code: static long getGenerationStampFromInlineChecksumFile(String blockName)
        throws IOException {
      String[] vals = StringUtils.split(blockName, '_');
      if (vals.length != 6) {
        // blk, blkid, genstamp, version, checksumtype, byte per checksum
        throw new IOException("unidentified block name format: " + blockName);
      }
      return Long.parseLong(vals[2]);
    }
docs: Return the generation stamp from the name of the block file.