port-arm/47463: ARM's disksubr_mbr.c is broken for non MBR disk.

[msaitoh%execsw.org@localhost]

>Number:         47463
>Category:       port-arm
>Synopsis:       ARM's disksubr_mbr.c is broken for non MBR disk.
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    port-arm-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jan 18 02:20:00 +0000 2013
>Originator:     SAITOH Masanobu
>Release:        6.0
>Organization:
>Environment:
arm ports which uses arm/arm/disksubr_mbr.c
>Description:
         Many ARM ports use their own function in arm/arm/disksubr_mbr.c
        to check MBR partition table instead of kern/subr_disk_mbr.c.
        It's hard to know perfectly whether the first sector is the MBR
        or normal boot sector but MI subr_disk_mbr.c is not so bad.
        For ARM dissubr_mbr.c, it's very poor to check whether the first
        sector is MBR or not. It checks only whether the last two bytes
        (offset 0x1fe - 0x1ff) has the magic number.

          We should check each partition table like MI subr_disk_mbr.c
         or switch to use it.
>How-To-Repeat:
        Inset USB FLASH memory which hash no MBR and use disklabel.
>Fix:
        Sync with kern/subr_disk_mbr.c or switch to use kern/subr_disk_mbr.c