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Re: [Qemu-block] [Qemu-devel] [PATCH v7 5/5] shutdown: Expose bool cause

From: Markus Armbruster
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v7 5/5] shutdown: Expose bool cause in SHUTDOWN and RESET events
Date: Tue, 09 May 2017 17:03:52 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux)

Eric Blake <address@hidden> writes:

> On 05/09/2017 07:07 AM, Markus Armbruster wrote:
>> Eric Blake <address@hidden> writes:
>>> Libvirt would like to be able to distinguish between a SHUTDOWN
>>> event triggered solely by guest request and one triggered by a
>>> SIGTERM or other action on the host.  While qemu_kill_report() was
>>> already able to give different output to stderr based on whether a
>>> shutdown was triggered by a host signal (but NOT by a host UI event,
>>> such as clicking the X on the window), that information was then
>>> lost to management.  The previous patches improved things to use an
>>> enum throughout all callsites, so now we have something ready to
>>> expose through QMP.
>>> Here is output from 'virsh qemu-monitor-event --loop' with the
>>> patch installed:
>>> event SHUTDOWN at 1492639680.731251 for domain fedora_13: {"guest":true}
>>> event STOP at 1492639680.732116 for domain fedora_13: <null>
>>> event SHUTDOWN at 1492639680.732830 for domain fedora_13: {"guest":false}
>>> Note that libvirt runs qemu with -no-quit: the first SHUTDOWN event
>> Do you mean -no-shutdown?
> Oh, right. (Too many synonyms to choose from).
>>> was triggered by an action I took directly in the guest (shutdown -h),
>>> at which point qemu stops the vcpus and waits for libvirt to do any
>>> final cleanups; the second SHUTDOWN event is the result of libvirt
>>> sending SIGTERM now that it has completed cleanup.
>> The double shutdown is a bit weird.  To avoid it, we'd have to
>> distinguish between guest shutdown and QEMU termination.  shutdown -h in
>> the guest triggers termination only when QEMU is configured that way.
>> SIGTERM triggers shutdown only when the guest is running.  The result
>> would be neater, but I'm not sure it's worth the extra effort.
> And libvirt is already handling the double event emission - it only
> exposes the first event to the end-user (which is the one that will have
> the correct guest-vs-host flag); the second event (which will always be
> host) is elided because libvirt already knows it passed on the first
> event.  So changing it is outside the scope of this series.


>>> +++ b/vl.c
>>> @@ -1705,8 +1705,8 @@ void qemu_system_reset(ShutdownCause reason)
>>>          qemu_devices_reset();
>>>      }
>>>      if (reason) {
>>> -        /* FIXME update event based on reason */
>>> -        qapi_event_send_reset(&error_abort);
>>> +        qapi_event_send_reset(reason >= SHUTDOWN_CAUSE_GUEST_SHUTDOWN,
>>> +                              &error_abort);
>> Exploits enum ordering.  A comment in the enum definition warning not to
>> reorder its members would be in order.  Defining a suitable predicate
>> right next to it would do, too.
> As in, adding this to sysemu.h?

Yes, right next to the typedef.

> static inline bool shutdown_caused_by_guest(ShutdownCause cause) {
>     return cause >= SHUTDOWN_CAUSE_GUEST_SHUTDOWN;
> }
> I can do that, if you like it.

Works for me.  A suitable comment in the enum would also work.

>> With at least the -no-quit in the commit message fixed (assuming it
>> needs fixing):
> Yes, it does need fixing.
>> Reviewed-by: Markus Armbruster <address@hidden>

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