Re: [Xen-devel] Re: [PATCH] Fix __XEN_INTERFACE_VERSION__ old config breakage

["Magnus Damm" <magnus.damm@xxxxxxxxx>]

On 4/7/06, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:
>
> On 7 Apr 2006, at 08:48, Magnus Damm wrote:
>
> >> Does this lead to a kernel that actually works (e.g., can you sgut it
> >> down without crashing)? I doubt it.
> >
> > I use a kernel config without CONFIG_XEN_INTERFACE_VERSION, and
> > building and running dom0 on x86 (in qemu) seems ok to me.
>
> I tried 'xm save' on such a domU and that doesn't work. The reason is
> that the kernel tree expects to be calling the new sched_op hypercall,
> but because the interface version gets defined to zero, it actually
> calls the old sched_op hypercall which takes different arguments. I
> also tried rebooting such a domU and that doesn't work (the guest is
> killed but not restarted) -- again because the old and new sched_op
> hypercall take their arguments in different ways.

Oh, I see. I did not test _that_ much. Good that you noticed.

> These problems are somewhat hidden I suppose, since you can boot and
> run happily with the domain for the most part, but it illustrates that
> if a guest is defining an obviously interface version we should fail
> the build, not build some inconsistent combination of guest kernel and
> hypervisor interface!

I'm afraid that I know too little about xen to say something about how
multiple interface versions are supposed to work, but I think your
plan of failing instead of building an inconsistent kernel sounds
good.

My main concern was that the code didn't build with my old config
file, and the error message produced by the c-compiler was far from
user friendly. If the kernel build should fail then I would prefer
some see some kind of #error message.

Thanks!

/ magnus

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