[Lguest] reserving interrupts

[ron minnich]

I thought I would drop this idea on the list so the kernel experts can
tell me if this is ok.

Problem: I need to reserve a few interrupts for guests that use a
SYSCALL_VECTOR other than 0x80. Currently, io_apic.c grabs just about
every interrupt there is, although (on my laptop) it uses few of them.

I am thinking to use pre_setup_arch_hook for this. It would check for
a list of values in a new reserved_interrupts parameter, and set a bit
in a bitmask (reserved_interrupts).

In the i8259.c and io_apic.c code, the check for SYSCALL_VECTOR would
remain, but an additional check against reserved_interrupts would be
added, and any interrupts in that mask would not be used by the
hardware.

Does this seem roughly ok?

I think it's pretty straightforward and might work well for other CPUs.

Thanks

ron