Re: [PATCH v3 22/30] qom: Factor out user_creatable_process_cmdline()

[Kevin Wolf]

Am 13.03.2021 um 09:41 hat Markus Armbruster geschrieben:
> Observation, not objection:
> 
> 1. QMP core parses JSON text into QObject, passes to generated
>    marshaller.
> 
> 2. Marshaller converts QObject to ObjectOptions with the QObject input
>    visitor, passes to qmp_object_add().
> 
> 3. qmp_object_add() wraps around user_creatable_add_qapi().
> 
> 4. user_creatable_add_qapi() converts right back to QObject with the
>    QObject output visitor.  It splits the result into qom_type, id and
>    the rest, and passes all three to user_creatable_add_type().
> 
> 5. user_creatable_add_type() performs a virtual visit with the QObject
>    input visitor.  The outermost object it visits itself, its children
>    it visits by calling object_property_set().
> 
> I sure hope we wouldn't write it this way from scratch :)
> 
> I think your patch is a reasonable step towards a QOM that is at peace
> with QAPI.  But there's plenty of work left.

Yes, obviously the conversion back to QObject is not great. There are
two reasons why we currently need it:

1. user_creatable_add_type() wants to iterate over all properties
   without knowing which properties exist. This should be fixed by not
   visiting the top level in user_creatable_add_type(), but moving this
   part to object-specific code (in the final state probably code
   generated from the QAPI schema).

2. We have ObjectOptions, but need to pass a visitor. We don't have a
   general purpose visitor that visits both sides. The clone visitor
   seems somewhat similar to what we need, but I seem to remember it was
   more restricted to its particular use case.

Kevin