rough-draft VKERNEL host-initiated shutdown patch

[Chris Turner]

Matthew Dillon wrote:
> 
>     This looks quite nice.  I just realized though that it isn't safe
>     to run reboot() (or probably ksignal either) from the idle halt
>     code, so scratch that part.

thanks. ok.

> 
>     We have to find a good place to put this.  I think what we may have
>     to do is create a kernel thread whos only job is to shut the kernel
>     down, and then check the mailbox from inside signalmailbox() and have
>     it wake the special kernel thread up.
> 
>     Would you like to have a go at that or would you like me to do it?

If the special thread doesn't need to do any other cleanup that I'm
likely unaware of, I can give it another shot this weekend.

Not yet knowing the overall code paths unfortunately means I'm
kind of coding this blind .. but I suppose the point is to learn as I go.

I assume the reason for the thread is that the way things are currently
called, the VK might not be in a consistent internal state when the
signal is delivered to init and/or init is rescheduled to run?

to clarify:

 - keep signal handler and shutdown function in the exception setup
 - create kthread somewhere ( main() ? platform init? )
 - remove checks from both idle loop / task switching areas
 - add check / wakeup logic to signalmailbox()

Thanks,

- Chris