netdev - Re: [PATCH 0/5] add initial io_uring

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Date:   Tue, 11 Apr 2023 08:41:15 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     David Ahern <dsahern@...nel.org>, Breno Leitao <leitao@...ian.org>
Cc:     Willem de Bruijn <willemb@...gle.com>, io-uring@...r.kernel.org,
        netdev@...r.kernel.org, kuba@...nel.org, asml.silence@...il.com,
        leit@...com, edumazet@...gle.com, pabeni@...hat.com,
        davem@...emloft.net, dccp@...r.kernel.org, mptcp@...ts.linux.dev,
        linux-kernel@...r.kernel.org, willemdebruijn.kernel@...il.com,
        matthieu.baerts@...sares.net, marcelo.leitner@...il.com
Subject: Re: [PATCH 0/5] add initial io_uring_cmd support for sockets

On 4/11/23 8:36?AM, David Ahern wrote:
> On 4/11/23 6:00 AM, Breno Leitao wrote:
>> I am not sure if avoiding io_uring details in network code is possible.
>>
>> The "struct proto"->uring_cmd callback implementation (tcp_uring_cmd()
>> in the TCP case) could be somewhere else, such as in the io_uring/
>> directory, but, I think it might be cleaner if these implementations are
>> closer to function assignment (in the network subsystem).
>>
>> And this function (tcp_uring_cmd() for instance) is the one that I am
>> planning to map io_uring CMDs to ioctls. Such as SOCKET_URING_OP_SIOCINQ
>> -> SIOCINQ.
>>
>> Please let me know if you have any other idea in mind.
> 
> I am not convinced that this io_uring_cmd is needed. This is one
> in-kernel subsystem calling into another, and there are APIs for that.
> All of this set is ioctl based and as Willem noted a little refactoring
> separates the get_user/put_user out so that in-kernel can call can be
> made with existing ops.

How do you want to wire it up then? We can't use fops->unlocked_ioctl()
obviously, and we already have ->uring_cmd() for this purpose.

I do think the right thing to do is have a common helper that returns
whatever value you want (or sets it), and split the ioctl parts into a
wrapper around that that simply copies in/out as needed. Then
->uring_cmd() could call that, or you could some exported function that
does supports that.

This works for the basic cases, though I do suspect we'll want to go
down the ->uring_cmd() at some point for more advanced cases or cases
that cannot sanely be done in an ioctl fashion.

-- 
Jens Axboe