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

[Yonghong Song <yonghong.song@linux.dev>]

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.

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
>
>