btrfs: don't show full path of bind mounts in subvol=

commit 3ef3959b29c4a5bd65526ab310a1a18ae533172a upstream.

Chris Murphy reported a problem where rpm ostree will bind mount a bunch
of things for whatever voodoo it's doing.  But when it does this
/proc/mounts shows something like

  /dev/sda /mnt/test btrfs rw,relatime,subvolid=256,subvol=/foo 0 0
  /dev/sda /mnt/test/baz btrfs rw,relatime,subvolid=256,subvol=/foo/bar 0 0

Despite subvolid=256 being subvol=/foo.  This is because we're just
spitting out the dentry of the mount point, which in the case of bind
mounts is the source path for the mountpoint.  Instead we should spit
out the path to the actual subvol.  Fix this by looking up the name for
the subvolid we have mounted.  With this fix the same test looks like
this

  /dev/sda /mnt/test btrfs rw,relatime,subvolid=256,subvol=/foo 0 0
  /dev/sda /mnt/test/baz btrfs rw,relatime,subvolid=256,subvol=/foo 0 0

Reported-by: Chris Murphy <chris@colorremedies.com>
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 712b93c84d90523425824f54bcf9ef0e4ead4098..4390250a7b55596a17ac1259081985aeb4c4ad0c 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1310,6 +1310,7 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
 {
        struct btrfs_fs_info *info = btrfs_sb(dentry->d_sb);
        const char *compress_type;
+       const char *subvol_name;
 
        if (btrfs_test_opt(info, DEGRADED))
                seq_puts(seq, ",degraded");
@@ -1396,8 +1397,13 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
                seq_puts(seq, ",ref_verify");
        seq_printf(seq, ",subvolid=%llu",
                  BTRFS_I(d_inode(dentry))->root->root_key.objectid);
-       seq_puts(seq, ",subvol=");
-       seq_dentry(seq, dentry, " \t\n\\");
+       subvol_name = btrfs_get_subvol_name_from_objectid(info,
+                       BTRFS_I(d_inode(dentry))->root->root_key.objectid);
+       if (!IS_ERR(subvol_name)) {
+               seq_puts(seq, ",subvol=");
+               seq_escape(seq, subvol_name, " \t\n\\");
+               kfree(subvol_name);
+       }
        return 0;
 }