Btrfs: Add new ioctl to add devices

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 8928649..7153dfa 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -388,6 +388,7 @@
 			goto error;
 		}
 
+		btrfs_sb(s)->fs_info->bdev_holder = fs_type;
 		s->s_flags |= MS_ACTIVE;
 	}