svn merge -c 1189901 from trunk for HDFS-2496.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23-PB@1229883 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -29,6 +29,8 @@ Release 0.23-PB - Unreleased
 
     HDFS-2488. Separate datatypes for InterDatanodeProtocol. (suresh)
 
+    HDFS-2496. Separate datatypes for DatanodeProtocol. (suresh)
+
   BUG FIXES
  
     HDFS-2481 Unknown protocol: org.apache.hadoop.hdfs.protocol.ClientProtocol (sanjay)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/ClientDatanodeProtocol.java

@@ -39,9 +39,6 @@ import org.apache.hadoop.security.token.TokenInfo;
     serverPrincipal = DFSConfigKeys.DFS_DATANODE_USER_NAME_KEY)
 @TokenInfo(BlockTokenSelector.class)
 public interface ClientDatanodeProtocol extends VersionedProtocol {
-  public static final Log LOG = LogFactory.getLog(ClientDatanodeProtocol.class);
-
-  
   /**
    * Until version 9, this class ClientDatanodeProtocol served as both
    * the client interface to the DN AND the RPC protocol used to 

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolR23Compatible/BlockWritable.java

@@ -92,4 +92,20 @@ public class BlockWritable implements Writable {
   public long getGenerationStamp() {
     return generationStamp;
   }
+  
+  public static Block[] convert(BlockWritable[] blocks) {
+    Block[] ret = new Block[blocks.length];
+    for (int i = 0; i < blocks.length; i++) {
+      ret[i] = blocks[i].convert();
+    }
+    return ret;
+  }
+  
+  public static BlockWritable[] convert(Block[] blocks) {
+    BlockWritable[] ret = new BlockWritable[blocks.length];
+    for (int i = 0; i < blocks.length; i++) {
+      ret[i] = BlockWritable.convert(blocks[i]);
+    }
+    return ret;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/BlockCommand.java

@@ -67,7 +67,6 @@ public class BlockCommand extends DatanodeCommand {
   public BlockCommand(int action, String poolId,
       List<BlockTargetPair> blocktargetlist) {
     super(action);
-
     this.poolId = poolId;
     blocks = new Block[blocktargetlist.size()]; 
     targets = new DatanodeInfo[blocks.length][];
@@ -85,10 +84,19 @@ public class BlockCommand extends DatanodeCommand {
    * @param blocks blocks related to the action
    */
   public BlockCommand(int action, String poolId, Block blocks[]) {
+    this(action, poolId, blocks, EMPTY_TARGET);
+  }
+
+  /**
+   * Create BlockCommand for the given action
+   * @param blocks blocks related to the action
+   */
+  public BlockCommand(int action, String poolId, Block[] blocks,
+      DatanodeInfo[][] targets) {
     super(action);
     this.poolId = poolId;
     this.blocks = blocks;
-    this.targets = EMPTY_TARGET;
+    this.targets = targets;
   }
   
   public String getBlockPoolId() {

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/BlockRecoveryCommand.java

@@ -117,8 +117,12 @@ public class BlockRecoveryCommand extends DatanodeCommand {
    * the specified capacity for recovering blocks.
    */
   public BlockRecoveryCommand(int capacity) {
+    this(new ArrayList<RecoveringBlock>(capacity));
+  }
+  
+  public BlockRecoveryCommand(Collection<RecoveringBlock> blocks) {
     super(DatanodeProtocol.DNA_RECOVERBLOCK);
-    recoveringBlocks = new ArrayList<RecoveringBlock>(capacity);
+    recoveringBlocks = blocks;
   }
 
   /**

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/DatanodeProtocol.java

@@ -22,10 +22,11 @@ import java.io.*;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
-import org.apache.hadoop.hdfs.protocol.Block;
 import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
 import org.apache.hadoop.hdfs.protocol.DatanodeID;
 import org.apache.hadoop.hdfs.protocol.LocatedBlock;
+import org.apache.hadoop.hdfs.protocolR23Compatible.ClientNamenodeWireProtocol;
+import org.apache.hadoop.hdfs.server.protocolR23Compatible.DatanodeWireProtocol;
 import org.apache.hadoop.ipc.VersionedProtocol;
 import org.apache.hadoop.security.KerberosInfo;
 
@@ -45,7 +46,14 @@ import org.apache.avro.reflect.Nullable;
 @InterfaceAudience.Private
 public interface DatanodeProtocol extends VersionedProtocol {
   /**
-   * 28: Add Balancer Bandwidth Command protocol.
+   * This class is used by both the Namenode (client) and BackupNode (server) 
+   * to insulate from the protocol serialization.
+   * 
+   * If you are adding/changing DN's interface then you need to 
+   * change both this class and ALSO
+   * {@link DatanodeWireProtocol}.
+   * These changes need to be done in a compatible fashion as described in 
+   * {@link ClientNamenodeWireProtocol}
    */
   public static final long versionID = 28L;
   

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocol/DatanodeRegistration.java

@@ -63,9 +63,14 @@ implements Writable, NodeRegistration {
    * Create DatanodeRegistration
    */
   public DatanodeRegistration(String nodeName) {
+    this(nodeName, new StorageInfo(), new ExportedBlockKeys());
+  }
+  
+  public DatanodeRegistration(String nodeName, StorageInfo info,
+      ExportedBlockKeys keys) {
     super(nodeName);
-    this.storageInfo = new StorageInfo();
+    this.storageInfo = info;
-    this.exportedKeys = new ExportedBlockKeys();
+    this.exportedKeys = keys;
   }
   
   public void setStorageInfo(StorageInfo storage) {

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/BalancerBandwidthCommandWritable.java

