#include <linux/netlink.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>

#define MAX_PAYLOAD 1024
#define NETLINK_USER 31

/* Some of these structs fields must be zeroed.
 * We could brute force memset them, but
 * TODO determine exactly which, and move into main. */
int sock_fd;
struct iovec iov;
struct msghdr msg;
struct nlmsghdr *nlh;
struct sockaddr_nl src_addr, dest_addr;

int main()
{
	sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_USER);
	if (sock_fd < 0) {
		perror("socket");
		return EXIT_FAILURE;
	}
	src_addr.nl_family = AF_NETLINK;
	src_addr.nl_pid = getpid();
	bind(sock_fd, (struct sockaddr *)&src_addr, sizeof(src_addr));
	dest_addr.nl_family = AF_NETLINK;
	nlh = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_PAYLOAD));
	memset(nlh, 0, NLMSG_SPACE(MAX_PAYLOAD));
	nlh->nlmsg_len = NLMSG_SPACE(MAX_PAYLOAD);
	nlh->nlmsg_pid = getpid();
	nlh->nlmsg_flags = 0;
	strcpy(NLMSG_DATA(nlh), "user request");
	iov.iov_base = (void *)nlh;
	iov.iov_len = nlh->nlmsg_len;
	msg.msg_name = (void *)&dest_addr;
	msg.msg_namelen = sizeof(dest_addr);
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
	printf("before sendmsg\n");
	sendmsg(sock_fd, &msg, 0);
	printf("after sendmsg\n");
	recvmsg(sock_fd, &msg, 0);
	printf("userland received: %s\n", (char *)NLMSG_DATA(nlh));
	close(sock_fd);
}