bin/60874: mount_union(8) references nonexistent content in fsck_ffs(8)

["rwhitlock22%gmail.com@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60874
>Category:       bin
>Synopsis:       mount_union(8) references nonexistent content in fsck_ffs(8)
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          doc-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Oct 14 00:40:00 +0000 2026
>Originator:     Robert Whitlock
>Release:        NetBSD current, Sept 24, 2026
>Organization:
>Environment:
NetBSD thinkpad 11.99.8 NetBSD 11.99.8 (GENERIC) #0: Thu Sep 24 21:53:47 UTC 2026  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64
>Description:
The BUGS section of mount_union(8) says that fsck_ffs(8) can be used to add whiteout support to an existing FFS file system using the -c option. While fsck_ffs(8) decribes the use of the -c option, there is no mention of how to view or change the state of whiteout support for a file system.
>How-To-Repeat:
Read mount_union(8) and fsck_ffs(8).
>Fix:
Find out how to determine whether a file system has whiteout support and document it somewhere.
Correct mount_union(8) to point to this information.