@@ -0,0 +1,107 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.server.protocol.BalancerBandwidthCommand;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeCommand;
+import org.apache.hadoop.io.Writable;
+import org.apache.hadoop.io.WritableFactories;
+import org.apache.hadoop.io.WritableFactory;
+
+/**
+ * Balancer bandwidth command instructs each datanode to change its value for
+ * the max amount of network bandwidth it may use during the block balancing
+ * operation.
+ * 
+ * The Balancer Bandwidth Command contains the new bandwidth value as its
+ * payload. The bandwidth value is in bytes per second.
+ */
+public class BalancerBandwidthCommandWritable extends DatanodeCommandWritable {
+  private final static long BBC_DEFAULTBANDWIDTH = 0L;
+
+  private long bandwidth;
+
+  /**
+   * Balancer Bandwidth Command constructor. Sets bandwidth to 0.
+   */
+  BalancerBandwidthCommandWritable() {
+    this(BBC_DEFAULTBANDWIDTH);
+  }
+
+  /**
+   * Balancer Bandwidth Command constructor.
+   * @param bandwidth Blanacer bandwidth in bytes per second.
+   */
+  public BalancerBandwidthCommandWritable(long bandwidth) {
+    super(DatanodeWireProtocol.DNA_BALANCERBANDWIDTHUPDATE);
+    this.bandwidth = bandwidth;
+  }
+
+  /**
+   * Get current value of the max balancer bandwidth in bytes per second.
+   * @return bandwidth Blanacer bandwidth in bytes per second for this datanode.
+   */
+  public long getBalancerBandwidthValue() {
+    return this.bandwidth;
+  }
+
+  // ///////////////////////////////////////////////
+  // Writable
+  // ///////////////////////////////////////////////
+  static { // register a ctor
+    WritableFactories.setFactory(BalancerBandwidthCommandWritable.class,
+        new WritableFactory() {
+          public Writable newInstance() {
+            return new BalancerBandwidthCommandWritable();
+          }
+        });
+  }
+
+  /**
+   * Writes the bandwidth payload to the Balancer Bandwidth Command packet.
+   * @param out DataOutput stream used for writing commands to the datanode.
+   * @throws IOException
+   */
+  public void write(DataOutput out) throws IOException {
+    super.write(out);
+    out.writeLong(this.bandwidth);
+  }
+
+  /**
+   * Reads the bandwidth payload from the Balancer Bandwidth Command packet.
+   * @param in DataInput stream used for reading commands to the datanode.
+   * @throws IOException
+   */
+  public void readFields(DataInput in) throws IOException {
+    super.readFields(in);
+    this.bandwidth = in.readLong();
+  }
+
+  @Override
+  public DatanodeCommand convert() {
+    return new BalancerBandwidthCommand(bandwidth);
+  }
+
+  public static DatanodeCommandWritable convert(BalancerBandwidthCommand cmd) {
+    return new BalancerBandwidthCommandWritable(cmd.getBalancerBandwidthValue());
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/BlockCommandWritable.java

@@ -0,0 +1,147 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+import java.util.List;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.protocol.Block;
+import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
+import org.apache.hadoop.hdfs.protocolR23Compatible.BlockWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.DatanodeInfoWritable;
+import org.apache.hadoop.hdfs.server.blockmanagement.DatanodeDescriptor.BlockTargetPair;
+import org.apache.hadoop.hdfs.server.protocol.BlockCommand;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeCommand;
+import org.apache.hadoop.io.Text;
+import org.apache.hadoop.io.Writable;
+import org.apache.hadoop.io.WritableFactories;
+import org.apache.hadoop.io.WritableFactory;
+
+/****************************************************
+ * A BlockCommand is an instruction to a datanode regarding some blocks under
+ * its control. It tells the DataNode to either invalidate a set of indicated
+ * blocks, or to copy a set of indicated blocks to another DataNode.
+ * 
+ ****************************************************/
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public class BlockCommandWritable extends DatanodeCommandWritable {
+
+  /**
+   * This constant is used to indicate that the block deletion does not need
+   * explicit ACK from the datanode. When a block is put into the list of blocks
+   * to be deleted, it's size is set to this constant. We assume that no block
+   * would actually have this size. Otherwise, we would miss ACKs for blocks
+   * with such size. Positive number is used for compatibility reasons.
+   */
+  public static final long NO_ACK = Long.MAX_VALUE;
+
+  String poolId;
+  BlockWritable blocks[];
+  DatanodeInfoWritable targets[][];
+
+  public BlockCommandWritable() {
+  }
+
+  /**
+   * Create BlockCommand for the given action
+   * 
+   * @param blocks blocks related to the action
+   */
+  public BlockCommandWritable(int action, String poolId, BlockWritable[] blocks,
+      DatanodeInfoWritable[][] targets) {
+    super(action);
+    this.poolId = poolId;
+    this.blocks = blocks;
+    this.targets = targets;
+  }
+
+  // /////////////////////////////////////////
+  // Writable
+  // /////////////////////////////////////////
+  static { // register a ctor
+    WritableFactories.setFactory(BlockCommandWritable.class,
+        new WritableFactory() {
+          public Writable newInstance() {
+            return new BlockCommandWritable();
+          }
+        });
+  }
+
+  @Override
+  public void write(DataOutput out) throws IOException {
+    super.write(out);
+    Text.writeString(out, poolId);
+    out.writeInt(blocks.length);
+    for (int i = 0; i < blocks.length; i++) {
+      blocks[i].write(out);
+    }
+    out.writeInt(targets.length);
+    for (int i = 0; i < targets.length; i++) {
+      out.writeInt(targets[i].length);
+      for (int j = 0; j < targets[i].length; j++) {
+        targets[i][j].write(out);
+      }
+    }
+  }
+
+  @Override
+  public void readFields(DataInput in) throws IOException {
+    super.readFields(in);
+    this.poolId = Text.readString(in);
+    this.blocks = new BlockWritable[in.readInt()];
+    for (int i = 0; i < blocks.length; i++) {
+      blocks[i] = new BlockWritable();
+      blocks[i].readFields(in);
+    }
+
+    this.targets = new DatanodeInfoWritable[in.readInt()][];
+    for (int i = 0; i < targets.length; i++) {
+      this.targets[i] = new DatanodeInfoWritable[in.readInt()];
+      for (int j = 0; j < targets[i].length; j++) {
+        targets[i][j] = new DatanodeInfoWritable();
+        targets[i][j].readFields(in);
+      }
+    }
+  }
+
+  @Override
+  public BlockCommand convert() {
+    DatanodeInfo[][] dinfo = new DatanodeInfo[targets.length][];
+    for (int i = 0; i < targets.length; i++) {
+      dinfo[i] = DatanodeInfoWritable.convertDatanodeInfo(targets[i]);
+    }
+    return new BlockCommand(getAction(), poolId, BlockWritable.convert(blocks),
+        dinfo);
+  }
+
+  public static BlockCommandWritable convert(BlockCommand cmd) {
+    if (cmd == null) return null;
+    DatanodeInfo[][] targets = cmd.getTargets();
+    DatanodeInfoWritable[][] dinfo = new DatanodeInfoWritable[targets.length][];
+    for (int i = 0; i < targets.length; i++) {
+      dinfo[i] = DatanodeInfoWritable.convertDatanodeInfo(targets[i]);
+    }
+    return new BlockCommandWritable(cmd.getAction(), cmd.getBlockPoolId(),
+        BlockWritable.convert(cmd.getBlocks()), dinfo);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/BlockRecoveryCommandWritable.java

