lib/model: Add fsync of files and directories, option to disable (fixes #3711)

lib/osutil/atomic.go

@@ -77,6 +77,11 @@ func (w *AtomicWriter) Close() error {
 	// Try to not leave temp file around, but ignore error.
 	defer os.Remove(w.next.Name())
 
+	if err := w.next.Sync(); err != nil {
+		w.err = err
+		return err
+	}
+
 	if err := w.next.Close(); err != nil {
 		w.err = err
 		return err
@@ -97,6 +102,8 @@ func (w *AtomicWriter) Close() error {
 		return err
 	}
 
+	SyncDir(filepath.Dir(w.next.Name()))
+
 	// Set w.err to return appropriately for any future operations.
 	w.err = ErrClosed