auth_zone_get_serial
if(!auth_zone_get_serial(z, &soa_serial)) {
int auth_zone_get_serial(struct auth_zone* z, uint32_t* serial);
if(auth_zone_get_serial(z, &serial)) {
have_old = (auth_zone_get_serial(old_z,
have_new = (auth_zone_get_serial(new_z,
if(!auth_zone_get_serial(z, &soa_serial)) {
int auth_zone_get_serial(struct auth_zone* z, uint32_t* serial);