Re: [Qemu-devel] QAPI conversion status and async commands support

[Luiz Capitulino]

On Wed, 07 Mar 2012 11:36:06 -0600
Anthony Liguori <address@hidden> wrote:

> On 03/07/2012 11:29 AM, Paolo Bonzini wrote:
> > Il 07/03/2012 17:36, Luiz Capitulino ha scritto:
> >> Hi there,
> >>
> >> In the last few weeks we've had some proposals for new QMP commands that 
> >> need
> >> to be asynchronous. As we lack a standard asynchronous API today, each 
> >> command
> >> ends up adding its own way to execute in the background.
> >>
> >> This multiplies the API complexity as each command has to be implemented 
> >> and
> >> learned by clients separately, with their own way of doing more or less the
> >> same things.
> >>
> >> The solution for this, envisioned for us for a long time now, is to 
> >> introduce
> >> an unified QMP API for asynchronous commands.
> >>
> >> But before doing this we have to:
> >>
> >>    1. Finish the commands conversion to the QAPI
> >>
> >>       This is almost done, the only missing commands are: 
> >> add_graphics_client,
> >>       do_closefd, do_device_add, do_device_del, do_getfd, do_migrate,
> >>       do_netdev_add, do_netdev_del, do_qmp_capabilities and do_screen_dump.
> >>
> >>       Note that do_migrate has already been posted to the list, and I have
> >>       the screendump more or less done. Also, Anthony has an old branch 
> >> where most
> >>       of the conversions are already done, they just need to be rebased&  
> >> tested.
> >>
> >>    2. Integrate the new QAPI server
> >>
> >>       Implemented by Anthony, may have missing pieces.
> >>
> >>    3. Implement async command support
> >>
> >>
> >> I think the missing commands to be converted can be done in around one 
> >> week,
> >> but unfortunately I've been busy at other things and will need a few days 
> >> to
> >> resume this work. Then there's the new QAPI server&  async support, which 
> >> I'm
> >> not sure how much time we'll need to integrate them, but we should have 
> >> this
> >> done for 1.1.
> >>
> >> The main question is: what should we do for the already posted async 
> >> commands?
> >> Should we hold them until we finish this work?
> >
> > I think yes, and we could even have a list of features without which 1.1
> > should not ship.  QOM buses, drive mirroring and QAPI async command
> > support may be them.  Perhaps qtest too.
> 
> Okay, let's get serious about what we can and can't do.
> 
> Hard freeze for 1.1 is May 1st which is roughly 6 weeks from now.
> 
> I think QOM buses can go in no problem along with qtest.  I would be okay 
> considering QOM buses a release blocker but probably not qtest.
> 
> I'm not really sure about drive mirroring.  Is the work already done such 
> that 
> we just need to talk about merging it?
> 
> With QAPI async command, I don't think 1.1 is a viable target.  We're not 
> just 
> talking about converting existing commands to QAPI, but also replacing the 
> QMP 
> server infrastructure.  I don't think that is a change that should be made at 
> the tail end of the development cycle.

I will have to agree with this, specially because I think the new server is
going to generate some fun discussions because iirc it has some novel
concepts. And those discussions burn a lot of time.

On top of that we also have the async API to design. I have some ideas in mind,
but again, design & review cycles take some time.

Having said that, I wonder if postponing want-to-be-async commands to 1.2 is
a good thing. Two solutions other than waiting:

 1. Add synchronous versions of them, if possible (I think this is possible
    for the dump command)

 2. Accept the ad-hoc async mechanism they introduce

Btw, probably needless to say but, I'd greatly appreciate and encourage anyone 
who
wants to join this effort and work on the conversions, new QMP server, etc...