RFC: Additional Directory for Extensions

From 5d5a0eb568b265bf48664bfa479dee7fd718cf03 Mon Sep 17 00:00:00 2001
From: "David E. Wheeler" <david@justatheory.com>
Date: Wed, 3 Apr 2024 09:27:48 -0400
Subject: [PATCH v1] Add extension_directory GUC

Based on a [patch] by Christophe Berg in the Debian Project, add a new
GUC, `extension_directory`, that prepends a path for extension loading.
This directory is prepended to paths when loading extensions (control
and SQL files), and to the `$libdir` directive when loading modules that
back functions. Changing the configuration requires a server restart,
and is visible only to super users.

  [patch]: https://salsa.debian.org/postgresql/postgresql/-/blob/17/debian/patches/extension_destdir?ref_type=heads
---
 src/backend/commands/extension.c              | 90 +++++++++++++++++++
 src/backend/utils/fmgr/dfmgr.c                | 29 +++++-
 src/backend/utils/misc/guc_tables.c           | 12 +++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/utils/guc.h                       |  1 +
 5 files changed, 133 insertions(+), 1 deletion(-)

diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index 77d8c9e186..fbe0e32aca 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -393,6 +393,16 @@ get_extension_control_filename(const char *extname)
 
 	get_share_path(my_exec_path, sharepath);
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		snprintf(result, MAXPGPATH, "%s%s/extension/%s.control",
+				 extension_destdir, sharepath, extname);
+		if (pg_file_exists(result))
+			return result;
+	}
 	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
 			 sharepath, extname);
 
@@ -432,6 +442,16 @@ get_extension_aux_control_filename(ExtensionControlFile *control,
 	scriptdir = get_extension_script_directory(control);
 
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		snprintf(result, MAXPGPATH, "%s%s/%s--%s.control",
+				 extension_destdir, scriptdir, control->name, version);
+		if (pg_file_exists(result))
+			return result;
+	}
 	snprintf(result, MAXPGPATH, "%s/%s--%s.control",
 			 scriptdir, control->name, version);
 
@@ -450,6 +470,23 @@ get_extension_script_filename(ExtensionControlFile *control,
 	scriptdir = get_extension_script_directory(control);
 
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		if (from_version)
+			snprintf(result, MAXPGPATH, "%s%s/%s--%s--%s.sql",
+					 extension_destdir, scriptdir, control->name, from_version, version);
+		else
+			snprintf(result, MAXPGPATH, "%s%s/%s--%s.sql",
+					 extension_destdir, scriptdir, control->name, version);
+		if (pg_file_exists(result))
+		{
+			pfree(scriptdir);
+			return result;
+		}
+	}
 	if (from_version)
 		snprintf(result, MAXPGPATH, "%s/%s--%s--%s.sql",
 				 scriptdir, control->name, from_version, version);
@@ -1209,6 +1246,59 @@ get_ext_ver_list(ExtensionControlFile *control)
 	DIR		   *dir;
 	struct dirent *de;
 
+	/*
+	 * If extension_destdir is set, try to find the files there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		char		location[MAXPGPATH];
+
+		snprintf(location, MAXPGPATH, "%s%s", extension_destdir,
+				get_extension_script_directory(control));
+		dir = AllocateDir(location);
+		while ((de = ReadDir(dir, location)) != NULL)
+		{
+			char	   *vername;
+			char	   *vername2;
+			ExtensionVersionInfo *evi;
+			ExtensionVersionInfo *evi2;
+
+			/* must be a .sql file ... */
+			if (!is_extension_script_filename(de->d_name))
+				continue;
+
+			/* ... matching extension name followed by separator */
+			if (strncmp(de->d_name, control->name, extnamelen) != 0 ||
+				de->d_name[extnamelen] != '-' ||
+				de->d_name[extnamelen + 1] != '-')
+				continue;
+
+			/* extract version name(s) from 'extname--something.sql' filename */
+			vername = pstrdup(de->d_name + extnamelen + 2);
+			*strrchr(vername, '.') = '\0';
+			vername2 = strstr(vername, "--");
+			if (!vername2)
+			{
+				/* It's an install, not update, script; record its version name */
+				evi = get_ext_ver_info(vername, &evi_list);
+				evi->installable = true;
+				continue;
+			}
+			*vername2 = '\0';		/* terminate first version */
+			vername2 += 2;			/* and point to second */
+
+			/* if there's a third --, it's bogus, ignore it */
+			if (strstr(vername2, "--"))
+				continue;
+
+			/* Create ExtensionVersionInfos and link them together */
+			evi = get_ext_ver_info(vername, &evi_list);
+			evi2 = get_ext_ver_info(vername2, &evi_list);
+			evi->reachable = lappend(evi->reachable, evi2);
+		}
+		FreeDir(dir);
+	}
+
 	location = get_extension_script_directory(control);
 	dir = AllocateDir(location);
 	while ((de = ReadDir(dir, location)) != NULL)
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index eafa0128ef..8dc17da5b5 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -35,6 +35,7 @@
 #include "miscadmin.h"
 #include "storage/fd.h"
 #include "storage/shmem.h"
+#include "utils/guc.h"
 #include "utils/hsearch.h"
 
 
@@ -415,7 +416,7 @@ expand_dynamic_library_name(const char *name)
 {
 	bool		have_slash;
 	char	   *new;
-	char	   *full;
+	char	   *full, *full2;
 
 	Assert(name);
 
@@ -430,6 +431,19 @@ expand_dynamic_library_name(const char *name)
 	else
 	{
 		full = substitute_libpath_macro(name);
+		/*
+		 * If extension_destdir is set, try to find the file there first
+		 */
+		if (*extension_destdir != '\0')
+		{
+			full2 = psprintf("%s%s", extension_destdir, full);
+			if (pg_file_exists(full2))
+			{
+				pfree(full);
+				return full2;
+			}
+			pfree(full2);
+		}
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -448,6 +462,19 @@ expand_dynamic_library_name(const char *name)
 	{
 		full = substitute_libpath_macro(new);
 		pfree(new);
+		/*
+		 * If extension_destdir is set, try to find the file there first
+		 */
+		if (*extension_destdir != '\0')
+		{
+			full2 = psprintf("%s%s", extension_destdir, full);
+			if (pg_file_exists(full2))
+			{
+				pfree(full);
+				return full2;
+			}
+			pfree(full2);
+		}
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index c12784cbec..f46e84db13 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -541,6 +541,7 @@ char	   *ConfigFileName;
 char	   *HbaFileName;
 char	   *IdentFileName;
 char	   *external_pid_file;
+char	   *extension_destdir;
 
 char	   *application_name;
 
@@ -4497,6 +4498,17 @@ struct config_string ConfigureNamesString[] =
 		check_canonical_path, NULL, NULL
 	},
 
+	{
+		{"extension_destdir", PGC_POSTMASTER, FILE_LOCATIONS,
+			gettext_noop("Path to prepend for extension loading."),
+			gettext_noop("This directory is prepended to paths when loading extensions (control and SQL files), and to the '$libdir' directive when loading modules that back functions. The location is made configurable to allow build-time testing of extensions that do not have been installed to their proper location yet."),
+			GUC_SUPERUSER_ONLY
+		},
+		&extension_destdir,
+		"",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"ssl_library", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows the name of the SSL library."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index baecde2841..d8df437554 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -771,6 +771,8 @@
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_destdir = ''			# prepend path when loading extensions
+					# and shared objects (added by Debian)
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index 8d1fe04078..9f198cf2b5 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -278,6 +278,7 @@ extern PGDLLIMPORT char *ConfigFileName;
 extern PGDLLIMPORT char *HbaFileName;
 extern PGDLLIMPORT char *IdentFileName;
 extern PGDLLIMPORT char *external_pid_file;
+extern PGDLLIMPORT char *extension_destdir;
 
 extern PGDLLIMPORT char *application_name;
 
-- 
2.44.0

From 71e466be3f27a1f90940d7b6c9def64eceea2cbd Mon Sep 17 00:00:00 2001
From: "David E. Wheeler" <david@justatheory.com>
Date: Thu, 4 Apr 2024 13:18:31 -0400
Subject: [PATCH v2] Add extension_directory GUC

Based on a [patch] by Christophe Berg in the Debian Project, add a new
GUC, `extension_directory`, that prepends a path for extension loading.
This directory is prepended to paths when loading extensions (control
and SQL files), and to the `$libdir` directive when loading modules that
back functions. Changing the configuration requires a server restart,
and is visible only to super users.

  [patch]: https://salsa.debian.org/postgresql/postgresql/-/blob/17/debian/patches/extension_destdir?ref_type=heads
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/extend.sgml                      |  5 +-
 src/backend/commands/extension.c              | 90 +++++++++++++++++++
 src/backend/utils/fmgr/dfmgr.c                | 29 +++++-
 src/backend/utils/misc/guc_tables.c           | 12 +++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/utils/guc.h                       |  1 +
 7 files changed, 152 insertions(+), 3 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 624518e0b0..5f131b87c5 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10379,6 +10379,22 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-extension-destdir" xreflabel="extension_destdir">
+      <term><varname>extension_destdir</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_destdir</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        This directory is prepended to paths when loading extensions (control
+        and SQL files), and to the '$libdir' directive when loading modules
+        that back functions. This parameter can only be set at server start.
+        For more information see <xref linkend="extend-extensions-files-directory"/>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      </variablelist>
     </sect2>
    </sect1>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 218940ee5c..bb29670777 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -668,8 +668,9 @@ RETURNS anycompatible AS ...
       <listitem>
        <para>
         The directory containing the extension's <acronym>SQL</acronym> script
-        file(s).  Unless an absolute path is given, the name is relative to
-        the installation's <literal>SHAREDIR</literal> directory.  The
+        file(s). Unless an absolute path is given, the name will be used to
+        search for the extension relative to the <xref linkend="guc-extension-destdir"/>
+        and the installation's <literal>SHAREDIR</literal> directory.  The
         default behavior is equivalent to specifying
         <literal>directory = 'extension'</literal>.
        </para>
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index 77d8c9e186..fbe0e32aca 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -393,6 +393,16 @@ get_extension_control_filename(const char *extname)
 
 	get_share_path(my_exec_path, sharepath);
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		snprintf(result, MAXPGPATH, "%s%s/extension/%s.control",
+				 extension_destdir, sharepath, extname);
+		if (pg_file_exists(result))
+			return result;
+	}
 	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
 			 sharepath, extname);
 
@@ -432,6 +442,16 @@ get_extension_aux_control_filename(ExtensionControlFile *control,
 	scriptdir = get_extension_script_directory(control);
 
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		snprintf(result, MAXPGPATH, "%s%s/%s--%s.control",
+				 extension_destdir, scriptdir, control->name, version);
+		if (pg_file_exists(result))
+			return result;
+	}
 	snprintf(result, MAXPGPATH, "%s/%s--%s.control",
 			 scriptdir, control->name, version);
 
@@ -450,6 +470,23 @@ get_extension_script_filename(ExtensionControlFile *control,
 	scriptdir = get_extension_script_directory(control);
 
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		if (from_version)
+			snprintf(result, MAXPGPATH, "%s%s/%s--%s--%s.sql",
+					 extension_destdir, scriptdir, control->name, from_version, version);
+		else
+			snprintf(result, MAXPGPATH, "%s%s/%s--%s.sql",
+					 extension_destdir, scriptdir, control->name, version);
+		if (pg_file_exists(result))
+		{
+			pfree(scriptdir);
+			return result;
+		}
+	}
 	if (from_version)
 		snprintf(result, MAXPGPATH, "%s/%s--%s--%s.sql",
 				 scriptdir, control->name, from_version, version);
@@ -1209,6 +1246,59 @@ get_ext_ver_list(ExtensionControlFile *control)
 	DIR		   *dir;
 	struct dirent *de;
 
+	/*
+	 * If extension_destdir is set, try to find the files there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		char		location[MAXPGPATH];
+
+		snprintf(location, MAXPGPATH, "%s%s", extension_destdir,
+				get_extension_script_directory(control));
+		dir = AllocateDir(location);
+		while ((de = ReadDir(dir, location)) != NULL)
+		{
+			char	   *vername;
+			char	   *vername2;
+			ExtensionVersionInfo *evi;
+			ExtensionVersionInfo *evi2;
+
+			/* must be a .sql file ... */
+			if (!is_extension_script_filename(de->d_name))
+				continue;
+
+			/* ... matching extension name followed by separator */
+			if (strncmp(de->d_name, control->name, extnamelen) != 0 ||
+				de->d_name[extnamelen] != '-' ||
+				de->d_name[extnamelen + 1] != '-')
+				continue;
+
+			/* extract version name(s) from 'extname--something.sql' filename */
+			vername = pstrdup(de->d_name + extnamelen + 2);
+			*strrchr(vername, '.') = '\0';
+			vername2 = strstr(vername, "--");
+			if (!vername2)
+			{
+				/* It's an install, not update, script; record its version name */
+				evi = get_ext_ver_info(vername, &evi_list);
+				evi->installable = true;
+				continue;
+			}
+			*vername2 = '\0';		/* terminate first version */
+			vername2 += 2;			/* and point to second */
+
+			/* if there's a third --, it's bogus, ignore it */
+			if (strstr(vername2, "--"))
+				continue;
+
+			/* Create ExtensionVersionInfos and link them together */
+			evi = get_ext_ver_info(vername, &evi_list);
+			evi2 = get_ext_ver_info(vername2, &evi_list);
+			evi->reachable = lappend(evi->reachable, evi2);
+		}
+		FreeDir(dir);
+	}
+
 	location = get_extension_script_directory(control);
 	dir = AllocateDir(location);
 	while ((de = ReadDir(dir, location)) != NULL)
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index eafa0128ef..8dc17da5b5 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -35,6 +35,7 @@
 #include "miscadmin.h"
 #include "storage/fd.h"
 #include "storage/shmem.h"
+#include "utils/guc.h"
 #include "utils/hsearch.h"
 
 
@@ -415,7 +416,7 @@ expand_dynamic_library_name(const char *name)
 {
 	bool		have_slash;
 	char	   *new;
-	char	   *full;
+	char	   *full, *full2;
 
 	Assert(name);
 
@@ -430,6 +431,19 @@ expand_dynamic_library_name(const char *name)
 	else
 	{
 		full = substitute_libpath_macro(name);
+		/*
+		 * If extension_destdir is set, try to find the file there first
+		 */
+		if (*extension_destdir != '\0')
+		{
+			full2 = psprintf("%s%s", extension_destdir, full);
+			if (pg_file_exists(full2))
+			{
+				pfree(full);
+				return full2;
+			}
+			pfree(full2);
+		}
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -448,6 +462,19 @@ expand_dynamic_library_name(const char *name)
 	{
 		full = substitute_libpath_macro(new);
 		pfree(new);
+		/*
+		 * If extension_destdir is set, try to find the file there first
+		 */
+		if (*extension_destdir != '\0')
+		{
+			full2 = psprintf("%s%s", extension_destdir, full);
+			if (pg_file_exists(full2))
+			{
+				pfree(full);
+				return full2;
+			}
+			pfree(full2);
+		}
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index c12784cbec..f46e84db13 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -541,6 +541,7 @@ char	   *ConfigFileName;
 char	   *HbaFileName;
 char	   *IdentFileName;
 char	   *external_pid_file;
+char	   *extension_destdir;
 
 char	   *application_name;
 
@@ -4497,6 +4498,17 @@ struct config_string ConfigureNamesString[] =
 		check_canonical_path, NULL, NULL
 	},
 
+	{
+		{"extension_destdir", PGC_POSTMASTER, FILE_LOCATIONS,
+			gettext_noop("Path to prepend for extension loading."),
+			gettext_noop("This directory is prepended to paths when loading extensions (control and SQL files), and to the '$libdir' directive when loading modules that back functions. The location is made configurable to allow build-time testing of extensions that do not have been installed to their proper location yet."),
+			GUC_SUPERUSER_ONLY
+		},
+		&extension_destdir,
+		"",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"ssl_library", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows the name of the SSL library."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index baecde2841..d8df437554 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -771,6 +771,8 @@
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_destdir = ''			# prepend path when loading extensions
+					# and shared objects (added by Debian)
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index 8d1fe04078..9f198cf2b5 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -278,6 +278,7 @@ extern PGDLLIMPORT char *ConfigFileName;
 extern PGDLLIMPORT char *HbaFileName;
 extern PGDLLIMPORT char *IdentFileName;
 extern PGDLLIMPORT char *external_pid_file;
+extern PGDLLIMPORT char *extension_destdir;
 
 extern PGDLLIMPORT char *application_name;
 
-- 
2.44.0

From f6c852a714dc2a3fcf08896cf24d99a9a488e5c8 Mon Sep 17 00:00:00 2001
From: "David E. Wheeler" <david@justatheory.com>
Date: Thu, 4 Apr 2024 13:18:31 -0400
Subject: [PATCH v3] Add extension_directory GUC

Based on a [patch] by Christophe Berg in the Debian Project, add a new
GUC, `extension_directory`, that prepends a path for extension loading.
This directory is prepended to paths when loading extensions (control
and SQL files), and to the `$libdir` directive when loading modules that
back functions. Changing the configuration requires a server restart,
and is visible only to super users.

  [patch]: https://salsa.debian.org/postgresql/postgresql/-/blob/17/debian/patches/extension_destdir?ref_type=heads
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/extend.sgml                      |  5 +-
 src/backend/commands/extension.c              | 90 +++++++++++++++++++
 src/backend/utils/fmgr/dfmgr.c                | 29 +++++-
 src/backend/utils/misc/guc_tables.c           | 12 +++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/utils/guc.h                       |  1 +
 7 files changed, 152 insertions(+), 3 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d8e1282e12..5cc0efe037 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10379,6 +10379,22 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-extension-destdir" xreflabel="extension_destdir">
+      <term><varname>extension_destdir</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_destdir</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        This directory is prepended to paths when loading extensions (control
+        and SQL files), and to the '$libdir' directive when loading modules
+        that back functions. This parameter can only be set at server start.
+        For more information see <xref linkend="extend-extensions-files-directory"/>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      </variablelist>
     </sect2>
    </sect1>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 218940ee5c..bb29670777 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -668,8 +668,9 @@ RETURNS anycompatible AS ...
       <listitem>
        <para>
         The directory containing the extension's <acronym>SQL</acronym> script
-        file(s).  Unless an absolute path is given, the name is relative to
-        the installation's <literal>SHAREDIR</literal> directory.  The
+        file(s). Unless an absolute path is given, the name will be used to
+        search for the extension relative to the <xref linkend="guc-extension-destdir"/>
+        and the installation's <literal>SHAREDIR</literal> directory.  The
         default behavior is equivalent to specifying
         <literal>directory = 'extension'</literal>.
        </para>
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index 77d8c9e186..fbe0e32aca 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -393,6 +393,16 @@ get_extension_control_filename(const char *extname)
 
 	get_share_path(my_exec_path, sharepath);
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		snprintf(result, MAXPGPATH, "%s%s/extension/%s.control",
+				 extension_destdir, sharepath, extname);
+		if (pg_file_exists(result))
+			return result;
+	}
 	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
 			 sharepath, extname);
 
@@ -432,6 +442,16 @@ get_extension_aux_control_filename(ExtensionControlFile *control,
 	scriptdir = get_extension_script_directory(control);
 
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		snprintf(result, MAXPGPATH, "%s%s/%s--%s.control",
+				 extension_destdir, scriptdir, control->name, version);
+		if (pg_file_exists(result))
+			return result;
+	}
 	snprintf(result, MAXPGPATH, "%s/%s--%s.control",
 			 scriptdir, control->name, version);
 
@@ -450,6 +470,23 @@ get_extension_script_filename(ExtensionControlFile *control,
 	scriptdir = get_extension_script_directory(control);
 
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		if (from_version)
+			snprintf(result, MAXPGPATH, "%s%s/%s--%s--%s.sql",
+					 extension_destdir, scriptdir, control->name, from_version, version);
+		else
+			snprintf(result, MAXPGPATH, "%s%s/%s--%s.sql",
+					 extension_destdir, scriptdir, control->name, version);
+		if (pg_file_exists(result))
+		{
+			pfree(scriptdir);
+			return result;
+		}
+	}
 	if (from_version)
 		snprintf(result, MAXPGPATH, "%s/%s--%s--%s.sql",
 				 scriptdir, control->name, from_version, version);
@@ -1209,6 +1246,59 @@ get_ext_ver_list(ExtensionControlFile *control)
 	DIR		   *dir;
 	struct dirent *de;
 
+	/*
+	 * If extension_destdir is set, try to find the files there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		char		location[MAXPGPATH];
+
+		snprintf(location, MAXPGPATH, "%s%s", extension_destdir,
+				get_extension_script_directory(control));
+		dir = AllocateDir(location);
+		while ((de = ReadDir(dir, location)) != NULL)
+		{
+			char	   *vername;
+			char	   *vername2;
+			ExtensionVersionInfo *evi;
+			ExtensionVersionInfo *evi2;
+
+			/* must be a .sql file ... */
+			if (!is_extension_script_filename(de->d_name))
+				continue;
+
+			/* ... matching extension name followed by separator */
+			if (strncmp(de->d_name, control->name, extnamelen) != 0 ||
+				de->d_name[extnamelen] != '-' ||
+				de->d_name[extnamelen + 1] != '-')
+				continue;
+
+			/* extract version name(s) from 'extname--something.sql' filename */
+			vername = pstrdup(de->d_name + extnamelen + 2);
+			*strrchr(vername, '.') = '\0';
+			vername2 = strstr(vername, "--");
+			if (!vername2)
+			{
+				/* It's an install, not update, script; record its version name */
+				evi = get_ext_ver_info(vername, &evi_list);
+				evi->installable = true;
+				continue;
+			}
+			*vername2 = '\0';		/* terminate first version */
+			vername2 += 2;			/* and point to second */
+
+			/* if there's a third --, it's bogus, ignore it */
+			if (strstr(vername2, "--"))
+				continue;
+
+			/* Create ExtensionVersionInfos and link them together */
+			evi = get_ext_ver_info(vername, &evi_list);
+			evi2 = get_ext_ver_info(vername2, &evi_list);
+			evi->reachable = lappend(evi->reachable, evi2);
+		}
+		FreeDir(dir);
+	}
+
 	location = get_extension_script_directory(control);
 	dir = AllocateDir(location);
 	while ((de = ReadDir(dir, location)) != NULL)
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index eafa0128ef..8dc17da5b5 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -35,6 +35,7 @@
 #include "miscadmin.h"
 #include "storage/fd.h"
 #include "storage/shmem.h"
+#include "utils/guc.h"
 #include "utils/hsearch.h"
 
 
@@ -415,7 +416,7 @@ expand_dynamic_library_name(const char *name)
 {
 	bool		have_slash;
 	char	   *new;
-	char	   *full;
+	char	   *full, *full2;
 
 	Assert(name);
 
@@ -430,6 +431,19 @@ expand_dynamic_library_name(const char *name)
 	else
 	{
 		full = substitute_libpath_macro(name);
+		/*
+		 * If extension_destdir is set, try to find the file there first
+		 */
+		if (*extension_destdir != '\0')
+		{
+			full2 = psprintf("%s%s", extension_destdir, full);
+			if (pg_file_exists(full2))
+			{
+				pfree(full);
+				return full2;
+			}
+			pfree(full2);
+		}
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -448,6 +462,19 @@ expand_dynamic_library_name(const char *name)
 	{
 		full = substitute_libpath_macro(new);
 		pfree(new);
+		/*
+		 * If extension_destdir is set, try to find the file there first
+		 */
+		if (*extension_destdir != '\0')
+		{
+			full2 = psprintf("%s%s", extension_destdir, full);
+			if (pg_file_exists(full2))
+			{
+				pfree(full);
+				return full2;
+			}
+			pfree(full2);
+		}
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index c68fdc008b..6c203edb11 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -542,6 +542,7 @@ char	   *ConfigFileName;
 char	   *HbaFileName;
 char	   *IdentFileName;
 char	   *external_pid_file;
+char	   *extension_destdir;
 
 char	   *application_name;
 
@@ -4508,6 +4509,17 @@ struct config_string ConfigureNamesString[] =
 		check_canonical_path, NULL, NULL
 	},
 
+	{
+		{"extension_destdir", PGC_POSTMASTER, FILE_LOCATIONS,
+			gettext_noop("Path to prepend for extension loading."),
+			gettext_noop("This directory is prepended to paths when loading extensions (control and SQL files), and to the '$libdir' directive when loading modules that back functions. The location is made configurable to allow build-time testing of extensions that do not have been installed to their proper location yet."),
+			GUC_SUPERUSER_ONLY
+		},
+		&extension_destdir,
+		"",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"ssl_library", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows the name of the SSL library."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2166ea4a87..bab263a3de 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -771,6 +771,8 @@
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_destdir = ''			# prepend path when loading extensions
+					# and shared objects (added by Debian)
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index 8d1fe04078..9f198cf2b5 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -278,6 +278,7 @@ extern PGDLLIMPORT char *ConfigFileName;
 extern PGDLLIMPORT char *HbaFileName;
 extern PGDLLIMPORT char *IdentFileName;
 extern PGDLLIMPORT char *external_pid_file;
+extern PGDLLIMPORT char *extension_destdir;
 
 extern PGDLLIMPORT char *application_name;
 
-- 
2.44.0

From 698bdd970c18585320b222ecc2b0906ace3177c6 Mon Sep 17 00:00:00 2001
From: "David E. Wheeler" <david@justatheory.com>
Date: Tue, 25 Jun 2024 18:28:27 -0400
Subject: [PATCH v4] Add extension_destdir GUC

Based on a [patch] by Christophe Berg in the Debian Project, add a new
GUC, `extension_destdir`, that prepends a directory prefix for extension
loading. This directory is prepended to the `SHAREDIR` paths when
loading extensions (control and SQL files), and to the `$libdir`
directive when loading modules that back functions. Changing the
configuration requires a server restart, and is visible only to super
users.

Also document the PGXS `DESTDIR` variable, which should be used to
install extensions into the proper destination directory.

  [patch]: https://salsa.debian.org/postgresql/postgresql/-/blob/17/debian/patches/extension_destdir?ref_type=heads
---
 doc/src/sgml/config.sgml                      | 35 ++++++++
 doc/src/sgml/extend.sgml                      | 12 ++-
 src/backend/commands/extension.c              | 90 +++++++++++++++++++
 src/backend/utils/fmgr/dfmgr.c                | 29 +++++-
 src/backend/utils/misc/guc_tables.c           | 12 +++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/utils/guc.h                       |  1 +
 7 files changed, 179 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 0c7a9082c5..350ed5b9c9 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10389,6 +10389,41 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-extension-destdir" xreflabel="extension_destdir">
+      <term><varname>extension_destdir</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_destdir</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies a directory prefix into which extensions should be
+        installed. When set, the postmaster will search this directory for an
+        extension before searching the default paths.
+       </para>
+
+       <para>
+        For example, this configuration:
+<programlisting>
+extension_destdir = '/mnt/extensions'
+</programlisting>
+        will allow <productname>PostgreSQL</productname> to first look for
+        extension control files, SQL files, and loadable modules installed in
+        <literal>/mnt/extensions</literal> and fall back on the
+        default directories if they're not found there.
+       </para>
+
+       <para>
+        Note that the files should be installed in their full paths under the
+        <varname>extension_destdir</varname> prefix. When using
+        <link linkend="extend-pgxs">PGXS</link> to install an extension, pass
+        the destination directory via the <varname>DESTDIR</varname> variable
+        to install the files in the proper location. For more information see
+        <xref linkend="extend-extensions-files-directory"/>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      </variablelist>
     </sect2>
    </sect1>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 218940ee5c..6653955d53 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -669,7 +669,8 @@ RETURNS anycompatible AS ...
        <para>
         The directory containing the extension's <acronym>SQL</acronym> script
         file(s).  Unless an absolute path is given, the name is relative to
-        the installation's <literal>SHAREDIR</literal> directory.  The
+        the <literal>SHAREDIR</literal> under the <xref linkend="guc-extension-destdir"/>
+        prefix and to the installation's <literal>SHAREDIR</literal> directory.  The
         default behavior is equivalent to specifying
         <literal>directory = 'extension'</literal>.
        </para>
@@ -1710,6 +1711,15 @@ include $(PGXS)
       </listitem>
      </varlistentry>
 
+     <varlistentry id="extend-pgxs-destdir">
+      <term><varname>DESTDIR</varname></term>
+      <listitem>
+       <para>
+        install all files under this directory prefix
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="extend-pgxs-no-installcheck">
       <term><varname>NO_INSTALLCHECK</varname></term>
       <listitem>
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index 1643c8c69a..f3b7735c5b 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -393,6 +393,16 @@ get_extension_control_filename(const char *extname)
 
 	get_share_path(my_exec_path, sharepath);
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		snprintf(result, MAXPGPATH, "%s%s/extension/%s.control",
+				 extension_destdir, sharepath, extname);
+		if (pg_file_exists(result))
+			return result;
+	}
 	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
 			 sharepath, extname);
 
@@ -432,6 +442,16 @@ get_extension_aux_control_filename(ExtensionControlFile *control,
 	scriptdir = get_extension_script_directory(control);
 
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		snprintf(result, MAXPGPATH, "%s%s/%s--%s.control",
+				 extension_destdir, scriptdir, control->name, version);
+		if (pg_file_exists(result))
+			return result;
+	}
 	snprintf(result, MAXPGPATH, "%s/%s--%s.control",
 			 scriptdir, control->name, version);
 
@@ -450,6 +470,23 @@ get_extension_script_filename(ExtensionControlFile *control,
 	scriptdir = get_extension_script_directory(control);
 
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		if (from_version)
+			snprintf(result, MAXPGPATH, "%s%s/%s--%s--%s.sql",
+					 extension_destdir, scriptdir, control->name, from_version, version);
+		else
+			snprintf(result, MAXPGPATH, "%s%s/%s--%s.sql",
+					 extension_destdir, scriptdir, control->name, version);
+		if (pg_file_exists(result))
+		{
+			pfree(scriptdir);
+			return result;
+		}
+	}
 	if (from_version)
 		snprintf(result, MAXPGPATH, "%s/%s--%s--%s.sql",
 				 scriptdir, control->name, from_version, version);
@@ -1209,6 +1246,59 @@ get_ext_ver_list(ExtensionControlFile *control)
 	DIR		   *dir;
 	struct dirent *de;
 
+	/*
+	 * If extension_destdir is set, try to find the files there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		char		location[MAXPGPATH];
+
+		snprintf(location, MAXPGPATH, "%s%s", extension_destdir,
+				get_extension_script_directory(control));
+		dir = AllocateDir(location);
+		while ((de = ReadDir(dir, location)) != NULL)
+		{
+			char	   *vername;
+			char	   *vername2;
+			ExtensionVersionInfo *evi;
+			ExtensionVersionInfo *evi2;
+
+			/* must be a .sql file ... */
+			if (!is_extension_script_filename(de->d_name))
+				continue;
+
+			/* ... matching extension name followed by separator */
+			if (strncmp(de->d_name, control->name, extnamelen) != 0 ||
+				de->d_name[extnamelen] != '-' ||
+				de->d_name[extnamelen + 1] != '-')
+				continue;
+
+			/* extract version name(s) from 'extname--something.sql' filename */
+			vername = pstrdup(de->d_name + extnamelen + 2);
+			*strrchr(vername, '.') = '\0';
+			vername2 = strstr(vername, "--");
+			if (!vername2)
+			{
+				/* It's an install, not update, script; record its version name */
+				evi = get_ext_ver_info(vername, &evi_list);
+				evi->installable = true;
+				continue;
+			}
+			*vername2 = '\0';		/* terminate first version */
+			vername2 += 2;			/* and point to second */
+
+			/* if there's a third --, it's bogus, ignore it */
+			if (strstr(vername2, "--"))
+				continue;
+
+			/* Create ExtensionVersionInfos and link them together */
+			evi = get_ext_ver_info(vername, &evi_list);
+			evi2 = get_ext_ver_info(vername2, &evi_list);
+			evi->reachable = lappend(evi->reachable, evi2);
+		}
+		FreeDir(dir);
+	}
+
 	location = get_extension_script_directory(control);
 	dir = AllocateDir(location);
 	while ((de = ReadDir(dir, location)) != NULL)
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 092004dcf3..25971b25b6 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -35,6 +35,7 @@
 #include "miscadmin.h"
 #include "storage/fd.h"
 #include "storage/shmem.h"
+#include "utils/guc.h"
 #include "utils/hsearch.h"
 
 
@@ -415,7 +416,7 @@ expand_dynamic_library_name(const char *name)
 {
 	bool		have_slash;
 	char	   *new;
-	char	   *full;
+	char	   *full, *full2;
 
 	Assert(name);
 
@@ -430,6 +431,19 @@ expand_dynamic_library_name(const char *name)
 	else
 	{
 		full = substitute_libpath_macro(name);
+		/*
+		 * If extension_destdir is set, try to find the file there first
+		 */
+		if (*extension_destdir != '\0')
+		{
+			full2 = psprintf("%s%s", extension_destdir, full);
+			if (pg_file_exists(full2))
+			{
+				pfree(full);
+				return full2;
+			}
+			pfree(full2);
+		}
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -448,6 +462,19 @@ expand_dynamic_library_name(const char *name)
 	{
 		full = substitute_libpath_macro(new);
 		pfree(new);
+		/*
+		 * If extension_destdir is set, try to find the file there first
+		 */
+		if (*extension_destdir != '\0')
+		{
+			full2 = psprintf("%s%s", extension_destdir, full);
+			if (pg_file_exists(full2))
+			{
+				pfree(full);
+				return full2;
+			}
+			pfree(full2);
+		}
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 46c258be28..8a3c6e2968 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -541,6 +541,7 @@ char	   *ConfigFileName;
 char	   *HbaFileName;
 char	   *IdentFileName;
 char	   *external_pid_file;
+char	   *extension_destdir;
 
 char	   *application_name;
 
@@ -4487,6 +4488,17 @@ struct config_string ConfigureNamesString[] =
 		check_canonical_path, NULL, NULL
 	},
 
+	{
+		{"extension_destdir", PGC_POSTMASTER, FILE_LOCATIONS,
+			gettext_noop("Path to prepend for extension loading."),
+			gettext_noop("This directory is prepended to paths when loading extensions (control and SQL files), and to the '$libdir' directive when loading modules that back functions. The location is made configurable to allow build-time testing of extensions that do not have been installed to their proper location yet."),
+			GUC_SUPERUSER_ONLY
+		},
+		&extension_destdir,
+		"",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"ssl_library", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows the name of the SSL library."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e0567de219..93a70487b6 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -771,6 +771,8 @@
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_destdir = ''			# prepend path when loading extensions
+					# and shared objects (added by Debian)
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index ff506bf48d..eaf0b4f337 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -277,6 +277,7 @@ extern PGDLLIMPORT char *ConfigFileName;
 extern PGDLLIMPORT char *HbaFileName;
 extern PGDLLIMPORT char *IdentFileName;
 extern PGDLLIMPORT char *external_pid_file;
+extern PGDLLIMPORT char *extension_destdir;
 
 extern PGDLLIMPORT char *application_name;
 
-- 
2.45.2

From c1a146b18187fa1ba96000815aab0a574e0110f2 Mon Sep 17 00:00:00 2001
From: "David E. Wheeler" <david@justatheory.com>
Date: Mon, 8 Jul 2024 11:58:45 -0400
Subject: [PATCH v5] Add extension_destdir GUC

Based on a [patch] by Christophe Berg in the Debian Project, add a new
GUC, `extension_destdir`, that prepends a directory prefix for extension
loading. This directory is prepended to the `SHAREDIR` paths when
loading extensions (control and SQL files), and to the `$libdir`
directive when loading modules that back functions. Requires a superuser
or user with the appropriate SET privilege.

