HADOOP-18193:Support nested mount points in INodeTree

Fixes #4181

Signed-off-by: Owen O'Malley <oomalley@linkedin.com>

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/viewfs/ConfigUtil.java

@@ -247,4 +247,22 @@ public static String getDefaultMountTableName(final Configuration conf) {
     return conf.get(Constants.CONFIG_VIEWFS_DEFAULT_MOUNT_TABLE_NAME_KEY,
         Constants.CONFIG_VIEWFS_DEFAULT_MOUNT_TABLE);
   }
+
+  /**
+   * Check the bool config whether nested mount point is supported. Default: true
+   * @param conf - from this conf
+   * @return whether nested mount point is supported
+   */
+  public static boolean isNestedMountPointSupported(final Configuration conf) {
+    return conf.getBoolean(Constants.CONFIG_NESTED_MOUNT_POINT_SUPPORTED, true);
+  }
+
+  /**
+   * Set the bool value isNestedMountPointSupported in config.
+   * @param conf - from this conf
+   * @param isNestedMountPointSupported - whether nested mount point is supported
+   */
+  public static void setIsNestedMountPointSupported(final Configuration conf, boolean isNestedMountPointSupported) {
+    conf.setBoolean(Constants.CONFIG_NESTED_MOUNT_POINT_SUPPORTED, isNestedMountPointSupported);
+  }
 }

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/viewfs/Constants.java

@@ -53,6 +53,11 @@ public interface Constants {
    */
   public static final String CONFIG_VIEWFS_DEFAULT_MOUNT_TABLE = "default";
 
+  /**
+   * Config to enable nested mount point in viewfs
+   */
+  String CONFIG_NESTED_MOUNT_POINT_SUPPORTED = CONFIG_VIEWFS_PREFIX + ".nested.mount.point.supported";
+
   /**
    * Config variable full prefix for the default mount table.
    */

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/viewfs/InodeTree.java

@@ -17,6 +17,10 @@
  */
 package org.apache.hadoop.fs.viewfs;
 
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.Set;
+import java.util.TreeSet;
 import java.util.function.Function;
 import org.apache.hadoop.util.Preconditions;
 import java.io.FileNotFoundException;
@@ -81,6 +85,8 @@ enum ResultKind {
   private List<RegexMountPoint<T>> regexMountPointList =
       new ArrayList<RegexMountPoint<T>>();
 
+  private final boolean isNestedMountPointSupported;
+
   public static class MountPoint<T> {
     String src;
     INodeLink<T> target;
@@ -99,7 +105,7 @@ public String getSource() {
     }
 
     /**
-     * Returns the target link.
+     * Returns the target INode link.
      * @return The target INode link
      */
     public INodeLink<T> getTarget() {
@@ -138,6 +144,14 @@ public INode(String pathToNode, UserGroupInformation aUgi) {
     boolean isLink() {
       return !isInternalDir();
     }
+
+    /**
+     * Return the link if isLink.
+     * @return will return null, for non links.
+     */
+    INodeLink<T> getLink() {
+      return null;
+    }
   }
 
   /**
@@ -212,6 +226,51 @@ void addLink(final String pathComponent, final INodeLink<T> link)
       }
       children.put(pathComponent, link);
     }
+
+    void addDirLink(final String pathComponent, final INodeDirLink<T> dirLink) {
+      children.put(pathComponent, dirLink);
+    }
+  }
+
+  /**
+   * Internal class to represent an INodeDir which also contains a INodeLink. This is used to support nested mount points
+   * where an INode is internalDir but points to a mount link. The class is a subclass of INodeDir and the semantics are
+   * as follows:
+   * isLink(): true
+   * isInternalDir(): true
+   * @param <T>
+   */
+  static class INodeDirLink<T> extends INodeDir<T> {
+    /**
+     * INodeLink wrapped in the INodeDir
+     */
+    private final INodeLink<T> link;
+
+    INodeDirLink(String pathToNode, UserGroupInformation aUgi, INodeLink<T> link) {
+      super(pathToNode, aUgi);
+      this.link = link;
+    }
+
+    @Override
+    INodeLink<T> getLink() {
+      return link;
+    }
+
+    /**
+     * True because the INodeDirLink also contains a INodeLink
+     */
+    @Override
+    boolean isLink() {
+      return true;
+    }
+
+    /**
+     * True because the INodeDirLink is internal node
+     */
+    @Override
+    boolean isInternalDir() {
+      return true;
+    }
   }
 
