Re: [Qemu-devel] [PATCH 7/9] qmp: Add runnability information to query-cpu-definitions

[Eduardo Habkost]

On Mon, May 09, 2016 at 10:54:53AM +0200, David Hildenbrand wrote:
> > Extend query-cpu-definitions schema to allow it to return two new
> > optional fields: "runnable" and "unavailable-features".
> > "runnable" will tell if the CPU model can be run in the current
> > host. "unavailable-features" will contain a list of CPU
> > properties that are preventing the CPU model from running in the
> > current host.
> > 
> > Cc: David Hildenbrand <address@hidden>
> > Cc: Michael Mueller <address@hidden>
> > Cc: Christian Borntraeger <address@hidden>
> > Cc: Cornelia Huck <address@hidden>
> > Cc: Jiri Denemark <address@hidden>
> > Cc: address@hidden
> > Signed-off-by: Eduardo Habkost <address@hidden>
> > ---
> >  qapi-schema.json | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/qapi-schema.json b/qapi-schema.json
> > index 54634c4..450e6e7 100644
> > --- a/qapi-schema.json
> > +++ b/qapi-schema.json
> > @@ -2948,11 +2948,19 @@
> >  # Virtual CPU definition.
> >  #
> >  # @name: the name of the CPU definition
> > +# @runnable: true if the CPU model is runnable using the current
> > +#            machine and accelerator. Optional. Since 2.6.
> > +# @unavailable-features: List of properties that prevent the CPU
> > +#                        model from running in the current host,
> > +#                        if @runnable is false. Optional.
> > +#                        Since 2.6.
> 
> Just FYI, on other architectures (e.g. s390x), other conditions (e.g. cpu
> generation) also define if a CPU model is runnable, so the pure availability 
> of
> features does not mean that a cpu model is runnable.
> 
> We could have runnable=false and unavailable-features being an empty list.

Even on those cases, can't the root cause be mapped to a QOM
property name (e.g. "cpu-generation"), even if it's property that
can't be changed by the user?

We could replace this with something more generic, like:

@runnability-blockers: List of attributes that prevent the CPU
  model from running in the current host.
  
  A list of QOM property names that represent CPU model
  attributes that prevent the CPU from running. If the QOM
  property is read-only, that means the CPU model can never run
  in the current host. If the property is read-write, it means
  that it MAY be possible to run the CPU model in the current
  host if that property is changed.
  
  Management software can use it as hints to suggest or choose an
  alternative for the user, or just to generate meaningful error
  messages explaining why the CPU model can't be used.

(I am looking for a better name than "runnability-blockers").

-- 
Eduardo