HDFS-5260. Merging change r1527113 from trunk to branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1527115 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/ByteBufferUtil.java

@@ -0,0 +1,113 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.fs;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.ByteBuffer;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.io.ByteBufferPool;
+
+import com.google.common.base.Preconditions;
+
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public final class ByteBufferUtil {
+
+  /**
+   * Determine if a stream can do a byte buffer read via read(ByteBuffer buf)
+   */
+  private static boolean streamHasByteBufferRead(InputStream stream) {
+    if (!(stream instanceof ByteBufferReadable)) {
+      return false;
+    }
+    if (!(stream instanceof FSDataInputStream)) {
+      return true;
+    }
+    return ((FSDataInputStream)stream).getWrappedStream() 
+        instanceof ByteBufferReadable;
+  }
+
+  /**
+   * Perform a fallback read.
+   */
+  public static ByteBuffer fallbackRead(
+      InputStream stream, ByteBufferPool bufferPool, int maxLength)
+          throws IOException {
+    if (bufferPool == null) {
+      throw new UnsupportedOperationException("zero-copy reads " +
+          "were not available, and you did not provide a fallback " +
+          "ByteBufferPool.");
+    }
+    boolean useDirect = streamHasByteBufferRead(stream);
+    ByteBuffer buffer = bufferPool.getBuffer(useDirect, maxLength);
+    if (buffer == null) {
+      throw new UnsupportedOperationException("zero-copy reads " +
+          "were not available, and the ByteBufferPool did not provide " +
+          "us with " + (useDirect ? "a direct" : "an indirect") +
+          "buffer.");
+    }
+    Preconditions.checkState(buffer.capacity() > 0);
+    Preconditions.checkState(buffer.isDirect() == useDirect);
+    maxLength = Math.min(maxLength, buffer.capacity());
+    boolean success = false;
+    try {
+      if (useDirect) {
+        buffer.clear();
+        buffer.limit(maxLength);
+        ByteBufferReadable readable = (ByteBufferReadable)stream;
+        int totalRead = 0;
+        while (true) {
+          if (totalRead >= maxLength) {
+            success = true;
+            break;
+          }
+          int nRead = readable.read(buffer);
+          if (nRead < 0) {
+            if (totalRead > 0) {
+              success = true;
+            }
+            break;
+          }
+          totalRead += nRead;
+        }
+        buffer.flip();
+      } else {
+        buffer.clear();
+        int nRead = stream.read(buffer.array(),
+            buffer.arrayOffset(), maxLength);
+        if (nRead >= 0) {
+          buffer.limit(nRead);
+          success = true;
+        }
+      }
+    } finally {
+      if (!success) {
+        // If we got an error while reading, or if we are at EOF, we 
+        // don't need the buffer any more.  We can give it back to the
+        // bufferPool.
+        bufferPool.putBuffer(buffer);
+        buffer = null;
+      }
+    }
+    return buffer;
+  }
+}

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FSDataInputStream.java

@@ -1,4 +1,5 @@
 /**
+ * 
  * 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
@@ -19,17 +20,29 @@ package org.apache.hadoop.fs;
 
 import java.io.*;
 import java.nio.ByteBuffer;
+import java.util.EnumSet;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.io.ByteBufferPool;
+import org.apache.hadoop.fs.ByteBufferUtil;
+import org.apache.hadoop.util.IdentityHashStore;
 
 /** Utility that wraps a {@link FSInputStream} in a {@link DataInputStream}
  * and buffers input through a {@link BufferedInputStream}. */
 @InterfaceAudience.Public
 @InterfaceStability.Stable
 public class FSDataInputStream extends DataInputStream
-    implements Seekable, PositionedReadable, Closeable,
-    ByteBufferReadable, HasFileDescriptor, CanSetDropBehind, CanSetReadahead {
+    implements Seekable, PositionedReadable, Closeable, 
+      ByteBufferReadable, HasFileDescriptor, CanSetDropBehind, CanSetReadahead,
+      HasEnhancedByteBufferAccess {
+  /**
+   * Map ByteBuffers that we have handed out to readers to ByteBufferPool 
+   * objects
+   */
+  private final IdentityHashStore<ByteBuffer, ByteBufferPool>
+    extendedReadBuffers
+      = new IdentityHashStore<ByteBuffer, ByteBufferPool>(0);
 
   public FSDataInputStream(InputStream in)
     throws IOException {
@@ -167,4 +180,45 @@ public class FSDataInputStream extends DataInputStream
           "support setting the drop-behind caching setting.");
     }
   }
+
+  @Override
+  public ByteBuffer read(ByteBufferPool bufferPool, int maxLength,
+      EnumSet<ReadOption> opts) 
+          throws IOException, UnsupportedOperationException {
+    try {
+      return ((HasEnhancedByteBufferAccess)in).read(bufferPool,
+          maxLength, opts);
+    }
+    catch (ClassCastException e) {
+      ByteBuffer buffer = ByteBufferUtil.
+          fallbackRead(this, bufferPool, maxLength);
+      if (buffer != null) {
+        extendedReadBuffers.put(buffer, bufferPool);
+      }
+      return buffer;
+    }
+  }
+
+  private static final EnumSet<ReadOption> EMPTY_READ_OPTIONS_SET =
+      EnumSet.noneOf(ReadOption.class);
+
+  final public ByteBuffer read(ByteBufferPool bufferPool, int maxLength)
+          throws IOException, UnsupportedOperationException {
+    return read(bufferPool, maxLength, EMPTY_READ_OPTIONS_SET);
+  }
+  
+  @Override
+  public void releaseBuffer(ByteBuffer buffer) {
+    try {
+      ((HasEnhancedByteBufferAccess)in).releaseBuffer(buffer);
+    }
+    catch (ClassCastException e) {
+      ByteBufferPool bufferPool = extendedReadBuffers.remove( buffer);
+      if (bufferPool == null) {
+        throw new IllegalArgumentException("tried to release a buffer " +
+            "that was not created by this stream.");
+      }
+      bufferPool.putBuffer(buffer);
+    }
+  }
 }

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FSInputStream.java

@@ -18,9 +18,11 @@
 package org.apache.hadoop.fs;
 
 import java.io.*;
+import java.nio.ByteBuffer;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.fs.ZeroCopyUnavailableException;
 
 /****************************************************************
  * FSInputStream is a generic old InputStream with a little bit

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/HasEnhancedByteBufferAccess.java

@@ -0,0 +1,79 @@
+/**
+ * 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.fs;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.EnumSet;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.io.ByteBufferPool;
+
+/**
+ * FSDataInputStreams implement this interface to provide enhanced
+ * byte buffer access.  Usually this takes the form of mmap support.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public interface HasEnhancedByteBufferAccess {
+  /**
+   * Get a ByteBuffer containing file data.
+   *
+   * This ByteBuffer may come from the stream itself, via a call like mmap,
+   * or it may come from the ByteBufferFactory which is passed in as an
+   * argument.
+   *
+   * @param factory
+   *            If this is non-null, it will be used to create a fallback
+   *            ByteBuffer when the stream itself cannot create one.
+   * @param maxLength
+   *            The maximum length of buffer to return.  We may return a buffer
+   *            which is shorter than this.
+   * @param opts
+   *            Options to use when reading.
+   *
+   * @return
+   *            We will return null on EOF (and only on EOF).
+   *            Otherwise, we will return a direct ByteBuffer containing at
+   *            least one byte.  You must free this ByteBuffer when you are 
+   *            done with it by calling releaseBuffer on it.
+   *            The buffer will continue to be readable until it is released 
+   *            in this manner.  However, the input stream's close method may
+   *            warn about unclosed buffers.
+   * @throws
+   *            IOException: if there was an error reading.
+   *            UnsupportedOperationException: if factory was null, and we
+   *            needed an external byte buffer.  UnsupportedOperationException
+   *            will never be thrown unless the factory argument is null.
+   */
+  public ByteBuffer read(ByteBufferPool factory, int maxLength,
+      EnumSet<ReadOption> opts)
+          throws IOException, UnsupportedOperationException;
+
+  /**
+   * Release a ByteBuffer which was created by the enhanced ByteBuffer read
+   * function. You must not continue using the ByteBuffer after calling this 
+   * function.
+   *
+   * @param buffer
+   *            The ByteBuffer to release.
+   */
+  public void releaseBuffer(ByteBuffer buffer);
+}

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/ReadOption.java

@@ -0,0 +1,34 @@
+/**
+ * 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.fs;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+
+/**
+ * Options that can be used when reading from a FileSystem.
+ */
+@InterfaceAudience.Public
+@InterfaceStability.Stable
+public enum ReadOption {
+  /**
+   * Skip checksums when reading.  This option may be useful when reading a file
+   * format that has built-in checksums, or for testing purposes.
+   */
+  SKIP_CHECKSUMS,
+}

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/ZeroCopyUnavailableException.java

@@ -0,0 +1,36 @@
+/**
+ * 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.fs;
+
+import java.io.IOException;
+
+public class ZeroCopyUnavailableException extends IOException {
+  private static final long serialVersionUID = 0L;
+
+  public ZeroCopyUnavailableException(String message) {
+    super(message);
+  }
+
+  public ZeroCopyUnavailableException(String message, Exception e) {
+    super(message, e);
+  }
+
+  public ZeroCopyUnavailableException(Exception e) {
+    super(e);
+  }
+}

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/ByteBufferPool.java

@@ -0,0 +1,48 @@
+/**
+ * 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.io;
+
+import java.nio.ByteBuffer;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+
+@InterfaceAudience.Public
+@InterfaceStability.Stable
+public interface ByteBufferPool {
+  /**
+   * Get a new direct ByteBuffer.  The pool can provide this from
+   * removing a buffer from its internal cache, or by allocating a 
+   * new buffer.
+   *
+   * @param direct     Whether the buffer should be direct.
+   * @param length     The minimum length the buffer will have.
+   * @return           A new ByteBuffer.  This ByteBuffer must be direct.
+   *                   Its capacity can be less than what was requested, but
+   *                   must be at least 1 byte.
+   */
+  ByteBuffer getBuffer(boolean direct, int length);
+
+  /**
+   * Release a buffer back to the pool.
+   * The pool may choose to put this buffer into its cache.
+   *
+   * @param buffer    a direct bytebuffer
+   */
+  void putBuffer(ByteBuffer buffer);
+}

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/ElasticByteBufferPool.java

@@ -0,0 +1,118 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.io;
+
+import com.google.common.collect.ComparisonChain;
+import org.apache.commons.lang.builder.HashCodeBuilder;
+
+import java.nio.ByteBuffer;
+import java.util.Map;
+import java.util.TreeMap;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+
+/**
+ * This is a simple ByteBufferPool which just creates ByteBuffers as needed.
+ * It also caches ByteBuffers after they're released.  It will always return
+ * the smallest cached buffer with at least the capacity you request.
+ * We don't try to do anything clever here like try to limit the maximum cache
+ * size.
+ */
+@InterfaceAudience.Public
+@InterfaceStability.Stable
+public final class ElasticByteBufferPool implements ByteBufferPool {
+  private static final class Key implements Comparable<Key> {
+    private final int capacity;
+    private final long insertionTime;
+
+    Key(int capacity, long insertionTime) {
+      this.capacity = capacity;
+      this.insertionTime = insertionTime;
+    }
+
+    @Override
+    public int compareTo(Key other) {
+      return ComparisonChain.start().
+          compare(capacity, other.capacity).
+          compare(insertionTime, other.insertionTime).
+          result();
+    }
+
+    @Override
+    public boolean equals(Object rhs) {
+      if (rhs == null) {
+        return false;
+      }
+      try {
+        Key o = (Key)rhs;
+        return (compareTo(o) == 0);
+      } catch (ClassCastException e) {
+        return false;
+      }
+    }
+
+    @Override
+    public int hashCode() {
+      return new HashCodeBuilder().
+          append(capacity).
+          append(insertionTime).
+          toHashCode();
+    }
+  }
+
+  private final TreeMap<Key, ByteBuffer> buffers =
+      new TreeMap<Key, ByteBuffer>();
+
+  private final TreeMap<Key, ByteBuffer> directBuffers =
+      new TreeMap<Key, ByteBuffer>();
+
+  private final TreeMap<Key, ByteBuffer> getBufferTree(boolean direct) {
+    return direct ? directBuffers : buffers;
+  }
+  
+  @Override
+  public synchronized ByteBuffer getBuffer(boolean direct, int length) {
+    TreeMap<Key, ByteBuffer> tree = getBufferTree(direct);
+    Map.Entry<Key, ByteBuffer> entry =
+        tree.ceilingEntry(new Key(length, 0));
+    if (entry == null) {
+      return direct ? ByteBuffer.allocateDirect(length) :
+                      ByteBuffer.allocate(length);
+    }
+    tree.remove(entry.getKey());
+    return entry.getValue();
+  }
+
+  @Override
+  public synchronized void putBuffer(ByteBuffer buffer) {
+    TreeMap<Key, ByteBuffer> tree = getBufferTree(buffer.isDirect());
+    while (true) {
+      Key key = new Key(buffer.capacity(), System.nanoTime());
+      if (!tree.containsKey(key)) {
+        tree.put(key, buffer);
+        return;
+      }
+      // Buffers are indexed by (capacity, time).
+      // If our key is not unique on the first try, we try again, since the
+      // time will be different.  Since we use nanoseconds, it's pretty
+      // unlikely that we'll loop even once, unless the system clock has a
+      // poor granularity.
+    }
+  }
+}

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

@@ -0,0 +1,197 @@
+/**
+ * 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 org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+
+import com.google.common.base.Preconditions;
+
+/**
+ * The IdentityHashStore stores (key, value) mappings in an array.
+ * It is similar to java.util.HashTable, but much more lightweight.
+ * Neither inserting nor removing an element ever leads to any garbage
+ * getting created (assuming the array doesn't need to be enlarged).
+ *
+ * Unlike HashTable, it compares keys using
+ * {@link System#identityHashCode(Object)} and the identity operator.
+ * This is useful for types like ByteBuffer which have expensive hashCode
+ * and equals operators.
+ *
+ * We use linear probing to resolve collisions.  This avoids the need for
+ * the overhead of linked list data structures.  It also means that it is
+ * expensive to attempt to remove an element that isn't there, since we
+ * have to look at the entire array to be sure that it doesn't exist.
+ *
+ * @param <K>    The key type to use.
+ * @param <V>    THe value type to use.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+@SuppressWarnings("unchecked")
+public final class IdentityHashStore<K, V> {
+  /**
+   * Even elements are keys; odd elements are values.
+   * The array has size 1 + Math.pow(2, capacity).
+   */
+  private Object buffer[];
+
+  private int numInserted = 0;
+
+  private int capacity;
+
+  /**
+   * The default maxCapacity value to use.
+   */
+  private static final int DEFAULT_MAX_CAPACITY = 2;
+
+  public IdentityHashStore(int capacity) {
+    Preconditions.checkArgument(capacity >= 0);
+    if (capacity == 0) {
+      this.capacity = 0;
+      this.buffer = null;
+    } else {
+      // Round the capacity we need up to a power of 2.
+      realloc((int)Math.pow(2,
+          Math.ceil(Math.log(capacity) / Math.log(2))));
+    }
+  }
+
+  private void realloc(int newCapacity) {
+    Preconditions.checkArgument(newCapacity > 0);
+    Object prevBuffer[] = buffer;
+    this.capacity = newCapacity;
+    // Each element takes two array slots -- one for the key, 
+    // and another for the value.  We also want a load factor 
+    // of 0.50.  Combine those together and you get 4 * newCapacity.
+    this.buffer = new Object[4 * newCapacity];
+    this.numInserted = 0;
+    if (prevBuffer != null) {
+      for (int i = 0; i < prevBuffer.length; i += 2) {
+        if (prevBuffer[i] != null) {
+          putInternal(prevBuffer[i], prevBuffer[i + 1]);
+        }
+      }
+    }
+  }
+
+  private void putInternal(Object k, Object v) {
+    int hash = System.identityHashCode(k);
+    final int numEntries = buffer.length / 2;
+    int index = hash % numEntries;
+    while (true) {
+      if (buffer[2 * index] == null) {
+        buffer[2 * index] = k;
+        buffer[1 + (2 * index)] = v;
+        numInserted++;
+        return;
+      }
+      index = (index + 1) % numEntries;
+    }
+  }
+
+  /**
+   * Add a new (key, value) mapping.
+   *
+   * Inserting a new (key, value) never overwrites a previous one.
+   * In other words, you can insert the same key multiple times and it will
+   * lead to multiple entries.
+   */
+  public void put(K k, V v) {
+    Preconditions.checkNotNull(k);
+    if (buffer == null) {
+      realloc(DEFAULT_MAX_CAPACITY);
+    } else if (numInserted + 1 > capacity) {
+      realloc(capacity * 2);
+    }
+    putInternal(k, v);
+  }
+
+  private int getElementIndex(K k) {
+    if (buffer == null) {
+      return -1;
+    }
+    final int numEntries = buffer.length / 2;
+    int hash = System.identityHashCode(k);
+    int index = hash % numEntries;
+    int firstIndex = index;
+    do {
+      if (buffer[2 * index] == k) {
+        return index;
+      }
+      index = (index + 1) % numEntries;
+    } while (index != firstIndex);
+    return -1;
+  }
+
+  /**
+   * Retrieve a value associated with a given key.
+   */
+  public V get(K k) {
+    int index = getElementIndex(k);
+    if (index < 0) {
+      return null;
+    }
+    return (V)buffer[1 + (2 * index)];
+  }
+
+  /**
+   * Retrieve a value associated with a given key, and delete the
+   * relevant entry.
+   */
+  public V remove(K k) {
+    int index = getElementIndex(k);
+    if (index < 0) {
+      return null;
+    }
+    V val = (V)buffer[1 + (2 * index)];
+    buffer[2 * index] = null;
+    buffer[1 + (2 * index)] = null;
+    numInserted--;
+    return val;
+  }
+
+  public boolean isEmpty() {
+    return numInserted == 0;
+  }
+
+  public int numElements() {
+    return numInserted;
+  }
+
+  public int capacity() {
+    return capacity;
+  }
+
+  public interface Visitor<K, V> {
+    void accept(K k, V v);
+  }
+
+  /**
+   * Visit all key, value pairs in the IdentityHashStore.
+   */
+  public void visitAll(Visitor<K, V> visitor) {
+    int length = buffer == null ? 0 : buffer.length;
+    for (int i = 0; i < length; i += 2) {
+      if (buffer[i] != null) {
+        visitor.accept((K)buffer[i], (V)buffer[i + 1]);
+      }
+    }
+  }
+}

