Btrfs: make subvolid=0 mount the original default root

Since theres not a good way to make sure the user sees the original default root
tree id, and not to mention it's 5 so is way different than any other volume,
just make subvol=0 mount the original default root.  This makes it a bit easier
for users to handle in the long run.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index f878337cee6f..9771eb8694b6 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -325,9 +325,15 @@ static int btrfs_parse_early_options(const char *options, fmode_t flags,
                         break;
                 case Opt_subvolid:
                         intarg = 0;
-                        match_int(&args[0], &intarg);
-                        if (intarg)
-                                *subvol_objectid = intarg;
+                        error = match_int(&args[0], &intarg);
+                        if (!error) {
+                                /* we want the original fs_tree */
+                                if (!intarg)
+                                        *subvol_objectid =
+                                                BTRFS_FS_TREE_OBJECTID;
+                                else
+                                        *subvol_objectid = intarg;
+                        }
                         break;
                 case Opt_device:
                         error = btrfs_scan_one_device(match_strdup(&args[0]),