netdev - Re: [PATCH bpf-next] bpf: Allow error injection for update_socket

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Message-ID: <f5c0d16e-73bc-4421-a634-099ea1eae4f7@linux.dev>
Date: Fri, 11 Apr 2025 11:06:07 -0700
From: Yonghong Song <yonghong.song@...ux.dev>
To: Geliang Tang <geliang@...nel.org>, Gang Yan <gang_yan@...mail.com>,
 Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, mptcp@...ts.linux.dev
Subject: Re: [PATCH bpf-next] bpf: Allow error injection for
 update_socket_protocol



On 4/9/25 2:17 AM, Geliang Tang wrote:
> Hi Yonghong,
>
> On Sun, 2024-08-25 at 21:05 -0700, Yonghong Song wrote:
>> On 8/25/24 8:29 PM, Gang Yan wrote:
>>> Hi Alexei:
>>> It's my honor to recieve your reply. The response to your concerns
>>> is attached below
>>> for your review.
>>> On Mon, Aug 26, 2024 at 10:57:12AM +0800, Gang Yan wrote:
>>>> On Thu, Aug 22, 2024 at 8:33 AM Jakub Kicinski wrote:
>>>>> On Thu, 22 Aug 2024 14:08:57 +0800 Gang Yan wrote:
>>>>>> diff --git a/net/socket.c b/net/socket.c
>>>>>> index fcbdd5bc47ac..63ce1caf75eb 100644
>>>>>> --- a/net/socket.c
>>>>>> +++ b/net/socket.c
>>>>>> @@ -1695,6 +1695,7 @@ __weak noinline int
>>>>>> update_socket_protocol(int family, int type, int protocol)
>>>>>> {
>>>>>> return protocol;
>>>>>> }
>>>>>> +ALLOW_ERROR_INJECTION(update_socket_protocol, ERRNO);
>>>>> IDK if this falls under BPF or directly net, but could you
>>>>> explain
>>>>> what test will use this? I'd prefer not to add test hooks into
>>>>> the
>>>>> kernel unless they are exercised by in-tree tests.
>>>> This looks unnecessary.
>>>> update_socket_protocol is already registered as fmodret.
>>>> There is even selftest that excises this feature:
>>>> tools/testing/selftests/bpf/progs/mptcpify.c
>>>>
>>>> It doesn't need to be part of the error-inject.
>>> The 'update_socket_protocol' is a BPF interface designed primarily
>>> to
>>> fix the socket protocol from TCP protocol to MPTCP protocol without
>>> requiring modifications to user-space application codes. However,
>>> when attempting to achieve this using the BCC tool in user-space,
>>> the BCC tool doesn't support 'fmod_ret'. Therefore, this patch aims
>>> to
>>> further expand capabilities, enabling the 'kprobe' method can
>>> overriding
>>> the update_socket_protocol interface.
>> Gang Yan, could you explore to add fmod_ret support in bcc? It should
>> be
>> similar to kfunc/kretfunc support. I am happy to review your patches.
> It took us some time to add this support in bcc, and we have recently
> completed it in [1]. We would be grateful if you could help review
> these patches.

Sounds good. I will take a look.

>
> Thanks,
> -Geliang
>
> [1]
> https://github.com/iovisor/bcc/pull/5274
>
>> Thanks,
>> Yonghong
>>
>>> As a Python developer, the BCC tool is a commonly utilized
>>> instrument for
>>> interacting with the kernel. If the kernel could permit the use of
>>> an
>>> error-inject method to modify the `update_socket_protocol`, it
>>> would significantly
>>> benefit the subsequent promotion and development of MPTCP
>>> applications.
>>> Thank you for considering this enhancement.
>>>
>>> Best wishes!
>>> Gang Yan
>>>
>>>
>