Re: [Qemu-devel] [Qemu-ppc] [QEMU-PPC] [PATCH V3 0/6] target/ppc: Rework spapr_caps

[Andrea Bolognani <abologna@redhat.com>]

On Wed, 2018-01-17 at 00:54 +1100, David Gibson wrote:
> > Correct me if I'm wrong, but it seems to me like there's no way
> > to figure out through QMP whether these new machine options can be
> > used for a given QEMU binary.
> 
> Uh, I don't think so.  These are machine options like any other (just
> constructed a bit differently).  So they'll appear in qemu -machine
> pseries,? and I believe that info can also be retrieved with QMP.

Yes, they will indeed show up in the output of -machine pseries,?
but there's AFAICT no way to retrieve them via QMP. And libvirt
can't afford to spawn a QEMU process for each machine type
implemented by each QEMU binary installed on the system just to
figure out what properties they support; in fact, we've been
pushing away from that approach - which was used initially - for
years and we're now at the point where we only fall back to it
for positively ancient QEMU versions. So the information needs
to be available through QMP for libvirt to consume it.

-- 
Andrea Bolognani / Red Hat / Virtualization