From: Pádraig Brady <[email protected]>

Date: Mon, 18 Aug 2014 16:59:26 +0000 (+0100)

Subject: df: improve mount point selection with inaccurate mount list

X-Git-Url: http://git.savannah.gnu.org/gitweb/?p=coreutils.git;a=commitdiff_plain;h=ed1a495b

df: improve mount point selection with inaccurate mount list

v8.23 has a test failure on Fedora rawhide build servers

in tests/df/skip-duplicate.sh.  This was due to no '/'

entry being output by df.  That was due to an inaccurate

/proc/mounts on the build environment as stat(/mnt/point)

identified all these /proc/mounts entries as having the

same device id:

  /                    rootfs

  /                    /dev/md1

  /dev                 devtmpfs

  /run                 tmpfs

  /boot                /dev/md0

  /proc/filesystems    /dev/md1

Since the device name on the right changes for a given id,

that causes the entries to be continually replaced, thus

resulting in no '/' entry.  I'm guessing this is due to

the mock environment bind mounting unneeded or sensitive

items to a dummy file on the host / (/dev/md1) though

have not looked into those details.

So rather than relying on an accurate /proc/mounts,

the attached patch takes a more conservative replacement

approach and only swaps a new device entry when the

mount point matches.  That should handle all practical

cases while also avoiding this situation.

* src/df.c (filter_mount_list): Only replace entries with

different device names when the mount point also matches.

---

diff --git a/src/df.c b/src/df.c

index 3ef5d33..e907b94 100644

--- src/df.c

+++ src/df.c

@@ -640,13 +640,18 @@ filter_mount_list (bool devices_only)

           if (devlist)

             {

-              /* ...let the shorter mountdir win.  */

+                  /* let "real" devices with '/' in the name win.  */

               if ((strchr (me->me_devname, '/')

                    && ! strchr (devlist->me->me_devname, '/'))

+                  /* let a shorter mountdir win.  */

                   || (strlen (devlist->me->me_mountdir)

                       > strlen (me->me_mountdir))

-                  /* or one overmounted on a different device.  */

-                  || ! STREQ (devlist->me->me_devname, me->me_devname))

+                  /* let an entry overmounted on a different device win...  */

+                  || (! STREQ (devlist->me->me_devname, me->me_devname)

+                      /* ... but only when matching an exsiting mount point, to

+                      avoid problematic replacement when given inaccurate mount

+                      lists, seen with some chroot environments for example.  */

+                      && STREQ (me->me_mountdir, devlist->me->me_mountdir)))

                 {

                   /* Discard mount entry for existing device.  */

                   discard_me = devlist->me;