kern/56271: default cgdroot setup doesn't work on systems using wedges

[ky0ko%disroot.org@localhost]

>Number:         56271
>Category:       kern
>Synopsis:       default cgdroot setup doesn't work on systems using wedges
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jun 23 08:35:00 +0000 2021
>Originator:     linear
>Release:        9.2
>Organization:
>Environment:
NetBSD  9.2 NetBSD 9.2 (GENERIC) #0: Wed May 12 13:15:55 UTC 2021  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64
>Description:
the default cgdroot setup does not work properly on systems that use wedges and a fake disklabel, such as amd64 uefi systems. it only attempts to mount wd0a or ld0a, which does not map to a valid filesystem - all the partitions are mapped to /dev/dkX instead.
>How-To-Repeat:

>Fix:
a quick fix would be to add dk0 (and maybe dk1) to the list of devices that it tries to mount.

a nicer fix would be not to have a hardcoded list at all but to instead implement a way for the bootloader to pass in the device name to try and mount. this would also work around the fact that the first partition (dk0) on uefi setups is generally msdosfs by necessity, and therefore not ideal for this setup