mptcp: add CurrEstab MIB counter support

Add a new MIB counter named MPTCP_MIB_CURRESTAB to count current
established MPTCP connections, similar to TCP_MIB_CURRESTAB. This is
useful to quickly list the number of MPTCP connections without having to
iterate over all of them.

This patch adds a new helper function mptcp_set_state(): if the state
switches from or to ESTABLISHED state, this newly added counter is
incremented. This helper is going to be used in the following patch.

Similar to MPTCP_INC_STATS(), a new helper called MPTCP_DEC_STATS() is
also needed to decrement a MIB counter.
Signed-off-by: Geliang Tang <geliang.tang@linux.dev>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts <matttbe@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/mib.c

@@ -66,6 +66,7 @@ static const struct snmp_mib mptcp_snmp_list[] = {
 	SNMP_MIB_ITEM("RcvWndShared", MPTCP_MIB_RCVWNDSHARED),
 	SNMP_MIB_ITEM("RcvWndConflictUpdate", MPTCP_MIB_RCVWNDCONFLICTUPDATE),
 	SNMP_MIB_ITEM("RcvWndConflict", MPTCP_MIB_RCVWNDCONFLICT),
+	SNMP_MIB_ITEM("MPCurrEstab", MPTCP_MIB_CURRESTAB),
 	SNMP_MIB_SENTINEL
 };
 

net/mptcp/mib.h

@@ -65,6 +65,7 @@ enum linux_mptcp_mib_field {
 					 * conflict with another subflow while updating msk rcv wnd
 					 */
 	MPTCP_MIB_RCVWNDCONFLICT,	/* Conflict with while updating msk rcv wnd */
+	MPTCP_MIB_CURRESTAB,		/* Current established MPTCP connections */
 	__MPTCP_MIB_MAX
 };
 
@@ -95,4 +96,11 @@ static inline void __MPTCP_INC_STATS(struct net *net,
 		__SNMP_INC_STATS(net->mib.mptcp_statistics, field);
 }
 
+static inline void MPTCP_DEC_STATS(struct net *net,
+				   enum linux_mptcp_mib_field field)
+{
+	if (likely(net->mib.mptcp_statistics))
+		SNMP_DEC_STATS(net->mib.mptcp_statistics, field);
+}
+
 bool mptcp_mib_alloc(struct net *net);

net/mptcp/protocol.c

@@ -2871,6 +2871,24 @@ void mptcp_subflow_shutdown(struct sock *sk, struct sock *ssk, int how)
 	release_sock(ssk);
 }
 
+void mptcp_set_state(struct sock *sk, int state)
+{
+	int oldstate = sk->sk_state;
+
+	switch (state) {
+	case TCP_ESTABLISHED:
+		if (oldstate != TCP_ESTABLISHED)
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_CURRESTAB);
+		break;
+
+	default:
+		if (oldstate == TCP_ESTABLISHED)
+			MPTCP_DEC_STATS(sock_net(sk), MPTCP_MIB_CURRESTAB);
+	}
+
+	inet_sk_state_store(sk, state);
+}
+
 static const unsigned char new_state[16] = {
 	/* current state:     new state:      action:	*/
 	[0 /* (Invalid) */] = TCP_CLOSE,

net/mptcp/protocol.h

@@ -641,6 +641,7 @@ bool __mptcp_close(struct sock *sk, long timeout);
 void mptcp_cancel_work(struct sock *sk);
 void __mptcp_unaccepted_force_close(struct sock *sk);
 void mptcp_set_owner_r(struct sk_buff *skb, struct sock *sk);
+void mptcp_set_state(struct sock *sk, int state);
 
 bool mptcp_addresses_equal(const struct mptcp_addr_info *a,
 			   const struct mptcp_addr_info *b, bool use_port);