《Linux TCP Implementation》.pdf

Basics of TCP implementation in Linux Charles 2014/12/05 Outlines  Basic skills to read kernel codes  Vim + Ctags  Grep: killer for function pointers  BSD Socket APIs  Server side: socket(), bind(), listen(), accept()  Client side: socket(), connect()  send(), recv()  Data strutures  socket, file descriptor(FD), sock  sock，inet_sock, inet_connection_sock, tcp_sock  sk_buff and routines operating on sk_buff  几个问题  区分struct socket和structsock，它们的缩写分别是：sock和sk  三次握手什么时候算完成了？  TCP/IP的包头具体是怎样封装并解封装的？  sock结构体嵌套了那么多层，是怎么分配内存的？ 0. An simple example 1. socket()  int socket (int family, int type, int protocol)  listenfd = socket(AF_INET, SOCK_STREAM, 0);  AF_INET: ipv4 address family SOCK_STREAM: socket type  If the protocol is 0, the family is instructed to select an appropriate default. 1.1 File descriptor, BSD socket and kernel sock 1.2 sock, inet_sock, tcp_sock  这些数据结构是一层一层嵌套的。  如果套用C++中类的概念：  sock 是父类，inet_sock是sock的子类  inet_connection_sock是inet_sock的子类  tcp_sock是inet_connection_sock的子类  因此经常有这样的转换 （一个指向父类的指针，是可以转化成一个指向子类的指针。C++类实现不过尔尔）  struct tcp_sock *tp = (struct tcp_sock *)sk; // 将一个sock *转换为tcp_sock *  如何分配内存的？  sk = sk_alloc(net, PF_INET, GFP_KERNEL, answer_port)  answer_port == tcp_port  sk = kmalloc(prot-obj_size, priority)  .obj_size == sizeof(struct tcp_sock)  细节请参考代码 1.3 Main routines of socket() 细节请参考源码 2. bind()  int bind(int sockfd, struct sockaddr *my_addr, int addrlen) /* diff with ‘sockaddr’, which is more general */ struct sockaddr_in serv_addr; memset(serv_addr, 0, sizeof(serv_addr)); serv_addr.sin_famil