HDFS-5631. Change BlockMetadataHeader.readHeader(..), ChunkChecksum class and constructor to public; and fix FsDatasetSpi to use generic type instead of FsVolumeImpl. Contributed by David Powell and Joe Pallas

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

@@ -136,6 +136,10 @@ Trunk (Unreleased)
     HDFS-7591. hdfs classpath command should support same options as hadoop
     classpath (Varun Saxena via Arpit Agarwal)
 
+    HDFS-5631. Change BlockMetadataHeader.readHeader(..), ChunkChecksum
+    class and constructor to public; and fix FsDatasetSpi to use generic type
+    instead of FsVolumeImpl.  (David Powell and Joe Pallas via szetszwo)
+
   OPTIMIZATIONS
 
   BUG FIXES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockMetadataHeader.java

@@ -162,7 +162,7 @@ public class BlockMetadataHeader {
    * The current file position will be altered by this method.
    * If an error occurs, the file is <em>not</em> closed.
    */
-  static BlockMetadataHeader readHeader(RandomAccessFile raf) throws IOException {
+  public static BlockMetadataHeader readHeader(RandomAccessFile raf) throws IOException {
     byte[] buf = new byte[getHeaderSize()];
     raf.seek(0);
     raf.readFully(buf, 0, buf.length);

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/ChunkChecksum.java

@@ -26,12 +26,12 @@ package org.apache.hadoop.hdfs.server.datanode;
  *     the checksum applies for the last chunk, or bytes 512 - 1023
  */
 
-class ChunkChecksum {
+public class ChunkChecksum {
   private final long dataLength;
   // can be null if not available
   private final byte[] checksum;
 
-  ChunkChecksum(long dataLength, byte[] checksum) {
+  public ChunkChecksum(long dataLength, byte[] checksum) {
     this.dataLength = dataLength;
     this.checksum = checksum;
   }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsDatasetSpi.java

@@ -503,7 +503,7 @@ public interface FsDatasetSpi<V extends FsVolumeSpi> extends FSDatasetMBean {
    * Callback from RamDiskAsyncLazyPersistService upon async lazy persist task end
    */
    public void onCompleteLazyPersist(String bpId, long blockId,
-      long creationTime, File[] savedFiles, FsVolumeImpl targetVolume);
+      long creationTime, File[] savedFiles, V targetVolume);
 
    /**
     * Callback from RamDiskAsyncLazyPersistService upon async lazy persist task fail

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/RamDiskAsyncLazyPersistService.java

@@ -229,14 +229,15 @@ class RamDiskAsyncLazyPersistService {
     @Override
     public void run() {
       boolean succeeded = false;
+      final FsDatasetImpl dataset = (FsDatasetImpl)datanode.getFSDataset();
       try {
         // No FsDatasetImpl lock for the file copy
         File targetFiles[] = FsDatasetImpl.copyBlockFiles(
             blockId, genStamp, metaFile, blockFile, lazyPersistDir, true);
 
         // Lock FsDataSetImpl during onCompleteLazyPersist callback
-        datanode.getFSDataset().onCompleteLazyPersist(bpId, blockId,
-            creationTime, targetFiles, targetVolume);
+        dataset.onCompleteLazyPersist(bpId, blockId,
+                creationTime, targetFiles, targetVolume);
         succeeded = true;
       } catch (Exception e){
         FsDatasetImpl.LOG.warn(
@@ -244,7 +245,7 @@ class RamDiskAsyncLazyPersistService {
             + bpId + "block Id: " + blockId, e);
       } finally {
         if (!succeeded) {
-          datanode.getFSDataset().onFailLazyPersist(bpId, blockId);
+          dataset.onFailLazyPersist(bpId, blockId);
         }
       }
     }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/SimulatedFSDataset.java

@@ -1253,7 +1253,7 @@ public class SimulatedFSDataset implements FsDatasetSpi<FsVolumeSpi> {
 
