TCP状态切换流程
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enum {
/*
* Description of States:
*
* TCP_SYN_SENT sent a connection request, waiting for ack
*
* TCP_SYN_RECV received a connection request, sent ack,
* waiting for final ack in three-way handshake.
*
* TCP_ESTABLISHED connection established
*
* TCP_FIN_WAIT1 our side has shutdown, waiting to complete
* transmission of remaining buffered data
*
* TCP_FIN_WAIT2 all buffered data sent, waiting for remote
* to shutdown
*
* TCP_CLOSING both sides have shutdown but we still have
* data we have to finish sending
*
* TCP_TIME_WAIT timeout to catch resent junk before entering
* closed, can only be entered from FIN_WAIT2
* or CLOSING. Required because the other end
* may not have gotten our last ACK causing it
* to retransmit the data packet (which we ignore)
*
* TCP_CLOSE_WAIT remote side has shutdown and is waiting for
* us to finish writing our data and to shutdown
* (we have to close() to move on to LAST_ACK)
*
* TCP_LAST_ACK out side has shutdown after remote has
* shutdown. There may still be data in our
* buffer that we have to finish sending
*
* TCP_CLOSE socket is finished
*/
* 连接已建立
*/
TCP_ESTABLISHED = 1,
/*
* 已发送SYN包
*/
TCP_SYN_SENT,
/*
* 已接收到SYN包
*/
TCP_SYN_RECV,
/*
* 执行主动关闭，已发送FIN包
*/
TCP_FIN_WAIT1,
/*
* 执行主动关闭，发送的FIN包后收到对端的ACK包
*/
TCP_FIN_WAIT2,
/*
* 执行主动关闭，，接收到对端的FIN包，并发送ACK包
*/
TCP_TIME_WAIT,
/*
* 连接初始状态
*/
TCP_CLOSE,
/*
* 执行被动关闭，接收到对端的FIN包，并发送ACK包
*/
TCP_CLOSE_WAIT,
/*
* 执行被动关闭，接收到FIN包后，发送自己的FIN包
*/
TCP_LAST_ACK,
/*
* 监听状态
*/
TCP_LISTEN,
/*
* 两端同时关闭，在发送FIN包后接收到对端的FIN包
*/
TCP_CLOSING, /* Now a valid state */
TCP_MAX_STATES /* Leave at the end! */
};
一、主动端
1、TCP_CLOSE ---->TCP_SYN_SENT
141 int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len) 142 { 143 struct sockaddr_in *usin = (struct sockaddr_in *)uaddr; 144 struct inet_sock *inet = inet_sk(sk); 145 struct tcp_sock *tp = tcp_sk(sk); 146 __be16 orig_sport, orig_dport; 147 __be32 daddr, nexthop; 148 struct flowi4 *fl4; 149 struct rtable *rt; 150 int err; 151 struct ip_options_rcu *inet_opt; 152 153 if (addr_len < sizeof(struct sockaddr_in)) 154 return -EINVAL; 155 156 if (usin->sin_family != AF_INET) 157 return -EAFNOSUPPORT; 158 159 nexthop = daddr = usin->sin_addr.s_addr; 160 inet_opt = rcu_dereference_protected(inet->inet_opt, 161 sock_owned_by_user(sk)); 162 if (inet_opt && inet_opt->opt.srr) { 163 if (!daddr) 164 return -EINVAL; 165 nexthop = inet_opt->opt.faddr; 166 } 167 168 orig_sport = inet->inet_sport; 169 orig_dport = usin->sin_port; 170 fl4 = &inet->cork.fl.u.ip4; 171 rt = ip_route_connect(fl4, nexthop, inet->inet_saddr, 172 RT_CONN_FLAGS(sk), sk->sk_bound_dev_if, 173 IPPROTO_TCP, 174 orig_sport, orig_dport, sk); 175 if (IS_ERR(rt)) { 176 err = PTR_ERR(rt); 177 if (err == -ENETUNREACH) 178 IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTNOROUTES); 179 return err; 180 } 181 182 if (rt->rt_flags & (RTCF_MULTICAST | RTCF_BROADCAST)) { 183 ip_rt_put(rt); 184 return -ENETUNREACH; 185 } 186 187 if (!inet_opt || !inet_opt->opt.srr) 188 daddr = fl4->daddr; 189 190 if (!inet->inet_saddr) 191 inet->inet_saddr = fl4->saddr; 192 sk_rcv_saddr_set(sk, inet->inet_saddr); 193 194 if (tp->rx_opt.ts_recent_stamp && inet->inet_daddr != daddr) { 195 /* Reset inherited state */ 196 tp->rx_opt.ts_recent = 0; 197 tp->rx_opt.ts_recent_stamp = 0; 198 if (likely(!tp->repair)) 199 tp->write_seq = 0; 200 } 201 202 if (tcp_death_row.sysctl_tw_recycle && 203 !tp->rx_opt.ts_recent_stamp && fl4->daddr == daddr) 204 tcp_fetch_timewait_stamp(sk, &rt->dst); 205 206 inet->inet_dport = usin->sin_port; 207 sk_daddr_set(sk, daddr); 208 209 inet_csk(sk)->icsk_ext_hdr_len = 0; 210 if (inet_opt) 211 inet_csk(sk)->icsk_ext_hdr_len = inet_opt->opt.optlen; 212 213 tp->rx_opt.mss_clamp = TCP_MSS_DEFAULT; 214 215 /* Socket identity is still unknown (sport may be zero). 