from netbsd:

from netbsd:
If the read or write request can fit into a 6-byte cdb, then
use a 6-byte cdb, otherwise use the 10-byte as before.
In sdattach(), make a note if the device is "ancient" (i.e.
inqbuf.version & SID_ANSII == 0).
Implement sdminphys(): if the device is "ancient", shorten the
transfer so it will fit into a 6-byte cdb.

In sdminphys(), add a comment about the semantics of the "length" field
in a 6-byte read/write cdb (namely, length == 0 really means 256), and
that we handle this conservatively by limiting the transfer to 255 blocks.
*sigh* One just never knows how a pre-scsi-1 device is going to behave.

Remove a couple of now unneeded assignments.