os-mac.h: implement fio_set_odirect()

Signed-off-by: Steven Noonan <snoonan@amazon.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/os/os-mac.h b/os/os-mac.h
index 1d67141..42e1fea 100644
--- a/os/os-mac.h
+++ b/os/os-mac.h
@@ -2,6 +2,7 @@
 #define FIO_OS_APPLE_H
 
 #include <errno.h>
+#include <fcntl.h>
 #include <sys/disk.h>
 #include <sys/sysctl.h>
 #include <sys/time.h>
@@ -107,6 +108,14 @@
 	return 0;
 }
 
+#define FIO_OS_DIRECTIO
+static inline int fio_set_odirect(int fd)
+{
+	if (fcntl(fd, F_NOCACHE, 1) == -1)
+		return errno;
+	return 0;
+}
+
 static inline int blockdev_size(struct fio_file *f, unsigned long long *bytes)
 {
     uint64_t temp = 1;