L1-A

[Doug Ward]

There seems to be confusion about how L1-A works.  Once the system is
booted, the L1-A sequence is  recognized in the kernel.  The kernel then
calls a routine in the PROM monitor to abort.  Actually, that's the same
routine that the kernel calls as the lasty thing it does during a halt.

At the cost of making system administration marginally harder, you can
disable L1-A in the kernel.  Then the only window of vulnerability will be
while the PROMS are in control and while boot is in control. 

For 4.0, look at:

zs_async.c:  zsa_xsint() -- this has code to detect breaks for terminal
				consoles and for unplugging the keyboard.

kbd.c:	  kbdinput() -- L1-A is caught here.

The part of the code you're interested in is the sequence of events
leading up to "montrap(*romp->v_abortent);".

The setup is pretty much the same in 3.x.

Personally, I think people who want UNIX machines without consoles and
people who want to power cycle hung machines instead of the "L1-A, g0"
sequence crazy, but I understand why the abort key is such a pain to
Universities.

	-daw