The code to walk through the list of discovered devices 
updates the index of the first device (sdev) when it should 
be updating the index of the currect device (tail).

Reference: /n/sources/patch/applied/boot-devsd-probe
Date: Tue Aug  8 17:24:09 CES 2006
Signed-off-by: ejsherry@cgl.uwaterloo.ca

--- /sys/src/boot/pc/devsd.c	Tue Aug  8 17:07:12 2006
+++ /sys/src/boot/pc/devsd.c	Tue Aug  8 17:07:11 2006
@@ -247,7 +247,7 @@
 		else
 			sdlist = sdev;
 		for(tail = sdev; tail->next != nil; tail = tail->next){
-			sdev->index = sdnunit;
+			tail->index = sdnunit;
 			sdnunit += tail->nunit;
 		}
 		tail->index = sdnunit;