   /**
@@ -320,6 +379,11 @@ boolean isInternalDir() {
       return false;
     }
 
+    @Override
+    INodeLink<T> getLink() {
+      return this;
+    }
+
     /**
      * Get the instance of FileSystem to use, creating one if needed.
      * @return An Initialized instance of T
@@ -376,10 +440,17 @@ private void createLink(final String src, final String target,
         newDir.setInternalDirFs(getTargetFileSystem(newDir));
         nextInode = newDir;
       }
-      if (nextInode.isLink()) {
+      if (!nextInode.isInternalDir()) {
-        // Error - expected a dir but got a link
+        if (isNestedMountPointSupported) {
-        throw new FileAlreadyExistsException("Path " + nextInode.fullPath +
+          // nested mount detected, add a new INodeDirLink that wraps existing INodeLink to INodeTree and override existing INodelink
-            " already exists as link");
+          INodeDirLink<T> dirLink = new INodeDirLink<T>(nextInode.fullPath, aUgi, (INodeLink<T>) nextInode);
+          curInode.addDirLink(iPath, dirLink);
+          curInode = dirLink;
+        } else {
+          // Error - expected a dir but got a link
+          throw new FileAlreadyExistsException("Path " + nextInode.fullPath +
+              " already exists as link");
+        }
       } else {
         assert(nextInode.isInternalDir());
         curInode = (INodeDir<T>) nextInode;
@@ -445,7 +516,7 @@ private INodeDir<T> getRootDir() {
   }
 
   private INodeLink<T> getRootLink() {
-    Preconditions.checkState(root.isLink());
+    Preconditions.checkState(!root.isInternalDir());
     return (INodeLink<T>)root;
   }
 
@@ -538,6 +609,7 @@ protected InodeTree(final Configuration config, final String viewName,
       mountTableName = ConfigUtil.getDefaultMountTableName(config);
     }
     homedirPrefix = ConfigUtil.getHomeDirValue(config, mountTableName);
+    isNestedMountPointSupported = ConfigUtil.isNestedMountPointSupported(config);
 
     boolean isMergeSlashConfigured = false;
     String mergeSlashTarget = null;
@@ -642,7 +714,8 @@ protected InodeTree(final Configuration config, final String viewName,
       getRootDir().setInternalDirFs(getTargetFileSystem(getRootDir()));
       getRootDir().setRoot(true);
       INodeLink<T> fallbackLink = null;
-      for (LinkEntry le : linkEntries) {
+
+      for (LinkEntry le : getLinkEntries(linkEntries)) {
         switch (le.getLinkType()) {
         case SINGLE_FALLBACK:
           if (fallbackLink != null) {
@@ -682,6 +755,32 @@ protected InodeTree(final Configuration config, final String viewName,
     }
   }
 
+  /**
+   * Get collection of linkEntry. Sort mount point based on alphabetical order of the src paths.
+   * The purpose is to group nested paths(shortest path always comes first) during INodeTree creation.
+   * E.g. /foo is nested with /foo/bar so an INodeDirLink will be created at /foo.
+   * @param linkEntries input linkEntries
+   * @return sorted linkEntries
+   */
+  private Collection<LinkEntry> getLinkEntries(List<LinkEntry> linkEntries) {
+    Set<LinkEntry> sortedLinkEntries = new TreeSet<>(new Comparator<LinkEntry>() {
+      @Override
+      public int compare(LinkEntry o1, LinkEntry o2) {
+        if (o1 == null) {
+          return -1;
+        }
+        if (o2 == null) {
+          return 1;
+        }
+        String src1 = o1.getSrc();
+        String src2=  o2.getSrc();
+        return src1.compareTo(src2);
+      }
+    });
+    sortedLinkEntries.addAll(linkEntries);
+    return sortedLinkEntries;
+  }
+
   private void checkMntEntryKeyEqualsTarget(
       String mntEntryKey, String targetMntEntryKey) throws IOException {
     if (!mntEntryKey.equals(targetMntEntryKey)) {
@@ -795,7 +894,7 @@ public ResolveResult<T> resolve(final String p, final boolean resolveLastCompone
      * been linked to the root directory of a file system.
      * The first non-slash path component should be name of the mount table.
      */
-    if (root.isLink()) {
+    if (!root.isInternalDir()) {
       Path remainingPath;
       StringBuilder remainingPathStr = new StringBuilder();
       // ignore first slash
@@ -818,10 +917,17 @@ public ResolveResult<T> resolve(final String p, final boolean resolveLastCompone
     }
 
     int i;
+    INodeDirLink<T> lastResolvedDirLink = null;
+    int lastResolvedDirLinkIndex = -1;
     // ignore first slash
     for (i = 1; i < path.length - (resolveLastComponent ? 0 : 1); i++) {
       INode<T> nextInode = curInode.resolveInternal(path[i]);
       if (nextInode == null) {
+        // first resolve to dirlink for nested mount point
+        if (isNestedMountPointSupported && lastResolvedDirLink != null) {
+          return new ResolveResult<T>(ResultKind.EXTERNAL_DIR, lastResolvedDirLink.getLink().getTargetFileSystem(),
+              lastResolvedDirLink.fullPath, getRemainingPath(path, i),true);
+        }
         if (hasFallbackLink()) {
           resolveResult = new ResolveResult<T>(ResultKind.EXTERNAL_DIR,
               getRootFallbackLink().getTargetFileSystem(), root.fullPath,
@@ -837,46 +943,54 @@ public ResolveResult<T> resolve(final String p, final boolean resolveLastCompone
         }
       }
 
