HDFS-6593. Move SnapshotDiffInfo out of INodeDirectorySnapshottable. Contributed by Jing Zhao.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1605169 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -473,6 +473,9 @@ Release 2.5.0 - UNRELEASED
 
     HDFS-6430. HTTPFS - Implement XAttr support. (Yi Liu via tucu)
 
+    HDFS-6593. Move SnapshotDiffInfo out of INodeDirectorySnapshottable.
+    (Jing Zhao via wheat9)
+
   OPTIMIZATIONS
 
     HDFS-6214. Webhdfs has poor throughput for files >2GB (daryn)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/SnapshotDiffReport.java

@@ -23,16 +23,14 @@ import java.util.List;
 
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.hdfs.DFSUtil;
-import org.apache.hadoop.hdfs.server.namenode.snapshot.INodeDirectorySnapshottable.SnapshotDiffInfo;
 
 import com.google.common.base.Objects;
 
 /**
  * This class represents to end users the difference between two snapshots of 
  * the same directory, or the difference between a snapshot of the directory and
- * its current state. Instead of capturing all the details of the diff, which 
+ * its current state. Instead of capturing all the details of the diff, this
- * is stored in {@link SnapshotDiffInfo}, this class only lists where the 
+ * class only lists where the changes happened and their types.
- * changes happened and their types.
  */
 public class SnapshotDiffReport {
   private final static String LINE_SEPARATOR = System.getProperty(

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

@@ -85,7 +85,18 @@ import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_REPLICATION_DEFAULT;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_REPLICATION_KEY;
 import static org.apache.hadoop.util.Time.now;
 
-import java.io.*;
+import java.io.BufferedWriter;
+import java.io.ByteArrayInputStream;
+import java.io.DataInput;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStreamWriter;
+import java.io.PrintWriter;
+import java.io.StringWriter;
 import java.lang.management.ManagementFactory;
 import java.net.InetAddress;
 import java.net.URI;
@@ -170,7 +181,6 @@ import org.apache.hadoop.hdfs.protocol.RollingUpgradeException;
 import org.apache.hadoop.hdfs.protocol.RollingUpgradeInfo;
 import org.apache.hadoop.hdfs.protocol.SnapshotAccessControlException;
 import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport;
-import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport.DiffReportEntry;
 import org.apache.hadoop.hdfs.protocol.SnapshottableDirectoryStatus;
 import org.apache.hadoop.hdfs.protocol.datatransfer.ReplaceDatanodeOnFailure;
 import org.apache.hadoop.hdfs.security.token.block.BlockTokenSecretManager;
@@ -208,7 +218,6 @@ import org.apache.hadoop.hdfs.server.namenode.ha.StandbyCheckpointer;
 import org.apache.hadoop.hdfs.server.namenode.metrics.FSNamesystemMBean;
 import org.apache.hadoop.hdfs.server.namenode.metrics.NameNodeMetrics;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.INodeDirectorySnapshottable;
-import org.apache.hadoop.hdfs.server.namenode.snapshot.INodeDirectorySnapshottable.SnapshotDiffInfo;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.Snapshot;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.SnapshotManager;
 import org.apache.hadoop.hdfs.server.namenode.startupprogress.Phase;
@@ -7484,7 +7493,7 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
    */
   SnapshotDiffReport getSnapshotDiffReport(String path,
       String fromSnapshot, String toSnapshot) throws IOException {
-    SnapshotDiffInfo diffs = null;
+    SnapshotDiffReport diffs;
     checkOperation(OperationCategory.READ);
     final FSPermissionChecker pc = getPermissionChecker();
     readLock();
@@ -7498,13 +7507,11 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
     } finally {
       readUnlock();
     }
-    
+
     if (auditLog.isInfoEnabled() && isExternalInvocation()) {
       logAuditEvent(true, "computeSnapshotDiff", null, null, null);
     }
-    return diffs != null ? diffs.generateReport() : new SnapshotDiffReport(
+    return diffs;
-        path, fromSnapshot, toSnapshot,
-        Collections.<DiffReportEntry> emptyList());
   }
   
