/**
 * 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.dfs;

import org.apache.commons.logging.*;

import org.apache.hadoop.conf.*;
import org.apache.hadoop.dfs.BlocksMap.BlockInfo;
import org.apache.hadoop.dfs.BlocksWithLocations.BlockWithLocations;
import org.apache.hadoop.dfs.namenode.metrics.FSNamesystemMBean;
import org.apache.hadoop.security.UnixUserGroupInformation;
import org.apache.hadoop.security.UserGroupInformation;
import org.apache.hadoop.util.*;
import org.apache.hadoop.mapred.StatusHttpServer;
import org.apache.hadoop.metrics.util.MBeanUtil;
import org.apache.hadoop.net.DNSToSwitchMapping;
import org.apache.hadoop.net.NetUtils;
import org.apache.hadoop.net.NetworkTopology;
import org.apache.hadoop.net.ScriptBasedMapping;
import org.apache.hadoop.dfs.LeaseManager.Lease;
import org.apache.hadoop.fs.ContentSummary;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.permission.*;
import org.apache.hadoop.ipc.Server;
import org.apache.hadoop.io.IOUtils;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.DataOutputStream;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.util.*;
import java.util.Map.Entry;
import java.util.concurrent.LinkedBlockingQueue;

import javax.management.NotCompliantMBeanException;
import javax.management.ObjectName;
import javax.management.StandardMBean;
import javax.security.auth.login.LoginException;

/***************************************************
 * FSNamesystem does the actual bookkeeping work for the
 * DataNode.
 *
 * It tracks several important tables.
 *
 * 1)  valid fsname --> blocklist  (kept on disk, logged)
 * 2)  Set of all valid blocks (inverted #1)
 * 3)  block --> machinelist (kept in memory, rebuilt dynamically from reports)
 * 4)  machine --> blocklist (inverted #2)
 * 5)  LRU cache of updated-heartbeat machines
 ***************************************************/
class FSNamesystem implements FSConstants, FSNamesystemMBean {
  public static final Log LOG = LogFactory.getLog("org.apache.hadoop.fs.FSNamesystem");
  public static final String AUDIT_FORMAT =
    "ugi=%s\t" +  // ugi
    "ip=%s\t" +   // remote IP
    "cmd=%s\t" +  // command
    "src=%s\t" +  // src path
    "dst=%s\t" +  // dst path (optional)
    "perm=%s";    // permissions (optional)

  private static final ThreadLocal<Formatter> auditFormatter =
    new ThreadLocal<Formatter>() {
      protected Formatter initialValue() {
        return new Formatter(new StringBuilder(AUDIT_FORMAT.length() * 4));
      }
  };

  private static final void logAuditEvent(UserGroupInformation ugi,
      InetAddress addr, String cmd, String src, String dst,
      FileStatus stat) {
    final Formatter fmt = auditFormatter.get();
    ((StringBuilder)fmt.out()).setLength(0);
    auditLog.info(fmt.format(AUDIT_FORMAT, ugi, addr, cmd, src, dst,
                  (stat == null)
                    ? null
                    : stat.getOwner() + ':' + stat.getGroup() + ':' +
                      stat.getPermission()
          ).toString());

  }

  public static final Log auditLog = LogFactory.getLog(
      "org.apache.hadoop.fs.FSNamesystem.audit");

  private boolean isPermissionEnabled;
  private UserGroupInformation fsOwner;
  private String supergroup;
  private PermissionStatus defaultPermission;
  // FSNamesystemMetrics counter variables
  private FSNamesystemMetrics myFSMetrics;
  private long capacityTotal = 0L, capacityUsed = 0L, capacityRemaining = 0L;
  private int totalLoad = 0;
  private long pendingReplicationBlocksCount = 0L, 
    underReplicatedBlocksCount = 0L, scheduledReplicationBlocksCount = 0L;

  //
  // Stores the correct file name hierarchy
  //
  FSDirectory dir;

  //
  // Mapping: Block -> { INode, datanodes, self ref } 
  // Updated only in response to client-sent information.
  //
  BlocksMap blocksMap = new BlocksMap();

  //
  // Store blocks-->datanodedescriptor(s) map of corrupt replicas
  //
  CorruptReplicasMap corruptReplicas = new CorruptReplicasMap();
    
  /**
   * Stores the datanode -> block map.  
   * <p>
   * Done by storing a set of {@link DatanodeDescriptor} objects, sorted by 
   * storage id. In order to keep the storage map consistent it tracks 
   * all storages ever registered with the namenode.
   * A descriptor corresponding to a specific storage id can be
   * <ul> 
   * <li>added to the map if it is a new storage id;</li>
   * <li>updated with a new datanode started as a replacement for the old one 
   * with the same storage id; and </li>
   * <li>removed if and only if an existing datanode is restarted to serve a
   * different storage id.</li>
   * </ul> <br>
   * The list of the {@link DatanodeDescriptor}s in the map is checkpointed
   * in the namespace image file. Only the {@link DatanodeInfo} part is 
   * persistent, the list of blocks is restored from the datanode block
   * reports. 
   * <p>
   * Mapping: StorageID -> DatanodeDescriptor
   */
  SortedMap<String, DatanodeDescriptor> datanodeMap = 
    new TreeMap<String, DatanodeDescriptor>();

  //
  // Keeps a Collection for every named machine containing
  // blocks that have recently been invalidated and are thought to live
  // on the machine in question.
  // Mapping: StorageID -> ArrayList<Block>
  //
  private Map<String, Collection<Block>> recentInvalidateSets = 
    new TreeMap<String, Collection<Block>>();

  //
  // Keeps a TreeSet for every named node.  Each treeset contains
  // a list of the blocks that are "extra" at that location.  We'll
  // eventually remove these extras.
  // Mapping: StorageID -> TreeSet<Block>
  //
  Map<String, Collection<Block>> excessReplicateMap = 
    new TreeMap<String, Collection<Block>>();

  //
  // For the HTTP browsing interface
  //
  StatusHttpServer infoServer;
  int infoPort;
  Date startTime;
    
  //
  Random r = new Random();

  /**
   * Stores a set of DatanodeDescriptor objects.
   * This is a subset of {@link #datanodeMap}, containing nodes that are 
   * considered alive.
   * The {@link HeartbeatMonitor} periodically checks for outdated entries,
   * and removes them from the list.
   */
  ArrayList<DatanodeDescriptor> heartbeats = new ArrayList<DatanodeDescriptor>();

  //
  // Store set of Blocks that need to be replicated 1 or more times.
  // We also store pending replication-orders.
  // Set of: Block
  //
  private UnderReplicatedBlocks neededReplications = new UnderReplicatedBlocks();
  private PendingReplicationBlocks pendingReplications;

  LeaseManager leaseManager = new LeaseManager(this); 

  //
  // Threaded object that checks to see if we have been
  // getting heartbeats from all clients. 
  //
  Daemon hbthread = null;   // HeartbeatMonitor thread
  Daemon lmthread = null;   // LeaseMonitor thread
  Daemon smmthread = null;  // SafeModeMonitor thread
  Daemon replthread = null;  // Replication thread
  Daemon resthread = null; //ResolutionMonitor thread
  
  private volatile boolean fsRunning = true;
  long systemStart = 0;

  //  The maximum number of replicates we should allow for a single block
  private int maxReplication;
  //  How many outgoing replication streams a given node should have at one time
  private int maxReplicationStreams;
  // MIN_REPLICATION is how many copies we need in place or else we disallow the write
  private int minReplication;
  // Default replication
  private int defaultReplication;
  // heartbeatRecheckInterval is how often namenode checks for expired datanodes
  private long heartbeatRecheckInterval;
  // heartbeatExpireInterval is how long namenode waits for datanode to report
  // heartbeat
  private long heartbeatExpireInterval;
  //replicationRecheckInterval is how often namenode checks for new replication work
  private long replicationRecheckInterval;
  // default block size of a file
  private long defaultBlockSize = 0;

  /**
   * Last block index used for replication work.
   */
  private int replIndex = 0;

  public static FSNamesystem fsNamesystemObject;
  private String localMachine;
  private int port;
  private SafeModeInfo safeMode;  // safe mode information
  private Host2NodesMap host2DataNodeMap = new Host2NodesMap();
    
  // datanode networktoplogy
  NetworkTopology clusterMap = new NetworkTopology();
  private DNSToSwitchMapping dnsToSwitchMapping;
  private LinkedBlockingQueue<DatanodeDescriptor> resolutionQueue = 
    new LinkedBlockingQueue <DatanodeDescriptor>();
  
  // for block replicas placement
  ReplicationTargetChooser replicator;

  private HostsFileReader hostsReader; 
  private Daemon dnthread = null;

  private long maxFsObjects = 0;          // maximum number of fs objects

  /**
   * The global generation stamp for this file system. 
   */
  private final GenerationStamp generationStamp = new GenerationStamp();

  // Ask Datanode only up to this many blocks to delete.
  private int blockInvalidateLimit = FSConstants.BLOCK_INVALIDATE_CHUNK;

  /**
   * FSNamesystem constructor.
   */
  FSNamesystem(NameNode nn, Configuration conf) throws IOException {
    try {
      initialize(nn, conf);
    } catch(IOException e) {
      LOG.error(getClass().getSimpleName() + " initialization failed.", e);
      close();
      throw e;
    }
  }

  /**
   * Initialize FSNamesystem.
   */
  private void initialize(NameNode nn, Configuration conf) throws IOException {
    this.systemStart = now();
    this.startTime = new Date(systemStart); 
    setConfigurationParameters(conf);

    this.localMachine = nn.getNameNodeAddress().getHostName();
    this.port = nn.getNameNodeAddress().getPort();
    this.registerMBean(conf); // register the MBean for the FSNamesystemStutus
    this.dir = new FSDirectory(this, conf);
    StartupOption startOpt = NameNode.getStartupOption(conf);
    this.dir.loadFSImage(getNamespaceDirs(conf), startOpt);
    long timeTakenToLoadFSImage = now() - systemStart;
    LOG.info("Finished loading FSImage in " + timeTakenToLoadFSImage + " msecs");
    NameNode.getNameNodeMetrics().fsImageLoadTime.set(
                              (int) timeTakenToLoadFSImage);
    this.safeMode = new SafeModeInfo(conf);
    setBlockTotal();
    pendingReplications = new PendingReplicationBlocks(
                            conf.getInt("dfs.replication.pending.timeout.sec", 
                                        -1) * 1000L);
    this.hbthread = new Daemon(new HeartbeatMonitor());
    this.lmthread = new Daemon(leaseManager.new Monitor());
    this.replthread = new Daemon(new ReplicationMonitor());
    this.resthread = new Daemon(new ResolutionMonitor());
    hbthread.start();
    lmthread.start();
    replthread.start();
    resthread.start();

    this.hostsReader = new HostsFileReader(conf.get("dfs.hosts",""),
                                           conf.get("dfs.hosts.exclude",""));
    this.dnthread = new Daemon(new DecommissionManager(this).new Monitor(
        conf.getInt("dfs.namenode.decommission.interval", 30),
        conf.getInt("dfs.namenode.decommission.nodes.per.interval", 5)));
    dnthread.start();

    this.dnsToSwitchMapping = (DNSToSwitchMapping)ReflectionUtils.newInstance(
        conf.getClass("topology.node.switch.mapping.impl", ScriptBasedMapping.class,
            DNSToSwitchMapping.class), conf);

    String infoAddr = 
      NetUtils.getServerAddress(conf, "dfs.info.bindAddress", 
                                "dfs.info.port", "dfs.http.address");
    InetSocketAddress infoSocAddr = NetUtils.createSocketAddr(infoAddr);
    String infoHost = infoSocAddr.getHostName();
    int tmpInfoPort = infoSocAddr.getPort();
    this.infoServer = new StatusHttpServer("dfs", infoHost, tmpInfoPort, 
                                            tmpInfoPort == 0);
    InetSocketAddress secInfoSocAddr = NetUtils.createSocketAddr(
        conf.get("dfs.https.address", infoHost + ":" + 0));
    Configuration sslConf = new Configuration(conf);
    sslConf.addResource(conf.get("https.keystore.info.rsrc", "sslinfo.xml"));
    String keyloc = sslConf.get("https.keystore.location");
    if (null != keyloc) {
      this.infoServer.addSslListener(secInfoSocAddr, keyloc,
          sslConf.get("https.keystore.password", ""),
          sslConf.get("https.keystore.keypassword", ""));
    }
    // assume same ssl port for all datanodes
    InetSocketAddress datanodeSslPort = NetUtils.createSocketAddr(
        conf.get("dfs.datanode.https.address", infoHost + ":" + 50475));
    this.infoServer.setAttribute("datanode.https.port",
        datanodeSslPort.getPort());
    this.infoServer.setAttribute("name.node", nn);
    this.infoServer.setAttribute("name.system.image", getFSImage());
    this.infoServer.setAttribute("name.conf", conf);
    this.infoServer.addServlet("fsck", "/fsck", FsckServlet.class);
    this.infoServer.addServlet("getimage", "/getimage", GetImageServlet.class);
    this.infoServer.addServlet("listPaths", "/listPaths/*", ListPathsServlet.class);
    this.infoServer.addServlet("data", "/data/*", FileDataServlet.class);
    this.infoServer.start();

    // The web-server port can be ephemeral... ensure we have the correct info
    this.infoPort = this.infoServer.getPort();
    conf.set("dfs.http.address", infoHost + ":" + infoPort);
    LOG.info("Web-server up at: " + infoHost + ":" + infoPort);
  }

  static Collection<File> getNamespaceDirs(Configuration conf) {
    Collection<String> dirNames = conf.getStringCollection("dfs.name.dir");
    if (dirNames.isEmpty())
      dirNames.add("/tmp/hadoop/dfs/name");
    Collection<File> dirs = new ArrayList<File>(dirNames.size());
    for(String name : dirNames) {
      dirs.add(new File(name));
    }
    return dirs;
  }

  /**
   * dirs is a list of directories where the filesystem directory state 
   * is stored
   */
  FSNamesystem(FSImage fsImage, Configuration conf) throws IOException {
    setConfigurationParameters(conf);
    this.dir = new FSDirectory(fsImage, this, conf);
  }

  /**
   * Initializes some of the members from configuration
   */
  private void setConfigurationParameters(Configuration conf) 
                                          throws IOException {
    fsNamesystemObject = this;
    try {
      fsOwner = UnixUserGroupInformation.login(conf);
    } catch (LoginException e) {
      throw new IOException(StringUtils.stringifyException(e));
    }
    LOG.info("fsOwner=" + fsOwner);

    this.supergroup = conf.get("dfs.permissions.supergroup", "supergroup");
    this.isPermissionEnabled = conf.getBoolean("dfs.permissions", true);
    LOG.info("supergroup=" + supergroup);
    LOG.info("isPermissionEnabled=" + isPermissionEnabled);
    short filePermission = (short)conf.getInt("dfs.upgrade.permission", 0777);
    this.defaultPermission = PermissionStatus.createImmutable(
        fsOwner.getUserName(), supergroup, new FsPermission(filePermission));


    this.replicator = new ReplicationTargetChooser(
                         conf.getBoolean("dfs.replication.considerLoad", true),
                         this,
                         clusterMap);
    this.defaultReplication = conf.getInt("dfs.replication", 3);
    this.maxReplication = conf.getInt("dfs.replication.max", 512);
    this.minReplication = conf.getInt("dfs.replication.min", 1);
    if (minReplication <= 0)
      throw new IOException(
                            "Unexpected configuration parameters: dfs.replication.min = " 
                            + minReplication
                            + " must be greater than 0");
    if (maxReplication >= (int)Short.MAX_VALUE)
      throw new IOException(
                            "Unexpected configuration parameters: dfs.replication.max = " 
                            + maxReplication + " must be less than " + (Short.MAX_VALUE));
    if (maxReplication < minReplication)
      throw new IOException(
                            "Unexpected configuration parameters: dfs.replication.min = " 
                            + minReplication
                            + " must be less than dfs.replication.max = " 
                            + maxReplication);
    this.maxReplicationStreams = conf.getInt("dfs.max-repl-streams", 2);
    long heartbeatInterval = conf.getLong("dfs.heartbeat.interval", 3) * 1000;
    this.heartbeatRecheckInterval = conf.getInt(
        "heartbeat.recheck.interval", 5 * 60 * 1000); // 5 minutes
    this.heartbeatExpireInterval = 2 * heartbeatRecheckInterval +
      10 * heartbeatInterval;
    this.replicationRecheckInterval = 
      conf.getInt("dfs.replication.interval", 3) * 1000L;
    this.defaultBlockSize = conf.getLong("dfs.block.size", DEFAULT_BLOCK_SIZE);
    this.maxFsObjects = conf.getLong("dfs.max.objects", 0);
    this.blockInvalidateLimit = Math.max(this.blockInvalidateLimit, 
                                         20*(int)(heartbeatInterval/1000));
  }

  /**
   * Return the default path permission when upgrading from releases with no
   * permissions (<=0.15) to releases with permissions (>=0.16)
   */
  protected PermissionStatus getUpgradePermission() {
    return defaultPermission;
  }
  
  /** Return the FSNamesystem object
   * 
   */
  public static FSNamesystem getFSNamesystem() {
    return fsNamesystemObject;
  } 

  NamespaceInfo getNamespaceInfo() {
    return new NamespaceInfo(dir.fsImage.getNamespaceID(),
                             dir.fsImage.getCTime(),
                             getDistributedUpgradeVersion());
  }

  /**
   * Close down this file system manager.
   * Causes heartbeat and lease daemons to stop; waits briefly for
   * them to finish, but a short timeout returns control back to caller.
   */
  public void close() {
    fsRunning = false;
    try {
      if (pendingReplications != null) pendingReplications.stop();
      if (infoServer != null) infoServer.stop();
      if (hbthread != null) hbthread.interrupt();
      if (replthread != null) replthread.interrupt();
      if (resthread != null) resthread.interrupt();
      if (dnthread != null) dnthread.interrupt();
      if (smmthread != null) smmthread.interrupt();
    } catch (InterruptedException ie) {
    } finally {
      // using finally to ensure we also wait for lease daemon
      try {
        if (lmthread != null) {
          lmthread.interrupt();
          lmthread.join(3000);
        }
        dir.close();
      } catch (InterruptedException ie) {
      } catch (IOException ie) {
        LOG.error("Error closing FSDirectory", ie);
        IOUtils.cleanup(LOG, dir);
      }
    }
  }

  /** Is this name system running? */
  boolean isRunning() {
    return fsRunning;
  }

  /**
   * Dump all metadata into specified file
   */
  void metaSave(String filename) throws IOException {
    checkSuperuserPrivilege();
    File file = new File(System.getProperty("hadoop.log.dir"), 
                         filename);
    PrintWriter out = new PrintWriter(new BufferedWriter(
                                                         new FileWriter(file, true)));
 