   @Override
   public void onCompleteLazyPersist(String bpId, long blockId,
-      long creationTime, File[] savedFiles, FsVolumeImpl targetVolume) {
+      long creationTime, File[] savedFiles, FsVolumeSpi targetVolume) {
     throw new UnsupportedOperationException();
   }
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalDatasetImpl.java

@@ -0,0 +1,409 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hdfs.server.datanode.extdataset;
+
+import java.io.*;
+import java.util.*;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.StorageType;
+import org.apache.hadoop.hdfs.protocol.Block;
+import org.apache.hadoop.hdfs.protocol.BlockListAsLongs;
+import org.apache.hadoop.hdfs.protocol.BlockLocalPathInfo;
+import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.protocol.HdfsBlocksMetadata;
+import org.apache.hadoop.hdfs.server.common.HdfsServerConstants.ReplicaState;
+import org.apache.hadoop.hdfs.server.datanode.*;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.LengthInputStream;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.ReplicaInputStreams;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.ReplicaOutputStreams;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.RollingLogs;
+import org.apache.hadoop.hdfs.server.protocol.BlockRecoveryCommand.RecoveringBlock;
+import org.apache.hadoop.hdfs.server.protocol.DatanodeStorage;
+import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
+import org.apache.hadoop.hdfs.server.protocol.ReplicaRecoveryInfo;
+import org.apache.hadoop.hdfs.server.protocol.StorageReport;
+import org.apache.hadoop.util.DiskChecker;
+import org.apache.hadoop.util.DiskChecker.DiskErrorException;
+
+public class ExternalDatasetImpl implements FsDatasetSpi<ExternalVolumeImpl> {
+
+  private final DatanodeStorage storage = new DatanodeStorage(
+      DatanodeStorage.generateUuid(), DatanodeStorage.State.NORMAL,
+      StorageType.DEFAULT);
+
+  @Override
+  public RollingLogs createRollingLogs(String bpid, String prefix)
+      throws IOException {
+    return new ExternalRollingLogs();
+  }
+
+  @Override
+  public List<ExternalVolumeImpl> getVolumes() {
+    return null;
+  }
+
+  @Override
+  public void addVolume(StorageLocation location, List<NamespaceInfo> nsInfos) throws IOException {
+
+  }
+
+  @Override
+  public void removeVolumes(Collection<StorageLocation> volumes) {
+
+  }
+
+  @Override
+  public DatanodeStorage getStorage(String storageUuid) {
+    return null;
+  }
+
+  @Override
+  public StorageReport[] getStorageReports(String bpid) throws IOException {
+    StorageReport[] result = new StorageReport[1];
+    result[0] = new StorageReport(storage, false, 0, 0, 0, 0);
+    return result;
+  }
+
+  @Override
+  public ExternalVolumeImpl getVolume(ExtendedBlock b) {
+    return null;
+  }
+
+  @Override
+  public Map<String, Object> getVolumeInfoMap() {
+    return null;
+  }
+
+  @Override
+  public List<FinalizedReplica> getFinalizedBlocks(String bpid) {
+    return null;
+  }
+
+  @Override
+  public List<FinalizedReplica> getFinalizedBlocksOnPersistentStorage(String bpid) {
+    return null;
+  }
+
+  @Override
+  public void checkAndUpdate(String bpid, long blockId, File diskFile,
+      File diskMetaFile, FsVolumeSpi vol) {
+  }
+
+  @Override
+  public LengthInputStream getMetaDataInputStream(ExtendedBlock b)
+      throws IOException {
+    return new LengthInputStream(null, 0);
+  }
+
+  @Override
