Hi Cornelia,
From: Cornelia Huck <cohuck@redhat.com> Sent: Tuesday, August 18, 2020 3:07 PM To: Daniel P. Berrangé <berrange@redhat.com> Cc: Jason Wang <jasowang@redhat.com>; Yan Zhao <yan.y.zhao@intel.com>; kvm@vger.kernel.org; libvir-list@redhat.com; qemu-devel@nongnu.org; Kirti Wankhede <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 <parav@mellanox.com>; jian-feng.ding@intel.com; dgilbert@redhat.com; zhenyuw@linux.intel.com; hejie.xu@intel.com; bao.yumeng@zte.com.cn; Alex Williamson <alex.williamson@redhat.com>; eskultet@redhat.com; smooney@redhat.com; intel-gvt- dev@lists.freedesktop.org; Jiri Pirko <jiri@mellanox.com>; dinechin@redhat.com; devel@ovirt.org Subject: Re: device compatibility interface for live migration with assigned devices
On Tue, 18 Aug 2020 10:16:28 +0100 Daniel P. Berrangé <berrange@redhat.com> 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.