diff --git a/prefs_interface.h b/prefs_interface.h
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--- /dev/null
+++ b/prefs_interface.h
@@ -0,0 +1,40 @@
+// 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_PREFS_INTERFACE_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_PREFS_INTERFACE_H__
+
+#include <string>
+
+namespace chromeos_update_engine {
+
+// The prefs interface allows access to a persistent preferences
+// store. The two reasons for providing this as an interface are
+// testing as well as easier switching to a new implementation in the
+// future, if necessary.
+
+class PrefsInterface {
+ public:
+  // Gets a string |value| associated with |key|. Returns true on
+  // success, false on failure (including when the |key| is not
+  // present in the store).
+  virtual bool GetString(const std::string& key, std::string* value) = 0;
+
+  // Associates |key| with a string |value|. Returns true on success,
+  // false otherwise.
+  virtual bool SetString(const std::string& key, const std::string& value) = 0;
+
+  // Gets an int64 |value| associated with |key|. Returns true on
+  // success, false on failure (including when the |key| is not
+  // present in the store).
+  virtual bool GetInt64(const std::string& key, int64_t* value) = 0;
+
+  // Associates |key| with an int64 |value|. Returns true on success,
+  // false otherwise.
+  virtual bool SetInt64(const std::string& key, const int64_t value) = 0;
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_PREFS_INTERFACE_H__