TCP Receive

Overview

Detail Flow (with code)

tcp_ipv4.c: Receive (tcp_v4_rcv function)

還記得skb與sock的關係吧?

int tcp_v4_rcv(struct sk_buff *skb)
{
    struct sock *sk;
    . . .

檢查sockets hash info，分析對應的sokk關係

有三種hash tables:

❑ Sockets that are fully connected.

❑ Sockets that are waiting for a connection (in the listen state).

❑ Sockets that are in the process of establishing a connection (using the three-way handshake discussed below).

    sk = __inet_lookup_skb(&tcp_hashinfo, skb, th->source, th->dest);
    . . .
    if (!sk)
        goto no_tcp_socket;

檢查sock有沒有被一些apps占用

沒有就放到prequeue裡面，然後呼叫tcp_v4_do_rcv()做後續處理

如果有，放到backlog

        if (!sock_owned_by_user(sk)) {
                 if (!tcp_prequeue(sk, skb))
                         ret = tcp_v4_do_rcv(sk, skb);
         } else if (unlikely(sk_add_backlog(sk, skb,
                 sk->sk_rcvbuf + sk->sk_sndbuf))) {
                 bh_unlock_sock(sk);
                 NET_INC_STATS_BH(net, LINUX_MIB_TCPBACKLOGDROP);
                 goto discard_and_relse;
         }

tcp_v4_do_rcv:

tcp_input.c

tcp_event_data_recv() : measuring the MSS and RTT

tcp_ack() : deals with incoming acks

• cleaning the retransmission queue
• marking the SACKed packets
• reacting to duplicate ACKs
• reordering detection
• reordering detection
• advancing congestion window