+  public long getLength(ExtendedBlock b) throws IOException {
+    return 0;
+  }
+
+  @Override
+  @Deprecated
+  public Replica getReplica(String bpid, long blockId) {
+    return new ExternalReplica();
+  }
+
+  @Override
+  public String getReplicaString(String bpid, long blockId) {
+    return null;
+  }
+
+  @Override
+  public Block getStoredBlock(String bpid, long blkid) throws IOException {
+    return new Block();
+  }
+
+  @Override
+  public InputStream getBlockInputStream(ExtendedBlock b, long seekOffset)
+      throws IOException {
+    return null;
+  }
+
+  @Override
+  public ReplicaInputStreams getTmpInputStreams(ExtendedBlock b, long blkoff,
+      long ckoff) throws IOException {
+    return new ReplicaInputStreams(FileDescriptor.in, FileDescriptor.in);
+  }
+
+  @Override
+  public ReplicaInPipelineInterface createTemporary(StorageType t, ExtendedBlock b)
+      throws IOException {
+    return new ExternalReplicaInPipeline();
+  }
+
+  @Override
+  public ReplicaInPipelineInterface createRbw(StorageType t, ExtendedBlock b, boolean tf)
+      throws IOException {
+    return new ExternalReplicaInPipeline();
+  }
+
+  @Override
+  public ReplicaInPipelineInterface recoverRbw(ExtendedBlock b, long newGS,
+      long minBytesRcvd, long maxBytesRcvd) throws IOException {
+    return new ExternalReplicaInPipeline();
+  }
+
+  @Override
+  public ReplicaInPipelineInterface convertTemporaryToRbw(
+      ExtendedBlock temporary) throws IOException {
+    return new ExternalReplicaInPipeline();
+  }
+
+  @Override
+  public ReplicaInPipelineInterface append(ExtendedBlock b, long newGS,
+      long expectedBlockLen) throws IOException {
+    return new ExternalReplicaInPipeline();
+  }
+
+  @Override
+  public ReplicaInPipelineInterface recoverAppend(ExtendedBlock b, long newGS,
+      long expectedBlockLen) throws IOException {
+    return new ExternalReplicaInPipeline();
+  }
+
+  @Override
+  public String recoverClose(ExtendedBlock b, long newGS, long expectedBlockLen)
+      throws IOException {
+    return null;
+  }
+
+  @Override
+  public void finalizeBlock(ExtendedBlock b) throws IOException {
+  }
+
+  @Override
+  public void unfinalizeBlock(ExtendedBlock b) throws IOException {
+  }
+
+  @Override
+  public Map<DatanodeStorage, BlockListAsLongs> getBlockReports(String bpid) {
+    final Map<DatanodeStorage, BlockListAsLongs> result =
+	new HashMap<DatanodeStorage, BlockListAsLongs>();
+
+    result.put(storage, new BlockListAsLongs(null, null));
+    return result;
+  }
+
+  @Override
+  public List<Long> getCacheReport(String bpid) {
+    return null;
+  }
+
+  @Override
+  public boolean contains(ExtendedBlock block) {
+    return false;
+  }
+
+  @Override
+  public void checkBlock(ExtendedBlock b, long minLength, ReplicaState state) throws ReplicaNotFoundException, UnexpectedReplicaStateException, FileNotFoundException, EOFException, IOException {
+
+  }
+
+  @Override
+  public boolean isValidBlock(ExtendedBlock b) {
+    return false;
+  }
+
+  @Override
+  public boolean isValidRbw(ExtendedBlock b) {
+    return false;
+  }
+
+  @Override
+  public void invalidate(String bpid, Block[] invalidBlks) throws IOException {
+  }
+
+  @Override
+  public void cache(String bpid, long[] blockIds) {
+  }
+
+  @Override
+  public void uncache(String bpid, long[] blockIds) {
+  }
+
+  @Override
+  public boolean isCached(String bpid, long blockId) {
+    return false;
