Wrap fsync(2) and fdatasync(2)

This adds two new functions in `System.Posix.Unistd`

 - `fileSynchronise` (aka `fsync(2)`), and
 - `fileSynchroniseDataOnly` (aka `fdatasync(2)`)

This is based on part of #7 and has been heavily refactored from its
original patch submission by Ricardo Catalinas Jiménez.

This also bumps version to 2.7.1.0 as a minor version bump is now needed.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

System/Posix/Unistd.hsc

+{-# LANGUAGE CApiFFI #-}
 {-# LANGUAGE NondecreasingIndentation #-}
 #ifdef __GLASGOW_HASKELL__
 {-# LANGUAGE Trustworthy #-}
@@ -27,6 +28,10 @@ module System.Posix.Unistd (
     -- * Sleeping
     sleep, usleep, nanosleep,
 
+    -- * File synchronisation
+    fileSynchronise,
+    fileSynchroniseDataOnly,
+
   {-
     ToDo from unistd.h:
       confstr,
@@ -55,8 +60,14 @@ import Foreign.C.Error
 import Foreign.C.String ( peekCString )
 import Foreign.C.Types
 import Foreign
+import System.Posix.Types
 import System.Posix.Internals
 
+#if !(HAVE_FSYNC && HAVE_FDATASYNC)
+import System.IO.Error ( ioeSetLocation )
+import GHC.IO.Exception ( unsupportedOperation )
+#endif
+
 -- -----------------------------------------------------------------------------
 -- System environment (uname())
 
@@ -206,3 +217,44 @@ sysconf n = do
 
 foreign import ccall unsafe "sysconf"
   c_sysconf :: CInt -> IO CLong
+
+-- -----------------------------------------------------------------------------
+-- File synchronization
+
+-- | Performs @fsync(2)@ operation on file-descriptor.
+--
+-- Throws 'IOError' (\"unsupported operation\") if platform does not
+-- provide @fsync(2)@ (use @#if HAVE_FSYNC@ CPP guard to
+-- detect availability).
+fileSynchronise :: Fd -> IO ()
+#if HAVE_FSYNC
+fileSynchronise fd = do
+  throwErrnoIfMinus1_ "fileSynchronise" (c_fsync fd)
+
+foreign import capi safe "unistd.h fsync"
+  c_fsync :: Fd -> IO CInt
+#else
+{-# WARNING fileSynchronise
+    "operation will throw exception (CPP guard: @#if HAVE_FSYNC@)" #-}
+fileSynchronise _ = ioError (ioeSetLocation unsupportedOperation
+                             "fileSynchronise")
+#endif
+
+-- | Performs @fdatasync(2)@ operation on file-descriptor.
+--
+-- Throws 'IOError' (\"unsupported operation\") if platform does not
+-- provide @fdatasync(2)@ (use @#if HAVE_FDATASYNC@ CPP guard to
+-- detect availability).
+fileSynchroniseDataOnly :: Fd -> IO ()
+#if HAVE_FDATASYNC
+fileSynchroniseDataOnly fd = do
+  throwErrnoIfMinus1_ "fileSynchroniseDataOnly" (c_fdatasync fd)
+
+foreign import capi safe "unistd.h fdatasync"
+  c_fdatasync :: Fd -> IO CInt
+#else
+{-# WARNING fileSynchroniseDataOnly
+    "operation will throw exception (CPP guard: @#if HAVE_FDATASYNC@)" #-}
+fileSynchroniseDataOnly _ = ioError (ioeSetLocation unsupportedOperation
+                                     "fileSynchroniseDataOnly")
+#endif

changelog.md

 # Changelog for [`unix` package](http://hackage.haskell.org/package/unix)
 
-## 2.7.0.2  *TBA*
+## 2.7.1.0  *Dec 2014*
 
   * Add support for `base-4.8.0.0`
   * Tighten `SafeHaskell` bounds for GHC 7.10+
@@ -17,6 +17,10 @@
   * `executeFile`: Fix `ENOTDIR` error for entries with non-directory
     components in `PATH` (and instead skip over non-directory `PATH`-elements)
 
+  * New functions in `System.Posix.Unistd`:
+     - `fileSynchronise` (aka `fsync(2)`), and
+     - `fileSynchroniseDataOnly` (aka `fdatasync(2)`)
+
 ## 2.7.0.1  *Mar 2014*
 
   * Bundled with GHC 7.8.1

configure.ac

@@ -67,6 +67,9 @@ AC_CHECK_FUNCS([lutimes futimes])
 # Additional temp functions
 AC_CHECK_FUNCS([mkstemps mkdtemp])
 
+# Functions for file synchronization and allocation control
+AC_CHECK_FUNCS([fsync fdatasync])
+
 # Avoid adding rt if absent or unneeded
 # shm_open needs -lrt on linux
 AC_SEARCH_LIBS(shm_open, rt, [AC_CHECK_FUNCS([shm_open shm_unlink])])

unix.cabal

 name:           unix
-version:        2.7.0.2
+version:        2.7.1.0
 -- NOTE: Don't forget to update ./changelog.md
 license:        BSD3
 license-file:   LICENSE