HDFS-15427. Merged ListStatus with Fallback target filesystem and InternalDirViewFS. Contributed by Uma Maheswara Rao G.

(cherry picked from commit 7c02d1889b)

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

@@ -374,7 +374,7 @@ abstract class InodeTree<T> {
       throws UnsupportedFileSystemException, URISyntaxException, IOException;
 
   protected abstract T getTargetFileSystem(INodeDir<T> dir)
-      throws URISyntaxException;
+      throws URISyntaxException, IOException;
 
   protected abstract T getTargetFileSystem(String settings, URI[] mergeFsURIs)
       throws UnsupportedFileSystemException, URISyntaxException, IOException;
@@ -393,7 +393,7 @@ abstract class InodeTree<T> {
     return rootFallbackLink != null;
   }
 
-  private INodeLink<T> getRootFallbackLink() {
+  protected INodeLink<T> getRootFallbackLink() {
     Preconditions.checkState(root.isInternalDir());
     return rootFallbackLink;
   }

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

@@ -291,7 +291,8 @@ public class ViewFileSystem extends FileSystem {
         @Override
         protected FileSystem getTargetFileSystem(final INodeDir<FileSystem> dir)
             throws URISyntaxException {
-          return new InternalDirOfViewFs(dir, creationTime, ugi, myUri, config);
+          return new InternalDirOfViewFs(dir, creationTime, ugi, myUri, config,
+              this);
         }
 
         @Override
@@ -518,10 +519,10 @@ public class ViewFileSystem extends FileSystem {
   /**
    * {@inheritDoc}
    *
-   * Note: listStatus on root("/") considers listing from fallbackLink if
+   * Note: listStatus considers listing from fallbackLink if available. If the
-   * available. If the same directory name is present in configured mount path
+   * same directory path is present in configured mount path as well as in
-   * as well as in fallback link, then only the configured mount path will be
+   * fallback fs, then only the fallback path will be listed in the returned
-   * listed in the returned result.
+   * result except for link.
    *
    * If any of the the immediate children of the given path f is a symlink(mount
    * link), the returned FileStatus object of that children would be represented
@@ -1125,11 +1126,13 @@ public class ViewFileSystem extends FileSystem {
     final UserGroupInformation ugi; // the user/group of user who created mtable
     final URI myUri;
     private final boolean showMountLinksAsSymlinks;
+    private InodeTree<FileSystem> fsState;
     
     public InternalDirOfViewFs(final InodeTree.INodeDir<FileSystem> dir,
         final long cTime, final UserGroupInformation ugi, URI uri,
-        Configuration config) throws URISyntaxException {
+        Configuration config, InodeTree fsState) throws URISyntaxException {
       myUri = uri;
+      this.fsState = fsState;
       try {
         initialize(myUri, config);
       } catch (IOException e) {
@@ -1225,7 +1228,8 @@ public class ViewFileSystem extends FileSystem {
         FileNotFoundException, IOException {
       checkPathIsSlash(f);
       FileStatus[] fallbackStatuses = listStatusForFallbackLink();
-      FileStatus[] result = new FileStatus[theInternalDir.getChildren().size()];
+      Set<FileStatus> linkStatuses = new HashSet<>();
+      Set<FileStatus> internalDirStatuses = new HashSet<>();
       int i = 0;
       for (Entry<String, INode<FileSystem>> iEntry :
           theInternalDir.getChildren().entrySet()) {
@@ -1238,11 +1242,10 @@ public class ViewFileSystem extends FileSystem {
             // To maintain backward compatibility, with default option(showing
             // mount links as symlinks), we will represent target link as
             // symlink and rest other properties are belongs to mount link only.
-            result[i++] =
+            linkStatuses.add(
                 new FileStatus(0, false, 0, 0, creationTime, creationTime,
                     PERMISSION_555, ugi.getShortUserName(),
-                    ugi.getPrimaryGroupName(), link.getTargetLink(),
+                    ugi.getPrimaryGroupName(), link.getTargetLink(), path));
-                    path);
             continue;
           }
 
