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/* Determine directory for shm/sem files. Linux version.
Copyright (C) 2000-2021 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
<https://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)
/* Make sure the table is freed if we want to free everything before
exiting. */
void
__shm_directory_freeres (void)
{
if (mountpoint.dir != defaultdir)
free (mountpoint.dir);
}
#endif
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