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 E4A07EE14D8 for ; Fri, 8 Sep 2023 12:03:07 +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 ED4E1335BD for ; Fri, 8 Sep 2023 12:03:06 +0000 (UTC) Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id DA72798662A for ; Fri, 8 Sep 2023 12:03:06 +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 CB99098646D; Fri, 8 Sep 2023 12:03:06 +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 BB0CE98644C for ; Fri, 8 Sep 2023 12:03:04 +0000 (UTC) X-Virus-Scanned: amavisd-new at kavi.com X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1694174582; x=1694779382; h=content-transfer-encoding:mime-version:message-id:in-reply-to:date :subject:cc:to:from:user-agent:references:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=usGbO52px+d14iZwGFx0u9Kcrr0MplJaiZE9VDoQlxE=; b=TM80PxGgZ5jkfGmfmy5AhxDIfqImCwj60mm6u4f0SCDUGhBk0S9eQ3qpNxE/Q4vKZe wr6ftxpXZ0AMP6toaIvzwDGx7BlYj2CchpW1HGApjpL9FIaKaJyHkwYzqvseXHTkeaE4 73g0mCCFJCat/MkKNLFOSrNyeKz1KFGR7AFw7VKvQZ66g812Ks32tdN8bURJxo1u4x2l 4z2hzDkhYJkdeAueaitT95DxO8L7y72cJewsbTh4/un4GP+xfwfeqnilpXNxOYkO4ZB6 xr34yrpT8wtDLE3K4sixsGxX+a2rc8ObIDOadSR/l5kEJj/i2dm/anLwFKalPxu3gmFG NSIQ== X-Gm-Message-State: AOJu0YytB6NLwZ9YVsMf0a/XEIAekJvpWCm0Du8FQQ9ru/7u4RZMkUoo 64c7V5V0xlCOxsOPNa3FF+aU5Q== X-Google-Smtp-Source: AGHT+IH8Fv8U/Yc7OdSqJBfJbSzcLVE2OE5vi3qQ+KnSLMI4qLmMpBGYPIxFXkvojWjnliwMGGtLgA== X-Received: by 2002:a05:6000:180b:b0:319:6caa:ada2 with SMTP id m11-20020a056000180b00b003196caaada2mr1672993wrh.47.1694174582462; Fri, 08 Sep 2023 05:03:02 -0700 (PDT) References: <20230901110018.3704459-1-alex.bennee@linaro.org> <87y1hlgdl4.fsf@linaro.org> <20230907192913.GD1560640@fedora> <87h6o517yh.fsf@linaro.org> User-agent: mu4e 1.11.17; emacs 29.1.50 From: Alex =?utf-8?Q?Benn=C3=A9e?= To: Stefan Hajnoczi Cc: Stefan Hajnoczi , Albert Esteve , slp@redhat.com, mst@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, qemu-devel@nongnu.org, virtio-dev@lists.oasis-open.org, virtio-comment@lists.oasis-open.org Date: Fri, 08 Sep 2023 12:59:49 +0100 In-reply-to: Message-ID: <87zg1wzxca.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [virtio-dev] [RFC PATCH v2] docs/interop: define PROBE feature for vhost-user VirtIO devices Stefan Hajnoczi writes: > On Fri, 8 Sept 2023 at 02:43, Alex Benn=C3=A9e w= rote: >> >> >> Stefan Hajnoczi writes: >> >> > On Tue, Sep 05, 2023 at 10:34:11AM +0100, Alex Benn=C3=A9e wrote: >> >> >> >> Albert Esteve writes: >> >> >> >> > This looks great! Thanks for this proposal. >> >> > >> >> > On Fri, Sep 1, 2023 at 1:00=E2=80=AFPM Alex Benn=C3=A9e wrote: >> >> > >> >> > Currently QEMU has to know some details about the VirtIO device >> >> > supported by a vhost-user daemon to be able to setup the guest. Th= is >> >> > makes it hard for QEMU to add support for additional vhost-user >> >> > daemons without adding specific stubs for each additional VirtIO >> >> > device. >> >> > >> >> > This patch suggests a new feature flag (VHOST_USER_PROTOCOL_F_PROB= 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. >> >> > >> >> > Together with the existing features VHOST_USER_PROTOCOL_F_STATUS a= nd >> >> > VHOST_USER_PROTOCOL_F_CONFIG we can create "standalone" vhost-user >> >> > daemons which are capable of handling all aspects of the VirtIO >> >> > transactions with only a generic stub on the QEMU side. These daem= ons >> >> > can also be used without QEMU in situations where there isn't a fu= ll >> >> > VMM managing their setup. >> >> > >> >> > Signed-off-by: Alex Benn=C3=A9e >> >> > >> >> > --- >> >> > v2 >> >> > - dropped F_STANDALONE in favour of F_PROBE >> >> > - split probe details across several messages >> >> > - probe messages don't automatically imply a standalone daemon >> >> > - add wording where probe details interact (F_MQ/F_CONFIG) >> >> > - define VMM and make clear QEMU is only one of many potential V= MMs >> >> > - reword commit message >> >> > --- >> >> > docs/interop/vhost-user.rst | 90 ++++++++++++++++++++++++++++++++= ----- >> >> > hw/virtio/vhost-user.c | 8 ++++ >> >> > 2 files changed, 88 insertions(+), 10 deletions(-) >> >> > >> >> > diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user= .rst >> >> > index 5a070adbc1..ba3b5e07b7 100644 >> >> > --- a/docs/interop/vhost-user.rst >> >> > +++ b/docs/interop/vhost-user.rst >> >> > @@ -7,6 +7,7 @@ Vhost-user Protocol >> >> > .. >> >> > Copyright 2014 Virtual Open Systems Sarl. >> >> > Copyright 2019 Intel Corporation >> >> > + Copyright 2023 Linaro Ltd >> >> > Licence: This work is licensed under the terms of the GNU GPL, >> >> > version 2 or later. See the COPYING file in the top-le= vel >> >> > directory. >> >> > @@ -27,17 +28,31 @@ The protocol defines 2 sides of the communicat= ion, *front-end* and >> >> > *back-end*. The *front-end* is the application that shares its vi= rtqueues, in >> >> > our case QEMU. The *back-end* is the consumer of the virtqueues. >> >> > >> >> > -In the current implementation QEMU is the *front-end*, and the *b= ack-end* >> >> > -is the external process consuming the virtio queues, for example a >> >> > -software Ethernet switch running in user space, such as Snabbswit= ch, >> >> > -or a block device back-end processing read & write to a virtual >> >> > -disk. In order to facilitate interoperability between various bac= k-end >> >> > -implementations, it is recommended to follow the :ref:`Backend pr= ogram >> >> > -conventions `. >> >> > +In the current implementation a Virtual Machine Manager (VMM) suc= h as >> >> > +QEMU is the *front-end*, and the *back-end* is the external proce= ss >> >> > +consuming the virtio queues, for example a software Ethernet swit= ch >> >> > +running in user space, such as Snabbswitch, or a block device bac= k-end >> >> > +processing read & write to a virtual disk. In order to facilitate >> >> > +interoperability between various back-end implementations, it is >> >> > +recommended to follow the :ref:`Backend program conventions >> >> > +`. >> >> > >> >> > The *front-end* and *back-end* can be either a client (i.e. conne= cting) or >> >> > server (listening) in the socket communication. >> >> > >> >> > +Probing device details >> >> > +---------------------- >> >> > + >> >> > +Traditionally the vhost-user daemon *back-end* shares configurati= on >> >> > +responsibilities with the VMM *front-end* which needs to know cer= tain >> >> > +key bits of information about the device. This means the VMM need= s to >> >> > +define at least a minimal stub for each VirtIO device it wants to >> >> > +support. If the daemon supports the right set of protocol feature= s the >> >> > +VMM can probe the daemon for the information it needs to setup the >> >> > +device. See :ref:`Probing features for standalone daemons >> >> > +` for more details. >> >> > + >> >> > + >> >> > Support for platforms other than Linux >> >> > -------------------------------------- >> >> > >> >> > @@ -316,6 +331,7 @@ replies. Here is a list of the ones that do: >> >> > * ``VHOST_USER_GET_VRING_BASE`` >> >> > * ``VHOST_USER_SET_LOG_BASE`` (if ``VHOST_USER_PROTOCOL_F_LOG_SHM= FD``) >> >> > * ``VHOST_USER_GET_INFLIGHT_FD`` (if ``VHOST_USER_PROTOCOL_F_INFL= IGHT_SHMFD``) >> >> > +* ``VHOST_USER_GET_BACKEND_SPECS`` (if ``VHOST_USER_PROTOCOL_F_ST= ANDALONE``) >> >> > >> >> > .. seealso:: >> >> > >> >> > @@ -396,9 +412,10 @@ must support changing some configuration aspe= cts on the fly. >> >> > Multiple queue support >> >> > ---------------------- >> >> > >> >> > -Many devices have a fixed number of virtqueues. In this case the= front-end >> >> > -already knows the number of available virtqueues without communic= ating with the >> >> > -back-end. >> >> > +Many devices have a fixed number of virtqueues. In this case the >> >> > +*front-end* usually already knows the number of available virtque= ues >> >> > +without communicating with the back-end. For standalone daemons t= his >> >> > +number can be can be probed with the ``VHOST_USER_GET_MIN_VQ`` me= ssage. >> >> > >> >> > Some devices do not have a fixed number of virtqueues. Instead t= he maximum >> >> > number of virtqueues is chosen by the back-end. The number can d= epend on host >> >> > @@ -885,6 +902,23 @@ Protocol features >> >> > #define VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS 15 >> >> > #define VHOST_USER_PROTOCOL_F_STATUS 16 >> >> > #define VHOST_USER_PROTOCOL_F_XEN_MMAP 17 >> >> > + #define VHOST_USER_PROTOCOL_F_PROBE 18 >> >> > + >> >> > +.. _probing_features: >> >> > + >> >> > +Probing