-      if (nextInode.isLink()) {
+      if (!nextInode.isInternalDir()) {
         final INodeLink<T> link = (INodeLink<T>) nextInode;
-        final Path remainingPath;
+        final Path remainingPath = getRemainingPath(path, i + 1);
-        if (i >= path.length - 1) {
-          remainingPath = SlashPath;
-        } else {
-          StringBuilder remainingPathStr =
-              new StringBuilder("/" + path[i + 1]);
-          for (int j = i + 2; j < path.length; ++j) {
-            remainingPathStr.append('/').append(path[j]);
-          }
-          remainingPath = new Path(remainingPathStr.toString());
-        }
         resolveResult = new ResolveResult<T>(ResultKind.EXTERNAL_DIR,
             link.getTargetFileSystem(), nextInode.fullPath, remainingPath,
             true);
         return resolveResult;
-      } else if (nextInode.isInternalDir()) {
+      } else {
         curInode = (INodeDir<T>) nextInode;
+        // track last resolved nest mount point.
+        if (isNestedMountPointSupported && nextInode.isLink()) {
+          lastResolvedDirLink = (INodeDirLink<T>) nextInode;
+          lastResolvedDirLinkIndex = i;
+        }
       }
     }
 
-    // We have resolved to an internal dir in mount table.
     Path remainingPath;
-    if (resolveLastComponent) {
+    if (isNestedMountPointSupported && lastResolvedDirLink != null) {
+      remainingPath = getRemainingPath(path, lastResolvedDirLinkIndex + 1);
+      resolveResult = new ResolveResult<T>(ResultKind.EXTERNAL_DIR, lastResolvedDirLink.getLink().getTargetFileSystem(),
+          lastResolvedDirLink.fullPath, remainingPath,true);
+    } else {
+      remainingPath = resolveLastComponent ? SlashPath : getRemainingPath(path, i);
+      resolveResult = new ResolveResult<T>(ResultKind.INTERNAL_DIR, curInode.getInternalDirFs(),
+          curInode.fullPath, remainingPath, false);
+    }
+    return resolveResult;
+  }
+
+  /**
+   * Return remaining path from specified index to the end of the path array.
+   * @param path An array of path components split by slash
+   * @param startIndex the specified start index of the path array
+   * @return remaining path.
+   */
+  private Path getRemainingPath(String[] path, int startIndex) {
+    Path remainingPath;
+    if (startIndex >= path.length) {
       remainingPath = SlashPath;
     } else {
-      // note we have taken care of when path is "/" above
+      StringBuilder remainingPathStr = new StringBuilder();
-      // for internal dirs rem-path does not start with / since the lookup
+      for (int j = startIndex; j < path.length; j++) {
-      // that follows will do a children.get(remaningPath) and will have to
+        remainingPathStr.append("/").append(path[j]);
-      // strip-out the initial /
-      StringBuilder remainingPathStr = new StringBuilder("/" + path[i]);
-      for (int j = i + 1; j < path.length; ++j) {
-        remainingPathStr.append('/').append(path[j]);
       }
       remainingPath = new Path(remainingPathStr.toString());
     }
-    resolveResult = new ResolveResult<T>(ResultKind.INTERNAL_DIR,
+    return remainingPath;
-        curInode.getInternalDirFs(), curInode.fullPath, remainingPath, false);
-    return resolveResult;
   }
 
   /**

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/viewfs/ViewFileSystem.java

@@ -1544,7 +1544,7 @@ public FileStatus[] listStatus(Path f) throws AccessControlException,
         INode<FileSystem> inode = iEntry.getValue();
         Path path = new Path(inode.fullPath).makeQualified(myUri, null);
         if (inode.isLink()) {
-          INodeLink<FileSystem> link = (INodeLink<FileSystem>) inode;
+          INodeLink<FileSystem> link = inode.getLink();
 
           if (showMountLinksAsSymlinks) {
             // To maintain backward compatibility, with default option(showing

