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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 AFEB5C001DF for ; Mon, 24 Jul 2023 18:09:08 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qNzzH-00078x-TY; Mon, 24 Jul 2023 14:08:51 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qNzzH-00078n-3D for qemu-devel@nongnu.org; Mon, 24 Jul 2023 14:08:51 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qNzzF-00026m-EW for qemu-devel@nongnu.org; Mon, 24 Jul 2023 14:08:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1690222128; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=vy0s3t2bKntxrw72io7NoadgGa/K+CMor+nXPDkE+vQ=; b=Td5Wdy33hee7PB7iop5DHD20ShBGnfBUkhR+gkqTy1oQKR3BGi2smnLJGiaCHupU6eCQJm btmo2vsZS/0D0BoORUNn5Z+7+T4llO6qjSrfgKrpOzOEcU7JgC9zO96NwMOMf2uEb+9pZ0 0RIlq7/1ZP24dFXSW94YTRbrlCu9808= Received: from mimecast-mx02.redhat.com (66.187.233.73 [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-695-SatHzKsSM66rfF1WWHDfMw-1; Mon, 24 Jul 2023 14:08:43 -0400 X-MC-Unique: SatHzKsSM66rfF1WWHDfMw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6A1913815F6B; Mon, 24 Jul 2023 18:08:42 +0000 (UTC) Received: from localhost (unknown [10.39.192.142]) by smtp.corp.redhat.com (Postfix) with ESMTP id B4DCE140E952; Mon, 24 Jul 2023 18:08:41 +0000 (UTC) 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 Subject: Re: [RFC PATCH] docs/interop: define STANDALONE protocol feature for vhost-user 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 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, 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 --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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