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Thu, 20 Aug 2026 09:16:49 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.12]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 65B1519560AB; Thu, 20 Aug 2026 09:16:48 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id ECA8021E6920; Thu, 20 Aug 2026 11:16:45 +0200 (CEST) From: Markus Armbruster To: Vladimir Sementsov-Ogievskiy Cc: jasowang@redhat.com, mst@redhat.com, peterx@redhat.com, farosas@suse.de, raphael.s.norwitz@gmail.com, bchaney@akamai.com, qemu-devel@nongnu.org, berrange@redhat.com, pbonzini@redhat.com, yc-core@yandex-team.ru, mark.caveayland@nutanix.com, Jason Wang , Eric Blake Subject: Re: [PATCH v21 15/16] net/tap: support local migration with virtio-net In-Reply-To: <20260819180201.1970193-16-vsementsov@yandex-team.ru> (Vladimir Sementsov-Ogievskiy's message of "Wed, 19 Aug 2026 21:01:58 +0300") References: <20260819180201.1970193-1-vsementsov@yandex-team.ru> <20260819180201.1970193-16-vsementsov@yandex-team.ru> Date: Thu, 20 Aug 2026 11:16:45 +0200 Message-ID: <87cxvd2ltu.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 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: 9 X-Spam_score: 0.9 X-Spam_bar: / X-Spam_report: (0.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.341, 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_H2=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development 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: > Support transferring of TAP state (including open fd). > > Add new property "x-permit-local-migration", which defines whether > local migration is actually permitted for this TAP device. > > Note that local-migration is enabled by global "local" migration > parameter, but individual devices may have additional options to > enable/disable it per device. > > The tricky thing is that we need to know whether to call open/connect in > TAP initialization code, i.e. we need to know the value of migration > parameter "local" when creating the TAP device. For incoming migration, > we can know only for TAP devices created with QMP after setting the > migration parameter with QMP. > > So the full picture is: > > On source, to start outgoing "local" migration you need: > > - migration parameter "local" set to true > - "x-permit-local-migration" TAP option set to true > > If at least one of these options is not set, TAP backend > doesn't participate in migration. > > On target, things are more difficult: > > Same, you need both "local" and "x-permit-local-migration" > be set. And same, if one of them is not set, TAP backend > is initialized as usual, and doesn't accept any incoming > state. > > Additionally, if you are going to set "local", it must be > set before creating the TAP device. If TAP device created > with "local" unset, it initializes as usual. If you enable > "local" after it and start incoming migration, it will fail > in .pre_load handler of TAP backend. > > Moreover, there are interface restrictions: if you create TAP > device when QEMU is in INCOMING state, and both "local" > and "x-permit-local-migration" set, most of TAP options are > not allowed, and script/downscript are required to be explicitly > disabled. > > Signed-off-by: Vladimir Sementsov-Ogievskiy > Reviewed-by: Ben Chaney QAPI schema Acked-by: Markus Armbruster