    //
    // Dump contents of neededReplication
    //
    synchronized (neededReplications) {
      out.println("Metasave: Blocks waiting for replication: " + 
                  neededReplications.size());
      for (Block block : neededReplications) {
        out.print(block);
        for (Iterator<DatanodeDescriptor> jt = blocksMap.nodeIterator(block);
             jt.hasNext();) {
          DatanodeDescriptor node = jt.next();
          out.print(" " + node + " : ");
        }
        out.println("");
      }
    }

    //
    // Dump blocks from pendingReplication
    //
    pendingReplications.metaSave(out);

    //
    // Dump blocks that are waiting to be deleted
    //
    dumpRecentInvalidateSets(out);

    //
    // Dump all datanodes
    //
    datanodeDump(out);

    out.flush();
    out.close();
  }

  long getDefaultBlockSize() {
    return defaultBlockSize;
  }
    
  /* get replication factor of a block */
  private int getReplication(Block block) {
    INodeFile fileINode = blocksMap.getINode(block);
    if (fileINode == null) { // block does not belong to any file
      return 0;
    }
    assert !fileINode.isDirectory() : "Block cannot belong to a directory.";
    return fileINode.getReplication();
  }

  /* updates a block in under replication queue */
  synchronized void updateNeededReplications(Block block,
                        int curReplicasDelta, int expectedReplicasDelta) {
    NumberReplicas repl = countNodes(block);
    int curExpectedReplicas = getReplication(block);
    neededReplications.update(block, 
                              repl.liveReplicas(), 
                              repl.decommissionedReplicas(),
                              curExpectedReplicas,
                              curReplicasDelta, expectedReplicasDelta);
  }

  /////////////////////////////////////////////////////////
  //
  // These methods are called by secondary namenodes
  //
  /////////////////////////////////////////////////////////
  /**
   * return a list of blocks & their locations on <code>datanode</code> whose
   * total size is <code>size</code>
   * 
   * @param datanode on which blocks are located
   * @param size total size of blocks
   */
  synchronized BlocksWithLocations getBlocks(DatanodeID datanode, long size)
      throws IOException {
    checkSuperuserPrivilege();

    DatanodeDescriptor node = getDatanode(datanode);
    if (node == null) {
      NameNode.stateChangeLog.warn("BLOCK* NameSystem.getBlocks: "
          + "Asking for blocks from an unrecorded node " + datanode.getName());
      throw new IllegalArgumentException(
          "Unexpected exception.  Got getBlocks message for datanode " + 
          datanode.getName() + ", but there is no info for it");
    }

    int numBlocks = node.numBlocks();
    if(numBlocks == 0) {
      return new BlocksWithLocations(new BlockWithLocations[0]);
    }
    Iterator<Block> iter = node.getBlockIterator();
    int startBlock = r.nextInt(numBlocks); // starting from a random block
    // skip blocks
    for(int i=0; i<startBlock; i++) {
      iter.next();
    }
    List<BlockWithLocations> results = new ArrayList<BlockWithLocations>();
    long totalSize = 0;
    while(totalSize<size && iter.hasNext()) {
      totalSize += addBlock(iter.next(), results);
    }
    if(totalSize<size) {
      iter = node.getBlockIterator(); // start from the beginning
      for(int i=0; i<startBlock&&totalSize<size; i++) {
        totalSize += addBlock(iter.next(), results);
      }
    }
    
    return new BlocksWithLocations(
        results.toArray(new BlockWithLocations[results.size()]));
  }
  
  /**
   * Get all valid locations of the block & add the block to results
   * return the length of the added block; 0 if the block is not added
   */
  private long addBlock(Block block, List<BlockWithLocations> results) {
    ArrayList<String> machineSet =
      new ArrayList<String>(blocksMap.numNodes(block));
    for(Iterator<DatanodeDescriptor> it = 
      blocksMap.nodeIterator(block); it.hasNext();) {
      String storageID = it.next().getStorageID();
      // filter invalidate replicas
      Collection<Block> blocks = recentInvalidateSets.get(storageID); 
      if(blocks==null || !blocks.contains(block)) {
        machineSet.add(storageID);
      }
    }
    if(machineSet.size() == 0) {
      return 0;
    } else {
      results.add(new BlockWithLocations(block, 
          machineSet.toArray(new String[machineSet.size()])));
      return block.getNumBytes();
    }
  }

  /////////////////////////////////////////////////////////
  //
  // These methods are called by HadoopFS clients
  //
  /////////////////////////////////////////////////////////
  /**
   * Set permissions for an existing file.
   * @throws IOException
   */
  public synchronized void setPermission(String src, FsPermission permission
      ) throws IOException {
    checkOwner(src);
    dir.setPermission(src, permission);
    getEditLog().logSync();
    if (auditLog.isInfoEnabled()) {
      final FileStatus stat = dir.getFileInfo(src);
      logAuditEvent(UserGroupInformation.getCurrentUGI(),
                    Server.getRemoteIp(),
                    "setPermission", src, null, stat);
    }
  }

  /**
   * Set owner for an existing file.
   * @throws IOException
   */
  public synchronized void setOwner(String src, String username, String group
      ) throws IOException {
    PermissionChecker pc = checkOwner(src);
    if (!pc.isSuper) {
      if (username != null && !pc.user.equals(username)) {
        throw new AccessControlException("Non-super user cannot change owner.");
      }
      if (group != null && !pc.containsGroup(group)) {
        throw new AccessControlException("User does not belong to " + group
            + " .");
      }
    }
    dir.setOwner(src, username, group);
    getEditLog().logSync();
    if (auditLog.isInfoEnabled()) {
      final FileStatus stat = dir.getFileInfo(src);
      logAuditEvent(UserGroupInformation.getCurrentUGI(),
                    Server.getRemoteIp(),
                    "setOwner", src, null, stat);
    }
  }

  /**
   * Get block locations within the specified range.
   * 
   * @see #getBlockLocations(String, long, long)
   */
  LocatedBlocks getBlockLocations(String clientMachine, String src,
      long offset, long length) throws IOException {
    if (isPermissionEnabled) {
      checkPathAccess(src, FsAction.READ);
    }

    LocatedBlocks blocks = getBlockLocations(src, offset, length);
    if (blocks != null) {
      //sort the blocks
      DatanodeDescriptor client = host2DataNodeMap.getDatanodeByHost(
          clientMachine);
      for (LocatedBlock b : blocks.getLocatedBlocks()) {
        clusterMap.pseudoSortByDistance(client, b.getLocations());
      }
    }
    return blocks;
  }

  /**
   * Get block locations within the specified range.
   * @see ClientProtocol#getBlockLocations(String, long, long)
   */
  LocatedBlocks getBlockLocations(String src, long offset, long length
      ) throws IOException {
    if (offset < 0) {
      throw new IOException("Negative offset is not supported. File: " + src );
    }
    if (length < 0) {
      throw new IOException("Negative length is not supported. File: " + src );
    }
    final LocatedBlocks ret = getBlockLocationsInternal(dir.getFileINode(src),
        offset, length, Integer.MAX_VALUE);  
    if (auditLog.isInfoEnabled()) {
      logAuditEvent(UserGroupInformation.getCurrentUGI(),
                    Server.getRemoteIp(),
                    "open", src, null, null);
    }
    return ret;
  }

  private synchronized LocatedBlocks getBlockLocationsInternal(INodeFile inode,
                                                       long offset, 
                                                       long length,
                                                       int nrBlocksToReturn) {
    if(inode == null) {
      return null;
    }
    Block[] blocks = inode.getBlocks();
    if (blocks == null) {
      return null;
    }
    if (blocks.length == 0) {
      return new LocatedBlocks(inode, new ArrayList<LocatedBlock>(blocks.length));
    }
    List<LocatedBlock> results;
    results = new ArrayList<LocatedBlock>(blocks.length);

    int curBlk = 0;
    long curPos = 0, blkSize = 0;
    int nrBlocks = (blocks[0].getNumBytes() == 0) ? 0 : blocks.length;
    for (curBlk = 0; curBlk < nrBlocks; curBlk++) {
      blkSize = blocks[curBlk].getNumBytes();
      assert blkSize > 0 : "Block of size 0";
      if (curPos + blkSize > offset) {
        break;
      }
      curPos += blkSize;
    }
    
    if (nrBlocks > 0 && curBlk == nrBlocks)   // offset >= end of file
      return null;
    
    long endOff = offset + length;
    
    do {
      // get block locations
      int numNodes = blocksMap.numNodes(blocks[curBlk]);
      int numCorruptNodes = countNodes(blocks[curBlk]).corruptReplicas();
      int numCorruptReplicas = corruptReplicas.numCorruptReplicas(blocks[curBlk]); 
      if (numCorruptNodes != numCorruptReplicas) {
        LOG.warn("Inconsistent number of corrupt replicas for " + 
            blocks[curBlk] + "blockMap has " + numCorruptNodes + 
            " but corrupt replicas map has " + numCorruptReplicas);
      }
      boolean blockCorrupt = (numCorruptNodes == numNodes);
      int numMachineSet = blockCorrupt ? numNodes : 
                            (numNodes - numCorruptNodes);
      DatanodeDescriptor[] machineSet = new DatanodeDescriptor[numMachineSet];
      if (numMachineSet > 0) {
        numNodes = 0;
        for(Iterator<DatanodeDescriptor> it = 
            blocksMap.nodeIterator(blocks[curBlk]); it.hasNext();) {
          DatanodeDescriptor dn = it.next();
          boolean replicaCorrupt = corruptReplicas.isReplicaCorrupt(blocks[curBlk], dn);
          if (blockCorrupt || (!blockCorrupt && !replicaCorrupt))
            machineSet[numNodes++] = dn;
        }
      }
      results.add(new LocatedBlock(blocks[curBlk], machineSet, curPos,
                  blockCorrupt));
      curPos += blocks[curBlk].getNumBytes();
      curBlk++;
    } while (curPos < endOff 
          && curBlk < blocks.length 
          && results.size() < nrBlocksToReturn);
    
    return new LocatedBlocks(inode, results);
  }

  /**
   * Set replication for an existing file.
   * 
   * The NameNode sets new replication and schedules either replication of 
   * under-replicated data blocks or removal of the eccessive block copies 
   * if the blocks are over-replicated.
   * 
   * @see ClientProtocol#setReplication(String, short)
   * @param src file name
   * @param replication new replication
   * @return true if successful; 
   *         false if file does not exist or is a directory
   */
  public boolean setReplication(String src, short replication) 
                                throws IOException {
    boolean status = setReplicationInternal(src, replication);
    getEditLog().logSync();
    if (status && auditLog.isInfoEnabled()) {
      logAuditEvent(UserGroupInformation.getCurrentUGI(),
                    Server.getRemoteIp(),
                    "setReplication", src, null, null);
    }
    return status;
  }

  private synchronized boolean setReplicationInternal(String src, 
                                             short replication
                                             ) throws IOException {
    if (isInSafeMode())
      throw new SafeModeException("Cannot set replication for " + src, safeMode);
    verifyReplication(src, replication, null);
    if (isPermissionEnabled) {
      checkPathAccess(src, FsAction.WRITE);
    }

    int[] oldReplication = new int[1];
    Block[] fileBlocks;
    fileBlocks = dir.setReplication(src, replication, oldReplication);
    if (fileBlocks == null)  // file not found or is a directory
      return false;
    int oldRepl = oldReplication[0];
    if (oldRepl == replication) // the same replication
      return true;

    // update needReplication priority queues
    LOG.info("Increasing replication for file " + src 
             + ". New replication is " + replication);
    for(int idx = 0; idx < fileBlocks.length; idx++)
      updateNeededReplications(fileBlocks[idx], 0, replication-oldRepl);
      
    if (oldRepl > replication) {  
      // old replication > the new one; need to remove copies
      LOG.info("Reducing replication for file " + src 
               + ". New replication is " + replication);
      for(int idx = 0; idx < fileBlocks.length; idx++)
        processOverReplicatedBlock(fileBlocks[idx], replication, null, null);
    }
    return true;
  }
    
  long getPreferredBlockSize(String filename) throws IOException {
    if (isPermissionEnabled) {
      checkTraverse(filename);
    }
    return dir.getPreferredBlockSize(filename);
  }
    
  /**
   * Check whether the replication parameter is within the range
   * determined by system configuration.
   */
  private void verifyReplication(String src, 
                                 short replication, 
                                 String clientName 
                                 ) throws IOException {
    String text = "file " + src 
      + ((clientName != null) ? " on client " + clientName : "")
      + ".\n"
      + "Requested replication " + replication;

    if (replication > maxReplication)
      throw new IOException(text + " exceeds maximum " + maxReplication);
      
    if (replication < minReplication)
      throw new IOException( 
                            text + " is less than the required minimum " + minReplication);
  }

  /**
   * Create a new file entry in the namespace.
   * 
   * @see ClientProtocol#create(String, FsPermission, String, boolean, short, long)
   * 
   * @throws IOException if file name is invalid
   *         {@link FSDirectory#isValidToCreate(String)}.
   */
  void startFile(String src, PermissionStatus permissions,
                 String holder, String clientMachine,
                 boolean overwrite, short replication, long blockSize
                ) throws IOException {
    startFileInternal(src, permissions, holder, clientMachine, overwrite,
                      replication, blockSize);
    getEditLog().logSync();
    if (auditLog.isInfoEnabled()) {
      final FileStatus stat = dir.getFileInfo(src);
      logAuditEvent(UserGroupInformation.getCurrentUGI(),
                    Server.getRemoteIp(),
                    "create", src, null, stat);
    }
  }

  private synchronized void startFileInternal(String src,
                                              PermissionStatus permissions,
                                              String holder, 
                                              String clientMachine, 
                                              boolean overwrite,
                                              short replication,
                                              long blockSize
                                              ) throws IOException {
    NameNode.stateChangeLog.debug("DIR* NameSystem.startFile: file "
                                  +src+" for "+holder+" at "+clientMachine);
    if (isInSafeMode())
      throw new SafeModeException("Cannot create file" + src, safeMode);
    if (!isValidName(src)) {
      throw new IOException("Invalid file name: " + src);
    }
    if (isPermissionEnabled) {
      if (overwrite && dir.exists(src)) {
        checkPathAccess(src, FsAction.WRITE);
      }
      else {
        checkAncestorAccess(src, FsAction.WRITE);
      }
    }

    try {
      INode myFile = dir.getFileINode(src);
      if (myFile != null && myFile.isUnderConstruction()) {
        INodeFileUnderConstruction pendingFile = (INodeFileUnderConstruction) myFile;
        //
        // If the file is under construction , then it must be in our
        // leases. Find the appropriate lease record.
        //
        Lease lease = leaseManager.getLease(new StringBytesWritable(holder));
        //
        // We found the lease for this file. And surprisingly the original
        // holder is trying to recreate this file. This should never occur.
        //
        if (lease != null) {
          throw new AlreadyBeingCreatedException(
                                                 "failed to create file " + src + " for " + holder +
                                                 " on client " + clientMachine + 
                                                 " because current leaseholder is trying to recreate file.");
        }
        //
        // Find the original holder.
        //
        lease = leaseManager.getLease(pendingFile.clientName);
        if (lease == null) {
          throw new AlreadyBeingCreatedException(
                                                 "failed to create file " + src + " for " + holder +
                                                 " on client " + clientMachine + 
                                                 " because pendingCreates is non-null but no leases found.");
        }
        //
        // If the original holder has not renewed in the last SOFTLIMIT 
        // period, then start lease recovery.
        //
        if (lease.expiredSoftLimit()) {
          LOG.info("startFile: recover lease " + lease + ", src=" + src);
          internalReleaseLease(lease, src);
        }
        throw new AlreadyBeingCreatedException("failed to create file " + src + " for " + holder +
                                               " on client " + clientMachine + 
                                               ", because this file is already being created by " +
                                               pendingFile.getClientName() + 
                                               " on " + pendingFile.getClientMachine());
      }

      try {
        verifyReplication(src, replication, clientMachine);
      } catch(IOException e) {
        throw new IOException("failed to create "+e.getMessage());
      }
      if (!dir.isValidToCreate(src)) {
        if (overwrite) {
          delete(src, true);
        } else {
          throw new IOException("failed to create file " + src 
                                +" on client " + clientMachine
                                +" either because the filename is invalid or the file exists");
        }
      }

      DatanodeDescriptor clientNode = 
        host2DataNodeMap.getDatanodeByHost(clientMachine);

      //
      // Now we can add the name to the filesystem. This file has no
      // blocks associated with it.
      //
      checkFsObjectLimit();

      // increment global generation stamp
      long genstamp = nextGenerationStamp();
      INodeFileUnderConstruction newNode = dir.addFile(src, permissions,
          replication, blockSize, holder, clientMachine, clientNode, genstamp);
      if (newNode == null) {
        throw new IOException("DIR* NameSystem.startFile: " +
                              "Unable to add file to namespace.");
      }
      leaseManager.addLease(newNode.clientName, src);
    } catch (IOException ie) {
      NameNode.stateChangeLog.warn("DIR* NameSystem.startFile: "
                                   +ie.getMessage());
      throw ie;
    }

    if (NameNode.stateChangeLog.isDebugEnabled()) {
      NameNode.stateChangeLog.debug("DIR* NameSystem.startFile: "
                                  +"add "+src+" to namespace for "+holder);
    }
  }

  /** append is not yet ready.  This method is for testing. */
  void appendFileInternal(String src, String holder, String clientMachine
      ) throws IOException {
    if (NameNode.stateChangeLog.isDebugEnabled()) {
      NameNode.stateChangeLog.debug("DIR* NameSystem.appendFile: file "
          +src+" for "+holder+" at "+clientMachine);
    }
    if (isInSafeMode())
      throw new SafeModeException("Cannot append file" + src, safeMode);
    if (!isValidName(src)) {
      throw new IOException("Invalid file name: " + src);
    }
    if (isPermissionEnabled) {
      checkPathAccess(src, FsAction.WRITE);
    }

    try {
      INodeFile f = dir.getFileINode(src);
      //assume f != null && !f.isUnderConstruction() && lease does not exist
      //TODO: remove the assumption 

      DatanodeDescriptor clientNode = host2DataNodeMap.getDatanodeByHost(
          clientMachine);
      INodeFileUnderConstruction newnode = f.toINodeFileUnderConstruction(
          holder, clientMachine, clientNode);

      dir.replaceNode(src, f, newnode);
      leaseManager.addLease(newnode.clientName, src);

    } catch (IOException ie) {
      NameNode.stateChangeLog.warn("DIR* NameSystem.appendFile: ", ie);
      throw ie;
    }

    if (NameNode.stateChangeLog.isDebugEnabled()) {
      NameNode.stateChangeLog.debug("DIR* NameSystem.appendFile: "
          +"add "+src+" to namespace for "+holder);
    }
  }

