HADOOP-17028. ViewFS should initialize mounted target filesystems lazily. Contributed by Abhishek Das (#2260)

(cherry picked from commit 1dd03cc4b5)

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

@@ -17,6 +17,7 @@
  */
 package org.apache.hadoop.fs.viewfs;
 
+import java.util.function.Function;
 import org.apache.hadoop.thirdparty.com.google.common.base.Preconditions;
 import java.io.FileNotFoundException;
 import java.io.IOException;
@@ -257,7 +258,10 @@ enum LinkType {
    */
   static class INodeLink<T> extends INode<T> {
     final URI[] targetDirLinkList;
-    final T targetFileSystem;   // file system object created from the link.
+    private T targetFileSystem;   // file system object created from the link.
+    // Function to initialize file system. Only applicable for simple links
+    private Function<URI, T> fileSystemInitMethod;
+    private final Object lock = new Object();
 
     /**
      * Construct a mergeLink or nfly.
@@ -273,11 +277,13 @@ static class INodeLink<T> extends INode<T> {
      * Construct a simple link (i.e. not a mergeLink).
      */
     INodeLink(final String pathToNode, final UserGroupInformation aUgi,
-        final T targetFs, final URI aTargetDirLink) {
+        Function<URI, T> createFileSystemMethod,
+        final URI aTargetDirLink) {
       super(pathToNode, aUgi);
-      targetFileSystem = targetFs;
+      targetFileSystem = null;
       targetDirLinkList = new URI[1];
       targetDirLinkList[0] = aTargetDirLink;
+      this.fileSystemInitMethod = createFileSystemMethod;
     }
 
     /**
@@ -298,7 +304,30 @@ boolean isInternalDir() {
       return false;
     }
 
-    public T getTargetFileSystem() {
+    /**
+     * Get the instance of FileSystem to use, creating one if needed.
+     * @return An Initialized instance of T
+     * @throws IOException
+     */
+    public T getTargetFileSystem() throws IOException {
+      if (targetFileSystem != null) {
+        return targetFileSystem;
+      }
+      // For non NFLY and MERGE links, we initialize the FileSystem when the
+      // corresponding mount path is accessed.
+      if (targetDirLinkList.length == 1) {
+        synchronized (lock) {
+          if (targetFileSystem != null) {
+            return targetFileSystem;
+          }
+          targetFileSystem = fileSystemInitMethod.apply(targetDirLinkList[0]);
+          if (targetFileSystem == null) {
+            throw new IOException(
+                "Could not initialize target File System for URI : " +
+                    targetDirLinkList[0]);
+          }
+        }
+      }
       return targetFileSystem;
     }
   }
@@ -359,7 +388,7 @@ private void createLink(final String src, final String target,
     switch (linkType) {
     case SINGLE:
       newLink = new INodeLink<T>(fullPath, aUgi,
-          getTargetFileSystem(new URI(target)), new URI(target));
+          initAndGetTargetFs(), new URI(target));
       break;
     case SINGLE_FALLBACK:
     case MERGE_SLASH:
@@ -385,8 +414,7 @@ private void createLink(final String src, final String target,
    * 3 abstract methods.
    * @throws IOException
    */
-  protected abstract T getTargetFileSystem(URI uri)
+  protected abstract Function<URI, T> initAndGetTargetFs();
-      throws UnsupportedFileSystemException, URISyntaxException, IOException;
 