216 * However we set state to SYN-SENT and not releasing socket 217 * lock select source port, enter ourselves into the hash tables and 218 * complete initialization after this. 219 */ 220 tcp_set_state(sk, TCP_SYN_SENT); 221 err = inet_hash_connect(&tcp_death_row, sk); 222 if (err) 223 goto failure; 224 225 inet_set_txhash(sk); 226 227 rt = ip_route_newports(fl4, rt, orig_sport, orig_dport, 228 inet->inet_sport, inet->inet_dport, sk); 229 if (IS_ERR(rt)) { 230 err = PTR_ERR(rt); 231 rt = NULL; 232 goto failure; 233 } 234 /* OK, now commit destination to socket. */ 235 sk->sk_gso_type = SKB_GSO_TCPV4; 236 sk_setup_caps(sk, &rt->dst); 237 238 if (!tp->write_seq && likely(!tp->repair)) 239 tp->write_seq = secure_tcp_sequence_number(inet->inet_saddr, 240 inet->inet_daddr, 241 inet->inet_sport, 242 usin->sin_port); 243 244 inet->inet_id = tp->write_seq ^ jiffies; 245 246 err = tcp_connect(sk); 247 248 rt = NULL; 249 if (err) 250 goto failure; 251 252 return 0; 253 254 failure: 255 /* 256 * This unhashes the socket and releases the local port, 257 * if necessary. 258 */ 259 tcp_set_state(sk, TCP_CLOSE); 260 ip_rt_put(rt); 261 sk->sk_route_caps = 0; 262 inet->inet_dport = 0; 263 return err; 264 } 265 EXPORT_SYMBOL(tcp_v4_connect);
2、TCP_SYN_SEND---->TCP_ESTABLISHED
5434 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, 5435 struct tcphdr *th, unsigned len) 5436 { 5437 u8 *hash_location; 5438 struct inet_connection_sock *icsk = inet_csk(sk); 5439 struct tcp_sock *tp = tcp_sk(sk); 5440 struct tcp_cookie_values *cvp = tp->cookie_values; 5441 int saved_clamp = tp->rx_opt.mss_clamp; 5442 5443 tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0); 5444 5445 if (th->ack) { 5446 /* rfc793: 5447 * "If the state is SYN-SENT then 5448 * first check the ACK bit 5449 * If the ACK bit is set 5450 * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send 5451 * a reset (unless the RST bit is set, if so drop 5452 * the segment and return)" 5453 * 5454 * We do not send data with SYN, so that RFC-correct 5455 * test reduces to: 5456 */ 5457 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt) 5458 goto reset_and_undo; 5459 5460 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && 5461 !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp, 5462 tcp_time_stamp)) { 5463 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED); 5464 goto reset_and_undo; 5465 } 5466 5467 /* Now ACK is acceptable. 5468 * 5469 * "If the RST bit is set 5470 * If the ACK was acceptable then signal the user "error: 5471 * connection reset", drop the segment, enter CLOSED state, 5472 * delete TCB, and return." 5473 */ 5474 5475 if (th->rst) { 5476 tcp_reset(sk); 5477 goto discard; 5478 } 5479 5480 /* rfc793: 5481 * "fifth, if neither of the SYN or RST bits is set then 5482 * drop the segment and return." 5483 * 5484 * See note below! 5485 * --ANK(990513) 5486 */ 5487 if (!th->syn) 5488 goto discard_and_undo; 5489 5490 /* rfc793: 5491 * "If the SYN bit is on ... 5492 * are acceptable then ... 5493 * (our SYN has been ACKed), change the connection 5494 * state to ESTABLISHED..." 5495 */ 5496 5497 TCP_ECN_rcv_synack(tp, th); 5498 5499 tp->snd_wl1 = TCP_SKB_CB(skb)->seq; 5500 tcp_ack(sk, skb, FLAG_SLOWPATH); 5501 5502 /* Ok.. it‘s good. Set up sequence numbers and 5503 * move to established. 5504 */ 5505 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; 5506 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; 5507 5508 /* RFC1323: The window in SYN & SYN/ACK segments is 5509 * never scaled. 