CustomScan support on readfuncs.c

 doc/src/sgml/custom-scan.sgml  | 53 +++++++++++++++++++++++++++++++++-----
 src/backend/nodes/copyfuncs.c  | 16 +++++++++++-
 src/backend/nodes/outfuncs.c   |  8 +++++-
 src/backend/nodes/readfuncs.c  | 58 ++++++++++++++++++++++++++++++++++++++++++
 src/backend/utils/fmgr/dfmgr.c | 21 +++++++++++++++
 src/include/fmgr.h             |  1 +
 src/include/nodes/plannodes.h  | 23 ++++++++++++++---
 7 files changed, 168 insertions(+), 12 deletions(-)

diff --git a/doc/src/sgml/custom-scan.sgml b/doc/src/sgml/custom-scan.sgml
index a229326..867b47e 100644
--- a/doc/src/sgml/custom-scan.sgml
+++ b/doc/src/sgml/custom-scan.sgml
@@ -195,11 +195,22 @@ typedef struct CustomScan
 
   <para>
    Plan trees must be able to be duplicated using <function>copyObject</>,
-   so all the data stored within the <quote>custom</> fields must consist of
-   nodes that that function can handle.  Furthermore, custom scan providers
-   cannot substitute a larger structure that embeds
-   a <structname>CustomScan</> for the structure itself, as would be possible
-   for a <structname>CustomPath</> or <structname>CustomScanState</>.
+   serialized using <function>nodeToString</> and deserialized using
+   <function>stringToNode</>, so so all the data stored within
+   the <quote>custom</> fields must consist of nodes that that function
+   can handle.
+   Furthermore, custom scan providers have to implement <quote>optional</>
+   callbacks if it defines substitute a larger structure that embeds
+   a <structname>CustomScan</> for the structure itself.
+  </para>
+
+  <para>
+   Also note that symbol name of the <structname>CustomScanMethods</> table
+   has to be visible to linker, because <function>stringToNode</>
+   reconstructs the <structfield>methods</> pointer using a pair of library
+   and symbol name. <function>INIT_CUSTOM_SCAN_METHODS</> initializes the
+   relevant fields, and expects custom-scan provider uses this macro on
+   <function>_PG_init</> timing.
   </para>
 
   <sect2 id="custom-scan-plan-callbacks">
@@ -228,8 +239,38 @@ void (*TextOutCustomScan) (StringInfo str,
     this custom plan node.  This callback is optional.  Since
     <function>nodeToString</> will automatically dump all fields in the
     structure, including the substructure of the <quote>custom</> fields,
-    there is usually not much need for this callback.
+    there is usually not much need for this callback, unless custom-scan
+    provider does not embed its 
+   </para>
+
+   <para>
+<programlisting>
+struct CustomScan *(*TextReadCustomScan)(void);
+</programlisting>
+    Allocate a <structname>CustomScan</> or larger structure embedding
+    <structname>CustomScan</>, and read its private fields generated by
+    <function>TextOutCustomScan</> callback.
+    This callback is optional, however, must be implemented if custom
+    scan provider makes additional output for support of plan-tree
+    serialization and deserialization.
+    This callback shall be invoked under <function>stringToNode</>
+    context, so <function>pg_strtok</> will give the next token.
    </para>
+
+   <para>
+<programlisting>
+struct CustomScan *(*NodeCopyCustomScan)(const struct CustomScan *from);
+</programlisting>
+    Allocate a <structname>CustomScan</> or larger structure embedding
+    <structname>CustomScan</>, and copies its private fields from the
+    original node.
+    This callback is optional, however, must be implemented if custom
+    scan provider extends <structname>CustomScan</> structure to save
+    its private fields for safety of <function>copyObject</>.
+    The common fields are duplicated by the backend, so all extension
+    needs to focus on is its private fields, if exists.
+   </para>
+
   </sect2>
  </sect1>
 
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 62355aa..05d23aa 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -637,7 +637,21 @@ _copyForeignScan(const ForeignScan *from)
 static CustomScan *
 _copyCustomScan(const CustomScan *from)
 {
-	CustomScan *newnode = makeNode(CustomScan);
+	const CustomScanMethods *methods = from->methods;
+	CustomScan *newnode;
+
+	/*
+	 * If custom-scan provider extends CustomScan node to save its private
+	 * data, it is role of the provider to allocate a new node that includes
+	 * the private fields.
+	 */
+	if (!methods->NodeCopyCustomScan)
+		newnode = makeNode(CustomScan);
+	else
+	{
+		newnode = methods->NodeCopyCustomScan(from);
+		Assert(IsA(newnode, CustomScan));
+	}
 
 	/*
 	 * copy node superclass fields
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index c91273c..7ed8118 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -599,8 +599,14 @@ _outCustomScan(StringInfo str, const CustomScan *node)
 	WRITE_NODE_FIELD(custom_private);
 	WRITE_NODE_FIELD(custom_scan_tlist);
 	WRITE_BITMAPSET_FIELD(custom_relids);
+
+	/* Dump library and symbol name instead of raw pointer */
 	appendStringInfoString(str, " :methods ");
-	_outToken(str, node->methods->CustomName);
+	_outToken(str, node->methods->methods_library_name);
+	appendStringInfoChar(str, ' ');
+	_outToken(str, node->methods->methods_symbol_name);
+
+	/* Also, private fields if any */
 	if (node->methods->TextOutCustomScan)
 		node->methods->TextOutCustomScan(str, node);
 }
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index ef88209..81449a2 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -28,6 +28,7 @@
 
