Unmapping video memory

[Kristoffer Eriksson]

I have a simple question, that I have been unable to find any answer to:
Is there any way to get rid of the video display memory again, once you
have mapped it into user space?

Maybe the answer is not as simple. A little background: I use SCO Xenix/386
2.3.1, with development system 2.2 (2.3 is not yet available around here).
The display memory of the video adapter can be mapped inte the adress space
of any process, using some ioctl:s described in screen(HW). Once this has
been done, the memory seems to hang around for ever. It does not go away
when the process forks (which seems reasonable), and not when it exec:s
another program either (which could be a natural time to drop it). And no
ioctl is documented to unmap the memory. Sbrk() does not know about this
memory, that I can determine.

I don't want this memory around when I spawn a shell from a process that
first mapped it in. The shell and subsequent programs should not have the
possibility to disturb the display. And furthermore, I suspect some kernel
bug involving mapped video memory, that I want to investigate further.

(The machine is an ALR 386/220.)
-- 
Kristoffer Eriksson, Peridot Konsult AB, Hagagatan 6, S-703 40 Oerebro, Sweden
Phone: +46 19-13 03 60   !  e-mail: ske at pkmab.se
Fax:   +46 19-11 51 03   !  or      ...{uunet,mcvax}!enea!kullmar!pkmab!ske