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Tsirkin" To: Markus Armbruster Cc: Hyman Huang , qemu-devel@nongnu.org, Eric Blake Subject: Re: [PATCH v4 0/3] Adjust the output of x-query-virtio-status Message-ID: <20240313070857-mutt-send-email-mst@kernel.org> References: <20240312121944-mutt-send-email-mst@kernel.org> <87h6hah7bb.fsf@pond.sub.org> <20240313051034-mutt-send-email-mst@kernel.org> <87msr2fp16.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87msr2fp16.fsf@pond.sub.org> Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.687, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 Wed, Mar 13, 2024 at 10:40:21AM +0100, Markus Armbruster wrote: > I could be awkward for the use case described in PATCH 1's commit > message: > > However, we sometimes want to compare features and status bits without > caring for their exact meaning. Say we want to verify the correctness > of the virtio negotiation between guest, QEMU, and OVS-DPDK. We can use > QMP command x-query-virtio-status to retrieve vhost-user net device > features, and the "ovs-vsctl list interface" command to retrieve > interface features. Without commit f3034ad71fc, we could then simply > compare the numbers. With this commit, we first have to map from the > strings back to the numeric encoding. So, consider how guest kernel presents features then. Do you happen to know? It's actually a binary string: static ssize_t features_show(struct device *_d, struct device_attribute *attr, char *buf) { struct virtio_device *dev = dev_to_virtio(_d); unsigned int i; ssize_t len = 0; /* We actually represent this as a bitstring, as it could be * arbitrary length in future. */ for (i = 0; i < sizeof(dev->features)*8; i++) len += sysfs_emit_at(buf, len, "%c", __virtio_test_bit(dev, i) ? '1' : '0'); len += sysfs_emit_at(buf, len, "\n"); return len; } static DEVICE_ATTR_RO(features); -- MST