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

[Jason Wang]

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)


>     - 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.


>    - subchannel_type (device_api is vfio-ccw)
>   
> vendor driver specific part: (optional)
>    - aggregator
>    - chpid_type
>    - remote_url


For "remote_url", just wonder if it's better to integrate or reuse the 
existing NVME management interface instead of duplicating it here. 
Otherwise it could be a burden for mgmt to learn. E.g vendor A may use 
"remote_url" but vendor B may use a different attribute.


> NOTE: vendors are free to add attributes in this part with a
> restriction that this attribute is able to be configured with the same
> name in sysfs too. e.g.


Sysfs works well for common attributes belongs to a class, but I'm not 
sure it can work well for device/vendor specific attributes. Does this 
mean mgmt need to iterate all the attributes in both src and dst?


> for aggregator, there must be a sysfs attribute in device node
> /sys/devices/pci0000:00/0000:00:02.0/882cc4da-dede-11e7-9180-078a62063ab1/intel_vgpu/aggregator,
> so that the userspace tool is able to configure the target device
> according to source device's aggregator attribute.
>
>
> (2) where and structure
> proposal 1:
> |- [path to device]
>    |--- migration
>    |     |--- self
>    |     |    |-software_version
>    |     |    |-device_api
>    |     |    |-type
>    |     |    |-[pci_id or subchannel_type]
>    |     |    |-<aggregator or chpid_type>
>    |     |--- compatible
>    |     |    |-software_version
>    |     |    |-device_api
>    |     |    |-type
>    |     |    |-[pci_id or subchannel_type]
>    |     |    |-<aggregator or chpid_type>
> multiple compatible is allowed.
> attributes should be ASCII text files, preferably with only one value
> per file.
>
>
> proposal 2: use bin_attribute.
> |- [path to device]
>    |--- migration
>    |     |--- self
>    |     |--- compatible
>
> so we can continue use multiline format. e.g.
> cat compatible
>    software_version=0.1.0
>    device_api=vfio_pci
>    type=i915-GVTg_V5_{val1:int:1,2,4,8}
>    pci_id=80865963
>    aggregator={val1}/2


So basically two questions:

- how hard to standardize sysfs API for dealing with compatibility check 
(to make it work for most types of devices)
- how hard for the mgmt to learn with a vendor specific attributes (vs 
existing management API)

Thanks


> Thanks
> Yan