Provide access to modules

With the provided functions it is possible to iterate over all loaded
modules or over all modules of a specific type.

include/maxscale/modules.h

@@ -121,4 +121,44 @@ void module_feedback_send(void*);
  */
 void moduleShowFeedbackReport(DCB *dcb);
 
+typedef struct mxs_module_iterator
+{
+    const char* type;
+    void* position;
+} MXS_MODULE_ITERATOR;
+
+/**
+ * @brief Returns an iterator to modules.
+ *
+ * @attention It is unspecified whether a module loaded after the iterator
+ *            was created, will be returned by the iterator. The behaviour
+ *            is undefined if a module is unloaded while an iteration is
+ *            being performed.
+ *
+ * @param type  The type of modules that should be returned. If NULL,
+ *              then all modules are returned.
+ *
+ * @return An iterator.
+ */
+MXS_MODULE_ITERATOR mxs_module_iterator_get(const char* type);
+
+/**
+ * @brief Indicates whether the iterator has a module to return.
+ *
+ * @param iterator  An iterator
+ *
+ * @return True if a subsequent call to @c mxs_module_iterator_get
+ *         will return a module.
+ */
+bool mxs_module_iterator_has_next(const MXS_MODULE_ITERATOR* iterator);
+
+/**
+ * @brief Returns the next module and advances the iterator.
+ *
+ * @param iterator  An iterator.
+ *
+ * @return A module if there was a module to return, NULL otherwise.
+ */
+MXS_MODULE* mxs_module_iterator_get_next(MXS_MODULE_ITERATOR* iterator);
+
 MXS_END_DECLS