Re: [PATCH v2] vfio: Add property documentation

[Joao Martins <joao.m.martins@oracle.com>]

On 11/03/2025 17:43, Cédric Le Goater wrote:
> 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.

Ok -- just sent it

	Joao