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,URIBL_BLOCKED,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 7FF1CC04AB1 for ; Thu, 9 May 2019 16:50:22 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 55DEF21019 for ; Thu, 9 May 2019 16:50:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 55DEF21019 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:57840 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOmFR-0002k5-Kk for qemu-devel@archiver.kernel.org; Thu, 09 May 2019 12:50:21 -0400 Received: from eggs.gnu.org ([209.51.188.92]:46381) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOmDt-0001zT-5n for qemu-devel@nongnu.org; Thu, 09 May 2019 12:48:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hOmDs-0004hZ-6v for qemu-devel@nongnu.org; Thu, 09 May 2019 12:48:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37702) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hOmDr-0004hG-Vv for qemu-devel@nongnu.org; Thu, 09 May 2019 12:48:44 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id 0DCCA3B712; Thu, 9 May 2019 16:48:42 +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 95FF11710E; Thu, 9 May 2019 16:48:28 +0000 (UTC) Date: Thu, 9 May 2019 17:48:26 +0100 From: "Dr. David Alan Gilbert" To: Cornelia Huck Message-ID: <20190509164825.GG2868@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> <20190509154857.GF2868@work-vm> <20190509175404.512ae7aa.cohuck@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190509175404.512ae7aa.cohuck@redhat.com> User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Thu, 09 May 2019 16:48:43 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2 1/2] vfio/mdev: add version attribute for mdev device X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: cjia@nvidia.com, kvm@vger.kernel.org, aik@ozlabs.ru, Zhengxiao.zx@alibaba-inc.com, shuangtai.tst@alibaba-inc.com, qemu-devel@nongnu.org, kwankhede@nvidia.com, eauger@redhat.com, yi.l.liu@intel.com, eskultet@redhat.com, ziye.yang@intel.com, mlevitsk@redhat.com, pasic@linux.ibm.com, libvir-list@redhat.com, arei.gonglei@huawei.com, felipe@nutanix.com, Ken.Xue@amd.com, kevin.tian@intel.com, Yan Zhao , zhenyuw@linux.intel.com, dinechin@redhat.com, Alex Williamson , intel-gvt-dev@lists.freedesktop.org, changpeng.liu@intel.com, linux-kernel@vger.kernel.org, zhi.a.wang@intel.com, jonathan.davies@nutanix.com, shaopeng.he@intel.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Cornelia Huck (cohuck@redhat.com) wrote: > On Thu, 9 May 2019 16:48:57 +0100 > "Dr. David Alan Gilbert" wrote: > > > * 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. > > So, what would be a reasonable approach? Userspace should first read > the version attributes on both devices (to find out whether migration > is supported at all), and only then figure out via writing whether they > are compatible? > > (Or just go ahead and try, if it does not care about the reason.) Well, I'm OK with something like writing to test whether it's compatible, it's just we need a better way of saying 'no'. I'm not sure if that involves reading back from somewhere after the write or what. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK