xfs: factor out everything but the filemap_write_and_wait from xfs_file_fsync

Hi,

Fsyncing is tricky business, so factor out the bits of the xfs_file_fsync
function that can be used from the I/O post-processing path.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 54a67dd..e63030f 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -153,25 +153,18 @@ xfs_dir_fsync(
 	return _xfs_log_force_lsn(mp, lsn, XFS_LOG_SYNC, NULL);
 }
 
+/*
+ * Returns 0 on success, -errno on failure.
+ */
 STATIC int
-xfs_file_fsync(
-	struct file		*file,
-	loff_t			start,
-	loff_t			end,
+do_xfs_file_fsync(
+	struct xfs_inode	*ip,
+	struct xfs_mount	*mp,
 	int			datasync)
 {
-	struct inode		*inode = file->f_mapping->host;
-	struct xfs_inode	*ip = XFS_I(inode);
-	struct xfs_mount	*mp = ip->i_mount;
-	int			error = 0;
 	int			log_flushed = 0;
 	xfs_lsn_t		lsn = 0;
-
-	trace_xfs_file_fsync(ip);
-
-	error = filemap_write_and_wait_range(inode->i_mapping, start, end);
-	if (error)
-		return error;
+	int			error = 0;
 
 	if (XFS_FORCED_SHUTDOWN(mp))
 		return -XFS_ERROR(EIO);
@@ -223,6 +216,27 @@ xfs_file_fsync(
 	return -error;
 }
 
+STATIC int
+xfs_file_fsync(
+	struct file		*file,
+	loff_t			start,
+	loff_t			end,
+	int			datasync)
+{
+	struct inode		*inode = file->f_mapping->host;
+	struct xfs_inode	*ip = XFS_I(inode);
+	struct xfs_mount	*mp = ip->i_mount;
+	int			error = 0;
+
+	trace_xfs_file_fsync(ip);
+
+	error = filemap_write_and_wait_range(inode->i_mapping, start, end);
+	if (error)
+		return error;
+
+	return do_xfs_file_fsync(ip, mp, datasync);
+}
+
 STATIC ssize_t
 xfs_file_aio_read(
 	struct kiocb		*iocb,