Re: [Qemu-devel] [RFC v5 0/2] virtio: introduce `info virtio' hmp command

[Jan Dakinevich <jan.dakinevich@virtuozzo.com>]

On Thu, 14 Dec 2017 12:05:19 +0100
Cornelia Huck <cohuck@redhat.com> wrote:

> On Tue, 12 Dec 2017 16:54:50 +0300
> Jan Dakinevich <jan.dakinevich@virtuozzo.com> wrote:
> 
> > I am going to reanimate works under this QMP/HMP. First of all, it
> > could be meaningful to settle what output would provide the QMP. I
> > would like to suggest the following description:
> > 
> > ##
> > # @VirtioFeature:
> > ##
> > {
> >     'struct': 'VirtioFeature',
> >     'data': {
> >         'name': 'str',
> >         'acked': 'bool'
> >     }
> > }
> > 
> > ##
> > # @VirtioInfo:
> > ##
> > {
> >     'struct': 'VirtioInfo',
> >     'data': {
> >         'qom-path': 'str',
> >         
> >         'status': 'uint8',
> >         'host-features': 'uint64',
> >         'guest-features': 'uint64',
> > 
> >         'status-names': ['str'],
> >         'common-features-names': ['VirtioFeature'],
> >         'device-features-names': ['VirtioFeature']
> >     }
> > }
> > 
> > ##
> > # @query-virtio:
> > ##
> > {
> >     'command': 'query-virtio',
> >     'data': {'*path': 'str'},
> >     'returns': ['VirtioInfo']
> > }
> > 
> > My final goal is to implement HMP which will print all exposed
> > virtio features (both common and device-specific) with their
> > acknowledgements, and virtio device configuration status. These are
> > provided by last 3 fields in @VirtioInfo.
> > 
> > For these who are going make own decision on features and status
> > bitmask, respective fields with raw values are preserved.
> 
> Looks sensible. What will you return an for the *-features-names
> fields if the status field indicates that negotiation is not yet done?
> (This has some fun interaction with the VERSION_1 feature bit...)
> 

Hmm... I was going to return current features and theirs
acknowledgments regardless if they were negotiated. Thus,
*-features-names would contain all exposed host features with `false'
in `acked' field.

> > 
> > So, I expect following data on the wire in response to
> > `query-virtio' command:
> > 
> > {
> >     "return": [
> >         {
> >             "qom-path":
> > "/machine/peripheral-anon/device[0]/virtio-backend", "status": 15,
> > "host-features": 6325010438, "guest-features": 5100273670,
> >             "status-names": [
> >                 "acknowledge", 
> >                 "driver", 
> >                 "driver-ok", 
> >                 "features-ok"
> >             ],
> >             "common-features-names": [
> >                 {"name": "notify-on-empty", "acked": false},
> >                 {"name": "any-layout", "acked": false},
> >                 {"name": "indirect-desc", "acked": true},
> >                 {"name": "event-idx", "acked": true},
> >                 {"name": "bad-feature", "acked": false},
> >                 {"name": "version-1", "acked": true}
> >             ],
> >             "device-features-names": [
> >                 {"name": "hotplug", "acked": true},
> >                 {"name": "change", "acked": true}
> 
> I suggest to use the #defines as names, especially as they are also
> used in the spec. Makes grepping easier.
> 

You mean, for example "VIRTIO_RING_F_EVENT_IDX" instead of "event-idx"
should be used. Right?

> >             ]
> >         }
> >     ]
> > }
> > 
> > 
> > Eric Blake, returning to your question which would probably appear
> > again after this mail:
> > 
> > >> +##
> > >> +# @query-virtio:
> > >> ...
> > >> +##
> > >> +{
> > >> +    'command': 'query-virtio',
> > >> +    'data': { '*path': 'str' },    
> > >
> > > Do we need filterable queries, or is it better to just have the
> > > command return info on all virtio devices at once and let the
> > > client filter the results as desired?  
> > 
> > I think it would be better to do here. I suppose, the client which
> > uses HMP will not be happy on filtering monitor output.
> 
> I think being able to optionally specify a path is the most flexible
> solution.



-- 
Best regards
Jan Dakinevich