writeback: show writeback reason with __print_symbolic

This makes the binary trace understandable by trace-cmd.

CC: Dave Chinner <david@fromorbit.com>
CC: Curt Wohlgemuth <curtw@google.com>
CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

fs/fs-writeback.c

@@ -47,17 +47,6 @@ struct wb_writeback_work {
 	struct completion *done;	/* set if the caller waits */
 };
 
-const char *wb_reason_name[] = {
-	[WB_REASON_BACKGROUND]		= "background",
-	[WB_REASON_TRY_TO_FREE_PAGES]	= "try_to_free_pages",
-	[WB_REASON_SYNC]		= "sync",
-	[WB_REASON_PERIODIC]		= "periodic",
-	[WB_REASON_LAPTOP_TIMER]	= "laptop_timer",
-	[WB_REASON_FREE_MORE_MEM]	= "free_more_memory",
-	[WB_REASON_FS_FREE_SPACE]	= "fs_free_space",
-	[WB_REASON_FORKER_THREAD]	= "forker_thread"
-};
-
 /*
  * Include the creation of the trace points after defining the
  * wb_writeback_work structure so that the definition remains local to this

include/trace/events/writeback.h

@@ -21,6 +21,16 @@
 		{I_REFERENCED,		"I_REFERENCED"}		\
 	)
 
+#define WB_WORK_REASON							\
+		{WB_REASON_BACKGROUND,		"background"},		\
+		{WB_REASON_TRY_TO_FREE_PAGES,	"try_to_free_pages"},	\
+		{WB_REASON_SYNC,		"sync"},		\
+		{WB_REASON_PERIODIC,		"periodic"},		\
+		{WB_REASON_LAPTOP_TIMER,	"laptop_timer"},	\
+		{WB_REASON_FREE_MORE_MEM,	"free_more_memory"},	\
+		{WB_REASON_FS_FREE_SPACE,	"fs_free_space"},	\
+		{WB_REASON_FORKER_THREAD,	"forker_thread"}
+
 struct wb_writeback_work;
 
 DECLARE_EVENT_CLASS(writeback_work_class,
@@ -55,7 +65,7 @@ DECLARE_EVENT_CLASS(writeback_work_class,
 		  __entry->for_kupdate,
 		  __entry->range_cyclic,
 		  __entry->for_background,
-		  wb_reason_name[__entry->reason]
+		  __print_symbolic(__entry->reason, WB_WORK_REASON)
 	)
 );
 #define DEFINE_WRITEBACK_WORK_EVENT(name) \
@@ -184,7 +194,8 @@ TRACE_EVENT(writeback_queue_io,
 		__entry->older,	/* older_than_this in jiffies */
 		__entry->age,	/* older_than_this in relative milliseconds */
 		__entry->moved,
-		wb_reason_name[__entry->reason])
+		__print_symbolic(__entry->reason, WB_WORK_REASON)
+	)
 );
 
 TRACE_EVENT(global_dirty_state,