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Re: tap interface address

On Mon, 11 Aug 2008, Quentin Garnier wrote:

> On Mon, Aug 11, 2008 at 02:23:50PM +0100, Iain Hibbert wrote:
> > Hi,
> >
> > Am trying to open a tap(4) device and get the interface address, but
> > SIOCGIFADDR does not work (though it seems that it should, looking at the
> > if_tap.c code and ether_ioctl()) No error is produced but nothing is
> I... doubt that.  tap_dev_ioctl() returns ENOTTY (as it should).  I'll
> try though, there might be a bug.

Mm, maybe you are right, but the program shows no error (is ENOTTY
rewritten to something else in the dev code?)

> > and I worked out how to change the physical address using SIOCSIFPHYADDR
> That won't work either if you do it on the fd returned by /dev/tap.

Sorry - yes, was using a socket (BTPROTO_L2CAP) for that.

If I try the SIOCGIFADDR through that socket I do get ENOTTY.

Interestingly, using socket(PF_INET, SOCK_STREAM, 0) gives EADDRNOTAVAIL
as does (PF_INET, SOCK_DGRAM, 0) but (PF_INET, SOCK_SEQPACKET, 0) is

I thought that the 'i' ioctls were diverted to the network stack?

I wonder if I need to prepare the sockaddr somehow?

> Iain, the way one is supposed to manipulate an interface is through a
> socket.  So you have to open a socket first (AF_INET is fine to do the
> SIOCSIFPHYADDR call, and you can use it later to set an ipv4 address on
> the interface and so on), and then do the ioctl calls on it.

dhclient will handle all that stuff. I just want to get the address

> I don't think I should blindly let ioctls go to tap_ioctl from the
> character device, but I guess I could at least allow my kludgy
> SIOCSIFPHYADDR.  Though usually if you're playing with a tap interface
> you'll need a socket at some point.

Well, you need the fd for the IO in any case..


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