  /**
   * The client would like to obtain an additional block for the indicated
   * filename (which is being written-to).  Return an array that consists
   * of the block, plus a set of machines.  The first on this list should
   * be where the client writes data.  Subsequent items in the list must
   * be provided in the connection to the first datanode.
   *
   * Make sure the previous blocks have been reported by datanodes and
   * are replicated.  Will return an empty 2-elt array if we want the
   * client to "try again later".
   */
  public LocatedBlock getAdditionalBlock(String src, 
                                         String clientName
                                         ) throws IOException {
    long fileLength, blockSize;
    int replication;
    DatanodeDescriptor clientNode = null;
    Block newBlock = null;

    NameNode.stateChangeLog.debug("BLOCK* NameSystem.getAdditionalBlock: file "
                                  +src+" for "+clientName);

    synchronized (this) {
      if (isInSafeMode()) {
        throw new SafeModeException("Cannot add block to " + src, safeMode);
      }

      // have we exceeded the configured limit of fs objects.
      checkFsObjectLimit();

      INodeFileUnderConstruction pendingFile  = checkLease(src, clientName);

      //
      // If we fail this, bad things happen!
      //
      if (!checkFileProgress(pendingFile, false)) {
        throw new NotReplicatedYetException("Not replicated yet:" + src);
      }
      fileLength = pendingFile.computeContentSummary().getLength();
      blockSize = pendingFile.getPreferredBlockSize();
      clientNode = pendingFile.getClientNode();
      replication = (int)pendingFile.getReplication();
    }

    // choose targets for the new block tobe allocated.
    DatanodeDescriptor targets[] = replicator.chooseTarget(replication,
                                                           clientNode,
                                                           null,
                                                           blockSize);
    if (targets.length < this.minReplication) {
      throw new IOException("File " + src + " could only be replicated to " +
                            targets.length + " nodes, instead of " +
                            minReplication);
    }

    // Allocate a new block and record it in the INode. 
    synchronized (this) {
      INodeFileUnderConstruction pendingFile  = checkLease(src, clientName);
      if (!checkFileProgress(pendingFile, false)) {
        throw new NotReplicatedYetException("Not replicated yet:" + src);
      }

      // allocate new block record block locations in INode.
      newBlock = allocateBlock(src, pendingFile);
      pendingFile.setTargets(targets);
      
      for (DatanodeDescriptor dn : targets) {
        dn.incBlocksScheduled();
      }      
    }
        
    // Create next block
    return new LocatedBlock(newBlock, targets, fileLength);
  }

  /**
   * The client would like to let go of the given block
   */
  public synchronized boolean abandonBlock(Block b, String src, String holder
      ) throws IOException {
    //
    // Remove the block from the pending creates list
    //
    NameNode.stateChangeLog.debug("BLOCK* NameSystem.abandonBlock: "
                                  +b+"of file "+src);
    INodeFileUnderConstruction file = checkLease(src, holder);
    dir.removeBlock(src, file, b);
    NameNode.stateChangeLog.debug("BLOCK* NameSystem.abandonBlock: "
                                    + b
                                    + " is removed from pendingCreates");
    return true;
  }
  
  // make sure that we still have the lease on this file
  private INodeFileUnderConstruction checkLease(String src, String holder
      ) throws IOException {
    INode file = dir.getFileINode(src);
    if (file == null) {
      Lease lease = leaseManager.getLease(new StringBytesWritable(holder));
      throw new LeaseExpiredException("No lease on " + src +
                                      " File does not exist. " +
                                      (lease != null ? lease.toString() :
                                       "Holder " + holder + 
                                       " does not have any open files."));
    }
    if (!file.isUnderConstruction()) {
      Lease lease = leaseManager.getLease(new StringBytesWritable(holder));
      throw new LeaseExpiredException("No lease on " + src + 
                                      " File is not open for writing. " +
                                      (lease != null ? lease.toString() :
                                       "Holder " + holder + 
                                       " does not have any open files."));
    }
    INodeFileUnderConstruction pendingFile = (INodeFileUnderConstruction)file;
    if (holder != null && !pendingFile.getClientName().equals(holder)) {
      throw new LeaseExpiredException("Lease mismatch on " + src + " owned by "
          + pendingFile.getClientName() + " but is accessed by " + holder);
    }
    return pendingFile;    
  }

  /**
   * The FSNamesystem will already know the blocks that make up the file.
   * Before we return, we make sure that all the file's blocks have 
   * been reported by datanodes and are replicated correctly.
   */
  public int completeFile(String src, String holder) throws IOException {
    int status = completeFileInternal(src, holder);
    getEditLog().logSync();
    return status;
  }

  private synchronized int completeFileInternal(String src, 
                                                String holder) throws IOException {
    NameNode.stateChangeLog.debug("DIR* NameSystem.completeFile: " + src + " for " + holder);
    if (isInSafeMode())
      throw new SafeModeException("Cannot complete file " + src, safeMode);
    INode iFile = dir.getFileINode(src);
    INodeFileUnderConstruction pendingFile = null;
    Block[] fileBlocks = null;

    if (iFile != null && iFile.isUnderConstruction()) {
      pendingFile = (INodeFileUnderConstruction) iFile;
      fileBlocks =  dir.getFileBlocks(src);
    }
    if (fileBlocks == null ) {    
      NameNode.stateChangeLog.warn("DIR* NameSystem.completeFile: "
                                   + "failed to complete " + src
                                   + " because dir.getFileBlocks() is null " + 
                                   " and pendingFile is " + 
                                   ((pendingFile == null) ? "null" : 
                                     ("from " + pendingFile.getClientMachine()))
                                  );                      
      return OPERATION_FAILED;
    } else if (!checkFileProgress(pendingFile, true)) {
      return STILL_WAITING;
    }

    finalizeINodeFileUnderConstruction(src, pendingFile);

    if (NameNode.stateChangeLog.isDebugEnabled()) {
      NameNode.stateChangeLog.debug("DIR* NameSystem.completeFile: " + src
                                  + " blocklist persisted");
    }
    return COMPLETE_SUCCESS;
  }

  /** 
   * Check all blocks of a file. If any blocks are lower than their intended
   * replication factor, then insert them into neededReplication
   */
  private void checkReplicationFactor(INodeFile file) {
    int numExpectedReplicas = file.getReplication();
    Block[] pendingBlocks = file.getBlocks();
    int nrBlocks = pendingBlocks.length;
    for (int i = 0; i < nrBlocks; i++) {
      // filter out containingNodes that are marked for decommission.
      NumberReplicas number = countNodes(pendingBlocks[i]);
      if (number.liveReplicas() < numExpectedReplicas) {
        neededReplications.add(pendingBlocks[i], 
                               number.liveReplicas(), 
                               number.decommissionedReplicas,
                               numExpectedReplicas);
      }
    }
  }

  static Random randBlockId = new Random();
    
  /**
   * Allocate a block at the given pending filename
   */
  private Block allocateBlock(String src, INode file) throws IOException {
    Block b = null;
    do {
      b = new Block(FSNamesystem.randBlockId.nextLong(), 0, 
                    getGenerationStamp());
    } while (isValidBlock(b));
    b = dir.addBlock(src, file, b);
    NameNode.stateChangeLog.info("BLOCK* NameSystem.allocateBlock: "
                                 +src+ ". "+b);
    return b;
  }

  /**
   * Check that the indicated file's blocks are present and
   * replicated.  If not, return false. If checkall is true, then check
   * all blocks, otherwise check only penultimate block.
   */
  synchronized boolean checkFileProgress(INodeFile v, boolean checkall) {
    if (checkall) {
      //
      // check all blocks of the file.
      //
      for (Block block: v.getBlocks()) {
        if (blocksMap.numNodes(block) < this.minReplication) {
          return false;
        }
      }
    } else {
      //
      // check the penultimate block of this file
      //
      Block b = v.getPenultimateBlock();
      if (b != null) {
        if (blocksMap.numNodes(b) < this.minReplication) {
          return false;
        }
      }
    }
    return true;
  }

  /**
   * Remove a datanode from the invalidatesSet
   * @param n datanode
   */
  private void removeFromInvalidates(DatanodeInfo n) {
    recentInvalidateSets.remove(n.getStorageID());
  }

  /**
   * Adds block to list of blocks which will be invalidated on 
   * specified datanode and log the move
   * @param b block
   * @param n datanode
   */
  private void addToInvalidates(Block b, DatanodeInfo n) {
    addToInvalidatesNoLog(b, n);
    NameNode.stateChangeLog.info("BLOCK* NameSystem.addToInvalidates: "
        + b.getBlockName() + " is added to invalidSet of " + n.getName());
  }

  /**
   * Adds block to list of blocks which will be invalidated on 
   * specified datanode
   * @param b block
   * @param n datanode
   */
  private void addToInvalidatesNoLog(Block b, DatanodeInfo n) {
    Collection<Block> invalidateSet = recentInvalidateSets.get(n.getStorageID());
    if (invalidateSet == null) {
      invalidateSet = new HashSet<Block>();
      recentInvalidateSets.put(n.getStorageID(), invalidateSet);
    }
    invalidateSet.add(b);
  }
  
  /**
   * Adds block to list of blocks which will be invalidated on 
   * all its datanodes.
   */
  private void addToInvalidates(Block b) {
    for (Iterator<DatanodeDescriptor> it = 
                                blocksMap.nodeIterator(b); it.hasNext();) {
      DatanodeDescriptor node = it.next();
      addToInvalidates(b, node);
    }
  }

  /**
   * dumps the contents of recentInvalidateSets
   */
  private synchronized void dumpRecentInvalidateSets(PrintWriter out) {
    int size = recentInvalidateSets.values().size();
    out.println("Metasave: Blocks waiting deletion from "+size+" datanodes.");
    if (size == 0) {
      return;
    }
    for(Map.Entry<String,Collection<Block>> entry : recentInvalidateSets.entrySet()) {
      Collection<Block> blocks = entry.getValue();
      if (blocks.size() > 0) {
        out.println(datanodeMap.get(entry.getKey()).getName() + blocks);
      }
    }
  }

  /**
   * Mark the block belonging to datanode as corrupt
   * @param blk Block to be marked as corrupt
   * @param datanode Datanode which holds the corrupt replica
   */
  public synchronized void markBlockAsCorrupt(Block blk, DatanodeInfo dn)
    throws IOException {
    DatanodeDescriptor node = getDatanode(dn);
    if (node == null) {
      throw new IOException("Cannot mark block" + blk.getBlockName() +
                            " as corrupt because datanode " + dn.getName() +
                            " does not exist. ");
    }
    
    if (!blocksMap.contains(blk, node)) {
      // Check if the replica is in the blockMap, if not 
      // ignore the request for now. This could happen when BlockScanner
      // thread of Datanode reports bad block before Block reports are sent
      // by the Datanode on startup
      NameNode.stateChangeLog.info("BLOCK NameSystem.markBlockAsCorrupt: " +
                                   "block " + blk + " could not be marked " +
                                   "as corrupt as it does not exists in " +
                                   "blocksMap");
    } else {
      INodeFile inode = blocksMap.getINode(blk);
      assert inode!=null : (blk + " in blocksMap must belongs to a file.");
      // Add this replica to corruptReplicas Map 
      corruptReplicas.addToCorruptReplicasMap(blk, node);
      if (countNodes(blk).liveReplicas()>inode.getReplication()) {
        // the block is over-replicated so invalidate the replicas immediately
        invalidateBlock(blk, node);
      } else {
        // add the block to neededReplication 
        updateNeededReplications(blk, -1, 0);
      }
    }
  }

  /**
   * Invalidates the given block on the given datanode.
   */
  public synchronized void invalidateBlock(Block blk, DatanodeInfo dn)
    throws IOException {
    NameNode.stateChangeLog.info("DIR* NameSystem.invalidateBlock: " 
                                 + blk + " on " 
                                 + dn.getName());
    DatanodeDescriptor node = getDatanode(dn);
    if (node == null) {
      throw new IOException("Cannot invalidate block " + blk +
                            " because datanode " + dn.getName() +
                            " does not exist.");
    }

    // Check how many copies we have of the block.  If we have at least one
    // copy on a live node, then we can delete it. 
    int count = countNodes(blk).liveReplicas();
    if (count > 1) {
      addToInvalidates(blk, dn);
      removeStoredBlock(blk, node);
      NameNode.stateChangeLog.debug("BLOCK* NameSystem.invalidateBlocks: "
                                   + blk + " on " 
                                   + dn.getName() + " listed for deletion.");
    } else {
      NameNode.stateChangeLog.info("BLOCK* NameSystem.invalidateBlocks: "
                                   + blk + " on " 
                                   + dn.getName() + " is the only copy and was not deleted.");
    }
  }

  ////////////////////////////////////////////////////////////////
  // Here's how to handle block-copy failure during client write:
  // -- As usual, the client's write should result in a streaming
  // backup write to a k-machine sequence.
  // -- If one of the backup machines fails, no worries.  Fail silently.
  // -- Before client is allowed to close and finalize file, make sure
  // that the blocks are backed up.  Namenode may have to issue specific backup
  // commands to make up for earlier datanode failures.  Once all copies
  // are made, edit namespace and return to client.
  ////////////////////////////////////////////////////////////////

  /** Change the indicated filename. */
  public boolean renameTo(String src, String dst) throws IOException {
    boolean status = renameToInternal(src, dst);
    getEditLog().logSync();
    if (status && auditLog.isInfoEnabled()) {
      final FileStatus stat = dir.getFileInfo(dst);
      logAuditEvent(UserGroupInformation.getCurrentUGI(),
                    Server.getRemoteIp(),
                    "rename", src, dst, stat);
    }
    return status;
  }

  private synchronized boolean renameToInternal(String src, String dst
      ) throws IOException {
    NameNode.stateChangeLog.debug("DIR* NameSystem.renameTo: " + src + " to " + dst);
    if (isInSafeMode())
      throw new SafeModeException("Cannot rename " + src, safeMode);
    if (!isValidName(dst)) {
      throw new IOException("Invalid name: " + dst);
    }

    if (isPermissionEnabled) {
      //We should not be doing this.  This is move() not renameTo().
      //but for now,
      String actualdst = dir.isDir(dst)?
          dst + Path.SEPARATOR + new Path(src).getName(): dst;
      checkParentAccess(src, FsAction.WRITE);
      checkAncestorAccess(actualdst, FsAction.WRITE);
    }

    DFSFileInfo dinfo = dir.getFileInfo(dst);
    if (dir.renameTo(src, dst)) {
      changeLease(src, dst, dinfo);     // update lease with new filename
      return true;
    }
    return false;
  }

  /**
   * Remove the indicated filename from namespace. If the filename 
   * is a directory (non empty) and recursive is set to false then throw exception.
   */
    public boolean delete(String src, boolean recursive) throws IOException {
      if ((!recursive) && (!dir.isDirEmpty(src))) {
        throw new IOException(src + " is non empty");
      }
      boolean status = deleteInternal(src, true, true);
      getEditLog().logSync();
      if (status && auditLog.isInfoEnabled()) {
        logAuditEvent(UserGroupInformation.getCurrentUGI(),
                      Server.getRemoteIp(),
                      "delete", src, null, null);
      }
      return status;
    }
    
  /**
   * An internal delete function that does not enforce safe mode
   */
  boolean deleteInSafeMode(String src) throws IOException {
    boolean status = deleteInternal(src, false, false);
    getEditLog().logSync();
    return status;
  }
  /**
   * Remove the indicated filename from the namespace.  This may
   * invalidate some blocks that make up the file.
   */
  synchronized boolean deleteInternal(String src, 
      boolean enforceSafeMode, boolean enforcePermission) throws IOException {
    if (NameNode.stateChangeLog.isDebugEnabled()) {
      NameNode.stateChangeLog.debug("DIR* NameSystem.delete: " + src);
    }
    if (enforceSafeMode && isInSafeMode())
      throw new SafeModeException("Cannot delete " + src, safeMode);
    if (enforcePermission && isPermissionEnabled) {
      checkPermission(src, false, null, FsAction.WRITE, null, FsAction.ALL);
    }

    return dir.delete(src) != null;
  }

  void removePathAndBlocks(String src, List<Block> blocks) throws IOException {
    leaseManager.removeLeaseWithPrefixPath(src);
    for(Block b : blocks) {
      blocksMap.removeINode(b);
      corruptReplicas.removeFromCorruptReplicasMap(b);
      addToInvalidates(b);
    }
  }

  /** Get the file info for a specific file.
   * @param src The string representation of the path to the file
   * @throws IOException if permission to access file is denied by the system 
   * @return object containing information regarding the file
   *         or null if file not found
   */
  DFSFileInfo getFileInfo(String src) throws IOException {
    if (isPermissionEnabled) {
      checkTraverse(src);
    }
    return dir.getFileInfo(src);
  }

  /**
   * Whether the pathname is valid.  Currently prohibits relative paths, 
   * and names which contain a ":" or "/" 
   */
  static boolean isValidName(String src) {
      
    // Path must be absolute.
    if (!src.startsWith(Path.SEPARATOR)) {
      return false;
    }
      
    // Check for ".." "." ":" "/"
    StringTokenizer tokens = new StringTokenizer(src, Path.SEPARATOR);
    while(tokens.hasMoreTokens()) {
      String element = tokens.nextToken();
      if (element.equals("..") || 
          element.equals(".")  ||
          (element.indexOf(":") >= 0)  ||
          (element.indexOf("/") >= 0)) {
        return false;
      }
    }
    return true;
  }
  /**
   * Create all the necessary directories
   */
  public boolean mkdirs(String src, PermissionStatus permissions
      ) throws IOException {
    boolean status = mkdirsInternal(src, permissions);
    getEditLog().logSync();
    if (status && auditLog.isInfoEnabled()) {
      final FileStatus stat = dir.getFileInfo(src);
      logAuditEvent(UserGroupInformation.getCurrentUGI(),
                    Server.getRemoteIp(),
                    "mkdirs", src, null, stat);
    }
    return status;
  }
    
  /**
   * Create all the necessary directories
   */
  private synchronized boolean mkdirsInternal(String src,
      PermissionStatus permissions) throws IOException {
    NameNode.stateChangeLog.debug("DIR* NameSystem.mkdirs: " + src);
    if (isPermissionEnabled) {
      checkTraverse(src);
    }
    if (dir.isDir(src)) {
      // all the users of mkdirs() are used to expect 'true' even if
      // a new directory is not created.
      return true;
    }
    if (isInSafeMode())
      throw new SafeModeException("Cannot create directory " + src, safeMode);
    if (!isValidName(src)) {
      throw new IOException("Invalid directory name: " + src);
    }
    if (isPermissionEnabled) {
      checkAncestorAccess(src, FsAction.WRITE);
    }