   private void checkSubtreeReadPermission(final FSPermissionChecker pc,

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

@@ -20,7 +20,6 @@ package org.apache.hadoop.hdfs.server.namenode.snapshot;
 import java.io.DataOutput;
 import java.io.IOException;
 import java.util.ArrayDeque;
-import java.util.ArrayList;
 import java.util.Deque;
 import java.util.HashMap;
 import java.util.Iterator;
@@ -29,8 +28,6 @@ import java.util.Map;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.hdfs.protocol.QuotaExceededException;
-import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport.DiffReportEntry;
-import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport.DiffType;
 import org.apache.hadoop.hdfs.server.namenode.Content;
 import org.apache.hadoop.hdfs.server.namenode.ContentSummaryComputationContext;
 import org.apache.hadoop.hdfs.server.namenode.FSImageSerialization;
@@ -41,7 +38,6 @@ import org.apache.hadoop.hdfs.server.namenode.INodeDirectoryAttributes;
 import org.apache.hadoop.hdfs.server.namenode.INodeFile;
 import org.apache.hadoop.hdfs.server.namenode.INodeReference;
 import org.apache.hadoop.hdfs.server.namenode.Quota;
-import org.apache.hadoop.hdfs.server.namenode.snapshot.INodeDirectorySnapshottable.SnapshotDiffInfo.RenameEntry;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.SnapshotFSImageFormat.ReferenceMap;
 import org.apache.hadoop.hdfs.util.Diff;
 import org.apache.hadoop.hdfs.util.Diff.Container;
@@ -161,43 +157,6 @@ public class DirectoryWithSnapshotFeature implements INode.Feature {
         }
       }
     }
-
-    /**
-     * Interpret the diff and generate a list of {@link DiffReportEntry}.
-     * @param parentPath The relative path of the parent.
-     * @param fromEarlier True indicates {@code diff=later-earlier},
-     *                    False indicates {@code diff=earlier-later}
-     * @return A list of {@link DiffReportEntry} as the diff report.
-     */
-    public List<DiffReportEntry> generateReport(byte[][] parentPath,
-        boolean fromEarlier, Map<Long, RenameEntry> renameMap) {
-      List<DiffReportEntry> list = new ArrayList<DiffReportEntry>();
-      List<INode> created = getList(ListType.CREATED);
-      List<INode> deleted = getList(ListType.DELETED);
-      byte[][] fullPath = new byte[parentPath.length + 1][];
-      System.arraycopy(parentPath, 0, fullPath, 0, parentPath.length);
-      for (INode cnode : created) {
-        RenameEntry entry = renameMap.get(cnode.getId());
-        if (entry == null || !entry.isRename()) {
-          fullPath[fullPath.length - 1] = cnode.getLocalNameBytes();
-          list.add(new DiffReportEntry(fromEarlier ? DiffType.CREATE
-              : DiffType.DELETE, fullPath));
-        }
-      }
-      for (INode dnode : deleted) {
-        RenameEntry entry = renameMap.get(dnode.getId());
-        if (entry != null && entry.isRename()) {
-          list.add(new DiffReportEntry(DiffType.RENAME,
-              fromEarlier ? entry.getSourcePath() : entry.getTargetPath(),
-              fromEarlier ? entry.getTargetPath() : entry.getSourcePath()));
-        } else {
-          fullPath[fullPath.length - 1] = dnode.getLocalNameBytes();
-          list.add(new DiffReportEntry(fromEarlier ? DiffType.DELETE
-              : DiffType.CREATE, fullPath));
-        }
-      }
-      return list;
-    }
   }
 
