diff --git a/CMakeLists.txt b/CMakeLists.txt
index 167a7ac..3d94a95 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,14 +4,18 @@ cmake_minimum_required(VERSION 2.8)
 
 include(FindOpenSSL)
 
+include_directories( ${grive_SOURCE_DIR}/src )
+
 add_executable( grive
 	src/main.cc
-	src/OAuth2.cc
-	src/Drive.cc
-	src/Collection.cc
+	src/drive/Collection.cc
+	src/drive/Drive.cc
+	src/protocol/Download.cc
 	src/protocol/HTTP.cc
 	src/protocol/Json.cc
-	src/protocol/Download.cc )
+	src/protocol/OAuth2.cc
+	src/util/OS.cc
+)
 
 target_link_libraries( grive
 	curl
diff --git a/src/Collection.cc b/src/drive/Collection.cc
similarity index 96%
rename from src/Collection.cc
rename to src/drive/Collection.cc
index f660dfc..8fc5ce5 100644
--- a/src/Collection.cc
+++ b/src/drive/Collection.cc
@@ -20,13 +20,10 @@
 #include "Collection.hh"
 
 #include "protocol/Json.hh"
+#include "util/OS.hh"
 
 #include <cassert>
 
-// OS specific library
-#include <sys/stat.h>
-#include <sys/types.h>
-
 // for debugging
 #include <iostream>
 
@@ -104,7 +101,8 @@ void Collection::Swap( Collection& coll )
 void Collection::CreateSubDir( const std::string& prefix )
 {
 	std::string dir = prefix + m_title ;
-	mkdir( dir.c_str(), 0700 ) ;
+// 	mkdir( dir.c_str(), 0700 ) ;
+	os::MakeDir( dir ) ;
 	
 	for ( std::vector<Collection*>::iterator i = m_child.begin() ; i != m_child.end() ; ++i )
 	{
diff --git a/src/Collection.hh b/src/drive/Collection.hh
similarity index 100%
rename from src/Collection.hh
rename to src/drive/Collection.hh
diff --git a/src/Drive.cc b/src/drive/Drive.cc
similarity index 99%
rename from src/Drive.cc
rename to src/drive/Drive.cc
index 60c0ca5..06267ca 100644
--- a/src/Drive.cc
+++ b/src/drive/Drive.cc
@@ -21,7 +21,7 @@
 
 #include "protocol/HTTP.hh"
 #include "protocol/Json.hh"
-#include "OAuth2.hh"
+#include "protocol/OAuth2.hh"
 
 // dependent libraries
 #include <openssl/evp.h>
diff --git a/src/Drive.hh b/src/drive/Drive.hh
similarity index 100%
rename from src/Drive.hh
rename to src/drive/Drive.hh
diff --git a/src/main.cc b/src/main.cc
index 4df7d9e..1d1c123 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -17,8 +17,8 @@
 	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */
 
-#include "OAuth2.hh"
-#include "Drive.hh"
+#include "drive/Drive.hh"
+#include "protocol/OAuth2.hh"
 #include "protocol/Json.hh"
 
 #include <cassert>
diff --git a/src/OAuth2.cc b/src/protocol/OAuth2.cc
similarity index 100%
rename from src/OAuth2.cc
rename to src/protocol/OAuth2.cc
diff --git a/src/OAuth2.hh b/src/protocol/OAuth2.hh
similarity index 100%
rename from src/OAuth2.hh
rename to src/protocol/OAuth2.hh
diff --git a/src/util/OS.cc b/src/util/OS.cc
new file mode 100644
index 0000000..a69dd2f
--- /dev/null
+++ b/src/util/OS.cc
@@ -0,0 +1,33 @@
+/*
+	grive: an GPL program to sync a local directory with Google Drive
+	Copyright (C) 2012  Wan Wai Ho
+
+	This program is free software; you can redistribute it and/or
+	modify it under the terms of the GNU General Public License
+	as published by the Free Software Foundation version 2
+	of the License.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with this program; if not, write to the Free Software
+	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+*/
+
+#include "OS.hh"
+
+// OS specific headers
+#include <sys/stat.h>
+#include <sys/types.h>
+
+namespace gr { namespace os {
+
+void MakeDir( const std::string& dir )
+{
+	mkdir( dir.c_str(), 0700 ) ;
+}
+
+} } // end of namespaces
diff --git a/src/util/OS.hh b/src/util/OS.hh
new file mode 100644
index 0000000..59d542e
--- /dev/null
+++ b/src/util/OS.hh
@@ -0,0 +1,28 @@
+/*
+	grive: an GPL program to sync a local directory with Google Drive
+	Copyright (C) 2012  Wan Wai Ho
+
+	This program is free software; you can redistribute it and/or
+	modify it under the terms of the GNU General Public License
+	as published by the Free Software Foundation version 2
+	of the License.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with this program; if not, write to the Free Software
+	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+*/
+
+#pragma once
+
+#include <string>
+
+namespace gr { namespace os {
+
+void MakeDir( const std::string& dir ) ;
+
+} } // end of namespaces