[PATCH v4 4/8] libtracefs: Add new API to check if instance exists

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

A new API is implemented:
 tracefs_instance_exists()
which can be used to check if ftrace instance with given name exists in
the system.

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 include/tracefs/tracefs.h      |  1 +
 lib/tracefs/tracefs-instance.c | 22 +++++++++++++++++++++-
 utest/tracefs-utest.c          |  2 ++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/include/tracefs/tracefs.h b/include/tracefs/tracefs.h
index 1cf8de48..ef806d3c 100644
--- a/include/tracefs/tracefs.h
+++ b/include/tracefs/tracefs.h
@@ -33,6 +33,7 @@ int tracefs_instance_file_write(struct tracefs_instance *instance,
 char *tracefs_instance_file_read(struct tracefs_instance *instance,
 				 char *file, int *psize);
 
+bool tracefs_instance_exists(const char *name);
 bool tracefs_file_exists(struct tracefs_instance *instance, char *name);
 bool tracefs_dir_exists(struct tracefs_instance *instance, char *name);
 
diff --git a/lib/tracefs/tracefs-instance.c b/lib/tracefs/tracefs-instance.c
index e37d93d1..06f33c35 100644
--- a/lib/tracefs/tracefs-instance.c
+++ b/lib/tracefs/tracefs-instance.c
@@ -257,7 +257,10 @@ static bool check_file_exists(struct tracefs_instance *instance,
 	int ret;
 
 	path = tracefs_instance_get_dir(instance);
-	snprintf(file, PATH_MAX, "%s/%s", path, name);
+	if (name)
+		snprintf(file, PATH_MAX, "%s/%s", path, name);
+	else
+		snprintf(file, PATH_MAX, "%s", path);
 	tracefs_put_tracing_file(path);
 	ret = stat(file, &st);
 	if (ret < 0)
@@ -266,6 +269,23 @@ static bool check_file_exists(struct tracefs_instance *instance,
 	return !dir == !S_ISDIR(st.st_mode);
 }
 
+/**
+ * tracefs_instance_exists - Check an instance with given name exists
+ * @name: name of the instance
+ *
+ * Returns true if the instance exists, false otherwise
+ *
+ */
+bool tracefs_instance_exists(const char *name)
+{
+	char file[PATH_MAX];
+
+	if (!name)
+		return false;
+	snprintf(file, PATH_MAX, "instances/%s", name);
+	return check_file_exists(NULL, file, true);
+}
+
 /**
  * tracefs_file_exists - Check if a file with given name exists in given instance
  * @instance: ftrace instance, can be NULL for the top instance
diff --git a/utest/tracefs-utest.c b/utest/tracefs-utest.c
index b5296963..2febdb88 100644
--- a/utest/tracefs-utest.c
+++ b/utest/tracefs-utest.c
@@ -197,6 +197,7 @@ static void test_instance_file(void)
 	CU_TEST(asprintf(&inst_dir, "%s/instances/%s", tdir, name) > 0);
 	CU_TEST(stat(inst_dir, &st) != 0);
 
+	CU_TEST(tracefs_instance_exists(name) == false);
 	instance = tracefs_instance_alloc(name);
 	CU_TEST(instance != NULL);
 	CU_TEST(stat(inst_dir, &st) != 0);
@@ -205,6 +206,7 @@ static void test_instance_file(void)
 	CU_TEST(strcmp(inst_name, name) == 0);
 
 	CU_TEST(tracefs_instance_create(instance) == 0);
+	CU_TEST(tracefs_instance_exists(name) == true);
 	CU_TEST(stat(inst_dir, &st) == 0);
 	CU_TEST(S_ISDIR(st.st_mode));
 
-- 
2.28.0