Also document the PGXS `DESTDIR` variable, which should be used to
install extensions into the proper destination directory.

  [patch]: https://salsa.debian.org/postgresql/postgresql/-/blob/17/debian/patches/extension_destdir?ref_type=heads
---
 doc/src/sgml/config.sgml                      | 37 ++++++++
 doc/src/sgml/extend.sgml                      | 12 ++-
 src/backend/commands/extension.c              | 90 +++++++++++++++++++
 src/backend/utils/fmgr/dfmgr.c                | 29 +++++-
 src/backend/utils/misc/guc_tables.c           | 12 +++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/utils/guc.h                       |  1 +
 7 files changed, 181 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index f627a3e63c..defe218007 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10389,6 +10389,43 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-extension-destdir" xreflabel="extension_destdir">
+      <term><varname>extension_destdir</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_destdir</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies a directory prefix into which extensions should be
+        installed. Only superusers and users with the appropriate
+        <literal>SET</literal> privilege can change this setting. When set,
+        the postmaster will search this directory for an extension before
+        searching the default paths.
+       </para>
+
+       <para>
+        For example, this configuration:
+<programlisting>
+extension_destdir = '/mnt/extensions'
+</programlisting>
+        will allow <productname>PostgreSQL</productname> to first look for
+        extension control files, SQL files, and loadable modules installed in
+        <literal>/mnt/extensions</literal> and fall back on the
+        default directories if they're not found there.
+       </para>
+
+       <para>
+        Note that the files should be installed in their full paths under the
+        <varname>extension_destdir</varname> prefix. When using
+        <link linkend="extend-pgxs">PGXS</link> to install an extension, pass
+        the destination directory via the <varname>DESTDIR</varname> variable
+        to install the files in the proper location. For more information see
+        <xref linkend="extend-extensions-files-directory"/>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      </variablelist>
     </sect2>
    </sect1>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 218940ee5c..6653955d53 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -669,7 +669,8 @@ RETURNS anycompatible AS ...
        <para>
         The directory containing the extension's <acronym>SQL</acronym> script
         file(s).  Unless an absolute path is given, the name is relative to
-        the installation's <literal>SHAREDIR</literal> directory.  The
+        the <literal>SHAREDIR</literal> under the <xref linkend="guc-extension-destdir"/>
+        prefix and to the installation's <literal>SHAREDIR</literal> directory.  The
         default behavior is equivalent to specifying
         <literal>directory = 'extension'</literal>.
        </para>
@@ -1710,6 +1711,15 @@ include $(PGXS)
       </listitem>
      </varlistentry>
 
+     <varlistentry id="extend-pgxs-destdir">
+      <term><varname>DESTDIR</varname></term>
+      <listitem>
+       <para>
+        install all files under this directory prefix
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="extend-pgxs-no-installcheck">
       <term><varname>NO_INSTALLCHECK</varname></term>
       <listitem>
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index 1643c8c69a..f3b7735c5b 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -393,6 +393,16 @@ get_extension_control_filename(const char *extname)
 
 	get_share_path(my_exec_path, sharepath);
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		snprintf(result, MAXPGPATH, "%s%s/extension/%s.control",
+				 extension_destdir, sharepath, extname);
+		if (pg_file_exists(result))
+			return result;
+	}
 	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
 			 sharepath, extname);
 
@@ -432,6 +442,16 @@ get_extension_aux_control_filename(ExtensionControlFile *control,
 	scriptdir = get_extension_script_directory(control);
 
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		snprintf(result, MAXPGPATH, "%s%s/%s--%s.control",
+				 extension_destdir, scriptdir, control->name, version);
+		if (pg_file_exists(result))
+			return result;
+	}
 	snprintf(result, MAXPGPATH, "%s/%s--%s.control",
 			 scriptdir, control->name, version);
 
@@ -450,6 +470,23 @@ get_extension_script_filename(ExtensionControlFile *control,
 	scriptdir = get_extension_script_directory(control);
 
 	result = (char *) palloc(MAXPGPATH);
+	/*
+	 * If extension_destdir is set, try to find the file there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		if (from_version)
+			snprintf(result, MAXPGPATH, "%s%s/%s--%s--%s.sql",
+					 extension_destdir, scriptdir, control->name, from_version, version);
+		else
+			snprintf(result, MAXPGPATH, "%s%s/%s--%s.sql",
+					 extension_destdir, scriptdir, control->name, version);
+		if (pg_file_exists(result))
+		{
+			pfree(scriptdir);
+			return result;
+		}
+	}
 	if (from_version)
 		snprintf(result, MAXPGPATH, "%s/%s--%s--%s.sql",
 				 scriptdir, control->name, from_version, version);
@@ -1209,6 +1246,59 @@ get_ext_ver_list(ExtensionControlFile *control)
 	DIR		   *dir;
 	struct dirent *de;
 
+	/*
+	 * If extension_destdir is set, try to find the files there first
+	 */
+	if (*extension_destdir != '\0')
+	{
+		char		location[MAXPGPATH];
+
+		snprintf(location, MAXPGPATH, "%s%s", extension_destdir,
+				get_extension_script_directory(control));
+		dir = AllocateDir(location);
+		while ((de = ReadDir(dir, location)) != NULL)
+		{
+			char	   *vername;
+			char	   *vername2;
+			ExtensionVersionInfo *evi;
+			ExtensionVersionInfo *evi2;
+
+			/* must be a .sql file ... */
+			if (!is_extension_script_filename(de->d_name))
+				continue;
+
+			/* ... matching extension name followed by separator */
+			if (strncmp(de->d_name, control->name, extnamelen) != 0 ||
+				de->d_name[extnamelen] != '-' ||
+				de->d_name[extnamelen + 1] != '-')
+				continue;
+
+			/* extract version name(s) from 'extname--something.sql' filename */
+			vername = pstrdup(de->d_name + extnamelen + 2);
+			*strrchr(vername, '.') = '\0';
+			vername2 = strstr(vername, "--");
+			if (!vername2)
+			{
+				/* It's an install, not update, script; record its version name */
+				evi = get_ext_ver_info(vername, &evi_list);
+				evi->installable = true;
+				continue;
+			}
+			*vername2 = '\0';		/* terminate first version */
+			vername2 += 2;			/* and point to second */
+
+			/* if there's a third --, it's bogus, ignore it */
+			if (strstr(vername2, "--"))
+				continue;
+
+			/* Create ExtensionVersionInfos and link them together */
+			evi = get_ext_ver_info(vername, &evi_list);
+			evi2 = get_ext_ver_info(vername2, &evi_list);
+			evi->reachable = lappend(evi->reachable, evi2);
+		}
+		FreeDir(dir);
+	}
+
 	location = get_extension_script_directory(control);
 	dir = AllocateDir(location);
 	while ((de = ReadDir(dir, location)) != NULL)
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 092004dcf3..25971b25b6 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -35,6 +35,7 @@
 #include "miscadmin.h"
 #include "storage/fd.h"
 #include "storage/shmem.h"
+#include "utils/guc.h"
 #include "utils/hsearch.h"
 
 
@@ -415,7 +416,7 @@ expand_dynamic_library_name(const char *name)
 {
 	bool		have_slash;
 	char	   *new;
-	char	   *full;
+	char	   *full, *full2;
 
 	Assert(name);
 
@@ -430,6 +431,19 @@ expand_dynamic_library_name(const char *name)
 	else
 	{
 		full = substitute_libpath_macro(name);
+		/*
+		 * If extension_destdir is set, try to find the file there first
+		 */
+		if (*extension_destdir != '\0')
+		{
+			full2 = psprintf("%s%s", extension_destdir, full);
+			if (pg_file_exists(full2))
+			{
+				pfree(full);
+				return full2;
+			}
+			pfree(full2);
+		}
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -448,6 +462,19 @@ expand_dynamic_library_name(const char *name)
 	{
 		full = substitute_libpath_macro(new);
 		pfree(new);
+		/*
+		 * If extension_destdir is set, try to find the file there first
+		 */
+		if (*extension_destdir != '\0')
+		{
+			full2 = psprintf("%s%s", extension_destdir, full);
+			if (pg_file_exists(full2))
+			{
+				pfree(full);
+				return full2;
+			}
+			pfree(full2);
+		}
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 630ed0f162..1f5430fd76 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -543,6 +543,7 @@ char	   *ConfigFileName;
 char	   *HbaFileName;
 char	   *IdentFileName;
 char	   *external_pid_file;
+char	   *extension_destdir;
 
 char	   *application_name;
 
@@ -4489,6 +4490,17 @@ struct config_string ConfigureNamesString[] =
 		check_canonical_path, NULL, NULL
 	},
 
+	{
+		{"extension_destdir", PGC_SUSET, FILE_LOCATIONS,
+			gettext_noop("Path to prepend for extension loading."),
+			gettext_noop("This directory is prepended to paths when loading extensions (control and SQL files), and to the '$libdir' directive when loading modules that back functions. The location is made configurable to allow build-time testing of extensions that do not have been installed to their proper location yet."),
+			GUC_SUPERUSER_ONLY
+		},
+		&extension_destdir,
+		"",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"ssl_library", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows the name of the SSL library."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 9ec9f97e92..152997e67e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -771,6 +771,8 @@
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_destdir = ''			# prepend path when loading extensions
+					# and shared objects (added by Debian)
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index ff506bf48d..eaf0b4f337 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -277,6 +277,7 @@ extern PGDLLIMPORT char *ConfigFileName;
 extern PGDLLIMPORT char *HbaFileName;
 extern PGDLLIMPORT char *IdentFileName;
 extern PGDLLIMPORT char *external_pid_file;
+extern PGDLLIMPORT char *extension_destdir;
 
 extern PGDLLIMPORT char *application_name;
 
-- 
2.45.2

From 08620bae551bb6b2e3a44aa3df4c8751ad06f804 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Mon, 11 Nov 2024 07:29:47 +0100
Subject: [PATCH v0] extension_control_path

The new GUC extension_control_path specifies a path to look for
extension control files.  The default value is $system, which looks in
the compiled-in location, as before.

The path search uses the same code and works in the same way as
dynamic_library_path.

Discussion: https://www.postgresql.org/message-id/flat/E7C7BFFB-8857-48D4-A71F-88B359FADCFD@justatheory.com
---
 doc/src/sgml/config.sgml                      | 13 ++++
 doc/src/sgml/extend.sgml                      |  1 +
 doc/src/sgml/ref/create_extension.sgml        |  1 +
 src/backend/commands/extension.c              | 56 ++++++++++++++--
 src/backend/utils/fmgr/dfmgr.c                | 64 +++++++++++--------
 src/backend/utils/misc/guc_tables.c           | 12 ++++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 src/include/commands/extension.h              |  2 +
 src/include/fmgr.h                            |  2 +
 9 files changed, 118 insertions(+), 34 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d54f9049569..c4790de7102 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10434,6 +10434,19 @@ <title>Other Defaults</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-extension-control-path" xreflabel="extension_control_path">
+      <term><varname>extension_control_path</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_control_path</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        TODO
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-gin-fuzzy-search-limit" xreflabel="gin_fuzzy_search_limit">
       <term><varname>gin_fuzzy_search_limit</varname> (<type>integer</type>)
       <indexterm>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 218940ee5ce..77a517d5167 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -635,6 +635,7 @@ <title>Extension Files</title>
     <primary>control file</primary>
    </indexterm>
 
+    <!-- TODO -->
     <para>
      The <command>CREATE EXTENSION</command> command relies on a control
      file for each extension, which must be named the same as the extension
diff --git a/doc/src/sgml/ref/create_extension.sgml b/doc/src/sgml/ref/create_extension.sgml
index ca2b80d669c..c26218f3adf 100644
--- a/doc/src/sgml/ref/create_extension.sgml
+++ b/doc/src/sgml/ref/create_extension.sgml
@@ -92,6 +92,7 @@ <title>Parameters</title>
         installed. <productname>PostgreSQL</productname> will create the
         extension using details from the file
         <literal>SHAREDIR/extension/</literal><replaceable class="parameter">extension_name</replaceable><literal>.control</literal>.
+        <!-- TODO -->
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index af6bd8ff426..b328e8e28f4 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -69,6 +69,9 @@
 #include "utils/varlena.h"
 
 
+/* GUC */
+char	   *Extension_control_path;
+
 /* Globally visible state variables */
 bool		creating_extension = false;
 Oid			CurrentExtensionObject = InvalidOid;
@@ -79,6 +82,7 @@ Oid			CurrentExtensionObject = InvalidOid;
 typedef struct ExtensionControlFile
 {
 	char	   *name;			/* name of the extension */
+	char	   *control_dir;	/* directory where control file was found */
 	char	   *directory;		/* directory for script files */
 	char	   *default_version;	/* default install target version, if any */
 	char	   *module_pathname;	/* string to substitute for
@@ -328,6 +332,9 @@ is_extension_script_filename(const char *filename)
 	return (extension != NULL) && (strcmp(extension, ".sql") == 0);
 }
 
+// TODO
+// This is now only for finding/listing available extensions.  Rewrite to use
+// path.  See further TODOs below.
 static char *
 get_extension_control_directory(void)
 {
@@ -341,16 +348,36 @@ get_extension_control_directory(void)
 	return result;
 }
 
+/*
+ * Find control file for extension with name in control->name, looking in the
+ * path.  Return the full file name, or NULL if not found.  If found, the
+ * directory is recorded in control->control_dir.
+ */
 static char *
-get_extension_control_filename(const char *extname)
+find_extension_control_filename(ExtensionControlFile *control)
 {
 	char		sharepath[MAXPGPATH];
+	char	   *system_dir;
+	char	   *basename;
 	char	   *result;
 
+	Assert(control->name);
+
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
-			 sharepath, extname);
+	system_dir = psprintf("%s/extension", sharepath);
+
+	basename = psprintf("%s.control", control->name);
+
+	result = find_in_path(basename, Extension_control_path, "extension_control_path", "$system", system_dir);
+
+	if (result)
+	{
+		const char *p;
+
+		p = strrchr(result, '/');
+		Assert(p);
+		control->control_dir = pnstrdup(result, p - result);
+	}
 
 	return result;
 }
@@ -366,7 +393,7 @@ get_extension_script_directory(ExtensionControlFile *control)
 	 * installation's share directory.
 	 */
 	if (!control->directory)
-		return get_extension_control_directory();
+		return pstrdup(control->control_dir);
 
 	if (is_absolute_path(control->directory))
 		return pstrdup(control->directory);
@@ -444,7 +471,15 @@ parse_extension_control_file(ExtensionControlFile *control,
 	if (version)
 		filename = get_extension_aux_control_filename(control, version);
 	else
-		filename = get_extension_control_filename(control->name);
+		filename = find_extension_control_filename(control);
+
+	if (!filename)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED), // XXX?
+				 errmsg("extension \"%s\" is not available", control->name),
+				 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+	}
 
 	if ((file = AllocateFile(filename, "r")) == NULL)
 	{
@@ -457,6 +492,7 @@ parse_extension_control_file(ExtensionControlFile *control,
 				return;
 			}
 
+			// TODO: this check is obsolete?
 			/* missing control file indicates extension is not installed */
 			ereport(ERROR,
 					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -2114,6 +2150,8 @@ RemoveExtensionById(Oid extId)
  * The system view pg_available_extensions provides a user interface to this
  * SRF, adding information about whether the extensions are installed in the
  * current DB.
+ *
+ * TODO
  */
 Datum
 pg_available_extensions(PG_FUNCTION_ARGS)
@@ -2194,6 +2232,8 @@ pg_available_extensions(PG_FUNCTION_ARGS)
  * The system view pg_available_extension_versions provides a user interface
  * to this SRF, adding information about which versions are installed in the
  * current DB.
+ *
+ * TODO
  */
 Datum
 pg_available_extension_versions(PG_FUNCTION_ARGS)
@@ -2366,6 +2406,8 @@ get_available_versions_for_extension(ExtensionControlFile *pcontrol,
  * directory.  That's not a bulletproof check, since the file might be
  * invalid, but this is only used for hints so it doesn't have to be 100%
  * right.
+ *
+ * TODO
  */
 bool
 extension_file_exists(const char *extensionName)
@@ -2445,6 +2487,8 @@ convert_requires_to_datum(List *requires)
 /*
  * This function reports the version update paths that exist for the
  * specified extension.
+ *
+ * TODO
  */
 Datum
 pg_extension_update_paths(PG_FUNCTION_ARGS)
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index c7aa789b51b..d348d30d9e4 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -81,8 +81,7 @@ static void incompatible_module_error(const char *libname,
 									  const Pg_magic_struct *module_magic_data) pg_attribute_noreturn();
 static char *expand_dynamic_library_name(const char *name);
 static void check_restricted_library_name(const char *name);
-static char *substitute_libpath_macro(const char *name);
-static char *find_in_dynamic_libpath(const char *basename);
+static char *substitute_path_macro(const char *str, const char *macro, const char *value);
 
 /* Magic structure that module needs to match to be accepted */
 static const Pg_magic_struct magic_data = PG_MODULE_MAGIC_DATA;
@@ -408,7 +407,7 @@ incompatible_module_error(const char *libname,
 /*
  * If name contains a slash, check if the file exists, if so return
  * the name.  Else (no slash) try to expand using search path (see
- * find_in_dynamic_libpath below); if that works, return the fully
+ * find_in_path below); if that works, return the fully
  * expanded file name.  If the previous failed, append DLSUFFIX and
  * try again.  If all fails, just return the original name.
  *
@@ -427,13 +426,13 @@ expand_dynamic_library_name(const char *name)
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(name);
+		full = find_in_path(name, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(name);
+		full = substitute_path_macro(name, "$libdir", pkglib_path);
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -443,14 +442,14 @@ expand_dynamic_library_name(const char *name)
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(new);
+		full = find_in_path(new, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		pfree(new);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(new);
+		full = substitute_path_macro(new, "$libdir", pkglib_path);
 		pfree(new);
 		if (pg_file_exists(full))
 			return full;
@@ -485,47 +484,56 @@ check_restricted_library_name(const char *name)
  * Result is always freshly palloc'd.
  */
 static char *
-substitute_libpath_macro(const char *name)
+substitute_path_macro(const char *str, const char *macro, const char *value)
 {
 	const char *sep_ptr;
 
-	Assert(name != NULL);
+	Assert(str != NULL);
+	Assert(macro[0] == '$');
 
-	/* Currently, we only recognize $libdir at the start of the string */
-	if (name[0] != '$')
-		return pstrdup(name);
+	/* Currently, we only recognize $macro at the start of the string */
+	if (str[0] != '$')
+		return pstrdup(str);
 
-	if ((sep_ptr = first_dir_separator(name)) == NULL)
-		sep_ptr = name + strlen(name);
+	if ((sep_ptr = first_dir_separator(str)) == NULL)
+		sep_ptr = str + strlen(str);
 
-	if (strlen("$libdir") != sep_ptr - name ||
-		strncmp(name, "$libdir", strlen("$libdir")) != 0)
+	if (strlen(macro) != sep_ptr - str ||
+		strncmp(str, macro, strlen(macro)) != 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_NAME),
-				 errmsg("invalid macro name in dynamic library path: %s",
-						name)));
+				 errmsg("invalid macro name in path: %s",
+						str)));
 
-	return psprintf("%s%s", pkglib_path, sep_ptr);
+	return psprintf("%s%s", value, sep_ptr);
 }
 
 
 /*
  * Search for a file called 'basename' in the colon-separated search
- * path Dynamic_library_path.  If the file is found, the full file name
+ * path given.  If the file is found, the full file name
  * is returned in freshly palloc'd memory.  If the file is not found,
  * return NULL.
+ *
+ * path_param is the name of the parameter that path came from, for error
+ * messages.
+ *
+ * macro and macro_val allow substituting a macro; see
+ * substitute_path_macro().
  */
-static char *
-find_in_dynamic_libpath(const char *basename)
+char *
+find_in_path(const char *basename, const char *path, const char *path_param,
+			 const char *macro, const char *macro_val)
 {
 	const char *p;
 	size_t		baselen;
 
 	Assert(basename != NULL);
 	Assert(first_dir_separator(basename) == NULL);
-	Assert(Dynamic_library_path != NULL);
+	Assert(path != NULL);
+	Assert(path_param != NULL);
 
-	p = Dynamic_library_path;
+	p = path;
 	if (strlen(p) == 0)
 		return NULL;
 
@@ -542,7 +550,7 @@ find_in_dynamic_libpath(const char *basename)
 		if (piece == p)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("zero-length component in parameter \"dynamic_library_path\"")));
+					 errmsg("zero-length component in parameter \"%s\"", path_param)));
 
 		if (piece == NULL)
 			len = strlen(p);
@@ -552,7 +560,7 @@ find_in_dynamic_libpath(const char *basename)
 		piece = palloc(len + 1);
 		strlcpy(piece, p, len + 1);
 
-		mangled = substitute_libpath_macro(piece);
+		mangled = substitute_path_macro(piece, macro, macro_val);
 		pfree(piece);
 
 		canonicalize_path(mangled);
@@ -561,13 +569,13 @@ find_in_dynamic_libpath(const char *basename)
 		if (!is_absolute_path(mangled))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("component in parameter \"dynamic_library_path\" is not an absolute path")));
+					 errmsg("component in parameter \"%s\" is not an absolute path", path_param)));
 
 		full = palloc(strlen(mangled) + 1 + baselen + 1);
 		sprintf(full, "%s/%s", mangled, basename);
 		pfree(mangled);
 
-		elog(DEBUG3, "find_in_dynamic_libpath: trying \"%s\"", full);
+		elog(DEBUG3, "%s: trying \"%s\"", __func__, full);
 
 		if (pg_file_exists(full))
 			return full;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 8a67f01200c..5a00b99daba 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -39,6 +39,7 @@
 #include "catalog/namespace.h"
 #include "catalog/storage.h"
 #include "commands/async.h"
+#include "commands/extension.h"
 #include "commands/event_trigger.h"
 #include "commands/tablespace.h"
 #include "commands/trigger.h"
@@ -4233,6 +4234,17 @@ struct config_string ConfigureNamesString[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"extension_control_path", PGC_SUSET, CLIENT_CONN_OTHER,
+			gettext_noop("Sets the path for extension control files."),
+			gettext_noop("TODO"),
+			GUC_SUPERUSER_ONLY
+		},
+		&Extension_control_path,
+		"$system",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"krb_server_keyfile", PGC_SIGHUP, CONN_AUTH_AUTH,
 			gettext_noop("Sets the location of the Kerberos server key file."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 39a3ac23127..518c4f40719 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -772,6 +772,7 @@
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_control_path = '$system'
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/commands/extension.h b/src/include/commands/extension.h
index c6f3f867eb7..fe8a97570ea 100644
--- a/src/include/commands/extension.h
+++ b/src/include/commands/extension.h
@@ -17,6 +17,8 @@
 #include "catalog/objectaddress.h"
 #include "parser/parse_node.h"
 
+/* GUC */
+extern PGDLLIMPORT char *Extension_control_path;
 
 /*
  * creating_extension is only true while running a CREATE EXTENSION or ALTER
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index 1e3795de4a8..2930b61cee5 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -740,6 +740,8 @@ extern bool CheckFunctionValidatorAccess(Oid validatorOid, Oid functionOid);
  */
 extern PGDLLIMPORT char *Dynamic_library_path;
 
+extern char *find_in_path(const char *basename, const char *path, const char *path_param,
+						  const char *macro, const char *macro_val);
 extern void *load_external_function(const char *filename, const char *funcname,
 									bool signalNotFound, void **filehandle);
 extern void *lookup_external_function(void *filehandle, const char *funcname);

base-commit: e7a9496de90657e2161f68b3a5a9b2d9b0b7bb07
-- 
2.47.0

From fdf1bd8abbb9aaff3747c57d653ef19f8be31fe8 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 5 Dec 2024 11:49:05 +0100
Subject: [PATCH v1] extension_control_path

The new GUC extension_control_path specifies a path to look for
extension control files.  The default value is $system, which looks in
the compiled-in location, as before.

The path search uses the same code and works in the same way as
dynamic_library_path.

Discussion: https://www.postgresql.org/message-id/flat/E7C7BFFB-8857-48D4-A71F-88B359FADCFD@justatheory.com

TODO: Some utility functions such as pg_available_extensions() are not
adjusted to be aware of the path yet.
---
 doc/src/sgml/config.sgml                      | 68 +++++++++++++++
 doc/src/sgml/extend.sgml                      | 19 ++--
 doc/src/sgml/ref/create_extension.sgml        |  6 +-
 src/Makefile.global.in                        | 19 ++--
 src/backend/commands/extension.c              | 87 ++++++++++++++-----
 src/backend/utils/fmgr/dfmgr.c                | 76 ++++++++++------
 src/backend/utils/misc/guc_tables.c           | 13 +++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 src/include/commands/extension.h              |  2 +
 src/include/fmgr.h                            |  2 +
 10 files changed, 230 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index e0c8325a39c..94ef9fb44d7 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10476,6 +10476,74 @@ <title>Other Defaults</title>
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-extension-control-path" xreflabel="extension_control_path">
+      <term><varname>extension_control_path</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_control_path</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        A path to search for extensions, specifically extension control files
+        (<filename><replaceable>name</replaceable>.control</filename>).  The
+        remaining extension script and secondary control files are then loaded
+        from the same directory where the primary control file was found.
+        See <xref linkend="extend-extensions-files"/> for details.
+       </para>
+
+       <para>
+        The value for <varname>extension_control_path</varname> must be a
+        list of absolute directory paths separated by colons (or semi-colons
+        on Windows).  If a list element starts
+        with the special string <literal>$system</literal>, the
+        compiled-in <productname>PostgreSQL</productname> extension
+        directory is substituted for <literal>$system</literal>; this
+        is where the extensions provided by the standard
+        <productname>PostgreSQL</productname> distribution are installed.
+        (Use <literal>pg_config --sharedir</literal> to find out the name of
+        this directory.) For example:
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:/home/my_project/share/extension:$system'
+</programlisting>
+        or, in a Windows environment:
+<programlisting>
+extension_control_path = 'C:\tools\postgresql\extension;H:\my_project\share\extension;$system'
+</programlisting>
+        Note that the path elements should typically end in
+        <literal>extension</literal> if the normal installation layouts are
+        followed.  (The value for <literal>$system</literal> already includes
+        the <literal>extension</literal> suffix.)
+       </para>
+
+       <para>
+        The default value for this parameter is
+        <literal>'$system'</literal>. If the value is set to an empty
+        string, the default <literal>'$system'</literal> is also assumed.
+       </para>
+
+       <para>
+        This parameter can be changed at run time by superusers and users
+        with the appropriate <literal>SET</literal> privilege, but a
+        setting done that way will only persist until the end of the
+        client connection, so this method should be reserved for
+        development purposes. The recommended way to set this parameter
+        is in the <filename>postgresql.conf</filename> configuration
+        file.
+       </para>
+
+       <para>
+        Note that if you set this parameter to be able to load extensions from
+        nonstandard locations, you will most likely also need to set <xref
+        linkend="guc-dynamic-library-path"/> to a correspondent location, for
+        example,
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:$system'
+dynamic_library_path = '/usr/local/lib/postgresql:$libdir'
+</programlisting>
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-gin-fuzzy-search-limit" xreflabel="gin_fuzzy_search_limit">
       <term><varname>gin_fuzzy_search_limit</varname> (<type>integer</type>)
       <indexterm>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 218940ee5ce..0a20d06abfb 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -649,6 +649,11 @@ <title>Extension Files</title>
      control file can specify a different directory for the script file(s).
     </para>
 
+    <para>
+     Additional locations for extension control files can be configured using
+     the parameter <xref linkend="guc-extension-control-path"/>.
+    </para>
+
     <para>
      The file format for an extension control file is the same as for the
      <filename>postgresql.conf</filename> file, namely a list of
@@ -669,9 +674,9 @@ <title>Extension Files</title>
        <para>
         The directory containing the extension's <acronym>SQL</acronym> script
         file(s).  Unless an absolute path is given, the name is relative to
-        the installation's <literal>SHAREDIR</literal> directory.  The
-        default behavior is equivalent to specifying
-        <literal>directory = 'extension'</literal>.
+        the installation's <literal>SHAREDIR</literal> directory.  By default,
+        the script files are looked for in the same directory where the
+        control file was found.
        </para>
       </listitem>
      </varlistentry>
@@ -719,8 +724,8 @@ <title>Extension Files</title>
        <para>
         The value of this parameter will be substituted for each occurrence
         of <literal>MODULE_PATHNAME</literal> in the script file(s).  If it is not
-        set, no substitution is made.  Typically, this is set to
-        <literal>$libdir/<replaceable>shared_library_name</replaceable></literal> and
+        set, no substitution is made.  Typically, this is set to just
+        <literal><replaceable>shared_library_name</replaceable></literal> and
         then <literal>MODULE_PATHNAME</literal> is used in <command>CREATE
         FUNCTION</command> commands for C-language functions, so that the script
         files do not need to hard-wire the name of the shared library.
@@ -1808,6 +1813,10 @@ <title>Extension Building Infrastructure</title>
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
+    You can also select a separate installation directory for your extension
+    by setting the <literal>make</literal> variable <varname>prefix</varname>
+    on the <literal>make</literal> command line.  (But this will then require
+    additional setup to get the server to find the extension there.)
    </para>
 
    <para>
diff --git a/doc/src/sgml/ref/create_extension.sgml b/doc/src/sgml/ref/create_extension.sgml
index ca2b80d669c..713abd9c494 100644
--- a/doc/src/sgml/ref/create_extension.sgml
+++ b/doc/src/sgml/ref/create_extension.sgml
@@ -90,8 +90,10 @@ <title>Parameters</title>
        <para>
         The name of the extension to be
         installed. <productname>PostgreSQL</productname> will create the
-        extension using details from the file
-        <literal>SHAREDIR/extension/</literal><replaceable class="parameter">extension_name</replaceable><literal>.control</literal>.
+        extension using details from the file <filename><replaceable
+        class="parameter">extension_name</replaceable>.control</filename>,
+        found via the server's extension control path (set by <xref
+        linkend="guc-extension-control-path"/>.)
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index eac3d001211..7c1bffbea07 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -87,9 +87,19 @@ endif # not PGXS
 #
 # In a PGXS build, we cannot use the values inserted into Makefile.global
 # by configure, since the installation tree may have been relocated.
-# Instead get the path values from pg_config.
+# Instead get the path values from pg_config.  But users can specify
+# prefix explicitly, if they want to select their own installation
+# location.
 
