getnetmaskbyaddr
if (getnetmaskbyaddr(ifaddr.sin_addr, &saddr->sin_addr) == 0) {
if (getnetmaskbyaddr(addr, &netmask) == 0) {
extern int getnetmaskbyaddr(struct in_addr, struct in_addr *);
} else if (getnetmaskbyaddr(in4,
if (getnetmaskbyaddr(sin->sin_addr, &m->sin_addr) == 0) {
if (getnetmaskbyaddr(hp, &tp) == 0) {
extern int getnetmaskbyaddr(const struct in_addr, struct in_addr *);