On Fri, 21 Aug 2020 11:14:41 +0800 Jason Wang <jasowang@xxxxxxxxxx> wrote: > On 2020/8/20 下午8:27, Cornelia Huck wrote: > > On Wed, 19 Aug 2020 17:28:38 +0800 > > Jason Wang <jasowang@xxxxxxxxxx> 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.