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/TestIdentityHashStore.java

@@ -0,0 +1,159 @@
+/**
+ * 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.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+
+import junit.framework.Assert;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.util.IdentityHashStore;
+import org.apache.hadoop.util.IdentityHashStore.Visitor;
+import org.junit.Test;
+
+public class TestIdentityHashStore {
+  private static final Log LOG = LogFactory.getLog(TestIdentityHashStore.class.getName());
+
+  private static class Key {
+    private final String name;
+
+    Key(String name) {
+      this.name = name;
+    }
+    
+    @Override
+    public int hashCode() {
+      throw new RuntimeException("should not be used!");
+    }
+    
+    @Override
+    public boolean equals(Object o) {
+      if (!(o instanceof Key)) {
+        return false;
+      }
+      Key other = (Key)o;
+      return name.equals(other.name);
+    }
+  }
+
+  @Test(timeout=60000)
+  public void testStartingWithZeroCapacity() {
+    IdentityHashStore<Key, Integer> store = 
+        new IdentityHashStore<Key, Integer>(0);
+    store.visitAll(new Visitor<Key, Integer>() {
+      @Override
+      public void accept(Key k, Integer v) {
+        Assert.fail("found key " + k + " in empty IdentityHashStore.");
+      }
+    });
+    Assert.assertTrue(store.isEmpty());
+    final Key key1 = new Key("key1");
+    Integer value1 = new Integer(100);
+    store.put(key1, value1);
+    Assert.assertTrue(!store.isEmpty());
+    Assert.assertEquals(value1, store.get(key1));
+    store.visitAll(new Visitor<Key, Integer>() {
+      @Override
+      public void accept(Key k, Integer v) {
+        Assert.assertEquals(key1, k);
+      }
+    });
+    Assert.assertEquals(value1, store.remove(key1));
+    Assert.assertTrue(store.isEmpty());
+  }
+  
+  @Test(timeout=60000)
+  public void testDuplicateInserts() {
+    IdentityHashStore<Key, Integer> store = 
+        new IdentityHashStore<Key, Integer>(4);
+    store.visitAll(new Visitor<Key, Integer>() {
+      @Override
+      public void accept(Key k, Integer v) {
+        Assert.fail("found key " + k + " in empty IdentityHashStore.");
+      }
+    });
+    Assert.assertTrue(store.isEmpty());
+    Key key1 = new Key("key1");
+    Integer value1 = new Integer(100);
+    Integer value2 = new Integer(200);
+    Integer value3 = new Integer(300);
+    store.put(key1, value1);
+    Key equalToKey1 = new Key("key1");
+
+    // IdentityHashStore compares by object equality, not equals()
+    Assert.assertNull(store.get(equalToKey1)); 
+
+    Assert.assertTrue(!store.isEmpty());
+    Assert.assertEquals(value1, store.get(key1));
+    store.put(key1, value2);
+    store.put(key1, value3);
+    final List<Integer> allValues = new LinkedList<Integer>();
+    store.visitAll(new Visitor<Key, Integer>() {
+      @Override
+      public void accept(Key k, Integer v) {
+        allValues.add(v);
+      }
+    });
+    Assert.assertEquals(3, allValues.size());
+    for (int i = 0; i < 3; i++) {
+      Integer value = store.remove(key1);
+      Assert.assertTrue(allValues.remove(value));
+    }
+    Assert.assertNull(store.remove(key1));
+    Assert.assertTrue(store.isEmpty());
+  }
+  
+  @Test(timeout=60000)
+  public void testAdditionsAndRemovals() {
+    IdentityHashStore<Key, Integer> store = 
+        new IdentityHashStore<Key, Integer>(0);
+    final int NUM_KEYS = 1000;
+    LOG.debug("generating " + NUM_KEYS + " keys");
+    final List<Key> keys = new ArrayList<Key>(NUM_KEYS);
+    for (int i = 0; i < NUM_KEYS; i++) {
+      keys.add(new Key("key " + i));
+    }
+    for (int i = 0; i < NUM_KEYS; i++) {
+      store.put(keys.get(i), i);
+    }
+    store.visitAll(new Visitor<Key, Integer>() {
+      @Override
+      public void accept(Key k, Integer v) {
+        Assert.assertTrue(keys.contains(k));
+      }
+    });
+    for (int i = 0; i < NUM_KEYS; i++) {
+      Assert.assertEquals(Integer.valueOf(i),
+          store.remove(keys.get(i)));
+    }
+    store.visitAll(new Visitor<Key, Integer>() {
+      @Override
+      public void accept(Key k, Integer v) {
+        Assert.fail("expected all entries to be removed");
+      }
+    });
+    Assert.assertTrue("expected the store to be " +
+        "empty, but found " + store.numElements() + " elements.",
+        store.isEmpty());
+    Assert.assertEquals(1024, store.capacity());
+  }
+  
+}

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

@@ -9,6 +9,9 @@ Release 2.3.0 - UNRELEASED
     HDFS-5122. Support failover and retry in WebHdfsFileSystem for NN HA.
     (Haohui Mai via jing9)
 
+    HDFS-4953. Enable HDFS local reads via mmap.
+    (Colin Patrick McCabe via wang).
+
   IMPROVEMENTS
 
     HDFS-4657.  Limit the number of blocks logged by the NN after a block
@@ -50,6 +53,12 @@ Release 2.3.0 - UNRELEASED
 
     HDFS-5240. Separate formatting from logging in the audit logger API (daryn)
 
+    HDFS-5191. Revisit zero-copy API in FSDataInputStream to make it more
+    intuitive.  (Contributed by Colin Patrick McCabe)
+
+    HDFS-5260. Merge zero-copy memory-mapped HDFS client reads to trunk and
+    branch-2. (cnauroth)
+
   OPTIMIZATIONS
 
     HDFS-5239.  Allow FSNamesystem lock fairness to be configurable (daryn)
@@ -72,6 +81,8 @@ Release 2.3.0 - UNRELEASED
     HDFS-5170. BlockPlacementPolicyDefault uses the wrong classname when
     alerting to enable debug logging. (Andrew Wang)
 
+    HDFS-5266. ElasticByteBufferPool#Key does not implement equals. (cnauroth)
+
 Release 2.2.0 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/dev-support/findbugsExcludeFile.xml

@@ -330,4 +330,14 @@
        <Method name="setDirInternal" />
        <Bug pattern="DM_STRING_CTOR" />
      </Match>
+    <Match>
+      <Class name="org.apache.hadoop.hdfs.client.ClientMmapManager" />
+      <Method name="create" />
+      <Bug pattern="UL_UNRELEASED_LOCK_EXCEPTION_PATH" />
+    </Match>
+    <Match>
+      <Class name="org.apache.hadoop.hdfs.client.ClientMmapManager" />
+      <Method name="create" />
+      <Bug pattern="UL_UNRELEASED_LOCK" />
+    </Match>
  </FindBugsFilter>

hadoop-hdfs-project/hadoop-hdfs/src/CMakeLists.txt

@@ -142,6 +142,7 @@ target_link_libraries(test_native_mini_dfs
 )
 
 add_executable(test_libhdfs_threaded
+    main/native/libhdfs/expect.c
     main/native/libhdfs/test_libhdfs_threaded.c
 )
 target_link_libraries(test_libhdfs_threaded
@@ -150,6 +151,16 @@ target_link_libraries(test_libhdfs_threaded
     pthread
 )
 
+add_executable(test_libhdfs_zerocopy
+    main/native/libhdfs/expect.c
+    main/native/libhdfs/test/test_libhdfs_zerocopy.c
+)
+target_link_libraries(test_libhdfs_zerocopy
+    hdfs
+    native_mini_dfs
+    pthread
+)
+
 IF(REQUIRE_LIBWEBHDFS)
     add_subdirectory(contrib/libwebhdfs)
 ENDIF(REQUIRE_LIBWEBHDFS)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReader.java

@@ -20,12 +20,16 @@ package org.apache.hadoop.hdfs;
 import java.io.IOException;
 
 import org.apache.hadoop.fs.ByteBufferReadable;
+import org.apache.hadoop.hdfs.client.ClientMmap;
+import org.apache.hadoop.hdfs.client.ClientMmapManager;
+import org.apache.hadoop.hdfs.protocol.LocatedBlock;
 
 /**
  * A BlockReader is responsible for reading a single block
  * from a single datanode.
  */
 public interface BlockReader extends ByteBufferReadable {
+  
 
   /* same interface as inputStream java.io.InputStream#read()
    * used by DFSInputStream#read()
@@ -81,4 +85,14 @@ public interface BlockReader extends ByteBufferReadable {
    *                      All short-circuit reads are also local.
    */
   boolean isShortCircuit();
+
+  /**
+   * Get a ClientMmap object for this BlockReader.
+   *
+   * @param curBlock      The current block.
+   * @return              The ClientMmap object, or null if mmap is not
+   *                      supported.
+   */
+  ClientMmap getClientMmap(LocatedBlock curBlock,
+        ClientMmapManager mmapManager);
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocal.java

@@ -22,11 +22,15 @@ import java.io.DataInputStream;
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.nio.ByteBuffer;
+import org.apache.hadoop.conf.Configuration;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.hdfs.client.ClientMmap;
+import org.apache.hadoop.hdfs.client.ClientMmapManager;
 import org.apache.hadoop.hdfs.protocol.DatanodeID;
 import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.protocol.LocatedBlock;
 import org.apache.hadoop.hdfs.server.datanode.BlockMetadataHeader;
 import org.apache.hadoop.hdfs.util.DirectBufferPool;
 import org.apache.hadoop.io.IOUtils;
@@ -87,6 +91,8 @@ class BlockReaderLocal implements BlockReader {
   private final ExtendedBlock block;
   
   private final FileInputStreamCache fisCache;
+  private ClientMmap clientMmap;
+  private boolean mmapDisabled;
   
   private static int getSlowReadBufferNumChunks(int bufSize,
       int bytesPerChecksum) {
@@ -113,6 +119,8 @@ class BlockReaderLocal implements BlockReader {
     this.datanodeID = datanodeID;
     this.block = block;
     this.fisCache = fisCache;
+    this.clientMmap = null;
+    this.mmapDisabled = false;
 
     // read and handle the common header here. For now just a version
     checksumIn.getChannel().position(0);
@@ -487,6 +495,10 @@ class BlockReaderLocal implements BlockReader {
 
   @Override
   public synchronized void close() throws IOException {
+    if (clientMmap != null) {
+      clientMmap.unref();
+      clientMmap = null;
+    }
     if (fisCache != null) {
       if (LOG.isDebugEnabled()) {
         LOG.debug("putting FileInputStream for " + filename +
@@ -534,4 +546,30 @@ class BlockReaderLocal implements BlockReader {
   public boolean isShortCircuit() {
     return true;
   }
+
+  @Override
+  public ClientMmap getClientMmap(LocatedBlock curBlock,
+      ClientMmapManager mmapManager) {
+    if (clientMmap == null) {
+      if (mmapDisabled) {
+        return null;
+      }
+      try {
+        clientMmap = mmapManager.fetch(datanodeID, block, dataIn);
+        if (clientMmap == null) {
+          mmapDisabled = true;
+          return null;
+        }
+      } catch (InterruptedException e) {
+        LOG.error("Interrupted while setting up mmap for " + filename, e);
+        Thread.currentThread().interrupt();
+        return null;
+      } catch (IOException e) {
+        LOG.error("unable to set up mmap for " + filename, e);
+        mmapDisabled = true;
+        return null;
+      }
+    }
+    return clientMmap;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocalLegacy.java

@@ -28,6 +28,8 @@ import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.Map;
 
+import org.apache.hadoop.hdfs.client.ClientMmap;
+import org.apache.hadoop.hdfs.client.ClientMmapManager;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.conf.Configuration;
@@ -35,6 +37,7 @@ import org.apache.hadoop.hdfs.protocol.BlockLocalPathInfo;
 import org.apache.hadoop.hdfs.protocol.ClientDatanodeProtocol;
 import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
 import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.protocol.LocatedBlock;
 import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
 import org.apache.hadoop.hdfs.server.datanode.BlockMetadataHeader;
 import org.apache.hadoop.hdfs.util.DirectBufferPool;
@@ -701,4 +704,10 @@ class BlockReaderLocalLegacy implements BlockReader {
   public boolean isShortCircuit() {
     return true;
   }
+
+  @Override
+  public ClientMmap getClientMmap(LocatedBlock curBlock,
+      ClientMmapManager mmapManager) {
+    return null;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSClient.java

@@ -106,6 +106,7 @@ import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.UnresolvedLinkException;
 import org.apache.hadoop.fs.VolumeId;
 import org.apache.hadoop.fs.permission.FsPermission;
+import org.apache.hadoop.hdfs.client.ClientMmapManager;
 import org.apache.hadoop.hdfs.client.HdfsDataInputStream;
 import org.apache.hadoop.hdfs.client.HdfsDataOutputStream;
 import org.apache.hadoop.hdfs.protocol.ClientProtocol;
@@ -208,7 +209,43 @@ public class DFSClient implements java.io.Closeable {
   private boolean shouldUseLegacyBlockReaderLocal;
   private final CachingStrategy defaultReadCachingStrategy;
   private final CachingStrategy defaultWriteCachingStrategy;
+  private ClientMmapManager mmapManager;
   
+  private static final ClientMmapManagerFactory MMAP_MANAGER_FACTORY =
+      new ClientMmapManagerFactory();
+
+  private static final class ClientMmapManagerFactory {
+    private ClientMmapManager mmapManager = null;
+    /**
+     * Tracks the number of users of mmapManager.
+     */
+    private int refcnt = 0;
+
+    synchronized ClientMmapManager get(Configuration conf) {
+      if (refcnt++ == 0) {
+        mmapManager = ClientMmapManager.fromConf(conf);
+      } else {
+        String mismatches = mmapManager.verifyConfigurationMatches(conf);
+        if (!mismatches.isEmpty()) {
+          LOG.warn("The ClientMmapManager settings you specified " +
+            "have been ignored because another thread created the " +
+            "ClientMmapManager first.  " + mismatches);
+        }
+      }
+      return mmapManager;
+    }
+    
+    synchronized void unref(ClientMmapManager mmapManager) {
+      if (this.mmapManager != mmapManager) {
+        throw new IllegalArgumentException();
+      }
+      if (--refcnt == 0) {
+        IOUtils.cleanup(LOG, mmapManager);
+        mmapManager = null;
+      }
+    }
+  }
+
   /**
    * DFSClient configuration 
    */
@@ -536,6 +573,7 @@ public class DFSClient implements java.io.Closeable {
         new CachingStrategy(readDropBehind, readahead);
     this.defaultWriteCachingStrategy =
         new CachingStrategy(writeDropBehind, readahead);
+    this.mmapManager = MMAP_MANAGER_FACTORY.get(conf);
   }
   
   /**
@@ -740,9 +778,12 @@ public class DFSClient implements java.io.Closeable {
   
   /** Abort and release resources held.  Ignore all errors. */
   void abort() {
+    if (mmapManager != null) {
+      MMAP_MANAGER_FACTORY.unref(mmapManager);
+      mmapManager = null;
+    }
     clientRunning = false;
     closeAllFilesBeingWritten(true);
-
     try {
       // remove reference to this client and stop the renewer,
       // if there is no more clients under the renewer.
@@ -786,6 +827,10 @@ public class DFSClient implements java.io.Closeable {
    */
   @Override
   public synchronized void close() throws IOException {
+    if (mmapManager != null) {
+      MMAP_MANAGER_FACTORY.unref(mmapManager);
+      mmapManager = null;
+    }
     if(clientRunning) {
       closeAllFilesBeingWritten(false);
       clientRunning = false;
@@ -2514,4 +2559,9 @@ public class DFSClient implements java.io.Closeable {
   public CachingStrategy getDefaultWriteCachingStrategy() {
     return defaultWriteCachingStrategy;
   }
+
+  @VisibleForTesting
+  public ClientMmapManager getMmapManager() {
+    return mmapManager;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -376,6 +376,12 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final int DFS_CLIENT_READ_SHORTCIRCUIT_BUFFER_SIZE_DEFAULT = 1024 * 1024;
   public static final String DFS_CLIENT_DOMAIN_SOCKET_DATA_TRAFFIC = "dfs.client.domain.socket.data.traffic";
   public static final boolean DFS_CLIENT_DOMAIN_SOCKET_DATA_TRAFFIC_DEFAULT = false;
+  public static final String DFS_CLIENT_MMAP_CACHE_SIZE = "dfs.client.mmap.cache.size";
+  public static final int DFS_CLIENT_MMAP_CACHE_SIZE_DEFAULT = 1024;
+  public static final String DFS_CLIENT_MMAP_CACHE_TIMEOUT_MS = "dfs.client.mmap.cache.timeout.ms";
+  public static final long DFS_CLIENT_MMAP_CACHE_TIMEOUT_MS_DEFAULT  = 15 * 60 * 1000;
+  public static final String DFS_CLIENT_MMAP_CACHE_THREAD_RUNS_PER_TIMEOUT = "dfs.client.mmap.cache.timeout.ms";
+  public static final int DFS_CLIENT_MMAP_CACHE_THREAD_RUNS_PER_TIMEOUT_DEFAULT  = 4;
 
   // property for fsimage compression
   public static final String DFS_IMAGE_COMPRESS_KEY = "dfs.image.compress";

