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[188.85.150.151]) by smtp.gmail.com with ESMTPSA id fm14-20020a05600c0c0e00b003fee8793911sm10881840wmb.44.2023.11.14.02.42.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Nov 2023 02:42:28 -0800 (PST) From: Juan Quintela To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Cc: Markus Armbruster , Peter Xu , qemu-devel@nongnu.org, Fabiano Rosas , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Thomas Huth Subject: Re: Configuring migration In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Tue, 14 Nov 2023 10:34:54 +0000") References: <878r8ajngg.fsf@pond.sub.org> <875y3dixzp.fsf@pond.sub.org> <8734yhgrzl.fsf@pond.sub.org> <877cnrjd71.fsf@pond.sub.org> <87zfzz82xq.fsf@secure.mitica> <87msvw6xm2.fsf_-_@pond.sub.org> <87pm0cochf.fsf@secure.mitica> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.3 (gnu/linux) Date: Tue, 14 Nov 2023 11:42:27 +0100 Message-ID: <87h6loobu4.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=170.10.129.124; envelope-from=quintela@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, T_SCC_BODY_TEXT_LINE=-0.01, T_SPF_TEMPERROR=0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Daniel P. Berrang=C3=A9 wrote: > On Tue, Nov 14, 2023 at 11:28:28AM +0100, Juan Quintela wrote: >> Daniel P. Berrang=C3=A9 wrote: >> > On Thu, Nov 02, 2023 at 03:25:25PM +0100, Markus Armbruster wrote: >> >> Now let's try to apply this to migration. >> >> >> >> As long as we can have just one migration, we need just one QAPI obje= ct >> >> to configure it. >> >>=20 >> >> We could create the object with -object / object_add. For convenienc= e, >> >> we'd probably want to create one with default configuration >> >> automatically on demand. >> >>=20 >> >> We could use qom-set to change configuration. If we're not comfortab= le >> >> with using qom-set for production, we could do something like >> >> blockdev-reopen instead. >> > >> > Do we even need to do this via a QAPI object ? >> > >> > Why are we not just making the obvious design change of passing everyt= hing >> > with the 'migrate' / 'migrate-incoming' commands that kick it off: >> > >> > ie: >> > >> > { 'command': 'migrate', >> > 'data': {'uri': 'str', >> > '*channels': [ 'MigrationChannel' ], >> > '*capabilities': [ 'MigrateCapability' ], >> > '*parameters': [ 'MigrateParameters' ], >> > '*detach': 'bool', '*resume': 'bool' } } >>=20 >> Once that we are doing incompatible changes: > > This is not incompatible - it is fully backcompatible with existing > usage initially, which should make it pretty trivial to introduce > to the code. Mgmt apps can carry on using migrate-set-capabilities > and migrate-set-parameters, and ignore these new 'capabilities' > and 'parameters' fields if desired. > > Only once we decide to deprecate migrate-set-capabilities, would > it become incompatible. Oh, I mean that the interface is incompatible. Not that we can't do the current one on top of this one. >> - resume can be another parameter > > Potentially yes, but 'resume' is conceptually different to all > the other capabilities and parameters, so I could see it remaining > as a distinct field as it is now It is conceptually different. But it is the _only_ one needed that capability. And putting that on the parameters and just checking it first will achieve the same result. I think that being special here don't help, for instance, to check for incompatible things, we need to also pass resume (it is only valid for postcopy). >> - detach is not needed. QMP don't use it, and HMP don't need to pass it >> to qmp_migrate() to make the non-detached implemntation. > > We could deprecate that today then. Yeap. Will do it. >> > (deprecated bits trimmed for clarity) >> > >> > and the counterpart: >> > >> > { 'command': 'migrate-incoming', >> > 'data': {'*uri': 'str', >> > '*channels': [ 'MigrationChannel' ], >> > '*capabilities': [ 'MigrateCapability' ], >> > '*parameters': [ 'MigrateParameters' ] } } >> > >> > such that the design is just like 99% of other commands which take >> > all their parameters directly. We already have 'migrate-set-parameters' >> > remaining for the runtime tunables, and can deprecate the usage of this >> > when migration is not already running, and similarly deprecate >> > migrate-set-capabilities. >>=20 >> This makes sense to me, but once that we change, we could try to merge >> capabilities and parameters. See my other email on this topic. >> Basically the distition is arbitrary, so just have one of them. >>=20 >> Or better, as I said in the other email, we have two types of >> parameters: >> - the ones that need to be set before migration starts >> - the ones that can be changed at any time >>=20 >> So to be simpler, I think that 1st set should be passed to the commands >> themselves and the others should only be set with >> migrate_set_parameters. > > As a mgmt app dev I don't want there to be an arbitrary distinction > between what I can pass with 'migrate' and what I have to use a > separate command for. If it ever wants to set the parameter that it "can" change after migration starts, it needs to know that they are different. Once told that, I don't write management apps and you do so I am not discussing further O:-) > If I'm starting a migration, I just want to > pass all the settings with the 'migrate' command. I should not have > to care about separate 'migrate-set-parameters' command at all, unless > I actually need to change something on the fly (many migrates will > never need this). What OpenStack/CNV do? If my memory is right, at least one of them used progressive downtimes every couple of iterations or something like that. Later, Juan. > With regards, > Daniel