Index: include/io.h
===================================================================
--- include/io.h	(revision 06f6615f7a871c8dba6b55c56185a726a2ebfa1a)
+++ include/io.h	(revision 7af8be4146b7665a3c5d25c39c1ecc2f3b0ff34f)
@@ -11,4 +11,10 @@
 #include "stdint.h"
 
+struct devtabl;
+struct channel;
+
+typedef int16_t (*chclo)(io_arg arg);
+typedef int16_t (*devop)(int8_t *name, int16_t flag, int16_t mode, struct channel *chp, struct devtabl *dp);
+
 struct channel {		/* channel table entry */
 
@@ -17,5 +23,5 @@
 	int8_t	c_ioctl;	/* ioctl routine index */
 	int8_t	c_seek;		/* seek routine index */
-	int16_t	(*c_close)();	/* close function pointer */
+	chclo	c_close;	/* close function pointer */
 	io_arg	c_arg;		/* argument to channel driver */
 };
@@ -27,5 +33,5 @@
 	int8_t	d_ioctl;	/* ioctl routine code */
 	int8_t	d_seek;		/* seek routine code */
-	int16_t	(*d_open)();	/* special open function */
+	devop	d_open;		/* special open function */
 };