tracing: Add needs_rec flag to event triggers

Add a new needs_rec flag for triggers that require unconditional
access to trace records in order to function.

Normally a trigger requires access to the contents of a trace record
only if it has a filter associated with it (since filters need the
contents of a record in order to make a filtering decision).  Some
types of triggers, such as 'hist' triggers, require access to trace
record contents independent of the presence of filters, so add a new
flag for those triggers.

Link: http://lkml.kernel.org/r/7be8fa38f9b90fdb6c47ca0f98d20a07b9fd512b.1449767187.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.h

@@ -1292,6 +1292,12 @@ struct event_trigger_ops {
  *	itself logs to the trace buffer, this flag should be set,
  *	otherwise it can be left unspecified.
  *
+ * @needs_rec: A flag that says whether or not this command needs
+ *	access to the trace record in order to perform its function,
+ *	regardless of whether or not it has a filter associated with
+ *	it (filters make a trigger require access to the trace record
+ *	but are not always present).
+ *
  * All the methods below, except for @set_filter(), must be
  * implemented.
  *
@@ -1332,6 +1338,7 @@ struct event_command {
 	char			*name;
 	enum event_trigger_type	trigger_type;
 	bool			post_trigger;
+	bool			needs_rec;
 	int			(*func)(struct event_command *cmd_ops,
 					struct trace_event_file *file,
 					char *glob, char *cmd, char *params);

kernel/trace/trace_events_trigger.c

@@ -493,7 +493,8 @@ void update_cond_flag(struct trace_event_file *file)
 	bool set_cond = false;
 
 	list_for_each_entry_rcu(data, &file->triggers, list) {
-		if (data->filter || data->cmd_ops->post_trigger) {
+		if (data->filter || data->cmd_ops->post_trigger ||
+		    data->cmd_ops->needs_rec) {
 			set_cond = true;
 			break;
 		}