public BlockCrcInfo blockCrcUpgradeGetBlockLocations(Block block) throws IOException
Get locations for a given block. This is used only during
Block Level CRC upgrades (HADOOP-1134), when a datanode node
misses the cluster wide distributed upgrade. It uses the same
BlockCrcInfo class, that is also used during distributed upgrade

 public  void blockReceived(DatanodeRegistration registration,
    Block[] blocks) throws IOException
blockReceived() allows the DataNode to tell the NameNode about
recently-received block data. For example, whenever client code
writes a new Block here, or another DataNode copies a Block to
this DataNode, it will call blockReceived().

 public DatanodeCommand blockReport(DatanodeRegistration registration,
    Block[] blocks) throws IOException
blockReport() tells the NameNode about all the locally-stored blocks.
The NameNode returns an array of Blocks that have become obsolete
and should be deleted. This function is meant to upload *all*
the locally-stored blocks. It's invoked upon startup and then
infrequently afterwards.

 public  void errorReport(DatanodeRegistration registration,
    int errorCode,
    String msg) throws IOException
errorReport() tells the NameNode about something that has gone
awry. Useful for debugging.

 public UpgradeCommand processUpgradeCommand(UpgradeCommand comm) throws IOException
This is a very general way to send a command to the name-node during
distributed upgrade process.

The generosity is because the variety of upgrade commands is unpredictable.
The reply from the name-node is also received in the form of an upgrade
command.

 public DatanodeRegistration register(DatanodeRegistration registration,
    String networkLocation) throws IOException
Register Datanode.

 public DatanodeCommand sendHeartbeat(DatanodeRegistration registration,
    long capacity,
    long remaining,
    int xmitsInProgress,
    int xceiverCount) throws IOException
sendHeartbeat() tells the NameNode that the DataNode is still
alive and well. Includes some status info, too.
It also gives the NameNode a chance to return a "DatanodeCommand" object.
A DatanodeCommand tells the DataNode to invalidate local block(s),
or to copy them to other DataNodes, etc.

 public NamespaceInfo versionRequest() throws IOException