随手记之TCP Keepalive笔记-tcp_keepalive_timer

这里可以找到大部分处理逻辑，net/ipv4/Tcp_timer.c:

static void tcp_keepalive_timer (unsigned long data)
{
     struct sock *sk = (struct sock *) data;
     struct inet_connection_sock *icsk = inet_csk(sk);
     struct tcp_sock *tp = tcp_sk(sk);
     __u32 elapsed;

     /* Only process if socket is not in use. */
     bh_lock_sock(sk);
     if (sock_owned_by_user(sk)) {
          /* Try again later. */
          inet_csk_reset_keepalive_timer (sk, HZ/20);
          goto out;
     }

     if (sk->sk_state == TCP_LISTEN) {
          tcp_synack_timer(sk);
          goto out;
     }
    // 关闭状态的处理
     if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
          if (tp->linger2 >= 0) {
               const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;

               if (tmo > 0) {
                    tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
                    goto out;
               }
          }
          tcp_send_active_reset(sk, GFP_ATOMIC);
          goto death;
     }

     if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
          goto out;

     elapsed = keepalive_time_when(tp);

     /* It is alive without keepalive 8) */
     if (tp->packets_out || sk->sk_send_head)
          goto resched;

     elapsed = tcp_time_stamp - tp->rcv_tstamp;

     if (elapsed >= keepalive_time_when(tp)) {
          if ((!tp->keepalive_probes && icsk->icsk_probes_out >= sysctl_tcp_keepalive_probes) ||
               (tp->keepalive_probes && icsk->icsk_probes_out >= tp->keepalive_probes)) {
               tcp_send_active_reset(sk, GFP_ATOMIC);
               tcp_write_err(sk); // 向上层应用汇报连接异常
               goto out;
          }
          if (tcp_write_wakeup(sk) <= 0) {
               icsk->icsk_probes_out++; // 这里仅仅是计数，并没有再次发送保活探测包
               elapsed = keepalive_intvl_when(tp);
          } else {
               /* If keepalive was lost due to local congestion,
               * try harder.
               */
               elapsed = TCP_RESOURCE_PROBE_INTERVAL;
          }
     } else {
          /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
          elapsed = keepalive_time_when(tp) - elapsed;
     }

     TCP_CHECK_TIMER(sk);
     sk_stream_mem_reclaim(sk);

resched:
     inet_csk_reset_keepalive_timer (sk, elapsed);
     goto out;

death:    
     tcp_done(sk);

out:
     bh_unlock_sock(sk);
     sock_put(sk);
}

http://www.blogjava.net/yongboy/archive/2015/04/14/424413.html