l2tp: add tracepoint infrastructure to core

The l2tp subsystem doesn't currently make use of tracepoints.

As a starting point for adding tracepoints, add skeleton infrastructure
for defining tracepoints for the subsystem, and for having them build
appropriately whether compiled into the kernel or built as a module.
Signed-off-by: Tom Parkin <tparkin@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/Makefile

@@ -5,6 +5,8 @@
 
 obj-$(CONFIG_L2TP) += l2tp_core.o
 
+CFLAGS_l2tp_core.o += -I$(src)
+
 # Build l2tp as modules if L2TP is M
 obj-$(subst y,$(CONFIG_L2TP),$(CONFIG_PPPOL2TP)) += l2tp_ppp.o
 obj-$(subst y,$(CONFIG_L2TP),$(CONFIG_L2TP_IP)) += l2tp_ip.o

net/l2tp/l2tp_core.c

@@ -62,6 +62,9 @@
 
 #include "l2tp_core.h"
 
+#define CREATE_TRACE_POINTS
+#include "trace.h"
+
 #define L2TP_DRV_VERSION	"V2.0"
 
 /* L2TP header constants */

net/l2tp/trace.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM l2tp
+
+#if !defined(_TRACE_L2TP_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_L2TP_H
+
+#endif /* _TRACE_L2TP_H */
+
+/* This part must be outside protection */
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+#undef TRACE_INCLUDE_FILE
+#define TRACE_INCLUDE_FILE trace
+#include <trace/define_trace.h>