HDFS-7884. Fix NullPointerException in BlockSender when the generation stamp provided by the client is larger than the one stored in the datanode. Contributed by Brahma Reddy Battula

(cherry picked from commit fe693b72dec703ecbf4ab3919d61d06ea8735a9e)
(cherry picked from commit 4c648779d69a668f5147b183af2d40d45d1227d2)

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

@@ -102,6 +102,10 @@ Release 2.6.1 - UNRELEASED
 
     HDFS-7930. commitBlockSynchronization() does not remove locations. (yliu)
 
+    HDFS-7884. Fix NullPointerException in BlockSender when the generation stamp
+    provided by the client is larger than the one stored in the datanode.
+    (Brahma Reddy Battula via szetszwo)
+
 Release 2.6.0 - 2014-11-18
 
   INCOMPATIBLE CHANGES

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

@@ -240,6 +240,13 @@ class BlockSender implements java.io.Closeable {
       if (replica.getGenerationStamp() < block.getGenerationStamp()) {
         throw new IOException("Replica gen stamp < block genstamp, block="
             + block + ", replica=" + replica);
+      } else if (replica.getGenerationStamp() > block.getGenerationStamp()) {
+        if (DataNode.LOG.isDebugEnabled()) {
+          DataNode.LOG.debug("Bumping up the client provided"
+              + " block's genstamp to latest " + replica.getGenerationStamp()
+              + " for block " + block);
+        }
+        block.setGenerationStamp(replica.getGenerationStamp());
       }
       if (replicaVisibleLength < 0) {
         throw new IOException("Replica is not readable, block="