HDFS-13250. RBF: Router to manage requests across multiple subclusters. Contributed by Inigo Goiri.

(cherry picked from commit 2caba999bb)
(cherry picked from commit 0db4b587c6)

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterRpcClient.java

@@ -768,6 +768,66 @@ public class RouterRpcClient {
     }
   }
 
+  /**
+   * Invoke method in all locations and return success if any succeeds.
+   *
+   * @param locations List of remote locations to call concurrently.
+   * @param method The remote method and parameters to invoke.
+   * @return If the call succeeds in any location.
+   * @throws IOException If any of the calls return an exception.
+   */
+  public <T extends RemoteLocationContext, R> boolean invokeAll(
+      final Collection<T> locations, final RemoteMethod method)
+          throws IOException {
+    boolean anyResult = false;
+    Map<T, Boolean> results =
+        invokeConcurrent(locations, method, false, false, Boolean.class);
+    for (Boolean value : results.values()) {
+      boolean result = value.booleanValue();
+      if (result) {
+        anyResult = true;
+      }
+    }
+    return anyResult;
+  }
+
+  /**
+   * Invoke multiple concurrent proxy calls to different clients. Returns an
+   * array of results.
+   *
+   * Re-throws exceptions generated by the remote RPC call as either
+   * RemoteException or IOException.
+   *
+   * @param <T> The type of the remote location.
+   * @param locations List of remote locations to call concurrently.
+   * @param method The remote method and parameters to invoke.
+   * @throws IOException If all the calls throw an exception.
+   */
+  public <T extends RemoteLocationContext, R> void invokeConcurrent(
+      final Collection<T> locations, final RemoteMethod method)
+          throws IOException {
+    invokeConcurrent(locations, method, void.class);
+  }
+
+  /**
+   * Invoke multiple concurrent proxy calls to different clients. Returns an
+   * array of results.
+   *
+   * Re-throws exceptions generated by the remote RPC call as either
+   * RemoteException or IOException.
+   *
+   * @param <T> The type of the remote location.
+   * @param locations List of remote locations to call concurrently.
+   * @param method The remote method and parameters to invoke.
+   * @return Result of invoking the method per subcluster: nsId -> result.
+   * @throws IOException If all the calls throw an exception.
+   */
+  public <T extends RemoteLocationContext, R> Map<T, R> invokeConcurrent(
+      final Collection<T> locations, final RemoteMethod method, Class<R> clazz)
+          throws IOException {
+    return invokeConcurrent(locations, method, false, false, clazz);
+  }
+
   /**
    * Invoke multiple concurrent proxy calls to different clients. Returns an
    * array of results.

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterRpcServer.java

@@ -510,6 +510,18 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol {
       throws IOException {
     checkOperation(OperationCategory.WRITE);
 
+    if (createParent && isPathAll(src)) {
+      int index = src.lastIndexOf(Path.SEPARATOR);
+      String parent = src.substring(0, index);
+      LOG.debug("Creating {} requires creating parent {}", src, parent);
+      FsPermission parentPermissions = getParentPermission(masked);
+      boolean success = mkdirs(parent, parentPermissions, createParent);
+      if (!success) {
+        // This shouldn't happen as mkdirs returns true or exception
+        LOG.error("Couldn't create parents for {}", src);
+      }
+    }
+
     RemoteLocation createLocation = getCreateLocation(src);
     RemoteMethod method = new RemoteMethod("create",
         new Class<?>[] {String.class, FsPermission.class, String.class,
@@ -521,6 +533,32 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol {
     return (HdfsFileStatus) rpcClient.invokeSingle(createLocation, method);
   }
 
+  /**
+   * Get the permissions for the parent of a child with given permissions. If
+   * the child has r--, we will set it to r-x.
+   * @param mask The permission mask of the child.
+   * @return The permission mask of the parent.
+   */
+  private static FsPermission getParentPermission(final FsPermission mask) {
+    FsPermission ret = new FsPermission(
+        applyExecute(mask.getUserAction()),
+        applyExecute(mask.getGroupAction()),
+        applyExecute(mask.getOtherAction()));
+    return ret;
+  }
+
+  /**
+   * Apply the execute permissions if it can be read.
+   * @param action Input permission.
+   * @return Output permission.
+   */
+  private static FsAction applyExecute(final FsAction action) {
+    if (action.and(FsAction.READ) == FsAction.READ) {
+      return action.or(FsAction.EXECUTE);
+    }
+    return action;
+  }
+
   /**
    * Get the location to create a file. It checks if the file already existed
    * in one of the locations.
@@ -580,7 +618,7 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol {
     RemoteMethod method = new RemoteMethod("append",
         new Class<?>[] {String.class, String.class, EnumSetWritable.class},
         new RemoteParam(), clientName, flag);
-    return (LastBlockWithStatus) rpcClient.invokeSequential(
+    return rpcClient.invokeSequential(
         locations, method, LastBlockWithStatus.class, null);
   }
 
@@ -643,7 +681,11 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol {
     RemoteMethod method = new RemoteMethod("setPermission",
         new Class<?>[] {String.class, FsPermission.class},
         new RemoteParam(), permissions);
-    rpcClient.invokeSequential(locations, method);
+    if (isPathAll(src)) {
+      rpcClient.invokeConcurrent(locations, method);
+    } else {
+      rpcClient.invokeSequential(locations, method);
+    }
   }
 
   @Override // ClientProtocol
@@ -655,7 +697,11 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol {
     RemoteMethod method = new RemoteMethod("setOwner",
         new Class<?>[] {String.class, String.class, String.class},
         new RemoteParam(), username, groupname);
-    rpcClient.invokeSequential(locations, method);
+    if (isPathAll(src)) {
+      rpcClient.invokeConcurrent(locations, method);
+    } else {
+      rpcClient.invokeSequential(locations, method);
+    }
   }
 
   /**
@@ -933,8 +979,12 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol {
     RemoteMethod method = new RemoteMethod("delete",
         new Class<?>[] {String.class, boolean.class}, new RemoteParam(),
         recursive);
-    return ((Boolean) rpcClient.invokeSequential(locations, method,
-        Boolean.class, Boolean.TRUE)).booleanValue();
+    if (isPathAll(src)) {
+      return rpcClient.invokeAll(locations, method);
+    } else {
+      return rpcClient.invokeSequential(locations, method,
+          Boolean.class, Boolean.TRUE).booleanValue();
+    }
   }
 
   @Override // ClientProtocol
@@ -943,6 +993,15 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol {
     checkOperation(OperationCategory.WRITE);
 
     final List<RemoteLocation> locations = getLocationsForPath(src, true);
+    RemoteMethod method = new RemoteMethod("mkdirs",
+        new Class<?>[] {String.class, FsPermission.class, boolean.class},
+        new RemoteParam(), masked, createParent);
+
+    // Create in all locations
+    if (isPathAll(src)) {
+      return rpcClient.invokeAll(locations, method);
+    }
+
     if (locations.size() > 1) {
       // Check if this directory already exists
       try {
@@ -959,9 +1018,6 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol {
     }
 
     RemoteLocation firstLocation = locations.get(0);
-    RemoteMethod method = new RemoteMethod("mkdirs",
-        new Class<?>[] {String.class, FsPermission.class, boolean.class},
-        new RemoteParam(), masked, createParent);
     return ((Boolean) rpcClient.invokeSingle(firstLocation, method))
         .booleanValue();
   }
@@ -1077,8 +1133,16 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol {
     final List<RemoteLocation> locations = getLocationsForPath(src, false);
     RemoteMethod method = new RemoteMethod("getFileInfo",
         new Class<?>[] {String.class}, new RemoteParam());
-    HdfsFileStatus ret = (HdfsFileStatus) rpcClient.invokeSequential(
-        locations, method, HdfsFileStatus.class, null);
+
+    HdfsFileStatus ret = null;
+    // If it's a directory, we check in all locations
+    if (isPathAll(src)) {
+      ret = getFileInfoAll(locations, method);
+    } else {
+      // Check for file information sequentially
+      ret = (HdfsFileStatus) rpcClient.invokeSequential(
+          locations, method, HdfsFileStatus.class, null);
+    }
 
     // If there is no real path, check mount points
     if (ret == null) {
@@ -1096,6 +1160,37 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol {
     return ret;
   }
 
