[PATCH] Shrink io_u a little

->index and ->seen can share the same space, they are both io engine
private.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index dc2f84b..921282c 100644
--- a/fio.h
+++ b/fio.h
@@ -66,14 +66,20 @@
 	char *buf;
 	unsigned int buflen;
 	unsigned long long offset;
-	unsigned int index;
 
 	unsigned int resid;
 	unsigned int error;
 
-	unsigned char seen;
 	unsigned char ddir;
 
+	/*
+	 * io engine private data
+	 */
+	union {
+		unsigned int index;
+		unsigned int seen;
+	};
+
 	struct fio_file *file;
 
 	struct list_head list;