code: private void validateBlockSize(byte[] descriptor) throws IOException {
          int blockSize = Util.getUInt16Both(descriptor, 129);
          if (blockSize != Constants.DEFAULT_BLOCK_SIZE) {
              throw new LoopFileSystemException("Invalid block size: " + blockSize);
          }
      }
docs: Check that the block size is what we expect.
  
  @param descriptor the descriptor bytes
  @throws IOException