   /**

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

@@ -21,22 +21,14 @@ import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.ArrayList;
 import java.util.Collections;
-import java.util.Comparator;
-import java.util.HashMap;
 import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
-import java.util.Map;
-import java.util.SortedMap;
-import java.util.TreeMap;
 
 import org.apache.hadoop.HadoopIllegalArgumentException;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.hdfs.DFSUtil;
 import org.apache.hadoop.hdfs.protocol.QuotaExceededException;
-import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport;
-import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport.DiffReportEntry;
-import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport.DiffType;
 import org.apache.hadoop.hdfs.protocol.SnapshotException;
 import org.apache.hadoop.hdfs.server.namenode.Content;
 import org.apache.hadoop.hdfs.server.namenode.ContentSummaryComputationContext;
@@ -56,7 +48,6 @@ import org.apache.hadoop.util.Time;
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
-import com.google.common.primitives.SignedBytes;
 
 /**
  * Directories where taking snapshots is allowed.
@@ -79,164 +70,6 @@ public class INodeDirectorySnapshottable extends INodeDirectory {
     }
     return (INodeDirectorySnapshottable)dir;
   }
-  
-  /**
-   * A class describing the difference between snapshots of a snapshottable
-   * directory.
-   */
-  public static class SnapshotDiffInfo {
-    /** Compare two inodes based on their full names */
-    public static final Comparator<INode> INODE_COMPARATOR = 
-        new Comparator<INode>() {
-      @Override
-      public int compare(INode left, INode right) {
-        if (left == null) {
-          return right == null ? 0 : -1;
-        } else {
-          if (right == null) {
-            return 1;
-          } else {
-            int cmp = compare(left.getParent(), right.getParent());
-            return cmp == 0 ? SignedBytes.lexicographicalComparator().compare(
-                left.getLocalNameBytes(), right.getLocalNameBytes()) : cmp;
-          }
-        }
-      }
-    };
-
-    static class RenameEntry {
-      private byte[][] sourcePath;
-      private byte[][] targetPath;
-
-      void setSource(INode source, byte[][] sourceParentPath) {
-        Preconditions.checkState(sourcePath == null);
-        sourcePath = new byte[sourceParentPath.length + 1][];
-        System.arraycopy(sourceParentPath, 0, sourcePath, 0,
-            sourceParentPath.length);
-        sourcePath[sourcePath.length - 1] = source.getLocalNameBytes();
-      }
-
-      void setTarget(INode target, byte[][] targetParentPath) {
-        targetPath = new byte[targetParentPath.length + 1][];
-        System.arraycopy(targetParentPath, 0, targetPath, 0,
-            targetParentPath.length);
-        targetPath[targetPath.length - 1] = target.getLocalNameBytes();
-      }
-
-      void setTarget(byte[][] targetPath) {
-        this.targetPath = targetPath;
-      }
-
-      boolean isRename() {
-        return sourcePath != null && targetPath != null;
-      }
-
-      byte[][] getSourcePath() {
-        return sourcePath;
-      }
-
-      byte[][] getTargetPath() {
-        return targetPath;
-      }
-    }
-
-    /** The root directory of the snapshots */
-    private final INodeDirectorySnapshottable snapshotRoot;
-    /** The starting point of the difference */
-    private final Snapshot from;
-    /** The end point of the difference */
-    private final Snapshot to;
-    /**
-     * A map recording modified INodeFile and INodeDirectory and their relative
-     * path corresponding to the snapshot root. Sorted based on their names.
-     */ 
-    private final SortedMap<INode, byte[][]> diffMap =
-        new TreeMap<INode, byte[][]>(INODE_COMPARATOR);
-    /**