-ifndef PGXS
+ifdef PGXS
+# Extension makefiles should set PG_CONFIG, but older ones might not
+ifndef PG_CONFIG
+PG_CONFIG = pg_config
+endif
+endif
+
+# This means: if ((not PGXS) or prefix)
+ifneq (,$(if $(PGXS),,1)$(prefix))
 
 # Note that prefix, exec_prefix, and datarootdir aren't defined in a PGXS build;
 # makefiles may only use the derived variables such as bindir.
@@ -147,11 +157,6 @@ localedir := @localedir@
 
 else # PGXS case
 
-# Extension makefiles should set PG_CONFIG, but older ones might not
-ifndef PG_CONFIG
-PG_CONFIG = pg_config
-endif
-
 bindir := $(shell $(PG_CONFIG) --bindir)
 datadir := $(shell $(PG_CONFIG) --sharedir)
 sysconfdir := $(shell $(PG_CONFIG) --sysconfdir)
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index af6bd8ff426..9115a48d25f 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -69,6 +69,9 @@
 #include "utils/varlena.h"
 
 
+/* GUC */
+char	   *Extension_control_path;
+
 /* Globally visible state variables */
 bool		creating_extension = false;
 Oid			CurrentExtensionObject = InvalidOid;
@@ -79,6 +82,7 @@ Oid			CurrentExtensionObject = InvalidOid;
 typedef struct ExtensionControlFile
 {
 	char	   *name;			/* name of the extension */
+	char	   *control_dir;	/* directory where control file was found */
 	char	   *directory;		/* directory for script files */
 	char	   *default_version;	/* default install target version, if any */
 	char	   *module_pathname;	/* string to substitute for
@@ -328,6 +332,12 @@ is_extension_script_filename(const char *filename)
 	return (extension != NULL) && (strcmp(extension, ".sql") == 0);
 }
 
+/*
+ * TODO
+ *
+ * This is now only for finding/listing available extensions.  Rewrite to use
+ * path.  See further TODOs below.
+ */
 static char *
 get_extension_control_directory(void)
 {
@@ -341,16 +351,45 @@ get_extension_control_directory(void)
 	return result;
 }
 
+/*
+ * Find control file for extension with name in control->name, looking in the
+ * path.  Return the full file name, or NULL if not found.  If found, the
+ * directory is recorded in control->control_dir.
+ */
 static char *
-get_extension_control_filename(const char *extname)
+find_extension_control_filename(ExtensionControlFile *control)
 {
 	char		sharepath[MAXPGPATH];
+	char	   *system_dir;
+	char	   *basename;
+	char	   *ecp;
 	char	   *result;
 
+	Assert(control->name);
+
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
-			 sharepath, extname);
+	system_dir = psprintf("%s/extension", sharepath);
+
+	basename = psprintf("%s.control", control->name);
+
+	/*
+	 * find_in_path() does nothing if the path value is empty.  This is the
+	 * historical behavior for dynamic_library_path, but it makes no sense for
+	 * extensions.  So in that case, substitute a default value.
+	 */
+	ecp = Extension_control_path;
+	if (strlen(ecp) == 0)
+		ecp = "$system";
+	result = find_in_path(basename, Extension_control_path, "extension_control_path", "$system", system_dir);
+
+	if (result)
+	{
+		const char *p;
+
+		p = strrchr(result, '/');
+		Assert(p);
+		control->control_dir = pnstrdup(result, p - result);
+	}
 
 	return result;
 }
@@ -366,7 +405,7 @@ get_extension_script_directory(ExtensionControlFile *control)
 	 * installation's share directory.
 	 */
 	if (!control->directory)
-		return get_extension_control_directory();
+		return pstrdup(control->control_dir);
 
 	if (is_absolute_path(control->directory))
 		return pstrdup(control->directory);
@@ -444,27 +483,25 @@ parse_extension_control_file(ExtensionControlFile *control,
 	if (version)
 		filename = get_extension_aux_control_filename(control, version);
 	else
-		filename = get_extension_control_filename(control->name);
+		filename = find_extension_control_filename(control);
+
+	if (!filename)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("extension \"%s\" is not available", control->name),
+				 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+	}
 
 	if ((file = AllocateFile(filename, "r")) == NULL)
 	{
-		if (errno == ENOENT)
+		/* no complaint for missing auxiliary file */
+		if (errno == ENOENT && version)
 		{
-			/* no complaint for missing auxiliary file */
-			if (version)
-			{
-				pfree(filename);
-				return;
-			}
-
-			/* missing control file indicates extension is not installed */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("extension \"%s\" is not available", control->name),
-					 errdetail("Could not open extension control file \"%s\": %m.",
-							   filename),
-					 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+			pfree(filename);
+			return;
 		}
+
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not open extension control file \"%s\": %m",
@@ -2114,6 +2151,8 @@ RemoveExtensionById(Oid extId)
  * The system view pg_available_extensions provides a user interface to this
  * SRF, adding information about whether the extensions are installed in the
  * current DB.
+ *
+ * TODO: make aware of path
  */
 Datum
 pg_available_extensions(PG_FUNCTION_ARGS)
@@ -2194,6 +2233,8 @@ pg_available_extensions(PG_FUNCTION_ARGS)
  * The system view pg_available_extension_versions provides a user interface
  * to this SRF, adding information about which versions are installed in the
  * current DB.
+ *
+ * TODO: make aware of path
  */
 Datum
 pg_available_extension_versions(PG_FUNCTION_ARGS)
@@ -2366,6 +2407,8 @@ get_available_versions_for_extension(ExtensionControlFile *pcontrol,
  * directory.  That's not a bulletproof check, since the file might be
  * invalid, but this is only used for hints so it doesn't have to be 100%
  * right.
+ *
+ * TODO: make aware of path
  */
 bool
 extension_file_exists(const char *extensionName)
@@ -2445,6 +2488,8 @@ convert_requires_to_datum(List *requires)
 /*
  * This function reports the version update paths that exist for the
  * specified extension.
+ *
+ * TODO: make aware of path
  */
 Datum
 pg_extension_update_paths(PG_FUNCTION_ARGS)
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 8e81ecc7491..2372d0944c0 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -71,8 +71,7 @@ static void incompatible_module_error(const char *libname,
 									  const Pg_magic_struct *module_magic_data) pg_attribute_noreturn();
 static char *expand_dynamic_library_name(const char *name);
 static void check_restricted_library_name(const char *name);
-static char *substitute_libpath_macro(const char *name);
-static char *find_in_dynamic_libpath(const char *basename);
+static char *substitute_path_macro(const char *str, const char *macro, const char *value);
 
 /* Magic structure that module needs to match to be accepted */
 static const Pg_magic_struct magic_data = PG_MODULE_MAGIC_DATA;
@@ -398,7 +397,7 @@ incompatible_module_error(const char *libname,
 /*
  * If name contains a slash, check if the file exists, if so return
  * the name.  Else (no slash) try to expand using search path (see
- * find_in_dynamic_libpath below); if that works, return the fully
+ * find_in_path below); if that works, return the fully
  * expanded file name.  If the previous failed, append DLSUFFIX and
  * try again.  If all fails, just return the original name.
  *
@@ -413,17 +412,25 @@ expand_dynamic_library_name(const char *name)
 
 	Assert(name);
 
+	/*
+	 * If the value starts with "$libdir/", strip that.  This is because many
+	 * extensions have hardcoded '$libdir/foo' as their library name, which
+	 * prevents using the path.
+	 */
+	if (strncmp(name, "$libdir/", 8) == 0)
+		name += 8;
+
 	have_slash = (first_dir_separator(name) != NULL);
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(name);
+		full = find_in_path(name, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(name);
+		full = substitute_path_macro(name, "$libdir", pkglib_path);
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -433,14 +440,14 @@ expand_dynamic_library_name(const char *name)
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(new);
+		full = find_in_path(new, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		pfree(new);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(new);
+		full = substitute_path_macro(new, "$libdir", pkglib_path);
 		pfree(new);
 		if (pg_file_exists(full))
 			return full;
@@ -475,47 +482,60 @@ check_restricted_library_name(const char *name)
  * Result is always freshly palloc'd.
  */
 static char *
-substitute_libpath_macro(const char *name)
+substitute_path_macro(const char *str, const char *macro, const char *value)
 {
 	const char *sep_ptr;
 
-	Assert(name != NULL);
+	Assert(str != NULL);
+	Assert(macro[0] == '$');
 
-	/* Currently, we only recognize $libdir at the start of the string */
-	if (name[0] != '$')
-		return pstrdup(name);
+	/* Currently, we only recognize $macro at the start of the string */
+	if (str[0] != '$')
+		return pstrdup(str);
 
-	if ((sep_ptr = first_dir_separator(name)) == NULL)
-		sep_ptr = name + strlen(name);
+	if ((sep_ptr = first_dir_separator(str)) == NULL)
+		sep_ptr = str + strlen(str);
 
-	if (strlen("$libdir") != sep_ptr - name ||
-		strncmp(name, "$libdir", strlen("$libdir")) != 0)
+	if (strlen(macro) != sep_ptr - str ||
+		strncmp(str, macro, strlen(macro)) != 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_NAME),
-				 errmsg("invalid macro name in dynamic library path: %s",
-						name)));
+				 errmsg("invalid macro name in path: %s",
+						str)));
 
-	return psprintf("%s%s", pkglib_path, sep_ptr);
+	return psprintf("%s%s", value, sep_ptr);
 }
 
 
 /*
  * Search for a file called 'basename' in the colon-separated search
- * path Dynamic_library_path.  If the file is found, the full file name
+ * path given.  If the file is found, the full file name
  * is returned in freshly palloc'd memory.  If the file is not found,
  * return NULL.
+ *
+ * path_param is the name of the parameter that path came from, for error
+ * messages.
+ *
+ * macro and macro_val allow substituting a macro; see
+ * substitute_path_macro().
  */
-static char *
-find_in_dynamic_libpath(const char *basename)
+char *
+find_in_path(const char *basename, const char *path, const char *path_param,
+			 const char *macro, const char *macro_val)
 {
 	const char *p;
 	size_t		baselen;
 
 	Assert(basename != NULL);
 	Assert(first_dir_separator(basename) == NULL);
-	Assert(Dynamic_library_path != NULL);
+	Assert(path != NULL);
+	Assert(path_param != NULL);
+
+	p = path;
 
-	p = Dynamic_library_path;
+	/*
+	 * If the path variable is empty, don't do a path search.
+	 */
 	if (strlen(p) == 0)
 		return NULL;
 
@@ -532,7 +552,7 @@ find_in_dynamic_libpath(const char *basename)
 		if (piece == p)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("zero-length component in parameter \"dynamic_library_path\"")));
+					 errmsg("zero-length component in parameter \"%s\"", path_param)));
 
 		if (piece == NULL)
 			len = strlen(p);
@@ -542,7 +562,7 @@ find_in_dynamic_libpath(const char *basename)
 		piece = palloc(len + 1);
 		strlcpy(piece, p, len + 1);
 
-		mangled = substitute_libpath_macro(piece);
+		mangled = substitute_path_macro(piece, macro, macro_val);
 		pfree(piece);
 
 		canonicalize_path(mangled);
@@ -551,13 +571,13 @@ find_in_dynamic_libpath(const char *basename)
 		if (!is_absolute_path(mangled))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("component in parameter \"dynamic_library_path\" is not an absolute path")));
+					 errmsg("component in parameter \"%s\" is not an absolute path", path_param)));
 
 		full = palloc(strlen(mangled) + 1 + baselen + 1);
 		sprintf(full, "%s/%s", mangled, basename);
 		pfree(mangled);
 
-		elog(DEBUG3, "find_in_dynamic_libpath: trying \"%s\"", full);
+		elog(DEBUG3, "%s: trying \"%s\"", __func__, full);
 
 		if (pg_file_exists(full))
 			return full;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 8cf1afbad20..5a280f62b77 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -39,6 +39,7 @@
 #include "catalog/namespace.h"
 #include "catalog/storage.h"
 #include "commands/async.h"
+#include "commands/extension.h"
 #include "commands/event_trigger.h"
 #include "commands/tablespace.h"
 #include "commands/trigger.h"
@@ -4252,6 +4253,18 @@ struct config_string ConfigureNamesString[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"extension_control_path", PGC_SUSET, CLIENT_CONN_OTHER,
+			gettext_noop("Sets the path for extension control files."),
+			gettext_noop("The remaining extension script and secondary control files are then loaded "
+						 "from the same directory where the primary control file was found."),
+			GUC_SUPERUSER_ONLY
+		},
+		&Extension_control_path,
+		"$system",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"krb_server_keyfile", PGC_SIGHUP, CONN_AUTH_AUTH,
 			gettext_noop("Sets the location of the Kerberos server key file."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index a2ac7575ca7..83e72b33fb7 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -774,6 +774,7 @@
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_control_path = '$system'
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/commands/extension.h b/src/include/commands/extension.h
index c6f3f867eb7..fe8a97570ea 100644
--- a/src/include/commands/extension.h
+++ b/src/include/commands/extension.h
@@ -17,6 +17,8 @@
 #include "catalog/objectaddress.h"
 #include "parser/parse_node.h"
 
+/* GUC */
+extern PGDLLIMPORT char *Extension_control_path;
 
 /*
  * creating_extension is only true while running a CREATE EXTENSION or ALTER
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index 1e3795de4a8..2930b61cee5 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -740,6 +740,8 @@ extern bool CheckFunctionValidatorAccess(Oid validatorOid, Oid functionOid);
  */
 extern PGDLLIMPORT char *Dynamic_library_path;
 
+extern char *find_in_path(const char *basename, const char *path, const char *path_param,
+						  const char *macro, const char *macro_val);
 extern void *load_external_function(const char *filename, const char *funcname,
 									bool signalNotFound, void **filehandle);
 extern void *lookup_external_function(void *filehandle, const char *funcname);

base-commit: 71cb352904c1833fe067d6f191269710fe2ca06f
-- 
2.47.1

From 092f300f31540fff85b116c25800182caec2a963 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 5 Dec 2024 11:49:05 +0100
Subject: [PATCH v2] extension_control_path

The new GUC extension_control_path specifies a path to look for
extension control files.  The default value is $system, which looks in
the compiled-in location, as before.

The path search uses the same code and works in the same way as
dynamic_library_path.

Discussion: https://www.postgresql.org/message-id/flat/E7C7BFFB-8857-48D4-A71F-88B359FADCFD@justatheory.com
---
 doc/src/sgml/config.sgml                      |  68 ++++
 doc/src/sgml/extend.sgml                      |  19 +-
 doc/src/sgml/ref/create_extension.sgml        |   6 +-
 src/Makefile.global.in                        |  19 +-
 src/backend/commands/extension.c              | 353 +++++++++++-------
 src/backend/utils/fmgr/dfmgr.c                |  76 ++--
 src/backend/utils/misc/guc_tables.c           |  13 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/commands/extension.h              |   2 +
 src/include/fmgr.h                            |   2 +
 src/test/modules/test_extensions/Makefile     |   1 +
 src/test/modules/test_extensions/meson.build  |   5 +
 .../t/001_extension_control_path.pl           |  54 +++
 13 files changed, 445 insertions(+), 174 deletions(-)
 create mode 100644 src/test/modules/test_extensions/t/001_extension_control_path.pl

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index a8354576108..cb67387243f 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10698,6 +10698,74 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-extension-control-path" xreflabel="extension_control_path">
+      <term><varname>extension_control_path</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_control_path</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        A path to search for extensions, specifically extension control files
+        (<filename><replaceable>name</replaceable>.control</filename>).  The
+        remaining extension script and secondary control files are then loaded
+        from the same directory where the primary control file was found.
+        See <xref linkend="extend-extensions-files"/> for details.
+       </para>
+
+       <para>
+        The value for <varname>extension_control_path</varname> must be a
+        list of absolute directory paths separated by colons (or semi-colons
+        on Windows).  If a list element starts
+        with the special string <literal>$system</literal>, the
+        compiled-in <productname>PostgreSQL</productname> extension
+        directory is substituted for <literal>$system</literal>; this
+        is where the extensions provided by the standard
+        <productname>PostgreSQL</productname> distribution are installed.
+        (Use <literal>pg_config --sharedir</literal> to find out the name of
+        this directory.) For example:
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:/home/my_project/share/extension:$system'
+</programlisting>
+        or, in a Windows environment:
+<programlisting>
+extension_control_path = 'C:\tools\postgresql\extension;H:\my_project\share\extension;$system'
+</programlisting>
+        Note that the path elements should typically end in
+        <literal>extension</literal> if the normal installation layouts are
+        followed.  (The value for <literal>$system</literal> already includes
+        the <literal>extension</literal> suffix.)
+       </para>
+
+       <para>
+        The default value for this parameter is
+        <literal>'$system'</literal>. If the value is set to an empty
+        string, the default <literal>'$system'</literal> is also assumed.
+       </para>
+
+       <para>
+        This parameter can be changed at run time by superusers and users
+        with the appropriate <literal>SET</literal> privilege, but a
+        setting done that way will only persist until the end of the
+        client connection, so this method should be reserved for
+        development purposes. The recommended way to set this parameter
+        is in the <filename>postgresql.conf</filename> configuration
+        file.
+       </para>
+
+       <para>
+        Note that if you set this parameter to be able to load extensions from
+        nonstandard locations, you will most likely also need to set <xref
+        linkend="guc-dynamic-library-path"/> to a correspondent location, for
+        example,
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:$system'
+dynamic_library_path = '/usr/local/lib/postgresql:$libdir'
+</programlisting>
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-gin-fuzzy-search-limit" xreflabel="gin_fuzzy_search_limit">
       <term><varname>gin_fuzzy_search_limit</varname> (<type>integer</type>)
       <indexterm>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index ba492ca27c0..64f8e133cae 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -649,6 +649,11 @@ RETURNS anycompatible AS ...
      control file can specify a different directory for the script file(s).
     </para>
 
+    <para>
+     Additional locations for extension control files can be configured using
+     the parameter <xref linkend="guc-extension-control-path"/>.
+    </para>
+
     <para>
      The file format for an extension control file is the same as for the
      <filename>postgresql.conf</filename> file, namely a list of
@@ -669,9 +674,9 @@ RETURNS anycompatible AS ...
        <para>
         The directory containing the extension's <acronym>SQL</acronym> script
         file(s).  Unless an absolute path is given, the name is relative to
-        the installation's <literal>SHAREDIR</literal> directory.  The
-        default behavior is equivalent to specifying
-        <literal>directory = 'extension'</literal>.
+        the installation's <literal>SHAREDIR</literal> directory.  By default,
+        the script files are looked for in the same directory where the
+        control file was found.
        </para>
       </listitem>
      </varlistentry>
@@ -719,8 +724,8 @@ RETURNS anycompatible AS ...
        <para>
         The value of this parameter will be substituted for each occurrence
         of <literal>MODULE_PATHNAME</literal> in the script file(s).  If it is not
-        set, no substitution is made.  Typically, this is set to
-        <literal>$libdir/<replaceable>shared_library_name</replaceable></literal> and
+        set, no substitution is made.  Typically, this is set to just
+        <literal><replaceable>shared_library_name</replaceable></literal> and
         then <literal>MODULE_PATHNAME</literal> is used in <command>CREATE
         FUNCTION</command> commands for C-language functions, so that the script
         files do not need to hard-wire the name of the shared library.
@@ -1804,6 +1809,10 @@ include $(PGXS)
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
+    You can also select a separate installation directory for your extension
+    by setting the <literal>make</literal> variable <varname>prefix</varname>
+    on the <literal>make</literal> command line.  (But this will then require
+    additional setup to get the server to find the extension there.)
    </para>
 
    <para>
diff --git a/doc/src/sgml/ref/create_extension.sgml b/doc/src/sgml/ref/create_extension.sgml
index ca2b80d669c..713abd9c494 100644
--- a/doc/src/sgml/ref/create_extension.sgml
+++ b/doc/src/sgml/ref/create_extension.sgml
@@ -90,8 +90,10 @@ CREATE EXTENSION [ IF NOT EXISTS ] <replaceable class="parameter">extension_name
        <para>
         The name of the extension to be
         installed. <productname>PostgreSQL</productname> will create the
-        extension using details from the file
-        <literal>SHAREDIR/extension/</literal><replaceable class="parameter">extension_name</replaceable><literal>.control</literal>.
+        extension using details from the file <filename><replaceable
+        class="parameter">extension_name</replaceable>.control</filename>,
+        found via the server's extension control path (set by <xref
+        linkend="guc-extension-control-path"/>.)
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index 3b620bac5ac..8fe9d61e82a 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -87,9 +87,19 @@ endif # not PGXS
 #
 # In a PGXS build, we cannot use the values inserted into Makefile.global
 # by configure, since the installation tree may have been relocated.
-# Instead get the path values from pg_config.
+# Instead get the path values from pg_config.  But users can specify
+# prefix explicitly, if they want to select their own installation
+# location.
 
-ifndef PGXS
+ifdef PGXS
+# Extension makefiles should set PG_CONFIG, but older ones might not
+ifndef PG_CONFIG
+PG_CONFIG = pg_config
+endif
+endif
+
+# This means: if ((not PGXS) or prefix)
+ifneq (,$(if $(PGXS),,1)$(prefix))
 
 # Note that prefix, exec_prefix, and datarootdir aren't defined in a PGXS build;
 # makefiles may only use the derived variables such as bindir.
@@ -147,11 +157,6 @@ localedir := @localedir@
 
 else # PGXS case
 
-# Extension makefiles should set PG_CONFIG, but older ones might not
-ifndef PG_CONFIG
-PG_CONFIG = pg_config
-endif
-
 bindir := $(shell $(PG_CONFIG) --bindir)
 datadir := $(shell $(PG_CONFIG) --sharedir)
 sysconfdir := $(shell $(PG_CONFIG) --sysconfdir)
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index d9bb4ce5f1e..362fa4a647a 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -51,6 +51,7 @@
 #include "commands/defrem.h"
 #include "commands/extension.h"
 #include "commands/schemacmds.h"
+#include "nodes/pg_list.h"
 #include "funcapi.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
@@ -69,6 +70,9 @@
 #include "utils/varlena.h"
 
 
+/* GUC */
+char	   *Extension_control_path;
+
 /* Globally visible state variables */
 bool		creating_extension = false;
 Oid			CurrentExtensionObject = InvalidOid;
@@ -79,6 +83,7 @@ Oid			CurrentExtensionObject = InvalidOid;
 typedef struct ExtensionControlFile
 {
 	char	   *name;			/* name of the extension */
+	char	   *control_dir;	/* directory where control file was found */
 	char	   *directory;		/* directory for script files */
 	char	   *default_version;	/* default install target version, if any */
 	char	   *module_pathname;	/* string to substitute for
@@ -328,29 +333,93 @@ is_extension_script_filename(const char *filename)
 	return (extension != NULL) && (strcmp(extension, ".sql") == 0);
 }
 
-static char *
-get_extension_control_directory(void)
+/*
+ * Return a list of directories declared on extension_control_path GUC.
+ */
+static List *
+get_extension_control_directories(void)
 {
 	char		sharepath[MAXPGPATH];
-	char	   *result;
+	char	   *system_dir;
+	char	   *ecp;
+	char	   *token;
+	char	   *path;
+	List	   *paths = NIL;
 
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension", sharepath);
 
-	return result;
+	system_dir = psprintf("%s/extension", sharepath);
+	ecp = system_dir;
+
+	if (strlen(Extension_control_path) == 0)
+	{
+		paths = lappend(paths, ecp);
+	}
+	else
+	{
+		/* Duplicate the string so we can modify it */
+		ecp = pstrdup(Extension_control_path);
+
+		token = strtok(ecp, ":");
+		while (token != NULL)
+		{
+			/* Duplicate location to store in paths */
+			if (strcmp(token, "$system") == 0)
+				path = pstrdup(system_dir);
+			else
+				path = pstrdup(token);
+
+			paths = lappend(paths, path);
+
+			token = strtok(NULL, ":");
+		}
+
+		pfree(system_dir);
+		pfree(ecp);
+	}
+
+	return paths;
 }
 
+/*
+ * Find control file for extension with name in control->name, looking in the
+ * path.  Return the full file name, or NULL if not found.  If found, the
+ * directory is recorded in control->control_dir.
+ */
 static char *
-get_extension_control_filename(const char *extname)
+find_extension_control_filename(ExtensionControlFile *control)
 {
 	char		sharepath[MAXPGPATH];
+	char	   *system_dir;
+	char	   *basename;
+	char	   *ecp;
 	char	   *result;
 
+	Assert(control->name);
+
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
-			 sharepath, extname);
+	system_dir = psprintf("%s/extension", sharepath);
+
+	basename = psprintf("%s.control", control->name);
+
+	/*
+	 * find_in_path() does nothing if the path value is empty.  This is the
+	 * historical behavior for dynamic_library_path, but it makes no sense for
+	 * extensions.  So in that case, substitute a default value.
+	 */
+	ecp = Extension_control_path;
+	if (strlen(ecp) == 0)
+		ecp = "$system";
+	result = find_in_path(basename, Extension_control_path, "extension_control_path", "$system", system_dir);
+
+	if (result)
+	{
+		const char *p;
+
+		p = strrchr(result, '/');
+		Assert(p);
+		control->control_dir = pnstrdup(result, p - result);
+	}
 
 	return result;
 }
@@ -366,7 +435,7 @@ get_extension_script_directory(ExtensionControlFile *control)
 	 * installation's share directory.
 	 */
 	if (!control->directory)
-		return get_extension_control_directory();
+		return pstrdup(control->control_dir);
 
 	if (is_absolute_path(control->directory))
 		return pstrdup(control->directory);
@@ -444,27 +513,25 @@ parse_extension_control_file(ExtensionControlFile *control,
 	if (version)
 		filename = get_extension_aux_control_filename(control, version);
 	else
-		filename = get_extension_control_filename(control->name);
+		filename = find_extension_control_filename(control);
+
+	if (!filename)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("extension \"%s\" is not available", control->name),
+				 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+	}
 
 	if ((file = AllocateFile(filename, "r")) == NULL)
 	{
-		if (errno == ENOENT)
+		/* no complaint for missing auxiliary file */
+		if (errno == ENOENT && version)
 		{
-			/* no complaint for missing auxiliary file */
-			if (version)
-			{
-				pfree(filename);
-				return;
-			}
-
-			/* missing control file indicates extension is not installed */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("extension \"%s\" is not available", control->name),
-					 errdetail("Could not open extension control file \"%s\": %m.",
-							   filename),
-					 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+			pfree(filename);
+			return;
 		}
+
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not open extension control file \"%s\": %m",
@@ -2121,68 +2188,75 @@ Datum
 pg_available_extensions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
 	DIR		   *dir;
 	struct dirent *de;
+	List	   *locations;
+	ListCell   *cell;
 
 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();
 
-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach(cell, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
-			Datum		values[3];
-			bool		nulls[3];
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;
+				Datum		values[3];
+				bool		nulls[3];
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			control = read_extension_control_file(extname);
+				control = read_extension_control_file(extname);
 
-			memset(values, 0, sizeof(values));
-			memset(nulls, 0, sizeof(nulls));
+				memset(values, 0, sizeof(values));
+				memset(nulls, 0, sizeof(nulls));
 
-			/* name */
-			values[0] = DirectFunctionCall1(namein,
-											CStringGetDatum(control->name));
-			/* default_version */
-			if (control->default_version == NULL)
-				nulls[1] = true;
-			else
-				values[1] = CStringGetTextDatum(control->default_version);
-			/* comment */
-			if (control->comment == NULL)
-				nulls[2] = true;
-			else
-				values[2] = CStringGetTextDatum(control->comment);
+				/* name */
+				values[0] = DirectFunctionCall1(namein,
+												CStringGetDatum(control->name));
+				/* default_version */
+				if (control->default_version == NULL)
+					nulls[1] = true;
+				else
+					values[1] = CStringGetTextDatum(control->default_version);
+				/* comment */
+				if (control->comment == NULL)
+					nulls[2] = true;
+				else
+					values[2] = CStringGetTextDatum(control->comment);
 
-			tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
-								 values, nulls);
-		}
+				tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
+									 values, nulls);
+			}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}
 
 	return (Datum) 0;
@@ -2201,51 +2275,57 @@ Datum
 pg_available_extension_versions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
+	List	   *locations;
+	ListCell   *cell;
 	DIR		   *dir;
 	struct dirent *de;
 
 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
-
-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
+	locations = get_extension_control_directories();
+	foreach(cell, locations)
 	{
-		/* do nothing */
-	}
-	else
-	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
+		{
+			/* do nothing */
+		}
+		else
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			/* read the control file */
-			control = read_extension_control_file(extname);
+				/* read the control file */
+				control = read_extension_control_file(extname);
 
-			/* scan extension's script directory for install scripts */
-			get_available_versions_for_extension(control, rsinfo->setResult,
-												 rsinfo->setDesc);
-		}
+				/* scan extension's script directory for install scripts */
+				get_available_versions_for_extension(control, rsinfo->setResult,
+													 rsinfo->setDesc);
+			}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}
 
 	return (Datum) 0;
@@ -2373,47 +2453,56 @@ bool
 extension_file_exists(const char *extensionName)
 {
 	bool		result = false;
-	char	   *location;
+	List	   *locations;
+	ListCell   *cell;
 	DIR		   *dir;
 	struct dirent *de;
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();
 
-	/*
-	 * If the control directory doesn't exist, we want to silently return
-	 * false.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach(cell, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * false.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
+		{
+			/* do nothing */
+		}
+		else
 		{
-			char	   *extname;
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				char	   *extname;
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			/* done if it matches request */
-			if (strcmp(extname, extensionName) == 0)
-			{
-				result = true;
-				break;
+				/* done if it matches request */
+				if (strcmp(extname, extensionName) == 0)
+				{
+					result = true;
+					break;
+				}
 			}
-		}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
+		if (result)
+			break;
 	}
 
 	return result;
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 87b233cb887..46a46715ec7 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -71,8 +71,7 @@ static void incompatible_module_error(const char *libname,
 									  const Pg_magic_struct *module_magic_data) pg_attribute_noreturn();
 static char *expand_dynamic_library_name(const char *name);
 static void check_restricted_library_name(const char *name);
-static char *substitute_libpath_macro(const char *name);
-static char *find_in_dynamic_libpath(const char *basename);
+static char *substitute_path_macro(const char *str, const char *macro, const char *value);
 
 /* Magic structure that module needs to match to be accepted */
 static const Pg_magic_struct magic_data = PG_MODULE_MAGIC_DATA;
@@ -398,7 +397,7 @@ incompatible_module_error(const char *libname,
 /*
  * If name contains a slash, check if the file exists, if so return
  * the name.  Else (no slash) try to expand using search path (see
- * find_in_dynamic_libpath below); if that works, return the fully
+ * find_in_path below); if that works, return the fully
  * expanded file name.  If the previous failed, append DLSUFFIX and
  * try again.  If all fails, just return the original name.
  *
@@ -413,17 +412,25 @@ expand_dynamic_library_name(const char *name)
 
 	Assert(name);
 
+	/*
+	 * If the value starts with "$libdir/", strip that.  This is because many
+	 * extensions have hardcoded '$libdir/foo' as their library name, which
+	 * prevents using the path.
+	 */
+	if (strncmp(name, "$libdir/", 8) == 0)
+		name += 8;
+
 	have_slash = (first_dir_separator(name) != NULL);
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(name);
+		full = find_in_path(name, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(name);
+		full = substitute_path_macro(name, "$libdir", pkglib_path);
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -433,14 +440,14 @@ expand_dynamic_library_name(const char *name)
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(new);
+		full = find_in_path(new, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		pfree(new);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(new);
+		full = substitute_path_macro(new, "$libdir", pkglib_path);
 		pfree(new);
 		if (pg_file_exists(full))
 			return full;
@@ -475,47 +482,60 @@ check_restricted_library_name(const char *name)
  * Result is always freshly palloc'd.
  */
 static char *
-substitute_libpath_macro(const char *name)
+substitute_path_macro(const char *str, const char *macro, const char *value)
 {
 	const char *sep_ptr;
 
-	Assert(name != NULL);
+	Assert(str != NULL);
+	Assert(macro[0] == '$');
 
-	/* Currently, we only recognize $libdir at the start of the string */
-	if (name[0] != '$')
-		return pstrdup(name);
+	/* Currently, we only recognize $macro at the start of the string */
+	if (str[0] != '$')
+		return pstrdup(str);
 
-	if ((sep_ptr = first_dir_separator(name)) == NULL)
-		sep_ptr = name + strlen(name);
+	if ((sep_ptr = first_dir_separator(str)) == NULL)
+		sep_ptr = str + strlen(str);
 
-	if (strlen("$libdir") != sep_ptr - name ||
-		strncmp(name, "$libdir", strlen("$libdir")) != 0)
+	if (strlen(macro) != sep_ptr - str ||
+		strncmp(str, macro, strlen(macro)) != 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_NAME),
-				 errmsg("invalid macro name in dynamic library path: %s",
-						name)));
+				 errmsg("invalid macro name in path: %s",
+						str)));
 
-	return psprintf("%s%s", pkglib_path, sep_ptr);
+	return psprintf("%s%s", value, sep_ptr);
 }
 
 
 /*
  * Search for a file called 'basename' in the colon-separated search
- * path Dynamic_library_path.  If the file is found, the full file name
+ * path given.  If the file is found, the full file name
  * is returned in freshly palloc'd memory.  If the file is not found,
  * return NULL.
+ *
+ * path_param is the name of the parameter that path came from, for error
+ * messages.
+ *
+ * macro and macro_val allow substituting a macro; see
+ * substitute_path_macro().
  */
-static char *
-find_in_dynamic_libpath(const char *basename)
+char *
+find_in_path(const char *basename, const char *path, const char *path_param,
+			 const char *macro, const char *macro_val)
 {
 	const char *p;
 	size_t		baselen;
 
 	Assert(basename != NULL);
 	Assert(first_dir_separator(basename) == NULL);
-	Assert(Dynamic_library_path != NULL);
+	Assert(path != NULL);
+	Assert(path_param != NULL);
+
+	p = path;
 
-	p = Dynamic_library_path;
+	/*
+	 * If the path variable is empty, don't do a path search.
+	 */
 	if (strlen(p) == 0)
 		return NULL;
 
