HDFS-5052. Add cacheRequest/uncacheRequest support to NameNode. (Contributed by Colin Patrick McCabe.)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-4949@1516669 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/Fallible.java

@@ -0,0 +1,53 @@
+/**
+ * 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.util;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+
+/**
+ * Contains either a value of type T, or an IOException.
+ *
+ * This can be useful as a return value for batch APIs that need granular
+ * error reporting.
+ */
+@InterfaceAudience.LimitedPrivate({"HDFS"})
+@InterfaceStability.Unstable
+public class Fallible<T> {
+  private final T val;
+  private final IOException ioe;
+
+  public Fallible(T val) {
+    this.val = val;
+    this.ioe = null;
+  }
+
+  public Fallible(IOException ioe) {
+    this.val = null;
+    this.ioe = ioe;
+  }
+
+  public T get() throws IOException {
+    if (ioe != null) {
+      throw new IOException(ioe);
+    }
+    return this.val;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-4949.txt

@@ -12,6 +12,9 @@ HDFS-4949 (Unreleased)
     HDFS-5051.  Propagate cache status information from the DataNode to the
     NameNode  (Andrew Wang via Colin Patrick McCabe)
 
+    HDFS-5052.  Add cacheRequest/uncacheRequest support to NameNode.
+    (contributed by Colin Patrick McCabe)
+
   OPTIMIZATIONS
 
   BUG FIXES

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

@@ -0,0 +1,78 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.protocol;
+
+import java.io.IOException;
+
+/**
+ * An exception which occurred when trying to add a path cache directive.
+ */
+public abstract class AddPathCacheDirectiveException extends IOException {
+  private static final long serialVersionUID = 1L;
+
+  private final PathCacheDirective directive;
+  
+  public AddPathCacheDirectiveException(String description,
+      PathCacheDirective directive) {
+    super(description);
+    this.directive = directive;
+  }
+
+  public PathCacheDirective getDirective() {
+    return directive;
+  }
+
+  public static final class EmptyPathError
+      extends AddPathCacheDirectiveException {
+    private static final long serialVersionUID = 1L;
+
+    public EmptyPathError(PathCacheDirective directive) {
+      super("empty path in directive " + directive, directive);
+    }
+  }
+
+  public static class InvalidPathNameError
+      extends AddPathCacheDirectiveException {
+    private static final long serialVersionUID = 1L;
+
+    public InvalidPathNameError(PathCacheDirective directive) {
+      super("can't handle non-absolute path name " + directive.getPath(),
+          directive);
+    }
+  }
+
+  public static class InvalidPoolNameError
+      extends AddPathCacheDirectiveException {
+    private static final long serialVersionUID = 1L;
+
+    public InvalidPoolNameError(PathCacheDirective directive) {
+      super("invalid pool name '" + directive.getPool() + "'", directive);
+    }
+  }
+
+  public static class UnexpectedAddPathCacheDirectiveException
+      extends AddPathCacheDirectiveException {
+    private static final long serialVersionUID = 1L;
+
+    public UnexpectedAddPathCacheDirectiveException(
+        PathCacheDirective directive) {
+      super("encountered an unexpected error when trying to " +
+          "add path cache directive " + directive, directive);
+    }
+  }
+};

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

@@ -19,6 +19,7 @@ package org.apache.hadoop.hdfs.protocol;
 
 import java.io.FileNotFoundException;
 import java.io.IOException;
+import java.util.List;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
@@ -30,6 +31,7 @@ import org.apache.hadoop.fs.InvalidPathException;
 import org.apache.hadoop.fs.Options;
 import org.apache.hadoop.fs.Options.Rename;
 import org.apache.hadoop.fs.ParentNotDirectoryException;
+import org.apache.hadoop.fs.RemoteIterator;
 import org.apache.hadoop.fs.UnresolvedLinkException;
 import org.apache.hadoop.fs.permission.FsPermission;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
@@ -46,6 +48,7 @@ import org.apache.hadoop.security.AccessControlException;
 import org.apache.hadoop.security.KerberosInfo;
 import org.apache.hadoop.security.token.Token;
 import org.apache.hadoop.security.token.TokenInfo;
+import org.apache.hadoop.util.Fallible;
 
 /**********************************************************************
  * ClientProtocol is used by user code via 
@@ -1093,5 +1096,53 @@ public interface ClientProtocol {
   @Idempotent
   public SnapshotDiffReport getSnapshotDiffReport(String snapshotRoot,
       String fromSnapshot, String toSnapshot) throws IOException;
+
+  /**
+   * Add some path cache directives to the CacheManager.
+   *
+   * @param directives
+   *          A list of all the path cache directives we want to add.
+   * @return
+   *          An list where each element is either a path cache entry that was
+   *          added, or an IOException exception describing why the directive
+   *          could not be added.
+   */
+  @AtMostOnce
+  public List<Fallible<PathCacheEntry>>
+    addPathCacheDirectives(List<PathCacheDirective> directives)
+      throws IOException;
+
+  /**
+   * Remove some path cache entries from the CacheManager.
+   *
+   * @param ids
+   *          A list of all the IDs we want to remove from the CacheManager.
+   * @return
+   *          An list where each element is either an ID that was removed,
+   *          or an IOException exception describing why the ID could not be
+   *          removed.
+   */
+  @AtMostOnce
+  public List<Fallible<Long>> removePathCacheEntries(List<Long> ids)
+      throws IOException;
+
+  /**
+   * List cached paths on the server.
+   *
+   * @param prevId
+   *          The previous ID that we listed, or 0 if this is the first call
+   *          to listPathCacheEntries.
+   * @param pool
+   *          The pool ID to list.  If this is the empty string, all pool ids
+   *          will be listed.
+   * @param maxRepliesPerRequest
+   *          The maximum number of replies to make in each request.
+   * @return
+   *          A RemoteIterator from which you can get PathCacheEntry objects.
+   *          Requests will be made as needed.
+   */
+  @Idempotent
+  public RemoteIterator<PathCacheEntry> listPathCacheEntries(long prevId,
+      String pool, int maxRepliesPerRequest) throws IOException;
 }
 