+  }
+
+  @Override
+  public void checkDataDir() throws DiskErrorException {
+    throw new DiskChecker.DiskErrorException(null);
+  }
+
+  @Override
+  public void shutdown() {
+  }
+
+  @Override
+  public void adjustCrcChannelPosition(ExtendedBlock b,
+      ReplicaOutputStreams outs, int checksumSize) throws IOException {
+  }
+
+  @Override
+  public boolean hasEnoughResource() {
+    return false;
+  }
+
+  @Override
+  public long getReplicaVisibleLength(ExtendedBlock block) throws IOException {
+    return 0;
+  }
+
+  @Override
+  public ReplicaRecoveryInfo initReplicaRecovery(RecoveringBlock rBlock)
+      throws IOException {
+    return new ReplicaRecoveryInfo(0, 0, 0, ReplicaState.FINALIZED);
+  }
+
+  @Override
+  public String updateReplicaUnderRecovery(ExtendedBlock oldBlock,
+      long recoveryId, long newBlockId, long newLength) throws IOException {
+    return null;
+  }
+
+  @Override
+  public void addBlockPool(String bpid, Configuration conf) throws IOException {
+  }
+
+  @Override
+  public void shutdownBlockPool(String bpid) {
+  }
+
+  @Override
+  public void deleteBlockPool(String bpid, boolean force) throws IOException {
+  }
+
+  @Override
+  public BlockLocalPathInfo getBlockLocalPathInfo(ExtendedBlock b)
+      throws IOException {
+    return new BlockLocalPathInfo(null, "file", "metafile");
+  }
+
+  @Override
+  public HdfsBlocksMetadata getHdfsBlocksMetadata(String bpid, long[] blockIds) throws IOException {
+    return new HdfsBlocksMetadata(null, null, null, null);
+  }
+
+  @Override
+  public void enableTrash(String bpid) {
+
+  }
+
+  @Override
+  public void restoreTrash(String bpid) {
+
+  }
+
+  @Override
+  public boolean trashEnabled(String bpid) {
+    return false;
+  }
+
+  @Override
+  public void setRollingUpgradeMarker(String bpid) throws IOException {
+
+  }
+
+  @Override
+  public void clearRollingUpgradeMarker(String bpid) throws IOException {
+
+  }
+
+  @Override
+  public void submitBackgroundSyncFileRangeRequest(ExtendedBlock block, FileDescriptor fd, long offset, long nbytes, int flags) {
+
+  }
+
+  @Override
+  public void onCompleteLazyPersist(String bpId, long blockId, long creationTime, File[] savedFiles, ExternalVolumeImpl targetVolume) {
+
+  }
+
+  @Override
+  public void onFailLazyPersist(String bpId, long blockId) {
+
+  }
+
+  @Override
+  public ReplicaInfo moveBlockAcrossStorage(ExtendedBlock block, StorageType targetStorageType) throws IOException {
+    return null;
+  }
+
+  @Override
+  public long getBlockPoolUsed(String bpid) throws IOException {
+    return 0;
+  }
+
+  @Override
+  public long getDfsUsed() throws IOException {
+    return 0;
+  }
+
+  @Override
+  public long getCapacity() throws IOException {
+    return 0;
+  }
+
+  @Override
+  public long getRemaining() throws IOException {
+    return 0;
+  }
+
+  @Override
+  public String getStorageInfo() {
+    return null;
+  }
+
+  @Override
+  public int getNumFailedVolumes() {
+    return 0;
+  }
+
+  @Override
+  public long getCacheUsed() {
+    return 0;
+  }
+
+  @Override
+  public long getCacheCapacity() {
+    return 0;
+  }
+
+  @Override
+  public long getNumBlocksCached() {
+    return 0;
+  }
+
+  @Override
+  public long getNumBlocksFailedToCache() {
+    return 0;
+  }
+
+  @Override
+  public long getNumBlocksFailedToUncache() {
+    return 0;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalReplica.java

