[libvirt] virtio network problems with kvm guests with 2.6.26 kernel

[Mark McLoughlin]

On Tue, 2009-09-29 at 15:20 -0400, Jim Paris wrote:

> Nevermind that, my conclusions were bogus.  Things still didn't quite add
> up, so I tracked down what's really going on here:
> 
> - Libvirt 0.7.1 (as packaged by Debian) has IFF_VNET_HDR support.
> - Qemu-kvm 0.11.0 (as built by myself) did NOT include IFF_VNET_HDR
>   support, because it was built against the older headers on my
>   system.
> 
> Libvirt assumes that if it can support IFF_VNET_HDR, and qemu is new
> enough, then qemu must support IFF_VNET_HDR too.  This assumption was
> wrong in my case, but it seems there's no easy way for libvirt to 
> figure out the correct thing to do.
> 
> Anyway, after updating the linux-libc-dev package and rebuilding 
> qemu-kvm, things work now.

Yeah, that makes some sense - we have no way of knowing whether qemu was
compiled with IFF_VNET_HDR support, all we can do is check that that
version of qemu would have support if compiled against headers with
IFF_VNET_HDR.

Thanks,
Mark.