Btrfs: prevent loops in the directory tree when creating snapshots

For a directory tree:

/mnt/subvolA/subvolB

btrfsctl -s /mnt/subvolA/subvolB /mnt

Will create a directory loop with subvolA under subvolB.  This
commit uses the forward refs for each subvol and snapshot to error out
before creating the loop.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index ad2cbe63503c..70b3dbb4de12 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1801,6 +1801,9 @@ int btrfs_drop_subtree(struct btrfs_trans_handle *trans,
                         struct extent_buffer *node,
                         struct extent_buffer *parent);
 /* root-item.c */
+int btrfs_find_root_ref(struct btrfs_root *tree_root,
+                   struct btrfs_path *path,
+                   u64 root_id, u64 ref_id);
 int btrfs_add_root_ref(struct btrfs_trans_handle *trans,
                        struct btrfs_root *tree_root,
                        u64 root_id, u8 type, u64 ref_id,