@@ -1258,11 +1261,12 @@ public class ViewFileSystem extends FileSystem {
             FileStatus status =
                 ((ChRootedFileSystem)link.getTargetFileSystem())
                 .getMyFs().getFileStatus(new Path(linkedPath));
-            result[i++] = new FileStatus(status.getLen(), status.isDirectory(),
+            linkStatuses.add(
+                new FileStatus(status.getLen(), status.isDirectory(),
                     status.getReplication(), status.getBlockSize(),
                     status.getModificationTime(), status.getAccessTime(),
-                status.getPermission(), status.getOwner(), status.getGroup(),
+                    status.getPermission(), status.getOwner(),
-                null, path);
+                    status.getGroup(), null, path));
           } catch (FileNotFoundException ex) {
             LOG.warn("Cannot get one of the children's(" + path
                 + ")  target path(" + link.getTargetFileSystem().getUri()
@@ -1270,52 +1274,59 @@ public class ViewFileSystem extends FileSystem {
             throw ex;
           }
         } else {
-          result[i++] =
+          internalDirStatuses.add(
               new FileStatus(0, true, 0, 0, creationTime, creationTime,
                   PERMISSION_555, ugi.getShortUserName(),
-                  ugi.getPrimaryGroupName(), path);
+                  ugi.getPrimaryGroupName(), path));
         }
       }
+      FileStatus[] internalDirStatusesMergedWithFallBack = internalDirStatuses
+          .toArray(new FileStatus[internalDirStatuses.size()]);
       if (fallbackStatuses.length > 0) {
-        return consolidateFileStatuses(fallbackStatuses, result);
+        internalDirStatusesMergedWithFallBack =
-      } else {
+            merge(fallbackStatuses, internalDirStatusesMergedWithFallBack);
-        return result;
       }
+      // Links will always have precedence than internalDir or fallback paths.
+      return merge(linkStatuses.toArray(new FileStatus[linkStatuses.size()]),
+          internalDirStatusesMergedWithFallBack);
     }
 
-    private FileStatus[] consolidateFileStatuses(FileStatus[] fallbackStatuses,
+    private FileStatus[] merge(FileStatus[] toStatuses,
-        FileStatus[] mountPointStatuses) {
+        FileStatus[] fromStatuses) {
       ArrayList<FileStatus> result = new ArrayList<>();
       Set<String> pathSet = new HashSet<>();
-      for (FileStatus status : mountPointStatuses) {
+      for (FileStatus status : toStatuses) {
         result.add(status);
         pathSet.add(status.getPath().getName());
       }
-      for (FileStatus status : fallbackStatuses) {
+      for (FileStatus status : fromStatuses) {
         if (!pathSet.contains(status.getPath().getName())) {
           result.add(status);
         }
       }
-      return result.toArray(new FileStatus[0]);
+      return result.toArray(new FileStatus[result.size()]);
     }
 
     private FileStatus[] listStatusForFallbackLink() throws IOException {
-      if (theInternalDir.isRoot() &&
+      if (this.fsState.getRootFallbackLink() != null) {
-          theInternalDir.getFallbackLink() != null) {
+        FileSystem linkedFallbackFs =
-        FileSystem linkedFs =
+            this.fsState.getRootFallbackLink().getTargetFileSystem();
-            theInternalDir.getFallbackLink().getTargetFileSystem();
+        Path p = Path.getPathWithoutSchemeAndAuthority(
-        // Fallback link is only applicable for root
+            new Path(theInternalDir.fullPath));
-        FileStatus[] statuses = linkedFs.listStatus(new Path("/"));
+        if (theInternalDir.isRoot() || linkedFallbackFs.exists(p)) {
+          FileStatus[] statuses = linkedFallbackFs.listStatus(p);
           for (FileStatus status : statuses) {
             // Fix the path back to viewfs scheme
+            Path pathFromConfiguredFallbackRoot =
+                new Path(p, status.getPath().getName());
             status.setPath(
-              new Path(myUri.toString(), status.getPath().getName()));
+                new Path(myUri.toString(), pathFromConfiguredFallbackRoot));
           }
           return statuses;
-      } else {
-        return new FileStatus[0];
         }
       }
+      return new FileStatus[0];
+    }
 
     @Override
     public boolean mkdirs(Path dir, FsPermission permission)

