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Date: Fri, 28 Mar 2025 15:02:50 +0000
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Subject: Re: SOCKET_URING_OP_GETSOCKOPT SOL_SOCKET restriction
To: Jens Axboe <axboe@kernel.dk>, Stefan Metzmacher <metze@samba.org>
Cc: io-uring <io-uring@vger.kernel.org>, Breno Leitao <leitao@debian.org>
References: <a41d8ee5-e859-4ec6-b01f-c0ea3d753704@samba.org>
<272ceaca-3e53-45ae-bbd4-2590f36c7ef8@kernel.dk>
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From: Pavel Begunkov <asml.silence@gmail.com>
In-Reply-To: <272ceaca-3e53-45ae-bbd4-2590f36c7ef8@kernel.dk>
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On 3/28/25 14:30, Jens Axboe wrote:
> On 3/28/25 8:27 AM, Stefan Metzmacher wrote:
>> Hi Jens,
>>
>> while playing with the kernel QUIC driver [1],
>> I noticed it does a lot of getsockopt() and setsockopt()
>> calls to sync the required state into and out of the kernel.
>>
>> My long term plan is to let the userspace quic handshake logic
>> work with SOCKET_URING_OP_GETSOCKOPT and SOCKET_URING_OP_SETSOCKOPT.
>>
>> The used level is SOL_QUIC and that won't work
>> as io_uring_cmd_getsockopt() has a restriction to
>> SOL_SOCKET, while there's no restriction in
>> io_uring_cmd_setsockopt().
>>
>> What's the reason to have that restriction?
>> And why is it only for the get path and not
>> the set path?
>
> There's absolutely no reason for that, looks like a pure oversight?!
Cc Breno, he can explain better, but IIRC that's because most
of set/get sockopt options expect user pointers to be passed in,
and io_uring wants to use kernel memory. It's plumbed for
SOL_SOCKET with sockptr_t, but there was a push back against
converting the rest.
The implications are not the uapi side. For example, io_uring
get/setsockopt returns err / len in a cqe->res. We can't do
that for SOL_SOCKET without the kernel pointer support, otherwise
io-uring uapi would need to get hacky. E.g. you'd need to
pass another user pointer is an SQE for socklen and read it
after completion.
--
Pavel Begunkov