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(p200300cfd746c5513d67278ec0a187a2.dip0.t-ipconnect.de. [2003:cf:d746:c551:3d67:278e:c0a1:87a2]) by smtp.gmail.com with ESMTPSA id x12-20020a5d444c000000b0032da022855fsm2423659wrr.111.2023.10.18.09.17.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Oct 2023 09:17:46 -0700 (PDT) Message-ID: Date: Wed, 18 Oct 2023 18:17:45 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH v4 3/8] vhost-user.rst: Clarify enabling/disabling vrings To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, virtio-fs@redhat.com, Stefan Hajnoczi , German Maglione , =?UTF-8?Q?Eugenio_P=c3=a9rez?= , Anton Kuchin References: <20231018081336-mutt-send-email-mst@kernel.org> Content-Language: en-US From: Hanna Czenczek In-Reply-To: <20231018081336-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=hreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -53 X-Spam_score: -5.4 X-Spam_bar: ----- X-Spam_report: (-5.4 / 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, NICE_REPLY_A=-3.339, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.29 Precedence: list List-Id: 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 18.10.23 14:14, Michael S. Tsirkin wrote: > On Wed, Oct 04, 2023 at 02:58:59PM +0200, Hanna Czenczek wrote: >> Currently, the vhost-user documentation says that rings are to be >> initialized in a disabled state when VHOST_USER_F_PROTOCOL_FEATURES is >> negotiated. However, by the time of feature negotiation, all rings have >> already been initialized, so it is not entirely clear what this means. >> >> At least the vhost-user-backend Rust crate's implementation interpreted >> it to mean that whenever this feature is negotiated, all rings are to >> put into a disabled state, which means that every SET_FEATURES call >> would disable all rings, effectively halting the device. This is >> problematic because the VHOST_F_LOG_ALL feature is also set or cleared >> this way, which happens during migration. Doing so should not halt the >> device. >> >> Other implementations have interpreted this to mean that the device is >> to be initialized with all rings disabled, and a subsequent SET_FEATURES >> call that does not set VHOST_USER_F_PROTOCOL_FEATURES will enable all of >> them. Here, SET_FEATURES will never disable any ring. >> >> This interpretation does not suffer the problem of unintentionally >> halting the device whenever features are set or cleared, so it seems >> better and more reasonable. >> >> We can clarify this in the documentation by making it explicit that the >> enabled/disabled state is tracked even while the vring is stopped. >> Every vring is initialized in a disabled state, and SET_FEATURES without >> VHOST_USER_F_PROTOCOL_FEATURES simply becomes one way to enable all >> vrings. >> >> Signed-off-by: Hanna Czenczek > > OK so I am expecting v5. My advice is to move patch 1 to end of patchset > so we can defer it if we want to. Already sent – I’ve just dropped patch 1, since it doesn’t add anything to the objective of the patch series itself: https://lists.nongnu.org/archive/html/qemu-devel/2023-10/msg04727.html Hanna