tracing: Add hist trigger 'execname' modifier

Allow users to have common_pid field values displayed as program names
in the output by appending '.execname' to a common_pid field name:

   # echo hist:keys=common_pid.execname ... \
              [ if filter] > event/trigger

Link: http://lkml.kernel.org/r/e172e81f10f5b8d1f08450e3763c850f39fbf698.1457029949.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.c

@@ -3857,7 +3857,8 @@ static const char readme_msg[] =
 	"\t    following modifiers to the field name, as applicable:\n\n"
 	"\t            .hex        display a number as a hex value\n"
 	"\t            .sym        display an address as a symbol\n"
-	"\t            .sym-offset display an address as a symbol and offset\n\n"
+	"\t            .sym-offset display an address as a symbol and offset\n"
+	"\t            .execname   display a common_pid as a program name\n\n"
 	"\t    The 'pause' parameter can be used to pause an existing hist\n"
 	"\t    trigger or to start a hist trigger but not log any events\n"
 	"\t    until told to do so.  'continue' can be used to start or\n"

kernel/trace/trace_events_hist.c

@@ -83,6 +83,7 @@ enum hist_field_flags {
 	HIST_FIELD_FL_HEX		= 8,
 	HIST_FIELD_FL_SYM		= 16,
 	HIST_FIELD_FL_SYM_OFFSET	= 32,
+	HIST_FIELD_FL_EXECNAME		= 64,
 };
 
 struct hist_trigger_attrs {
@@ -232,6 +233,73 @@ static struct hist_trigger_attrs *parse_hist_trigger_attrs(char *trigger_str)
 	return ERR_PTR(ret);
 }
 
+static inline void save_comm(char *comm, struct task_struct *task)
+{
+	if (!task->pid) {
+		strcpy(comm, "<idle>");
+		return;
+	}
+
+	if (WARN_ON_ONCE(task->pid < 0)) {
+		strcpy(comm, "<XXX>");
+		return;
+	}
+
+	memcpy(comm, task->comm, TASK_COMM_LEN);
+}
+
+static void hist_trigger_elt_comm_free(struct tracing_map_elt *elt)
+{
+	kfree((char *)elt->private_data);
+}
+
+static int hist_trigger_elt_comm_alloc(struct tracing_map_elt *elt)
+{
+	struct hist_trigger_data *hist_data = elt->map->private_data;
+	struct hist_field *key_field;
+	unsigned int i;
+
+	for_each_hist_key_field(i, hist_data) {
+		key_field = hist_data->fields[i];
+
+		if (key_field->flags & HIST_FIELD_FL_EXECNAME) {
+			unsigned int size = TASK_COMM_LEN + 1;
+
+			elt->private_data = kzalloc(size, GFP_KERNEL);
+			if (!elt->private_data)
+				return -ENOMEM;
+			break;
+		}
+	}
+
+	return 0;
+}
+
+static void hist_trigger_elt_comm_copy(struct tracing_map_elt *to,
+				       struct tracing_map_elt *from)
+{
+	char *comm_from = from->private_data;
+	char *comm_to = to->private_data;
+
+	if (comm_from)
+		memcpy(comm_to, comm_from, TASK_COMM_LEN + 1);
+}
+
+static void hist_trigger_elt_comm_init(struct tracing_map_elt *elt)
+{
+	char *comm = elt->private_data;
+
+	if (comm)
+		save_comm(comm, current);
+}
+
+static const struct tracing_map_ops hist_trigger_elt_comm_ops = {
+	.elt_alloc	= hist_trigger_elt_comm_alloc,
+	.elt_copy	= hist_trigger_elt_comm_copy,
+	.elt_free	= hist_trigger_elt_comm_free,
+	.elt_init	= hist_trigger_elt_comm_init,
+};
+
 static void destroy_hist_field(struct hist_field *hist_field)
 {
 	kfree(hist_field);
@@ -403,6 +471,9 @@ static int create_key_field(struct hist_trigger_data *hist_data,
 			flags |= HIST_FIELD_FL_SYM;
 		else if (strcmp(field_str, "sym-offset") == 0)
 			flags |= HIST_FIELD_FL_SYM_OFFSET;
+		else if ((strcmp(field_str, "execname") == 0) &&
+			 (strcmp(field_name, "common_pid") == 0))
+			flags |= HIST_FIELD_FL_EXECNAME;
 		else {
 			ret = -EINVAL;
 			goto out;
@@ -624,11 +695,27 @@ static int create_tracing_map_fields(struct hist_trigger_data *hist_data)
 	return 0;
 }
 
+static bool need_tracing_map_ops(struct hist_trigger_data *hist_data)
+{
+	struct hist_field *key_field;
+	unsigned int i;
+
+	for_each_hist_key_field(i, hist_data) {
+		key_field = hist_data->fields[i];
+
+		if (key_field->flags & HIST_FIELD_FL_EXECNAME)
+			return true;
+	}
+
+	return false;
+}
+
 static struct hist_trigger_data *
 create_hist_data(unsigned int map_bits,
 		 struct hist_trigger_attrs *attrs,
 		 struct trace_event_file *file)
 {
+	const struct tracing_map_ops *map_ops = NULL;
 	struct hist_trigger_data *hist_data;
 	int ret = 0;
 
@@ -646,8 +733,11 @@ create_hist_data(unsigned int map_bits,
 	if (ret)
 		goto free;
 
+	if (need_tracing_map_ops(hist_data))
+		map_ops = &hist_trigger_elt_comm_ops;
+
 	hist_data->map = tracing_map_create(map_bits, hist_data->key_size,
-					    NULL, hist_data);
+					    map_ops, hist_data);
 	if (IS_ERR(hist_data->map)) {
 		ret = PTR_ERR(hist_data->map);
 		hist_data->map = NULL;
@@ -758,6 +848,12 @@ hist_trigger_entry_print(struct seq_file *m,
 			sprint_symbol(str, uval);
 			seq_printf(m, "%s: [%llx] %-55s",
 				   key_field->field->name, uval, str);
+		} else if (key_field->flags & HIST_FIELD_FL_EXECNAME) {
+			char *comm = elt->private_data;
+
+			uval = *(u64 *)(key + key_field->offset);
+			seq_printf(m, "%s: %-16s[%10llu]",
+				   key_field->field->name, comm, uval);
 		} else if (key_field->flags & HIST_FIELD_FL_STRING) {
 			seq_printf(m, "%s: %-50s", key_field->field->name,
 				   (char *)(key + key_field->offset));
@@ -877,6 +973,8 @@ static const char *get_hist_field_flags(struct hist_field *hist_field)
 		flags_str = "sym";
 	else if (hist_field->flags & HIST_FIELD_FL_SYM_OFFSET)
 		flags_str = "sym-offset";
+	else if (hist_field->flags & HIST_FIELD_FL_EXECNAME)
+		flags_str = "execname";
 
 	return flags_str;
 }