   protected abstract T getTargetFileSystem(INodeDir<T> dir)
       throws URISyntaxException, IOException;
@@ -589,7 +617,7 @@ protected InodeTree(final Configuration config, final String viewName,
     if (isMergeSlashConfigured) {
       Preconditions.checkNotNull(mergeSlashTarget);
       root = new INodeLink<T>(mountTableName, ugi,
-          getTargetFileSystem(new URI(mergeSlashTarget)),
+          initAndGetTargetFs(),
           new URI(mergeSlashTarget));
       mountPoints.add(new MountPoint<T>("/", (INodeLink<T>) root));
       rootFallbackLink = null;
@@ -608,8 +636,7 @@ protected InodeTree(final Configuration config, final String viewName,
                 + "not allowed.");
           }
           fallbackLink = new INodeLink<T>(mountTableName, ugi,
-              getTargetFileSystem(new URI(le.getTarget())),
+              initAndGetTargetFs(), new URI(le.getTarget()));
-              new URI(le.getTarget()));
           continue;
         case REGEX:
           addRegexMountEntry(le);
@@ -634,9 +661,8 @@ protected InodeTree(final Configuration config, final String viewName,
           new StringBuilder("Empty mount table detected for ").append(theUri)
               .append(" and considering itself as a linkFallback.");
       FileSystem.LOG.info(msg.toString());
-      rootFallbackLink =
+      rootFallbackLink = new INodeLink<T>(mountTableName, ugi,
-          new INodeLink<T>(mountTableName, ugi, getTargetFileSystem(theUri),
+          initAndGetTargetFs(), theUri);
-              theUri);
       getRootDir().addFallbackLink(rootFallbackLink);
     }
   }
@@ -734,10 +760,10 @@ boolean isLastInternalDirLink() {
    * @param p - input path
    * @param resolveLastComponent
    * @return ResolveResult which allows further resolution of the remaining path
-   * @throws FileNotFoundException
+   * @throws IOException
    */
   ResolveResult<T> resolve(final String p, final boolean resolveLastComponent)
-      throws FileNotFoundException {
+      throws IOException {
     ResolveResult<T> resolveResult = null;
     String[] path = breakIntoPathComponents(p);
     if (path.length <= 1) { // special case for when path is "/"
@@ -881,19 +907,20 @@ protected ResolveResult<T> buildResolveResultForRegexMountPoint(
       ResultKind resultKind, String resolvedPathStr,
       String targetOfResolvedPathStr, Path remainingPath) {
     try {
-      T targetFs = getTargetFileSystem(
+      T targetFs = initAndGetTargetFs()
-          new URI(targetOfResolvedPathStr));
+          .apply(new URI(targetOfResolvedPathStr));
-      return new ResolveResult<T>(resultKind, targetFs, resolvedPathStr,
+      if (targetFs == null) {
-          remainingPath, true);
-    } catch (IOException ex) {
         LOGGER.error(String.format(
-          "Got Exception while build resolve result."
+            "Not able to initialize target file system."
                 + " ResultKind:%s, resolvedPathStr:%s,"
                 + " targetOfResolvedPathStr:%s, remainingPath:%s,"
                 + " will return null.",
-          resultKind, resolvedPathStr, targetOfResolvedPathStr, remainingPath),
+            resultKind, resolvedPathStr, targetOfResolvedPathStr,
-          ex);
+            remainingPath));
         return null;
+      }
+      return new ResolveResult<T>(resultKind, targetFs, resolvedPathStr,
+          remainingPath, true);
     } catch (URISyntaxException uex) {
       LOGGER.error(String.format(
           "Got Exception while build resolve result."

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

@@ -26,10 +26,12 @@
 import static org.apache.hadoop.fs.viewfs.Constants.CONFIG_VIEWFS_MOUNT_LINKS_AS_SYMLINKS_DEFAULT;
 import static org.apache.hadoop.fs.viewfs.Constants.PERMISSION_555;
 
+import java.util.function.Function;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.security.PrivilegedExceptionAction;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -302,7 +304,7 @@ public void initialize(final URI theUri, final Configuration conf)
     enableInnerCache = config.getBoolean(CONFIG_VIEWFS_ENABLE_INNER_CACHE,
         CONFIG_VIEWFS_ENABLE_INNER_CACHE_DEFAULT);
     FsGetter fsGetter = fsGetter();
-    final InnerCache innerCache = new InnerCache(fsGetter);
+    cache = new InnerCache(fsGetter);
     // Now build  client side view (i.e. client side mount table) from config.
     final String authority = theUri.getAuthority();
     String tableName = authority;
@@ -318,15 +320,32 @@ public void initialize(final URI theUri, final Configuration conf)
       fsState = new InodeTree<FileSystem>(conf, tableName, myUri,
           initingUriAsFallbackOnNoMounts) {
         @Override
-        protected FileSystem getTargetFileSystem(final URI uri)
+        protected Function<URI, FileSystem> initAndGetTargetFs() {
-          throws URISyntaxException, IOException {
+          return new Function<URI, FileSystem>() {
+            @Override
+            public FileSystem apply(final URI uri) {
               FileSystem fs;
+              try {
+                fs = ugi.doAs(new PrivilegedExceptionAction<FileSystem>() {
+                  @Override
+                  public FileSystem run() throws IOException {
                     if (enableInnerCache) {
-            fs = innerCache.get(uri, config);
+                      synchronized (cache) {
-          } else {
+                        return cache.get(uri, config);
-            fs = fsGetter.get(uri, config);
                       }
+                    } else {
+                      return fsGetter().get(uri, config);
+                    }
+                  }
+                });
                 return new ChRootedFileSystem(fs, uri);
+              } catch (IOException | InterruptedException ex) {
+                LOG.error("Could not initialize the underlying FileSystem "
+                    + "object. Exception: " + ex.toString());
+              }
+              return null;
+            }
+          };
         }
 
