HDFS-7831. Fix the starting index and end condition of the loop in FileDiffList.findEarlierSnapshotBlocks(). Contributed by Konstantin Shvachko.

(cherry picked from commit 73bcfa99af61e5202f030510db8954c17cba43cc)

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

@@ -717,6 +717,9 @@ Release 2.7.0 - UNRELEASED
     HDFS-7008. xlator should be closed upon exit from DFSAdmin#genericRefresh().
     (ozawa)
 
+    HDFS-7831. Fix the starting index and end condition of the loop in
+    FileDiffList.findEarlierSnapshotBlocks(). (Konstantin Shvachko via jing9)
+
     BREAKDOWN OF HDFS-7584 SUBTASKS AND RELATED JIRAS
 
       HDFS-7720. Quota by Storage Type API, tools and ClientNameNode

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/snapshot/FileDiffList.java

@@ -63,7 +63,7 @@ public class FileDiffList extends
     List<FileDiff> diffs = this.asList();
     int i = Collections.binarySearch(diffs, snapshotId);
     BlockInfoContiguous[] blocks = null;
-    for(i = i >= 0 ? i : -i; i < diffs.size(); i--) {
+    for(i = i >= 0 ? i : -i-2; i >= 0; i--) {
       blocks = diffs.get(i).getBlocks();
       if(blocks != null) {
         break;