 #include <math.h>
 
+#include "fmgr.h"
 #include "nodes/parsenodes.h"
 #include "nodes/plannodes.h"
 #include "nodes/readfuncs.h"
@@ -1849,6 +1850,61 @@ _readForeignScan(void)
 }
 
 /*
+ * _readCustomScan
+ */
+static CustomScan *
+_readCustomScan(void)
+{
+	READ_TEMP_LOCALS();
+	CustomScan		local_temp;
+	CustomScan	   *local_node = &local_temp;
+	char		   *library_name;
+	char		   *symbol_name;
+	const CustomScanMethods *methods;
+
+	NodeSetTag(local_node, T_CustomScan);
+	ReadCommonScan(&local_node->scan);
+
+	READ_UINT_FIELD(flags);
+	READ_NODE_FIELD(custom_plans);
+	READ_NODE_FIELD(custom_exprs);
+	READ_NODE_FIELD(custom_private);
+	READ_NODE_FIELD(custom_scan_tlist);
+	READ_BITMAPSET_FIELD(custom_relids);
+
+	/*
+	 * Reconstruction of methods using library and symbol name
+	 */
+	token = pg_strtok(&length);		/* skip methods: */
+	token = pg_strtok(&length);		/* methods_library_name */
+	library_name = nullable_string(token, length);
+	token = pg_strtok(&length);		/* methods_symbol_name */
+	symbol_name = nullable_string(token, length);
+
+	methods = (const CustomScanMethods *)
+		load_external_function(library_name, symbol_name, true, NULL);
+	Assert(strcmp(methods->methods_library_name, library_name) == 0 &&
+		   strcmp(methods->methods_symbol_name, symbol_name) == 0);
+
+	/*
+	 * Then, read private fields if any. Elsewhere, just construct
+	 * a usual CustomScan node.
+	 */
+	if (!methods->TextReadCustomScan)
+		local_node = makeNode(CustomScan);
+	else
+	{
+		local_node = methods->TextReadCustomScan();
+		Assert(IsA(local_node, CustomScan));
+	}
+	/* move the common field of CustomScan */
+	memcpy(local_node, &local_temp, offsetof(CustomScan, methods));
+	local_node->methods = methods;
+
+	READ_DONE();
+}
+
+/*
  * ReadCommonJoin
  *	Assign the basic stuff of all nodes that inherit from Join
  */
@@ -2388,6 +2444,8 @@ parseNodeString(void)
 		return_value = _readWorkTableScan();
 	else if (MATCH("FOREIGNSCAN", 11))
 		return_value = _readForeignScan();
+	else if (MATCH("CUSTOMSCAN", 10))
+		return_value = _readCustomScan();
 	else if (MATCH("JOIN", 4))
 		return_value = _readJoin();
 	else if (MATCH("NESTLOOP", 8))
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index cd3db87..f343cfc 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -80,6 +80,8 @@ 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;
 
+/* Library filename on which PG_init() is currently processed */
+static const *current_library_filename = NULL;
 
 /*
  * Load the specified dynamic-link library file, and look for a function
@@ -277,8 +279,16 @@ internal_load_library(const char *libname)
 		 */
 		PG_init = (PG_init_t) pg_dlsym(file_scanner->handle, "_PG_init");
 		if (PG_init)
+		{
+			const char *saved_library_name = current_library_filename;
+
+			current_library_filename = file_scanner->filename;
+
 			(*PG_init) ();
 
+			current_library_filename = saved_library_name;
+		}
+
 		/* OK to link it into list */
 		if (file_list == NULL)
 			file_list = file_scanner;
@@ -291,6 +301,17 @@ internal_load_library(const char *libname)
 }
 
 /*
+ * Inform extensions their own filename, at the time of PG_init()
+ */
+const char *
+get_current_library_filename(void)
+{
+	if (!current_library_filename)
+		elog(ERROR, "Not in the context of _PG_init");
+	return current_library_filename;
+}
+
+/*
  * Report a suitable error for an incompatible magic block.
  */
 static void
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index 808d142..116ca4d 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -645,6 +645,7 @@ extern void **find_rendezvous_variable(const char *varName);
 extern Size EstimateLibraryStateSpace(void);
 extern void SerializeLibraryState(Size maxsize, char *start_address);
 extern void RestoreLibraryState(char *start_address);
+extern const char *get_current_library_filename(void);
 
 /*
  * Support for aggregate functions
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index cc259f1..4c64b51 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -535,24 +535,39 @@ typedef struct ForeignScan
  * custom_private, custom_scan_tlist, and custom_relids fields.  The
  * convention of setting scan.scanrelid to zero for joins applies as well.
  *
- * Note that since Plan trees can be copied, custom scan providers *must*
- * fit all plan data they need into those fields; embedding CustomScan in
- * a larger struct will not work.
+ * Note that Plan trees can be copied, displayed and read using node
+ * functions, thus, custom scan provider *must* support relevant callbacks
+ * if provider wants to embed CustomScan in a larger struct to save private
+ * fields.
  * ----------------
  */
 struct CustomScan;
 
 typedef struct CustomScanMethods
 {
+	/* to be set by INIT_CUSTOM_SCAN_METHODS */
 	const char *CustomName;
+	const char *methods_library_name;
+	const char *methods_symbol_name;
 
 	/* Create execution state (CustomScanState) from a CustomScan plan node */
 	Node	   *(*CreateCustomScanState) (struct CustomScan *cscan);
-	/* Optional: print custom_xxx fields in some special way */
+	/* Optional: print private fields in some special way */
 	void		(*TextOutCustomScan) (StringInfo str,
 											  const struct CustomScan *node);
+	/* Optional: read and construct the private fields above */
+	struct CustomScan *(*TextReadCustomScan)(void);
+	/* Optional: copy the original including private fields */
+	struct CustomScan *(*NodeCopyCustomScan)(const struct CustomScan *from);
 } CustomScanMethods;
 
