Add code to make handling domain poweroff/reboot symmetrical
between paravirtualized and fully virtualized.

A paravirtualized domain uses sched_op to shut down and set the
reason code. This will send a VIRQ_DOM_EXC, which can be
handled in dom0 by control software.  In some ways, this resembles
SIGCHILD/waitpid, and is a reasonable model.

The fully virtualized case has qemu invoke xm directly. This is a
different path than paravirtualized. It also removes
decision and policy making choices from the rest of the control
software and places it within qemu. When any dom0 logic
eventually gets a VIRQ_DOM_EXC, the information about the
domain is gone having been destroyed by xm.

It would be useful if all shutdown/reboot operations were
symmetrical from domain 0's point of view. One approach
would be to redefine sched_op to handle other domains than
the current domain, but this seemed excessive. Another
approach, which is what this patch implements, adds
a DOM0 hypervisor call very similar to the existing
DOM0_DESTROYDOMAIN, called DOM0_SHUTDOWNDOMAIN, which handles
the shutdown and reason -- basically, just like a
paravirtualized system.

Like DOM0_DESTROYDOMAIN, add a xenctrl wrapper, and have qemu
call it.

With this change, both domain types shutdown/reboot using
the same dom0 management logic. All control decisions are
removed from qemu, which now simply handles the request
and reason. At a very high level, the flow is "notify of
shutdown and reason", "send VIRQ_DOM_EXC", process, and
destroy domain.  Paravirtualized and fully-virtualized
domains would differ slightly in the first step of
notification.  Paravirtualized continues to use sched_op,
fully virtualized uses DOM0_SHUTDOWNDOMAIN. The rest
of the steps would be identical in both cases.

Or, back to the opening sentence, make the operations as
symmetrical as possible.

(As a freebie, #if 0 some very verbose logging code in qemu.
  Totally unrelated, but as long as I was there...)

Signed-off-by: Ben Thomas (ben@virtualiron.com)


-- 
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Ben Thomas                                         Virtual Iron Software
bthomas@virtualiron.com                            Tower 1, Floor 2
978-849-1214                                       900 Chelmsford Street
                                                    Lowell, MA 01851