Re: [Qemu-devel] [PATCH v4 7/8] qmp: Support abstract classes on device-list-properties

[Jiri Denemark <jdenemar@redhat.com>]

On Tue, Nov 08, 2016 at 08:29:41 +0100, Markus Armbruster wrote:
> Eduardo Habkost <ehabkost@redhat.com> writes:
> > libvirt wants to know if the QEMU binary supports a given -cpu
> > option (normally CPU features that can be enabled/disabled using
> > "+foo"/"-foo").
> 
> The obvious way to check whether a specific CPU supports it is to
> introspect that CPU.
> 
> The obvious way to check whether all CPUs of interest support it
> (assuming that is a productive question) is to introspect all CPUs of
> interest.  Works regardless of whether the option is inherited, which is
> really an implementation detail.

As Eduardo said, libvirt wants to know whether it can use a given CPU
feature with current QEMU binary. In -cpu help, we can see a list of
models and features QEMU understands, but we need to get similar info
via QMP. CPU models are easy, but how do we get the list of CPU
features? If introspection is the way to get it, I'm fine with that,
just beware that we don't actually know the name of the CPU object
(Westmere-x86_64-cpu), we only know the name of the CPU model
(Westmere). So if the object name is needed, we need to query the
mapping from CPU model names to CPU object names.

Jirka