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

@@ -44,6 +44,7 @@ import org.apache.hadoop.fs.FSDataInputStream;
 import org.apache.hadoop.fs.FSDataOutputStream;
 import org.apache.hadoop.fs.FileAlreadyExistsException;
 import org.apache.hadoop.fs.FileChecksum;
+import org.apache.hadoop.fs.FileContext;
 import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FsConstants;
 import org.apache.hadoop.fs.FsServerDefaults;
@@ -236,7 +237,8 @@ public class ViewFs extends AbstractFileSystem {
       @Override
       protected AbstractFileSystem getTargetFileSystem(
           final INodeDir<AbstractFileSystem> dir) throws URISyntaxException {
-        return new InternalDirOfViewFs(dir, creationTime, ugi, getUri());
+        return new InternalDirOfViewFs(dir, creationTime, ugi, getUri(), this,
+            config);
       }
 
       @Override
@@ -455,6 +457,11 @@ public class ViewFs extends AbstractFileSystem {
   /**
    * {@inheritDoc}
    *
+   * Note: listStatus considers listing from fallbackLink if available. If the
+   * same directory path is present in configured mount path as well as in
+   * fallback fs, then only the fallback path will be listed in the returned
+   * result except for link.
+   *
    * If any of the the immediate children of the given path f is a symlink(mount
    * link), the returned FileStatus object of that children would be represented
    * as a symlink. It will not be resolved to the target path and will not get
@@ -880,15 +887,20 @@ public class ViewFs extends AbstractFileSystem {
     final long creationTime; // of the the mount table
     final UserGroupInformation ugi; // the user/group of user who created mtable
     final URI myUri; // the URI of the outer ViewFs
+    private InodeTree<AbstractFileSystem> fsState;
+    private Configuration conf;
 
     public InternalDirOfViewFs(final InodeTree.INodeDir<AbstractFileSystem> dir,
-        final long cTime, final UserGroupInformation ugi, final URI uri)
+        final long cTime, final UserGroupInformation ugi, final URI uri,
+        InodeTree fsState, Configuration conf)
       throws URISyntaxException {
       super(FsConstants.VIEWFS_URI, FsConstants.VIEWFS_SCHEME, false, -1);
       theInternalDir = dir;
       creationTime = cTime;
       this.ugi = ugi;
       myUri = uri;
+      this.fsState = fsState;
+      this.conf = conf;
     }
 
     static private void checkPathIsSlash(final Path f) throws IOException {
@@ -1015,7 +1027,8 @@ public class ViewFs extends AbstractFileSystem {
     public FileStatus[] listStatus(final Path f) throws IOException {
       checkPathIsSlash(f);
       FileStatus[] fallbackStatuses = listStatusForFallbackLink();
-      FileStatus[] result = new FileStatus[theInternalDir.getChildren().size()];
+      Set<FileStatus> linkStatuses = new HashSet<>();
+      Set<FileStatus> internalDirStatuses = new HashSet<>();
       int i = 0;
       for (Entry<String, INode<AbstractFileSystem>> iEntry :
           theInternalDir.getChildren().entrySet()) {
@@ -1029,11 +1042,10 @@ public class ViewFs extends AbstractFileSystem {
             // To maintain backward compatibility, with default option(showing
             // mount links as symlinks), we will represent target link as
             // symlink and rest other properties are belongs to mount link only.
-            result[i++] =
+            linkStatuses.add(
                 new FileStatus(0, false, 0, 0, creationTime, creationTime,
                     PERMISSION_555, ugi.getShortUserName(),
-                    ugi.getPrimaryGroupName(), link.getTargetLink(),
+                    ugi.getPrimaryGroupName(), link.getTargetLink(), path));
-                    path);
             continue;
           }
 
@@ -1049,11 +1061,12 @@ public class ViewFs extends AbstractFileSystem {
             FileStatus status =
                 ((ChRootedFs) link.getTargetFileSystem()).getMyFs()
                     .getFileStatus(new Path(linkedPath));
-            result[i++] = new FileStatus(status.getLen(), status.isDirectory(),
+            linkStatuses.add(
+                new FileStatus(status.getLen(), status.isDirectory(),
                     status.getReplication(), status.getBlockSize(),
                     status.getModificationTime(), status.getAccessTime(),
-                status.getPermission(), status.getOwner(), status.getGroup(),
+                    status.getPermission(), status.getOwner(),
-                null, path);
+                    status.getGroup(), null, path));
           } catch (FileNotFoundException ex) {
             LOG.warn("Cannot get one of the children's(" + path
                 + ")  target path(" + link.getTargetFileSystem().getUri()
@@ -1061,52 +1074,63 @@ public class ViewFs extends AbstractFileSystem {
             throw ex;
           }
         } else {
-          result[i++] =
+          internalDirStatuses.add(
               new FileStatus(0, true, 0, 0, creationTime, creationTime,
                   PERMISSION_555, ugi.getShortUserName(),
-                  ugi.getGroupNames()[0], path);
+                  ugi.getPrimaryGroupName(), path));
-        }
-      }
-      if (fallbackStatuses.length > 0) {
-        return consolidateFileStatuses(fallbackStatuses, result);
-      } else {
-        return result;
         }
       }
 
