tracing: Add README information for synthetic_events file

Add an entry with a basic description of events/synthetic_events along
with a simple example.

Link: https://lkml.kernel.org/r/3c7f178cf95aaeebc01eda7d95600dd937233eb7.1601848695.git.zanussi@kernel.org
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3f2533adae72a485b4130fafacac490b3ad3c189..73fd0e0c0f39e1324a9def644b792557ae7d55f8 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5249,7 +5249,12 @@ static const char readme_msg[] =
        "\t        trace(<synthetic_event>,param list)  - generate synthetic event\n"
        "\t        save(field,...)                      - save current event fields\n"
 #ifdef CONFIG_TRACER_SNAPSHOT
-       "\t        snapshot()                           - snapshot the trace buffer\n"
+       "\t        snapshot()                           - snapshot the trace buffer\n\n"
+#endif
+#ifdef CONFIG_SYNTH_EVENTS
+       "  events/synthetic_events\t- Create/append/remove/show synthetic events\n"
+       "\t  Write into this file to define/undefine new synthetic events.\n"
+       "\t     example: echo 'myevent u64 lat; char name[]' >> synthetic_events\n"
 #endif
 #endif
 ;