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Thu, 16 Oct 2025 10:56:49 +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 2838618004D4; Thu, 16 Oct 2025 10:56:49 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id A514821E6A27; Thu, 16 Oct 2025 12:56:46 +0200 (CEST) From: Markus Armbruster To: Vladimir Sementsov-Ogievskiy Cc: mst@redhat.com, jasowang@redhat.com, peterx@redhat.com, farosas@suse.de, sw@weilnetz.de, eblake@redhat.com, thuth@redhat.com, philmd@linaro.org, berrange@redhat.com, qemu-devel@nongnu.org, michael.roth@amd.com, steven.sistare@oracle.com, leiyang@redhat.com, davydov-max@yandex-team.ru, yc-core@yandex-team.ru, raphael.s.norwitz@gmail.com Subject: Re: [PATCH v8 16/19] qapi: introduce backend-transfer migration parameter In-Reply-To: <20251015132136.1083972-17-vsementsov@yandex-team.ru> (Vladimir Sementsov-Ogievskiy's message of "Wed, 15 Oct 2025 16:21:32 +0300") References: <20251015132136.1083972-1-vsementsov@yandex-team.ru> <20251015132136.1083972-17-vsementsov@yandex-team.ru> Date: Thu, 16 Oct 2025 12:56:46 +0200 Message-ID: <87a51rgln5.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_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, 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: , 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: > This parameter enables backend-transfer feature: all devices > which support it will migrate their backends (for example a TAP > device, by passing open file descriptor to migration channel). > > Currently no such devices, so the new parameter is a noop. > > Next commit will add support for virtio-net, to migrate its > TAP backend. > > Signed-off-by: Vladimir Sementsov-Ogievskiy [...] > diff --git a/qapi/migration.json b/qapi/migration.json > index be0f3fcc12..35601a1f87 100644 > --- a/qapi/migration.json > +++ b/qapi/migration.json > @@ -951,9 +951,16 @@ > # is @cpr-exec. The first list element is the program's filename, > # the remainder its arguments. (Since 10.2) > # > +# @backend-transfer: Enable backend-transfer feature for devices that Either "Enable the backend transfer feature" or "Enable backend transfer" > +# supports it. In general that means that backend state and its support > +# file descriptors are passed to the destination in the migraton > +# channel (which must be a UNIX socket). Individual devices > +# declare the support for backend-transfer by per-device > +# backend-transfer option. (Since 10.2) > +# I'm not sure I understand this. What is a "per-device backend-transfer option"? Is it a device property? If yes, I guess the device declares its capability to do this by having this property. Correct? Does the property's value matter? How? > # Features: > # > -# @unstable: Members @x-checkpoint-delay and > +# @unstable: Members @backend-transfer, @x-checkpoint-delay and > # @x-vcpu-dirty-limit-period are experimental. > # > # Since: 2.4 > @@ -978,7 +985,8 @@ > 'mode', > 'zero-page-detection', > 'direct-io', > - 'cpr-exec-command'] } > + 'cpr-exec-command', > + { 'name': 'backend-transfer', 'features': ['unstable'] } ] } > > ## > # @MigrateSetParameters: [...]