add missing tun/tap utility routines

src/tuntap.c

@@ -0,0 +1,42 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+#include <sys/socket.h>
+#include <sys/ioctl.h>
+
+#include <linux/if_tun.h>
+#include <linux/if.h>
+
+int tun_alloc(char *dev)
+  {
+      struct ifreq ifr;
+      int fd, err;
+
+      fd = open("/dev/net/tun", O_RDWR);
+	if (fd < 0)
+		return fd;
+        // return tun_alloc_old(dev);
+
+      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|IFF_NO_PI; 
+      if( *dev )
+         strncpy(ifr.ifr_name, dev, IFNAMSIZ);
+
+      if( (err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0 ){
+         close(fd);
+         return err;
+      }
+#if 0
+      strcpy(dev, ifr.ifr_name);
+#endif
+      return fd;
+  }