#include <stdio.h>#include <sys/types.h>#include <sys/fcntl.h>#include <sys/errno.h>#include <sys/socket.h>#include <netinet/in.h>extern int errno;#define SERV_TCP_PORT   6000main(){	int fd;	struct sockaddr_in	my_addr;	void			echo_serv (int);	bzero((char *) &my_addr, sizeof(my_addr));	my_addr.sin_family      = AF_INET;	my_addr.sin_addr.s_addr = htonl (INADDR_ANY);	my_addr.sin_port        = htons(SERV_TCP_PORT);	fd = net_open ("/dev/udp", O_RDWR);	fd = net_bind (fd, &my_addr, sizeof (struct sockaddr_in));	echo_serv (fd);	exit (0);	/* not reached */}voidecho_serv (int fd){	struct sockaddr_in	fm_addr;	char			buf[512];	int			n;	while (1)	{		n = net_recv (fd, buf, sizeof (buf),				&fm_addr, sizeof (struct sockaddr_in));		net_send (fd, buf, n,				&fm_addr, sizeof (struct sockaddr_in));	}}