linux网络编程之socket(十六)
5、msg_control:是一个指向cmsghdr 结构体的指针 struct cmsghdr { socklen_t cmsg_len; /* data byte count, including header */ int cmsg_level; /* originating protocol */ int cmsg_type; /* protocol- specific type */ /* followed by unsigned char cmsg_data[]; */ }; 6、msg_controllen :参见下图,即cmsghdr 结构体可能不止一个; 7、flags : 一般设置为0即可; 为了对齐,可能存在一些填充字节,跟每个系统的实现有关,但我们不必关心,可以通过一些函数宏来获取相关的值, 如下: #include <sys/socket.h> struct cmsghdr *CMSG_FIRSTHDR(struct msghdr *msgh); struct cmsghdr *CMSG_NXTHDR(struct msghdr *msgh, struct cmsghdr *cmsg); size_t CMSG_ALIGN(size_t length); size_t CMSG_SPACE (size_t length); size_t CMSG_LEN(size_t length); unsigned char *CMSG_DATA(struct cmsghdr *cmsg); 下面通过封装两个函数,send_fd 和 recv_fd 来进一步认识这些函数宏 的作用: void send_fd(int sock_fd, int send_fd) { int ret; struct msghdr msg; struct cmsghdr *p_cmsg; struct iovec vec; char cmsgbuf[CMSG_SPACE(sizeof(send_fd))]; int *p_fds; char sendchar = 0; msg.msg_control = cmsgbuf; msg.msg_controllen = sizeof(cmsgbuf); p_cmsg = CMSG_FIRSTHDR(&msg); p_cmsg->cmsg_level = SOL_SOCKET; p_cmsg->cmsg_type = SCM_RIGHTS; p_cmsg->cmsg_len = CMSG_LEN(sizeof(send_fd)); p_fds = (int *)CMSG_DATA(p_cmsg); *p_fds = send_fd; // 通过传递辅助数据的方式传递文件描述符 msg.msg_name = NULL; msg.msg_namelen = 0; msg.msg_iov = &vec; msg.msg_iovlen = 1; //主要目的不是传递数据,故只传1个字符 msg.msg_flags = 0; vec.iov_base = &sendchar; vec.iov_len = sizeof(sendchar); ret = sendmsg(sock_fd, &msg, 0); if (ret != 1) ERR_EXIT("sendmsg"); } int recv_fd(const int sock_fd) { int ret; struct msghdr msg; char recvchar; struct iovec vec; int recv_fd; char cmsgbuf[CMSG_SPACE(sizeof(recv_fd))]; struct cmsghdr *p_cmsg; int *p_fd; vec.iov_base = &recvchar; vec.iov_len = sizeof(recvchar); msg.msg_name = NULL; msg.msg_namelen = 0; msg.msg_iov = &vec; msg.msg_iovlen = 1; msg.msg_control = cmsgbuf; msg.msg_controllen = sizeof(cmsgbuf); msg.msg_flags = 0; p_fd = (int *)CMSG_DATA(CMSG_FIRSTHDR(&msg)); *p_fd = -1; ret = recvmsg(sock_fd, &msg, 0); if (ret != 1) ERR_EXIT("recvmsg"); p_cmsg = CMSG_FIRSTHDR(&msg); if (p_cmsg == NULL) ERR_EXIT("no passed fd"); p_fd = (int *)CMSG_DATA(p_cmsg); recv_fd = *p_fd; if (recv_fd == -1) ERR_EXIT("no passed fd"); return recv_fd; } (编辑:温州站长网) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |