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Fri, 28 Mar 2025 19:41:12 +0000
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Date: Fri, 28 Mar 2025 20:41:10 +0100
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Subject: Re: SOCKET_URING_OP_GETSOCKOPT SOL_SOCKET restriction
To: Pavel Begunkov <asml.silence@gmail.com>, Jens Axboe <axboe@kernel.dk>
Cc: io-uring <io-uring@vger.kernel.org>, Breno Leitao <leitao@debian.org>
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From: Stefan Metzmacher <metze@samba.org>
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Am 28.03.25 um 18:21 schrieb Pavel Begunkov:
> On 3/28/25 17:18, Pavel Begunkov wrote:
>> On 3/28/25 16:34, Jens Axboe wrote:
>>> On 3/28/25 9:02 AM, Pavel Begunkov wrote:
>>>> 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.
>>>
>>> Gah yes, now I remember. What's pretty annoying though, as it leaves the
>>> get/setsockopt parts less useful than they should be, compared to the
>>> regular syscalls.
>>>
>>> Did we ever ponder ways of getting this sorted out on the net side?
>>
>> I remember Breno looking at several different options.
>>
>> Breno, can you remind me, why can't we convert ->getsockopt to
>> take a normal kernel ptr for length while passing a user ptr
>> for value as before?
>
> Similar to this:
>
> getsockopt_syscall(void __user *len_uptr) {
> int klen;
>
> copy_from_user(&klen, len_uptr);
> ->getsockopt(&klen);
> copy_to_user(len_uptr, &klen);
> }
Yes, I was thinking about something similar.
I'll give it a go next week.
Thanks!
metze