static int get_extra_mirror_from_replace(struct btrfs_fs_info *fs_info,
					 u64 logical, u64 length,
					 u64 srcdev_devid, int *mirror_num,
					 u64 *physical)
{
	struct btrfs_bio *bbio = NULL;
	int num_stripes;
	int index_srcdev = 0;
	int found = 0;
	u64 physical_of_found = 0;
	int i;
	int ret = 0;

	ret = __btrfs_map_block(fs_info, BTRFS_MAP_GET_READ_MIRRORS,
				logical, &length, &bbio, 0, 0);
	if (ret) {
		ASSERT(bbio == NULL);
		return ret;
	}

	num_stripes = bbio->num_stripes;
	if (*mirror_num > num_stripes) {
		/*
		 * BTRFS_MAP_GET_READ_MIRRORS does not contain this mirror,
		 * that means that the requested area is not left of the left
		 * cursor
		 */
		btrfs_put_bbio(bbio);
		return -EIO;
	}

	/*
	 * process the rest of the function using the mirror_num of the source
	 * drive. Therefore look it up first.  At the end, patch the device
	 * pointer to the one of the target drive.
	 */
	for (i = 0; i < num_stripes; i++) {
		if (bbio->stripes[i].dev->devid != srcdev_devid)
			continue;

		/*
		 * In case of DUP, in order to keep it simple, only add the
		 * mirror with the lowest physical address
		 */
		if (found &&
		    physical_of_found <= bbio->stripes[i].physical)
			continue;

		index_srcdev = i;
		found = 1;
		physical_of_found = bbio->stripes[i].physical;
	}

	btrfs_put_bbio(bbio);

	ASSERT(found);
	if (!found)
		return -EIO;

	*mirror_num = index_srcdev + 1;
	*physical = physical_of_found;
	return ret;
}