[PATCH 1/5] tracing: use union to simplify the trace_event_functions initialization

From: Wei Yang
Date: Thu Jul 02 2020 - 22:06:23 EST


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@xxxxxxxxxxxxxxxxx>
---
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)