5510 */ 5511 tp->snd_wnd = ntohs(th->window); 5512 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq); 5513 5514 if (!tp->rx_opt.wscale_ok) { 5515 tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0; 5516 tp->window_clamp = min(tp->window_clamp, 65535U); 5517 } 5518 5519 if (tp->rx_opt.saw_tstamp) { 5520 tp->rx_opt.tstamp_ok = 1; 5521 tp->tcp_header_len = 5522 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 5523 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; 5524 tcp_store_ts_recent(tp); 5525 } else { 5526 tp->tcp_header_len = sizeof(struct tcphdr); 5527 } 5528 5529 if (tcp_is_sack(tp) && sysctl_tcp_fack) 5530 tcp_enable_fack(tp); 5531 5532 tcp_mtup_init(sk); 5533 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 5534 tcp_initialize_rcv_mss(sk); 5535 5536 /* Remember, tcp_poll() does not lock socket! 5537 * Change state from SYN-SENT only after copied_seq 5538 * is initialized. */ 5539 tp->copied_seq = tp->rcv_nxt; 5540 5541 if (cvp != NULL && 5542 cvp->cookie_pair_size > 0 && 5543 tp->rx_opt.cookie_plus > 0) { 5544 int cookie_size = tp->rx_opt.cookie_plus 5545 - TCPOLEN_COOKIE_BASE; 5546 int cookie_pair_size = cookie_size 5547 + cvp->cookie_desired; 5548 5549 /* A cookie extension option was sent and returned. 5550 * Note that each incoming SYNACK replaces the 5551 * Responder cookie. The initial exchange is most 5552 * fragile, as protection against spoofing relies 5553 * entirely upon the sequence and timestamp (above). 5554 * This replacement strategy allows the correct pair to 5555 * pass through, while any others will be filtered via 5556 * Responder verification later. 5557 */ 5558 if (sizeof(cvp->cookie_pair) >= cookie_pair_size) { 5559 memcpy(&cvp->cookie_pair[cvp->cookie_desired], 5560 hash_location, cookie_size); 5561 cvp->cookie_pair_size = cookie_pair_size; 5562 } 5563 } 5564 5565 smp_mb(); 5566 tcp_set_state(sk, TCP_ESTABLISHED); 5567 5568 security_inet_conn_established(sk, skb); 5569 5570 /* Make sure socket is routed, for correct metrics. */ 5571 icsk->icsk_af_ops->rebuild_header(sk); 5572 5573 tcp_init_metrics(sk); 5574 5575 tcp_init_congestion_control(sk); 5576 5577 /* Prevent spurious tcp_cwnd_restart() on first data 5578 * packet. 5579 */ 5580 tp->lsndtime = tcp_time_stamp; 5581 5582 tcp_init_buffer_space(sk); 5583 5584 if (sock_flag(sk, SOCK_KEEPOPEN)) 5585 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp)); 5586 5587 if (!tp->rx_opt.snd_wscale) 5588 __tcp_fast_path_on(tp, tp->snd_wnd); 5589 else 5590 tp->pred_flags = 0; 5591 5592 if (!sock_flag(sk, SOCK_DEAD)) { 5593 sk->sk_state_change(sk); 5594 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT); 5595 } 5596 5597 if (sk->sk_write_pending || 5598 icsk->icsk_accept_queue.rskq_defer_accept || 5599 icsk->icsk_ack.pingpong) { 5600 /* Save one ACK. Data will be ready after 5601 * several ticks, if write_pending is set. 5602 * 5603 * It may be deleted, but with this feature tcpdumps 5604 * look so _wonderfully_ clever, that I was not able 5605 * to stand against the temptation 8) --ANK 5606 */ 5607 inet_csk_schedule_ack(sk); 5608 icsk->icsk_ack.lrcvtime = tcp_time_stamp; 5609 icsk->icsk_ack.ato = TCP_ATO_MIN; 5610 tcp_incr_quickack(sk); 5611 tcp_enter_quickack_mode(sk); 5612 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, 5613 TCP_DELACK_MAX, TCP_RTO_MAX); 5614 5615 discard: 5616 __kfree_skb(skb); 5617 return 0; 5618 } else { 5619 tcp_send_ack(sk); 5620 } 5621 return -1; 5622 } 5623 5624 /* No ACK in the segment */ 5625 5626 if (th->rst) { 5627 /* rfc793: 5628 * "If the RST bit is set 5629 * 5630 * Otherwise (no ACK) drop the segment and return." 