btrfs: Don't allow subvolid >= (1 << BTRFS_QGROUP_LEVEL_SHIFT) to be created

Btrfs will create qgroup on subvolume creation if quota is enabled, but
qgroup uses the high bits(currently 16 bits) as level, to build the
inheritance.

However it is fully possible a subvolume can be created with a
subvolumeid larger than 1 << BTRFS_QGROUP_LEVEL_SHIFT, so it will be
considered as level 1 and can't be assigned to other qgroup in level 1.

This patch will prevent such things so qgroup inheritance will not be
screwed up.
The downside is very clear, btrfs subvolume number limit will decrease
from (u64 max - 256(fisrt free objectid) - 256(last free objectid)) to
(u48 max -256(first free objectid)).
But we still have near u48(that's 15 digits in dec), so that should not
be a huge problem.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 8b851ac7c3fabac2057d8bf9022c892096b0bb79..6f364e1d8d3d1e9c08e246dbc1df443be49c33fd 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -4219,7 +4219,8 @@ int btree_readahead_hook(struct btrfs_root *root, struct extent_buffer *eb,
 static inline int is_fstree(u64 rootid)
 {
        if (rootid == BTRFS_FS_TREE_OBJECTID ||
-           (s64)rootid >= (s64)BTRFS_FIRST_FREE_OBJECTID)
+           ((s64)rootid >= (s64)BTRFS_FIRST_FREE_OBJECTID &&
+             !btrfs_qgroup_level(rootid)))
                return 1;
        return 0;
 }

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 2e66d8e76f322268577c97b2f5c686518f7256b4..e38b645c50151f1f0c376743cf00da0a01098525 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -456,6 +456,13 @@ static noinline int create_subvol(struct inode *dir,
        if (ret)
                return ret;
 
+       /*
+        * Don't create subvolume whose level is not zero. Or qgroup will be
+        * screwed up since it assume subvolme qgroup's level to be 0.
+        */
+       if (btrfs_qgroup_level(objectid))
+               return -ENOSPC;
+
        btrfs_init_block_rsv(&block_rsv, BTRFS_BLOCK_RSV_TEMP);
        /*
         * The same as the snapshot creation, please see the comment