src/find-mount-point.c

   1 /* find-mount-point.c -- find the root mount point for a file.
   2    Copyright (C) 2010-2016 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  16
  17 #include <config.h>
  18 #include <sys/types.h>
  19
  20 #include "system.h"
  21 #include "error.h"
  22 #include "save-cwd.h"
  23 #include "xgetcwd.h"
  24 #include "find-mount-point.h"
  25
  26 /* Return the root mountpoint of the file system on which FILE exists, in
  27    malloced storage.  FILE_STAT should be the result of stating FILE.
  28    Give a diagnostic and return NULL if unable to determine the mount point.
  29    Exit if unable to restore current working directory.  */
  30 extern char *
  31 find_mount_point (char const *file, struct stat const *file_stat)
  32 {
  33   struct saved_cwd cwd;
  34   struct stat last_stat;
  35   char *mp = NULL;              /* The malloc'd mount point.  */
  36
  37   if (save_cwd (&cwd) != 0)
  38     {
  39       error (0, errno, _("cannot get current directory"));
  40       return NULL;
  41     }
  42
  43   if (S_ISDIR (file_stat->st_mode))
  44     /* FILE is a directory, so just chdir there directly.  */
  45     {
  46       last_stat = *file_stat;
  47       if (chdir (file) < 0)
  48         {
  49           error (0, errno, _("cannot change to directory %s"), quoteaf (file));
  50           return NULL;
  51         }
  52     }
  53   else
  54     /* FILE is some other kind of file; use its directory.  */
  55     {
  56       char *xdir = dir_name (file);
  57       char *dir;
  58       ASSIGN_STRDUPA (dir, xdir);
  59       free (xdir);
  60
  61       if (chdir (dir) < 0)
  62         {
  63           error (0, errno, _("cannot change to directory %s"), quoteaf (dir));
  64           return NULL;
  65         }
  66
  67       if (stat (".", &last_stat) < 0)
  68         {
  69           error (0, errno, _("cannot stat current directory (now %s)"),
  70                  quoteaf (dir));
  71           goto done;
  72         }
  73     }
  74
  75   /* Now walk up FILE's parents until we find another file system or /,
  76      chdiring as we go.  LAST_STAT holds stat information for the last place
  77      we visited.  */
  78   while (true)
  79     {
  80       struct stat st;
  81       if (stat ("..", &st) < 0)
  82         {
  83           error (0, errno, _("cannot stat %s"), quoteaf (".."));
  84           goto done;
  85         }
  86       if (st.st_dev != last_stat.st_dev || st.st_ino == last_stat.st_ino)
  87         /* cwd is the mount point.  */
  88         break;
  89       if (chdir ("..") < 0)
  90         {
  91           error (0, errno, _("cannot change to directory %s"), quoteaf (".."));
  92           goto done;
  93         }
  94       last_stat = st;
  95     }
  96
  97   /* Finally reached a mount point, see what it's called.  */
  98   mp = xgetcwd ();
  99
 100 done:
 101   /* Restore the original cwd.  */
 102   {
 103     int save_errno = errno;
 104     if (restore_cwd (&cwd) != 0)
 105       error (EXIT_FAILURE, errno,
 106              _("failed to return to initial working directory"));
 107     free_cwd (&cwd);
 108     errno = save_errno;
 109   }
 110
 111   return mp;
 112 }