@@ -532,7 +552,7 @@ find_in_dynamic_libpath(const char *basename)
 		if (piece == p)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("zero-length component in parameter \"dynamic_library_path\"")));
+					 errmsg("zero-length component in parameter \"%s\"", path_param)));
 
 		if (piece == NULL)
 			len = strlen(p);
@@ -542,7 +562,7 @@ find_in_dynamic_libpath(const char *basename)
 		piece = palloc(len + 1);
 		strlcpy(piece, p, len + 1);
 
-		mangled = substitute_libpath_macro(piece);
+		mangled = substitute_path_macro(piece, macro, macro_val);
 		pfree(piece);
 
 		canonicalize_path(mangled);
@@ -551,13 +571,13 @@ find_in_dynamic_libpath(const char *basename)
 		if (!is_absolute_path(mangled))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("component in parameter \"dynamic_library_path\" is not an absolute path")));
+					 errmsg("component in parameter \"%s\" is not an absolute path", path_param)));
 
 		full = palloc(strlen(mangled) + 1 + baselen + 1);
 		sprintf(full, "%s/%s", mangled, basename);
 		pfree(mangled);
 
-		elog(DEBUG3, "find_in_dynamic_libpath: trying \"%s\"", full);
+		elog(DEBUG3, "%s: trying \"%s\"", __func__, full);
 
 		if (pg_file_exists(full))
 			return full;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 690bf96ef03..c587e53078e 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -39,6 +39,7 @@
 #include "catalog/namespace.h"
 #include "catalog/storage.h"
 #include "commands/async.h"
+#include "commands/extension.h"
 #include "commands/event_trigger.h"
 #include "commands/tablespace.h"
 #include "commands/trigger.h"
@@ -4305,6 +4306,18 @@ struct config_string ConfigureNamesString[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"extension_control_path", PGC_SUSET, CLIENT_CONN_OTHER,
+			gettext_noop("Sets the path for extension control files."),
+			gettext_noop("The remaining extension script and secondary control files are then loaded "
+						 "from the same directory where the primary control file was found."),
+			GUC_SUPERUSER_ONLY
+		},
+		&Extension_control_path,
+		"$system",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"krb_server_keyfile", PGC_SIGHUP, CONN_AUTH_AUTH,
 			gettext_noop("Sets the location of the Kerberos server key file."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e771d87da1f..92d14f728b2 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -790,6 +790,7 @@ autovacuum_worker_slots = 16	# autovacuum worker slots to allocate
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_control_path = '$system'
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/commands/extension.h b/src/include/commands/extension.h
index 0b636405120..24419bfb5c9 100644
--- a/src/include/commands/extension.h
+++ b/src/include/commands/extension.h
@@ -17,6 +17,8 @@
 #include "catalog/objectaddress.h"
 #include "parser/parse_node.h"
 
+/* GUC */
+extern PGDLLIMPORT char *Extension_control_path;
 
 /*
  * creating_extension is only true while running a CREATE EXTENSION or ALTER
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index e609ea875a7..5811307a82c 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -740,6 +740,8 @@ extern bool CheckFunctionValidatorAccess(Oid validatorOid, Oid functionOid);
  */
 extern PGDLLIMPORT char *Dynamic_library_path;
 
+extern char *find_in_path(const char *basename, const char *path, const char *path_param,
+						  const char *macro, const char *macro_val);
 extern void *load_external_function(const char *filename, const char *funcname,
 									bool signalNotFound, void **filehandle);
 extern void *lookup_external_function(void *filehandle, const char *funcname);
diff --git a/src/test/modules/test_extensions/Makefile b/src/test/modules/test_extensions/Makefile
index 1dbec14cba3..a3591bf3d2f 100644
--- a/src/test/modules/test_extensions/Makefile
+++ b/src/test/modules/test_extensions/Makefile
@@ -28,6 +28,7 @@ DATA = test_ext1--1.0.sql test_ext2--1.0.sql test_ext3--1.0.sql \
        test_ext_req_schema3--1.0.sql
 
 REGRESS = test_extensions test_extdepend
+TAP_TESTS = 1
 
 # force C locale for output stability
 NO_LOCALE = 1
diff --git a/src/test/modules/test_extensions/meson.build b/src/test/modules/test_extensions/meson.build
index dd7ec0ce56b..3c7e378bf35 100644
--- a/src/test/modules/test_extensions/meson.build
+++ b/src/test/modules/test_extensions/meson.build
@@ -57,4 +57,9 @@ tests += {
     ],
     'regress_args': ['--no-locale'],
   },
+  'tap': {
+    'tests': [
+      't/001_extension_control_path.pl',
+    ],
+  },
 }
diff --git a/src/test/modules/test_extensions/t/001_extension_control_path.pl b/src/test/modules/test_extensions/t/001_extension_control_path.pl
new file mode 100644
index 00000000000..659fdcfce56
--- /dev/null
+++ b/src/test/modules/test_extensions/t/001_extension_control_path.pl
@@ -0,0 +1,54 @@
+# Copyright (c) 2024-2025, PostgreSQL Global Development Group
+
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Utils;
+use PostgreSQL::Test::Cluster;
+use Test::More;
+
+my $node = PostgreSQL::Test::Cluster->new('node');
+
+$node->init;
+
+# Create a temporary directory for the extension control file
+my $ext_dir = PostgreSQL::Test::Utils::tempdir();
+my $ext_name = "test_custom_ext_paths";
+my $control_file = "$ext_dir/$ext_name.control";
+my $sql_file = "$ext_dir/$ext_name--1.0.sql";
+
+# Create .control .sql file
+open my $cf, '>', $control_file or die "Could not create control file: $!";
+print $cf "default_version = '1.0'\n";
+print $cf "relocatable = true\n";
+close $cf;
+
+# Create --1.0.sql file
+open my $sqlf, '>', $sql_file or die "Could not create sql file: $!";
+print $sqlf "/* $sql_file */'\n";
+print $sqlf "-- complain if script is sourced in psql, rather than via CREATE EXTENSION\n";
+print $sqlf qq'\\echo Use "CREATE EXTENSION $ext_name" to load this file. \\quit\n';
+close $sqlf;
+
+$node->append_conf(
+	'postgresql.conf', qq{
+extension_control_path = '\$system:$ext_dir'
+});
+
+# Start node
+$node->start;
+
+my $ecp = $node->safe_psql('postgres', 'show extension_control_path;');
+
+is($ecp, "\$system:$ext_dir");
+
+my $ret = $node->safe_psql(
+	'postgres',
+	"select count(1) > 0 as ok from pg_available_extensions where name = '$ext_name'");
+is($ret, "t", "Expected to list available extension on a custom extension control path directory");
+
+my $ret2 = $node->safe_psql(
+	'postgres',
+	"select count(1) > 0 as ok from pg_available_extension_versions where name = '$ext_name'");
+is($ret2, "t", "Expected to list available extension with version on a custom extension control path directory");
+
+done_testing();
-- 
2.39.5 (Apple Git-154)

From 1f5f8ed0f23b436e73e4e4624f2c788f9a60f40a Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 5 Dec 2024 11:49:05 +0100
Subject: [PATCH v3] extension_control_path

The new GUC extension_control_path specifies a path to look for
extension control files.  The default value is $system, which looks in
the compiled-in location, as before.

The path search uses the same code and works in the same way as
dynamic_library_path.

Discussion: https://www.postgresql.org/message-id/flat/E7C7BFFB-8857-48D4-A71F-88B359FADCFD@justatheory.com
---
 doc/src/sgml/config.sgml                      |  68 ++++
 doc/src/sgml/extend.sgml                      |  19 +-
 doc/src/sgml/ref/create_extension.sgml        |   6 +-
 src/Makefile.global.in                        |  19 +-
 src/backend/commands/extension.c              | 348 +++++++++++-------
 src/backend/utils/fmgr/dfmgr.c                |  76 ++--
 src/backend/utils/misc/guc_tables.c           |  13 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/commands/extension.h              |   2 +
 src/include/fmgr.h                            |   2 +
 src/test/modules/test_extensions/Makefile     |   1 +
 src/test/modules/test_extensions/meson.build  |   5 +
 .../t/001_extension_control_path.pl           |  54 +++
 13 files changed, 440 insertions(+), 174 deletions(-)
 create mode 100644 src/test/modules/test_extensions/t/001_extension_control_path.pl

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index a8354576108..cb67387243f 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10698,6 +10698,74 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-extension-control-path" xreflabel="extension_control_path">
+      <term><varname>extension_control_path</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_control_path</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        A path to search for extensions, specifically extension control files
+        (<filename><replaceable>name</replaceable>.control</filename>).  The
+        remaining extension script and secondary control files are then loaded
+        from the same directory where the primary control file was found.
+        See <xref linkend="extend-extensions-files"/> for details.
+       </para>
+
+       <para>
+        The value for <varname>extension_control_path</varname> must be a
+        list of absolute directory paths separated by colons (or semi-colons
+        on Windows).  If a list element starts
+        with the special string <literal>$system</literal>, the
+        compiled-in <productname>PostgreSQL</productname> extension
+        directory is substituted for <literal>$system</literal>; this
+        is where the extensions provided by the standard
+        <productname>PostgreSQL</productname> distribution are installed.
+        (Use <literal>pg_config --sharedir</literal> to find out the name of
+        this directory.) For example:
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:/home/my_project/share/extension:$system'
+</programlisting>
+        or, in a Windows environment:
+<programlisting>
+extension_control_path = 'C:\tools\postgresql\extension;H:\my_project\share\extension;$system'
+</programlisting>
+        Note that the path elements should typically end in
+        <literal>extension</literal> if the normal installation layouts are
+        followed.  (The value for <literal>$system</literal> already includes
+        the <literal>extension</literal> suffix.)
+       </para>
+
+       <para>
+        The default value for this parameter is
+        <literal>'$system'</literal>. If the value is set to an empty
+        string, the default <literal>'$system'</literal> is also assumed.
+       </para>
+
+       <para>
+        This parameter can be changed at run time by superusers and users
+        with the appropriate <literal>SET</literal> privilege, but a
+        setting done that way will only persist until the end of the
+        client connection, so this method should be reserved for
+        development purposes. The recommended way to set this parameter
+        is in the <filename>postgresql.conf</filename> configuration
+        file.
+       </para>
+
+       <para>
+        Note that if you set this parameter to be able to load extensions from
+        nonstandard locations, you will most likely also need to set <xref
+        linkend="guc-dynamic-library-path"/> to a correspondent location, for
+        example,
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:$system'
+dynamic_library_path = '/usr/local/lib/postgresql:$libdir'
+</programlisting>
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-gin-fuzzy-search-limit" xreflabel="gin_fuzzy_search_limit">
       <term><varname>gin_fuzzy_search_limit</varname> (<type>integer</type>)
       <indexterm>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index ba492ca27c0..64f8e133cae 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -649,6 +649,11 @@ RETURNS anycompatible AS ...
      control file can specify a different directory for the script file(s).
     </para>
 
+    <para>
+     Additional locations for extension control files can be configured using
+     the parameter <xref linkend="guc-extension-control-path"/>.
+    </para>
+
     <para>
      The file format for an extension control file is the same as for the
      <filename>postgresql.conf</filename> file, namely a list of
@@ -669,9 +674,9 @@ RETURNS anycompatible AS ...
        <para>
         The directory containing the extension's <acronym>SQL</acronym> script
         file(s).  Unless an absolute path is given, the name is relative to
-        the installation's <literal>SHAREDIR</literal> directory.  The
-        default behavior is equivalent to specifying
-        <literal>directory = 'extension'</literal>.
+        the installation's <literal>SHAREDIR</literal> directory.  By default,
+        the script files are looked for in the same directory where the
+        control file was found.
        </para>
       </listitem>
      </varlistentry>
@@ -719,8 +724,8 @@ RETURNS anycompatible AS ...
        <para>
         The value of this parameter will be substituted for each occurrence
         of <literal>MODULE_PATHNAME</literal> in the script file(s).  If it is not
-        set, no substitution is made.  Typically, this is set to
-        <literal>$libdir/<replaceable>shared_library_name</replaceable></literal> and
+        set, no substitution is made.  Typically, this is set to just
+        <literal><replaceable>shared_library_name</replaceable></literal> and
         then <literal>MODULE_PATHNAME</literal> is used in <command>CREATE
         FUNCTION</command> commands for C-language functions, so that the script
         files do not need to hard-wire the name of the shared library.
@@ -1804,6 +1809,10 @@ include $(PGXS)
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
+    You can also select a separate installation directory for your extension
+    by setting the <literal>make</literal> variable <varname>prefix</varname>
+    on the <literal>make</literal> command line.  (But this will then require
+    additional setup to get the server to find the extension there.)
    </para>
 
    <para>
diff --git a/doc/src/sgml/ref/create_extension.sgml b/doc/src/sgml/ref/create_extension.sgml
index ca2b80d669c..713abd9c494 100644
--- a/doc/src/sgml/ref/create_extension.sgml
+++ b/doc/src/sgml/ref/create_extension.sgml
@@ -90,8 +90,10 @@ CREATE EXTENSION [ IF NOT EXISTS ] <replaceable class="parameter">extension_name
        <para>
         The name of the extension to be
         installed. <productname>PostgreSQL</productname> will create the
-        extension using details from the file
-        <literal>SHAREDIR/extension/</literal><replaceable class="parameter">extension_name</replaceable><literal>.control</literal>.
+        extension using details from the file <filename><replaceable
+        class="parameter">extension_name</replaceable>.control</filename>,
+        found via the server's extension control path (set by <xref
+        linkend="guc-extension-control-path"/>.)
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index 3b620bac5ac..8fe9d61e82a 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -87,9 +87,19 @@ endif # not PGXS
 #
 # In a PGXS build, we cannot use the values inserted into Makefile.global
 # by configure, since the installation tree may have been relocated.
-# Instead get the path values from pg_config.
+# Instead get the path values from pg_config.  But users can specify
+# prefix explicitly, if they want to select their own installation
+# location.
 
-ifndef PGXS
+ifdef PGXS
+# Extension makefiles should set PG_CONFIG, but older ones might not
+ifndef PG_CONFIG
+PG_CONFIG = pg_config
+endif
+endif
+
+# This means: if ((not PGXS) or prefix)
+ifneq (,$(if $(PGXS),,1)$(prefix))
 
 # Note that prefix, exec_prefix, and datarootdir aren't defined in a PGXS build;
 # makefiles may only use the derived variables such as bindir.
@@ -147,11 +157,6 @@ localedir := @localedir@
 
 else # PGXS case
 
-# Extension makefiles should set PG_CONFIG, but older ones might not
-ifndef PG_CONFIG
-PG_CONFIG = pg_config
-endif
-
 bindir := $(shell $(PG_CONFIG) --bindir)
 datadir := $(shell $(PG_CONFIG) --sharedir)
 sysconfdir := $(shell $(PG_CONFIG) --sysconfdir)
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index d9bb4ce5f1e..7e8a28e4064 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -51,6 +51,7 @@
 #include "commands/defrem.h"
 #include "commands/extension.h"
 #include "commands/schemacmds.h"
+#include "nodes/pg_list.h"
 #include "funcapi.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
@@ -69,6 +70,9 @@
 #include "utils/varlena.h"
 
 
+/* GUC */
+char	   *Extension_control_path;
+
 /* Globally visible state variables */
 bool		creating_extension = false;
 Oid			CurrentExtensionObject = InvalidOid;
@@ -79,6 +83,7 @@ Oid			CurrentExtensionObject = InvalidOid;
 typedef struct ExtensionControlFile
 {
 	char	   *name;			/* name of the extension */
+	char	   *control_dir;	/* directory where control file was found */
 	char	   *directory;		/* directory for script files */
 	char	   *default_version;	/* default install target version, if any */
 	char	   *module_pathname;	/* string to substitute for
@@ -328,29 +333,88 @@ is_extension_script_filename(const char *filename)
 	return (extension != NULL) && (strcmp(extension, ".sql") == 0);
 }
 
-static char *
-get_extension_control_directory(void)
+/*
+ * Return a list of directories declared on extension_control_path GUC.
+ */
+static List *
+get_extension_control_directories(void)
 {
 	char		sharepath[MAXPGPATH];
-	char	   *result;
+	char	   *system_dir;
+	char	   *ecp;
+	char	   *token;
+	char	   *path;
+	List	   *paths = NIL;
 
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension", sharepath);
 
-	return result;
+	system_dir = psprintf("%s/extension", sharepath);
+
+	if (strlen(Extension_control_path) == 0)
+	{
+		paths = lappend(paths, system_dir);
+	}
+	else
+	{
+		/* Duplicate the string so we can modify it */
+		ecp = pstrdup(Extension_control_path);
+
+		/* Consume each path between ':' */
+		for (token = strtok(ecp, ":"); token != NULL; token = strtok(NULL, ":"))
+		{
+			if (strcmp(token, "$system") == 0)
+				path = system_dir;
+			else
+				path = pstrdup(token);
+
+			paths = lappend(paths, path);
+		}
+
+		pfree(ecp);
+	}
+
+	return paths;
 }
 
+/*
+ * Find control file for extension with name in control->name, looking in the
+ * path.  Return the full file name, or NULL if not found.  If found, the
+ * directory is recorded in control->control_dir.
+ */
 static char *
-get_extension_control_filename(const char *extname)
+find_extension_control_filename(ExtensionControlFile *control)
 {
 	char		sharepath[MAXPGPATH];
+	char	   *system_dir;
+	char	   *basename;
+	char	   *ecp;
 	char	   *result;
 
+	Assert(control->name);
+
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
-			 sharepath, extname);
+	system_dir = psprintf("%s/extension", sharepath);
+
+	basename = psprintf("%s.control", control->name);
+
+	/*
+	 * find_in_path() does nothing if the path value is empty.  This is the
+	 * historical behavior for dynamic_library_path, but it makes no sense for
+	 * extensions.  So in that case, substitute a default value.
+	 */
+	ecp = Extension_control_path;
+	if (strlen(ecp) == 0)
+		ecp = "$system";
+	result = find_in_path(basename, Extension_control_path, "extension_control_path", "$system", system_dir);
+
+	if (result)
+	{
+		const char *p;
+
+		p = strrchr(result, '/');
+		Assert(p);
+		control->control_dir = pnstrdup(result, p - result);
+	}
 
 	return result;
 }
@@ -366,7 +430,7 @@ get_extension_script_directory(ExtensionControlFile *control)
 	 * installation's share directory.
 	 */
 	if (!control->directory)
-		return get_extension_control_directory();
+		return pstrdup(control->control_dir);
 
 	if (is_absolute_path(control->directory))
 		return pstrdup(control->directory);
@@ -444,27 +508,25 @@ parse_extension_control_file(ExtensionControlFile *control,
 	if (version)
 		filename = get_extension_aux_control_filename(control, version);
 	else
-		filename = get_extension_control_filename(control->name);
+		filename = find_extension_control_filename(control);
+
+	if (!filename)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("extension \"%s\" is not available", control->name),
+				 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+	}
 
 	if ((file = AllocateFile(filename, "r")) == NULL)
 	{
-		if (errno == ENOENT)
+		/* no complaint for missing auxiliary file */
+		if (errno == ENOENT && version)
 		{
-			/* no complaint for missing auxiliary file */
-			if (version)
-			{
-				pfree(filename);
-				return;
-			}
-
-			/* missing control file indicates extension is not installed */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("extension \"%s\" is not available", control->name),
-					 errdetail("Could not open extension control file \"%s\": %m.",
-							   filename),
-					 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+			pfree(filename);
+			return;
 		}
+
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not open extension control file \"%s\": %m",
@@ -2121,68 +2183,75 @@ Datum
 pg_available_extensions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
 	DIR		   *dir;
 	struct dirent *de;
+	List	   *locations;
+	ListCell   *cell;
 
 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();
 
-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach(cell, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
-			Datum		values[3];
-			bool		nulls[3];
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;
+				Datum		values[3];
+				bool		nulls[3];
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			control = read_extension_control_file(extname);
+				control = read_extension_control_file(extname);
 
-			memset(values, 0, sizeof(values));
-			memset(nulls, 0, sizeof(nulls));
+				memset(values, 0, sizeof(values));
+				memset(nulls, 0, sizeof(nulls));
 
-			/* name */
-			values[0] = DirectFunctionCall1(namein,
-											CStringGetDatum(control->name));
-			/* default_version */
-			if (control->default_version == NULL)
-				nulls[1] = true;
-			else
-				values[1] = CStringGetTextDatum(control->default_version);
-			/* comment */
-			if (control->comment == NULL)
-				nulls[2] = true;
-			else
-				values[2] = CStringGetTextDatum(control->comment);
+				/* name */
+				values[0] = DirectFunctionCall1(namein,
+												CStringGetDatum(control->name));
+				/* default_version */
+				if (control->default_version == NULL)
+					nulls[1] = true;
+				else
+					values[1] = CStringGetTextDatum(control->default_version);
+				/* comment */
+				if (control->comment == NULL)
+					nulls[2] = true;
+				else
+					values[2] = CStringGetTextDatum(control->comment);
 
-			tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
-								 values, nulls);
-		}
+				tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
+									 values, nulls);
+			}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}
 
 	return (Datum) 0;
@@ -2201,51 +2270,57 @@ Datum
 pg_available_extension_versions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
+	List	   *locations;
+	ListCell   *cell;
 	DIR		   *dir;
 	struct dirent *de;
 
 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
-
-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	locations = get_extension_control_directories();
+	foreach(cell, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
+		{
+			/* do nothing */
+		}
+		else
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			/* read the control file */
-			control = read_extension_control_file(extname);
+				/* read the control file */
+				control = read_extension_control_file(extname);
 
-			/* scan extension's script directory for install scripts */
-			get_available_versions_for_extension(control, rsinfo->setResult,
-												 rsinfo->setDesc);
-		}
+				/* scan extension's script directory for install scripts */
+				get_available_versions_for_extension(control, rsinfo->setResult,
+													 rsinfo->setDesc);
+			}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}
 
 	return (Datum) 0;
@@ -2373,47 +2448,56 @@ bool
 extension_file_exists(const char *extensionName)
 {
 	bool		result = false;
-	char	   *location;
+	List	   *locations;
+	ListCell   *cell;
 	DIR		   *dir;
 	struct dirent *de;
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();
 
-	/*
-	 * If the control directory doesn't exist, we want to silently return
-	 * false.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach(cell, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * false.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			char	   *extname;
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				char	   *extname;
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			/* done if it matches request */
-			if (strcmp(extname, extensionName) == 0)
-			{
-				result = true;
-				break;
+				/* done if it matches request */
+				if (strcmp(extname, extensionName) == 0)
+				{
+					result = true;
+					break;
+				}
 			}
-		}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
+		if (result)
+			break;
 	}
 
 	return result;
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 87b233cb887..46a46715ec7 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -71,8 +71,7 @@ static void incompatible_module_error(const char *libname,
 									  const Pg_magic_struct *module_magic_data) pg_attribute_noreturn();
 static char *expand_dynamic_library_name(const char *name);
 static void check_restricted_library_name(const char *name);
-static char *substitute_libpath_macro(const char *name);
-static char *find_in_dynamic_libpath(const char *basename);
+static char *substitute_path_macro(const char *str, const char *macro, const char *value);
 
 /* Magic structure that module needs to match to be accepted */
 static const Pg_magic_struct magic_data = PG_MODULE_MAGIC_DATA;
@@ -398,7 +397,7 @@ incompatible_module_error(const char *libname,
 /*
  * If name contains a slash, check if the file exists, if so return
  * the name.  Else (no slash) try to expand using search path (see
- * find_in_dynamic_libpath below); if that works, return the fully
+ * find_in_path below); if that works, return the fully
  * expanded file name.  If the previous failed, append DLSUFFIX and
  * try again.  If all fails, just return the original name.
  *
@@ -413,17 +412,25 @@ expand_dynamic_library_name(const char *name)
 
 	Assert(name);
 
+	/*
+	 * If the value starts with "$libdir/", strip that.  This is because many
+	 * extensions have hardcoded '$libdir/foo' as their library name, which
+	 * prevents using the path.
+	 */
+	if (strncmp(name, "$libdir/", 8) == 0)
+		name += 8;
+
 	have_slash = (first_dir_separator(name) != NULL);
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(name);
+		full = find_in_path(name, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(name);
+		full = substitute_path_macro(name, "$libdir", pkglib_path);
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -433,14 +440,14 @@ expand_dynamic_library_name(const char *name)
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(new);
+		full = find_in_path(new, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		pfree(new);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(new);
+		full = substitute_path_macro(new, "$libdir", pkglib_path);
 		pfree(new);
 		if (pg_file_exists(full))
 			return full;
@@ -475,47 +482,60 @@ check_restricted_library_name(const char *name)
  * Result is always freshly palloc'd.
  */
 static char *
-substitute_libpath_macro(const char *name)
+substitute_path_macro(const char *str, const char *macro, const char *value)
 {
 	const char *sep_ptr;
 
-	Assert(name != NULL);
+	Assert(str != NULL);
+	Assert(macro[0] == '$');
 
-	/* Currently, we only recognize $libdir at the start of the string */
-	if (name[0] != '$')
-		return pstrdup(name);
+	/* Currently, we only recognize $macro at the start of the string */
+	if (str[0] != '$')
+		return pstrdup(str);
 
-	if ((sep_ptr = first_dir_separator(name)) == NULL)
-		sep_ptr = name + strlen(name);
+	if ((sep_ptr = first_dir_separator(str)) == NULL)
+		sep_ptr = str + strlen(str);
 
-	if (strlen("$libdir") != sep_ptr - name ||
-		strncmp(name, "$libdir", strlen("$libdir")) != 0)
+	if (strlen(macro) != sep_ptr - str ||
+		strncmp(str, macro, strlen(macro)) != 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_NAME),
-				 errmsg("invalid macro name in dynamic library path: %s",
-						name)));
+				 errmsg("invalid macro name in path: %s",
+						str)));
 
-	return psprintf("%s%s", pkglib_path, sep_ptr);
+	return psprintf("%s%s", value, sep_ptr);
 }
 
 
 /*
  * Search for a file called 'basename' in the colon-separated search
- * path Dynamic_library_path.  If the file is found, the full file name
+ * path given.  If the file is found, the full file name
  * is returned in freshly palloc'd memory.  If the file is not found,
  * return NULL.
+ *
+ * path_param is the name of the parameter that path came from, for error
+ * messages.
+ *
+ * macro and macro_val allow substituting a macro; see
+ * substitute_path_macro().
  */
-static char *
-find_in_dynamic_libpath(const char *basename)
+char *
+find_in_path(const char *basename, const char *path, const char *path_param,
+			 const char *macro, const char *macro_val)
 {
 	const char *p;
 	size_t		baselen;
 
 	Assert(basename != NULL);
 	Assert(first_dir_separator(basename) == NULL);
-	Assert(Dynamic_library_path != NULL);
+	Assert(path != NULL);
+	Assert(path_param != NULL);
+
+	p = path;
 
-	p = Dynamic_library_path;
+	/*
+	 * If the path variable is empty, don't do a path search.
+	 */
 	if (strlen(p) == 0)
 		return NULL;
 
@@ -532,7 +552,7 @@ find_in_dynamic_libpath(const char *basename)
 		if (piece == p)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("zero-length component in parameter \"dynamic_library_path\"")));
+					 errmsg("zero-length component in parameter \"%s\"", path_param)));
 
 		if (piece == NULL)
 			len = strlen(p);
@@ -542,7 +562,7 @@ find_in_dynamic_libpath(const char *basename)
 		piece = palloc(len + 1);
 		strlcpy(piece, p, len + 1);
 
-		mangled = substitute_libpath_macro(piece);
+		mangled = substitute_path_macro(piece, macro, macro_val);
 		pfree(piece);
 
 		canonicalize_path(mangled);
@@ -551,13 +571,13 @@ find_in_dynamic_libpath(const char *basename)
 		if (!is_absolute_path(mangled))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("component in parameter \"dynamic_library_path\" is not an absolute path")));
+					 errmsg("component in parameter \"%s\" is not an absolute path", path_param)));
 
 		full = palloc(strlen(mangled) + 1 + baselen + 1);
 		sprintf(full, "%s/%s", mangled, basename);
 		pfree(mangled);
 
-		elog(DEBUG3, "find_in_dynamic_libpath: trying \"%s\"", full);
+		elog(DEBUG3, "%s: trying \"%s\"", __func__, full);
 
 		if (pg_file_exists(full))
 			return full;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 690bf96ef03..c587e53078e 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -39,6 +39,7 @@
 #include "catalog/namespace.h"
 #include "catalog/storage.h"
 #include "commands/async.h"
+#include "commands/extension.h"
 #include "commands/event_trigger.h"
 #include "commands/tablespace.h"
 #include "commands/trigger.h"
@@ -4305,6 +4306,18 @@ struct config_string ConfigureNamesString[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"extension_control_path", PGC_SUSET, CLIENT_CONN_OTHER,
+			gettext_noop("Sets the path for extension control files."),
+			gettext_noop("The remaining extension script and secondary control files are then loaded "
+						 "from the same directory where the primary control file was found."),
+			GUC_SUPERUSER_ONLY
+		},
+		&Extension_control_path,
+		"$system",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"krb_server_keyfile", PGC_SIGHUP, CONN_AUTH_AUTH,
 			gettext_noop("Sets the location of the Kerberos server key file."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e771d87da1f..92d14f728b2 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -790,6 +790,7 @@ autovacuum_worker_slots = 16	# autovacuum worker slots to allocate
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_control_path = '$system'
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/commands/extension.h b/src/include/commands/extension.h
index 0b636405120..24419bfb5c9 100644
--- a/src/include/commands/extension.h
+++ b/src/include/commands/extension.h
@@ -17,6 +17,8 @@
 #include "catalog/objectaddress.h"
 #include "parser/parse_node.h"
 
+/* GUC */
+extern PGDLLIMPORT char *Extension_control_path;
 
 /*
  * creating_extension is only true while running a CREATE EXTENSION or ALTER
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index e609ea875a7..5811307a82c 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -740,6 +740,8 @@ extern bool CheckFunctionValidatorAccess(Oid validatorOid, Oid functionOid);
  */
 extern PGDLLIMPORT char *Dynamic_library_path;
 
+extern char *find_in_path(const char *basename, const char *path, const char *path_param,
+						  const char *macro, const char *macro_val);
 extern void *load_external_function(const char *filename, const char *funcname,
 									bool signalNotFound, void **filehandle);
 extern void *lookup_external_function(void *filehandle, const char *funcname);
diff --git a/src/test/modules/test_extensions/Makefile b/src/test/modules/test_extensions/Makefile
index 1dbec14cba3..a3591bf3d2f 100644
--- a/src/test/modules/test_extensions/Makefile
+++ b/src/test/modules/test_extensions/Makefile
@@ -28,6 +28,7 @@ DATA = test_ext1--1.0.sql test_ext2--1.0.sql test_ext3--1.0.sql \
        test_ext_req_schema3--1.0.sql
 
 REGRESS = test_extensions test_extdepend
+TAP_TESTS = 1
 
 # force C locale for output stability
 NO_LOCALE = 1
diff --git a/src/test/modules/test_extensions/meson.build b/src/test/modules/test_extensions/meson.build
index dd7ec0ce56b..3c7e378bf35 100644
--- a/src/test/modules/test_extensions/meson.build
+++ b/src/test/modules/test_extensions/meson.build
@@ -57,4 +57,9 @@ tests += {
     ],
     'regress_args': ['--no-locale'],
   },
+  'tap': {
+    'tests': [
+      't/001_extension_control_path.pl',
+    ],
+  },
 }
diff --git a/src/test/modules/test_extensions/t/001_extension_control_path.pl b/src/test/modules/test_extensions/t/001_extension_control_path.pl
new file mode 100644
index 00000000000..659fdcfce56
--- /dev/null
+++ b/src/test/modules/test_extensions/t/001_extension_control_path.pl
@@ -0,0 +1,54 @@
+# Copyright (c) 2024-2025, PostgreSQL Global Development Group
+
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Utils;
+use PostgreSQL::Test::Cluster;
+use Test::More;
+
+my $node = PostgreSQL::Test::Cluster->new('node');
+
+$node->init;
+
+# Create a temporary directory for the extension control file
+my $ext_dir = PostgreSQL::Test::Utils::tempdir();
+my $ext_name = "test_custom_ext_paths";
+my $control_file = "$ext_dir/$ext_name.control";
+my $sql_file = "$ext_dir/$ext_name--1.0.sql";
+
+# Create .control .sql file
+open my $cf, '>', $control_file or die "Could not create control file: $!";
+print $cf "default_version = '1.0'\n";
+print $cf "relocatable = true\n";
+close $cf;
+
+# Create --1.0.sql file
+open my $sqlf, '>', $sql_file or die "Could not create sql file: $!";
+print $sqlf "/* $sql_file */'\n";
+print $sqlf "-- complain if script is sourced in psql, rather than via CREATE EXTENSION\n";
+print $sqlf qq'\\echo Use "CREATE EXTENSION $ext_name" to load this file. \\quit\n';
+close $sqlf;
+
+$node->append_conf(
+	'postgresql.conf', qq{
+extension_control_path = '\$system:$ext_dir'
+});
+
+# Start node
+$node->start;
+
+my $ecp = $node->safe_psql('postgres', 'show extension_control_path;');
+
+is($ecp, "\$system:$ext_dir");
+
+my $ret = $node->safe_psql(
+	'postgres',
+	"select count(1) > 0 as ok from pg_available_extensions where name = '$ext_name'");
+is($ret, "t", "Expected to list available extension on a custom extension control path directory");
+
+my $ret2 = $node->safe_psql(
+	'postgres',
+	"select count(1) > 0 as ok from pg_available_extension_versions where name = '$ext_name'");
+is($ret2, "t", "Expected to list available extension with version on a custom extension control path directory");
+
+done_testing();
-- 
2.39.5 (Apple Git-154)

From 21606ffcfbc99bed8a5f8883b954f3f095b22910 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 5 Dec 2024 11:49:05 +0100
Subject: [PATCH v4] extension_control_path

The new GUC extension_control_path specifies a path to look for
extension control files.  The default value is $system, which looks in
the compiled-in location, as before.

