udpsend.c

关于UDP方面的东西。。看不懂就算了。不适合基础者。

/* udpsend.c - udpsend */

#include <conf.h>
#include <kernel.h>
#include <network.h>
#include <igmp.h>

/*------------------------------------------------------------------------
 *  udpsend  -  send one UDP datagram to a given IP address
 *------------------------------------------------------------------------
 */
int
udpsend(IPaddr fip, u_short fport, u_short lport, struct ep *pep,
	unsigned datalen, Bool docksum)
{
	struct	ip	*pip = (struct ip *) pep->ep_data;
	struct	udp	*pudp = (struct udp *) pip->ip_data;
	struct	route	*prt;
	struct  hg	*phg;
	int		ttl = IP_TTL;

	pudp->u_src = lport;
	pudp->u_dst = fport;
	pudp->u_len = U_HLEN+datalen;
	pudp->u_cksum = 0;
	udph2net(pudp);
	pep->ep_order &= ~EPO_UDP;
	if (docksum) {
		prt = rtget(fip, RTF_LOCAL);
		if (prt == NULL) {
			IpOutNoRoutes++;
			freebuf(pep);
			return SYSERR;
		}
		pip->ip_dst = fip;
		if (prt->rt_ifnum == NI_LOCAL)
			pip->ip_src = pip->ip_dst;
		else
			pip->ip_src = nif[prt->rt_ifnum].ni_ip;
		rtfree(prt);
		pudp->u_cksum = udpcksum(pep, U_HLEN+datalen);
		if (pudp->u_cksum == 0)
			pudp->u_cksum = ~0;
	}
	UdpOutDatagrams++;
	if (IP_CLASSD(fip)) {
		wait(HostGroup.hi_mutex);
		phg = hglookup(NI_PRIMARY, fip);
		if (phg)
			ttl = phg->hg_ttl;
		else
			ttl = 1;
		signal(HostGroup.hi_mutex);
	}
	return ipsend(fip, pep, U_HLEN+datalen, IPT_UDP, IPP_NORMAL, ttl);
}