* sysv_shmem.c
* Implement shared memory using SysV facilities
*
- * These routines represent a fairly thin layer on top of SysV shared
- * memory functionality.
+ * These routines used to be a fairly thin layer on top of SysV shared
+ * memory functionality. With the addition of anonymous-shmem logic,
+ * they're a bit fatter now. We still require a SysV shmem block to
+ * exist, though, because mmap'd shmem provides no way to find out how
+ * many processes are attached, which we need for interlocking purposes.
*
- * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/port/sysv_shmem.c,v 1.21 2003/10/13 22:47:15 momjian Exp $
+ * src/backend/port/sysv_shmem.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
-#include <errno.h>
#include <signal.h>
#include <unistd.h>
#include <sys/file.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
#ifdef HAVE_SYS_IPC_H
#include <sys/ipc.h>
#endif
#ifdef HAVE_SYS_SHM_H
#include <sys/shm.h>
#endif
-#ifdef HAVE_KERNEL_OS_H
-#include <kernel/OS.h>
-#endif
#include "miscadmin.h"
+#include "portability/mem.h"
+#include "storage/dsm.h"
+#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/pg_shmem.h"
+#include "utils/guc.h"
+#include "utils/pidfile.h"
+
+
+/*
+ * As of PostgreSQL 9.3, we normally allocate only a very small amount of
+ * System V shared memory, and only for the purposes of providing an
+ * interlock to protect the data directory. The real shared memory block
+ * is allocated using mmap(). This works around the problem that many
+ * systems have very low limits on the amount of System V shared memory
+ * that can be allocated. Even a limit of a few megabytes will be enough
+ * to run many copies of PostgreSQL without needing to adjust system settings.
+ *
+ * We assume that no one will attempt to run PostgreSQL 9.3 or later on
+ * systems that are ancient enough that anonymous shared memory is not
+ * supported, such as pre-2.4 versions of Linux. If that turns out to be
+ * false, we might need to add compile and/or run-time tests here and do this
+ * only if the running kernel supports it.
+ *
+ * However, we must always disable this logic in the EXEC_BACKEND case, and
+ * fall back to the old method of allocating the entire segment using System V
+ * shared memory, because there's no way to attach an anonymous mmap'd segment
+ * to a process after exec(). Since EXEC_BACKEND is intended only for
+ * developer use, this shouldn't be a big problem. Because of this, we do
+ * not worry about supporting anonymous shmem in the EXEC_BACKEND cases below.
+ */
+#ifndef EXEC_BACKEND
+#define USE_ANONYMOUS_SHMEM
+#endif
-typedef int IpcMemoryId; /* shared memory ID returned by shmget(2) */
-#define IPCProtection (0600) /* access/modify by user only */
+typedef key_t IpcMemoryKey; /* shared memory key passed to shmget(2) */
+typedef int IpcMemoryId; /* shared memory ID returned by shmget(2) */
-IpcMemoryKey UsedShmemSegID = 0;
+unsigned long UsedShmemSegID = 0;
void *UsedShmemSegAddr = NULL;
-static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, uint32 size);
+#ifdef USE_ANONYMOUS_SHMEM
+static Size AnonymousShmemSize;
+static void *AnonymousShmem = NULL;
+#endif
+
+static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
static void IpcMemoryDetach(int status, Datum shmaddr);
static void IpcMemoryDelete(int status, Datum shmId);
static PGShmemHeader *PGSharedMemoryAttach(IpcMemoryKey key,
* print out an error and abort. Other types of errors are not recoverable.
*/
static void *
-InternalIpcMemoryCreate(IpcMemoryKey memKey, uint32 size)
+InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
{
IpcMemoryId shmid;
+ void *requestedAddress = NULL;
void *memAddress;
+ /*
+ * Normally we just pass requestedAddress = NULL to shmat(), allowing the
+ * system to choose where the segment gets mapped. But in an EXEC_BACKEND
+ * build, it's possible for whatever is chosen in the postmaster to not
+ * work for backends, due to variations in address space layout. As a
+ * rather klugy workaround, allow the user to specify the address to use
+ * via setting the environment variable PG_SHMEM_ADDR. (If this were of
+ * interest for anything except debugging, we'd probably create a cleaner
+ * and better-documented way to set it, such as a GUC.)
