tracing: Add alternative synthetic event trace action syntax

Add a 'trace(synthetic_event_name, params)' alternative to
synthetic_event_name(params).

Currently, the syntax used for generating synthetic events is to
invoke synthetic_event_name(params) i.e. use the synthetic event name
as a function call.

Users requested a new form that more explicitly shows that the
synthetic event is in effect being traced.  In this version, a new
'trace()' keyword is used, and the synthetic event name is passed in
as the first argument.

In addition, for the sake of consistency with other actions, change
the documention to emphasize the trace() form over the function-call
form, which remains documented as equivalent.

Link: http://lkml.kernel.org/r/d082773e50232a001480cf837679a1e01c1a2eb7.1550100284.git.tom.zanussi@linux.intel.com

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

2 files changed, 39 insertions, 5 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index be6779f963c6..0460cc0f28fd 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4918,7 +4918,7 @@ static const char readme_msg[] =
 	"\t        onmax(var)               - invoke if var exceeds current max\n"
 	"\t        onchange(var)            - invoke action if var changes\n\n"
 	"\t    The available actions are:\n\n"
-	"\t        <synthetic_event>(param list)        - generate synthetic event\n"
+	"\t        trace(<synthetic_event>,param list)  - generate synthetic event\n"
 	"\t        save(field,...)                      - save current event fields\n"
 #ifdef CONFIG_TRACER_SNAPSHOT
 	"\t        snapshot()                           - snapshot the trace buffer\n"
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 2f3323ca9d24..66386ba1425f 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -419,6 +419,8 @@ struct action_data {
 	 */
 	unsigned int		var_ref_idx;
 	struct synth_event	*synth_event;
+	bool			use_trace_keyword;
+	char			*synth_event_name;
 
 	union {
 		struct {
@@ -3700,6 +3702,8 @@ static void action_data_destroy(struct action_data *data)
 	if (data->synth_event)
 		data->synth_event->ref--;
 
+	kfree(data->synth_event_name);
+
 	kfree(data);
 }
 
@@ -3781,6 +3785,7 @@ static int track_data_create(struct hist_trigger_data *hist_data,
 static int parse_action_params(char *params, struct action_data *data)
 {
 	char *param, *saved_param;
+	bool first_param = true;
 	int ret = 0;
 
 	while (params) {
@@ -3809,6 +3814,13 @@ static int parse_action_params(char *params, struct action_data *data)
 			goto out;
 		}
 
+		if (first_param && data->use_trace_keyword) {
+			data->synth_event_name = saved_param;
+			first_param = false;
+			continue;
+		}
+		first_param = false;
+
 		data->params[data->n_params++] = saved_param;
 	}
  out:
@@ -3886,6 +3898,9 @@ static int action_parse(char *str, struct action_data *data,
 	} else {
 		char *params = strsep(&str, ")");
 
+		if (str_has_prefix(action_name, "trace"))
+			data->use_trace_keyword = true;
+
 		if (params) {
 			ret = parse_action_params(params, data);
 			if (ret)
@@ -4088,13 +4103,19 @@ static int trace_action_create(struct hist_trigger_data *hist_data,
 	unsigned int i, var_ref_idx;
 	unsigned int field_pos = 0;
 	struct synth_event *event;
+	char *synth_event_name;
 	int ret = 0;
 
 	lockdep_assert_held(&event_mutex);
 
-	event = find_synth_event(data->action_name);
+	if (data->use_trace_keyword)
+		synth_event_name = data->synth_event_name;
+	else
+		synth_event_name = data->action_name;
+
+	event = find_synth_event(synth_event_name);
 	if (!event) {
-		hist_err("trace action: Couldn't find synthetic event: ", data->action_name);
+		hist_err("trace action: Couldn't find synthetic event: ", synth_event_name);
 		return -EINVAL;
 	}
 
@@ -4841,8 +4862,10 @@ static void print_action_spec(struct seq_file *m,
 				seq_puts(m, ",");
 		}
 	} else if (data->action == ACTION_TRACE) {
+		if (data->use_trace_keyword)
+			seq_printf(m, "%s", data->synth_event_name);
 		for (i = 0; i < data->n_params; i++) {
-			if (i)
+			if (i || data->use_trace_keyword)
 				seq_puts(m, ",");
 			seq_printf(m, "%s", data->params[i]);
 		}
@@ -4890,6 +4913,7 @@ static bool actions_match(struct hist_trigger_data *hist_data,
 	for (i = 0; i < hist_data->n_actions; i++) {
 		struct action_data *data = hist_data->actions[i];
 		struct action_data *data_test = hist_data_test->actions[i];
+		char *action_name, *action_name_test;
 
 		if (data->handler != data_test->handler)
 			return false;
@@ -4904,7 +4928,17 @@ static bool actions_match(struct hist_trigger_data *hist_data,
 				return false;
 		}
 
-		if (strcmp(data->action_name, data_test->action_name) != 0)
+		if (data->use_trace_keyword)
+			action_name = data->synth_event_name;
+		else
+			action_name = data->action_name;
+
+		if (data_test->use_trace_keyword)
+			action_name_test = data_test->synth_event_name;
+		else
+			action_name_test = data_test->action_name;
+
+		if (strcmp(action_name, action_name_test) != 0)
 			return false;
 
 		if (data->handler == HANDLER_ONMATCH) {