The path search uses the same code and works in the same way as
dynamic_library_path.

Discussion: https://www.postgresql.org/message-id/flat/E7C7BFFB-8857-48D4-A71F-88B359FADCFD@justatheory.com
---
 doc/src/sgml/config.sgml                      |  68 ++++
 doc/src/sgml/extend.sgml                      |  19 +-
 doc/src/sgml/ref/create_extension.sgml        |   6 +-
 src/Makefile.global.in                        |  19 +-
 src/backend/commands/extension.c              | 348 +++++++++++-------
 src/backend/utils/fmgr/dfmgr.c                |  76 ++--
 src/backend/utils/misc/guc_tables.c           |  13 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/commands/extension.h              |   2 +
 src/include/fmgr.h                            |   2 +
 src/test/modules/test_extensions/Makefile     |   1 +
 src/test/modules/test_extensions/meson.build  |   5 +
 .../t/001_extension_control_path.pl           |  56 +++
 13 files changed, 442 insertions(+), 174 deletions(-)
 create mode 100644 src/test/modules/test_extensions/t/001_extension_control_path.pl

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index a8354576108..cb67387243f 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10698,6 +10698,74 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-extension-control-path" xreflabel="extension_control_path">
+      <term><varname>extension_control_path</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_control_path</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        A path to search for extensions, specifically extension control files
+        (<filename><replaceable>name</replaceable>.control</filename>).  The
+        remaining extension script and secondary control files are then loaded
+        from the same directory where the primary control file was found.
+        See <xref linkend="extend-extensions-files"/> for details.
+       </para>
+
+       <para>
+        The value for <varname>extension_control_path</varname> must be a
+        list of absolute directory paths separated by colons (or semi-colons
+        on Windows).  If a list element starts
+        with the special string <literal>$system</literal>, the
+        compiled-in <productname>PostgreSQL</productname> extension
+        directory is substituted for <literal>$system</literal>; this
+        is where the extensions provided by the standard
+        <productname>PostgreSQL</productname> distribution are installed.
+        (Use <literal>pg_config --sharedir</literal> to find out the name of
+        this directory.) For example:
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:/home/my_project/share/extension:$system'
+</programlisting>
+        or, in a Windows environment:
+<programlisting>
+extension_control_path = 'C:\tools\postgresql\extension;H:\my_project\share\extension;$system'
+</programlisting>
+        Note that the path elements should typically end in
+        <literal>extension</literal> if the normal installation layouts are
+        followed.  (The value for <literal>$system</literal> already includes
+        the <literal>extension</literal> suffix.)
+       </para>
+
+       <para>
+        The default value for this parameter is
+        <literal>'$system'</literal>. If the value is set to an empty
+        string, the default <literal>'$system'</literal> is also assumed.
+       </para>
+
+       <para>
+        This parameter can be changed at run time by superusers and users
+        with the appropriate <literal>SET</literal> privilege, but a
+        setting done that way will only persist until the end of the
+        client connection, so this method should be reserved for
+        development purposes. The recommended way to set this parameter
+        is in the <filename>postgresql.conf</filename> configuration
+        file.
+       </para>
+
+       <para>
+        Note that if you set this parameter to be able to load extensions from
+        nonstandard locations, you will most likely also need to set <xref
+        linkend="guc-dynamic-library-path"/> to a correspondent location, for
+        example,
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:$system'
+dynamic_library_path = '/usr/local/lib/postgresql:$libdir'
+</programlisting>
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-gin-fuzzy-search-limit" xreflabel="gin_fuzzy_search_limit">
       <term><varname>gin_fuzzy_search_limit</varname> (<type>integer</type>)
       <indexterm>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index ba492ca27c0..64f8e133cae 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -649,6 +649,11 @@ RETURNS anycompatible AS ...
      control file can specify a different directory for the script file(s).
     </para>
 
+    <para>
+     Additional locations for extension control files can be configured using
+     the parameter <xref linkend="guc-extension-control-path"/>.
+    </para>
+
     <para>
      The file format for an extension control file is the same as for the
      <filename>postgresql.conf</filename> file, namely a list of
@@ -669,9 +674,9 @@ RETURNS anycompatible AS ...
        <para>
         The directory containing the extension's <acronym>SQL</acronym> script
         file(s).  Unless an absolute path is given, the name is relative to
-        the installation's <literal>SHAREDIR</literal> directory.  The
-        default behavior is equivalent to specifying
-        <literal>directory = 'extension'</literal>.
+        the installation's <literal>SHAREDIR</literal> directory.  By default,
+        the script files are looked for in the same directory where the
+        control file was found.
        </para>
       </listitem>
      </varlistentry>
@@ -719,8 +724,8 @@ RETURNS anycompatible AS ...
        <para>
         The value of this parameter will be substituted for each occurrence
         of <literal>MODULE_PATHNAME</literal> in the script file(s).  If it is not
-        set, no substitution is made.  Typically, this is set to
-        <literal>$libdir/<replaceable>shared_library_name</replaceable></literal> and
+        set, no substitution is made.  Typically, this is set to just
+        <literal><replaceable>shared_library_name</replaceable></literal> and
         then <literal>MODULE_PATHNAME</literal> is used in <command>CREATE
         FUNCTION</command> commands for C-language functions, so that the script
         files do not need to hard-wire the name of the shared library.
@@ -1804,6 +1809,10 @@ include $(PGXS)
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
+    You can also select a separate installation directory for your extension
+    by setting the <literal>make</literal> variable <varname>prefix</varname>
+    on the <literal>make</literal> command line.  (But this will then require
+    additional setup to get the server to find the extension there.)
    </para>
 
    <para>
diff --git a/doc/src/sgml/ref/create_extension.sgml b/doc/src/sgml/ref/create_extension.sgml
index ca2b80d669c..713abd9c494 100644
--- a/doc/src/sgml/ref/create_extension.sgml
+++ b/doc/src/sgml/ref/create_extension.sgml
@@ -90,8 +90,10 @@ CREATE EXTENSION [ IF NOT EXISTS ] <replaceable class="parameter">extension_name
        <para>
         The name of the extension to be
         installed. <productname>PostgreSQL</productname> will create the
-        extension using details from the file
-        <literal>SHAREDIR/extension/</literal><replaceable class="parameter">extension_name</replaceable><literal>.control</literal>.
+        extension using details from the file <filename><replaceable
+        class="parameter">extension_name</replaceable>.control</filename>,
+        found via the server's extension control path (set by <xref
+        linkend="guc-extension-control-path"/>.)
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index 3b620bac5ac..8fe9d61e82a 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -87,9 +87,19 @@ endif # not PGXS
 #
 # In a PGXS build, we cannot use the values inserted into Makefile.global
 # by configure, since the installation tree may have been relocated.
-# Instead get the path values from pg_config.
+# Instead get the path values from pg_config.  But users can specify
+# prefix explicitly, if they want to select their own installation
+# location.
 
-ifndef PGXS
+ifdef PGXS
+# Extension makefiles should set PG_CONFIG, but older ones might not
+ifndef PG_CONFIG
+PG_CONFIG = pg_config
+endif
+endif
+
+# This means: if ((not PGXS) or prefix)
+ifneq (,$(if $(PGXS),,1)$(prefix))
 
 # Note that prefix, exec_prefix, and datarootdir aren't defined in a PGXS build;
 # makefiles may only use the derived variables such as bindir.
@@ -147,11 +157,6 @@ localedir := @localedir@
 
 else # PGXS case
 
-# Extension makefiles should set PG_CONFIG, but older ones might not
-ifndef PG_CONFIG
-PG_CONFIG = pg_config
-endif
-
 bindir := $(shell $(PG_CONFIG) --bindir)
 datadir := $(shell $(PG_CONFIG) --sharedir)
 sysconfdir := $(shell $(PG_CONFIG) --sysconfdir)
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index d9bb4ce5f1e..7e8a28e4064 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -51,6 +51,7 @@
 #include "commands/defrem.h"
 #include "commands/extension.h"
 #include "commands/schemacmds.h"
+#include "nodes/pg_list.h"
 #include "funcapi.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
@@ -69,6 +70,9 @@
 #include "utils/varlena.h"
 
 
+/* GUC */
+char	   *Extension_control_path;
+
 /* Globally visible state variables */
 bool		creating_extension = false;
 Oid			CurrentExtensionObject = InvalidOid;
@@ -79,6 +83,7 @@ Oid			CurrentExtensionObject = InvalidOid;
 typedef struct ExtensionControlFile
 {
 	char	   *name;			/* name of the extension */
+	char	   *control_dir;	/* directory where control file was found */
 	char	   *directory;		/* directory for script files */
 	char	   *default_version;	/* default install target version, if any */
 	char	   *module_pathname;	/* string to substitute for
@@ -328,29 +333,88 @@ is_extension_script_filename(const char *filename)
 	return (extension != NULL) && (strcmp(extension, ".sql") == 0);
 }
 
-static char *
-get_extension_control_directory(void)
+/*
+ * Return a list of directories declared on extension_control_path GUC.
+ */
+static List *
+get_extension_control_directories(void)
 {
 	char		sharepath[MAXPGPATH];
-	char	   *result;
+	char	   *system_dir;
+	char	   *ecp;
+	char	   *token;
+	char	   *path;
+	List	   *paths = NIL;
 
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension", sharepath);
 
-	return result;
+	system_dir = psprintf("%s/extension", sharepath);
+
+	if (strlen(Extension_control_path) == 0)
+	{
+		paths = lappend(paths, system_dir);
+	}
+	else
+	{
+		/* Duplicate the string so we can modify it */
+		ecp = pstrdup(Extension_control_path);
+
+		/* Consume each path between ':' */
+		for (token = strtok(ecp, ":"); token != NULL; token = strtok(NULL, ":"))
+		{
+			if (strcmp(token, "$system") == 0)
+				path = system_dir;
+			else
+				path = pstrdup(token);
+
+			paths = lappend(paths, path);
+		}
+
+		pfree(ecp);
+	}
+
+	return paths;
 }
 
+/*
+ * Find control file for extension with name in control->name, looking in the
+ * path.  Return the full file name, or NULL if not found.  If found, the
+ * directory is recorded in control->control_dir.
+ */
 static char *
-get_extension_control_filename(const char *extname)
+find_extension_control_filename(ExtensionControlFile *control)
 {
 	char		sharepath[MAXPGPATH];
+	char	   *system_dir;
+	char	   *basename;
+	char	   *ecp;
 	char	   *result;
 
+	Assert(control->name);
+
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
-			 sharepath, extname);
+	system_dir = psprintf("%s/extension", sharepath);
+
+	basename = psprintf("%s.control", control->name);
+
+	/*
+	 * find_in_path() does nothing if the path value is empty.  This is the
+	 * historical behavior for dynamic_library_path, but it makes no sense for
+	 * extensions.  So in that case, substitute a default value.
+	 */
+	ecp = Extension_control_path;
+	if (strlen(ecp) == 0)
+		ecp = "$system";
+	result = find_in_path(basename, Extension_control_path, "extension_control_path", "$system", system_dir);
+
+	if (result)
+	{
+		const char *p;
+
+		p = strrchr(result, '/');
+		Assert(p);
+		control->control_dir = pnstrdup(result, p - result);
+	}
 
 	return result;
 }
@@ -366,7 +430,7 @@ get_extension_script_directory(ExtensionControlFile *control)
 	 * installation's share directory.
 	 */
 	if (!control->directory)
-		return get_extension_control_directory();
+		return pstrdup(control->control_dir);
 
 	if (is_absolute_path(control->directory))
 		return pstrdup(control->directory);
@@ -444,27 +508,25 @@ parse_extension_control_file(ExtensionControlFile *control,
 	if (version)
 		filename = get_extension_aux_control_filename(control, version);
 	else
-		filename = get_extension_control_filename(control->name);
+		filename = find_extension_control_filename(control);
+
+	if (!filename)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("extension \"%s\" is not available", control->name),
+				 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+	}
 
 	if ((file = AllocateFile(filename, "r")) == NULL)
 	{
-		if (errno == ENOENT)
+		/* no complaint for missing auxiliary file */
+		if (errno == ENOENT && version)
 		{
-			/* no complaint for missing auxiliary file */
-			if (version)
-			{
-				pfree(filename);
-				return;
-			}
-
-			/* missing control file indicates extension is not installed */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("extension \"%s\" is not available", control->name),
-					 errdetail("Could not open extension control file \"%s\": %m.",
-							   filename),
-					 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+			pfree(filename);
+			return;
 		}
+
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not open extension control file \"%s\": %m",
@@ -2121,68 +2183,75 @@ Datum
 pg_available_extensions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
 	DIR		   *dir;
 	struct dirent *de;
+	List	   *locations;
+	ListCell   *cell;
 
 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();
 
-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach(cell, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
-			Datum		values[3];
-			bool		nulls[3];
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;
+				Datum		values[3];
+				bool		nulls[3];
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			control = read_extension_control_file(extname);
+				control = read_extension_control_file(extname);
 
-			memset(values, 0, sizeof(values));
-			memset(nulls, 0, sizeof(nulls));
+				memset(values, 0, sizeof(values));
+				memset(nulls, 0, sizeof(nulls));
 
-			/* name */
-			values[0] = DirectFunctionCall1(namein,
-											CStringGetDatum(control->name));
-			/* default_version */
-			if (control->default_version == NULL)
-				nulls[1] = true;
-			else
-				values[1] = CStringGetTextDatum(control->default_version);
-			/* comment */
-			if (control->comment == NULL)
-				nulls[2] = true;
-			else
-				values[2] = CStringGetTextDatum(control->comment);
+				/* name */
+				values[0] = DirectFunctionCall1(namein,
+												CStringGetDatum(control->name));
+				/* default_version */
+				if (control->default_version == NULL)
+					nulls[1] = true;
+				else
+					values[1] = CStringGetTextDatum(control->default_version);
+				/* comment */
+				if (control->comment == NULL)
+					nulls[2] = true;
+				else
+					values[2] = CStringGetTextDatum(control->comment);
 
-			tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
-								 values, nulls);
-		}
+				tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
+									 values, nulls);
+			}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}
 
 	return (Datum) 0;
@@ -2201,51 +2270,57 @@ Datum
 pg_available_extension_versions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
+	List	   *locations;
+	ListCell   *cell;
 	DIR		   *dir;
 	struct dirent *de;
 
 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
-
-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	locations = get_extension_control_directories();
+	foreach(cell, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
+		{
+			/* do nothing */
+		}
+		else
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			/* read the control file */
-			control = read_extension_control_file(extname);
+				/* read the control file */
+				control = read_extension_control_file(extname);
 
-			/* scan extension's script directory for install scripts */
-			get_available_versions_for_extension(control, rsinfo->setResult,
-												 rsinfo->setDesc);
-		}
+				/* scan extension's script directory for install scripts */
+				get_available_versions_for_extension(control, rsinfo->setResult,
+													 rsinfo->setDesc);
+			}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}
 
 	return (Datum) 0;
@@ -2373,47 +2448,56 @@ bool
 extension_file_exists(const char *extensionName)
 {
 	bool		result = false;
-	char	   *location;
+	List	   *locations;
+	ListCell   *cell;
 	DIR		   *dir;
 	struct dirent *de;
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();
 
-	/*
-	 * If the control directory doesn't exist, we want to silently return
-	 * false.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach(cell, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * false.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			char	   *extname;
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				char	   *extname;
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			/* done if it matches request */
-			if (strcmp(extname, extensionName) == 0)
-			{
-				result = true;
-				break;
+				/* done if it matches request */
+				if (strcmp(extname, extensionName) == 0)
+				{
+					result = true;
+					break;
+				}
 			}
-		}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
+		if (result)
+			break;
 	}
 
 	return result;
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 87b233cb887..46a46715ec7 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -71,8 +71,7 @@ static void incompatible_module_error(const char *libname,
 									  const Pg_magic_struct *module_magic_data) pg_attribute_noreturn();
 static char *expand_dynamic_library_name(const char *name);
 static void check_restricted_library_name(const char *name);
-static char *substitute_libpath_macro(const char *name);
-static char *find_in_dynamic_libpath(const char *basename);
+static char *substitute_path_macro(const char *str, const char *macro, const char *value);
 
 /* Magic structure that module needs to match to be accepted */
 static const Pg_magic_struct magic_data = PG_MODULE_MAGIC_DATA;
@@ -398,7 +397,7 @@ incompatible_module_error(const char *libname,
 /*
  * If name contains a slash, check if the file exists, if so return
  * the name.  Else (no slash) try to expand using search path (see
- * find_in_dynamic_libpath below); if that works, return the fully
+ * find_in_path below); if that works, return the fully
  * expanded file name.  If the previous failed, append DLSUFFIX and
  * try again.  If all fails, just return the original name.
  *
@@ -413,17 +412,25 @@ expand_dynamic_library_name(const char *name)
 
 	Assert(name);
 
+	/*
+	 * If the value starts with "$libdir/", strip that.  This is because many
+	 * extensions have hardcoded '$libdir/foo' as their library name, which
+	 * prevents using the path.
+	 */
+	if (strncmp(name, "$libdir/", 8) == 0)
+		name += 8;
+
 	have_slash = (first_dir_separator(name) != NULL);
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(name);
+		full = find_in_path(name, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(name);
+		full = substitute_path_macro(name, "$libdir", pkglib_path);
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -433,14 +440,14 @@ expand_dynamic_library_name(const char *name)
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(new);
+		full = find_in_path(new, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		pfree(new);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(new);
+		full = substitute_path_macro(new, "$libdir", pkglib_path);
 		pfree(new);
 		if (pg_file_exists(full))
 			return full;
@@ -475,47 +482,60 @@ check_restricted_library_name(const char *name)
  * Result is always freshly palloc'd.
  */
 static char *
-substitute_libpath_macro(const char *name)
+substitute_path_macro(const char *str, const char *macro, const char *value)
 {
 	const char *sep_ptr;
 
-	Assert(name != NULL);
+	Assert(str != NULL);
+	Assert(macro[0] == '$');
 
-	/* Currently, we only recognize $libdir at the start of the string */
-	if (name[0] != '$')
-		return pstrdup(name);
+	/* Currently, we only recognize $macro at the start of the string */
+	if (str[0] != '$')
+		return pstrdup(str);
 
-	if ((sep_ptr = first_dir_separator(name)) == NULL)
-		sep_ptr = name + strlen(name);
+	if ((sep_ptr = first_dir_separator(str)) == NULL)
+		sep_ptr = str + strlen(str);
 
-	if (strlen("$libdir") != sep_ptr - name ||
-		strncmp(name, "$libdir", strlen("$libdir")) != 0)
+	if (strlen(macro) != sep_ptr - str ||
+		strncmp(str, macro, strlen(macro)) != 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_NAME),
-				 errmsg("invalid macro name in dynamic library path: %s",
-						name)));
+				 errmsg("invalid macro name in path: %s",
+						str)));
 
-	return psprintf("%s%s", pkglib_path, sep_ptr);
+	return psprintf("%s%s", value, sep_ptr);
 }
 
 
 /*
  * Search for a file called 'basename' in the colon-separated search
- * path Dynamic_library_path.  If the file is found, the full file name
+ * path given.  If the file is found, the full file name
  * is returned in freshly palloc'd memory.  If the file is not found,
  * return NULL.
+ *
+ * path_param is the name of the parameter that path came from, for error
+ * messages.
+ *
+ * macro and macro_val allow substituting a macro; see
+ * substitute_path_macro().
  */
-static char *
-find_in_dynamic_libpath(const char *basename)
+char *
+find_in_path(const char *basename, const char *path, const char *path_param,
+			 const char *macro, const char *macro_val)
 {
 	const char *p;
 	size_t		baselen;
 
 	Assert(basename != NULL);
 	Assert(first_dir_separator(basename) == NULL);
-	Assert(Dynamic_library_path != NULL);
+	Assert(path != NULL);
+	Assert(path_param != NULL);
+
+	p = path;
 
-	p = Dynamic_library_path;
+	/*
+	 * If the path variable is empty, don't do a path search.
+	 */
 	if (strlen(p) == 0)
 		return NULL;
 
@@ -532,7 +552,7 @@ find_in_dynamic_libpath(const char *basename)
 		if (piece == p)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("zero-length component in parameter \"dynamic_library_path\"")));
+					 errmsg("zero-length component in parameter \"%s\"", path_param)));
 
 		if (piece == NULL)
 			len = strlen(p);
@@ -542,7 +562,7 @@ find_in_dynamic_libpath(const char *basename)
 		piece = palloc(len + 1);
 		strlcpy(piece, p, len + 1);
 
-		mangled = substitute_libpath_macro(piece);
+		mangled = substitute_path_macro(piece, macro, macro_val);
 		pfree(piece);
 
 		canonicalize_path(mangled);
@@ -551,13 +571,13 @@ find_in_dynamic_libpath(const char *basename)
 		if (!is_absolute_path(mangled))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("component in parameter \"dynamic_library_path\" is not an absolute path")));
+					 errmsg("component in parameter \"%s\" is not an absolute path", path_param)));
 
 		full = palloc(strlen(mangled) + 1 + baselen + 1);
 		sprintf(full, "%s/%s", mangled, basename);
 		pfree(mangled);
 
-		elog(DEBUG3, "find_in_dynamic_libpath: trying \"%s\"", full);
+		elog(DEBUG3, "%s: trying \"%s\"", __func__, full);
 
 		if (pg_file_exists(full))
 			return full;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 690bf96ef03..c587e53078e 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -39,6 +39,7 @@
 #include "catalog/namespace.h"
 #include "catalog/storage.h"
 #include "commands/async.h"
+#include "commands/extension.h"
 #include "commands/event_trigger.h"
 #include "commands/tablespace.h"
 #include "commands/trigger.h"
@@ -4305,6 +4306,18 @@ struct config_string ConfigureNamesString[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"extension_control_path", PGC_SUSET, CLIENT_CONN_OTHER,
+			gettext_noop("Sets the path for extension control files."),
+			gettext_noop("The remaining extension script and secondary control files are then loaded "
+						 "from the same directory where the primary control file was found."),
+			GUC_SUPERUSER_ONLY
+		},
+		&Extension_control_path,
+		"$system",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"krb_server_keyfile", PGC_SIGHUP, CONN_AUTH_AUTH,
 			gettext_noop("Sets the location of the Kerberos server key file."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e771d87da1f..92d14f728b2 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -790,6 +790,7 @@ autovacuum_worker_slots = 16	# autovacuum worker slots to allocate
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_control_path = '$system'
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/commands/extension.h b/src/include/commands/extension.h
index 0b636405120..24419bfb5c9 100644
--- a/src/include/commands/extension.h
+++ b/src/include/commands/extension.h
@@ -17,6 +17,8 @@
 #include "catalog/objectaddress.h"
 #include "parser/parse_node.h"
 
+/* GUC */
+extern PGDLLIMPORT char *Extension_control_path;
 
 /*
  * creating_extension is only true while running a CREATE EXTENSION or ALTER
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index e609ea875a7..5811307a82c 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -740,6 +740,8 @@ extern bool CheckFunctionValidatorAccess(Oid validatorOid, Oid functionOid);
  */
 extern PGDLLIMPORT char *Dynamic_library_path;
 
+extern char *find_in_path(const char *basename, const char *path, const char *path_param,
+						  const char *macro, const char *macro_val);
 extern void *load_external_function(const char *filename, const char *funcname,
 									bool signalNotFound, void **filehandle);
 extern void *lookup_external_function(void *filehandle, const char *funcname);
diff --git a/src/test/modules/test_extensions/Makefile b/src/test/modules/test_extensions/Makefile
index 1dbec14cba3..a3591bf3d2f 100644
--- a/src/test/modules/test_extensions/Makefile
+++ b/src/test/modules/test_extensions/Makefile
@@ -28,6 +28,7 @@ DATA = test_ext1--1.0.sql test_ext2--1.0.sql test_ext3--1.0.sql \
        test_ext_req_schema3--1.0.sql
 
 REGRESS = test_extensions test_extdepend
+TAP_TESTS = 1
 
 # force C locale for output stability
 NO_LOCALE = 1
diff --git a/src/test/modules/test_extensions/meson.build b/src/test/modules/test_extensions/meson.build
index dd7ec0ce56b..3c7e378bf35 100644
--- a/src/test/modules/test_extensions/meson.build
+++ b/src/test/modules/test_extensions/meson.build
@@ -57,4 +57,9 @@ tests += {
     ],
     'regress_args': ['--no-locale'],
   },
+  'tap': {
+    'tests': [
+      't/001_extension_control_path.pl',
+    ],
+  },
 }
diff --git a/src/test/modules/test_extensions/t/001_extension_control_path.pl b/src/test/modules/test_extensions/t/001_extension_control_path.pl
new file mode 100644
index 00000000000..74747b3e9f4
--- /dev/null
+++ b/src/test/modules/test_extensions/t/001_extension_control_path.pl
@@ -0,0 +1,56 @@
+# Copyright (c) 2024-2025, PostgreSQL Global Development Group
+
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Utils;
+use PostgreSQL::Test::Cluster;
+use Test::More;
+
+my $node = PostgreSQL::Test::Cluster->new('node');
+
+$node->init;
+
+# Create a temporary directory for the extension control file
+my $ext_dir = PostgreSQL::Test::Utils::tempdir();
+my $ext_name = "test_custom_ext_paths";
+my $control_file = "$ext_dir/$ext_name.control";
+my $sql_file = "$ext_dir/$ext_name--1.0.sql";
+
+# Create .control .sql file
+open my $cf, '>', $control_file or die "Could not create control file: $!";
+print $cf "default_version = '1.0'\n";
+print $cf "relocatable = true\n";
+close $cf;
+
+# Create --1.0.sql file
+open my $sqlf, '>', $sql_file or die "Could not create sql file: $!";
+print $sqlf "/* $sql_file */'\n";
+print $sqlf "-- complain if script is sourced in psql, rather than via CREATE EXTENSION\n";
+print $sqlf qq'\\echo Use "CREATE EXTENSION $ext_name" to load this file. \\quit\n';
+close $sqlf;
+
+# Use the correct separator and escape \ when running on Windows.
+my $sep = $windows_os ? ";" : ":";
+$node->append_conf(
+    'postgresql.conf', qq{
+extension_control_path = '\$system$sep@{[ $windows_os ? ($ext_dir =~ s/\\/\\\\/gr) : $ext_dir ]}'
+});
+
+# Start node
+$node->start;
+
+my $ecp = $node->safe_psql('postgres', 'show extension_control_path;');
+
+is($ecp, "\$system$sep$ext_dir");
+
+my $ret = $node->safe_psql(
+	'postgres',
+	"select count(1) > 0 as ok from pg_available_extensions where name = '$ext_name'");
+is($ret, "t", "Expected to list available extension on a custom extension control path directory");
+
+my $ret2 = $node->safe_psql(
+	'postgres',
+	"select count(1) > 0 as ok from pg_available_extension_versions where name = '$ext_name'");
+is($ret2, "t", "Expected to list available extension with version on a custom extension control path directory");
+
+done_testing();
-- 
2.39.5 (Apple Git-154)

From 96f7be3962ceb3caccfcec5473bf5fcf9c9d666e Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 5 Dec 2024 11:49:05 +0100
Subject: [PATCH v5] extension_control_path

The new GUC extension_control_path specifies a path to look for
extension control files.  The default value is $system, which looks in
the compiled-in location, as before.

The path search uses the same code and works in the same way as
dynamic_library_path.

Discussion: https://www.postgresql.org/message-id/flat/E7C7BFFB-8857-48D4-A71F-88B359FADCFD@justatheory.com
---
 doc/src/sgml/config.sgml                      |  68 ++++
 doc/src/sgml/extend.sgml                      |  19 +-
 doc/src/sgml/ref/create_extension.sgml        |   6 +-
 src/Makefile.global.in                        |  19 +-
 src/backend/commands/extension.c              | 348 +++++++++++-------
 src/backend/utils/fmgr/dfmgr.c                |  76 ++--
 src/backend/utils/misc/guc_tables.c           |  13 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/commands/extension.h              |   2 +
 src/include/fmgr.h                            |   2 +
 src/test/modules/test_extensions/Makefile     |   1 +
 src/test/modules/test_extensions/meson.build  |   5 +
 .../t/001_extension_control_path.pl           |  67 ++++
 13 files changed, 453 insertions(+), 174 deletions(-)
 create mode 100644 src/test/modules/test_extensions/t/001_extension_control_path.pl

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index e55700f35b8..69c23f17aef 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10726,6 +10726,74 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-extension-control-path" xreflabel="extension_control_path">
+      <term><varname>extension_control_path</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_control_path</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        A path to search for extensions, specifically extension control files
+        (<filename><replaceable>name</replaceable>.control</filename>).  The
+        remaining extension script and secondary control files are then loaded
+        from the same directory where the primary control file was found.
+        See <xref linkend="extend-extensions-files"/> for details.
+       </para>
+
+       <para>
+        The value for <varname>extension_control_path</varname> must be a
+        list of absolute directory paths separated by colons (or semi-colons
+        on Windows).  If a list element starts
+        with the special string <literal>$system</literal>, the
+        compiled-in <productname>PostgreSQL</productname> extension
+        directory is substituted for <literal>$system</literal>; this
+        is where the extensions provided by the standard
+        <productname>PostgreSQL</productname> distribution are installed.
+        (Use <literal>pg_config --sharedir</literal> to find out the name of
+        this directory.) For example:
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:/home/my_project/share/extension:$system'
+</programlisting>
+        or, in a Windows environment:
+<programlisting>
+extension_control_path = 'C:\tools\postgresql\extension;H:\my_project\share\extension;$system'
+</programlisting>
+        Note that the path elements should typically end in
+        <literal>extension</literal> if the normal installation layouts are
+        followed.  (The value for <literal>$system</literal> already includes
+        the <literal>extension</literal> suffix.)
+       </para>
+
+       <para>
+        The default value for this parameter is
+        <literal>'$system'</literal>. If the value is set to an empty
+        string, the default <literal>'$system'</literal> is also assumed.
+       </para>
+
+       <para>
+        This parameter can be changed at run time by superusers and users
+        with the appropriate <literal>SET</literal> privilege, but a
+        setting done that way will only persist until the end of the
+        client connection, so this method should be reserved for
+        development purposes. The recommended way to set this parameter
+        is in the <filename>postgresql.conf</filename> configuration
+        file.
+       </para>
+
+       <para>
+        Note that if you set this parameter to be able to load extensions from
+        nonstandard locations, you will most likely also need to set <xref
+        linkend="guc-dynamic-library-path"/> to a correspondent location, for
+        example,
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:$system'
+dynamic_library_path = '/usr/local/lib/postgresql:$libdir'
+</programlisting>
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-gin-fuzzy-search-limit" xreflabel="gin_fuzzy_search_limit">
       <term><varname>gin_fuzzy_search_limit</varname> (<type>integer</type>)
       <indexterm>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index ba492ca27c0..64f8e133cae 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -649,6 +649,11 @@ RETURNS anycompatible AS ...
      control file can specify a different directory for the script file(s).
     </para>
 
+    <para>
+     Additional locations for extension control files can be configured using
+     the parameter <xref linkend="guc-extension-control-path"/>.
+    </para>
+
     <para>
      The file format for an extension control file is the same as for the
      <filename>postgresql.conf</filename> file, namely a list of
@@ -669,9 +674,9 @@ RETURNS anycompatible AS ...
        <para>
         The directory containing the extension's <acronym>SQL</acronym> script
         file(s).  Unless an absolute path is given, the name is relative to
-        the installation's <literal>SHAREDIR</literal> directory.  The
-        default behavior is equivalent to specifying
-        <literal>directory = 'extension'</literal>.
+        the installation's <literal>SHAREDIR</literal> directory.  By default,
+        the script files are looked for in the same directory where the
+        control file was found.
        </para>
       </listitem>
      </varlistentry>
@@ -719,8 +724,8 @@ RETURNS anycompatible AS ...
        <para>
         The value of this parameter will be substituted for each occurrence
         of <literal>MODULE_PATHNAME</literal> in the script file(s).  If it is not
-        set, no substitution is made.  Typically, this is set to
-        <literal>$libdir/<replaceable>shared_library_name</replaceable></literal> and
+        set, no substitution is made.  Typically, this is set to just
+        <literal><replaceable>shared_library_name</replaceable></literal> and
         then <literal>MODULE_PATHNAME</literal> is used in <command>CREATE
         FUNCTION</command> commands for C-language functions, so that the script
         files do not need to hard-wire the name of the shared library.
@@ -1804,6 +1809,10 @@ include $(PGXS)
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
+    You can also select a separate installation directory for your extension
+    by setting the <literal>make</literal> variable <varname>prefix</varname>
+    on the <literal>make</literal> command line.  (But this will then require
+    additional setup to get the server to find the extension there.)
    </para>
 
    <para>
diff --git a/doc/src/sgml/ref/create_extension.sgml b/doc/src/sgml/ref/create_extension.sgml
index ca2b80d669c..713abd9c494 100644
--- a/doc/src/sgml/ref/create_extension.sgml
+++ b/doc/src/sgml/ref/create_extension.sgml
@@ -90,8 +90,10 @@ CREATE EXTENSION [ IF NOT EXISTS ] <replaceable class="parameter">extension_name
        <para>
         The name of the extension to be
         installed. <productname>PostgreSQL</productname> will create the
-        extension using details from the file
-        <literal>SHAREDIR/extension/</literal><replaceable class="parameter">extension_name</replaceable><literal>.control</literal>.
+        extension using details from the file <filename><replaceable
+        class="parameter">extension_name</replaceable>.control</filename>,
+        found via the server's extension control path (set by <xref
+        linkend="guc-extension-control-path"/>.)
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index 3b620bac5ac..8fe9d61e82a 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -87,9 +87,19 @@ endif # not PGXS
 #
 # In a PGXS build, we cannot use the values inserted into Makefile.global
 # by configure, since the installation tree may have been relocated.
-# Instead get the path values from pg_config.
+# Instead get the path values from pg_config.  But users can specify
+# prefix explicitly, if they want to select their own installation
+# location.
 
