Btrfs: add all ioctl checks before user change for quota operations

Since all the quota configurations are loaded in memory, and we can
have ioctl checks before operating in the disk. It is safe to do such
things because qgroup_ioctl_lock is held outside.

Without these extra checks firstly, it should be ok to do user change
for quota operations. For example:

if we want to add an existed qgroup, we will do:
	->add_qgroup_item()
		->add_qgroup_rb()

add_qgroup_item() will return -EEXIST to us, however, qgroups are all
in memory, why not check them in memory firstly.
Signed-off-by: Wang Shilong <wangsl-fnst@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/qgroup.c

@@ -956,6 +956,7 @@ int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans,
 	struct btrfs_root *quota_root;
 	struct btrfs_qgroup *parent;
 	struct btrfs_qgroup *member;
+	struct btrfs_qgroup_list *list;
 	int ret = 0;
 
 	mutex_lock(&fs_info->qgroup_ioctl_lock);
@@ -971,6 +972,14 @@ int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans,
 		goto out;
 	}
 
+	/* check if such qgroup relation exist firstly */
+	list_for_each_entry(list, &member->groups, next_group) {
+		if (list->group == parent) {
+			ret = -EEXIST;
+			goto out;
+		}
+	}
+
 	ret = add_qgroup_relation_item(trans, quota_root, src, dst);
 	if (ret)
 		goto out;
@@ -993,6 +1002,9 @@ int btrfs_del_qgroup_relation(struct btrfs_trans_handle *trans,
 			      struct btrfs_fs_info *fs_info, u64 src, u64 dst)
 {
 	struct btrfs_root *quota_root;
+	struct btrfs_qgroup *parent;
+	struct btrfs_qgroup *member;
+	struct btrfs_qgroup_list *list;
 	int ret = 0;
 	int err;
 
@@ -1003,6 +1015,21 @@ int btrfs_del_qgroup_relation(struct btrfs_trans_handle *trans,
 		goto out;
 	}
 
+	member = find_qgroup_rb(fs_info, src);
+	parent = find_qgroup_rb(fs_info, dst);
+	if (!member || !parent) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* check if such qgroup relation exist firstly */
+	list_for_each_entry(list, &member->groups, next_group) {
+		if (list->group == parent)
+			goto exist;
+	}
+	ret = -ENOENT;
+	goto out;
+exist:
 	ret = del_qgroup_relation_item(trans, quota_root, src, dst);
 	err = del_qgroup_relation_item(trans, quota_root, dst, src);
 	if (err && !ret)
@@ -1010,7 +1037,6 @@ int btrfs_del_qgroup_relation(struct btrfs_trans_handle *trans,
 
 	spin_lock(&fs_info->qgroup_lock);
 	del_relation_rb(fs_info, src, dst);
-
 	spin_unlock(&fs_info->qgroup_lock);
 out:
 	mutex_unlock(&fs_info->qgroup_ioctl_lock);
@@ -1030,8 +1056,15 @@ int btrfs_create_qgroup(struct btrfs_trans_handle *trans,
 		ret = -EINVAL;
 		goto out;
 	}
+	qgroup = find_qgroup_rb(fs_info, qgroupid);
+	if (qgroup) {
+		ret = -EEXIST;
+		goto out;
+	}
 
 	ret = add_qgroup_item(trans, quota_root, qgroupid);
+	if (ret)
+		goto out;
 
 	spin_lock(&fs_info->qgroup_lock);
 	qgroup = add_qgroup_rb(fs_info, qgroupid);
@@ -1058,15 +1091,18 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans,
 		goto out;
 	}
 
-	/* check if there are no relations to this qgroup */
 	qgroup = find_qgroup_rb(fs_info, qgroupid);
-	if (qgroup) {
-		if (!list_empty(&qgroup->groups) || !list_empty(&qgroup->members)) {
+	if (!qgroup) {
+		ret = -ENOENT;
+		goto out;
+	} else {
+		/* check if there are no relations to this qgroup */
+		if (!list_empty(&qgroup->groups) ||
+		    !list_empty(&qgroup->members)) {
 			ret = -EBUSY;
 			goto out;
 		}
 	}
-
 	ret = del_qgroup_item(trans, quota_root, qgroupid);
 
 	spin_lock(&fs_info->qgroup_lock);