+  /**
+   * Get the file info from all the locations.
+   *
+   * @param locations Locations to check.
+   * @param method The file information method to run.
+   * @return The first file info if it's a file, the directory if it's
+   *         everywhere.
+   * @throws IOException If all the locations throw an exception.
+   */
+  private HdfsFileStatus getFileInfoAll(final List<RemoteLocation> locations,
+      final RemoteMethod method) throws IOException {
+
+    // Get the file info from everybody
+    Map<RemoteLocation, HdfsFileStatus> results =
+        rpcClient.invokeConcurrent(locations, method, HdfsFileStatus.class);
+
+    // We return the first file
+    HdfsFileStatus dirStatus = null;
+    for (RemoteLocation loc : locations) {
+      HdfsFileStatus fileStatus = results.get(loc);
+      if (fileStatus != null) {
+        if (!fileStatus.isDirectory()) {
+          return fileStatus;
+        } else if (dirStatus == null) {
+          dirStatus = fileStatus;
+        }
+      }
+    }
+    return dirStatus;
+  }
+
   @Override // ClientProtocol
   public boolean isFileClosed(String src) throws IOException {
     checkOperation(OperationCategory.READ);
@@ -2071,6 +2166,27 @@ public class RouterRpcServer extends AbstractService implements ClientProtocol {
     }
   }
 
+  /**
+   * Check if a path should be in all subclusters.
+   *
+   * @param path Path to check.
+   * @return If a path should be in all subclusters.
+   */
+  private boolean isPathAll(final String path) {
+    if (subclusterResolver instanceof MountTableResolver) {
+      try {
+        MountTableResolver mountTable = (MountTableResolver)subclusterResolver;
+        MountTable entry = mountTable.getMountPoint(path);
+        if (entry != null) {
+          return entry.isAll();
+        }
+      } catch (IOException e) {
+        LOG.error("Cannot get mount point: {}", e.getMessage());
+      }
+    }
+    return false;
+  }
+
   /**
    * Check if a path is in a read only mount point.
    *

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/store/records/MountTable.java

@@ -37,8 +37,6 @@ import org.apache.hadoop.hdfs.server.federation.router.RouterQuotaUsage;
 import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
 import org.apache.hadoop.hdfs.server.namenode.NameNode;
 import org.apache.hadoop.security.UserGroupInformation;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 /**
  * Data schema for
@@ -50,7 +48,6 @@ import org.slf4j.LoggerFactory;
  */
 public abstract class MountTable extends BaseRecord {
 
-  private static final Logger LOG = LoggerFactory.getLogger(MountTable.class);
   public static final String ERROR_MSG_NO_SOURCE_PATH =
       "Invalid entry, no source path specified ";
   public static final String ERROR_MSG_MUST_START_WITH_BACK_SLASH =
@@ -417,6 +414,16 @@ public abstract class MountTable extends BaseRecord {
     return false;
   }
 
+  /**
+   * Check if a mount table spans all locations.
+   * @return If the mount table spreads across all locations.
+   */
+  public boolean isAll() {
+    DestinationOrder order = getDestOrder();
+    return order == DestinationOrder.HASH_ALL ||
+        order == DestinationOrder.RANDOM;
+  }
+
   /**
    * Normalize a path for that filesystem.
    *

hadoop-hdfs-project/hadoop-hdfs-rbf/src/test/java/org/apache/hadoop/hdfs/server/federation/router/TestRouterAllResolver.java