+ */
+#ifdef EXEC_BACKEND
+ {
+ char *pg_shmem_addr = getenv("PG_SHMEM_ADDR");
+
+ if (pg_shmem_addr)
+ requestedAddress = (void *) strtoul(pg_shmem_addr, NULL, 0);
+ }
+#endif
+
shmid = shmget(memKey, size, IPC_CREAT | IPC_EXCL | IPCProtection);
if (shmid < 0)
{
+ int shmget_errno = errno;
+
/*
- * Fail quietly if error indicates a collision with existing
- * segment. One would expect EEXIST, given that we said IPC_EXCL,
- * but perhaps we could get a permission violation instead? Also,
- * EIDRM might occur if an old seg is slated for destruction but
- * not gone yet.
+ * Fail quietly if error indicates a collision with existing segment.
+ * One would expect EEXIST, given that we said IPC_EXCL, but perhaps
+ * we could get a permission violation instead? Also, EIDRM might
+ * occur if an old seg is slated for destruction but not gone yet.
*/
- if (errno == EEXIST || errno == EACCES
+ if (shmget_errno == EEXIST || shmget_errno == EACCES
#ifdef EIDRM
- || errno == EIDRM
+ || shmget_errno == EIDRM
#endif
)
return NULL;
/*
- * Else complain and abort
+ * Some BSD-derived kernels are known to return EINVAL, not EEXIST, if
+ * there is an existing segment but it's smaller than "size" (this is
+ * a result of poorly-thought-out ordering of error tests). To
+ * distinguish between collision and invalid size in such cases, we
+ * make a second try with size = 0. These kernels do not test size
+ * against SHMMIN in the preexisting-segment case, so we will not get
+ * EINVAL a second time if there is such a segment.
*/
+ if (shmget_errno == EINVAL)
+ {
+ shmid = shmget(memKey, 0, IPC_CREAT | IPC_EXCL | IPCProtection);
+
+ if (shmid < 0)
+ {
+ /* As above, fail quietly if we verify a collision */
+ if (errno == EEXIST || errno == EACCES
+#ifdef EIDRM
+ || errno == EIDRM
+#endif
+ )
+ return NULL;
+ /* Otherwise, fall through to report the original error */
+ }
+ else
+ {
+ /*
+ * On most platforms we cannot get here because SHMMIN is
+ * greater than zero. However, if we do succeed in creating a
+ * zero-size segment, free it and then fall through to report
+ * the original error.
+ */
+ if (shmctl(shmid, IPC_RMID, NULL) < 0)
+ elog(LOG, "shmctl(%d, %d, 0) failed: %m",
+ (int) shmid, IPC_RMID);
+ }
+ }
+
+ /*
+ * Else complain and abort.
+ *
+ * Note: at this point EINVAL should mean that either SHMMIN or SHMMAX
+ * is violated. SHMALL violation might be reported as either ENOMEM
+ * (BSDen) or ENOSPC (Linux); the Single Unix Spec fails to say which
+ * it should be. SHMMNI violation is ENOSPC, per spec. Just plain
+ * not-enough-RAM is ENOMEM.
+ */
+ errno = shmget_errno;
ereport(FATAL,
(errmsg("could not create shared memory segment: %m"),
- errdetail("Failed system call was shmget(key=%d, size=%u, 0%o).",
- (int) memKey, size,
- IPC_CREAT | IPC_EXCL | IPCProtection),
- (errno == EINVAL) ?
