/* Determine directory for shm/sem files.  Linux version.

   Copyright (C) 2000-2018 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)

/* 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