Re: df: auto fs's don't show in normal df

[Jim Meyering]

Jim Meyering <address@hidden> wrote:
> Burton Windle <address@hidden> wrote:
>> Hello. I recently started using Ext3, and based on advice on the LKML,
>> changed my /etc/fstab to mount / as auto (incase I didn't have ext2
>> support). This was tested on 2.4.16, as well as 2.5.1-pre4.
>>
>> Now, my / partition doesn't show up in 'df' unless I do 'df -a' or
>> explictly as for /
>>
>> If I change my /etc/fstab to mount / as ext3 instead of auto, it works
>> again.
>
> Thanks for the report.
> However, this doesn't seem to be a problem with df.
>
> I suspect that you're not using new enough tools like mount
> or a new enough libc.  I've just created an ext3 partition,
> marked it as `auto' in /etc/fstab, and rebooted.  Now, df lists
> it and df -T shows its type as `ext3'.
>
> I'm using libc-2.2.4, mount-2.11m, e2fsck-1.25, and linux-2.4.16.

I now know that this problem arises only when / is of type ext3.
There's an ongoing discussion about how to fix this on the ext3-users
mailing list.  IMHO it's not a problem with df.  df ignores entries
of type `auto' because historically those have been duplicate entries
associated with certain types of automount systems.  If you're really set
on using df with the current set-up, you might want to try the following
truly kludgey patch that works only if you have procfs.  It's relative
to the latest test release:

  ftp://alpha.gnu.org/gnu/fetish/fileutils-4.1.3.tar.gz

I've barely tested that patch, so treat it with caution.
Since I expect mount (or something) to be fixed,  I don't plan to
check in this change -- it'd just bloat the code unnecessarily.

You can always change fstab to specify ext3 instead of auto if you
really care (and be careful to change it if you change to a kernel
that's not ext3-aware).

Index: mountlist.c
===================================================================
RCS file: /fetish/fileutils/lib/mountlist.c,v
retrieving revision 1.37
diff -u -p -u -p -r1.37 mountlist.c
--- mountlist.c 2001/11/17 13:50:40     1.37
+++ mountlist.c 2001/12/09 21:46:22
@@ -33,6 +33,7 @@ void free ();
 #else
 # include <strings.h>
 #endif
+#include "getstr.h"
 #include "xalloc.h"
 
 #ifndef strstr
@@ -145,6 +146,8 @@ extern int errno;
 #include "mountlist.h"
 #include "unlocked-io.h"
 
+#define STREQ(s1, s2) ((strcmp (s1, s2) == 0))
+
 #ifdef MOUNTED_GETMNTENT1      /* 4.3BSD, SunOS, HP-UX, Dynix, Irix.  */
 /* Return the value of the hexadecimal number represented by CP.
    No prefix (like '0x') or suffix (like 'h') is expected to be
@@ -171,6 +174,82 @@ xatoi (char *cp)
     }
   return val;
 }
+
+#define CLOSE_AND_RETURN(Fp, String) \
+  do { fclose (Fp); return String; } while (0)
+
+/* This is a kludge to determine the real type of the root file system
+   when it is recorded as `auto' in /etc/fstab and /etc/mtab (by mount).
+   As far as I know, this happens only for the root partition on Linux
+   systems when that partition is of type ext3 and when its type is
+   listed as `auto' in /etc/fstab.  Until mount is fixed, this should help.
+
+   Return in malloc'd storage the type of the root file system as recorded
+   in /proc/mounts.  Each line in that file is expected to look like this:
+
+   /dev/scsi/host0/bus0/target0/lun0/part4 / ext3 rw 0 0
+
+   where there is no leading white space, and there is a single space
+   between tokens.  This function reads /proc/mounts and returns the
+   type, `ext3' in the above example.  If no matching line is found,
+   or if the file can't be opened, or if getstr can't allocate space,
+   return NULL.  */
+static char *
+resolve_root_mount_type (char const *proc_mount_file)
+{
+  FILE *fp = fopen (proc_mount_file, "r");
+  if (!fp)
+    return NULL;
+
+  while (1)
+    {
+      /* skip first sequence of non-spaces */
+      while (1)
+       {
+         int c = fgetc (fp);
+         if (c == ' ')
+           break;
+         if (c == EOF)
+           CLOSE_AND_RETURN (fp, NULL);
+       }
+
+      /* The next sequence of non-spaces is the mount point.
+        Skip this line if it's not `/'.  */
+      int ch = fgetc (fp);
+      if (ch == '/' && fgetc (fp) == ' ')
+       {
+         /* This sequence of non-spaces is the file system type.  */
+         char *fs_name = NULL;
+         size_t fs_name_alloc;
+         int fs_name_len = getstr (&fs_name, &fs_name_alloc, fp, ' ', 0, 0);
+         fclose (fp);
+         if (fs_name_len <= 1)
+           return NULL;
+         if (fs_name[fs_name_len - 1] != ' ')
+           {
+             free (fs_name);
+             return NULL;
+           }
+         fs_name[--fs_name_len] = '\0';
+
+         return fs_name;
+       }
+
+      if (ch == EOF)
+       CLOSE_AND_RETURN (fp, NULL);
+
+      /* read up to and including the next newline */
+      while (1)
+       {
+         int c = fgetc (fp);
+         if (c == '\n')
+           break;
+         if (c == EOF)
+           CLOSE_AND_RETURN (fp, NULL);
+       }
+    }
+}
+
 #endif /* MOUNTED_GETMNTENT1.  */
 
 #if MOUNTED_GETMNTINFO
@@ -352,10 +431,14 @@ read_filesystem_list (int need_fs_type)
 
     while ((mnt = getmntent (fp)))
       {
+       char *t;
        me = (struct mount_entry *) xmalloc (sizeof (struct mount_entry));
        me->me_devname = xstrdup (mnt->mnt_fsname);
        me->me_mountdir = xstrdup (mnt->mnt_dir);
-       me->me_type = xstrdup (mnt->mnt_type);
+       me->me_type = ((STREQ (mnt->mnt_type, "auto")
+                       && STREQ (mnt->mnt_dir, "/")
+                       && (t = resolve_root_mount_type ("/proc/mounts")))
+                      ? t : xstrdup (mnt->mnt_type));
        me->me_dummy = ME_DUMMY (me->me_devname, me->me_type);
        me->me_remote = ME_REMOTE (me->me_devname, me->me_type);
        devopt = strstr (mnt->mnt_opts, "dev=");