netdev - [PATCH net-next 1/6] mptcp: pm: netlink: only add server-side attr when true

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Message-Id: <20250919-net-next-mptcp-server-side-flag-v1-1-a97a5d561a8b@kernel.org>
Date: Fri, 19 Sep 2025 14:08:58 +0200
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: Mat Martineau <martineau@...nel.org>, Geliang Tang <geliang@...nel.org>, 
 Donald Hunter <donald.hunter@...il.com>, Jakub Kicinski <kuba@...nel.org>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Shuah Khan <shuah@...nel.org>
Cc: netdev@...r.kernel.org, mptcp@...ts.linux.dev, 
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
Subject: [PATCH net-next 1/6] mptcp: pm: netlink: only add server-side attr
 when true

This attribute is a boolean. No need to add it to set it to 'false'.

Indeed, the default value when this attribute is not set is naturally
'false'. A few bytes can then be saved by not adding this attribute if
the connection is not on the server side.

This prepares the future deprecation of its attribute, in favour of a
new flag.

Reviewed-by: Geliang Tang <geliang@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 Documentation/netlink/specs/mptcp_pm.yaml         | 4 ++--
 include/uapi/linux/mptcp_pm.h                     | 4 ++--
 net/mptcp/pm_netlink.c                            | 4 +++-
 tools/testing/selftests/net/mptcp/userspace_pm.sh | 2 +-
 4 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/Documentation/netlink/specs/mptcp_pm.yaml b/Documentation/netlink/specs/mptcp_pm.yaml
index d1b4829b580ad09baf4afd73b67abd7b4ef6883a..fc47a2931014c0304efd3215cc24485ea22e1ede 100644
--- a/Documentation/netlink/specs/mptcp_pm.yaml
+++ b/Documentation/netlink/specs/mptcp_pm.yaml
@@ -28,13 +28,13 @@ definitions:
           traffic-patterns it can take a long time until the
           MPTCP_EVENT_ESTABLISHED is sent.
           Attributes: token, family, saddr4 | saddr6, daddr4 | daddr6, sport,
-          dport, server-side, [flags].
+          dport, [server-side], [flags].
       -
         name: established
         doc: >-
           A MPTCP connection is established (can start new subflows).
           Attributes: token, family, saddr4 | saddr6, daddr4 | daddr6, sport,
-          dport, server-side, [flags].
+          dport, [server-side], [flags].
       -
         name: closed
         doc: >-
diff --git a/include/uapi/linux/mptcp_pm.h b/include/uapi/linux/mptcp_pm.h
index 7359d34da446b94be148b363079120db03ba8549..bf44a5cf5b5a1e6d789632682a9bedbf8090feb9 100644
--- a/include/uapi/linux/mptcp_pm.h
+++ b/include/uapi/linux/mptcp_pm.h
@@ -16,10 +16,10 @@
  *   good time to allocate memory and send ADD_ADDR if needed. Depending on the
  *   traffic-patterns it can take a long time until the MPTCP_EVENT_ESTABLISHED
  *   is sent. Attributes: token, family, saddr4 | saddr6, daddr4 | daddr6,
- *   sport, dport, server-side, [flags].
+ *   sport, dport, [server-side], [flags].
  * @MPTCP_EVENT_ESTABLISHED: A MPTCP connection is established (can start new
  *   subflows). Attributes: token, family, saddr4 | saddr6, daddr4 | daddr6,
- *   sport, dport, server-side, [flags].
+ *   sport, dport, [server-side], [flags].
  * @MPTCP_EVENT_CLOSED: A MPTCP connection has stopped. Attribute: token.
  * @MPTCP_EVENT_ANNOUNCED: A new address has been announced by the peer.
  *   Attributes: token, rem_id, family, daddr4 | daddr6 [, dport].
diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 483ddbb9ec406a3e965376ee5a833ae295896a02..33a6bf536c020b59717472aca2d38add26255419 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -413,7 +413,9 @@ static int mptcp_event_created(struct sk_buff *skb,
 	if (err)
 		return err;
 
-	if (nla_put_u8(skb, MPTCP_ATTR_SERVER_SIDE, READ_ONCE(msk->pm.server_side)))
+	/* only set when it is the server side */
+	if (READ_ONCE(msk->pm.server_side) &&
+	    nla_put_u8(skb, MPTCP_ATTR_SERVER_SIDE, 1))
 		return -EMSGSIZE;
 
 	if (READ_ONCE(msk->pm.remote_deny_join_id0))
diff --git a/tools/testing/selftests/net/mptcp/userspace_pm.sh b/tools/testing/selftests/net/mptcp/userspace_pm.sh
index 3d45991f24ede919264185e3b5c2a3b95c1dcc85..87323942cb8a0779717e6c0cb6be46314d303d26 100755
--- a/tools/testing/selftests/net/mptcp/userspace_pm.sh
+++ b/tools/testing/selftests/net/mptcp/userspace_pm.sh
@@ -241,7 +241,7 @@ make_connection()
 
 	print_test "Established IP${is_v6} MPTCP Connection ns2 => ns1"
 	if [ "${client_token}" != "" ] && [ "${server_token}" != "" ] &&
-	   [ "${client_serverside}" = 0 ] && [ "${server_serverside}" = 1 ] &&
+	   [ "${client_serverside:-0}" = 0 ] && [ "${server_serverside:-0}" = 1 ] &&
 	   [ "${client_nojoin:-0}" = 0 ] && [ "${server_nojoin:-0}" = 1 ]
 	then
 		test_pass

-- 
2.51.0