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(p200300cfd70866e5a5d0fe9228997179.dip0.t-ipconnect.de. [2003:cf:d708:66e5:a5d0:fe92:2899:7179]) by smtp.gmail.com with ESMTPSA id dx12-20020a170906a84c00b009b977bea1dcsm2427925ejb.23.2023.10.06.00.48.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Oct 2023 00:48:15 -0700 (PDT) Message-ID: <00272da3-0a48-5544-6ba8-5dfde00be241@redhat.com> Date: Fri, 6 Oct 2023 09:48:14 +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: [Virtio-fs] (no subject) To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, virtio-fs@redhat.com, =?UTF-8?Q?Eugenio_P=c3=a9rez?= , Anton Kuchin References: <20231004125904.110781-1-hreitz@redhat.com> <20231004125904.110781-2-hreitz@redhat.com> <20231005170852.GB1342722@fedora> <20231005131352-mutt-send-email-mst@kernel.org> Content-Language: en-US From: Hanna Czenczek In-Reply-To: <20231005131352-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=hreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -62 X-Spam_score: -6.3 X-Spam_bar: ------ X-Spam_report: (-6.3 / 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=-4.219, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=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 05.10.23 19:15, Michael S. Tsirkin wrote: > On Thu, Oct 05, 2023 at 01:08:52PM -0400, Stefan Hajnoczi wrote: >> On Wed, Oct 04, 2023 at 02:58:57PM +0200, Hanna Czenczek wrote: >>> There is no clearly defined purpose for the virtio status byte in >>> vhost-user: For resetting, we already have RESET_DEVICE; and for virtio >>> feature negotiation, we have [GS]ET_FEATURES. With the REPLY_ACK >>> protocol extension, it is possible for SET_FEATURES to return errors >>> (SET_PROTOCOL_FEATURES may be called before SET_FEATURES). >>> >>> As for implementations, SET_STATUS is not widely implemented. dpdk does >>> implement it, but only uses it to signal feature negotiation failure. >>> While it does log reset requests (SET_STATUS 0) as such, it effectively >>> ignores them, in contrast to RESET_OWNER (which is deprecated, and today >>> means the same thing as RESET_DEVICE). >>> >>> While qemu superficially has support for [GS]ET_STATUS, it does not >>> forward the guest-set status byte, but instead just makes it up >>> internally, and actually completely ignores what the back-end returns, >>> only using it as the template for a subsequent SET_STATUS to add single >>> bits to it. Notably, after setting FEATURES_OK, it never reads it back >>> to see whether the flag is still set, which is the only way in which >>> dpdk uses the status byte. >>> >>> As-is, no front-end or back-end can rely on the other side handling this >>> field in a useful manner, and it also provides no practical use over >>> other mechanisms the vhost-user protocol has, which are more clearly >>> defined. Deprecate it. >>> >>> Suggested-by: Stefan Hajnoczi >>> Signed-off-by: Hanna Czenczek >>> --- >>> docs/interop/vhost-user.rst | 28 +++++++++++++++++++++------- >>> 1 file changed, 21 insertions(+), 7 deletions(-) >> Reviewed-by: Stefan Hajnoczi > > SET_STATUS is the only way to signal failure to acknowledge FEATURES_OK. > The fact current backends never check errors does not mean they never > will. So no, not applying this. Can this not be done with REPLY_ACK?  I.e., with the following message order: 1. GET_FEATURES to find out whether VHOST_USER_F_PROTOCOL_FEATURES is present 2. GET_PROTOCOL_FEATURES to hopefully get VHOST_USER_PROTOCOL_F_REPLY_ACK 3. SET_PROTOCOL_FEATURES to set VHOST_USER_PROTOCOL_F_REPLY_ACK 4. SET_FEATURES with need_reply If not, the problem is that qemu has sent SET_STATUS 0 for a while when the vCPUs are stopped, which generally seems to request a device reset.  If we don’t state at least that SET_STATUS 0 is to be ignored, back-ends that will implement SET_STATUS later may break with at least these qemu versions.  But documenting that a particular use of the status byte is to be ignored would be really strange. Hanna