bin/56942: fsck_ffs can't replay wapbl journals to memory

[dholland%NetBSD.org@localhost]

>Number:         56942
>Category:       bin
>Synopsis:       fsck_ffs can't replay wapbl journals to memory
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jul 27 01:05:00 +0000 2022
>Originator:     David A. Holland
>Release:        NetBSD 9.99.99 (20220726)
>Organization:
>Environment:
n/a
>Description:

I discovered recently that although fsck_ffs -n claims it's replaying
the journal, it actually doesn't, because fsck doesn't have the
infrastructure necessary to support replaying the journal without
writing to disk.

I fixed the prints so it no longer claims this; however, since running
fsck without having replayed the journal isn't especially meaningful
or helpful, it would be better to add this functionality.

>How-To-Repeat:

crash, fsck -n, observe inconsistencies, mount and unmount (which
replays the journal), fsck -n again, inconsistencies have disappeared.

>Fix:

SMOP but not entirely trivial :-|