Re: [PATCH 04/14] qapi: add a 'command-features' pragma

[Markus Armbruster]

Daniel P. Berrangé <berrange@redhat.com> writes:

> On Fri, Jul 12, 2024 at 10:07:34AM +0200, Markus Armbruster wrote:
>> Daniel P. Berrangé <berrange@redhat.com> writes:
>> 
>> > The 'command-features' pragma allows for defining additional
>> > special features that are unique to a particular QAPI schema
>> > instance and its implementation.
>> 
>> So far, we have special features (predefined, known to the generator and
>> treated specially), and normal features (user-defined, not known to the
>> generator).  You create a new kind in between: user-defined, not known
>> to the generator, yet treated specially (I guess?).  Hmm.
>> 
>> Could you at least hint at indented use here?  What special treatment do
>> you have in mind?
>
> Essentially, these features are a way to attach metadata to commands that
> the server side impl can later query. This eliminates the need to hardcode
> lists of commands, such as in QGA which hardcodes a list of commands which
> are safe to use when filesystems are frozen. This is illustrated later in
> this series.

Please update docs/devel/qapi-code-gen.rst section "Pragma directives",
and maybe section "Features".

I'm not sure conflating the new kind of feature with existing special
features is a good idea.  I need to review more of the series before I
can make up my mind.