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java

@@ -24,6 +24,7 @@ import java.net.Socket;
 import java.nio.ByteBuffer;
 import java.util.AbstractMap;
 import java.util.ArrayList;
+import java.util.EnumSet;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -36,11 +37,15 @@ import java.util.concurrent.ConcurrentHashMap;
 import org.apache.commons.io.IOUtils;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.fs.ByteBufferReadable;
+import org.apache.hadoop.fs.ByteBufferUtil;
 import org.apache.hadoop.fs.CanSetDropBehind;
 import org.apache.hadoop.fs.CanSetReadahead;
 import org.apache.hadoop.fs.ChecksumException;
 import org.apache.hadoop.fs.FSInputStream;
+import org.apache.hadoop.fs.HasEnhancedByteBufferAccess;
+import org.apache.hadoop.fs.ReadOption;
 import org.apache.hadoop.fs.UnresolvedLinkException;
+import org.apache.hadoop.hdfs.client.ClientMmap;
 import org.apache.hadoop.hdfs.net.DomainPeer;
 import org.apache.hadoop.hdfs.net.Peer;
 import org.apache.hadoop.hdfs.net.TcpPeerServer;
@@ -54,12 +59,14 @@ import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
 import org.apache.hadoop.hdfs.security.token.block.InvalidBlockTokenException;
 import org.apache.hadoop.hdfs.server.datanode.CachingStrategy;
 import org.apache.hadoop.hdfs.server.datanode.ReplicaNotFoundException;
+import org.apache.hadoop.io.ByteBufferPool;
 import org.apache.hadoop.ipc.RPC;
 import org.apache.hadoop.ipc.RemoteException;
 import org.apache.hadoop.net.NetUtils;
 import org.apache.hadoop.net.unix.DomainSocket;
 import org.apache.hadoop.security.AccessControlException;
 import org.apache.hadoop.security.token.Token;
+import org.apache.hadoop.util.IdentityHashStore;
 
 import com.google.common.annotations.VisibleForTesting;
 
@@ -69,7 +76,8 @@ import com.google.common.annotations.VisibleForTesting;
  ****************************************************************/
 @InterfaceAudience.Private
 public class DFSInputStream extends FSInputStream
-implements ByteBufferReadable, CanSetDropBehind, CanSetReadahead {
+implements ByteBufferReadable, CanSetDropBehind, CanSetReadahead,
+    HasEnhancedByteBufferAccess {
   @VisibleForTesting
   static boolean tcpReadsDisabledForTesting = false;
   private final PeerCache peerCache;
@@ -87,17 +95,28 @@ implements ByteBufferReadable, CanSetDropBehind, CanSetReadahead {
   private CachingStrategy cachingStrategy;
   private final ReadStatistics readStatistics = new ReadStatistics();
 
+  /**
+   * Track the ByteBuffers that we have handed out to readers.
+   * 
+   * The value type can be either ByteBufferPool or ClientMmap, depending on
+   * whether we this is a memory-mapped buffer or not.
+   */
+  private final IdentityHashStore<ByteBuffer, Object>
+      extendedReadBuffers = new IdentityHashStore<ByteBuffer, Object>(0);
+
   public static class ReadStatistics {
     public ReadStatistics() {
       this.totalBytesRead = 0;
       this.totalLocalBytesRead = 0;
       this.totalShortCircuitBytesRead = 0;
+      this.totalZeroCopyBytesRead = 0;
     }
 
     public ReadStatistics(ReadStatistics rhs) {
       this.totalBytesRead = rhs.getTotalBytesRead();
       this.totalLocalBytesRead = rhs.getTotalLocalBytesRead();
       this.totalShortCircuitBytesRead = rhs.getTotalShortCircuitBytesRead();
+      this.totalZeroCopyBytesRead = rhs.getTotalZeroCopyBytesRead();
     }
 
     /**
@@ -123,6 +142,13 @@ implements ByteBufferReadable, CanSetDropBehind, CanSetReadahead {
     public long getTotalShortCircuitBytesRead() {
       return totalShortCircuitBytesRead;
     }
+    
+    /**
+     * @return The total number of zero-copy bytes read.
+     */
+    public long getTotalZeroCopyBytesRead() {
+      return totalZeroCopyBytesRead;
+    }
 
     /**
      * @return The total number of bytes read which were not local.
@@ -145,12 +171,21 @@ implements ByteBufferReadable, CanSetDropBehind, CanSetReadahead {
       this.totalLocalBytesRead += amt;
       this.totalShortCircuitBytesRead += amt;
     }
+
+    void addZeroCopyBytes(long amt) {
+      this.totalBytesRead += amt;
+      this.totalLocalBytesRead += amt;
+      this.totalShortCircuitBytesRead += amt;
+      this.totalZeroCopyBytesRead += amt;
+    }
     
     private long totalBytesRead;
 
     private long totalLocalBytesRead;
 
     private long totalShortCircuitBytesRead;
+
+    private long totalZeroCopyBytesRead;
   }
   
   private final FileInputStreamCache fileInputStreamCache;
@@ -587,6 +622,20 @@ implements ByteBufferReadable, CanSetDropBehind, CanSetReadahead {
     }
     dfsClient.checkOpen();
 
+    if (!extendedReadBuffers.isEmpty()) {
+      final StringBuilder builder = new StringBuilder();
+      extendedReadBuffers.visitAll(new IdentityHashStore.Visitor<ByteBuffer, Object>() {
+        private String prefix = "";
+        @Override
+        public void accept(ByteBuffer k, Object v) {
+          builder.append(prefix).append(k);
+          prefix = ", ";
+        }
+      });
+      DFSClient.LOG.warn("closing file " + src + ", but there are still " +
+          "unreleased ByteBuffers allocated by read().  " +
+          "Please release " + builder.toString() + ".");
+    }
     if (blockReader != null) {
       blockReader.close();
       blockReader = null;
@@ -1393,4 +1442,100 @@ implements ByteBufferReadable, CanSetDropBehind, CanSetReadahead {
     this.cachingStrategy.setDropBehind(dropBehind);
     closeCurrentBlockReader();
   }
+
+  @Override
+  public synchronized ByteBuffer read(ByteBufferPool bufferPool,
+      int maxLength, EnumSet<ReadOption> opts) 
+          throws IOException, UnsupportedOperationException {
+    assert(maxLength > 0);
+    if (((blockReader == null) || (blockEnd == -1)) &&
+          (pos < getFileLength())) {
+      /*
+       * If we don't have a blockReader, or the one we have has no more bytes
+       * left to read, we call seekToBlockSource to get a new blockReader and
+       * recalculate blockEnd.  Note that we assume we're not at EOF here
+       * (we check this above).
+       */
+      if ((!seekToBlockSource(pos)) || (blockReader == null)) {
+        throw new IOException("failed to allocate new BlockReader " +
+            "at position " + pos);
+      }
+    }
+    boolean canSkipChecksums = opts.contains(ReadOption.SKIP_CHECKSUMS);
+    if (canSkipChecksums) {
+      ByteBuffer buffer = tryReadZeroCopy(maxLength);
+      if (buffer != null) {
+        return buffer;
+      }
+    }
+    ByteBuffer buffer = ByteBufferUtil.
+        fallbackRead(this, bufferPool, maxLength);
+    if (buffer != null) {
+      extendedReadBuffers.put(buffer, bufferPool);
+    }
+    return buffer;
+  }
+
+  private synchronized ByteBuffer tryReadZeroCopy(int maxLength)
+      throws IOException {
+    // Java ByteBuffers can't be longer than 2 GB, because they use
+    // 4-byte signed integers to represent capacity, etc.
+    // So we can't mmap the parts of the block higher than the 2 GB offset.
+    // FIXME: we could work around this with multiple memory maps.
+    // See HDFS-5101.
+    long blockEnd32 = Math.min(Integer.MAX_VALUE, blockEnd);
+    long curPos = pos;
+    long blockLeft = blockEnd32 - curPos + 1;
+    if (blockLeft <= 0) {
+      if (DFSClient.LOG.isDebugEnabled()) {
+        DFSClient.LOG.debug("unable to perform a zero-copy read from offset " +
+          curPos + " of " + src + "; blockLeft = " + blockLeft +
+          "; blockEnd32 = " + blockEnd32 + ", blockEnd = " + blockEnd +
+          "; maxLength = " + maxLength);
+      }
+      return null;
+    }
+    int length = Math.min((int)blockLeft, maxLength);
+    long blockStartInFile = currentLocatedBlock.getStartOffset();
+    long blockPos = curPos - blockStartInFile;
+    long limit = blockPos + length;
+    ClientMmap clientMmap =
+        blockReader.getClientMmap(currentLocatedBlock,
+            dfsClient.getMmapManager());
+    if (clientMmap == null) {
+      if (DFSClient.LOG.isDebugEnabled()) {
+        DFSClient.LOG.debug("unable to perform a zero-copy read from offset " +
+          curPos + " of " + src + "; BlockReader#getClientMmap returned " +
+          "null.");
+      }
+      return null;
+    }
+    seek(pos + length);
+    ByteBuffer buffer = clientMmap.getMappedByteBuffer().asReadOnlyBuffer();
+    buffer.position((int)blockPos);
+    buffer.limit((int)limit);
+    clientMmap.ref();
+    extendedReadBuffers.put(buffer, clientMmap);
+    readStatistics.addZeroCopyBytes(length);
+    if (DFSClient.LOG.isDebugEnabled()) {
+      DFSClient.LOG.debug("readZeroCopy read " + maxLength + " bytes from " +
+          "offset " + curPos + " via the zero-copy read path.  " +
+          "blockEnd = " + blockEnd);
+    }
+    return buffer;
+  }
+
+  @Override
+  public synchronized void releaseBuffer(ByteBuffer buffer) {
+    Object val = extendedReadBuffers.remove(buffer);
+    if (val == null) {
+      throw new IllegalArgumentException("tried to release a buffer " +
+          "that was not created by this stream, " + buffer);
+    }
+    if (val instanceof ClientMmap) {
+      ((ClientMmap)val).unref();
+    } else if (val instanceof ByteBufferPool) {
+      ((ByteBufferPool)val).putBuffer(buffer);
+    }
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/RemoteBlockReader.java

@@ -27,9 +27,12 @@ import java.nio.ByteBuffer;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.fs.FSInputChecker;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hdfs.client.ClientMmap;
+import org.apache.hadoop.hdfs.client.ClientMmapManager;
 import org.apache.hadoop.hdfs.net.Peer;
 import org.apache.hadoop.hdfs.protocol.DatanodeID;
 import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.protocol.LocatedBlock;
 import org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtoUtil;
 import org.apache.hadoop.hdfs.protocol.datatransfer.PacketHeader;
 import org.apache.hadoop.hdfs.protocol.datatransfer.Sender;
@@ -485,4 +488,10 @@ public class RemoteBlockReader extends FSInputChecker implements BlockReader {
   public boolean isShortCircuit() {
     return false;
   }
+
+  @Override
+  public ClientMmap getClientMmap(LocatedBlock curBlock,
+      ClientMmapManager mmapManager) {
+    return null;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/RemoteBlockReader2.java

@@ -29,9 +29,12 @@ import java.nio.channels.ReadableByteChannel;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.hdfs.client.ClientMmap;
+import org.apache.hadoop.hdfs.client.ClientMmapManager;
 import org.apache.hadoop.hdfs.net.Peer;
 import org.apache.hadoop.hdfs.protocol.DatanodeID;
 import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.protocol.LocatedBlock;
 import org.apache.hadoop.hdfs.protocol.datatransfer.DataTransferProtoUtil;
 import org.apache.hadoop.hdfs.protocol.datatransfer.PacketHeader;
 import org.apache.hadoop.hdfs.protocol.datatransfer.PacketReceiver;
@@ -40,7 +43,6 @@ import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.BlockOpResponseP
 import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ClientReadStatusProto;
 import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.ReadOpChecksumInfoProto;
 import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.Status;
-import org.apache.hadoop.hdfs.security.token.block.DataEncryptionKey;
 import org.apache.hadoop.hdfs.protocolPB.PBHelper;
 import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
 import org.apache.hadoop.hdfs.security.token.block.InvalidBlockTokenException;
@@ -451,4 +453,10 @@ public class RemoteBlockReader2  implements BlockReader {
   public boolean isShortCircuit() {
     return false;
   }
+
+  @Override
+  public ClientMmap getClientMmap(LocatedBlock curBlock,
+      ClientMmapManager manager) {
+    return null;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/client/ClientMmap.java

@@ -0,0 +1,166 @@
+/**
+ * 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.client;
+
+import java.io.FileInputStream;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.hdfs.protocol.DatanodeID;
+import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+
+import java.io.IOException;
+import java.lang.ref.WeakReference;
+import java.nio.MappedByteBuffer;
+import java.nio.channels.FileChannel.MapMode;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import com.google.common.annotations.VisibleForTesting;
+
+/**
+ * A memory-mapped region used by an HDFS client.
+ * 
+ * This class includes a reference count and some other information used by
+ * ClientMmapManager to track and cache mmaps.
+ */
+@InterfaceAudience.Private
+public class ClientMmap {
+  static final Log LOG = LogFactory.getLog(ClientMmap.class);
+  
+  /**
+   * A reference to the manager of this mmap.
+   * 
+   * This is only a weak reference to help minimize the damange done by
+   * code which leaks references accidentally.
+   */
+  private final WeakReference<ClientMmapManager> manager;
+  
+  /**
+   * The actual mapped memory region.
+   */
+  private final MappedByteBuffer map;
+  
+  /**
+   * A reference count tracking how many threads are using this object.
+   */
+  private final AtomicInteger refCount = new AtomicInteger(1);
+
+  /**
+   * Block pertaining to this mmap
+   */
+  private final ExtendedBlock block;
+  
+  /**
+   * The DataNode where this mmap came from.
+   */
+  private final DatanodeID datanodeID;
+
+  /**
+   * The monotonic time when this mmap was last evictable.
+   */
+  private long lastEvictableTimeNs;
+
+  public static ClientMmap load(ClientMmapManager manager, FileInputStream in, 
+      ExtendedBlock block, DatanodeID datanodeID) 
+          throws IOException {
+    MappedByteBuffer map =
+        in.getChannel().map(MapMode.READ_ONLY, 0,
+            in.getChannel().size());
+    return new ClientMmap(manager, map, block, datanodeID);
+  }
+
+  private ClientMmap(ClientMmapManager manager, MappedByteBuffer map, 
+        ExtendedBlock block, DatanodeID datanodeID) 
+            throws IOException {
+    this.manager = new WeakReference<ClientMmapManager>(manager);
+    this.map = map;
+    this.block = block;
+    this.datanodeID = datanodeID;
+    this.lastEvictableTimeNs = 0;
+  }
+
+  /**
+   * Decrement the reference count on this object.
+   * Should be called with the ClientMmapManager lock held.
+   */
+  public void unref() {
+    int count = refCount.decrementAndGet();
+    if (count < 0) {
+      throw new IllegalArgumentException("can't decrement the " +
+          "reference count on this ClientMmap lower than 0.");
+    } else if (count == 0) {
+      ClientMmapManager man = manager.get();
+      if (man == null) {
+        unmap();
+      } else {
+        man.makeEvictable(this);
+      }
+    }
+  }
+
+  /**
+   * Increment the reference count on this object.
+   *
+   * @return     The new reference count.
+   */
+  public int ref() {
+    return refCount.getAndIncrement();
+  }
+
+  @VisibleForTesting
+  public ExtendedBlock getBlock() {
+    return block;
+  }
+
+  DatanodeID getDatanodeID() {
+    return datanodeID;
+  }
+
+  public MappedByteBuffer getMappedByteBuffer() {
+    return map;
+  }
+
+  public void setLastEvictableTimeNs(long lastEvictableTimeNs) {
+    this.lastEvictableTimeNs = lastEvictableTimeNs;
+  }
+
+  public long getLastEvictableTimeNs() {
+    return this.lastEvictableTimeNs;
+  }
+
+  /**
+   * Unmap the memory region.
+   *
+   * There isn't any portable way to unmap a memory region in Java.
+   * So we use the sun.nio method here.
+   * Note that unmapping a memory region could cause crashes if code
+   * continues to reference the unmapped code.  However, if we don't
+   * manually unmap the memory, we are dependent on the finalizer to
+   * do it, and we have no idea when the finalizer will run.
+   */
+  void unmap() {
+    assert(refCount.get() == 0);
+    if (map instanceof sun.nio.ch.DirectBuffer) {
+      final sun.misc.Cleaner cleaner =
+          ((sun.nio.ch.DirectBuffer) map).cleaner();
+      cleaner.clean();
+    }
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/client/ClientMmapManager.java