+#define INIT_CUSTOM_SCAN_METHODS(methods, name)							\
+	do {																\
+		methods.CustomName = (name);									\
+		methods.methods_library_name = get_current_library_filename();	\
+		methods.methods_symbol_name = #methods;							\
+	} while(0)
+
 typedef struct CustomScan
 {
 	Scan		scan;

 src/cuda_control.c |  24 +-------
 src/gpuscan.c      | 167 ++++++++++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 148 insertions(+), 43 deletions(-)

diff --git a/src/cuda_control.c b/src/cuda_control.c
index 4d29591..de5e3a3 100644
--- a/src/cuda_control.c
+++ b/src/cuda_control.c
@@ -1372,7 +1372,7 @@ launch_pending_tasks(GpuTaskState *gts)
  *
  */
 static bool
-__waitfor_ready_tasks(GpuTaskState *gts)
+waitfor_ready_tasks(GpuTaskState *gts)
 {
 	bool	retry_next = true;
 	bool	wait_latch = true;
@@ -1459,28 +1459,6 @@ __waitfor_ready_tasks(GpuTaskState *gts)
 	return retry_next;
 }
 
-static bool
-waitfor_ready_tasks(GpuTaskState *gts)
-{
-	bool	save_set_latch_on_sigusr1 = set_latch_on_sigusr1;
-	bool	status;
-
-	set_latch_on_sigusr1 = true;
-	PG_TRY();
-	{
-		status = __waitfor_ready_tasks(gts);
-	}
-	PG_CATCH();
-	{
-		set_latch_on_sigusr1 = save_set_latch_on_sigusr1;
-		PG_RE_THROW();
-	}
-	PG_END_TRY();
-	set_latch_on_sigusr1 = save_set_latch_on_sigusr1;
-
-	return status;
-}
-
 /*
  * gpucontext_health_check
  *
diff --git a/src/gpuscan.c b/src/gpuscan.c
index 7fb11a7..5a8e633 100644
--- a/src/gpuscan.c
+++ b/src/gpuscan.c
@@ -19,6 +19,7 @@
 #include "access/xact.h"
 #include "catalog/pg_namespace.h"
 #include "miscadmin.h"
+#include "nodes/readfuncs.h"
 #include "optimizer/cost.h"
 #include "optimizer/pathnode.h"
 #include "optimizer/paths.h"
@@ -35,9 +36,9 @@
 
 static set_rel_pathlist_hook_type	set_rel_pathlist_next;
 static CustomPathMethods		gpuscan_path_methods;
-static CustomScanMethods		gpuscan_plan_methods;
+CustomScanMethods				gpuscan_plan_methods;
 static PGStromExecMethods		gpuscan_exec_methods;
-static CustomScanMethods		bulkscan_plan_methods;
+CustomScanMethods				bulkscan_plan_methods;
 static PGStromExecMethods		bulkscan_exec_methods;
 static bool						enable_gpuscan;
 
@@ -61,6 +62,15 @@ typedef struct {
 	List	   *dev_quals;		/* qualifiers to be run on device */
 } GpuScanInfo;
 
+typedef struct {
+	CustomScan	cscan;
+	char	   *kern_source;
+	int32		extra_flags;
+	List	   *used_params;
+	List	   *used_vars;
+	List	   *dev_quals;
+} GpuScanPlan;
+
 static inline void
 form_gpuscan_info(CustomScan *cscan, GpuScanInfo *gscan_info)
 {
@@ -502,7 +512,7 @@ create_gpuscan_plan(PlannerInfo *root,
 					List *clauses,
 					List *custom_children)
 {
-	CustomScan	   *cscan;
+	GpuScanPlan	   *gscan;
 	GpuScanInfo		gs_info;
 	List		   *host_quals = NIL;
 	List		   *dev_quals = NIL;
@@ -543,23 +553,29 @@ create_gpuscan_plan(PlannerInfo *root,
 	/*
 	 * Construction of GpuScanPlan node; on top of CustomPlan node
 	 */
-	cscan = makeNode(CustomScan);
-	cscan->scan.plan.targetlist = tlist;
-	cscan->scan.plan.qual = host_quals;
-	cscan->scan.plan.lefttree = NULL;
-	cscan->scan.plan.righttree = NULL;
-	cscan->scan.scanrelid = rel->relid;
-
-	gs_info.kern_source = kern_source;
-	gs_info.extra_flags = context.extra_flags | DEVKERNEL_NEEDS_GPUSCAN;
-	gs_info.used_params = context.used_params;
-	gs_info.used_vars = context.used_vars;
-	gs_info.dev_quals = dev_quals;
-	form_gpuscan_info(cscan, &gs_info);
-	cscan->flags = best_path->flags;
-	cscan->methods = &gpuscan_plan_methods;
-
-	return &cscan->scan.plan;
+	gscan = palloc0(sizeof(GpuScanPlan));
+	NodeSetTag(gscan, T_CustomScan);
+
+	gscan->cscan.scan.plan.targetlist = tlist;
+	gscan->cscan.scan.plan.qual = host_quals;
+	gscan->cscan.scan.plan.lefttree = NULL;
+	gscan->cscan.scan.plan.righttree = NULL;
+	gscan->cscan.scan.scanrelid = rel->relid;
+	gscan->kern_source = kern_source;
+	gscan->extra_flags = context.extra_flags | DEVKERNEL_NEEDS_GPUSCAN;
+	gscan->used_vars = context.used_vars;
+	gscan->dev_quals = dev_quals;
+	gscan->cscan.flags = best_path->flags;
+	gscan->cscan.methods = &gpuscan_plan_methods;
+
+	gs_info.kern_source = gscan->kern_source;
+	gs_info.extra_flags = gscan->extra_flags;
+	gs_info.used_params = gscan->used_params;
+	gs_info.used_vars = gscan->used_vars;
+	gs_info.dev_quals = gscan->dev_quals;
+	form_gpuscan_info(&gscan->cscan, &gs_info);
+
+	return &gscan->cscan.scan.plan;
 }
 
