Re: [Qemu-devel] [PATCH v1 00/23] QAPI Infrastructure Round 1

[Luiz Capitulino]

On Wed, 18 May 2011 09:43:37 -0500
Michael Roth <address@hidden> wrote:

> On 05/18/2011 08:46 AM, Luiz Capitulino wrote:
> > On Tue, 17 May 2011 19:51:47 -0500
> > Michael Roth<address@hidden>  wrote:
> >
> >> These apply on top of master, and can also be obtained from:
> >> git://repo.or.cz/qemu/mdroth.git qapi_round1_v1
> >
> > Nice to see this moving forward.
> >
> >> These patches are a backport of some of the QAPI-related work from 
> >> Anthony's
> >> glib tree. The main goal is to get the basic code generation 
> >> infrastructure in
> >> place so that it can be used by the guest agent to implement a QMP-like 
> >> guest
> >> interface, and so that future work regarding the QMP conversion to QAPI 
> >> can be
> >> decoupled from the infrastructure bits.
> >>
> >> Round1 incorporates the following components from Anthony's tree:
> >>
> >>   - Pulls in GLib libraries (core GLib, GThreads, and GIO)
> >>
> >>   - Adds code to do exception-like error propagation
> >>
> >>   - New error reporting functions
> >>
> >>   - Schema-based code generation for QAPI types and synchronous QMP 
> >> commands
> >>     using visiter patterns to cut reduce the amount of code generated by 
> >> the
> >>     previous scripts. This is just infrastructure, QMP will remain 
> >> untouched
> >>     until the actual conversion efforts are underway. Only a set of unit 
> >> tests
> >>     and, in the guest, virtagent, will utilize this infrastructure 
> >> initially.
> >
> > This series introduces quite a lot of infrastructure w/o adding a single 
> > real
> > user. This has some disadvantages, the most important one being that we 
> > can't
> > test it for real (unit-tests are important, but don't replace real usage).
> > Another disadvantage is that, reviewers don't actually see how this is 
> > going to
> > be used and can't comment on API level improvements/bugs.
> 
> The guest agent user will mirror the QMP user pretty closely, but I 
> could see why it'd be nice to have an actual QMP user as part of the 
> series. I think we decided on IRC that an incremental QMP conversion 
> wouldn't be the best route and should instead be done as part of a 
> single concerted effort. So one approach I would propose is to have 
> example conversions tacked on to the end of this series.

Yes, that would be good.

> So for this series we'd have 1 or 2 example conversions for synchronous 
> QMP functions. Future infrastructure patches could provide examples for 
> async QMP/proxied QMP/QMP event/qcfg/etc users as the relevant 
> infrastructure bits are added.

I think the examples have to use all the added infrastructure. For example,
if you're not adding async commands, then we'd have to drop the async support
from the series.

I'm tempted to say that we should try to reduce the code generator (and all
the infrastructure around it) to generated only the bits that are going to be
used by the examples. But I'm not sure if the work involved is worth it.

> So long as the example conversions capture the general use cases, we'd 
> still be able to decouple conversion efforts from infrastructure (with 
> any corner cases fixed as a part of those efforts), while allowing the 
> infrastructure code to be reviewed in the proper context.

Yes.

> > I prefer an incremental approach. We could try to split this series in 
> > smaller
> > parts and change current QMP to use that parts. This will make review easier
> > and will make it possible to do incremental testing too.
> >
> 
> I could split the code conversion stuff out into a separate series. So 
> we'd have:

Looks good to me.

> Round 1: error-related changes

I'm already taking care of this one. I hope to have patches soon. The problem
here is that I'm very serious about testing and am going to test each
converted handler. Unfortunately, most of the testing is done by hand today :(
but kvm-autotest has some support for testing error paths and libvirt has a
more general suite too.

> Round 2: json-related changes

I think I saw patches flying on the list, did you submit then? Do they
depend on the error stuff?

> Round 3: code conversion infra + examples
> 
> If we take the approach mentioned above, anyway.
> 
> Otherwise I don't see how we could decouple any QMP conversion efforts 
> from infrastructure (which I think was considered desirable). In terms 
> of the code generation it's basically all or nothing, with the exception 
> of the unit tests we've added. Did you have something else in mind?

Your plan looks good to me. I mean, maybe it' me who's is still catching up
with all that stuff and want it to go slower so that I can fully absorb it
and try to make sure it won't break anything before it's merged.

On the other hand, we might want to discuss errors separately for example,
as it's not specified to QMP.