-ifndef PGXS
+ifdef PGXS
+# Extension makefiles should set PG_CONFIG, but older ones might not
+ifndef PG_CONFIG
+PG_CONFIG = pg_config
+endif
+endif
+
+# This means: if ((not PGXS) or prefix)
+ifneq (,$(if $(PGXS),,1)$(prefix))
 
 # Note that prefix, exec_prefix, and datarootdir aren't defined in a PGXS build;
 # makefiles may only use the derived variables such as bindir.
@@ -147,11 +157,6 @@ localedir := @localedir@
 
 else # PGXS case
 
-# Extension makefiles should set PG_CONFIG, but older ones might not
-ifndef PG_CONFIG
-PG_CONFIG = pg_config
-endif
-
 bindir := $(shell $(PG_CONFIG) --bindir)
 datadir := $(shell $(PG_CONFIG) --sharedir)
 sysconfdir := $(shell $(PG_CONFIG) --sysconfdir)
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index d9bb4ce5f1e..7e8a28e4064 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -51,6 +51,7 @@
 #include "commands/defrem.h"
 #include "commands/extension.h"
 #include "commands/schemacmds.h"
+#include "nodes/pg_list.h"
 #include "funcapi.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
@@ -69,6 +70,9 @@
 #include "utils/varlena.h"
 
 
+/* GUC */
+char	   *Extension_control_path;
+
 /* Globally visible state variables */
 bool		creating_extension = false;
 Oid			CurrentExtensionObject = InvalidOid;
@@ -79,6 +83,7 @@ Oid			CurrentExtensionObject = InvalidOid;
 typedef struct ExtensionControlFile
 {
 	char	   *name;			/* name of the extension */
+	char	   *control_dir;	/* directory where control file was found */
 	char	   *directory;		/* directory for script files */
 	char	   *default_version;	/* default install target version, if any */
 	char	   *module_pathname;	/* string to substitute for
@@ -328,29 +333,88 @@ is_extension_script_filename(const char *filename)
 	return (extension != NULL) && (strcmp(extension, ".sql") == 0);
 }
 
-static char *
-get_extension_control_directory(void)
+/*
+ * Return a list of directories declared on extension_control_path GUC.
+ */
+static List *
+get_extension_control_directories(void)
 {
 	char		sharepath[MAXPGPATH];
-	char	   *result;
+	char	   *system_dir;
+	char	   *ecp;
+	char	   *token;
+	char	   *path;
+	List	   *paths = NIL;
 
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension", sharepath);
 
-	return result;
+	system_dir = psprintf("%s/extension", sharepath);
+
+	if (strlen(Extension_control_path) == 0)
+	{
+		paths = lappend(paths, system_dir);
+	}
+	else
+	{
+		/* Duplicate the string so we can modify it */
+		ecp = pstrdup(Extension_control_path);
+
+		/* Consume each path between ':' */
+		for (token = strtok(ecp, ":"); token != NULL; token = strtok(NULL, ":"))
+		{
+			if (strcmp(token, "$system") == 0)
+				path = system_dir;
+			else
+				path = pstrdup(token);
+
+			paths = lappend(paths, path);
+		}
+
+		pfree(ecp);
+	}
+
+	return paths;
 }
 
+/*
+ * Find control file for extension with name in control->name, looking in the
+ * path.  Return the full file name, or NULL if not found.  If found, the
+ * directory is recorded in control->control_dir.
+ */
 static char *
-get_extension_control_filename(const char *extname)
+find_extension_control_filename(ExtensionControlFile *control)
 {
 	char		sharepath[MAXPGPATH];
+	char	   *system_dir;
+	char	   *basename;
+	char	   *ecp;
 	char	   *result;
 
+	Assert(control->name);
+
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
-			 sharepath, extname);
+	system_dir = psprintf("%s/extension", sharepath);
+
+	basename = psprintf("%s.control", control->name);
+
+	/*
+	 * find_in_path() does nothing if the path value is empty.  This is the
+	 * historical behavior for dynamic_library_path, but it makes no sense for
+	 * extensions.  So in that case, substitute a default value.
+	 */
+	ecp = Extension_control_path;
+	if (strlen(ecp) == 0)
+		ecp = "$system";
+	result = find_in_path(basename, Extension_control_path, "extension_control_path", "$system", system_dir);
+
+	if (result)
+	{
+		const char *p;
+
+		p = strrchr(result, '/');
+		Assert(p);
+		control->control_dir = pnstrdup(result, p - result);
+	}
 
 	return result;
 }
@@ -366,7 +430,7 @@ get_extension_script_directory(ExtensionControlFile *control)
 	 * installation's share directory.
 	 */
 	if (!control->directory)
-		return get_extension_control_directory();
+		return pstrdup(control->control_dir);
 
 	if (is_absolute_path(control->directory))
 		return pstrdup(control->directory);
@@ -444,27 +508,25 @@ parse_extension_control_file(ExtensionControlFile *control,
 	if (version)
 		filename = get_extension_aux_control_filename(control, version);
 	else
-		filename = get_extension_control_filename(control->name);
+		filename = find_extension_control_filename(control);
+
+	if (!filename)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("extension \"%s\" is not available", control->name),
+				 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+	}
 
 	if ((file = AllocateFile(filename, "r")) == NULL)
 	{
-		if (errno == ENOENT)
+		/* no complaint for missing auxiliary file */
+		if (errno == ENOENT && version)
 		{
-			/* no complaint for missing auxiliary file */
-			if (version)
-			{
-				pfree(filename);
-				return;
-			}
-
-			/* missing control file indicates extension is not installed */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("extension \"%s\" is not available", control->name),
-					 errdetail("Could not open extension control file \"%s\": %m.",
-							   filename),
-					 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+			pfree(filename);
+			return;
 		}
+
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not open extension control file \"%s\": %m",
@@ -2121,68 +2183,75 @@ Datum
 pg_available_extensions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
 	DIR		   *dir;
 	struct dirent *de;
+	List	   *locations;
+	ListCell   *cell;
 
 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();
 
-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach(cell, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
-			Datum		values[3];
-			bool		nulls[3];
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;
+				Datum		values[3];
+				bool		nulls[3];
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			control = read_extension_control_file(extname);
+				control = read_extension_control_file(extname);
 
-			memset(values, 0, sizeof(values));
-			memset(nulls, 0, sizeof(nulls));
+				memset(values, 0, sizeof(values));
+				memset(nulls, 0, sizeof(nulls));
 
-			/* name */
-			values[0] = DirectFunctionCall1(namein,
-											CStringGetDatum(control->name));
-			/* default_version */
-			if (control->default_version == NULL)
-				nulls[1] = true;
-			else
-				values[1] = CStringGetTextDatum(control->default_version);
-			/* comment */
-			if (control->comment == NULL)
-				nulls[2] = true;
-			else
-				values[2] = CStringGetTextDatum(control->comment);
+				/* name */
+				values[0] = DirectFunctionCall1(namein,
+												CStringGetDatum(control->name));
+				/* default_version */
+				if (control->default_version == NULL)
+					nulls[1] = true;
+				else
+					values[1] = CStringGetTextDatum(control->default_version);
+				/* comment */
+				if (control->comment == NULL)
+					nulls[2] = true;
+				else
+					values[2] = CStringGetTextDatum(control->comment);
 
-			tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
-								 values, nulls);
-		}
+				tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
+									 values, nulls);
+			}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}
 
 	return (Datum) 0;
@@ -2201,51 +2270,57 @@ Datum
 pg_available_extension_versions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
+	List	   *locations;
+	ListCell   *cell;
 	DIR		   *dir;
 	struct dirent *de;
 
 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
-
-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	locations = get_extension_control_directories();
+	foreach(cell, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
+		{
+			/* do nothing */
+		}
+		else
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			/* read the control file */
-			control = read_extension_control_file(extname);
+				/* read the control file */
+				control = read_extension_control_file(extname);
 
-			/* scan extension's script directory for install scripts */
-			get_available_versions_for_extension(control, rsinfo->setResult,
-												 rsinfo->setDesc);
-		}
+				/* scan extension's script directory for install scripts */
+				get_available_versions_for_extension(control, rsinfo->setResult,
+													 rsinfo->setDesc);
+			}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}
 
 	return (Datum) 0;
@@ -2373,47 +2448,56 @@ bool
 extension_file_exists(const char *extensionName)
 {
 	bool		result = false;
-	char	   *location;
+	List	   *locations;
+	ListCell   *cell;
 	DIR		   *dir;
 	struct dirent *de;
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();
 
-	/*
-	 * If the control directory doesn't exist, we want to silently return
-	 * false.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach(cell, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		char	   *location = (char *) lfirst(cell);
+
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * false.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			char	   *extname;
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				char	   *extname;
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			/* done if it matches request */
-			if (strcmp(extname, extensionName) == 0)
-			{
-				result = true;
-				break;
+				/* done if it matches request */
+				if (strcmp(extname, extensionName) == 0)
+				{
+					result = true;
+					break;
+				}
 			}
-		}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
+		if (result)
+			break;
 	}
 
 	return result;
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 87b233cb887..46a46715ec7 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -71,8 +71,7 @@ static void incompatible_module_error(const char *libname,
 									  const Pg_magic_struct *module_magic_data) pg_attribute_noreturn();
 static char *expand_dynamic_library_name(const char *name);
 static void check_restricted_library_name(const char *name);
-static char *substitute_libpath_macro(const char *name);
-static char *find_in_dynamic_libpath(const char *basename);
+static char *substitute_path_macro(const char *str, const char *macro, const char *value);
 
 /* Magic structure that module needs to match to be accepted */
 static const Pg_magic_struct magic_data = PG_MODULE_MAGIC_DATA;
@@ -398,7 +397,7 @@ incompatible_module_error(const char *libname,
 /*
  * If name contains a slash, check if the file exists, if so return
  * the name.  Else (no slash) try to expand using search path (see
- * find_in_dynamic_libpath below); if that works, return the fully
+ * find_in_path below); if that works, return the fully
  * expanded file name.  If the previous failed, append DLSUFFIX and
  * try again.  If all fails, just return the original name.
  *
@@ -413,17 +412,25 @@ expand_dynamic_library_name(const char *name)
 
 	Assert(name);
 
+	/*
+	 * If the value starts with "$libdir/", strip that.  This is because many
+	 * extensions have hardcoded '$libdir/foo' as their library name, which
+	 * prevents using the path.
+	 */
+	if (strncmp(name, "$libdir/", 8) == 0)
+		name += 8;
+
 	have_slash = (first_dir_separator(name) != NULL);
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(name);
+		full = find_in_path(name, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(name);
+		full = substitute_path_macro(name, "$libdir", pkglib_path);
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -433,14 +440,14 @@ expand_dynamic_library_name(const char *name)
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(new);
+		full = find_in_path(new, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		pfree(new);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(new);
+		full = substitute_path_macro(new, "$libdir", pkglib_path);
 		pfree(new);
 		if (pg_file_exists(full))
 			return full;
@@ -475,47 +482,60 @@ check_restricted_library_name(const char *name)
  * Result is always freshly palloc'd.
  */
 static char *
-substitute_libpath_macro(const char *name)
+substitute_path_macro(const char *str, const char *macro, const char *value)
 {
 	const char *sep_ptr;
 
-	Assert(name != NULL);
+	Assert(str != NULL);
+	Assert(macro[0] == '$');
 
-	/* Currently, we only recognize $libdir at the start of the string */
-	if (name[0] != '$')
-		return pstrdup(name);
+	/* Currently, we only recognize $macro at the start of the string */
+	if (str[0] != '$')
+		return pstrdup(str);
 
-	if ((sep_ptr = first_dir_separator(name)) == NULL)
-		sep_ptr = name + strlen(name);
+	if ((sep_ptr = first_dir_separator(str)) == NULL)
+		sep_ptr = str + strlen(str);
 
-	if (strlen("$libdir") != sep_ptr - name ||
-		strncmp(name, "$libdir", strlen("$libdir")) != 0)
+	if (strlen(macro) != sep_ptr - str ||
+		strncmp(str, macro, strlen(macro)) != 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_NAME),
-				 errmsg("invalid macro name in dynamic library path: %s",
-						name)));
+				 errmsg("invalid macro name in path: %s",
+						str)));
 
-	return psprintf("%s%s", pkglib_path, sep_ptr);
+	return psprintf("%s%s", value, sep_ptr);
 }
 
 
 /*
  * Search for a file called 'basename' in the colon-separated search
- * path Dynamic_library_path.  If the file is found, the full file name
+ * path given.  If the file is found, the full file name
  * is returned in freshly palloc'd memory.  If the file is not found,
  * return NULL.
+ *
+ * path_param is the name of the parameter that path came from, for error
+ * messages.
+ *
+ * macro and macro_val allow substituting a macro; see
+ * substitute_path_macro().
  */
-static char *
-find_in_dynamic_libpath(const char *basename)
+char *
+find_in_path(const char *basename, const char *path, const char *path_param,
+			 const char *macro, const char *macro_val)
 {
 	const char *p;
 	size_t		baselen;
 
 	Assert(basename != NULL);
 	Assert(first_dir_separator(basename) == NULL);
-	Assert(Dynamic_library_path != NULL);
+	Assert(path != NULL);
+	Assert(path_param != NULL);
+
+	p = path;
 
-	p = Dynamic_library_path;
+	/*
+	 * If the path variable is empty, don't do a path search.
+	 */
 	if (strlen(p) == 0)
 		return NULL;
 
@@ -532,7 +552,7 @@ find_in_dynamic_libpath(const char *basename)
 		if (piece == p)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("zero-length component in parameter \"dynamic_library_path\"")));
+					 errmsg("zero-length component in parameter \"%s\"", path_param)));
 
 		if (piece == NULL)
 			len = strlen(p);
@@ -542,7 +562,7 @@ find_in_dynamic_libpath(const char *basename)
 		piece = palloc(len + 1);
 		strlcpy(piece, p, len + 1);
 
-		mangled = substitute_libpath_macro(piece);
+		mangled = substitute_path_macro(piece, macro, macro_val);
 		pfree(piece);
 
 		canonicalize_path(mangled);
@@ -551,13 +571,13 @@ find_in_dynamic_libpath(const char *basename)
 		if (!is_absolute_path(mangled))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("component in parameter \"dynamic_library_path\" is not an absolute path")));
+					 errmsg("component in parameter \"%s\" is not an absolute path", path_param)));
 
 		full = palloc(strlen(mangled) + 1 + baselen + 1);
 		sprintf(full, "%s/%s", mangled, basename);
 		pfree(mangled);
 
-		elog(DEBUG3, "find_in_dynamic_libpath: trying \"%s\"", full);
+		elog(DEBUG3, "%s: trying \"%s\"", __func__, full);
 
 		if (pg_file_exists(full))
 			return full;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index ad25cbb39c5..c357a5304ae 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -39,6 +39,7 @@
 #include "catalog/namespace.h"
 #include "catalog/storage.h"
 #include "commands/async.h"
+#include "commands/extension.h"
 #include "commands/event_trigger.h"
 #include "commands/tablespace.h"
 #include "commands/trigger.h"
@@ -4314,6 +4315,18 @@ struct config_string ConfigureNamesString[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"extension_control_path", PGC_SUSET, CLIENT_CONN_OTHER,
+			gettext_noop("Sets the path for extension control files."),
+			gettext_noop("The remaining extension script and secondary control files are then loaded "
+						 "from the same directory where the primary control file was found."),
+			GUC_SUPERUSER_ONLY
+		},
+		&Extension_control_path,
+		"$system",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"krb_server_keyfile", PGC_SIGHUP, CONN_AUTH_AUTH,
 			gettext_noop("Sets the location of the Kerberos server key file."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 5362ff80519..24eaeb3dc6b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -791,6 +791,7 @@ autovacuum_worker_slots = 16	# autovacuum worker slots to allocate
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_control_path = '$system'
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/commands/extension.h b/src/include/commands/extension.h
index 0b636405120..24419bfb5c9 100644
--- a/src/include/commands/extension.h
+++ b/src/include/commands/extension.h
@@ -17,6 +17,8 @@
 #include "catalog/objectaddress.h"
 #include "parser/parse_node.h"
 
+/* GUC */
+extern PGDLLIMPORT char *Extension_control_path;
 
 /*
  * creating_extension is only true while running a CREATE EXTENSION or ALTER
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index e609ea875a7..5811307a82c 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -740,6 +740,8 @@ extern bool CheckFunctionValidatorAccess(Oid validatorOid, Oid functionOid);
  */
 extern PGDLLIMPORT char *Dynamic_library_path;
 
+extern char *find_in_path(const char *basename, const char *path, const char *path_param,
+						  const char *macro, const char *macro_val);
 extern void *load_external_function(const char *filename, const char *funcname,
 									bool signalNotFound, void **filehandle);
 extern void *lookup_external_function(void *filehandle, const char *funcname);
diff --git a/src/test/modules/test_extensions/Makefile b/src/test/modules/test_extensions/Makefile
index 1dbec14cba3..a3591bf3d2f 100644
--- a/src/test/modules/test_extensions/Makefile
+++ b/src/test/modules/test_extensions/Makefile
@@ -28,6 +28,7 @@ DATA = test_ext1--1.0.sql test_ext2--1.0.sql test_ext3--1.0.sql \
        test_ext_req_schema3--1.0.sql
 
 REGRESS = test_extensions test_extdepend
+TAP_TESTS = 1
 
 # force C locale for output stability
 NO_LOCALE = 1
diff --git a/src/test/modules/test_extensions/meson.build b/src/test/modules/test_extensions/meson.build
index dd7ec0ce56b..3c7e378bf35 100644
--- a/src/test/modules/test_extensions/meson.build
+++ b/src/test/modules/test_extensions/meson.build
@@ -57,4 +57,9 @@ tests += {
     ],
     'regress_args': ['--no-locale'],
   },
+  'tap': {
+    'tests': [
+      't/001_extension_control_path.pl',
+    ],
+  },
 }
diff --git a/src/test/modules/test_extensions/t/001_extension_control_path.pl b/src/test/modules/test_extensions/t/001_extension_control_path.pl
new file mode 100644
index 00000000000..f857e2140df
--- /dev/null
+++ b/src/test/modules/test_extensions/t/001_extension_control_path.pl
@@ -0,0 +1,67 @@
+# Copyright (c) 2024-2025, PostgreSQL Global Development Group
+
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Utils;
+use PostgreSQL::Test::Cluster;
+use Test::More;
+
+my $node = PostgreSQL::Test::Cluster->new('node');
+
+$node->init;
+
+# Create a temporary directory for the extension control file
+my $ext_dir = PostgreSQL::Test::Utils::tempdir();
+my $ext_name = "test_custom_ext_paths";
+my $control_file = "$ext_dir/$ext_name.control";
+my $sql_file = "$ext_dir/$ext_name--1.0.sql";
+
+# Create .control .sql file
+open my $cf, '>', $control_file or die "Could not create control file: $!";
+print $cf "comment = 'Test extension_control_path'\n";
+print $cf "default_version = '1.0'\n";
+print $cf "relocatable = true\n";
+close $cf;
+
+# Create --1.0.sql file
+open my $sqlf, '>', $sql_file or die "Could not create sql file: $!";
+print $sqlf "/* $sql_file */\n";
+print $sqlf "-- complain if script is sourced in psql, rather than via CREATE EXTENSION\n";
+print $sqlf qq'\\echo Use "CREATE EXTENSION $ext_name" to load this file. \\quit\n';
+close $sqlf;
+
+# Use the correct separator and escape \ when running on Windows.
+my $sep = $windows_os ? ";" : ":";
+$node->append_conf(
+    'postgresql.conf', qq{
+extension_control_path = '\$system$sep@{[ $windows_os ? ($ext_dir =~ s/\\/\\\\/gr) : $ext_dir ]}'
+});
+
+# Start node
+$node->start;
+
+my $ecp = $node->safe_psql('postgres', 'show extension_control_path;');
+
+is($ecp, "\$system$sep$ext_dir", "Custom extension control directory path configured");
+
+$node->safe_psql(
+	'postgres',
+	"CREATE EXTENSION $ext_name");
+
+my $ret = $node->safe_psql(
+	'postgres',
+	"select * from pg_available_extensions where name = '$ext_name'");
+is(
+	$ret,
+	"test_custom_ext_paths|1.0|1.0|Test extension_control_path",
+	"Extension is installed correctly on pg_available_extensions");
+
+my $ret2 = $node->safe_psql(
+	'postgres',
+	"select * from pg_available_extension_versions where name = '$ext_name'");
+is(
+	$ret2,
+	"test_custom_ext_paths|1.0|t|t|f|t|||Test extension_control_path",
+	"Extension is installed correctly on pg_available_extension_versions");
+
+done_testing();
-- 
2.39.5 (Apple Git-154)

From 35c2106558095e74359cec58b9631fa19ed937b3 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 6 Mar 2025 14:28:08 +0100
Subject: [PATCH] Use foreach_ptr

---
 src/backend/commands/extension.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index 7e8a28e4064..4bdb20aaf54 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -51,10 +51,10 @@
 #include "commands/defrem.h"
 #include "commands/extension.h"
 #include "commands/schemacmds.h"
-#include "nodes/pg_list.h"
 #include "funcapi.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
+#include "nodes/pg_list.h"
 #include "nodes/queryjumble.h"
 #include "storage/fd.h"
 #include "tcop/utility.h"
@@ -2183,20 +2183,17 @@ Datum
 pg_available_extensions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	List	   *locations;
 	DIR		   *dir;
 	struct dirent *de;
-	List	   *locations;
-	ListCell   *cell;
 
 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);
 
 	locations = get_extension_control_directories();
 
-	foreach(cell, locations)
+	foreach_ptr(char, location, locations)
 	{
-		char	   *location = (char *) lfirst(cell);
-
 		dir = AllocateDir(location);
 
 		/*
@@ -2271,7 +2268,6 @@ pg_available_extension_versions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
 	List	   *locations;
-	ListCell   *cell;
 	DIR		   *dir;
 	struct dirent *de;
 
@@ -2279,10 +2275,9 @@ pg_available_extension_versions(PG_FUNCTION_ARGS)
 	InitMaterializedSRF(fcinfo, 0);
 
 	locations = get_extension_control_directories();
-	foreach(cell, locations)
-	{
-		char	   *location = (char *) lfirst(cell);
 
+	foreach_ptr(char, location, locations)
+	{
 		dir = AllocateDir(location);
 
 		/*
@@ -2449,16 +2444,13 @@ extension_file_exists(const char *extensionName)
 {
 	bool		result = false;
 	List	   *locations;
-	ListCell   *cell;
 	DIR		   *dir;
 	struct dirent *de;
 
 	locations = get_extension_control_directories();
 
-	foreach(cell, locations)
+	foreach_ptr(char, location, locations)
 	{
-		char	   *location = (char *) lfirst(cell);
-
 		dir = AllocateDir(location);
 
 		/*
-- 
2.48.1

From f0ed47907ab40d3201dfaad6d29f57155337dc2c Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 5 Dec 2024 11:49:05 +0100
Subject: [PATCH v6] extension_control_path

The new GUC extension_control_path specifies a path to look for
extension control files.  The default value is $system, which looks in
the compiled-in location, as before.

The path search uses the same code and works in the same way as
dynamic_library_path.

Discussion: https://www.postgresql.org/message-id/flat/E7C7BFFB-8857-48D4-A71F-88B359FADCFD@justatheory.com
---
 doc/src/sgml/config.sgml                      |  68 ++++
 doc/src/sgml/extend.sgml                      |  19 +-
 doc/src/sgml/ref/create_extension.sgml        |   6 +-
 src/Makefile.global.in                        |  19 +-
 src/backend/commands/extension.c              | 356 +++++++++++-------
 src/backend/utils/fmgr/dfmgr.c                |  77 ++--
 src/backend/utils/misc/guc_tables.c           |  13 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/commands/extension.h              |   2 +
 src/include/fmgr.h                            |   5 +
 src/test/modules/test_extensions/Makefile     |   1 +
 src/test/modules/test_extensions/meson.build  |   5 +
 .../t/001_extension_control_path.pl           |  77 ++++
 13 files changed, 475 insertions(+), 174 deletions(-)
 create mode 100644 src/test/modules/test_extensions/t/001_extension_control_path.pl

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d2fa5f7d1a9..9fec78db6f7 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10725,6 +10725,74 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-extension-control-path" xreflabel="extension_control_path">
+      <term><varname>extension_control_path</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_control_path</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        A path to search for extensions, specifically extension control files
+        (<filename><replaceable>name</replaceable>.control</filename>).  The
+        remaining extension script and secondary control files are then loaded
+        from the same directory where the primary control file was found.
+        See <xref linkend="extend-extensions-files"/> for details.
+       </para>
+
+       <para>
+        The value for <varname>extension_control_path</varname> must be a
+        list of absolute directory paths separated by colons (or semi-colons
+        on Windows).  If a list element starts
+        with the special string <literal>$system</literal>, the
+        compiled-in <productname>PostgreSQL</productname> extension
+        directory is substituted for <literal>$system</literal>; this
+        is where the extensions provided by the standard
+        <productname>PostgreSQL</productname> distribution are installed.
+        (Use <literal>pg_config --sharedir</literal> to find out the name of
+        this directory.) For example:
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:/home/my_project/share/extension:$system'
+</programlisting>
+        or, in a Windows environment:
+<programlisting>
+extension_control_path = 'C:\tools\postgresql\extension;H:\my_project\share\extension;$system'
+</programlisting>
+        Note that the path elements should typically end in
+        <literal>extension</literal> if the normal installation layouts are
+        followed.  (The value for <literal>$system</literal> already includes
+        the <literal>extension</literal> suffix.)
+       </para>
+
+       <para>
+        The default value for this parameter is
+        <literal>'$system'</literal>. If the value is set to an empty
+        string, the default <literal>'$system'</literal> is also assumed.
+       </para>
+
+       <para>
+        This parameter can be changed at run time by superusers and users
+        with the appropriate <literal>SET</literal> privilege, but a
+        setting done that way will only persist until the end of the
+        client connection, so this method should be reserved for
+        development purposes. The recommended way to set this parameter
+        is in the <filename>postgresql.conf</filename> configuration
+        file.
+       </para>
+
+       <para>
+        Note that if you set this parameter to be able to load extensions from
+        nonstandard locations, you will most likely also need to set <xref
+        linkend="guc-dynamic-library-path"/> to a correspondent location, for
+        example,
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:$system'
+dynamic_library_path = '/usr/local/lib/postgresql:$libdir'
+</programlisting>
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-gin-fuzzy-search-limit" xreflabel="gin_fuzzy_search_limit">
       <term><varname>gin_fuzzy_search_limit</varname> (<type>integer</type>)
       <indexterm>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index ba492ca27c0..64f8e133cae 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -649,6 +649,11 @@ RETURNS anycompatible AS ...
      control file can specify a different directory for the script file(s).
     </para>
 
+    <para>
+     Additional locations for extension control files can be configured using
+     the parameter <xref linkend="guc-extension-control-path"/>.
+    </para>
+
     <para>
      The file format for an extension control file is the same as for the
      <filename>postgresql.conf</filename> file, namely a list of
@@ -669,9 +674,9 @@ RETURNS anycompatible AS ...
        <para>
         The directory containing the extension's <acronym>SQL</acronym> script
         file(s).  Unless an absolute path is given, the name is relative to
-        the installation's <literal>SHAREDIR</literal> directory.  The
-        default behavior is equivalent to specifying
-        <literal>directory = 'extension'</literal>.
+        the installation's <literal>SHAREDIR</literal> directory.  By default,
+        the script files are looked for in the same directory where the
+        control file was found.
        </para>
       </listitem>
      </varlistentry>
@@ -719,8 +724,8 @@ RETURNS anycompatible AS ...
        <para>
         The value of this parameter will be substituted for each occurrence
         of <literal>MODULE_PATHNAME</literal> in the script file(s).  If it is not
-        set, no substitution is made.  Typically, this is set to
-        <literal>$libdir/<replaceable>shared_library_name</replaceable></literal> and
+        set, no substitution is made.  Typically, this is set to just
+        <literal><replaceable>shared_library_name</replaceable></literal> and
         then <literal>MODULE_PATHNAME</literal> is used in <command>CREATE
         FUNCTION</command> commands for C-language functions, so that the script
         files do not need to hard-wire the name of the shared library.
@@ -1804,6 +1809,10 @@ include $(PGXS)
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
+    You can also select a separate installation directory for your extension
+    by setting the <literal>make</literal> variable <varname>prefix</varname>
+    on the <literal>make</literal> command line.  (But this will then require
+    additional setup to get the server to find the extension there.)
    </para>
 
    <para>
diff --git a/doc/src/sgml/ref/create_extension.sgml b/doc/src/sgml/ref/create_extension.sgml
index ca2b80d669c..713abd9c494 100644
--- a/doc/src/sgml/ref/create_extension.sgml
+++ b/doc/src/sgml/ref/create_extension.sgml
@@ -90,8 +90,10 @@ CREATE EXTENSION [ IF NOT EXISTS ] <replaceable class="parameter">extension_name
        <para>
         The name of the extension to be
         installed. <productname>PostgreSQL</productname> will create the
-        extension using details from the file
-        <literal>SHAREDIR/extension/</literal><replaceable class="parameter">extension_name</replaceable><literal>.control</literal>.
+        extension using details from the file <filename><replaceable
+        class="parameter">extension_name</replaceable>.control</filename>,
+        found via the server's extension control path (set by <xref
+        linkend="guc-extension-control-path"/>.)
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index 3b620bac5ac..8fe9d61e82a 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -87,9 +87,19 @@ endif # not PGXS
 #
 # In a PGXS build, we cannot use the values inserted into Makefile.global
 # by configure, since the installation tree may have been relocated.
-# Instead get the path values from pg_config.
+# Instead get the path values from pg_config.  But users can specify
+# prefix explicitly, if they want to select their own installation
+# location.
 
