* Markus Armbruster (arm...@redhat.com) wrote: > "Dr. David Alan Gilbert" <d...@treblig.org> writes: > > > * Markus Armbruster (arm...@redhat.com) wrote: > >> Philippe Mathieu-Daudé <phi...@linaro.org> writes: > >> > >> > Hi Daniel, Dave, Markus & Thomas. > >> > > >> > On 4/6/24 06:58, Markus Armbruster wrote: > >> >> "Dr. David Alan Gilbert" <d...@treblig.org> writes: > >> >>> * Daniel P. Berrangé (berra...@redhat.com) wrote: > >> >>>> On Fri, May 31, 2024 at 06:47:45AM +0200, Thomas Huth wrote: > >> >>>>> On 30/05/2024 09.45, Philippe Mathieu-Daudé wrote: > >> >>>>>> We are trying to unify all qemu-system-FOO to a single binary. > >> >>>>>> In order to do that we need to remove QAPI target specific code. > >> >>>>>> > >> >>>>>> @dump-skeys is only available on qemu-system-s390x. This series > >> >>>>>> rename it as @dump-s390-skey, making it available on other > >> >>>>>> binaries. We take care of backward compatibility via deprecation. > >> >>>>>> > >> >>>>>> Philippe Mathieu-Daudé (4): > >> >>>>>> hw/s390x: Introduce the @dump-s390-skeys QMP command > >> >>>>>> hw/s390x: Introduce the 'dump_s390_skeys' HMP command > >> >>>>>> hw/s390x: Deprecate the HMP 'dump_skeys' command > >> >>>>>> hw/s390x: Deprecate the QMP @dump-skeys command > >> >>>>> > >> >>>>> Why do we have to rename the command? Just for the sake of it? I > >> >>>>> think > >> >>>>> renaming HMP commands is maybe ok, but breaking the API in QMP is > >> >>>>> something > >> >>>>> you should consider twice. > >> > > >> > I'm looking at how to include this command in the new "single binary". > >> > > >> > Markus explained in an earlier series, just expanding this command as > >> > stub to targets that don't implement it is not backward compatible and > >> > breaks QMP introspection. Currently on s390x we get a result, on other > >> > targets the command doesn't exist. If we add a stubs, then other targets > >> > return something (even if it is an empty list), confusing management > >> > interface. > >> > >> Loss of introspection precision is a concern, not a hard "no". > >> > >> We weigh all the concerns, and pick a solution we hate the least :) > >> > >> > So this approach use to deprecate process to include a new command > >> > which behaves differently on non-s390x targets. > >> > > >> > If we don't care for this particular case, better. However I'd still > >> > like to discuss this approach for other target-specific commands. > >> > > >> >> PRO rename: the command's tie to S390 is them immediately obvious, which > >> >> may be useful when the command becomes available in qemu-systems capable > >> >> of running other targets. > >> >> > >> >> CON rename: users need to adapt. > >> >> > >> >> What are the users? Not libvirt, as far as I can tell. > >> > > >> > Years ago we said, "all HMP must be based on QMP". > >> > >> In practice, it's closer to "HMP must be base on QMP when the > >> functionality does or should exist in QMP." > >> > >> > Now we realize HMP > >> > became stable because QMP-exposed, although not consumed externally... > >> > >> I'm afraid I didn't get this part. > >> > >> > Does the concept of "internal QMP commands" makes sense for HMP debug > >> > ones? (Looking at a way to not expose them). We could use the "x-" > >> > prefix to not care about stable / backward compat, but what is the point > >> > of exposing to QMP commands that will never be accessed there? > >> > > >> >>>> That was going to be my question too. Seems like its possible to > >> >>>> simply > >> >>>> stub out the existing command for other targets. > >> >> > >> >> That's going to happen whether we rename the commands or not. > >> >> > >> >>> Are these commands really supposed to be stable, or are they just debug > >> >>> commands? If they are debug, then add the x- and don't worry too much. > >> > > >> > OK. > >> > > >> >> docs/devel/qapi-code-gen.rst: > >> >> > >> >> Names beginning with ``x-`` used to signify "experimental". This > >> >> convention has been replaced by special feature "unstable". > >> >> > >> >> Feature "unstable" is what makes something unstable, and is what > >> >> machines should check. > >> > > >> > What I mentioned earlier could be 'Feature "internal" or "debug"'. > >> > >> What's the difference to "unstable"? > > > > It should be clear *why* something is marked x- - something that's > > marked 'x-' because the feature is still in development is expected to shake > > out at some point, and the interface designed so it can. > > (and at some point the developer should get a prod to be asked whethere the > > x- can be removed). > > That's different from it permenantly being x- because it's expected to > > change as the needs of the people debugging change. > > When you add special feature 'unstable', the tooling insists you cover > it in the doc comment. Review should then ensure the doc comment > explains why it is unstable. Examples: > > # @unstable: Member @x-perf is experimental. > > # @unstable: This command is meant for debugging.
OK, that makes some sense. Dave > > Dave > > > >> >> An "x-" prefix may still be useful for humans. Machines should *not* > >> >> key on the prefix. It's unreliable anyway: InputBarrierProperties > >> >> member @x-origin is stable despite it's name. Renames to gain or lose > >> >> the prefix may or may not be worth the bother. > >> > > >> > Could follow the rules and be renamed as "origin-coordinate-x". > >> > >> I don't think it's worth the trouble. The "x-" prefix is now strictly > >> for humans, and humans can figure out what the x- in @x-origin, > >> @y-origin means. > >> > >> [...] > >> > -- -----Open up your eyes, open up your mind, open up your code ------- / Dr. David Alan Gilbert | Running GNU/Linux | Happy \ \ dave @ treblig.org | | In Hex / \ _________________________|_____ http://www.treblig.org |_______/
