HADOOP-13840. Implement getUsed() for ViewFileSystem. Contributed by Manoj Govindassamy.

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

@@ -858,6 +858,24 @@ public FsStatus getStatus(Path p) throws IOException {
     return res.targetFileSystem.getStatus(p);
   }
 
+  /**
+   * Return the total size of all files under "/", if {@link
+   * Constants#CONFIG_VIEWFS_LINK_MERGE_SLASH} is supported and is a valid
+   * mount point. Else, throw NotInMountpointException.
+   *
+   * @throws IOException
+   */
+  @Override
+  public long getUsed() throws IOException {
+    InodeTree.ResolveResult<FileSystem> res = fsState.resolve(
+        getUriPath(InodeTree.SlashPath), true);
+    if (res.isInternalDir()) {
+      throw new NotInMountpointException(InodeTree.SlashPath, "getUsed");
+    } else {
+      return res.targetFileSystem.getUsed();
+    }
+  }
+
   /**
    * An instance of this class represents an internal dir of the viewFs
    * that is internal dir of the mount table.

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

@@ -1108,4 +1108,33 @@ public Object run() throws IOException {
       }
     });
   }
+
+  @Test
+  public void testUsed() throws IOException {
+    try {
+      fsView.getUsed();
+      fail("ViewFileSystem getUsed() should fail for slash root path when the" +
+          " slash root mount point is not configured.");
+    } catch (NotInMountpointException e) {
+      // expected exception.
+    }
+    long usedSpaceByPathViaViewFs = fsView.getUsed(new Path("/user"));
+    long usedSpaceByPathViaTargetFs =
+        fsTarget.getUsed(new Path(targetTestRoot, "user"));
+    assertEquals("Space used not matching between ViewFileSystem and " +
+        "the mounted FileSystem!",
+        usedSpaceByPathViaTargetFs, usedSpaceByPathViaViewFs);
+
+    Path mountDataRootPath = new Path("/data");
+    String fsTargetFileName = "debug.log";
+    Path fsTargetFilePath = new Path(targetTestRoot, "data/debug.log");
+    Path mountDataFilePath = new Path(mountDataRootPath, fsTargetFileName);
+    fileSystemTestHelper.createFile(fsTarget, fsTargetFilePath);
+
+    usedSpaceByPathViaViewFs = fsView.getUsed(mountDataFilePath);
+    usedSpaceByPathViaTargetFs = fsTarget.getUsed(fsTargetFilePath);
+    assertEquals("Space used not matching between ViewFileSystem and " +
+        "the mounted FileSystem!",
+        usedSpaceByPathViaTargetFs, usedSpaceByPathViaViewFs);
+  }
 }