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

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Date:   Tue, 11 Apr 2023 09:10:32 -0600
From:   David Ahern <dsahern@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>, 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 8:41 AM, Jens Axboe wrote:
> 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.
> 

My meta point is that there are uapis today to return this information
to applications (and I suspect this is just the start of more networking
changes - both data retrieval and adjusting settings). io_uring is
wanting to do this on behalf of the application without a syscall. That
makes io_uring yet another subsystem / component managing a socket. Any
change to the networking stack required by io_uring should be usable by
all other in-kernel socket owners or managers. ie., there is no reason
for io_uring specific code here.