四次挥手过程分析上【V5.8，正常流程】 1、客户端主动断开连接，状态从TCP_ESTABLISHED变为TCP_FIN_WAIT1，发送FIN包给服务端 A、状态变为TCP_FIN_WAIT1 tcp_close->tcp_close_state ->tcp_set_state(sk, new_state[TCP_ESTABLISHED])，也就是TCP_FIN_WAIT1 B、发送FIN包 tcp_close->tcp_close_state ->tcp_send_fin 2、服务端收到FIN包，状态从TCP_ESTABLISHED变为TCP_CLOSE_WAIT，并返回ACK包 A、状态变为TCP_CLOSE_WAIT 【tcp_protocol.handler】tcp_v4_rcv->tcp_v4_do_rcv->tcp_rcv_established ->tcp_data_queue ->->tcp_fin ->->->inet_csk_schedule_ack; 安排ack ->->->sk->sk_shutdown |= RCV_SHUTDOWN; 模拟了close ->->->sock_set_flag(sk, SOCK_DONE); ->->->case TCP_ESTABLISHED: ->->->tcp_set_state(sk, TCP_CLOSE_WAIT); 修改状态 ->->inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW; ACS是否立即发送 B、发送ACK包 【tcp_protocol.handler】tcp_v4_rcv->tcp_v4_do_rcv->tcp_rcv_established【接上面】 ->tcp_ack_snd_check->__tcp_ack_snd_check->tcp_send_ack 3、客户端收到ACK包，状态从TCP_FIN_WAIT1变为TCP_FIN_WAIT2，然后被替换为状态TCP_TIME_WAIT，子状态TCP_FIN_WAIT2 【tcp_protocol.handler】tcp_v4_rcv->tcp_v4_do_rcv->tcp_rcv_state_process ->case TCP_FIN_WAIT1: ->tcp_set_state(sk, TCP_FIN_WAIT2); ->tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); ->->tw = inet_twsk_alloc(sk, tcp_death_row, state); ->->->tw->tw_state = TCP_TIME_WAIT; ->->->tw->tw_substate = TCP_FIN_WAIT2; ->->->timer_setup(&tw->tw_timer, tw_timer_handler, TIMER_PINNED); 4、服务端状态从TCP_CLOSE_WAIT变为TCP_LAST_ACK，发送FIN包 A、状态变为TCP_LAST_ACK tcp_close->tcp_close_state ->tcp_set_state(sk, new_state[TCP_CLOSE_WAIT])，也就是TCP_LAST_ACK B、发送FIN包 tcp_close->tcp_close_state ->tcp_send_fin

三次握手过程分析【V5.8，正常流程】 1、客户端发起第一次握手，状态调变为TCP_SYN_SENT，发送SYN包 connect->__sys_connect->__sys_connect_file->【sock->ops->connect】tcp_v4_connect A、状态变化 ->tcp_set_state(sk, TCP_SYN_SENT); B、发送SYN ->tcp_connect->tcp_send_syn_data 2、服务端收到客户端的SYN包，初始化socket，状态从TCP_LISTEN变为TCP_NEW_SYN_RECV，发送第二次握手SYN_ACK包 A、收到连接，初始化socket accept->__sys_accept4->__sys_accept4_file->【sock->ops->accept】inet_csk_accept B、收到SYN，改变状态 【tcp_protocol.handler】tcp_v4_rcv->tcp_v4_do_rcv->tcp_rcv_state_process-> ->case TCP_LISTEN: ->[sock->ops->conn_request]tcp_v4_conn_request->tcp_conn_request ->->inet_reqsk_alloc ->->->ireq->ireq_state = TCP_NEW_SYN_RECV; C、发送SYN_ACK包 ->[sock->ops->conn_request]tcp_v4_conn_request->tcp_conn_request【和B路径一样】 ->->【af_ops->send_synack】tcp_v4_send_synack ->->->tcp_make_synack ->->->__tcp_v4_send_check 3、客户端收到SYN_ACK包，状态从TCP_SYN_SENT变为TCP_ESTABLISHED，并发送ACK包 A、收到SYN_ACK包 【tcp_protocol.handler】tcp_v4_rcv->tcp_v4_do_rcv->tcp_rcv_state_process ->case TCP_SYN_SENT: ->tcp_rcv_synsent_state_process->tcp_finish_connect ->->tcp_set_state(sk, TCP_ESTABLISHED); B、发送ACK包 ->tcp_rcv_synsent_state_process->tcp_send_ack->__tcp_send_ack 4、服务端收到ACK包，状态从TCP_NEW_SYN_RECV变为TCP_SYN_RECV【实际上是新建了一个sock】 【tcp_protocol.handler】tcp_v4_rcv-> ->if (sk->sk_state == TCP_NEW_SYN_RECV) ->tcp_check_req ->->【inet_csk(sk)->icsk_af_ops->syn_recv_sock】tcp_v4_syn_recv_sock->tcp_create_openreq_child->inet_csk_clone_lock ->->->inet_sk_set_state(newsk, TCP_SYN_RECV); 5、服务端状态从TCP_SYN_RECV变为TCP_ESTABLISHED 【tcp_protocol.handler】tcp_v4_rcv->tcp_v4_do_rcv->tcp_rcv_state_process ->case TCP_SYN_RECV: ->tcp_set_state(sk, TCP_ESTABLISHED); 只看没调，有问题的欢迎各位小伙伴指出。