9fs kfs on a diskless terminal causes disk/kfs to suicide
when it fails to open the device. This patch adds a check.

I cannot see how this will prevent kfs standalone machines
from booting but somone who knows more should think about it.

-Steve

Reference: /n/sources/patch/applied/kfs-dev-exists
Date: Fri Jan 28 15:58:28 CET 2005

--- /sys/src/cmd/disk/kfs/main.c	Fri Jan 28 15:58:28 2005
+++ /sys/src/cmd/disk/kfs/main.c	Fri Jan 28 15:58:28 2005
@@ -97,6 +97,9 @@
 
 	cmdfd = 2;
 
+	if (access(wrenfile, 6) == -1)
+		sysfatal("%s cannot access device\n", wrenfile);
+
 	formatinit();
 	sublockinit();