Make the distinction between "parameter import" which merges parameters, and "parameter load" which blows away any current changes.

apps/systemcmds/eeprom/eeprom.c

@@ -216,7 +216,7 @@ eeprom_load(const char *name)
 	if (fd < 0)
 		err(1, "open '%s'", name);
 
-	int result = param_import(fd);
+	int result = param_load(fd);
 	close(fd);
 
 	if (result < 0)

apps/systemlib/param/param.c

@@ -178,6 +178,22 @@ param_find_changed(param_t param) {
 	return s;
 }
 
+static void
+param_notify_changes(void)
+{
+	struct parameter_update_s pup = { .timestamp = hrt_absolute_time() };
+
+	/*
+	 * If we don't have a handle to our topic, create one now; otherwise
+	 * just publish.
+	 */
+	if (param_topic == -1) {
+		param_topic = orb_advertise(ORB_ID(parameter_update), &pup);
+	} else {
+		orb_publish(ORB_ID(parameter_update), param_topic, &pup);
+	}
+}
+
 param_t
 param_find(const char *name)
 {
@@ -390,24 +406,50 @@ out:
 	 * If we set something, now that we have unlocked, go ahead and advertise that
 	 * a thing has been set.
 	 */
-	if (params_changed) {
-		struct parameter_update_s pup = { .timestamp = hrt_absolute_time() };
-
-		/*
-		 * If we don't have a handle to our topic, create one now; otherwise
-		 * just publish.
-		 */
-		if (param_topic == -1) {
-			param_topic = orb_advertise(ORB_ID(parameter_update), &pup);
-		} else {
-			orb_publish(ORB_ID(parameter_update), param_topic, &pup);
-		}
-
-	}
+	if (params_changed)
+		param_notify_changes();
 
 	return result;
 }
 
+void
+param_reset(param_t param)
+{
+	struct param_wbuf_s *s = NULL;
+
+	param_lock();
+
+	if (handle_in_range(param)) {
+
+		/* look for a saved value */
+		s = param_find_changed(param);
+
+		/* if we found one, erase it */
+		if (s != NULL) {
+			int pos = utarry_eltidx(param_values, s);
+			utarray_erase(param_values, pos, 1);
+		}
+	}
+	param_unlock();
+
+	if (s != NULL)
+		param_notify_changes();
+}
+
+void
+param_reset_all(void)
+{
+	param_lock();
+
+	if (param_values != NULL) {
+		utarray_free(param_values);
+	}
+
+	param_unlock();
+
+	param_notify_changes();
+}
+
 int
 param_export(int fd, bool only_unsaved)
 {
@@ -619,9 +661,17 @@ param_import(int fd)
 out:
 	if (result < 0)
 		debug("BSON error decoding parameters");
+
 	return result;
 }
 
+int
+param_load(int fd)
+{
+	param_reset_all();
+	return param_import(fd);
+}
+
 void
 param_foreach(void (*func)(void *arg, param_t param), void *arg, bool only_changed)
 {

apps/systemlib/param/param.h

@@ -148,15 +148,31 @@ __EXPORT size_t		param_size(param_t param) __attribute__((const));
 __EXPORT int		param_get(param_t param, void *val);
 
 /**
- * Set the scalar value of a parameter.
+ * Set the value of a parameter.
  *
  * @param param		A handle returned by param_find or passed by param_foreach.
  * @param val		The value to set; assumed to point to a variable of the parameter type.
- *			For structures, the pointer is assumed to point to a copy of the structure.
+ *			For structures, the pointer is assumed to point to a structure to be copied.
  * @return		Zero if the parameter's value could be set from a scalar, nonzero otherwise.
  */
 __EXPORT int		param_set(param_t param, const void *val);
 
+/**
+ * Reset a parameter to its default value.
+ *
+ * This function frees any storage used by struct parameters, but scalar parameters 
+ *
+ * @param param		A handle returned by param_find or passed by param_foreach.
+ */
+__EXPORT void		param_reset(param_t param);
+
+/**
+ * Reset all parameters to their default values.
+ *
+ * This function also releases the storage used by struct parameters.
+ */
+__EXPORT void		param_reset_all(void);
+
 /**
  * Export changed parameters to a file.
  *
@@ -169,12 +185,26 @@ __EXPORT int		param_export(int fd, bool only_unsaved);
 /**
  * Import parameters from a file, discarding any unrecognized parameters.
  *
+ * This function merges the imported parameters with the current parameter set.
+ *
  * @param fd		File descriptor to import from.  (Currently expected to be a file.)
  * @return		Zero on success, nonzero if an error occurred during import.
  *			Note that in the failure case, parameters may be inconsistent.
  */
 __EXPORT int		param_import(int fd);
 
+/**
+ * Load parameters from a file.
+ *
+ * This function resets all parameters to their default values, then loads new
+ * values from a file.
+ *
+ * @param fd		File descriptor to import from.  (Currently expected to be a file.)
+ * @return		Zero on success, nonzero if an error occurred during import.
+ *			Note that in the failure case, parameters may be inconsistent.
+ */
+__EXPORT int		param_load(int fd);
+
 /**
  * Apply a function to each parameter.
  *