@@ -0,0 +1,482 @@
+/**
+ * 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.client;
+
+import java.io.Closeable;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.lang.ref.WeakReference;
+import java.util.Iterator;
+import java.util.TreeMap;
+import java.util.Map.Entry;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_CLIENT_MMAP_CACHE_SIZE;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_CLIENT_MMAP_CACHE_SIZE_DEFAULT;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_CLIENT_MMAP_CACHE_TIMEOUT_MS;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_CLIENT_MMAP_CACHE_TIMEOUT_MS_DEFAULT;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_CLIENT_MMAP_CACHE_THREAD_RUNS_PER_TIMEOUT;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_CLIENT_MMAP_CACHE_THREAD_RUNS_PER_TIMEOUT_DEFAULT;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.protocol.DatanodeID;
+import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.io.IOUtils;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.ComparisonChain;
+import com.google.common.util.concurrent.ThreadFactoryBuilder;
+
+/**
+ * Tracks mmap instances used on an HDFS client.
+ *
+ * mmaps can be used concurrently by multiple threads at once.
+ * mmaps cannot be closed while they are in use.
+ *
+ * The cache is important for performance, because the first time an mmap is
+ * created, the page table entries (PTEs) are not yet set up.
+ * Even when reading data that is entirely resident in memory, reading an
+ * mmap the second time is faster.
+ */
+@InterfaceAudience.Private
+public class ClientMmapManager implements Closeable {
+  public static final Log LOG = LogFactory.getLog(ClientMmapManager.class);
+
+  private boolean closed = false;
+
+  private final int cacheSize;
+
+  private final long timeoutNs;
+
+  private final int runsPerTimeout;
+
+  private final Lock lock = new ReentrantLock();
+  
+  /**
+   * Maps block, datanode_id to the client mmap object.
+   * If the ClientMmap is in the process of being loaded,
+   * {@link Waitable<ClientMmap>#await()} will block.
+   *
+   * Protected by the ClientMmapManager lock.
+   */
+  private final TreeMap<Key, Waitable<ClientMmap>> mmaps =
+      new TreeMap<Key, Waitable<ClientMmap>>();
+
+  /**
+   * Maps the last use time to the client mmap object.
+   * We ensure that each last use time is unique by inserting a jitter of a
+   * nanosecond or two if necessary.
+   * 
+   * Protected by the ClientMmapManager lock.
+   * ClientMmap objects that are in use are never evictable.
+   */
+  private final TreeMap<Long, ClientMmap> evictable =
+      new TreeMap<Long, ClientMmap>();
+
+  private final ScheduledThreadPoolExecutor executor = 
+      new ScheduledThreadPoolExecutor(1, new ThreadFactoryBuilder().
+          setDaemon(true).setNameFormat("ClientMmapManager").
+          build());
+  
+  /**
+   * The CacheCleaner for this ClientMmapManager.  We don't create this
+   * and schedule it until it becomes necessary.
+   */
+  private CacheCleaner cacheCleaner;
+
+  /**
+   * Factory method to create a ClientMmapManager from a Hadoop
+   * configuration.
+   */
+  public static ClientMmapManager fromConf(Configuration conf) {
+    return new ClientMmapManager(conf.getInt(DFS_CLIENT_MMAP_CACHE_SIZE,
+      DFS_CLIENT_MMAP_CACHE_SIZE_DEFAULT),
+      conf.getLong(DFS_CLIENT_MMAP_CACHE_TIMEOUT_MS,
+        DFS_CLIENT_MMAP_CACHE_TIMEOUT_MS_DEFAULT),
+      conf.getInt(DFS_CLIENT_MMAP_CACHE_THREAD_RUNS_PER_TIMEOUT,
+        DFS_CLIENT_MMAP_CACHE_THREAD_RUNS_PER_TIMEOUT_DEFAULT));
+  }
+
+  public ClientMmapManager(int cacheSize, long timeoutMs, int runsPerTimeout) {
+    this.cacheSize = cacheSize;
+    this.timeoutNs = timeoutMs * 1000000;
+    this.runsPerTimeout = runsPerTimeout;
+  }
+  
+  long getTimeoutMs() {
+    return this.timeoutNs / 1000000;
+  }
+
+  int getRunsPerTimeout() {
+    return this.runsPerTimeout;
+  }
+  
+  public String verifyConfigurationMatches(Configuration conf) {
+    StringBuilder bld = new StringBuilder();
+    int cacheSize = conf.getInt(DFS_CLIENT_MMAP_CACHE_SIZE,
+                    DFS_CLIENT_MMAP_CACHE_SIZE_DEFAULT);
+    if (this.cacheSize != cacheSize) {
+      bld.append("You specified a cache size of ").append(cacheSize).
+          append(", but the existing cache size is ").append(this.cacheSize).
+          append(".  ");
+    }
+    long timeoutMs = conf.getLong(DFS_CLIENT_MMAP_CACHE_TIMEOUT_MS,
+        DFS_CLIENT_MMAP_CACHE_TIMEOUT_MS_DEFAULT);
+    if (getTimeoutMs() != timeoutMs) {
+      bld.append("You specified a cache timeout of ").append(timeoutMs).
+          append(" ms, but the existing cache timeout is ").
+          append(getTimeoutMs()).append("ms").append(".  ");
+    }
+    int runsPerTimeout = conf.getInt(
+        DFS_CLIENT_MMAP_CACHE_THREAD_RUNS_PER_TIMEOUT,
+        DFS_CLIENT_MMAP_CACHE_THREAD_RUNS_PER_TIMEOUT_DEFAULT);
+    if (getRunsPerTimeout() != runsPerTimeout) {
+      bld.append("You specified ").append(runsPerTimeout).
+          append(" runs per timeout, but the existing runs per timeout is ").
+          append(getTimeoutMs()).append(".  ");
+    }
+    return bld.toString();
+  }
+
+  private static class Waitable<T> {
+    private T val;
+    private final Condition cond;
+
+    public Waitable(Condition cond) {
+      this.val = null;
+      this.cond = cond;
+    }
+
+    public T await() throws InterruptedException {
+      while (this.val == null) {
+        this.cond.await();
+      }
+      return this.val;
+    }
+
+    public void provide(T val) {
+      this.val = val;
+      this.cond.signalAll();
+    }
+  }
+
+  private static class Key implements Comparable<Key> {
+    private final ExtendedBlock block;
+    private final DatanodeID datanode;
+    
+    Key(ExtendedBlock block, DatanodeID datanode) {
+      this.block = block;
+      this.datanode = datanode;
+    }
+
+    /**
+     * Compare two ClientMmap regions that we're storing.
+     *
+     * When we append to a block, we bump the genstamp.  It is important to 
+     * compare the genStamp here.  That way, we will not return a shorter 
+     * mmap than required.
+     */
+    @Override
+    public int compareTo(Key o) {
+      return ComparisonChain.start().
+          compare(block.getBlockId(), o.block.getBlockId()).
+          compare(block.getGenerationStamp(), o.block.getGenerationStamp()).
+          compare(block.getBlockPoolId(), o.block.getBlockPoolId()).
+          compare(datanode, o.datanode).
+          result();
+    }
+
+    @Override
+    public boolean equals(Object rhs) {
+      if (rhs == null) {
+        return false;
+      }
+      try {
+        Key o = (Key)rhs;
+        return (compareTo(o) == 0);
+      } catch (ClassCastException e) {
+        return false;
+      }
+    }
+
+    @Override
+    public int hashCode() {
+      return block.hashCode() ^ datanode.hashCode();
+    }
+  }
+
+  /**
+   * Thread which handles expiring mmaps from the cache.
+   */
+  private static class CacheCleaner implements Runnable, Closeable {
+    private WeakReference<ClientMmapManager> managerRef;
+    private ScheduledFuture<?> future;
+    
+    CacheCleaner(ClientMmapManager manager) {
+      this.managerRef= new WeakReference<ClientMmapManager>(manager);
+    }
+
+    @Override
+    public void run() {
+      ClientMmapManager manager = managerRef.get();
+      if (manager == null) return;
+      long curTime = System.nanoTime();
+      try {
+        manager.lock.lock();
+        manager.evictStaleEntries(curTime);
+      } finally {
+        manager.lock.unlock();
+      }
+    }
+    
+    void setFuture(ScheduledFuture<?> future) {
+      this.future = future;
+    }
+
+    @Override
+    public void close() throws IOException {
+      future.cancel(false);
+    }
+  }
+
+  /**
+   * Evict entries which are older than curTime + timeoutNs from the cache.
+   *
+   * NOTE: you must call this function with the lock held.
+   */
+  private void evictStaleEntries(long curTime) {
+    if (closed) {
+      return;
+    }
+    Iterator<Entry<Long, ClientMmap>> iter =
+        evictable.entrySet().iterator(); 
+    while (iter.hasNext()) {
+      Entry<Long, ClientMmap> entry = iter.next();
+      if (entry.getKey() + timeoutNs >= curTime) {
+        return;
+      }
+      ClientMmap mmap = entry.getValue();
+      Key key = new Key(mmap.getBlock(), mmap.getDatanodeID());
+      mmaps.remove(key);
+      iter.remove();
+      mmap.unmap();
+    }
+  }
+
+  /**
+   * Evict one mmap object from the cache.
+   *
+   * NOTE: you must call this function with the lock held.
+   *
+   * @return                  True if an object was evicted; false if none
+   *                          could be evicted.
+   */
+  private boolean evictOne() {
+    Entry<Long, ClientMmap> entry = evictable.pollFirstEntry();
+    if (entry == null) {
+      // We don't want to try creating another mmap region, because the
+      // cache is full.
+      return false;
+    }
+    ClientMmap evictedMmap = entry.getValue(); 
+    Key evictedKey = new Key(evictedMmap.getBlock(), 
+                             evictedMmap.getDatanodeID());
+    mmaps.remove(evictedKey);
+    evictedMmap.unmap();
+    return true;
+  }
+
+  /**
+   * Create a new mmap object.
+   * 
+   * NOTE: you must call this function with the lock held.
+   *
+   * @param key              The key which describes this mmap.
+   * @param in               The input stream to use to create the mmap.
+   * @return                 The new mmap object, or null if there were
+   *                         insufficient resources.
+   * @throws IOException     If there was an I/O error creating the mmap.
+   */
+  private ClientMmap create(Key key, FileInputStream in) throws IOException {
+    if (mmaps.size() + 1 > cacheSize) {
+      if (!evictOne()) {
+        LOG.warn("mmap cache is full (with " + cacheSize + " elements) and " +
+              "nothing is evictable.  Ignoring request for mmap with " +
+              "datanodeID=" + key.datanode + ", " + "block=" + key.block);
+        return null;
+      }
+    }
+    // Create the condition variable that other threads may wait on.
+    Waitable<ClientMmap> waitable =
+        new Waitable<ClientMmap>(lock.newCondition());
+    mmaps.put(key, waitable);
+    // Load the entry
+    boolean success = false;
+    ClientMmap mmap = null;
+    try {
+      try {
+        lock.unlock();
+        mmap = ClientMmap.load(this, in, key.block, key.datanode);
+      } finally {
+        lock.lock();
+      }
+      if (cacheCleaner == null) {
+        cacheCleaner = new CacheCleaner(this);
+        ScheduledFuture<?> future = 
+            executor.scheduleAtFixedRate(cacheCleaner,
+                timeoutNs, timeoutNs / runsPerTimeout, TimeUnit.NANOSECONDS);
+        cacheCleaner.setFuture(future);
+      }
+      success = true;
+    } finally {
+      if (!success) {
+        LOG.warn("failed to create mmap for datanodeID=" + key.datanode +
+                  ", " + "block=" + key.block);
+        mmaps.remove(key);
+      }
+      waitable.provide(mmap);
+    }
+    if (LOG.isDebugEnabled()) {
+      LOG.info("created a new ClientMmap for block " + key.block +
+          " on datanode " + key.datanode);
+    }
+    return mmap;
+  }
+
+  /**
+   * Get or create an mmap region.
+   * 
+   * @param node       The DataNode that owns the block for this mmap region.
+   * @param block      The block ID, block pool ID, and generation stamp of 
+   *                     the block we want to read.
+   * @param in         An open file for this block.  This stream is only used
+   *                     if we have to create a new mmap; if we use an
+   *                     existing one, it is ignored.
+   *
+   * @return           The client mmap region.
+   */
+  public ClientMmap fetch(DatanodeID datanodeID, ExtendedBlock block,
+      FileInputStream in) throws IOException, InterruptedException {
+    LOG.debug("fetching mmap with datanodeID=" + datanodeID + ", " +
+        "block=" + block);
+    Key key = new Key(block, datanodeID);
+    ClientMmap mmap = null;
+    try {
+      lock.lock();
+      if (closed) {
+        throw new IOException("ClientMmapManager is closed.");
+      }
+      while (mmap == null) {
+        Waitable<ClientMmap> entry = mmaps.get(key);
+        if (entry == null) {
+          return create(key, in);
+        }
+        mmap = entry.await();
+      }
+      if (mmap.ref() == 1) {
+        // When going from nobody using the mmap (ref = 0) to somebody
+        // using the mmap (ref = 1), we must make the mmap un-evictable.
+        evictable.remove(mmap.getLastEvictableTimeNs());
+      }
+    }
+    finally {
+      lock.unlock();
+    }
+    if (LOG.isDebugEnabled()) {
+      LOG.debug("reusing existing mmap with datanodeID=" + datanodeID +
+              ", " + "block=" + block);
+    }
+    return mmap;
+  }
+
+  /**
+   * Make an mmap evictable.
+   * 
+   * When an mmap is evictable, it may be removed from the cache if necessary.
+   * mmaps can only be evictable if nobody is using them.
+   *
+   * @param mmap             The mmap to make evictable.
+   */
+  void makeEvictable(ClientMmap mmap) {
+    try {
+      lock.lock();
+      if (closed) {
+        // If this ClientMmapManager is closed, then don't bother with the
+        // cache; just close the mmap.
+        mmap.unmap();
+        return;
+      }
+      long now = System.nanoTime();
+      while (evictable.containsKey(now)) {
+        now++;
+      }
+      mmap.setLastEvictableTimeNs(now);
+      evictable.put(now, mmap);
+    } finally {
+      lock.unlock();
+    }
+  }
+
+  @Override
+  public void close() throws IOException {
+    try {
+      lock.lock();
+      closed = true;
+      IOUtils.cleanup(LOG, cacheCleaner);
+
+      // Unmap all the mmaps that nobody is using.
+      // The ones which are in use will be unmapped just as soon as people stop
+      // using them.
+      evictStaleEntries(Long.MAX_VALUE);
+
+      executor.shutdown();
+    } finally {
+      lock.unlock();
+    }
+  }
+
+  @VisibleForTesting
+  public interface ClientMmapVisitor {
+    void accept(ClientMmap mmap);
+  }
+
+  @VisibleForTesting
+  public synchronized void visitMmaps(ClientMmapVisitor visitor)
+      throws InterruptedException {
+    for (Waitable<ClientMmap> entry : mmaps.values()) {
+      visitor.accept(entry.await());
+    }
+  }
+
+  public void visitEvictable(ClientMmapVisitor visitor)
+      throws InterruptedException {
+    for (ClientMmap mmap : evictable.values()) {
+      visitor.accept(mmap);
+    }
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/expect.c

@@ -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.
+ */
+
+#include "expect.h"
+#include "hdfs.h"
+
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int expectFileStats(hdfsFile file,
+      uint64_t expectedTotalBytesRead,
+      uint64_t expectedTotalLocalBytesRead,
+      uint64_t expectedTotalShortCircuitBytesRead,
+      uint64_t expectedTotalZeroCopyBytesRead)
+{
+    struct hdfsReadStatistics *stats = NULL;
+    EXPECT_ZERO(hdfsFileGetReadStatistics(file, &stats));
+    fprintf(stderr, "expectFileStats(expectedTotalBytesRead=%"PRId64", "
+            "expectedTotalLocalBytesRead=%"PRId64", "
+            "expectedTotalShortCircuitBytesRead=%"PRId64", "
+            "expectedTotalZeroCopyBytesRead=%"PRId64", "
+            "totalBytesRead=%"PRId64", "
+            "totalLocalBytesRead=%"PRId64", "
+            "totalShortCircuitBytesRead=%"PRId64", "
+            "totalZeroCopyBytesRead=%"PRId64")\n",
+            expectedTotalBytesRead,
+            expectedTotalLocalBytesRead,
+            expectedTotalShortCircuitBytesRead,
+            expectedTotalZeroCopyBytesRead,
+            stats->totalBytesRead,
+            stats->totalLocalBytesRead,
+            stats->totalShortCircuitBytesRead,
+            stats->totalZeroCopyBytesRead);
+    if (expectedTotalBytesRead != UINT64_MAX) {
+        EXPECT_INT64_EQ(expectedTotalBytesRead, stats->totalBytesRead);
+    }
+    if (expectedTotalLocalBytesRead != UINT64_MAX) {
+        EXPECT_INT64_EQ(expectedTotalLocalBytesRead,
+                      stats->totalLocalBytesRead);
+    }
+    if (expectedTotalShortCircuitBytesRead != UINT64_MAX) {
+        EXPECT_INT64_EQ(expectedTotalShortCircuitBytesRead,
+                      stats->totalShortCircuitBytesRead);
+    }
+    if (expectedTotalZeroCopyBytesRead != UINT64_MAX) {
+        EXPECT_INT64_EQ(expectedTotalZeroCopyBytesRead,
+                      stats->totalZeroCopyBytesRead);
+    }
+    hdfsFileFreeReadStatistics(stats);
+    return 0;
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/expect.h

@@ -19,16 +19,19 @@
 #ifndef LIBHDFS_NATIVE_TESTS_EXPECT_H
 #define LIBHDFS_NATIVE_TESTS_EXPECT_H
 
+#include <inttypes.h>
 #include <stdio.h>
 
+struct hdfsFile_internal;
+
 #define EXPECT_ZERO(x) \
     do { \
         int __my_ret__ = x; \
         if (__my_ret__) { \
             int __my_errno__ = errno; \
-            fprintf(stderr, "TEST_ERROR: failed on line %d with return " \
+            fprintf(stderr, "TEST_ERROR: failed on %s:%d with return " \
 		    "code %d (errno: %d): got nonzero from %s\n", \
-		    __LINE__, __my_ret__, __my_errno__, #x); \
+		    __FILE__, __LINE__, __my_ret__, __my_errno__, #x); \
             return __my_ret__; \
         } \
     } while (0);
@@ -38,9 +41,9 @@
         void* __my_ret__ = x; \
         int __my_errno__ = errno; \
         if (__my_ret__ != NULL) { \
-            fprintf(stderr, "TEST_ERROR: failed on line %d (errno: %d): " \
+            fprintf(stderr, "TEST_ERROR: failed on %s:%d (errno: %d): " \
 		    "got non-NULL value %p from %s\n", \
-		    __LINE__, __my_errno__, __my_ret__, #x); \
+		    __FILE__, __LINE__, __my_errno__, __my_ret__, #x); \
             return -1; \
         } \
     } while (0);
@@ -50,8 +53,8 @@
         void* __my_ret__ = x; \
         int __my_errno__ = errno; \
         if (__my_ret__ == NULL) { \
-            fprintf(stderr, "TEST_ERROR: failed on line %d (errno: %d): " \
-		    "got NULL from %s\n", __LINE__, __my_errno__, #x); \
+            fprintf(stderr, "TEST_ERROR: failed on %s:%d (errno: %d): " \
+		    "got NULL from %s\n", __FILE__, __LINE__, __my_errno__, #x); \
             return -1; \
         } \
     } while (0);
@@ -61,15 +64,16 @@
         int __my_ret__ = x; \
         int __my_errno__ = errno; \
         if (__my_ret__ != -1) { \
-            fprintf(stderr, "TEST_ERROR: failed on line %d with return " \
-                "code %d (errno: %d): expected -1 from %s\n", __LINE__, \
+            fprintf(stderr, "TEST_ERROR: failed on %s:%d with return " \
+                "code %d (errno: %d): expected -1 from %s\n", \
+                    __FILE__, __LINE__, \
                 __my_ret__, __my_errno__, #x); \
             return -1; \
         } \
         if (__my_errno__ != e) { \
-            fprintf(stderr, "TEST_ERROR: failed on line %d with return " \
+            fprintf(stderr, "TEST_ERROR: failed on %s:%d with return " \
                 "code %d (errno: %d): expected errno = %d from %s\n", \
-                __LINE__, __my_ret__, __my_errno__, e, #x); \
+                __FILE__, __LINE__, __my_ret__, __my_errno__, e, #x); \
             return -1; \
 	} \
     } while (0);
@@ -79,9 +83,9 @@
         int __my_ret__ = x; \
         int __my_errno__ = errno; \
         if (!__my_ret__) { \
-            fprintf(stderr, "TEST_ERROR: failed on line %d with return " \
-		    "code %d (errno: %d): got zero from %s\n", __LINE__, \
-                __my_ret__, __my_errno__, #x); \
+            fprintf(stderr, "TEST_ERROR: failed on %s:%d with return " \
+              "code %d (errno: %d): got zero from %s\n", __FILE__, __LINE__, \
+              __my_ret__, __my_errno__, #x); \
             return -1; \
         } \
     } while (0);
@@ -91,9 +95,9 @@
         int __my_ret__ = x; \
         int __my_errno__ = errno; \
         if (__my_ret__ < 0) { \
-            fprintf(stderr, "TEST_ERROR: failed on line %d with return " \
+            fprintf(stderr, "TEST_ERROR: failed on %s:%d with return " \
                 "code %d (errno: %d): got negative return from %s\n", \
-		    __LINE__, __my_ret__, __my_errno__, #x); \
+                __FILE__, __LINE__, __my_ret__, __my_errno__, #x); \
             return __my_ret__; \
         } \
     } while (0);
@@ -103,9 +107,21 @@
         int __my_ret__ = y; \
         int __my_errno__ = errno; \
         if (__my_ret__ != (x)) { \
-            fprintf(stderr, "TEST_ERROR: failed on line %d with return " \
+            fprintf(stderr, "TEST_ERROR: failed on %s:%d with return " \
               "code %d (errno: %d): expected %d\n", \
-               __LINE__, __my_ret__, __my_errno__, (x)); \
+               __FILE__, __LINE__, __my_ret__, __my_errno__, (x)); \
+            return -1; \
+        } \
+    } while (0);
+
+#define EXPECT_INT64_EQ(x, y) \
+    do { \
+        int64_t __my_ret__ = y; \
+        int __my_errno__ = errno; \
+        if (__my_ret__ != (x)) { \
+            fprintf(stderr, "TEST_ERROR: failed on %s:%d with return " \
+              "value %"PRId64" (errno: %d): expected %"PRId64"\n", \
+               __FILE__, __LINE__, __my_ret__, __my_errno__, (x)); \
             return -1; \
         } \
     } while (0);
@@ -117,4 +133,17 @@
     ret = -errno; \
     } while (ret == -EINTR);
 
