uORB: Add API to check if a topic exists yet

src/modules/uORB/uORB.cpp

@@ -41,6 +41,7 @@
 #include <drivers/device/device.h>
 
 #include <sys/types.h>
+#include <sys/stat.h>
 #include <stdint.h>
 #include <stdbool.h>
 #include <string.h>
@@ -1196,6 +1197,25 @@ node_open(Flavor f, const struct orb_metadata *meta, const void *data, bool adve
 
 } // namespace
 
+int
+orb_exists(const struct orb_metadata *meta, int instance)
+{
+	/*
+	 * Generate the path to the node and try to open it.
+	 */
+	char path[orb_maxpath];
+	int inst = instance;
+	int ret = node_mkpath(path, PUBSUB, meta, &inst);
+
+	if (ret != OK) {
+		errno = -ret;
+		return ERROR;
+	}
+
+	struct stat buffer;
+	return stat(path, &buffer);
+}
+
 orb_advert_t
 orb_advertise(const struct orb_metadata *meta, const void *data)
 {

src/modules/uORB/uORB.h

@@ -318,6 +318,15 @@ extern int	orb_check(int handle, bool *updated) __EXPORT;
  */
 extern int	orb_stat(int handle, uint64_t *time) __EXPORT;
 
+/**
+ * Check if a topic has already been created.
+ *
+ * @param meta		ORB topic metadata.
+ * @param instance	ORB instance
+ * @return		OK if the topic exists, ERROR otherwise with errno set accordingly.
+ */
+extern int	orb_exists(const struct orb_metadata *meta, int instance) __EXPORT;
+
 /**
  * Return the priority of the topic
  *