Message-Id: <20250925-net-next-mptcp-c-flag-laminar-v1-6-ad126cc47c6b@kernel.org>
Date: Thu, 25 Sep 2025 12:32:41 +0200
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>, Shuah Khan <shuah@...nel.org>, 
 Martin KaFai Lau <martin.lau@...ux.dev>
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 06/15] mptcp: pm: in-kernel: rename 'subflows_max'
 to 'limit_extra_subflows'

A few variables linked to the in-kernel Path-Manager are confusing, and
it would help current and future developers, to clarify them.

One of them is 'subflows_max', which in fact represents the limit of
extra subflows: the limit set via 'ip mptcp limit subflows X' for
example. It is not linked to the maximum number of created / possible
subflows.

While at it, add an additional name for the corresponding variable in
MPTCP INFO: mptcpi_limit_extra_subflows. Not to break the current uAPI,
the new name is added as a 'define' pointing to the former name. This
will then also help userspace devs.

No functional changes intended.

Reviewed-by: Geliang Tang <geliang@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 include/uapi/linux/mptcp.h |  1 +
 net/mptcp/pm.c             | 12 ++++++------
 net/mptcp/pm_kernel.c      | 48 ++++++++++++++++++++++++----------------------
 net/mptcp/protocol.h       |  6 +++---
 net/mptcp/sockopt.c        |  4 ++--
 5 files changed, 37 insertions(+), 34 deletions(-)

diff --git a/include/uapi/linux/mptcp.h b/include/uapi/linux/mptcp.h
index f807c8dba56e7eb278fce0ad3184de3d0e24399b..314200c61f150da445ff87debb154bfd98f324fc 100644
--- a/include/uapi/linux/mptcp.h
+++ b/include/uapi/linux/mptcp.h
@@ -46,6 +46,7 @@ struct mptcp_info {
 	__u8	mptcpi_add_addr_signal;
 	__u8	mptcpi_add_addr_accepted;
 	__u8	mptcpi_subflows_max;
+	#define mptcpi_limit_extra_subflows mptcpi_subflows_max
 	__u8	mptcpi_add_addr_signal_max;
 	__u8	mptcpi_add_addr_accepted_max;
 	__u32	mptcpi_flags;
diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index 332e96bdadc0b936704188e5c9666cba97817b16..502f6c235e06c3f6fdca9dcf3a1d7b8e97fb9df6 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -483,7 +483,7 @@ void mptcp_pm_new_connection(struct mptcp_sock *msk, const struct sock *ssk, int
 bool mptcp_pm_allow_new_subflow(struct mptcp_sock *msk)
 {
 	struct mptcp_pm_data *pm = &msk->pm;
-	unsigned int subflows_max;
+	unsigned int limit_extra_subflows;
 	int ret = 0;
 
 	if (mptcp_pm_is_userspace(msk)) {
@@ -496,10 +496,10 @@ bool mptcp_pm_allow_new_subflow(struct mptcp_sock *msk)
 		return false;
 	}
 
-	subflows_max = mptcp_pm_get_subflows_max(msk);
+	limit_extra_subflows = mptcp_pm_get_limit_extra_subflows(msk);
 
 	pr_debug("msk=%p subflows=%d max=%d allow=%d\n", msk,
-		 pm->extra_subflows, subflows_max,
+		 pm->extra_subflows, limit_extra_subflows,
 		 READ_ONCE(pm->accept_subflow));
 
 	/* try to avoid acquiring the lock below */
@@ -508,8 +508,8 @@ bool mptcp_pm_allow_new_subflow(struct mptcp_sock *msk)
 
 	spin_lock_bh(&pm->lock);
 	if (READ_ONCE(pm->accept_subflow)) {
-		ret = pm->extra_subflows < subflows_max;
-		if (ret && ++pm->extra_subflows == subflows_max)
+		ret = pm->extra_subflows < limit_extra_subflows;
+		if (ret && ++pm->extra_subflows == limit_extra_subflows)
 			WRITE_ONCE(pm->accept_subflow, false);
 	}
 	spin_unlock_bh(&pm->lock);
@@ -1029,7 +1029,7 @@ void mptcp_pm_data_reset(struct mptcp_sock *msk)
 	WRITE_ONCE(pm->pm_type, pm_type);
 
 	if (pm_type == MPTCP_PM_TYPE_KERNEL) {
-		bool subflows_allowed = !!mptcp_pm_get_subflows_max(msk);
+		bool subflows_allowed = !!mptcp_pm_get_limit_extra_subflows(msk);
 
 		/* pm->work_pending must be only be set to 'true' when
 		 * pm->pm_type is set to MPTCP_PM_TYPE_KERNEL
diff --git a/net/mptcp/pm_kernel.c b/net/mptcp/pm_kernel.c
index 20bee6fc06259a0211782c94c1693ffe79dae1b6..db0d254d0e6b903fd8b920eb4cda628a811f7d58 100644
--- a/net/mptcp/pm_kernel.c
+++ b/net/mptcp/pm_kernel.c
@@ -23,7 +23,7 @@ struct pm_nl_pernet {
 	unsigned int		add_addr_signal_max;
 	unsigned int		add_addr_accept_max;
 	unsigned int		local_addr_max;
-	unsigned int		subflows_max;
+	unsigned int		limit_extra_subflows;
 	unsigned int		next_id;
 	DECLARE_BITMAP(id_bitmap, MPTCP_PM_MAX_ADDR_ID + 1);
 };
@@ -62,13 +62,13 @@ unsigned int mptcp_pm_get_add_addr_accept_max(const struct mptcp_sock *msk)
 }
 EXPORT_SYMBOL_GPL(mptcp_pm_get_add_addr_accept_max);
 
-unsigned int mptcp_pm_get_subflows_max(const struct mptcp_sock *msk)
+unsigned int mptcp_pm_get_limit_extra_subflows(const struct mptcp_sock *msk)
 {
 	struct pm_nl_pernet *pernet = pm_nl_get_pernet_from_msk(msk);
 
-	return READ_ONCE(pernet->subflows_max);
+	return READ_ONCE(pernet->limit_extra_subflows);
 }
-EXPORT_SYMBOL_GPL(mptcp_pm_get_subflows_max);
+EXPORT_SYMBOL_GPL(mptcp_pm_get_limit_extra_subflows);
 
 unsigned int mptcp_pm_get_local_addr_max(const struct mptcp_sock *msk)
 {
@@ -190,10 +190,10 @@ fill_remote_addresses_fullmesh(struct mptcp_sock *msk,
 	DECLARE_BITMAP(unavail_id, MPTCP_PM_MAX_ADDR_ID + 1);
 	struct sock *sk = (struct sock *)msk, *ssk;
 	struct mptcp_subflow_context *subflow;
-	unsigned int subflows_max;
+	unsigned int limit_extra_subflows;
 	int i = 0;
 
-	subflows_max = mptcp_pm_get_subflows_max(msk);
+	limit_extra_subflows = mptcp_pm_get_limit_extra_subflows(msk);
 
 	/* Forbid creation of new subflows matching existing ones, possibly
 	 * already created by incoming ADD_ADDR
@@ -221,7 +221,7 @@ fill_remote_addresses_fullmesh(struct mptcp_sock *msk,
 		msk->pm.extra_subflows++;
 		i++;
 
-		if (msk->pm.extra_subflows >= subflows_max)
+		if (msk->pm.extra_subflows >= limit_extra_subflows)
 			break;
 	}
 
@@ -274,18 +274,18 @@ __lookup_addr(struct pm_nl_pernet *pernet, const struct mptcp_addr_info *info)
 static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 {
 	struct sock *sk = (struct sock *)msk;
+	unsigned int limit_extra_subflows;
 	unsigned int add_addr_signal_max;
 	bool signal_and_subflow = false;
 	unsigned int local_addr_max;
 	struct pm_nl_pernet *pernet;
 	struct mptcp_pm_local local;
-	unsigned int subflows_max;
 
 	pernet = pm_nl_get_pernet(sock_net(sk));
 
 	add_addr_signal_max = mptcp_pm_get_add_addr_signal_max(msk);
 	local_addr_max = mptcp_pm_get_local_addr_max(msk);
-	subflows_max = mptcp_pm_get_subflows_max(msk);
+	limit_extra_subflows = mptcp_pm_get_limit_extra_subflows(msk);
 
 	/* do lazy endpoint usage accounting for the MPC subflows */
 	if (unlikely(!(msk->pm.status & BIT(MPTCP_PM_MPC_ENDPOINT_ACCOUNTED))) && msk->first) {
@@ -313,7 +313,7 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 	pr_debug("local %d:%d signal %d:%d subflows %d:%d\n",
 		 msk->pm.local_addr_used, local_addr_max,
 		 msk->pm.add_addr_signaled, add_addr_signal_max,
-		 msk->pm.extra_subflows, subflows_max);
+		 msk->pm.extra_subflows, limit_extra_subflows);
 
