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[82.30.61.225]) by smtp.gmail.com with ESMTPSA id c25sm2442946wml.37.2021.10.06.07.28.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 Oct 2021 07:28:01 -0700 (PDT) Date: Wed, 6 Oct 2021 15:27:59 +0100 From: "Dr. David Alan Gilbert" To: "Michael S. Tsirkin" Subject: Re: [PATCH v0 0/2] virtio-blk and vhost-user-blk cross-device migration Message-ID: References: <20211005161008.iq5ao7t2sdqeo6kc@habkost.net> <20211005175503-mutt-send-email-mst@kernel.org> <20211006041419-mutt-send-email-mst@kernel.org> <20211006043314-mutt-send-email-mst@kernel.org> <20211006081653-mutt-send-email-mst@kernel.org> <20211006093707-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: <20211006093707-mutt-send-email-mst@kernel.org> User-Agent: Mutt/2.0.7 (2021-05-04) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@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=170.10.133.124; envelope-from=dgilbert@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=-0.05, 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_HELO_NONE=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, Denis Plotnikov , Eduardo Habkost , qemu-block@nongnu.org, qemu-devel@nongnu.org, raphael.norwitz@nutanix.com, Roman Kagan , yc-core@yandex-team.ru, pbonzini@redhat.com, Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Michael S. Tsirkin (mst@redhat.com) wrote: > On Wed, Oct 06, 2021 at 02:29:37PM +0100, Dr. David Alan Gilbert wrote: > > * Michael S. Tsirkin (mst@redhat.com) wrote: > > > On Wed, Oct 06, 2021 at 09:43:52AM +0100, Dr. David Alan Gilbert wrote: > > > > * Michael S. Tsirkin (mst@redhat.com) wrote: > > > > > On Wed, Oct 06, 2021 at 09:28:50AM +0100, Dr. David Alan Gilbert wrote: > > > > > > To me it feels the same as the distinction between vhost-kernel and qemu > > > > > > backended virtio that we get in net and others - in principal it's just > > > > > > another implementation. > > > > > > > > > > In net it's actually like this. Same -device, a different netdev. > > > > > > > > > > > A tricky part is guaranteeing the set of visible virtio features between > > > > > > implementations; we have that problem when we use vhost-kernel and run > > > > > > on a newer/older kernel and gain virtio features; the same will be true > > > > > > with vhost-user implementations. > > > > > > > > > > That's not new but yes we need to work on this. > > > > > > > > > > > But this would make the structure of a vhost-user implementation quite > > > > > > different. > > > > > > > > > > > > Dave > > > > > > > > > > Right. That's why I'm reluctant to just add a new device type that > > > > > has special compatibility requirements. > > > > > > > > Hmm but there's already another layer of hack^Wabstraction in there isn't there - > > > > there's already: > > > > virtio-blk-pci > > > > virtio-blk-device > > > > > > > > created when the user specifies a virtio-blk device? > > > > > > > > Dave > > > > > > virtio-*-pci is there because it was felt these devices look > > > differently from e.g. virtio-ccw so should have a different name. > > > virtio-blk-device is an internal thingy, users and guests have no idea. > > > > Right, so to do what we're asking here, should we keep the > > virtio-blk-pci and instantiate virtio-blk-vhost-user instead of > > virtio-blk-device? > > > > Dave > > I guess that's possible, but we need to pass a bunch of parameters. > -drive is probably the right want to do that, right? I'm not sure about -drive - isn't that very tied into the block layer? Dave > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > MST > > > > > > > > > > > > > > > > > -- > > > > > > > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > > > > > > > > > > > > > -- > > > > > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > > > > > > > > > -- > > > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > > > > > -- > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK