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

[Yan Zhao]

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 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.

> 
> >    - 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.
> 
it's vendor driver specific.
vendor specific attributes are inevitable, and that's why we are
discussing here of a way to standardizing of it.
our goal is that mgmt can use it without understanding the meaning of vendor
specific attributes.

> 
> > 
> > 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?
>
no. just attributes under migration directory.

> 
> > 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)
sorry, I just know we are in the process of standardizing of it :)

> - how hard for the mgmt to learn with a vendor specific attributes (vs
> existing management API)
what is existing management API?

Thanks