 	/* check first for announce */
 	if (msk->pm.add_addr_signaled < add_addr_signal_max) {
@@ -353,7 +353,7 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 subflow:
 	/* check if should create a new subflow */
 	while (msk->pm.local_addr_used < local_addr_max &&
-	       msk->pm.extra_subflows < subflows_max) {
+	       msk->pm.extra_subflows < limit_extra_subflows) {
 		struct mptcp_addr_info addrs[MPTCP_PM_ADDR_MAX];
 		bool fullmesh;
 		int i, nr;
@@ -402,14 +402,15 @@ fill_local_addresses_vec_fullmesh(struct mptcp_sock *msk,
 				  bool c_flag_case)
 {
 	struct pm_nl_pernet *pernet = pm_nl_get_pernet_from_msk(msk);
-	unsigned int subflows_max = mptcp_pm_get_subflows_max(msk);
 	struct sock *sk = (struct sock *)msk;
 	struct mptcp_pm_addr_entry *entry;
+	unsigned int limit_extra_subflows;
 	struct mptcp_addr_info mpc_addr;
 	struct mptcp_pm_local *local;
 	int i = 0;
 
 	mptcp_local_address((struct sock_common *)msk, &mpc_addr);
+	limit_extra_subflows = mptcp_pm_get_limit_extra_subflows(msk);
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(entry, &pernet->local_addr_list, list) {
@@ -444,7 +445,7 @@ fill_local_addresses_vec_fullmesh(struct mptcp_sock *msk,
 		msk->pm.extra_subflows++;
 		i++;
 
-		if (msk->pm.extra_subflows >= subflows_max)
+		if (msk->pm.extra_subflows >= limit_extra_subflows)
 			break;
 	}
 	rcu_read_unlock();
@@ -459,13 +460,14 @@ fill_local_addresses_vec_c_flag(struct mptcp_sock *msk,
 {
 	unsigned int local_addr_max = mptcp_pm_get_local_addr_max(msk);
 	struct pm_nl_pernet *pernet = pm_nl_get_pernet_from_msk(msk);
-	unsigned int subflows_max = mptcp_pm_get_subflows_max(msk);
 	struct sock *sk = (struct sock *)msk;
+	unsigned int limit_extra_subflows;
 	struct mptcp_addr_info mpc_addr;
 	struct mptcp_pm_local *local;
 	int i = 0;
 
 	mptcp_local_address((struct sock_common *)msk, &mpc_addr);
+	limit_extra_subflows = mptcp_pm_get_limit_extra_subflows(msk);
 
 	while (msk->pm.local_addr_used < local_addr_max) {
 		local = &locals[i];
@@ -486,7 +488,7 @@ fill_local_addresses_vec_c_flag(struct mptcp_sock *msk,
 		msk->pm.extra_subflows++;
 		i++;
 
-		if (msk->pm.extra_subflows >= subflows_max)
+		if (msk->pm.extra_subflows >= limit_extra_subflows)
 			break;
 	}
 
@@ -544,14 +546,14 @@ static void mptcp_pm_nl_add_addr_received(struct mptcp_sock *msk)
 {
 	struct mptcp_pm_local locals[MPTCP_PM_ADDR_MAX];
 	struct sock *sk = (struct sock *)msk;
+	unsigned int limit_extra_subflows;
 	unsigned int add_addr_accept_max;
 	struct mptcp_addr_info remote;
-	unsigned int subflows_max;
 	bool sf_created = false;
 	int i, nr;
 
 	add_addr_accept_max = mptcp_pm_get_add_addr_accept_max(msk);
-	subflows_max = mptcp_pm_get_subflows_max(msk);
+	limit_extra_subflows = mptcp_pm_get_limit_extra_subflows(msk);
 
 	pr_debug("accepted %d:%d remote family %d\n",
 		 msk->pm.add_addr_accepted, add_addr_accept_max,
@@ -586,7 +588,7 @@ static void mptcp_pm_nl_add_addr_received(struct mptcp_sock *msk)
 		if (remote.id)
 			msk->pm.add_addr_accepted++;
 		if (msk->pm.add_addr_accepted >= add_addr_accept_max ||
-		    msk->pm.extra_subflows >= subflows_max)
+		    msk->pm.extra_subflows >= limit_extra_subflows)
 			WRITE_ONCE(msk->pm.accept_addr, false);
 	}
 }
@@ -1285,13 +1287,13 @@ int mptcp_pm_nl_set_limits_doit(struct sk_buff *skb, struct genl_info *info)
 	if (ret)
 		goto unlock;
 
-	subflows = pernet->subflows_max;
+	subflows = pernet->limit_extra_subflows;
 	ret = parse_limit(info, MPTCP_PM_ATTR_SUBFLOWS, &subflows);
 	if (ret)
 		goto unlock;
 
