HDFS-7383. DataNode.requestShortCircuitFdsForRead may throw NullPointerException. Contributed by Tsz Wo Nicholas Sze.

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

@@ -155,6 +155,9 @@ Release 2.7.0 - UNRELEASED
     HDFS-7366. BlockInfo should take replication as an short in the constructor.
     (Li Lu via wheat9)
 
+    HDFS-7383. DataNode.requestShortCircuitFdsForRead may throw 
+    NullPointerException. (szetszwo via suresh)
+
 Release 2.6.0 - UNRELEASED
 
   INCOMPATIBLE CHANGES

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

@@ -1550,7 +1550,7 @@ public class DataNode extends ReconfigurableBase
     
     try {
       fis[0] = (FileInputStream)data.getBlockInputStream(blk, 0);
-      fis[1] = (FileInputStream)data.getMetaDataInputStream(blk).getWrappedStream();
+      fis[1] = DatanodeUtil.getMetaDataInputStream(blk, data);
     } catch (ClassCastException e) {
       LOG.debug("requestShortCircuitFdsForRead failed", e);
       throw new ShortCircuitFdsUnsupportedException("This DataNode's " +

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

@@ -18,10 +18,15 @@
 package org.apache.hadoop.hdfs.server.datanode;
 
 import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
 import java.io.IOException;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.hdfs.protocol.Block;
+import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi;
+import org.apache.hadoop.hdfs.server.datanode.fsdataset.LengthInputStream;
 
 /** Provide utility methods for Datanode. */
 @InterfaceAudience.Private
@@ -114,4 +119,20 @@ public class DatanodeUtil {
         DataStorage.BLOCK_SUBDIR_PREFIX + d2;
     return new File(root, path);
   }
+
+  /**
+   * @return the FileInputStream for the meta data of the given block.
+   * @throws FileNotFoundException
+   *           if the file not found.
+   * @throws ClassCastException
+   *           if the underlying input stream is not a FileInputStream.
+   */
+  public static FileInputStream getMetaDataInputStream(
+      ExtendedBlock b, FsDatasetSpi<?> data) throws IOException {
+    final LengthInputStream lin = data.getMetaDataInputStream(b);
+    if (lin == null) {
+      throw new FileNotFoundException("Meta file for " + b + " not found.");
+    }
+    return (FileInputStream)lin.getWrappedStream();
+  }
 }

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

@@ -51,6 +51,7 @@ import org.apache.hadoop.hdfs.ExtendedBlockId;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.protocol.BlockListAsLongs;
 import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
+import org.apache.hadoop.hdfs.server.datanode.DatanodeUtil;
 import org.apache.hadoop.io.nativeio.NativeIO;
 import org.apache.hadoop.util.Time;
 import org.slf4j.Logger;
@@ -373,8 +374,7 @@ public class FsDatasetCache {
         reservedBytes = true;
         try {
           blockIn = (FileInputStream)dataset.getBlockInputStream(extBlk, 0);
-          metaIn = (FileInputStream)dataset.getMetaDataInputStream(extBlk)
+          metaIn = DatanodeUtil.getMetaDataInputStream(extBlk, dataset);
-              .getWrappedStream();
         } catch (ClassCastException e) {
           LOG.warn("Failed to cache " + key +
               ": Underlying blocks are not backed by files.", e);