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Wed, 15 Oct 2025 07:55:54 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.19]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4E3851800451; Wed, 15 Oct 2025 07:55:53 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id C77B621E6A27; Wed, 15 Oct 2025 09:55:50 +0200 (CEST) From: Markus Armbruster To: Vladimir Sementsov-Ogievskiy Cc: marcandre.lureau@redhat.com, pbonzini@redhat.com, berrange@redhat.com, eduardo@habkost.net, qemu-devel@nongnu.org, raphael@enfabrica.net, yc-core@yandex-team.ru, d-tatianin@yandex-team.ru Subject: Re: [PATCH v3 7/7] chardev: introduce DEFINE_PROP_CHR_NO_CONNECT In-Reply-To: <2df28aa4-d979-4659-a1ca-33d9cba94fb1@yandex-team.ru> (Vladimir Sementsov-Ogievskiy's message of "Wed, 15 Oct 2025 10:11:16 +0300") References: <20251014152644.954762-1-vsementsov@yandex-team.ru> <20251014152644.954762-8-vsementsov@yandex-team.ru> <87tt00irg0.fsf@pond.sub.org> <2df28aa4-d979-4659-a1ca-33d9cba94fb1@yandex-team.ru> Date: Wed, 15 Oct 2025 09:55:50 +0200 Message-ID: <87ldlcfvjt.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=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: 2.1.29 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-bounces+qemu-devel=archiver.kernel.org@nongnu.org Vladimir Sementsov-Ogievskiy writes: > On 15.10.25 09:56, Markus Armbruster wrote: >> Vladimir Sementsov-Ogievskiy writes: >> >>> For further vhost-user-blk backend-transfer migration realization we >>> want to give it (vhost-user-blk) a possibility (and responsibility) to >>> decide when do connect. >>> >>> For incoming migration we'll need to postpone connect at least until >>> early stage of migrate-incoming command, when we already know all >>> migration parameters and can decide, are we going to do incoming >>> backend-transfer (and get chardev fd from incoming stream), or we >>> finally need to connect. >>> >>> With this patch, we only provide new macro, to define chardev property, >>> later it will be used in vhost-user-blk instead of DEFINE_PROP_CHR. >> >> There is no "later" in this series. >> The new macro is called DEFINE_PROP_CHR_NO_CONNECT(). >> >>> Then, vhost-user-blk will call qemu_chr_connect() by hand when needed >>> (for example through qemu_chr_fe_wait_connected(), which is already >>> called in vhost_user_blk_realize_connect()). >>> >>> Signed-off-by: Vladimir Sementsov-Ogievskiy >> >> Excuse my quick & ignorant questions... >> >> I understand ChardevClass provides either methods init() and connect(), >> or method open(). >> >> Is a ChardevClass providing open() usable with >> DEFINE_PROP_CHR_NO_CONNECT()? > > Good question. It's usable, but it will work like simple DEFINE_PROP_CHR. > I should improve it somehow. Better is to fail than go unexpected way. > >> Is a ChardevClass providing init() and connect() usable with >> DEFINE_PROP_CHR()? > > Yes, and works correctly. > >> Could the code do the right thing based on presence of open() vs. init() >> and connect() instead of DEFINE_PROP_CHR() >> vs. DEFINE_PROP_CHR_NO_CONNECT()? >> > > No, because, the frontend should be prepared to work with new _NO_CONNECT (e.g., > call _connect() by hand when needed). There are a lot of frontends, which > expect already connected backend, updating them all would be big (and > unnecessary) work. QMP command {"execute": "qom-list-types", "arguments": {"implements": "chardev"}} shows me 23 subtypes of "chardev". Could miss a few not in this build. Converting them all would be work. It's not a prohibitive amount of work, though. Whether it's worth our while is not for me to judge.