Re: [Qemu-devel] [Xen-devel] [PATCH RFC v2 4/4] xen/MSI: re-expose masking capability

[Stefano Stabellini]

On Mon, 14 Dec 2015, Jan Beulich wrote:
> >>> On 11.12.15 at 17:56, <address@hidden> wrote:
> > On Fri, 2015-12-11 at 16:44 +0000, Stefano Stabellini wrote:
> >>  
> >> It is not possible to do this at runtime. I think we should do this at
> >> compile time because in any case it is not supported to run a QEMU built
> >> for a given Xen version on a different Xen version.
> > 
> > I am currently working pretty hard to make this possible in the future, it
> > would be a shame to add another reason it wasn't possible at this stage.
> 
> And I don't think it's not possible - if anything, the infrastructure to
> do so is just missing. I'm definitely not going to make this a build time
> check, since I deem it very wrong namely when considering
> --with-system-qemu (as in that case there shouldn't be any
> dependency on the precise Xen tools versions in use - using plural
> intentionally here to point out the possibility of multiple ones being
> present).

Compile time checks are indeed suboptimal, but so are runtime checks:
what if we backport the fix to more Xen releases? What if we revert the
fix on the Xen tree for any reason?

I think that a feature flag is the best course of action.