 /*
@@ -639,6 +655,100 @@ gpuscan_create_scan_state(CustomScan *cscan)
 	return (Node *) gss;
 }
 
+/* copy and paste from outfuncs.c */
+static void
+_outToken(StringInfo str, const char *s)
+{
+	if (s == NULL || *s == '\0')
+	{
+		appendStringInfoString(str, "<>");
+		return;
+	}
+
+	/*
+	 * Look for characters or patterns that are treated specially by read.c
+	 * (either in pg_strtok() or in nodeRead()), and therefore need a
+	 * protective backslash.
+	 */
+	/* These characters only need to be quoted at the start of the string */
+	if (*s == '<' ||
+		*s == '\"' ||
+		isdigit((unsigned char) *s) ||
+		((*s == '+' || *s == '-') &&
+		 (isdigit((unsigned char) s[1]) || s[1] == '.')))
+		appendStringInfoChar(str, '\\');
+	while (*s)
+	{
+		/* These chars must be backslashed anywhere in the string */
+		if (*s == ' ' || *s == '\n' || *s == '\t' ||
+			*s == '(' || *s == ')' || *s == '{' || *s == '}' ||
+			*s == '\\')
+			appendStringInfoChar(str, '\\');
+		appendStringInfoChar(str, *s++);
+	}
+}
+
+static void
+gpuscan_textout(StringInfo str, const CustomScan *node)
+{
+	GpuScanPlan	   *gscan = (GpuScanPlan *) node;
+
+	appendStringInfo(str, " :kern_source ");
+	_outToken(str, gscan->kern_source);
+	appendStringInfo(str, " :extra_flags %u", gscan->extra_flags);
+	appendStringInfo(str, " :used_params %s",
+					 nodeToString(gscan->used_params));
+	appendStringInfo(str, " :used_vars %s",
+					 nodeToString(gscan->used_vars));
+	appendStringInfo(str, " :dev_quals %s",
+					 nodeToString(gscan->dev_quals));
+}
+
+static CustomScan *
+gpuscan_textread(void)
+{
+	GpuScanPlan	   *gscan = palloc0(sizeof(GpuScanPlan));
+	char		   *token;
+	int				length;
+
+	NodeSetTag(gscan, T_CustomScan);
+	/* kern_source */
+	token = pg_strtok(&length);
+	token = pg_strtok(&length);
+	gscan->kern_source = (length > 0 ? debackslash(token, length) : NULL);
+	/* extra_flags */
+	token = pg_strtok(&length);
+	token = pg_strtok(&length);
+	gscan->extra_flags = (cl_uint)strtoul(token, NULL, 10);
+	/* used_params */
+	token = pg_strtok(&length);
+	gscan->used_params = nodeRead(NULL, 0);
+	/* used_vars */
+	token = pg_strtok(&length);
+	gscan->used_vars = nodeRead(NULL, 0);
+	/* dev_quals */
+	token = pg_strtok(&length);
+	gscan->dev_quals = nodeRead(NULL, 0);
+
+	return &gscan->cscan;
+}
+
+static CustomScan *
+gpuscan_nodecopy(const CustomScan *__from)
+{
+	GpuScanPlan	   *from = (GpuScanPlan *) __from;
+	GpuScanPlan	   *to = palloc0(sizeof(GpuScanPlan));
+
+	NodeSetTag(to, T_CustomScan);
+	to->kern_source = (from->kern_source ? pstrdup(from->kern_source) : NULL);
+	to->extra_flags = from->extra_flags;
+	to->used_params = copyObject(from->used_params);
+	to->used_vars = copyObject(from->used_vars);
+	to->dev_quals = copyObject(from->dev_quals);
+
+	return &to->cscan;
+}
+
 static void
 gpuscan_begin(CustomScanState *node, EState *estate, int eflags)
 {
@@ -646,6 +756,15 @@ gpuscan_begin(CustomScanState *node, EState *estate, int eflags)
 	GpuContext	   *gcontext = NULL;
 	GpuScanState   *gss = (GpuScanState *) node;
 	GpuScanInfo	   *gs_info = deform_gpuscan_info(node->ss.ps.plan);
+	CustomScan	   *dplan;
+	char		   *str_1;
+	char		   *str_2;
+
+	dplan = stringToNode(nodeToString(copyObject(node->ss.ps.plan)));
+	str_1 = nodeToString(node->ss.ps.plan);
+	str_2 = nodeToString(dplan);
+	elog(INFO, "str_1 => %s", str_1);
+	elog(INFO, "str_2 => %s", str_2);
 
