The 4kn support in current bios specific biosdisk.c is broken, as the code
is only implementing the support for the 512B sector size.
This work is bilding the support for custom size sectors, we still do assume
the requested data to be multiple of 512B blocks and we only do address the
biosdisk.c interface here.
For reference, see also:
https://www.illumos.org/issues/8303
https://www.illumos.org/rb/r/547
As of the time of the creation this diff, the GELI bits are not done, so
this is not yet the complete review.