tracing: add comments to explain TRACE_EVENT out of protection
The commit:
commit 5ac35daa9343936038a3c9c4f4d6d3fe6a2a7bd8
Author: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
tracing/events: fix the include file dependencies
Moved the TRACE_EVENT out of the ifdef protection of tracepoints.h
but uses the define of TRACE_EVENT itself as protection. This patch
adds comments to explain why.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 8170985..0341f2e 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -180,7 +180,15 @@
}
#define PARAMS(args...) args
-#endif
+
+#endif /* _LINUX_TRACEPOINT_H */
+
+/*
+ * Note: we keep the TRACE_EVENT outside the include file ifdef protection.
+ * This is due to the way trace events work. If a file includes two
+ * trace event headers under one "CREATE_TRACE_POINTS" the first include
+ * will override the TRACE_EVENT and break the second include.
+ */
#ifndef TRACE_EVENT
/*
@@ -287,4 +295,5 @@
#define TRACE_EVENT(name, proto, args, struct, assign, print) \
DECLARE_TRACE(name, PARAMS(proto), PARAMS(args))
-#endif
+
+#endif /* ifdef TRACE_EVENT (see note above) */