Re: [PATCH 1/9] qapi: New special feature flag "unstable"

[Dr. David Alan Gilbert]

* Kevin Wolf (kwolf@redhat.com) wrote:
> Am 25.10.2021 um 07:25 hat Markus Armbruster geschrieben:
> > By convention, names starting with "x-" are experimental.  The parts
> > of external interfaces so named may be withdrawn or changed
> > incompatibly in future releases.
> > 
> > Drawback: promoting something from experimental to stable involves a
> > name change.  Client code needs to be updated.
> > 
> > Moreover, the convention is not universally observed:
> > 
> > * QOM type "input-barrier" has properties "x-origin", "y-origin".
> >   Looks accidental, but it's ABI since 4.2.
> > 
> > * QOM types "memory-backend-file", "memory-backend-memfd",
> >   "memory-backend-ram", and "memory-backend-epc" have a property
> >   "x-use-canonical-path-for-ramblock-id" that is documented to be
> >   stable despite its name.
> > 
> > We could document these exceptions, but documentation helps only
> > humans.  We want to recognize "unstable" in code, like "deprecated".
> > 
> > Replace the convention by a new special feature flag "unstable".  It
> > will be recognized by the QAPI generator, like the existing feature
> > flag "deprecated", and unlike regular feature flags.
> > 
> > This commit updates documentation and prepares tests.  The next commit
> > updates the QAPI schema.  The remaining patches update the QAPI
> > generator and wire up -compat policy checking.
> > 
> > Signed-off-by: Markus Armbruster <armbru@redhat.com>
> 
> Obviously, replacing the old convention gets rid of the old drawbacks,
> but adds a new one: While using x- makes it very obvious for a human
> user that this is an unstable feature, a feature flag in the schema will
> almost certainly go unnoticed in manual use.

Agreed, I'd keep the x- as well.

Having said that, the x- represents a few different things (that we
don't currently distinguish):
  - experimental
  - for internal use
  - for debugging/human use

Dave

> Kevin
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK