code: boolean addBlock(BlockInfo b) {
      int dnIndex = b.addNode(this);
      if(dnIndex < 0)
        return false;
      // add to the head of the data-node list
      blockList = b.listInsert(blockList, this, dnIndex);
      numOfBlocks++;
      return true;
    }
docs: Add data-node to the block.
  Add block to the head of the list of blocks belonging to the data-node.