Re: [PATCH v15 09/11] machine: adding s390 topology to query-cpu-fast

[Daniel P . Berrangé]

On Mon, Feb 06, 2023 at 01:41:44PM +0100, Thomas Huth wrote:
> On 01/02/2023 14.20, Pierre Morel wrote:
> > S390x provides two more topology containers above the sockets,
> > books and drawers.
> > 
> > Let's add these CPU attributes to the QAPI command query-cpu-fast.
> > 
> > Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> > ---
> >   qapi/machine.json          | 13 ++++++++++---
> >   hw/core/machine-qmp-cmds.c |  2 ++
> >   2 files changed, 12 insertions(+), 3 deletions(-)
> > 
> > diff --git a/qapi/machine.json b/qapi/machine.json
> > index 3036117059..e36c39e258 100644
> > --- a/qapi/machine.json
> > +++ b/qapi/machine.json
> > @@ -53,11 +53,18 @@
> >   #
> >   # Additional information about a virtual S390 CPU
> >   #
> > -# @cpu-state: the virtual CPU's state
> > +# @cpu-state: the virtual CPU's state (since 2.12)
> > +# @dedicated: the virtual CPU's dedication (since 8.0)
> > +# @polarity: the virtual CPU's polarity (since 8.0)
> >   #
> >   # Since: 2.12
> >   ##
> > -{ 'struct': 'CpuInfoS390', 'data': { 'cpu-state': 'CpuS390State' } }
> > +{ 'struct': 'CpuInfoS390',
> > +    'data': { 'cpu-state': 'CpuS390State',
> > +              'dedicated': 'bool',
> > +              'polarity': 'int'
> 
> I think it would also be better to mark the new fields as optional and only
> return them if the guest has the topology enabled, to avoid confusing
> clients that were written before this change.

FWIW, I would say that the general expectation of QMP clients is that
they must *always* expect new fields to appear in dicts that are
returned in QMP replies. We add new fields at will on a frequent basis.

So personally I'd keep life simple and unconditionally report the new
fields.

With regards,
Daniel
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