Add specific knob for controlling fallocate() usage

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index 119dc09..bdc1708 100644
--- a/fio.h
+++ b/fio.h
@@ -227,6 +227,7 @@
 	unsigned int file_service_type;
 	unsigned int group_reporting;
 	unsigned int fadvise_hint;
+	unsigned int fallocate;
 	unsigned int zero_buffers;
 	unsigned int refill_buffers;
 	unsigned int time_based;