(i had to make a small but disgusting change to the MI scsi code,
   because there isn't a way to find out which target/unit a particular
   device is on, well, at least not when dk_establish() is called. i'm
   searching for a better change to the scsi code, but nothing looks
   better at the moment.)

One of the other ports (Amiga, I think), after some discussion with
me, added a routine to the SCSI code that will look up the device's
unit number based on a bus:target:lun triplet.  This is very easy to
do.