HDFS-13101. Yet another fsimage corruption related to snapshot. Contributed by Shashikant Banerjee.

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

@@ -39,6 +39,7 @@
 import org.apache.hadoop.hdfs.server.blockmanagement.BlockUnderConstructionFeature;
 import org.apache.hadoop.hdfs.DFSUtil;
 import org.apache.hadoop.hdfs.server.namenode.INodeReference.DstReference;
+import org.apache.hadoop.hdfs.server.namenode.INodeReference.WithCount;
 import org.apache.hadoop.hdfs.server.namenode.INodeReference.WithName;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.Snapshot;
 import org.apache.hadoop.hdfs.util.Diff;
@@ -646,6 +647,18 @@ public INodeReference getParentReference() {
     return parent == null || !parent.isReference()? null: (INodeReference)parent;
   }
 
+  /**
+   * @return true if this is a reference and the reference count is 1;
+   *         otherwise, return false.
+   */
+  public boolean isLastReference() {
+    final INodeReference ref = getParentReference();
+    if (!(ref instanceof WithCount)) {
+      return false;
+    }
+    return ((WithCount)ref).getReferenceCount() == 1;
+  }
+
   /** Set parent directory */
   public final void setParent(INodeDirectory parent) {
     this.parent = parent;

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

@@ -903,6 +903,14 @@ public void dumpTreeRecursively(PrintWriter out, StringBuilder prefix,
       prefix.setLength(prefix.length() - 2);
       prefix.append("  ");
     }
+
+    final DirectoryWithSnapshotFeature snapshotFeature =
+        getDirectoryWithSnapshotFeature();
+    if (snapshotFeature != null) {
+      out.print(prefix);
+      out.print(snapshotFeature);
+    }
+    out.println();
     dumpTreeRecursively(out, prefix, new Iterable<SnapshotAndINode>() {
       final Iterator<INode> i = getChildrenList(snapshot).iterator();
       

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

@@ -1046,6 +1046,18 @@ public void dumpTreeRecursively(PrintWriter out, StringBuilder prefix,
     out.print(", blocks=");
     out.print(blocks.length == 0 ? null: blocks[0]);
     out.println();
+
+    final FileWithSnapshotFeature snapshotFeature =
+        getFileWithSnapshotFeature();
+    if (snapshotFeature != null) {
+      if (prefix.length() >= 2) {
+        prefix.setLength(prefix.length() - 2);
+        prefix.append("  ");
+      }
+      out.print(prefix);
+      out.print(snapshotFeature);
+    }
+    out.println();
   }
 
   /**

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

@@ -314,6 +314,19 @@ public Iterator<D> iterator() {
 
   @Override
   public String toString() {
-    return getClass().getSimpleName() + ": " + (diffs != null ? diffs : "[]");
+    if (diffs != null) {
+      final StringBuilder b =
+          new StringBuilder(getClass().getSimpleName()).append("@")
+              .append(Integer.toHexString(hashCode())).append(": ");
+      b.append("[");
+      for (D d : diffs) {
+        b.append(d).append(", ");
+      }
+      b.setLength(b.length() - 2);
+      b.append("]");
+      return b.toString();
+    } else {
+      return "";
+    }
   }
 }

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

@@ -739,6 +739,12 @@ public void cleanDirectory(INode.ReclaimContext reclaimContext,
           // were created before "prior" will be covered by the later 
           // cleanSubtreeRecursively call.
           if (priorCreated != null) {
+            if (currentINode.isLastReference()) {
+              // if this is the last reference, the created list can be
+              // destroyed.
+              priorDiff.getChildrenDiff().destroyCreatedList(
+                  reclaimContext, currentINode);
+            } else {
               // we only check the node originally in prior's created list
               for (INode cNode : priorDiff.diff.getCreatedUnmodifiable()) {
                 if (priorCreated.containsKey(cNode)) {
@@ -746,7 +752,7 @@ public void cleanDirectory(INode.ReclaimContext reclaimContext,
                 }
               }
             }
-          
+          }
           // When a directory is moved from the deleted list of the posterior
           // diff to the deleted list of this diff, we need to destroy its
           // descendants that were 1) created after taking this diff and 2)
@@ -770,4 +776,9 @@ public void cleanDirectory(INode.ReclaimContext reclaimContext,
       reclaimContext.quotaDelta().addQuotaDirUpdate(currentINode, current);
     }
   }
+
+  @Override
+  public String toString() {
+    return "" + diffs;
+  }
 }

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

@@ -225,4 +225,9 @@ public void collectBlocksAndClear(
       file.collectBlocksBeyondSnapshot(snapshotBlocks,
                                        reclaimContext.collectedBlocks());
   }
+
+  @Override
+  public String toString() {
+    return "" + diffs;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestFSImageWithSnapshot.java

