Enable hash check of used parameters to verify integrity of GCS local copy

src/modules/mavlink/mavlink_parameters.cpp

@@ -44,6 +44,8 @@
 #include "mavlink_parameters.h"
 #include "mavlink_main.h"
 
+#define HASH_PARAM "_HASH_CHECK"
+
 MavlinkParametersManager::MavlinkParametersManager(Mavlink *mavlink) : MavlinkStream(mavlink),
 	_send_all_index(-1),
 	_rc_param_map_pub(nullptr),
@@ -121,13 +123,27 @@ MavlinkParametersManager::handle_message(const mavlink_message_t *msg)
 
 				/* when no index is given, loop through string ids and compare them */
 				if (req_read.param_index < 0) {
-					/* local name buffer to enforce null-terminated string */
-					char name[MAVLINK_MSG_PARAM_VALUE_FIELD_PARAM_ID_LEN + 1];
-					strncpy(name, req_read.param_id, MAVLINK_MSG_PARAM_VALUE_FIELD_PARAM_ID_LEN);
-					/* enforce null termination */
-					name[MAVLINK_MSG_PARAM_VALUE_FIELD_PARAM_ID_LEN] = '\0';
-					/* attempt to find parameter and send it */
-					send_param(param_find_no_notification(name));
+					if (strncmp(req_read.param_id, HASH_PARAM, MAVLINK_MSG_PARAM_VALUE_FIELD_PARAM_ID_LEN) == 0) {
+						/* return hash check for cached params */
+						uint32_t hash = param_hash_check();
+
+						/* build the one-off response message */
+						mavlink_param_value_t msg;
+						msg.param_count = param_count_used();
+						msg.param_index = -1;
+						strncpy(msg.param_id, HASH_PARAM, MAVLINK_MSG_PARAM_VALUE_FIELD_PARAM_ID_LEN);
+						msg.param_type = MAV_PARAM_TYPE_UINT32;
+						memcpy(&msg.param_value, &hash, sizeof(hash));
+						_mavlink->send_message(MAVLINK_MSG_ID_PARAM_VALUE, &msg);
+					} else {
+						/* local name buffer to enforce null-terminated string */
+						char name[MAVLINK_MSG_PARAM_VALUE_FIELD_PARAM_ID_LEN + 1];
+						strncpy(name, req_read.param_id, MAVLINK_MSG_PARAM_VALUE_FIELD_PARAM_ID_LEN);
+						/* enforce null termination */
+						name[MAVLINK_MSG_PARAM_VALUE_FIELD_PARAM_ID_LEN] = '\0';
+						/* attempt to find parameter and send it */
+						send_param(param_find_no_notification(name));
+					}
 
 				} else {
 					/* when index is >= 0, send this parameter again */

src/modules/systemlib/param/param.c

@@ -65,6 +65,8 @@
 #include "uORB/topics/parameter_update.h"
 #include "px4_parameters.h"
 
+#include <crc32.h>
+
 #if 0
 # define debug(fmt, args...)		do { warnx(fmt, ##args); } while(0)
 #else
@@ -1035,3 +1037,25 @@ param_foreach(void (*func)(void *arg, param_t param), void *arg, bool only_chang
 		func(arg, param);
 	}
 }
+
+uint32_t param_hash_check(void)
+{
+	uint32_t param_hash = 0;
+
+	param_lock();
+
+	/* compute the CRC32 over all string param names and 4 byte values */
+	for (param_t param = 0; handle_in_range(param); param++) {
+		if (!param_used(param)) {
+			continue;
+		}
+		const char *name = param_name(param);
+		const void *val = param_get_value_ptr(param);
+		param_hash = crc32part((const uint8_t*)name, strlen(name), param_hash);
+		param_hash = crc32part(val, sizeof(union param_value_u), param_hash);
+	}
+
+	param_unlock();
+
+	return param_hash;
+}

src/modules/systemlib/param/param.h

@@ -333,6 +333,13 @@ __EXPORT int 		param_save_default(void);
  */
 __EXPORT int 		param_load_default(void);
 
+/**
+ * Generate the hash of all parameters and their values
+ *
+ * @return		CRC32 hash of all param_ids and values
+ */
+__EXPORT uint32_t	param_hash_check(void);
+
 /*
  * Macros creating static parameter definitions.
  *