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dkim=none (message not signed) header.d=none;redhat.com; dmarc=none action=none header.from=virtuozzo.com; Received: from AM7PR08MB5494.eurprd08.prod.outlook.com (2603:10a6:20b:dc::15) by AM6PR08MB4788.eurprd08.prod.outlook.com (2603:10a6:20b:c4::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4195.27; Tue, 8 Jun 2021 11:46:52 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::f928:f4f2:77c0:74b4]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::f928:f4f2:77c0:74b4%9]) with mapi id 15.20.4195.030; Tue, 8 Jun 2021 11:46:52 +0000 Subject: Re: [PATCH v2 3/3] qapi: deprecate drive-backup To: Markus Armbruster Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, libvir-list@redhat.com, jsnow@redhat.com, eblake@redhat.com, xiechanglong.d@gmail.com, wencongyang2@huawei.com, nshirokovskiy@virtuozzo.com, pkrempa@redhat.com, den@openvz.org, yur@virtuozzo.com, dim@virtuozzo.com, berrange@redhat.com, kchamart@redhat.com References: <20210505135803.67896-1-vsementsov@virtuozzo.com> <20210505135803.67896-4-vsementsov@virtuozzo.com> <87eedc1ugb.fsf@dusky.pond.sub.org> From: Vladimir Sementsov-Ogievskiy Message-ID: <3c1c05c3-87ec-c665-00ae-0c0ca312e5bc@virtuozzo.com> Date: Tue, 8 Jun 2021 14:46:49 +0300 User-Agent: Mozilla/5.0 (X11; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR03-VE1-obe.outbound.protection.outlook.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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 08.06.2021 14:12, Markus Armbruster wrote: > Vladimir Sementsov-Ogievskiy writes: > > [...] > >> TODO: We also need to deprecate drive-backup transaction action.. >> But union members in QAPI doesn't support 'deprecated' feature. I tried >> to dig a bit, but failed :/ Markus, could you please help with it? At >> least by advice? > > There are two closely related things in play here: the union branch and > the corresponding enum value. > > So far, the QAPI schema language doesn't support tacking feature flags > to either. > > If an enum value is deprecated, any union branches corresponding to it > must also be deprecated (because their use requires using the deprecated > enum value). > > The converse is not true, but I can't see a use for deprecating a union > branch without also deprecating the enum member. > > I think we can implement feature flags just for enum members, then > document that 'deprecated' enum value implies corresponding union > branches are also deprecated. > > I have unfinished patches implementing feature flags for enum members. > > Since TransactionAction is a simple union, the corresponding enum is > implicit. We can make it explicit by converting to a flat union. > Simple unions need to die anyway. Does BlockStatsSpecific from qapi/block-core.json a correct example of flat union you mean? I can make patch to convert TransactionAction to be similar if that helps (discriminator field should be called "type", yes?). > > Does this make sense? > Yes if it helps) Did you also look at John's https://gitlab.com/jsnow/qemu/-/commits/hack-deprecate-union-branches/ ? I hope you and John will send patches that you have, I'll help with reviewing (keep me in CC), and finally we'll get the feature. -- Best regards, Vladimir