From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from ws5-mx01.kavi.com (ws5-mx01.kavi.com [34.193.7.191]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id AA937C001B0 for ; Mon, 24 Jul 2023 18:08:50 +0000 (UTC) Received: from lists.oasis-open.org (oasis.ws5.connectedcommunity.org [10.110.1.242]) by ws5-mx01.kavi.com (Postfix) with ESMTP id C5D24C622E for ; Mon, 24 Jul 2023 18:08:49 +0000 (UTC) Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id A7E3798653D for ; Mon, 24 Jul 2023 18:08:49 +0000 (UTC) Received: from host09.ws5.connectedcommunity.org (host09.ws5.connectedcommunity.org [10.110.1.97]) by lists.oasis-open.org (Postfix) with QMQP id 8F3C09864BD; Mon, 24 Jul 2023 18:08:49 +0000 (UTC) Mailing-List: contact virtio-dev-help@lists.oasis-open.org; run by ezmlm List-ID: Sender: Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 7BBA5986509 for ; Mon, 24 Jul 2023 18:08:49 +0000 (UTC) X-Virus-Scanned: amavisd-new at kavi.com X-MC-Unique: SatHzKsSM66rfF1WWHDfMw-1 Date: Mon, 24 Jul 2023 14:08:39 -0400 From: Stefan Hajnoczi To: "Michael S. Tsirkin" Cc: Stefan Hajnoczi , Alex =?iso-8859-1?Q?Benn=E9e?= , qemu-devel@nongnu.org, virtio-dev@lists.oasis-open.org, slp@redhat.com, marcandre.lureau@redhat.com, viresh.kumar@linaro.org, sgarzare@redhat.com, takahiro.akashi@linaro.org, erik.schilling@linaro.org, manos.pitsidianakis@linaro.org, mathieu.poirier@linaro.org Message-ID: <20230724180839.GC222590@fedora> References: <20230704123600.1808604-1-alex.bennee@linaro.org> <20230706124347-mutt-send-email-mst@kernel.org> <20230720195837.GJ210977@fedora> <20230720171321-mutt-send-email-mst@kernel.org> <20230720182128-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="o5VRGi/hTISP7+bi" Content-Disposition: inline In-Reply-To: <20230720182128-mutt-send-email-mst@kernel.org> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 Subject: [virtio-dev] Re: [RFC PATCH] docs/interop: define STANDALONE protocol feature for vhost-user --o5VRGi/hTISP7+bi Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jul 20, 2023 at 06:22:08PM -0400, Michael S. Tsirkin wrote: > On Thu, Jul 20, 2023 at 05:31:03PM -0400, Stefan Hajnoczi wrote: > > On Thu, 20 Jul 2023 at 17:15, Michael S. Tsirkin wrote: > > > > > > On Thu, Jul 20, 2023 at 03:58:37PM -0400, Stefan Hajnoczi wrote: > > > > On Thu, Jul 06, 2023 at 12:48:20PM -0400, Michael S. Tsirkin wrote: > > > > > On Tue, Jul 04, 2023 at 01:36:00PM +0100, Alex Benn=E9e wrote: > > > > > > Currently QEMU has to know some details about the back-end to b= e able > > > > > > to setup the guest. While various parts of the setup can be del= egated > > > > > > to the backend (for example config handling) this is a very pie= cemeal > > > > > > approach. > > > > > > > > > > > This patch suggests a new feature flag (VHOST_USER_PROTOCOL_F_S= TANDALONE) > > > > > > which the back-end can advertise which allows a probe message t= o be > > > > > > sent to get all the details QEMU needs to know in one message. > > > > > > > > > > The reason we do piecemeal is that these existing pieces can be r= eused > > > > > as others evolve or fall by wayside. > > > > > > > > > > For example, I can think of instances where you want to connect > > > > > specifically to e.g. networking backend, and specify it > > > > > on command line. Reasons could be many, e.g. for debugging, > > > > > or to prevent connecting to wrong device on wrong channel > > > > > (kind of like type safety). > > > > > > > > > > What is the reason to have 1 message? startup latency? > > > > > How about we allow pipelining several messages then? > > > > > Will be easier. > > > > > > > > This flag effectively says that the back-end is a full VIRTIO device > > > > with a Device Status Register, Configuration Space, Virtqueues, the > > > > device type, etc. This is different from previous vhost-user devices > > > > which sometimes just offloaded certain virtqueues without providing= the > > > > full VIRTIO device (parts were emulated in the VMM). > > > > > > > > So for example, a vhost-user-net device does not support the contro= lq. > > > > Alex's "standalone" device is a mode where the vhost-user protocol = is > > > > used but the back-end must implement a full virtio-net device. > > > > Standalone devices are like vDPA device in this respect. > > > > > > > > I think it is important to have a protocol feature bit that adverti= ses > > > > that this is a standalone device, since the semantics are different= for > > > > traditional vhost-user-net devices. > > > > > > Not sure what that would gain as compared to a feature bit per > > > message as we did previously. > >=20 > > Having a single feature bit makes it easier to distinguish between a > > traditional vhost-user device and a standalone device. > >=20 > > For example, the presence of VHOST_USER_F_GET_DEVICE_ID doesn't tell > > you whether this device is a standalone device that is appropriate for > > a new generic QEMU --device vhost-user-device feature that Alex is > > working on. It could be a traditional vhost-user device that is not > > standalone but implements the VHOST_USER_GET_DEVICE_ID message. > >=20 > > How will we detect standalone devices? It will be messy if there is no > > single feature bit that advertises that this back-end is a standalone > > device. > >=20 > > Stefan >=20 > Looks like standalone implies some 5-6 messages to be supported. > So just test the 6 bits are all ones. It's not clear to me that the individual bits together mean this is really a standalone device, but let's go with individual commands and see if a front-end can distinguish standalone devices or not. If not, then we can still add "standalone" feature bit before merging the code. 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