 	/* gpuscan should not have inner/outer plan right now */
 	Assert(outerPlan(node) == NULL);
@@ -969,10 +1088,18 @@ pgstrom_init_gpuscan(void)
 	memset(&gpuscan_plan_methods, 0, sizeof(gpuscan_plan_methods));
 	gpuscan_plan_methods.CustomName			= "GpuScan";
 	gpuscan_plan_methods.CreateCustomScanState = gpuscan_create_scan_state;
+	gpuscan_plan_methods.TextOutCustomScan	= gpuscan_textout;
+	gpuscan_plan_methods.TextReadCustomScan	= gpuscan_textread;
+	gpuscan_plan_methods.NodeCopyCustomScan	= gpuscan_nodecopy;
+	INIT_CUSTOM_SCAN_METHODS(gpuscan_plan_methods, "GpuScan");
 
 	memset(&bulkscan_plan_methods, 0, sizeof(bulkscan_plan_methods));
 	bulkscan_plan_methods.CustomName		= "BulkScan";
 	bulkscan_plan_methods.CreateCustomScanState = gpuscan_create_scan_state;
+	bulkscan_plan_methods.TextOutCustomScan	= gpuscan_textout;
+	bulkscan_plan_methods.TextReadCustomScan= gpuscan_textread;
+	bulkscan_plan_methods.NodeCopyCustomScan= gpuscan_nodecopy;
+	INIT_CUSTOM_SCAN_METHODS(bulkscan_plan_methods, "GpuScan");
 
 	/* setup exec methods */
 	memset(&gpuscan_exec_methods, 0, sizeof(gpuscan_exec_methods));

 doc/src/sgml/custom-scan.sgml | 25 +++++++++++++++++++++----
 src/backend/nodes/copyfuncs.c | 16 +++++++++++++++-
 src/backend/nodes/readfuncs.c | 22 +++++++++++++++++-----
 src/include/nodes/plannodes.h | 11 +++++++----
 4 files changed, 60 insertions(+), 14 deletions(-)

diff --git a/doc/src/sgml/custom-scan.sgml b/doc/src/sgml/custom-scan.sgml
index af0dd56..21a9ace 100644
--- a/doc/src/sgml/custom-scan.sgml
+++ b/doc/src/sgml/custom-scan.sgml
@@ -197,9 +197,11 @@ typedef struct CustomScan
    Plan trees must be able to be duplicated using <function>copyObject</>,
    serialized using <function>nodeToString</> and deserialized using
    <function>stringToNode</>.
+   <structname>CustomScan</> can be located on head of larger structure
+   to keep private fields of custom scan provider.
    Thus, if custom scan provider implements <function>TextOutCustomScan</>
    to dump its private fields its own way, it also has responsibility of
-   <function>TextReadCustomScan</> to clean out these tokens.
+   <function>TextReadCustomScan</> to reconstruct the private structure.
   </para>
   <para>
    Like any other fields, <structfield>methods</> pointer of the
@@ -251,16 +253,31 @@ void (*TextOutCustomScan) (StringInfo str,
 
    <para>
 <programlisting>
-void (*TextReadCustomScan)(CustomScan *node);
+CustomScan *(*TextReadCustomScan)(void);
 </programlisting>
-    Reads the private fields of supplied <structname>CustomScan</> node
-    generated by <function>TextOutCustomScan</> callback.
+    Allocate a <structname>CustomScan</> or larger structure embedding
+    <structname>CustomScan</>, and read its private fields generated by
+    <function>TextOutCustomScan</> callback.
     This callback is optional, however, must be implemented if custom
     scan provider makes additional output for support of plan-tree
     serialization and deserialization.
     This callback shall be invoked under <function>stringToNode</>
     context, so <function>pg_strtok</> will give the next token.
    </para>
+
+   <para>
+<programlisting>
+CustomScan *(*NodeCopyCustomScan)(const struct CustomScan *from);
+</programlisting>
+    Allocate a <structname>CustomScan</> or larger structure embedding
+    <structname>CustomScan</>, and copies its private fields from the
+    original node.
+    This callback is optional, however, must be implemented if custom
+    scan provider extends <structname>CustomScan</> structure to save
+    its private fields for safety of <function>copyObject</>.
+    The common fields are duplicated by the backend, so all extension
+    needs to focus on is its private fields, if exists.
+   </para>
   </sect2>
  </sect1>
 
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index c176ff9..ba58f3f 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -661,7 +661,21 @@ _copyForeignScan(const ForeignScan *from)
 static CustomScan *
 _copyCustomScan(const CustomScan *from)
 {
-	CustomScan *newnode = makeNode(CustomScan);
+	const CustomScanMethods *methods = from->methods;
+	CustomScan *newnode;
+
+	/*
+	 * If custom-scan provider extends CustomScan node to save its private
+	 * data, it is role of the provider to allocate a new node that includes
+	 * the private fields.
+	 */
+	if (!methods->NodeCopyCustomScan)
+		newnode = makeNode(CustomScan);
+	else
+	{
+		newnode = methods->NodeCopyCustomScan(from);
+		Assert(IsA(newnode, CustomScan));
+	}
 
 	/*
 	 * copy node superclass fields
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 8e6e3d6..8e99703 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -1812,11 +1812,14 @@ _readForeignScan(void)
 static CustomScan *
 _readCustomScan(void)
 {
-	READ_LOCALS(CustomScan);
+	READ_TEMP_LOCALS();
+	CustomScan	local_temp;
+	CustomScan *local_node = &local_temp;
 	char	   *library_name;
 	char	   *symbol_name;
 	const CustomScanMethods *methods;
 
+	NodeSetTag(local_node, T_CustomScan);
 	ReadCommonScan(&local_node->scan);
 
 	READ_UINT_FIELD(flags);
@@ -1842,11 +1845,20 @@ _readCustomScan(void)
 	local_node->methods = methods;
 
