TCP定时器 之 重传/延迟ACK/保活 定时器初始化

创建socket时会创建传输控制块，之后调用初始化函数对控制块进行初始化，其中包括对定时器的初始化，tcp会调用tcp_init_xmit_timers函数来初始化这些定时器，本文将详细分析tcp_init_xmit_timers函数；

下面为这种情况的函数调用关系：

 /**
  * inet_create
  *  |-->sk->sk_prot->init
  *         |-->tcp_v4_init_sock
  *                |-->tcp_init_sock
  *                      |-->tcp_init_xmit_timers
  */

tcp_init_xmit_timers函数将三个定时器回调传入到inet_csk_init_xmit_timers函数；

 void tcp_init_xmit_timers(struct sock *sk)
 {
     inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
                   &tcp_keepalive_timer);
 }

inet_csk_init_xmit_timers函数将重传定时器icsk_retransmit_timer的回调设置为retransmit_handler，将延迟ack定时器icsk_delack_timer的回调设置为delack_handler，将sk_timer定时器设置wei为keepalive_handler，注: sk_timer为共用定时器，会在连接处于不同状态下设置不同的定时器回调；

 /*
  * Using different timers for retransmit, delayed acks and probes
  * We may wish use just one timer maintaining a list of expire jiffies
  * to optimize.
  */
 void inet_csk_init_xmit_timers(struct sock *sk,
                    void (*retransmit_handler)(unsigned long),
                    void (*delack_handler)(unsigned long),
                    void (*keepalive_handler)(unsigned long))
 {
     struct inet_connection_sock *icsk = inet_csk(sk);

     setup_timer(&icsk->icsk_retransmit_timer, retransmit_handler,
             (unsigned long)sk);
     setup_timer(&icsk->icsk_delack_timer, delack_handler,
             (unsigned long)sk);
     setup_timer(&sk->sk_timer, keepalive_handler, (unsigned long)sk);
     icsk->icsk_pending = icsk->icsk_ack.pending = ;
 }

——————–我是分割线——————–

定时器初始化的另外一条调用路径是开启fastopen的情况，本文不做讨论，补充在尾部；

 /**
 *tcp_v4_rcv
 * |-->tcp_v4_do_rcv
 *       |-->tcp_rcv_state_process
 *              |-->tcp_v4_conn_request
 *                    |-->tcp_try_fastopen
 *                            |-->tcp_fastopen_create_child
 *                                    |-->tcp_v4_syn_recv_sock
 *                                            |-->tcp_create_openreq_child
 *                                                    |-->tcp_init_xmit_timers
 */