Re: [PATCH v2] vfio: Add property documentation

["Cédric Le Goater" <clg@redhat.com>]

On 3/11/25 17:44, Joao Martins wrote:
> On 05/03/2025 13:13, Cédric Le Goater wrote:
>> Joao,
>>
>> On 3/5/25 12:16, Joao Martins wrote:
>>> On 14/02/2025 13:05, Cédric Le Goater wrote:
>>>> +Kirti
>>>> +Joao
>>>>
>>>> On 2/13/25 22:45, Alex Williamson wrote:
>>>>>> +
>>>>>> +    /*
>>>>>> +     * Migration support
>>>>>> +     */
>>>>>> +    object_class_property_set_description(klass, /* 5.2 */
>>>>>> +                                          "x-pre-copy-dirty-page-tracking",
>>>>>> +                                          "Disable dirty pages tracking
>>>>>> during iterative phase");
>>>>>> +    object_class_property_set_description(klass, /* 9.1 */
>>>>>> +                                          "x-device-dirty-page-tracking",
>>>>>> +                                          "Disable device dirty page
>>>>>> tracking and use container-based dirty page tracking");
>>>>> These are really debug as well, right?  They just happen to be
>>>>> migration related debug.
>>>>
>>>> I suppose so. I would rather keep them under the migration topic
>>>> and add 'debug' in the comment.
>>>>
>>>> Changes :
>>>>
>>>>     commit bb0990d1740f ("vfio: Change default dirty pages tracking behavior
>>>> during migration")
>>>>     commit 30b916778517 ("vfio/common: Allow disabling device dirty page
>>>> tracking")
>>>>
>>>> do not explicitly explain why these properties are useful in any way.
>>>>
>>>> Kirti, Joao, could you ?
>>>
>>> Sorry for the extreme delay but I was out travelling for the past 3 weeks for
>>> vacation and work.
>>>
>>> The property is marked as x- but my intent was both debug/testing and to have
>>> something that allows me to select the dirty tracker between device vs platform
>>> dirty tracker if something is wrong with say VF dirty tracker or if there's some
>>> limitations around it. These days we actually use it a lot as my default to have
>>> IOMMU dirty tracker in use. I wouldn't label it exclusively as '(debug)' just
>>> yet.
>>>
>>> The precopy option might be to avoid dirty tracking at all and it's generally
>>> useful when you don't have dirty tracking at all or say snapshots or 'offline
>>> migration'. But I have never seen real use of it, or need for that matter,
>>> except the early days of VFIO migration during testing.
>>
>> Could you please send a patch on top of :
>>
>>    https://lore.kernel.org/qemu-devel/20250217173455.449983-1-clg@redhat.com/
>>
>> This would be great to keep the information in the git history.
> 
> I'll send a patch shortly.

I am about to send a last PR. I will check in the evening
for your update.

Thanks,

C.