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

@@ -0,0 +1,110 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.protocol;
+
+import java.io.IOException;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ComparisonChain;
+
+import org.apache.commons.lang.builder.HashCodeBuilder;
+import org.apache.hadoop.hdfs.DFSUtil;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.EmptyPathError;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.InvalidPoolNameError;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.InvalidPathNameError;
+
+/**
+ * A directive to add a path to a cache pool.
+ */
+public class PathCacheDirective implements Comparable<PathCacheDirective> {
+  private final String path;
+
+  private final String pool;
+
+  public PathCacheDirective(String path, String pool) throws IOException {
+    Preconditions.checkNotNull(path);
+    Preconditions.checkNotNull(pool);
+    this.path = path;
+    this.pool = pool;
+  }
+
+  /**
+   * @return The path used in this request.
+   */
+  public String getPath() {
+    return path;
+  }
+
+  /**
+   * @return The pool used in this request.
+   */
+  public String getPool() {
+    return pool;
+  }
+
+  /**
+   * Check if this PathCacheDirective is valid.
+   * 
+   * @throws IOException
+   *     If this PathCacheDirective is not valid.
+   */
+  public void validate() throws IOException {
+    if (path.isEmpty()) {
+      throw new EmptyPathError(this);
+    }
+    if (DFSUtil.isValidName(path)) {
+      throw new InvalidPathNameError(this);
+    }
+
+    if (pool.isEmpty()) {
+      throw new InvalidPoolNameError(this);
+    }
+  }
+
+  @Override
+  public int compareTo(PathCacheDirective rhs) {
+    return ComparisonChain.start().
+        compare(pool, rhs.getPool()).
+        compare(path, rhs.getPath()).
+        result();
+  }
+
+  @Override
+  public int hashCode() {
+    return new HashCodeBuilder().append(path).append(pool).hashCode();
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    try {
+      PathCacheDirective other = (PathCacheDirective)o;
+      return other.compareTo(this) == 0;
+    } catch (ClassCastException e) {
+      return false;
+    }
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder builder = new StringBuilder();
+    builder.append("{ path:").append(path).
+      append(", pool:").append(pool).
+      append(" }");
+    return builder.toString();
+  }
+};

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

@@ -0,0 +1,75 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.protocol;
+
+import org.apache.commons.lang.builder.EqualsBuilder;
+import org.apache.commons.lang.builder.HashCodeBuilder;
+
+import com.google.common.base.Preconditions;
+
+/**
+ * An entry in the NameNode's path cache.
+ */
+public final class PathCacheEntry {
+  private final long entryId;
+  private final PathCacheDirective directive;
+
+  public PathCacheEntry(long entryId, PathCacheDirective directive) {
+    Preconditions.checkArgument(entryId > 0);
+    this.entryId = entryId;
+    this.directive = directive;
+  }
+
+  public long getEntryId() {
+    return entryId;
+  }
+
+  public PathCacheDirective getDirective() {
+    return directive;
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    try {
+      PathCacheEntry other = (PathCacheEntry)o;
+      return new EqualsBuilder().
+          append(this.entryId, other.entryId).
+          append(this.directive, other.directive).
+          isEquals();
+    } catch (ClassCastException e) {
+      return false;
+    }
+  }
+
+  @Override
+  public int hashCode() {
+    return new HashCodeBuilder().
+        append(entryId).
+        append(directive).
+        hashCode();
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder builder = new StringBuilder();
+    builder.append("{ entryId:").append(entryId).
+        append(", directive:").append(directive.toString()).
+        append(" }");
+    return builder.toString();
+  }
+};

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

@@ -0,0 +1,68 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.protocol;
+
+import java.io.IOException;
+
+import com.google.common.base.Preconditions;
+
+/**
+ * An exception which occurred when trying to remove a path cache entry.
+ */
+public abstract class RemovePathCacheEntryException extends IOException {
+  private static final long serialVersionUID = 1L;
+
+  private final long entryId;
+
+  public RemovePathCacheEntryException(String description, long entryId) {
+    super(description);
+    this.entryId = entryId;
+  }
+    
+  public long getEntryId() {
+    return this.entryId;
+  }
+
+  public final static class InvalidIdException
+      extends RemovePathCacheEntryException {
+    private static final long serialVersionUID = 1L;
+
+    public InvalidIdException(long entryId) {
+      super("invalid cache path entry id " + entryId, entryId);
+    }
+  }
+
+  public final static class NoSuchIdException
+      extends RemovePathCacheEntryException {
+    private static final long serialVersionUID = 1L;
+
+    public NoSuchIdException(long entryId) {
+      super("there is no path cache entry with id " + entryId, entryId);
+    }
+  }
+
+  public final static class UnexpectedRemovePathCacheEntryException
+      extends RemovePathCacheEntryException {
+    private static final long serialVersionUID = 1L;
+
+    public UnexpectedRemovePathCacheEntryException(long id) {
+      super("encountered an unexpected error when trying to " +
+          "remove path cache entry id " + id, id);
+    }
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientNamenodeProtocolServerSideTranslatorPB.java

@@ -18,6 +18,7 @@
 package org.apache.hadoop.hdfs.protocolPB;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.List;
 
