Re: [PATCH mptcp-next v4 2/4] mptcp: propagate RECVERR sockopts to subflows

[Matthieu Baerts <matttbe@kernel.org>]

On 27/04/2026 23:10, David Carlier wrote:
> Propagate IP_RECVERR/IP_RECVERR_RFC4884 and
> IPV6_RECVERR/IPV6_RECVERR_RFC4884 from the MPTCP socket to existing
> and future subflows. The setsockopt path forwards each option to
> every subflow via mptcp_setsockopt_all_sf(); newly-joining subflows
> inherit the four RECVERR bits through sync_socket_options() now that
> MPTCP_INET_FLAGS_MASK covers them.
> 
> Suggested-by: Paolo Abeni <pabeni@redhat.com>
> Assisted-by: Codex:gpt-5
> Signed-off-by: David Carlier <devnexen@gmail.com>
> ---
>  net/mptcp/sockopt.c | 97 ++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 79 insertions(+), 18 deletions(-)
> 
> diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
> index 41c9dc9cf95e..171e83e66a97 100644
> --- a/net/mptcp/sockopt.c
> +++ b/net/mptcp/sockopt.c

(...)

> @@ -388,6 +394,41 @@ static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname,
>  	return -EOPNOTSUPP;
>  }
>  
> +static int mptcp_setsockopt_all_sf(struct mptcp_sock *msk, int level,
> +				   int optname, sockptr_t optval,
> +				   unsigned int optlen)
> +{
> +	struct mptcp_subflow_context *subflow;
> +	int ret = 0;
> +
> +	mptcp_for_each_subflow(msk, subflow) {
> +		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
> +
> +		ret = tcp_setsockopt(ssk, level, optname, optval, optlen);
> +		if (ret)
> +			break;
> +	}
> +	return ret;
> +}
> +
> +#if IS_ENABLED(CONFIG_IPV6)
> +static int mptcp_setsockopt_v6_recverr(struct mptcp_sock *msk, int optname,
> +				       sockptr_t optval, unsigned int optlen)
> +{
> +	struct sock *sk = (struct sock *)msk;
> +	int ret;
> +
> +	ret = ipv6_setsockopt(sk, SOL_IPV6, optname, optval, optlen);
> +	if (ret)
> +		return ret;
> +
> +	lock_sock(sk);
> +	ret = mptcp_setsockopt_all_sf(msk, SOL_IPV6, optname, optval, optlen);
> +	release_sock(sk);
> +	return ret;
> +}
> +#endif

Maybe you could have one generic helper to call xxx_setsockopt() on the
MPTCP socket, and then call mptcp_setsockopt_all_sf(). You can pass the
level, and call the right function.

(...)

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.