I have a SCSI-2 DDS2 tape drive which I'd like to set up to use either
in compressing or non-compressing mode by selecting a different minor
device number.

The existing common SCSI tape code will remember what density codes were
set for a particular minor device, but this tape drive selects
compression modes via a mode select on a particular device-specific
compression page.

DEC's scsi drivers allow a mode page template to be stored for each
{tape device, minor device #} pair, so that you could store a mode page
for non-compressing on the "low density" minor number, and a compressing
selection mode page for a "high density" minor number.

I'm thinking of doing something similar for the NetBSD scsi tape driver,
perhaps allowing an ioctl() on a particular device to execute and store
a particular mode select page.

I'd like to hear comments on whether this should be (a) a compile-time
option (compiled in mode-select page templates), (b) a run-time option
(user-land program specifies a mode-select page via ioctl(2) syscall),
or (c) something else.

==John