+/**
+ * Test that an HDFS file has the given statistics.
+ *
+ * Any parameter can be set to UINT64_MAX to avoid checking it.
+ *
+ * @return 0 on success; error code otherwise
+ */
+int expectFileStats(struct hdfsFile_internal *file,
+      uint64_t expectedTotalBytesRead,
+      uint64_t expectedTotalLocalBytesRead,
+      uint64_t expectedTotalShortCircuitBytesRead,
+      uint64_t expectedTotalZeroCopyBytesRead);
+
 #endif

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/hdfs.c

@@ -39,6 +39,7 @@
 #define JAVA_NET_ISA    "java/net/InetSocketAddress"
 #define JAVA_NET_URI    "java/net/URI"
 #define JAVA_STRING     "java/lang/String"
+#define READ_OPTION     "org/apache/hadoop/fs/ReadOption"
 
 #define JAVA_VOID       "V"
 
@@ -143,6 +144,15 @@ int hdfsFileGetReadStatistics(hdfsFile file,
         goto done;
     }
     s->totalShortCircuitBytesRead = jVal.j;
+    jthr = invokeMethod(env, &jVal, INSTANCE, readStats,
+                  "org/apache/hadoop/hdfs/DFSInputStream$ReadStatistics",
+                  "getTotalZeroCopyBytesRead", "()J");
+    if (jthr) {
+        ret = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+            "hdfsFileGetReadStatistics: getTotalZeroCopyBytesRead failed");
+        goto done;
+    }
+    s->totalZeroCopyBytesRead = jVal.j;
     *stats = s;
     s = NULL;
     ret = 0;
@@ -183,6 +193,25 @@ void hdfsFileDisableDirectRead(hdfsFile file)
     file->flags &= ~HDFS_FILE_SUPPORTS_DIRECT_READ;
 }
 
+int hdfsDisableDomainSocketSecurity(void)
+{
+    jthrowable jthr;
+    JNIEnv* env = getJNIEnv();
+    if (env == NULL) {
+      errno = EINTERNAL;
+      return -1;
+    }
+    jthr = invokeMethod(env, NULL, STATIC, NULL,
+            "org/apache/hadoop/net/unix/DomainSocket",
+            "disableBindPathValidation", "()V");
+    if (jthr) {
+        errno = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+            "DomainSocket#disableBindPathValidation");
+        return -1;
+    }
+    return 0;
+}
+
 /**
  * hdfsJniEnv: A wrapper struct to be used as 'value'
  * while saving thread -> JNIEnv* mappings
@@ -220,40 +249,6 @@ static jthrowable constructNewObjectOfPath(JNIEnv *env, const char *path,
     return NULL;
 }
 
-/**
- * Set a configuration value.
- *
- * @param env               The JNI environment
- * @param jConfiguration    The configuration object to modify
- * @param key               The key to modify
- * @param value             The value to set the key to
- *
- * @return                  NULL on success; exception otherwise
- */
-static jthrowable hadoopConfSetStr(JNIEnv *env, jobject jConfiguration,
-        const char *key, const char *value)
-{
-    jthrowable jthr;
-    jstring jkey = NULL, jvalue = NULL;
-
-    jthr = newJavaStr(env, key, &jkey);
-    if (jthr)
-        goto done;
-    jthr = newJavaStr(env, value, &jvalue);
-    if (jthr)
-        goto done;
-    jthr = invokeMethod(env, NULL, INSTANCE, jConfiguration,
-            HADOOP_CONF, "set", JMETHOD2(JPARAM(JAVA_STRING),
-                                         JPARAM(JAVA_STRING), JAVA_VOID),
-            jkey, jvalue);
-    if (jthr)
-        goto done;
-done:
-    destroyLocalReference(env, jkey);
-    destroyLocalReference(env, jvalue);
-    return jthr;
-}
-
 static jthrowable hadoopConfGetStr(JNIEnv *env, jobject jConfiguration,
         const char *key, char **val)
 {
@@ -2108,6 +2103,395 @@ int hdfsUtime(hdfsFS fs, const char* path, tTime mtime, tTime atime)
     return 0;
 }
 
+/**
+ * Zero-copy options.
+ *
+ * We cache the EnumSet of ReadOptions which has to be passed into every
+ * readZero call, to avoid reconstructing it each time.  This cache is cleared
+ * whenever an element changes.
+ */
+struct hadoopRzOptions
+{
+    JNIEnv *env;
+    int skipChecksums;
+    jobject byteBufferPool;
+    jobject cachedEnumSet;
+};
+
+struct hadoopRzOptions *hadoopRzOptionsAlloc(void)
+{
+    struct hadoopRzOptions *opts;
+    JNIEnv *env;
+
+    env = getJNIEnv();
+    if (!env) {
+        // Check to make sure the JNI environment is set up properly.
+        errno = EINTERNAL;
+        return NULL;
+    }
+    opts = calloc(1, sizeof(struct hadoopRzOptions));
+    if (!opts) {
+        errno = ENOMEM;
+        return NULL;
+    }
+    return opts;
+}
+
+static void hadoopRzOptionsClearCached(JNIEnv *env,
+        struct hadoopRzOptions *opts)
+{
+    if (!opts->cachedEnumSet) {
+        return;
+    }
+    (*env)->DeleteGlobalRef(env, opts->cachedEnumSet);
+    opts->cachedEnumSet = NULL;
+}
+
+int hadoopRzOptionsSetSkipChecksum(
+        struct hadoopRzOptions *opts, int skip)
+{
+    JNIEnv *env;
+    env = getJNIEnv();
+    if (!env) {
+        errno = EINTERNAL;
+        return -1;
+    }
+    hadoopRzOptionsClearCached(env, opts);
+    opts->skipChecksums = !!skip;
+    return 0;
+}
+
+int hadoopRzOptionsSetByteBufferPool(
+        struct hadoopRzOptions *opts, const char *className)
+{
+    JNIEnv *env;
+    jthrowable jthr;
+    jobject byteBufferPool = NULL;
+
+    env = getJNIEnv();
+    if (!env) {
+        errno = EINTERNAL;
+        return -1;
+    }
+
+    // Note: we don't have to call hadoopRzOptionsClearCached in this
+    // function, since the ByteBufferPool is passed separately from the
+    // EnumSet of ReadOptions.
+
+    jthr = constructNewObjectOfClass(env, &byteBufferPool, className, "()V");
+    if (jthr) {
+        printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+            "hadoopRzOptionsSetByteBufferPool(className=%s): ", className);
+        errno = EINVAL;
+        return -1;
+    }
+    if (opts->byteBufferPool) {
+        // Delete any previous ByteBufferPool we had.
+        (*env)->DeleteGlobalRef(env, opts->byteBufferPool);
+    }
+    opts->byteBufferPool = byteBufferPool;
+    return 0;
+}
+
+void hadoopRzOptionsFree(struct hadoopRzOptions *opts)
+{
+    JNIEnv *env;
+    env = getJNIEnv();
+    if (!env) {
+        return;
+    }
+    hadoopRzOptionsClearCached(env, opts);
+    if (opts->byteBufferPool) {
+        (*env)->DeleteGlobalRef(env, opts->byteBufferPool);
+        opts->byteBufferPool = NULL;
+    }
+    free(opts);
+}
+
+struct hadoopRzBuffer
+{
+    jobject byteBuffer;
+    uint8_t *ptr;
+    int32_t length;
+    int direct;
+};
+
+static jthrowable hadoopRzOptionsGetEnumSet(JNIEnv *env,
+        struct hadoopRzOptions *opts, jobject *enumSet)
+{
+    jthrowable jthr = NULL;
+    jobject enumInst = NULL, enumSetObj = NULL;
+    jvalue jVal;
+
+    if (opts->cachedEnumSet) {
+        // If we cached the value, return it now.
+        *enumSet = opts->cachedEnumSet;
+        goto done;
+    }
+    if (opts->skipChecksums) {
+        jthr = fetchEnumInstance(env, READ_OPTION,
+                  "SKIP_CHECKSUMS", &enumInst);
+        if (jthr) {
+            goto done;
+        }
+        jthr = invokeMethod(env, &jVal, STATIC, NULL,
+                "java/util/EnumSet", "of",
+                "(Ljava/lang/Enum;)Ljava/util/EnumSet;", enumInst);
+        if (jthr) {
+            goto done;
+        }
+        enumSetObj = jVal.l;
+    } else {
+        jclass clazz = (*env)->FindClass(env, READ_OPTION);
+        if (!clazz) {
+            jthr = newRuntimeError(env, "failed "
+                    "to find class for %s", READ_OPTION);
+            goto done;
+        }
+        jthr = invokeMethod(env, &jVal, STATIC, NULL,
+                "java/util/EnumSet", "noneOf",
+                "(Ljava/lang/Class;)Ljava/util/EnumSet;", clazz);
+        enumSetObj = jVal.l;
+    }
+    // create global ref
+    opts->cachedEnumSet = (*env)->NewGlobalRef(env, enumSetObj);
+    if (!opts->cachedEnumSet) {
+        jthr = getPendingExceptionAndClear(env);
+        goto done;
+    }
+    *enumSet = opts->cachedEnumSet;
+    jthr = NULL;
+done:
+    (*env)->DeleteLocalRef(env, enumInst);
+    (*env)->DeleteLocalRef(env, enumSetObj);
+    return jthr;
+}
+
+static int hadoopReadZeroExtractBuffer(JNIEnv *env,
+        const struct hadoopRzOptions *opts, struct hadoopRzBuffer *buffer)
+{
+    int ret;
+    jthrowable jthr;
+    jvalue jVal;
+    uint8_t *directStart;
+    void *mallocBuf = NULL;
+    jint position;
+    jarray array = NULL;
+
+    jthr = invokeMethod(env, &jVal, INSTANCE, buffer->byteBuffer,
+                     "java/nio/ByteBuffer", "remaining", "()I");
+    if (jthr) {
+        ret = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                "hadoopReadZeroExtractBuffer: ByteBuffer#remaining failed: ");
+        goto done;
+    }
+    buffer->length = jVal.i;
+    jthr = invokeMethod(env, &jVal, INSTANCE, buffer->byteBuffer,
+                     "java/nio/ByteBuffer", "position", "()I");
+    if (jthr) {
+        ret = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                "hadoopReadZeroExtractBuffer: ByteBuffer#position failed: ");
+        goto done;
+    }
+    position = jVal.i;
+    directStart = (*env)->GetDirectBufferAddress(env, buffer->byteBuffer);
+    if (directStart) {
+        // Handle direct buffers.
+        buffer->ptr = directStart + position;
+        buffer->direct = 1;
+        ret = 0;
+        goto done;
+    }
+    // Handle indirect buffers.
+    // The JNI docs don't say that GetDirectBufferAddress throws any exceptions
+    // when it fails.  However, they also don't clearly say that it doesn't.  It
+    // seems safest to clear any pending exceptions here, to prevent problems on
+    // various JVMs.
+    (*env)->ExceptionClear(env);
+    if (!opts->byteBufferPool) {
+        fputs("hadoopReadZeroExtractBuffer: we read through the "
+                "zero-copy path, but failed to get the address of the buffer via "
+                "GetDirectBufferAddress.  Please make sure your JVM supports "
+                "GetDirectBufferAddress.\n", stderr);
+        ret = ENOTSUP;
+        goto done;
+    }
+    // Get the backing array object of this buffer.
+    jthr = invokeMethod(env, &jVal, INSTANCE, buffer->byteBuffer,
+                     "java/nio/ByteBuffer", "array", "()[B");
+    if (jthr) {
+        ret = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                "hadoopReadZeroExtractBuffer: ByteBuffer#array failed: ");
+        goto done;
+    }
+    array = jVal.l;
+    if (!array) {
+        fputs("hadoopReadZeroExtractBuffer: ByteBuffer#array returned NULL.",
+              stderr);
+        ret = EIO;
+        goto done;
+    }
+    mallocBuf = malloc(buffer->length);
+    if (!mallocBuf) {
+        fprintf(stderr, "hadoopReadZeroExtractBuffer: failed to allocate %d bytes of memory\n",
+                buffer->length);
+        ret = ENOMEM;
+        goto done;
+    }
+    (*env)->GetByteArrayRegion(env, array, position, buffer->length, mallocBuf);
+    jthr = (*env)->ExceptionOccurred(env);
+    if (jthr) {
+        ret = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                "hadoopReadZeroExtractBuffer: GetByteArrayRegion failed: ");
+        goto done;
+    }
+    buffer->ptr = mallocBuf;
+    buffer->direct = 0;
+    ret = 0;
+
+done:
+    free(mallocBuf);
+    (*env)->DeleteLocalRef(env, array);
+    return ret;
+}
+
+static int translateZCRException(JNIEnv *env, jthrowable exc)
+{
+    int ret;
+    char *className = NULL;
+    jthrowable jthr = classNameOfObject(exc, env, &className);
+
+    if (jthr) {
+        fputs("hadoopReadZero: failed to get class name of "
+                "exception from read().\n", stderr);
+        destroyLocalReference(env, exc);
+        destroyLocalReference(env, jthr);
+        ret = EIO;
+        goto done;
+    }
+    if (!strcmp(className, "java.lang.UnsupportedOperationException")) {
+        ret = EPROTONOSUPPORT;
+        goto done;
+    }
+    ret = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+            "hadoopZeroCopyRead: ZeroCopyCursor#read failed");
+done:
+    free(className);
+    return ret;
+}
+
+struct hadoopRzBuffer* hadoopReadZero(hdfsFile file,
+            struct hadoopRzOptions *opts, int32_t maxLength)
+{
+    JNIEnv *env;
+    jthrowable jthr = NULL;
+    jvalue jVal;
+    jobject enumSet = NULL, byteBuffer = NULL;
+    struct hadoopRzBuffer* buffer = NULL;
+    int ret;
+
+    env = getJNIEnv();
+    if (!env) {
+        errno = EINTERNAL;
+        return NULL;
+    }
+    if (file->type != INPUT) {
+        fputs("Cannot read from a non-InputStream object!\n", stderr);
+        ret = EINVAL;
+        goto done;
+    }
+    buffer = calloc(1, sizeof(struct hadoopRzBuffer));
+    if (!buffer) {
+        ret = ENOMEM;
+        goto done;
+    }
+    jthr = hadoopRzOptionsGetEnumSet(env, opts, &enumSet);
+    if (jthr) {
+        ret = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                "hadoopReadZero: hadoopRzOptionsGetEnumSet failed: ");
+        goto done;
+    }
+    jthr = invokeMethod(env, &jVal, INSTANCE, file->file, HADOOP_ISTRM, "read",
+        "(Lorg/apache/hadoop/io/ByteBufferPool;ILjava/util/EnumSet;)"
+        "Ljava/nio/ByteBuffer;", opts->byteBufferPool, maxLength, enumSet);
+    if (jthr) {
+        ret = translateZCRException(env, jthr);
+        goto done;
+    }
+    byteBuffer = jVal.l;
+    if (!byteBuffer) {
+        buffer->byteBuffer = NULL;
+        buffer->length = 0;
+        buffer->ptr = NULL;
+    } else {
+        buffer->byteBuffer = (*env)->NewGlobalRef(env, byteBuffer);
+        if (!buffer->byteBuffer) {
+            ret = printPendingExceptionAndFree(env, PRINT_EXC_ALL,
+                "hadoopReadZero: failed to create global ref to ByteBuffer");
+            goto done;
+        }
+        ret = hadoopReadZeroExtractBuffer(env, opts, buffer);
+        if (ret) {
+            goto done;
+        }
+    }
+    ret = 0;
+done:
+    (*env)->DeleteLocalRef(env, byteBuffer);
+    if (ret) {
+        if (buffer) {
+            if (buffer->byteBuffer) {
+                (*env)->DeleteGlobalRef(env, buffer->byteBuffer);
+            }
+            free(buffer);
+        }
+        errno = ret;
+        return NULL;
+    } else {
+        errno = 0;
+    }
+    return buffer;
+}
+
+int32_t hadoopRzBufferLength(const struct hadoopRzBuffer *buffer)
+{
+    return buffer->length;
+}
+
+const void *hadoopRzBufferGet(const struct hadoopRzBuffer *buffer)
+{
+    return buffer->ptr;
+}
+
+void hadoopRzBufferFree(hdfsFile file, struct hadoopRzBuffer *buffer)
+{
+    jvalue jVal;
+    jthrowable jthr;
+    JNIEnv* env;
+    
+    env = getJNIEnv();
+    if (env == NULL) {
+        errno = EINTERNAL;
+        return;
+    }
+    if (buffer->byteBuffer) {
+        jthr = invokeMethod(env, &jVal, INSTANCE, file->file,
+                    HADOOP_ISTRM, "releaseBuffer",
+                    "(Ljava/nio/ByteBuffer;)V", buffer->byteBuffer);
+        if (jthr) {
+            printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                    "hadoopRzBufferFree: releaseBuffer failed: ");
+            // even on error, we have to delete the reference.
+        }
+        (*env)->DeleteGlobalRef(env, buffer->byteBuffer);
+    }
+    if (!buffer->direct) {
+        free(buffer->ptr);
+    }
+    memset(buffer, 0, sizeof(*buffer));
+    free(buffer);
+}
+
 char***
 hdfsGetHosts(hdfsFS fs, const char* path, tOffset start, tOffset length)
 {

