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

[Gang Yan <gang_yan@foxmail.com>]

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.

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