Hi!

quoted

I think the biggest areas of practical concern would be:

 - Can this mechanism ever, under any circumstance corrupt any real
   data, destroy the MBR or do other nasties. Can you think of any
   additional fail-safe measures where you could _further robustify
   the BIOS calls_ to make sure it can never go to the wrong
   sector(s)? I really do not want to think of trusting a BIOS to
   _write to my disk_.

It's quite unlikely but I wouldn't say it's completely impossible.
It's common for ATA controllers to have dual modes of operation - the
old IDE compatible interface by emulation which is used by BIOS and
older operating systems and newer interface (ahci) to be used by
modern OS.  Some need to be explicitly switched and some just need to
be accessed carefully.  If the controller is accessed by bIOS after
switched to ahci or commands are in progress via ahci, anything can
happen.

Could we read the log area, first, verify it contains signature, write
it back?
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html