[PATCH 0/4] Allow MMIO regions to be exported through dma-buf

[Christian König]

Am 19.08.22 um 15:39 schrieb Jason Gunthorpe:
> On Fri, Aug 19, 2022 at 03:33:04PM +0200, Christian König wrote:
>
>>>>> So we could delete the try_buf and just rely on move being safe on
>>>>> partially destroyed dma_buf's as part of the API design.
>>>> I think that might be the more defensive approach. A comment on the
>>>> dma_buf_move_notify() function should probably be a good idea.
>>> IMHO, it is an anti-pattern. The caller should hold a strong reference
>>> on an object before invoking any API surface. Upgrading a weak
>>> reference to a strong reference requires the standard "try get" API.
>>>
>>> But if you feel strongly I don't mind dropping the try_get around move.
>> Well I see it as well that both approaches are not ideal, but my gut feeling
>> tells me that just documenting that dma_buf_move_notify() can still be
>> called as long as the release callback wasn't called yet is probably the
>> better approach.
> The comment would say something like:
>
>   "dma_resv_lock(), dma_buf_move_notify(), dma_resv_unlock() may be
>    called with a 0 refcount so long as ops->release() hasn't returned"
>
> Which is a really abnormal API design, IMHO.

Mhm, Daniel or other do you have any opinion on that as well?

Thanks,
Christian.

>
> Jason