 	/*
-	 * Read custom fields if any. Number of tokens has to be equivalent
-	 * to the output of TextOutCustomScan
+	 * Then, read private data fields and reconstruct a struct that
+	 * contains CustomScan on its head, if any. Elsewhere, construct
+	 * usual CustomScan node.
 	 */
-	if (methods->TextReadCustomScan)
-		methods->TextReadCustomScan(local_node);
+	if (!methods->TextReadCustomScan)
+		local_node = makeNode(CustomScan);
+	else
+	{
+		local_node = methods->TextReadCustomScan();
+		Assert(IsA(local_node, CustomScan));
+	}
+	/* move the common field of CustomScan */
+	memcpy(local_node, &local_temp, offsetof(CustomScan, methods));
+	local_node->methods = methods;
 
 	READ_DONE();
 }
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index b3f90fb..908c029 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -542,9 +542,10 @@ typedef struct ForeignScan
  * custom_private, custom_scan_tlist, and custom_relids fields.  The
  * convention of setting scan.scanrelid to zero for joins applies as well.
  *
- * Note that since Plan trees can be copied, custom scan providers *must*
- * fit all plan data they need into those fields; embedding CustomScan in
- * a larger struct will not work.
+ * Note that Plan trees can be copied, displayed and read using node
+ * functions, thus, custom scan provider *must* support relevant callbacks
+ * if provider wants to embed CustomScan in a larger struct to save private
+ * fields.
  * ----------------
  */
 struct CustomScan;
@@ -562,7 +563,9 @@ typedef struct CustomScanMethods
 	void		(*TextOutCustomScan) (StringInfo str,
 											  const struct CustomScan *node);
 	/* Optional: read the private fields printed in special way */
-	void		(*TextReadCustomScan) (struct CustomScan *cscan);
+	struct CustomScan *(*TextReadCustomScan)(void);
+	/* Optional: copy the original including private fields */
+	struct CustomScan *(*NodeCopyCustomScan)(const struct CustomScan *from);
 } CustomScanMethods;
 
 #define INIT_CUSTOM_SCAN_METHODS(methods, name)							\

 doc/src/sgml/custom-scan.sgml  | 41 +++++++++++++++++++++++++++++++-----
 src/backend/nodes/outfuncs.c   |  8 ++++++-
 src/backend/nodes/readfuncs.c  | 48 ++++++++++++++++++++++++++++++++++++++++++
 src/backend/utils/fmgr/dfmgr.c | 21 ++++++++++++++++++
 src/include/fmgr.h             |  1 +
 src/include/nodes/plannodes.h  | 14 +++++++++++-
 6 files changed, 126 insertions(+), 7 deletions(-)

diff --git a/doc/src/sgml/custom-scan.sgml b/doc/src/sgml/custom-scan.sgml
index a229326..af0dd56 100644
--- a/doc/src/sgml/custom-scan.sgml
+++ b/doc/src/sgml/custom-scan.sgml
@@ -195,11 +195,29 @@ typedef struct CustomScan
 
   <para>
    Plan trees must be able to be duplicated using <function>copyObject</>,
-   so all the data stored within the <quote>custom</> fields must consist of
-   nodes that that function can handle.  Furthermore, custom scan providers
-   cannot substitute a larger structure that embeds
-   a <structname>CustomScan</> for the structure itself, as would be possible
-   for a <structname>CustomPath</> or <structname>CustomScanState</>.
+   serialized using <function>nodeToString</> and deserialized using
+   <function>stringToNode</>.
+   Thus, if custom scan provider implements <function>TextOutCustomScan</>
+   to dump its private fields its own way, it also has responsibility of
+   <function>TextReadCustomScan</> to clean out these tokens.
+  </para>
+  <para>
+   Like any other fields, <structfield>methods</> pointer of the
+   <structname>CustomScanMethods</> also has to be restored, however,
+   nobody can ensure a particular shared library that contains the custom
+   scan provider is loaded exactly same address, for example, when
+   <structname>CustomScan</> node is deserialized on the background worker
+   under the control of <structname>Gather</>.
+
+   Thus, here is a few additional interface contract. The first one is
+   symbol name of the <structname>CustomScanMethods</> table has to be
+   visible to linker; that means the variable should not be declared as
+   static, because <function>stringToNode</> reconstructs the
+   <structfield>methods</> pointer using a pair of library and symbol
+   name. The second one is, <structname>CustomScanMethods</> table also
+   has to be initialized using <function>INIT_CUSTOM_SCAN_METHODS</>
+   macro on <function>_PG_init</>, to assign exact library and symbol
+   name to be referenced.
   </para>
 
   <sect2 id="custom-scan-plan-callbacks">
@@ -230,6 +248,19 @@ void (*TextOutCustomScan) (StringInfo str,
     structure, including the substructure of the <quote>custom</> fields,
     there is usually not much need for this callback.
    </para>
+
+   <para>
+<programlisting>
+void (*TextReadCustomScan)(CustomScan *node);
+</programlisting>
+    Reads the private fields of supplied <structname>CustomScan</> node
+    generated by <function>TextOutCustomScan</> callback.
+    This callback is optional, however, must be implemented if custom
+    scan provider makes additional output for support of plan-tree
+    serialization and deserialization.
+    This callback shall be invoked under <function>stringToNode</>
+    context, so <function>pg_strtok</> will give the next token.
+   </para>
   </sect2>
  </sect1>
 
