linux TCP/IP协议栈 ---ip_local_deliver_finish()

1. /* 如果忽略掉原始套接字和IPSec，则该函数仅仅是根据IP头部中的协议字段选择上层L4协议，并交给它来处理*/
2. static int ip_local_deliver_finish(struct sk_buff *skb)
3. {
4.     /* 跳过IP头部 */
5.     __skb_pull(skb, ip_hdrlen(skb));
6. 
   
7.     /* Point into the IP datagram, just past the header. */
8.     /* 设置传输层头部位置 */
9.     skb_reset_transport_header(skb);
10. 
    
11.     rcu_read_lock();
12.     {
13.         /* Note: See raw.c and net/raw.h, RAWV4_HTABLE_SIZE==MAX_INET_PROTOS */
14.         int protocol = ip_hdr(skb)->protocol;
15.         int hash;
16.         struct sock *raw_sk;
17.         struct net_protocol *ipprot;
18. 
    
19.     resubmit:
20.     /* 这个hash根本不是哈希值，仅仅只是inet_protos数组中的下表而已 */
21.         hash = protocol & (MAX_INET_PROTOS - 1);
22.         raw_sk = sk_head(&raw_v4_htable[hash]);
23. 
    
24.         /* If there maybe a raw socket we must check - if not we
25.          * don't care less
26.          */
27.     /* 原始套接字？？ 忽略... */
28.         if (raw_sk && !raw_v4_input(skb, ip_hdr(skb), hash))
29.             raw_sk = NULL;
30.     /* 查找注册的L4层协议处理结构。 */
31.         if ((ipprot = rcu_dereference(inet_protos[hash])) != NULL) {
32.             int ret;
33.     /* 启用了安全策略，则交给IPSec */
34.             if (!ipprot->no_policy) {
35.                 if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
36.                     kfree_skb(skb);
37.                     goto out;
38.                 }
39.                 nf_reset(skb);
40.             }
41.     /* 调用L4层协议处理函数 */
42.     /* 通常会是tcp_v4_rcv, udp_rcv, icmp_rcv和igmp_rcv */
43.     /* 如果注册了其他的L4层协议处理，则会进行相应的调用。 */
44.             ret = ipprot->handler(skb);
45.             if (ret < 0) {
46.                 protocol = -ret;
47.                 goto resubmit;
48.             }
49.             IP_INC_STATS_BH(IPSTATS_MIB_INDELIVERS);
50.         } else {
51.             if (!raw_sk) {    /* 无原始套接字，提交给IPSec */
52.                 if (xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
53.                     IP_INC_STATS_BH(IPSTATS_MIB_INUNKNOWNPROTOS);
54.                     icmp_send(skb, ICMP_DEST_UNREACH,
55.                          ICMP_PROT_UNREACH, 0);
56.                 }
57.             } else
58.                 IP_INC_STATS_BH(IPSTATS_MIB_INDELIVERS);
59.             kfree_skb(skb);
60.         }
61.     }
62.  out:
63.     rcu_read_unlock();
64. 
    
65.     return 0;
66. }