+ errdetail("Failed system call was shmget(key=%lu, size=%zu, 0%o).",
+ (unsigned long) memKey, size,
+ IPC_CREAT | IPC_EXCL | IPCProtection),
+ (shmget_errno == EINVAL) ?
errhint("This error usually means that PostgreSQL's request for a shared memory "
- "segment exceeded your kernel's SHMMAX parameter. You can either "
- "reduce the request size or reconfigure the kernel with larger SHMMAX. "
- "To reduce the request size (currently %u bytes), reduce "
- "PostgreSQL's shared_buffers parameter (currently %d) and/or "
- "its max_connections parameter (currently %d).\n"
- "If the request size is already small, it's possible that it is less than "
- "your kernel's SHMMIN parameter, in which case raising the request size or "
- "reconfiguring SHMMIN is called for.\n"
+ "segment exceeded your kernel's SHMMAX parameter, or possibly that "
+ "it is less than "
+ "your kernel's SHMMIN parameter.\n"
"The PostgreSQL documentation contains more information about shared "
- "memory configuration.",
- size, NBuffers, MaxBackends) : 0,
- (errno == ENOMEM) ?
+ "memory configuration.") : 0,
+ (shmget_errno == ENOMEM) ?
errhint("This error usually means that PostgreSQL's request for a shared "
- "memory segment exceeded available memory or swap space. "
- "To reduce the request size (currently %u bytes), reduce "
- "PostgreSQL's shared_buffers parameter (currently %d) and/or "
- "its max_connections parameter (currently %d).\n"
+ "memory segment exceeded your kernel's SHMALL parameter. You might need "
+ "to reconfigure the kernel with larger SHMALL.\n"
"The PostgreSQL documentation contains more information about shared "
- "memory configuration.",
- size, NBuffers, MaxBackends) : 0,
- (errno == ENOSPC) ?
- errhint("This error does *not* mean that you have run out of disk space. "
+ "memory configuration.") : 0,
+ (shmget_errno == ENOSPC) ?
+ errhint("This error does *not* mean that you have run out of disk space. "
"It occurs either if all available shared memory IDs have been taken, "
"in which case you need to raise the SHMMNI parameter in your kernel, "
"or because the system's overall limit for shared memory has been "
- "reached. If you cannot increase the shared memory limit, "
- "reduce PostgreSQL's shared memory request (currently %u bytes), "
- "by reducing its shared_buffers parameter (currently %d) and/or "
- "its max_connections parameter (currently %d).\n"
+ "reached.\n"
"The PostgreSQL documentation contains more information about shared "
- "memory configuration.",
- size, NBuffers, MaxBackends) : 0));
+ "memory configuration.") : 0));
}
/* Register on-exit routine to delete the new segment */
on_shmem_exit(IpcMemoryDelete, Int32GetDatum(shmid));
/* OK, should be able to attach to the segment */
-#if defined(solaris) && defined(__sparc__)
- /* use intimate shared memory on SPARC Solaris */
- memAddress = shmat(shmid, 0, SHM_SHARE_MMU);
-#else
- memAddress = shmat(shmid, 0, 0);
-#endif
+ memAddress = shmat(shmid, requestedAddress, PG_SHMAT_FLAGS);
if (memAddress == (void *) -1)
- elog(FATAL, "shmat(id=%d) failed: %m", shmid);
+ elog(FATAL, "shmat(id=%d, addr=%p, flags=0x%x) failed: %m",
+ shmid, requestedAddress, PG_SHMAT_FLAGS);
/* Register on-exit routine to detach new segment before deleting */
on_shmem_exit(IpcMemoryDetach, PointerGetDatum(memAddress));
- /* Record key and ID in lockfile for data directory. */
- RecordSharedMemoryInLockFile((unsigned long) memKey,
- (unsigned long) shmid);
+ /*
+ * Store shmem key and ID in data directory lockfile. Format to try to
+ * keep it the same length always (trailing junk in the lockfile won't
+ * hurt, but might confuse humans).