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 3e75cd1..775ac95 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -612,8 +612,14 @@ _outCustomScan(StringInfo str, const CustomScan *node)
 	WRITE_NODE_FIELD(custom_private);
 	WRITE_NODE_FIELD(custom_scan_tlist);
 	WRITE_BITMAPSET_FIELD(custom_relids);
+
+	/* Dump library and symbol name instead of raw pointer */
 	appendStringInfoString(str, " :methods ");
-	_outToken(str, node->methods->CustomName);
+	_outToken(str, node->methods->methods_library_name);
+	appendStringInfoChar(str, ' ');
+	_outToken(str, node->methods->methods_symbol_name);
+
+	/* Also, private fields if any */
 	if (node->methods->TextOutCustomScan)
 		node->methods->TextOutCustomScan(str, node);
 }
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 94ba6dc..8e6e3d6 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -28,6 +28,7 @@
 
 #include <math.h>
 
+#include "fmgr.h"
 #include "nodes/parsenodes.h"
 #include "nodes/plannodes.h"
 #include "nodes/readfuncs.h"
@@ -1806,6 +1807,51 @@ _readForeignScan(void)
 }
 
 /*
+ * _readCustomScan
+ */
+static CustomScan *
+_readCustomScan(void)
+{
+	READ_LOCALS(CustomScan);
+	char	   *library_name;
+	char	   *symbol_name;
+	const CustomScanMethods *methods;
+
+	ReadCommonScan(&local_node->scan);
+
+	READ_UINT_FIELD(flags);
+	READ_NODE_FIELD(custom_plans);
+	READ_NODE_FIELD(custom_exprs);
+	READ_NODE_FIELD(custom_private);
+	READ_NODE_FIELD(custom_scan_tlist);
+	READ_BITMAPSET_FIELD(custom_relids);
+
+	/*
+	 * Reconstruction of methods using library and symbol name
+	 */
+	token = pg_strtok(&length);		/* skip methods: */
+	token = pg_strtok(&length);		/* methods_library_name */
+	library_name = nullable_string(token, length);
+	token = pg_strtok(&length);		/* methods_symbol_name */
+	symbol_name = nullable_string(token, length);
+
+	methods = (const CustomScanMethods *)
+		load_external_function(library_name, symbol_name, true, NULL);
+	Assert(strcmp(methods->methods_library_name, library_name) == 0 &&
+		   strcmp(methods->methods_symbol_name, symbol_name) == 0);
+	local_node->methods = methods;
+
+	/*
+	 * Read custom fields if any. Number of tokens has to be equivalent
+	 * to the output of TextOutCustomScan
+	 */
+	if (methods->TextReadCustomScan)
+		methods->TextReadCustomScan(local_node);
+
+	READ_DONE();
+}
+
+/*
  * ReadCommonJoin
  *	Assign the basic stuff of all nodes that inherit from Join
  */
@@ -2361,6 +2407,8 @@ parseNodeString(void)
 		return_value = _readWorkTableScan();
 	else if (MATCH("FOREIGNSCAN", 11))
 		return_value = _readForeignScan();
+	else if (MATCH("CUSTOMSCAN", 10))
+		return_value = _readCustomScan();
 	else if (MATCH("JOIN", 4))
 		return_value = _readJoin();
 	else if (MATCH("NESTLOOP", 8))
diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index cd3db87..f343cfc 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -80,6 +80,8 @@ 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;
 
+/* Library filename on which PG_init() is currently processed */
+static const *current_library_filename = NULL;
 
 /*
  * Load the specified dynamic-link library file, and look for a function
@@ -277,8 +279,16 @@ internal_load_library(const char *libname)
 		 */
 		PG_init = (PG_init_t) pg_dlsym(file_scanner->handle, "_PG_init");
 		if (PG_init)
+		{
+			const char *saved_library_name = current_library_filename;
+
+			current_library_filename = file_scanner->filename;
+
 			(*PG_init) ();
 
+			current_library_filename = saved_library_name;
+		}
+
 		/* OK to link it into list */
 		if (file_list == NULL)
 			file_list = file_scanner;
@@ -291,6 +301,17 @@ internal_load_library(const char *libname)
 }
 
 /*
+ * Inform extensions their own filename, at the time of PG_init()
+ */
+const char *
+get_current_library_filename(void)
+{
+	if (!current_library_filename)
+		elog(ERROR, "Not in the context of _PG_init");
+	return current_library_filename;
+}
+
+/*
  * Report a suitable error for an incompatible magic block.
  */
 static void
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index 808d142..116ca4d 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -645,6 +645,7 @@ extern void **find_rendezvous_variable(const char *varName);
 extern Size EstimateLibraryStateSpace(void);
 extern void SerializeLibraryState(Size maxsize, char *start_address);
 extern void RestoreLibraryState(char *start_address);
+extern const char *get_current_library_filename(void);
 
 /*
  * Support for aggregate functions
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 6b28c8e..b3f90fb 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -551,15 +551,27 @@ struct CustomScan;
 
 typedef struct CustomScanMethods
 {
+	/* to be set by INIT_CUSTOM_SCAN_METHODS */
 	const char *CustomName;
+	const char *methods_library_name;
+	const char *methods_symbol_name;
 
 	/* Create execution state (CustomScanState) from a CustomScan plan node */
 	Node	   *(*CreateCustomScanState) (struct CustomScan *cscan);
-	/* Optional: print custom_xxx fields in some special way */
+	/* Optional: print private fields in some special way */
 	void		(*TextOutCustomScan) (StringInfo str,
 											  const struct CustomScan *node);
+	/* Optional: read the private fields printed in special way */
+	void		(*TextReadCustomScan) (struct CustomScan *cscan);
 } CustomScanMethods;
 