@@ -0,0 +1,118 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.server.protocol.BlockRecoveryCommand;
+import org.apache.hadoop.hdfs.server.protocol.BlockRecoveryCommand.RecoveringBlock;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeCommand;
+import org.apache.hadoop.io.Writable;
+import org.apache.hadoop.io.WritableFactories;
+import org.apache.hadoop.io.WritableFactory;
+
+/**
+ * BlockRecoveryCommand is an instruction to a data-node to recover the
+ * specified blocks.
+ * 
+ * The data-node that receives this command treats itself as a primary data-node
+ * in the recover process.
+ * 
+ * Block recovery is identified by a recoveryId, which is also the new
+ * generation stamp, which the block will have after the recovery succeeds.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public class BlockRecoveryCommandWritable extends DatanodeCommandWritable {
+  Collection<RecoveringBlockWritable> recoveringBlocks;
+
+  /**
+   * Create empty BlockRecoveryCommand.
+   */
+  public BlockRecoveryCommandWritable() { }
+
+  /**
+   * Create BlockRecoveryCommand with the specified capacity for recovering
+   * blocks.
+   */
+  public BlockRecoveryCommandWritable(int capacity) {
+    this(new ArrayList<RecoveringBlockWritable>(capacity));
+  }
+  
+  public BlockRecoveryCommandWritable(Collection<RecoveringBlockWritable> blocks) {
+    super(DatanodeWireProtocol.DNA_RECOVERBLOCK);
+    recoveringBlocks = blocks;
+  }
+
+  // /////////////////////////////////////////
+  // Writable
+  // /////////////////////////////////////////
+  static { // register a ctor
+    WritableFactories.setFactory(BlockRecoveryCommandWritable.class,
+        new WritableFactory() {
+          public Writable newInstance() {
+            return new BlockRecoveryCommandWritable();
+          }
+        });
+  }
+
+  public void write(DataOutput out) throws IOException {
+    super.write(out);
+    out.writeInt(recoveringBlocks.size());
+    for (RecoveringBlockWritable block : recoveringBlocks) {
+      block.write(out);
+    }
+  }
+
+  public void readFields(DataInput in) throws IOException {
+    super.readFields(in);
+    int numBlocks = in.readInt();
+    recoveringBlocks = new ArrayList<RecoveringBlockWritable>(numBlocks);
+    for (int i = 0; i < numBlocks; i++) {
+      RecoveringBlockWritable b = new RecoveringBlockWritable();
+      b.readFields(in);
+      recoveringBlocks.add(b);
+    }
+  }
+
+  @Override
+  public DatanodeCommand convert() {
+    Collection<RecoveringBlock> blks = 
+        new ArrayList<RecoveringBlock>(recoveringBlocks.size());
+    for (RecoveringBlockWritable b : recoveringBlocks) {
+      blks.add(b.convert());
+    }
+    return new BlockRecoveryCommand(blks);
+  }
+
+  public static BlockRecoveryCommandWritable convert(BlockRecoveryCommand cmd) {
+    if (cmd == null) return null;
+    Collection<RecoveringBlockWritable> blks = 
+        new ArrayList<RecoveringBlockWritable>(cmd.getRecoveringBlocks().size());
+    for (RecoveringBlock b : cmd.getRecoveringBlocks()) {
+      blks.add(RecoveringBlockWritable.convert(b));
+    }
+    return new BlockRecoveryCommandWritable(blks);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/DatanodeCommandHelper.java

@@ -0,0 +1,73 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.hdfs.server.protocol.BalancerBandwidthCommand;
+import org.apache.hadoop.hdfs.server.protocol.BlockCommand;
+import org.apache.hadoop.hdfs.server.protocol.BlockRecoveryCommand;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeCommand;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeProtocol;
+import org.apache.hadoop.hdfs.server.protocol.FinalizeCommand;
+import org.apache.hadoop.hdfs.server.protocol.KeyUpdateCommand;
+import org.apache.hadoop.hdfs.server.protocol.UpgradeCommand;
+
+/**
+ * Class for translating DatanodeCommandWritable to and from DatanodeCommand.
+ */
+class DatanodeCommandHelper {
+  public static final Log LOG = LogFactory.getLog(DatanodeCommandHelper.class);
+  
+  private DatanodeCommandHelper() {
+    /* Private constructor to prevent instantiation */
+  }
+  
+  static DatanodeCommand convert(DatanodeCommandWritable cmd) {
+    return cmd.convert();
+  }
+  
+  /**
+   * Given a subclass of {@link DatanodeCommand} return the corresponding
+   * writable type.
+   */
+  static DatanodeCommandWritable convert(DatanodeCommand cmd) {
+    switch (cmd.getAction()) {
+    case DatanodeProtocol.DNA_BALANCERBANDWIDTHUPDATE:
+      return BalancerBandwidthCommandWritable
+          .convert((BalancerBandwidthCommand) cmd);
+    
+    case DatanodeProtocol.DNA_FINALIZE:
+      return FinalizeCommandWritable.convert((FinalizeCommand)cmd);
+    case DatanodeProtocol.DNA_ACCESSKEYUPDATE:
+      return KeyUpdateCommandWritable.convert((KeyUpdateCommand)cmd);
+    case DatanodeProtocol.DNA_REGISTER:
+      return RegisterCommandWritable.REGISTER;
+    case DatanodeProtocol.DNA_TRANSFER:
+    case DatanodeProtocol.DNA_INVALIDATE:
+      return BlockCommandWritable.convert((BlockCommand)cmd);
+    case UpgradeCommand.UC_ACTION_START_UPGRADE:
+      return UpgradeCommandWritable.convert((UpgradeCommand)cmd);
+    case DatanodeProtocol.DNA_RECOVERBLOCK:
+      return BlockRecoveryCommandWritable.convert((BlockRecoveryCommand)cmd);
+    default:
+      LOG.warn("Unknown DatanodeCommand action - " + cmd.getAction());
+      return null;
+    }
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/DatanodeCommandWritable.java

@@ -0,0 +1,58 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeCommand;
+
+/**
+ * Base class for data-node command.
+ * Issued by the name-node to notify data-nodes what should be done.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public abstract class DatanodeCommandWritable extends ServerCommandWritable {
+  public DatanodeCommandWritable() {
+    super();
+  }
+  
+  DatanodeCommandWritable(int action) {
+    super(action);
+  }
+
+  /** Method to convert from writable type to internal type */
+  public abstract DatanodeCommand convert();
+
+  public static DatanodeCommandWritable[] convert(DatanodeCommand[] cmds) {
+    DatanodeCommandWritable[] ret = new DatanodeCommandWritable[cmds.length];
+    for (int i = 0; i < cmds.length; i++) {
+      ret[i] = DatanodeCommandHelper.convert(cmds[i]);
+    }
+    return ret;
+  }
+
+  public static DatanodeCommand[] convert(DatanodeCommandWritable[] cmds) {
+    if (cmds == null) return null;
+    DatanodeCommand[] ret = new DatanodeCommand[cmds.length];
+    for (int i = 0; i < cmds.length; i++) {
+      ret[i] = cmds[i].convert();
+    }
+    return ret;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/DatanodeProtocolServerSideTranslatorR23.java