-    private FileStatus[] consolidateFileStatuses(FileStatus[] fallbackStatuses,
+      FileStatus[] internalDirStatusesMergedWithFallBack = internalDirStatuses
-        FileStatus[] mountPointStatuses) {
+          .toArray(new FileStatus[internalDirStatuses.size()]);
+      if (fallbackStatuses.length > 0) {
+        internalDirStatusesMergedWithFallBack =
+            merge(fallbackStatuses, internalDirStatusesMergedWithFallBack);
+      }
+
+      // Links will always have precedence than internalDir or fallback paths.
+      return merge(linkStatuses.toArray(new FileStatus[linkStatuses.size()]),
+          internalDirStatusesMergedWithFallBack);
+    }
+
+    private FileStatus[] merge(FileStatus[] toStatuses,
+        FileStatus[] fromStatuses) {
       ArrayList<FileStatus> result = new ArrayList<>();
       Set<String> pathSet = new HashSet<>();
-      for (FileStatus status : mountPointStatuses) {
+      for (FileStatus status : toStatuses) {
         result.add(status);
         pathSet.add(status.getPath().getName());
       }
-      for (FileStatus status : fallbackStatuses) {
+      for (FileStatus status : fromStatuses) {
         if (!pathSet.contains(status.getPath().getName())) {
           result.add(status);
         }
       }
-      return result.toArray(new FileStatus[0]);
+      return result.toArray(new FileStatus[result.size()]);
     }
 
     private FileStatus[] listStatusForFallbackLink() throws IOException {
-      if (theInternalDir.isRoot() &&
+      if (fsState.getRootFallbackLink() != null) {
-          theInternalDir.getFallbackLink() != null) {
+        AbstractFileSystem linkedFallbackFs =
-        AbstractFileSystem linkedFs =
+            fsState.getRootFallbackLink().getTargetFileSystem();
-            theInternalDir.getFallbackLink().getTargetFileSystem();
+        Path p = Path.getPathWithoutSchemeAndAuthority(
+            new Path(theInternalDir.fullPath));
+        if (theInternalDir.isRoot() || FileContext
+            .getFileContext(linkedFallbackFs, conf).util().exists(p)) {
           // Fallback link is only applicable for root
-        FileStatus[] statuses = linkedFs.listStatus(new Path("/"));
+          FileStatus[] statuses = linkedFallbackFs.listStatus(p);
           for (FileStatus status : statuses) {
             // Fix the path back to viewfs scheme
+            Path pathFromConfiguredFallbackRoot =
+                new Path(p, status.getPath().getName());
             status.setPath(
-              new Path(myUri.toString(), status.getPath().getName()));
+                new Path(myUri.toString(), pathFromConfiguredFallbackRoot));
           }
           return statuses;
-      } else {
-        return new FileStatus[0];
         }
       }
+      return new FileStatus[0];
+    }
 
     @Override
     public void mkdir(final Path dir, final FsPermission permission,

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/fs/viewfs/TestViewFileSystemLinkFallback.java

