ocfs2: fix ocfs2_sync_file() if filesystem is readonly

If filesystem is readonly, there is no need to flush drive's caches or
force any uncommitted transactions.

[akpm@linux-foundation.org: return -EROFS, not 0]
Signed-off-by: Younger Liu <younger.liucn@gmail.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/file.c

@@ -185,6 +185,9 @@ static int ocfs2_sync_file(struct file *file, loff_t start, loff_t end,
 			      file->f_path.dentry->d_name.name,
 			      (unsigned long long)datasync);
 
+	if (ocfs2_is_hard_readonly(osb) || ocfs2_is_soft_readonly(osb))
+		return -EROFS;
+
 	err = filemap_write_and_wait_range(inode->i_mapping, start, end);
 	if (err)
 		return err;