I recently ran into some extent buffer indexing issue which turned to be
my fault in code I was working on. But while looking into these I found
an old patch from Lachlan McIlroy that tried to fix various issue in
that area. I went through them slowly to understand what's going on and
ended up with this series. The first patch is not actually related but
touches the area and was in my queue so I've decided to include it.
The second patch removes the if_lastex field in struct xfs_ifork as it's
not actually needed and just makes the code using it confusing. The
following patches fixes various places that feed too large indices into
xfs_iext_get_ext or xfs_iext_idx_to_irec, and the last patch finally
adds asserts into these to catch the incorrect accesses.