-     * A map capturing the detailed difference about file creation/deletion.
-     * Each key indicates a directory whose children have been changed between
-     * the two snapshots, while its associated value is a {@link ChildrenDiff}
-     * storing the changes (creation/deletion) happened to the children (files).
-     */
-    private final Map<INodeDirectory, ChildrenDiff> dirDiffMap = 
-        new HashMap<INodeDirectory, ChildrenDiff>();
-
-    private final Map<Long, RenameEntry> renameMap =
-        new HashMap<Long, RenameEntry>();
-
-    SnapshotDiffInfo(INodeDirectorySnapshottable snapshotRoot, Snapshot start,
-        Snapshot end) {
-      this.snapshotRoot = snapshotRoot;
-      this.from = start;
-      this.to = end;
-    }
-    
-    /** Add a dir-diff pair */
-    private void addDirDiff(INodeDirectory dir, byte[][] relativePath,
-        ChildrenDiff diff) {
-      dirDiffMap.put(dir, diff);
-      diffMap.put(dir, relativePath);
-      // detect rename
-      for (INode created : diff.getList(ListType.CREATED)) {
-        if (created.isReference()) {
-          RenameEntry entry = getEntry(created.getId());
-          if (entry.getTargetPath() == null) {
-            entry.setTarget(created, relativePath);
-          }
-        }
-      }
-      for (INode deleted : diff.getList(ListType.DELETED)) {
-        if (deleted instanceof INodeReference.WithName) {
-          RenameEntry entry = getEntry(deleted.getId());
-          entry.setSource(deleted, relativePath);
-        }
-      }
-    }
-
-    private RenameEntry getEntry(long inodeId) {
-      RenameEntry entry = renameMap.get(inodeId);
-      if (entry == null) {
-        entry = new RenameEntry();
-        renameMap.put(inodeId, entry);
-      }
-      return entry;
-    }
-
-    private void setRenameTarget(long inodeId, byte[][] path) {
-      getEntry(inodeId).setTarget(path);
-    }
-
-    /** Add a modified file */ 
-    private void addFileDiff(INodeFile file, byte[][] relativePath) {
-      diffMap.put(file, relativePath);
-    }
-    
-    /** @return True if {@link #from} is earlier than {@link #to} */
-    private boolean isFromEarlier() {
-      return Snapshot.ID_COMPARATOR.compare(from, to) < 0;
-    }
-    
-    /**
-     * Generate a {@link SnapshotDiffReport} based on detailed diff information.
-     * @return A {@link SnapshotDiffReport} describing the difference
-     */
-    public SnapshotDiffReport generateReport() {
-      List<DiffReportEntry> diffReportList = new ArrayList<DiffReportEntry>();
-      for (INode node : diffMap.keySet()) {
-        diffReportList.add(new DiffReportEntry(DiffType.MODIFY, diffMap
-            .get(node), null));
-        if (node.isDirectory()) {
-          ChildrenDiff dirDiff = dirDiffMap.get(node);
-          List<DiffReportEntry> subList = dirDiff.generateReport(
-              diffMap.get(node), isFromEarlier(), renameMap);
-          diffReportList.addAll(subList);
-        }
-      }
-      return new SnapshotDiffReport(snapshotRoot.getFullPathName(),
-          Snapshot.getSnapshotName(from), Snapshot.getSnapshotName(to),
-          diffReportList);
-    }
-  }
 
   /**
    * Snapshots of this directory in ascending order of snapshot names.
@@ -496,9 +329,9 @@ public class INodeDirectorySnapshottable extends INodeDirectory {
   private void computeDiffRecursively(INode node, List<byte[]> parentPath,
       SnapshotDiffInfo diffReport) {
     final Snapshot earlierSnapshot = diffReport.isFromEarlier() ?
-        diffReport.from : diffReport.to;
+        diffReport.getFrom() : diffReport.getTo();
     final Snapshot laterSnapshot = diffReport.isFromEarlier() ?
-        diffReport.to : diffReport.from;
+        diffReport.getTo() : diffReport.getFrom();
     byte[][] relativePath = parentPath.toArray(new byte[parentPath.size()][]);
     if (node.isDirectory()) {
       final ChildrenDiff diff = new ChildrenDiff();

