public DataInputStream readRootIndex(HFileBlock blk, final int numEntries) throws IOException {
      DataInputStream in = blk.getByteStream();
      readRootIndex(in, numEntries);
      return in;
    }
Read in the root-level index from the given input stream. Must match what was written into
the root level by {@link BlockIndexWriter#writeIndexBlocks(FSDataOutputStream)} at the offset
that function returned.
@param blk        the HFile block
@param numEntries the number of root-level index entries
@return the buffered input stream or wrapped byte input stream
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlockIndex.java