netdev - Re: IORING_SEND_NOTIF_USER_DATA (was Re: IORING_CQE_F

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Date:   Fri, 21 Oct 2022 10:27:29 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Stefan Metzmacher <metze@...ba.org>,
        io-uring <io-uring@...r.kernel.org>, Jens Axboe <axboe@...nel.dk>
Cc:     Jakub Kicinski <kuba@...nel.org>, netdev <netdev@...r.kernel.org>,
        Dylan Yudaken <dylany@...com>
Subject: Re: IORING_SEND_NOTIF_USER_DATA (was Re: IORING_CQE_F_COPIED)

On 10/21/22 09:32, Stefan Metzmacher wrote:
> Hi Pavel,
> 
>>>>> Experimenting with this stuff lets me wish to have a way to
>>>>> have a different 'user_data' field for the notif cqe,
>>>>> maybe based on a IORING_RECVSEND_ flag, it may make my life
>>>>> easier and would avoid some complexity in userspace...
>>>>> As I need to handle retry on short writes even with MSG_WAITALL
>>>>> as EINTR and other errors could cause them.
>>>>>
>>>>> What do you think?
>>>
>>> Any comment on this?
>>>
>>> IORING_SEND_NOTIF_USER_DATA could let us use
>>> notif->cqe.user_data = sqe->addr3;
>>
>> I'd rather not use the last available u64, tbh, that was the
>> reason for not adding a second user_data in the first place.
> 
> As far as I can see io_send_zc_prep has this:
> 
>          if (unlikely(READ_ONCE(sqe->__pad2[0]) || READ_ONCE(sqe->addr3)))
>                  return -EINVAL;
> 
> both are u64...

Hah, true, completely forgot about that one

-- 
Pavel Begunkov