How to open utun device in OS X

open_utun.c

#include <netinet/in.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/kern_control.h>
#include <net/if_utun.h>
#include <sys/ioctl.h>
#include <sys/kern_event.h>

int open_utun(int num) {
	int err;
	int fd;
	struct sockaddr_ctl addr;
	struct ctl_info info;

	fd = socket(PF_SYSTEM, SOCK_DGRAM, SYSPROTO_CONTROL);
	if (fd < 0) {
		return fd;
	}
	memset(&info, 0, sizeof (info));
	strncpy(info.ctl_name, UTUN_CONTROL_NAME, strlen(UTUN_CONTROL_NAME));
	err = ioctl(fd, CTLIOCGINFO, &info);
	if (err < 0) {
		close(fd);
		return err;
	}

	addr.sc_id = info.ctl_id;
	addr.sc_len = sizeof(addr);
	addr.sc_family = AF_SYSTEM;
	addr.ss_sysaddr = AF_SYS_CONTROL;
	addr.sc_unit = num + 1; // utunX where X is sc.sc_unit -1

	err = connect(fd, (struct sockaddr*)&addr, sizeof(addr));
	if (err < 0) {
		// this utun is in use
		close(fd);
		return err;
	}

	return fd;
}

int main(void) {
	int fd;
	for (int num = 0; num < 255; ++num) {
		fd = open_utun();
		if (fd >= 0) {
			break;
		}
	}
	// hava fun
}