[PATCH 5.10.y] mptcp: mib: count MPJ with backup flag

["Matthieu Baerts (NGI0)" <matttbe@kernel.org>]

commit 4dde0d72ccec500c60c798e036b852e013d6e124 upstream.

Without such counters, it is difficult to easily debug issues with MPJ
not having the backup flags on production servers.

This is not strictly a fix, but it eases to validate the following
patches without requiring to take packet traces, to query ongoing
connections with Netlink with admin permissions, or to guess by looking
at the behaviour of the packet scheduler. Also, the modification is self
contained, isolated, well controlled, and the increments are done just
after others, there from the beginning. It looks then safe, and helpful
to backport this.

Fixes: 4596a2c1b7f5 ("mptcp: allow creating non-backup subflows")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
[ Conflicts in subflow.c because the context has changed in
  commit b3ea6b272d79 ("mptcp: consolidate initial ack seq generation")
  and commit 5bc56388c74f ("mptcp: add port number check for MP_JOIN")
  which are not in this version. These commits are unrelated to this
  modification. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/mib.c     | 2 ++
 net/mptcp/mib.h     | 2 ++
 net/mptcp/subflow.c | 6 ++++++
 3 files changed, 10 insertions(+)

diff --git a/net/mptcp/mib.c b/net/mptcp/mib.c
index b921cbdd9aaa..f4034e000f3e 100644
--- a/net/mptcp/mib.c
+++ b/net/mptcp/mib.c
@@ -16,7 +16,9 @@ static const struct snmp_mib mptcp_snmp_list[] = {
 	SNMP_MIB_ITEM("MPTCPRetrans", MPTCP_MIB_RETRANSSEGS),
 	SNMP_MIB_ITEM("MPJoinNoTokenFound", MPTCP_MIB_JOINNOTOKEN),
 	SNMP_MIB_ITEM("MPJoinSynRx", MPTCP_MIB_JOINSYNRX),
+	SNMP_MIB_ITEM("MPJoinSynBackupRx", MPTCP_MIB_JOINSYNBACKUPRX),
 	SNMP_MIB_ITEM("MPJoinSynAckRx", MPTCP_MIB_JOINSYNACKRX),
+	SNMP_MIB_ITEM("MPJoinSynAckBackupRx", MPTCP_MIB_JOINSYNACKBACKUPRX),
 	SNMP_MIB_ITEM("MPJoinSynAckHMacFailure", MPTCP_MIB_JOINSYNACKMAC),
 	SNMP_MIB_ITEM("MPJoinAckRx", MPTCP_MIB_JOINACKRX),
 	SNMP_MIB_ITEM("MPJoinAckHMacFailure", MPTCP_MIB_JOINACKMAC),
diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h
index 47bcecce1106..a9f43ff00b3c 100644
--- a/net/mptcp/mib.h
+++ b/net/mptcp/mib.h
@@ -9,7 +9,9 @@ enum linux_mptcp_mib_field {
 	MPTCP_MIB_RETRANSSEGS,		/* Segments retransmitted at the MPTCP-level */
 	MPTCP_MIB_JOINNOTOKEN,		/* Received MP_JOIN but the token was not found */
 	MPTCP_MIB_JOINSYNRX,		/* Received a SYN + MP_JOIN */
+	MPTCP_MIB_JOINSYNBACKUPRX,	/* Received a SYN + MP_JOIN + backup flag */
 	MPTCP_MIB_JOINSYNACKRX,		/* Received a SYN/ACK + MP_JOIN */
+	MPTCP_MIB_JOINSYNACKBACKUPRX,	/* Received a SYN/ACK + MP_JOIN + backup flag */
 	MPTCP_MIB_JOINSYNACKMAC,	/* HMAC was wrong on SYN/ACK + MP_JOIN */
 	MPTCP_MIB_JOINACKRX,		/* Received an ACK + MP_JOIN */
 	MPTCP_MIB_JOINACKMAC,		/* HMAC was wrong on ACK + MP_JOIN */
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index a59c731d7fed..f4067484727e 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -135,6 +135,9 @@ static void subflow_init_req(struct request_sock *req,
 			return;
 	} else if (mp_opt.mp_join) {
 		SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINSYNRX);
+
+		if (mp_opt.backup)
+			SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINSYNBACKUPRX);
 	}
 
 	if (mp_opt.mp_capable && listener->request_mptcp) {
@@ -347,6 +350,9 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 
 		subflow->mp_join = 1;
 		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINSYNACKRX);
+
+		if (subflow->backup)
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINSYNACKBACKUPRX);
 	} else if (mptcp_check_fallback(sk)) {
 fallback:
 		mptcp_rcv_space_init(mptcp_sk(parent), sk);
-- 
2.45.2