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

Geliang Tang posted 2 patches 7 months, 2 weeks ago
[PATCH mptcp-next v3 2/2] mptcp: add TCP_MAXSEG sockopt support
Posted by Geliang Tang 7 months, 2 weeks ago 
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,
+					 sockptr_t optval, unsigned int optlen)
+{
+	struct mptcp_subflow_context *subflow;
+
+	mptcp_for_each_subflow(msk, subflow) {
+		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
+		int ret = 0;
+
+		ret = tcp_setsockopt(ssk, level, optname, optval, optlen);
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+
 static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
 				    sockptr_t optval, unsigned int optlen)
 {
@@ -859,6 +875,11 @@ static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
 						 &msk->keepalive_cnt,
 						 val);
 		break;
+	case TCP_MAXSEG:
+		msk->maxseg = val;
+		ret = mptcp_setsockopt_all_subflows(msk, SOL_TCP, optname,
+						    optval, optlen);
+		break;
 	default:
 		ret = -ENOPROTOOPT;
 	}
@@ -1406,6 +1427,9 @@ static int mptcp_getsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
 		return mptcp_put_int_option(msk, optval, optlen, msk->notsent_lowat);
 	case TCP_IS_MPTCP:
 		return mptcp_put_int_option(msk, optval, optlen, 1);
+	case TCP_MAXSEG:
+		return mptcp_getsockopt_first_sf_only(msk, SOL_TCP, optname,
+						      optval, optlen);
 	}
 	return -EOPNOTSUPP;
 }
@@ -1552,6 +1576,7 @@ static void sync_socket_options(struct mptcp_sock *msk, struct sock *ssk)
 	tcp_sock_set_keepidle_locked(ssk, msk->keepalive_idle);
 	tcp_sock_set_keepintvl(ssk, msk->keepalive_intvl);
 	tcp_sock_set_keepcnt(ssk, msk->keepalive_cnt);
+	tcp_sock_set_maxseg(ssk, msk->maxseg);
 
 	inet_assign_bit(TRANSPARENT, ssk, inet_test_bit(TRANSPARENT, sk));
 	inet_assign_bit(FREEBIND, ssk, inet_test_bit(FREEBIND, sk));
-- 
2.43.0
Re: [PATCH mptcp-next v3 2/2] mptcp: add TCP_MAXSEG sockopt support
Posted by Matthieu Baerts 7 months, 2 weeks ago 

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.
Re: [PATCH mptcp-next v3 2/2] mptcp: add TCP_MAXSEG sockopt support
Posted by Matthieu Baerts 7 months, 2 weeks ago 
Hi Geliang,

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.

Might be good to add:

  The get part looks at the value on the first subflow, to be as closed
  as possible to TCP. Only one value can be returned for the cached MSS,
  so this can come only from one subflow.

The rest looks good to me:

Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

I can do the modification when applying the patch.

Note that I will not send them upstream before the addition of the
packetdrill test in our other repo.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.
Re: [PATCH mptcp-next v3 2/2] mptcp: add TCP_MAXSEG sockopt support
Posted by Geliang Tang 7 months, 1 week ago 
Hi Matt,

On Wed, 2025-04-30 at 10:55 +0200, Matthieu Baerts wrote:
> Hi Geliang,
> 
> 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.
> 
> Might be good to add:
> 
>   The get part looks at the value on the first subflow, to be as
> closed
>   as possible to TCP. Only one value can be returned for the cached
> MSS,
>   so this can come only from one subflow.
> 
> The rest looks good to me:
> 
> Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> 
> I can do the modification when applying the patch.
> 
> Note that I will not send them upstream before the addition of the
> packetdrill test in our other repo.

Thanks for applying these patches for me.

They can be WIP on the export branch until I add the packetdrill test,
which I have already started working on.

Thanks,
-Geliang

> 
> Cheers,
> Matt

Patchew 2.1-devel-b67e4c2

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