[PATCH v3 20/33] tracing: Add hist trigger action hook

[Tom Zanussi]

Add a hook for executing extra actions whenever a histogram entry is
added or updated.

The default 'action' when a hist entry is added to a histogram is to
update the set of values associated with it.  Some applications may
want to perform additional actions at that point, such as generate
another event, or compare and save a maximum.

Add a simple framework for doing that; specific actions will be
implemented on top of it in later patches.

Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
---
 kernel/trace/trace_events_hist.c | 91 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 88 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 6dcef22..f1e60fb 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -33,6 +33,7 @@ typedef u64 (*hist_field_fn_t) (struct hist_field *field,
 
 #define HIST_FIELD_OPERANDS_MAX	2
 #define HIST_FIELDS_MAX		(TRACING_MAP_FIELDS_MAX + TRACING_MAP_VARS_MAX)
+#define HIST_ACTIONS_MAX	8
 
 enum field_op_id {
 	FIELD_OP_NONE,
@@ -241,6 +242,9 @@ struct hist_trigger_attrs {
 	char		*assignment_str[TRACING_MAP_VARS_MAX];
 	unsigned int	n_assignments;
 
+	char		*action_str[HIST_ACTIONS_MAX];
+	unsigned int	n_actions;
+
 	struct var_defs	var_defs;
 };
 
@@ -261,6 +265,21 @@ struct hist_trigger_data {
 	bool				remove;
 	struct hist_field               *var_refs[TRACING_MAP_VARS_MAX];
 	unsigned int			n_var_refs;
+
+	struct action_data		*actions[HIST_ACTIONS_MAX];
+	unsigned int			n_actions;
+};
+
+struct action_data;
+
+typedef void (*action_fn_t) (struct hist_trigger_data *hist_data,
+			     struct tracing_map_elt *elt, void *rec,
+			     struct ring_buffer_event *rbe,
+			     struct action_data *data, u64 *var_ref_vals);
+
+struct action_data {
+	action_fn_t		fn;
+	unsigned int		var_ref_idx;
 };
 
 static u64 hist_field_timestamp(struct hist_field *hist_field,
@@ -710,6 +729,9 @@ static void destroy_hist_trigger_attrs(struct hist_trigger_attrs *attrs)
 	for (i = 0; i < attrs->n_assignments; i++)
 		kfree(attrs->assignment_str[i]);
 
+	for (i = 0; i < attrs->n_actions; i++)
+		kfree(attrs->action_str[i]);
+
 	kfree(attrs->name);
 	kfree(attrs->sort_key_str);
 	kfree(attrs->keys_str);
@@ -717,6 +739,16 @@ static void destroy_hist_trigger_attrs(struct hist_trigger_attrs *attrs)
 	kfree(attrs);
 }
 
+static int parse_action(char *str, struct hist_trigger_attrs *attrs)
+{
+	int ret = 0;
+
+	if (attrs->n_actions >= HIST_ACTIONS_MAX)
+		return ret;
+
+	return ret;
+}
+
 static int parse_assignment(char *str, struct hist_trigger_attrs *attrs)
 {
 	int ret = 0;
@@ -800,8 +832,9 @@ static struct hist_trigger_attrs *parse_hist_trigger_attrs(char *trigger_str)
 		else if (strcmp(str, "clear") == 0)
 			attrs->clear = true;
 		else {
-			ret = -EINVAL;
-			goto free;
+			ret = parse_action(str, attrs);
+			if (ret)
+				goto free;
 		}
 	}
 
@@ -1949,11 +1982,42 @@ static int create_sort_keys(struct hist_trigger_data *hist_data)
 	return ret;
 }
 
+static void destroy_actions(struct hist_trigger_data *hist_data)
+{
+	unsigned int i;
+
+	for (i = 0; i < hist_data->n_actions; i++) {
+		struct action_data *data = hist_data->actions[i];
+
+		kfree(data);
+	}
+}
+
+static int create_actions(struct hist_trigger_data *hist_data,
+			  struct trace_event_file *file)
+{
+	unsigned int i;
+	int ret = 0;
+	char *str;
+
+	for (i = 0; i < hist_data->attrs->n_actions; i++) {
+		str = hist_data->attrs->action_str[i];
+	}
+
+	return ret;
+}
+
 static void destroy_hist_data(struct hist_trigger_data *hist_data)
 {
+	if (!hist_data)
+		return;
+
 	destroy_hist_trigger_attrs(hist_data->attrs);
 	destroy_hist_fields(hist_data);
 	tracing_map_destroy(hist_data->map);
+
+	destroy_actions(hist_data);
+
 	kfree(hist_data);
 }
 
@@ -2112,6 +2176,20 @@ static inline void add_to_key(char *compound_key, void *key,
 	memcpy(compound_key + key_field->offset, key, size);
 }
 
+static void
+hist_trigger_actions(struct hist_trigger_data *hist_data,
+		     struct tracing_map_elt *elt, void *rec,
+		     struct ring_buffer_event *rbe, u64 *var_ref_vals)
+{
+	struct action_data *data;
+	unsigned int i;
+
+	for (i = 0; i < hist_data->n_actions; i++) {
+		data = hist_data->actions[i];
+		data->fn(hist_data, elt, rec, rbe, data, var_ref_vals);
+	}
+}
+
 static void event_hist_trigger(struct event_trigger_data *data, void *rec,
 			       struct ring_buffer_event *rbe)
 {
@@ -2167,6 +2245,9 @@ static void event_hist_trigger(struct event_trigger_data *data, void *rec,
 		return;
 
 	hist_trigger_elt_update(hist_data, elt, rec, rbe, var_ref_vals);
+
+	if (resolve_var_refs(hist_data, key, var_ref_vals, true))
+		hist_trigger_actions(hist_data, elt, rec, rbe, var_ref_vals);
 }
 
 static void hist_trigger_stacktrace_print(struct seq_file *m,
@@ -2942,6 +3023,10 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	if (has_hist_vars(hist_data))
 		save_hist_vars(hist_data);
 
+	ret = create_actions(hist_data, file);
+	if (ret)
+		goto out_unreg;
+
 	ret = tracing_map_init(hist_data->map);
 	if (ret)
 		goto out_unreg;
@@ -2963,8 +3048,8 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	remove_hist_vars(hist_data);
 
 	kfree(trigger_data);
-
 	destroy_hist_data(hist_data);
+
 	goto out;
 }
 
-- 
1.9.3