Re: [PATCH 1/1] net: fix vnet_hdr bustage with slirp

[Mark McLoughlin <markmc@redhat.com>]

On Fri, 2009-08-07 at 13:51 +0200, Arnd Bergmann wrote:
> On Friday 07 August 2009, Mark McLoughlin wrote:
> > slirp has started using VLANClientState::opaque and this has caused the
> > kvm specific tap_has_vnet_hdr() hack to break because we blindly use
> > this opaque pointer even if it is not a tap client.
> > 
> > Add yet another hack to check that we're actually getting called with a
> > tap client.
> > 
> > [Needed on stable-0.11 too]
> > 
> > Signed-off-by: Mark McLoughlin <markmc@redhat.com>
> 
> Jens and I discovered the same bug before, but then we forgot about
> sending a fix (sorry). Your patch should work fine as a workaround,
> but I wonder if it is the right solution. 
> 
> The abstraction of struct VLANClientState is otherwise done through
> function pointers taking the VLANClientState pointer as their
> first argument. IMHO a cleaner abstraction would be to do the same
> for tap_has_vnet_hdr(), like the patch below, and similar for
> other functions passing 'opaque' pointers.

Indeed, but using vc->vlan->first_client is a great big hole in the
abstraction as it is.

The vnet_hdr code in qemu-kvm.git is a hack which we plan to
(eventually) replace by allowing a nic to be paired directly with a
backend.

Your patch is fine, but I'd suggest since both are a hack we stick with
mine since it'll reduce merge conflicts. Both hacks will go away
eventually, anyway.

Thanks,
Mark.