+ */
+ {
+ char line[64];
+
+ sprintf(line, "%9lu %9lu",
+ (unsigned long) memKey, (unsigned long) shmid);
+ AddToDataDirLockFile(LOCK_FILE_LINE_SHMEM_KEY, line);
+ }
return memAddress;
}
/****************************************************************************/
/* IpcMemoryDetach(status, shmaddr) removes a shared memory segment */
-/* from process' address spaceq */
+/* from process' address space */
/* (called as an on_shmem_exit callback, hence funny argument list) */
/****************************************************************************/
static void
IpcMemoryDetach(int status, Datum shmaddr)
{
+ /* Detach System V shared memory block. */
if (shmdt(DatumGetPointer(shmaddr)) < 0)
elog(LOG, "shmdt(%p) failed: %m", DatumGetPointer(shmaddr));
}
static void
IpcMemoryDelete(int status, Datum shmId)
{
- if (shmctl(DatumGetInt32(shmId), IPC_RMID, (struct shmid_ds *) NULL) < 0)
+ if (shmctl(DatumGetInt32(shmId), IPC_RMID, NULL) < 0)
elog(LOG, "shmctl(%d, %d, 0) failed: %m",
DatumGetInt32(shmId), IPC_RMID);
}
* PGSharedMemoryIsInUse
*
* Is a previously-existing shmem segment still existing and in use?
+ *
+ * The point of this exercise is to detect the case where a prior postmaster
+ * crashed, but it left child backends that are still running. Therefore
+ * we only care about shmem segments that are associated with the intended
+ * DataDir. This is an important consideration since accidental matches of
+ * shmem segment IDs are reasonably common.
*/
bool
PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
{
IpcMemoryId shmId = (IpcMemoryId) id2;
struct shmid_ds shmStat;
+ struct stat statbuf;
+ PGShmemHeader *hdr;
/*
- * We detect whether a shared memory segment is in use by seeing
- * whether it (a) exists and (b) has any processes are attached to it.
- *
- * If we are unable to perform the stat operation for a reason other than
- * nonexistence of the segment (most likely, because it doesn't belong
- * to our userid), assume it is in use.
+ * We detect whether a shared memory segment is in use by seeing whether
+ * it (a) exists and (b) has any processes attached to it.
*/
if (shmctl(shmId, IPC_STAT, &shmStat) < 0)
{
/*
* EINVAL actually has multiple possible causes documented in the
- * shmctl man page, but we assume it must mean the segment no
- * longer exists.
+ * shmctl man page, but we assume it must mean the segment no longer
+ * exists.
*/
if (errno == EINVAL)
return false;
- /* Else assume segment is in use */
+
+ /*
+ * EACCES implies that the segment belongs to some other userid, which
+ * means it is not a Postgres shmem segment (or at least, not one that
+ * is relevant to our data directory).
+ */
+ if (errno == EACCES)
+ return false;
+
+ /*
+ * Some Linux kernel versions (in fact, all of them as of July 2007)
+ * sometimes return EIDRM when EINVAL is correct. The Linux kernel
+ * actually does not have any internal state that would justify
+ * returning EIDRM, so we can get away with assuming that EIDRM is
+ * equivalent to EINVAL on that platform.
+ */
+#ifdef HAVE_LINUX_EIDRM_BUG
+ if (errno == EIDRM)
+ return false;
+#endif
+
+ /*
+ * Otherwise, we had better assume that the segment is in use. The
+ * only likely case is EIDRM, which implies that the segment has been
+ * IPC_RMID'd but there are still processes attached to it.
+ */
return true;
}
- /* If it has attached processes, it's in use */
- if (shmStat.shm_nattch != 0)
- return true;
- return false;
+
+ /* If it has no attached processes, it's not in use */
+ if (shmStat.shm_nattch == 0)
+ return false;
+
+ /*
+ * Try to attach to the segment and see if it matches our data directory.
+ * This avoids shmid-conflict problems on machines that are running
+ * several postmasters under the same userid.
+ */
+ if (stat(DataDir, &statbuf) < 0)
+ return true; /* if can't stat, be conservative */
+
+ hdr = (PGShmemHeader *) shmat(shmId, NULL, PG_SHMAT_FLAGS);
+
+ if (hdr == (PGShmemHeader *) -1)
+ return true; /* if can't attach, be conservative */
+
+ if (hdr->magic != PGShmemMagic ||
+ hdr->device != statbuf.st_dev ||
+ hdr->inode != statbuf.st_ino)
+ {
+ /*
+ * It's either not a Postgres segment, or not one for my data
+ * directory. In either case it poses no threat.
