int btrfs_uuid_scan_kthread(void *data)
{
	struct btrfs_fs_info *fs_info = data;
	struct btrfs_root *root = fs_info->tree_root;
	struct btrfs_key key;
	struct btrfs_path *path = NULL;
	int ret = 0;
	struct extent_buffer *eb;
	int slot;
	struct btrfs_root_item root_item;
	u32 item_size;
	struct btrfs_trans_handle *trans = NULL;
	bool closing = false;

	path = btrfs_alloc_path();
	if (!path) {
		ret = -ENOMEM;
		goto out;
	}

	key.objectid = 0;
	key.type = BTRFS_ROOT_ITEM_KEY;
	key.offset = 0;

	while (1) {
		if (btrfs_fs_closing(fs_info)) {
			closing = true;
			break;
		}
		ret = btrfs_search_forward(root, &key, path,
				BTRFS_OLDEST_GENERATION);
		if (ret) {
			if (ret > 0)
				ret = 0;
			break;
		}

		if (key.type != BTRFS_ROOT_ITEM_KEY ||
		    (key.objectid < BTRFS_FIRST_FREE_OBJECTID &&
		     key.objectid != BTRFS_FS_TREE_OBJECTID) ||
		    key.objectid > BTRFS_LAST_FREE_OBJECTID)
			goto skip;

		eb = path->nodes[0];
		slot = path->slots[0];
		item_size = btrfs_item_size_nr(eb, slot);
		if (item_size < sizeof(root_item))
			goto skip;

		read_extent_buffer(eb, &root_item,
				   btrfs_item_ptr_offset(eb, slot),
				   (int)sizeof(root_item));
		if (btrfs_root_refs(&root_item) == 0)
			goto skip;

		if (!btrfs_is_empty_uuid(root_item.uuid) ||
		    !btrfs_is_empty_uuid(root_item.received_uuid)) {
			if (trans)
				goto update_tree;

			btrfs_release_path(path);
			/*
			 * 1 - subvol uuid item
			 * 1 - received_subvol uuid item
			 */
			trans = btrfs_start_transaction(fs_info->uuid_root, 2);
			if (IS_ERR(trans)) {
				ret = PTR_ERR(trans);
				break;
			}
			continue;
		} else {
			goto skip;
		}
update_tree:
		btrfs_release_path(path);
		if (!btrfs_is_empty_uuid(root_item.uuid)) {
			ret = btrfs_uuid_tree_add(trans, root_item.uuid,
						  BTRFS_UUID_KEY_SUBVOL,
						  key.objectid);
			if (ret < 0) {
				btrfs_warn(fs_info, "uuid_tree_add failed %d",
					ret);
				break;
			}
		}

		if (!btrfs_is_empty_uuid(root_item.received_uuid)) {
			ret = btrfs_uuid_tree_add(trans,
						  root_item.received_uuid,
						 BTRFS_UUID_KEY_RECEIVED_SUBVOL,
						  key.objectid);
			if (ret < 0) {
				btrfs_warn(fs_info, "uuid_tree_add failed %d",
					ret);
				break;
			}
		}

skip:
		btrfs_release_path(path);
		if (trans) {
			ret = btrfs_end_transaction(trans);
			trans = NULL;
			if (ret)
				break;
		}

		if (key.offset < (u64)-1) {
			key.offset++;
		} else if (key.type < BTRFS_ROOT_ITEM_KEY) {
			key.offset = 0;
			key.type = BTRFS_ROOT_ITEM_KEY;
		} else if (key.objectid < (u64)-1) {
			key.offset = 0;
			key.type = BTRFS_ROOT_ITEM_KEY;
			key.objectid++;
		} else {
			break;
		}
		cond_resched();
	}

out:
	btrfs_free_path(path);
	if (trans && !IS_ERR(trans))
		btrfs_end_transaction(trans);
	if (ret)
		btrfs_warn(fs_info, "btrfs_uuid_scan_kthread failed %d", ret);
	else if (!closing)
		set_bit(BTRFS_FS_UPDATE_UUID_TREE_GEN, &fs_info->flags);
	up(&fs_info->uuid_tree_rescan_sem);
	return 0;
}