Re: How to initiate power-off in quest with new microvm machine type

[Sergio Lopez]

Peter Maydell <address@hidden> writes:

> On Tue, 12 Nov 2019 at 15:22, Waldek Kozaczuk <address@hidden> wrote:
>>
>> Hi,
>>
>> I am referring to the machine type described here - 
>> https://github.com/qemu/qemu/blob/master/docs/microvm.rst. I would like to 
>> know how to initiate power-off sequence from a guest given that ACPI is not 
>> available. On firecracker the only way is generating Ctrl-Alt-Del keyboard 
>> event by writing proper value to the keyboard controller port 0xfe like so:
>>
>> outb(0x64, 0xfe);
>>
>> What is the corresponding mechanism on QEMU with microvm machine?

To shut down the VM from the guest I can think of two options (that we
should probably add to the documentation):

 1. Add "-no-reboot" to the QEMU command line (you'd also need this for
 the keyboard based method) and trigger a triple fault. If you're
 running Linux, you can make this the default by passing "reboot=t" to
 the kernel command line.

 2. Add an isa-debug-exit device and write to its port in a similar way
 you do with the keyboard. There's no need for adding "-no-reboot" to
 the command line, as this will cause QEMU to exit immediately.

That said, we can easily add a knob for attaching a i8042 keyboard to
the microvm machine type. I'm not entirely convinced that this is really
necessary, but if it makes people's life easier, it may be worth it.

Sergio.

> I've cc'd the maintainers of the microvm machine, who hopefully
> will know the answer.
>
> thanks
> -- PMM