@@ -0,0 +1,170 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.protocolR23Compatible.DatanodeIDWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.ExtendedBlockWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.LocatedBlockWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.NamespaceInfoWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.ProtocolSignatureWritable;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeProtocol;
+import org.apache.hadoop.ipc.ProtocolSignature;
+import org.apache.hadoop.ipc.RPC;
+
+/**
+ * This class is used on the server side. Calls come across the wire for the
+ * protocol family of Release 23 onwards. This class translates the R23 data
+ * types to the native data types used inside the NN as specified in the generic
+ * DatanodeProtocol.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Stable
+public class DatanodeProtocolServerSideTranslatorR23 implements
+    DatanodeWireProtocol {
+  final private DatanodeProtocol server;
+
+  /**
+   * Constructor
+   * @param server - the NN server
+   * @throws IOException
+   */
+  public DatanodeProtocolServerSideTranslatorR23(DatanodeProtocol server)
+      throws IOException {
+    this.server = server;
+  }
+
+  /**
+   * The client side will redirect getProtocolSignature to
+   * getProtocolSignature2.
+   * 
+   * However the RPC layer below on the Server side will call getProtocolVersion
+   * and possibly in the future getProtocolSignature. Hence we still implement
+   * it even though the end client's call will never reach here.
+   */
+  @Override
+  public ProtocolSignature getProtocolSignature(String protocol,
+      long clientVersion, int clientMethodsHash) throws IOException {
+    /**
+     * Don't forward this to the server. The protocol version and signature is
+     * that of {@link DatanodeProtocol}
+     * 
+     */
+    if (!protocol.equals(RPC.getProtocolName(DatanodeWireProtocol.class))) {
+      throw new IOException("Namenode Serverside implements " +
+          RPC.getProtocolName(DatanodeWireProtocol.class) +
+          ". The following requested protocol is unknown: " + protocol);
+    }
+
+    return ProtocolSignature.getProtocolSignature(clientMethodsHash,
+        DatanodeWireProtocol.versionID, DatanodeWireProtocol.class);
+  }
+
+  @Override
+  public ProtocolSignatureWritable 
+          getProtocolSignature2(
+      String protocol, long clientVersion, int clientMethodsHash)
+      throws IOException {
+    /**
+     * Don't forward this to the server. The protocol version and signature is
+     * that of {@link DatanodeProtocol}
+     */
+    return ProtocolSignatureWritable.convert(
+        this.getProtocolSignature(protocol, clientVersion, clientMethodsHash));
+  }
+
+  @Override
+  public long getProtocolVersion(String protocol, long clientVersion)
+      throws IOException {
+    if (protocol.equals(RPC.getProtocolName(DatanodeWireProtocol.class))) {
+      return DatanodeWireProtocol.versionID;
+    }
+    throw new IOException("Namenode Serverside implements " +
+        RPC.getProtocolName(DatanodeWireProtocol.class) +
+        ". The following requested protocol is unknown: " + protocol);
+  }
+
+  @Override
+  public DatanodeRegistrationWritable registerDatanode(
+      DatanodeRegistrationWritable registration) throws IOException {
+    return DatanodeRegistrationWritable.convert(server
+        .registerDatanode(registration.convert()));
+  }
+
+  @Override
+  public DatanodeCommandWritable[] sendHeartbeat(
+      DatanodeRegistrationWritable registration, long capacity, long dfsUsed,
+      long remaining, long blockPoolUsed, int xmitsInProgress,
+      int xceiverCount, int failedVolumes) throws IOException {
+    return DatanodeCommandWritable.convert(server.sendHeartbeat(
+        registration.convert(), capacity, dfsUsed, remaining, blockPoolUsed,
+        xmitsInProgress, xceiverCount, failedVolumes));
+  }
+
+  @Override
+  public DatanodeCommandWritable blockReport(
+      DatanodeRegistrationWritable registration, String poolId, long[] blocks)
+      throws IOException {
+    return DatanodeCommandHelper.convert(server.blockReport(
+        registration.convert(), poolId, blocks));
+  }
+
+  @Override
+  public void blockReceivedAndDeleted(
+      DatanodeRegistrationWritable registration, String poolId,
+      ReceivedDeletedBlockInfoWritable[] receivedAndDeletedBlocks)
+      throws IOException {
+    server.blockReceivedAndDeleted(registration.convert(), poolId,
+        ReceivedDeletedBlockInfoWritable.convert(receivedAndDeletedBlocks));
+  }
+
+  @Override
+  public void errorReport(DatanodeRegistrationWritable registration,
+      int errorCode, String msg) throws IOException {
+    server.errorReport(registration.convert(), errorCode, msg);
+  }
+
+  @Override
+  public NamespaceInfoWritable versionRequest() throws IOException {
+    return NamespaceInfoWritable.convert(server.versionRequest());
+  }
+
+  @Override
+  public UpgradeCommandWritable processUpgradeCommand(
+      UpgradeCommandWritable comm) throws IOException {
+    return UpgradeCommandWritable.convert(server.processUpgradeCommand(comm.convert()));
+  }
+
+  @Override
+  public void reportBadBlocks(LocatedBlockWritable[] blocks) throws IOException {
+    server.reportBadBlocks(LocatedBlockWritable.convertLocatedBlock(blocks));
+  }
+
+  @Override
+  public void commitBlockSynchronization(ExtendedBlockWritable block,
+      long newgenerationstamp, long newlength, boolean closeFile,
+      boolean deleteblock, DatanodeIDWritable[] newtargets) throws IOException {
+    server.commitBlockSynchronization(
+        ExtendedBlockWritable.convertExtendedBlock(block), newgenerationstamp,
+        newlength, closeFile, deleteblock,
+        DatanodeIDWritable.convertDatanodeID(newtargets));
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/DatanodeProtocolTranslatorR23.java

