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

[Kevin Wolf]

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 of external interfaces so named may be withdrawn or changed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.

Kevin