amd64/159222: unusual behavior writing boot0 from single user mode

[tim newsham]

>Number:         159222
>Category:       amd64
>Synopsis:       unusual behavior writing boot0 from single user mode
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    freebsd-amd64
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Wed Jul 27 06:30:08 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator:     tim newsham
>Release:        8.2
>Organization:
>Environment:
FreeBSD hpsux.x0d99.com 8.2-RELEASE FreeBSD 8.2-RELEASE #0: Thu Feb 17 02:41:51 UTC 2011     root at mason.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  amd64

>Description:
I boot single user, then I run "df" to see which disk is root.  Then I run:

   # fdisk -B -b /boot/boot0 /dev/da0

when its done it says "/boot/boot0: Device not configured" (error varies)
and then afterwards most commands I type (like "ls") ellicit: "vnode_pager_getpages: I/O read error" from the kernel.

I get the same behavior on my real machine as well as in vmware.  The vmware has a clean 8.2 release installed off of DVD (8.2 release disk) and then updated with "freebsd-update".

>How-To-Repeat:
Install 8.2 release for amd64.
Update with freebsd-update (I don't know if this matters).
Boot single user.
Run "fdisk -B -b /boot/boot0 /dev/da0" (or whatever the root disk drive is).
Run "ls" after it completes.
>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted: