Re: [PATCH 1/1] io_uring/zctx: separate notification user_data

[Pavel Begunkov <asml.silence@gmail.com>]

On 2/16/26 15:10, Jens Axboe wrote:
> On 2/16/26 4:48 AM, Pavel Begunkov wrote:
>> People previously asked for the notification CQE to have a different
>> user_data value from the main request completion. It's useful to
>> separate buffer and request handling logic and avoid separately
>> refcounting the request.
>>
>> Let the user pass the notification user_data in sqe->addr3. If zero,
>> it'll inherit sqe->user_data as before. It doesn't change the rules for
>> when the user can expect a notification CQE, and it should still check
>> the IORING_CQE_F_MORE flag.
> 
> This should use and sqe->ioprio flag to manage it, otherwise you're
> excluding 0. Which may not be important in and of itself, but the
> flag approach is expected way to do this.

What's the benefit? It's not unreasonable to exclude zero, it won't
limit any use cases, and it's not new either (i.e. buffer tags).
On the other hand, the user will now have to modify two fields
instead of one, which is cleaner. And you're taking one extra bit
out of 16bit ->ioprio, which is not critical if it's all going to
be flags, but it wouldn't be an outrageous idea to take 8 bits
out of it for some index, for example.

-- 
Pavel Begunkov