+ */
+ shmdt((void *) hdr);
+ return false;
+ }
+
+ /* Trouble --- looks a lot like there's still live backends */
+ shmdt((void *) hdr);
+
+ return true;
+}
+
+#ifdef USE_ANONYMOUS_SHMEM
+
+#ifdef MAP_HUGETLB
+
+/*
+ * Identify the huge page size to use.
+ *
+ * Some Linux kernel versions have a bug causing mmap() to fail on requests
+ * that are not a multiple of the hugepage size. Versions without that bug
+ * instead silently round the request up to the next hugepage multiple ---
+ * and then munmap() fails when we give it a size different from that.
+ * So we have to round our request up to a multiple of the actual hugepage
+ * size to avoid trouble.
+ *
+ * Doing the round-up ourselves also lets us make use of the extra memory,
+ * rather than just wasting it. Currently, we just increase the available
+ * space recorded in the shmem header, which will make the extra usable for
+ * purposes such as additional locktable entries. Someday, for very large
+ * hugepage sizes, we might want to think about more invasive strategies,
+ * such as increasing shared_buffers to absorb the extra space.
+ *
+ * Returns the (real or assumed) page size into *hugepagesize,
+ * and the hugepage-related mmap flags to use into *mmap_flags.
+ *
+ * Currently *mmap_flags is always just MAP_HUGETLB. Someday, on systems
+ * that support it, we might OR in additional bits to specify a particular
+ * non-default huge page size.
+ */
+static void
+GetHugePageSize(Size *hugepagesize, int *mmap_flags)
+{
+ /*
+ * If we fail to find out the system's default huge page size, assume it
+ * is 2MB. This will work fine when the actual size is less. If it's
+ * more, we might get mmap() or munmap() failures due to unaligned
+ * requests; but at this writing, there are no reports of any non-Linux
+ * systems being picky about that.
+ */
+ *hugepagesize = 2 * 1024 * 1024;
+ *mmap_flags = MAP_HUGETLB;
+
+ /*
+ * System-dependent code to find out the default huge page size.
+ *
+ * On Linux, read /proc/meminfo looking for a line like "Hugepagesize:
+ * nnnn kB". Ignore any failures, falling back to the preset default.
+ */
+#ifdef __linux__
+ {
+ FILE *fp = AllocateFile("/proc/meminfo", "r");
+ char buf[128];
+ unsigned int sz;
+ char ch;
+
+ if (fp)
+ {
+ while (fgets(buf, sizeof(buf), fp))
+ {
+ if (sscanf(buf, "Hugepagesize: %u %c", &sz, &ch) == 2)
+ {
+ if (ch == 'k')
+ {
+ *hugepagesize = sz * (Size) 1024;
+ break;
+ }
+ /* We could accept other units besides kB, if needed */
+ }
+ }
+ FreeFile(fp);
+ }
+ }
+#endif /* __linux__ */
}
+#endif /* MAP_HUGETLB */
+
+/*
+ * Creates an anonymous mmap()ed shared memory segment.
+ *
+ * Pass the requested size in *size. This function will modify *size to the
+ * actual size of the allocation, if it ends up allocating a segment that is
+ * larger than requested.
+ */
+static void *
+CreateAnonymousSegment(Size *size)
+{
+ Size allocsize = *size;
+ void *ptr = MAP_FAILED;
+ int mmap_errno = 0;
+
+#ifndef MAP_HUGETLB
+ /* PGSharedMemoryCreate should have dealt with this case */
+ Assert(huge_pages != HUGE_PAGES_ON);
+#else
+ if (huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY)
+ {
+ /*
+ * Round up the request size to a suitable large value.