5631 */ 5632 5633 goto discard_and_undo; 5634 } 5635 5636 /* PAWS check. */ 5637 if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && 5638 tcp_paws_reject(&tp->rx_opt, 0)) 5639 goto discard_and_undo; 5640 5641 if (th->syn) { 5642 /* We see SYN without ACK. It is attempt of 5643 * simultaneous connect with crossed SYNs. 5644 * Particularly, it can be connect to self. 5645 */ 5646 tcp_set_state(sk, TCP_SYN_RECV); 5647 5648 if (tp->rx_opt.saw_tstamp) { 5649 tp->rx_opt.tstamp_ok = 1; 5650 tcp_store_ts_recent(tp); 5651 tp->tcp_header_len = 5652 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 5653 } else { 5654 tp->tcp_header_len = sizeof(struct tcphdr); 5655 } 5656 5657 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; 5658 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; 5659 5660 /* RFC1323: The window in SYN & SYN/ACK segments is 5661 * never scaled. 5662 */ 5663 tp->snd_wnd = ntohs(th->window); 5664 tp->snd_wl1 = TCP_SKB_CB(skb)->seq; 5665 tp->max_window = tp->snd_wnd; 5666 5667 TCP_ECN_rcv_syn(tp, th); 5668 5669 tcp_mtup_init(sk); 5670 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 5671 tcp_initialize_rcv_mss(sk); 5672 5673 tcp_send_synack(sk); 5674 #if 0 5675 /* Note, we could accept data and URG from this segment. 5676 * There are no obstacles to make this. 5677 * 5678 * However, if we ignore data in ACKless segments sometimes, 5679 * we have no reasons to accept it sometimes. 5680 * Also, seems the code doing it in step6 of tcp_rcv_state_process 5681 * is not flawless. So, discard packet for sanity. 5682 * Uncomment this return to process the data. 5683 */ 5684 return -1; 5685 #else 5686 goto discard; 5687 #endif 5688 } 5689 /* "fifth, if neither of the SYN or RST bits is set then 5690 * drop the segment and return." 5691 */ 5692 5693 discard_and_undo: 5694 tcp_clear_options(&tp->rx_opt); 5695 tp->rx_opt.mss_clamp = saved_clamp; 5696 goto discard; 5697 5698 reset_and_undo: 5699 tcp_clear_options(&tp->rx_opt); 5700 tp->rx_opt.mss_clamp = saved_clamp; 5701 return 1; 5702 }
二、被动打开
1、TCP_CLOSE ----> TCP_LISTEN
794 int inet_csk_listen_start(struct sock *sk, const int nr_table_entries) 795 { 796 struct inet_sock *inet = inet_sk(sk); 797 struct inet_connection_sock *icsk = inet_csk(sk); 798 int rc = reqsk_queue_alloc(&icsk->icsk_accept_queue, nr_table_entries); 799 800 if (rc != 0) 801 return rc; 802 803 sk->sk_max_ack_backlog = 0; 804 sk->sk_ack_backlog = 0; 805 inet_csk_delack_init(sk); 806 807 /* There is race window here: we announce ourselves listening, 808 * but this transition is still not validated by get_port(). 809 * It is OK, because this socket enters to hash table only 810 * after validation is complete. 811 */ 812 sk->sk_state = TCP_LISTEN; 813 if (!sk->sk_prot->get_port(sk, inet->inet_num)) { 814 inet->inet_sport = htons(inet->inet_num); 815 816 sk_dst_reset(sk); 817 sk->sk_prot->hash(sk); 818 819 return 0; 820 } 821 822 sk->sk_state = TCP_CLOSE; 823 __reqsk_queue_destroy(&icsk->icsk_accept_queue); 824 return -EADDRINUSE; 825 }
2、TCP_LISTEN ----> TCP_SYN_RCVE
5434 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, 5435 struct tcphdr *th, unsigned len) 5436 { 5437 u8 *hash_location; 5438 struct inet_connection_sock *icsk = inet_csk(sk); 5439 struct tcp_sock *tp = tcp_sk(sk); 5440 struct tcp_cookie_values *cvp = tp->cookie_values; 5441 int saved_clamp = tp->rx_opt.mss_clamp; 5442 5443 tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0); 5444 5445 if (th->ack) { 5446 /* rfc793: 5447 * "If the state is SYN-SENT then 5448 * first check the ACK bit 5449 * If the ACK bit is set 5450 * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send 5451 * a reset (unless the RST bit is set, if so drop 5452 * the segment and return)" 5453 * 5454 * We do not send data with SYN, so that RFC-correct 5455 * test reduces to: 5456 */ 5457 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt) 5458 goto reset_and_undo; 5459 5460 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && 5461 !