[PATCH export v3 1/4] mptcp: add MPFailFallback MIB

[Chenguang Zhao <chenguang.zhao@linux.dev>]

From: Chenguang Zhao <zhaochenguang@kylinos.cn>

Add a dedicated MIB to track TCP fallbacks triggered by receiving
MP_FAIL. A follow-up change will use it from
mptcp_pm_mp_fail_received() via mptcp_try_fallback().

Fixes: c65c2e3bae69 ("mptcp: track fallbacks accurately via mibs")
Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
---
 net/mptcp/mib.c | 1 +
 net/mptcp/mib.h | 1 +
 2 files changed, 2 insertions(+)

diff --git a/net/mptcp/mib.c b/net/mptcp/mib.c
index 608cb568897c..3e1bb4ff07b7 100644
--- a/net/mptcp/mib.c
+++ b/net/mptcp/mib.c
@@ -90,6 +90,7 @@ static const struct snmp_mib mptcp_snmp_list[] = {
 	SNMP_MIB_ITEM("DssFallback", MPTCP_MIB_DSSFALLBACK),
 	SNMP_MIB_ITEM("DssReset", MPTCP_MIB_DSSRESET),
 	SNMP_MIB_ITEM("SimultConnectFallback", MPTCP_MIB_SIMULTCONNFALLBACK),
+	SNMP_MIB_ITEM("MPFailFallback", MPTCP_MIB_MPFAILFALLBACK),
 	SNMP_MIB_ITEM("FallbackFailed", MPTCP_MIB_FALLBACKFAILED),
 	SNMP_MIB_ITEM("WinProbe", MPTCP_MIB_WINPROBE),
 	SNMP_MIB_ITEM("BacklogDrop", MPTCP_MIB_BACKLOGDROP),
diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h
index 1ebdb55e9534..89ebf7086cc6 100644
--- a/net/mptcp/mib.h
+++ b/net/mptcp/mib.h
@@ -93,6 +93,7 @@ enum linux_mptcp_mib_field {
 	MPTCP_MIB_DSSFALLBACK,		/* Bad or missing DSS */
 	MPTCP_MIB_DSSRESET,		/* MP_RST: bad data mapping */
 	MPTCP_MIB_SIMULTCONNFALLBACK,	/* Simultaneous connect */
+	MPTCP_MIB_MPFAILFALLBACK,	/* Received MP_FAIL, fallback to TCP */
 	MPTCP_MIB_FALLBACKFAILED,	/* Can't fallback due to msk status */
 	MPTCP_MIB_WINPROBE,		/* MPTCP-level zero window probe */
 	MPTCP_MIB_BACKLOGDROP,		/* Backlog over memory limit */
-- 
2.25.1