@@ -0,0 +1,402 @@
+/**
+ * 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.federation.router;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.IOException;
+import java.net.URI;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FSDataInputStream;
+import org.apache.hadoop.fs.FSDataOutputStream;
+import org.apache.hadoop.fs.FileStatus;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hdfs.server.federation.RouterConfigBuilder;
+import org.apache.hadoop.hdfs.server.federation.RouterDFSCluster.NamenodeContext;
+import org.apache.hadoop.hdfs.server.federation.RouterDFSCluster.RouterContext;
+import org.apache.hadoop.hdfs.server.federation.StateStoreDFSCluster;
+import org.apache.hadoop.hdfs.server.federation.resolver.MountTableManager;
+import org.apache.hadoop.hdfs.server.federation.resolver.MultipleDestinationMountTableResolver;
+import org.apache.hadoop.hdfs.server.federation.resolver.order.DestinationOrder;
+import org.apache.hadoop.hdfs.server.federation.store.StateStoreService;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.AddMountTableEntryRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.AddMountTableEntryResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetMountTableEntriesRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetMountTableEntriesResponse;
+import org.apache.hadoop.hdfs.server.federation.store.records.MountTable;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+/**
+ * Tests the use of the resolvers that write in all subclusters from the
+ * Router. It supports:
+ * <li>HashResolver
+ * <li>RandomResolver.
+ */
+public class TestRouterAllResolver {
+
+  /** Directory that will be in a HASH_ALL mount point. */
+  private static final String TEST_DIR_HASH_ALL = "/hashall";
+  /** Directory that will be in a HASH_ALL mount point. */
+  private static final String TEST_DIR_RANDOM = "/random";
+
+  /** Number of namespaces. */
+  private static final int NUM_NAMESPACES = 2;
+
+
+  /** Mini HDFS clusters with Routers and State Store. */
+  private static StateStoreDFSCluster cluster;
+  /** Router for testing. */
+  private static RouterContext routerContext;
+  /** Router/federated filesystem. */
+  private static FileSystem routerFs;
+  /** Filesystem for each namespace. */
+  private static List<FileSystem> nsFss = new LinkedList<>();
+
+
+  @Before
+  public void setup() throws Exception {
+    // 2 nameservices with 1 namenode each (no HA needed for this test)
+    cluster = new StateStoreDFSCluster(
+        false, NUM_NAMESPACES, MultipleDestinationMountTableResolver.class);
+
+    // Start NNs and DNs and wait until ready
+    cluster.startCluster();
+
+    // Build and start a Router with: State Store + Admin + RPC
+    Configuration routerConf = new RouterConfigBuilder()
+        .stateStore()
+        .admin()
+        .rpc()
+        .build();
+    cluster.addRouterOverrides(routerConf);
+    cluster.startRouters();
+    routerContext = cluster.getRandomRouter();
+
+    // Register and verify all NNs with all routers
+    cluster.registerNamenodes();
+    cluster.waitNamenodeRegistration();
+
+    // Setup the test mount point
+    createMountTableEntry(TEST_DIR_HASH_ALL, DestinationOrder.HASH_ALL);
+    createMountTableEntry(TEST_DIR_RANDOM, DestinationOrder.RANDOM);
+
+    // Get filesystems for federated and each namespace
+    routerFs = routerContext.getFileSystem();
+    for (String nsId : cluster.getNameservices()) {
+      List<NamenodeContext> nns = cluster.getNamenodes(nsId);
+      for (NamenodeContext nn : nns) {
+        FileSystem nnFs = nn.getFileSystem();
+        nsFss.add(nnFs);
+      }
+    }
+    assertEquals(NUM_NAMESPACES, nsFss.size());
+  }
+
+  @After
+  public void cleanup() {
+    cluster.shutdown();
+    cluster = null;
+    routerContext = null;
+    routerFs = null;
+    nsFss.clear();
+  }
+
+  @Test
+  public void testHashAll() throws Exception {
+    testAll(TEST_DIR_HASH_ALL);
+  }
+
+  @Test
+  public void testRandomAll() throws Exception {
+    testAll(TEST_DIR_RANDOM);
+  }
+
+  /**
+   * Tests that the resolver spreads files across subclusters in the whole
+   * tree.
+   * @throws Exception If the resolver is not working.
+   */
+  private void testAll(final String path) throws Exception {
+
+    // Create directories in different levels
+    routerFs.mkdirs(new Path(path + "/dir0"));
+    routerFs.mkdirs(new Path(path + "/dir1"));
+    routerFs.mkdirs(new Path(path + "/dir2/dir20"));
+    routerFs.mkdirs(new Path(path + "/dir2/dir21"));
+    routerFs.mkdirs(new Path(path + "/dir2/dir22"));
+    routerFs.mkdirs(new Path(path + "/dir2/dir22/dir220"));
+    routerFs.mkdirs(new Path(path + "/dir2/dir22/dir221"));
+    routerFs.mkdirs(new Path(path + "/dir2/dir22/dir222"));
+    assertDirsEverywhere(path, 9);
+
+    // Create 14 files at different levels of the tree
+    createTestFile(routerFs, path + "/dir0/file1.txt");
+    createTestFile(routerFs, path + "/dir0/file2.txt");
+    createTestFile(routerFs, path + "/dir1/file2.txt");
+    createTestFile(routerFs, path + "/dir1/file3.txt");
+    createTestFile(routerFs, path + "/dir2/dir20/file4.txt");
+    createTestFile(routerFs, path + "/dir2/dir20/file5.txt");
+    createTestFile(routerFs, path + "/dir2/dir21/file6.txt");
+    createTestFile(routerFs, path + "/dir2/dir21/file7.txt");
+    createTestFile(routerFs, path + "/dir2/dir22/file8.txt");
+    createTestFile(routerFs, path + "/dir2/dir22/file9.txt");
+    createTestFile(routerFs, path + "/dir2/dir22/dir220/file10.txt");
+    createTestFile(routerFs, path + "/dir2/dir22/dir220/file11.txt");
+    createTestFile(routerFs, path + "/dir2/dir22/dir220/file12.txt");
+    createTestFile(routerFs, path + "/dir2/dir22/dir220/file13.txt");
+    assertDirsEverywhere(path, 9);
+    assertFilesDistributed(path, 14);
+
+    // Test append
+    String testFile = path + "/dir2/dir22/dir220/file-append.txt";
+    createTestFile(routerFs, testFile);
+    Path testFilePath = new Path(testFile);
+    assertTrue("Created file is too small",
+        routerFs.getFileStatus(testFilePath).getLen() > 50);
+    appendTestFile(routerFs, testFile);
+    assertTrue("Append file is too small",
+        routerFs.getFileStatus(testFilePath).getLen() > 110);
+    assertDirsEverywhere(path, 9);
+    assertFilesDistributed(path, 15);
+
+    // Removing a directory should remove it from every subcluster
+    routerFs.delete(new Path(path + "/dir2/dir22/dir220"), true);
+    assertDirsEverywhere(path, 8);
+    assertFilesDistributed(path, 10);
+
+    // Removing all sub directories
+    routerFs.delete(new Path(path + "/dir0"), true);
+    routerFs.delete(new Path(path + "/dir1"), true);
+    routerFs.delete(new Path(path + "/dir2"), true);
+    assertDirsEverywhere(path, 0);
+    assertFilesDistributed(path, 0);
+  }
+
+  /**
+   * Directories in HASH_ALL mount points must be in every namespace.
+   * @param path Path to check under.
+   * @param expectedNumDirs Expected number of directories.
+   * @throws IOException If it cannot check the directories.
+   */
+  private void assertDirsEverywhere(String path, int expectedNumDirs)
+      throws IOException {
+
+    // Check for the directories in each filesystem
+    List<FileStatus> files = listRecursive(routerFs, path);
+    int numDirs = 0;
+    for (FileStatus file : files) {
+      if (file.isDirectory()) {
+        numDirs++;
+
+        Path dirPath = file.getPath();
+        Path checkPath = getRelativePath(dirPath);
+        for (FileSystem nsFs : nsFss) {
+          FileStatus fileStatus1 = nsFs.getFileStatus(checkPath);
+          assertTrue(file + " should be a directory",
+              fileStatus1.isDirectory());
+        }
+      }
+    }
+    assertEquals(expectedNumDirs, numDirs);
+  }
+
+  /**
+   * Check that the files are somewhat spread across namespaces.
+   * @param path Path to check under.
+   * @param expectedNumFiles Number of files expected.
+   * @throws IOException If the files cannot be checked.
+   */
+  private void assertFilesDistributed(String path, int expectedNumFiles)
+      throws IOException {
+
+    // Check where the files went
+    List<FileStatus> routerFiles = listRecursive(routerFs, path);
+    List<List<FileStatus>> nssFiles = new LinkedList<>();
+    for (FileSystem nsFs : nsFss) {
+      List<FileStatus> nsFiles = listRecursive(nsFs, path);
+      nssFiles.add(nsFiles);
+    }
+
+    // We should see all the files in the federated view
+    int numRouterFiles = getNumTxtFiles(routerFiles);
+    assertEquals(numRouterFiles, expectedNumFiles);
+
+    // All the files should be spread somewhat evenly across subclusters
+    List<Integer> numNsFiles = new LinkedList<>();
+    int sumNsFiles = 0;
+    for (int i = 0; i < NUM_NAMESPACES; i++) {
+      List<FileStatus> nsFiles = nssFiles.get(i);
+      int numFiles = getNumTxtFiles(nsFiles);
+      numNsFiles.add(numFiles);
+      sumNsFiles += numFiles;
+    }
+    assertEquals(numRouterFiles, sumNsFiles);
+    if (expectedNumFiles > 0) {
+      for (int numFiles : numNsFiles) {
+        assertTrue("Files not distributed: " + numNsFiles, numFiles > 0);
+      }
+    }
+  }
+
+  /**
