tracing: Update some tracing_map constants and comments

Make it clear exactly how many keys and values are supported through
better defines, and add 1 to the vals count, since normally clients
want support for at least a hitcount and two other values.

Also, note the error return value for tracing_map_add_key/val_field()
in the comments.

Link: http://lkml.kernel.org/r/6696fa02ebc716aa344c27a571a2afaa25e5b4d4.1457029949.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/tracing_map.c

@@ -163,7 +163,7 @@ static int tracing_map_add_field(struct tracing_map *map,
  * tracing_map_update_sum() or reading it via tracing_map_read_sum().
  *
  * Return: The index identifying the field in the map and associated
- * tracing_map_elts.
+ * tracing_map_elts, or -EINVAL on error.
  */
 int tracing_map_add_sum_field(struct tracing_map *map)
 {
@@ -184,7 +184,7 @@ int tracing_map_add_sum_field(struct tracing_map *map)
  * the key referenced by this key field resides.
  *
  * Return: The index identifying the field in the map and associated
- * tracing_map_elts.
+ * tracing_map_elts, or -EINVAL on error.
  */
 int tracing_map_add_key_field(struct tracing_map *map,
 			      unsigned int offset,

kernel/trace/tracing_map.h

@@ -5,9 +5,10 @@
 #define TRACING_MAP_BITS_MAX		17
 #define TRACING_MAP_BITS_MIN		7
 
-#define TRACING_MAP_FIELDS_MAX		4
 #define TRACING_MAP_KEYS_MAX		2
-
+#define TRACING_MAP_VALS_MAX		3
+#define TRACING_MAP_FIELDS_MAX		(TRACING_MAP_KEYS_MAX + \
+					 TRACING_MAP_VALS_MAX)
 #define TRACING_MAP_SORT_KEYS_MAX	2
 
 typedef int (*tracing_map_cmp_fn_t) (void *val_a, void *val_b);