ipt_dscp.c

这个linux源代码是很全面的~基本完整了~使用c编译的~由于时间问题我没有亲自测试~但就算用来做参考资料也是非常好的

/* iptables module for setting the IPv4 DSCP field, Version 1.8
 *
 * (C) 2002 by Harald Welte <[e-mail]>
 * based on ipt_FTOS.c (C) 2000 by Matthew G. Marsh <[e-mail]>
 * This software is distributed under GNU GPL v2, 1991
 * 
 * See RFC2474 for a description of the DSCP field within the IP Header.
 *
 * ipt_DSCP.c,v 1.8 2002/08/06 18:41:57 laforge Exp
*/

#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <net/checksum.h>

#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv4/ipt_DSCP.h>

MODULE_AUTHOR("Harald Welte <[e-mail]>");
MODULE_DESCRIPTION("IP tables DSCP modification module");
MODULE_LICENSE("GPL");

static unsigned int
target(struct sk_buff **pskb,
       unsigned int hooknum,
       const struct net_device *in,
       const struct net_device *out,
       const void *targinfo,
       void *userinfo)
{
	struct iphdr *iph = (*pskb)->nh.iph;
	const struct ipt_DSCP_info *dinfo = targinfo;
	u_int8_t sh_dscp = ((dinfo->dscp << IPT_DSCP_SHIFT) & IPT_DSCP_MASK);


	if ((iph->tos & IPT_DSCP_MASK) != sh_dscp) {
		u_int16_t diffs[2];

		/* raw socket (tcpdump) may have clone of incoming
		 * skb: don't disturb it --RR */
		if (skb_cloned(*pskb) && !(*pskb)->sk) {
			struct sk_buff *nskb = skb_copy(*pskb, GFP_ATOMIC);
			if (!nskb)
				return NF_DROP;
			kfree_skb(*pskb);
			*pskb = nskb;
			iph = (*pskb)->nh.iph;
		}

		diffs[0] = htons(iph->tos) ^ 0xFFFF;