    // validate that we have enough inodes. This is, at best, a 
    // heuristic because the mkdirs() operation migth need to 
    // create multiple inodes.
    checkFsObjectLimit();

    if (!dir.mkdirs(src, permissions, false, now())) {
      throw new IOException("Invalid directory name: " + src);
    }
    return true;
  }

  ContentSummary getContentSummary(String src) throws IOException {
    if (isPermissionEnabled) {
      checkPermission(src, false, null, null, null, FsAction.READ_EXECUTE);
    }
    return dir.getContentSummary(src);
  }

  /**
   * Set the quota for a directory.
   * @param path The string representation of the path to the directory
   * @param quota The limit of the number of names in or below the directory
   * @throws IOException if the path is not a directory or the number of
   * existing names in or below the directory is greater than the given quota
   */
  void setQuota(String path, long quota) throws IOException {
    if (isPermissionEnabled) {
      checkSuperuserPrivilege();
    }
    
    dir.setQuota(path, quota);
    getEditLog().logSync();
  }
  
  /**
   * Remove the quota for a directory
   * @param path The string representation of the path to the directory
   * @throws IOException if the path is not a directory
   */
  void clearQuota(String path) throws IOException {
    if (isPermissionEnabled) {
      checkSuperuserPrivilege();
    }
    
    dir.clearQuota(path);
    getEditLog().logSync();
  }
  
  /** Persist all metadata about this file.
   * @param src The string representation of the path
   * @param clientName The string representation of the client
   * @throws IOException if path does not exist
   */
  void fsync(String src, String clientName) throws IOException {

    NameNode.stateChangeLog.info("BLOCK* NameSystem.fsync: file "
                                  + src + " for " + clientName);
    synchronized (this) {
      if (isInSafeMode()) {
        throw new SafeModeException("Cannot fsync file " + src, safeMode);
      }
      INodeFileUnderConstruction pendingFile  = checkLease(src, clientName);
      dir.persistBlocks(src, pendingFile);
    }
  }

  /**
   * Move a file that is being written to be immutable.
   * @param src The filename
   * @param holder The datanode that was creating the file
   */
  void internalReleaseLease(Lease lease, String src) throws IOException {
    LOG.info("Recovering lease=" + lease + ", src=" + src);

    INodeFile iFile = dir.getFileINode(src);
    if (iFile == null) {
      final String message = "DIR* NameSystem.internalReleaseCreate: "
        + "attempt to release a create lock on "
        + src + " file does not exist.";
      NameNode.stateChangeLog.warn(message);
      throw new IOException(message);
    }
    if (!iFile.isUnderConstruction()) {
      final String message = "DIR* NameSystem.internalReleaseCreate: "
        + "attempt to release a create lock on "
        + src + " but file is already closed.";
      NameNode.stateChangeLog.warn(message);
      throw new IOException(message);
    }

    INodeFileUnderConstruction pendingFile = (INodeFileUnderConstruction) iFile;

    // Initialize lease recovery for pendingFile. If there are no blocks 
    // associated with this file, then reap lease immediately. Otherwise 
    // renew the lease and trigger lease recovery.
    if (pendingFile.getTargets() == null ||
        pendingFile.getTargets().length == 0) {
      if (pendingFile.getBlocks().length == 0) {
        finalizeINodeFileUnderConstruction(src, pendingFile);
        NameNode.stateChangeLog.warn("BLOCK*"
          + " internalReleaseLease: No blocks found, lease removed.");
        return;
      }
      // setup the Inode.targets for the last block from the blocksMap
      //
      Block[] blocks = pendingFile.getBlocks();
      Block last = blocks[blocks.length-1];
      DatanodeDescriptor[] targets = 
         new DatanodeDescriptor[blocksMap.numNodes(last)];
      Iterator<DatanodeDescriptor> it = blocksMap.nodeIterator(last);
      for (int i = 0; it != null && it.hasNext(); i++) {
        targets[i] = it.next();
      }
      pendingFile.setTargets(targets);
    }
    // start lease recovery of the last block for this file.
    pendingFile.assignPrimaryDatanode();
    leaseManager.renewLease(lease);
  }

  private void finalizeINodeFileUnderConstruction(String src,
      INodeFileUnderConstruction pendingFile) throws IOException {
    leaseManager.removeLease(pendingFile.clientName, src);

    // The file is no longer pending.
    // Create permanent INode, update blockmap
    INodeFile newFile = pendingFile.convertToInodeFile();
    dir.replaceNode(src, pendingFile, newFile);

    // close file and persist block allocations for this file
    dir.closeFile(src, newFile);

    checkReplicationFactor(newFile);
  }

  synchronized void commitBlockSynchronization(Block lastblock,
      long newgenerationstamp, long newlength,
      boolean closeFile, boolean deleteblock, DatanodeID[] newtargets
      ) throws IOException {
    LOG.info("commitBlockSynchronization(lastblock=" + lastblock
          + ", newgenerationstamp=" + newgenerationstamp
          + ", newlength=" + newlength
          + ", newtargets=" + Arrays.asList(newtargets)
          + ", closeFile=" + closeFile
          + ", deleteBlock=" + deleteblock
          + ")");
    final BlockInfo oldblockinfo = blocksMap.getStoredBlock(lastblock);
    if (oldblockinfo == null) {
      throw new IOException("Block (=" + lastblock + ") not found");
    }
    INodeFile iFile = oldblockinfo.getINode();
    if (!iFile.isUnderConstruction()) {
      throw new IOException("Unexpected block (=" + lastblock
          + ") since the file (=" + iFile.getLocalName()
          + ") is not under construction");
    }
    INodeFileUnderConstruction pendingFile = (INodeFileUnderConstruction)iFile;

    // Remove old block from blocks map. This always have to be done
    // because the generation stamp of this block is changing.
    blocksMap.removeBlock(oldblockinfo);

    if (deleteblock) {
      pendingFile.removeBlock(lastblock);
    }
    else {
      // update last block, construct newblockinfo and add it to the blocks map
      lastblock.set(lastblock.blkid, newlength, newgenerationstamp);
      final BlockInfo newblockinfo = blocksMap.addINode(lastblock, pendingFile);

      // find the DatanodeDescriptor objects
      // There should be no locations in the blocksMap till now because the
      // file is underConstruction
      DatanodeDescriptor[] descriptors = null;
      if (newtargets.length > 0) {
        descriptors = new DatanodeDescriptor[newtargets.length];
        for(int i = 0; i < newtargets.length; i++) {
          descriptors[i] = getDatanode(newtargets[i]);
        }
      }
      if (closeFile) {
        // the file is getting closed. Insert block locations into blocksMap.
        // Otherwise fsck will report these blocks as MISSING, especially if the
        // blocksReceived from Datanodes take a long time to arrive.
        for (int i = 0; i < descriptors.length; i++) {
          descriptors[i].addBlock(newblockinfo);
        }
        pendingFile.setLastBlock(newblockinfo, null);
      } else {
        // add locations into the INodeUnderConstruction
        pendingFile.setLastBlock(newblockinfo, descriptors);
      }
    }

    // Return if this commit does not want to close the file
    String src = leaseManager.findPath(pendingFile);
    if (!closeFile) {
      LOG.info("commitBlockSynchronization(" + lastblock + ") successful");
      return;
    }
    
    //remove lease, close file
    finalizeINodeFileUnderConstruction(src, pendingFile);
    getEditLog().logSync();
    LOG.info("commitBlockSynchronization(newblock=" + lastblock
          + ", file=" + src
          + ", newgenerationstamp=" + newgenerationstamp
          + ", newlength=" + newlength
          + ", newtargets=" + Arrays.asList(newtargets) + ") successful");
  }


  /**
   * Renew the lease(s) held by the given client
   */
  void renewLease(String holder) throws IOException {
    if (isInSafeMode())
      throw new SafeModeException("Cannot renew lease for " + holder, safeMode);
    leaseManager.renewLease(holder);
  }

  /**
   * Get a listing of all files at 'src'.  The Object[] array
   * exists so we can return file attributes (soon to be implemented)
   */
  public DFSFileInfo[] getListing(String src) throws IOException {
    if (isPermissionEnabled) {
      if (dir.isDir(src)) {
        checkPathAccess(src, FsAction.READ_EXECUTE);
      }
      else {
        checkTraverse(src);
      }
    }
    if (auditLog.isInfoEnabled()) {
      logAuditEvent(UserGroupInformation.getCurrentUGI(),
                    Server.getRemoteIp(),
                    "listStatus", src, null, null);
    }
    return dir.getListing(src);
  }

  public void addToResolutionQueue(DatanodeDescriptor d) {
    while (!resolutionQueue.add(d)) {
      LOG.warn("Couldn't add to the Resolution queue now. Will " +
               "try again");
      try {
        Thread.sleep(2000);
      } catch (InterruptedException ie) {}
    }
  }
  
  private class ResolutionMonitor implements Runnable {
    public void run() {
      try {
        while (fsRunning) {
          try {
            List <DatanodeDescriptor> datanodes = 
              new ArrayList<DatanodeDescriptor>(resolutionQueue.size());
            // Block if the queue is empty
            datanodes.add(resolutionQueue.take());
            resolutionQueue.drainTo(datanodes);
            List<String> dnHosts = new ArrayList<String>(datanodes.size());
            for (DatanodeDescriptor d : datanodes) {
              dnHosts.add(d.getName());
            }
            List<String> rName = dnsToSwitchMapping.resolve(dnHosts);
            if (rName == null) {
              LOG.error("The resolve call returned null! Using " + 
                  NetworkTopology.DEFAULT_RACK + " for some hosts");
              rName = new ArrayList<String>(dnHosts.size());
              for (int i = 0; i < dnHosts.size(); i++) {
                rName.add(NetworkTopology.DEFAULT_RACK);
              }
            }
            int i = 0;
            for (String m : rName) {
              DatanodeDescriptor d = datanodes.get(i++); 
              d.setNetworkLocation(m);
              clusterMap.add(d);
            }
          } catch (InterruptedException e) {
              FSNamesystem.LOG.debug("ResolutionMonitor thread received " +
                                     "InterruptException. " + e);
          }
        }
      } catch (Exception e) {
        FSNamesystem.LOG.error(StringUtils.stringifyException(e));
      }
    }
  }
  
  /**
   * Has the block report of the datanode represented by nodeReg been processed
   * yet.
   * @param nodeReg
   * @return true or false
   */
  synchronized boolean blockReportProcessed(DatanodeRegistration nodeReg)
  throws IOException {
    return getDatanode(nodeReg).getBlockReportProcessed();
  }
  
  /**
   * Has the datanode been resolved to a switch/rack
   */
  synchronized boolean isResolved(DatanodeRegistration dnReg) {
    try {
      return !getDatanode(dnReg).getNetworkLocation()
            .equals(NetworkTopology.UNRESOLVED);
    } catch (IOException ie) {
      return false;
    }
  }
    
  /////////////////////////////////////////////////////////
  //
  // These methods are called by datanodes
  //
  /////////////////////////////////////////////////////////
  /**
   * Register Datanode.
   * <p>
   * The purpose of registration is to identify whether the new datanode
   * serves a new data storage, and will report new data block copies,
   * which the namenode was not aware of; or the datanode is a replacement
   * node for the data storage that was previously served by a different
   * or the same (in terms of host:port) datanode.
   * The data storages are distinguished by their storageIDs. When a new
   * data storage is reported the namenode issues a new unique storageID.
   * <p>
   * Finally, the namenode returns its namespaceID as the registrationID
   * for the datanodes. 
   * namespaceID is a persistent attribute of the name space.
   * The registrationID is checked every time the datanode is communicating
   * with the namenode. 
   * Datanodes with inappropriate registrationID are rejected.
   * If the namenode stops, and then restarts it can restore its 
   * namespaceID and will continue serving the datanodes that has previously
   * registered with the namenode without restarting the whole cluster.
   * 
   * @see DataNode#register()
   */
  public synchronized void registerDatanode(DatanodeRegistration nodeReg
                                            ) throws IOException {

    if (!verifyNodeRegistration(nodeReg)) {
      throw new DisallowedDatanodeException(nodeReg);
    }

    String dnAddress = Server.getRemoteAddress();
    if (dnAddress == null) {
      // Mostly called inside an RPC.
      // But if not, use address passed by the data-node.
      dnAddress = nodeReg.getHost();
    }      

    String hostName = nodeReg.getHost();
      
    // update the datanode's name with ip:port
    DatanodeID dnReg = new DatanodeID(dnAddress + ":" + nodeReg.getPort(),
                                      nodeReg.getStorageID(),
                                      nodeReg.getInfoPort(),
                                      nodeReg.getIpcPort());
    nodeReg.updateRegInfo(dnReg);
      
    NameNode.stateChangeLog.info(
                                 "BLOCK* NameSystem.registerDatanode: "
                                 + "node registration from " + nodeReg.getName()
                                 + " storage " + nodeReg.getStorageID());

    DatanodeDescriptor nodeS = datanodeMap.get(nodeReg.getStorageID());
    DatanodeDescriptor nodeN = host2DataNodeMap.getDatanodeByName(nodeReg.getName());
      
    if (nodeN != null && nodeN != nodeS) {
      NameNode.LOG.info("BLOCK* NameSystem.registerDatanode: "
                        + "node from name: " + nodeN.getName());
      // nodeN previously served a different data storage, 
      // which is not served by anybody anymore.
      removeDatanode(nodeN);
      // physically remove node from datanodeMap
      wipeDatanode(nodeN);
      nodeN = null;
    }

    if (nodeS != null) {
      if (nodeN == nodeS) {
        // The same datanode has been just restarted to serve the same data 
        // storage. We do not need to remove old data blocks, the delta will
        // be calculated on the next block report from the datanode
        NameNode.stateChangeLog.debug("BLOCK* NameSystem.registerDatanode: "
                                      + "node restarted.");
      } else {
        // nodeS is found
        /* The registering datanode is a replacement node for the existing 
          data storage, which from now on will be served by a new node.
          If this message repeats, both nodes might have same storageID 
          by (insanely rare) random chance. User needs to restart one of the
          nodes with its data cleared (or user can just remove the StorageID
          value in "VERSION" file under the data directory of the datanode,
          but this is might not work if VERSION file format has changed 
       */        
        NameNode.stateChangeLog.info( "BLOCK* NameSystem.registerDatanode: "
                                      + "node " + nodeS.getName()
                                      + " is replaced by " + nodeReg.getName() + 
                                      " with the same storageID " +
                                      nodeReg.getStorageID());
      }
      // update cluster map
      clusterMap.remove(nodeS);
      nodeS.updateRegInfo(nodeReg);
      nodeS.setHostName(hostName);
      nodeS.setNetworkLocation(NetworkTopology.UNRESOLVED);
      nodeS.setBlockReportProcessed(false);
      addToResolutionQueue(nodeS);
        
      // also treat the registration message as a heartbeat
      synchronized(heartbeats) {
        if( !heartbeats.contains(nodeS)) {
          heartbeats.add(nodeS);
          //update its timestamp
          nodeS.updateHeartbeat(0L, 0L, 0L, 0);
          nodeS.isAlive = true;
        }
      }
      return;
    } 

    // this is a new datanode serving a new data storage
    if (nodeReg.getStorageID().equals("")) {
      // this data storage has never been registered
      // it is either empty or was created by pre-storageID version of DFS
      nodeReg.storageID = newStorageID();
      NameNode.stateChangeLog.debug(
                                    "BLOCK* NameSystem.registerDatanode: "
                                    + "new storageID " + nodeReg.getStorageID() + " assigned.");
    }
    // register new datanode
    DatanodeDescriptor nodeDescr 
      = new DatanodeDescriptor(nodeReg, NetworkTopology.UNRESOLVED, hostName);
    unprotectedAddDatanode(nodeDescr);
    addToResolutionQueue(nodeDescr);
      
    // also treat the registration message as a heartbeat
    synchronized(heartbeats) {
      heartbeats.add(nodeDescr);
      nodeDescr.isAlive = true;
      // no need to update its timestamp
      // because its is done when the descriptor is created
    }
    return;
  }
    
  /**
   * Get registrationID for datanodes based on the namespaceID.
   * 
   * @see #registerDatanode(DatanodeRegistration)
   * @see FSImage#newNamespaceID()
   * @return registration ID
   */
  public String getRegistrationID() {
    return Storage.getRegistrationID(dir.fsImage);
  }
    
  /**
   * Generate new storage ID.
   * 
   * @return unique storage ID
   * 
   * Note: that collisions are still possible if somebody will try 
   * to bring in a data storage from a different cluster.
   */
  private String newStorageID() {
    String newID = null;
    while(newID == null) {
      newID = "DS" + Integer.toString(r.nextInt());
      if (datanodeMap.get(newID) != null)
        newID = null;
    }
    return newID;
  }
    
  private boolean isDatanodeDead(DatanodeDescriptor node) {
    return (node.getLastUpdate() <
            (now() - heartbeatExpireInterval));
  }
    
  private void setDatanodeDead(DatanodeDescriptor node) throws IOException {
    node.setLastUpdate(0);
  }

  /**
   * The given node has reported in.  This method should:
   * 1) Record the heartbeat, so the datanode isn't timed out
   * 2) Adjust usage stats for future block allocation
   * 
   * If a substantial amount of time passed since the last datanode 
   * heartbeat then request an immediate block report.  
   * 
   * @return a datanode command 
   * @throws IOException
   */
  DatanodeCommand handleHeartbeat(DatanodeRegistration nodeReg,
      long capacity, long dfsUsed, long remaining,
      int xceiverCount, int xmitsInProgress) throws IOException {
    DatanodeCommand cmd = null;
    synchronized (heartbeats) {
      synchronized (datanodeMap) {
        DatanodeDescriptor nodeinfo = null;
        try {
          nodeinfo = getDatanode(nodeReg);
        } catch(UnregisteredDatanodeException e) {
          return DatanodeCommand.REGISTER;
        }
          
        // Check if this datanode should actually be shutdown instead. 
        if (nodeinfo != null && shouldNodeShutdown(nodeinfo)) {
          setDatanodeDead(nodeinfo);
          throw new DisallowedDatanodeException(nodeinfo);
        }

        if (nodeinfo == null || !nodeinfo.isAlive) {
          return DatanodeCommand.REGISTER;
        }

        updateStats(nodeinfo, false);
        nodeinfo.updateHeartbeat(capacity, dfsUsed, remaining, xceiverCount);
        updateStats(nodeinfo, true);
        
