TCP定时器 之 重传/延迟ACK/保活 定时器初始化

Posted 2020-12-02 wanpengcoder

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：

1 /**
2  * inet_create
3  *  |-->sk->sk_prot->init
4  *         |-->tcp_v4_init_sock
5  *                |-->tcp_init_sock
6  *                      |-->tcp_init_xmit_timers
7  */

 

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

1 void tcp_init_xmit_timers(struct sock *sk)
2 {
3     inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
4                   &tcp_keepalive_timer);
5 }

 

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；

 1 /*
 2  * Using different timers for retransmit, delayed acks and probes
 3  * We may wish use just one timer maintaining a list of expire jiffies
 4  * to optimize.
 5  */
 6 void inet_csk_init_xmit_timers(struct sock *sk,
 7                    void (*retransmit_handler)(unsigned long),
 8                    void (*delack_handler)(unsigned long),
 9                    void (*keepalive_handler)(unsigned long))
10 {
11     struct inet_connection_sock *icsk = inet_csk(sk);
12 
13     setup_timer(&icsk->icsk_retransmit_timer, retransmit_handler,
14             (unsigned long)sk);
15     setup_timer(&icsk->icsk_delack_timer, delack_handler,
16             (unsigned long)sk);
17     setup_timer(&sk->sk_timer, keepalive_handler, (unsigned long)sk);
18     icsk->icsk_pending = icsk->icsk_ack.pending = 0;
19 }

 

——————–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；

 1 /**
 2 *tcp_v4_rcv
 3 * |-->tcp_v4_do_rcv
 4 *       |-->tcp_rcv_state_process
 5 *              |-->tcp_v4_conn_request
 6 *                    |-->tcp_try_fastopen
 7 *                            |-->tcp_fastopen_create_child                       
 8 *                                    |-->tcp_v4_syn_recv_sock
 9 *                                            |-->tcp_create_openreq_child
10 *                                                    |-->tcp_init_xmit_timers
11 */