netdev - Re: IORING_SEND_NOTIF_USER_DATA (was Re: IORING_CQE_F

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Date:   Fri, 21 Oct 2022 10:32:16 +0200
From:   Stefan Metzmacher <metze@...ba.org>
To:     Pavel Begunkov <asml.silence@...il.com>,
        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)

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...

metze