Re: [Qemu-devel] per-machine vs per-qemu-version compat_props macros (was Re: acpi:ich9: add memory hotplug handling)

[Marcel Apfelbaum]

On Tue, 2014-06-24 at 14:55 -0300, Eduardo Habkost wrote:
> On Tue, Jun 24, 2014 at 05:47:53PM +0100, Peter Maydell wrote:
> > On 24 June 2014 17:44, Eduardo Habkost <address@hidden> wrote:
> > > (I would go even further and say that no compat_props bit need to be
> > > specific to a machine-type family, and they are simply tied to the code
> > > included in a QEMU version. So every PC_COMPAT_* bit could go to a
> > > common QEMU_COMPAT_<version> macro, that could be reusable by all
> > > machine-types, and there's no need PC-specific compat macros.)
> > 
> > What if different machines in a particular release had the
> > property set to different defaults?
> 
> I never saw that happen, and I don't think it is even likely: default
> values set in instance_init, and compat_props are applied just after
> instance_init, before object_new() returns. So a machine-type would need
> to find a way to change fields after instance_init but before
> compat_props are applied.
> 
> Anyway, if a machine-type really needs that, it can still have its own
> set of compat macros to implement machine-type-specific compat_props. My
> point is that there's no need for that on the PC code today.
> 
+1

As discussed in today's KVM call, compat props per version is the best
approach.

Thanks,
Marcel