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Re: Fixing tap(4) behaviour

On Sat, Nov 29, 2008 at 03:55:49PM -0500, Arnaud Lacombe wrote:
> On Sat, Nov 29, 2008 at 3:21 PM, Quentin Garnier <> 
> wrote:
> > On Sat, Nov 29, 2008 at 03:05:46PM -0500, Arnaud Lacombe wrote:
> >> Hi Folks,
> >>
> >> People currently using qemu(1) need to use a dirty static fd-based
> >> trick to link the created interface to qemu(1). This is due to the
> >> fact that 1) qemu doesn't check the return value of the stat(2)
> >> syscall and 2) our tap(4) cloner device provide nothing to know the
> >> created interface's unit. I fixed this by making the cloner device
> >
> > That's not true.  You should have read tap(4)'s manual page.
> true, my bad.
> > Besides,
> > I have always told people how qemu was supposed to do that, and I think
> > that someone had actually made a patch for qemu at some point but I
> > guess it was lost.
> >
> Only FreeBSD and us have implemented TAPGIFNAME.

I don't know what others do.  When I did tap(4), Linux, FreeBSD and
OpenBSD already had three very different interfaces.

> Beside that, this do not solve the problem of the behavior of the
> stat(2) syscall on a cloner device.

Right.  I was pointing out that the premise for the work was incorrect,
which doesn't mean the work itself isn't useful.  One thing to note,
though, is that it is a bad idea to derive the name of the interface
from the unit number, because we might want to make it possible to
change interface names in the future, which means the network interface
name and the device name might differ.  Which is why TAPGIFNAME takes an
ifreq, which is something you can actually feed to a socket ioctl

Now, if your git stuff could provide an easy way to get a diff...  But I
might have missed something in your initial mail.

Quentin Garnier - -
"See the look on my face from staying too long in one place
[...] every time the morning breaks I know I'm closer to falling"
KT Tunstall, Saving My Face, Drastic Fantastic, 2007.

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