Better handling of file creation vs existing files

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index 5173464..5098ff8 100644
--- a/fio.h
+++ b/fio.h
@@ -222,6 +222,7 @@
 	FIO_FILE_OPEN		= 1 << 0,	/* file is open */
 	FIO_FILE_UNLINK		= 1 << 1,	/* unlink on close */
 	FIO_FILE_CLOSING	= 1 << 2,	/* file being closed */
+	FIO_FILE_EXISTS		= 1 << 3,	/* no need to create */
 };
 
 /*