Hi Cornelia, > From: Cornelia Huck <cohuck@xxxxxxxxxx> > Sent: Tuesday, August 18, 2020 3:07 PM > To: Daniel P. Berrangé <berrange@xxxxxxxxxx> > Cc: Jason Wang <jasowang@xxxxxxxxxx>; Yan Zhao > <yan.y.zhao@xxxxxxxxx>; kvm@xxxxxxxxxxxxxxx; libvir-list@xxxxxxxxxx; > qemu-devel@xxxxxxxxxx; Kirti Wankhede <kwankhede@xxxxxxxxxx>; > eauger@xxxxxxxxxx; xin-ran.wang@xxxxxxxxx; corbet@xxxxxxx; openstack- > discuss@xxxxxxxxxxxxxxxxxxx; shaohe.feng@xxxxxxxxx; kevin.tian@xxxxxxxxx; > Parav Pandit <parav@xxxxxxxxxxxx>; jian-feng.ding@xxxxxxxxx; > dgilbert@xxxxxxxxxx; zhenyuw@xxxxxxxxxxxxxxx; hejie.xu@xxxxxxxxx; > bao.yumeng@xxxxxxxxxx; Alex Williamson <alex.williamson@xxxxxxxxxx>; > eskultet@xxxxxxxxxx; smooney@xxxxxxxxxx; intel-gvt- > dev@xxxxxxxxxxxxxxxxxxxxx; Jiri Pirko <jiri@xxxxxxxxxxxx>; > dinechin@xxxxxxxxxx; devel@xxxxxxxxx > Subject: Re: device compatibility interface for live migration with assigned > devices > > On Tue, 18 Aug 2020 10:16:28 +0100 > Daniel P. Berrangé <berrange@xxxxxxxxxx> 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? > > [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.] > > > > > > > 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.) > > > > > 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 > ? Please refer to my previous email which has more example and details.
