#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/time.h>
#include <sys/types.h>

#include <netinet/if_ether.h>
#include <linux/if.h>
#include <linux/if_tun.h>

#define max(a,b) ((a)>(b) ? (a):(b))

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

      if( (fd = open("/dev/net/tun", O_RDWR)) < 0 )
         return -1;

      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_TAP | IFF_NO_PI;
      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[])
{
   char dev1[7], dev2[7], buf[1600];
   int f1,f2,l,fm;
   fd_set fds;
 
   strcpy(dev1,"tap%d");
   strcpy(dev2,"tap%d");
   if (((f1 = tun_alloc(dev1)) < 0) || ((f2 = tun_alloc(dev2)) < 0)) {
     printf("Cannot allocate TAP device\n");
     exit(1);
   }
   printf("Allocated devices: %s and %s\n", dev1, dev2);

   fm = max(f1, f2) + 1;
/*
   ioctl(f1, TUNSETNOCSUM, 1); 
   ioctl(f2, TUNSETNOCSUM, 1); 
*/
   while(1){
	FD_ZERO(&fds);
        FD_SET(f1, &fds);
        FD_SET(f2, &fds);

	select(fm, &fds, NULL, NULL, NULL);

	if( FD_ISSET(f1, &fds) ) {
	   l = read(f1,buf,sizeof(buf));
	   printf("Got %i bytes from %s\n", l, dev1);
           write(f2,buf,l);
	}
	if( FD_ISSET(f2, &fds) ) {
	   l = read(f2,buf,sizeof(buf));
	   printf("Got %i bytes from %s\n", l, dev2);
           write(f1,buf,l);
	}
   }
}