@@ -18,6 +18,7 @@
 package org.apache.hadoop.fs.viewfs;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
@@ -36,6 +37,7 @@ import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.FileSystemTestHelper;
 import org.apache.hadoop.fs.FsConstants;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.permission.FsPermission;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.MiniDFSCluster;
 import org.apache.hadoop.hdfs.MiniDFSNNTopology;
@@ -343,8 +345,8 @@ public class TestViewFileSystemLinkFallback extends ViewFileSystemBaseTest {
         afterFallback.add(stat.getPath());
       }
       afterFallback.removeAll(beforeFallback);
-      assertTrue("The same directory name in fallback link should be shaded",
+      assertEquals("The same directory name in fallback link should be shaded",
-          afterFallback.size() == 1);
+          1, afterFallback.size());
       Path[] fallbackArray = new Path[afterFallback.size()];
       // Only user1 should be listed as fallback link
       Path expected = new Path(viewFsUri.toString(), "user1");
@@ -359,4 +361,249 @@ public class TestViewFileSystemLinkFallback extends ViewFileSystemBaseTest {
       assertTrue(vfs.getFileStatus(childDir).isDirectory());
     }
   }
+
+  /**
+   * Tests ListStatus on non-link parent with fallback configured.
+   * =============================Example.======================================
+   * ===== Fallback path tree =============== Mount Path Tree ==================
+   * ===========================================================================
+   * *             /            *****               /          *****************
+   * *            /             *****              /           *****************
+   * *          user1           *****          user1           *****************
+   * *           /              *****          /               *****************
+   * *         hive             *****        hive              *****************
+   * *       /      \           *****       /                  *****************
+   * * warehouse    warehouse1  *****  warehouse               *****************
+   * * (-rwxr--r--)             ***** (-r-xr--r--)             *****************
+   * *     /                    *****    /                     *****************
+   * * partition-0              ***** partition-0              *****************
+   * ===========================================================================
+   * ===========================================================================
+   * ***         ls /user1/hive                                        *********
+   * ***         viewfs://default/user1/hive/warehouse (-rwxr--r--)    *********
+   * ***         viewfs://default/user1/hive/warehouse1                *********
+   * ===========================================================================
+   */
+  @Test
+  public void testListingWithFallbackLinkWithSameMountDirectoryTree()
+      throws Exception {
+    Configuration conf = new Configuration();
+    conf.setBoolean(Constants.CONFIG_VIEWFS_MOUNT_LINKS_AS_SYMLINKS, false);
+    ConfigUtil.addLink(conf, "/user1/hive/warehouse/partition-0",
+        new Path(targetTestRoot.toString()).toUri());
+    // Creating multiple directories path under the fallback directory.
+    // "/user1/hive/warehouse/partition-0" directory already exists as
+    // configured mount point.
+    Path dir1 = new Path(targetTestRoot,
+        "fallbackDir/user1/hive/warehouse/partition-0");
+    Path dir2 = new Path(targetTestRoot, "fallbackDir/user1/hive/warehouse1");
+    fsTarget.mkdirs(dir1);
+    fsTarget.mkdirs(dir2);
+    fsTarget.setPermission(new Path(targetTestRoot, "fallbackDir/user1/hive/"),
+        FsPermission.valueOf("-rwxr--r--"));
+    URI viewFsUri = new URI(FsConstants.VIEWFS_SCHEME,
+        Constants.CONFIG_VIEWFS_DEFAULT_MOUNT_TABLE, "/", null, null);
+
+    HashSet<Path> beforeFallback = new HashSet<>();
+    try (FileSystem vfs = FileSystem.get(viewFsUri, conf)) {
+      for (FileStatus stat : vfs
+          .listStatus(new Path(viewFsUri.toString(), "/user1/hive/"))) {
+        beforeFallback.add(stat.getPath());
+      }
+    }
+    ConfigUtil
+        .addLinkFallback(conf, new Path(targetTestRoot, "fallbackDir").toUri());
+
+    try (FileSystem vfs = FileSystem.get(viewFsUri, conf)) {
+      HashSet<Path> afterFallback = new HashSet<>();
+      for (FileStatus stat : vfs
+          .listStatus(new Path(viewFsUri.toString(), "/user1/hive/"))) {
+        afterFallback.add(stat.getPath());
+        if (dir1.getName().equals(stat.getPath().getName())) {
+          // make sure fallback dir listed out with correct permissions, but not
+          // with link permissions.
+          assertEquals(FsPermission.valueOf("-rwxr--r--"),
+              stat.getPermission());
+        }
+      }
+      //
+      //viewfs://default/user1/hive/warehouse
+      afterFallback.removeAll(beforeFallback);
+      assertEquals("The same directory name in fallback link should be shaded",
+          1, afterFallback.size());
+    }
+  }
+
+  /**
+   * Tests ListStatus on link parent with fallback configured.
+   * =============================Example.======================================
+   * ===== Fallback path tree =============== Mount Path Tree ==================
+   * ===========================================================================
+   * *             /            *****               /                 **********
+   * *            /             *****              /                  **********
+   * *          user1           *****          user1                  **********
+   * *           /              *****          /                      **********
+   * *         hive             *****        hive                     **********
+   * *       /      \           *****       /                         **********
+   * * warehouse    warehouse1  *****  warehouse                      **********
+   * * (-rwxr--r--)             ***** (-r-xr--r--)                    **********
+   * *     /                    *****    /                            **********
+   * * partition-0              ***** partition-0 ---> targetTestRoot **********
+   * *                          ***** (-r-xr--r--)      (-rwxr--rw-)  **********
+   * ===========================================================================
+   * ===========================================================================
+   * ***       ls /user1/hive/warehouse                                       **
+   * ***       viewfs://default/user1/hive/warehouse/partition-0 (-rwxr--rw-) **
+   * ===========================================================================
+   */
+  @Test
+  public void testLSOnLinkParentWithFallbackLinkWithSameMountDirectoryTree()
+      throws Exception {
+    Configuration conf = new Configuration();
+    conf.setBoolean(Constants.CONFIG_VIEWFS_MOUNT_LINKS_AS_SYMLINKS, false);
+    ConfigUtil.addLink(conf, "/user1/hive/warehouse/partition-0",
+        new Path(targetTestRoot.toString()).toUri());
+    // Creating multiple directories path under the fallback directory.
+    // "/user1/hive/warehouse/partition-0" directory already exists as
+    // configured mount point.
+    Path dir1 = new Path(targetTestRoot,
+        "fallbackDir/user1/hive/warehouse/partition-0");
+    Path dir2 = new Path(targetTestRoot, "fallbackDir/user1/hive/warehouse1");
+    fsTarget.mkdirs(dir1);
+    fsTarget.mkdirs(dir2);
+    fsTarget.setPermission(new Path(targetTestRoot,
+            "fallbackDir/user1/hive/warehouse/partition-0"),
+        FsPermission.valueOf("-rwxr--r--"));
+    fsTarget.setPermission(targetTestRoot, FsPermission.valueOf("-rwxr--rw-"));
+    URI viewFsUri = new URI(FsConstants.VIEWFS_SCHEME,
+        Constants.CONFIG_VIEWFS_DEFAULT_MOUNT_TABLE, "/", null, null);
+
+    HashSet<Path> beforeFallback = new HashSet<>();
+    try (FileSystem vfs = FileSystem.get(viewFsUri, conf)) {
+      for (FileStatus stat : vfs.listStatus(
+          new Path(viewFsUri.toString(), "/user1/hive/warehouse/"))) {
+        beforeFallback.add(stat.getPath());
+      }
+    }
+    ConfigUtil
+        .addLinkFallback(conf, new Path(targetTestRoot, "fallbackDir").toUri());
+
+    try (FileSystem vfs = FileSystem.get(viewFsUri, conf)) {
+      HashSet<Path> afterFallback = new HashSet<>();
+      for (FileStatus stat : vfs.listStatus(
+          new Path(viewFsUri.toString(), "/user1/hive/warehouse/"))) {
+        afterFallback.add(stat.getPath());
+        if (dir1.getName().equals(stat.getPath().getName())) {
+          // make sure fallback dir listed out with correct permissions, but not
+          // with link permissions.
+          assertEquals(FsPermission.valueOf("-rwxr--rw-"),
+              stat.getPermission());
+        }
+      }
+      afterFallback.removeAll(beforeFallback);
+      assertEquals("Just to make sure paths are same.", 0,
+          afterFallback.size());
+    }
+  }
+
+  /**
+   * Tests ListStatus on root with fallback configured.
+   * =============================Example.=======================================
+   * ===== Fallback path tree =============== Mount Path Tree ==================
+   * ===========================================================================