         @Override
@@ -350,13 +369,6 @@ protected FileSystem getTargetFileSystem(final String settings,
     } catch (URISyntaxException e) {
       throw new IOException("URISyntax exception: " + theUri);
     }
-
-    if (enableInnerCache) {
-      // All fs instances are created and cached on startup. The cache is
-      // readonly after the initialize() so the concurrent access of the cache
-      // is safe.
-      cache = innerCache;
-    }
   }
 
   /**
@@ -908,11 +920,36 @@ public void removeXAttr(Path path, String name) throws IOException {
   public void setVerifyChecksum(final boolean verifyChecksum) { 
     List<InodeTree.MountPoint<FileSystem>> mountPoints = 
         fsState.getMountPoints();
+    Map<String, FileSystem> fsMap = initializeMountedFileSystems(mountPoints);
     for (InodeTree.MountPoint<FileSystem> mount : mountPoints) {
-      mount.target.targetFileSystem.setVerifyChecksum(verifyChecksum);
+      fsMap.get(mount.src).setVerifyChecksum(verifyChecksum);
     }
   }
 
+  /**
+   * Initialize the target filesystem for all mount points.
+   * @param mountPoints The mount points
+   * @return Mapping of mount point and the initialized target filesystems
+   * @throws RuntimeException when the target file system cannot be initialized
+   */
+  private Map<String, FileSystem> initializeMountedFileSystems(
+      List<InodeTree.MountPoint<FileSystem>> mountPoints) {
+    FileSystem fs = null;
+    Map<String, FileSystem> fsMap = new HashMap<>(mountPoints.size());
+    for (InodeTree.MountPoint<FileSystem> mount : mountPoints) {
+      try {
+        fs = mount.target.getTargetFileSystem();
+        fsMap.put(mount.src, fs);
+      } catch (IOException ex) {
+        String errMsg = "Not able to initialize FileSystem for mount path " +
+            mount.src + " with exception " + ex;
+        LOG.error(errMsg);
+        throw new RuntimeException(errMsg, ex);
+      }
+    }
+    return fsMap;
+  }
+  
   @Override
   public long getDefaultBlockSize() {
     throw new NotInMountpointException("getDefaultBlockSize");
@@ -936,6 +973,9 @@ public long getDefaultBlockSize(Path f) {
       return res.targetFileSystem.getDefaultBlockSize(res.remainingPath);
     } catch (FileNotFoundException e) {
       throw new NotInMountpointException(f, "getDefaultBlockSize"); 
+    } catch (IOException e) {
+      throw new RuntimeException("Not able to initialize fs in "
+          + " getDefaultBlockSize for path " + f + " with exception", e);
     }
   }
 
@@ -947,6 +987,9 @@ public short getDefaultReplication(Path f) {
       return res.targetFileSystem.getDefaultReplication(res.remainingPath);
     } catch (FileNotFoundException e) {
       throw new NotInMountpointException(f, "getDefaultReplication"); 
+    } catch (IOException e) {
+      throw new RuntimeException("Not able to initialize fs in "
+          + " getDefaultReplication for path " + f + " with exception", e);
     }
   }
 