@@ -0,0 +1,65 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hdfs.server.datanode.extdataset;
+
+import org.apache.hadoop.hdfs.server.common.HdfsServerConstants.ReplicaState;
+import org.apache.hadoop.hdfs.server.datanode.Replica;
+
+public class ExternalReplica implements Replica {
+
+  @Override
+  public long getBlockId() {
+    return 0;
+  }
+
+  @Override
+  public long getGenerationStamp() {
+    return 0;
+  }
+
+  @Override
+  public ReplicaState getState() {
+    return ReplicaState.FINALIZED;
+  }
+
+  @Override
+  public long getNumBytes() {
+    return 0;
+  }
+
+  @Override
+  public long getBytesOnDisk() {
+    return 0;
+  }
+
+  @Override
+  public long getVisibleLength() {
+    return 0;
+  }
+
+  @Override
+  public String getStorageUuid() {
+    return null;
+  }
+
+  @Override
+  public boolean isOnTransientStorage() {
+    return false;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalReplicaInPipeline.java

@@ -0,0 +1,97 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hdfs.server.datanode.extdataset;
+
+import java.io.IOException;
+import org.apache.hadoop.hdfs.server.common.HdfsServerConstants.ReplicaState;
+import org.apache.hadoop.hdfs.server.datanode.ChunkChecksum;
+import org.apache.hadoop.hdfs.server.datanode.ReplicaInPipelineInterface;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.ReplicaOutputStreams;
+import org.apache.hadoop.util.DataChecksum;
+
+public class ExternalReplicaInPipeline implements ReplicaInPipelineInterface {
+
+  @Override
+  public void setNumBytes(long bytesReceived) {
+  }
+
+  @Override
+  public long getBytesAcked() {
+    return 0;
+  }
+
+  @Override
+  public void setBytesAcked(long bytesAcked) {
+  }
+
+  @Override
+  public void setLastChecksumAndDataLen(long dataLength, byte[] lastChecksum) {
+  }
+
+  @Override
+  public ChunkChecksum getLastChecksumAndDataLen() {
+    return new ChunkChecksum(0, null);
+  }
+
+  @Override
+  public ReplicaOutputStreams createStreams(boolean isCreate,
+      DataChecksum requestedChecksum) throws IOException {
+    return new ReplicaOutputStreams(null, null, requestedChecksum, false);
+  }
+
+  @Override
+  public long getBlockId() {
+    return 0;
+  }
+
+  @Override
+  public long getGenerationStamp() {
+    return 0;
+  }
+
+  @Override
+  public ReplicaState getState() {
+    return ReplicaState.FINALIZED;
+  }
+
+  @Override
+  public long getNumBytes() {
+    return 0;
+  }
+
+  @Override
+  public long getBytesOnDisk() {
+    return 0;
+  }
+
+  @Override
+  public long getVisibleLength() {
+    return 0;
+  }
+
+  @Override
+  public String getStorageUuid() {
+    return null;
+  }
+
+  @Override
+  public boolean isOnTransientStorage() {
+    return false;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalRollingLogs.java

@@ -0,0 +1,92 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hdfs.server.datanode.extdataset;
+
+import java.io.IOException;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.RollingLogs;
+
+public class ExternalRollingLogs implements RollingLogs {
+
+  private class ExternalLineIterator implements LineIterator {
+    @Override
+    public boolean isPrevious() {
+      return false;
+    }
+
+    @Override
+    public boolean isLastReadFromPrevious() {
+      return false;
+    }
+
+    @Override
+    public boolean hasNext() {
+      return false;
+    }
+
+    @Override
+    public String next() {
+      return null;
+    }
+
+    @Override
+    public void remove() {
+    }
+
+    @Override
+    public void close() throws IOException {
+    }
+  }
+
+  private class ExternalAppender implements Appender {
+    @Override
+    public Appendable append(CharSequence cs) throws IOException {
+      return null;
+    }
+
+    @Override
+    public Appendable append(CharSequence cs, int i, int i1)
+	throws IOException {
+      return null;
+    }
+
+    @Override
+    public Appendable append(char c) throws IOException {
+      return null;
+    }
+
+    @Override
+    public void close() throws IOException {
+    }
+  }
+
+  @Override
+  public LineIterator iterator(boolean skipPrevious) throws IOException {
+    return new ExternalLineIterator();
+  }
+
+  @Override
+  public Appender appender() {
+    return new ExternalAppender();
+  }
+
+  @Override
+  public boolean roll() throws IOException {
+    return false;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/ExternalVolumeImpl.java

