It seems that the mode sense function in st.c isn't there to do a mode
sense. It is there to read the tape density and probably some other
parameters that just happen to require a mode sense. It is not possible
to ask the st_mode_sense function to return any code pages at all, which
rather begs the question 'why bother?' There is a scsipi_mode_sense function,
but the st driver seems to ignore it. 

Does anybody mind if I tidy this up while I work with Manuel Bouyer on
the ATAPI tape code? I expect it's just bit rot.

Cheers
Lloyd