/*
* InternalIpcMemoryCreate(memKey, size)
*
* Attempt to create a new shared memory segment with the specified key.
* Will fail (return NULL) if such a segment already exists. If successful,
* attach the segment to the current process and return its attached address.
* On success, callbacks are registered with on_shmem_exit to detach and
* delete the segment when on_shmem_exit is called.
*
* If we fail with a failure code other than collision-with-existing-segment,
* print out an error and abort. Other types of errors are not recoverable.
*/
static void *
InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
{
IpcMemoryId shmid;
void *memAddress;
shmid = shmget(memKey, size, IPC_CREAT | IPC_EXCL | IPCProtection);
if (shmid < 0)
{
/*
* 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
#ifdef EIDRM
|| errno == EIDRM
#endif
)
return NULL;
/*
* Else complain and abort
*/
ereport(FATAL,
(errmsg("could not create shared memory segment: %m"),
errdetail("Failed system call was shmget(key=%lu, size=%lu, 0%o).",
(unsigned long) memKey, (unsigned long) size,
IPC_CREAT | IPC_EXCL | IPCProtection),
(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 %lu 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"
"The PostgreSQL documentation contains more information about shared "
"memory configuration.",
(unsigned long) size, NBuffers, MaxBackends) : 0,
(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 %lu bytes), reduce "
"PostgreSQL's shared_buffers parameter (currently %d) and/or "
"its max_connections parameter (currently %d).\n"
"The PostgreSQL documentation contains more information about shared "
"memory configuration.",
(unsigned long) size, NBuffers, MaxBackends) : 0,
(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 %lu bytes), "
"by reducing its shared_buffers parameter (currently %d) and/or "
"its max_connections parameter (currently %d).\n"
"The PostgreSQL documentation contains more information about shared "
"memory configuration.",
(unsigned long) size, NBuffers, MaxBackends) : 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 */
memAddress = shmat(shmid, NULL, PG_SHMAT_FLAGS);
if (memAddress == (void *) -1)
elog(FATAL, "shmat(id=%d) failed: %m", shmid);
/* 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);
return memAddress;
}
/*
* InternalIpcMemoryCreate(memKey, size)
*
* Attempt to create a new shared memory segment with the specified key.
* Will fail (return NULL) if such a segment already exists. If successful,
* attach the segment to the current process and return its attached address.
* On success, callbacks are registered with on_shmem_exit to detach and
* delete the segment when on_shmem_exit is called.
*
* If we fail with a failure code other than collision-with-existing-segment,
* print out an error and abort. Other types of errors are not recoverable.
*/
static void *
InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
{
IpcMemoryId shmid;
void *memAddress;
shmid = shmget(memKey, size, IPC_CREAT | IPC_EXCL | IPCProtection);
if (shmid < 0)
{
/*
* 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
#ifdef EIDRM
|| errno == EIDRM
#endif
)
return NULL;
/*
* 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 (errno == EINVAL)
{
int save_errno = errno;
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);
}
errno = save_errno;
}
/*
* 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.
*/
ereport(FATAL,
(errmsg("could not create shared memory segment: %m"),
errdetail("Failed system call was shmget(key=%lu, size=%lu, 0%o).",
(unsigned long) memKey, (unsigned long) size,
IPC_CREAT | IPC_EXCL | IPCProtection),
(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 %lu 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"
"The PostgreSQL documentation contains more information about shared "
"memory configuration.",
(unsigned long) size, NBuffers, MaxBackends) : 0,
(errno == ENOMEM) ?
errhint("This error usually means that PostgreSQL's request for a shared "
"memory segment exceeded available memory or swap space, "
"or exceeded your kernel's SHMALL parameter. You can either "
"reduce the request size or reconfigure the kernel with larger SHMALL. "
"To reduce the request size (currently %lu bytes), reduce "
"PostgreSQL's shared_buffers parameter (currently %d) and/or "
"its max_connections parameter (currently %d).\n"
"The PostgreSQL documentation contains more information about shared "
"memory configuration.",
(unsigned long) size, NBuffers, MaxBackends) : 0,
(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 %lu bytes), "
"by reducing its shared_buffers parameter (currently %d) and/or "
"its max_connections parameter (currently %d).\n"
"The PostgreSQL documentation contains more information about shared "
"memory configuration.",
(unsigned long) size, NBuffers, MaxBackends) : 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 */
memAddress = shmat(shmid, NULL, PG_SHMAT_FLAGS);
if (memAddress == (void *) -1)
elog(FATAL, "shmat(id=%d) failed: %m", shmid);
/* 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);
return memAddress;
}