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/hdfs.h

@@ -36,6 +36,8 @@
 #define EINTERNAL 255 
 #endif
 
+#define ELASTIC_BYTE_BUFFER_POOL_CLASS \
+  "org/apache/hadoop/io/ElasticByteBufferPool"
 
 /** All APIs set errno to meaningful values */
 
@@ -65,6 +67,10 @@ extern  "C" {
     struct hdfsFile_internal;
     typedef struct hdfsFile_internal* hdfsFile;
 
+    struct hadoopRzOptions;
+
+    struct hadoopRzBuffer;
+
     /**
      * Determine if a file is open for read.
      *
@@ -85,6 +91,7 @@ extern  "C" {
       uint64_t totalBytesRead;
       uint64_t totalLocalBytesRead;
       uint64_t totalShortCircuitBytesRead;
+      uint64_t totalZeroCopyBytesRead;
     };
 
     /**
@@ -680,7 +687,107 @@ extern  "C" {
      * @return 0 on success else -1
      */
     int hdfsUtime(hdfsFS fs, const char* path, tTime mtime, tTime atime);
-    
+
+    /**
+     * Allocate a zero-copy options structure.
+     *
+     * You must free all options structures allocated with this function using
+     * hadoopRzOptionsFree.
+     *
+     * @return            A zero-copy options structure, or NULL if one could
+     *                    not be allocated.  If NULL is returned, errno will
+     *                    contain the error number.
+     */
+    struct hadoopRzOptions *hadoopRzOptionsAlloc(void);
+
+    /**
+     * Determine whether we should skip checksums in read0.
+     *
+     * @param opts        The options structure.
+     * @param skip        Nonzero to skip checksums sometimes; zero to always
+     *                    check them.
+     *
+     * @return            0 on success; -1 plus errno on failure.
+     */
+    int hadoopRzOptionsSetSkipChecksum(
+            struct hadoopRzOptions *opts, int skip);
+
+    /**
+     * Set the ByteBufferPool to use with read0.
+     *
+     * @param opts        The options structure.
+     * @param className   If this is NULL, we will not use any
+     *                    ByteBufferPool.  If this is non-NULL, it will be
+     *                    treated as the name of the pool class to use.
+     *                    For example, you can use
+     *                    ELASTIC_BYTE_BUFFER_POOL_CLASS.
+     *
+     * @return            0 if the ByteBufferPool class was found and
+     *                    instantiated;
+     *                    -1 plus errno otherwise.
+     */
+    int hadoopRzOptionsSetByteBufferPool(
+            struct hadoopRzOptions *opts, const char *className);
+
+    /**
+     * Free a hadoopRzOptionsFree structure.
+     *
+     * @param opts        The options structure to free.
+     *                    Any associated ByteBufferPool will also be freed.
+     */
+    void hadoopRzOptionsFree(struct hadoopRzOptions *opts);
+
+    /**
+     * Perform a byte buffer read.
+     * If possible, this will be a zero-copy (mmap) read.
+     *
+     * @param file       The file to read from.
+     * @param opts       An options structure created by hadoopRzOptionsAlloc.
+     * @param maxLength  The maximum length to read.  We may read fewer bytes
+     *                   than this length.
+     *
+     * @return           On success, returns a new hadoopRzBuffer.
+     *                   This buffer will continue to be valid and readable
+     *                   until it is released by readZeroBufferFree.  Failure to
+     *                   release a buffer will lead to a memory leak.
+     *
+     *                   NULL plus an errno code on an error.
+     *                   errno = EOPNOTSUPP indicates that we could not do a
+     *                   zero-copy read, and there was no ByteBufferPool
+     *                   supplied.
+     */
+    struct hadoopRzBuffer* hadoopReadZero(hdfsFile file,
+            struct hadoopRzOptions *opts, int32_t maxLength);
+
+    /**
+     * Determine the length of the buffer returned from readZero.
+     *
+     * @param buffer     a buffer returned from readZero.
+     * @return           the length of the buffer.
+     */
+    int32_t hadoopRzBufferLength(const struct hadoopRzBuffer *buffer);
+
+    /**
+     * Get a pointer to the raw buffer returned from readZero.
+     *
+     * To find out how many bytes this buffer contains, call
+     * hadoopRzBufferLength.
+     *
+     * @param buffer     a buffer returned from readZero.
+     * @return           a pointer to the start of the buffer.  This will be
+     *                   NULL when end-of-file has been reached.
+     */
+    const void *hadoopRzBufferGet(const struct hadoopRzBuffer *buffer);
+
+    /**
+     * Release a buffer obtained through readZero.
+     *
+     * @param file       The hdfs stream that created this buffer.  This must be
+     *                   the same stream you called hadoopReadZero on.
+     * @param buffer     The buffer to release.
+     */
+    void hadoopRzBufferFree(hdfsFile file, struct hadoopRzBuffer *buffer);
+
 #ifdef __cplusplus
 }
 #endif

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/hdfs_test.h

@@ -48,6 +48,15 @@ extern  "C" {
      * @param file     The HDFS file
      */
     void hdfsFileDisableDirectRead(struct hdfsFile_internal *file);
+
+    /**
+     * Disable domain socket security checks.
+     *
+     * @param          0 if domain socket security was disabled;
+     *                 -1 if not.
+     */
+    int hdfsDisableDomainSocketSecurity(void); 
+
 #ifdef __cplusplus
 }
 #endif

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/jni_helper.c

@@ -608,3 +608,73 @@ JNIEnv* getJNIEnv(void)
     return env;
 }
 
+int javaObjectIsOfClass(JNIEnv *env, jobject obj, const char *name)
+{
+    jclass clazz;
+    int ret;
+
+    clazz = (*env)->FindClass(env, name);
+    if (!clazz) {
+        printPendingExceptionAndFree(env, PRINT_EXC_ALL,
+            "javaObjectIsOfClass(%s)", name);
+        return -1;
+    }
+    ret = (*env)->IsInstanceOf(env, obj, clazz);
+    (*env)->DeleteLocalRef(env, clazz);
+    return ret == JNI_TRUE ? 1 : 0;
+}
+
+jthrowable hadoopConfSetStr(JNIEnv *env, jobject jConfiguration,
+        const char *key, const char *value)
+{
+    jthrowable jthr;
+    jstring jkey = NULL, jvalue = NULL;
+
+    jthr = newJavaStr(env, key, &jkey);
+    if (jthr)
+        goto done;
+    jthr = newJavaStr(env, value, &jvalue);
+    if (jthr)
+        goto done;
+    jthr = invokeMethod(env, NULL, INSTANCE, jConfiguration,
+            "org/apache/hadoop/conf/Configuration", "set", 
+            "(Ljava/lang/String;Ljava/lang/String;)V",
+            jkey, jvalue);
+    if (jthr)
+        goto done;
+done:
+    (*env)->DeleteLocalRef(env, jkey);
+    (*env)->DeleteLocalRef(env, jvalue);
+    return jthr;
+}
+
+jthrowable fetchEnumInstance(JNIEnv *env, const char *className,
+                         const char *valueName, jobject *out)
+{
+    jclass clazz;
+    jfieldID fieldId;
+    jobject jEnum;
+    char prettyClass[256];
+
+    clazz = (*env)->FindClass(env, className);
+    if (!clazz) {
+        return newRuntimeError(env, "fetchEnum(%s, %s): failed to find class.",
+                className, valueName);
+    }
+    if (snprintf(prettyClass, sizeof(prettyClass), "L%s;", className)
+          >= sizeof(prettyClass)) {
+        return newRuntimeError(env, "fetchEnum(%s, %s): class name too long.",
+                className, valueName);
+    }
+    fieldId = (*env)->GetStaticFieldID(env, clazz, valueName, prettyClass);
+    if (!fieldId) {
+        return getPendingExceptionAndClear(env);
+    }
+    jEnum = (*env)->GetStaticObjectField(env, clazz, fieldId);
+    if (!jEnum) {
+        return getPendingExceptionAndClear(env);
+    }
+    *out = jEnum;
+    return NULL;
+}
+

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/jni_helper.h

@@ -114,6 +114,47 @@ jthrowable classNameOfObject(jobject jobj, JNIEnv *env, char **name);
  * */
 JNIEnv* getJNIEnv(void);
 
+/**
+ * Figure out if a Java object is an instance of a particular class.
+ *
+ * @param env  The Java environment.
+ * @param obj  The object to check.
+ * @param name The class name to check.
+ *
+ * @return     -1 if we failed to find the referenced class name.
+ *             0 if the object is not of the given class.
+ *             1 if the object is of the given class.
+ */
+int javaObjectIsOfClass(JNIEnv *env, jobject obj, const char *name);
+
+/**
+ * Set a value in a configuration object.
+ *
+ * @param env               The JNI environment
+ * @param jConfiguration    The configuration object to modify
+ * @param key               The key to modify
+ * @param value             The value to set the key to
+ *
+ * @return                  NULL on success; exception otherwise
+ */
+jthrowable hadoopConfSetStr(JNIEnv *env, jobject jConfiguration,
+        const char *key, const char *value);
+
+/**
+ * Fetch an instance of an Enum.
+ *
+ * @param env               The JNI environment.
+ * @param className         The enum class name.
+ * @param valueName         The name of the enum value
+ * @param out               (out param) on success, a local reference to an
+ *                          instance of the enum object.  (Since Java enums are
+ *                          singletones, this is also the only instance.)
+ *
+ * @return                  NULL on success; exception otherwise
+ */
+jthrowable fetchEnumInstance(JNIEnv *env, const char *className,
+                             const char *valueName, jobject *out);
+
 #endif /*LIBHDFS_JNI_HELPER_H*/
 
 /**

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/native_mini_dfs.c

@@ -17,14 +17,19 @@
  */
 
 #include "exception.h"
+#include "hdfs.h"
+#include "hdfs_test.h"
 #include "jni_helper.h"
 #include "native_mini_dfs.h"
 
 #include <errno.h>
 #include <jni.h>
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/types.h>
+#include <unistd.h>
 
 #define MINIDFS_CLUSTER_BUILDER "org/apache/hadoop/hdfs/MiniDFSCluster$Builder"
 #define MINIDFS_CLUSTER "org/apache/hadoop/hdfs/MiniDFSCluster"
@@ -39,8 +44,44 @@ struct NativeMiniDfsCluster {
      * The NativeMiniDfsCluster object
      */
     jobject obj;
+
+    /**
+     * Path to the domain socket, or the empty string if there is none.
+     */
+    char domainSocketPath[PATH_MAX];
 };
 
+static jthrowable nmdConfigureShortCircuit(JNIEnv *env,
+              struct NativeMiniDfsCluster *cl, jobject cobj)
+{
+    jthrowable jthr;
+    char *tmpDir;
+
+    int ret = hdfsDisableDomainSocketSecurity();
+    if (ret) {
+        return newRuntimeError(env, "failed to disable hdfs domain "
+                               "socket security: error %d", ret);
+    }
+    jthr = hadoopConfSetStr(env, cobj, "dfs.client.read.shortcircuit", "true");
+    if (jthr) {
+        return jthr;
+    }
+    tmpDir = getenv("TMPDIR");
+    if (!tmpDir) {
+        tmpDir = "/tmp";
+    }
+    snprintf(cl->domainSocketPath, PATH_MAX, "%s/native_mini_dfs.sock.%d.%d",
+             tmpDir, getpid(), rand());
+    snprintf(cl->domainSocketPath, PATH_MAX, "%s/native_mini_dfs.sock.%d.%d",
+             tmpDir, getpid(), rand());
+    jthr = hadoopConfSetStr(env, cobj, "dfs.domain.socket.path",
+                            cl->domainSocketPath);
+    if (jthr) {
+        return jthr;
+    }
+    return NULL;
+}
+
 struct NativeMiniDfsCluster* nmdCreate(struct NativeMiniDfsConf *conf)
 {
     struct NativeMiniDfsCluster* cl = NULL;
@@ -81,6 +122,28 @@ struct NativeMiniDfsCluster* nmdCreate(struct NativeMiniDfsConf *conf)
             goto error;
         }
     }
+    if (jthr) {
+        printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                              "nmdCreate: Configuration::setBoolean");
+        goto error;
+    }
+    // Disable 'minimum block size' -- it's annoying in tests.
+    (*env)->DeleteLocalRef(env, jconfStr);
+    jconfStr = NULL;
+    jthr = newJavaStr(env, "dfs.namenode.fs-limits.min-block-size", &jconfStr);
+    if (jthr) {
+        printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                              "nmdCreate: new String");
+        goto error;
+    }
+    jthr = invokeMethod(env, NULL, INSTANCE, cobj, HADOOP_CONF,
+                        "setLong", "(Ljava/lang/String;J)V", jconfStr, 0LL);
+    if (jthr) {
+        printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                              "nmdCreate: Configuration::setLong");
+        goto error;
+    }
+    // Creae MiniDFSCluster object
     jthr = constructNewObjectOfClass(env, &bld, MINIDFS_CLUSTER_BUILDER,
                     "(L"HADOOP_CONF";)V", cobj);
     if (jthr) {
@@ -88,6 +151,14 @@ struct NativeMiniDfsCluster* nmdCreate(struct NativeMiniDfsConf *conf)
             "nmdCreate: NativeMiniDfsCluster#Builder#Builder");
         goto error;
     }
+    if (conf->configureShortCircuit) {
+        jthr = nmdConfigureShortCircuit(env, cl, cobj);
+        if (jthr) {
+            printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                "nmdCreate: nmdConfigureShortCircuit error");
+            goto error;
+        }
+    }
     jthr = invokeMethod(env, &val, INSTANCE, bld, MINIDFS_CLUSTER_BUILDER,
             "format", "(Z)L" MINIDFS_CLUSTER_BUILDER ";", conf->doFormat);
     if (jthr) {
@@ -272,3 +343,29 @@ error_dlr_nn:
     
     return ret;
 }
+
+int nmdConfigureHdfsBuilder(struct NativeMiniDfsCluster *cl,
+                            struct hdfsBuilder *bld)
+{
+    int port, ret;
+
+    hdfsBuilderSetNameNode(bld, "localhost");
+    port = nmdGetNameNodePort(cl);
+    if (port < 0) {
+      fprintf(stderr, "nmdGetNameNodePort failed with error %d\n", -port);
+      return EIO;
+    }
+    hdfsBuilderSetNameNodePort(bld, port);
+    if (cl->domainSocketPath[0]) {
+      ret = hdfsBuilderConfSetStr(bld, "dfs.client.read.shortcircuit", "true");
+      if (ret) {
+          return ret;
+      }
+      ret = hdfsBuilderConfSetStr(bld, "dfs.domain.socket.path",
+                            cl->domainSocketPath);
+      if (ret) {
+          return ret;
+      }
+    }
+    return 0;
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/native_mini_dfs.h

@@ -21,6 +21,7 @@
 
 #include <jni.h> /* for jboolean */
 
+struct hdfsBuilder;
 struct NativeMiniDfsCluster; 
 
 /**
@@ -28,17 +29,24 @@ struct NativeMiniDfsCluster;
  */
 struct NativeMiniDfsConf {
     /**
-     * Nonzero if the cluster should be formatted prior to startup
+     * Nonzero if the cluster should be formatted prior to startup.
      */
     jboolean doFormat;
+
     /**
      * Whether or not to enable webhdfs in MiniDfsCluster
      */
     jboolean webhdfsEnabled;
+
     /**
      * The http port of the namenode in MiniDfsCluster
      */
     jint namenodeHttpPort;
+
+    /**
+     * Nonzero if we should configure short circuit.
+     */
+    jboolean configureShortCircuit;
 };
 
 /**
@@ -84,7 +92,7 @@ void nmdFree(struct NativeMiniDfsCluster* cl);
  *
  * @return          the port, or a negative error code
  */
-int nmdGetNameNodePort(const struct NativeMiniDfsCluster *cl);
+int nmdGetNameNodePort(const struct NativeMiniDfsCluster *cl); 
 
 /**
  * Get the http address that's in use by the given (non-HA) nativeMiniDfs
@@ -101,4 +109,14 @@ int nmdGetNameNodePort(const struct NativeMiniDfsCluster *cl);
 int nmdGetNameNodeHttpAddress(const struct NativeMiniDfsCluster *cl,
                                int *port, const char **hostName);
 
+/**
+ * Configure the HDFS builder appropriately to connect to this cluster.
+ *
+ * @param bld       The hdfs builder
+ *
+ * @return          the port, or a negative error code
+ */
+int nmdConfigureHdfsBuilder(struct NativeMiniDfsCluster *cl,
+                            struct hdfsBuilder *bld);
+
 #endif

hadoop-hdfs-project/hadoop-hdfs/src/main/native/libhdfs/test/test_libhdfs_zerocopy.c

@@ -0,0 +1,233 @@
+/**
+ * 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.
+ */
+
+#include "expect.h"
+#include "hdfs.h"
+#include "native_mini_dfs.h"
+
+#include <errno.h>
+#include <inttypes.h>
+#include <semaphore.h>
+#include <pthread.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+
+#define TO_STR_HELPER(X) #X
+#define TO_STR(X) TO_STR_HELPER(X)
+
+#define TEST_FILE_NAME_LENGTH 128
+#define TEST_ZEROCOPY_FULL_BLOCK_SIZE 4096
+#define TEST_ZEROCOPY_LAST_BLOCK_SIZE 3215
+#define TEST_ZEROCOPY_NUM_BLOCKS 6
+#define SMALL_READ_LEN 16
+
+#define ZC_BUF_LEN 32768
+
+static uint8_t *getZeroCopyBlockData(int blockIdx)
+{
+    uint8_t *buf = malloc(TEST_ZEROCOPY_FULL_BLOCK_SIZE);
+    int i;
+    if (!buf) {
+        fprintf(stderr, "malloc(%d) failed\n", TEST_ZEROCOPY_FULL_BLOCK_SIZE);
+        exit(1);
+    }
+    for (i = 0; i < TEST_ZEROCOPY_FULL_BLOCK_SIZE; i++) {
+      buf[i] = blockIdx + (i % 17);
+    }
+    return buf;
+}
+
+static int getZeroCopyBlockLen(int blockIdx)
+{
+    if (blockIdx >= TEST_ZEROCOPY_NUM_BLOCKS) {
+        return 0;
+    } else if (blockIdx == (TEST_ZEROCOPY_NUM_BLOCKS - 1)) {
+        return TEST_ZEROCOPY_LAST_BLOCK_SIZE;
+    } else {
+        return TEST_ZEROCOPY_FULL_BLOCK_SIZE;
+    }
+}
+
+static void printBuf(const uint8_t *buf, size_t len) __attribute__((unused));
+
+static void printBuf(const uint8_t *buf, size_t len)
+{
+  size_t i;
+
+  for (i = 0; i < len; i++) {
+    fprintf(stderr, "%02x", buf[i]);
+  }
+  fprintf(stderr, "\n");
+}
+
+static int doTestZeroCopyReads(hdfsFS fs, const char *fileName)
+{
+    hdfsFile file = NULL;
+    struct hadoopRzOptions *opts = NULL;
+    struct hadoopRzBuffer *buffer = NULL;
+    uint8_t *block;
+
+    file = hdfsOpenFile(fs, fileName, O_RDONLY, 0, 0, 0);
+    EXPECT_NONNULL(file);
+    opts = hadoopRzOptionsAlloc();
+    EXPECT_NONNULL(opts);
+    EXPECT_ZERO(hadoopRzOptionsSetSkipChecksum(opts, 1));
+    /* haven't read anything yet */
+    EXPECT_ZERO(expectFileStats(file, 0LL, 0LL, 0LL, 0LL));
+    block = getZeroCopyBlockData(0);
+    EXPECT_NONNULL(block);
+    /* first read is half of a block. */
+    buffer = hadoopReadZero(file, opts, TEST_ZEROCOPY_FULL_BLOCK_SIZE / 2);
+    EXPECT_NONNULL(buffer);
+    EXPECT_INT_EQ(TEST_ZEROCOPY_FULL_BLOCK_SIZE / 2,
+          hadoopRzBufferLength(buffer));
+    EXPECT_ZERO(memcmp(hadoopRzBufferGet(buffer), block,
+          TEST_ZEROCOPY_FULL_BLOCK_SIZE / 2));
+    hadoopRzBufferFree(file, buffer);
+    /* read the next half of the block */
+    buffer = hadoopReadZero(file, opts, TEST_ZEROCOPY_FULL_BLOCK_SIZE / 2);
+    EXPECT_NONNULL(buffer);
+    EXPECT_INT_EQ(TEST_ZEROCOPY_FULL_BLOCK_SIZE / 2,
+          hadoopRzBufferLength(buffer));
+    EXPECT_ZERO(memcmp(hadoopRzBufferGet(buffer),
+          block + (TEST_ZEROCOPY_FULL_BLOCK_SIZE / 2),
+          TEST_ZEROCOPY_FULL_BLOCK_SIZE / 2));
+    hadoopRzBufferFree(file, buffer);
+    free(block);
+    EXPECT_ZERO(expectFileStats(file, TEST_ZEROCOPY_FULL_BLOCK_SIZE, 
+              TEST_ZEROCOPY_FULL_BLOCK_SIZE,
+              TEST_ZEROCOPY_FULL_BLOCK_SIZE,
+              TEST_ZEROCOPY_FULL_BLOCK_SIZE));
+    /* Now let's read just a few bytes. */
+    buffer = hadoopReadZero(file, opts, SMALL_READ_LEN);
+    EXPECT_NONNULL(buffer);
+    EXPECT_INT_EQ(SMALL_READ_LEN, hadoopRzBufferLength(buffer));
+    block = getZeroCopyBlockData(1);
+    EXPECT_NONNULL(block);
+    EXPECT_ZERO(memcmp(block, hadoopRzBufferGet(buffer), SMALL_READ_LEN));
+    hadoopRzBufferFree(file, buffer);
+    EXPECT_INT_EQ(TEST_ZEROCOPY_FULL_BLOCK_SIZE + SMALL_READ_LEN,
+                  hdfsTell(fs, file));
+    EXPECT_ZERO(expectFileStats(file,
+          TEST_ZEROCOPY_FULL_BLOCK_SIZE + SMALL_READ_LEN,
+          TEST_ZEROCOPY_FULL_BLOCK_SIZE + SMALL_READ_LEN,
+          TEST_ZEROCOPY_FULL_BLOCK_SIZE + SMALL_READ_LEN,
+          TEST_ZEROCOPY_FULL_BLOCK_SIZE + SMALL_READ_LEN));
+
+    /* Clear 'skip checksums' and test that we can't do zero-copy reads any
+     * more.  Since there is no ByteBufferPool set, we should fail with
+     * EPROTONOSUPPORT.
+     */
+    EXPECT_ZERO(hadoopRzOptionsSetSkipChecksum(opts, 0));
+    EXPECT_NULL(hadoopReadZero(file, opts, TEST_ZEROCOPY_FULL_BLOCK_SIZE));
+    EXPECT_INT_EQ(EPROTONOSUPPORT, errno);
+
+    /* Now set a ByteBufferPool and try again.  It should succeed this time. */
+    EXPECT_ZERO(hadoopRzOptionsSetByteBufferPool(opts,
+          ELASTIC_BYTE_BUFFER_POOL_CLASS));
+    buffer = hadoopReadZero(file, opts, TEST_ZEROCOPY_FULL_BLOCK_SIZE);
+    EXPECT_NONNULL(buffer);
+    EXPECT_INT_EQ(TEST_ZEROCOPY_FULL_BLOCK_SIZE, hadoopRzBufferLength(buffer));
+    EXPECT_ZERO(expectFileStats(file,
+          (2 * TEST_ZEROCOPY_FULL_BLOCK_SIZE) + SMALL_READ_LEN,
+          (2 * TEST_ZEROCOPY_FULL_BLOCK_SIZE) + SMALL_READ_LEN,
+          (2 * TEST_ZEROCOPY_FULL_BLOCK_SIZE) + SMALL_READ_LEN,
+          TEST_ZEROCOPY_FULL_BLOCK_SIZE + SMALL_READ_LEN));
+    EXPECT_ZERO(memcmp(block + SMALL_READ_LEN, hadoopRzBufferGet(buffer),
+        TEST_ZEROCOPY_FULL_BLOCK_SIZE - SMALL_READ_LEN));
+    free(block);
+    block = getZeroCopyBlockData(2);
+    EXPECT_NONNULL(block);
+    EXPECT_ZERO(memcmp(block, hadoopRzBufferGet(buffer) +
+        (TEST_ZEROCOPY_FULL_BLOCK_SIZE - SMALL_READ_LEN), SMALL_READ_LEN));
+    hadoopRzBufferFree(file, buffer);
+    free(block);
+    hadoopRzOptionsFree(opts);
+    EXPECT_ZERO(hdfsCloseFile(fs, file));
+    return 0;
+}
+
+static int createZeroCopyTestFile(hdfsFS fs, char *testFileName,
+                                  size_t testFileNameLen)
+{
+    int blockIdx, blockLen;
+    hdfsFile file;
+    uint8_t *data;
+
+    snprintf(testFileName, testFileNameLen, "/zeroCopyTestFile.%d.%d",
+             getpid(), rand());
+    file = hdfsOpenFile(fs, testFileName, O_WRONLY, 0, 1,
+                        TEST_ZEROCOPY_FULL_BLOCK_SIZE);
+    EXPECT_NONNULL(file);
+    for (blockIdx = 0; blockIdx < TEST_ZEROCOPY_NUM_BLOCKS; blockIdx++) {
+        blockLen = getZeroCopyBlockLen(blockIdx);
+        data = getZeroCopyBlockData(blockIdx);
+        EXPECT_NONNULL(data);
+        EXPECT_INT_EQ(blockLen, hdfsWrite(fs, file, data, blockLen));
+    }
+    EXPECT_ZERO(hdfsCloseFile(fs, file));
+    return 0;
+}
+
+/**
+ * Test that we can write a file with libhdfs and then read it back
+ */
+int main(void)
+{
+    int port;
+    struct NativeMiniDfsConf conf = {
+        .doFormat = 1,
+        .configureShortCircuit = 1,
+    };
+    char testFileName[TEST_FILE_NAME_LENGTH];
+    hdfsFS fs;
+    struct NativeMiniDfsCluster* cl;
+    struct hdfsBuilder *bld;
+
+    cl = nmdCreate(&conf);
+    EXPECT_NONNULL(cl);
+    EXPECT_ZERO(nmdWaitClusterUp(cl));
+    port = nmdGetNameNodePort(cl);
+    if (port < 0) {
+        fprintf(stderr, "TEST_ERROR: test_zerocopy: "
+                "nmdGetNameNodePort returned error %d\n", port);
+        return EXIT_FAILURE;
+    }
+    bld = hdfsNewBuilder();
+    EXPECT_NONNULL(bld);
+    EXPECT_ZERO(nmdConfigureHdfsBuilder(cl, bld));
+    hdfsBuilderSetForceNewInstance(bld);
+    hdfsBuilderConfSetStr(bld, "dfs.block.size",
+                          TO_STR(TEST_ZEROCOPY_FULL_BLOCK_SIZE));
+    /* ensure that we'll always get our mmaps */
+    hdfsBuilderConfSetStr(bld, "dfs.client.read.shortcircuit.skip.checksum",
+                          "true");
+    fs = hdfsBuilderConnect(bld);
+    EXPECT_NONNULL(fs);
+    EXPECT_ZERO(createZeroCopyTestFile(fs, testFileName,
+          TEST_FILE_NAME_LENGTH));
+    EXPECT_ZERO(doTestZeroCopyReads(fs, testFileName));
+    EXPECT_ZERO(hdfsDisconnect(fs));
+    EXPECT_ZERO(nmdShutdown(cl));
+    nmdFree(cl);
+    fprintf(stderr, "TEST_SUCCESS\n"); 
+    return EXIT_SUCCESS;
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -1415,4 +1415,32 @@
 	  linearly increases.
 	</description>
 </property>
+
+<property>
+  <name>dfs.client.mmap.cache.size</name>
+  <value>1024</value>
+  <description>
+    When zero-copy reads are used, the DFSClient keeps a cache of recently used
+    memory mapped regions.  This parameter controls the maximum number of
+    entries that we will keep in that cache.
+
+    If this is set to 0, we will not allow mmap.
+
+    The larger this number is, the more file descriptors we will potentially
+    use for memory-mapped files.  mmaped files also use virtual address space.
+    You may need to increase your ulimit virtual address space limits before
+    increasing the client mmap cache size.
+  </description>
+</property>
+
+<property>
+  <name>dfs.client.mmap.cache.timeout.ms</name>
+  <value>900000</value>
+  <description>
+    The minimum length of time that we will keep an mmap entry in the cache
+    between uses.  If an entry is in the cache longer than this, and nobody
+    uses it, it will be removed by a background thread.
+  </description>
+</property>
+
 </configuration>

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/fs/TestEnhancedByteBufferAccess.java

