param save: Add a blocking API for param saves to be used from shell.

src/lib/parameters/autosave.cpp

@@ -110,10 +110,22 @@ void ParamAutosave::Run()
 	}
 
 	PX4_DEBUG("Autosaving params");
-	int ret = param_save_default();
+	int ret = param_save_default(false);
 
-	if (ret != 0) {
-		PX4_ERR("param auto save failed (%i)", ret);
+	if (ret != PX4_OK) {
+		// re-request to be saved in the future, try 3 times at most
+		if (_retry_count < 3) {
+			_retry_count++;
+			PX4_INFO("param auto save unavailable (%i), retrying..", ret);
+			request();
+
+		} else {
+			PX4_ERR("param auto save failed (%i)", ret);
+			_retry_count = 0;
+		}
+
+	} else {
+		_retry_count = 0;
 	}
 }
 

src/lib/parameters/autosave.h

@@ -59,5 +59,6 @@ public:
 private:
 	hrt_abstime _last_timestamp{0};
 	px4::atomic_bool _scheduled{false};
+	int _retry_count{0};
 	bool _disabled{false};
 };

src/lib/parameters/param.h

@@ -400,13 +400,17 @@ __EXPORT const char	*param_get_backup_file(void);
 
 /**
  * Save parameters to the default file.
+ *
  * Note: this method requires a large amount of stack size!
  *
  * This function saves all parameters with non-default values.
  *
- * @return		Zero on success.
+ * @param blocking	If true, in case the default file is busy, the function blocks
+ * 			until the file is available for writing.
+ *
+ * @return		Zero on success, -EWOULDBLOCK if the file is busy and blocking is false.
  */
-__EXPORT int 		param_save_default(void);
+__EXPORT int 		param_save_default(bool blocking);
 
 /**
  * Load parameters from the default parameter file.

src/lib/parameters/parameters.cpp

@@ -698,14 +698,19 @@ const char *param_get_backup_file()
 static int param_export_internal(int fd, param_filter_func filter);
 static int param_verify(int fd);
 
-int param_save_default()
+int param_save_default(bool blocking)
 {
 	PX4_DEBUG("param_save_default");
 
 	// take the file lock
-	if (pthread_mutex_trylock(&file_mutex) != 0) {
-		PX4_ERR("param_save_default: file lock failed (already locked)");
-		return PX4_ERROR;
+	if (blocking) {
+		pthread_mutex_lock(&file_mutex);
+
+	} else {
+		if (pthread_mutex_trylock(&file_mutex) != 0) {
+			PX4_DEBUG("param_save_default: file lock failed (already locked)");
+			return -EWOULDBLOCK;
+		}
 	}
 
 	int shutdown_lock_ret = px4_shutdown_lock();

src/lib/parameters/parameters_ioctl.cpp

@@ -168,7 +168,7 @@ int	param_ioctl(unsigned int cmd, unsigned long arg)
 
 	case PARAMIOCSAVEDEFAULT: {
 			paramiocsavedefault_t *data = (paramiocsavedefault_t *)arg;
-			data->ret = param_save_default();
+			data->ret = param_save_default(data->blocking);
 		}
 		break;
 

src/lib/parameters/parameters_ioctl.h

@@ -140,6 +140,7 @@ typedef struct paramiocresetgroup {
 
 #define PARAMIOCSAVEDEFAULT	_PARAMIOC(15)
 typedef struct paramiocsavedefault {
+	bool blocking;
 	int ret;
 } paramiocsavedefault_t;
 

src/lib/parameters/usr_parameters_if.cpp

@@ -187,9 +187,9 @@ param_reset_specific(const char *resets[], int num_resets)
 	boardctl(PARAMIOCRESETGROUP, reinterpret_cast<unsigned long>(&data));
 }
 
-int param_save_default()
+int param_save_default(bool blocking)
 {
-	paramiocsavedefault_t data = {PX4_ERROR};
+	paramiocsavedefault_t data = {blocking, PX4_ERROR};
 	boardctl(PARAMIOCSAVEDEFAULT, reinterpret_cast<unsigned long>(&data));
 	return data.ret;
 }