@@ -22,6 +22,7 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.io.PrintWriter;
 import java.util.ArrayList;
 import java.util.EnumSet;
 import java.util.List;
@@ -64,7 +65,7 @@ public class TestFSImageWithSnapshot {
   }
 
   static final long seed = 0;
-  static final short NUM_DATANODES = 3;
+  static final short NUM_DATANODES = 1;
   static final int BLOCKSIZE = 1024;
   static final long txid = 1;
 
@@ -511,4 +512,101 @@ public void testSaveLoadImageAfterSnapshotDeletion()
     fsn = cluster.getNamesystem();
     hdfs = cluster.getFileSystem();
   }
+
+  void rename(Path src, Path dst) throws Exception {
+    printTree("Before rename " + src + " -> " + dst);
+    hdfs.rename(src, dst);
+    printTree("After rename " + src + " -> " + dst);
+  }
+
+  void createFile(Path directory, String filename) throws Exception {
+    final Path f = new Path(directory, filename);
+    DFSTestUtil.createFile(hdfs, f, 0, NUM_DATANODES, seed);
+  }
+
+  void appendFile(Path directory, String filename) throws Exception {
+    final Path f = new Path(directory, filename);
+    DFSTestUtil.appendFile(hdfs, f, "more data");
+    printTree("appended " + f);
+  }
+
+  void deleteSnapshot(Path directory, String snapshotName) throws Exception {
+    hdfs.deleteSnapshot(directory, snapshotName);
+    printTree("deleted snapshot " + snapshotName);
+  }
+
+  @Test (timeout=60000)
+  public void testDoubleRename() throws Exception {
+    final Path parent = new Path("/parent");
+    hdfs.mkdirs(parent);
+    final Path sub1 = new Path(parent, "sub1");
+    final Path sub1foo = new Path(sub1, "foo");
+    hdfs.mkdirs(sub1);
+    hdfs.mkdirs(sub1foo);
+    createFile(sub1foo, "file0");
+
+    printTree("before s0");
+    hdfs.allowSnapshot(parent);
+    hdfs.createSnapshot(parent, "s0");
+
+    createFile(sub1foo, "file1");
+    createFile(sub1foo, "file2");
+
+    final Path sub2 = new Path(parent, "sub2");
+    hdfs.mkdirs(sub2);
+    final Path sub2foo = new Path(sub2, "foo");
+    // mv /parent/sub1/foo to /parent/sub2/foo
+    rename(sub1foo, sub2foo);
+
+    hdfs.createSnapshot(parent, "s1");
+    hdfs.createSnapshot(parent, "s2");
+    printTree("created snapshots: s1, s2");
+
+    appendFile(sub2foo, "file1");
+    createFile(sub2foo, "file3");
+
+    final Path sub3 = new Path(parent, "sub3");
+    hdfs.mkdirs(sub3);
+    // mv /parent/sub2/foo to /parent/sub3/foo
+    rename(sub2foo, sub3);
+
+    hdfs.delete(sub3,  true);
+    printTree("deleted " + sub3);
+
+    deleteSnapshot(parent, "s1");
+    restartCluster();
+
+    deleteSnapshot(parent, "s2");
+    restartCluster();
+  }
+
+  void restartCluster() throws Exception {
+    final File before = dumpTree2File("before.txt");
+
+    hdfs.setSafeMode(SafeModeAction.SAFEMODE_ENTER);
+    hdfs.saveNamespace();
+    hdfs.setSafeMode(SafeModeAction.SAFEMODE_LEAVE);
+
+    cluster.shutdown();
+    cluster = new MiniDFSCluster.Builder(conf).format(false)
+        .numDataNodes(NUM_DATANODES).build();
+    cluster.waitActive();
+    fsn = cluster.getNamesystem();
+    hdfs = cluster.getFileSystem();
+    final File after = dumpTree2File("after.txt");
+    SnapshotTestHelper.compareDumpedTreeInFile(before, after, true);
+  }
+
+  private final PrintWriter output = new PrintWriter(System.out, true);
+  private int printTreeCount = 0;
+
+  String printTree(String label) throws Exception {
+    output.println();
+    output.println();
+    output.println("***** " + printTreeCount++ + ": " + label);
+    final String b =
+        fsn.getFSDirectory().getINode("/").dumpTreeRecursively().toString();
+    output.println(b);
+    return b;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/snapshot/SnapshotTestHelper.java

@@ -245,8 +245,7 @@ private static void compareDumpedTreeInFile(File file1, File file2,
            "\\{blockUCState=\\w+, primaryNodeIndex=[-\\d]+, replicas=\\[\\]\\}",
            "");
         }
-        
-        assertEquals(line1, line2);
+        assertEquals(line1.trim(), line2.trim());
       }
       Assert.assertNull(reader1.readLine());
       Assert.assertNull(reader2.readLine());