diff --git a/extent_mapper.h b/extent_mapper.h
new file mode 100755
index 0000000..acdd418
--- /dev/null
+++ b/extent_mapper.h
@@ -0,0 +1,22 @@
+// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_EXTENT_MAPPER_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_EXTENT_MAPPER_H__
+
+#include <string>
+#include <vector>
+#include "update_engine/update_metadata.pb.h"
+
+namespace chromeos_update_engine {
+
+namespace extent_mapper {
+
+bool ExtentsForFileFibmap(const std::string& path, std::vector<Extent>* out);
+
+}  // namespace extent_mapper
+
+}  // namespace chromeos_update_engine
+
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_EXTENT_MAPPER_H__