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mptcp: add TCP_MAXSEG sockopt support

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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. 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.

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>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20250719-net-next-mptcp-tcp_maxseg-v2-3-8c910fbc5307@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Geliang Tang 2025-07-19 00:06:58 +02:00 committed by Jakub Kicinski
parent 51a62199a8
commit 51c5fd09e1
2 changed files with 27 additions and 0 deletions
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1
net/mptcp/protocol.h
View File

@ -326,6 +326,7 @@ 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;

26
net/mptcp/sockopt.c
View File

@ -798,6 +798,23 @@ static int mptcp_setsockopt_first_sf_only(struct mptcp_sock *msk, int level, int
return ret;
}
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;
}
static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
sockptr_t optval, unsigned int optlen)
{
@ -859,6 +876,11 @@ 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_sf(msk, SOL_TCP, optname, optval,
optlen);
break;
default:
ret = -ENOPROTOOPT;
}
@ -1406,6 +1428,9 @@ 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 +1577,7 @@ 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));