vdev_label_read_config
nvl = vdev_label_read_config(&vtmp, UINT64_MAX);
extern nvlist_t *vdev_label_read_config(vdev_t *vd, uint64_t txg);
if ((label = vdev_label_read_config(vd, txg)) == NULL) {
if ((label = vdev_label_read_config(vd, -1ULL)) == NULL) {
*config = vdev_label_read_config(cb.ubl_vd, ub->ub_txg);
*config = vdev_label_read_config(cb.ubl_vd, UINT64_MAX);
if ((label = vdev_label_read_config(vd, -1ULL)) == NULL)