netdev - Re: [PATCH bpf-next] mptcp: Add struct mptcp_sock definition when CONFIG

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Date:   Mon, 11 Jul 2022 14:21:17 -0700 (PDT)
From:   Mat Martineau <mathew.j.martineau@...ux.intel.com>
To:     Jiri Olsa <jolsa@...nel.org>
cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Matthieu Baerts <matthieu.baerts@...sares.net>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Geliang Tang <geliang.tang@...e.com>, mptcp@...ts.linux.dev
Subject: Re: [PATCH bpf-next] mptcp: Add struct mptcp_sock definition when
 CONFIG_MPTCP is disabled

On Mon, 11 Jul 2022, Jiri Olsa wrote:

> The btf_sock_ids array needs struct mptcp_sock BTF ID for
> the bpf_skc_to_mptcp_sock helper.
>
> When CONFIG_MPTCP is disabled, the 'struct mptcp_sock' is not
> defined and resolve_btfids will complain with:
>
>  BTFIDS  vmlinux
> WARN: resolve_btfids: unresolved symbol mptcp_sock
>
> Adding empty difinition for struct mptcp_sock when CONFIG_MPTCP
> is disabled.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
> include/net/mptcp.h | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/include/net/mptcp.h b/include/net/mptcp.h
> index ac9cf7271d46..25741a52c666 100644
> --- a/include/net/mptcp.h
> +++ b/include/net/mptcp.h
> @@ -59,6 +59,10 @@ struct mptcp_addr_info {
> 	};
> };
>
> +#if !IS_ENABLED(CONFIG_MPTCP)
> +struct mptcp_sock { };
> +#endif

The only use of struct mptcp_sock I see with !CONFIG_MPTCP is from this 
stub at the end of mptcp.h:

static inline struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk) { return NULL; }

It's normally defined in net/mptcp/protocol.h for the MPTCP subsystem 
code.

The conditional could be added on the line before the stub to make it 
clear that the empty struct is associated with that inline stub.

> +
> struct mptcp_out_options {
> #if IS_ENABLED(CONFIG_MPTCP)
> 	u16 suboptions;
> -- 
> 2.35.3
>
>

--
Mat Martineau
Intel