@@ -0,0 +1,193 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.protocol.AlreadyBeingCreatedException;
+import org.apache.hadoop.hdfs.protocol.DatanodeID;
+import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.protocol.HdfsConstants;
+import org.apache.hadoop.hdfs.protocol.LocatedBlock;
+import org.apache.hadoop.hdfs.protocolR23Compatible.DatanodeIDWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.ExtendedBlockWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.LocatedBlockWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.ProtocolSignatureWritable;
+import org.apache.hadoop.hdfs.server.namenode.NameNode;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeCommand;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeProtocol;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeRegistration;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.hdfs.server.protocol.ReceivedDeletedBlockInfo;
+import org.apache.hadoop.hdfs.server.protocol.UpgradeCommand;
+import org.apache.hadoop.io.retry.RetryPolicies;
+import org.apache.hadoop.io.retry.RetryPolicy;
+import org.apache.hadoop.io.retry.RetryProxy;
+import org.apache.hadoop.ipc.ProtocolSignature;
+import org.apache.hadoop.ipc.RPC;
+import org.apache.hadoop.ipc.RemoteException;
+import org.apache.hadoop.net.NetUtils;
+import org.apache.hadoop.security.UserGroupInformation;
+
+/**
+ * This class forwards NN's ClientProtocol calls as RPC calls to the NN server
+ * while translating from the parameter types used in ClientProtocol to those
+ * used in protocolR23Compatile.*.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Stable
+public class DatanodeProtocolTranslatorR23 implements
+    DatanodeProtocol, Closeable {
+  final private DatanodeWireProtocol rpcProxy;
+
+  private static DatanodeWireProtocol createNamenode(
+      InetSocketAddress nameNodeAddr, Configuration conf,
+      UserGroupInformation ugi) throws IOException {
+    return RPC.getProxy(DatanodeWireProtocol.class,
+        DatanodeWireProtocol.versionID, nameNodeAddr, ugi, conf,
+        NetUtils.getSocketFactory(conf, DatanodeWireProtocol.class));
+  }
+
+  /** Create a {@link NameNode} proxy */
+  static DatanodeWireProtocol createNamenodeWithRetry(
+      DatanodeWireProtocol rpcNamenode) {
+    RetryPolicy createPolicy = RetryPolicies
+        .retryUpToMaximumCountWithFixedSleep(5,
+            HdfsConstants.LEASE_SOFTLIMIT_PERIOD, TimeUnit.MILLISECONDS);
+
+    Map<Class<? extends Exception>, RetryPolicy> remoteExceptionToPolicyMap = 
+        new HashMap<Class<? extends Exception>, RetryPolicy>();
+    remoteExceptionToPolicyMap.put(AlreadyBeingCreatedException.class,
+        createPolicy);
+
+    Map<Class<? extends Exception>, RetryPolicy> exceptionToPolicyMap = 
+        new HashMap<Class<? extends Exception>, RetryPolicy>();
+    exceptionToPolicyMap.put(RemoteException.class, RetryPolicies
+        .retryByRemoteException(RetryPolicies.TRY_ONCE_THEN_FAIL,
+            remoteExceptionToPolicyMap));
+    RetryPolicy methodPolicy = RetryPolicies.retryByException(
+        RetryPolicies.TRY_ONCE_THEN_FAIL, exceptionToPolicyMap);
+    Map<String, RetryPolicy> methodNameToPolicyMap = new HashMap<String, RetryPolicy>();
+
+    methodNameToPolicyMap.put("create", methodPolicy);
+
+    return (DatanodeWireProtocol) RetryProxy.create(
+        DatanodeWireProtocol.class, rpcNamenode, methodNameToPolicyMap);
+  }
+
+  public DatanodeProtocolTranslatorR23(InetSocketAddress nameNodeAddr,
+      Configuration conf) throws IOException {
+    UserGroupInformation ugi = UserGroupInformation.getCurrentUser();
+    rpcProxy = createNamenodeWithRetry(createNamenode(nameNodeAddr, conf, ugi));
+  }
+
+  @Override
+  public void close() {
+    RPC.stopProxy(rpcProxy);
+  }
+
+  @Override
+  public long getProtocolVersion(String protocolName, long clientVersion)
+      throws IOException {
+    return rpcProxy.getProtocolVersion(protocolName, clientVersion);
+  }
+
+  @Override
+  public ProtocolSignature getProtocolSignature(String protocol,
+      long clientVersion, int clientMethodsHash) throws IOException {
+    return ProtocolSignatureWritable.convert(rpcProxy.getProtocolSignature2(
+        protocol, clientVersion, clientMethodsHash));
+  }
+
+  @Override
+  public DatanodeRegistration registerDatanode(DatanodeRegistration registration)
+      throws IOException {
+    return rpcProxy.registerDatanode(
+        DatanodeRegistrationWritable.convert(registration)).convert();
+  }
+
+  @Override
+  public DatanodeCommand[] sendHeartbeat(DatanodeRegistration registration,
+      long capacity, long dfsUsed, long remaining, long blockPoolUsed,
+      int xmitsInProgress, int xceiverCount, int failedVolumes)
+      throws IOException {
+    return DatanodeCommandWritable.convert(rpcProxy.sendHeartbeat(
+            DatanodeRegistrationWritable.convert(registration), capacity,
+            dfsUsed, remaining, blockPoolUsed, xmitsInProgress, xceiverCount,
+            failedVolumes));
+  }
+
+  @Override
+  public DatanodeCommand blockReport(DatanodeRegistration registration,
+      String poolId, long[] blocks) throws IOException {
+    return rpcProxy.blockReport(
+        DatanodeRegistrationWritable.convert(registration), poolId, blocks)
+        .convert();
+  }
+
+  @Override
+  public void blockReceivedAndDeleted(DatanodeRegistration registration,
+      String poolId, ReceivedDeletedBlockInfo[] receivedAndDeletedBlocks)
+      throws IOException {
+    rpcProxy.blockReceivedAndDeleted(
+        DatanodeRegistrationWritable.convert(registration), poolId,
+        ReceivedDeletedBlockInfoWritable.convert(receivedAndDeletedBlocks));
+  }
+
+  @Override
+  public void errorReport(DatanodeRegistration registration, int errorCode,
+      String msg) throws IOException {
+    rpcProxy.errorReport(DatanodeRegistrationWritable.convert(registration),
+        errorCode, msg);
+  }
+
+  @Override
+  public NamespaceInfo versionRequest() throws IOException {
+    return rpcProxy.versionRequest().convert();
+  }
+
+  @Override
+  public UpgradeCommand processUpgradeCommand(UpgradeCommand cmd)
+      throws IOException {
+    return rpcProxy.processUpgradeCommand(UpgradeCommandWritable.convert(cmd))
+        .convert();
+  }
+
+  @Override
+  public void reportBadBlocks(LocatedBlock[] blocks) throws IOException {
+    rpcProxy.reportBadBlocks(LocatedBlockWritable.convertLocatedBlock(blocks));
+  }
+
+  @Override
+  public void commitBlockSynchronization(ExtendedBlock block,
+      long newgenerationstamp, long newlength, boolean closeFile,
+      boolean deleteblock, DatanodeID[] newtargets) throws IOException {
+    rpcProxy.commitBlockSynchronization(
+        ExtendedBlockWritable.convertExtendedBlock(block), newgenerationstamp,
+        newlength, closeFile, deleteblock,
+        DatanodeIDWritable.convertDatanodeID(newtargets));
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/DatanodeRegistrationWritable.java

