Btrfs: fix wrong reserved space when deleting a snapshot/subvolume

When deleting a snapshot/subvolume, we need remove root ref/backref,
dir entries and update the dir inode, so we must reserve free space
for those operations.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/ioctl.c

@@ -2064,6 +2064,8 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 	struct btrfs_root *dest = NULL;
 	struct btrfs_ioctl_vol_args *vol_args;
 	struct btrfs_trans_handle *trans;
+	struct btrfs_block_rsv block_rsv;
+	u64 qgroup_reserved;
 	int namelen;
 	int ret;
 	int err = 0;
@@ -2153,12 +2155,23 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 	if (err)
 		goto out_up_write;
 
+	btrfs_init_block_rsv(&block_rsv, BTRFS_BLOCK_RSV_TEMP);
+	/*
+	 * One for dir inode, two for dir entries, two for root
+	 * ref/backref.
+	 */
+	err = btrfs_subvolume_reserve_metadata(root, &block_rsv,
+					       5, &qgroup_reserved);
+	if (err)
+		goto out_up_write;
+
 	trans = btrfs_start_transaction(root, 0);
 	if (IS_ERR(trans)) {
 		err = PTR_ERR(trans);
-		goto out_up_write;
+		goto out_release;
 	}
-	trans->block_rsv = &root->fs_info->global_block_rsv;
+	trans->block_rsv = &block_rsv;
+	trans->bytes_reserved = block_rsv.size;
 
 	ret = btrfs_unlink_subvol(trans, root, dir,
 				dest->root_key.objectid,
@@ -2188,10 +2201,14 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 		}
 	}
 out_end_trans:
+	trans->block_rsv = NULL;
+	trans->bytes_reserved = 0;
 	ret = btrfs_end_transaction(trans, root);
 	if (ret && !err)
 		err = ret;
 	inode->i_flags |= S_DEAD;
+out_release:
+	btrfs_subvolume_release_metadata(root, &block_rsv, qgroup_reserved);
 out_up_write:
 	up_write(&root->fs_info->subvol_sem);
 out_unlock: