[PATCH v5 5/5] libtraceevent: Add tep_print_selected_fields()

["Yordan Karadzhov (VMware)" <y.karadz@gmail.com>]

The new method can print only a subset of the unique data fields of
the trace event. The print format is derived from the parsing tokens
(tep_print_parse objects) of the event.

Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
---
 src/event-parse.c | 26 ++++++++++++++++++++++----
 src/event-parse.h |  3 +++
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/src/event-parse.c b/src/event-parse.c
index 7831e74..3b93138 100644
--- a/src/event-parse.c
+++ b/src/event-parse.c
@@ -5454,20 +5454,38 @@ void tep_print_field(struct trace_seq *s, void *data,
 	_tep_print_field(s, data, field, NULL);
 }
 
-void tep_print_fields(struct trace_seq *s, void *data,
-		      int size __maybe_unused, struct tep_event *event)
+static inline void
+print_selected_fields(struct trace_seq *s, void *data,
+		      struct tep_event *event,
+		      unsigned long long ignore_mask)
 {
 	struct tep_print_parse *parse = event->print_fmt.print_cache;
 	struct tep_format_field *field;
+	unsigned long long field_mask = 1;
 
 	field = event->format.fields;
-	while (field) {
+	for (;field; field = field->next, field_mask *= 2) {
+		if (field_mask & ignore_mask)
+			continue;
+
 		trace_seq_printf(s, " %s=", field->name);
 		_tep_print_field(s, data, field, &parse);
-		field = field->next;
 	}
 }
 
+void tep_print_selected_fields(struct trace_seq *s, void *data,
+			       struct tep_event *event,
+			       unsigned long long ignore_mask)
+{
+	print_selected_fields(s, data, event, ignore_mask);
+}
+
+void tep_print_fields(struct trace_seq *s, void *data,
+		      int size __maybe_unused, struct tep_event *event)
+{
+	print_selected_fields(s, data, event, 0);
+}
+
 static int print_function(struct trace_seq *s, const char *format,
 			  void *data, int size, struct tep_event *event,
 			  struct tep_print_arg *arg)
diff --git a/src/event-parse.h b/src/event-parse.h
index d4a876f..e3638cf 100644
--- a/src/event-parse.h
+++ b/src/event-parse.h
@@ -545,6 +545,9 @@ int tep_cmdline_pid(struct tep_handle *tep, struct tep_cmdline *cmdline);
 
 void tep_print_field(struct trace_seq *s, void *data,
 		     struct tep_format_field *field);
+void tep_print_selected_fields(struct trace_seq *s, void *data,
+			       struct tep_event *event,
+			       unsigned long long ignore_mask);
 void tep_print_fields(struct trace_seq *s, void *data,
 		      int size __maybe_unused, struct tep_event *event);
 int tep_strerror(struct tep_handle *tep, enum tep_errno errnum,
-- 
2.30.2