Linux套接字发送和接收整数数组

Question

我试图通过linux套接字使用c++传递整数数组(文件描述符)。

我使用cmgs(3)和seccomp_unotify(2)编写了以下发送和接收函数:

发送:

static bool send_fds(int socket)  // send array of fds by socket
{
int myfds[] = {568, 519, 562, 572, 569 ,566}; //static values for testing
struct msghdr msg = { 0 };
struct cmsghdr *cmsg;
char iobuf[1];
struct iovec io = {
.iov_base = iobuf,
.iov_len = sizeof(iobuf)
};
union {
char buf[CMSG_SPACE(sizeof(myfds))];
struct cmsghdr align;
} u;
msg.msg_iov = &io;
msg.msg_iovlen = 1;
msg.msg_control = u.buf;
msg.msg_controllen = sizeof(u.buf);

cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN(sizeof(myfds));
memcpy(CMSG_DATA(cmsg), &myfds, sizeof(myfds));
if (sendmsg (socket, &msg, 0) < 0)
{
return false;
}
return true;
}

收到:

static int * read_fds(int sockfd)
{
struct msghdr msgh;
struct iovec iov;
int data[6], fd[6];
ssize_t nr;
union {
char   buf[CMSG_SPACE(sizeof(fd))];
struct cmsghdr align;
} controlMsg;
struct cmsghdr *cmsgp;
msgh.msg_name = NULL;
msgh.msg_namelen = 0;
msgh.msg_iov = &iov;
msgh.msg_iovlen = 1;
iov.iov_base = &data;
iov.iov_len = sizeof(fd);
msgh.msg_control = controlMsg.buf;
msgh.msg_controllen = sizeof(controlMsg.buf);
recvmsg(sockfd, &msgh, 0);
cmsgp = CMSG_FIRSTHDR(&msgh);
memcpy(&fd, CMSG_DATA(cmsgp), sizeof(int)*6);
return fd;
}

无论我发送什么，接收函数中的数组都被[8,9,10,11,12,13]填充。

我做错了什么?

Answer 1

From Cloudflare blog:

技术上你不发送"文件描述符"。您在代码中处理的"文件描述符"只是进程的本地文件描述符表的索引，该表依次指向操作系统的打开文件表，最终指向表示文件的vnode。因此，其他进程观察到的"文件描述符"很可能具有不同的数值，尽管指向相同的文件。