用戶態(tài)對accept的標準使用方法： if ((client_fd = accept(sockfd, (struct sockaddr *)&remote_addr, &sin_size)) == -1){//accept()函數(shù)讓server接收客戶的連接請求perror("accept Error\n");continue;} sockfd是通過socket系統(tǒng)調(diào)用，而且經(jīng)過listen過的套接字： sockfd = socket(AF_INET, SOCK_STREAM, 0) listen(sockfd, 128)remote_addr將會存儲遠端設備的地址信息。/** For accept, we attempt to create a new socket, set up the link* with the client, wake up the client, then return the new* connected fd. We collect the address of the connector in kernel* space and move it to user at the very end. This is unclean because* we open the socket then return an error.** 1003.1g adds the ability to recvmsg() to query connection pending* status to recvmsg. We need to add that support in a way thats* clean when we restucture accept also.*/asmlinkage long sys_accept(int fd, struct sockaddr __user *upeer_sockaddr,int __user *upeer_addrlen) {struct socket *sock, *newsock;struct file *newfile;int err, len, newfd, fput_needed;char address[MAX_SOCK_ADDR];//通過監(jiān)聽套接字的描寫敘述符fd，找到監(jiān)聽套接字sock = sockfd_lookup_light(fd, &err, &fput_needed);if (!sock)goto out;err = -ENFILE; //創(chuàng)建新的socket，即心的套接字，它將被client_fd 描寫敘述，用于數(shù)據(jù)傳輸， //也就是accept系統(tǒng)調(diào)用返回值client_fd 所相應的套接口if (!(newsock = sock_alloc()))goto out_put;//繼承l(wèi)isten_fd相應的的一些屬性，包含套接字類型，和操作。 //不難理解，listen_fd和client_fd 相應的套接口都是tcp，這些不用一一賦值，直接用listen_fd的屬性就可以。newsock->type = sock->type;newsock->ops = sock->ops;/** We don't need try_module_get here, as the listening socket (sock)* has the protocol module (sock->ops->owner) held.*/ //不懂__module_get(newsock->ops->owner);//創(chuàng)建新的file，然后返回newfd ，這個fd就是待會被返回的client_fd //到如今為止，這個newfd和newfile是有關聯(lián)的。newfd = sock_alloc_fd(&newfile);if (unlikely(newfd < 0)) {err = newfd;sock_release(newsock);goto out_put;} //使得這個newsock綁定剛才新建的newfile //即如今為止，newfd newfile newsock之間是有關聯(lián)的err = sock_attach_fd(newsock, newfile);if (err < 0)goto out_fd_simple;err = security_socket_accept(sock, newsock);if (err)goto out_fd; //newsock是socket結(jié)構體，sock->ops->accept的目的是為newsock關聯(lián)一個sock結(jié)構體 //即三次握手結(jié)束后，新建的sock傳輸控制塊，它等待用戶accept系統(tǒng)調(diào)用“領養(yǎng)”它。 //sock->ops->accept相應的函數(shù)是inet_accepterr = sock->ops->accept(sock, newsock, sock->file->f_flags);if (err < 0)goto out_fd;if (upeer_sockaddr) {if (newsock->ops->getname(newsock, (struct sockaddr *)address,&len, 2) < 0) {err = -ECONNABORTED;goto out_fd;}err = move_addr_to_user(address, len, upeer_sockaddr,upeer_addrlen);if (err < 0)goto out_fd;} ......................................... }/** Accept a pending connection. The TCP layer now gives BSD semantics.*/ int inet_accept(struct socket *sock, struct socket *newsock, int flags) { //第一個參數(shù)sock是監(jiān)聽套接字代表的套接字 //newsock是剛才我們新建的套接字，用以描寫敘述數(shù)據(jù)傳輸 //顯然，此函數(shù)的目的，是找到通過套接字，找到套接字上掛著的以及完畢三次握手的sk //這個被找到的sk，將被關聯(lián)到newsock//sk1 是監(jiān)聽套接字相應的傳輸控制塊struct sock *sk1 = sock->sk;int err = -EINVAL;//sk2(三次握手后建立的傳輸控制塊) 是掛在sk1(監(jiān)聽套接字的傳輸控制塊) 中的完畢三次握手后的sk // sk1->sk_prot->accept 相應的函數(shù)是inet_csk_acceptstruct sock *sk2 = sk1->sk_prot->accept(sk1, flags, &err);if (!sk2)goto do_err;lock_sock(sk2);WARN_ON(!((1 << sk2->sk_state) &(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT | TCPF_CLOSE)));//這個被找到的sk，將被關聯(lián)到newsock //三次握手后建立的傳輸控制塊sk(sock 結(jié)構體)，是不正確應不論什么socket結(jié)構體的，所以我們關聯(lián)上 //這樣三次握手后建立的傳輸控制塊sk，就和文件系統(tǒng)有關聯(lián)了 //關聯(lián)上后，我們就能對其調(diào)用send，recvfrom等系統(tǒng)調(diào)用了sock_graft(sk2, newsock);newsock->state = SS_CONNECTED;err = 0;release_sock(sk2); do_err:return err; }/** This will accept the next outstanding connection.*/ //inet_csk_accept的功能時獲取建立3次握手后的sk，一次調(diào)用返回一個sk struct sock *inet_csk_accept(struct sock *sk, int flags, int *err) { //第一個參數(shù)是監(jiān)聽套接字相應的傳輸控制塊。struct inet_connection_sock *icsk = inet_csk(sk);struct sock *newsk;int error;lock_sock(sk);/* We need to make sure that this socket is listening,* and that it has something pending.*/error = -EINVAL; //假設你傳進的參數(shù)正確，監(jiān)聽套接字相應的傳輸控制塊的狀態(tài)，肯定是TCP_LISTENif (sk->sk_state != TCP_LISTEN)goto out_err;/* Find already established connection */ //icsk->icsk_accept_queue掛的是request_sock，request_sock上掛的就是三次握手后新建的sk //reqsk_queue_empty(&icsk->icsk_accept_queue)推斷是否空，就進入if，怎樣設置為堵塞，則休眠if (reqsk_queue_empty(&icsk->icsk_accept_queue)) {long timeo = sock_rcvtimeo(sk, flags & O_NONBLOCK);/* If this is a non blocking socket don't sleep */error = -EAGAIN;if (!timeo)goto out_err;error = inet_csk_wait_for_connect(sk, timeo);if (error)goto out_err;}//reqsk_queue_get_child的邏輯是： //1：取出icsk_accept_queue的request_sock，然后取出request_sock中的sk //2：listen的sk中，sk_ack_backlog計數(shù)減一，sk->sk_ack_backlog--，由于sk_ack_backlog有上限。 //3：刪除request_sock //4：return取出的sknewsk = reqsk_queue_get_child(&icsk->icsk_accept_queue, sk);WARN_ON(newsk->sk_state == TCP_SYN_RECV); out:release_sock(sk);return newsk; out_err:newsk = NULL;*err = error;goto out; }

轉(zhuǎn)載于:https://www.cnblogs.com/mfrbuaa/p/3901351.html

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