docs/attachments/LUCENE-3788/LUCENE-3788.patch

diff --git a/lucene/core/src/java/org/apache/lucene/index/DirectoryBased.java b/lucene/core/src/java/org/apache/lucene/index/DirectoryBased.java
new file mode 100644
index 0000000..913a71d
--- /dev/null
+++ b/lucene/core/src/java/org/apache/lucene/index/DirectoryBased.java
@@ -0,0 +1,32 @@
+package org.apache.lucene.index;
+
+/**
+ * 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.
+ */
+
+import org.apache.lucene.store.Directory;
+
+/**
+ * Marks {@link IndexReader}-s that are reading their data from
+ * {@link Directory}.
+ */
+public interface DirectoryBased {
+
+  /**
+   * Return {@link Directory} that is the source of data for this {@link IndexReader}.
+   */
+  public Directory directory();
+}
diff --git a/lucene/core/src/java/org/apache/lucene/index/DirectoryReader.java b/lucene/core/src/java/org/apache/lucene/index/DirectoryReader.java
index 6cb1c37..3b77d10 100644
--- a/lucene/core/src/java/org/apache/lucene/index/DirectoryReader.java
+++ b/lucene/core/src/java/org/apache/lucene/index/DirectoryReader.java
@@ -54,7 +54,7 @@ import org.apache.lucene.store.Directory;
  {@link AtomicReader}, see {@link #subReaders} and
  {@link #getSequentialSubReaders}.
 */
-public abstract class DirectoryReader extends BaseMultiReader<AtomicReader> {
+public abstract class DirectoryReader extends BaseMultiReader<AtomicReader> implements DirectoryBased {
   public static final int DEFAULT_TERMS_INDEX_DIVISOR = 1;
 
   protected final Directory directory;