kernel refuse to mount a filesystem read-write (booting a system
multiuser with critical filesystems read-only is bad):
Add a check_wapbl() which will check some WAPBL values in the superblock,
and try to read the journal via wapbl_replay_start() if there is one.
pfatal() if one of these fail (abort boot if in preen mode,
as "CONTINUE" otherwise). In non-preen mode the bogus journal will
be cleared.
check_wapbl() is always called if the superblock supports WAPBL.
Even if FS_DOWAPBL is not there, there could be flags asking the
kernel to clear or create a log with bogus values which would cause the
kernel refuse to mount the filesystem.
Discussed in
http://mail-index.netbsd.org/tech-kern/2009/08/17/msg005896.html
and followups.
cab6cd67bc