Add fsck_flags config option

[luporl]

Summary

On UFS with SU+J, sometimes fsck's default recovery from journal marks the filesystem as clean but some errors remain.

With SU only, default fsck in preen mode sometimes thinks all errors have been fixed but some still remain.

To address the issues above, this change proposes a new config option: fsck_flags.
By default it's set to -p, but the user may change it to -y or -f -y, for instance, to force a full fsck after a system crash.

Test Plan

On a system where the root filesystem is UFS with SU, add fsck_flags="-y" to rc.conf.
Force a panic with:
sysctl debug.kdb.panic=1
Reboot and check that a full fsck is performed.

[mckusick]

With the above suggested changes, I agree with this proposal.

libexec/rc/rc.conf

104 ↗

(On Diff #69570)

I suggest adding a comment such as

fsck_flags="-p" # may be changed to -f (or -f -y) to force a full fsck

libexec/rc/rc.d/fsck

28 ↗

(On Diff #69570)

Delete (safely?). Background fsck can only be run with -p

41 ↗

(On Diff #69570)

Delete (safely?). Background fsck can only be run with -p

[luporl]

Address review's comments

[mckusick]

Looks good to me.