HADOOP-18169. getDelegationTokens in ViewFs should also fetch the token from fallback FS (#4094)

HADOOP-18169. getDelegationTokens in ViewFs should also fetch the token from the fallback FS

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

@@ -746,6 +746,17 @@ public class ViewFs extends AbstractFileSystem {
         result.addAll(tokens);
       }
     }
+
+    // Add tokens from fallback FS
+    if (this.fsState.getRootFallbackLink() != null) {
+      AbstractFileSystem rootFallbackFs =
+          this.fsState.getRootFallbackLink().getTargetFileSystem();
+      List<Token<?>> tokens = rootFallbackFs.getDelegationTokens(renewer);
+      if (tokens != null) {
+        result.addAll(tokens);
+      }
+    }
+
     return result;
   }
 

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

@@ -29,6 +29,7 @@ import java.net.URI;
 import java.net.URISyntaxException;
 import java.util.EnumSet;
 
+import java.util.List;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.AbstractFileSystem;
 import org.apache.hadoop.fs.FileAlreadyExistsException;
@@ -45,6 +46,7 @@ import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.DistributedFileSystem;
 import org.apache.hadoop.hdfs.MiniDFSCluster;
 import org.apache.hadoop.hdfs.MiniDFSNNTopology;
+import org.apache.hadoop.security.token.Token;
 import org.apache.hadoop.test.LambdaTestUtils;
 import org.junit.AfterClass;
 import org.junit.Assert;
@@ -182,6 +184,26 @@ public class TestViewFsLinkFallback {
     assertTrue(fsTarget.exists(test));
   }
 
+  /**
+   * Test getDelegationToken when fallback is configured.
+   */
+  @Test
+  public void testGetDelegationToken() throws IOException {
+    Configuration conf = new Configuration();
+    conf.setBoolean(Constants.CONFIG_VIEWFS_MOUNT_LINKS_AS_SYMLINKS, false);
+    ConfigUtil.addLink(conf, "/user",
+        new Path(targetTestRoot.toString(), "user").toUri());
+    ConfigUtil.addLink(conf, "/data",
+        new Path(targetTestRoot.toString(), "data").toUri());
+    ConfigUtil.addLinkFallback(conf, targetTestRoot.toUri());
+
+    FileContext fcView =
+        FileContext.getFileContext(FsConstants.VIEWFS_URI, conf);
+    List<Token<?>> tokens = fcView.getDelegationTokens(new Path("/"), "tester");
+    // Two tokens from the two mount points and one token from fallback
+    assertEquals(3, tokens.size());
+  }
+
   /**
    * Tests that when the parent dirs does not exist in fallback but the parent
    * dir is same as mount internal directory, then we create parent structure