        //check lease recovery
        if (cmd == null) {
          cmd = nodeinfo.getLeaseRecoveryCommand(Integer.MAX_VALUE);
        }
        //check pending replication
        if (cmd == null) {
          cmd = nodeinfo.getReplicationCommand(
              maxReplicationStreams - xmitsInProgress);
        }
        //check block invalidation
        if (cmd == null) {
          cmd = nodeinfo.getInvalidateBlocks(blockInvalidateLimit);
        }
      }
    }

    // If the datanode has (just) been resolved and we haven't ever processed 
    // a block report from it yet, ask for one now.
    if (!blockReportProcessed(nodeReg)) {
      // If we never processed a block report from this datanode, we shouldn't
      // have any work for that as well
      assert(cmd == null);
      if (isResolved(nodeReg)) {
        return DatanodeCommand.BLOCKREPORT;
      }
    }
    //check distributed upgrade
    if (cmd == null) {
      cmd = getDistributedUpgradeCommand();
    }
    return cmd;
  }

  private void updateStats(DatanodeDescriptor node, boolean isAdded) {
    //
    // The statistics are protected by the heartbeat lock
    //
    assert(Thread.holdsLock(heartbeats));
    if (isAdded) {
      capacityTotal += node.getCapacity();
      capacityUsed += node.getDfsUsed();
      capacityRemaining += node.getRemaining();
      totalLoad += node.getXceiverCount();
    } else {
      capacityTotal -= node.getCapacity();
      capacityUsed -= node.getDfsUsed();
      capacityRemaining -= node.getRemaining();
      totalLoad -= node.getXceiverCount();
    }
  }
  /**
   * Periodically calls heartbeatCheck().
   */
  class HeartbeatMonitor implements Runnable {
    /**
     */
    public void run() {
      while (fsRunning) {
        try {
          heartbeatCheck();
        } catch (Exception e) {
          FSNamesystem.LOG.error(StringUtils.stringifyException(e));
        }
        try {
          Thread.sleep(heartbeatRecheckInterval);
        } catch (InterruptedException ie) {
        }
      }
    }
  }

  /**
   * Periodically calls computeReplicationWork().
   */
  class ReplicationMonitor implements Runnable {
    static final int INVALIDATE_WORK_PCT_PER_ITERATION = 32;
    static final float REPLICATION_WORK_MULTIPLIER_PER_ITERATION = 2;
    public void run() {
      while (fsRunning) {
        try {
          computeDatanodeWork();
          processPendingReplications();
          Thread.sleep(replicationRecheckInterval);
        } catch (InterruptedException ie) {
          LOG.warn("ReplicationMonitor thread received InterruptedException." + ie);
          break;
        } catch (IOException ie) {
          LOG.warn("ReplicationMonitor thread received exception. " + ie);
        } catch (Throwable t) {
          LOG.warn("ReplicationMonitor thread received Runtime exception. " + t);
          Runtime.getRuntime().exit(-1);
        }
      }
    }
  }

  /////////////////////////////////////////////////////////
  //
  // These methods are called by the Namenode system, to see
  // if there is any work for registered datanodes.
  //
  /////////////////////////////////////////////////////////
  /**
   * Compute block replication and block invalidation work 
   * that can be scheduled on data-nodes.
   * The datanode will be informed of this work at the next heartbeat.
   * 
   * @return number of blocks scheduled for replication or removal.
   */
  int computeDatanodeWork() throws IOException {
    int workFound = 0;
    int blocksToProcess = 0;
    int nodesToProcess = 0;
    // blocks should not be replicated or removed if safe mode is on
    if (isInSafeMode())
      return workFound;
    synchronized(heartbeats) {
      blocksToProcess = (int)(heartbeats.size() 
          * ReplicationMonitor.REPLICATION_WORK_MULTIPLIER_PER_ITERATION);
      nodesToProcess = (int)Math.ceil((double)heartbeats.size() 
          * ReplicationMonitor.INVALIDATE_WORK_PCT_PER_ITERATION / 100);
    }

    workFound = computeReplicationWork(blocksToProcess); 
    
    // Update FSNamesystemMetrics counters
    pendingReplicationBlocksCount = pendingReplications.size();
    underReplicatedBlocksCount = neededReplications.size();
    scheduledReplicationBlocksCount = workFound;
    
    if(workFound == 0)
      workFound = computeInvalidateWork(nodesToProcess);
    return workFound;
  }

  private int computeInvalidateWork(int nodesToProcess) {
    int blockCnt = 0;
    for(int nodeCnt = 0; nodeCnt < nodesToProcess; nodeCnt++ ) {
      int work = invalidateWorkForOneNode();
      if(work == 0)
        break;
      blockCnt += work;
    }
    return blockCnt;
  }

  /**
   * Scan blocks in {@link #neededReplications} and assign replication
   * work to data-nodes they belong to. 
   * 
   * The number of process blocks equals either twice the number of live 
   * data-nodes or the number of under-replicated blocks whichever is less.
   * 
   * @return number of blocks scheduled for replication during this iteration.
   */
  private synchronized int computeReplicationWork(
                                  int blocksToProcess) throws IOException {
    int scheduledReplicationCount = 0;

    synchronized(neededReplications) {
      // # of blocks to process equals either twice the number of live 
      // data-nodes or the number of under-replicated blocks whichever is less
      blocksToProcess = Math.min(blocksToProcess, neededReplications.size());
      if(blocksToProcess == 0)
        return scheduledReplicationCount;

      // Go through all blocks that need replications.
      // Select source and target nodes for replication.
      Iterator<Block> neededReplicationsIterator = neededReplications.iterator();
      // skip to the first unprocessed block, which is at replIndex 
      for(int i=0; i < replIndex && neededReplicationsIterator.hasNext(); i++) {
        neededReplicationsIterator.next();
      }
      // process blocks
      for(int blkCnt = 0; blkCnt < blocksToProcess; blkCnt++, replIndex++) {
        if( ! neededReplicationsIterator.hasNext()) {
          // start from the beginning
          replIndex = 0;
          blocksToProcess = Math.min(blocksToProcess, neededReplications.size());
          if(blkCnt >= blocksToProcess)
            break;
          neededReplicationsIterator = neededReplications.iterator();
          assert neededReplicationsIterator.hasNext() : 
                                  "neededReplications should not be empty.";
        }

        Block block = neededReplicationsIterator.next();

        // block should belong to a file
        INodeFile fileINode = blocksMap.getINode(block);
        if(fileINode == null) { // abandoned block 
          neededReplicationsIterator.remove(); // remove from neededReplications
          replIndex--;
          continue;
        }
        int requiredReplication = fileINode.getReplication(); 

        // get a source data-node
        List<DatanodeDescriptor> containingNodes =
                                          new ArrayList<DatanodeDescriptor>();
        NumberReplicas numReplicas = new NumberReplicas();
        DatanodeDescriptor srcNode = 
          chooseSourceDatanode(block, containingNodes, numReplicas);
        if(srcNode == null) // block can not be replicated from any node
          continue;

        // do not schedule more if enough replicas is already pending
        int numEffectiveReplicas = numReplicas.liveReplicas() +
                                pendingReplications.getNumReplicas(block);
        if(numEffectiveReplicas >= requiredReplication) {
          neededReplicationsIterator.remove(); // remove from neededReplications
          replIndex--;
          NameNode.stateChangeLog.info("BLOCK* "
              + "Removing block " + block
              + " from neededReplications as it has enough replicas.");
          continue;
        }

        // choose replication targets
        int maxTargets = 
          maxReplicationStreams - srcNode.getNumberOfBlocksToBeReplicated();
        assert maxTargets > 0 : "Datanode " + srcNode.getName() 
              + " should have not been selected as a source for replication.";
        DatanodeDescriptor targets[] = replicator.chooseTarget(
            Math.min(requiredReplication - numEffectiveReplicas, maxTargets),
            srcNode, containingNodes, null, block.getNumBytes());
        if(targets.length == 0)
          continue;
        // Add block to the to be replicated list
        srcNode.addBlockToBeReplicated(block, targets);
        scheduledReplicationCount++;

        for (DatanodeDescriptor dn : targets) {
          dn.incBlocksScheduled();
        }
        
        // Move the block-replication into a "pending" state.
        // The reason we use 'pending' is so we can retry
        // replications that fail after an appropriate amount of time.
        if(numEffectiveReplicas + targets.length >= requiredReplication) {
          neededReplicationsIterator.remove(); // remove from neededReplications
          replIndex--;
          pendingReplications.add(block, targets.length);
          NameNode.stateChangeLog.debug(
              "BLOCK* block " + block
              + " is moved from neededReplications to pendingReplications");
        }
        if (NameNode.stateChangeLog.isInfoEnabled()) {
          StringBuffer targetList = new StringBuffer("datanode(s)");
          for (int k = 0; k < targets.length; k++) {
            targetList.append(' ');
            targetList.append(targets[k].getName());
          }
          NameNode.stateChangeLog.info(
                    "BLOCK* ask "
                    + srcNode.getName() + " to replicate "
                    + block + " to " + targetList);
          NameNode.stateChangeLog.debug(
                    "BLOCK* neededReplications = " + neededReplications.size()
                    + " pendingReplications = " + pendingReplications.size());
        }
      }
    }
    return scheduledReplicationCount;
  }

  /**
   * Parse the data-nodes the block belongs to and choose one,
   * which will be the replication source.
   * 
   * We prefer nodes that are in DECOMMISSION_INPROGRESS state to other nodes
   * since the former do not have write traffic and hence are less busy.
   * We do not use already decommissioned nodes as a source.
   * Otherwise we choose a random node among those that did not reach their 
   * replication limit.
   * 
   * In addition form a list of all nodes containing the block
   * and calculate its replication numbers.
   */
  private DatanodeDescriptor chooseSourceDatanode(
                                    Block block,
                                    List<DatanodeDescriptor> containingNodes,
                                    NumberReplicas numReplicas) {
    containingNodes.clear();
    DatanodeDescriptor srcNode = null;
    int live = 0;
    int decommissioned = 0;
    int corrupt = 0;
    int excess = 0;
    Iterator<DatanodeDescriptor> it = blocksMap.nodeIterator(block);
    Collection<DatanodeDescriptor> nodesCorrupt = corruptReplicas.getNodes(block);
    while(it.hasNext()) {
      DatanodeDescriptor node = it.next();
      Collection<Block> excessBlocks = 
        excessReplicateMap.get(node.getStorageID());
      if ((nodesCorrupt != null) && (nodesCorrupt.contains(node)))
        corrupt++;
      else if (node.isDecommissionInProgress() || node.isDecommissioned())
        decommissioned++;
      else if (excessBlocks != null && excessBlocks.contains(block)) {
        excess++;
      } else {
        live++;
      }
      containingNodes.add(node);
      // Check if this replica is corrupt
      // If so, do not select the node as src node
      if ((nodesCorrupt != null) && nodesCorrupt.contains(node))
        continue;
      if(node.getNumberOfBlocksToBeReplicated() >= maxReplicationStreams)
        continue; // already reached replication limit
      // the block must not be scheduled for removal on srcNode
      if(excessBlocks != null && excessBlocks.contains(block))
        continue;
      // never use already decommissioned nodes
      if(node.isDecommissioned())
        continue;
      // we prefer nodes that are in DECOMMISSION_INPROGRESS state
      if(node.isDecommissionInProgress() || srcNode == null) {
        srcNode = node;
        continue;
      }
      if(srcNode.isDecommissionInProgress())
        continue;
      // switch to a different node randomly
      // this to prevent from deterministically selecting the same node even
      // if the node failed to replicate the block on previous iterations
      if(r.nextBoolean())
        srcNode = node;
    }
    if(numReplicas != null)
      numReplicas.initialize(live, decommissioned, corrupt, excess);
    return srcNode;
  }

  /**
   * Get blocks to invalidate for the first node 
   * in {@link #recentInvalidateSets}.
   * 
   * @return number of blocks scheduled for removal during this iteration.
   */
  private synchronized int invalidateWorkForOneNode() {
    // blocks should not be replicated or removed if safe mode is on
    if (isInSafeMode())
      return 0;
    if(recentInvalidateSets.isEmpty())
      return 0;
    // get blocks to invalidate for the first node
    String firstNodeId = recentInvalidateSets.keySet().iterator().next();
    assert firstNodeId != null;
    DatanodeDescriptor dn = datanodeMap.get(firstNodeId);
    Collection<Block> invalidateSet = recentInvalidateSets.remove(firstNodeId);
 
    if(invalidateSet == null || dn == null)
      return 0;

    ArrayList<Block> blocksToInvalidate = 
      new ArrayList<Block>(blockInvalidateLimit);

    // # blocks that can be sent in one message is limited
    Iterator<Block> it = invalidateSet.iterator();
    for(int blkCount = 0; blkCount < blockInvalidateLimit && it.hasNext();
                                                                blkCount++) {
      blocksToInvalidate.add(it.next());
      it.remove();
    }

    // If we could not send everything in this message, reinsert this item
    // into the collection.
    if(it.hasNext())
      recentInvalidateSets.put(firstNodeId, invalidateSet);

    dn.addBlocksToBeInvalidated(blocksToInvalidate);

    if(NameNode.stateChangeLog.isInfoEnabled()) {
      StringBuffer blockList = new StringBuffer();
      for(Block blk : blocksToInvalidate) {
        blockList.append(' ');
        blockList.append(blk);
      }
      NameNode.stateChangeLog.info("BLOCK* ask "
          + dn.getName() + " to delete " + blockList);
    }
    return blocksToInvalidate.size();
  }

  void setNodeReplicationLimit(int limit) {
    this.maxReplicationStreams = limit;
  }

  /**
   * If there were any replication requests that timed out, reap them
   * and put them back into the neededReplication queue
   */
  void processPendingReplications() {
    Block[] timedOutItems = pendingReplications.getTimedOutBlocks();
    if (timedOutItems != null) {
      synchronized (this) {
        for (int i = 0; i < timedOutItems.length; i++) {
          NumberReplicas num = countNodes(timedOutItems[i]);
          neededReplications.add(timedOutItems[i], 
                                 num.liveReplicas(),
                                 num.decommissionedReplicas(),
                                 getReplication(timedOutItems[i]));
        }
      }
      /* If we know the the target datanodes where the replication timedout,
       * we could invoke decBlocksScheduled() on it. Its ok for now.
       */
    }
  }

  /**
   * remove a datanode descriptor
   * @param nodeID datanode ID
   */
  synchronized public void removeDatanode(DatanodeID nodeID) 
    throws IOException {
    DatanodeDescriptor nodeInfo = getDatanode(nodeID);
    if (nodeInfo != null) {
      removeDatanode(nodeInfo);
    } else {
      NameNode.stateChangeLog.warn("BLOCK* NameSystem.removeDatanode: "
                                   + nodeID.getName() + " does not exist");
    }
  }
  
  /**
   * remove a datanode descriptor
   * @param nodeInfo datanode descriptor
   */
  private void removeDatanode(DatanodeDescriptor nodeInfo) {
    synchronized (heartbeats) {
      if (nodeInfo.isAlive) {
        updateStats(nodeInfo, false);
        heartbeats.remove(nodeInfo);
        nodeInfo.isAlive = false;
      }
    }

    for (Iterator<Block> it = nodeInfo.getBlockIterator(); it.hasNext();) {
      removeStoredBlock(it.next(), nodeInfo);
    }
    unprotectedRemoveDatanode(nodeInfo);
    clusterMap.remove(nodeInfo);
  }

  void unprotectedRemoveDatanode(DatanodeDescriptor nodeDescr) {
    nodeDescr.resetBlocks();
    removeFromInvalidates(nodeDescr);
    NameNode.stateChangeLog.debug(
                                  "BLOCK* NameSystem.unprotectedRemoveDatanode: "
                                  + nodeDescr.getName() + " is out of service now.");
  }
    
  void unprotectedAddDatanode(DatanodeDescriptor nodeDescr) {
    /* To keep host2DataNodeMap consistent with datanodeMap,
       remove  from host2DataNodeMap the datanodeDescriptor removed
       from datanodeMap before adding nodeDescr to host2DataNodeMap.
    */
    host2DataNodeMap.remove(
                            datanodeMap.put(nodeDescr.getStorageID(), nodeDescr));
    host2DataNodeMap.add(nodeDescr);
      
    NameNode.stateChangeLog.debug(
                                  "BLOCK* NameSystem.unprotectedAddDatanode: "
                                  + "node " + nodeDescr.getName() + " is added to datanodeMap.");
  }

  /**
   * Physically remove node from datanodeMap.
   * 
   * @param nodeID node
   */
  void wipeDatanode(DatanodeID nodeID) throws IOException {
    String key = nodeID.getStorageID();
    host2DataNodeMap.remove(datanodeMap.remove(key));
    NameNode.stateChangeLog.debug(
                                  "BLOCK* NameSystem.wipeDatanode: "
                                  + nodeID.getName() + " storage " + key 
                                  + " is removed from datanodeMap.");
  }

  FSImage getFSImage() {
    return dir.fsImage;
  }

  FSEditLog getEditLog() {
    return getFSImage().getEditLog();
  }

  /**
   * Check if there are any expired heartbeats, and if so,
   * whether any blocks have to be re-replicated.
   * While removing dead datanodes, make sure that only one datanode is marked
   * dead at a time within the synchronized section. Otherwise, a cascading
   * effect causes more datanodes to be declared dead.
   */
  void heartbeatCheck() {
    boolean allAlive = false;
    while (!allAlive) {
      boolean foundDead = false;
      DatanodeID nodeID = null;

      // locate the first dead node.
      synchronized(heartbeats) {
        for (Iterator<DatanodeDescriptor> it = heartbeats.iterator();
             it.hasNext();) {
          DatanodeDescriptor nodeInfo = it.next();
          if (isDatanodeDead(nodeInfo)) {
            foundDead = true;
            nodeID = nodeInfo;
            break;
          }
        }
      }

      // acquire the fsnamesystem lock, and then remove the dead node.
      if (foundDead) {
        synchronized (this) {
          synchronized(heartbeats) {
            synchronized (datanodeMap) {
              DatanodeDescriptor nodeInfo = null;
              try {
                nodeInfo = getDatanode(nodeID);
              } catch (IOException e) {
                nodeInfo = null;
              }
              if (nodeInfo != null && isDatanodeDead(nodeInfo)) {
                NameNode.stateChangeLog.info("BLOCK* NameSystem.heartbeatCheck: "
                                             + "lost heartbeat from " + nodeInfo.getName());
                removeDatanode(nodeInfo);
              }
            }
          }
        }
      }
      allAlive = !foundDead;
    }
  }
    