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/viewfs/ViewFs.java

@@ -1098,8 +1098,7 @@ public FileStatus getFileLinkStatus(final Path f)
       }
       FileStatus result;
       if (inode.isLink()) {
-        INodeLink<AbstractFileSystem> inodelink = 
+        INodeLink<AbstractFileSystem> inodelink = inode.getLink();
-          (INodeLink<AbstractFileSystem>) inode;
         try {
           String linkedPath = inodelink.getTargetFileSystem()
               .getUri().getPath();
@@ -1169,8 +1168,7 @@ public FileStatus[] listStatus(final Path f) throws IOException {
         INode<AbstractFileSystem> inode = iEntry.getValue();
         Path path = new Path(inode.fullPath).makeQualified(myUri, null);
         if (inode.isLink()) {
-          INodeLink<AbstractFileSystem> link = 
+          INodeLink<AbstractFileSystem> link = inode.getLink();
-            (INodeLink<AbstractFileSystem>) inode;
 
           if (showMountLinksAsSymlinks) {
             // To maintain backward compatibility, with default option(showing

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/viewfs/TestNestedMountPoint.java

@@ -0,0 +1,365 @@
+/**
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.fs.viewfs;
+
+import java.net.URI;
+import java.util.List;
+import java.util.function.Function;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.FsConstants;
+import org.apache.hadoop.fs.Path;
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+
+/**
+ * Unit test of nested mount point support in INodeTree
+ */
+public class TestNestedMountPoint {
+  private InodeTree inodeTree;
+  private Configuration conf;
+  private String mtName;
+  private URI fsUri;
+
+  static class TestNestMountPointFileSystem {
+    public URI getUri() {
+      return uri;
+    }
+
+    private URI uri;
+
+    TestNestMountPointFileSystem(URI uri) {
+      this.uri = uri;
+    }
+  }
+
+  static class TestNestMountPointInternalFileSystem extends TestNestMountPointFileSystem {
+    TestNestMountPointInternalFileSystem(URI uri) {
+      super(uri);
+    }
+  }
+
+  private static final URI LINKFALLBACK_TARGET = URI.create("hdfs://nn00");
+  private static final URI NN1_TARGET = URI.create("hdfs://nn01/a/b");
+  private static final URI NN2_TARGET = URI.create("hdfs://nn02/a/b/e");
+  private static final URI NN3_TARGET = URI.create("hdfs://nn03/a/b/c/d");
+  private static final URI NN4_TARGET = URI.create("hdfs://nn04/a/b/c/d/e");
+  private static final URI NN5_TARGET = URI.create("hdfs://nn05/b/c/d/e");
+  private static final URI NN6_TARGET = URI.create("hdfs://nn06/b/c/d/e/f");
+
+  @Before
+  public void setUp() throws Exception {
+    conf = new Configuration();
+    mtName = TestNestedMountPoint.class.getName();
+    ConfigUtil.setIsNestedMountPointSupported(conf, true);
+    ConfigUtil.addLink(conf, mtName, "/a/b", NN1_TARGET);
+    ConfigUtil.addLink(conf, mtName, "/a/b/e", NN2_TARGET);
+    ConfigUtil.addLink(conf, mtName, "/a/b/c/d", NN3_TARGET);
+    ConfigUtil.addLink(conf, mtName, "/a/b/c/d/e", NN4_TARGET);
+    ConfigUtil.addLink(conf, mtName, "/b/c/d/e", NN5_TARGET);
+    ConfigUtil.addLink(conf, mtName, "/b/c/d/e/f", NN6_TARGET);
+    ConfigUtil.addLinkFallback(conf, mtName, LINKFALLBACK_TARGET);
+
+    fsUri = new URI(FsConstants.VIEWFS_SCHEME, mtName, "/", null, null);
+
+    inodeTree = new InodeTree<TestNestedMountPoint.TestNestMountPointFileSystem>(conf,
+        mtName, fsUri, false) {
+      @Override
+      protected Function<URI, TestNestedMountPoint.TestNestMountPointFileSystem> initAndGetTargetFs() {
+        return new Function<URI, TestNestMountPointFileSystem>() {
+          @Override
+          public TestNestedMountPoint.TestNestMountPointFileSystem apply(URI uri) {
+            return new TestNestMountPointFileSystem(uri);
+          }
+        };
+      }
+
+      // For intenral dir fs
+      @Override
+      protected TestNestedMountPoint.TestNestMountPointInternalFileSystem getTargetFileSystem(
+          final INodeDir<TestNestedMountPoint.TestNestMountPointFileSystem> dir) {
+        return new TestNestMountPointInternalFileSystem(fsUri);
+      }
+
+      @Override
+      protected TestNestedMountPoint.TestNestMountPointInternalFileSystem getTargetFileSystem(
+          final String settings, final URI[] mergeFsURIList) {
+        return new TestNestMountPointInternalFileSystem(null);
+      }
+    };
+  }
+
+  @After
+  public void tearDown() throws Exception {
+    inodeTree = null;
+  }
+
+  @Test
+  public void testPathResolveToLink() throws Exception {
+    // /a/b/c/d/e/f resolves to /a/b/c/d/e and /f
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/a/b/c/d/e/f", true);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/a/b/c/d/e", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/f"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN4_TARGET, ((TestNestMountPointFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult.isLastInternalDirLink());
+
+    // /a/b/c/d/e resolves to /a/b/c/d/e and /
+    InodeTree.ResolveResult resolveResult2 = inodeTree.resolve("/a/b/c/d/e", true);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult2.kind);
+    Assert.assertEquals("/a/b/c/d/e", resolveResult2.resolvedPath);
+    Assert.assertEquals(new Path("/"), resolveResult2.remainingPath);
+    Assert.assertTrue(resolveResult2.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN4_TARGET, ((TestNestMountPointFileSystem) resolveResult2.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult2.isLastInternalDirLink());
+
+    // /a/b/c/d/e/f/g/h/i resolves to /a/b/c/d/e and /f/g/h/i
+    InodeTree.ResolveResult resolveResult3 = inodeTree.resolve("/a/b/c/d/e/f/g/h/i", true);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult3.kind);
