Re: [Qemu-devel] [RFC PATCH qemu] qmp: Add qom-list-properties to list QOM object properties

[David Gibson]

On Tue, Jan 23, 2018 at 11:08:31AM +0100, Andrea Bolognani wrote:
> On Fri, 2018-01-19 at 15:34 +0100, Andrea Bolognani wrote:
> > > > This won't solve the libvirt problem we were discussing, because it
> > > > needs an existing instance of the object.  libvirt wants to know the
> > > > machine properties *without* instantiating an instance.
> > > 
> > > My patch works with types, it creates an instance for a short time itself,
> > > this is why it does not do a thing for "pseries" as it is not a type and
> > > prints properties for the "pseries-2.12-machine" type.
> > 
> > Yeah, I took this for a spin and can confirm that it's pretty much
> > exactly what I was thinking about. The fact that the QMP command
> > instantiates objects behind the scenes is not an issue, at least
> > from libvirt's point of view: device-list-properties does the same
> > thing and we already use it quite happily; what matters is that we
> > can call this, along with all the other capabilities-collecting
> > QMP commands, in one go and on a single QEMU instance.
> 
> David, I know you're busy with linux.conf.au, but it would be
> really helpful if you could carve out five minutes to look over
> Alexey's proposal again, with my reply above in mind, and let us
> know whether it looks a reasonable design. Doesn't have to be a
> review, just a quick feedback on the high-level idea.

It looks ok, I think, but I don't think I'm really the right person to
ask.  I do wonder if creating a throwaway instance could cause
trouble, especially for something like machine that might well have
gotten away with having global side-effects in the past.  I think we
need to talk with someone who knows more about qom and qapi - Markus
seems the obvious choice.

> I'm moving forward with the libvirt implementation of pSeries
> capabilities and I would have to start implementing support for
> this new QMP command, well, pretty much... Right now :) But I'd
> rather not start at all if I'm just going to have to scrap
> everything later.

Yeah, unfortunately because its part of the core infrastructure, not
power specific, this isn't something I can make call on.

-- 
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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