HDFS-9290. DFSClient#callAppend() is not backward compatible for slightly older NameNodes. Contributed by Tony Wu.

(cherry picked from commit b9e0417bdf2b9655dc4256bdb43683eca1ab46be)

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

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

@@ -72,6 +72,9 @@ Release 2.7.2 - UNRELEASED
     HDFS-9220. Reading small file (< 512 bytes) that is open for append fails
     due to incorrect checksum (Jing Zhao via kihwal)
 
+    HDFS-9290. DFSClient#callAppend() is not backward compatible for slightly
+    older NameNodes. (Tony Wu via kihwal)
+
 Release 2.7.1 - 2015-07-06
 
   INCOMPATIBLE CHANGES

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

@@ -1807,9 +1807,15 @@ public class DFSClient implements java.io.Closeable, RemotePeerFactory,
     try {
       LastBlockWithStatus blkWithStatus = namenode.append(src, clientName,
           new EnumSetWritable<>(flag, CreateFlag.class));
+      HdfsFileStatus status = blkWithStatus.getFileStatus();
+      if (status == null) {
+        DFSClient.LOG.debug("NameNode is on an older version, request file " +
+            "info with additional RPC call for file: " + src);
+        status = getFileInfo(src);
+      }
       return DFSOutputStream.newStreamForAppend(this, src, flag, buffersize,
           progress, blkWithStatus.getLastBlock(),
-          blkWithStatus.getFileStatus(), dfsClientConf.createChecksum(),
+          status, dfsClientConf.createChecksum(),
           favoredNodes);
     } catch(RemoteException re) {
       throw re.unwrapRemoteException(AccessControlException.class,