myip_forward.c

一个基于linux的TCP/IP协议栈的实现

static inline int myip_forward_finish(struct sk_buff *skb)
{
	struct ip_options * opt	= &(IPCB(skb)->opt);

	//MYIP_INC_STATS_BH(IPSTATS_MIB_OUTFORWDATAGRAMS);

	//if( unlikely(opt->optlen) )
	//	ip_forward_options(skb);

	return dst_output(skb);
}

int myip_forward(struct sk_buff *skb)
{
	struct iphdr *iph;
	struct rtable *rt;
	struct ip_options * opt	= &(IPCB(skb)->opt);
	printk(KERN_INFO "forward the packet!\n");
	//if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
	//	goto drop;

	//if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
	//	return NET_RX_SUCCESS;

	if (skb->pkt_type != PACKET_HOST)
		goto drop;

	skb->ip_summed = CHECKSUM_NONE;
	if (skb->nh.iph->ttl <= 1)
		goto too_many_hops;

	//if (!xfrm4_route_forward(skb))
	//	goto drop;

	rt = (struct rtable*)skb->dst;

	if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway)
		goto sr_failed;

	if (skb_cow(skb, LL_RESERVED_SPACE(rt->u.dst.dev)+rt->u.dst.header_len))
		goto drop;
	iph = skb->nh.iph;

	ip_decrease_ttl(iph);

	//if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr)
	//	ip_rt_send_redirect(skb);

	//skb->priority = rt_tos2priority(iph->tos);

	return NF_HOOK(MY_PF_INET, NF_IP_FORWARD, skb, skb->dev, rt->u.dst.dev,
					myip_forward_finish);

sr_failed:
	//icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
	goto drop;

too_many_hops:
	/* Tell the sender its packet died... */
	//icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
drop:
	kfree_skb(skb);
	return NET_RX_DROP;
}