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=-2.4 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,T_HK_NAME_DR,USER_AGENT_MUTT autolearn=unavailable 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 25B07C04AB1 for ; Thu, 9 May 2019 15:49:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 023A62173C for ; Thu, 9 May 2019 15:49:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726644AbfEIPtQ (ORCPT ); Thu, 9 May 2019 11:49:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:17718 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726561AbfEIPtP (ORCPT ); Thu, 9 May 2019 11:49:15 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CFA953079B73; Thu, 9 May 2019 15:49:14 +0000 (UTC) Received: from work-vm (ovpn-116-174.ams2.redhat.com [10.36.116.174]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 347CF5B681; Thu, 9 May 2019 15:49:00 +0000 (UTC) Date: Thu, 9 May 2019 16:48:57 +0100 From: "Dr. David Alan Gilbert" To: Cornelia Huck Cc: Alex Williamson , Yan Zhao , intel-gvt-dev@lists.freedesktop.org, arei.gonglei@huawei.com, aik@ozlabs.ru, Zhengxiao.zx@alibaba-inc.com, shuangtai.tst@alibaba-inc.com, qemu-devel@nongnu.org, eauger@redhat.com, yi.l.liu@intel.com, ziye.yang@intel.com, mlevitsk@redhat.com, pasic@linux.ibm.com, felipe@nutanix.com, changpeng.liu@intel.com, Ken.Xue@amd.com, jonathan.davies@nutanix.com, shaopeng.he@intel.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, libvir-list@redhat.com, eskultet@redhat.com, kevin.tian@intel.com, zhenyuw@linux.intel.com, zhi.a.wang@intel.com, cjia@nvidia.com, kwankhede@nvidia.com, berrange@redhat.com, dinechin@redhat.com Subject: Re: [PATCH v2 1/2] vfio/mdev: add version attribute for mdev device Message-ID: <20190509154857.GF2868@work-vm> References: <20190506014514.3555-1-yan.y.zhao@intel.com> <20190506014904.3621-1-yan.y.zhao@intel.com> <20190507151826.502be009@x1.home> <20190509173839.2b9b2b46.cohuck@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190509173839.2b9b2b46.cohuck@redhat.com> User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Thu, 09 May 2019 15:49:15 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org * Cornelia Huck (cohuck@redhat.com) wrote: > On Tue, 7 May 2019 15:18:26 -0600 > Alex Williamson wrote: > > > On Sun, 5 May 2019 21:49:04 -0400 > > Yan Zhao wrote: > > > > + Errno: > > > + If vendor driver wants to claim a mdev device incompatible to all other mdev > > > + devices, it should not register version attribute for this mdev device. But if > > > + a vendor driver has already registered version attribute and it wants to claim > > > + a mdev device incompatible to all other mdev devices, it needs to return > > > + -ENODEV on access to this mdev device's version attribute. > > > + If a mdev device is only incompatible to certain mdev devices, write of > > > + incompatible mdev devices's version strings to its version attribute should > > > + return -EINVAL; > > > > I think it's best not to define the specific errno returned for a > > specific situation, let the vendor driver decide, userspace simply > > needs to know that an errno on read indicates the device does not > > support migration version comparison and that an errno on write > > indicates the devices are incompatible or the target doesn't support > > migration versions. > > I think I have to disagree here: It's probably valuable to have an > agreed error for 'cannot migrate at all' vs 'cannot migrate between > those two particular devices'. Userspace might want to do different > things (e.g. trying with different device pairs). Trying to stuff these things down an errno seems a bad idea; we can't get much information that way. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK