ip_route_me_harder 函数的作用
如题。求教ip_route_me_harder函数的功能。/* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */13 int ip_route_me_harder(struct sk_buff *skb, unsigned addr_type)
14 {
15 const struct iphdr *iph = ip_hdr(skb);
16 struct rtable *rt;
17 struct flowi fl = {};
18 struct dst_entry *odst;
19 unsigned int hh_len;
20 unsigned int type;
21
22 type = inet_addr_type(&init_net, iph->saddr);
23 if (addr_type == RTN_UNSPEC)
24 addr_type = type;
25
26 /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
27 * packets with foreign saddr to appear on the NF_INET_LOCAL_OUT hook.
28 */
29 if (addr_type == RTN_LOCAL) {
30 fl.nl_u.ip4_u.daddr = iph->daddr;
31 if (type == RTN_LOCAL)
32 fl.nl_u.ip4_u.saddr = iph->saddr;
33 fl.nl_u.ip4_u.tos = RT_TOS(iph->tos);
34 fl.oif = skb->sk ? skb->sk->sk_bound_dev_if : 0;
35 fl.mark = skb->mark;
36 if (ip_route_output_key(&init_net, &rt, &fl) != 0)
37 return -1;
38
39 /* Drop old route. */
40 dst_release(skb->dst);
41 skb->dst = &rt->u.dst;
42 } else {
43 /* non-local src, find valid iif to satisfy
44 * rp-filter when calling ip_route_input. */
45 fl.nl_u.ip4_u.daddr = iph->saddr;
46 if (ip_route_output_key(&init_net, &rt, &fl) != 0)
47 return -1;
48
49 odst = skb->dst;
50 if (ip_route_input(skb, iph->daddr, iph->saddr,
51 RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
52 dst_release(&rt->u.dst);
53 return -1;
54 }
55 dst_release(&rt->u.dst);
56 dst_release(odst);
57 }
58
59 if (skb->dst->error)
60 return -1;
61
62 #ifdef CONFIG_XFRM
63 if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
64 xfrm_decode_session(skb, &fl, AF_INET) == 0)
65 if (xfrm_lookup(&skb->dst, &fl, skb->sk, 0))
66 return -1;
67 #endif
68
69 /* Change in oif may mean change in hh_len. */
70 hh_len = skb->dst->dev->hard_header_len;
71 if (skb_headroom(skb) < hh_len &&
72 pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
73 return -1;
74
75 return 0;
76 }代码看得一知半解的。 我也想知道这个函数的作用，网上资料很少，求助！谢谢 请问，您知道什么意思了吗，这个函数，能不能给讲一下，谢谢了 感觉是一种hack手段，netfilter引入之后针对原有标准layer-3转发流程的hack。
nat（或者其它mangle逻辑）增加了修改目的ip的操作，有可能导致之前的路由结果无效，因此在某些情况下需要重新进行选路。
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