+ */
+ Size hugepagesize;
+ int mmap_flags;
+
+ GetHugePageSize(&hugepagesize, &mmap_flags);
+
+ if (allocsize % hugepagesize != 0)
+ allocsize += hugepagesize - (allocsize % hugepagesize);
+
+ ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
+ PG_MMAP_FLAGS | mmap_flags, -1, 0);
+ mmap_errno = errno;
+ if (huge_pages == HUGE_PAGES_TRY && ptr == MAP_FAILED)
+ elog(DEBUG1, "mmap(%zu) with MAP_HUGETLB failed, huge pages disabled: %m",
+ allocsize);
+ }
+#endif
+
+ if (ptr == MAP_FAILED && huge_pages != HUGE_PAGES_ON)
+ {
+ /*
+ * Use the original size, not the rounded-up value, when falling back
+ * to non-huge pages.
+ */
+ allocsize = *size;
+ ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
+ PG_MMAP_FLAGS, -1, 0);
+ mmap_errno = errno;
+ }
+
+ if (ptr == MAP_FAILED)
+ {
+ errno = mmap_errno;
+ ereport(FATAL,
+ (errmsg("could not map anonymous shared memory: %m"),
+ (mmap_errno == ENOMEM) ?
+ errhint("This error usually means that PostgreSQL's request "
+ "for a shared memory segment exceeded available memory, "
+ "swap space, or huge pages. To reduce the request size "
+ "(currently %zu bytes), reduce PostgreSQL's shared "
+ "memory usage, perhaps by reducing shared_buffers or "
+ "max_connections.",
+ *size) : 0));
+ }
+
+ *size = allocsize;
+ return ptr;
+}
+
+/*
+ * AnonymousShmemDetach --- detach from an anonymous mmap'd block
+ * (called as an on_shmem_exit callback, hence funny argument list)
+ */
+static void
+AnonymousShmemDetach(int status, Datum arg)
+{
+ /* Release anonymous shared memory block, if any. */
+ if (AnonymousShmem != NULL)
+ {
+ if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
+ elog(LOG, "munmap(%p, %zu) failed: %m",
+ AnonymousShmem, AnonymousShmemSize);
+ AnonymousShmem = NULL;
+ }
+}
+
+#endif /* USE_ANONYMOUS_SHMEM */
/*
* PGSharedMemoryCreate
*
* Create a shared memory segment of the given size and initialize its
* standard header. Also, register an on_shmem_exit callback to release
- * the storage. For an exec'ed backend, it just attaches.
+ * the storage.
*
* Dead Postgres segments are recycled if found, but we do not fail upon
- * collision with non-Postgres shmem segments. The idea here is to detect and
+ * collision with non-Postgres shmem segments. The idea here is to detect and
* re-use keys that may have been assigned by a crashed postmaster or backend.
*
* makePrivate means to always create a new segment, rather than attach to
* or recycle any existing segment.
*
* The port number is passed for possible use as a key (for SysV, we use
- * it to generate the starting shmem key). In a standalone backend,
+ * it to generate the starting shmem key). In a standalone backend,
* zero will be passed.
*/
PGShmemHeader *
-PGSharedMemoryCreate(uint32 size, bool makePrivate, int port)
+PGSharedMemoryCreate(Size size, bool makePrivate, int port,
+ PGShmemHeader **shim)
{
IpcMemoryKey NextShmemSegID;
void *memAddress;
PGShmemHeader *hdr;
IpcMemoryId shmid;
+ struct stat statbuf;
+ Size sysvsize;
+
+ /* Complain if hugepages demanded but we can't possibly support them */
+#if !defined(USE_ANONYMOUS_SHMEM) || !defined(MAP_HUGETLB)
+ if (huge_pages == HUGE_PAGES_ON)
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("huge pages not supported on this platform")));
+#endif
/* Room for a header? */
Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
- /* Just attach and return the pointer */
- if (ExecBackend && UsedShmemSegAddr != NULL && !makePrivate)
- {
- if ((hdr = PGSharedMemoryAttach(UsedShmemSegID, &shmid)) == NULL)
- elog(FATAL, "could not attach to proper memory at fixed address: shmget(key=%d, addr=%p) failed: %m",
- (int) UsedShmemSegID, UsedShmemSegAddr);
- return hdr;
- }
+#ifdef USE_ANONYMOUS_SHMEM
+ AnonymousShmem = CreateAnonymousSegment(&size);
+ AnonymousShmemSize = size;
+
+ /* Register on-exit routine to unmap the anonymous segment */
+ on_shmem_exit(AnonymousShmemDetach, (Datum) 0);
+
+ /* Now we need only allocate a minimal-sized SysV shmem block. */
+ sysvsize = sizeof(PGShmemHeader);
+#else
+ sysvsize = size;
+#endif
+
+ /* Make sure PGSharedMemoryAttach doesn't fail without need */
+ UsedShmemSegAddr = NULL;
/* Loop till we find a free IPC key */
NextShmemSegID = port * 1000;
for (NextShmemSegID++;; NextShmemSegID++)
{
/* Try to create new segment */
- memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
+ memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
if (memAddress)
break; /* successful create and attach */
}
/*
- * 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. This probably shouldn't fail, but if it does, assume
- * the segment belongs to someone else after all, and continue
- * quietly.
