writeback: Export enums used by tracepoint to user space

The enums used in tracepoints for __print_symbolic() do not have their
values shown in the tracepoint format files and this makes it difficult
for user space tools to convert the binary values to the strings they
are to represent.

Add TRACE_DEFINE_ENUM(x) macros to export the enum names to their values
to make the tracing output from user space tools more robust.

Link: http://lkml.kernel.org/r/20150403013802.220157513@goodmis.org

Cc: Dave Chinner <dchinner@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/trace/events/writeback.h

@@ -23,15 +23,32 @@
 		{I_REFERENCED,		"I_REFERENCED"}		\
 	)
 
+/* enums need to be exported to user space */
+#undef EM
+#undef EMe
+#define EM(a,b) 	TRACE_DEFINE_ENUM(a);
+#define EMe(a,b)	TRACE_DEFINE_ENUM(a);
+
 #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"}
+	EM( WB_REASON_BACKGROUND,		"background")		\
+	EM( WB_REASON_TRY_TO_FREE_PAGES,	"try_to_free_pages")	\
+	EM( WB_REASON_SYNC,			"sync")			\
+	EM( WB_REASON_PERIODIC,			"periodic")		\
+	EM( WB_REASON_LAPTOP_TIMER,		"laptop_timer")		\
+	EM( WB_REASON_FREE_MORE_MEM,		"free_more_memory")	\
+	EM( WB_REASON_FS_FREE_SPACE,		"fs_free_space")	\
+	EMe(WB_REASON_FORKER_THREAD,		"forker_thread")
+
+WB_WORK_REASON
+
+/*
+ * Now redefine the EM() and EMe() macros to map the enums to the strings
+ * that will be printed in the output.
+ */
+#undef EM
+#undef EMe
+#define EM(a,b)		{ a, b },
+#define EMe(a,b)	{ a, b }
 
 struct wb_writeback_work;