 import org.apache.hadoop.classification.InterfaceAudience;
@@ -25,6 +26,14 @@ import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.fs.ContentSummary;
 import org.apache.hadoop.fs.FsServerDefaults;
 import org.apache.hadoop.fs.Options.Rename;
+import org.apache.hadoop.fs.RemoteIterator;
+import org.apache.hadoop.hdfs.protocol.PathCacheDirective;
+import org.apache.hadoop.hdfs.protocol.PathCacheEntry;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.EmptyPathError;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.InvalidPathNameError;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.InvalidPoolNameError;
+import org.apache.hadoop.hdfs.protocol.RemovePathCacheEntryException.InvalidIdException;
+import org.apache.hadoop.hdfs.protocol.RemovePathCacheEntryException.NoSuchIdException;
 import org.apache.hadoop.hdfs.protocol.ClientProtocol;
 import org.apache.hadoop.hdfs.protocol.CorruptFileBlocks;
 import org.apache.hadoop.hdfs.protocol.DirectoryListing;
@@ -37,6 +46,10 @@ import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.Abando
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AbandonBlockResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AddBlockRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AddBlockResponseProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.PathCacheDirectiveProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AddPathCacheDirectiveErrorProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AddPathCacheDirectivesRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AddPathCacheDirectivesResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AllowSnapshotRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AllowSnapshotResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AppendRequestProto;
@@ -92,6 +105,9 @@ import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.GetSna
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.GetSnapshottableDirListingResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.IsFileClosedRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.IsFileClosedResponseProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ListPathCacheEntriesElementProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ListPathCacheEntriesRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ListPathCacheEntriesResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ListCorruptFileBlocksRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ListCorruptFileBlocksResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.MetaSaveRequestProto;
@@ -102,6 +118,9 @@ import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.Recove
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RecoverLeaseResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RefreshNodesRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RefreshNodesResponseProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RemovePathCacheEntryErrorProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RemovePathCacheEntriesRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RemovePathCacheEntriesResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.Rename2RequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.Rename2ResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RenameRequestProto;
@@ -142,6 +161,7 @@ import org.apache.hadoop.hdfs.protocol.proto.HdfsProtos.LocatedBlockProto;
 import org.apache.hadoop.hdfs.security.token.block.DataEncryptionKey;
 import org.apache.hadoop.hdfs.security.token.delegation.DelegationTokenIdentifier;
 import org.apache.hadoop.hdfs.server.namenode.INodeId;
+import org.apache.hadoop.hdfs.server.namenode.UnsupportedActionException;
 import org.apache.hadoop.io.Text;
 import org.apache.hadoop.security.proto.SecurityProtos.CancelDelegationTokenRequestProto;
 import org.apache.hadoop.security.proto.SecurityProtos.CancelDelegationTokenResponseProto;
@@ -150,6 +170,7 @@ import org.apache.hadoop.security.proto.SecurityProtos.GetDelegationTokenRespons
 import org.apache.hadoop.security.proto.SecurityProtos.RenewDelegationTokenRequestProto;
 import org.apache.hadoop.security.proto.SecurityProtos.RenewDelegationTokenResponseProto;
 import org.apache.hadoop.security.token.Token;
+import org.apache.hadoop.util.Fallible;
 
 import com.google.protobuf.RpcController;
 import com.google.protobuf.ServiceException;
@@ -1004,4 +1025,94 @@ public class ClientNamenodeProtocolServerSideTranslatorPB implements
     }
   }
 
+  @Override
+  public AddPathCacheDirectivesResponseProto addPathCacheDirectives(RpcController controller,
+      AddPathCacheDirectivesRequestProto request) throws ServiceException {
+    try {
+      ArrayList<PathCacheDirective> input =
+          new ArrayList<PathCacheDirective>(request.getElementsCount());
+      for (int i = 0; i < request.getElementsCount(); i++) {
+        PathCacheDirectiveProto proto = request.getElements(i);
+        input.add(new PathCacheDirective(proto.getPath(), proto.getPool()));
+      }
+      List<Fallible<PathCacheEntry>> output = server.addPathCacheDirectives(input);
+      AddPathCacheDirectivesResponseProto.Builder builder =
+         AddPathCacheDirectivesResponseProto.newBuilder();
+      for (int idx = 0; idx < output.size(); idx++) {
+        try {
+          PathCacheEntry entry = output.get(idx).get();
+          builder.addResults(entry.getEntryId());
+        } catch (EmptyPathError ioe) {
+          builder.addResults(AddPathCacheDirectiveErrorProto.
+              EMPTY_PATH_ERROR_VALUE);
+        } catch (InvalidPathNameError ioe) {
+          builder.addResults(AddPathCacheDirectiveErrorProto.
+              INVALID_PATH_NAME_ERROR_VALUE);
+        } catch (InvalidPoolNameError ioe) {
+          builder.addResults(AddPathCacheDirectiveErrorProto.
+              INVALID_POOL_NAME_ERROR_VALUE);
+        } catch (IOException ioe) {
+          builder.addResults(AddPathCacheDirectiveErrorProto.
+              UNEXPECTED_ADD_ERROR_VALUE);
+        }
+      }
+      return builder.build();
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+  }
+
+  @Override
+  public RemovePathCacheEntriesResponseProto removePathCacheEntries(
+      RpcController controller, RemovePathCacheEntriesRequestProto request)
+      throws ServiceException {
+    try {
+      List<Fallible<Long>> output =
+         server.removePathCacheEntries(request.getElementsList());
+      RemovePathCacheEntriesResponseProto.Builder builder =
+         RemovePathCacheEntriesResponseProto.newBuilder();
+      for (int idx = 0; idx < output.size(); idx++) {
+        try {
+          long id = output.get(idx).get();
+          builder.addResults(id);
+        } catch (InvalidIdException ioe) {
+          builder.addResults(RemovePathCacheEntryErrorProto.
+              INVALID_CACHED_PATH_ID_ERROR_VALUE);
+        } catch (NoSuchIdException ioe) {
+          builder.addResults(RemovePathCacheEntryErrorProto.
+              NO_SUCH_CACHED_PATH_ID_ERROR_VALUE);
+        } catch (IOException ioe) {
+          builder.addResults(RemovePathCacheEntryErrorProto.
+              UNEXPECTED_REMOVE_ERROR_VALUE);
+        }
+      }
+      return builder.build();
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+  }
+
+  @Override
+  public ListPathCacheEntriesResponseProto listPathCacheEntries(RpcController controller,
+      ListPathCacheEntriesRequestProto request) throws ServiceException {
+    try {
+      RemoteIterator<PathCacheEntry> iter =
+         server.listPathCacheEntries(request.getPrevId(),
+             request.getPool(),
+             request.getMaxReplies());
+      ListPathCacheEntriesResponseProto.Builder builder =
+          ListPathCacheEntriesResponseProto.newBuilder();
+      while (iter.hasNext()) {
+        PathCacheEntry entry = iter.next();
+        builder.addElements(
+            ListPathCacheEntriesElementProto.newBuilder().
+              setId(entry.getEntryId()).
+              setPath(entry.getDirective().getPath()).
+              setPool(entry.getDirective().getPool()));
+      }
+      return builder.build();
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientNamenodeProtocolTranslatorPB.java

@@ -20,7 +20,10 @@ package org.apache.hadoop.hdfs.protocolPB;
 import java.io.Closeable;
 import java.io.FileNotFoundException;
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.List;
+import java.util.NoSuchElementException;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
@@ -30,9 +33,19 @@ import org.apache.hadoop.fs.FileAlreadyExistsException;
 import org.apache.hadoop.fs.FsServerDefaults;
 import org.apache.hadoop.fs.Options.Rename;
 import org.apache.hadoop.fs.ParentNotDirectoryException;
+import org.apache.hadoop.fs.RemoteIterator;
 import org.apache.hadoop.fs.UnresolvedLinkException;
 import org.apache.hadoop.fs.permission.FsPermission;
 import org.apache.hadoop.hdfs.protocol.AlreadyBeingCreatedException;
+import org.apache.hadoop.hdfs.protocol.PathCacheDirective;
+import org.apache.hadoop.hdfs.protocol.PathCacheEntry;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.EmptyPathError;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.InvalidPathNameError;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.InvalidPoolNameError;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.UnexpectedAddPathCacheDirectiveException;
+import org.apache.hadoop.hdfs.protocol.RemovePathCacheEntryException.InvalidIdException;
+import org.apache.hadoop.hdfs.protocol.RemovePathCacheEntryException.NoSuchIdException;
+import org.apache.hadoop.hdfs.protocol.RemovePathCacheEntryException.UnexpectedRemovePathCacheEntryException;
 import org.apache.hadoop.hdfs.protocol.ClientProtocol;
 import org.apache.hadoop.hdfs.protocol.CorruptFileBlocks;
 import org.apache.hadoop.hdfs.protocol.DSQuotaExceededException;
@@ -50,6 +63,10 @@ import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport;
 import org.apache.hadoop.hdfs.protocol.SnapshottableDirectoryStatus;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AbandonBlockRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AddBlockRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.PathCacheDirectiveProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AddPathCacheDirectiveErrorProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AddPathCacheDirectivesRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AddPathCacheDirectivesResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AllowSnapshotRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AppendRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.AppendResponseProto;
@@ -87,11 +104,18 @@ import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.GetSna
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.GetSnapshottableDirListingRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.GetSnapshottableDirListingResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.IsFileClosedRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ListPathCacheEntriesElementProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ListPathCacheEntriesRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ListPathCacheEntriesRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ListPathCacheEntriesResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ListCorruptFileBlocksRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.MetaSaveRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.MkdirsRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RecoverLeaseRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RefreshNodesRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RemovePathCacheEntriesRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RemovePathCacheEntriesResponseProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RemovePathCacheEntryErrorProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.Rename2RequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RenameRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RenameSnapshotRequestProto;
@@ -127,6 +151,7 @@ import org.apache.hadoop.security.proto.SecurityProtos.GetDelegationTokenRequest
 import org.apache.hadoop.security.proto.SecurityProtos.GetDelegationTokenResponseProto;
 import org.apache.hadoop.security.proto.SecurityProtos.RenewDelegationTokenRequestProto;
 import org.apache.hadoop.security.token.Token;
+import org.apache.hadoop.util.Fallible;
 
