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[93.172.224.64]) by smtp.gmail.com with ESMTPSA id x16sm2056174ejj.8.2021.10.04.08.11.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Oct 2021 08:11:03 -0700 (PDT) Date: Mon, 4 Oct 2021 11:11:00 -0400 From: "Michael S. Tsirkin" To: Denis Plotnikov Subject: Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration Message-ID: <20211004110855-mutt-send-email-mst@kernel.org> References: <20211004150731.191270-1-den-plotnikov@yandex-team.ru> MIME-Version: 1.0 In-Reply-To: <20211004150731.191270-1-den-plotnikov@yandex-team.ru> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.066, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001, T_SPF_HELO_TEMPERROR=0.01 autolearn=unavailable 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: , Cc: kwolf@redhat.com, yc-core@yandex-team.ru, qemu-devel@nongnu.org, qemu-block@nongnu.org, raphael.norwitz@nutanix.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Oct 04, 2021 at 06:07:29PM +0300, Denis Plotnikov wrote: > It might be useful for the cases when a slow block layer should be replaced > with a more performant one on running VM without stopping, i.e. with very low > downtime comparable with the one on migration. > > It's possible to achive that for two reasons: > > 1.The VMStates of "virtio-blk" and "vhost-user-blk" are almost the same. > They consist of the identical VMSTATE_VIRTIO_DEVICE and differs from > each other in the values of migration service fields only. > 2.The device driver used in the guest is the same: virtio-blk > > In the series cross-migration is achieved by adding a new type. > The new type uses virtio-blk VMState instead of vhost-user-blk specific > VMstate, also it implements migration save/load callbacks to be compatible > with migration stream produced by "virtio-blk" device. > > Adding the new type instead of modifying the existing one is convenent. > It ease to differ the new virtio-blk-compatible vhost-user-blk > device from the existing non-compatible one using qemu machinery without any > other modifiactions. That gives all the variety of qemu device related > constraints out of box. Hmm I'm not sure I understand. What is the advantage for the user? What if vhost-user-blk became an alias for vhost-user-virtio-blk? We could add some hacks to make it compatible for old machine types. > 0001: adds new type "vhost-user-virtio-blk" > 0002: add new type "vhost-user-virtio-blk-pci" > > Denis Plotnikov (2): > vhost-user-blk: add a new vhost-user-virtio-blk type > vhost-user-blk-pci: add new pci device type to support > vhost-user-virtio-blk > > hw/block/vhost-user-blk.c | 63 ++++++++++++++++++++++++++++++ > hw/virtio/vhost-user-blk-pci.c | 43 ++++++++++++++++++-- > include/hw/virtio/vhost-user-blk.h | 2 + > 3 files changed, 105 insertions(+), 3 deletions(-) > > -- > 2.25.1