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 X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B4598C433E1 for ; Wed, 19 Aug 2020 02:54:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 89E6A2076E for ; Wed, 19 Aug 2020 02:54:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OiJFqrqU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726852AbgHSCyd (ORCPT ); Tue, 18 Aug 2020 22:54:33 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:30080 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726718AbgHSCyc (ORCPT ); Tue, 18 Aug 2020 22:54:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1597805670; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=OyfXHDOh3tadbBcQyUmurCPsA+lHPesiQMeXAJCp/nc=; b=OiJFqrqUeN8hDTapH/ujMRVmOQtv/EPJs7ua6I52WuT2TPZrnonb0zYfwvpgDQpMxvnmWH 0xmAYRwY+wdzM+UCytm7+tKTTHNEwEdvUNR+Xn5Kht88CtZ5cTzYL1jUq5Qh6a1W+fml5J xt6ILlqrzTjQVHSS9lWmZXdByLxBjv4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-207-Ay-EfPfqMQ6MMOO5kbt_wg-1; Tue, 18 Aug 2020 22:54:29 -0400 X-MC-Unique: Ay-EfPfqMQ6MMOO5kbt_wg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7656381F030; Wed, 19 Aug 2020 02:54:26 +0000 (UTC) Received: from [10.72.13.88] (ovpn-13-88.pek2.redhat.com [10.72.13.88]) by smtp.corp.redhat.com (Postfix) with ESMTP id D15481B47B; Wed, 19 Aug 2020 02:54:08 +0000 (UTC) Subject: Re: device compatibility interface for live migration with assigned devices To: Cornelia Huck , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= Cc: Yan Zhao , kvm@vger.kernel.org, libvir-list@redhat.com, qemu-devel@nongnu.org, kwankhede@nvidia.com, eauger@redhat.com, xin-ran.wang@intel.com, corbet@lwn.net, openstack-discuss@lists.openstack.org, shaohe.feng@intel.com, kevin.tian@intel.com, Parav Pandit , jian-feng.ding@intel.com, dgilbert@redhat.com, zhenyuw@linux.intel.com, hejie.xu@intel.com, bao.yumeng@zte.com.cn, Alex Williamson , eskultet@redhat.com, smooney@redhat.com, intel-gvt-dev@lists.freedesktop.org, Jiri Pirko , dinechin@redhat.com, devel@ovirt.org References: <20200805075647.GB2177@nanopsycho> <20200805093338.GC30485@joy-OptiPlex-7040> <20200805105319.GF2177@nanopsycho> <20200810074631.GA29059@joy-OptiPlex-7040> <20200814051601.GD15344@joy-OptiPlex-7040> <20200818085527.GB20215@redhat.com> <3a073222-dcfe-c02d-198b-29f6a507b2e1@redhat.com> <20200818091628.GC20215@redhat.com> <20200818113652.5d81a392.cohuck@redhat.com> From: Jason Wang Message-ID: Date: Wed, 19 Aug 2020 10:54:07 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200818113652.5d81a392.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2020/8/18 下午5:36, Cornelia Huck wrote: > On Tue, 18 Aug 2020 10:16:28 +0100 > Daniel P. Berrangé wrote: > >> On Tue, Aug 18, 2020 at 05:01:51PM +0800, Jason Wang wrote: >>> On 2020/8/18 下午4:55, Daniel P. Berrangé wrote: >>> >>> On Tue, Aug 18, 2020 at 11:24:30AM +0800, Jason Wang wrote: >>> >>> On 2020/8/14 下午1:16, Yan Zhao wrote: >>> >>> On Thu, Aug 13, 2020 at 12:24:50PM +0800, Jason Wang wrote: >>> >>> On 2020/8/10 下午3:46, Yan Zhao wrote: >>> we actually can also retrieve the same information through sysfs, .e.g >>> >>> |- [path to device] >>> |--- migration >>> | |--- self >>> | | |---device_api >>> | | |---mdev_type >>> | | |---software_version >>> | | |---device_id >>> | | |---aggregator >>> | |--- compatible >>> | | |---device_api >>> | | |---mdev_type >>> | | |---software_version >>> | | |---device_id >>> | | |---aggregator >>> >>> >>> Yes but: >>> >>> - You need one file per attribute (one syscall for one attribute) >>> - Attribute is coupled with kobject > Is that really that bad? You have the device with an embedded kobject > anyway, and you can just put things into an attribute group? Yes, but all of this could be done via devlink(netlink) as well with low overhead. > > [Also, I think that self/compatible split in the example makes things > needlessly complex. Shouldn't semantic versioning and matching already > cover nearly everything? That's my question as well. E.g for virtio, versioning may not even work, some of features are negotiated independently: Source features: A, B, C Dest features: A, B, C, E We just need to make sure the dest features is a superset of source then all set. > I would expect very few cases that are more > complex than that. Maybe the aggregation stuff, but I don't think we > need that self/compatible split for that, either.] > >>> All of above seems unnecessary. >>> >>> Another point, as we discussed in another thread, it's really hard to make >>> sure the above API work for all types of devices and frameworks. So having a >>> vendor specific API looks much better. >>> >>> From the POV of userspace mgmt apps doing device compat checking / migration, >>> we certainly do NOT want to use different vendor specific APIs. We want to >>> have an API that can be used / controlled in a standard manner across vendors. >>> >>> Yes, but it could be hard. E.g vDPA will chose to use devlink (there's a >>> long debate on sysfs vs devlink). So if we go with sysfs, at least two >>> APIs needs to be supported ... >> NB, I was not questioning devlink vs sysfs directly. If devlink is related >> to netlink, I can't say I'm enthusiastic as IMKE sysfs is easier to deal >> with. I don't know enough about devlink to have much of an opinion though. >> The key point was that I don't want the userspace APIs we need to deal with >> to be vendor specific. > From what I've seen of devlink, it seems quite nice; but I understand > why sysfs might be easier to deal with (especially as there's likely > already a lot of code using it.) > > I understand that some users would like devlink because it is already > widely used for network drivers (and some others), but I don't think > the majority of devices used with vfio are network (although certainly > a lot of them are.) Note that though devlink could be popular only in network devices, netlink is widely used by a lot of subsystesm (e.g SCSI). Thanks > >> What I care about is that we have a *standard* userspace API for performing >> device compatibility checking / state migration, for use by QEMU/libvirt/ >> OpenStack, such that we can write code without countless vendor specific >> code paths. >> >> If there is vendor specific stuff on the side, that's fine as we can ignore >> that, but the core functionality for device compat / migration needs to be >> standardized. > To summarize: > - choose one of sysfs or devlink > - have a common interface, with a standardized way to add > vendor-specific attributes > ?