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

@@ -0,0 +1,242 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.namenode.snapshot;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport;
+import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport.DiffReportEntry;
+import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport.DiffType;
+import org.apache.hadoop.hdfs.server.namenode.INode;
+import org.apache.hadoop.hdfs.server.namenode.INodeDirectory;
+import org.apache.hadoop.hdfs.server.namenode.INodeFile;
+import org.apache.hadoop.hdfs.server.namenode.INodeReference;
+import org.apache.hadoop.hdfs.server.namenode.snapshot.DirectoryWithSnapshotFeature.ChildrenDiff;
+import org.apache.hadoop.hdfs.util.Diff.ListType;
+
+import com.google.common.base.Preconditions;
+import com.google.common.primitives.SignedBytes;
+
+/**
+ * A class describing the difference between snapshots of a snapshottable
+ * directory.
+ */
+class SnapshotDiffInfo {
+  /** Compare two inodes based on their full names */
+  public static final Comparator<INode> INODE_COMPARATOR =
+      new Comparator<INode>() {
+    @Override
+    public int compare(INode left, INode right) {
+      if (left == null) {
+        return right == null ? 0 : -1;
+      } else {
+        if (right == null) {
+          return 1;
+        } else {
+          int cmp = compare(left.getParent(), right.getParent());
+          return cmp == 0 ? SignedBytes.lexicographicalComparator().compare(
+              left.getLocalNameBytes(), right.getLocalNameBytes()) : cmp;
+        }
+      }
+    }
+  };
+
+  static class RenameEntry {
+    private byte[][] sourcePath;
+    private byte[][] targetPath;
+
+    void setSource(INode source, byte[][] sourceParentPath) {
+      Preconditions.checkState(sourcePath == null);
+      sourcePath = new byte[sourceParentPath.length + 1][];
+      System.arraycopy(sourceParentPath, 0, sourcePath, 0,
+          sourceParentPath.length);
+      sourcePath[sourcePath.length - 1] = source.getLocalNameBytes();
+    }
+
+    void setTarget(INode target, byte[][] targetParentPath) {
+      targetPath = new byte[targetParentPath.length + 1][];
+      System.arraycopy(targetParentPath, 0, targetPath, 0,
+          targetParentPath.length);
+      targetPath[targetPath.length - 1] = target.getLocalNameBytes();
+    }
+
+    void setTarget(byte[][] targetPath) {
+      this.targetPath = targetPath;
+    }
+
+    boolean isRename() {
+      return sourcePath != null && targetPath != null;
+    }
+
+    byte[][] getSourcePath() {
+      return sourcePath;
+    }
+
+    byte[][] getTargetPath() {
+      return targetPath;
+    }
+  }
+
+  /** The root directory of the snapshots */
+  private final INodeDirectorySnapshottable snapshotRoot;
+  /** The starting point of the difference */
+  private final Snapshot from;
+  /** The end point of the difference */
+  private final Snapshot to;
+  /**
+   * A map recording modified INodeFile and INodeDirectory and their relative
+   * path corresponding to the snapshot root. Sorted based on their names.
+   */
+  private final SortedMap<INode, byte[][]> diffMap =
+      new TreeMap<INode, byte[][]>(INODE_COMPARATOR);
+  /**
+   * A map capturing the detailed difference about file creation/deletion.
+   * Each key indicates a directory whose children have been changed between
+   * the two snapshots, while its associated value is a {@link ChildrenDiff}
+   * storing the changes (creation/deletion) happened to the children (files).
+   */
+  private final Map<INodeDirectory, ChildrenDiff> dirDiffMap =
+      new HashMap<INodeDirectory, ChildrenDiff>();
+
+  private final Map<Long, RenameEntry> renameMap =
+      new HashMap<Long, RenameEntry>();
+
+  SnapshotDiffInfo(INodeDirectorySnapshottable snapshotRoot, Snapshot start,
+      Snapshot end) {
+    this.snapshotRoot = snapshotRoot;
+    this.from = start;
+    this.to = end;
+  }
+
+  /** Add a dir-diff pair */
+  void addDirDiff(INodeDirectory dir, byte[][] relativePath, ChildrenDiff diff) {