  /**
   * The given node is reporting all its blocks.  Use this info to 
   * update the (machine-->blocklist) and (block-->machinelist) tables.
   */
  public synchronized void processReport(DatanodeID nodeID, 
                                         BlockListAsLongs newReport
                                        ) throws IOException {
    long startTime = now();
    if (NameNode.stateChangeLog.isDebugEnabled()) {
      NameNode.stateChangeLog.debug("BLOCK* NameSystem.processReport: "
                             + "from " + nodeID.getName()+" " + 
                             newReport.getNumberOfBlocks()+" blocks");
    }
    DatanodeDescriptor node = getDatanode(nodeID);
    if (node == null) {
      throw new IOException("ProcessReport from unregisterted node: "
                            + nodeID.getName());
    }

    // Check if this datanode should actually be shutdown instead.
    if (shouldNodeShutdown(node)) {
      setDatanodeDead(node);
      throw new DisallowedDatanodeException(node);
    }
    
    if (node.getNetworkLocation().equals(NetworkTopology.UNRESOLVED)) {
      LOG.info("Ignoring block report from " + nodeID.getName() + 
          " because rack location for this datanode is still to be resolved."); 
      return; //drop the block report if the dn hasn't been resolved
    }

    node.setBlockReportProcessed(true);
    //
    // Modify the (block-->datanode) map, according to the difference
    // between the old and new block report.
    //
    Collection<Block> toAdd = new LinkedList<Block>();
    Collection<Block> toRemove = new LinkedList<Block>();
    Collection<Block> toInvalidate = new LinkedList<Block>();
    node.reportDiff(blocksMap, newReport, toAdd, toRemove, toInvalidate);
        
    for (Block b : toRemove) {
      removeStoredBlock(b, node);
    }
    for (Block b : toAdd) {
      addStoredBlock(b, node, null);
    }
    for (Block b : toInvalidate) {
      NameNode.stateChangeLog.info("BLOCK* NameSystem.processReport: block " 
          + b + " on " + node.getName() + " size " + b.getNumBytes()
          + " does not belong to any file.");
      addToInvalidates(b, node);
    }
    NameNode.getNameNodeMetrics().blockReport.inc((int) (now() - startTime));
  }

  /**
   * Modify (block-->datanode) map.  Remove block from set of 
   * needed replications if this takes care of the problem.
   * @return the block that is stored in blockMap.
   */
  synchronized Block addStoredBlock(Block block, 
                                    DatanodeDescriptor node,
                                    DatanodeDescriptor delNodeHint) {
    BlockInfo storedBlock = blocksMap.getStoredBlock(block);
    if(storedBlock == null || storedBlock.getINode() == null) {
      // If this block does not belong to anyfile, then we are done.
      NameNode.stateChangeLog.info("BLOCK* NameSystem.addStoredBlock: "
                                   + "addStoredBlock request received for " 
                                   + block + " on " + node.getName()
                                   + " size " + block.getNumBytes()
                                   + " But it does not belong to any file.");
      // we could add this block to invalidate set of this datanode. 
      // it will happen in next block report otherwise.
      return block;      
    }
     
    // add block to the data-node
    boolean added = node.addBlock(storedBlock);
    
    assert storedBlock != null : "Block must be stored by now";

    if (block != storedBlock) {
      if (block.getNumBytes() >= 0) {
        long cursize = storedBlock.getNumBytes();
        if (cursize == 0) {
          storedBlock.setNumBytes(block.getNumBytes());
        } else if (cursize != block.getNumBytes()) {
          LOG.warn("Inconsistent size for block " + block + 
                   " reported from " + node.getName() + 
                   " current size is " + cursize +
                   " reported size is " + block.getNumBytes());
          try {
            if (cursize > block.getNumBytes()) {
              // new replica is smaller in size than existing block.
              // Mark the new replica as corrupt.
              LOG.warn("Mark new replica " + block + " from " + node.getName() + 
                  "as corrupt because its length is shorter than existing ones");
              markBlockAsCorrupt(block, node);
            } else {
              // new replica is larger in size than existing block.
              // Mark pre-existing replicas as corrupt.
              int numNodes = blocksMap.numNodes(block);
              int count = 0;
              DatanodeDescriptor nodes[] = new DatanodeDescriptor[numNodes];
              Iterator<DatanodeDescriptor> it = blocksMap.nodeIterator(block);
              for (; it != null && it.hasNext(); ) {
                DatanodeDescriptor dd = it.next();
                if (!dd.equals(node)) {
                  nodes[count++] = dd;
                }
              }
              for (int j = 0; j < count; j++) {
                LOG.warn("Mark existing replica " + block + " from " + node.getName() + 
                " as corrupt because its length is shorter than the new one");
                markBlockAsCorrupt(block, nodes[j]);
              }
              //
              // change the size of block in blocksMap
              //
              storedBlock = blocksMap.getStoredBlock(block); //extra look up!
              if (storedBlock == null) {
                LOG.warn("Block " + block + 
                   " reported from " + node.getName() + 
                   " does not exist in blockMap. Surprise! Surprise!");
              } else {
                storedBlock.setNumBytes(block.getNumBytes());
              }
            }
          } catch (IOException e) {
            LOG.warn("Error in deleting bad block " + block + e);
          }
        }
      }
      block = storedBlock;
    }
    assert storedBlock == block : "Block must be stored by now";
        
    int curReplicaDelta = 0;
        
    if (added) {
      curReplicaDelta = 1;
      // 
      // At startup time, because too many new blocks come in
      // they take up lots of space in the log file. 
      // So, we log only when namenode is out of safemode.
      //
      if (!isInSafeMode()) {
        NameNode.stateChangeLog.info("BLOCK* NameSystem.addStoredBlock: "
                                      +"blockMap updated: "+node.getName()+" is added to "+block+" size "+block.getNumBytes());
      }
    } else {
      NameNode.stateChangeLog.warn("BLOCK* NameSystem.addStoredBlock: "
                                   + "Redundant addStoredBlock request received for " 
                                   + block + " on " + node.getName()
                                   + " size " + block.getNumBytes());
    }

    // filter out containingNodes that are marked for decommission.
    NumberReplicas num = countNodes(storedBlock);
    int numLiveReplicas = num.liveReplicas();
    int numCurrentReplica = numLiveReplicas
      + pendingReplications.getNumReplicas(block);

    // check whether safe replication is reached for the block
    incrementSafeBlockCount(numCurrentReplica);
 
    //
    // if file is being actively written to, then do not check 
    // replication-factor here. It will be checked when the file is closed.
    //
    INodeFile fileINode = null;
    fileINode = storedBlock.getINode();
    if (fileINode.isUnderConstruction()) {
      return block;
    }

    // do not handle mis-replicated blocks during startup
    if(isInSafeMode())
      return block;

    // handle underReplication/overReplication
    short fileReplication = fileINode.getReplication();
    if (numCurrentReplica >= fileReplication) {
      neededReplications.remove(block, numCurrentReplica, 
                                num.decommissionedReplicas, fileReplication);
    } else {
      updateNeededReplications(block, curReplicaDelta, 0);
    }
    if (numCurrentReplica > fileReplication) {
      processOverReplicatedBlock(block, fileReplication, node, delNodeHint);
    }
    // If the file replication has reached desired value
    // we can remove any corrupt replicas the block may have
    int corruptReplicasCount = corruptReplicas.numCorruptReplicas(block); 
    int numCorruptNodes = num.corruptReplicas();
    if ( numCorruptNodes != corruptReplicasCount) {
      LOG.warn("Inconsistent number of corrupt replicas for " + 
          block + "blockMap has " + numCorruptNodes + 
          " but corrupt replicas map has " + corruptReplicasCount);
    }
    if ((corruptReplicasCount > 0) && (numLiveReplicas >= fileReplication)) 
      invalidateCorruptReplicas(block);
    return block;
  }

  /**
   * Invalidate corrupt replicas.
   * <p>
   * This will remove the replicas from the block's location list,
   * add them to {@link #recentInvalidateSets} so that they could be further
   * deleted from the respective data-nodes,
   * and remove the block from corruptReplicasMap.
   * <p>
   * This method should be called when the block has sufficient
   * number of live replicas.
   *
   * @param blk Block whose corrupt replicas need to be invalidated
   */
  void invalidateCorruptReplicas(Block blk) {
    Collection<DatanodeDescriptor> nodes = corruptReplicas.getNodes(blk);
    boolean gotException = false;
    if (nodes == null)
      return;
    for (Iterator<DatanodeDescriptor> it = nodes.iterator(); it.hasNext(); ) {
      DatanodeDescriptor node = it.next();
      try {
        invalidateBlock(blk, node);
      } catch (IOException e) {
        NameNode.stateChangeLog.info("NameNode.invalidateCorruptReplicas " +
                                      "error in deleting bad block " + blk +
                                      " on " + node + e);
        gotException = true;
      }
    }
    // Remove the block from corruptReplicasMap
    if (!gotException)
      corruptReplicas.removeFromCorruptReplicasMap(blk);
  }

  /**
   * For each block in the name-node verify whether it belongs to any file,
   * over or under replicated. Place it into the respective queue.
   */
  private synchronized void processMisReplicatedBlocks() {
    long nrInvalid = 0, nrOverReplicated = 0, nrUnderReplicated = 0;
    neededReplications.clear();
    for(BlocksMap.BlockInfo block : blocksMap.getBlocks()) {
      INodeFile fileINode = block.getINode();
      if(fileINode == null) {
        // block does not belong to any file
        nrInvalid++;
        addToInvalidates(block);
        continue;
      }
      // calculate current replication
      short expectedReplication = fileINode.getReplication();
      NumberReplicas num = countNodes(block);
      int numCurrentReplica = num.liveReplicas();
      // add to under-replicated queue if need to be
      if (neededReplications.add(block, 
                                 numCurrentReplica,
                                 num.decommissionedReplicas(),
                                 expectedReplication)) {
        nrUnderReplicated++;
      }

      if (numCurrentReplica > expectedReplication) {
        // over-replicated block
        nrOverReplicated++;
        processOverReplicatedBlock(block, expectedReplication, null, null);
      }
    }
    LOG.info("Total number of blocks = " + blocksMap.size());
    LOG.info("Number of invalid blocks = " + nrInvalid);
    LOG.info("Number of under-replicated blocks = " + nrUnderReplicated);
    LOG.info("Number of  over-replicated blocks = " + nrOverReplicated);
  }

  /**
   * Find how many of the containing nodes are "extra", if any.
   * If there are any extras, call chooseExcessReplicates() to
   * mark them in the excessReplicateMap.
   */
  private void processOverReplicatedBlock(Block block, short replication, 
      DatanodeDescriptor addedNode, DatanodeDescriptor delNodeHint) {
    if(addedNode == delNodeHint) {
      delNodeHint = null;
    }
    Collection<DatanodeDescriptor> nonExcess = new ArrayList<DatanodeDescriptor>();
    Collection<DatanodeDescriptor> corruptNodes = corruptReplicas.getNodes(block);
    for (Iterator<DatanodeDescriptor> it = blocksMap.nodeIterator(block); 
         it.hasNext();) {
      DatanodeDescriptor cur = it.next();
      Collection<Block> excessBlocks = excessReplicateMap.get(cur.getStorageID());
      if (excessBlocks == null || !excessBlocks.contains(block)) {
        if (!cur.isDecommissionInProgress() && !cur.isDecommissioned()) {
          // exclude corrupt replicas
          if (corruptNodes == null || !corruptNodes.contains(cur)) {
            nonExcess.add(cur);
          }
        }
      }
    }
    chooseExcessReplicates(nonExcess, block, replication, 
        addedNode, delNodeHint);    
  }

  /**
   * We want "replication" replicates for the block, but we now have too many.  
   * In this method, copy enough nodes from 'srcNodes' into 'dstNodes' such that:
   *
   * srcNodes.size() - dstNodes.size() == replication
   *
   * We pick node that make sure that replicas are spread across racks and
   * also try hard to pick one with least free space.
   * The algorithm is first to pick a node with least free space from nodes
   * that are on a rack holding more than one replicas of the block.
   * So removing such a replica won't remove a rack. 
   * If no such a node is available,
   * then pick a node with least free space
   */
  void chooseExcessReplicates(Collection<DatanodeDescriptor> nonExcess, 
                              Block b, short replication,
                              DatanodeDescriptor addedNode,
                              DatanodeDescriptor delNodeHint) {
    // first form a rack to datanodes map and
    HashMap<String, ArrayList<DatanodeDescriptor>> rackMap =
      new HashMap<String, ArrayList<DatanodeDescriptor>>();
    for (Iterator<DatanodeDescriptor> iter = nonExcess.iterator();
         iter.hasNext();) {
      DatanodeDescriptor node = iter.next();
      String rackName = node.getNetworkLocation();
      ArrayList<DatanodeDescriptor> datanodeList = rackMap.get(rackName);
      if(datanodeList==null) {
        datanodeList = new ArrayList<DatanodeDescriptor>();
      }
      datanodeList.add(node);
      rackMap.put(rackName, datanodeList);
    }
    
    // split nodes into two sets
    // priSet contains nodes on rack with more than one replica
    // remains contains the remaining nodes
    ArrayList<DatanodeDescriptor> priSet = new ArrayList<DatanodeDescriptor>();
    ArrayList<DatanodeDescriptor> remains = new ArrayList<DatanodeDescriptor>();
    for( Iterator<Entry<String, ArrayList<DatanodeDescriptor>>> iter = 
      rackMap.entrySet().iterator(); iter.hasNext(); ) {
      Entry<String, ArrayList<DatanodeDescriptor>> rackEntry = iter.next();
      ArrayList<DatanodeDescriptor> datanodeList = rackEntry.getValue(); 
      if( datanodeList.size() == 1 ) {
        remains.add(datanodeList.get(0));
      } else {
        priSet.addAll(datanodeList);
      }
    }
    
    // pick one node to delete that favors the delete hint
    // otherwise pick one with least space from priSet if it is not empty
    // otherwise one node with least space from remains
    boolean firstOne = true;
    while (nonExcess.size() - replication > 0) {
      DatanodeInfo cur = null;
      long minSpace = Long.MAX_VALUE;

      // check if we can del delNodeHint
      if (firstOne && delNodeHint !=null && nonExcess.contains(delNodeHint) &&
            (priSet.contains(delNodeHint) || (addedNode != null && !priSet.contains(addedNode))) ) {
          cur = delNodeHint;
      } else { // regular excessive replica removal
        Iterator<DatanodeDescriptor> iter = 
          priSet.isEmpty() ? remains.iterator() : priSet.iterator();
          while( iter.hasNext() ) {
            DatanodeDescriptor node = iter.next();
            long free = node.getRemaining();

            if (minSpace > free) {
              minSpace = free;
              cur = node;
            }
          }
      }

      firstOne = false;
      // adjust rackmap, priSet, and remains
      String rack = cur.getNetworkLocation();
      ArrayList<DatanodeDescriptor> datanodes = rackMap.get(rack);
      datanodes.remove(cur);
      if(datanodes.isEmpty()) {
        rackMap.remove(rack);
      }
      if( priSet.remove(cur) ) {
        if (datanodes.size() == 1) {
          priSet.remove(datanodes.get(0));
          remains.add(datanodes.get(0));
        }
      } else {
        remains.remove(cur);
      }

      nonExcess.remove(cur);

      Collection<Block> excessBlocks = excessReplicateMap.get(cur.getStorageID());
      if (excessBlocks == null) {
        excessBlocks = new TreeSet<Block>();
        excessReplicateMap.put(cur.getStorageID(), excessBlocks);
      }
      excessBlocks.add(b);
      NameNode.stateChangeLog.debug("BLOCK* NameSystem.chooseExcessReplicates: "
                                    +"("+cur.getName()+", "+b+") is added to excessReplicateMap");

      //
      // The 'excessblocks' tracks blocks until we get confirmation
      // that the datanode has deleted them; the only way we remove them
      // is when we get a "removeBlock" message.  
      //
      // The 'invalidate' list is used to inform the datanode the block 
      // should be deleted.  Items are removed from the invalidate list
      // upon giving instructions to the namenode.
      //
      addToInvalidatesNoLog(b, cur);
      NameNode.stateChangeLog.info("BLOCK* NameSystem.chooseExcessReplicates: "
                +"("+cur.getName()+", "+b+") is added to recentInvalidateSets");
    }
  }

  /**
   * Modify (block-->datanode) map.  Possibly generate 
   * replication tasks, if the removed block is still valid.
   */
  synchronized void removeStoredBlock(Block block, DatanodeDescriptor node) {
    NameNode.stateChangeLog.debug("BLOCK* NameSystem.removeStoredBlock: "
                                  +block + " from "+node.getName());
    if (!blocksMap.removeNode(block, node)) {
      NameNode.stateChangeLog.debug("BLOCK* NameSystem.removeStoredBlock: "
                                    +block+" has already been removed from node "+node);
      return;
    }
        
    //
    // It's possible that the block was removed because of a datanode
    // failure.  If the block is still valid, check if replication is
    // necessary.  In that case, put block on a possibly-will-
    // be-replicated list.
    //
    INode fileINode = blocksMap.getINode(block);
    if (fileINode != null) {
      decrementSafeBlockCount(block);
      updateNeededReplications(block, -1, 0);
    }

    //
    // We've removed a block from a node, so it's definitely no longer
    // in "excess" there.
    //
    Collection<Block> excessBlocks = excessReplicateMap.get(node.getStorageID());
    if (excessBlocks != null) {
      excessBlocks.remove(block);
      NameNode.stateChangeLog.debug("BLOCK* NameSystem.removeStoredBlock: "
                                    +block+" is removed from excessBlocks");
      if (excessBlocks.size() == 0) {
        excessReplicateMap.remove(node.getStorageID());
      }
    }
    
    // Remove the replica from corruptReplicas
    corruptReplicas.removeFromCorruptReplicasMap(block, node);
  }

  /**
   * The given node is reporting that it received a certain block.
   */
  public synchronized void blockReceived(DatanodeID nodeID,  
                                         Block block,
                                         String delHint
                                         ) throws IOException {
    DatanodeDescriptor node = getDatanode(nodeID);
    if (node == null) {
      NameNode.stateChangeLog.warn("BLOCK* NameSystem.blockReceived: "
                                   + block + " is received from an unrecorded node " 
                                   + nodeID.getName());
      throw new IllegalArgumentException(
                                         "Unexpected exception.  Got blockReceived message from node " 
                                         + block + ", but there is no info for it");
    }
        
    if (NameNode.stateChangeLog.isDebugEnabled()) {
      NameNode.stateChangeLog.debug("BLOCK* NameSystem.blockReceived: "
                                    +block+" is received from " + nodeID.getName());
    }

    // Check if this datanode should actually be shutdown instead.
    if (shouldNodeShutdown(node)) {
      setDatanodeDead(node);
      throw new DisallowedDatanodeException(node);
    }

    // decrement number of blocks scheduled to this datanode.
    node.decBlocksScheduled();
    
