hammer2_get_volume
vol = hammer2_get_volume(bref->data_off);
vol = hammer2_get_volume(bref->data_off);
vol = hammer2_get_volume(data_off);
while ((vol = hammer2_get_volume(loff)) != NULL) {
vol = hammer2_get_volume(bref->data_off);
hammer2_volume_t *hammer2_get_volume(hammer2_off_t offset);
hammer2_volume_t *hammer2_get_volume(hammer2_dev_t *hmp, hammer2_off_t offset);
vol = hammer2_get_volume(hmp, pbase);