Re: [Discuss-gnuradio] Re: tun/tap OS X for tunneling

[Mark Kuhr]

I've got a small update on this.

To read the tap devices on OS X, just issue the os.open command.

self.tap_fd = os.open("/dev/tap0", os.O_RDWR)

Once this open is completed, you can setup the interface with  
ifconfig.  Spawning this off into a subprocess with popen works well  
inside the script.

To write to the tap device, just use os.write(self.tap_fd,DATA)

The ioctl command is challenging since it is implemented differently  
as previously discussed.  The request constant (second argument) used  
by the osxtuntap kernel extensions are different from Linux.  Two  
request constants are used and defined as follows:

#define TUNSIFHEAD _IOW('t', 96, int)
#define TUNGIFHEAD _IOR('t', 97, int)

Translated they become the following:

TUNSIFHEAD = 2147775584
TUNGIFHEAD = 1074033761

So, in tunnel.py, you can modify the ioctl command to be as follows on  
os x and it should not crash.

ifs = ioctl(tun, TUNSIFHEAD, struct.pack("16sH", "gr%d", mode))

I think it is possible to create a cross-platform abstraction of this  
functionality that manages the differences between the OSs.  Maybe a  
tun/tap module that is part of gnuradio, however the reliance on  
external pieces such as the os x tun tap kernel extensions could be  
problematic.  Might want to roll that into the code base as well to  
maintain some control of the versioning.



On Jan 6, 2009, at 12:00 PM, Eric Blossom wrote:

> On Tue, Jan 06, 2009 at 09:52:14AM -0800, Johnathan Corgan wrote:
> > On Tue, Jan 6, 2009 at 8:59 AM, Ed Criscuolo
> > <address@hidden> wrote:
> >
> > > There also seems to be a fundamental difference between the
> > > way the TUN/TAP driver works on the two OS's.
> >
> > Ah, then it's not so easy.  It would be very useful to GNU Radio to
> > have a cross-platform implementation of this functionality, written  
> > in
> > C++, that abstracts the differences and presents a simple
> > write/callback API.  I've written a TAP/TUN mblock that has the right
> > C++ guts that could be extracted and reused, but it would still have
> > the same problem on OS X.
> >
> > -Johnathan
>
> IIRC there was a discussion about an OS neutral wrapper for tap/tun
> several months back.   I don't remember any solution being found,
> proposed or built.
>
> Eric
>
>
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