-ifndef PGXS
+ifdef PGXS
+# Extension makefiles should set PG_CONFIG, but older ones might not
+ifndef PG_CONFIG
+PG_CONFIG = pg_config
+endif
+endif
+
+# This means: if ((not PGXS) or prefix)
+ifneq (,$(if $(PGXS),,1)$(prefix))
 
 # Note that prefix, exec_prefix, and datarootdir aren't defined in a PGXS build;
 # makefiles may only use the derived variables such as bindir.
@@ -147,11 +157,6 @@ localedir := @localedir@
 
 else # PGXS case
 
-# Extension makefiles should set PG_CONFIG, but older ones might not
-ifndef PG_CONFIG
-PG_CONFIG = pg_config
-endif
-
 bindir := $(shell $(PG_CONFIG) --bindir)
 datadir := $(shell $(PG_CONFIG) --sharedir)
 sysconfdir := $(shell $(PG_CONFIG) --sysconfdir)
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index d9bb4ce5f1e..a45389807de 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -54,6 +54,7 @@
 #include "funcapi.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
+#include "nodes/pg_list.h"
 #include "nodes/queryjumble.h"
 #include "storage/fd.h"
 #include "tcop/utility.h"
@@ -69,6 +70,9 @@
 #include "utils/varlena.h"
 
 
+/* GUC */
+char	   *Extension_control_path;
+
 /* Globally visible state variables */
 bool		creating_extension = false;
 Oid			CurrentExtensionObject = InvalidOid;
@@ -79,6 +83,7 @@ Oid			CurrentExtensionObject = InvalidOid;
 typedef struct ExtensionControlFile
 {
 	char	   *name;			/* name of the extension */
+	char	   *control_dir;	/* directory where control file was found */
 	char	   *directory;		/* directory for script files */
 	char	   *default_version;	/* default install target version, if any */
 	char	   *module_pathname;	/* string to substitute for
@@ -328,29 +333,106 @@ is_extension_script_filename(const char *filename)
 	return (extension != NULL) && (strcmp(extension, ".sql") == 0);
 }
 
-static char *
-get_extension_control_directory(void)
+/*
+ * Return a list of directories declared on extension_control_path GUC.
+ */
+static List *
+get_extension_control_directories(void)
 {
 	char		sharepath[MAXPGPATH];
-	char	   *result;
+	char	   *system_dir;
+	char	   *ecp;
+	List	   *paths = NIL;
 
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension", sharepath);
 
-	return result;
+	system_dir = psprintf("%s/extension", sharepath);
+
+	if (strlen(Extension_control_path) == 0)
+	{
+		paths = lappend(paths, system_dir);
+	}
+	else
+	{
+		/* Duplicate the string so we can modify it */
+		ecp = pstrdup(Extension_control_path);
+
+		{
+			for (;;)
+			{
+				int			len;
+				char	   *mangled;
+				char	   *piece = first_path_var_separator(ecp);
+
+				/* Get the length of the next path on ecp */
+				if (piece == NULL)
+					len = strlen(ecp);
+				else
+					len = piece - ecp;
+
+				/* Copy the next path found on ecp */
+				piece = palloc(len + 1);
+				strlcpy(piece, ecp, len + 1);
+
+				/* Substitute the path macro if needed */
+				mangled = substitute_path_macro(piece, "$system", system_dir);
+				pfree(piece);
+
+				/* Canonicalize the path based on the OS and add to the list */
+				canonicalize_path(mangled);
+				paths = lappend(paths, mangled);
+
+				/* Break if ecp is empty or move to the next path on ecp */
+				if (ecp[len] == '\0')
+					break;
+				else
+					ecp += len + 1;
+			}
+		}
+	}
+
+	return paths;
 }
 
+/*
+ * Find control file for extension with name in control->name, looking in the
+ * path.  Return the full file name, or NULL if not found.  If found, the
+ * directory is recorded in control->control_dir.
+ */
 static char *
-get_extension_control_filename(const char *extname)
+find_extension_control_filename(ExtensionControlFile *control)
 {
 	char		sharepath[MAXPGPATH];
+	char	   *system_dir;
+	char	   *basename;
+	char	   *ecp;
 	char	   *result;
 
+	Assert(control->name);
+
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
-			 sharepath, extname);
+	system_dir = psprintf("%s/extension", sharepath);
+
+	basename = psprintf("%s.control", control->name);
+
+	/*
+	 * find_in_path() does nothing if the path value is empty.  This is the
+	 * historical behavior for dynamic_library_path, but it makes no sense for
+	 * extensions.  So in that case, substitute a default value.
+	 */
+	ecp = Extension_control_path;
+	if (strlen(ecp) == 0)
+		ecp = "$system";
+	result = find_in_path(basename, Extension_control_path, "extension_control_path", "$system", system_dir);
+
+	if (result)
+	{
+		const char *p;
+
+		p = strrchr(result, '/');
+		Assert(p);
+		control->control_dir = pnstrdup(result, p - result);
+	}
 
 	return result;
 }
@@ -366,7 +448,7 @@ get_extension_script_directory(ExtensionControlFile *control)
 	 * installation's share directory.
 	 */
 	if (!control->directory)
-		return get_extension_control_directory();
+		return pstrdup(control->control_dir);
 
 	if (is_absolute_path(control->directory))
 		return pstrdup(control->directory);
@@ -444,27 +526,25 @@ parse_extension_control_file(ExtensionControlFile *control,
 	if (version)
 		filename = get_extension_aux_control_filename(control, version);
 	else
-		filename = get_extension_control_filename(control->name);
+		filename = find_extension_control_filename(control);
+
+	if (!filename)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("extension \"%s\" is not available", control->name),
+				 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+	}
 
 	if ((file = AllocateFile(filename, "r")) == NULL)
 	{
-		if (errno == ENOENT)
+		/* no complaint for missing auxiliary file */
+		if (errno == ENOENT && version)
 		{
-			/* no complaint for missing auxiliary file */
-			if (version)
-			{
-				pfree(filename);
-				return;
-			}
-
-			/* missing control file indicates extension is not installed */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("extension \"%s\" is not available", control->name),
-					 errdetail("Could not open extension control file \"%s\": %m.",
-							   filename),
-					 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+			pfree(filename);
+			return;
 		}
+
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not open extension control file \"%s\": %m",
@@ -2121,68 +2201,72 @@ Datum
 pg_available_extensions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
+	List	   *locations;
 	DIR		   *dir;
 	struct dirent *de;
 
 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();
 
-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach_ptr(char, location, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
-			Datum		values[3];
-			bool		nulls[3];
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;
+				Datum		values[3];
+				bool		nulls[3];
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			control = read_extension_control_file(extname);
+				control = read_extension_control_file(extname);
 
-			memset(values, 0, sizeof(values));
-			memset(nulls, 0, sizeof(nulls));
+				memset(values, 0, sizeof(values));
+				memset(nulls, 0, sizeof(nulls));
 
-			/* name */
-			values[0] = DirectFunctionCall1(namein,
-											CStringGetDatum(control->name));
-			/* default_version */
-			if (control->default_version == NULL)
-				nulls[1] = true;
-			else
-				values[1] = CStringGetTextDatum(control->default_version);
-			/* comment */
-			if (control->comment == NULL)
-				nulls[2] = true;
-			else
-				values[2] = CStringGetTextDatum(control->comment);
+				/* name */
+				values[0] = DirectFunctionCall1(namein,
+												CStringGetDatum(control->name));
+				/* default_version */
+				if (control->default_version == NULL)
+					nulls[1] = true;
+				else
+					values[1] = CStringGetTextDatum(control->default_version);
+				/* comment */
+				if (control->comment == NULL)
+					nulls[2] = true;
+				else
+					values[2] = CStringGetTextDatum(control->comment);
 
-			tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
-								 values, nulls);
-		}
+				tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
+									 values, nulls);
+			}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}
 
 	return (Datum) 0;
@@ -2201,51 +2285,55 @@ Datum
 pg_available_extension_versions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
+	List	   *locations;
 	DIR		   *dir;
 	struct dirent *de;
 
 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();
 
-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach_ptr(char, location, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			/* read the control file */
-			control = read_extension_control_file(extname);
+				/* read the control file */
+				control = read_extension_control_file(extname);
 
-			/* scan extension's script directory for install scripts */
-			get_available_versions_for_extension(control, rsinfo->setResult,
-												 rsinfo->setDesc);
-		}
+				/* scan extension's script directory for install scripts */
+				get_available_versions_for_extension(control, rsinfo->setResult,
+													 rsinfo->setDesc);
+			}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}
 
 	return (Datum) 0;
@@ -2373,47 +2461,53 @@ bool
 extension_file_exists(const char *extensionName)
 {
 	bool		result = false;
-	char	   *location;
+	List	   *locations;
 	DIR		   *dir;
 	struct dirent *de;
 
-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();
 
-	/*
-	 * If the control directory doesn't exist, we want to silently return
-	 * false.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach_ptr(char, location, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * false.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
+		{
+			/* do nothing */
+		}
+		else
 		{
-			char	   *extname;
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				char	   *extname;
 
-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;
 
-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';
 
-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;
 
-			/* done if it matches request */
-			if (strcmp(extname, extensionName) == 0)
-			{
-				result = true;
-				break;
+				/* done if it matches request */
+				if (strcmp(extname, extensionName) == 0)
+				{
+					result = true;
+					break;
+				}
 			}
-		}
 
-		FreeDir(dir);
+			FreeDir(dir);
+		}
+		if (result)
+			break;
 	}
 
 	return result;
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 87b233cb887..ca12e954ea2 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -71,8 +71,6 @@ static void incompatible_module_error(const char *libname,
 									  const Pg_magic_struct *module_magic_data) pg_attribute_noreturn();
 static char *expand_dynamic_library_name(const char *name);
 static void check_restricted_library_name(const char *name);
-static char *substitute_libpath_macro(const char *name);
-static char *find_in_dynamic_libpath(const char *basename);
 
 /* Magic structure that module needs to match to be accepted */
 static const Pg_magic_struct magic_data = PG_MODULE_MAGIC_DATA;
@@ -398,7 +396,7 @@ incompatible_module_error(const char *libname,
 /*
  * If name contains a slash, check if the file exists, if so return
  * the name.  Else (no slash) try to expand using search path (see
- * find_in_dynamic_libpath below); if that works, return the fully
+ * find_in_path below); if that works, return the fully
  * expanded file name.  If the previous failed, append DLSUFFIX and
  * try again.  If all fails, just return the original name.
  *
@@ -413,17 +411,25 @@ expand_dynamic_library_name(const char *name)
 
 	Assert(name);
 
+	/*
+	 * If the value starts with "$libdir/", strip that.  This is because many
+	 * extensions have hardcoded '$libdir/foo' as their library name, which
+	 * prevents using the path.
+	 */
+	if (strncmp(name, "$libdir/", 8) == 0)
+		name += 8;
+
 	have_slash = (first_dir_separator(name) != NULL);
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(name);
+		full = find_in_path(name, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(name);
+		full = substitute_path_macro(name, "$libdir", pkglib_path);
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -433,14 +439,14 @@ expand_dynamic_library_name(const char *name)
 
 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(new);
+		full = find_in_path(new, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		pfree(new);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(new);
+		full = substitute_path_macro(new, "$libdir", pkglib_path);
 		pfree(new);
 		if (pg_file_exists(full))
 			return full;
@@ -474,48 +480,61 @@ check_restricted_library_name(const char *name)
  * Substitute for any macros appearing in the given string.
  * Result is always freshly palloc'd.
  */
-static char *
-substitute_libpath_macro(const char *name)
+char *
+substitute_path_macro(const char *str, const char *macro, const char *value)
 {
 	const char *sep_ptr;
 
-	Assert(name != NULL);
+	Assert(str != NULL);
+	Assert(macro[0] == '$');
 
-	/* Currently, we only recognize $libdir at the start of the string */
-	if (name[0] != '$')
-		return pstrdup(name);
+	/* Currently, we only recognize $macro at the start of the string */
+	if (str[0] != '$')
+		return pstrdup(str);
 
-	if ((sep_ptr = first_dir_separator(name)) == NULL)
-		sep_ptr = name + strlen(name);
+	if ((sep_ptr = first_dir_separator(str)) == NULL)
+		sep_ptr = str + strlen(str);
 
-	if (strlen("$libdir") != sep_ptr - name ||
-		strncmp(name, "$libdir", strlen("$libdir")) != 0)
+	if (strlen(macro) != sep_ptr - str ||
+		strncmp(str, macro, strlen(macro)) != 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_NAME),
-				 errmsg("invalid macro name in dynamic library path: %s",
-						name)));
+				 errmsg("invalid macro name in path: %s",
+						str)));
 
-	return psprintf("%s%s", pkglib_path, sep_ptr);
+	return psprintf("%s%s", value, sep_ptr);
 }
 
 
 /*
  * Search for a file called 'basename' in the colon-separated search
- * path Dynamic_library_path.  If the file is found, the full file name
+ * path given.  If the file is found, the full file name
  * is returned in freshly palloc'd memory.  If the file is not found,
  * return NULL.
+ *
+ * path_param is the name of the parameter that path came from, for error
+ * messages.
+ *
+ * macro and macro_val allow substituting a macro; see
+ * substitute_path_macro().
  */
-static char *
-find_in_dynamic_libpath(const char *basename)
+char *
+find_in_path(const char *basename, const char *path, const char *path_param,
+			 const char *macro, const char *macro_val)
 {
 	const char *p;
 	size_t		baselen;
 
 	Assert(basename != NULL);
 	Assert(first_dir_separator(basename) == NULL);
-	Assert(Dynamic_library_path != NULL);
+	Assert(path != NULL);
+	Assert(path_param != NULL);
+
+	p = path;
 
-	p = Dynamic_library_path;
+	/*
+	 * If the path variable is empty, don't do a path search.
+	 */
 	if (strlen(p) == 0)
 		return NULL;
 
@@ -532,7 +551,7 @@ find_in_dynamic_libpath(const char *basename)
 		if (piece == p)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("zero-length component in parameter \"dynamic_library_path\"")));
+					 errmsg("zero-length component in parameter \"%s\"", path_param)));
 
 		if (piece == NULL)
 			len = strlen(p);
@@ -542,7 +561,7 @@ find_in_dynamic_libpath(const char *basename)
 		piece = palloc(len + 1);
 		strlcpy(piece, p, len + 1);
 
-		mangled = substitute_libpath_macro(piece);
+		mangled = substitute_path_macro(piece, macro, macro_val);
 		pfree(piece);
 
 		canonicalize_path(mangled);
@@ -551,13 +570,13 @@ find_in_dynamic_libpath(const char *basename)
 		if (!is_absolute_path(mangled))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("component in parameter \"dynamic_library_path\" is not an absolute path")));
+					 errmsg("component in parameter \"%s\" is not an absolute path", path_param)));
 
 		full = palloc(strlen(mangled) + 1 + baselen + 1);
 		sprintf(full, "%s/%s", mangled, basename);
 		pfree(mangled);
 
-		elog(DEBUG3, "find_in_dynamic_libpath: trying \"%s\"", full);
+		elog(DEBUG3, "%s: trying \"%s\"", __func__, full);
 
 		if (pg_file_exists(full))
 			return full;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index ad25cbb39c5..c357a5304ae 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -39,6 +39,7 @@
 #include "catalog/namespace.h"
 #include "catalog/storage.h"
 #include "commands/async.h"
+#include "commands/extension.h"
 #include "commands/event_trigger.h"
 #include "commands/tablespace.h"
 #include "commands/trigger.h"
@@ -4314,6 +4315,18 @@ struct config_string ConfigureNamesString[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"extension_control_path", PGC_SUSET, CLIENT_CONN_OTHER,
+			gettext_noop("Sets the path for extension control files."),
+			gettext_noop("The remaining extension script and secondary control files are then loaded "
+						 "from the same directory where the primary control file was found."),
+			GUC_SUPERUSER_ONLY
+		},
+		&Extension_control_path,
+		"$system",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"krb_server_keyfile", PGC_SIGHUP, CONN_AUTH_AUTH,
 			gettext_noop("Sets the location of the Kerberos server key file."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2d1de9c37bd..d22ef6ef47b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -791,6 +791,7 @@ autovacuum_worker_slots = 16	# autovacuum worker slots to allocate
 # - Other Defaults -
 
 #dynamic_library_path = '$libdir'
+#extension_control_path = '$system'
 #gin_fuzzy_search_limit = 0
 
 
diff --git a/src/include/commands/extension.h b/src/include/commands/extension.h
index 0b636405120..24419bfb5c9 100644
--- a/src/include/commands/extension.h
+++ b/src/include/commands/extension.h
@@ -17,6 +17,8 @@
 #include "catalog/objectaddress.h"
 #include "parser/parse_node.h"
 
+/* GUC */
+extern PGDLLIMPORT char *Extension_control_path;
 
 /*
  * creating_extension is only true while running a CREATE EXTENSION or ALTER
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index e609ea875a7..442c50d6b90 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -740,6 +740,8 @@ extern bool CheckFunctionValidatorAccess(Oid validatorOid, Oid functionOid);
  */
 extern PGDLLIMPORT char *Dynamic_library_path;
 
+extern char *find_in_path(const char *basename, const char *path, const char *path_param,
+						  const char *macro, const char *macro_val);
 extern void *load_external_function(const char *filename, const char *funcname,
 									bool signalNotFound, void **filehandle);
 extern void *lookup_external_function(void *filehandle, const char *funcname);
@@ -749,6 +751,9 @@ extern Size EstimateLibraryStateSpace(void);
 extern void SerializeLibraryState(Size maxsize, char *start_address);
 extern void RestoreLibraryState(char *start_address);
 
+extern char *
+substitute_path_macro(const char *str, const char *macro, const char *value);
+
 /*
  * Support for aggregate functions
  *
diff --git a/src/test/modules/test_extensions/Makefile b/src/test/modules/test_extensions/Makefile
index 1dbec14cba3..a3591bf3d2f 100644
--- a/src/test/modules/test_extensions/Makefile
+++ b/src/test/modules/test_extensions/Makefile
@@ -28,6 +28,7 @@ DATA = test_ext1--1.0.sql test_ext2--1.0.sql test_ext3--1.0.sql \
        test_ext_req_schema3--1.0.sql
 
 REGRESS = test_extensions test_extdepend
+TAP_TESTS = 1
 
 # force C locale for output stability
 NO_LOCALE = 1
diff --git a/src/test/modules/test_extensions/meson.build b/src/test/modules/test_extensions/meson.build
index dd7ec0ce56b..3c7e378bf35 100644
--- a/src/test/modules/test_extensions/meson.build
+++ b/src/test/modules/test_extensions/meson.build
@@ -57,4 +57,9 @@ tests += {
     ],
     'regress_args': ['--no-locale'],
   },
+  'tap': {
+    'tests': [
+      't/001_extension_control_path.pl',
+    ],
+  },
 }
diff --git a/src/test/modules/test_extensions/t/001_extension_control_path.pl b/src/test/modules/test_extensions/t/001_extension_control_path.pl
new file mode 100644
index 00000000000..19c9ed9748b
--- /dev/null
+++ b/src/test/modules/test_extensions/t/001_extension_control_path.pl
@@ -0,0 +1,77 @@
+# Copyright (c) 2024-2025, PostgreSQL Global Development Group
+
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Utils;
+use PostgreSQL::Test::Cluster;
+use Test::More;
+
+my $node = PostgreSQL::Test::Cluster->new('node');
+
+$node->init;
+
+# Create a temporary directory for the extension control file
+my $ext_dir = PostgreSQL::Test::Utils::tempdir();
+my $ext_name = "test_custom_ext_paths";
+my $control_file = "$ext_dir/$ext_name.control";
+my $sql_file = "$ext_dir/$ext_name--1.0.sql";
+
+# Create .control .sql file
+open my $cf, '>', $control_file or die "Could not create control file: $!";
+print $cf "comment = 'Test extension_control_path'\n";
+print $cf "default_version = '1.0'\n";
+print $cf "relocatable = true\n";
+close $cf;
+
+# Create --1.0.sql file
+open my $sqlf, '>', $sql_file or die "Could not create sql file: $!";
+print $sqlf "/* $sql_file */\n";
+print $sqlf "-- complain if script is sourced in psql, rather than via CREATE EXTENSION\n";
+print $sqlf qq'\\echo Use "CREATE EXTENSION $ext_name" to load this file. \\quit\n';
+close $sqlf;
+
+# Use the correct separator and escape \ when running on Windows.
+my $sep = $windows_os ? ";" : ":";
+$node->append_conf(
+    'postgresql.conf', qq{
+extension_control_path = '\$system$sep@{[ $windows_os ? ($ext_dir =~ s/\\/\\\\/gr) : $ext_dir ]}'
+});
+
+# Start node
+$node->start;
+
+my $ecp = $node->safe_psql('postgres', 'show extension_control_path;');
+
+is($ecp, "\$system$sep$ext_dir", "Custom extension control directory path configured");
+
+$node->safe_psql(
+	'postgres',
+	"CREATE EXTENSION $ext_name");
+
+my $ret = $node->safe_psql(
+	'postgres',
+	"select * from pg_available_extensions where name = '$ext_name'");
+is(
+	$ret,
+	"test_custom_ext_paths|1.0|1.0|Test extension_control_path",
+	"Extension is installed correctly on pg_available_extensions");
+
+my $ret2 = $node->safe_psql(
+	'postgres',
+	"select * from pg_available_extension_versions where name = '$ext_name'");
+is(
+	$ret2,
+	"test_custom_ext_paths|1.0|t|t|f|t|||Test extension_control_path",
+	"Extension is installed correctly on pg_available_extension_versions");
+
+# Ensure that extensions installed on $system is still visible when using with
+# custom extension control path.
+my $ret3 = $node->safe_psql(
+	'postgres',
+	"select count(*) > 0 as ok from pg_available_extensions where name = 'amcheck'");
+is(
+	$ret3,
+	"t",
+	"\$system extension is installed correctly on pg_available_extensions");
+
+done_testing();
-- 
2.39.5 (Apple Git-154)

From a0e8ae7af182cf5f37442b85c42b9c40d84419bb Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Thu, 5 Dec 2024 11:49:05 +0100
Subject: [PATCH v7] extension_control_path

The new GUC extension_control_path specifies a path to look for
extension control files.  The default value is $system, which looks in
the compiled-in location, as before.

The path search uses the same code and works in the same way as
dynamic_library_path.

Discussion: https://www.postgresql.org/message-id/flat/E7C7BFFB-8857-48D4-A71F-88B359FADCFD@justatheory.com
---
 doc/src/sgml/config.sgml                      |  68 +++
 doc/src/sgml/extend.sgml                      |  19 +-
 doc/src/sgml/ref/create_extension.sgml        |   6 +-
 src/Makefile.global.in                        |  19 +-
 src/backend/commands/extension.c              | 416 ++++++++++++------
 src/backend/utils/fmgr/dfmgr.c                |  77 ++--
 src/backend/utils/misc/guc_tables.c           |  13 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/commands/extension.h              |   2 +
 src/include/fmgr.h                            |   5 +
 src/test/modules/test_extensions/Makefile     |   1 +
 src/test/modules/test_extensions/meson.build  |   5 +
 .../t/001_extension_control_path.pl           |  86 ++++
 13 files changed, 535 insertions(+), 183 deletions(-)
 create mode 100644 src/test/modules/test_extensions/t/001_extension_control_path.pl

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d2fa5f7d1a9..9fec78db6f7 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -10725,6 +10725,74 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </listitem>
      </varlistentry>

+     <varlistentry id="guc-extension-control-path" xreflabel="extension_control_path">
+      <term><varname>extension_control_path</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>extension_control_path</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        A path to search for extensions, specifically extension control files
+        (<filename><replaceable>name</replaceable>.control</filename>).  The
+        remaining extension script and secondary control files are then loaded
+        from the same directory where the primary control file was found.
+        See <xref linkend="extend-extensions-files"/> for details.
+       </para>
+
+       <para>
+        The value for <varname>extension_control_path</varname> must be a
+        list of absolute directory paths separated by colons (or semi-colons
+        on Windows).  If a list element starts
+        with the special string <literal>$system</literal>, the
+        compiled-in <productname>PostgreSQL</productname> extension
+        directory is substituted for <literal>$system</literal>; this
+        is where the extensions provided by the standard
+        <productname>PostgreSQL</productname> distribution are installed.
+        (Use <literal>pg_config --sharedir</literal> to find out the name of
+        this directory.) For example:
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:/home/my_project/share/extension:$system'
+</programlisting>
+        or, in a Windows environment:
+<programlisting>
+extension_control_path = 'C:\tools\postgresql\extension;H:\my_project\share\extension;$system'
+</programlisting>
+        Note that the path elements should typically end in
+        <literal>extension</literal> if the normal installation layouts are
+        followed.  (The value for <literal>$system</literal> already includes
+        the <literal>extension</literal> suffix.)
+       </para>
+
+       <para>
+        The default value for this parameter is
+        <literal>'$system'</literal>. If the value is set to an empty
+        string, the default <literal>'$system'</literal> is also assumed.
+       </para>
+
+       <para>
+        This parameter can be changed at run time by superusers and users
+        with the appropriate <literal>SET</literal> privilege, but a
+        setting done that way will only persist until the end of the
+        client connection, so this method should be reserved for
+        development purposes. The recommended way to set this parameter
+        is in the <filename>postgresql.conf</filename> configuration
+        file.
+       </para>
+
+       <para>
+        Note that if you set this parameter to be able to load extensions from
+        nonstandard locations, you will most likely also need to set <xref
+        linkend="guc-dynamic-library-path"/> to a correspondent location, for
+        example,
+<programlisting>
+extension_control_path = '/usr/local/share/postgresql/extension:$system'
+dynamic_library_path = '/usr/local/lib/postgresql:$libdir'
+</programlisting>
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-gin-fuzzy-search-limit" xreflabel="gin_fuzzy_search_limit">
       <term><varname>gin_fuzzy_search_limit</varname> (<type>integer</type>)
       <indexterm>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index ba492ca27c0..64f8e133cae 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -649,6 +649,11 @@ RETURNS anycompatible AS ...
      control file can specify a different directory for the script file(s).
     </para>

+    <para>
+     Additional locations for extension control files can be configured using
+     the parameter <xref linkend="guc-extension-control-path"/>.
+    </para>
+
     <para>
      The file format for an extension control file is the same as for the
      <filename>postgresql.conf</filename> file, namely a list of
@@ -669,9 +674,9 @@ RETURNS anycompatible AS ...
        <para>
         The directory containing the extension's <acronym>SQL</acronym> script
         file(s).  Unless an absolute path is given, the name is relative to
-        the installation's <literal>SHAREDIR</literal> directory.  The
-        default behavior is equivalent to specifying
-        <literal>directory = 'extension'</literal>.
+        the installation's <literal>SHAREDIR</literal> directory.  By default,
+        the script files are looked for in the same directory where the
+        control file was found.
        </para>
       </listitem>
      </varlistentry>
@@ -719,8 +724,8 @@ RETURNS anycompatible AS ...
        <para>
         The value of this parameter will be substituted for each occurrence
         of <literal>MODULE_PATHNAME</literal> in the script file(s).  If it is not
-        set, no substitution is made.  Typically, this is set to
-        <literal>$libdir/<replaceable>shared_library_name</replaceable></literal> and
+        set, no substitution is made.  Typically, this is set to just
+        <literal><replaceable>shared_library_name</replaceable></literal> and
         then <literal>MODULE_PATHNAME</literal> is used in <command>CREATE
         FUNCTION</command> commands for C-language functions, so that the script
         files do not need to hard-wire the name of the shared library.
@@ -1804,6 +1809,10 @@ include $(PGXS)
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
+    You can also select a separate installation directory for your extension
+    by setting the <literal>make</literal> variable <varname>prefix</varname>
+    on the <literal>make</literal> command line.  (But this will then require
+    additional setup to get the server to find the extension there.)
    </para>

    <para>
diff --git a/doc/src/sgml/ref/create_extension.sgml b/doc/src/sgml/ref/create_extension.sgml
index ca2b80d669c..713abd9c494 100644
--- a/doc/src/sgml/ref/create_extension.sgml
+++ b/doc/src/sgml/ref/create_extension.sgml
@@ -90,8 +90,10 @@ CREATE EXTENSION [ IF NOT EXISTS ] <replaceable class="parameter">extension_name
        <para>
         The name of the extension to be
         installed. <productname>PostgreSQL</productname> will create the
-        extension using details from the file
-        <literal>SHAREDIR/extension/</literal><replaceable class="parameter">extension_name</replaceable><literal>.control</literal>.
+        extension using details from the file <filename><replaceable
+        class="parameter">extension_name</replaceable>.control</filename>,
+        found via the server's extension control path (set by <xref
+        linkend="guc-extension-control-path"/>.)
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index 3b620bac5ac..8fe9d61e82a 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -87,9 +87,19 @@ endif # not PGXS
 #
 # In a PGXS build, we cannot use the values inserted into Makefile.global
 # by configure, since the installation tree may have been relocated.
-# Instead get the path values from pg_config.
+# Instead get the path values from pg_config.  But users can specify
+# prefix explicitly, if they want to select their own installation
+# location.

-ifndef PGXS
+ifdef PGXS
+# Extension makefiles should set PG_CONFIG, but older ones might not
+ifndef PG_CONFIG
+PG_CONFIG = pg_config
+endif
+endif
+
+# This means: if ((not PGXS) or prefix)
+ifneq (,$(if $(PGXS),,1)$(prefix))

 # Note that prefix, exec_prefix, and datarootdir aren't defined in a PGXS build;
 # makefiles may only use the derived variables such as bindir.
@@ -147,11 +157,6 @@ localedir := @localedir@

 else # PGXS case

-# Extension makefiles should set PG_CONFIG, but older ones might not
-ifndef PG_CONFIG
-PG_CONFIG = pg_config
-endif
-
 bindir := $(shell $(PG_CONFIG) --bindir)
 datadir := $(shell $(PG_CONFIG) --sharedir)
 sysconfdir := $(shell $(PG_CONFIG) --sysconfdir)
diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index d9bb4ce5f1e..aa45f4810b8 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -54,6 +54,7 @@
 #include "funcapi.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
+#include "nodes/pg_list.h"
 #include "nodes/queryjumble.h"
 #include "storage/fd.h"
 #include "tcop/utility.h"
@@ -69,6 +70,9 @@
 #include "utils/varlena.h"


+/* GUC */
+char	   *Extension_control_path;
+
 /* Globally visible state variables */
 bool		creating_extension = false;
 Oid			CurrentExtensionObject = InvalidOid;
@@ -79,6 +83,7 @@ Oid			CurrentExtensionObject = InvalidOid;
 typedef struct ExtensionControlFile
 {
 	char	   *name;			/* name of the extension */
+	char	   *control_dir;	/* directory where control file was found */
 	char	   *directory;		/* directory for script files */
 	char	   *default_version;	/* default install target version, if any */
 	char	   *module_pathname;	/* string to substitute for
@@ -147,6 +152,8 @@ static void ExecAlterExtensionContentsRecurse(AlterExtensionContentsStmt *stmt,
 											  ObjectAddress object);
 static char *read_whole_file(const char *filename, int *length);

+static ExtensionControlFile *new_ExtensionControlFile(const char *extname);
+

 /*
  * get_extension_oid - given an extension name, look up the OID
@@ -328,29 +335,104 @@ is_extension_script_filename(const char *filename)
 	return (extension != NULL) && (strcmp(extension, ".sql") == 0);
 }

-static char *
-get_extension_control_directory(void)
+/*
+ * Return a list of directories declared on extension_control_path GUC.
+ */
+static List *
+get_extension_control_directories(void)
 {
 	char		sharepath[MAXPGPATH];
-	char	   *result;
+	char	   *system_dir;
+	char	   *ecp;
+	List	   *paths = NIL;

 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension", sharepath);

-	return result;
+	system_dir = psprintf("%s/extension", sharepath);
+
+	if (strlen(Extension_control_path) == 0)
+	{
+		paths = lappend(paths, system_dir);
+	}
+	else
+	{
+		/* Duplicate the string so we can modify it */
+		ecp = pstrdup(Extension_control_path);
+
+		for (;;)
+		{
+			int			len;
+			char	   *mangled;
+			char	   *piece = first_path_var_separator(ecp);
+
+			/* Get the length of the next path on ecp */
+			if (piece == NULL)
+				len = strlen(ecp);
+			else
+				len = piece - ecp;
+
+			/* Copy the next path found on ecp */
+			piece = palloc(len + 1);
+			strlcpy(piece, ecp, len + 1);
+
+			/* Substitute the path macro if needed */
+			mangled = substitute_path_macro(piece, "$system", system_dir);
+			pfree(piece);
+
+			/* Canonicalize the path based on the OS and add to the list */
+			canonicalize_path(mangled);
+			paths = lappend(paths, mangled);
+
+			/* Break if ecp is empty or move to the next path on ecp */
+			if (ecp[len] == '\0')
+				break;
+			else
+				ecp += len + 1;
+		}
+	}
+
+	return paths;
 }

+/*
+ * Find control file for extension with name in control->name, looking in the
+ * path.  Return the full file name, or NULL if not found.  If found, the
+ * directory is recorded in control->control_dir.
+ */
 static char *
-get_extension_control_filename(const char *extname)
+find_extension_control_filename(ExtensionControlFile *control)
 {
 	char		sharepath[MAXPGPATH];
+	char	   *system_dir;
+	char	   *basename;
+	char	   *ecp;
 	char	   *result;

+	Assert(control->name);
+
 	get_share_path(my_exec_path, sharepath);
-	result = (char *) palloc(MAXPGPATH);
-	snprintf(result, MAXPGPATH, "%s/extension/%s.control",
-			 sharepath, extname);
+	system_dir = psprintf("%s/extension", sharepath);
+
+	basename = psprintf("%s.control", control->name);
+
+	/*
+	 * find_in_path() does nothing if the path value is empty.  This is the
+	 * historical behavior for dynamic_library_path, but it makes no sense for
+	 * extensions.  So in that case, substitute a default value.
+	 */
+	ecp = Extension_control_path;
+	if (strlen(ecp) == 0)
+		ecp = "$system";
+	result = find_in_path(basename, ecp, "extension_control_path", "$system", system_dir);
+
+	if (result)
+	{
+		const char *p;
+
+		p = strrchr(result, '/');
+		Assert(p);
+		control->control_dir = pnstrdup(result, p - result);
+	}

 	return result;
 }
@@ -366,7 +448,7 @@ get_extension_script_directory(ExtensionControlFile *control)
 	 * installation's share directory.
 	 */
 	if (!control->directory)
-		return get_extension_control_directory();
+		return pstrdup(control->control_dir);

 	if (is_absolute_path(control->directory))
 		return pstrdup(control->directory);
@@ -424,6 +506,11 @@ get_extension_script_filename(ExtensionControlFile *control,
  * fields of *control.  We parse primary file if version == NULL,
  * else the optional auxiliary file for that version.
  *
+ * The control file will be search on Extension_control_path paths if
+ * control->control_dir is NULL, otherwise it will use the value of control_dir
+ * to read and parse the .control file, so it assume that the control_dir is a
+ * valid path for the control file being parsed.
+ *
  * Control files are supposed to be very short, half a dozen lines,
  * so we don't worry about memory allocation risks here.  Also we don't
  * worry about what encoding it's in; all values are expected to be ASCII.
@@ -444,27 +531,52 @@ parse_extension_control_file(ExtensionControlFile *control,
 	if (version)
 		filename = get_extension_aux_control_filename(control, version);
 	else
-		filename = get_extension_control_filename(control->name);
-
-	if ((file = AllocateFile(filename, "r")) == NULL)
 	{
-		if (errno == ENOENT)
+		/*
+		 * Skip searching if control_dir is already set. We assume that
+		 * control_dir is set correctly to find the .control file, otherwise
+		 * ereport extension not available error.
+		 */
+		if (control->control_dir != NULL)
 		{
-			/* no complaint for missing auxiliary file */
-			if (version)
+			/*
+			 * Don't forget to consider path separator, .control suffix and
+			 * null terminator.
+			 */
+			filename = palloc(strlen(control->control_dir) + 1 + strlen(control->name) + 8 + 1);
+			sprintf(filename, "%s/%s.control", control->control_dir, control->name);
+
+			if (!pg_file_exists(filename))
 			{
+				/*
+				 * Extension is not available. Free the memory and set to NULL
+				 * for ereporting.
+				 */
 				pfree(filename);
-				return;
+				filename = NULL;
 			}
+		}
+		else
+			filename = find_extension_control_filename(control);
+	}

