uORB: Provide used group count

src/modules/uORB/uORB.cpp

@@ -260,6 +260,20 @@ int  orb_exists(const struct orb_metadata *meta, int instance)
 	return uORB::Manager::get_instance()->orb_exists(meta, instance);
 }
 
+/**
+ * Get the number of published instances of a topic group
+ *
+ * @param meta    ORB topic metadata.
+ * @return    The number of published instances of this topic
+ */
+int  orb_group_count(const struct orb_metadata *meta)
+{
+	unsigned group_count = 0;
+	while (!uORB::Manager::get_instance()->orb_exists(meta, group_count++)) {};
+
+	return group_count;
+}
+
 /**
  * Return the priority of the topic
  *

src/modules/uORB/uORB.h

@@ -328,6 +328,14 @@ extern int	orb_stat(int handle, uint64_t *time) __EXPORT;
  */
 extern int	orb_exists(const struct orb_metadata *meta, int instance) __EXPORT;
 
+/**
+ * Get the number of published instances of a topic group
+ *
+ * @param meta    ORB topic metadata.
+ * @return    The number of published instances of this topic
+ */
+extern int	orb_group_count(const struct orb_metadata *meta) __EXPORT;
+
 /**
  * Return the priority of the topic
  *