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Re: device compatibility interface for live migration with assigned devices



On Thu, 20 Aug 2020 08:18:10 +0800
Yan Zhao <yan y zhao intel com> wrote:

> On Wed, Aug 19, 2020 at 11:50:21AM -0600, Alex Williamson wrote:
> <...>
> > > > > > What I care about is that we have a *standard* userspace API for
> > > > > > performing device compatibility checking / state migration, for use by
> > > > > > QEMU/libvirt/ OpenStack, such that we can write code without countless
> > > > > > vendor specific code paths.
> > > > > >
> > > > > > If there is vendor specific stuff on the side, that's fine as we can
> > > > > > ignore that, but the core functionality for device compat / migration
> > > > > > needs to be standardized.    
> > > > > 
> > > > > To summarize:
> > > > > - choose one of sysfs or devlink
> > > > > - have a common interface, with a standardized way to add
> > > > >   vendor-specific attributes
> > > > > ?    
> > > > 
> > > > Please refer to my previous email which has more example and details.    
> > > hi Parav,
> > > the example is based on a new vdpa tool running over netlink, not based
> > > on devlink, right?
> > > For vfio migration compatibility, we have to deal with both mdev and physical
> > > pci devices, I don't think it's a good idea to write a new tool for it, given
> > > we are able to retrieve the same info from sysfs and there's already an
> > > mdevctl from Alex (https://github.com/mdevctl/mdevctl).
> > > 
> > > 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)
> > >    - 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)  
> > 
> > As noted previously, the parent PCI ID should not matter for an mdev
> > device, if a vendor has a dependency on matching the parent device PCI
> > ID, that's a vendor specific restriction.  An mdev device can also
> > expose a vfio-pci device API without the parent device being PCI.  For
> > a physical PCI device, shouldn't the PCI ID be encompassed in the
> > signature?  Thanks,
> >   
> you are right. I need to put the PCI ID as a vendor specific field.
> I didn't do that because I wanted all fields in vendor specific to be
> configurable by management tools, so they can configure the target device
> according to the value of a vendor specific field even they don't know
> the meaning of the field.
> But maybe they can just ignore the field when they can't find a matching
> writable field to configure the target.


If fields can be ignored, what's the point of reporting them?  Seems
it's no longer a requirement.  Thanks,

Alex


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


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