@@ -0,0 +1,113 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.protocolR23Compatible.DatanodeIDWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.ExportedBlockKeysWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.StorageInfoWritable;
+import org.apache.hadoop.hdfs.security.token.block.ExportedBlockKeys;
+import org.apache.hadoop.hdfs.server.common.StorageInfo;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeRegistration;
+import org.apache.hadoop.io.Writable;
+import org.apache.hadoop.io.WritableFactories;
+import org.apache.hadoop.io.WritableFactory;
+
+/** 
+ * DatanodeRegistration class contains all information the name-node needs
+ * to identify and verify a data-node when it contacts the name-node.
+ * This information is sent by data-node with each communication request.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public class DatanodeRegistrationWritable implements Writable {
+  static {                                      // register a ctor
+    WritableFactories.setFactory
+      (DatanodeRegistrationWritable.class,
+       new WritableFactory() {
+         public Writable newInstance() { return new DatanodeRegistrationWritable(); }
+       });
+  }
+
+  private DatanodeIDWritable datanodeId;
+  private StorageInfoWritable storageInfo;
+  private ExportedBlockKeysWritable exportedKeys;
+
+  /**
+   * Default constructor.
+   */
+  public DatanodeRegistrationWritable() {
+    this("", new StorageInfo(), new ExportedBlockKeys());
+  }
+  
+  /**
+   * Create DatanodeRegistration
+   */
+  public DatanodeRegistrationWritable(String nodeName, StorageInfo info,
+      ExportedBlockKeys keys) {
+    this.datanodeId = new DatanodeIDWritable(nodeName);
+    this.storageInfo = StorageInfoWritable.convert(info);
+    this.exportedKeys = ExportedBlockKeysWritable.convert(keys);
+  }
+  
+  /////////////////////////////////////////////////
+  // Writable
+  /////////////////////////////////////////////////
+  /** {@inheritDoc} */
+  public void write(DataOutput out) throws IOException {
+    datanodeId.write(out);
+
+    //TODO: move it to DatanodeID once HADOOP-2797 has been committed
+    out.writeShort(datanodeId.ipcPort);
+
+    storageInfo.write(out);
+    exportedKeys.write(out);
+  }
+
+  /** {@inheritDoc} */
+  public void readFields(DataInput in) throws IOException {
+    datanodeId.readFields(in);
+
+    //TODO: move it to DatanodeID once HADOOP-2797 has been committed
+    datanodeId.ipcPort = in.readShort() & 0x0000ffff;
+
+    storageInfo.readFields(in);
+    exportedKeys.readFields(in);
+  }
+
+  public DatanodeRegistration convert() {
+    DatanodeRegistration dnReg = new DatanodeRegistration(datanodeId.name,
+        storageInfo.convert(), exportedKeys.convert());
+    dnReg.setIpcPort(datanodeId.ipcPort);
+    return dnReg;
+  }
+
+  public static DatanodeRegistrationWritable convert(DatanodeRegistration dnReg) {
+    if (dnReg == null) return null;
+    DatanodeRegistrationWritable ret = new DatanodeRegistrationWritable(
+        dnReg.getName(), dnReg.storageInfo, dnReg.exportedKeys);
+    ret.datanodeId.ipcPort = dnReg.ipcPort;
+    return ret;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/DatanodeWireProtocol.java

@@ -0,0 +1,183 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.IOException;
+
+import org.apache.avro.reflect.Nullable;
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.protocol.ClientProtocol;
+import org.apache.hadoop.hdfs.protocol.LocatedBlock;
+import org.apache.hadoop.hdfs.protocolR23Compatible.ClientNamenodeWireProtocol;
+import org.apache.hadoop.hdfs.protocolR23Compatible.DatanodeIDWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.ExtendedBlockWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.LocatedBlockWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.NamespaceInfoWritable;
+import org.apache.hadoop.hdfs.protocolR23Compatible.ProtocolSignatureWritable;
+import org.apache.hadoop.ipc.VersionedProtocol;
+import org.apache.hadoop.security.KerberosInfo;
+
+/**********************************************************************
+ * Protocol that a DFS datanode uses to communicate with the NameNode.
+ * It's used to upload current load information and block reports.
+ *
+ * The only way a NameNode can communicate with a DataNode is by
+ * returning values from these functions.
+ *
+ **********************************************************************/
+@KerberosInfo(
+    serverPrincipal = DFSConfigKeys.DFS_NAMENODE_USER_NAME_KEY, 
+    clientPrincipal = DFSConfigKeys.DFS_DATANODE_USER_NAME_KEY)
+@InterfaceAudience.Private
+public interface DatanodeWireProtocol extends VersionedProtocol {
+  /**
+   * The  rules for changing this protocol are the same as that for
+   * {@link ClientNamenodeWireProtocol} - see that java file for details.
+   */
+  public static final long versionID = 28L;
+  
+  // error code
+  final static int NOTIFY = 0;
+  final static int DISK_ERROR = 1; // there are still valid volumes on DN
+  final static int INVALID_BLOCK = 2;
+  final static int FATAL_DISK_ERROR = 3; // no valid volumes left on DN
+
+  /**
+   * Determines actions that data node should perform 
+   * when receiving a datanode command. 
+   */
+  final static int DNA_UNKNOWN = 0;    // unknown action   
+  final static int DNA_TRANSFER = 1;   // transfer blocks to another datanode
+  final static int DNA_INVALIDATE = 2; // invalidate blocks
+  final static int DNA_SHUTDOWN = 3;   // shutdown node
+  final static int DNA_REGISTER = 4;   // re-register
+  final static int DNA_FINALIZE = 5;   // finalize previous upgrade
+  final static int DNA_RECOVERBLOCK = 6;  // request a block recovery
+  final static int DNA_ACCESSKEYUPDATE = 7;  // update access key
+  final static int DNA_BALANCERBANDWIDTHUPDATE = 8; // update balancer bandwidth
+  
+  /** 
+   * Register Datanode.
+   * @return updated {@link DatanodeRegistrationWritable}, which contains 
+   * new storageID if the datanode did not have one and
+   * registration ID for further communication.
+   */
+  public DatanodeRegistrationWritable registerDatanode(
+      DatanodeRegistrationWritable registration) 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 
+   * an array of "DatanodeCommand" objects.
+   * A DatanodeCommand tells the DataNode to invalidate local block(s), 
+   * or to copy them to other DataNodes, etc.
+   * @param registration datanode registration information
+   * @param capacity total storage capacity available at the datanode
+   * @param dfsUsed storage used by HDFS
+   * @param remaining remaining storage available for HDFS
+   * @param blockPoolUsed storage used by the block pool
+   * @param xmitsInProgress number of transfers from this datanode to others
+   * @param xceiverCount number of active transceiver threads
+   * @param failedVolumes number of failed volumes
+   * @throws IOException on error
+   */
+  @Nullable
+  public DatanodeCommandWritable[] sendHeartbeat(
+      DatanodeRegistrationWritable registration, long capacity, long dfsUsed,
+      long remaining, long blockPoolUsed, int xmitsInProgress,
+      int xceiverCount, int failedVolumes) 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.
+   * @param registration
+   * @param poolId - the block pool ID for the blocks
+   * @param blocks - the block list as an array of longs.
+   *     Each block is represented as 2 longs.
+   *     This is done instead of Block[] to reduce memory used by block reports.
+   *     
+   * @return - the next command for DN to process.
+   * @throws IOException
+   */
+  public DatanodeCommandWritable blockReport(
+      DatanodeRegistrationWritable registration, String poolId, long[] blocks)
+      throws IOException;
+    
+  /**
+   * blockReceivedAndDeleted() allows the DataNode to tell the NameNode about
+   * recently-received and -deleted block data. 
+   * 
+   * For the case of received blocks, a hint for preferred replica to be 
+   * deleted when there is any excessive blocks is provided.
+   * For example, whenever client code
+   * writes a new Block here, or another DataNode copies a Block to
+   * this DataNode, it will call blockReceived().
+   */
+  public void blockReceivedAndDeleted(
+      DatanodeRegistrationWritable registration, String poolId,
+      ReceivedDeletedBlockInfoWritable[] receivedAndDeletedBlocks)
+      throws IOException;
+
+  /**
+   * errorReport() tells the NameNode about something that has gone
+   * awry.  Useful for debugging.
+   */
+  public void errorReport(DatanodeRegistrationWritable registration,
+      int errorCode, String msg) throws IOException;
+    
+  public NamespaceInfoWritable versionRequest() 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. 
+   * 
+   * @return a reply in the form of an upgrade command
+   */
+  UpgradeCommandWritable processUpgradeCommand(UpgradeCommandWritable comm)
+      throws IOException;
+  
+  /**
+   * same as {@link ClientProtocol#reportBadBlocks(LocatedBlock[])}
+   * }
+   */
+  public void reportBadBlocks(LocatedBlockWritable[] blocks) throws IOException;
+  
+  /**
+   * Commit block synchronization in lease recovery
+   */
+  public void commitBlockSynchronization(ExtendedBlockWritable block,
+      long newgenerationstamp, long newlength, boolean closeFile,
+      boolean deleteblock, DatanodeIDWritable[] newtargets) throws IOException;
+  
+  /**
+   * This method is defined to get the protocol signature using 
+   * the R23 protocol - hence we have added the suffix of 2 the method name
+   * to avoid conflict.
+   */
+  public ProtocolSignatureWritable getProtocolSignature2(String protocol,
+      long clientVersion, int clientMethodsHash) throws IOException;
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/FinalizeCommandWritable.java

