add getDiskSize

Couldn't find anything that exposed this for Windows.

Utility/DiskFree.hs

@@ -1,13 +1,16 @@
 {- disk free space checking 
  -
- - Copyright 2012 Joey Hess <joey@kitenet.net>
+ - Copyright 2012, 2014 Joey Hess <joey@kitenet.net>
  -
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
 {-# LANGUAGE ForeignFunctionInterface, CPP #-}
 
-module Utility.DiskFree ( getDiskFree ) where
+module Utility.DiskFree (
+	getDiskFree,
+	getDiskSize
+) where
 
 #ifdef WITH_CLIBS
 
@@ -20,9 +23,12 @@ import Foreign.C.Error
 foreign import ccall safe "libdiskfree.h diskfree" c_diskfree
 	:: CString -> IO CULLong
 
-getDiskFree :: FilePath -> IO (Maybe Integer)
-getDiskFree path = withFilePath path $ \c_path -> do
-	free <- c_diskfree c_path
+foreign import ccall safe "libdiskfree.h disksize" c_disksize
+	:: CString -> IO CULLong
+
+getVal :: (CString -> IO CULLong) -> FilePath -> IO (Maybe Integer)
+getVal getter path = withFilePath path $ \c_path -> do
+	free <- getter c_path
 	ifM (safeErrno <$> getErrno)
 		( return $ Just $ toInteger free
 		, return Nothing
@@ -30,6 +36,12 @@ getDiskFree path = withFilePath path $ \c_path -> do
   where
 	safeErrno (Errno v) = v == 0
 
+getDiskFree :: FilePath -> IO (Maybe Integer)
+getDiskFree = getVal c_diskfree
+
+getDiskSize :: FilePath -> IO (Maybe Integer)
+getDiskSize = getVal c_disksize
+
 #else
 #ifdef mingw32_HOST_OS
 
@@ -41,6 +53,9 @@ getDiskFree :: FilePath -> IO (Maybe Integer)
 getDiskFree path = catchMaybeIO $ do
 	(sectors, bytes, nfree, _ntotal) <- getDiskFreeSpace (Just path)
 	return $ toInteger sectors * toInteger bytes * toInteger nfree
+
+getDiskSize :: FilePath -> IO (Maybe Integer)
+getDiskSize _ = return Nothing
 #else
 
 #warning Building without disk free space checking support
@@ -48,5 +63,8 @@ getDiskFree path = catchMaybeIO $ do
 getDiskFree :: FilePath -> IO (Maybe Integer)
 getDiskFree _ = return Nothing
 
+getDiskSize :: FilePath -> IO (Maybe Integer)
+getDiskSize _ = return Nothing
+
 #endif
 #endif