Re: df displays wrong figures for network mounts

[Paul Eggert]

Bruno Haible <address@hidden> writes:

> The mistake that 'df' did is: When it climbed up directories until it
> found a mount point
>   /smb/ibook/data/temp
>   /smb/ibook/data
>   /smb/ibook
> it only considered mount points on the current host (linuix), but ignored
> mount points and symbolic links on the machine that exports the filesystem.

Thanks for reporting this.  I don't see an easy way around this
problem in general, since df assumes the POSIX semantics where every
file in the same file system (i.e., every file with the same device
number) has the same file system statistics.

That being said, it's easy to cajole "df" to use statfs (or statvfs or
whatever) on the file that the user originally specified, instead of
the root of the locally mounted file system.  This is better for other
reasons, too, as it generates better diagnostics.  I installed this
patch into CVS coreutils.  I don't think it'll fix the problem in
general, but does it fix your particular problem?

2005-08-16  Paul Eggert  <address@hidden>

        * src/df.c (show_dev): New arg STAT_FILE.  All uses changed.
        This sometimes gives better results on networked file systems
        that do not respect POSIX semantics.  Problem reported by
        Bruno Haible.

Index: df.c
===================================================================
RCS file: /fetish/cu/src/df.c,v
retrieving revision 1.167
retrieving revision 1.168
diff -p -u -r1.167 -r1.168
--- df.c        2 Jun 2005 05:12:59 -0000       1.167
+++ df.c        16 Aug 2005 20:33:40 -0000      1.168
@@ -253,17 +253,22 @@ df_readable (bool negative, uintmax_t n,
 /* Display a space listing for the disk device with absolute file name DISK.
    If MOUNT_POINT is non-NULL, it is the name of the root of the
    file system on DISK.
+   If STAT_FILE is non-null, it is the name of a file within the file
+   system that the user originally asked for; this provides better
+   diagnostics, and sometimes it provides better results on networked
+   file systems that give different free-space results depending on
+   where in the file system you probe.
    If FSTYPE is non-NULL, it is the type of the file system on DISK.
    If MOUNT_POINT is non-NULL, then DISK may be NULL -- certain systems may
    not be able to produce statistics in this case.
    ME_DUMMY and ME_REMOTE are the mount entry flags.  */
 
 static void
-show_dev (const char *disk, const char *mount_point, const char *fstype,
+show_dev (char const *disk, char const *mount_point,
+         char const *stat_file, char const *fstype,
          bool me_dummy, bool me_remote)
 {
   struct fs_usage fsu;
-  const char *stat_file;
   char buf[3][LONGEST_HUMAN_READABLE + 2];
   int width;
   int use_width;
@@ -290,7 +295,8 @@ show_dev (const char *disk, const char *
      program reports on the file system that the special file is on.
      It would be better to report on the unmounted file system,
      but statfs doesn't do that on most systems.  */
-  stat_file = mount_point ? mount_point : disk;
+  if (!stat_file)
+    stat_file = mount_point ? mount_point : disk;
 
   if (get_fs_usage (stat_file, disk, &fsu))
     {
@@ -530,7 +536,7 @@ show_disk (char const *disk)
 
   if (best_match)
     {
-      show_dev (best_match->me_devname, best_match->me_mountdir,
+      show_dev (best_match->me_devname, best_match->me_mountdir, NULL,
                best_match->me_type, best_match->me_dummy,
                best_match->me_remote);
       return true;
@@ -628,7 +634,7 @@ show_point (const char *point, const str
       }
 
   if (best_match)
-    show_dev (best_match->me_devname, best_match->me_mountdir,
+    show_dev (best_match->me_devname, best_match->me_mountdir, point,
              best_match->me_type, best_match->me_dummy, best_match->me_remote);
   else
     {
@@ -640,7 +646,7 @@ show_point (const char *point, const str
       char *mp = find_mount_point (point, statp);
       if (mp)
        {
-         show_dev (NULL, mp, NULL, false, false);
+         show_dev (NULL, mp, NULL, NULL, false, false);
          free (mp);
        }
     }
@@ -668,7 +674,7 @@ show_all_entries (void)
   struct mount_entry *me;
 
   for (me = mount_list; me; me = me->me_next)
-    show_dev (me->me_devname, me->me_mountdir, me->me_type,
+    show_dev (me->me_devname, me->me_mountdir, NULL, me->me_type,
              me->me_dummy, me->me_remote);
 }