@@ -979,8 +1022,9 @@ public QuotaUsage getQuotaUsage(Path f) throws IOException {
   public void setWriteChecksum(final boolean writeChecksum) { 
     List<InodeTree.MountPoint<FileSystem>> mountPoints = 
         fsState.getMountPoints();
+    Map<String, FileSystem> fsMap = initializeMountedFileSystems(mountPoints);
     for (InodeTree.MountPoint<FileSystem> mount : mountPoints) {
-      mount.target.targetFileSystem.setWriteChecksum(writeChecksum);
+      fsMap.get(mount.src).setWriteChecksum(writeChecksum);
     }
   }
 
@@ -988,17 +1032,24 @@ public void setWriteChecksum(final boolean writeChecksum) {
   public FileSystem[] getChildFileSystems() {
     List<InodeTree.MountPoint<FileSystem>> mountPoints =
         fsState.getMountPoints();
+    Map<String, FileSystem> fsMap = initializeMountedFileSystems(mountPoints);
     Set<FileSystem> children = new HashSet<FileSystem>();
     for (InodeTree.MountPoint<FileSystem> mountPoint : mountPoints) {
-      FileSystem targetFs = mountPoint.target.targetFileSystem;
+      FileSystem targetFs = fsMap.get(mountPoint.src);
       children.addAll(Arrays.asList(targetFs.getChildFileSystems()));
     }
 
-    if (fsState.isRootInternalDir() && fsState.getRootFallbackLink() != null) {
+    try {
+      if (fsState.isRootInternalDir() &&
+          fsState.getRootFallbackLink() != null) {
         children.addAll(Arrays.asList(
-          fsState.getRootFallbackLink().targetFileSystem
+            fsState.getRootFallbackLink().getTargetFileSystem()
                 .getChildFileSystems()));
       }
+    } catch (IOException ex) {
+      LOG.error("Could not add child filesystems for source path "
+          + fsState.getRootFallbackLink().fullPath + " with exception " + ex);
+    }
     return children.toArray(new FileSystem[]{});
   }
   

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

@@ -308,7 +308,7 @@ public MountPathInfo<FileSystem> getMountPathInfo(Path path,
       FileSystem fs = res.isInternalDir() ?
           (fsState.getRootFallbackLink() != null ?
               ((ChRootedFileSystem) fsState
-                  .getRootFallbackLink().targetFileSystem).getMyFs() :
+                  .getRootFallbackLink().getTargetFileSystem()).getMyFs() :
               fsGetter().get(path.toUri(), conf)) :
           ((ChRootedFileSystem) res.targetFileSystem).getMyFs();
       return new MountPathInfo<FileSystem>(res.remainingPath, res.resolvedPath,
@@ -350,8 +350,13 @@ public FileSystem getFallbackFileSystem() {
     if (fsState.getRootFallbackLink() == null) {
       return null;
     }
-    return ((ChRootedFileSystem) fsState.getRootFallbackLink().targetFileSystem)
+    try {
-        .getMyFs();
+      return ((ChRootedFileSystem) fsState.getRootFallbackLink()
+          .getTargetFileSystem()).getMyFs();
+    } catch (IOException ex) {
+      LOG.error("Could not get fallback filesystem ");
+    }
+    return null;
   }
 
 }

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

@@ -21,10 +21,12 @@
 import static org.apache.hadoop.fs.viewfs.Constants.CONFIG_VIEWFS_MOUNT_LINKS_AS_SYMLINKS_DEFAULT;
 import static org.apache.hadoop.fs.viewfs.Constants.PERMISSION_555;
 
+import java.util.function.Function;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.security.PrivilegedExceptionAction;
 import java.util.ArrayList;
 import java.util.EnumSet;
 import java.util.HashSet;
@@ -237,15 +239,32 @@ public ViewFs(final Configuration conf) throws IOException,
         initingUriAsFallbackOnNoMounts) {
 
