#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <linux/if_tun.h>
#include <linux/sched.h>

int main(int argc, char **argv)
{
	struct ifreq ifr;
	pid_t pid, ppid = getpid();
	int fd;

	fd = open("/dev/net/tun", O_RDWR);
	if (fd < 0) {
		perror("open tun");
		exit(1);
	}

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

	ifr.ifr_flags = (IFF_TUN | IFF_NO_PI);
	if (ioctl(fd, TUNSETIFF, &ifr) < 0) {
		perror("TUNSETIFF");
		exit(1);
	}

	pid = fork();
	if (pid < 0) {
		perror("fork");
		exit(1);
	}
	if (!pid) {
		char *cmd;
		close(fd);
		if (unshare(CLONE_NEWNET) < 0) {
			perror("unshare");
			exit(1);
		}
		/* Wait for the tun device to be given to us... */
		sleep(2);
		
		fd = open("/dev/net/tun", O_RDWR);
		if (fd < 0) {
			perror("open tun");
			exit(1);
		}
		memset(&ifr, 0, sizeof(ifr));

		ifr.ifr_flags = (IFF_TUN | IFF_NO_PI);
		if (ioctl(fd, TUNSETIFF, &ifr) < 0) {
			perror("TUNSETIFF");
			exit(1);
		}
		printf("Open %s in child\n", ifr.ifr_name);

		if (asprintf(&cmd, "/sbin/ip link set %s netns %d",
			     ifr.ifr_name, ppid) < 0) {
			perror("asprintf");
			exit(1);
		}
		printf("%s\n", cmd);
		if (system(cmd)) {
			perror("give tun to parent");
			exit(1);
		}
		sleep(1);
		printf("child bye\n");
		exit(0);
	} else {
		/* Wait for the unshare() */
		char *cmd;

		if (asprintf(&cmd, "/sbin/ip link set %s netns %d",
			     ifr.ifr_name, pid) < 0) {
			perror("asprintf");
			exit(1);
		}
		sleep(1);
		printf("%s\n", cmd);
		if (system(cmd)) {
			perror("give tun to child");
			exit(1);
		}
		free(cmd);
		sleep(1);

		/* Yeah, too lazy to pass the real name back */
		printf("del tun1\n");
		sleep(1);
		system("/sbin/ip link del tun1");
		close(fd);
	}
	return 0;
}