 import com.google.protobuf.ByteString;
 import com.google.protobuf.ServiceException;
@@ -982,4 +1007,170 @@ public class ClientNamenodeProtocolTranslatorPB implements
       throw ProtobufHelper.getRemoteException(e);
     }
   }
+
+  private static IOException addPathCacheDirectivesError(long code,
+      PathCacheDirective directive) {
+    if (code == AddPathCacheDirectiveErrorProto.EMPTY_PATH_ERROR_VALUE) {
+      return new EmptyPathError(directive);
+    } else if (code == AddPathCacheDirectiveErrorProto.
+        INVALID_PATH_NAME_ERROR_VALUE) {
+      return new InvalidPathNameError(directive);
+    } else if (code == AddPathCacheDirectiveErrorProto.
+        INVALID_POOL_NAME_ERROR_VALUE) {
+      return new InvalidPoolNameError(directive);
+    } else {
+      return new UnexpectedAddPathCacheDirectiveException(directive);
+    }
+  }
+  
+  @Override
+  public List<Fallible<PathCacheEntry>> addPathCacheDirectives(
+        List<PathCacheDirective> directives) throws IOException {
+    try {
+      AddPathCacheDirectivesRequestProto.Builder builder =
+          AddPathCacheDirectivesRequestProto.newBuilder();
+      for (PathCacheDirective directive : directives) {
+        builder.addElements(PathCacheDirectiveProto.newBuilder().
+            setPath(directive.getPath()).
+            setPool(directive.getPool()).
+            build());
+      }
+      AddPathCacheDirectivesResponseProto result = 
+          rpcProxy.addPathCacheDirectives(null, builder.build());
+      int resultsCount = result.getResultsCount();
+      ArrayList<Fallible<PathCacheEntry>> results = 
+          new ArrayList<Fallible<PathCacheEntry>>(resultsCount);
+      for (int i = 0; i < resultsCount; i++) {
+        PathCacheDirective directive = directives.get(i);
+        long code = result.getResults(i);
+        if (code > 0) {
+          results.add(new Fallible<PathCacheEntry>(
+                new PathCacheEntry(code, directive)));
+        } else {
+          results.add(new Fallible<PathCacheEntry>(
+                addPathCacheDirectivesError(code, directive))); 
+        }
+      }
+      return results;
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+  
+  private static IOException removePathCacheEntriesError(long code, long id) {
+    if (code == RemovePathCacheEntryErrorProto.
+        INVALID_CACHED_PATH_ID_ERROR_VALUE) {
+      return new InvalidIdException(id);
+    } else if (code == RemovePathCacheEntryErrorProto.
+        NO_SUCH_CACHED_PATH_ID_ERROR_VALUE) {
+      return new NoSuchIdException(id);
+    } else {
+      return new UnexpectedRemovePathCacheEntryException(id);
+    }
+  }
+
+  @Override
+  public List<Fallible<Long>> removePathCacheEntries(List<Long> ids)
+      throws IOException {
+    try {
+      RemovePathCacheEntriesRequestProto.Builder builder =
+          RemovePathCacheEntriesRequestProto.newBuilder();
+      for (Long id : ids) {
+        builder.addElements(id);
+      }
+      RemovePathCacheEntriesResponseProto result = 
+          rpcProxy.removePathCacheEntries(null, builder.build());
+      int resultsCount = result.getResultsCount();
+      ArrayList<Fallible<Long>> results = 
+          new ArrayList<Fallible<Long>>(resultsCount);
+      for (int i = 0; i < resultsCount; i++) {
+        long code = result.getResults(i);
+        if (code > 0) {
+          results.add(new Fallible<Long>(code));
+        } else {
+          results.add(new Fallible<Long>(
+              removePathCacheEntriesError(code, ids.get(i))));
+        }
+      }
+      return results;
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
+
+  private class PathCacheEntriesIterator
+      implements RemoteIterator<PathCacheEntry> {
+    private long prevId;
+    private final String pool;
+    private final int repliesPerRequest;
+    private ListPathCacheEntriesResponseProto response;
+    private int idx;
+
+    public PathCacheEntriesIterator(long prevId, String pool,
+        int repliesPerRequest) {
+      this.prevId = prevId;
+      this.pool = pool;
+      this.repliesPerRequest = repliesPerRequest;
+      this.response = null;
+      this.idx = -1;
+    }
+
+    private void makeRequest() throws IOException {
+      idx = 0;
+      response = null;
+      try {
+        ListPathCacheEntriesRequestProto req =
+            ListPathCacheEntriesRequestProto.newBuilder().
+              setPrevId(prevId).
+              setPool(pool).
+              setMaxReplies(repliesPerRequest).
+              build();
+        response = rpcProxy.listPathCacheEntries(null, req);
+        if (response.getElementsCount() == 0) {
+          response = null;
+        }
+      } catch (ServiceException e) {
+        throw ProtobufHelper.getRemoteException(e);
+      }
+    }
+
+    private void makeRequestIfNeeded() throws IOException {
+      if (idx == -1) {
+        makeRequest();
+      } else if ((response != null) && (idx >= response.getElementsCount())) {
+        if (response.getHasMore()) {
+          makeRequest();
+        } else {
+          response = null;
+        }
+      }
+    }
+
+    @Override
+    public boolean hasNext() throws IOException {
+      makeRequestIfNeeded();
+      return (response != null);
+    }
+
+    @Override
+    public PathCacheEntry next() throws IOException {
+      makeRequestIfNeeded();
+      if (response == null) {
+        throw new NoSuchElementException();
+      }
+      ListPathCacheEntriesElementProto elementProto =
+        response.getElements(idx);
+      prevId = elementProto.getId();
+      idx++;
+      return new PathCacheEntry(elementProto.getId(), 
+          new PathCacheDirective(elementProto.getPath(),
+              elementProto.getPool()));
+    }
+  }
+
+  @Override
+  public RemoteIterator<PathCacheEntry> listPathCacheEntries(long prevId,
+      String pool, int repliesPerRequest) throws IOException {
+    return new PathCacheEntriesIterator(prevId, pool, repliesPerRequest);
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/CacheManager.java