+ * 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,
+ * 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, (struct shmid_ds *) NULL) < 0)
+ if (shmctl(shmid, IPC_RMID, NULL) < 0)
continue;
/*
* Now try again to create the segment.
*/
- memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
+ memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
if (memAddress)
break; /* successful create and attach */
/*
- * Can only get here if some other process managed to create the
- * same shmem key before we did. Let him have that one, loop
- * around to try next key.
+ * Can only get here if some other process managed to create the same
+ * shmem key before we did. Let him have that one, loop around to try
+ * next key.
*/
}
/*
- * OK, we created a new segment. Mark it as created by this process.
- * The order of assignments here is critical so that another Postgres
- * process can't see the header as valid but belonging to an invalid
- * PID!
+ * OK, we created a new segment. Mark it as created by this process. The
+ * order of assignments here is critical so that another Postgres process
+ * can't see the header as valid but belonging to an invalid PID!
*/
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)
+ ereport(FATAL,
+ (errcode_for_file_access(),
+ errmsg("could not stat data directory \"%s\": %m",
+ DataDir)));
+ hdr->device = statbuf.st_dev;
+ hdr->inode = statbuf.st_ino;
/*
* Initialize space allocation status for segment.
*/
hdr->totalsize = size;
hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
+ *shim = hdr;
+ /* Save info for possible future use */
+ UsedShmemSegAddr = memAddress;
+ UsedShmemSegID = (unsigned long) NextShmemSegID;
- if (ExecBackend && UsedShmemSegAddr == NULL && !makePrivate)
+ /*
+ * If AnonymousShmem is NULL here, then we're not using anonymous shared
+ * memory, and should return a pointer to the System V shared memory
+ * block. Otherwise, the System V shared memory block is only a shim, and
+ * we must return a pointer to the real block.
+ */
+#ifdef USE_ANONYMOUS_SHMEM
+ if (AnonymousShmem == NULL)
+ return hdr;
+ memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
+ return (PGShmemHeader *) AnonymousShmem;
+#else
+ return hdr;
+#endif
+}
+
+#ifdef EXEC_BACKEND
+
+/*
+ * PGSharedMemoryReAttach
+ *
+ * This is called during startup of a postmaster child process to re-attach to
+ * an already existing shared memory segment. This is needed only in the
+ * EXEC_BACKEND case; otherwise postmaster children inherit the shared memory
+ * segment attachment via fork().
+ *
+ * UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
+ * routine. The caller must have already restored them to the postmaster's
+ * values.
