[PATCH v6 14/15] tracing: Add alternative synthetic event trace action syntax

[Tom Zanussi]

From: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>

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.

Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
---
 Documentation/trace/histogram.rst | 21 ++++++++++++++++++++
 kernel/trace/trace.c              |  1 +
 kernel/trace/trace_events_hist.c  | 42 +++++++++++++++++++++++++++++++++++----
 3 files changed, 60 insertions(+), 4 deletions(-)

diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst
index 1a42ba2ec51c..b964dfc31cec 100644
--- a/Documentation/trace/histogram.rst
+++ b/Documentation/trace/histogram.rst
@@ -1874,6 +1874,7 @@ The available handlers are:
 The available actions are:
 
   - <synthetic_event_name>(param list)         - generate synthetic event
+  - trace(<synthetic_event_name>,(param list)) - generate synthetic event
   - save(field,...)                            - save current event fields
   - snapshot()                                 - snapshot the trace buffer
 
@@ -1881,6 +1882,10 @@ The following commonly-used handler.action pairs are available:
 
   - onmatch(matching.event).<synthetic_event_name>(param list)
 
+    or
+
+  - onmatch(matching.event).trace(<synthetic_event_name>,(param list))
+
     The 'onmatch(matching.event).<synthetic_event_name>(params)' hist
     trigger action is invoked whenever an event matches and the
     histogram entry would be added or updated.  It causes the named
@@ -1889,6 +1894,16 @@ The following commonly-used handler.action pairs are available:
     that consists of the values contained in those variables at the
     time the invoking event was hit.
 
+    There are two equivalent forms available for generating synthetic
+    events.  In the first form, the synthetic event name is used as if
+    it were a function name.  For example, if the synthetic event name
+    is 'wakeup_latency', the wakeup_latency event would be generated
+    by invoking it as if it were a function call, with the event field
+    values passed in as arguments: wakeup_latency(arg1,arg2).  The
+    second form simply uses the 'trace' keyword as the function name
+    and passes in the synthetic event name as the first argument,
+    followed by the field values: trace(wakeup_latency,arg1,arg2).
+
     The 'param list' consists of one or more parameters which may be
     either variables or fields defined on either the 'matching.event'
     or the target event.  The variables or fields specified in the
@@ -1928,6 +1943,12 @@ The following commonly-used handler.action pairs are available:
               wakeup_new_test($testpid) if comm=="cyclictest"' >> \
               /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/trigger
 
+    Or, equivalently, using the 'trace' keyword syntax:
+
+    # echo 'hist:keys=$testpid:testpid=pid:onmatch(sched.sched_wakeup_new).\
+            trace(wakeup_new_test,$testpid) if comm=="cyclictest"' >> \
+            /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/trigger
+
     Creating and displaying a histogram based on those events is now
     just a matter of using the fields and new synthetic event in the
     tracing/events/synthetic directory, as usual::
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b1158d26880e..242cbf558884 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4880,6 +4880,7 @@ static const char readme_msg[] =
 	"\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"
 	"\t        snapshot()                           - snapshot the trace buffer\n"
 #endif
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 90f1a0cf34c0..05234538505e 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -352,6 +352,8 @@ struct action_data {
 
 	unsigned int		var_ref_idx;
 	struct synth_event	*synth_event;
+	bool			use_trace_keyword;
+	char			*synth_event_name;
 
 	union {
 		struct {
@@ -3584,6 +3586,8 @@ static void action_data_destroy(struct action_data *data)
 	if (data->synth_event)
 		data->synth_event->ref--;
 
+	kfree(data->synth_event_name);
+
 	kfree(data);
 
 	mutex_unlock(&synth_event_mutex);
@@ -3678,6 +3682,7 @@ 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) {
@@ -3706,6 +3711,13 @@ 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:
@@ -3789,6 +3801,9 @@ static int action_parse(char *str, struct action_data *data,
 	} else {
 		char *params = strsep(&str, ")");
 
+		if (strncmp(action_name, "trace", strlen("trace")) == 0)
+			data->use_trace_keyword = true;
+
 		if (params) {
 			ret = parse_action_params(params, data);
 			if (ret)
@@ -4007,13 +4022,19 @@ 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;
 
 	mutex_lock(&synth_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);
 		mutex_unlock(&synth_event_mutex);
 		return -EINVAL;
 	}
@@ -4781,8 +4802,10 @@ 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]);
 		}
@@ -4830,6 +4853,7 @@ 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;
@@ -4844,7 +4868,17 @@ 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) {
-- 
2.14.1