+    Assert.assertEquals("/a/b/c/d/e", resolveResult3.resolvedPath);
+    Assert.assertEquals(new Path("/f/g/h/i"), resolveResult3.remainingPath);
+    Assert.assertTrue(resolveResult3.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN4_TARGET, ((TestNestMountPointFileSystem) resolveResult3.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult3.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testPathResolveToLinkNotResolveLastComponent() throws Exception {
+    // /a/b/c/d/e/f resolves to /a/b/c/d/e and /f
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/a/b/c/d/e/f", false);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/a/b/c/d/e", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/f"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN4_TARGET, ((TestNestMountPointFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult.isLastInternalDirLink());
+
+    // /a/b/c/d/e resolves to /a/b/c/d and /e
+    InodeTree.ResolveResult resolveResult2 = inodeTree.resolve("/a/b/c/d/e", false);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult2.kind);
+    Assert.assertEquals("/a/b/c/d", resolveResult2.resolvedPath);
+    Assert.assertEquals(new Path("/e"), resolveResult2.remainingPath);
+    Assert.assertTrue(resolveResult2.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN3_TARGET, ((TestNestMountPointFileSystem) resolveResult2.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult2.isLastInternalDirLink());
+
+    // /a/b/c/d/e/f/g/h/i resolves to /a/b/c/d/e and /f/g/h/i
+    InodeTree.ResolveResult resolveResult3 = inodeTree.resolve("/a/b/c/d/e/f/g/h/i", false);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult3.kind);
+    Assert.assertEquals("/a/b/c/d/e", resolveResult3.resolvedPath);
+    Assert.assertEquals(new Path("/f/g/h/i"), resolveResult3.remainingPath);
+    Assert.assertTrue(resolveResult3.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN4_TARGET, ((TestNestMountPointFileSystem) resolveResult3.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult3.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testPathResolveToDirLink() throws Exception {
+    // /a/b/c/d/f resolves to /a/b/c/d, /f
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/a/b/c/d/f", true);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/a/b/c/d", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/f"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN3_TARGET, ((TestNestMountPointFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult.isLastInternalDirLink());
+
+    // /a/b/c/d resolves to /a/b/c/d and /
+    InodeTree.ResolveResult resolveResult2 = inodeTree.resolve("/a/b/c/d", true);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult2.kind);
+    Assert.assertEquals("/a/b/c/d", resolveResult2.resolvedPath);
+    Assert.assertEquals(new Path("/"), resolveResult2.remainingPath);
+    Assert.assertTrue(resolveResult2.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN3_TARGET, ((TestNestMountPointFileSystem) resolveResult2.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult2.isLastInternalDirLink());
+
+    // /a/b/c/d/f/g/h/i resolves to /a/b/c/d and /f/g/h/i
+    InodeTree.ResolveResult resolveResult3 = inodeTree.resolve("/a/b/c/d/f/g/h/i", true);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult3.kind);
+    Assert.assertEquals("/a/b/c/d", resolveResult3.resolvedPath);
+    Assert.assertEquals(new Path("/f/g/h/i"), resolveResult3.remainingPath);
+    Assert.assertTrue(resolveResult3.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN3_TARGET, ((TestNestMountPointFileSystem) resolveResult3.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult3.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testPathResolveToDirLinkNotResolveLastComponent() throws Exception {
+    // /a/b/c/d/f resolves to /a/b/c/d, /f
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/a/b/c/d/f", false);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/a/b/c/d", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/f"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN3_TARGET, ((TestNestMountPointFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult.isLastInternalDirLink());
+
+    // /a/b/c/d resolves to /a/b and /c/d
+    InodeTree.ResolveResult resolveResult2 = inodeTree.resolve("/a/b/c/d", false);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult2.kind);
+    Assert.assertEquals("/a/b", resolveResult2.resolvedPath);
+    Assert.assertEquals(new Path("/c/d"), resolveResult2.remainingPath);
+    Assert.assertTrue(resolveResult2.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN1_TARGET, ((TestNestMountPointFileSystem) resolveResult2.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult2.isLastInternalDirLink());
+
+    // /a/b/c/d/f/g/h/i resolves to /a/b/c/d and /f/g/h/i
+    InodeTree.ResolveResult resolveResult3 = inodeTree.resolve("/a/b/c/d/f/g/h/i", false);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult3.kind);
+    Assert.assertEquals("/a/b/c/d", resolveResult3.resolvedPath);
+    Assert.assertEquals(new Path("/f/g/h/i"), resolveResult3.remainingPath);
+    Assert.assertTrue(resolveResult3.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN3_TARGET, ((TestNestMountPointFileSystem) resolveResult3.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult3.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testMultiNestedMountPointsPathResolveToDirLink() throws Exception {
+    // /a/b/f resolves to /a/b and /f
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/a/b/f", true);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/a/b", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/f"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN1_TARGET, ((TestNestMountPointFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult.isLastInternalDirLink());
