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 555BBEB64D9 for ; Fri, 7 Jul 2023 09:57:33 +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 77FCB2B039 for ; Fri, 7 Jul 2023 09:57:32 +0000 (UTC) Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 4D1E098680D for ; Fri, 7 Jul 2023 09:57:32 +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 3140E984091; Fri, 7 Jul 2023 09:57:32 +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 1E3949867EB for ; Fri, 7 Jul 2023 09:57:32 +0000 (UTC) X-Virus-Scanned: amavisd-new at kavi.com X-MC-Unique: ZEDXxeMIP2WYetnp9Km6cA-1 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688723846; x=1691315846; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=/dIX253dVfraFuoXO78AeOKruzKxsZtte4eZK0L+66I=; b=EgIoMiAnqkJZryHwNfoaXEdKaNyAoYjnOF5yoDRV/ziHPtIwvcJXt07rgNIRYgBO1s vVHipVodmvRQw2nV+wqSTRYmYhsF3ygnUnHO5k6gA5dQAiwy/VMnkTLFsAk0ZAuatAhj thuAnBqkync3Ihg9p7HjBAGkCyxcsUrTgoBd8a6dDsjcok9IP+z1rkSacZQ4ZNhNtv9P tQcR048dOPFP0at1C1qxWXxaclzBspWd3d4wpUn8HsBfCOJeeZ1QNw+16eD7+PIXOP9e Svkasb1BWMf02ZQhQR5/9ClgRxyL53vYnP8yEYVFcXdBDR8h9MYO35J7W6ZBgTpF38p4 BCww== X-Gm-Message-State: ABy/qLbNxSv3UANlJQFPIlqQb3xUaY2hGJl8djRkp484hUiOQVyNG97e ct0xFoKeVzVbdjEF49WLvqXpv682r6zXV4/U8uprw4+zJvUb+cOmOFwqoH1Ad/9TB9CTs9btaP2 4Uwy/DnMEMZfFDx4b1q02isg4VkFl X-Received: by 2002:adf:fc4e:0:b0:314:10d8:b491 with SMTP id e14-20020adffc4e000000b0031410d8b491mr3698236wrs.67.1688723845816; Fri, 07 Jul 2023 02:57:25 -0700 (PDT) X-Google-Smtp-Source: APBJJlERWKNZgkUMMqALvFBDmlw5jND4B8XuLB6IlHMKB0k0yTjunZn48hyqZBSGBWFIzHzElcC3ig== X-Received: by 2002:adf:fc4e:0:b0:314:10d8:b491 with SMTP id e14-20020adffc4e000000b0031410d8b491mr3698220wrs.67.1688723845511; Fri, 07 Jul 2023 02:57:25 -0700 (PDT) Date: Fri, 7 Jul 2023 05:57:21 -0400 From: "Michael S. Tsirkin" To: Alex =?iso-8859-1?Q?Benn=E9e?= Cc: qemu-devel@nongnu.org, virtio-dev@lists.oasis-open.org, slp@redhat.com, marcandre.lureau@redhat.com, stefanha@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: <20230707055141-mutt-send-email-mst@kernel.org> References: <20230704123600.1808604-1-alex.bennee@linaro.org> <20230706124347-mutt-send-email-mst@kernel.org> <87ilawdtug.fsf@linaro.org> MIME-Version: 1.0 In-Reply-To: <87ilawdtug.fsf@linaro.org> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Subject: [virtio-dev] Re: [RFC PATCH] docs/interop: define STANDALONE protocol feature for vhost-user On Fri, Jul 07, 2023 at 08:58:00AM +0100, Alex Bennée wrote: > > "Michael S. Tsirkin" writes: > > > On Tue, Jul 04, 2023 at 01:36:00PM +0100, Alex Bennée 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. > > > >> This patch suggests a new feature flag (VHOST_USER_PROTOCOL_F_STANDALONE) > >> 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. > > > > The reason we do piecemeal is that these existing pieces can be reused > > as others evolve or fall by wayside. > > Sure I have no objection in principle but we then turn code like: > > if (dev->protocol_features & (1ULL << VHOST_USER_PROTOCOL_F_STANDALONE)) { > err = vhost_user_get_backend_specs(dev, errp); > if (err < 0) { > error_setg_errno(errp, EPROTO, "vhost_get_backend_specs failed"); > return -EPROTO; > } > } > > to > > if (dev->protocol_features & (1ULL << VHOST_USER_PROTOCOL_F_ID) && > dev->protocol_features & (1ULL << VHOST_USER_PROTOCOL_F_CFGSZ) && > dev->protocol_features & (1ULL << VHOST_USER_PROTOCOL_F_MINVQ) && > dev->protocol_features & (1ULL << VHOST_USER_PROTOCOL_F_MAXVQ) > ) { > err = vhost_user_get_virtio_id(dev, errp); > if (err < 0) { > error_setg_errno(errp, EPROTO, "vhost_get_backend_id failed"); > return -EPROTO; > } > err = vhost_user_get_virtio_cfgsz(dev, errp); > if (err < 0) { > error_setg_errno(errp, EPROTO, "vhost_get_backend_cfgsz failed"); > return -EPROTO; > } > err = vhost_user_get_virtio_minvq(dev, errp); > if (err < 0) { > error_setg_errno(errp, EPROTO, "vhost_get_backend_minvq failed"); > return -EPROTO; > } > err = vhost_user_get_virtio_maxvq(dev, errp); > if (err < 0) { > error_setg_errno(errp, EPROTO, "vhost_get_backend_maxvq failed"); > return -EPROTO; > } > dev->specs.valid = true; > } > > for little gain IMHO. > > > 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). > > I don't quite follow what you are trying to say here. That some or all of these might be better on qemu command line not come from backend. Then we'll want to *send* it to backend. All this at our discretion without protocol changes. > > What is the reason to have 1 message? startup latency? > > How about we allow pipelining several messages then? > > Will be easier. > > I'm not overly worried about performance because this is all at > start-up. I am worried about excessive complexity though. We already > have quite a lot of interacting protocol messages. > > > > > > >> > >> Signed-off-by: Alex Bennée > >> > >> --- > >> Initial RFC for discussion. I intend to prototype this work with QEMU > >> and one of the rust-vmm vhost-user daemons. > >> --- > >> docs/interop/vhost-user.rst | 37 +++++++++++++++++++++++++++++++++++++ > >> hw/virtio/vhost-user.c | 8 ++++++++ > >> 2 files changed, 45 insertions(+) > >> > >> diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst > >> index 5a070adbc1..85b1b1583a 100644 > >> --- a/docs/interop/vhost-user.rst > >> +++ b/docs/interop/vhost-user.rst > >> @@ -275,6 +275,21 @@ Inflight description > >> > >> :queue size: a 16-bit size of virtqueues > >> > >> +Backend specifications > >> +^^^^^^^^^^^^^^^^^^^^^^ > >> + > >> ++-----------+-------------+------------+------------+ > >> +| device id | config size | min_vqs | max_vqs | > >> ++-----------+-------------+------------+------------+ > >> + > >> +:device id: a 32-bit value holding the VirtIO device ID > >> + > >> +:config size: a 32-bit value holding the config size (see ``VHOST_USER_GET_CONFIG``) > >> + > >> +:min_vqs: a 32-bit value holding the minimum number of vqs supported > >> + > >> +:max_vqs: a 32-bit value holding the maximum number of vqs supported, must be >= min_vqs > >> + > > > > looks like a weird set of info. > > It's basically the information you need for -device vhost-user-device to > start-up (and what is essentially the information set by the stubs as > they start-up). > > > why would we want # of vqs and not their sizes? > > I thought the vring's themselves where allocated by the driver. We only > need to the number of vqs so we can allocate the tracking structures. size is specified by device though > > why config size but not config itself? > > We already have GET_CONFIG and SET_CONFIG but without knowing the size > of the config space we can't properly set it up. I don't get it. each message includes size already. > > > -- > Alex Bennée > 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