recv_peek偷窥函数和UNIX域间文件描述符传递sendmsg、recvmsg

/**
 * recv_peek - 仅仅查看套接字缓冲区数据，但不移除数据
 * @sockfd: 套接字
 * @buf: 接收缓冲区
 * @len: 长度
 * 成功返回>=0，失败返回-1
 */
ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
while (1)
{
int ret = recv(sockfd, buf, len, MSG_PEEK);
if (ret == -1 && errno == EINTR)
continue;
return ret;
}

}

//往sock_fd发送fd描述符
void send_fd(int sock_fd, int fd)
{
int ret;
struct msghdr msg;
struct cmsghdr *p_cmsg;
struct iovec vec;
char cmsgbuf[CMSG_SPACE(sizeof(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(fd));
p_fds = (int*)CMSG_DATA(p_cmsg);
*p_fds = fd;


msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = &vec;
msg.msg_iovlen = 1;
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");
}


//从sock_fd接收fd描述符
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;
}