Re: [Qemu-devel] [Qemu-ppc] [QEMU-PPC] [PATCH V3 0/6] target/ppc: Rework spapr_caps

[David Gibson]

On Wed, Jan 17, 2018 at 09:54:57AM +0100, Andrea Bolognani wrote:
> On Wed, 2018-01-17 at 10:26 +1100, Alexey Kardashevskiy wrote:
> > On 17/01/18 09:34, David Gibson wrote:
> > > On Tue, Jan 16, 2018 at 03:46:20PM +0100, Andrea Bolognani wrote:
> > > > On Wed, 2018-01-17 at 00:54 +1100, David Gibson wrote:
> > > > > > Correct me if I'm wrong, but it seems to me like there's no way
> > > > > > to figure out through QMP whether these new machine options can be
> > > > > > used for a given QEMU binary.
> > > > > 
> > > > > Uh, I don't think so.  These are machine options like any other (just
> > > > > constructed a bit differently).  So they'll appear in qemu -machine
> > > > > pseries,? and I believe that info can also be retrieved with QMP.
> > > > 
> > > > Yes, they will indeed show up in the output of -machine pseries,?
> > > > but there's AFAICT no way to retrieve them via QMP.
> > > 
> > > Really!?  I thought introspecting object properties was QMP's bread
> > > and butter.
> > 
> > On a guest started with '-S':
> > {"execute": "qom-list", "arguments": {"path": "/machine"}}
> > 
> > returns:
> > {   'return': [   {'name': 'graphics', 'type': 'bool'},
> [...]
> >                   {'name': 'cap-dfp', 'type': 'bool'},
> >                   {'name': 'cap-htm', 'type': 'bool'},
> >                   {'name': 'cap-vsx', 'type': 'bool'},
> >                   {'name': 'vfio-no-msix-emulation', 'type': 'bool'},
> >                   {'name': 'kvm-type', 'type': 'string'},
> >                   {'name': 'max-cpu-compat', 'type': 'string'},
> [...]
> >                   {'name': 'resize-hpt', 'type': 'string'}]}
> > 
> > but still requires a running qemu, yes.
> 
> That's not a problem in itself; however, AFAICT the guest in
> question also needs to be started with -machine pseries in order
> for the above to work, which means it's not usable due to the
> scalability issues mentioned earlier in the thread. We run QEMU
> with -machine none, a single time, to probe for capabilities.
> 
> I looked further and device-list-properties looks like it would
> do the trick; however it doesn't seem to work for machines:
> 
>   {"execute": "device-list-properties",
>    "arguments": {"typename": "spapr-2.11-machine"}}
>   {"error": {"class": "GenericError",
>              "desc": "Parameter 'typename' expects device"}}
> 
> It works fine for the likes of virtio-scsi-pci and even
> power9_v2.0-powerpc64-cpu, though. Any ideas? :)

I'm guessing it's because machines aren't descended from TYPE_DEVICE.

Dammit.  I really can't see a reasonable way of addressing this other
than improving qapi in general to have a way of reporting machine
class properties.  Adding something ad-hoc for just these properties
of this machine seems like madness.

Nor can I think of a place to put these that would be both sensible
and more discoverable with existing mechanisms.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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