mptcp建连过程
创建 socket
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| inet_create
tcp_v4_init_sock
tcp_init_sock
mptcp_init_tcp_sock {
if (!mptcp_init_failed && sysctl_mptcp_enabled == MPTCP_SYSCTL)
mptcp_enable_sock(sk);
}
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所以listen之后再设置mptcp_enable=0，需要restart才能生效
发送syn
只加 option
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| tcp_connect {
tcp_connect_init {
tp->request_mptcp = 1;
}
tcp_transmit_skb
tcp_syn_options
mptcp_syn_options {
if (is_master_tp(tp)) {
opts->mptcp_options |= OPTION_MP_CAPABLE | OPTION_TYPE_SYN;
...
} else {
opts->mptcp_options |= OPTION_MP_JOIN | OPTION_TYPE_SYN;
}
}
}
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接收syn, 发送synack
只加 option
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| tcp_synack_options
mptcp_synack_options {
/* MPCB not yet set - thus it's a new MPTCP-session */
if (!mtreq->is_sub) {
opts->mptcp_options |= OPTION_MP_CAPABLE | OPTION_TYPE_SYNACK;
} else {
opts->mptcp_options |= OPTION_MP_JOIN | OPTION_TYPE_SYNACK;
}
}
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接收synack
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| tcp_v4_do_rcv {
sk->sk_state == TCP_SYN_SENT
tcp_rcv_state_process {
queued = tcp_rcv_synsent_state_process(sk, skb, th, len) {
if (tp->request_mptcp || mptcp(tp)) {
ret = mptcp_rcv_synsent_state_process(sk, &sk, skb, &mopt);
// 这个会创建出一个新的sk叫master_sk，原来的sk改为meta_sk
// master_sk 和 meta_sk 的五元组一样，meta_sk 从hash表中删去，master_sk 加入hash表
// 也就是说，和应用层通信的是meta_sk，tcp通信用master_sk
}
tcp_set_state(sk, TCP_ESTABLISHED);
tcp_send_ack(sk) {
mptcp_established_options {
if (unlikely(tp->mptcp->include_mpc)) {
opts->mptcp_options |= OPTION_MP_CAPABLE | OPTION_TYPE_ACK;
}
}
}
if (is_meta_sk(sk)) {
mptcp_update_metasocket(tp->meta_sk);
// 客户端建连成功
}
}
}
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接收ack
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| tcp_child_process {
tcp_rcv_state_process {
if (!tcp_validate_incoming(sk, skb, th, 0))
return 0;
/* step 5: check the ACK field */
if (th->ack) {
int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH) > 0;
switch (sk->sk_state) {
case TCP_SYN_RECV:
tcp_set_state(sk, TCP_ESTABLISHED);
}
case TCP_ESTABLISHED:
tcp_data_queue(sk, skb);
queued = 1;
break;
}
}
if (mptcp(tp)) {
if (is_master_tp(tp)) {
mptcp_update_metasocket(mptcp_meta_sk(sk));
// 服务端建连成功
}
}
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