@@ -0,0 +1,75 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hdfs.server.datanode.extdataset;
+
+import java.io.File;
+import java.io.IOException;
+import org.apache.hadoop.hdfs.StorageType;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
+
+public class ExternalVolumeImpl implements FsVolumeSpi {
+
+  @Override
+  public String[] getBlockPoolList() {
+    return null;
+  }
+
+  @Override
+  public long getAvailable() throws IOException {
+    return 0;
+  }
+
+  @Override
+  public String getBasePath() {
+    return null;
+  }
+
+  @Override
+  public String getPath(String bpid) throws IOException {
+    return null;
+  }
+
+  @Override
+  public File getFinalizedDir(String bpid) throws IOException {
+    return null;
+  }
+
+  @Override
+  public String getStorageID() {
+    return null;
+  }
+
+  @Override
+  public StorageType getStorageType() {
+    return StorageType.DEFAULT;
+  }
+
+  @Override
+  public boolean isTransientStorage() {
+    return false;
+  }
+
+  @Override
+  public void reserveSpaceForRbw(long bytesToReserve) {
+  }
+
+  @Override
+  public void releaseReservedSpace(long bytesToRelease) {
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/extdataset/TestExternalDataset.java

@@ -0,0 +1,97 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hdfs.server.datanode.extdataset;
+
+import org.apache.hadoop.hdfs.server.datanode.Replica;
+import org.apache.hadoop.hdfs.server.datanode.ReplicaInPipelineInterface;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsVolumeSpi;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.RollingLogs;
+import org.junit.Test;
+
+/**
+ * Tests the ability to create external FsDatasetSpi implementations.
+ *
+ * The purpose of this suite of tests is to ensure that it is possible to
+ * construct subclasses of FsDatasetSpi outside the Hadoop tree
+ * (specifically, outside of the org.apache.hadoop.hdfs.server.datanode
+ * package).  This consists of creating subclasses of the two key classes
+ * (FsDatasetSpi and FsVolumeSpi) *and* instances or subclasses of any
+ * classes/interfaces their methods need to produce.  If methods are added
+ * to or changed in any superclasses, or if constructors of other classes
+ * are changed, this package will fail to compile.  In fixing this
+ * compilation error, any new class dependencies should receive the same
+ * treatment.
+ *
+ * It is worth noting what these tests do *not* accomplish.  Just as
+ * important as being able to produce instances of the appropriate classes
+ * is being able to access all necessary methods on those classes as well
+ * as on any additional classes accepted as inputs to FsDatasetSpi's
+ * methods.  It wouldn't be correct to mandate all methods be public, as
+ * that would defeat encapsulation.  Moreover, there is no natural
+ * mechanism that would prevent a manually-constructed list of methods
+ * from becoming stale.  Rather than creating tests with no clear means of
+ * maintaining them, this problem is left unsolved for now.
+ *
+ * Lastly, though merely compiling this package should signal success,
+ * explicit testInstantiate* unit tests are included below so as to have a
+ * tangible means of referring to each case.
+ */
+public class TestExternalDataset {
+
+  /**
+   * Tests instantiating an FsDatasetSpi subclass.
+   */
+  @Test
+  public void testInstantiateDatasetImpl() throws Throwable {
+    FsDatasetSpi<?> inst = new ExternalDatasetImpl();
+  }
+
+  /**
+   * Tests instantiating a Replica subclass.
+   */
+  @Test
+  public void testIntantiateExternalReplica() throws Throwable {
+    Replica inst = new ExternalReplica();
+  }
+
+  /**
+   * Tests instantiating a ReplicaInPipelineInterface subclass.
+   */
+  @Test
+  public void testInstantiateReplicaInPipeline() throws Throwable {
+    ReplicaInPipelineInterface inst = new ExternalReplicaInPipeline();
+  }
+
+  /**
+   * Tests instantiating a RollingLogs subclass.
+   */
+  @Test
+  public void testInstantiateRollingLogs() throws Throwable {
+    RollingLogs inst = new ExternalRollingLogs();
+  }
+
+  /**
+   * Tests instantiating an FsVolumeSpi subclass.
+   */
+  @Test
+  public void testInstantiateVolumeImpl() throws Throwable {
+    FsVolumeSpi inst = new ExternalVolumeImpl();
+  }
+}