Re: [Qemu-devel] [Bug 1217339] [PATCH] Unix signal to send ACPI-shutdown to Guest

[Daniel P. Berrange]

On Wed, Mar 15, 2017 at 06:45:57PM +0000, Peter Maydell wrote:
> On 15 March 2017 at 18:08, Daniel P. Berrange <address@hidden> wrote:
> > On Wed, Mar 15, 2017 at 06:00:40PM +0000, Peter Maydell wrote:
> >> On 15 March 2017 at 17:46, Simon <address@hidden> wrote:
> >> > OK for not using SIGHUP and keep SIGTERM, SIGINT and SIGHUP to have the
> >> > same behavior.
> >> >
> >> > SIGQUIT is reserved for core files generation.
> >> >
> >> > SIGUSR1 is already used in 'util/qemu-progress.c' to trigger a report
> >> > on ongoing jobs, so it does not seem usable.
> >> >
> >> > SIGUSR2 is temporarily used in 'util/coroutine-sigaltstack.c' which
> >> > takes care however to preserve the original handler. I did not saw
> >> > any other place where it is used, so it seems to be a better candidate.
> >>
> >> I don't think we can use SIGUSR2 here -- as you say, it's used
> >> in the sigaltstack version of coroutines, and so there would
> >> be races if the user tried to use SIGUSR2 to power down the
> >> machine while we happened to be starting a new coroutine.
> >>
> >> SIGUSR1 is also no good, as it is used by main-loop.c as
> >> the SIG_IPI.
> >
> > Which means we'd be into the realm of having to pick  SIGRTMIN + N for
> > some arbitrary N >= 0
> 
> That's pretty nasty. Why can't we use SIGHUP, again?

Because QEMU already designate that as doing an immediate stop - ie it'll
allow QEMU block layer to flush pending I/O, but it will not wait for the
guest to shutdown.  If we change that behaviour we'll break anyone who
is already relying on SIGHUP - qemu might never exit at all if the guest
ignores the ACPI request


Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://entangle-photo.org       -o-    http://search.cpan.org/~danberr/ :|