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

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)

>>>> >>> sorry, I don't understand here, why virtio devices need to use vfio interface? >> >> I don't see any reason that virtio devices can't be used by VFIO. Do you? >> >> Actually, virtio devices have been used by VFIO for many years: >> >> - passthrough a hardware virtio devices to userspace(VM) drivers >> - using virtio PMD inside guest >> > So, what's different for it vs passing through a physical hardware via VFIO? The difference is in the guest, the device could be either real hardware or emulated ones. > even though the features are negotiated dynamically, could you explain > why it would cause software_version not work? Virtio device 1 supports feature A, B, C Virtio device 2 supports feature B, C, D So you can't migrate a guest from device 1 to device 2. And it's impossible to model the features with versions.

> > >>> I think this thread is discussing about vfio related devices. >>> >>>>> - 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.

Thanks for the patience. Since sysfs is uABI, when accepted, we need support it forever. That's why we need to be careful.