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glibc/sysdeps/unix/sysv/linux/shm-directory.c
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/* Determine directory for shm/sem files. Linux version. | |
Copyright (C) 2000-2016 Free Software Foundation, Inc. | |
This file is part of the GNU C Library. | |
The GNU C Library is free software; you can redistribute it and/or | |
modify it under the terms of the GNU Lesser General Public | |
License as published by the Free Software Foundation; either | |
version 2.1 of the License, or (at your option) any later version. | |
The GNU C Library is distributed in the hope that it will be useful, | |
but WITHOUT ANY WARRANTY; without even the implied warranty of | |
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
Lesser General Public License for more details. | |
You should have received a copy of the GNU Lesser General Public | |
License along with the GNU C Library; if not, see | |
<http://www.gnu.org/licenses/>. */ | |
#include "shm-directory.h" | |
#include <errno.h> | |
#include <mntent.h> | |
#include <paths.h> | |
#include <stdio.h> | |
#include <string.h> | |
#include <sys/statfs.h> | |
#include <libc-lock.h> | |
#include "linux_fsinfo.h" | |
/* Mount point of the shared memory filesystem. */ | |
static struct | |
{ | |
char *dir; | |
size_t dirlen; | |
} mountpoint; | |
/* This is the default directory. */ | |
static const char defaultdir[] = "/dev/shm/"; | |
/* Protect the `mountpoint' variable above. */ | |
__libc_once_define (static, once); | |
/* Determine where the shmfs is mounted (if at all). */ | |
static void | |
where_is_shmfs (void) | |
{ | |
char buf[512]; | |
struct statfs f; | |
struct mntent resmem; | |
struct mntent *mp; | |
FILE *fp; | |
/* The canonical place is /dev/shm. This is at least what the | |
documentation tells everybody to do. */ | |
if (__statfs (defaultdir, &f) == 0 && (f.f_type == SHMFS_SUPER_MAGIC | |
|| f.f_type == RAMFS_MAGIC)) | |
{ | |
/* It is in the normal place. */ | |
mountpoint.dir = (char *) defaultdir; | |
mountpoint.dirlen = sizeof (defaultdir) - 1; | |
return; | |
} | |
/* OK, do it the hard way. Look through the /proc/mounts file and if | |
this does not exist through /etc/fstab to find the mount point. */ | |
fp = __setmntent ("/proc/mounts", "r"); | |
if (__glibc_unlikely (fp == NULL)) | |
{ | |
fp = __setmntent (_PATH_MNTTAB, "r"); | |
if (__glibc_unlikely (fp == NULL)) | |
/* There is nothing we can do. Blind guesses are not helpful. */ | |
return; | |
} | |
/* Now read the entries. */ | |
while ((mp = __getmntent_r (fp, &resmem, buf, sizeof buf)) != NULL) | |
/* The original name is "shm" but this got changed in early Linux | |
2.4.x to "tmpfs". */ | |
if (strcmp (mp->mnt_type, "tmpfs") == 0 | |
|| strcmp (mp->mnt_type, "shm") == 0) | |
{ | |
/* Found it. There might be more than one place where the | |
filesystem is mounted but one is enough for us. */ | |
size_t namelen; | |
/* First make sure this really is the correct entry. At least | |
some versions of the kernel give wrong information because | |
of the implicit mount of the shmfs for SysV IPC. */ | |
if (__statfs (mp->mnt_dir, &f) != 0 || (f.f_type != SHMFS_SUPER_MAGIC | |
&& f.f_type != RAMFS_MAGIC)) | |
continue; | |
namelen = strlen (mp->mnt_dir); | |
if (namelen == 0) | |
/* Hum, maybe some crippled entry. Keep on searching. */ | |
continue; | |
mountpoint.dir = (char *) malloc (namelen + 2); | |
if (mountpoint.dir != NULL) | |
{ | |
char *cp = __mempcpy (mountpoint.dir, mp->mnt_dir, namelen); | |
if (cp[-1] != '/') | |
*cp++ = '/'; | |
*cp = '\0'; | |
mountpoint.dirlen = cp - mountpoint.dir; | |
} | |
break; | |
} | |
/* Close the stream. */ | |
__endmntent (fp); | |
} | |
const char * | |
__shm_directory (size_t *len) | |
{ | |
/* Determine where the shmfs is mounted. */ | |
__libc_once (once, where_is_shmfs); | |
/* If we don't know the mount points there is nothing we can do. Ever. */ | |
if (__glibc_unlikely (mountpoint.dir == NULL)) | |
{ | |
__set_errno (ENOSYS); | |
return NULL; | |
} | |
*len = mountpoint.dirlen; | |
return mountpoint.dir; | |
} | |
#if IS_IN (libpthread) | |
hidden_def (__shm_directory) | |
#endif | |
/* Make sure the table is freed if we want to free everything before | |
exiting. */ | |
libc_freeres_fn (freeit) | |
{ | |
if (mountpoint.dir != defaultdir) | |
free (mountpoint.dir); | |
} |