+   * Create a test file in the filesystem and check if it was written.
+   * @param fs Filesystem.
+   * @param filename Name of the file to create.
+   * @throws IOException If it cannot create the file.
+   */
+  private static void createTestFile(
+      final FileSystem fs, final String filename)throws IOException {
+
+    final Path path = new Path(filename);
+
+    // Write the data
+    FSDataOutputStream os = fs.create(path);
+    os.writeUTF("Test data " + filename);
+    os.close();
+
+    // Read the data and check
+    FSDataInputStream is = fs.open(path);
+    String read = is.readUTF();
+    assertEquals("Test data " + filename, read);
+    is.close();
+  }
+
+  /**
+   * Append to a test file in the filesystem and check if we appended.
+   * @param fs Filesystem.
+   * @param filename Name of the file to append to.
+   * @throws IOException
+   */
+  private static void appendTestFile(
+      final FileSystem fs, final String filename) throws IOException {
+    final Path path = new Path(filename);
+
+    // Write the data
+    FSDataOutputStream os = fs.append(path);
+    os.writeUTF("Test append data " + filename);
+    os.close();
+
+    // Read the data previous data
+    FSDataInputStream is = fs.open(path);
+    String read = is.readUTF();
+    assertEquals(read, "Test data " + filename);
+    // Read the new data and check
+    read = is.readUTF();
+    assertEquals(read, "Test append data " + filename);
+    is.close();
+  }
+
+  /**
+   * Count the number of text files in a list.
+   * @param files File list.
+   * @return Number of .txt files.
+   */
+  private static int getNumTxtFiles(final List<FileStatus> files) {
+    int numFiles = 0;
+    for (FileStatus file : files) {
+      if (file.getPath().getName().endsWith(".txt")) {
+        numFiles++;
+      }
+    }
+    return numFiles;
+  }
+
+  /**
+   * Get the relative path within a filesystem (removes the filesystem prefix).
+   * @param path Path to check.
+   * @return File within the filesystem.
+   */
+  private static Path getRelativePath(final Path path) {
+    URI uri = path.toUri();
+    String uriPath = uri.getPath();
+    return new Path(uriPath);
+  }
+
+  /**
+   * Get the list the files/dirs under a path.
+   * @param fs Filesystem to check in.
+   * @param path Path to check for.
+   * @return List of files.
+   * @throws IOException If it cannot list the files.
+   */
+  private List<FileStatus> listRecursive(
+      final FileSystem fs, final String path) throws IOException {
+    List<FileStatus> ret = new LinkedList<>();
+    List<Path> temp = new LinkedList<>();
+    temp.add(new Path(path));
+    while (!temp.isEmpty()) {
+      Path p = temp.remove(0);
+      for (FileStatus fileStatus : fs.listStatus(p)) {
+        ret.add(fileStatus);
+        if (fileStatus.isDirectory()) {
+          temp.add(fileStatus.getPath());
+        }
+      }
+    }
+    return ret;
+  }
+
+  /**
+   * Add a mount table entry in all nameservices and wait until it is
+   * available in all routers.
+   * @param mountPoint Name of the mount point.
+   * @param order Order of the mount table entry.
+   * @throws Exception If the entry could not be created.
+   */
+  private void createMountTableEntry(
+      final String mountPoint, final DestinationOrder order) throws Exception {
+
+    RouterClient admin = routerContext.getAdminClient();
+    MountTableManager mountTable = admin.getMountTableManager();
+    Map<String, String> destMap = new HashMap<>();
+    for (String nsId : cluster.getNameservices()) {
+      destMap.put(nsId, mountPoint);
+    }
+    MountTable newEntry = MountTable.newInstance(mountPoint, destMap);
+    newEntry.setDestOrder(order);
+    AddMountTableEntryRequest addRequest =
+        AddMountTableEntryRequest.newInstance(newEntry);
+    AddMountTableEntryResponse addResponse =
+        mountTable.addMountTableEntry(addRequest);
+    boolean created = addResponse.getStatus();
+    assertTrue(created);
+
+    // Refresh the caches to get the mount table
+    Router router = routerContext.getRouter();
+    StateStoreService stateStore = router.getStateStore();
+    stateStore.refreshCaches(true);
+
+    // Check for the path
+    GetMountTableEntriesRequest getRequest =
+        GetMountTableEntriesRequest.newInstance(mountPoint);
+    GetMountTableEntriesResponse getResponse =
+        mountTable.getMountTableEntries(getRequest);
+    List<MountTable> entries = getResponse.getEntries();
+    assertEquals(1, entries.size());
+    assertEquals(mountPoint, entries.get(0).getSourcePath());
+  }
+}