From 59a667f079c9b040c23921e4c43fae94b88776f2 Mon Sep 17 00:00:00 2001
From: Tristan Partin <tristan@neon.tech>
Date: Fri, 13 Oct 2023 14:00:44 -0500
Subject: [PATCH v1 2/5] Allow extensions to override the global storage
 manager

---
 src/backend/storage/smgr/md.c     | 2 +-
 src/backend/storage/smgr/smgr.c   | 5 ++++-
 src/backend/utils/init/miscinit.c | 2 ++
 src/include/storage/md.h          | 2 ++
 src/include/storage/smgr.h        | 2 ++
 5 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 66a93101ab..13ec9da236 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -140,7 +140,7 @@ void mdsmgr_register(void)
 {
 	/* magnetic disk */
 	f_smgr md_smgr = (f_smgr) {
-		.name = "md",
+		.name = MdSMgrName,
 		.smgr_init = mdinit,
 		.smgr_shutdown = NULL,
 		.smgr_open = mdopen,
diff --git a/src/backend/storage/smgr/smgr.c b/src/backend/storage/smgr/smgr.c
index b586e6e25a..0814330b8a 100644
--- a/src/backend/storage/smgr/smgr.c
+++ b/src/backend/storage/smgr/smgr.c
@@ -37,6 +37,9 @@ static int NSmgr = 0;
 
 static Size LargestSMgrRelationSize = 0;
 
+char *storage_manager_string;
+SMgrId storage_manager_id;
+
 /*
  * Each backend has a hashtable that stores all extant SMgrRelation objects.
  * In addition, "unowned" SMgrRelation objects are chained together in a list.
@@ -182,7 +185,7 @@ smgropen(RelFileLocator rlocator, BackendId backend)
 		for (int i = 0; i <= MAX_FORKNUM; ++i)
 			reln->smgr_cached_nblocks[i] = InvalidBlockNumber;
 
-		reln->smgr_which = MdSMgrId;	/* we only have md.c at present */
+		reln->smgr_which = storage_manager_id;
 
 		/* implementation-specific initialization */
 		smgrsw[reln->smgr_which].smgr_open(reln);
diff --git a/src/backend/utils/init/miscinit.c b/src/backend/utils/init/miscinit.c
index 4ec7619302..f44f511f69 100644
--- a/src/backend/utils/init/miscinit.c
+++ b/src/backend/utils/init/miscinit.c
@@ -1871,6 +1871,8 @@ void
 register_builtin_dynamic_managers(void)
 {
 	mdsmgr_register();
+
+	storage_manager_id = MdSMgrId;
 }
 
 /*
diff --git a/src/include/storage/md.h b/src/include/storage/md.h
index 734bae07e1..fdafb2c8e3 100644
--- a/src/include/storage/md.h
+++ b/src/include/storage/md.h
@@ -19,6 +19,8 @@
 #include "storage/smgr.h"
 #include "storage/sync.h"
 
+#define MdSMgrName "md"
+
 /* registration function for md storage manager */
 extern void mdsmgr_register(void);
 extern SMgrId MdSMgrId;
diff --git a/src/include/storage/smgr.h b/src/include/storage/smgr.h
index 95927b8bdd..ee4fc27265 100644
--- a/src/include/storage/smgr.h
+++ b/src/include/storage/smgr.h
@@ -22,6 +22,8 @@ typedef uint8 SMgrId;
 
 #define MaxSMgrId UINT8_MAX
 
+extern PGDLLIMPORT SMgrId storage_manager_id;
+
 /*
  * smgr.c maintains a table of SMgrRelation objects, which are essentially
  * cached file handles.  An SMgrRelation is created (if not already present)
-- 
Tristan Partin
Neon (https://neon.tech)