+
+    // /a/b resolves to /a/b and /
+    InodeTree.ResolveResult resolveResult2 = inodeTree.resolve("/a/b", true);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult2.kind);
+    Assert.assertEquals("/a/b", resolveResult2.resolvedPath);
+    Assert.assertEquals(new Path("/"), resolveResult2.remainingPath);
+    Assert.assertTrue(resolveResult2.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN1_TARGET, ((TestNestMountPointFileSystem) resolveResult2.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult2.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testMultiNestedMountPointsPathResolveToDirLinkNotResolveLastComponent() throws Exception {
+    // /a/b/f resolves to /a/b and /f
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/a/b/f", false);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/a/b", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/f"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN1_TARGET, ((TestNestMountPointFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult.isLastInternalDirLink());
+
+    // /a/b resolves to /a and /b
+    InodeTree.ResolveResult resolveResult2 = inodeTree.resolve("/a/b", false);
+    Assert.assertEquals(InodeTree.ResultKind.INTERNAL_DIR, resolveResult2.kind);
+    Assert.assertEquals("/a", resolveResult2.resolvedPath);
+    Assert.assertEquals(new Path("/b"), resolveResult2.remainingPath);
+    Assert.assertTrue(resolveResult2.targetFileSystem instanceof TestNestMountPointInternalFileSystem);
+    Assert.assertEquals(fsUri, ((TestNestMountPointInternalFileSystem) resolveResult2.targetFileSystem).getUri());
+    Assert.assertFalse(resolveResult2.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testPathResolveToDirLinkLastComponentInternalDir() throws Exception {
+    // /a/b/c resolves to /a/b and /c
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/a/b/c", true);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/a/b", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/c"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN1_TARGET, ((TestNestMountPointFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testPathResolveToDirLinkLastComponentInternalDirNotResolveLastComponent() throws Exception {
+    // /a/b/c resolves to /a/b and /c
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/a/b/c", false);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/a/b", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/c"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(NN1_TARGET, ((TestNestMountPointFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertTrue(resolveResult.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testPathResolveToLinkFallBack() throws Exception {
+    // /a/e resolves to linkfallback
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/a/e", true);
+    Assert.assertEquals(InodeTree.ResultKind.EXTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/a/e"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointFileSystem);
+    Assert.assertEquals(LINKFALLBACK_TARGET, ((TestNestMountPointFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertFalse(resolveResult.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testPathNotResolveToLinkFallBackNotResolveLastComponent() throws Exception {
+    // /a/e resolves to internalDir instead of linkfallback
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/a/e", false);
+    Assert.assertEquals(InodeTree.ResultKind.INTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/a", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/e"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointInternalFileSystem);
+    Assert.assertEquals(fsUri, ((TestNestMountPointInternalFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertFalse(resolveResult.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testPathResolveToInternalDir() throws Exception {
+    // /b/c resolves to internal dir
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/b/c", true);
+    Assert.assertEquals(InodeTree.ResultKind.INTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/b/c", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointInternalFileSystem);
+    Assert.assertEquals(fsUri, ((TestNestMountPointInternalFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertFalse(resolveResult.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testPathResolveToInternalDirNotResolveLastComponent() throws Exception {
+    // /b/c resolves to internal dir
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/b/c", false);
+    Assert.assertEquals(InodeTree.ResultKind.INTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/b", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/c"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointInternalFileSystem);
+    Assert.assertEquals(fsUri, ((TestNestMountPointInternalFileSystem) resolveResult.targetFileSystem).getUri());
+    Assert.assertFalse(resolveResult.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testSlashResolveToInternalDir() throws Exception {
+    // / resolves to internal dir
+    InodeTree.ResolveResult resolveResult = inodeTree.resolve("/", true);
+    Assert.assertEquals(InodeTree.ResultKind.INTERNAL_DIR, resolveResult.kind);
+    Assert.assertEquals("/", resolveResult.resolvedPath);
+    Assert.assertEquals(new Path("/"), resolveResult.remainingPath);
+    Assert.assertTrue(resolveResult.targetFileSystem instanceof TestNestMountPointInternalFileSystem);
+    Assert.assertFalse(resolveResult.isLastInternalDirLink());
+  }
+
+  @Test
+  public void testInodeTreeMountPoints() throws Exception {
+    List<InodeTree.MountPoint<FileSystem>> mountPoints = inodeTree.getMountPoints();
+    Assert.assertEquals(6, mountPoints.size());
+  }
+}

