On Tue, Oct 26, 2021 at 05:15:10PM +0200, Markus Armbruster wrote: > Daniel P. Berrangé <berrange@xxxxxxxxxx> writes: > > > On Tue, Oct 26, 2021 at 11:37:19AM +0200, Markus Armbruster wrote: > >> Kevin Wolf <kwolf@xxxxxxxxxx> writes: > >> > >> > 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 of external interfaces so named may be withdrawn or changed 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@xxxxxxxxxx> > >> > > >> > 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. > >> > >> I thought about this, but neglected to put it in writing. My bad. > >> > >> Manual use of unstable interfaces is mostly fine. Human users can adapt > >> to changing interfaces. HMP works that way. > >> > >> Management applications are better off with a feature flag than with a > >> naming convention we sometimes ignore. > > > > We will sometimes ignore/forget the feature flag too though, so I'm > > not convinced there's much difference there. > > -compat unstable-input=reject,unstable-output=hide should help you stay > on the straight & narrow :) That's from the pov of the mgmt app. I meant from the POV of QEMU maintainers forgetting to add "unstable" flag, just as they might forget to add a "x-" prefix. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
