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 1B728C001DE for ; Thu, 20 Jul 2023 19:59:52 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qMZnk-0000Br-AF; Thu, 20 Jul 2023 15:59:04 -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 1qMZni-0000BO-J0 for qemu-devel@nongnu.org; Thu, 20 Jul 2023 15:59:02 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qMZnh-0004X2-26 for qemu-devel@nongnu.org; Thu, 20 Jul 2023 15:59:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1689883139; 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=HYVMeM6kZVR+OlIn6wXPChfp1WxiF2Vf8eMU13lCAEM=; b=avhWMeuYEE+4y9E7lCuNKUJmubPqvZEGkpSPZsm3Pf8I9L+wDc4Gjoa7buR5nIHFYmZMzQ dxY+QpQgQZRZAYzk8u24+9ZxXKYjfQvxKibgAD7dT9zpbTKEWqmiABdXMphuCXG/H3ks2G hTqFYi0shExmBPx98CfxSy8b0pWWZew= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-422-rOCc9eh6MjmAnkY4mda72A-1; Thu, 20 Jul 2023 15:58:54 -0400 X-MC-Unique: rOCc9eh6MjmAnkY4mda72A-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 0C2BB185A78B; Thu, 20 Jul 2023 19:58:40 +0000 (UTC) Received: from localhost (unknown [10.39.194.253]) by smtp.corp.redhat.com (Postfix) with ESMTP id 69EB51454142; Thu, 20 Jul 2023 19:58:39 +0000 (UTC) Date: Thu, 20 Jul 2023 15:58:37 -0400 From: Stefan Hajnoczi To: "Michael S. Tsirkin" Cc: 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: <20230720195837.GJ210977@fedora> References: <20230704123600.1808604-1-alex.bennee@linaro.org> <20230706124347-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="y3Pyr4rpz3fA5NCs" Content-Disposition: inline In-Reply-To: <20230706124347-mutt-send-email-mst@kernel.org> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 Received-SPF: pass client-ip=170.10.133.124; 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 --y3Pyr4rpz3fA5NCs Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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 be able > > to setup the guest. While various parts of the setup can be delegated > > to the backend (for example config handling) this is a very piecemeal > > approach. >=20 > > This patch suggests a new feature flag (VHOST_USER_PROTOCOL_F_STANDALON= E) > > which the back-end can advertise which allows a probe message to be > > sent to get all the details QEMU needs to know in one message. >=20 > The reason we do piecemeal is that these existing pieces can be reused > as others evolve or fall by wayside. >=20 > 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). >=20 > 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 controlq. 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 advertises that this is a standalone device, since the semantics are different for traditional vhost-user-net devices. However, I think having a single message is inflexible and duplicates existing vhost-user protocol messages like VHOST_USER_GET_QUEUE_NUM. I would prefer VHOST_USER_GET_DEVICE_ID and other messages. Stefan --y3Pyr4rpz3fA5NCs Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmS5ke0ACgkQnKSrs4Gr c8hj3wf+OxDIxO3gPzNYxNljVy5Q+tGdkNsGXwheOv7mDLm3fRfKUpJLlFbUz7uG lgx9e/arw5qy885ZkOA9ElHVuAEA283hk2WpnGGhW8oh3pSN9aZHx2p/cNRWBSx/ XsjghkSF0GwDXOWfhACGwVySezmpIU7lmp52XfyPNKn06u6PA6psRBQsJpr1HuHx wt8Mck6AvhETrpBG9kzJgqFK3EDxdN4sBvbh3Yi1v+Z1AaQfWMNsmWgU1v/B+NYz 0PDGcHAlrBvIBNWRQrE/PcUf7163Mn/5XLDKaavN2udfNi/BUhifTpso9q4Jbd+J Oezp7UpOgKRdFAcw/JOssBQJ+WfU9w== =XMod -----END PGP SIGNATURE----- --y3Pyr4rpz3fA5NCs--