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

[Jamie Lokier <jamie@shareable.org>]

Alex Williamson wrote:
> 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,

I would parse uname -r - it's not hard, Linux versions have always
matched %d.%d.%d, and map in a standard way to a 32-bit integer for
easy comparisons.

A few QEMU releases later, someone will run the new version on a
2.6.26 to 2.6.28 host.

It's quite usual in my experience to run a QEMU that's much newer than
the corresponding host kernel, because upgrading host is a big deal
(if you only have one or two) due to being heavily used, whereas
upgrading QEMU/KVM is much easier as you can do it one VM guest at a time.

-- Jamie