Can anyone help me decypher the following code :

int tun_alloc(char *dev)
  {
      struct ifreq ifr;
      int fd, err;
      if( (fd = open("/dev/net/tun", O_RDWR)) < 0 )
         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;
      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;
  }

This is an example code found in TUN/TAP documentation. I need to do some network diagnosing programs and i plan to use Freepascal to do the job.

Opening the TUN/TAP (/dev/net/tun) without the ioctl call is not doing the job, but i dont know how to do this with pascal equivalent code...

Thanks in advance and sorry for any inconvenience...

En/na Jorge Aldo G. de F. Junior ha escrit:

Opening the TUN/TAP (/dev/net/tun) without the ioctl call is not doing the job, but i dont know how to do this with pascal equivalent code...

There's an fpioctl function in freepascal (never used it though):

http://www.freepascal.org/docs-html/rtl/baseunix/fpioctl.html

Bye

i already knew about fpioctl, but the ioctl example uses some macros to get the correct code, but i dont understand how

theres a python equivalent code that works, but i cant decypher this :

(Python code)

TUNSETIFF = 0x400454ca
IFF_TUN = 0x0001
IFF_TAP = 0x0002

TUNMODE = IFF_TUN

f = os.open("/dev/net/tun", os.O_RDWR)
ifs = ioctl(f, TUNSETIFF, struct.pack("16sH", "toto%d", TUNMODE)) ifname = ifs[:16].strip("\x00")

becomes (Pascal Code);
TUNSETIFF := $400454ca;
IFF_TUN := $0001; // TUN is a pseudo-ip device
IFF_TAP := $0002; // TAP is a pseudo-ethernet device
F := TFileStream.Create('/dev/net/tun', fmOpenReadWrite);
IFS := fpioctl(F.Handle, TUNSETIFF, ???);
IFNAME := ????

This makes the handle behave as a virtual network interface (allowing packet injection/reception from userland) and returns the correct interface name so as to allow passing it to scripts, ifconfig etc...

2009/10/3 Jorge Aldo G. de F. Junior :

First, you need to get a pascal definition of struct ifreq, so look in /usr/include/linux/if.h and translate it to pascal (or try and use h2pas).

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

You will have to use fpopen here.

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

Use fillchar.

These flags are defined int /sys/include/linux/if_tun.h.

ifr.ifr_flags = IFF_TUN; if( *dev ) strncpy(ifr.ifr_name, dev, IFNAMSIZ);

ifr_name is defined to be ifr_ifrn.ifrn_name in if.h.

if( (err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0 ){

lol. TUNSETIFF (_IOW('T', 202, int)) is generated by the various macros in /usr/include/asm-generic/ioctl.h. Work it out, or write a c program to give you the number. Then use fpioctl.

The rest should be straight forward.

Henry

ifreq becomes

Const

TUNSETIFF = $400454ca
IFF_TUN = $0001
IFF_TAP = $0002

type
     ifreq = record
          ifr_ifrn : record
              case longint of
                 0 : ( ifrn_name : array[0..15] of char );
              end;
          ifr_ifru : record
              case longint of
                 0 : ( ifru_addr : sockaddr );
                 1 : ( ifru_dstaddr : sockaddr );
                 2 : ( ifru_broadaddr : sockaddr );
                 3 : ( ifru_netmask : sockaddr );
                 4 : ( ifru_hwaddr : sockaddr );
                 5 : ( ifru_flags : smallint );
                 6 : ( ifru_ivalue : longint );
                 7 : ( ifru_mtu : longint );
                 8 : ( ifru_map : ifmap );
                 9 : ( ifru_slave : array[0..15] of char );
                 10 : ( ifru_newname : array[0..15] of char );
                 11 : ( ifru_data : __caddr_t );
              end;
       end;

now i need to translate sockaddr, ifmap, __caddr_t etc

but thanks !

2009/10/5 Henry Vermaak

What is the reason of the first case statement in the record? There is only one variant so you can omit it.

thats h2pas result of compilling this structure into pascal. But thanks for the tip.

2009/10/7 Jürgen Hestermann