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

[Kashyap Chamarthy]

On Mon, Oct 25, 2021 at 07:25:24AM +0200, Markus Armbruster wrote:
> 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 of external interfaces so named may be withdrawn or changed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.

Looks like there's another stable property with an "x-" prefix:
"x-remote-object", part of QOM type @RemoteObjectProperties.

Given the above "x-" properties are now stable, I take it that they
cannot be renamed now, as they might break any tools using them?  My
guess is the tedious way is not worth it: deprecate them, and add the
non-x variants as "synonyms".  
 
> 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.

FWIW, sounds good to me.

> 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>
> ---
>  docs/devel/qapi-code-gen.rst            | 9 ++++++---
>  tests/qapi-schema/qapi-schema-test.json | 7 +++++--
>  tests/qapi-schema/qapi-schema-test.out  | 5 +++++
>  3 files changed, 16 insertions(+), 5 deletions(-)

[...]

-- 
/kashyap