zpool_read_label
if (zpool_read_label(h->fd, &h->config, &num_labels) != 0) {
if (zpool_read_label(fd, &config, NULL) != 0) {
zpool_read_label(fd, &label, NULL) != 0) {
if (zpool_read_label(fd, &config, NULL) != 0 && errno == ENOMEM) {
extern int zpool_read_label(int, nvlist_t **, int *);
error = zpool_read_label(fd, &config, &num_labels);