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp, 5462 tcp_time_stamp)) { 5463 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED); 5464 goto reset_and_undo; 5465 } 5466 5467 /* Now ACK is acceptable. 5468 * 5469 * "If the RST bit is set 5470 * If the ACK was acceptable then signal the user "error: 5471 * connection reset", drop the segment, enter CLOSED state, 5472 * delete TCB, and return." 5473 */ 5474 5475 if (th->rst) { 5476 tcp_reset(sk); 5477 goto discard; 5478 } 5479 5480 /* rfc793: 5481 * "fifth, if neither of the SYN or RST bits is set then 5482 * drop the segment and return." 5483 * 5484 * See note below! 5485 * --ANK(990513) 5486 */ 5487 if (!th->syn) 5488 goto discard_and_undo; 5489 5490 /* rfc793: 5491 * "If the SYN bit is on ... 5492 * are acceptable then ... 5493 * (our SYN has been ACKed), change the connection 5494 * state to ESTABLISHED..." 5495 */ 5496 5497 TCP_ECN_rcv_synack(tp, th); 5498 5499 tp->snd_wl1 = TCP_SKB_CB(skb)->seq; 5500 tcp_ack(sk, skb, FLAG_SLOWPATH); 5501 5502 /* Ok.. it‘s good. Set up sequence numbers and 5503 * move to established. 5504 */ 5505 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; 5506 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; 5507 5508 /* RFC1323: The window in SYN & SYN/ACK segments is 5509 * never scaled. 5510 */ 5511 tp->snd_wnd = ntohs(th->window); 5512 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq); 5513 5514 if (!tp->rx_opt.wscale_ok) { 5515 tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0; 5516 tp->window_clamp = min(tp->window_clamp, 65535U); 5517 } 5518 5519 if (tp->rx_opt.saw_tstamp) { 5520 tp->rx_opt.tstamp_ok = 1; 5521 tp->tcp_header_len = 5522 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 5523 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; 5524 tcp_store_ts_recent(tp); 5525 } else { 5526 tp->tcp_header_len = sizeof(struct tcphdr); 5527 } 5528 5529 if (tcp_is_sack(tp) && sysctl_tcp_fack) 5530 tcp_enable_fack(tp); 5531 5532 tcp_mtup_init(sk); 5533 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 5534 tcp_initialize_rcv_mss(sk); 5535 5536 /* Remember, tcp_poll() does not lock socket! 5537 * Change state from SYN-SENT only after copied_seq 5538 * is initialized. */ 5539 tp->copied_seq = tp->rcv_nxt; 5540 5541 if (cvp != NULL && 5542 cvp->cookie_pair_size > 0 && 5543 tp->rx_opt.cookie_plus > 0) { 5544 int cookie_size = tp->rx_opt.cookie_plus 5545 - TCPOLEN_COOKIE_BASE; 5546 int cookie_pair_size = cookie_size 5547 + cvp->cookie_desired; 5548 5549 /* A cookie extension option was sent and returned. 5550 * Note that each incoming SYNACK replaces the 5551 * Responder cookie. The initial exchange is most 5552 * fragile, as protection against spoofing relies 5553 * entirely upon the sequence and timestamp (above). 5554 * This replacement strategy allows the correct pair to 5555 * pass through, while any others will be filtered via 5556 * Responder verification later. 5557 */ 5558 if (sizeof(cvp->cookie_pair) >= cookie_pair_size) { 5559 memcpy(&cvp->cookie_pair[cvp->cookie_desired], 5560 hash_location, cookie_size); 5561 cvp->cookie_pair_size = cookie_pair_size; 5562 } 5563 } 5564 5565 smp_mb(); 5566 tcp_set_state(sk, TCP_ESTABLISHED); 5567 5568以上是关于TCP状态切换流程的主要内容，如果未能解决你的问题，请参考以下文章