diff --git a/kernel/file.h b/kernel/file.h
index 5cf15a2..b076d1d 100644
--- a/kernel/file.h
+++ b/kernel/file.h
@@ -9,6 +9,9 @@ struct file {
   short major;       // FD_DEVICE
 };
 
+#define major(dev)  ((dev) >> 16 & 0xFFFF)
+#define minor(dev)  ((dev) & 0xFFFF)
+#define	mkdev(m,n)  ((uint)((m)<<16| (n)))
 
 // in-memory copy of an inode
 struct inode {