[PATCH v4 7/8] trace-cmd: Add new libtrasefs API to get the current trace clock

["Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>]

A new API is added to tracefs library:
	tracefs_get_clock()
It reads the trace_clock file from the ftrace file system, parses it
and returns a string with the current trace clock. The returned string
must be freed by free().

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 include/tracefs/tracefs.h      |  2 ++
 lib/tracefs/tracefs-instance.c | 35 ++++++++++++++++++++++++++++++++++
 tracecmd/trace-stat.c          | 27 +++++---------------------
 utest/tracefs-utest.c          | 30 ++++++++++++++++++++++++++++-
 4 files changed, 71 insertions(+), 23 deletions(-)

diff --git a/include/tracefs/tracefs.h b/include/tracefs/tracefs.h
index bcf3dd64..3358e33d 100644
--- a/include/tracefs/tracefs.h
+++ b/include/tracefs/tracefs.h
@@ -57,4 +57,6 @@ struct tep_handle *tracefs_local_events_system(const char *tracing_dir,
 int tracefs_fill_local_events(const char *tracing_dir,
 			       struct tep_handle *tep, int *parsing_failures);
 
+char *tracefs_get_clock(struct tracefs_instance *instance);
+
 #endif /* _TRACE_FS_H */
diff --git a/lib/tracefs/tracefs-instance.c b/lib/tracefs/tracefs-instance.c
index d05e08b1..e9e24ef8 100644
--- a/lib/tracefs/tracefs-instance.c
+++ b/lib/tracefs/tracefs-instance.c
@@ -418,3 +418,38 @@ out:
 	tracefs_put_tracing_file(path);
 	return fret;
 }
+
+/**
+ * tracefs_get_clock - Get the current trace clock
+ * @instance: ftrace instance, can be NULL for the top instance
+ *
+ * Returns the current trace clock of the given instance, or NULL in
+ * case of an error.
+ * The return string must be freed by free()
+ */
+char *tracefs_get_clock(struct tracefs_instance *instance)
+{
+	char *all_clocks = NULL;
+	char *ret = NULL;
+	int bytes = 0;
+	char *clock;
+	char *cont;
+
+	all_clocks  = tracefs_instance_file_read(instance, "trace_clock", &bytes);
+	if (!all_clocks || !bytes)
+		goto out;
+
+	clock = strstr(all_clocks, "[");
+	if (!clock)
+		goto out;
+	clock++;
+	cont = strstr(clock, "]");
+	if (!cont)
+		goto out;
+	*cont = '\0';
+
+	ret = strdup(clock);
+out:
+	free(all_clocks);
+	return ret;
+}
diff --git a/tracecmd/trace-stat.c b/tracecmd/trace-stat.c
index e6678eab..31127872 100644
--- a/tracecmd/trace-stat.c
+++ b/tracecmd/trace-stat.c
@@ -710,33 +710,16 @@ static void report_buffers(struct buffer_instance *instance)
 
 static void report_clock(struct buffer_instance *instance)
 {
-	char *str;
-	char *cont;
+	struct tracefs_instance *tracefs = instance ? instance->tracefs : NULL;
 	char *clock;
 
-	str = get_instance_file_content(instance, "trace_clock");
-	if (!str)
-		return;
-
-	clock = strstr(str, "[");
-	if (!clock)
-		goto out;
-	clock++;
-
-	cont = strstr(clock, "]");
-	if (!cont) /* should never happen */
-		goto out;
-
-	*cont = '\0';
+	clock = tracefs_get_clock(tracefs);
 
 	/* Default clock is "local", only show others */
-	if (strcmp(clock, "local") == 0)
-		goto out;
+	if (clock && !strcmp(clock, "local") == 0)
+		printf("\nClock: %s\n", clock);
 
-	printf("\nClock: %s\n", clock);
-
- out:
-	free(str);
+	free(clock);
 }
 
 static void report_cpumask(struct buffer_instance *instance)
diff --git a/utest/tracefs-utest.c b/utest/tracefs-utest.c
index c42fea12..78eda481 100644
--- a/utest/tracefs-utest.c
+++ b/utest/tracefs-utest.c
@@ -511,6 +511,33 @@ static void test_instances_walk(void)
 	}
 }
 
+static void current_clock_check(const char *clock)
+{
+	int size = 0;
+	char *clocks;
+	char *str;
+
+	clocks = tracefs_instance_file_read(test_instance, "trace_clock", &size);
+	CU_TEST(clocks != NULL);
+	CU_TEST(size > strlen(clock));
+	str = strstr(clocks, clock);
+	CU_TEST(str != NULL);
+	CU_TEST(str != clocks);
+	CU_TEST(*(str - 1) == '[');
+	CU_TEST(*(str + strlen(clock)) == ']');
+	free(clocks);
+}
+
+static void test_get_clock(void)
+{
+	const char *clock;
+
+	clock = tracefs_get_clock(test_instance);
+	CU_TEST(clock != NULL);
+	current_clock_check(clock);
+	free((char *)clock);
+}
+
 static int test_suite_destroy(void)
 {
 	tracefs_instance_destroy(test_instance);
@@ -556,5 +583,6 @@ void test_tracefs_lib(void)
 		    test_local_events);
 	CU_add_test(suite, "tracefs_instances_walk API",
 		    test_instances_walk);
-
+	CU_add_test(suite, "tracefs_get_clock API",
+		    test_get_clock);
 }
-- 
2.28.0