+ */
+void
+PGSharedMemoryReAttach(void)
+{
+ IpcMemoryId shmid;
+ void *hdr;
+ void *origUsedShmemSegAddr = UsedShmemSegAddr;
+
+ Assert(UsedShmemSegAddr != NULL);
+ Assert(IsUnderPostmaster);
+
+#ifdef __CYGWIN__
+ /* cygipc (currently) appears to not detach on exec. */
+ PGSharedMemoryDetach();
+ UsedShmemSegAddr = origUsedShmemSegAddr;
+#endif
+
+ elog(DEBUG3, "attaching to %p", UsedShmemSegAddr);
+ hdr = (void *) PGSharedMemoryAttach((IpcMemoryKey) UsedShmemSegID, &shmid);
+ if (hdr == NULL)
+ elog(FATAL, "could not reattach to shared memory (key=%d, addr=%p): %m",
+ (int) UsedShmemSegID, UsedShmemSegAddr);
+ 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 */
+}
+
+/*
+ * PGSharedMemoryNoReAttach
+ *
+ * This is called during startup of a postmaster child process when we choose
+ * *not* to re-attach to the existing shared memory segment. We must clean up
+ * to leave things in the appropriate state. This is not used in the non
+ * EXEC_BACKEND case, either.
+ *
+ * The child process startup logic might or might not call PGSharedMemoryDetach
+ * after this; make sure that it will be a no-op if called.
+ *
+ * UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
+ * routine. The caller must have already restored them to the postmaster's
+ * values.
+ */
+void
+PGSharedMemoryNoReAttach(void)
+{
+ Assert(UsedShmemSegAddr != NULL);
+ Assert(IsUnderPostmaster);
+
+#ifdef __CYGWIN__
+ /* cygipc (currently) appears to not detach on exec. */
+ PGSharedMemoryDetach();
+#endif
+
+ /* For cleanliness, reset UsedShmemSegAddr to show we're not attached. */
+ UsedShmemSegAddr = NULL;
+ /* And the same for UsedShmemSegID. */
+ UsedShmemSegID = 0;
+}
+
+#endif /* EXEC_BACKEND */
+
+/*
+ * PGSharedMemoryDetach
+ *
+ * Detach from the shared memory segment, if still attached. This is not
+ * intended to be called explicitly by the process that originally created the
+ * segment (it will have on_shmem_exit callback(s) registered to do that).
+ * Rather, this is for subprocesses that have inherited an attachment and want
+ * to get rid of it.
+ *
+ * UsedShmemSegID and UsedShmemSegAddr are implicit parameters to this
+ * routine, also AnonymousShmem and AnonymousShmemSize.
+ */
+void
+PGSharedMemoryDetach(void)
+{
+ if (UsedShmemSegAddr != NULL)
{
- UsedShmemSegAddr = memAddress;
- UsedShmemSegID = NextShmemSegID;
+ if ((shmdt(UsedShmemSegAddr) < 0)
+#if defined(EXEC_BACKEND) && defined(__CYGWIN__)
+ /* Work-around for cygipc exec bug */
+ && shmdt(NULL) < 0
+#endif
+ )
+ elog(LOG, "shmdt(%p) failed: %m", UsedShmemSegAddr);
+ UsedShmemSegAddr = NULL;
}
- return hdr;
+#ifdef USE_ANONYMOUS_SHMEM
+ if (AnonymousShmem != NULL)
+ {
+ if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
+ elog(LOG, "munmap(%p, %zu) failed: %m",
+ AnonymousShmem, AnonymousShmemSize);
+ AnonymousShmem = NULL;
+ }
+#endif
}
if ((*shmid = shmget(key, sizeof(PGShmemHeader), 0)) < 0)
return NULL;
- hdr = (PGShmemHeader *) shmat(*shmid,
- UsedShmemSegAddr,
-#if defined(solaris) && defined(__sparc__)
- /* use intimate shared memory on Solaris */
- SHM_SHARE_MMU
-#else
- 0
-#endif
- );
+ hdr = (PGShmemHeader *) shmat(*shmid, UsedShmemSegAddr, PG_SHMAT_FLAGS);
if (hdr == (PGShmemHeader *) -1)
return NULL; /* failed: must be some other app's */
if (hdr->magic != PGShmemMagic)
{
- shmdt(hdr);
+ shmdt((void *) hdr);
return NULL; /* segment belongs to a non-Postgres app */
}
projects / postgresql / blobdiff