    // get the deletion hint node
    DatanodeDescriptor delHintNode = null;
    if(delHint!=null && delHint.length()!=0) {
      delHintNode = datanodeMap.get(delHint);
      if(delHintNode == null) {
        NameNode.stateChangeLog.warn("BLOCK* NameSystem.blockReceived: "
            + block
            + " is expected to be removed from an unrecorded node " 
            + delHint);
      }
    }

    //
    // Modify the blocks->datanode map and node's map.
    // 
    pendingReplications.remove(block);
    addStoredBlock(block, node, delHintNode );
  }

  long[] getStats() throws IOException {
    checkSuperuserPrivilege();
    synchronized(heartbeats) {
      return new long[]
            {getCapacityTotal(), getCapacityUsed(), getCapacityRemaining()};
    }
  }

  /**
   * Total raw bytes including non-dfs used space.
   */
  public long getCapacityTotal() {
    synchronized (heartbeats) {
      return this.capacityTotal;
    }
  }

  /**
   * Total used space by data nodes
   */
  public long getCapacityUsed() {
    synchronized(heartbeats){
      return this.capacityUsed;
    }
  }
  /**
   * Total non-used raw bytes.
   */
  public long getCapacityRemaining() {
    synchronized (heartbeats) {
      return this.capacityRemaining;
    }
  }

  /**
   * Total number of connections.
   */
  public int getTotalLoad() {
    synchronized (heartbeats) {
      return this.totalLoad;
    }
  }

  int getNumberOfDatanodes(DatanodeReportType type) {
    return getDatanodeListForReport(type).size(); 
  }

  private synchronized ArrayList<DatanodeDescriptor> getDatanodeListForReport(
                                                      DatanodeReportType type) {                  
    
    boolean listLiveNodes = type == DatanodeReportType.ALL ||
                            type == DatanodeReportType.LIVE;
    boolean listDeadNodes = type == DatanodeReportType.ALL ||
                            type == DatanodeReportType.DEAD;

    HashMap<String, String> mustList = new HashMap<String, String>();
    
    if (listDeadNodes) {
      //first load all the nodes listed in include and exclude files.
      for (Iterator<String> it = hostsReader.getHosts().iterator(); 
           it.hasNext();) {
        mustList.put(it.next(), "");
      }
      for (Iterator<String> it = hostsReader.getExcludedHosts().iterator(); 
           it.hasNext();) {
        mustList.put(it.next(), "");
      }
    }
   
    ArrayList<DatanodeDescriptor> nodes = null;
    
    synchronized (datanodeMap) {
      nodes = new ArrayList<DatanodeDescriptor>(datanodeMap.size() + 
                                                mustList.size());
      
      for(Iterator<DatanodeDescriptor> it = datanodeMap.values().iterator(); 
                                                               it.hasNext();) {
        DatanodeDescriptor dn = it.next();
        boolean isDead = isDatanodeDead(dn);
        if ( (isDead && listDeadNodes) || (!isDead && listLiveNodes) ) {
          nodes.add(dn);
        }
        //Remove any form of the this datanode in include/exclude lists.
        mustList.remove(dn.getName());
        mustList.remove(dn.getHost());
        mustList.remove(dn.getHostName());
      }
    }
    
    if (listDeadNodes) {
      for (Iterator<String> it = mustList.keySet().iterator(); it.hasNext();) {
        DatanodeDescriptor dn = 
            new DatanodeDescriptor(new DatanodeID(it.next()));
        dn.setLastUpdate(0);
        nodes.add(dn);
      }
    }
    
    return nodes;
  }

  public synchronized DatanodeInfo[] datanodeReport( DatanodeReportType type
      ) throws AccessControlException {
    checkSuperuserPrivilege();

    ArrayList<DatanodeDescriptor> results = getDatanodeListForReport(type);
    DatanodeInfo[] arr = new DatanodeInfo[results.size()];
    for (int i=0; i<arr.length; i++) {
      arr[i] = new DatanodeInfo(results.get(i));
    }
    return arr;
  }
    
  /**
   */
  public synchronized void DFSNodesStatus(ArrayList<DatanodeDescriptor> live, 
                                          ArrayList<DatanodeDescriptor> dead) {

    ArrayList<DatanodeDescriptor> results = 
                            getDatanodeListForReport(DatanodeReportType.ALL);    
    for(Iterator<DatanodeDescriptor> it = results.iterator(); it.hasNext();) {
      DatanodeDescriptor node = it.next();
      if (isDatanodeDead(node))
        dead.add(node);
      else
        live.add(node);
    }
  }

  /**
   * Prints information about all datanodes.
   */
  private synchronized void datanodeDump(PrintWriter out) {
    synchronized (datanodeMap) {
      out.println("Metasave: Number of datanodes: " + datanodeMap.size());
      for(Iterator<DatanodeDescriptor> it = datanodeMap.values().iterator(); it.hasNext();) {
        DatanodeDescriptor node = it.next();
        out.println(node.dumpDatanode());
      }
    }
  }

  /**
   * Start decommissioning the specified datanode. 
   */
  private void startDecommission (DatanodeDescriptor node) 
    throws IOException {

    if (!node.isDecommissionInProgress() && !node.isDecommissioned()) {
      LOG.info("Start Decommissioning node " + node.name);
      node.startDecommission();
      //
      // all the blocks that reside on this node have to be 
      // replicated.
      Iterator<Block> decommissionBlocks = node.getBlockIterator();
      while(decommissionBlocks.hasNext()) {
        Block block = decommissionBlocks.next();
        updateNeededReplications(block, -1, 0);
      }
    }
  }

  /**
   * Stop decommissioning the specified datanodes.
   */
  public void stopDecommission (DatanodeDescriptor node) 
    throws IOException {
    LOG.info("Stop Decommissioning node " + node.name);
    node.stopDecommission();
  }

  /** 
   */
  public DatanodeInfo getDataNodeInfo(String name) {
    return datanodeMap.get(name);
  }
  /** 
   */
  public String getDFSNameNodeMachine() {
    return localMachine;
  }
  /**
   */ 
  public int getDFSNameNodePort() {
    return port;
  }
  /**
   */
  public Date getStartTime() {
    return startTime;
  }
    
  short getMaxReplication()     { return (short)maxReplication; }
  short getMinReplication()     { return (short)minReplication; }
  short getDefaultReplication() { return (short)defaultReplication; }
    
  /**
   * A immutable object that stores the number of live replicas and
   * the number of decommissined Replicas.
   */
  static class NumberReplicas {
    private int liveReplicas;
    private int decommissionedReplicas;
    private int corruptReplicas;
    private int excessReplicas;

    NumberReplicas() {
      initialize(0, 0, 0, 0);
    }

    NumberReplicas(int live, int decommissioned, int corrupt, int excess) {
      initialize(live, decommissioned, corrupt, excess);
    }

    void initialize(int live, int decommissioned, int corrupt, int excess) {
      liveReplicas = live;
      decommissionedReplicas = decommissioned;
      corruptReplicas = corrupt;
      excessReplicas = excess;
    }

    int liveReplicas() {
      return liveReplicas;
    }
    int decommissionedReplicas() {
      return decommissionedReplicas;
    }
    int corruptReplicas() {
      return corruptReplicas;
    }
    int excessReplicas() {
      return excessReplicas;
    }
  } 

  /**
   * Counts the number of nodes in the given list into active and
   * decommissioned counters.
   */
  private NumberReplicas countNodes(Block b,
                                    Iterator<DatanodeDescriptor> nodeIter) {
    int count = 0;
    int live = 0;
    int corrupt = 0;
    int excess = 0;
    Collection<DatanodeDescriptor> nodesCorrupt = corruptReplicas.getNodes(b);
    while ( nodeIter.hasNext() ) {
      DatanodeDescriptor node = nodeIter.next();
      if ((nodesCorrupt != null) && (nodesCorrupt.contains(node))) {
        corrupt++;
      }
      else if (node.isDecommissionInProgress() || node.isDecommissioned()) {
        count++;
      }
      else  {
        Collection<Block> blocksExcess = 
          excessReplicateMap.get(node.getStorageID());
        if (blocksExcess != null && blocksExcess.contains(b)) {
          excess++;
        } else {
          live++;
        }
      }
    }
    return new NumberReplicas(live, count, corrupt, excess);
  }

  /**
   * Return the number of nodes that are live and decommissioned.
   */
  NumberReplicas countNodes(Block b) {
    return countNodes(b, blocksMap.nodeIterator(b));
  }

  /**
   * Return true if there are any blocks on this node that have not
   * yet reached their replication factor. Otherwise returns false.
   */
  private boolean isReplicationInProgress(DatanodeDescriptor srcNode) {
    boolean status = false;
    for(final Iterator<Block> i = srcNode.getBlockIterator(); i.hasNext(); ) {
      final Block block = i.next();
      INode fileINode = blocksMap.getINode(block);

      if (fileINode != null) {
        NumberReplicas num = countNodes(block);
        int curReplicas = num.liveReplicas();
        int curExpectedReplicas = getReplication(block);
        if (curExpectedReplicas > curReplicas) {
          status = true;
          if (!neededReplications.contains(block) &&
            pendingReplications.getNumReplicas(block) == 0) {
            //
            // These blocks have been reported from the datanode
            // after the startDecommission method has been executed. These
            // blocks were in flight when the decommission was started.
            //
            neededReplications.update(block, 
                                      curReplicas,
                                      num.decommissionedReplicas(),
                                      curExpectedReplicas,
                                      -1, 0);
          }
        }
      }
    }
    return status;
  }

  /**
   * Change, if appropriate, the admin state of a datanode to 
   * decommission completed. Return true if decommission is complete.
   */
  boolean checkDecommissionStateInternal(DatanodeDescriptor node) {
    //
    // Check to see if all blocks in this decommissioned
    // node has reached their target replication factor.
    //
    if (node.isDecommissionInProgress()) {
      if (!isReplicationInProgress(node)) {
        node.setDecommissioned();
        LOG.info("Decommission complete for node " + node.name);
      }
    }
    if (node.isDecommissioned()) {
      return true;
    }
    return false;
  }

  /** 
   * Keeps track of which datanodes are allowed to connect to the namenode.
   */
  private boolean inHostsList(DatanodeID node) {
    Set<String> hostsList = hostsReader.getHosts();
    return (hostsList.isEmpty() || 
            hostsList.contains(node.getName()) || 
            hostsList.contains(node.getHost()) ||
            ((node instanceof DatanodeInfo) && 
             hostsList.contains(((DatanodeInfo)node).getHostName())));
  }


  private boolean inExcludedHostsList(DatanodeID node) {
    Set<String> excludeList = hostsReader.getExcludedHosts();
    return (excludeList.contains(node.getName()) ||
            excludeList.contains(node.getHost()) ||
            ((node instanceof DatanodeInfo) && 
             excludeList.contains(((DatanodeInfo)node).getHostName())));
  }

  /**
   * Rereads the files to update the hosts and exclude lists.  It
   * checks if any of the hosts have changed states:
   * 1. Added to hosts  --> no further work needed here.
   * 2. Removed from hosts --> mark AdminState as decommissioned. 
   * 3. Added to exclude --> start decommission.
   * 4. Removed from exclude --> stop decommission.
   */
  void refreshNodes() throws IOException {
    checkSuperuserPrivilege();
    hostsReader.refresh();
    synchronized (this) {
      for (Iterator<DatanodeDescriptor> it = datanodeMap.values().iterator();
           it.hasNext();) {
        DatanodeDescriptor node = it.next();
        // Check if not include.
        if (!inHostsList(node)) {
          node.setDecommissioned();  // case 2.
        } else {
          if (inExcludedHostsList(node)) {
            if (!node.isDecommissionInProgress() && 
                !node.isDecommissioned()) {
              startDecommission(node);   // case 3.
            }
          } else {
            if (node.isDecommissionInProgress() || 
                node.isDecommissioned()) {
              stopDecommission(node);   // case 4.
            } 
          }
        }
      }
    } 
      
  }
    
  void finalizeUpgrade() throws IOException {
    checkSuperuserPrivilege();
    getFSImage().finalizeUpgrade();
  }

  /**
   * Checks if the node is not on the hosts list.  If it is not, then
   * it will be ignored.  If the node is in the hosts list, but is also 
   * on the exclude list, then it will be decommissioned.
   * Returns FALSE if node is rejected for registration. 
   * Returns TRUE if node is registered (including when it is on the 
   * exclude list and is being decommissioned). 
   */
  public synchronized boolean verifyNodeRegistration(DatanodeRegistration nodeReg) 
    throws IOException {
    if (!inHostsList(nodeReg)) {
      return false;    
    }
    if (inExcludedHostsList(nodeReg)) {
      DatanodeDescriptor node = getDatanode(nodeReg);
      if (node == null) {
        throw new IOException("verifyNodeRegistration: unknown datanode " +
                              nodeReg.getName());
      }
      if (!checkDecommissionStateInternal(node)) {
        startDecommission(node);
      }
    } 
    return true;
  }
    
  /**
   * Checks if the Admin state bit is DECOMMISSIONED.  If so, then 
   * we should shut it down. 
   * 
   * Returns true if the node should be shutdown.
   */
  private boolean shouldNodeShutdown(DatanodeDescriptor node) {
    return (node.isDecommissioned());
  }
    
  /**
   * Get data node by storage ID.
   * 
   * @param nodeID
   * @return DatanodeDescriptor or null if the node is not found.
   * @throws IOException
   */
  public DatanodeDescriptor getDatanode(DatanodeID nodeID) throws IOException {
    UnregisteredDatanodeException e = null;
    DatanodeDescriptor node = datanodeMap.get(nodeID.getStorageID());
    if (node == null) 
      return null;
    if (!node.getName().equals(nodeID.getName())) {
      e = new UnregisteredDatanodeException(nodeID, node);
      NameNode.stateChangeLog.fatal("BLOCK* NameSystem.getDatanode: "
                                    + e.getLocalizedMessage());
      throw e;
    }
    return node;
  }
    
  /** Stop at and return the datanode at index (used for content browsing)*/
  @Deprecated
  private DatanodeDescriptor getDatanodeByIndex(int index) {
    int i = 0;
    for (DatanodeDescriptor node : datanodeMap.values()) {
      if (i == index) {
        return node;
      }
      i++;
    }
    return null;
  }
    
  @Deprecated
  public String randomDataNode() {
    int size = datanodeMap.size();
    int index = 0;
    if (size != 0) {
      index = r.nextInt(size);
      for(int i=0; i<size; i++) {
        DatanodeDescriptor d = getDatanodeByIndex(index);
        if (d != null && !d.isDecommissioned() && !isDatanodeDead(d) &&
            !d.isDecommissionInProgress()) {
          return d.getHost() + ":" + d.getInfoPort();
        }
        index = (index + 1) % size;
      }
    }
    return null;
  }

  public DatanodeDescriptor getRandomDatanode() {
    return replicator.chooseTarget(1, null, null, 0)[0];
  }
    
  public int getNameNodeInfoPort() {
    return infoPort;
  }

  /**
   * SafeModeInfo contains information related to the safe mode.
   * <p>
   * An instance of {@link SafeModeInfo} is created when the name node
   * enters safe mode.
   * <p>
   * During name node startup {@link SafeModeInfo} counts the number of
   * <em>safe blocks</em>, those that have at least the minimal number of
   * replicas, and calculates the ratio of safe blocks to the total number
   * of blocks in the system, which is the size of
   * {@link FSNamesystem#blocksMap}. When the ratio reaches the
   * {@link #threshold} it starts the {@link SafeModeMonitor} daemon in order
   * to monitor whether the safe mode {@link #extension} is passed.
   * Then it leaves safe mode and destroys itself.
   * <p>
   * If safe mode is turned on manually then the number of safe blocks is
   * not tracked because the name node is not intended to leave safe mode
   * automatically in the case.
   *
   * @see ClientProtocol#setSafeMode(FSConstants.SafeModeAction)
   * @see SafeModeMonitor
   */
  class SafeModeInfo {
    // configuration fields
    /** Safe mode threshold condition %.*/
    private double threshold;
    /** Safe mode extension after the threshold. */
    private int extension;
    /** Min replication required by safe mode. */
    private int safeReplication;
      
    // internal fields
    /** Time when threshold was reached.
     * 
     * <br>-1 safe mode is off
     * <br> 0 safe mode is on, but threshold is not reached yet 
     */
    private long reached = -1;  
    /** Total number of blocks. */
    int blockTotal; 
    /** Number of safe blocks. */
    private int blockSafe;
    /** time of the last status printout */
    private long lastStatusReport = 0;
      
    /**
     * Creates SafeModeInfo when the name node enters
     * automatic safe mode at startup.
     *  
     * @param conf configuration
     */
    SafeModeInfo(Configuration conf) {
      this.threshold = conf.getFloat("dfs.safemode.threshold.pct", 0.95f);
      this.extension = conf.getInt("dfs.safemode.extension", 0);
      this.safeReplication = conf.getInt("dfs.replication.min", 1);
      this.blockTotal = 0; 
      this.blockSafe = 0;
    }

    /**
     * Creates SafeModeInfo when safe mode is entered manually.
     *
     * The {@link #threshold} is set to 1.5 so that it could never be reached.
     * {@link #blockTotal} is set to -1 to indicate that safe mode is manual.
     * 
     * @see SafeModeInfo
     */
    private SafeModeInfo() {
      this.threshold = 1.5f;  // this threshold can never be riched
      this.extension = Integer.MAX_VALUE;
      this.safeReplication = Short.MAX_VALUE + 1; // more than maxReplication
      this.blockTotal = -1;
      this.blockSafe = -1;
      this.reached = -1;
      enter();
      reportStatus("STATE* Safe mode is ON.", true);
    }
      
    /**
     * Check if safe mode is on.
     * @return true if in safe mode
     */
    synchronized boolean isOn() {
      try {
        assert isConsistent() : " SafeMode: Inconsistent filesystem state: "
          + "Total num of blocks, active blocks, or "
          + "total safe blocks don't match.";
      } catch(IOException e) {
        System.err.print(StringUtils.stringifyException(e));
      }
      return this.reached >= 0;
    }
      
    /**
     * Enter safe mode.
     */
    void enter() {
      this.reached = 0;
    }
      