@@ -0,0 +1,165 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.namenode;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.SortedMap;
+import java.util.TreeMap;
+import java.util.Map.Entry;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.protocol.PathCacheDirective;
+import org.apache.hadoop.hdfs.protocol.PathCacheEntry;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.UnexpectedAddPathCacheDirectiveException;
+import org.apache.hadoop.hdfs.protocol.RemovePathCacheEntryException.InvalidIdException;
+import org.apache.hadoop.hdfs.protocol.RemovePathCacheEntryException.NoSuchIdException;
+import org.apache.hadoop.hdfs.protocol.RemovePathCacheEntryException.UnexpectedRemovePathCacheEntryException;
+import org.apache.hadoop.util.Fallible;
+
+/**
+ * The Cache Manager handles caching on DataNodes.
+ */
+final class CacheManager {
+  public static final Log LOG = LogFactory.getLog(CacheManager.class);
+
+  /**
+   * Cache entries, sorted by ID.
+   *
+   * listPathCacheEntries relies on the ordering of elements in this map 
+   * to track what has already been listed by the client.
+   */
+  private final TreeMap<Long, PathCacheEntry> entriesById =
+      new TreeMap<Long, PathCacheEntry>();
+
+  /**
+   * Cache entries, sorted by directive.
+   */
+  private final TreeMap<PathCacheDirective, PathCacheEntry> entriesByDirective =
+      new TreeMap<PathCacheDirective, PathCacheEntry>();
+
+  /**
+   * The entry ID to use for a new entry.
+   */
+  private long nextEntryId;
+
+  CacheManager(FSDirectory dir, Configuration conf) {
+    // TODO: support loading and storing of the CacheManager state
+    clear();
+  }
+
+  synchronized void clear() {
+    entriesById.clear();
+    entriesByDirective.clear();
+    nextEntryId = 1;
+  }
+
+  synchronized long getNextEntryId() throws IOException {
+    if (nextEntryId == Long.MAX_VALUE) {
+      throw new IOException("no more available IDs");
+    }
+    return nextEntryId++;
+  }
+
+  private synchronized Fallible<PathCacheEntry> addDirective(
+        PathCacheDirective directive) {
+    try {
+      directive.validate();
+    } catch (IOException ioe) {
+      return new Fallible<PathCacheEntry>(ioe);
+    }
+    // Check if we already have this entry.
+    PathCacheEntry existing = entriesByDirective.get(directive);
+    if (existing != null) {
+      // Entry already exists: return existing entry.
+      return new Fallible<PathCacheEntry>(existing);
+    }
+    // Add a new entry with the next available ID.
+    PathCacheEntry entry;
+    try {
+      entry = new PathCacheEntry(getNextEntryId(), directive);
+    } catch (IOException ioe) {
+      return new Fallible<PathCacheEntry>(
+          new UnexpectedAddPathCacheDirectiveException(directive));
+    }
+    entriesByDirective.put(directive, entry);
+    entriesById.put(entry.getEntryId(), entry);
+    return new Fallible<PathCacheEntry>(entry);
+  }
+
+  public synchronized List<Fallible<PathCacheEntry>> addDirectives(
+      List<PathCacheDirective> directives) {
+    ArrayList<Fallible<PathCacheEntry>> results = 
+        new ArrayList<Fallible<PathCacheEntry>>(directives.size());
+    for (PathCacheDirective directive: directives) {
+      results.add(addDirective(directive));
+    }
+    return results;
+  }
+
+  private synchronized Fallible<Long> removeEntry(long entryId) {
+    // Check for invalid IDs.
+    if (entryId <= 0) {
+      return new Fallible<Long>(new InvalidIdException(entryId));
+    }
+    // Find the entry.
+    PathCacheEntry existing = entriesById.get(entryId);
+    if (existing == null) {
+      return new Fallible<Long>(new NoSuchIdException(entryId));
+    }
+    // Remove the corresponding entry in entriesByDirective.
+    if (entriesByDirective.remove(existing.getDirective()) == null) {
+      return new Fallible<Long>(
+          new UnexpectedRemovePathCacheEntryException(entryId));
+    }
+    entriesById.remove(entryId);
+    return new Fallible<Long>(entryId);
+  }
+
+  public synchronized List<Fallible<Long>> removeEntries(List<Long> entryIds) {
+    ArrayList<Fallible<Long>> results = 
+        new ArrayList<Fallible<Long>>(entryIds.size());
+    for (Long entryId : entryIds) {
+      results.add(removeEntry(entryId));
+    }
+    return results;
+  }
+
+  public synchronized List<PathCacheEntry> listPathCacheEntries(long prevId,
+      String pool, int maxReplies) {
+    final int MAX_PRE_ALLOCATED_ENTRIES = 16;
+    ArrayList<PathCacheEntry> replies =
+        new ArrayList<PathCacheEntry>(Math.min(MAX_PRE_ALLOCATED_ENTRIES, maxReplies));
+    int numReplies = 0;
+    SortedMap<Long, PathCacheEntry> tailMap = entriesById.tailMap(prevId + 1);
+    for (Entry<Long, PathCacheEntry> cur : tailMap.entrySet()) {
+      if (numReplies >= maxReplies) {
+        return replies;
+      }
+      if (pool.isEmpty() || cur.getValue().getDirective().
+            getPool().equals(pool)) {
+        replies.add(cur.getValue());
+        numReplies++;
+      }
+    }
+    return replies;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -129,6 +129,7 @@ import org.apache.hadoop.fs.Options;
 import org.apache.hadoop.fs.Options.Rename;
 import org.apache.hadoop.fs.ParentNotDirectoryException;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.RemoteIterator;
 import org.apache.hadoop.fs.UnresolvedLinkException;
 import org.apache.hadoop.fs.permission.FsAction;
 import org.apache.hadoop.fs.permission.FsPermission;
@@ -141,6 +142,8 @@ import org.apache.hadoop.hdfs.HAUtil;
 import org.apache.hadoop.hdfs.HdfsConfiguration;
 import org.apache.hadoop.hdfs.protocol.AlreadyBeingCreatedException;
 import org.apache.hadoop.hdfs.protocol.Block;
+import org.apache.hadoop.hdfs.protocol.PathCacheDirective;
+import org.apache.hadoop.hdfs.protocol.PathCacheEntry;
 import org.apache.hadoop.hdfs.protocol.ClientProtocol;
 import org.apache.hadoop.hdfs.protocol.DatanodeID;
 import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
@@ -223,6 +226,7 @@ import org.apache.hadoop.security.token.Token;
 import org.apache.hadoop.security.token.delegation.DelegationKey;
 import org.apache.hadoop.util.Daemon;
 import org.apache.hadoop.util.DataChecksum;
+import org.apache.hadoop.util.Fallible;
 import org.apache.hadoop.util.StringUtils;
 import org.apache.hadoop.util.Time;
 import org.apache.hadoop.util.VersionInfo;
@@ -360,6 +364,7 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
   FSDirectory dir;
   private final BlockManager blockManager;
   private final SnapshotManager snapshotManager;
+  private final CacheManager cacheManager;
   private final DatanodeStatistics datanodeStatistics;
 
   // Block pool ID used by this namenode
@@ -687,6 +692,7 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
       this.dtSecretManager = createDelegationTokenSecretManager(conf);
       this.dir = new FSDirectory(fsImage, this, conf);
       this.snapshotManager = new SnapshotManager(dir);
+      this.cacheManager= new CacheManager(dir, conf);
       this.safeMode = new SafeModeInfo(conf);
       this.auditLoggers = initAuditLoggers(conf);
       this.isDefaultAuditLogger = auditLoggers.size() == 1 &&
@@ -6741,6 +6747,20 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
     }
   }
 
+  List<Fallible<PathCacheEntry>> addPathCacheDirectives(
+      List<PathCacheDirective> directives) {
+    return cacheManager.addDirectives(directives);
+  }
+
+  List<Fallible<Long>> removePathCacheEntries(List<Long> ids) {
+    return cacheManager.removeEntries(ids);
+  }
+
+  List<PathCacheEntry> listPathCacheEntries(long startId, String pool,
+      int maxReplies) {
+    return cacheManager.listPathCacheEntries(startId, pool, maxReplies);
+  }
+
   /**
    * Default AuditLogger implementation; used when no access logger is
    * defined in the config file. It can also be explicitly listed in the
@@ -6777,7 +6797,9 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
         auditLog.info(sb);
       }
     }
-
   }
 
+  public CacheManager getCacheManager() {
+    return cacheManager;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeRpcServer.java

