@Override
 public FileSystemReference fileFromDescriptor(String descriptor) {
   return runtime.fileFromDescriptor(descriptor);
 }
 @Override
 public FileSystemReference commitTempFile(
     FileSystemReference sourceFile, long fileId, String fileName) {
   return runtime.commitTempFile(sourceFile, fileId, fileName);
 }
 @Override
 public boolean isFsPersistent() {
   return runtime.isFsPersistent();
 }
 @Override
 public FileSystemReference createTempFile() {
   return runtime.createTempFile();
 }