TIME_WAIT状态下对接收到的数据包如何处理 - c++编程基础

CP_TW_SUCCESS;
}
}
inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
TCP_TIMEWAIT_LEN);

if (tmp_opt.saw_tstamp) {
tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
tcptw->tw_ts_recent_stamp = get_seconds();
}

inet_twsk_put(tw);
return TCP_TW_SUCCESS;
}

if (!paws_reject &&
(TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
(TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
/* In window segment, it may be only reset or bare ack. */
if (th->rst) {
/* This is TIME_WAIT assassination, in two flavors.
* Oh well... nobody has a sufficient solution to this
* protocol bug yet.
*/
if (sysctl_tcp_rfc1337 == 0) {
kill:
inet_twsk_deschedule(tw, &tcp_death_row);
inet_twsk_put(tw);
return TCP_TW_SUCCESS;
}
}
inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
TCP_TIMEWAIT_LEN);

if (tmp_opt.saw_tstamp) {
tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
tcptw->tw_ts_recent_stamp = get_seconds();
}

inet_twsk_put(tw);
return TCP_TW_SUCCESS;
} 如果是RST包的话，并且系统配置sysctl_tcp_rfc1337（默认情况下为0，参见/proc/sys/net/ipv4/tcp_rfc1337）的值为0，这时会立即释放time_wait传输控制块，丢掉接收的RST包。
如果是ACK包，则会启动TIME_WAIT定时器后丢掉接收到的ACK包。
接下来是对SYN包的处理。前面提到了，如果在TIME_WAIT状态下接收到序列号比上一个连接的结束序列号大的SYN包，可以接受，并建立新的连接，下面这段代码就是来处理这样的情况：
[cpp]
if (th->syn && !th->rst && !th->ack && !paws_reject &&
(after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
(tmp_opt.saw_tstamp &&
(s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
if (isn == 0)
isn++;
TCP_SKB_CB(skb)->when = isn;
return TCP_TW_SYN;
}

if (th->syn && !th->rst && !th->ack && !paws_reject &&
(after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
(tmp_opt.saw_tstamp &&
(s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
if (isn == 0)
isn++;
TCP_SKB_CB(skb)->when = isn;
return TCP_TW_SYN;
} 当返回TCP_TW_SYN时，在tcp_v4_rcv()中会立即释放time_wait控制块，并且开始进行正常的连接建立过程。
如果数据包不是上述几种类型的包，可能的情况有：
1、不是有效的SYN包。不考虑时间戳的话，就是序列号在上一次连接的结束序列号之前
2、ACK包，起始序列号不是下一个要接收的序列号
3、RST包，起始序列号不是下一个要接收的序列号
4、带数据的SKB包
这几种情况由以下代码处理：
[cpp]
if (!th->rst) {
/* In this case we must reset the TIMEWAIT timer.
*
* If it is ACKless SYN it may be both old duplicate
* and new good SYN with random sequence number * Do not reschedule in the last case.
*/
if (paws_reject || th->ack)
inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
TCP_TIMEWAIT_LEN);

/* Send ACK. Note, we do not put the bucket,
* it will be released by caller.
*/
return TCP_TW_ACK;
}
inet_twsk_put(tw);
return TCP_TW_SUCCESS;

if (!th->rst) {
/* In this case we must reset the TIMEWAIT timer.
*
* If it is ACKless SYN it may be both old duplicate
* and new good SYN with random sequence number * Do not reschedule in the last case.
*/
if (paws_reject || th->ack)

TIME_WAIT状态下对接收到的数据包如何处理 (五)