log_writer_file: call fsync after reliable transfer

ensures watchdog data is flushed immediately

src/modules/logger/log_writer_file.cpp

@@ -369,7 +369,8 @@ void LogWriterFile::run()
 			const hrt_abstime now = hrt_absolute_time();
 
 			/* call fsync periodically to minimize potential loss of data */
-			const bool call_fsync = ++poll_count >= 100 || now - last_fsync > 1_s;
+			const bool call_fsync = ++poll_count >= 100 || now - last_fsync > 1_s || _want_fsync.load();
+			_want_fsync.store(false);
 
 			if (call_fsync) {
 				last_fsync = now;

src/modules/logger/log_writer_file.h

@@ -120,6 +120,10 @@ public:
 
 	void set_need_reliable_transfer(bool need_reliable)
 	{
+		if (!need_reliable && _need_reliable_transfer) {
+			_want_fsync.store(true);
+		}
+
 		_need_reliable_transfer = need_reliable;
 	}
 
@@ -210,6 +214,7 @@ private:
 
 	px4::atomic_bool	_exit_thread{false};
 	bool			_need_reliable_transfer{false};
+	px4::atomic_bool	_want_fsync{false};
 	pthread_mutex_t		_mtx;
 	pthread_cond_t		_cv;
 	pthread_t _thread = 0;