netdev - Re: [PATCH bpf-next v8 1/4] bpf: Add update_socket

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Date: Thu, 3 Aug 2023 14:53:38 +0200
From: Simon Horman <horms@...nel.org>
To: Geliang Tang <geliang.tang@...e.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Florent Revest <revest@...omium.org>,
	Brendan Jackman <jackmanb@...omium.org>,
	Matthieu Baerts <matthieu.baerts@...sares.net>,
	Mat Martineau <martineau@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	John Johansen <john.johansen@...onical.com>,
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Stephen Smalley <stephen.smalley.work@...il.com>,
	Eric Paris <eparis@...isplace.org>, Mykola Lysenko <mykolal@...com>,
	Shuah Khan <shuah@...nel.org>, bpf@...r.kernel.org,
	netdev@...r.kernel.org, mptcp@...ts.linux.dev,
	apparmor@...ts.ubuntu.com, linux-security-module@...r.kernel.org,
	selinux@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v8 1/4] bpf: Add update_socket_protocol hook

On Thu, Aug 03, 2023 at 03:30:39PM +0800, Geliang Tang wrote:
> Add a hook named update_socket_protocol in __sys_socket(), for bpf
> progs to attach to and update socket protocol. One user case is to
> force legacy TCP apps to create and use MPTCP sockets instead of
> TCP ones.
> 
> Define a mod_ret set named bpf_mptcp_fmodret_ids, add the hook
> update_socket_protocol into this set, and register it in
> bpf_mptcp_kfunc_init().
> 
> Signed-off-by: Geliang Tang <geliang.tang@...e.com>

...

> diff --git a/net/socket.c b/net/socket.c
> index 2b0e54b2405c..586a437d7a5e 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -1644,11 +1644,36 @@ struct file *__sys_socket_file(int family, int type, int protocol)
>  	return sock_alloc_file(sock, flags, NULL);
>  }
>  
> +/**

Hi Geliang Tang,

nit: The format of the text below is not in kernel doc format,
     so it is probably better if the comment begins with '/*'
     rather than '/**'.

> + *	A hook for bpf progs to attach to and update socket protocol.
> + *
> + *	A static noinline declaration here could cause the compiler to
> + *	optimize away the function. A global noinline declaration will
> + *	keep the definition, but may optimize away the callsite.
> + *	Therefore, __weak is needed to ensure that the call is still
> + *	emitted, by telling the compiler that we don't know what the
> + *	function might eventually be.
> + *
> + *	__diag_* below are needed to dismiss the missing prototype warning.
> + */

...