netdev - [PATCH net-next v2] mptcp: allow overridden write

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Message-Id: <20260206-net-next-mptcp-write_space-override-v2-1-e0b12be818c6@kernel.org>
Date: Fri, 06 Feb 2026 14:09:24 +0100
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: Mat Martineau <martineau@...nel.org>, Geliang Tang <geliang@...nel.org>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org, mptcp@...ts.linux.dev, 
 linux-kernel@...r.kernel.org, Gang Yan <yangang@...inos.cn>, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>, 
 Geliang Tang <geliang@...nel.org>
Subject: [PATCH net-next v2] mptcp: allow overridden write_space to be
 invoked

From: Geliang Tang <tanggeliang@...inos.cn>

Future extensions with psock will override their own sk->sk_write_space
callback. This patch ensures that the overridden sk_write_space can be
invoked by MPTCP.

INDIRECT_CALL is used to keep the default path optimised.

Note that sk->sk_write_space was never called directly with MPTCP
sockets, so changing it to sk_stream_write_space in the init, and using
it from mptcp_write_space() is not supposed to change the current
behaviour.

This patch is shared early to ease discussions around future RFC and
avoid confusions with this "fix" that is needed for different future
extensions.

Suggested-by: Paolo Abeni <pabeni@...hat.com>
Co-developed-by: Gang Yan <yangang@...inos.cn>
Signed-off-by: Gang Yan <yangang@...inos.cn>
Signed-off-by: Geliang Tang <tanggeliang@...inos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
v2: set sk->sk_write_space to sk_stream_write_space (Review assistant)
v1: https://lore.kernel.org/20260203-net-next-mptcp-misc-feat-6-20-v1-7-31ec8bfc56d1@kernel.org
---
 net/mptcp/protocol.c | 1 +
 net/mptcp/protocol.h | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index e0b4745bbaa9..cf1852b99963 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3058,6 +3058,7 @@ static int mptcp_init_sock(struct sock *sk)
 	sk_sockets_allocated_inc(sk);
 	sk->sk_rcvbuf = READ_ONCE(net->ipv4.sysctl_tcp_rmem[1]);
 	sk->sk_sndbuf = READ_ONCE(net->ipv4.sysctl_tcp_wmem[1]);
+	sk->sk_write_space = sk_stream_write_space;

 	return 0;
 }
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index f4bfe91ca7f9..0bd1ee860316 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -975,7 +975,7 @@ static inline void mptcp_write_space(struct sock *sk)
 	/* pairs with memory barrier in mptcp_poll */
 	smp_mb();
 	if (mptcp_stream_memory_free(sk, 1))
-		sk_stream_write_space(sk);
+		INDIRECT_CALL_1(sk->sk_write_space, sk_stream_write_space, sk);
 }

 static inline void __mptcp_sync_sndbuf(struct sock *sk)

---
base-commit: 24cf78c738318f3d2b961a1ab4b3faf1eca860d7
change-id: 20260206-net-next-mptcp-write_space-override-b70ad5842211

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@...nel.org>