Re: [ovirt-devel] Re: device compatibility interface for live migration with assigned devices

On Fri, 21 Aug 2020 11:14:41 +0800 Jason Wang <jasowang(a)redhat.com&gt; wrote: > On 2020/8/20 下午8:27, Cornelia Huck wrote: >> On Wed, 19 Aug 2020 17:28:38 +0800 >> Jason Wang <jasowang(a)redhat.com&gt; wrote: >> >>> On 2020/8/19 下午4:13, Yan Zhao wrote: >>>> On Wed, Aug 19, 2020 at 03:39:50PM +0800, Jason Wang wrote: >>>>> On 2020/8/19 下午2:59, Yan Zhao wrote: >>>>>> On Wed, Aug 19, 2020 at 02:57:34PM +0800, Jason Wang wrote: >>>>>>> On 2020/8/19 上午11:30, Yan Zhao wrote: >>>>>>>> hi All, >>>>>>>> could we decide that sysfs is the interface that every VFIO vendor driver >>>>>>>> needs to provide in order to support vfio live migration, otherwise the >>>>>>>> userspace management tool would not list the device into the compatible >>>>>>>> list? >>>>>>>> >>>>>>>> if that's true, let's move to the standardizing of the sysfs interface. >>>>>>>> (1) content >>>>>>>> common part: (must) >>>>>>>> - software_version: (in major.minor.bugfix scheme) >>>>>>> This can not work for devices whose features can be negotiated/advertised >>>>>>> independently. (E.g virtio devices) >> I thought the 'software_version' was supposed to describe kind of a >> 'protocol version' for the data we transmit? I.e., you add a new field, >> you bump the version number. > > Ok, but since we mandate backward compatibility of uABI, is this really > worth to have a version for sysfs? (Searching on sysfs shows no examples > like this) I was not thinking about the sysfs interface, but rather about the data that is sent over while migrating. E.g. we find out that sending some auxiliary data is a good idea and bump to version 1.1.0; version 1.0.0 cannot deal with the extra data, but version 1.1.0 can deal with the older data stream. (...)

>>>>>>>> - device_api: vfio-pci or vfio-ccw ... >>>>>>>> - type: mdev type for mdev device or >>>>>>>> a signature for physical device which is a counterpart for >>>>>>>> mdev type. >>>>>>>> >>>>>>>> device api specific part: (must) >>>>>>>> - pci id: pci id of mdev parent device or pci id of physical pci >>>>>>>> device (device_api is vfio-pci)API here. >>>>>>> So this assumes a PCI device which is probably not true. >>>>>>> >>>>>> for device_api of vfio-pci, why it's not true? >>>>>> >>>>>> for vfio-ccw, it's subchannel_type. >>>>> Ok but having two different attributes for the same file is not good idea. >>>>> How mgmt know there will be a 3rd type? >>>> that's why some attributes need to be common. e.g. >>>> device_api: it's common because mgmt need to know it's a pci device or a >>>> ccw device. and the api type is already defined vfio.h. >>>> (The field is agreed by and actually suggested by Alex in previous mail) >>>> type: mdev_type for mdev. if mgmt does not understand it, it would not >>>> be able to create one compatible mdev device. >>>> software_version: mgmt can compare the major and minor if it understands >>>> this fields. >>> I think it would be helpful if you can describe how mgmt is expected to >>> work step by step with the proposed sysfs API. This can help people to >>> understand. >> My proposal would be: >> - check that device_api matches >> - check possible device_api specific attributes >> - check that type matches [I don't think the combination of mdev types >> and another attribute to determine compatibility is a good idea; > > Any reason for this? Actually if we only use mdev type to detect the > compatibility, it would be much more easier. Otherwise, we are actually > re-inventing mdev types. > > E.g can we have the same mdev types with different device_api and other > attributes? In the end, the mdev type is represented as a string; but I'm not sure we can expect that two types with the same name, but a different device_api are related in any way. If we e.g. compare vfio-pci and vfio-ccw, they are fundamentally different. I was mostly concerned about the aggregation proposal, where type A + aggregation value b might be compatible with type B + aggregation value a.

> >> actually, the current proposal confuses me every time I look at it] >> - check that software_version is compatible, assuming semantic >> versioning >> - check possible type-specific attributes > > I'm not sure if this is too complicated. And I suspect there will be > vendor specific attributes: > > - for compatibility check: I think we should either modeling everything > via mdev type or making it totally vendor specific. Having something in > the middle will bring a lot of burden FWIW, I'm for a strict match on mdev type, and flexibility in per-type attributes.

> - for provisioning: it's still not clear. As shown in this proposal, for > NVME we may need to set remote_url, but unless there will be a subclass > (NVME) in the mdev (which I guess not), we can't prevent vendor from > using another attribute name, in this case, tricks like attributes > iteration in some sub directory won't work. So even if we had some > common API for compatibility check, the provisioning API is still vendor > specific ... Yes, I'm not sure how to deal with the "same thing for different vendors" problem. We can try to make sure that in-kernel drivers play nicely, but not much more.