网络编程api总结

1、socket函数创建一个socket连接，此时该socket连接为主动式。 fd(int)->fd(struct fd)->file->sock；sock->file

2、bind函数把socket与ip和端口绑定，并且把socket连接从 主动式 改为 被动式，成为服务端，只能够接受客户端的连接，不能发起连接。

3、listen函数开始监听socket，开始接受客户端的连接，不会阻塞（或者只会因为锁阻塞）；backlog参数：建立连接的全连接队列大小限制；未完成三次握手的半连接队列有另外的参数限制

4、accpet函数从全连接队列取出 new sd，，然后开始工作。默认可阻塞（浅度睡眠），可以在sd创建后设置 不阻塞 属性；https://blog.csdn.net/tanyjin/article/details/69403220

5、connet函数发起三次握手建立连接，在三次握手期间也分为阻塞和非阻塞两种。

ipv4源码参考：

 static int inet_csk_wait_for_connect(struct sock *sk, long timeo)
 {
     struct inet_connection_sock *icsk = inet_csk(sk);
     DEFINE_WAIT(wait);
     int err;

     /*
      * True wake-one mechanism for incoming connections: only
      * one process gets woken up, not the 'whole herd'.
      * Since we do not 'race & poll' for established sockets
      * anymore, the common case will execute the loop only once.
      *
      * Subtle issue: "add_wait_queue_exclusive()" will be added
      * after any current non-exclusive waiters, and we know that
      * it will always _stay_ after any new non-exclusive waiters
      * because all non-exclusive waiters are added at the
      * beginning of the wait-queue. As such, it's ok to "drop"
      * our exclusiveness temporarily when we get woken up without
      * having to remove and re-insert us on the wait queue.
      */
     for (;;) {
         prepare_to_wait_exclusive(sk_sleep(sk), &wait,
                       TASK_INTERRUPTIBLE);
         release_sock(sk);
         if (reqsk_queue_empty(&icsk->icsk_accept_queue))
             timeo = schedule_timeout(timeo);
         sched_annotate_sleep();
         lock_sock(sk);
         err = ;
         if (!reqsk_queue_empty(&icsk->icsk_accept_queue))
             break;
         err = -EINVAL;
         if (sk->sk_state != TCP_LISTEN)
             break;
         err = sock_intr_errno(timeo);
         if (signal_pending(current))
             break;
         err = -EAGAIN;
         if (!timeo)
             break;
     }
     finish_wait(sk_sleep(sk), &wait);
     return err;
 }

5、connet函数从

源码参考：

ipv4代码路径：linux/net/ipv4/af_inet.c

初始化代码：

 static int __init inet_init(void)
      ---proto_register(&tcp_prot, );
      ---inet_register_protosw(q);

关键数据结构的值，sd的操作全部在里面：

 static struct inet_protosw inetsw_array[] =
 {
     {
         .type =       SOCK_STREAM,
         .protocol =   IPPROTO_TCP,
         .prot =       &tcp_prot,
         .ops =        &inet_stream_ops,
         .flags =      INET_PROTOSW_PERMANENT |
                   INET_PROTOSW_ICSK,
     },

     {
         .type =       SOCK_DGRAM,
         .protocol =   IPPROTO_UDP,
         .prot =       &udp_prot,
         .ops =        &inet_dgram_ops,
         .flags =      INET_PROTOSW_PERMANENT,
        },

        {
         .type =       SOCK_DGRAM,
         .protocol =   IPPROTO_ICMP,
         .prot =       &ping_prot,
         .ops =        &inet_sockraw_ops,
         .flags =      INET_PROTOSW_REUSE,
        },

        {
            .type =       SOCK_RAW,
            .protocol =   IPPROTO_IP,    /* wild card */
            .prot =       &raw_prot,
            .ops =        &inet_sockraw_ops,
            .flags =      INET_PROTOSW_REUSE,
        }
 };