@@ -0,0 +1,530 @@
+/**
+ * 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.fs;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.InputStream;
+import java.nio.ByteBuffer;
+import java.util.concurrent.TimeoutException;
+import java.util.Arrays;
+import java.util.EnumSet;
+import java.util.Random;
+
+import org.apache.commons.lang.SystemUtils;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.fs.FSDataInputStream;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.DFSTestUtil;
+import org.apache.hadoop.hdfs.DistributedFileSystem;
+import org.apache.hadoop.hdfs.HdfsConfiguration;
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.hdfs.client.ClientMmap;
+import org.apache.hadoop.hdfs.client.ClientMmapManager;
+import org.apache.hadoop.hdfs.client.HdfsDataInputStream;
+import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.io.ByteBufferPool;
+import org.apache.hadoop.io.ElasticByteBufferPool;
+import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.io.nativeio.NativeIO;
+import org.apache.hadoop.net.unix.DomainSocket;
+import org.apache.hadoop.net.unix.TemporarySocketDirectory;
+import org.apache.hadoop.test.GenericTestUtils;
+import org.junit.Assert;
+import org.junit.Assume;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import com.google.common.base.Preconditions;
+import com.google.common.base.Supplier;
+
+/**
+ * This class tests if EnhancedByteBufferAccess works correctly.
+ */
+public class TestEnhancedByteBufferAccess {
+  private static final Log LOG =
+      LogFactory.getLog(TestEnhancedByteBufferAccess.class.getName());
+
+  static TemporarySocketDirectory sockDir;
+
+  @BeforeClass
+  public static void init() {
+    sockDir = new TemporarySocketDirectory();
+    DomainSocket.disableBindPathValidation();
+  }
+
+  private static byte[] byteBufferToArray(ByteBuffer buf) {
+    byte resultArray[] = new byte[buf.remaining()];
+    buf.get(resultArray);
+    buf.flip();
+    return resultArray;
+  }
+  
+  public static HdfsConfiguration initZeroCopyTest() {
+    Assume.assumeTrue(NativeIO.isAvailable());
+    Assume.assumeTrue(SystemUtils.IS_OS_UNIX);
+    HdfsConfiguration conf = new HdfsConfiguration();
+    conf.setBoolean(DFSConfigKeys.DFS_CLIENT_READ_SHORTCIRCUIT_KEY, true);
+    conf.setLong(DFSConfigKeys.DFS_BLOCK_SIZE_KEY, 4096);
+    conf.setInt(DFSConfigKeys.DFS_CLIENT_MMAP_CACHE_SIZE, 3);
+    conf.setLong(DFSConfigKeys.DFS_CLIENT_MMAP_CACHE_TIMEOUT_MS, 100);
+    conf.set(DFSConfigKeys.DFS_DOMAIN_SOCKET_PATH_KEY,
+        new File(sockDir.getDir(),
+          "TestRequestMmapAccess._PORT.sock").getAbsolutePath());
+    conf.setBoolean(DFSConfigKeys.
+        DFS_CLIENT_READ_SHORTCIRCUIT_SKIP_CHECKSUM_KEY, true);
+    return conf;
+  }
+
+  @Test
+  public void testZeroCopyReads() throws Exception {
+    HdfsConfiguration conf = initZeroCopyTest();
+    MiniDFSCluster cluster = null;
+    final Path TEST_PATH = new Path("/a");
+    FSDataInputStream fsIn = null;
+    final int TEST_FILE_LENGTH = 12345;
+    
+    FileSystem fs = null;
+    try {
+      cluster = new MiniDFSCluster.Builder(conf).numDataNodes(1).build();
+      cluster.waitActive();
+      fs = cluster.getFileSystem();
+      DFSTestUtil.createFile(fs, TEST_PATH,
+          TEST_FILE_LENGTH, (short)1, 7567L);
+      try {
+        DFSTestUtil.waitReplication(fs, TEST_PATH, (short)1);
+      } catch (InterruptedException e) {
+        Assert.fail("unexpected InterruptedException during " +
+            "waitReplication: " + e);
+      } catch (TimeoutException e) {
+        Assert.fail("unexpected TimeoutException during " +
+            "waitReplication: " + e);
+      }
+      fsIn = fs.open(TEST_PATH);
+      byte original[] = new byte[TEST_FILE_LENGTH];
+      IOUtils.readFully(fsIn, original, 0, TEST_FILE_LENGTH);
+      fsIn.close();
+      fsIn = fs.open(TEST_PATH);
+      ByteBuffer result = fsIn.read(null, 4096,
+          EnumSet.of(ReadOption.SKIP_CHECKSUMS));
+      Assert.assertEquals(4096, result.remaining());
+      HdfsDataInputStream dfsIn = (HdfsDataInputStream)fsIn;
+      Assert.assertEquals(4096,
+          dfsIn.getReadStatistics().getTotalBytesRead());
+      Assert.assertEquals(4096,
+          dfsIn.getReadStatistics().getTotalZeroCopyBytesRead());
+      Assert.assertArrayEquals(Arrays.copyOfRange(original, 0, 4096),
+          byteBufferToArray(result));
+      fsIn.releaseBuffer(result);
+    } finally {
+      if (fsIn != null) fsIn.close();
+      if (fs != null) fs.close();
+      if (cluster != null) cluster.shutdown();
+    }
+  }
+  
+  @Test
+  public void testShortZeroCopyReads() throws Exception {
+    HdfsConfiguration conf = initZeroCopyTest();
+    MiniDFSCluster cluster = null;
+    final Path TEST_PATH = new Path("/a");
+    FSDataInputStream fsIn = null;
+    final int TEST_FILE_LENGTH = 12345;
+    
+    FileSystem fs = null;
+    try {
+      cluster = new MiniDFSCluster.Builder(conf).numDataNodes(1).build();
+      cluster.waitActive();
+      fs = cluster.getFileSystem();
+      DFSTestUtil.createFile(fs, TEST_PATH, TEST_FILE_LENGTH, (short)1, 7567L);
+      try {
+        DFSTestUtil.waitReplication(fs, TEST_PATH, (short)1);
+      } catch (InterruptedException e) {
+        Assert.fail("unexpected InterruptedException during " +
+            "waitReplication: " + e);
+      } catch (TimeoutException e) {
+        Assert.fail("unexpected TimeoutException during " +
+            "waitReplication: " + e);
+      }
+      fsIn = fs.open(TEST_PATH);
+      byte original[] = new byte[TEST_FILE_LENGTH];
+      IOUtils.readFully(fsIn, original, 0, TEST_FILE_LENGTH);
+      fsIn.close();
+      fsIn = fs.open(TEST_PATH);
+
+      // Try to read 8192, but only get 4096 because of the block size.
+      HdfsDataInputStream dfsIn = (HdfsDataInputStream)fsIn;
+      ByteBuffer result =
+        dfsIn.read(null, 8192, EnumSet.of(ReadOption.SKIP_CHECKSUMS));
+      Assert.assertEquals(4096, result.remaining());
+      Assert.assertEquals(4096,
+          dfsIn.getReadStatistics().getTotalBytesRead());
+      Assert.assertEquals(4096,
+          dfsIn.getReadStatistics().getTotalZeroCopyBytesRead());
+      Assert.assertArrayEquals(Arrays.copyOfRange(original, 0, 4096),
+          byteBufferToArray(result));
+      dfsIn.releaseBuffer(result);
+      
+      // Try to read 4097, but only get 4096 because of the block size.
+      result = 
+          dfsIn.read(null, 4097, EnumSet.of(ReadOption.SKIP_CHECKSUMS));
+      Assert.assertEquals(4096, result.remaining());
+      Assert.assertArrayEquals(Arrays.copyOfRange(original, 4096, 8192),
+          byteBufferToArray(result));
+      dfsIn.releaseBuffer(result);
+    } finally {
+      if (fsIn != null) fsIn.close();
+      if (fs != null) fs.close();
+      if (cluster != null) cluster.shutdown();
+    }
+  }
+
+  @Test
+  public void testZeroCopyReadsNoFallback() throws Exception {
+    HdfsConfiguration conf = initZeroCopyTest();
+    MiniDFSCluster cluster = null;
+    final Path TEST_PATH = new Path("/a");
+    FSDataInputStream fsIn = null;
+    final int TEST_FILE_LENGTH = 12345;
+    
+    FileSystem fs = null;
+    try {
+      cluster = new MiniDFSCluster.Builder(conf).numDataNodes(1).build();
+      cluster.waitActive();
+      fs = cluster.getFileSystem();
+      DFSTestUtil.createFile(fs, TEST_PATH,
+          TEST_FILE_LENGTH, (short)1, 7567L);
+      try {
+        DFSTestUtil.waitReplication(fs, TEST_PATH, (short)1);
+      } catch (InterruptedException e) {
+        Assert.fail("unexpected InterruptedException during " +
+            "waitReplication: " + e);
+      } catch (TimeoutException e) {
+        Assert.fail("unexpected TimeoutException during " +
+            "waitReplication: " + e);
+      }
+      fsIn = fs.open(TEST_PATH);
+      byte original[] = new byte[TEST_FILE_LENGTH];
+      IOUtils.readFully(fsIn, original, 0, TEST_FILE_LENGTH);
+      fsIn.close();
+      fsIn = fs.open(TEST_PATH);
+      HdfsDataInputStream dfsIn = (HdfsDataInputStream)fsIn;
+      ByteBuffer result;
+      try {
+        result = dfsIn.read(null, 4097, EnumSet.noneOf(ReadOption.class));
+        Assert.fail("expected UnsupportedOperationException");
+      } catch (UnsupportedOperationException e) {
+        // expected
+      }
+      result = dfsIn.read(null, 4096, EnumSet.of(ReadOption.SKIP_CHECKSUMS));
+      Assert.assertEquals(4096, result.remaining());
+      Assert.assertEquals(4096,
+          dfsIn.getReadStatistics().getTotalBytesRead());
+      Assert.assertEquals(4096,
+          dfsIn.getReadStatistics().getTotalZeroCopyBytesRead());
+      Assert.assertArrayEquals(Arrays.copyOfRange(original, 0, 4096),
+          byteBufferToArray(result));
+    } finally {
+      if (fsIn != null) fsIn.close();
+      if (fs != null) fs.close();
+      if (cluster != null) cluster.shutdown();
+    }
+  }
+
+  private static class CountingVisitor
+      implements ClientMmapManager.ClientMmapVisitor {
+    int count = 0;
+
+    @Override
+    public void accept(ClientMmap mmap) {
+      count++;
+    }
+
+    public void reset() {
+      count = 0;
+    }
+  }
+
+  @Test
+  public void testZeroCopyMmapCache() throws Exception {
+    HdfsConfiguration conf = initZeroCopyTest();
+    MiniDFSCluster cluster = null;
+    final Path TEST_PATH = new Path("/a");
+    final int TEST_FILE_LENGTH = 16385;
+    final int RANDOM_SEED = 23453;
+    FSDataInputStream fsIn = null;
+    ByteBuffer results[] = { null, null, null, null, null };
+    
+    DistributedFileSystem fs = null;
+    try {
+      cluster = new MiniDFSCluster.Builder(conf).numDataNodes(1).build();
+      cluster.waitActive();
+      fs = cluster.getFileSystem();
+      DFSTestUtil.createFile(fs, TEST_PATH,
+          TEST_FILE_LENGTH, (short)1, RANDOM_SEED);
+      try {
+        DFSTestUtil.waitReplication(fs, TEST_PATH, (short)1);
+      } catch (InterruptedException e) {
+        Assert.fail("unexpected InterruptedException during " +
+            "waitReplication: " + e);
+      } catch (TimeoutException e) {
+        Assert.fail("unexpected TimeoutException during " +
+            "waitReplication: " + e);
+      }
+      fsIn = fs.open(TEST_PATH);
+      byte original[] = new byte[TEST_FILE_LENGTH];
+      IOUtils.readFully(fsIn, original, 0, TEST_FILE_LENGTH);
+      fsIn.close();
+      fsIn = fs.open(TEST_PATH);
+      final ClientMmapManager mmapManager = fs.getClient().getMmapManager();
+      final CountingVisitor countingVisitor = new CountingVisitor();
+      mmapManager.visitMmaps(countingVisitor);
+      Assert.assertEquals(0, countingVisitor.count);
+      mmapManager.visitEvictable(countingVisitor);
+      Assert.assertEquals(0, countingVisitor.count);
+      results[0] = fsIn.read(null, 4096,
+          EnumSet.of(ReadOption.SKIP_CHECKSUMS));
+      fsIn.seek(0);
+      results[1] = fsIn.read(null, 4096,
+          EnumSet.of(ReadOption.SKIP_CHECKSUMS));
+      mmapManager.visitMmaps(countingVisitor);
+      Assert.assertEquals(1, countingVisitor.count);
+      countingVisitor.reset();
+      mmapManager.visitEvictable(countingVisitor);
+      Assert.assertEquals(0, countingVisitor.count);
+      countingVisitor.reset();
+
+      // The mmaps should be of the first block of the file.
+      final ExtendedBlock firstBlock = DFSTestUtil.getFirstBlock(fs, TEST_PATH);
+      mmapManager.visitMmaps(new ClientMmapManager.ClientMmapVisitor() {
+        @Override
+        public void accept(ClientMmap mmap) {
+          Assert.assertEquals(firstBlock, mmap.getBlock());
+        }
+      });
+
+      // Read more blocks.
+      results[2] = fsIn.read(null, 4096,
+          EnumSet.of(ReadOption.SKIP_CHECKSUMS));
+      results[3] = fsIn.read(null, 4096,
+          EnumSet.of(ReadOption.SKIP_CHECKSUMS));
+      try {
+        results[4] = fsIn.read(null, 4096,
+            EnumSet.of(ReadOption.SKIP_CHECKSUMS));
+        Assert.fail("expected UnsupportedOperationException");
+      } catch (UnsupportedOperationException e) {
+        // expected
+      }
+
+      // we should have 3 mmaps, 0 evictable
+      mmapManager.visitMmaps(countingVisitor);
+      Assert.assertEquals(3, countingVisitor.count);
+      countingVisitor.reset();
+      mmapManager.visitEvictable(countingVisitor);
+      Assert.assertEquals(0, countingVisitor.count);
+
+      // After we close the cursors, the mmaps should be evictable for 
+      // a brief period of time.  Then, they should be closed (we're 
+      // using a very quick timeout)
+      for (ByteBuffer buffer : results) {
+        if (buffer != null) {
+          fsIn.releaseBuffer(buffer);
+        }
+      }
+      GenericTestUtils.waitFor(new Supplier<Boolean>() {
+        public Boolean get() {
+          countingVisitor.reset();
+          try {
+            mmapManager.visitEvictable(countingVisitor);
+          } catch (InterruptedException e) {
+            e.printStackTrace();
+            return false;
+          }
+          return (0 == countingVisitor.count);
+        }
+      }, 10, 10000);
+      countingVisitor.reset();
+      mmapManager.visitMmaps(countingVisitor);
+      Assert.assertEquals(0, countingVisitor.count);
+    } finally {
+      if (fsIn != null) fsIn.close();
+      if (fs != null) fs.close();
+      if (cluster != null) cluster.shutdown();
+    }
+  }
+
+  /**
+   * Test HDFS fallback reads.  HDFS streams support the ByteBufferReadable
+   * interface.
+   */
+  @Test
+  public void testHdfsFallbackReads() throws Exception {
+    HdfsConfiguration conf = initZeroCopyTest();
+    MiniDFSCluster cluster = null;
+    final Path TEST_PATH = new Path("/a");
+    final int TEST_FILE_LENGTH = 16385;
+    final int RANDOM_SEED = 23453;
+    FSDataInputStream fsIn = null;
+    
+    DistributedFileSystem fs = null;
+    try {
+      cluster = new MiniDFSCluster.Builder(conf).numDataNodes(1).build();
+      cluster.waitActive();
+      fs = cluster.getFileSystem();
+      DFSTestUtil.createFile(fs, TEST_PATH,
+          TEST_FILE_LENGTH, (short)1, RANDOM_SEED);
+      try {
+        DFSTestUtil.waitReplication(fs, TEST_PATH, (short)1);
+      } catch (InterruptedException e) {
+        Assert.fail("unexpected InterruptedException during " +
+            "waitReplication: " + e);
+      } catch (TimeoutException e) {
+        Assert.fail("unexpected TimeoutException during " +
+            "waitReplication: " + e);
+      }
+      fsIn = fs.open(TEST_PATH);
+      byte original[] = new byte[TEST_FILE_LENGTH];
+      IOUtils.readFully(fsIn, original, 0, TEST_FILE_LENGTH);
+      fsIn.close();
+      fsIn = fs.open(TEST_PATH);
+      testFallbackImpl(fsIn, original);
+    } finally {
+      if (fsIn != null) fsIn.close();
+      if (fs != null) fs.close();
+      if (cluster != null) cluster.shutdown();
+    }
+  }
+
+  private static class RestrictedAllocatingByteBufferPool
+      implements ByteBufferPool {
+    private final boolean direct;
+
+    RestrictedAllocatingByteBufferPool(boolean direct) {
+      this.direct = direct;
+    }
+    @Override
+    public ByteBuffer getBuffer(boolean direct, int length) {
+      Preconditions.checkArgument(this.direct == direct);
+      return direct ? ByteBuffer.allocateDirect(length) :
+        ByteBuffer.allocate(length);
+    }
+    @Override
+    public void putBuffer(ByteBuffer buffer) {
+    }
+  }
+  
+  private static void testFallbackImpl(InputStream stream,
+      byte original[]) throws Exception {
+    RestrictedAllocatingByteBufferPool bufferPool =
+        new RestrictedAllocatingByteBufferPool(
+            stream instanceof ByteBufferReadable);
+
+    ByteBuffer result = ByteBufferUtil.fallbackRead(stream, bufferPool, 10);
+    Assert.assertEquals(10, result.remaining());
+    Assert.assertArrayEquals(Arrays.copyOfRange(original, 0, 10),
+        byteBufferToArray(result));
+
+    result = ByteBufferUtil.fallbackRead(stream, bufferPool, 5000);
+    Assert.assertEquals(5000, result.remaining());
+    Assert.assertArrayEquals(Arrays.copyOfRange(original, 10, 5010),
+        byteBufferToArray(result));
+
+    result = ByteBufferUtil.fallbackRead(stream, bufferPool, 9999999);
+    Assert.assertEquals(11375, result.remaining());
+    Assert.assertArrayEquals(Arrays.copyOfRange(original, 5010, 16385),
+        byteBufferToArray(result));
+
+    result = ByteBufferUtil.fallbackRead(stream, bufferPool, 10);
+    Assert.assertNull(result);
+  }
+
+  /**
+   * Test the {@link ByteBufferUtil#fallbackRead} function directly.
+   */
+  @Test
+  public void testFallbackRead() throws Exception {
+    HdfsConfiguration conf = initZeroCopyTest();
+    MiniDFSCluster cluster = null;
+    final Path TEST_PATH = new Path("/a");
+    final int TEST_FILE_LENGTH = 16385;
+    final int RANDOM_SEED = 23453;
+    FSDataInputStream fsIn = null;
+    
+    DistributedFileSystem fs = null;
+    try {
+      cluster = new MiniDFSCluster.Builder(conf).numDataNodes(1).build();
+      cluster.waitActive();
+      fs = cluster.getFileSystem();
+      DFSTestUtil.createFile(fs, TEST_PATH,
+          TEST_FILE_LENGTH, (short)1, RANDOM_SEED);
+      try {
+        DFSTestUtil.waitReplication(fs, TEST_PATH, (short)1);
+      } catch (InterruptedException e) {
+        Assert.fail("unexpected InterruptedException during " +
+            "waitReplication: " + e);
+      } catch (TimeoutException e) {
+        Assert.fail("unexpected TimeoutException during " +
+            "waitReplication: " + e);
+      }
+      fsIn = fs.open(TEST_PATH);
+      byte original[] = new byte[TEST_FILE_LENGTH];
+      IOUtils.readFully(fsIn, original, 0, TEST_FILE_LENGTH);
+      fsIn.close();
+      fsIn = fs.open(TEST_PATH);
+      testFallbackImpl(fsIn, original);
+    } finally {
+      if (fsIn != null) fsIn.close();
+      if (fs != null) fs.close();
+      if (cluster != null) cluster.shutdown();
+    }
+  }
+
+  /**
+   * Test fallback reads on a stream which does not support the
+   * ByteBufferReadable * interface.
+   */
+  @Test
+  public void testIndirectFallbackReads() throws Exception {
+    final File TEST_DIR = new File(
+      System.getProperty("test.build.data","build/test/data"));
+    final String TEST_PATH = TEST_DIR + File.separator +
+        "indirectFallbackTestFile";
+    final int TEST_FILE_LENGTH = 16385;
+    final int RANDOM_SEED = 23453;
+    FileOutputStream fos = null;
+    FileInputStream fis = null;
+    try {
+      fos = new FileOutputStream(TEST_PATH);
+      Random random = new Random(RANDOM_SEED);
+      byte original[] = new byte[TEST_FILE_LENGTH];
+      random.nextBytes(original);
+      fos.write(original);
+      fos.close();
+      fos = null;
+      fis = new FileInputStream(TEST_PATH);
+      testFallbackImpl(fis, original);
+    } finally {
+      IOUtils.cleanup(LOG, fos, fis);
+      new File(TEST_PATH).delete();
+    }
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestBlockReaderLocal.java

@@ -25,7 +25,6 @@ import java.io.RandomAccessFile;
 import java.nio.ByteBuffer;
 import java.util.concurrent.TimeoutException;
 
-import org.apache.hadoop.hdfs.DFSInputStream.ReadStatistics;
 import org.apache.hadoop.fs.ChecksumException;
 import org.apache.hadoop.fs.FSDataInputStream;
 import org.apache.hadoop.fs.FileSystem;
@@ -36,11 +35,26 @@ import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
 import org.apache.hadoop.io.IOUtils;
 import org.apache.hadoop.net.unix.DomainSocket;
 import org.apache.hadoop.net.unix.TemporarySocketDirectory;
+import org.junit.AfterClass;
 import org.junit.Assert;
 import org.junit.Assume;
+import org.junit.BeforeClass;
 import org.junit.Test;
 
 public class TestBlockReaderLocal {
+  private static TemporarySocketDirectory sockDir;
+  
+  @BeforeClass
+  public static void init() {
+    sockDir = new TemporarySocketDirectory();
+    DomainSocket.disableBindPathValidation();
+  }
+  
+  @AfterClass
+  public static void shutdown() throws IOException {
+    sockDir.close();
+  }
+  
   public static void assertArrayRegionsEqual(byte []buf1, int off1, byte []buf2,
       int off2, int len) {
     for (int i = 0; i < len; i++) {
@@ -100,10 +114,11 @@ public class TestBlockReaderLocal {
     FSDataInputStream fsIn = null;
     byte original[] = new byte[BlockReaderLocalTest.TEST_LENGTH];
     
+    FileSystem fs = null;
     try {
       cluster = new MiniDFSCluster.Builder(conf).numDataNodes(1).build();
       cluster.waitActive();
-      FileSystem fs = cluster.getFileSystem();
+      fs = cluster.getFileSystem();
       DFSTestUtil.createFile(fs, TEST_PATH,
           BlockReaderLocalTest.TEST_LENGTH, (short)1, RANDOM_SEED);
       try {
@@ -138,6 +153,7 @@ public class TestBlockReaderLocal {
       test.doTest(blockReaderLocal, original);
     } finally {
       if (fsIn != null) fsIn.close();
+      if (fs != null) fs.close();
       if (cluster != null) cluster.shutdown();
       if (dataIn != null) dataIn.close();
       if (checkIn != null) checkIn.close();
@@ -382,10 +398,11 @@ public class TestBlockReaderLocal {
     final long RANDOM_SEED = 4567L;
     FSDataInputStream fsIn = null;
     byte original[] = new byte[BlockReaderLocalTest.TEST_LENGTH];
+    FileSystem fs = null;
     try {
       cluster = new MiniDFSCluster.Builder(conf).numDataNodes(1).build();
       cluster.waitActive();
-      FileSystem fs = cluster.getFileSystem();
+      fs = cluster.getFileSystem();
       DFSTestUtil.createFile(fs, TEST_PATH,
           BlockReaderLocalTest.TEST_LENGTH, (short)1, RANDOM_SEED);
       try {
@@ -417,6 +434,7 @@ public class TestBlockReaderLocal {
     } finally {
       DFSInputStream.tcpReadsDisabledForTesting = false;
       if (fsIn != null) fsIn.close();
+      if (fs != null) fs.close();
       if (cluster != null) cluster.shutdown();
       if (sockDir != null) sockDir.close();
     }