Re: [PATCH mptcp-next v3 2/2] mptcp: add TCP_MAXSEG sockopt support

[Matthieu Baerts <matttbe@kernel.org>]

On 30/04/2025 07:49, Geliang Tang wrote:
> From: Geliang Tang <tanggeliang@kylinos.cn>
> 
> The TCP_MAXSEG socket option is currently not supported by MPTCP, mainly
> because it has never been requested before. But there are still valid
> use-cases, e.g. with HAProxy.
> 
> This patch adds its support in MPTCP by propagating the value to all
> subflows.
> 
> Similar to mptcp_setsockopt_first_sf_only(), a generic helper
> mptcp_setsockopt_all_subflows() is added to set sockopt for each
> subflows of the mptcp socket.
> 
> Add a new member for struct mptcp_sock to store the TCP_MAXSEG value,
> and return this value in getsockopt.
> 
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/515
> Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
> ---
>  net/mptcp/protocol.h |  1 +
>  net/mptcp/sockopt.c  | 25 +++++++++++++++++++++++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
> index 64aa091cb685..91aaed17fe56 100644
> --- a/net/mptcp/protocol.h
> +++ b/net/mptcp/protocol.h
> @@ -327,6 +327,7 @@ struct mptcp_sock {
>  	int		keepalive_cnt;
>  	int		keepalive_idle;
>  	int		keepalive_intvl;
> +	int		maxseg;
>  	struct work_struct work;
>  	struct sk_buff  *ooo_last_skb;
>  	struct rb_root  out_of_order_queue;
> diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
> index afa54fba51e2..5a002dd05cc9 100644
> --- a/net/mptcp/sockopt.c
> +++ b/net/mptcp/sockopt.c
> @@ -798,6 +798,22 @@ static int mptcp_setsockopt_first_sf_only(struct mptcp_sock *msk, int level, int
>  	return ret;
>  }
>  
> +static int mptcp_setsockopt_all_subflows(struct mptcp_sock *msk, int level, int optname,

Checkpatch was complaining about this line because we were over 80
chars. I just did a modification to avoid that, and while at it, I also
use 'mptcp_setsockopt_all_sf', similar to 'first_sf_only' and what was
suggested there:

https://patchwork.kernel.org/project/mptcp/patch/20230707-mptcp-unify-sockopt-issue-353-v1-5-693e15c06646@tessares.net/

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