Define OS preferred IO engine

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/options.c b/options.c
index 67d0d2d..de2d037 100644
--- a/options.c
+++ b/options.c
@@ -918,7 +918,7 @@
 		.type	= FIO_OPT_STR_STORE,
 		.off1	= td_var_offset(ioengine),
 		.help	= "IO engine to use",
-		.def	= "sync",
+		.def	= FIO_PREFERRED_ENGINE,
 		.posval	= {
 			  { .ival = "sync",
 			    .help = "Use read/write",
diff --git a/os/os-windows.h b/os/os-windows.h
index 9edacf3..e790a51 100644
--- a/os/os-windows.h
+++ b/os/os-windows.h
@@ -22,6 +22,8 @@
 

 #define OS_CLOCK CLOCK_REALTIME

 

+#define FIO_PREFERRED_ENGINE	"windowsaio"

+

 typedef off_t off64_t;

 

 typedef struct {

diff --git a/os/os.h b/os/os.h
index 92b6950..1569e40 100644
--- a/os/os.h
+++ b/os/os.h
@@ -102,6 +102,10 @@
 #define fio_lookup_raw(dev, majdev, mindev)	1
 #endif
 
+#ifndef FIO_PREFERRED_ENGINE
+#define FIO_PREFERRED_ENGINE	"sync"
+#endif
+
 #ifndef FIO_HAVE_BLKTRACE
 static inline int is_blktrace(const char *fname)
 {