zfs_rlookup
if (zfs_rlookup(spa, dev->root_guid, rootname)) {
if (zfs_rlookup(spa, dev->root_guid, rootname)) {
static int zfs_rlookup(const spa_t *spa, uint64_t objnum, char *result);
zfs_rlookup(spa, rootid, bootfs) == 0) {