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Wed, 04 Feb 2026 09:21:06 -0800 (PST) Date: Wed, 4 Feb 2026 12:21:05 -0500 From: Peter Xu To: Vladimir Sementsov-Ogievskiy Cc: jasowang@redhat.com, mst@redhat.com, pbonzini@redhat.com, berrange@redhat.com, thuth@redhat.com, armbru@redhat.com, eblake@redhat.com, farosas@suse.de, zhao1.liu@intel.com, wangyanan55@huawei.com, philmd@linaro.org, marcel.apfelbaum@gmail.com, eduardo@habkost.net, davydov-max@yandex-team.ru, qemu-devel@nongnu.org, yc-core@yandex-team.ru, leiyang@redhat.com, raphael.s.norwitz@gmail.com, bchaney@akamai.com Subject: Re: [PATCH v10 3/8] qapi: add backend-transfer migration parameter Message-ID: References: <20260201162001.296328-1-vsementsov@yandex-team.ru> <20260201162001.296328-4-vsementsov@yandex-team.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260201162001.296328-4-vsementsov@yandex-team.ru> Received-SPF: pass client-ip=170.10.133.124; envelope-from=peterx@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_H2=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: 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 On Sun, Feb 01, 2026 at 07:19:55PM +0300, Vladimir Sementsov-Ogievskiy wrote: > # @migrate-set-parameters: > @@ -1004,6 +1005,13 @@ > # 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 > +# supports it. In general that means that backend state and its > +# 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 11.0) I still think it'll be nice to either have "local" in the name of parameter or at least document it with crystal clear terms. I used to suggest fd-passing, but maybe you wanted to emphasize there's more than fds to be migrated at least for tap? Then it can still be "local-backend-transfer", because nobody stops a device to transfer backend states in a remote migration either.. so "backend-transfer" seems to also work for remote migrations, but it is not. Or at least mentioned explicitly in the comment, saying this is a local migration / upgrade. If you could at least update the doc on the locality attribute for the migration (one way or another..), feel free to take: Acked-by: Peter Xu If you decide to rename, that's even better. Thanks, -- Peter Xu