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[79.182.31.92]) by smtp.gmail.com with ESMTPSA id 207sm278946wme.13.2020.06.29.08.45.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 29 Jun 2020 08:45:38 -0700 (PDT) Date: Mon, 29 Jun 2020 11:45:35 -0400 From: "Michael S. Tsirkin" To: Cornelia Huck Subject: Re: [PATCH RFC] virtio-fs: force virtio 1.x usage Message-ID: <20200629114515-mutt-send-email-mst@kernel.org> References: <20200629102758.421552-1-cohuck@redhat.com> <20200629104948-mutt-send-email-mst@kernel.org> <20200629173933.35cea40f.cohuck@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200629173933.35cea40f.cohuck@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=205.139.110.120; envelope-from=mst@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/29 01:10:03 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: "Dr. David Alan Gilbert" , Stefan Hajnoczi , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jun 29, 2020 at 05:39:33PM +0200, Cornelia Huck wrote: > On Mon, 29 Jun 2020 10:53:23 -0400 > "Michael S. Tsirkin" wrote: > > > On Mon, Jun 29, 2020 at 12:27:58PM +0200, Cornelia Huck wrote: > > > virtio-fs devices are only specified for virtio-1, so it is unclear > > > how a legacy or transitional device should behave. > > > > > > Signed-off-by: Cornelia Huck > > > --- > > > > > > Forcing off legacy now (after the virtio-fs device has already been > > > available) may have unintended consequences, therefore RFC. > > > > > > By default, a virtio-pci device uses 'AUTO' for disable_legacy, which > > > will resolve to different values based upon which bus the device has > > > been plugged. Therefore, forcing disable_legacy may result in the same > > > device or a quite different one. > > > > > > Even though pre-virtio-1 behaviour of virtio-fs devices is simply not > > > specified, toggling disable_legacy will have implications for the BAR > > > layout, IIRC, and therefore a guest might end up getting a different > > > device, even if it always used it with virtio-1 anyway. > > > > > > Not sure what the best way to solve this problem is. Adding a compat > > > property for disable_legacy=AUTO may be the right thing to do, but I'm > > > not quite clear if there are any further implications here. > > > > Well I notice that this device is not migrateable. > > So I think that we can just switch it over and be done with it. > > Oh, that makes things easier. (I'm wondering if libvirt already > configures this correctly?) > > > > > > > > Whatever we do here, we should make sure that the ccw incarnation of > > > this device indeed forces virtio-1. > > > > I agree. I notice that the API virtio_pci_force_virtio_1 turned out > > to be too fragile. I propose that instead we have a whitelist of > > devices which can be legacy or transitional. Force rest to modern. > > Also, there are further complications because the mechanism is per > transport, and therefore easy to miss. > > bool virtio_legacy_allowed(VirtIODevice *vdev) > { > switch (vdev->device_id) { > case <...>: > > return true; > default: > return false; > } > > Seems straightforward enough. Agreed. virtio spec has the list. > > > > > > > --- > > > hw/virtio/vhost-user-fs-pci.c | 1 + > > > 1 file changed, 1 insertion(+) > > > > > > diff --git a/hw/virtio/vhost-user-fs-pci.c b/hw/virtio/vhost-user-fs-pci.c > > > index e11c889d82b3..244205edf765 100644 > > > --- a/hw/virtio/vhost-user-fs-pci.c > > > +++ b/hw/virtio/vhost-user-fs-pci.c > > > @@ -44,6 +44,7 @@ static void vhost_user_fs_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp) > > > vpci_dev->nvectors = dev->vdev.conf.num_request_queues + 2; > > > } > > > > > > + virtio_pci_force_virtio_1(vpci_dev); > > > qdev_realize(vdev, BUS(&vpci_dev->bus), errp); > > > } > > > > > > -- > > > 2.25.4 > >