Re: [Qemu-devel] vhost_net.c broken by --kerneldir

[Michael S. Tsirkin]

On Thu, Aug 26, 2010 at 05:15:35PM +0200, Arnd Bergmann wrote:
> On Wednesday 25 August 2010, Hollis Blanchard wrote:
> > > We only recently fixed the kernel to have this warning in types.h, which
> > > triggers more often than kernel.h, where it used to be before. In 2.6.35
> > > and before, you consequently would not have noticed the problem.
> > >    
> > 
> > Thanks Arnd, that explains it.
> > 
> > It looks like the --kerneldir option needs to be re-thought.
> 
> Yes. I believe that we should just kill that option, since there is
> no reason for building with set of headers from a different kernel
> than the one your glibc normally uses.

As others pointed out, it's very useful for development.
I would suggest we do what qemu-kvm.git does instead, and
keep a copy of some headers in qemu tree.
This way developer just copies the header into qemu tree,
and we can get rid of a bunch of ifdefs in code.

> You obviously need copies of some headers to match qemu code, e.g.
> the kvm headers, but for those we have run-time compatibility code
> in qemu. Building with a newer kernel header is pointless because
> qemu would not use any of the features that were added after the
> release of the qemu tree you are trying to build. Building with
> an older kernel header is equally pointless because all it would
> do is to require #ifdef magic in qemu that ends up preventing you
> from using all features of new kernels.
> 
>       Arnd