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



> 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 <dahi linux vnet ibm com>
> > > Cc: Michael Mueller <mimu linux vnet ibm com>
> > > Cc: Christian Borntraeger <borntraeger de ibm com>
> > > Cc: Cornelia Huck <cornelia huck de ibm com>
> > > Cc: Jiri Denemark <jdenemar redhat com>
> > > Cc: libvir-list redhat com
> > > Signed-off-by: Eduardo Habkost <ehabkost redhat com>
> > > ---
> > >  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?

In the current state, no.

So I think for runnable=false:
a) unavailable-features set -> can be made runnable
b) unavailable-features not set -> cannot be made runnable

would be enough.

> 
> 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").
> 



David


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