linux-kernel - [PATCH 1/5] tracing: use union to simplify the trace_event

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Date:   Fri,  3 Jul 2020 10:06:08 +0800
From:   Wei Yang <richard.weiyang@...ux.alibaba.com>
To:     rostedt@...dmis.org, mingo@...hat.com
Cc:     linux-kernel@...r.kernel.org,
        Wei Yang <richard.weiyang@...ux.alibaba.com>
Subject: [PATCH 1/5] tracing: use union to simplify the trace_event_functions initialization

There are for 4 fields in trace_event_functions with the same type of
trace_print_func. Initialize them in register_trace_event() one by one
looks redundant.

Let's take advantage of union to simplify the procedure.

Signed-off-by: Wei Yang <richard.weiyang@...ux.alibaba.com>
---
 include/linux/trace_events.h | 13 +++++++++----
 kernel/trace/trace_output.c  | 14 +++++---------
 2 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 5c6943354049..1a421246f4a2 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -122,10 +122,15 @@ typedef enum print_line_t (*trace_print_func)(struct trace_iterator *iter,
 				      int flags, struct trace_event *event);
 
 struct trace_event_functions {
-	trace_print_func	trace;
-	trace_print_func	raw;
-	trace_print_func	hex;
-	trace_print_func	binary;
+	union {
+		struct {
+			trace_print_func	trace;
+			trace_print_func	raw;
+			trace_print_func	hex;
+			trace_print_func	binary;
+		};
+		trace_print_func print_funcs[4];
+	};
 };
 
 struct trace_event {
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 73976de7f8cc..47bf9f042b97 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -728,7 +728,7 @@ void trace_event_read_unlock(void)
 int register_trace_event(struct trace_event *event)
 {
 	unsigned key;
-	int ret = 0;
+	int i, ret = 0;
 
 	down_write(&trace_event_sem);
 
@@ -770,14 +770,10 @@ int register_trace_event(struct trace_event *event)
 			goto out;
 	}
 
-	if (event->funcs->trace == NULL)
-		event->funcs->trace = trace_nop_print;
-	if (event->funcs->raw == NULL)
-		event->funcs->raw = trace_nop_print;
-	if (event->funcs->hex == NULL)
-		event->funcs->hex = trace_nop_print;
-	if (event->funcs->binary == NULL)
-		event->funcs->binary = trace_nop_print;
+	for (i = 0; i < ARRAY_SIZE(event->funcs->print_funcs); i++) {
+		if (!event->funcs->print_funcs[i])
+			event->funcs->print_funcs[i] = trace_nop_print;
+	}
 
 	key = event->type & (EVENT_HASHSIZE - 1);
 
-- 
2.20.1 (Apple Git-117)