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Mon, 30 Nov 2020 10:21:08 +0100 (CET) From: Markus Armbruster To: Peter Krempa Subject: Re: [PATCH for-6.0 6/6] qapi: Deprecate 'query-kvm' References: <20201116131011.26607-1-r.bolshakov@yadro.com> <20201116131011.26607-7-r.bolshakov@yadro.com> <20201127105059.GC1596141@redhat.com> <20201127112154.GA105758@angien.pipo.sk> <20201127114512.GE67322@SPB-NB-133.local> <20201127121809.GB105758@angien.pipo.sk> <87h7paoldm.fsf@dusky.pond.sub.org> <20201127163013.GD105758@angien.pipo.sk> Date: Mon, 30 Nov 2020 10:21:08 +0100 In-Reply-To: <20201127163013.GD105758@angien.pipo.sk> (Peter Krempa's message of "Fri, 27 Nov 2020 17:30:13 +0100") Message-ID: <87zh2zi4jf.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.496, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: libvir-list@redhat.com, Peter Maydell , Roman Bolshakov , Habkost , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Peter Krempa writes: > On Fri, Nov 27, 2020 at 16:44:05 +0100, Markus Armbruster wrote: >> Peter Krempa writes: >> >> > On Fri, Nov 27, 2020 at 14:45:12 +0300, Roman Bolshakov wrote: >> >> On Fri, Nov 27, 2020 at 12:21:54PM +0100, Peter Krempa wrote: > > [...] > >> > As you can see this has an issue when we have to add support for a >> > unreleased interface, which may change during the dev cycle or plainly >> > forget that something got deprecated as we've already added an override. >> > >> > This mainly comes from libvirt trying to keep on top of the changes so >> > we refresh the QMP schema during qemu's dev cycle multiple times. >> > >> > Obviously the argument that we try to depend on unreleased functionality >> > can be used, but that would be to detrement of progress IMO. >> >> I understand your concerns. >> >> We have a somewhat similar problem in QEMU: there's nothing to remind us >> later on that the old interface still needs to be deprecated. > > Oh, yes. That's basically the same thing. > > The thing is that changes to the new interface are very rare, but very > real. Since I don't really want to increase the burden for any normal > scenario. > > I'd also very much like to keep libvirt pulling in snapshots of qemu's > capabilities/qapi schema etc throughout the development cycle. It allows > us to adapt faster and develop features simultaneously. > > This unfortunately undermines my own arguments partially as libvirt > regularly develops features on top of unreleased qemu features so we are > regularly risking very similar circumstances. The small but important > difference though is, that releasing a broken feature is not as bad as > breaking an existing feature. > > As a conclusion of the above I'd basically prefer a sort of gentleman's > agreement, that new APIs become 'somewhat' stable at the moment the > commit deprecating the old interface hits upstream. > > The 'somewhat'-stable API would mean that any changes to the new API > should be consulted with libvirt so that we can either give a go-ahead > that we didn't adapt yet, disable the adaptation until the changes can > be done, or another compromise depending on what's the state. > > I know it's hard to enforce, but probably the cheapest in terms of > drawbacks any other solution would be. We can and should try. Can we flag problematic interface changes automatically? Semantic changes, no. What about changes visible in query-qmp-schema? > I'll probably keep notifying patchsets which implement and deprecate old > api at the same time to keep in mind that we need to be kept in touch, > but I really don't want to impose any kind of extra process to > development on either side. Thanks!