+    dirDiffMap.put(dir, diff);
+    diffMap.put(dir, relativePath);
+    // detect rename
+    for (INode created : diff.getList(ListType.CREATED)) {
+      if (created.isReference()) {
+        RenameEntry entry = getEntry(created.getId());
+        if (entry.getTargetPath() == null) {
+          entry.setTarget(created, relativePath);
+        }
+      }
+    }
+    for (INode deleted : diff.getList(ListType.DELETED)) {
+      if (deleted instanceof INodeReference.WithName) {
+        RenameEntry entry = getEntry(deleted.getId());
+        entry.setSource(deleted, relativePath);
+      }
+    }
+  }
+
+  Snapshot getFrom() {
+    return from;
+  }
+
+  Snapshot getTo() {
+    return to;
+  }
+
+  private RenameEntry getEntry(long inodeId) {
+    RenameEntry entry = renameMap.get(inodeId);
+    if (entry == null) {
+      entry = new RenameEntry();
+      renameMap.put(inodeId, entry);
+    }
+    return entry;
+  }
+
+  void setRenameTarget(long inodeId, byte[][] path) {
+    getEntry(inodeId).setTarget(path);
+  }
+
+  /** Add a modified file */
+  void addFileDiff(INodeFile file, byte[][] relativePath) {
+    diffMap.put(file, relativePath);
+  }
+
+  /** @return True if {@link #from} is earlier than {@link #to} */
+  boolean isFromEarlier() {
+    return Snapshot.ID_COMPARATOR.compare(from, to) < 0;
+  }
+
+  /**
+   * Generate a {@link SnapshotDiffReport} based on detailed diff information.
+   * @return A {@link SnapshotDiffReport} describing the difference
+   */
+  public SnapshotDiffReport generateReport() {
+    List<DiffReportEntry> diffReportList = new ArrayList<DiffReportEntry>();
+    for (INode node : diffMap.keySet()) {
+      diffReportList.add(new DiffReportEntry(DiffType.MODIFY, diffMap
+          .get(node), null));
+      if (node.isDirectory()) {
+        List<DiffReportEntry> subList = generateReport(dirDiffMap.get(node),
+            diffMap.get(node), isFromEarlier(), renameMap);
+        diffReportList.addAll(subList);
+      }
+    }
+    return new SnapshotDiffReport(snapshotRoot.getFullPathName(),
+        Snapshot.getSnapshotName(from), Snapshot.getSnapshotName(to),
+        diffReportList);
+  }
+
+  /**
+   * Interpret the ChildrenDiff and generate a list of {@link DiffReportEntry}.
+   * @param dirDiff The ChildrenDiff.
+   * @param parentPath The relative path of the parent.
+   * @param fromEarlier True indicates {@code diff=later-earlier},
+   *                    False indicates {@code diff=earlier-later}
+   * @param renameMap A map containing information about rename operations.
+   * @return A list of {@link DiffReportEntry} as the diff report.
+   */
+  private List<DiffReportEntry> generateReport(ChildrenDiff dirDiff,
+      byte[][] parentPath, boolean fromEarlier, Map<Long, RenameEntry> renameMap) {
+    List<DiffReportEntry> list = new ArrayList<DiffReportEntry>();
+    List<INode> created = dirDiff.getList(ListType.CREATED);
+    List<INode> deleted = dirDiff.getList(ListType.DELETED);
+    byte[][] fullPath = new byte[parentPath.length + 1][];
+    System.arraycopy(parentPath, 0, fullPath, 0, parentPath.length);
+    for (INode cnode : created) {
+      RenameEntry entry = renameMap.get(cnode.getId());
+      if (entry == null || !entry.isRename()) {
+        fullPath[fullPath.length - 1] = cnode.getLocalNameBytes();
+        list.add(new DiffReportEntry(fromEarlier ? DiffType.CREATE
+            : DiffType.DELETE, fullPath));
+      }
+    }
+    for (INode dnode : deleted) {
+      RenameEntry entry = renameMap.get(dnode.getId());
+      if (entry != null && entry.isRename()) {
+        list.add(new DiffReportEntry(DiffType.RENAME,
+            fromEarlier ? entry.getSourcePath() : entry.getTargetPath(),
+            fromEarlier ? entry.getTargetPath() : entry.getSourcePath()));
+      } else {
+        fullPath[fullPath.length - 1] = dnode.getLocalNameBytes();
+        list.add(new DiffReportEntry(fromEarlier ? DiffType.DELETE
+            : DiffType.CREATE, fullPath));
+      }
+    }
+    return list;
+  }
+}