-			/* missing control file indicates extension is not installed */
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("extension \"%s\" is not available", control->name),
-					 errdetail("Could not open extension control file \"%s\": %m.",
-							   filename),
-					 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+	if (!filename)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("extension \"%s\" is not available", control->name),
+				 errhint("The extension must first be installed on the system where PostgreSQL is running.")));
+	}
+
+	if ((file = AllocateFile(filename, "r")) == NULL)
+	{
+		/* no complaint for missing auxiliary file */
+		if (errno == ENOENT && version)
+		{
+			pfree(filename);
+			return;
 		}
+
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not open extension control file \"%s\": %m",
@@ -603,17 +715,7 @@ parse_extension_control_file(ExtensionControlFile *control,
 static ExtensionControlFile *
 read_extension_control_file(const char *extname)
 {
-	ExtensionControlFile *control;
-
-	/*
-	 * Set up default values.  Pointer fields are initially null.
-	 */
-	control = (ExtensionControlFile *) palloc0(sizeof(ExtensionControlFile));
-	control->name = pstrdup(extname);
-	control->relocatable = false;
-	control->superuser = true;
-	control->trusted = false;
-	control->encoding = -1;
+	ExtensionControlFile *control = new_ExtensionControlFile(extname);

 	/*
 	 * Parse the primary control file.
@@ -2121,68 +2223,75 @@ Datum
 pg_available_extensions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
+	List	   *locations;
 	DIR		   *dir;
 	struct dirent *de;

 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);

-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();

-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
-	{
-		/* do nothing */
-	}
-	else
+	foreach_ptr(char, location, locations)
 	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
-			Datum		values[3];
-			bool		nulls[3];
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;
+				Datum		values[3];
+				bool		nulls[3];

-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;

-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';

-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;

-			control = read_extension_control_file(extname);
+				control = new_ExtensionControlFile(extname);
+				control->control_dir = pstrdup(location);

-			memset(values, 0, sizeof(values));
-			memset(nulls, 0, sizeof(nulls));
+				parse_extension_control_file(control, NULL);

-			/* name */
-			values[0] = DirectFunctionCall1(namein,
-											CStringGetDatum(control->name));
-			/* default_version */
-			if (control->default_version == NULL)
-				nulls[1] = true;
-			else
-				values[1] = CStringGetTextDatum(control->default_version);
-			/* comment */
-			if (control->comment == NULL)
-				nulls[2] = true;
-			else
-				values[2] = CStringGetTextDatum(control->comment);
+				memset(values, 0, sizeof(values));
+				memset(nulls, 0, sizeof(nulls));

-			tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
-								 values, nulls);
-		}
+				/* name */
+				values[0] = DirectFunctionCall1(namein,
+												CStringGetDatum(control->name));
+				/* default_version */
+				if (control->default_version == NULL)
+					nulls[1] = true;
+				else
+					values[1] = CStringGetTextDatum(control->default_version);
+				/* comment */
+				if (control->comment == NULL)
+					nulls[2] = true;
+				else
+					values[2] = CStringGetTextDatum(control->comment);
+
+				tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
+									 values, nulls);
+			}

-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}

 	return (Datum) 0;
@@ -2201,51 +2310,55 @@ Datum
 pg_available_extension_versions(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	char	   *location;
+	List	   *locations;
 	DIR		   *dir;
 	struct dirent *de;

 	/* Build tuplestore to hold the result rows */
 	InitMaterializedSRF(fcinfo, 0);

-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();

-	/*
-	 * If the control directory doesn't exist, we want to silently return an
-	 * empty set.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
+	foreach_ptr(char, location, locations)
 	{
-		/* do nothing */
-	}
-	else
-	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * an empty set.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			ExtensionControlFile *control;
-			char	   *extname;
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				ExtensionControlFile *control;
+				char	   *extname;

-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;

-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';

-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;

-			/* read the control file */
-			control = read_extension_control_file(extname);
+				/* read the control file */
+				control = read_extension_control_file(extname);

-			/* scan extension's script directory for install scripts */
-			get_available_versions_for_extension(control, rsinfo->setResult,
-												 rsinfo->setDesc);
-		}
+				/* scan extension's script directory for install scripts */
+				get_available_versions_for_extension(control, rsinfo->setResult,
+													 rsinfo->setDesc);
+			}

-		FreeDir(dir);
+			FreeDir(dir);
+		}
 	}

 	return (Datum) 0;
@@ -2373,47 +2486,53 @@ bool
 extension_file_exists(const char *extensionName)
 {
 	bool		result = false;
-	char	   *location;
+	List	   *locations;
 	DIR		   *dir;
 	struct dirent *de;

-	location = get_extension_control_directory();
-	dir = AllocateDir(location);
+	locations = get_extension_control_directories();

-	/*
-	 * If the control directory doesn't exist, we want to silently return
-	 * false.  Any other error will be reported by ReadDir.
-	 */
-	if (dir == NULL && errno == ENOENT)
+	foreach_ptr(char, location, locations)
 	{
-		/* do nothing */
-	}
-	else
-	{
-		while ((de = ReadDir(dir, location)) != NULL)
+		dir = AllocateDir(location);
+
+		/*
+		 * If the control directory doesn't exist, we want to silently return
+		 * false.  Any other error will be reported by ReadDir.
+		 */
+		if (dir == NULL && errno == ENOENT)
 		{
-			char	   *extname;
+			/* do nothing */
+		}
+		else
+		{
+			while ((de = ReadDir(dir, location)) != NULL)
+			{
+				char	   *extname;

-			if (!is_extension_control_filename(de->d_name))
-				continue;
+				if (!is_extension_control_filename(de->d_name))
+					continue;

-			/* extract extension name from 'name.control' filename */
-			extname = pstrdup(de->d_name);
-			*strrchr(extname, '.') = '\0';
+				/* extract extension name from 'name.control' filename */
+				extname = pstrdup(de->d_name);
+				*strrchr(extname, '.') = '\0';

-			/* ignore it if it's an auxiliary control file */
-			if (strstr(extname, "--"))
-				continue;
+				/* ignore it if it's an auxiliary control file */
+				if (strstr(extname, "--"))
+					continue;

-			/* done if it matches request */
-			if (strcmp(extname, extensionName) == 0)
-			{
-				result = true;
-				break;
+				/* done if it matches request */
+				if (strcmp(extname, extensionName) == 0)
+				{
+					result = true;
+					break;
+				}
 			}
-		}

-		FreeDir(dir);
+			FreeDir(dir);
+		}
+		if (result)
+			break;
 	}

 	return result;
@@ -3691,3 +3810,20 @@ read_whole_file(const char *filename, int *length)
 	*length = bytes_to_read;
 	return buf;
 }
+
+static ExtensionControlFile *
+new_ExtensionControlFile(const char *extname)
+{
+	/*
+	 * Set up default values.  Pointer fields are initially null.
+	 */
+	ExtensionControlFile *control = (ExtensionControlFile *) palloc0(sizeof(ExtensionControlFile));
+
+	control->name = pstrdup(extname);
+	control->relocatable = false;
+	control->superuser = true;
+	control->trusted = false;
+	control->encoding = -1;
+
+	return control;
+}
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 87b233cb887..ca12e954ea2 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -71,8 +71,6 @@ static void incompatible_module_error(const char *libname,
 									  const Pg_magic_struct *module_magic_data) pg_attribute_noreturn();
 static char *expand_dynamic_library_name(const char *name);
 static void check_restricted_library_name(const char *name);
-static char *substitute_libpath_macro(const char *name);
-static char *find_in_dynamic_libpath(const char *basename);

 /* Magic structure that module needs to match to be accepted */
 static const Pg_magic_struct magic_data = PG_MODULE_MAGIC_DATA;
@@ -398,7 +396,7 @@ incompatible_module_error(const char *libname,
 /*
  * If name contains a slash, check if the file exists, if so return
  * the name.  Else (no slash) try to expand using search path (see
- * find_in_dynamic_libpath below); if that works, return the fully
+ * find_in_path below); if that works, return the fully
  * expanded file name.  If the previous failed, append DLSUFFIX and
  * try again.  If all fails, just return the original name.
  *
@@ -413,17 +411,25 @@ expand_dynamic_library_name(const char *name)

 	Assert(name);

+	/*
+	 * If the value starts with "$libdir/", strip that.  This is because many
+	 * extensions have hardcoded '$libdir/foo' as their library name, which
+	 * prevents using the path.
+	 */
+	if (strncmp(name, "$libdir/", 8) == 0)
+		name += 8;
+
 	have_slash = (first_dir_separator(name) != NULL);

 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(name);
+		full = find_in_path(name, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(name);
+		full = substitute_path_macro(name, "$libdir", pkglib_path);
 		if (pg_file_exists(full))
 			return full;
 		pfree(full);
@@ -433,14 +439,14 @@ expand_dynamic_library_name(const char *name)

 	if (!have_slash)
 	{
-		full = find_in_dynamic_libpath(new);
+		full = find_in_path(new, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
 		pfree(new);
 		if (full)
 			return full;
 	}
 	else
 	{
-		full = substitute_libpath_macro(new);
+		full = substitute_path_macro(new, "$libdir", pkglib_path);
 		pfree(new);
 		if (pg_file_exists(full))
 			return full;
@@ -474,48 +480,61 @@ check_restricted_library_name(const char *name)
  * Substitute for any macros appearing in the given string.
  * Result is always freshly palloc'd.
  */
-static char *
-substitute_libpath_macro(const char *name)
+char *
+substitute_path_macro(const char *str, const char *macro, const char *value)
 {
 	const char *sep_ptr;

-	Assert(name != NULL);
+	Assert(str != NULL);
+	Assert(macro[0] == '$');

-	/* Currently, we only recognize $libdir at the start of the string */
-	if (name[0] != '$')
-		return pstrdup(name);
+	/* Currently, we only recognize $macro at the start of the string */
+	if (str[0] != '$')
+		return pstrdup(str);

-	if ((sep_ptr = first_dir_separator(name)) == NULL)
-		sep_ptr = name + strlen(name);
+	if ((sep_ptr = first_dir_separator(str)) == NULL)
+		sep_ptr = str + strlen(str);

-	if (strlen("$libdir") != sep_ptr - name ||
-		strncmp(name, "$libdir", strlen("$libdir")) != 0)
+	if (strlen(macro) != sep_ptr - str ||
+		strncmp(str, macro, strlen(macro)) != 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_NAME),
-				 errmsg("invalid macro name in dynamic library path: %s",
-						name)));
+				 errmsg("invalid macro name in path: %s",
+						str)));

-	return psprintf("%s%s", pkglib_path, sep_ptr);
+	return psprintf("%s%s", value, sep_ptr);
 }


 /*
  * Search for a file called 'basename' in the colon-separated search
- * path Dynamic_library_path.  If the file is found, the full file name
+ * path given.  If the file is found, the full file name
  * is returned in freshly palloc'd memory.  If the file is not found,
  * return NULL.
+ *
+ * path_param is the name of the parameter that path came from, for error
+ * messages.
+ *
+ * macro and macro_val allow substituting a macro; see
+ * substitute_path_macro().
  */
-static char *
-find_in_dynamic_libpath(const char *basename)
+char *
+find_in_path(const char *basename, const char *path, const char *path_param,
+			 const char *macro, const char *macro_val)
 {
 	const char *p;
 	size_t		baselen;

 	Assert(basename != NULL);
 	Assert(first_dir_separator(basename) == NULL);
-	Assert(Dynamic_library_path != NULL);
+	Assert(path != NULL);
+	Assert(path_param != NULL);
+
+	p = path;

-	p = Dynamic_library_path;
+	/*
+	 * If the path variable is empty, don't do a path search.
+	 */
 	if (strlen(p) == 0)
 		return NULL;

@@ -532,7 +551,7 @@ find_in_dynamic_libpath(const char *basename)
 		if (piece == p)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("zero-length component in parameter \"dynamic_library_path\"")));
+					 errmsg("zero-length component in parameter \"%s\"", path_param)));

 		if (piece == NULL)
 			len = strlen(p);
@@ -542,7 +561,7 @@ find_in_dynamic_libpath(const char *basename)
 		piece = palloc(len + 1);
 		strlcpy(piece, p, len + 1);

-		mangled = substitute_libpath_macro(piece);
+		mangled = substitute_path_macro(piece, macro, macro_val);
 		pfree(piece);

 		canonicalize_path(mangled);
@@ -551,13 +570,13 @@ find_in_dynamic_libpath(const char *basename)
 		if (!is_absolute_path(mangled))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("component in parameter \"dynamic_library_path\" is not an absolute path")));
+					 errmsg("component in parameter \"%s\" is not an absolute path", path_param)));

 		full = palloc(strlen(mangled) + 1 + baselen + 1);
 		sprintf(full, "%s/%s", mangled, basename);
 		pfree(mangled);

-		elog(DEBUG3, "find_in_dynamic_libpath: trying \"%s\"", full);
+		elog(DEBUG3, "%s: trying \"%s\"", __func__, full);

 		if (pg_file_exists(full))
 			return full;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index ad25cbb39c5..c357a5304ae 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -39,6 +39,7 @@
 #include "catalog/namespace.h"
 #include "catalog/storage.h"
 #include "commands/async.h"
+#include "commands/extension.h"
 #include "commands/event_trigger.h"
 #include "commands/tablespace.h"
 #include "commands/trigger.h"
@@ -4314,6 +4315,18 @@ struct config_string ConfigureNamesString[] =
 		NULL, NULL, NULL
 	},

+	{
+		{"extension_control_path", PGC_SUSET, CLIENT_CONN_OTHER,
+			gettext_noop("Sets the path for extension control files."),
+			gettext_noop("The remaining extension script and secondary control files are then loaded "
+						 "from the same directory where the primary control file was found."),
+			GUC_SUPERUSER_ONLY
+		},
+		&Extension_control_path,
+		"$system",
+		NULL, NULL, NULL
+	},
+
 	{
 		{"krb_server_keyfile", PGC_SIGHUP, CONN_AUTH_AUTH,
 			gettext_noop("Sets the location of the Kerberos server key file."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2d1de9c37bd..d22ef6ef47b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -791,6 +791,7 @@ autovacuum_worker_slots = 16	# autovacuum worker slots to allocate
 # - Other Defaults -

 #dynamic_library_path = '$libdir'
+#extension_control_path = '$system'
 #gin_fuzzy_search_limit = 0


diff --git a/src/include/commands/extension.h b/src/include/commands/extension.h
index 0b636405120..24419bfb5c9 100644
--- a/src/include/commands/extension.h
+++ b/src/include/commands/extension.h
@@ -17,6 +17,8 @@
 #include "catalog/objectaddress.h"
 #include "parser/parse_node.h"

+/* GUC */
+extern PGDLLIMPORT char *Extension_control_path;

 /*
  * creating_extension is only true while running a CREATE EXTENSION or ALTER
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index e609ea875a7..442c50d6b90 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -740,6 +740,8 @@ extern bool CheckFunctionValidatorAccess(Oid validatorOid, Oid functionOid);
  */
 extern PGDLLIMPORT char *Dynamic_library_path;

+extern char *find_in_path(const char *basename, const char *path, const char *path_param,
+						  const char *macro, const char *macro_val);
 extern void *load_external_function(const char *filename, const char *funcname,
 									bool signalNotFound, void **filehandle);
 extern void *lookup_external_function(void *filehandle, const char *funcname);
@@ -749,6 +751,9 @@ extern Size EstimateLibraryStateSpace(void);
 extern void SerializeLibraryState(Size maxsize, char *start_address);
 extern void RestoreLibraryState(char *start_address);

+extern char *
+substitute_path_macro(const char *str, const char *macro, const char *value);
+
 /*
  * Support for aggregate functions
  *
diff --git a/src/test/modules/test_extensions/Makefile b/src/test/modules/test_extensions/Makefile
index 1dbec14cba3..a3591bf3d2f 100644
--- a/src/test/modules/test_extensions/Makefile
+++ b/src/test/modules/test_extensions/Makefile
@@ -28,6 +28,7 @@ DATA = test_ext1--1.0.sql test_ext2--1.0.sql test_ext3--1.0.sql \
        test_ext_req_schema3--1.0.sql

 REGRESS = test_extensions test_extdepend
+TAP_TESTS = 1

 # force C locale for output stability
 NO_LOCALE = 1
diff --git a/src/test/modules/test_extensions/meson.build b/src/test/modules/test_extensions/meson.build
index dd7ec0ce56b..3c7e378bf35 100644
--- a/src/test/modules/test_extensions/meson.build
+++ b/src/test/modules/test_extensions/meson.build
@@ -57,4 +57,9 @@ tests += {
     ],
     'regress_args': ['--no-locale'],
   },
+  'tap': {
+    'tests': [
+      't/001_extension_control_path.pl',
+    ],
+  },
 }
diff --git a/src/test/modules/test_extensions/t/001_extension_control_path.pl b/src/test/modules/test_extensions/t/001_extension_control_path.pl
new file mode 100644
index 00000000000..1cf01fca57d
--- /dev/null
+++ b/src/test/modules/test_extensions/t/001_extension_control_path.pl
@@ -0,0 +1,86 @@
+# Copyright (c) 2024-2025, PostgreSQL Global Development Group
+
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Utils;
+use PostgreSQL::Test::Cluster;
+use Test::More;
+
+my $node = PostgreSQL::Test::Cluster->new('node');
+
+$node->init;
+
+# Create a temporary directory for the extension control file
+my $ext_dir = PostgreSQL::Test::Utils::tempdir();
+my $ext_name = "test_custom_ext_paths";
+my $control_file = "$ext_dir/$ext_name.control";
+my $sql_file = "$ext_dir/$ext_name--1.0.sql";
+
+# Create .control .sql file
+open my $cf, '>', $control_file or die "Could not create control file: $!";
+print $cf "comment = 'Test extension_control_path'\n";
+print $cf "default_version = '1.0'\n";
+print $cf "relocatable = true\n";
+close $cf;
+
+# Create --1.0.sql file
+open my $sqlf, '>', $sql_file or die "Could not create sql file: $!";
+print $sqlf "/* $sql_file */\n";
+print $sqlf "-- complain if script is sourced in psql, rather than via CREATE EXTENSION\n";
+print $sqlf qq'\\echo Use "CREATE EXTENSION $ext_name" to load this file. \\quit\n';
+close $sqlf;
+
+# Use the correct separator and escape \ when running on Windows.
+my $sep = $windows_os ? ";" : ":";
+$node->append_conf(
+    'postgresql.conf', qq{
+extension_control_path = '\$system$sep@{[ $windows_os ? ($ext_dir =~ s/\\/\\\\/gr) : $ext_dir ]}'
+});
+
+# Start node
+$node->start;
+
+my $ecp = $node->safe_psql('postgres', 'show extension_control_path;');
+
+is($ecp, "\$system$sep$ext_dir", "Custom extension control directory path configured");
+
+$node->safe_psql(
+	'postgres',
+	"CREATE EXTENSION $ext_name");
+
+my $ret = $node->safe_psql(
+	'postgres',
+	"select * from pg_available_extensions where name = '$ext_name'");
+is(
+	$ret,
+	"test_custom_ext_paths|1.0|1.0|Test extension_control_path",
+	"Extension is installed correctly on pg_available_extensions");
+
+my $ret2 = $node->safe_psql(
+	'postgres',
+	"select * from pg_available_extension_versions where name = '$ext_name'");
+is(
+	$ret2,
+	"test_custom_ext_paths|1.0|t|t|f|t|||Test extension_control_path",
+	"Extension is installed correctly on pg_available_extension_versions");
+
+# Ensure that extensions installed on $system is still visible when using with
+# custom extension control path.
+my $ret3 = $node->safe_psql(
+	'postgres',
+	"select count(*) > 0 as ok from pg_available_extensions where name = 'amcheck'");
+is(
+	$ret3,
+	"t",
+	"\$system extension is installed correctly on pg_available_extensions");
+
+
+my $ret4 = $node->safe_psql(
+	'postgres',
+	"set extension_control_path = ''; select count(*) > 0 as ok from pg_available_extensions where name = 'amcheck'");
+is(
+	$ret4,
+	"t",
+	"\$system extension is installed correctly on pg_available_extensions with empty extension_control_path");
+
+done_testing();
--
2.39.5 (Apple Git-154)

From e0ffe63f621463662d13bf21e9431a78a3391349 Mon Sep 17 00:00:00 2001
From: "David E. Wheeler" <david@justatheory.com>
Date: Wed, 19 Mar 2025 13:18:33 -0400
Subject: [PATCH v1] Flesh out docs for the `prefix` make variable

The variable is a bit magical in how it requires "postgresql" or "pgsql"
to be part of the path, and files end up in its `share` and `lib`
subdirectories. So mention all that and show an example of setting
`extension_control_path` and `dynamic_library_path` to use those
locations.
---
 doc/src/sgml/extend.sgml | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 64f8e133cae..4e75a01fae4 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -1809,10 +1809,35 @@ include $(PGXS)
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
-    You can also select a separate installation directory for your extension
-    by setting the <literal>make</literal> variable <varname>prefix</varname>
-    on the <literal>make</literal> command line.  (But this will then require
-    additional setup to get the server to find the extension there.)
+   </para>
+
+   <para>
+    You can also select a separate directory prefix in which to install your
+    extension's files by setting the <literal>make</literal> variable
+    <varname>prefix</varname> when executing <literal>make install</literal>
+    like so:
+<programlisting>
+make install prefix=/etc/postgresql
+</programlisting>
+    This will install the control SQL files into
+    <literal>/etc/postgresql/share</literal> and shared modules into
+    <literal>/etc/postgresql/lib</literal>. If the prefix does not
+    include the strings <literal>postgresql</literal> or
+    <literal>pgsql</literal>, such as:
+<programlisting>
+make install prefix=/etc/extras
+</programlisting>
+    Then the <literal>postgresql</literal> directory will be appended io the
+    prefix, installing the control SQL files into
+    <literal>/etc/extras/postgresql/share</literal> and shared modules into
+    <literal>/etc/extras/postgresql/lib</literal>. Either way, you'll need to
+    set <xref linkend="guc-extension-control-path"/> and <xref
+    linkend="guc-dynamic-library-path"/> to allow
+    <productname>PostgreSQL</productname> to find the files:
+</programlisting>
+extension_control_path = '/etc/extras/postgresql/share/extension:$system'
+dynamic_library_path = '/etc/extras/postgresql/lib:$libdir'
+ </programlisting>
    </para>
 
    <para>
-- 
2.48.1

From 4fa81f1c04df649b183e1e55053662a35109d0b6 Mon Sep 17 00:00:00 2001
From: Matheus Alcantara <mths.dev@pm.me>
Date: Wed, 19 Mar 2025 16:15:43 -0300
Subject: [PATCH v1] Fix extension control path tests

Change expected extension to be installed from amcheck to plpgsql since
not all build farm animals has the contrib module installed.
---
 .../modules/test_extensions/t/001_extension_control_path.pl   | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/test/modules/test_extensions/t/001_extension_control_path.pl b/src/test/modules/test_extensions/t/001_extension_control_path.pl
index 7160009739a..c186c1470f7 100644
--- a/src/test/modules/test_extensions/t/001_extension_control_path.pl
+++ b/src/test/modules/test_extensions/t/001_extension_control_path.pl
@@ -64,14 +64,14 @@ is( $ret2,
 # Ensure that extensions installed on $system is still visible when using with
 # custom extension control path.
 my $ret3 = $node->safe_psql('postgres',
-	"select count(*) > 0 as ok from pg_available_extensions where name = 'amcheck'"
+	"select count(*) > 0 as ok from pg_available_extensions where name = 'plpgsql'"
 );
 is($ret3, "t",
 	"\$system extension is installed correctly on pg_available_extensions");
 
 
 my $ret4 = $node->safe_psql('postgres',
-	"set extension_control_path = ''; select count(*) > 0 as ok from pg_available_extensions where name = 'amcheck'"
+	"set extension_control_path = ''; select count(*) > 0 as ok from pg_available_extensions where name = 'plpgsql'"
 );
 is($ret4, "t",
 	"\$system extension is installed correctly on pg_available_extensions with empty extension_control_path"
-- 
2.39.5 (Apple Git-154)

From 448a03ac53fd145eb5da63c96ac99a99876de642 Mon Sep 17 00:00:00 2001
From: "David E. Wheeler" <david@justatheory.com>
Date: Thu, 24 Apr 2025 18:57:26 -0400
Subject: [PATCH v2] Flesh out docs for the `prefix` make variable

The variable is a bit magical in how it requires "postgresql" or "pgsql"
to be part of the path, and files end up in its `share` and `lib`
subdirectories. So mention all that and show an example of setting
`extension_control_path` and `dynamic_library_path` to use those
locations.
---
 doc/src/sgml/extend.sgml | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 64f8e133cae..4e75a01fae4 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -1809,10 +1809,35 @@ include $(PGXS)
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
-    You can also select a separate installation directory for your extension
-    by setting the <literal>make</literal> variable <varname>prefix</varname>
-    on the <literal>make</literal> command line.  (But this will then require
-    additional setup to get the server to find the extension there.)
+   </para>
+
+   <para>
+    You can also select a separate directory prefix in which to install your
+    extension's files by setting the <literal>make</literal> variable
+    <varname>prefix</varname> when executing <literal>make install</literal>
+    like so:
+<programlisting>
+make install prefix=/etc/postgresql
+</programlisting>
+    This will install the control SQL files into
+    <literal>/etc/postgresql/share</literal> and shared modules into
+    <literal>/etc/postgresql/lib</literal>. If the prefix does not
+    include the strings <literal>postgresql</literal> or
+    <literal>pgsql</literal>, such as:
+<programlisting>
+make install prefix=/etc/extras
+</programlisting>
+    Then the <literal>postgresql</literal> directory will be appended io the
+    prefix, installing the control SQL files into
+    <literal>/etc/extras/postgresql/share</literal> and shared modules into
+    <literal>/etc/extras/postgresql/lib</literal>. Either way, you'll need to
+    set <xref linkend="guc-extension-control-path"/> and <xref
+    linkend="guc-dynamic-library-path"/> to allow
+    <productname>PostgreSQL</productname> to find the files:
+</programlisting>
+extension_control_path = '/etc/extras/postgresql/share/extension:$system'
+dynamic_library_path = '/etc/extras/postgresql/lib:$libdir'
+ </programlisting>
    </para>
 
    <para>
-- 
2.48.1

From d49d3445ca5bdde436713dc8a2ae7707683851e3 Mon Sep 17 00:00:00 2001
From: "David E. Wheeler" <david@justatheory.com>
Date: Fri, 25 Apr 2025 15:22:23 -0400
Subject: [PATCH v3] Flesh out docs for the `prefix` make variable

The variable is a bit magical in how it requires "postgresql" or "pgsql"
to be part of the path, and files end up in its `share` and `lib`
subdirectories. So mention all that and show an example of setting
`extension_control_path` and `dynamic_library_path` to use those
locations.
---
 doc/src/sgml/extend.sgml | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 64f8e133cae..05063d4e7bc 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -1809,10 +1809,35 @@ include $(PGXS)
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
-    You can also select a separate installation directory for your extension
-    by setting the <literal>make</literal> variable <varname>prefix</varname>
-    on the <literal>make</literal> command line.  (But this will then require
-    additional setup to get the server to find the extension there.)
+   </para>
+
+   <para>
+    You can also select a separate directory prefix in which to install your
+    extension's files by setting the <literal>make</literal> variable
+    <varname>prefix</varname> when executing <literal>make install</literal>
+    like so:
+<programlisting>
+make install prefix=/usr/local/postgresql
+</programlisting>
+    This will install the control SQL files into
+    <literal>/usr/local/postgresql/share</literal> and shared modules into
+    <literal>/usr/local/postgresql/lib</literal>. If the prefix does not
+    include the strings <literal>postgres</literal> or
+    <literal>pgsql</literal>, such as:
+<programlisting>
+make install prefix=/usr/local/extras
+</programlisting>
+    Then the <literal>postgresql</literal> directory will be appended io the
+    prefix, installing the control and SQL files into
+    <literal>/usr/local/extras/postgresql/share/extension</literal> and shared
+    modules into <literal>/usr/local/extras/postgresql/lib</literal>. Either
+    way, you'll need to set <xref linkend="guc-extension-control-path"/> and
+    <xref linkend="guc-dynamic-library-path"/> to allow
+    <productname>PostgreSQL</productname> to find the files:
+</programlisting>
+extension_control_path = '/usr/local/extras/postgresql/share/extension:$system'
+dynamic_library_path = '/usr/local/extras/postgresql/lib:$libdir'
+ </programlisting>
    </para>
 
    <para>
-- 
2.48.1

From 8ff0470bd6b1110c43e9852c5196139df7b2734e Mon Sep 17 00:00:00 2001
From: "David E. Wheeler" <david@justatheory.com>
Date: Mon, 28 Apr 2025 17:13:20 -0400
Subject: [PATCH v4] Flesh out docs for the `prefix` make variable

The variable is a bit magical in how it requires "postgresql" or "pgsql"
to be part of the path, and files end up in its `share` and `lib`
subdirectories. So mention all that and show an example of setting
`extension_control_path` and `dynamic_library_path` to use those
locations.
---
 doc/src/sgml/extend.sgml | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 64f8e133cae..68358a5b15f 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -1809,10 +1809,35 @@ include $(PGXS)
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
-    You can also select a separate installation directory for your extension
-    by setting the <literal>make</literal> variable <varname>prefix</varname>
-    on the <literal>make</literal> command line.  (But this will then require
-    additional setup to get the server to find the extension there.)
+   </para>
+
+   <para>
+    You can also select a separate directory prefix in which to install your
+    extension's files by setting the <literal>make</literal> variable
+    <varname>prefix</varname> when executing <literal>make install</literal>
+    like so:
+<programlisting>
+make install prefix=/usr/local/postgresql
+</programlisting>
+    This will install the control SQL files into
+    <literal>/usr/local/postgresql/share</literal> and shared modules into
+    <literal>/usr/local/postgresql/lib</literal>. If the prefix does not
+    include the strings <literal>postgres</literal> or
+    <literal>pgsql</literal>, such as:
+<programlisting>
+make install prefix=/usr/local/extras
+</programlisting>
+    Then the <literal>postgresql</literal> directory will be appended io the
+    prefix, installing the control and SQL files into
+    <literal>/usr/local/extras/postgresql/share/extension</literal> and shared
+    modules into <literal>/usr/local/extras/postgresql/lib</literal>. Either
+    way, you'll need to set <xref linkend="guc-extension-control-path"/> and
+    <xref linkend="guc-dynamic-library-path"/> to allow
+    <productname>PostgreSQL</productname> to find the files:
+</programlisting>
+extension_control_path = '/usr/local/extras/postgresql/share:$system'
+dynamic_library_path = '/usr/local/extras/postgresql/lib:$libdir'
+ </programlisting>
    </para>
 
    <para>
-- 
2.49.0

From 53e4f4173d62f8d30938e75274ab4b7b1074a290 Mon Sep 17 00:00:00 2001
From: "David E. Wheeler" <david@justatheory.com>
Date: Tue, 29 Apr 2025 09:58:12 -0400
Subject: [PATCH v5] Flesh out docs for the `prefix` make variable

The variable is a bit magical in how it requires "postgresql" or "pgsql"
to be part of the path, and files end up in its `share` and `lib`
subdirectories. So mention all that and show an example of setting
`extension_control_path` and `dynamic_library_path` to use those
locations.
---
 doc/src/sgml/extend.sgml | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 64f8e133cae..4ffb337e0a2 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -1809,10 +1809,35 @@ include $(PGXS)
     setting <varname>PG_CONFIG</varname> to point to its
     <command>pg_config</command> program, either within the makefile
     or on the <literal>make</literal> command line.
-    You can also select a separate installation directory for your extension
-    by setting the <literal>make</literal> variable <varname>prefix</varname>
-    on the <literal>make</literal> command line.  (But this will then require
-    additional setup to get the server to find the extension there.)
+   </para>
+
+   <para>
+    You can also select a separate directory prefix in which to install your
+    extension's files by setting the <literal>make</literal> variable
+    <varname>prefix</varname> when executing <literal>make install</literal>
+    like so:
+<programlisting>
+make install prefix=/usr/local/postgresql
+</programlisting>
+    This will install the control SQL files into
+    <literal>/usr/local/postgresql/share</literal> and shared modules into
+    <literal>/usr/local/postgresql/lib</literal>. If the prefix does not
+    include the strings <literal>postgres</literal> or
+    <literal>pgsql</literal>, such as:
+<programlisting>
+make install prefix=/usr/local/extras
+</programlisting>
+    Then the <literal>postgresql</literal> directory will be appended to the
+    prefix, installing the control and SQL files into
+    <literal>/usr/local/extras/postgresql/share/extension</literal> and shared
+    modules into <literal>/usr/local/extras/postgresql/lib</literal>. Either
+    way, you'll need to set <xref linkend="guc-extension-control-path"/> and
+    <xref linkend="guc-dynamic-library-path"/> to allow
+    <productname>PostgreSQL</productname> to find the files:
+</programlisting>
+extension_control_path = '/usr/local/extras/postgresql/share:$system'
+dynamic_library_path = '/usr/local/extras/postgresql/lib:$libdir'
+ </programlisting>
    </para>
 
    <para>
-- 
2.49.0