device compatibility interface for live migration with assigned devices

Jason Wang jasowang at
Wed Aug 5 08:02:48 UTC 2020

On 2020/8/5 下午3:56, Jiri Pirko wrote:
> Wed, Aug 05, 2020 at 04:41:54AM CEST, jasowang at wrote:
>> On 2020/8/5 上午10:16, Yan Zhao wrote:
>>> On Wed, Aug 05, 2020 at 10:22:15AM +0800, Jason Wang wrote:
>>>> On 2020/8/5 上午12:35, Cornelia Huck wrote:
>>>>> [sorry about not chiming in earlier]
>>>>> On Wed, 29 Jul 2020 16:05:03 +0800
>>>>> Yan Zhao <yan.y.zhao at> wrote:
>>>>>> On Mon, Jul 27, 2020 at 04:23:21PM -0600, Alex Williamson wrote:
>>>>> (...)
>>>>>>> Based on the feedback we've received, the previously proposed interface
>>>>>>> is not viable.  I think there's agreement that the user needs to be
>>>>>>> able to parse and interpret the version information.  Using json seems
>>>>>>> viable, but I don't know if it's the best option.  Is there any
>>>>>>> precedent of markup strings returned via sysfs we could follow?
>>>>> I don't think encoding complex information in a sysfs file is a viable
>>>>> approach. Quoting Documentation/filesystems/sysfs.rst:
>>>>> "Attributes should be ASCII text files, preferably with only one value
>>>>> per file. It is noted that it may not be efficient to contain only one
>>>>> value per file, so it is socially acceptable to express an array of
>>>>> values of the same type.
>>>>> Mixing types, expressing multiple lines of data, and doing fancy
>>>>> formatting of data is heavily frowned upon."
>>>>> Even though this is an older file, I think these restrictions still
>>>>> apply.
>>>> +1, that's another reason why devlink(netlink) is better.
>>> hi Jason,
>>> do you have any materials or sample code about devlink, so we can have a good
>>> study of it?
>>> I found some kernel docs about it but my preliminary study didn't show me the
>>> advantage of devlink.
>> CC Jiri and Parav for a better answer for this.
>> My understanding is that the following advantages are obvious (as I replied
>> in another thread):
>> - existing users (NIC, crypto, SCSI, ib), mature and stable
>> - much better error reporting (ext_ack other than string or errno)
>> - namespace aware
>> - do not couple with kobject
> Jason, what is your use case?

I think the use case is to report device compatibility for live 
migration. Yan proposed a simple sysfs based migration version first, 
but it looks not sufficient and something based on JSON is discussed.

Yan, can you help to summarize the discussion so far for Jiri as a 


>> Thanks
>>> Thanks
>>> Yan

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