@@ -31,6 +31,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.List;
+import java.util.NoSuchElementException;
 
 import org.apache.commons.logging.Log;
 import org.apache.hadoop.HadoopIllegalArgumentException;
@@ -44,6 +45,7 @@ import org.apache.hadoop.fs.InvalidPathException;
 import org.apache.hadoop.fs.Options;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.ParentNotDirectoryException;
+import org.apache.hadoop.fs.RemoteIterator;
 import org.apache.hadoop.fs.UnresolvedLinkException;
 import org.apache.hadoop.fs.permission.FsPermission;
 import org.apache.hadoop.fs.permission.PermissionStatus;
@@ -58,6 +60,8 @@ import org.apache.hadoop.hdfs.DFSUtil;
 import org.apache.hadoop.hdfs.HDFSPolicyProvider;
 import org.apache.hadoop.hdfs.protocol.AlreadyBeingCreatedException;
 import org.apache.hadoop.hdfs.protocol.BlockListAsLongs;
+import org.apache.hadoop.hdfs.protocol.PathCacheDirective;
+import org.apache.hadoop.hdfs.protocol.PathCacheEntry;
 import org.apache.hadoop.hdfs.protocol.CorruptFileBlocks;
 import org.apache.hadoop.hdfs.protocol.DatanodeID;
 import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
@@ -133,6 +137,7 @@ import org.apache.hadoop.security.token.Token;
 import org.apache.hadoop.tools.proto.GetUserMappingsProtocolProtos.GetUserMappingsProtocolService;
 import org.apache.hadoop.tools.protocolPB.GetUserMappingsProtocolPB;
 import org.apache.hadoop.tools.protocolPB.GetUserMappingsProtocolServerSideTranslatorPB;
+import org.apache.hadoop.util.Fallible;
 import org.apache.hadoop.util.VersionInfo;
 import org.apache.hadoop.util.VersionUtil;
 
@@ -1200,4 +1205,81 @@ class NameNodeRpcServer implements NamenodeProtocols {
     metrics.incrSnapshotDiffReportOps();
     return report;
   }
+
+  @Override
+  public List<Fallible<PathCacheEntry>> addPathCacheDirectives(
+      List<PathCacheDirective> paths) throws IOException {
+    return namesystem.addPathCacheDirectives(paths);
+  }
+
+  @Override
+  public List<Fallible<Long>> removePathCacheEntries(List<Long> ids)
+      throws IOException {
+    return namesystem.removePathCacheEntries(ids);
+  }
+
+  private class PathCacheEntriesIterator
+      implements RemoteIterator<PathCacheEntry> {
+    private long prevId;
+    private final String pool;
+    private final int repliesPerRequest;
+    private List<PathCacheEntry> entries;
+    private int idx;
+
+    public PathCacheEntriesIterator(long prevId, String pool,
+        int repliesPerRequest) {
+      this.prevId = prevId;
+      this.pool = pool;
+      this.repliesPerRequest = repliesPerRequest;
+      this.entries = null;
+      this.idx = -1;
+    }
+
+    private void makeRequest() throws IOException {
+      idx = 0;
+      entries = null;
+      entries = namesystem.listPathCacheEntries(prevId, pool,
+          repliesPerRequest);
+      if (entries.isEmpty()) {
+        entries = null;
+      }
+    }
+
+    private void makeRequestIfNeeded() throws IOException {
+      if (idx == -1) {
+        makeRequest();
+      } else if ((entries != null) && (idx >= entries.size())) {
+        if (entries.size() < repliesPerRequest) {
+          // Last time, we got fewer entries than requested.
+          // So we should be at the end.
+          entries = null;
+        } else {
+          makeRequest();
+        }
+      }
+    }
+
+    @Override
+    public boolean hasNext() throws IOException {
+      makeRequestIfNeeded();
+      return (entries != null);
+    }
+
+    @Override
+    public PathCacheEntry next() throws IOException {
+      makeRequestIfNeeded();
+      if (entries == null) {
+        throw new NoSuchElementException();
+      }
+      PathCacheEntry entry = entries.get(idx++);
+      prevId = entry.getEntryId();
+      return entry;
+    }
+  }
+  
+  @Override
+  public RemoteIterator<PathCacheEntry> listPathCacheEntries(long prevId, String pool,
+      int maxReplies) throws IOException {
+    return new PathCacheEntriesIterator(prevId, pool, maxReplies);
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/proto/ClientNamenodeProtocol.proto

@@ -363,6 +363,57 @@ message IsFileClosedResponseProto {
   required bool result = 1;
 }
 
+message PathCacheDirectiveProto {
+  required string path = 1;
+  required string pool = 2;
+}
+
+message AddPathCacheDirectivesRequestProto {
+  repeated PathCacheDirectiveProto elements = 1;
+}
+
+message AddPathCacheDirectivesResponseProto {
+  repeated int64 results = 1 [packed=true];
+}
+
+enum AddPathCacheDirectiveErrorProto {
+  EMPTY_PATH_ERROR = -1;
+  INVALID_PATH_NAME_ERROR = -2;
+  INVALID_POOL_NAME_ERROR = -3;
+  UNEXPECTED_ADD_ERROR = -4;
+}
+
+message RemovePathCacheEntriesRequestProto {
+  repeated int64 elements = 1 [packed=true];
+}
+
+message RemovePathCacheEntriesResponseProto {
+  repeated int64 results = 1 [packed=true];
+}
+
+enum RemovePathCacheEntryErrorProto {
+  INVALID_CACHED_PATH_ID_ERROR = -1;
+  NO_SUCH_CACHED_PATH_ID_ERROR = -2;
+  UNEXPECTED_REMOVE_ERROR = -3;
+}
+
+message ListPathCacheEntriesRequestProto {
+  required int64 prevId = 1;
+  required string pool = 2;
+  optional int32 maxReplies = 3;
+}
+
+message ListPathCacheEntriesElementProto {
+  required int64 id = 1;
+  required string path = 2;
+  required string pool = 3;
+}
+
+message ListPathCacheEntriesResponseProto {
+  repeated ListPathCacheEntriesElementProto elements = 1;
+  required bool hasMore = 2;
+}
+
 message GetFileLinkInfoRequestProto {
   required string src = 1;
 }
@@ -544,6 +595,12 @@ service ClientNamenodeProtocol {
       returns(ListCorruptFileBlocksResponseProto);
   rpc metaSave(MetaSaveRequestProto) returns(MetaSaveResponseProto);
   rpc getFileInfo(GetFileInfoRequestProto) returns(GetFileInfoResponseProto);
+  rpc addPathCacheDirectives(AddPathCacheDirectivesRequestProto)
+      returns (AddPathCacheDirectivesResponseProto);
+  rpc removePathCacheEntries(RemovePathCacheEntriesRequestProto)
+      returns (RemovePathCacheEntriesResponseProto);
+  rpc listPathCacheEntries(ListPathCacheEntriesRequestProto)
+      returns (ListPathCacheEntriesResponseProto);
   rpc getFileLinkInfo(GetFileLinkInfoRequestProto)
       returns(GetFileLinkInfoResponseProto);
   rpc getContentSummary(GetContentSummaryRequestProto)

