Re: [Qemu-devel] [PATCH 3/3] qmp: add architecture specific cpu data for query-cpus-fast

[Luiz Capitulino <lcapitulino@redhat.com>]

On Tue, 13 Feb 2018 13:30:02 +0100
Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com> wrote:

> On 12.02.2018 19:15, Luiz Capitulino wrote:
> > On Mon, 12 Feb 2018 13:14:32 +0100
> > Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com> wrote:
> >   
> >> -{ 'struct': 'CpuInfoFast',
> >> -  'data': {'cpu-index': 'int', 'qom-path': 'str',
> >> -           'thread-id': 'int', '*props': 'CpuInstanceProperties' } }
> >> +{ 'union': 'CpuInfoFast',
> >> +  'base': {'cpu-index': 'int', 'qom-path': 'str',
> >> +           'thread-id': 'int', '*props': 'CpuInstanceProperties',
> >> +           'arch': 'CpuInfoArch' },
> >> +  'discriminator': 'arch',
> >> +  'data': { 'x86': 'CpuInfoOther',
> >> +            'sparc': 'CpuInfoOther',
> >> +            'ppc': 'CpuInfoOther',
> >> +            'mips': 'CpuInfoOther',
> >> +            'tricore': 'CpuInfoOther',
> >> +            's390': 'CpuInfoS390Fast',
> >> +            'other': 'CpuInfoOther' } }  
> > 
> > Consider this a minor comment (and QMP maintainers can give a much
> > better advice than me), but I think this arch list has problems. For
> > one thing, it's incomplete. And the second problem is the 'other'
> > field. What happens when QEMU starts supporting a new arch? 'other'
> > becomes the new arch. Is this compatible? I don't know.  
> This seems to be the customary approach, see
> https://lists.gnu.org/archive/html/qemu-devel/2018-02/msg01986.html
> > 
> > I don't know if this would work with the QAPI, but you could have
> > a '*arch-data' field in the CpuInfoFast definition, like:
> > 
> > 'data': { ..., '*arch-data': 'CpuInfoFastArchData' }
> > 
> > where 'CpuInfoFastArchData' is defined by each arch that supports
> > the field. An arch supporting the field could also export a
> > query_cpus_fast_arch() function, which is called by qmp_query_cpus_fast().
> >   
> I had it like this in my first reply to your initial patch. However,
> that adds an additional hierarchy level in the return data. This
> prevents clients like libvirt to reuse the data extraction code when
> they switch over to using query-cpus-fast.

OK, fair enough.