tuntest.c

/* 
 * Based on example code at https://www.kernel.org/doc/Documentation/networking/tuntap.txt
 *
 * Simple program to create a tun device, then wait forever. No external dependencies, except libc.
 * 
 * Compiling: gcc tuntest.c -o tuntest
 */

#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <linux/if.h>
#include <linux/if_tun.h>

int tun_alloc(char *dev)
{
    struct ifreq ifr;
    int fd, err;

    if( (fd = open("/dev/net/tun", O_RDWR)) < 0 )
        return 0;

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

    /* Flags: IFF_TUN   - TUN device (no Ethernet headers)
     *        IFF_TAP   - TAP device
     *
     *        IFF_NO_PI - Do not provide packet information
     */
    ifr.ifr_flags = IFF_TUN;
    if( *dev )
        strncpy(ifr.ifr_name, dev, IFNAMSIZ);

    if( (err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0 ){
        close(fd);
        return err;
    }
    strcpy(dev, ifr.ifr_name);
    return fd;
}

int main(int argc, char** argv) {
    int fd;
    char* dev = strdup("tuntest");
    fd = tun_alloc(dev);
    while(1) sleep(1000);
}