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/viewfs/TestViewFsConfig.java

@@ -32,6 +32,7 @@ public class TestViewFsConfig {
   @Test(expected = FileAlreadyExistsException.class)
   public void testInvalidConfig() throws IOException, URISyntaxException {
     Configuration conf = new Configuration();
+    ConfigUtil.setIsNestedMountPointSupported(conf, false);
     ConfigUtil.addLink(conf, "/internalDir/linkToDir2",
         new Path("file:///dir2").toUri());
     ConfigUtil.addLink(conf, "/internalDir/linkToDir2/linkToDir3",

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/viewfs/ViewFileSystemBaseTest.java

@@ -460,6 +460,148 @@ public void testRenameAcrossMounts4() throws IOException {
         .assertIsFile(fsTarget, new Path(targetTestRoot, "data/fooBar"));
   }
 
+
+  // rename across nested mount points that point to same target also fail
+  @Test
+  public void testRenameAcrossNestedMountPointSameTarget() throws IOException {
+    setUpNestedMountPoint();
+    fileSystemTestHelper.createFile(fsView, "/user/foo");
+    try {
+      // Nested mount points point to the same target should fail
+      // /user -> /user
+      // /user/userA -> /user
+      // Rename strategy: SAME_MOUNTPOINT
+      fsView.rename(new Path("/user/foo"), new Path("/user/userA/foo"));
+      ContractTestUtils.fail("IOException is not thrown on rename operation");
+    } catch (IOException e) {
+      GenericTestUtils
+          .assertExceptionContains("Renames across Mount points not supported",
+              e);
+    }
+  }
+
+
+  // rename across nested mount points fail if the mount link targets are different
+  // even if the targets are part of the same target FS
+  @Test
+  public void testRenameAcrossMountPointDifferentTarget() throws IOException {
+    setUpNestedMountPoint();
+    fileSystemTestHelper.createFile(fsView, "/data/foo");
+    // /data -> /data
+    // /data/dataA -> /dataA
+    // Rename strategy: SAME_MOUNTPOINT
+    try {
+      fsView.rename(new Path("/data/foo"), new Path("/data/dataA/fooBar"));
+      ContractTestUtils.fail("IOException is not thrown on rename operation");
+    } catch (IOException e) {
+      GenericTestUtils
+          .assertExceptionContains("Renames across Mount points not supported",
+              e);
+    }
+  }
+
+  // RenameStrategy SAME_TARGET_URI_ACROSS_MOUNTPOINT enabled
+  // to rename across nested mount points that point to same target URI
+  @Test
+  public void testRenameAcrossNestedMountPointSameTargetUriAcrossMountPoint() throws IOException {
+    setUpNestedMountPoint();
+    //  /user/foo -> /user
+    // /user/userA/fooBarBar -> /user
+    // Rename strategy: SAME_TARGET_URI_ACROSS_MOUNTPOINT
+    Configuration conf2 = new Configuration(conf);
+    conf2.set(Constants.CONFIG_VIEWFS_RENAME_STRATEGY,
+        ViewFileSystem.RenameStrategy.SAME_TARGET_URI_ACROSS_MOUNTPOINT
+            .toString());
+    FileSystem fsView2 = FileSystem.newInstance(FsConstants.VIEWFS_URI, conf2);
+    fileSystemTestHelper.createFile(fsView2, "/user/foo");
+    fsView2.rename(new Path("/user/foo"), new Path("/user/userA/fooBarBar"));
+    ContractTestUtils.assertPathDoesNotExist(fsView2, "src should not exist after rename",
+        new Path("/user/foo"));
+    ContractTestUtils.assertPathDoesNotExist(fsTarget, "src should not exist after rename",
+        new Path(targetTestRoot, "user/foo"));
+    ContractTestUtils.assertIsFile(fsView2, fileSystemTestHelper.getTestRootPath(fsView2, "/user/userA/fooBarBar"));
+    ContractTestUtils.assertIsFile(fsTarget, new Path(targetTestRoot, "user/fooBarBar"));
+  }
+
+  // RenameStrategy SAME_FILESYSTEM_ACROSS_MOUNTPOINT enabled
+  // to rename across mount points where the mount link targets are different
+  // but are part of the same target FS
+  @Test
+  public void testRenameAcrossNestedMountPointSameFileSystemAcrossMountPoint() throws IOException {