 	WRITE_ONCE(pernet->add_addr_accept_max, rcv_addrs);
-	WRITE_ONCE(pernet->subflows_max, subflows);
+	WRITE_ONCE(pernet->limit_extra_subflows, subflows);
 
 unlock:
 	spin_unlock_bh(&pernet->lock);
@@ -1318,7 +1320,7 @@ int mptcp_pm_nl_get_limits_doit(struct sk_buff *skb, struct genl_info *info)
 		goto fail;
 
 	if (nla_put_u32(msg, MPTCP_PM_ATTR_SUBFLOWS,
-			READ_ONCE(pernet->subflows_max)))
+			READ_ONCE(pernet->limit_extra_subflows)))
 		goto fail;
 
 	genlmsg_end(msg, reply);
@@ -1427,7 +1429,7 @@ bool mptcp_pm_nl_check_work_pending(struct mptcp_sock *msk)
 {
 	struct pm_nl_pernet *pernet = pm_nl_get_pernet_from_msk(msk);
 
-	if (msk->pm.extra_subflows == mptcp_pm_get_subflows_max(msk) ||
+	if (msk->pm.extra_subflows == mptcp_pm_get_limit_extra_subflows(msk) ||
 	    (find_next_and_bit(pernet->id_bitmap, msk->pm.id_avail_bitmap,
 			       MPTCP_PM_MAX_ADDR_ID + 1, 0) == MPTCP_PM_MAX_ADDR_ID + 1)) {
 		WRITE_ONCE(msk->pm.work_pending, false);
@@ -1462,7 +1464,7 @@ static int __net_init pm_nl_init_net(struct net *net)
 	INIT_LIST_HEAD_RCU(&pernet->local_addr_list);
 
 	/* Cit. 2 subflows ought to be enough for anybody. */
-	pernet->subflows_max = 2;
+	pernet->limit_extra_subflows = 2;
 	pernet->next_id = 1;
 	pernet->stale_loss_cnt = 4;
 	spin_lock_init(&pernet->lock);
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index ca68f9a7580149e43139ec6cc61a1e0b966e7a22..4c777f87b0497ed623f0d51bf1f87cfa011cf0eb 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -1182,13 +1182,13 @@ void mptcp_pm_worker(struct mptcp_sock *msk);
 void __mptcp_pm_kernel_worker(struct mptcp_sock *msk);
 unsigned int mptcp_pm_get_add_addr_signal_max(const struct mptcp_sock *msk);
 unsigned int mptcp_pm_get_add_addr_accept_max(const struct mptcp_sock *msk);
-unsigned int mptcp_pm_get_subflows_max(const struct mptcp_sock *msk);
+unsigned int mptcp_pm_get_limit_extra_subflows(const struct mptcp_sock *msk);
 unsigned int mptcp_pm_get_local_addr_max(const struct mptcp_sock *msk);
 
 /* called under PM lock */
 static inline void __mptcp_pm_close_subflow(struct mptcp_sock *msk)
 {
-	if (--msk->pm.extra_subflows < mptcp_pm_get_subflows_max(msk))
+	if (--msk->pm.extra_subflows < mptcp_pm_get_limit_extra_subflows(msk))
 		WRITE_ONCE(msk->pm.accept_subflow, true);
 }
 
@@ -1204,7 +1204,7 @@ static inline bool mptcp_pm_add_addr_c_flag_case(struct mptcp_sock *msk)
 	return READ_ONCE(msk->pm.remote_deny_join_id0) &&
 	       msk->pm.local_addr_used == 0 &&
 	       mptcp_pm_get_add_addr_accept_max(msk) == 0 &&
-	       msk->pm.extra_subflows < mptcp_pm_get_subflows_max(msk);
+	       msk->pm.extra_subflows < mptcp_pm_get_limit_extra_subflows(msk);
 }
 
 void mptcp_sockopt_sync_locked(struct mptcp_sock *msk, struct sock *ssk);
diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 17966da80239d731de925f3e4211b3ee00f802e4..4e82bcfcd34e3a1dffb05799cf181ee2940e75d7 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -972,8 +972,8 @@ void mptcp_diag_fill_info(struct mptcp_sock *msk, struct mptcp_info *info)
 
 	/* The following limits only make sense for the in-kernel PM */
 	if (mptcp_pm_is_kernel(msk)) {
-		info->mptcpi_subflows_max =
-			mptcp_pm_get_subflows_max(msk);
+		info->mptcpi_limit_extra_subflows =
+			mptcp_pm_get_limit_extra_subflows(msk);
 		info->mptcpi_add_addr_signal_max =
 			mptcp_pm_get_add_addr_signal_max(msk);
 		info->mptcpi_add_addr_accepted_max =

-- 
2.51.0

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