install/54582: sysinst cannot find disklabel on 9.0_BETA/x68k

[isaki%pastel-flower.jp@localhost]

>Number:         54582
>Category:       install
>Synopsis:       sysinst cannot find disklabel on 9.0_BETA/x68k
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Sep 28 03:25:00 +0000 2019
>Originator:     Tetsuya Isaki
>Release:        9.0_BETA
>Organization:
>Environment:
NetBSD/x68k 9.0_BETA (20190913)
>Description:
On 9.0_BETA/x68k, sysinst cannot find disklabel so that upgrade
installation fails.

  NetBSD-9.0_BETA Install System
  ==> b: Upgrade NetBSD on a hard disk

  Ok, let's upgrade NetBSD on your hard disk. ...
  ==> b: Yes

  On which disk do you want to upgrade NetBSD?
  ==> b: sd0 (2.0G)

  No root partition defined.  Cannot continue
    Hit enter to continue

x68k kernel has used Human68k partition if BSD partition is empty for
long time.  Human68k is X680x0's native OS.
But 9.0 sysinst only reads BSD disklabel directly on raw disk image
and does not fallback to MD partition like kernel does.

According to sys/arch/x68k/include/disklabel.h,
BSD disklabel exists at +64 bytes offset from beginning of the disk and
Human68k partition exists at +2048 bytes offset from beginning.
In fact, my disk which is installed 8.0 (or prior release) has Human68k
partition and no BSD disklabel.

# dd if=/dev/rsd0c bs=1024 count=3 | hexdump -C
 :
00000030  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000400  60 00 00 0c 6d 62 6f 6f  74 20 30 2e 31 00 4f fb  |`...mboot 0.1.O.|
 :
00000800  58 36 38 4b 00 00 00 20  00 1f fc 00 00 1f fc 00  |X68K... ........|
00000810  42 53 44 20 66 66 73 20  00 00 00 20 00 1f b8 00  |BSD ffs ... ....|
00000820  42 53 44 20 73 77 61 70  02 1f b8 20 00 00 43 e0  |BSD swap... ..C.|
00000830  00 00 00 00 00 00 00 00  01 00 00 00 00 00 00 00  |................|
*
>How-To-Repeat:
Boot 9.0_BETA/x68k sysinst and try upgrade installation.
>Fix: