diff --git a/util.cpp b/util.cpp
new file mode 100644
index 0000000..cf9ef81
--- /dev/null
+++ b/util.cpp
@@ -0,0 +1,72 @@
+/**
+ * Copyright 2017 Google Inc.
+ *
+ * Licensed 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.
+ */
+
+#include <string>
+
+#include "util.hpp"
+
+
+static constexpr auto external_sensor =
+    "/xyz/openbmc_project/extsensors/"; // type/
+static constexpr auto openbmc_sensor = "/xyz/openbmc_project/"; // type/
+static constexpr auto sysfs = "/sys/";
+
+
+IOInterfaceType GetWriteInterfaceType(const std::string& path)
+{
+    std::string::size_type n;
+
+    if (path.empty() || "None" == path)
+    {
+        return IOInterfaceType::NONE;
+    }
+
+    if (path.find(sysfs) != std::string::npos)
+    {
+        // A sysfs read sensor.
+        return IOInterfaceType::SYSFS;
+    }
+
+    return IOInterfaceType::UNKNOWN;
+}
+
+IOInterfaceType GetReadInterfaceType(const std::string& path)
+{
+    std::string::size_type n;
+
+    if (path.empty() || "None" == path)
+    {
+        return IOInterfaceType::NONE;
+    }
+
+    if (path.find(external_sensor) != std::string::npos)
+    {
+        return IOInterfaceType::EXTERNAL;
+    }
+
+    if (path.find(openbmc_sensor) != std::string::npos)
+    {
+        return IOInterfaceType::DBUSPASSIVE;
+    }
+
+    if (path.find(sysfs) != std::string::npos)
+    {
+        return IOInterfaceType::SYSFS;
+    }
+
+    return IOInterfaceType::UNKNOWN;
+}
+