bin/56975: fsck_ffs(8) doesn't mention level 5 filesystems

[kre%munnari.OZ.AU@localhost]

>Number:         56975
>Category:       bin
>Synopsis:       fsck_ffs(8) doesn't mention level 5 filesystems
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          doc-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Aug 22 11:55:00 +0000 2022
>Originator:     kre%munnari.OZ.AU@localhost
>Release:        NetBSD 9.99.99
>Organization:
>Environment:
System: NetBSD jacaranda.noi.kre.to 9.99.99 NetBSD 9.99.99 (JACARANDA:1.1-20220811) #17: Sat Aug 13 18:11:47 +07 2022 kre%jacaranda.noi.kre.to@localhost:/usr/obj/testing/kernels/amd64/JACARANDA amd64
Architecture: x86_64
Machine: amd64
>Description:
	The man page for fsck_ffs describes the -c option:

    -c level        Convert the FFSv1 file system to the level level.
                           Note that the level of a file system can only be
                           raised.  There are currently five levels defined:

	and then goes on to describe levels 0 .. 4, and then:

		    Note that FFSv2 file systems are always level 4.

Yet, when I look at one of my filesystems, I see:

file system: /dev/rdk28
format  FFSv2
endian  little-endian
[...]
cylgrp  dynamic inodes  FFSv2   sblock  FFSv2   fslevel 5
[...]

(created by newfs -O2 on a 9.99.9x system (.97 or .98 when it was created).

>How-To-Repeat:
	RTFM.   Examine modern (newly created) filesystems.

>Fix:
	Could someone who knows what the difference between level 4 and
	level 5 is please describe it in fsck_ffs(8) - either in the
	description of the -c option (if -c 5 works, or should work),
	in a new section for thet option for FFSv2, or elsewhere (perhaps
	in that sentence about UFSv2 always being level 4, which obviously
	needs correcting anyway, if the -c option is not intended to be
	used to change a FFSv2 from level 4 to level 5.

	Or, perhaps all FFSv2 are level 5, and always have been, and all
	that is needed is s/4/5/ in that sentence.

	If a FFSv1 can be made level 5, then the intro to the description
	of the -c option probably needs changing, to stop implying that it
	is only relevant to FFSv1 filesystems (assuming that a 4->5 conversion
	for a FFSv2 is possible).