Btrfs: prevent qgroup destroy when there are still relations

Currently you can just destroy a qgroup even though it is in use by other qgroups
or has qgroups assigned to it. This patch prevents destruction of qgroups unless
they are completely unused. Otherwise destroy will return EBUSY.

Reported-by: Eric Hopper <hopper@omnifarious.org>
Signed-off-by: Arne Jansen <sensille@gmx.net>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 28f2b39f6a25d338565fa00b526c667d3542e0a0..a5c856234323241c22dde18e1ee072c8bed3ccaa 100644 (file)
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -963,17 +963,28 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans,
                        struct btrfs_fs_info *fs_info, u64 qgroupid)
 {
        struct btrfs_root *quota_root;
+       struct btrfs_qgroup *qgroup;
        int ret = 0;
 
        quota_root = fs_info->quota_root;
        if (!quota_root)
                return -EINVAL;
 
+       /* check if there are no relations to this qgroup */
+       spin_lock(&fs_info->qgroup_lock);
+       qgroup = find_qgroup_rb(fs_info, qgroupid);
+       if (qgroup) {
+               if (!list_empty(&qgroup->groups) || !list_empty(&qgroup->members)) {
+                       spin_unlock(&fs_info->qgroup_lock);
+                       return -EBUSY;
+               }
+       }
+       spin_unlock(&fs_info->qgroup_lock);
+
        ret = del_qgroup_item(trans, quota_root, qgroupid);
 
        spin_lock(&fs_info->qgroup_lock);
        del_qgroup_rb(quota_root->fs_info, qgroupid);
-
        spin_unlock(&fs_info->qgroup_lock);
 
        return ret;