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Tue, 18 Aug 2020 09:36:54 +0000 (UTC) Date: Tue, 18 Aug 2020 11:36:52 +0200 From: Cornelia Huck To: "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" Subject: Re: device compatibility interface for live migration with assigned devices Message-ID: <20200818113652.5d81a392.cohuck@redhat.com> In-Reply-To: <20200818091628.GC20215@redhat.com> 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> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Received-SPF: none client-ip=205.139.110.120; envelope-from=cohuck@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/18 03:19:25 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm@vger.kernel.org, libvir-list@redhat.com, Jason Wang , 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, Yan Zhao , 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 , smooney@redhat.com, intel-gvt-dev@lists.freedesktop.org, eskultet@redhat.com, Jiri Pirko , dinechin@redhat.com, devel@ovirt.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 18 Aug 2020 10:16:28 +0100 Daniel P. Berrang=C3=A9 wrote: > On Tue, Aug 18, 2020 at 05:01:51PM +0800, Jason Wang wrote: > > On 2020/8/18 =E4=B8=8B=E5=8D=884:55, Daniel P. Berrang=C3=A9 wrote: > >=20 > > On Tue, Aug 18, 2020 at 11:24:30AM +0800, Jason Wang wrote: > >=20 > > On 2020/8/14 =E4=B8=8B=E5=8D=881:16, Yan Zhao wrote: > >=20 > > On Thu, Aug 13, 2020 at 12:24:50PM +0800, Jason Wang wrote: > >=20 > > On 2020/8/10 =E4=B8=8B=E5=8D=883:46, Yan Zhao wrote: =20 >=20 > > we actually can also retrieve the same information through sysfs, .e.g > >=20 > > |- [path to device] > > |--- migration > > | |--- self > > | | |---device_api > > | | |---mdev_type > > | | |---software_version > > | | |---device_id > > | | |---aggregator > > | |--- compatible > > | | |---device_api > > | | |---mdev_type > > | | |---software_version > > | | |---device_id > > | | |---aggregator > >=20 > >=20 > > Yes but: > >=20 > > - 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? [Also, I think that self/compatible split in the example makes things needlessly complex. Shouldn't semantic versioning and matching already cover nearly everything? 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.] > >=20 > > All of above seems unnecessary. > >=20 > > 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 ha= ving a > > vendor specific API looks much better. > >=20 > > From the POV of userspace mgmt apps doing device compat checking / mig= ration, > > we certainly do NOT want to use different vendor specific APIs. We wan= t to > > have an API that can be used / controlled in a standard manner across = vendors. > >=20 > > 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 t= wo > > APIs needs to be supported ... =20 >=20 > 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 wi= th > to be vendor specific. =46rom 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.) >=20 > What I care about is that we have a *standard* userspace API for performi= ng > device compatibility checking / state migration, for use by QEMU/libvirt/ > OpenStack, such that we can write code without countless vendor specific > code paths. >=20 > If there is vendor specific stuff on the side, that's fine as we can igno= re > 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 ?