Get rid of the dynamic shared memory state file.

Instead of storing the ID of the dynamic shared memory control
segment in a file within the data directory, store it in the main
control segment.  This avoids a number of nasty corner cases,
most seriously that doing an online backup and then using it on
the same machine (e.g. to fire up a standby) would result in the
standby clobbering all of the master's dynamic shared memory
segments.

Per complaints from Heikki Linnakangas, Fujii Masao, and Tom
Lane.

Author: robertmhaas

src/backend/port/sysv_shmem.c

@@ -30,6 +30,7 @@
 
 #include "miscadmin.h"
 #include "portability/mem.h"
+#include "storage/dsm.h"
 #include "storage/ipc.h"
 #include "storage/pg_shmem.h"
 #include "utils/guc.h"
@@ -421,7 +422,8 @@ CreateAnonymousSegment(Size *size)
  * zero will be passed.
  */
 PGShmemHeader *
-PGSharedMemoryCreate(Size size, bool makePrivate, int port)
+PGSharedMemoryCreate(Size size, bool makePrivate, int port,
+					 PGShmemHeader **shim)
 {
 	IpcMemoryKey NextShmemSegID;
 	void	   *memAddress;
@@ -509,10 +511,13 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
 
 		/*
 		 * The segment appears to be from a dead Postgres process, or from a
-		 * previous cycle of life in this same process.  Zap it, if possible.
+		 * previous cycle of life in this same process.  Zap it, if possible,
+		 * and any associated dynamic shared memory segments, as well.
 		 * This probably shouldn't fail, but if it does, assume the segment
 		 * belongs to someone else after all, and continue quietly.
 		 */
+		if (hdr->dsm_control != 0)
+			dsm_cleanup_using_control_segment(hdr->dsm_control);
 		shmdt(memAddress);
 		if (shmctl(shmid, IPC_RMID, NULL) < 0)
 			continue;
@@ -539,6 +544,7 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
 	hdr = (PGShmemHeader *) memAddress;
 	hdr->creatorPID = getpid();
 	hdr->magic = PGShmemMagic;
+	hdr->dsm_control = 0;
 
 	/* Fill in the data directory ID info, too */
 	if (stat(DataDir, &statbuf) < 0)
@@ -554,6 +560,7 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
 	 */
 	hdr->totalsize = size;
 	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
+	*shim = hdr;
 
 	/* Save info for possible future use */
 	UsedShmemSegAddr = memAddress;
@@ -608,6 +615,7 @@ PGSharedMemoryReAttach(void)
 	if (hdr != origUsedShmemSegAddr)
 		elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
 			 hdr, origUsedShmemSegAddr);
+	dsm_set_control_handle(((PGShmemHeader *) hdr)->dsm_control);
 
 	UsedShmemSegAddr = hdr;		/* probably redundant */
 }

src/backend/port/win32_shmem.c

@@ -117,7 +117,8 @@ PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
  *
  */
 PGShmemHeader *
-PGSharedMemoryCreate(Size size, bool makePrivate, int port)
+PGSharedMemoryCreate(Size size, bool makePrivate, int port,
+					 PGShmemHeader **shim)
 {
 	void	   *memAddress;
 	PGShmemHeader *hdr;
@@ -245,12 +246,14 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
 	 */
 	hdr->totalsize = size;
 	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
+	hdr->dsm_control = 0;
 
 	/* Save info for possible future use */
 	UsedShmemSegAddr = memAddress;
 	UsedShmemSegSize = size;
 	UsedShmemSegID = hmap2;
 
+	*shim = NULL;
 	return hdr;
 }
 
@@ -289,6 +292,7 @@ PGSharedMemoryReAttach(void)
 			 hdr, origUsedShmemSegAddr);
 	if (hdr->magic != PGShmemMagic)
 		elog(FATAL, "reattaching to shared memory returned non-PostgreSQL memory");
+	dsm_set_control_handle(hdr->dsm_control);
 
 	UsedShmemSegAddr = hdr;		/* probably redundant */
 }