+   * *          /       /          *****               /                     ***
+   * *         /       /           *****              /                      ***
+   * *      user1    user2         *****           user1 ---> targetTestRoot ***
+   * *(-r-xr--r--)   (-r-xr--r--)  *****                      (-rwxr--rw-)   ***
+   * ===========================================================================
+   * ===========================================================================
+   * ***       ls /user1/hive/warehouse                                       **
+   * ***       viewfs://default/user1(-rwxr--rw-)                             **
+   * ***       viewfs://default/user2(-r-xr--r--)                             **
+   * ===========================================================================
+   */
+  @Test
+  public void testLSOnRootWithFallbackLinkWithSameMountDirectories()
+      throws Exception {
+    Configuration conf = new Configuration();
+    conf.setBoolean(Constants.CONFIG_VIEWFS_MOUNT_LINKS_AS_SYMLINKS, false);
+    ConfigUtil
+        .addLink(conf, "/user1", new Path(targetTestRoot.toString()).toUri());
+    // Creating multiple directories path under the fallback directory.
+    // "/user1" directory already exists as configured mount point.
+    Path dir1 = new Path(targetTestRoot, "fallbackDir/user1");
+    Path dir2 = new Path(targetTestRoot, "fallbackDir/user2");
+    fsTarget.mkdirs(dir1);
+    fsTarget.mkdirs(dir2, FsPermission.valueOf("-rwxr--r--"));
+    fsTarget.setPermission(targetTestRoot, FsPermission.valueOf("-rwxr--rw-"));
+    URI viewFsUri = new URI(FsConstants.VIEWFS_SCHEME,
+        Constants.CONFIG_VIEWFS_DEFAULT_MOUNT_TABLE, "/", null, null);
+
+    HashSet<Path> beforeFallback = new HashSet<>();
+    try (FileSystem vfs = FileSystem.get(viewFsUri, conf)) {
+      for (FileStatus stat : vfs
+          .listStatus(new Path(viewFsUri.toString(), "/"))) {
+        beforeFallback.add(stat.getPath());
+      }
+    }
+    ConfigUtil
+        .addLinkFallback(conf, new Path(targetTestRoot, "fallbackDir").toUri());
+
+    try (FileSystem vfs = FileSystem.get(viewFsUri, conf)) {
+      HashSet<Path> afterFallback = new HashSet<>();
+      for (FileStatus stat : vfs
+          .listStatus(new Path(viewFsUri.toString(), "/"))) {
+        afterFallback.add(stat.getPath());
+        if (dir1.getName().equals(stat.getPath().getName())) {
+          // make sure fallback dir listed out with correct permissions, but not
+          // with link permissions.
+          assertEquals(FsPermission.valueOf("-rwxr--rw-"),
+              stat.getPermission());
+        } else {
+          assertEquals("Path is: " + stat.getPath(),
+              FsPermission.valueOf("-rwxr--r--"), stat.getPermission());
+        }
+      }
+      afterFallback.removeAll(beforeFallback);
+      assertEquals(1, afterFallback.size());
+      assertEquals("/user2 dir from fallback should be listed.", "user2",
+          afterFallback.iterator().next().getName());
+    }
+  }
+
+  @Test
+  public void testLSOnLinkParentWhereMountLinkMatchesWithAFileUnderFallback()
+      throws Exception {
+    Configuration conf = new Configuration();
+    conf.setBoolean(Constants.CONFIG_VIEWFS_MOUNT_LINKS_AS_SYMLINKS, true);
+    ConfigUtil.addLink(conf, "/user1/hive/warehouse/part-0",
+        new Path(targetTestRoot.toString()).toUri());
+    // Create a file path in fallback matching to the path of mount link.
+    Path file1 =
+        new Path(targetTestRoot, "fallbackDir/user1/hive/warehouse/part-0");
+    fsTarget.createNewFile(file1);
+    Path dir2 = new Path(targetTestRoot, "fallbackDir/user1/hive/warehouse1");
+    fsTarget.mkdirs(dir2);
+    URI viewFsUri = new URI(FsConstants.VIEWFS_SCHEME,
+        Constants.CONFIG_VIEWFS_DEFAULT_MOUNT_TABLE, "/", null, null);
+
+    ConfigUtil
+        .addLinkFallback(conf, new Path(targetTestRoot, "fallbackDir").toUri());
+
+    try (FileSystem vfs = FileSystem.get(viewFsUri, conf)) {
+      for (FileStatus stat : vfs.listStatus(
+          new Path(viewFsUri.toString(), "/user1/hive/warehouse/"))) {
+        if (file1.getName().equals(stat.getPath().getName())) {
+          // Link represents as symlink.
+          assertFalse(stat.isFile());
+          assertFalse(stat.isDirectory());
+          assertTrue(stat.isSymlink());
+          Path fileUnderDir = new Path(stat.getPath(), "check");
+          assertTrue(vfs.mkdirs(fileUnderDir)); // Creating dir under target
+          assertTrue(fsTarget
+              .exists(new Path(targetTestRoot, fileUnderDir.getName())));
+        }
+      }
+    }
+  }
 }