add varargchk to io.h to allow use outside pci.c
extend %T to be used with tbdf == BUSUNKNOWN
without this change BUSUNKNOWN -> type < 0
which results in a negative index with bustypes[].
for example, an ide device could be BUSUNKNOWN
or a valid pci or isa device.

Reference: /n/sources/patch/applied/tbdffmt
Date: Mon Jul 13 04:53:50 CES 2009
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/pc/pci.c	Mon Jul 13 04:53:36 2009
+++ /sys/src/9/pc/pci.c	Mon Jul 13 04:53:33 2009
@@ -60,7 +60,7 @@
 static Lock pcicfglock;
 static Lock pcicfginitlock;
 static int pcicfgmode = -1;
-static int pcimaxbno = 7;
+static int pcimaxbno = 15;
 static int pcimaxdno;
 static Pcidev* pciroot;
 static Pcidev* pcilist;
@@ -97,13 +97,12 @@
 	"XPRESS",
 };
 
-#pragma	varargck	type	"T"	int
-
 static int
 tbdffmt(Fmt* fmt)
 {
 	char *p;
-	int l, r, type, tbdf;
+	int l, r;
+	uint type, tbdf;
 
 	if((p = malloc(READSTR)) == nil)
 		return fmtstrcpy(fmt, "(tbdfconv)");
@@ -111,13 +110,17 @@
 	switch(fmt->r){
 	case 'T':
 		tbdf = va_arg(fmt->args, int);
-		type = BUSTYPE(tbdf);
-		if(type < nelem(bustypes))
-			l = snprint(p, READSTR, bustypes[type]);
-		else
-			l = snprint(p, READSTR, "%d", type);
-		snprint(p+l, READSTR-l, ".%d.%d.%d",
-			BUSBNO(tbdf), BUSDNO(tbdf), BUSFNO(tbdf));
+		if(tbdf == BUSUNKNOWN)
+			snprint(p, READSTR, "unknown");
+		else{
+			type = BUSTYPE(tbdf);
+			if(type < nelem(bustypes))
+				l = snprint(p, READSTR, bustypes[type]);
+			else
+				l = snprint(p, READSTR, "%d", type);
+			snprint(p+l, READSTR-l, ".%d.%d.%d",
+				BUSBNO(tbdf), BUSDNO(tbdf), BUSFNO(tbdf));
+		}
 		break;
 
 	default:
--- /sys/src/9/pc/io.h	Mon Jul 13 04:53:43 2009
+++ /sys/src/9/pc/io.h	Mon Jul 13 04:53:41 2009
@@ -369,3 +369,6 @@
 	int	time;
 	PCMmap	mmap[4];	/* maps, last is always for the kernel */
 };
+
+#pragma varargck	type	"T"	int
+#pragma varargck	type	"T"	uint