[libvirt] [RFC 00/28] s390x CPU models: exposing features

[Eduardo Habkost]

On Tue, Jun 21, 2016 at 11:09:49PM +0200, Jiri Denemark wrote:
[...]
> > 1) "query-cpu-model-expansion model=host" vs "query-host-cpu":
> > 
> > I still don't think we want to set in stone that "the result the
> > guest sees when using -cpu host" is always the same as "what the
> > host supports running".
> > 
> > For example: let's assume a given architecture have two features
> > (A and B) that are both supported by the host but can never be
> > enabled together. For actual "-cpu host" usage, QEMU would have
> > to choose between enabling A and B. For querying host
> > capabilities, we still want to let management software know that
> > either A or B are supported.
> 
> What libvirt is really interested in is the guest CPU which would be
> used with -cpu host. This is actually what I thought query-host-cpu was
> all about. Perhaps because there's no difference for x86.

In that case, I think it makes sense to just extend
query-cpu-definitions or use "query-cpu-model-expansion
model=host" instead of a query-host-cpu command.

Probably query-cpu-model-expansion is better than just extending
query-cpu-definitions, because it would allow the expansion of
extra CPU options, like "host,migratable=off".

-- 
Eduardo