From ab96a0838dafbfea77382135914feadbfd03cf53 Mon Sep 17 00:00:00 2001
From: Kihwal Lee <kihwal@apache.org>
Date: Thu, 6 Feb 2014 15:45:47 +0000
Subject: [PATCH] HDFS-5881. Fix skip() of the short-circuit local
 reader(legacy). Contributed by Kihwal Lee.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1565310 13f79535-47bb-0310-9956-ffa450edef68
---
 hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt               | 2 ++
 .../org/apache/hadoop/hdfs/BlockReaderLocalLegacy.java    | 6 +++---
 .../main/java/org/apache/hadoop/hdfs/DFSInputStream.java  | 8 ++++++++
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 0ad51b7569..2720c7ddd1 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -337,6 +337,8 @@ Release 2.4.0 - UNRELEASED
     HDFS-5709. Improve NameNode upgrade with existing reserved paths and path
     components. (Andrew Wang via atm)
 
+    HDFS-5881. Fix skip() of the short-circuit local reader(legacy). (kihwal)
+
 Release 2.3.0 - UNRELEASED
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocalLegacy.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocalLegacy.java
index 2f66193361..ffc4eb9f8e 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocalLegacy.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/BlockReaderLocalLegacy.java
@@ -629,7 +629,7 @@ public synchronized long skip(long n) throws IOException {
         skipBuf = new byte[bytesPerChecksum];
       }
       int ret = read(skipBuf, 0, (int)(n - remaining));
-      return ret;
+      return (remaining + ret);
     }
   
     // optimize for big gap: discard the current buffer, skip to
@@ -660,9 +660,9 @@ public synchronized long skip(long n) throws IOException {
     int ret = read(skipBuf, 0, myOffsetFromChunkBoundary);
 
     if (ret == -1) {  // EOS
-      return toskip;
+      return (toskip + remaining);
     } else {
-      return (toskip + ret);
+      return (toskip + remaining + ret);
     }
   }
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java
index 73861bc8ad..438030eaa9 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java
@@ -1345,6 +1345,14 @@ public synchronized void seek(long targetPos) throws IOException {
           pos += blockReader.skip(diff);
           if (pos == targetPos) {
             done = true;
+          } else {
+            // The range was already checked. If the block reader returns
+            // something unexpected instead of throwing an exception, it is
+            // most likely a bug. 
+            String errMsg = "BlockReader failed to seek to " + 
+                targetPos + ". Instead, it seeked to " + pos + ".";
+            DFSClient.LOG.warn(errMsg);
+            throw new IOException(errMsg);
           }
         } catch (IOException e) {//make following read to retry
           if(DFSClient.LOG.isDebugEnabled()) {