From 51a62199a8aaac0d1645b1dd8e670a6f35aead81 Mon Sep 17 00:00:00 2001 From: Geliang Tang Date: Sat, 19 Jul 2025 00:06:57 +0200 Subject: [PATCH] tcp: add tcp_sock_set_maxseg Add a helper tcp_sock_set_maxseg() to directly set the TCP_MAXSEG sockopt from kernel space. This new helper will be used in the following patch from MPTCP. Signed-off-by: Geliang Tang Acked-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20250719-net-next-mptcp-tcp_maxseg-v2-2-8c910fbc5307@kernel.org Signed-off-by: Jakub Kicinski --- include/linux/tcp.h | 1 + net/ipv4/tcp.c | 23 ++++++++++++++--------- 2 files changed, 15 insertions(+), 9 deletions(-) diff --git a/include/linux/tcp.h b/include/linux/tcp.h index 1a5737b3753d0..57e478bfaef20 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -621,6 +621,7 @@ void tcp_sock_set_nodelay(struct sock *sk); void tcp_sock_set_quickack(struct sock *sk, int val); int tcp_sock_set_syncnt(struct sock *sk, int val); int tcp_sock_set_user_timeout(struct sock *sk, int val); +int tcp_sock_set_maxseg(struct sock *sk, int val); static inline bool dst_tcp_usec_ts(const struct dst_entry *dst) { diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 31149a0ac8491..71a956fbfc553 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -3751,6 +3751,19 @@ int tcp_set_window_clamp(struct sock *sk, int val) return 0; } +int tcp_sock_set_maxseg(struct sock *sk, int val) +{ + /* Values greater than interface MTU won't take effect. However + * at the point when this call is done we typically don't yet + * know which interface is going to be used + */ + if (val && (val < TCP_MIN_MSS || val > MAX_TCP_WINDOW)) + return -EINVAL; + + tcp_sk(sk)->rx_opt.user_mss = val; + return 0; +} + /* * Socket option code for TCP. */ @@ -3883,15 +3896,7 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname, switch (optname) { case TCP_MAXSEG: - /* Values greater than interface MTU won't take effect. However - * at the point when this call is done we typically don't yet - * know which interface is going to be used - */ - if (val && (val < TCP_MIN_MSS || val > MAX_TCP_WINDOW)) { - err = -EINVAL; - break; - } - tp->rx_opt.user_mss = val; + err = tcp_sock_set_maxseg(sk, val); break; case TCP_NODELAY: -- 2.47.2