+#define INIT_CUSTOM_SCAN_METHODS(methods, name)							\
+	do {																\
+		methods.CustomName = (name);									\
+		methods.methods_library_name = get_current_library_filename();	\
+		methods.methods_symbol_name = #methods;							\
+	} while(0)
+
 typedef struct CustomScan
 {
 	Scan		scan;

 doc/src/sgml/custom-scan.sgml | 16 +++-------------
 src/backend/nodes/outfuncs.c  |  7 ++++---
 src/backend/nodes/readfuncs.c | 41 +++++++++++++++++++++++++++++++++++++++++
 src/include/nodes/plannodes.h |  5 ++---
 4 files changed, 50 insertions(+), 19 deletions(-)

diff --git a/doc/src/sgml/custom-scan.sgml b/doc/src/sgml/custom-scan.sgml
index a229326..d042adb 100644
--- a/doc/src/sgml/custom-scan.sgml
+++ b/doc/src/sgml/custom-scan.sgml
@@ -83,7 +83,9 @@ typedef struct CustomPath
     print the custom path will work as designed.  <structfield>methods</> must
     point to a (usually statically allocated) object implementing the required
     custom path methods, of which there are currently only two, as further
-    detailed below.
+    detailed below. Also note that this field shall be serialized using
+    a pair of library name and symbol name, thus, method variable has to
+    be resolvable by linker.
   </para>
 
   <para>
@@ -218,18 +220,6 @@ Node *(*CreateCustomScanState) (CustomScan *cscan);
     the <function>BeginCustomScan</> callback will be invoked to give the
     custom scan provider a chance to do whatever else is needed.
    </para>
-
-   <para>
-<programlisting>
-void (*TextOutCustomScan) (StringInfo str,
-                           const CustomScan *node);
-</programlisting>
-    Generate additional output when <function>nodeToString</> is invoked on
-    this custom plan node.  This callback is optional.  Since
-    <function>nodeToString</> will automatically dump all fields in the
-    structure, including the substructure of the <quote>custom</> fields,
-    there is usually not much need for this callback.
-   </para>
   </sect2>
  </sect1>
 
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 3e75cd1..af6674c 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -612,10 +612,11 @@ _outCustomScan(StringInfo str, const CustomScan *node)
 	WRITE_NODE_FIELD(custom_private);
 	WRITE_NODE_FIELD(custom_scan_tlist);
 	WRITE_BITMAPSET_FIELD(custom_relids);
+	/* Dump library and symbol name instead of raw pointer */
 	appendStringInfoString(str, " :methods ");
-	_outToken(str, node->methods->CustomName);
-	if (node->methods->TextOutCustomScan)
-		node->methods->TextOutCustomScan(str, node);
+	_outToken(str, node->methods->methodsLibraryName);
+	appendStringInfoChar(str, ' ');
+	_outToken(str, node->methods->methodsSymbolName);
 }
 
 static void
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 94ba6dc..d143dac 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -28,6 +28,7 @@
 
 #include <math.h>
 
+#include "fmgr.h"
 #include "nodes/parsenodes.h"
 #include "nodes/plannodes.h"
 #include "nodes/readfuncs.h"
@@ -1806,6 +1807,44 @@ _readForeignScan(void)
 }
 
 /*
+ * _readCustomScan
+ */
+static CustomScan *
+_readCustomScan(void)
+{
+	READ_LOCALS(CustomScan);
+	char	   *library_name;
+	char	   *symbol_name;
+	const CustomScanMethods *methods;
+
+	ReadCommonScan(&local_node->scan);
+
+	READ_UINT_FIELD(flags);
+	READ_NODE_FIELD(custom_plans);
+	READ_NODE_FIELD(custom_exprs);
+	READ_NODE_FIELD(custom_private);
+	READ_NODE_FIELD(custom_scan_tlist);
+	READ_BITMAPSET_FIELD(custom_relids);
+
+	/*
+	 * Reconstruction of methods using library and symbol name
+	 */
+	token = pg_strtok(&length);		/* skip methods: */
+	token = pg_strtok(&length);		/* methodsLibraryName */
+	library_name = nullable_string(token, length);
+	token = pg_strtok(&length);		/* methodsSymbolName */
+	symbol_name = nullable_string(token, length);
+
+	methods = (const CustomScanMethods *)
+		load_external_function(library_name, symbol_name, true, NULL);
+	Assert(strcmp(methods->methodsLibraryName, library_name) == 0 &&
+		   strcmp(methods->methodsSymbolName, symbol_name) == 0);
+	local_node->methods = methods;
+
+	READ_DONE();
+}
+
+/*
  * ReadCommonJoin
  *	Assign the basic stuff of all nodes that inherit from Join
  */
@@ -2361,6 +2400,8 @@ parseNodeString(void)
 		return_value = _readWorkTableScan();
 	else if (MATCH("FOREIGNSCAN", 11))
 		return_value = _readForeignScan();
+	else if (MATCH("CUSTOMSCAN", 10))
+		return_value = _readCustomScan();
 	else if (MATCH("JOIN", 4))
 		return_value = _readJoin();
 	else if (MATCH("NESTLOOP", 8))
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 6b28c8e..5ecc2d1 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -552,12 +552,11 @@ struct CustomScan;
 typedef struct CustomScanMethods
 {
 	const char *CustomName;
+	const char *methodsLibraryName;
+	const char *methodsSymbolName;
 
 	/* Create execution state (CustomScanState) from a CustomScan plan node */
 	Node	   *(*CreateCustomScanState) (struct CustomScan *cscan);
-	/* Optional: print custom_xxx fields in some special way */
-	void		(*TextOutCustomScan) (StringInfo str,
-											  const struct CustomScan *node);
 } CustomScanMethods;
 
 typedef struct CustomScan