add_fd
add_fd(fd_loop);
add_fd(fd_ppp);
extern void add_fd __P((int)); /* Add fd to set to wait for */
return add_fd(data, sock, CONN_UDP, process_packet);
return add_fd(data, sock, CONN_TCP_LISTENER, accept_tcp_connection);
return add_fd(data, sock, CONN_TCP, process_tcp_connection);