features for standalone daemons >> >> > +--------------------------------------- >> >> > + >> >> > +The protocol feature ``VHOST_USER_PROTOCOL_F_PROBE`` enables a nu= mber >> >> > +of additional messages which allow the *front-end* to probe detai= ls >> >> > +about the VirtIO device from the *back-end*. However for a *back-= end* >> >> > +to be described as standalone it must also support: >> >> > + >> >> > + * ``VHOST_USER_PROTOCOL_F_STATUS`` >> >> > + * ``VHOST_USER_PROTOCOL_F_CONFIG`` (if there is a config space) >> >> > + >> >> > +which are required to ensure the *back-end* daemon can operate >> >> > +without the *front-end* managing some aspects of its configuratio= n. >> >> > >> >> > Front-end message types >> >> > ----------------------- >> >> > @@ -1440,6 +1474,42 @@ Front-end message types >> >> > query the back-end for its device status as defined in the Virt= io >> >> > specification. >> >> > >> >> > +``VHOST_USER_GET_DEVICE_ID`` >> >> > + :id: 41 >> >> > + :request payload: N/A >> >> > + :reply payload: ``u32`` >> >> > + >> >> > + When the ``VHOST_USER_PROTOCOL_F_PROBE`` protocol feature has b= een >> >> > + successfully negotiated, this message is submitted by the front= -end >> >> > + to query what VirtIO device the back-end support. This is inten= ded >> >> > + to remove the need for the front-end to know ahead of time what= the >> >> > + VirtIO device the backend emulates is. >> >> > + >> >> > +``VHOST_USER_GET_CONFIG_SIZE`` >> >> > + :id: 42 >> >> > + :request payload: N/A >> >> > + :reply payload: ``u32`` >> >> > + >> >> > + When the ``VHOST_USER_PROTOCOL_F_PROBE`` protocol feature has b= een >> >> > + successfully negotiated, this message is submitted by the front= -end >> >> > + to query the size of the VirtIO device's config space. This is >> >> > + intended to remove the need for the front-end to know ahead of = time >> >> > + what the size is. Replying with 0 when >> >> > + ``VHOST_USER_PROTOCOL_F_CONFIG`` has been negotiated would indi= cate >> >> > + an bug. >> >> > + >> >> > +``VHOST_USER_GET_MIN_VQ`` >> >> > + :id: 43 >> >> > + :request payload: N/A >> >> > + :reply payload: ``u32`` >> >> > + >> >> > + When the ``VHOST_USER_PROTOCOL_F_PROBE`` protocol feature has b= een >> >> > + successfully negotiated, this message is submitted by the front= -end to >> >> > + query minimum number of VQ's required to support the device. A >> >> > + device may support more than this number of VQ's if it advertis= es >> >> > + the ``VHOST_USER_PROTOCOL_F_MQ`` protocol feature. Reporting a >> >> > + number greater than the result of ``VHOST_USER_GET_QUEUE_NUM`` = would >> >> > + indicate a bug. >> >> > >> >> > Maybe I lack some background, but not sure what min_vq is here? >> >> >> >> There will be a minimum number of queues you need to support the devi= ce. >> >> For example the virtio-sound spec specifies you need four queues: >> >> control, event, tx, rx >> > >> > I don't understand why the front-end needs to know that? The backend >> > already reports the number of queues and not all of them need to be >> > initialized by the driver. >> >> But how many don't need to be initialised? We can't just skip: >> >> /* Allocate queues */ >> vub->vqs =3D g_ptr_array_sized_new(vub->num_vqs); >> for (int i =3D 0; i < vub->num_vqs; i++) { >> g_ptr_array_add(vub->vqs, >> virtio_add_queue(vdev, vub->vq_size, vub_handle_= output)); >> } >> >> Or are you saying just require probe-able backends to support >> VHOST_USER_PROTOCOL_F_MQ and have it always report the minimmum number >> of queues if it is not a MQ capable device? > > The front-end should prepare to allow the maximum number of virtqueues > returned by VHOST_USER_GET_QUEUE_NUM (VHOST_USER_PROTOCOL_F_MQ). > > VIRTIO Transports have a way to query the maximum number of queues but > not a way to query the minimum number of queues. Why is the minimum > necessary? It seems excessive to automatically create the maximum number of VQs. I guess for backends that don't support the MQ feature (i.e. a variable number of VQs) we could just say VHOST_USER_GET_QUEUE_NUM =3D=3D min. But now we are overloading a different message originally added for something else. --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org