+    setUpNestedMountPoint();
+    // /data/foo -> /data
+    // /data/dataA/fooBar -> /dataA
+    // Rename strategy: SAME_FILESYSTEM_ACROSS_MOUNTPOINT
+    Configuration conf2 = new Configuration(conf);
+    conf2.set(Constants.CONFIG_VIEWFS_RENAME_STRATEGY,
+        ViewFileSystem.RenameStrategy.SAME_FILESYSTEM_ACROSS_MOUNTPOINT
+            .toString());
+    FileSystem fsView2 = FileSystem.newInstance(FsConstants.VIEWFS_URI, conf2);
+    fileSystemTestHelper.createFile(fsView2, "/data/foo");
+    fsView2.rename(new Path("/data/foo"), new Path("/data/dataB/fooBar"));
+    ContractTestUtils
+        .assertPathDoesNotExist(fsView2, "src should not exist after rename",
+            new Path("/data/foo"));
+    ContractTestUtils
+        .assertPathDoesNotExist(fsTarget, "src should not exist after rename",
+            new Path(targetTestRoot, "data/foo"));
+    ContractTestUtils.assertIsFile(fsView2,
+        fileSystemTestHelper.getTestRootPath(fsView2, "/user/fooBar"));
+    ContractTestUtils
+        .assertIsFile(fsTarget, new Path(targetTestRoot, "user/fooBar"));
+  }
+
+  @Test
+  public void testOperationsThroughNestedMountPointsInternal()
+      throws IOException {
+    setUpNestedMountPoint();
+    // Create file with nested mount point
+    fileSystemTestHelper.createFile(fsView, "/user/userB/foo");
+    Assert.assertTrue("Created file should be type file",
+        fsView.getFileStatus(new Path("/user/userB/foo")).isFile());
+    Assert.assertTrue("Target of created file should be type file",
+        fsTarget.getFileStatus(new Path(targetTestRoot,"userB/foo")).isFile());
+
+    // Delete the created file with nested mount point
+    Assert.assertTrue("Delete should succeed",
+        fsView.delete(new Path("/user/userB/foo"), false));
+    Assert.assertFalse("File should not exist after delete",
+        fsView.exists(new Path("/user/userB/foo")));
+    Assert.assertFalse("Target File should not exist after delete",
+        fsTarget.exists(new Path(targetTestRoot,"userB/foo")));
+
+    // Create file with a 2 component dirs with nested mount point
+    fileSystemTestHelper.createFile(fsView, "/internalDir/linkToDir2/linkToDir2/foo");
+    Assert.assertTrue("Created file should be type file",
+        fsView.getFileStatus(new Path("/internalDir/linkToDir2/linkToDir2/foo")).isFile());
+    Assert.assertTrue("Target of created file should be type file",
+        fsTarget.getFileStatus(new Path(targetTestRoot,"linkToDir2/foo")).isFile());
+
+    // Delete the created file with nested mount point
+    Assert.assertTrue("Delete should succeed",
+        fsView.delete(new Path("/internalDir/linkToDir2/linkToDir2/foo"), false));
+    Assert.assertFalse("File should not exist after delete",
+        fsView.exists(new Path("/internalDir/linkToDir2/linkToDir2/foo")));
+    Assert.assertFalse("Target File should not exist after delete",
+        fsTarget.exists(new Path(targetTestRoot,"linkToDir2/foo")));
+  }
+
+  private void setUpNestedMountPoint() throws IOException {
+    // Enable nested mount point, ViewFilesystem should support both non-nested and nested mount points
+    ConfigUtil.setIsNestedMountPointSupported(conf, true);
+    ConfigUtil.addLink(conf, "/user/userA",
+        new Path(targetTestRoot, "user").toUri());
+    ConfigUtil.addLink(conf, "/user/userB",
+        new Path(targetTestRoot, "userB").toUri());
+    ConfigUtil.addLink(conf, "/data/dataA",
+        new Path(targetTestRoot, "dataA").toUri());
+    ConfigUtil.addLink(conf, "/data/dataB",
+        new Path(targetTestRoot, "user").toUri());
+    ConfigUtil.addLink(conf, "/internalDir/linkToDir2/linkToDir2",
+        new Path(targetTestRoot,"linkToDir2").toUri());
+    fsView = FileSystem.get(FsConstants.VIEWFS_URI, conf);
+  }
+
   static protected boolean SupportsBlocks = false; //  local fs use 1 block
                                                    // override for HDFS
   @Test