While I was auditing the code in xfs_repair that adds feature bits to
existing V5 filesystems, I decided to have a look at how online fsck
handles feature bits, and I found a few problems:

1) ATTR2 is added to the primary super when an xattr is set to a file,
but that isn't consistently propagated to secondary supers.  This isn't
a corruption, merely a discrepancy that repair will fix if it ever has
to restore the primary from a secondary.  Hence, if we find a mismatch
on a secondary, this is a preen condition, not a corruption.

2) There are more compat and ro_compat features now than there used to
be, but we mask off the newer features from testing.  This means we
ignore inconsistencies in the INOBTCOUNT and BIGTIME features, which is
wrong.  Get rid of the masking and compare directly.

3) NEEDSREPAIR, when set on a secondary, is ignored by everyone.  Hence
a mismatch here should also be flagged for preening, and online repair
should clear the flag.  Right now we ignore it due to (2).

4) log_incompat features are ephemeral, since we can clear the feature
bit as soon as the log no longer contains live records for a particular
log feature.  As such, the only copy we care about is the one in the
primary super.  If we find any bits set in the secondary super, we
should flag that for preening, and clear the bits if the user elects to
repair it.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>