fd_puller.c

#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/fcntl.h>
#include <sys/un.h>
#include <stdbool.h>
#include <stdio.h>
#include <errno.h>
#include <stdint.h>
#include <unistd.h>

struct cmsgbuf
{
    struct cmsghdr hdr;
    int fd;
};

static bool push_handle(int socket, int fd)
{
    char empty = '!';
    struct iovec nothing = {
        .iov_base = &empty,
        .iov_len = 1,
    };

    struct cmsgbuf msgbuf;
    struct msghdr msg = {
        .msg_name = NULL,
        .msg_namelen = 0,
        .msg_iov = &nothing,
        .msg_iovlen = 1,
        .msg_flags = 0,
        .msg_control = &msgbuf,
        .msg_controllen = CMSG_LEN(sizeof(int)),
    };

    struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
    cmsg->cmsg_len = msg.msg_controllen;
    cmsg->cmsg_level = SOL_SOCKET;
    cmsg->cmsg_type = SCM_RIGHTS;
    int *dfd = (int*)CMSG_DATA(cmsg);
    *dfd = fd;

    fprintf(stderr, "Sending FD %d\n", fd);
    int ret = sendmsg(socket, &msg, MSG_DONTWAIT | MSG_NOSIGNAL);
    return ret > 0;
}

int main(int argc, char *argv[])
{
    if (argc != 2)
        return 1;

    fprintf(stderr, "Running test ...\n");

    int ret = 0;
    int fd = open(argv[1], O_RDWR);
    if (fd < 0)
        return 1;

    push_handle(0, fd);
    close(fd);
    return ret;
}