I've tried to make a patch for
HBASE-21879, most of work seems to be fine, but the trouble is:
HFileBlock#validateChecksum can only accept ByteBuffer as its input, while after the
HBASE-21916, we will use an ourself-defined ByteBuff (which can be SingleByteBuff or MultiByteBuff).
Now, need to create our own ByteBuff checksum validation method, should not be so hard but an separate issue will be more clearer.