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Problem with ioctl(fd, TUNSETIFF, ...)

DISCUSSION Eric Brower 1 participant 1 message Jan 30, 2004

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Eric Brower

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The definition of TUNSETIF is:

   #define TUNSETIFF     _IOW('T', 202, int)

indicating the argument is an "int" rather than a "struct ifreq*". This
trickery (as I understand it) would work on 32-bit systems, but not
64-bit.

The .../arch/sparc64/kernel/ioctl32.c translation for this ioctl is "COMPATIBLE_IOCTL" which would be correct if an int was really expected, but is not correct when a struct ifreq* is passed. There are already translations in ioctl32.c to deal with an argument of type struct ifreq*, so you might wish to take a look at them and change the COMPATIBLE_IOCTL entry to an appropriate HANDLE_IOCTL entry. Take a look at dev_ifsioc() for starters.

I've cc'd the ultralinux list, which is more appropriate for this matter.

E

Quoted 62 lines · Erwann Abalea

Hello,

I wanted to install OpenVPN on my firewall machine (an Ultra1 running 2.4.18), but unfortunately, I failed.

I managed to track the failing code, and tried to find equivalent known-to-be-good code (found in the Linux Kernel documentation, in networking/tuntap.txt).

The following code fails:
-----
int tun_alloc(char *dev)
{
struct ifreq ifr;
int fd, err;

  if ((fd = open("/dev/net/tun", O_RDWR)) < 0)
  {
    perror("Unable to open /dev/net/tun");
    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_TUN;

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

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

  {
    close(fd);
    perror("ioctl(fd, TUNSETIFF, ...) error");
    return err;

}
strcpy(dev, ifr.ifr_name);
return fd;
}
-----

I tested this in a small program (just add a main() asking for an argument, and call the tun_alloc() with the given argument). It fails on 2 ultrasparc machines (an U1 and an U2 running the same kernel version, the U1 also has the IPVS patch applied), and works on a standard PC also running the 2.4.18 kernel. Tun/Tap support is compiled in (if it wasn't, the failure would have been at the open() call).

What I get is:
-----
Opening tun0
ioctl(fd, TUNSETIFF, ...) error: : Invalid argument
-----

I also get something in my syslog.log file:

Jan 30 15:15:39 herisson kernel: sys32_ioctl(tun:4329): Unknown cmd fd(3) cmd(800454ca) arg(effffc70)

What am I doing wrong?