@@ -0,0 +1,88 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeCommand;
+import org.apache.hadoop.hdfs.server.protocol.FinalizeCommand;
+import org.apache.hadoop.io.Writable;
+import org.apache.hadoop.io.WritableFactories;
+import org.apache.hadoop.io.WritableFactory;
+import org.apache.hadoop.io.WritableUtils;
+
+/**
+ * A FinalizeCommand is an instruction from namenode to finalize the previous
+ * upgrade to a datanode
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public class FinalizeCommandWritable extends DatanodeCommandWritable {
+  // /////////////////////////////////////////
+  // Writable
+  // /////////////////////////////////////////
+  static { // register a ctor
+    WritableFactories.setFactory(FinalizeCommandWritable.class,
+        new WritableFactory() {
+          public Writable newInstance() {
+            return new FinalizeCommandWritable();
+          }
+        });
+  }
+
+  String blockPoolId;
+
+  private FinalizeCommandWritable() {
+    this(null);
+  }
+
+  public FinalizeCommandWritable(String bpid) {
+    super(DatanodeWireProtocol.DNA_FINALIZE);
+    blockPoolId = bpid;
+  }
+
+  public String getBlockPoolId() {
+    return blockPoolId;
+  }
+
+  @Override
+  public void readFields(DataInput in) throws IOException {
+    blockPoolId = WritableUtils.readString(in);
+  }
+
+  @Override
+  public void write(DataOutput out) throws IOException {
+    WritableUtils.writeString(out, blockPoolId);
+  }
+
+  @Override
+  public DatanodeCommand convert() {
+    return new FinalizeCommand(blockPoolId);
+  }
+
+  public static FinalizeCommandWritable convert(FinalizeCommand cmd) {
+    if (cmd == null) {
+      return null;
+    }
+    return new FinalizeCommandWritable(cmd.getBlockPoolId());
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/KeyUpdateCommandWritable.java

@@ -0,0 +1,87 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.protocolR23Compatible.ExportedBlockKeysWritable;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeCommand;
+import org.apache.hadoop.hdfs.server.protocol.KeyUpdateCommand;
+import org.apache.hadoop.io.Writable;
+import org.apache.hadoop.io.WritableFactories;
+import org.apache.hadoop.io.WritableFactory;
+
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public class KeyUpdateCommandWritable extends DatanodeCommandWritable {
+  private ExportedBlockKeysWritable keys;
+
+  KeyUpdateCommandWritable() {
+    this(new ExportedBlockKeysWritable());
+  }
+
+  public KeyUpdateCommandWritable(ExportedBlockKeysWritable keys) {
+    super(DatanodeWireProtocol.DNA_ACCESSKEYUPDATE);
+    this.keys = keys;
+  }
+
+  public ExportedBlockKeysWritable getExportedKeys() {
+    return this.keys;
+  }
+
+  // ///////////////////////////////////////////////
+  // Writable
+  // ///////////////////////////////////////////////
+  static { // register a ctor
+    WritableFactories.setFactory(KeyUpdateCommandWritable.class,
+        new WritableFactory() {
+          public Writable newInstance() {
+            return new KeyUpdateCommandWritable();
+          }
+        });
+  }
+
+  @Override
+  public void write(DataOutput out) throws IOException {
+    super.write(out);
+    keys.write(out);
+  }
+
+  @Override
+  public void readFields(DataInput in) throws IOException {
+    super.readFields(in);
+    keys.readFields(in);
+  }
+
+  @Override
+  public DatanodeCommand convert() {
+    return new KeyUpdateCommand(keys.convert());
+  }
+
+  public static KeyUpdateCommandWritable convert(KeyUpdateCommand cmd) {
+    if (cmd == null) {
+      return null;
+    }
+    return new KeyUpdateCommandWritable(ExportedBlockKeysWritable.convert(cmd
+        .getExportedKeys()));
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/ReceivedDeletedBlockInfoWritable.java