    /**
     * Leave safe mode.
     * <p>
     * Switch to manual safe mode if distributed upgrade is required.<br>
     * Check for invalid, under- & over-replicated blocks in the end of startup.
     */
    synchronized void leave(boolean checkForUpgrades) {
      if(checkForUpgrades) {
        // verify whether a distributed upgrade needs to be started
        boolean needUpgrade = false;
        try {
          needUpgrade = startDistributedUpgradeIfNeeded();
        } catch(IOException e) {
          FSNamesystem.LOG.error(StringUtils.stringifyException(e));
        }
        if(needUpgrade) {
          // switch to manual safe mode
          safeMode = new SafeModeInfo();
          return;
        }
      }
      // verify blocks replications
      processMisReplicatedBlocks();
      long timeInSafemode = now() - systemStart;
      NameNode.stateChangeLog.info("STATE* Leaving safe mode after " 
                                    + timeInSafemode/1000 + " secs.");
      NameNode.getNameNodeMetrics().safeModeTime.set((int) timeInSafemode);
      
      if (reached >= 0) {
        NameNode.stateChangeLog.info("STATE* Safe mode is OFF."); 
      }
      reached = -1;
      safeMode = null;
      NameNode.stateChangeLog.info("STATE* Network topology has "
                                   +clusterMap.getNumOfRacks()+" racks and "
                                   +clusterMap.getNumOfLeaves()+ " datanodes");
      NameNode.stateChangeLog.info("STATE* UnderReplicatedBlocks has "
                                   +neededReplications.size()+" blocks");
    }
      
    /** 
     * Safe mode can be turned off iff 
     * the threshold is reached and 
     * the extension time have passed.
     * @return true if can leave or false otherwise.
     */
    synchronized boolean canLeave() {
      if (reached == 0)
        return false;
      if (now() - reached < extension) {
        reportStatus("STATE* Safe mode ON.", false);
        return false;
      }
      return !needEnter();
    }
      
    /** 
     * There is no need to enter safe mode 
     * if DFS is empty or {@link #threshold} == 0
     */
    boolean needEnter() {
      return getSafeBlockRatio() < threshold;
    }
      
    /**
     * Ratio of the number of safe blocks to the total number of blocks 
     * to be compared with the threshold.
     */
    private float getSafeBlockRatio() {
      return (blockTotal == 0 ? 1 : (float)blockSafe/blockTotal);
    }
      
    /**
     * Check and trigger safe mode if needed. 
     */
    private void checkMode() {
      if (needEnter()) {
        enter();
        reportStatus("STATE* Safe mode ON.", false);
        return;
      }
      // the threshold is reached
      if (!isOn() ||                           // safe mode is off
          extension <= 0 || threshold <= 0) {  // don't need to wait
        this.leave(true); // leave safe mode
        return;
      }
      if (reached > 0) {  // threshold has already been reached before
        reportStatus("STATE* Safe mode ON.", false);
        return;
      }
      // start monitor
      reached = now();
      smmthread = new Daemon(new SafeModeMonitor());
      smmthread.start();
      reportStatus("STATE* Safe mode extension entered.", true);
    }
      
    /**
     * Set total number of blocks.
     */
    synchronized void setBlockTotal(int total) {
      this.blockTotal = total; 
      checkMode();
    }
      
    /**
     * Increment number of safe blocks if current block has 
     * reached minimal replication.
     * @param replication current replication 
     */
    synchronized void incrementSafeBlockCount(short replication) {
      if ((int)replication == safeReplication)
        this.blockSafe++;
      checkMode();
    }
      
    /**
     * Decrement number of safe blocks if current block has 
     * fallen below minimal replication.
     * @param replication current replication 
     */
    synchronized void decrementSafeBlockCount(short replication) {
      if (replication == safeReplication-1)
        this.blockSafe--;
      checkMode();
    }

    /**
     * Check if safe mode was entered manually or at startup.
     */
    boolean isManual() {
      return extension == Integer.MAX_VALUE;
    }

    /**
     * Set manual safe mode.
     */
    void setManual() {
      extension = Integer.MAX_VALUE;
    }

    /**
     * A tip on how safe mode is to be turned off: manually or automatically.
     */
    String getTurnOffTip() {
      String leaveMsg = "Safe mode will be turned off automatically";
      if(reached < 0)
        return "Safe mode is OFF.";
      if(isManual()) {
        if(getDistributedUpgradeState())
          return leaveMsg + " upon completion of " + 
            "the distributed upgrade: upgrade progress = " + 
            getDistributedUpgradeStatus() + "%";
        leaveMsg = "Use \"hadoop dfs -safemode leave\" to turn safe mode off";
      }
      if(blockTotal < 0)
        return leaveMsg + ".";
      String safeBlockRatioMsg = 
        String.format("The ratio of reported blocks %.4f has " +
          (reached == 0 ? "not " : "") + "reached the threshold %.4f. ",
          getSafeBlockRatio(), threshold) + leaveMsg;
      if(reached == 0 || isManual())  // threshold is not reached or manual
        return safeBlockRatioMsg + ".";
      // extension period is in progress
      return safeBlockRatioMsg + " in " 
            + Math.abs(reached + extension - now())/1000 + " seconds.";
    }

    /**
     * Print status every 20 seconds.
     */
    private void reportStatus(String msg, boolean rightNow) {
      long curTime = now();
      if(!rightNow && (curTime - lastStatusReport < 20 * 1000))
        return;
      NameNode.stateChangeLog.info(msg + " \n" + getTurnOffTip());
      lastStatusReport = curTime;
    }

    /**
     * Returns printable state of the class.
     */
    public String toString() {
      String resText = "Current safe block ratio = " 
        + getSafeBlockRatio() 
        + ". Target threshold = " + threshold
        + ". Minimal replication = " + safeReplication + ".";
      if (reached > 0) 
        resText += " Threshold was reached " + new Date(reached) + ".";
      return resText;
    }
      
    /**
     * Checks consistency of the class state.
     * This is costly and currently called only in assert.
     */
    boolean isConsistent() throws IOException {
      if (blockTotal == -1 && blockSafe == -1) {
        return true; // manual safe mode
      }
      int activeBlocks = blocksMap.size();
      for(Iterator<Collection<Block>> it = 
            recentInvalidateSets.values().iterator(); it.hasNext();) {
        activeBlocks -= it.next().size();
      }
      return (blockTotal == activeBlocks) ||
        (blockSafe >= 0 && blockSafe <= blockTotal);
    }
  }
    
  /**
   * Periodically check whether it is time to leave safe mode.
   * This thread starts when the threshold level is reached.
   *
   */
  class SafeModeMonitor implements Runnable {
    /** interval in msec for checking safe mode: {@value} */
    private static final long recheckInterval = 1000;
      
    /**
     */
    public void run() {
      while (fsRunning && (safeMode != null && !safeMode.canLeave())) {
        try {
          Thread.sleep(recheckInterval);
        } catch (InterruptedException ie) {
        }
      }
      // leave safe mode and stop the monitor
      try {
        leaveSafeMode(true);
      } catch(SafeModeException es) { // should never happen
        String msg = "SafeModeMonitor may not run during distributed upgrade.";
        assert false : msg;
        throw new RuntimeException(msg, es);
      }
      smmthread = null;
    }
  }
    
  /**
   * Current system time.
   * @return current time in msec.
   */
  static long now() {
    return System.currentTimeMillis();
  }
    
  boolean setSafeMode(SafeModeAction action) throws IOException {
    if (action != SafeModeAction.SAFEMODE_GET) {
      checkSuperuserPrivilege();
      switch(action) {
      case SAFEMODE_LEAVE: // leave safe mode
        leaveSafeMode(false);
        break;
      case SAFEMODE_ENTER: // enter safe mode
        enterSafeMode();
        break;
      }
    }
    return isInSafeMode();
  }

  /**
   * Check whether the name node is in safe mode.
   * @return true if safe mode is ON, false otherwise
   */
  boolean isInSafeMode() {
    if (safeMode == null)
      return false;
    return safeMode.isOn();
  }
    
  /**
   * Increment number of blocks that reached minimal replication.
   * @param replication current replication 
   */
  void incrementSafeBlockCount(int replication) {
    if (safeMode == null)
      return;
    safeMode.incrementSafeBlockCount((short)replication);
  }

  /**
   * Decrement number of blocks that reached minimal replication.
   */
  void decrementSafeBlockCount(Block b) {
    if (safeMode == null) // mostly true
      return;
    safeMode.decrementSafeBlockCount((short)countNodes(b).liveReplicas());
  }

  /**
   * Set the total number of blocks in the system. 
   */
  void setBlockTotal() {
    if (safeMode == null)
      return;
    safeMode.setBlockTotal(blocksMap.size());
  }

  /**
   * Get the total number of blocks in the system. 
   */
  public long getBlocksTotal() {
    return blocksMap.size();
  }

  /**
   * Enter safe mode manually.
   * @throws IOException
   */
  synchronized void enterSafeMode() throws IOException {
    if (!isInSafeMode()) {
      safeMode = new SafeModeInfo();
      return;
    }
    safeMode.setManual();
    NameNode.stateChangeLog.info("STATE* Safe mode is ON. " 
                                + safeMode.getTurnOffTip());
  }

  /**
   * Leave safe mode.
   * @throws IOException
   */
  synchronized void leaveSafeMode(boolean checkForUpgrades) throws SafeModeException {
    if (!isInSafeMode()) {
      NameNode.stateChangeLog.info("STATE* Safe mode is already OFF."); 
      return;
    }
    if(getDistributedUpgradeState())
      throw new SafeModeException("Distributed upgrade is in progress",
                                  safeMode);
    safeMode.leave(checkForUpgrades);
  }
    
  String getSafeModeTip() {
    if (!isInSafeMode())
      return "";
    return safeMode.getTurnOffTip();
  }

  long getEditLogSize() throws IOException {
    return getEditLog().getEditLogSize();
  }

  synchronized CheckpointSignature rollEditLog() throws IOException {
    if (isInSafeMode()) {
      throw new SafeModeException("Checkpoint not created",
                                  safeMode);
    }
    LOG.info("Roll Edit Log from " + Server.getRemoteAddress());
    return getFSImage().rollEditLog();
  }

  synchronized void rollFSImage() throws IOException {
    if (isInSafeMode()) {
      throw new SafeModeException("Checkpoint not created",
                                  safeMode);
    }
    LOG.info("Roll FSImage from " + Server.getRemoteAddress());
    getFSImage().rollFSImage();
  }

  /**
   * Returns whether the given block is one pointed-to by a file.
   */
  private boolean isValidBlock(Block b) {
    return (blocksMap.getINode(b) != null);
  }

  // Distributed upgrade manager
  UpgradeManagerNamenode upgradeManager = new UpgradeManagerNamenode();

  UpgradeStatusReport distributedUpgradeProgress(UpgradeAction action 
                                                 ) throws IOException {
    return upgradeManager.distributedUpgradeProgress(action);
  }

  UpgradeCommand processDistributedUpgradeCommand(UpgradeCommand comm) throws IOException {
    return upgradeManager.processUpgradeCommand(comm);
  }

  int getDistributedUpgradeVersion() {
    return upgradeManager.getUpgradeVersion();
  }

  UpgradeCommand getDistributedUpgradeCommand() throws IOException {
    return upgradeManager.getBroadcastCommand();
  }

  boolean getDistributedUpgradeState() {
    return upgradeManager.getUpgradeState();
  }

  short getDistributedUpgradeStatus() {
    return upgradeManager.getUpgradeStatus();
  }

  boolean startDistributedUpgradeIfNeeded() throws IOException {
    return upgradeManager.startUpgrade();
  }

  PermissionStatus createFsOwnerPermissions(FsPermission permission) {
    return new PermissionStatus(fsOwner.getUserName(), supergroup, permission);
  }

  private PermissionChecker checkOwner(String path) throws AccessControlException {
    return checkPermission(path, true, null, null, null, null);
  }

  private PermissionChecker checkPathAccess(String path, FsAction access
      ) throws AccessControlException {
    return checkPermission(path, false, null, null, access, null);
  }

  private PermissionChecker checkParentAccess(String path, FsAction access
      ) throws AccessControlException {
    return checkPermission(path, false, null, access, null, null);
  }

  private PermissionChecker checkAncestorAccess(String path, FsAction access
      ) throws AccessControlException {
    return checkPermission(path, false, access, null, null, null);
  }

  private PermissionChecker checkTraverse(String path
      ) throws AccessControlException {
    return checkPermission(path, false, null, null, null, null);
  }

  private void checkSuperuserPrivilege() throws AccessControlException {
    if (isPermissionEnabled) {
      PermissionChecker pc = new PermissionChecker(
          fsOwner.getUserName(), supergroup);
      if (!pc.isSuper) {
        throw new AccessControlException("Superuser privilege is required");
      }
    }
  }

  /**
   * Check whether current user have permissions to access the path.
   * For more details of the parameters, see
   * {@link PermissionChecker#checkPermission(String, INodeDirectory, boolean, FsAction, FsAction, FsAction, FsAction)}.
   */
  private PermissionChecker checkPermission(String path, boolean doCheckOwner,
      FsAction ancestorAccess, FsAction parentAccess, FsAction access,
      FsAction subAccess) throws AccessControlException {
    PermissionChecker pc = new PermissionChecker(
        fsOwner.getUserName(), supergroup);
    if (!pc.isSuper) {
      dir.waitForReady();
      pc.checkPermission(path, dir.rootDir, doCheckOwner,
          ancestorAccess, parentAccess, access, subAccess);
    }
    return pc;
  }

  /**
   * Check to see if we have exceeded the limit on the number
   * of inodes.
   */
  void checkFsObjectLimit() throws IOException {
    if (maxFsObjects != 0 &&
        maxFsObjects <= dir.totalInodes() + getBlocksTotal()) {
      throw new IOException("Exceeded the configured number of objects " +
                             maxFsObjects + " in the filesystem.");
    }
  }

  /**
   * Get the total number of objects in the system. 
   */
  long getMaxObjects() {
    return maxFsObjects;
  }

  public long getFilesTotal() {
    return this.dir.totalInodes();
  }

  public long getPendingReplicationBlocks() {
    return pendingReplicationBlocksCount;
  }

  public long getUnderReplicatedBlocks() {
    return underReplicatedBlocksCount;
  }

  public long getScheduledReplicationBlocks() {
    return scheduledReplicationBlocksCount;
  }

  public String getFSState() {
    return isInSafeMode() ? "safeMode" : "Operational";
  }
  
  private ObjectName mbeanName;
  /**
   * Register the FSNamesystem MBean
   */
  void registerMBean(Configuration conf) {
    // We wrap to bypass standard mbean naming convetion.
    // This wraping can be removed in java 6 as it is more flexible in 
    // package naming for mbeans and their impl.
    StandardMBean bean;
    try {
      myFSMetrics = new FSNamesystemMetrics(conf);
      bean = new StandardMBean(this,FSNamesystemMBean.class);
      mbeanName = MBeanUtil.registerMBean("NameNode", "FSNamesystemStatus", bean);
    } catch (NotCompliantMBeanException e) {
      e.printStackTrace();
    }

    LOG.info("Registered FSNamesystemStatusMBean");
  }

  /**
   * get FSNamesystemMetrics
   */
  public FSNamesystemMetrics getFSNamesystemMetrics() {
    return myFSMetrics;
  }

  /**
   * shutdown FSNamesystem
   */
  public void shutdown() {
    if (mbeanName != null)
      MBeanUtil.unregisterMBean(mbeanName);
  }
  

  /**
   * Number of live data nodes
   * @return Number of live data nodes
   */
  public int numLiveDataNodes() {
    int numLive = 0;
    synchronized (datanodeMap) {   
      for(Iterator<DatanodeDescriptor> it = datanodeMap.values().iterator(); 
                                                               it.hasNext();) {
        DatanodeDescriptor dn = it.next();
        if (!isDatanodeDead(dn) ) {
          numLive++;
        }
      }
    }
    return numLive;
  }
  

  /**
   * Number of dead data nodes
   * @return Number of dead data nodes
   */
  public int numDeadDataNodes() {
    int numDead = 0;
    synchronized (datanodeMap) {   
      for(Iterator<DatanodeDescriptor> it = datanodeMap.values().iterator(); 
                                                               it.hasNext();) {
        DatanodeDescriptor dn = it.next();
        if (isDatanodeDead(dn) ) {
          numDead++;
        }
      }
    }
    return numDead;
  }

  /**
   * Sets the generation stamp for this filesystem
   */
  void setGenerationStamp(long stamp) {
    generationStamp.setStamp(stamp);
  }

  /**
   * Gets the generation stamp for this filesystem
   */
  long getGenerationStamp() {
    return generationStamp.getStamp();
  }

  /**
   * Increments, logs and then returns the stamp
   */
  long nextGenerationStamp() {
    long gs = generationStamp.nextStamp();
    getEditLog().logGenerationStamp(gs);
    return gs;
  }

  /**
   * Verifies that the block is associated with a file that has a lease.
   * Increments, logs and then returns the stamp
   */
  synchronized long nextGenerationStampForBlock(Block block) throws IOException {
    BlockInfo storedBlock = blocksMap.getStoredBlock(block);
    if (storedBlock == null) {
      String msg = block + " is already commited, storedBlock == null.";
      LOG.info(msg);
      throw new IOException(msg);
    }
    INodeFile fileINode = storedBlock.getINode();
    if (!fileINode.isUnderConstruction()) {
      String msg = block + " is already commited, !fileINode.isUnderConstruction().";
      LOG.info(msg);
      throw new IOException(msg);
    }
    if (!((INodeFileUnderConstruction)fileINode).setLastRecoveryTime(now())) {
      String msg = block + " is beening recovered, ignoring this request.";
      LOG.info(msg);
      throw new IOException(msg);
    }
    return nextGenerationStamp();
  }

  // rename was successful. If any part of the renamed subtree had
  // files that were being written to, update with new filename.
  //
  void changeLease(String src, String dst, DFSFileInfo dinfo) 
                   throws IOException {
    String overwrite;
    String replaceBy;

    boolean destinationExisted = true;
    if (dinfo == null) {
      destinationExisted = false;
    }

    if (destinationExisted && dinfo.isDir()) {
      Path spath = new Path(src);
      overwrite = spath.getParent().toString() + Path.SEPARATOR;
      replaceBy = dst + Path.SEPARATOR;
    } else {
      overwrite = src;
      replaceBy = dst;
    }

    leaseManager.changeLease(src, dst, overwrite, replaceBy);
  }
           
  /**
   * Serializes leases. 
   */
  void saveFilesUnderConstruction(DataOutputStream out) throws IOException {
    synchronized (leaseManager) {
      out.writeInt(leaseManager.countPath()); // write the size

      for (Lease lease : leaseManager.getSortedLeases()) {
        Collection<StringBytesWritable> files = lease.getPaths();
        for (Iterator<StringBytesWritable> i = files.iterator(); i.hasNext();){
          String path = i.next().getString();

          // verify that path exists in namespace
          INode node = dir.getFileINode(path);
          if (node == null) {
            throw new IOException("saveLeases found path " + path +
                                  " but no matching entry in namespace.");
          }
          if (!node.isUnderConstruction()) {
            throw new IOException("saveLeases found path " + path +
                                  " but is not under construction.");
          }
          INodeFileUnderConstruction cons = (INodeFileUnderConstruction) node;
          FSImage.writeINodeUnderConstruction(out, cons, path);
        }
      }
    }
  }
}