device compatibility interface for live migration with assigned devices

Eric Farman farman at
Thu Aug 13 19:02:53 UTC 2020

On 8/13/20 11:33 AM, Cornelia Huck wrote:
> On Fri, 7 Aug 2020 13:59:42 +0200
> Cornelia Huck <cohuck at> wrote:
>> On Wed, 05 Aug 2020 12:35:01 +0100
>> Sean Mooney <smooney at> wrote:
>>> On Wed, 2020-08-05 at 12:53 +0200, Jiri Pirko wrote:  
>>>> Wed, Aug 05, 2020 at 11:33:38AM CEST, yan.y.zhao at wrote:    
>> (...)
>>>>>    software_version: device driver's version.
>>>>>               in <major>.<minor>[.bugfix] scheme, where there is no
>>>>> 	       compatibility across major versions, minor versions have
>>>>> 	       forward compatibility (ex. 1-> 2 is ok, 2 -> 1 is not) and
>>>>> 	       bugfix version number indicates some degree of internal
>>>>> 	       improvement that is not visible to the user in terms of
>>>>> 	       features or compatibility,
>>>>> vendor specific attributes: each vendor may define different attributes
>>>>>   device id : device id of a physical devices or mdev's parent pci device.
>>>>>               it could be equal to pci id for pci devices
>>>>>   aggregator: used together with mdev_type. e.g. aggregator=2 together
>>>>>               with i915-GVTg_V5_4 means 2*1/4=1/2 of a gen9 Intel
>>>>> 	       graphics device.
>>>>>   remote_url: for a local NVMe VF, it may be configured with a remote
>>>>>               url of a remote storage and all data is stored in the
>>>>> 	       remote side specified by the remote url.
>>>>>   ...    
>>> just a minor not that i find ^ much more simmple to understand then
>>> the current proposal with self and compatiable.
>>> if i have well defiend attibute that i can parse and understand that allow
>>> me to calulate the what is and is not compatible that is likely going to
>>> more useful as you wont have to keep maintianing a list of other compatible
>>> devices every time a new sku is released.
>>> in anycase thank for actully shareing ^ as it make it simpler to reson about what
>>> you have previously proposed.  
>> So, what would be the most helpful format? A 'software_version' field
>> that follows the conventions outlined above, and other (possibly
>> optional) fields that have to match?
> Just to get a different perspective, I've been trying to come up with
> what would be useful for a very different kind of device, namely
> vfio-ccw. (Adding Eric to cc: for that.)
> software_version makes sense for everybody, so it should be a standard
> attribute.
> For the vfio-ccw type, we have only one vendor driver (vfio-ccw_IO).
> Given a subchannel A, we want to make sure that subchannel B has a
> reasonable chance of being compatible. I guess that means:
> - same subchannel type (I/O)
> - same chpid type (e.g. all FICON; I assume there are no 'mixed' setups
>   -- Eric?)


> - same number of chpids? Maybe we can live without that and just inject
>   some machine checks, I don't know. Same chpid numbers is something we
>   cannot guarantee, especially if we want to migrate cross-CEC (to
>   another machine.)

I think we'd live without it, because I wouldn't expect it to be
consistent between systems.

> Other possibly interesting information is not available at the
> subchannel level (vfio-ccw is a subchannel driver.)

I presume you're alluding to the DASD uid (dasdinfo -x) here?

> So, looking at a concrete subchannel on one of my machines, it would
> look something like the following:
> <common>
> software_version=1.0.0
> type=vfio-ccw          <-- would be vfio-pci on the example above
> <vfio-ccw specific>
> subchannel_type=0
> <vfio-ccw_IO specific>
> chpid_type=0x1a
> chpid_mask=0xf0        <-- not sure if needed/wanted
> Does that make sense?

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