zfs_set_bootenv
zfs_set_bootenv(bdev, benv);
int zfs_set_bootenv(void *, nvlist_t *);
rv = zfs_set_bootenv(vdev, spa->spa_bootenv);
(void) zfs_set_bootenv(vdev, benv);
rv = zfs_set_bootenv(vdev, spa->spa_bootenv);