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

@@ -30,9 +30,11 @@ import java.util.concurrent.atomic.AtomicInteger;
 import javax.management.ObjectName;
 
 import org.apache.hadoop.hdfs.DFSUtil;
+import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport;
 import org.apache.hadoop.hdfs.protocol.SnapshotException;
 import org.apache.hadoop.hdfs.protocol.SnapshotInfo;
 import org.apache.hadoop.hdfs.protocol.SnapshottableDirectoryStatus;
+import org.apache.hadoop.hdfs.protocol.SnapshotDiffReport.DiffReportEntry;
 import org.apache.hadoop.hdfs.server.namenode.FSDirectory;
 import org.apache.hadoop.hdfs.server.namenode.FSImageFormat;
 import org.apache.hadoop.hdfs.server.namenode.FSNamesystem;
@@ -40,7 +42,6 @@ import org.apache.hadoop.hdfs.server.namenode.INode;
 import org.apache.hadoop.hdfs.server.namenode.INode.BlocksMapUpdateInfo;
 import org.apache.hadoop.hdfs.server.namenode.INodeDirectory;
 import org.apache.hadoop.hdfs.server.namenode.INodesInPath;
-import org.apache.hadoop.hdfs.server.namenode.snapshot.INodeDirectorySnapshottable.SnapshotDiffInfo;
 import org.apache.hadoop.metrics2.util.MBeans;
 
 /**
@@ -361,12 +362,13 @@ public class SnapshotManager implements SnapshotStatsMXBean {
    * Compute the difference between two snapshots of a directory, or between a
    * snapshot of the directory and its current tree.
    */
-  public SnapshotDiffInfo diff(final String path, final String from,
+  public SnapshotDiffReport diff(final String path, final String from,
       final String to) throws IOException {
     if ((from == null || from.isEmpty())
         && (to == null || to.isEmpty())) {
       // both fromSnapshot and toSnapshot indicate the current tree
-      return null;
+      return new SnapshotDiffReport(path, from, to,
+          Collections.<DiffReportEntry> emptyList());
     }
 
     // Find the source root directory path where the snapshots were taken.
@@ -374,8 +376,10 @@ public class SnapshotManager implements SnapshotStatsMXBean {
     INodesInPath inodesInPath = fsdir.getINodesInPath4Write(path.toString());
     final INodeDirectorySnapshottable snapshotRoot = INodeDirectorySnapshottable
         .valueOf(inodesInPath.getLastINode(), path);
-    
+
-    return snapshotRoot.computeDiff(from, to);
+    final SnapshotDiffInfo diffs = snapshotRoot.computeDiff(from, to);
+    return diffs != null ? diffs.generateReport() : new SnapshotDiffReport(
+        path, from, to, Collections.<DiffReportEntry> emptyList());
   }
   
   public void clearSnapshottableDirs() {