res_gethostbyaddr
extern struct hostent *res_gethostbyaddr(const char *addr, int len, int type);
he = res_gethostbyaddr((char*)(&sa2sin(addr)->sin_addr),
he = res_gethostbyaddr(
#define gethostbyaddr res_gethostbyaddr /* libnsl */
#define gethostbyaddr res_gethostbyaddr