传输层

struct proto

struct tcp_prot位于文件net/ipv4/tcp_ipv4.c

struct proto tcp_prot = {

.name = "TCP",

.owner = THIS_MODULE,

.close = tcp_close,

.connect = tcp_v4_connect,

.disconnect = tcp_disconnect,

.accept = inet_csk_accept,

.ioctl = tcp_ioctl,

.init = tcp_v4_init_sock,

.destroy = tcp_v4_destroy_sock,

.shutdown = tcp_shutdown,

.setsockopt = tcp_setsockopt,

.getsockopt = tcp_getsockopt,

.recvmsg = tcp_recvmsg,

.sendmsg = tcp_sendmsg,

.sendpage = tcp_sendpage,

...

};

tcp_sendmsg

tcp_sendmsg

//向队列尾添加一个struct sk_buff *skb

struct sk_buff *skb = tcp_write_queue_tail(sk);

//并使用sk中的数据初始化这个skb

skb_add_data_nocache(sk, skb, from, copy);

tcp_init_xmit_timers

inet_csk_init_xmit_timers(sk, &tcp_write_timer...) => tcp_write_timer

tcp_write_timer_handler(sk)

tcp_retransmit_timer(sk)

//从队列尾取出一块skb进行传输

tcp_retransmit_skb(sk, tcp_write_queue_head(sk))

__tcp_retransmit_skb(sk, skb)

tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC)

struct inet_connection_sock *icsk = inet_csk(sk);

icsk->icsk_af_ops->queue_xmit(skb, ...)

网络层

struct inet_connection_sock_af_ops

tcp_sendmsg最终调用了结构体icsk_af_ops中queue_xmit来传输队列中的skb，结构体icsk_af_ops是这么来的：

const struct inet_connection_sock_af_ops ipv4_specific = {

.queue_xmit = ip_queue_xmit,

.send_check = tcp_v4_send_check,

.rebuild_header = inet_sk_rebuild_header,

.sk_rx_dst_set = inet_sk_rx_dst_set,

.conn_request = tcp_v4_conn_request,

.syn_recv_sock = tcp_v4_syn_recv_sock,

.net_header_len = sizeof(struct iphdr),

.setsockopt = ip_setsockopt,

.getsockopt = ip_getsockopt,

.addr2sockaddr = inet_csk_addr2sockaddr,

.sockaddr_len = sizeof(struct sockaddr_in),

.bind_conflict = inet_csk_bind_conflict,

};

tcp_v4_init_sock(struct sock *sk)

struct inet_connection_sock *icsk = inet_csk(sk);

icsk->icsk_af_ops = &ipv4_specific;

ip_queue_xmit

//dst.output赋值

tcp_v4_conn_request

inet_csk_route_req

ip_route_output_flow

__ip_route_output_key

__mkroute_output

rth->dst.output = ip_output

//使用dsp.output=ip_out来发送数据

ip_queue_xmit

ip_local_out(skb)

dst_output(skb)

skb_dst(skb)->output(skb) == ip_out

ip_finish_output

ip_fragment(skb, ip_finish_output2)

ip_finish_output2(skb)

dst_neigh_output

neigh_hh_output

dev_queue_xmit(skb)