[RFC PATCH v4 2/3] tools lib traceevent: Add function to get dynamic arrays length

[He Kuang <hekuang@huawei.com>]

To print a trace event with a dynamic array, __print_array(array, len,
element_size) requires the number of items in the array, which can be
got by the helper function __get_dynamic_array_len(), currently it is
not an available function in the function list in process_function().

Add new arg type PRINT_DYNAMIC_ARRAY_LEN which returns the array
length embedded in the __data_loc_##item field to eval_num_arg().

Signed-off-by: He Kuang <hekuang@huawei.com>
---
 tools/lib/traceevent/event-parse.c                 | 52 ++++++++++++++++++++++
 tools/lib/traceevent/event-parse.h                 |  1 +
 .../util/scripting-engines/trace-event-python.c    |  1 +
 3 files changed, 54 insertions(+)

diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
index cc25f05..55fc3b6c 100644
--- a/tools/lib/traceevent/event-parse.c
+++ b/tools/lib/traceevent/event-parse.c
@@ -783,6 +783,7 @@ static void free_arg(struct print_arg *arg)
 		free(arg->bitmask.bitmask);
 		break;
 	case PRINT_DYNAMIC_ARRAY:
+	case PRINT_DYNAMIC_ARRAY_LEN:
 		free(arg->dynarray.index);
 		break;
 	case PRINT_OP:
@@ -2655,6 +2656,42 @@ process_dynamic_array(struct event_format *event, struct print_arg *arg, char **
 }
 
 static enum event_type
+process_dynamic_array_len(struct event_format *event, struct print_arg *arg,
+			  char **tok)
+{
+	struct format_field *field;
+	enum event_type type;
+	char *token;
+
+	if (read_expect_type(EVENT_ITEM, &token) < 0)
+		goto out_free;
+
+	arg->type = PRINT_DYNAMIC_ARRAY_LEN;
+
+	/* Find the field */
+	field = pevent_find_field(event, token);
+	if (!field)
+		goto out_free;
+
+	arg->dynarray.field = field;
+	arg->dynarray.index = 0;
+
+	if (read_expected(EVENT_DELIM, ")") < 0)
+		goto out_err;
+
+	type = read_token(&token);
+	*tok = token;
+
+	return type;
+
+ out_free:
+	free_token(token);
+ out_err:
+	*tok = NULL;
+	return EVENT_ERROR;
+}
+
+static enum event_type
 process_paren(struct event_format *event, struct print_arg *arg, char **tok)
 {
 	struct print_arg *item_arg;
@@ -2901,6 +2938,10 @@ process_function(struct event_format *event, struct print_arg *arg,
 		free_token(token);
 		return process_dynamic_array(event, arg, tok);
 	}
+	if (strcmp(token, "__get_dynamic_array_len") == 0) {
+		free_token(token);
+		return process_dynamic_array_len(event, arg, tok);
+	}
 
 	func = find_func_handler(event->pevent, token);
 	if (func) {
@@ -3581,6 +3622,17 @@ eval_num_arg(void *data, int size, struct event_format *event, struct print_arg
 			goto out_warning_op;
 		}
 		break;
+	case PRINT_DYNAMIC_ARRAY_LEN:
+		offset = pevent_read_number(pevent,
+					    data + arg->dynarray.field->offset,
+					    arg->dynarray.field->size);
+		/*
+		 * The actual length of the dynamic array is stored
+		 * in the top half of the field, and the offset
+		 * is in the bottom half of the 32 bit field.
+		 */
+		val = (unsigned long long)(offset >> 16);
+		break;
 	case PRINT_DYNAMIC_ARRAY:
 		/* Without [], we pass the address to the dynamic data */
 		offset = pevent_read_number(pevent,
diff --git a/tools/lib/traceevent/event-parse.h b/tools/lib/traceevent/event-parse.h
index 063b197..94543aa 100644
--- a/tools/lib/traceevent/event-parse.h
+++ b/tools/lib/traceevent/event-parse.h
@@ -294,6 +294,7 @@ enum print_arg_type {
 	PRINT_OP,
 	PRINT_FUNC,
 	PRINT_BITMASK,
+	PRINT_DYNAMIC_ARRAY_LEN,
 };
 
 struct print_arg {
diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c
index ace2484..d309341 100644
--- a/tools/perf/util/scripting-engines/trace-event-python.c
+++ b/tools/perf/util/scripting-engines/trace-event-python.c
@@ -253,6 +253,7 @@ static void define_event_symbols(struct event_format *event,
 	case PRINT_DYNAMIC_ARRAY:
 	case PRINT_FUNC:
 	case PRINT_BITMASK:
+	case PRINT_DYNAMIC_ARRAY_LEN:
 		/* we should warn... */
 		return;
 	}
-- 
1.8.5.2