ssize_t read(int fd, void *buf, size_t count);
ssize_t recv(int sockfd, void *buf, size_t len, int flags);
ssize_t write(int fd, const void *buf, size_t count);
ssize_t send(int sockfd, const void *buf, size_t len, int flags);
分区 12 - tcp状态转换-select-poll 的第 2 页
