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

[Daniel P . Berrangé]

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.

> 
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >  scripts/qapi/parser.py | 2 ++
> >  scripts/qapi/source.py | 2 ++
> >  2 files changed, 4 insertions(+)
> >
> > diff --git a/scripts/qapi/parser.py b/scripts/qapi/parser.py
> > index 7b13a583ac..36a9046243 100644
> > --- a/scripts/qapi/parser.py
> > +++ b/scripts/qapi/parser.py
> > @@ -243,6 +243,8 @@ def check_list_str(name: str, value: object) -> 
> > List[str]:
> >              pragma.documentation_exceptions = check_list_str(name, value)
> >          elif name == 'member-name-exceptions':
> >              pragma.member_name_exceptions = check_list_str(name, value)
> > +        elif name == 'command-features':
> > +            pragma.command_features = check_list_str(name, value)
> >          else:
> >              raise QAPISemError(info, "unknown pragma '%s'" % name)
> >  
> > diff --git a/scripts/qapi/source.py b/scripts/qapi/source.py
> > index 7b379fdc92..07c2958ac4 100644
> > --- a/scripts/qapi/source.py
> > +++ b/scripts/qapi/source.py
> > @@ -28,6 +28,8 @@ def __init__(self) -> None:
> >          self.documentation_exceptions: List[str] = []
> >          # Types whose member names may violate case conventions
> >          self.member_name_exceptions: List[str] = []
> > +        # Arbitrary extra features recorded against commands
> > +        self.command_features: List[str] = []
> >  
> >  
> >  class QAPISourceInfo:
> 

With regards,
Daniel
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