[Qemu-devel] Re: [PATCH 0/4] qemu: TAP filtering support

[Alex Williamson <alex.williamson@hp.com>]

On Wed, 2009-02-11 at 20:19 +0000, Mark McLoughlin wrote:
> On Wed, 2009-02-11 at 12:51 -0700, Alex Williamson wrote:
> > >   - What do we need rxfilter=on|off on the command line for?
> > 
> > Primarily because the current tun driver in Linux has a bug that it can
> > drop unicast packets requested to be included in the filter if it
> > overflows the exact match table.
> > 
> > http://www.spinics.net/lists/netdev/msg88451.html
> 
> Oh dear. Does this suggest we should make rxfilter=off the default?
> 
> Is there any way we can automatically detect we're running on a broken
> kernel?

TUNSETTXFITLER has only existed since 2.6.26, so the ioctl will fail on
anything older and it will be disabled anyway.  The patch will fix .29
and should get rolled into .28 stable, so we're looking at an exposure
of 2 kernel releases.  Unfortunately a few community distros went out on
those kernels, so perhaps the prudent approach would be to make the
default disabled until we're a few releases beyond.  I don't know any
way you could detect it outside of ugly parsing of uname -r.  Thanks,

Alex