@@ -0,0 +1,95 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.protocolR23Compatible.BlockWritable;
+import org.apache.hadoop.hdfs.server.protocol.ReceivedDeletedBlockInfo;
+import org.apache.hadoop.io.Text;
+import org.apache.hadoop.io.Writable;
+
+/**
+ * A data structure to store Block and delHints together, used to send
+ * received/deleted ACKs.
+ */
+public class ReceivedDeletedBlockInfoWritable implements Writable {
+  BlockWritable block;
+  String delHints;
+
+  public final static String TODELETE_HINT = "-";
+
+  public ReceivedDeletedBlockInfoWritable() {
+  }
+
+  public ReceivedDeletedBlockInfoWritable(BlockWritable blk, String delHints) {
+    this.block = blk;
+    this.delHints = delHints;
+  }
+
+  @Override
+  public void write(DataOutput out) throws IOException {
+    this.block.write(out);
+    Text.writeString(out, this.delHints);
+  }
+
+  @Override
+  public void readFields(DataInput in) throws IOException {
+    this.block = new BlockWritable();
+    this.block.readFields(in);
+    this.delHints = Text.readString(in);
+  }
+
+  public String toString() {
+    return block.toString() + ", delHint: " + delHints;
+  }
+
+  public static ReceivedDeletedBlockInfo[] convert(
+      ReceivedDeletedBlockInfoWritable[] rdBlocks) {
+    ReceivedDeletedBlockInfo[] ret = 
+        new ReceivedDeletedBlockInfo[rdBlocks.length];
+    for (int i = 0; i < rdBlocks.length; i++) {
+      ret[i] = rdBlocks[i].convert();
+    }
+    return ret;
+  }
+  
+  public static ReceivedDeletedBlockInfoWritable[] convert(
+      ReceivedDeletedBlockInfo[] blocks) {
+    ReceivedDeletedBlockInfoWritable[] ret = 
+        new ReceivedDeletedBlockInfoWritable[blocks.length];
+    for (int i = 0; i < blocks.length; i++) {
+      ret[i] = convert(blocks[i]);
+    }
+    return ret;
+  }
+
+  public ReceivedDeletedBlockInfo convert() {
+    return new ReceivedDeletedBlockInfo(block.convert(), delHints);
+  }
+
+  public static ReceivedDeletedBlockInfoWritable convert(
+      ReceivedDeletedBlockInfo b) {
+    if (b == null) return null;
+    return new ReceivedDeletedBlockInfoWritable(BlockWritable.convert(b
+        .getBlock()), b.getDelHints());
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/RegisterCommandWritable.java

@@ -0,0 +1,69 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeCommand;
+import org.apache.hadoop.hdfs.server.protocol.RegisterCommand;
+import org.apache.hadoop.io.Writable;
+import org.apache.hadoop.io.WritableFactories;
+import org.apache.hadoop.io.WritableFactory;
+
+/**
+ * A RegisterCommand is an instruction to a datanode to register with the
+ * namenode.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public class RegisterCommandWritable extends DatanodeCommandWritable {
+  public static final RegisterCommandWritable REGISTER = 
+      new RegisterCommandWritable();
+  
+  // /////////////////////////////////////////
+  // Writable
+  // /////////////////////////////////////////
+  static { // register a ctor
+    WritableFactories.setFactory(RegisterCommandWritable.class,
+        new WritableFactory() {
+          public Writable newInstance() {
+            return new RegisterCommandWritable();
+          }
+        });
+  }
+
+  public RegisterCommandWritable() {
+    super(DatanodeWireProtocol.DNA_REGISTER);
+  }
+
+  @Override
+  public void readFields(DataInput in) { /* Nothing to read */
+  }
+
+  @Override
+  public void write(DataOutput out) { /* Nothing to write */
+  }
+
+  @Override
+  public DatanodeCommand convert() {
+    return RegisterCommand.REGISTER;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/ServerCommandWritable.java

@@ -0,0 +1,75 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.io.Writable;
+
+/**
+ * Base class for a server command.
+ * Issued by the name-node to notify other servers what should be done.
+ * Commands are defined by actions defined in respective protocols.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public abstract class ServerCommandWritable implements Writable {
+  private int action;
+
+  /**
+   * Unknown server command constructor.
+   * Creates a command with action 0.
+   */
+  public ServerCommandWritable() {
+    this(0);
+  }
+
+  /**
+   * Create a command for the specified action.
+   * Actions are protocol specific.
+   * @param action
+   */
+  public ServerCommandWritable(int action) {
+    this.action = action;
+  }
+
+  /**
+   * Get server command action.
+   * @return action code.
+   */
+  public int getAction() {
+    return this.action;
+  }
+
+  ///////////////////////////////////////////
+  // Writable
+  ///////////////////////////////////////////
+  @Override
+  public void write(DataOutput out) throws IOException {
+    out.writeInt(this.action);
+  }
+
+  @Override
+  public void readFields(DataInput in) throws IOException {
+    this.action = in.readInt();
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/protocolR23Compatible/UpgradeCommandWritable.java

@@ -0,0 +1,106 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.protocolR23Compatible;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.server.protocol.UpgradeCommand;
+import org.apache.hadoop.io.Writable;
+import org.apache.hadoop.io.WritableFactories;
+import org.apache.hadoop.io.WritableFactory;
+
+/**
+ * This as a generic distributed upgrade command.
+ * 
+ * During the upgrade cluster components send upgrade commands to each other
+ * in order to obtain or share information with them.
+ * It is supposed that each upgrade defines specific upgrade command by
+ * deriving them from this class.
+ * The upgrade command contains version of the upgrade, which is verified 
+ * on the receiving side and current status of the upgrade.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public class UpgradeCommandWritable extends DatanodeCommandWritable {
+  final static int UC_ACTION_UNKNOWN = DatanodeWireProtocol.DNA_UNKNOWN;
+  public final static int UC_ACTION_REPORT_STATUS = 100; // report upgrade status
+  public final static int UC_ACTION_START_UPGRADE = 101; // start upgrade
+
+  private int version;
+  private short upgradeStatus;
+
+  public UpgradeCommandWritable() {
+    super(UC_ACTION_UNKNOWN);
+    this.version = 0;
+    this.upgradeStatus = 0;
+  }
+
+  public UpgradeCommandWritable(int action, int version, short status) {
+    super(action);
+    this.version = version;
+    this.upgradeStatus = status;
+  }
+
+  public int getVersion() {
+    return this.version;
+  }
+
+  public short getCurrentStatus() {
+    return this.upgradeStatus;
+  }
+
+  /////////////////////////////////////////////////
+  // Writable
+  /////////////////////////////////////////////////
+  static {                                      // register a ctor
+    WritableFactories.setFactory
+      (UpgradeCommandWritable.class,
+       new WritableFactory() {
+         public Writable newInstance() { return new UpgradeCommandWritable(); }
+       });
+  }
+
+  @Override
+  public void write(DataOutput out) throws IOException {
+    super.write(out);
+    out.writeInt(this.version);
+    out.writeShort(this.upgradeStatus);
+  }
+
+  @Override
+  public void readFields(DataInput in) throws IOException {
+    super.readFields(in);
+    this.version = in.readInt();
+    this.upgradeStatus = in.readShort();
+  }
+
+  @Override
+  public UpgradeCommand convert() {
+    return new UpgradeCommand(getAction(), version, upgradeStatus);
+  }
+
+  public static UpgradeCommandWritable convert(UpgradeCommand cmd) {
+    if (cmd == null) return null;
+    return new UpgradeCommandWritable(cmd.getAction(), cmd.getVersion(),
+        cmd.getCurrentStatus());
+  }
+}