Re: [PATCH v2] vfio: Add property documentation

["Cédric Le Goater" <clg@redhat.com>]

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.

Thanks,

C.