       @Override
-      protected AbstractFileSystem getTargetFileSystem(final URI uri)
+      protected Function<URI, AbstractFileSystem> initAndGetTargetFs() {
-        throws URISyntaxException, UnsupportedFileSystemException {
+        return new Function<URI, AbstractFileSystem>() {
+          @Override
+          public AbstractFileSystem apply(final URI uri) {
+            AbstractFileSystem fs;
+            try {
+              fs = ugi.doAs(
+                  new PrivilegedExceptionAction<AbstractFileSystem>() {
+                    @Override
+                    public AbstractFileSystem run() throws IOException {
+                      return AbstractFileSystem.createFileSystem(uri, config);
+                    }
+                  });
               String pathString = uri.getPath();
               if (pathString.isEmpty()) {
                 pathString = "/";
               }
-          return new ChRootedFs(
+              return new ChRootedFs(fs, new Path(pathString));
-              AbstractFileSystem.createFileSystem(uri, config),
+            } catch (IOException | URISyntaxException |
-              new Path(pathString));
+                InterruptedException ex) {
+              LOG.error("Could not initialize underlying FileSystem object"
+                  +" for uri " + uri + "with exception: " + ex.toString());
+            }
+            return null;
+          }
+        };
       }
 
       @Override
@@ -719,7 +738,8 @@ public List<Token<?>> getDelegationTokens(String renewer) throws IOException {
     List<Token<?>> result = new ArrayList<Token<?>>(initialListSize);
     for ( int i = 0; i < mountPoints.size(); ++i ) {
       List<Token<?>> tokens = 
-        mountPoints.get(i).target.targetFileSystem.getDelegationTokens(renewer);
+          mountPoints.get(i).target.getTargetFileSystem()
+              .getDelegationTokens(renewer);
       if (tokens != null) {
         result.addAll(tokens);
       }

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

@@ -17,6 +17,7 @@
  */
 package org.apache.hadoop.fs.viewfs;
 
+import java.util.function.Function;
 import java.io.IOException;
 import java.net.URI;
 import java.util.Map;
@@ -63,10 +64,15 @@ public void setUp() throws Exception {
     inodeTree = new InodeTree<TestRegexMountPointFileSystem>(conf,
         TestRegexMountPoint.class.getName(), null, false) {
       @Override
-      protected TestRegexMountPointFileSystem getTargetFileSystem(
+      protected Function<URI, TestRegexMountPointFileSystem>
-          final URI uri) {
+          initAndGetTargetFs() {
+        return new Function<URI, TestRegexMountPointFileSystem>() {
+          @Override
+          public TestRegexMountPointFileSystem apply(URI uri) {
             return new TestRegexMountPointFileSystem(uri);
           }
+        };
+      }
 
       @Override
       protected TestRegexMountPointFileSystem getTargetFileSystem(

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

@@ -17,6 +17,7 @@
  */
 package org.apache.hadoop.fs.viewfs;
 
+import java.util.function.Function;
 import java.io.IOException;
 import java.net.URI;
 import java.net.URISyntaxException;
@@ -42,7 +43,7 @@ class Foo {
     new InodeTree<Foo>(conf, null, null, false) {
 
       @Override
-      protected Foo getTargetFileSystem(final URI uri) {
+      protected Function<URI, Foo> initAndGetTargetFs() {
         return null;
       }
 

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

@@ -66,6 +66,7 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import static org.apache.hadoop.fs.FileSystemTestHelper.*;
+import static org.apache.hadoop.fs.viewfs.Constants.CONFIG_VIEWFS_ENABLE_INNER_CACHE;
 import static org.apache.hadoop.fs.viewfs.Constants.PERMISSION_555;
 
 import org.junit.After;
@@ -1354,6 +1355,8 @@ public void testChildrenFileSystemLeak() throws Exception {
     final int cacheSize = TestFileUtil.getCacheSize();
     ViewFileSystem viewFs = (ViewFileSystem) FileSystem
         .get(new URI("viewfs://" + clusterName + "/"), config);
+    viewFs.resolvePath(
+        new Path(String.format("viewfs://%s/%s", clusterName, "/user")));
     assertEquals(cacheSize + 1, TestFileUtil.getCacheSize());
     viewFs.close();
     assertEquals(cacheSize, TestFileUtil.getCacheSize());
@@ -1430,4 +1433,45 @@ public void testGetContentSummaryWithFileInLocalFS() throws Exception {
           summaryAfter.getLength());
     }
   }
+
+  @Test
+  public void testTargetFileSystemLazyInitialization() throws Exception {
+    final String clusterName = "cluster" + new Random().nextInt();
+    Configuration config = new Configuration(conf);
+    config.setBoolean(CONFIG_VIEWFS_ENABLE_INNER_CACHE, false);
+    config.setClass("fs.mockfs.impl",
+        TestChRootedFileSystem.MockFileSystem.class, FileSystem.class);
+    ConfigUtil.addLink(config, clusterName, "/user",
+        URI.create("mockfs://mockauth1/mockpath"));
+    ConfigUtil.addLink(config, clusterName,
+        "/mock", URI.create("mockfs://mockauth/mockpath"));
+
+    final int cacheSize = TestFileUtil.getCacheSize();
+    ViewFileSystem viewFs = (ViewFileSystem) FileSystem
+        .get(new URI("viewfs://" + clusterName + "/"), config);
+
+    // As no inner file system instance has been initialized,
+    // cache size will remain the same
+    // cache is disabled for viewfs scheme, so the viewfs:// instance won't
+    // go in the cache even after the initialization
+    assertEquals(cacheSize, TestFileUtil.getCacheSize());
+
+    // This resolve path will initialize the file system corresponding
+    // to the mount table entry of the path "/user"
+    viewFs.resolvePath(
+        new Path(String.format("viewfs://%s/%s", clusterName, "/user")));
+
+    // Cache size will increase by 1.
+    assertEquals(cacheSize + 1, TestFileUtil.getCacheSize());
+    // This resolve path will initialize the file system corresponding
+    // to the mount table entry of the path "/mock"
+    viewFs.resolvePath(new Path(String.format("viewfs://%s/%s", clusterName,
+        "/mock")));
+    // One more file system instance will get initialized.
+    assertEquals(cacheSize + 2, TestFileUtil.getCacheSize());
+    viewFs.close();
+    // Initialized FileSystem instances will not be removed from cache as
+    // viewfs inner cache is disabled
+    assertEquals(cacheSize + 2, TestFileUtil.getCacheSize());
+  }
 }

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

@@ -21,8 +21,11 @@
 import java.io.IOException;
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.security.PrivilegedExceptionAction;
 import java.util.EnumSet;
 
+import java.util.HashMap;
+import java.util.Map;
 import javax.security.auth.login.LoginException;
 
 import org.apache.hadoop.conf.Configuration;
@@ -39,6 +42,7 @@
 import org.apache.hadoop.fs.FsShell;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.contract.ContractTestUtils;
+import org.apache.hadoop.fs.permission.FsPermission;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.DFSTestUtil;
 import org.apache.hadoop.hdfs.MiniDFSCluster;
@@ -46,6 +50,7 @@
 import org.apache.hadoop.hdfs.client.CreateEncryptionZoneFlag;
 import org.apache.hadoop.hdfs.client.HdfsAdmin;
 import org.apache.hadoop.io.IOUtils;
+import org.apache.hadoop.security.AccessControlException;
 import org.apache.hadoop.security.UserGroupInformation;
 import org.apache.hadoop.test.GenericTestUtils;
 import static org.apache.hadoop.fs.CommonConfigurationKeysPublic.FS_TRASH_INTERVAL_KEY;
@@ -406,4 +411,72 @@ private void testNflyRepair(NflyFSystem.NflyKey repairKey)
       }
     }
   }
+
+  @Test
+  public void testTargetFileSystemLazyInitializationWithUgi() throws Exception {
+    final Map<String, FileSystem> map = new HashMap<>();
+    final Path user1Path = new Path("/data/user1");
+
+    // Scenario - 1: Create FileSystem with the current user context
+    // Both mkdir and delete should be successful
+    FileSystem fs = FileSystem.get(FsConstants.VIEWFS_URI, conf);
+    fs.mkdirs(user1Path);
+    fs.delete(user1Path, false);
+
+    // Scenario - 2: Create FileSystem with the a different user context
+    final UserGroupInformation userUgi = UserGroupInformation
+        .createUserForTesting("user1@HADOOP.COM", new String[]{"hadoop"});
+    userUgi.doAs(new PrivilegedExceptionAction<Object>() {
+      @Override
+      public Object run() throws IOException {
+        UserGroupInformation ugi = UserGroupInformation.getCurrentUser();
+        String doAsUserName = ugi.getUserName();
+        assertEquals(doAsUserName, "user1@HADOOP.COM");
+
+        FileSystem viewFS = FileSystem.get(FsConstants.VIEWFS_URI, conf);
+        map.put("user1", viewFS);
+        return null;
+      }
+    });
+
+    // Try creating a directory with the file context created by a different ugi
+    // Though we are running the mkdir with the current user context, the
+    // target filesystem will be instantiated by the ugi with which the
+    // file context was created.
+    try {
+      FileSystem otherfs = map.get("user1");
+      otherfs.mkdirs(user1Path);
+      fail("This mkdir should fail");
+    } catch (AccessControlException ex) {
+      // Exception is expected as the FileSystem was created with ugi of user1
+      // So when we are trying to access the /user/user1 path for the first
+      // time, the corresponding file system is initialized and it tries to
+      // execute the task with ugi with which the FileSystem was created.
+    }
+
+    // Change the permission of /data path so that user1 can create a directory
+    fsTarget.setOwner(new Path(targetTestRoot, "data"),
+        "user1", "test2");
+    // set permission of target to allow rename to target
+    fsTarget.setPermission(new Path(targetTestRoot, "data"),
+        new FsPermission("775"));
+
+    userUgi.doAs(new PrivilegedExceptionAction<Object>() {
+      @Override
+      public Object run() throws IOException {
+        FileSystem viewFS = FileSystem.get(FsConstants.VIEWFS_URI, conf);
+        map.put("user1", viewFS);
+        return null;
+      }
+    });
+
+    // Although we are running with current user context, and current user
+    // context does not have write permission, we are able to create the
+    // directory as its using ugi of user1 which has write permission.
+    FileSystem otherfs = map.get("user1");
+    otherfs.mkdirs(user1Path);
+    String owner = otherfs.getFileStatus(user1Path).getOwner();
+    assertEquals("The owner did not match ", owner, userUgi.getShortUserName());
+    otherfs.delete(user1Path, false);
+  }
 }

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

@@ -35,7 +35,6 @@
 import org.apache.hadoop.fs.FsConstants;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.RawLocalFileSystem;
-import org.apache.hadoop.fs.UnsupportedFileSystemException;
 import org.apache.hadoop.hdfs.DistributedFileSystem;
 import org.apache.hadoop.hdfs.MiniDFSCluster;
 import org.apache.hadoop.test.LambdaTestUtils;
@@ -206,7 +205,8 @@ public void testMountLinkWithNonExistentLink(boolean expectFsInitFailure)
         new String[] {nonExistTargetPath.toUri().toString()}, conf);
     if (expectFsInitFailure) {
       LambdaTestUtils.intercept(IOException.class, () -> {
-        FileSystem.get(conf);
+        FileSystem fs = FileSystem.get(conf);
+        fs.resolvePath(new Path(userFolder));
       });
     } else {
       try (FileSystem fs = FileSystem.get(conf)) {
@@ -397,7 +397,7 @@ public void testCreateOnRoot(boolean fallbackExist) throws Exception {
    * Unset fs.viewfs.overload.scheme.target.hdfs.impl property.
    * So, OverloadScheme target fs initialization will fail.
    */
-  @Test(expected = UnsupportedFileSystemException.class, timeout = 30000)
+  @Test(expected = IOException.class, timeout = 30000)
   public void testInvalidOverloadSchemeTargetFS() throws Exception {
     final Path hdfsTargetPath = new Path(defaultFSURI + HDFS_USER_FOLDER);
     String mountTableIfSet = conf.get(Constants.CONFIG_VIEWFS_MOUNTTABLE_PATH);

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

@@ -21,18 +21,28 @@
 import java.io.IOException;
 import java.net.URISyntaxException;
 
+import java.security.PrivilegedExceptionAction;
+import java.util.HashMap;
+import java.util.Map;
 import javax.security.auth.login.LoginException;
 
 import org.apache.hadoop.fs.FileContext;
 import org.apache.hadoop.fs.FileContextTestHelper;
+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.HdfsConfiguration;
 import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.security.AccessControlException;
 import org.apache.hadoop.security.UserGroupInformation;
 import org.junit.AfterClass;
 import org.junit.Before;
 import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
 
 public class TestViewFsHdfs extends ViewFsBaseTest {
 
@@ -86,4 +96,72 @@ int getExpectedDelegationTokenCount() {
     return 8;
   }
 
+  @Test
+  public void testTargetFileSystemLazyInitialization() throws Exception {
+    final Map<String, FileContext> map = new HashMap<>();
+    final Path user1Path = new Path("/data/user1");
+
+    // Scenario - 1: Create FileContext with the current user context
+    // Both mkdir and delete should be successful
+    FileContext fs = FileContext.getFileContext(FsConstants.VIEWFS_URI, conf);
+    fs.mkdir(user1Path, FileContext.DEFAULT_PERM, false);
+    fs.delete(user1Path, false);
+
+    // Scenario - 2: Create FileContext with the a different user context
+    final UserGroupInformation userUgi = UserGroupInformation
+        .createUserForTesting("user1@HADOOP.COM", new String[]{"hadoop"});
+    userUgi.doAs(new PrivilegedExceptionAction<Object>() {
+      @Override
+      public Object run() throws IOException {
+        UserGroupInformation ugi = UserGroupInformation.getCurrentUser();
+        String doAsUserName = ugi.getUserName();
+        assertEquals(doAsUserName, "user1@HADOOP.COM");
+
+        FileContext viewFS = FileContext.getFileContext(
+            FsConstants.VIEWFS_URI, conf);
+        map.put("user1", viewFS);
+        return null;
+      }
+    });
+
+    // Try creating a directory with the file context created by a different ugi
+    // Though we are running the mkdir with the current user context, the
+    // target filesystem will be instantiated by the ugi with which the
+    // file context was created.
+    try {
+      FileContext otherfs = map.get("user1");
+      otherfs.mkdir(user1Path, FileContext.DEFAULT_PERM, false);
+      fail("This mkdir should fail");
+    } catch (AccessControlException ex) {
+      // Exception is expected as the FileContext was created with ugi of user1
+      // So when we are trying to access the /user/user1 path for the first
+      // time, the corresponding file system is initialized and it tries to
+      // execute the task with ugi with which the FileContext was created.
+    }
+
+    // Change the permission of /data path so that user1 can create a directory
+    fcView.setOwner(new Path("/data"), "user1", "test2");
+    // set permission of target to allow rename to target
+    fcView.setPermission(new Path("/data"), new FsPermission("775"));
+
+    userUgi.doAs(new PrivilegedExceptionAction<Object>() {
+      @Override
+      public Object run() throws IOException {
+        FileContext viewFS = FileContext.getFileContext(
+            FsConstants.VIEWFS_URI, conf);
+        map.put("user1", viewFS);
+        return null;
+      }
+    });
+
+    // Although we are running with current user context, and current user
+    // context does not have write permission, we are able to create the
+    // directory as its using ugi of user1 which has write permission.
+    FileContext otherfs = map.get("user1");
+    otherfs.mkdir(user1Path, FileContext.DEFAULT_PERM, false);
+    String owner = otherfs.getFileStatus(user1Path).getOwner();
+    assertEquals("The owner did not match ", owner, userUgi.getShortUserName());
+    otherfs.delete(user1Path, false);
+  }
+ 
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/tools/TestViewFileSystemOverloadSchemeWithDFSAdmin.java

@@ -198,13 +198,15 @@ public void testSaveNamespaceWithoutSpecifyingFS() throws Exception {
    */
   @Test
   public void testSafeModeWithWrongFS() throws Exception {
+    String wrongFsUri = "hdfs://nonExistent";
     final Path hdfsTargetPath =
-        new Path("hdfs://nonExistent" + HDFS_USER_FOLDER);
+        new Path(wrongFsUri + HDFS_USER_FOLDER);
     addMountLinks(defaultFSURI.getHost(), new String[] {HDFS_USER_FOLDER},
         new String[] {hdfsTargetPath.toUri().toString()}, conf);
     final DFSAdmin dfsAdmin = new DFSAdmin(conf);
     redirectStream();
-    int ret = ToolRunner.run(dfsAdmin, new String[] {"-safemode", "enter" });
+    int ret = ToolRunner.run(dfsAdmin,
+        new String[] {"-fs", wrongFsUri, "-safemode", "enter" });
     assertEquals(-1, ret);
     assertErrMsg("safemode: java.net.UnknownHostException: nonExistent", 0);
   }