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestPathCacheRequests.java

@@ -0,0 +1,150 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.namenode;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+
+import junit.framework.Assert;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.RemoteIterator;
+import org.apache.hadoop.hdfs.HdfsConfiguration;
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.EmptyPathError;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.InvalidPoolNameError;
+import org.apache.hadoop.hdfs.protocol.AddPathCacheDirectiveException.InvalidPathNameError;
+import org.apache.hadoop.hdfs.protocol.RemovePathCacheEntryException.InvalidIdException;
+import org.apache.hadoop.hdfs.protocol.PathCacheDirective;
+import org.apache.hadoop.hdfs.protocol.PathCacheEntry;
+import org.apache.hadoop.hdfs.protocol.RemovePathCacheEntryException.NoSuchIdException;
+import org.apache.hadoop.hdfs.server.protocol.NamenodeProtocols;
+import org.apache.hadoop.util.Fallible;
+import org.junit.Test;
+
+public class TestPathCacheRequests {
+  static final Log LOG = LogFactory.getLog(TestPathCacheRequests.class);
+
+  private static void validateListAll(
+      RemoteIterator<PathCacheEntry> iter,
+      long id0, long id1, long id2) throws Exception {
+    Assert.assertEquals(new PathCacheEntry(id0,
+        new PathCacheDirective("/alpha", "pool1")),
+        iter.next());
+    Assert.assertEquals(new PathCacheEntry(id1,
+        new PathCacheDirective("/beta", "pool2")),
+        iter.next());
+    Assert.assertEquals(new PathCacheEntry(id2,
+        new PathCacheDirective("/gamma", "pool1")),
+        iter.next());
+    Assert.assertFalse(iter.hasNext());
+  }
+
+  @Test
+  public void testSetAndGet() throws Exception {
+    Configuration conf = new HdfsConfiguration();
+    MiniDFSCluster cluster = null;
+
+    try {
+      cluster = new MiniDFSCluster.Builder(conf).numDataNodes(1).build();
+      cluster.waitActive();
+      NamenodeProtocols proto = cluster.getNameNodeRpc();
+      List<Fallible<PathCacheEntry>> addResults1 = 
+          proto.addPathCacheDirectives(Arrays.asList(
+            new PathCacheDirective[] {
+        new PathCacheDirective("/alpha", "pool1"),
+        new PathCacheDirective("/beta", "pool2"),
+        new PathCacheDirective("", "pool3")
+      }));
+      long ids1[] = new long[2];
+      ids1[0] = addResults1.get(0).get().getEntryId();
+      ids1[1] = addResults1.get(1).get().getEntryId();
+      try {
+        addResults1.get(2).get();
+        Assert.fail("expected an error when adding an empty path");
+      } catch (IOException ioe) {
+        Assert.assertTrue(ioe.getCause() instanceof EmptyPathError);
+      }
+
+      List<Fallible<PathCacheEntry>> addResults2 = 
+          proto.addPathCacheDirectives(Arrays.asList(
+            new PathCacheDirective[] {
+        new PathCacheDirective("/alpha", "pool1"),
+        new PathCacheDirective("/theta", ""),
+        new PathCacheDirective("bogus", "pool1"),
+        new PathCacheDirective("/gamma", "pool1")
+      }));
+      long id = addResults2.get(0).get().getEntryId();
+      Assert.assertEquals("expected to get back the same ID as last time " +
+          "when re-adding an existing path cache directive.", ids1[0], id);
+      try {
+        addResults2.get(1).get();
+        Assert.fail("expected an error when adding a path cache " +
+            "directive with an empty pool name.");
+      } catch (IOException ioe) {
+        Assert.assertTrue(ioe.getCause() instanceof InvalidPoolNameError);
+      }
+      try {
+        addResults2.get(2).get();
+        Assert.fail("expected an error when adding a path cache " +
+            "directive with a non-absolute path name.");
+      } catch (IOException ioe) {
+        Assert.assertTrue(ioe.getCause() instanceof InvalidPathNameError);
+      }
+      long ids2[] = new long[1];
+      ids2[0] = addResults2.get(3).get().getEntryId();
+
+      RemoteIterator<PathCacheEntry> iter =
+          proto.listPathCacheEntries(0, "", 100);
+      validateListAll(iter, ids1[0], ids1[1], ids2[0]);
+      iter = proto.listPathCacheEntries(0, "", 1);
+      validateListAll(iter, ids1[0], ids1[1], ids2[0]);
+      iter = proto.listPathCacheEntries(0, "pool3", 1);
+      Assert.assertFalse(iter.hasNext());
+      iter = proto.listPathCacheEntries(0, "pool2", 4444);
+      Assert.assertEquals(addResults1.get(1).get(),
+          iter.next());
+      Assert.assertFalse(iter.hasNext());
+
+      List<Fallible<Long>> removeResults1 = 
+          proto.removePathCacheEntries(Arrays.asList(
+            new Long[] { ids1[1], -42L, 999999L }));
+      Assert.assertEquals(Long.valueOf(ids1[1]),
+          removeResults1.get(0).get());
+      try {
+        removeResults1.get(1).get();
+        Assert.fail("expected an error when removing a negative ID");
+      } catch (IOException ioe) {
+        Assert.assertTrue(ioe.getCause() instanceof InvalidIdException);
+      }
+      try {
+        removeResults1.get(2).get();
+        Assert.fail("expected an error when removing a nonexistent ID");
+      } catch (IOException ioe) {
+        Assert.assertTrue(ioe.getCause() instanceof NoSuchIdException);
+      }
+      iter = proto.listPathCacheEntries(0, "pool2", 4444);
+      Assert.assertFalse(iter.hasNext());
+    } finally {
+      if (cluster != null) { cluster.shutdown(); }
+    }
+  }
+}