libxfs: be more forgiving of a v4 secondary sb w/ junk in v5 fields
[userspace port]
Today, if xfs_sb_read_verify encounters a v4 superblock
with junk past v4 fields which includes data in sb_crc,
it will be treated as a failing checksum and a significant
corruption.
There are known prior bugs which leave junk at the end
of the V4 superblock; we don't need to actually fail the
verification in this case if other checks pan out ok.
So if this is a secondary superblock, and the primary
superblock doesn't indicate that this is a V5 filesystem,
don't treat this as an actual checksum failure.
We should probably check the garbage condition as
we do in xfs_repair, and possibly warn about it
or self-heal, but that's a different scope of work.
Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>