/*

 * Utility to send fds via Unix domain socket

 *

 * Copyright 2011, 2018 Yuya Nishihara <yuya@tcha.org>

 *

 * This software may be used and distributed according to the terms of the

 * GNU General Public License version 2 or any later version.

 */

#include <errno.h>

#include <stdlib.h>

#include <string.h>

#include <sys/socket.h>

#include <sys/types.h>

#define MAX_FD_LEN 10

/*

 * Sends the given fds with 1-byte dummy payload.

 *

 * Returns the number of bytes sent on success, -1 on error and errno is set

 * appropriately.

 */

ssize_t sendfds(int sockfd, const int *fds, size_t fdlen)

{

	char dummy[1] = {0};

	struct iovec iov = {dummy, sizeof(dummy)};

	char fdbuf[CMSG_SPACE(sizeof(fds[0]) * MAX_FD_LEN)];

	struct msghdr msgh;

	struct cmsghdr *cmsg;

	/* just use a fixed-size buffer since we'll never send tons of fds */

	if (fdlen > MAX_FD_LEN) {

		errno = EINVAL;

		return -1;

	}

	memset(&msgh, 0, sizeof(msgh));

	msgh.msg_iov = &iov;

	msgh.msg_iovlen = 1;

	msgh.msg_control = fdbuf;

	msgh.msg_controllen = CMSG_SPACE(sizeof(fds[0]) * fdlen);

	cmsg = CMSG_FIRSTHDR(&msgh);

	cmsg->cmsg_level = SOL_SOCKET;

	cmsg->cmsg_type = SCM_RIGHTS;

	cmsg->cmsg_len = CMSG_LEN(sizeof(fds[0]) * fdlen);

	memcpy(CMSG_DATA(cmsg), fds, sizeof(fds[0]) * fdlen);

	msgh.msg_controllen = cmsg->cmsg_len;

	return sendmsg(sockfd, &msgh, 0);

}