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Fri, 30 Jan 2026 16:31:12 +0000 (UTC) Received: from localhost (unknown [10.67.32.74]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C336619560A2; Fri, 30 Jan 2026 16:31:09 +0000 (UTC) From: Cornelia Huck To: Eric Farman , Halil Pasic , Vladimir Sementsov-Ogievskiy Cc: mst@redhat.com, sgarzare@redhat.com, raphael@enfabrica.net, qemu-devel@nongnu.org, yc-core@yandex-team.ru, d-tatianin@yandex-team.ru, Richard Henderson , Ilya Leoshkevich , David Hildenbrand , Thomas Huth , Christian Borntraeger , Matthew Rosato , "open list:virtio-ccw" Subject: Re: [PATCH v4 08/23] virtio: move common part of _set_guest_notifier to generic code In-Reply-To: <28313ff2e6fc34f45304ba19b8b9380fc4ba167d.camel@linux.ibm.com> Organization: "Red Hat GmbH, Sitz: Werner-von-Siemens-Ring 12, D-85630 Grasbrunn, Handelsregister: Amtsgericht =?utf-8?Q?M=C3=BCnchen=2C?= HRB 153243, =?utf-8?Q?Gesch=C3=A4ftsf=C3=BChrer=3A?= Ryan Barnhart, Charles Cachera, Avril Crosse O'Flaherty" References: <20260119185228.203296-1-vsementsov@yandex-team.ru> <20260119185228.203296-9-vsementsov@yandex-team.ru> <20260124000624.1bd7c9c1.pasic@linux.ibm.com> <26198787-a1da-4858-8656-f5006d153d6e@yandex-team.ru> <20260126230026.2664d565.pasic@linux.ibm.com> <28313ff2e6fc34f45304ba19b8b9380fc4ba167d.camel@linux.ibm.com> User-Agent: Notmuch/0.39 (https://notmuchmail.org) Date: Fri, 30 Jan 2026 17:31:04 +0100 Message-ID: <87ecn7t647.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.129.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-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: qemu development 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 Fri, Jan 30 2026, Eric Farman wrote: > On Mon, 2026-01-26 at 23:00 +0100, Halil Pasic wrote: >> On Mon, 26 Jan 2026 19:40:09 +0300 >> Vladimir Sementsov-Ogievskiy wrote: >> >> > > > +/** >> > > > + * virtio_queue_set_guest_notifier - set/unset queue or config guest >> > > > + * notifier >> > > > + * >> > > > + * @vdev: the VirtIO device >> > > > + * @n: queue number, or VIRTIO_CONFIG_IRQ_IDX to set config notifer >> > > >> > > Semantically are mixing queue numbers and interrupt indexes here. >> > >> > That's preexisting logic in virtio_pci_set_guest_notifier_fd_handler(). >> > >> > But, you are right, that's doesn't answer the question, is it good to share >> > the logic with mmio and ccw. >> > >> > Is config notifier only pci specific, or similar feature may appear in future >> > for mmio and/or ccw? >> >> AFAIR there is no notifier for ccw. A possible explanation for >> that is, that AFAIK that config space notifications (device -> driver) >> are always classic I/O interrupts while queue indicators can be so called >> adapter I/O interrupts and irqfd is only available for adapter I/O >> interrupts. >> >> If you like you can have a look at >> "4.3.2.6 Setting Up Indicators" in >> https://docs.oasis-open.org/virtio/virtio/v1.3/csd01/virtio-v1.3-csd01.html#x1-1940003 >> >> I see no reason why virtio_config_guest_notifier_read() based, i.e >> !irqfd virtio config notifier should not exist or would not work. And I >> guess it is needed for certain vhost things. But nevertheless, I can't >> find the place where a virtio-ccw config notifier is set up. >> >> Eric, what is your opinion on this? My current thinking is that >> virtio-ccw not having a config notifier is basically a bug. > > (Sorry that I missed this; thanks for the ping, Halil) > > Yeah, we don't have have such a config notifier and I don't recall the history behind it. Adapter interrupts were not a thing for virtio-ccw in the beginning (we only added the airq infrastructure later IIRC, so all interrupts were "classic" subchannel-based interrupts.) > But I don't know that it's a bug; spec points out config notifications for ccw come as unsolicited > interrupts versus config notifier, so not having one is fine by me as far as this refactoring goes. > I'll add it to a list of things to play around with, though. I think I agree. (Although my brain is already more than halfway into the weekend...)