Re: [Qemu-devel] [PATCH v5 3/4] shutdown: Add source information to SHUTDOWN and RESET

[Markus Armbruster <armbru@redhat.com>]

Eric Blake <eblake@redhat.com> 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() is
> already able to tell 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 after being printed
> to stderr.  The previous patch prepped things to use an enum
> internally; now it's time to wire it up through all callers, and
> to extend the SHUTDOWN and RESET events to report the details.
>
> Enhance the shutdown request path to take a parameter of which
> way it is being triggered, and update ALL callers.  It would have
> been less churn to keep the common case with no arguments as
> meaning guest-triggered, and only modified the host-triggered
> code paths, via a wrapper function, but then we'd still have to
> audit that I didn't miss any host-triggered spots; changing the
> signature forces us to double-check that I correctly categorized
> all callers.
>
> Since command line options can change whether a guest reset request
> causes an actual reset vs. a shutdown, it's easy to also add the
> information to the RESET event, even though libvirt has not yet
> expressed a need to know that.
>
> For the moment, we keep the enum ShutdownCause for internal use
> only, and merely expose a single boolean of 'guest':true|false
> to the QMP client; this is because we don't yet have evidence that
> the further distinctions will be useful, or whether the addition
> of new enum members would cause problems to clients coded to an
> older version of the enum.
>
> Update expected iotest outputs to match the new data.
>
> 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
> 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 replay driver needs a followup patch if we want to be able to
> faithfully replay the difference between a host- and guest-initiated
> shutdown (for now, the replayed event is always attributed to host).

I'd prefer to get this right from the start, but that requires input
from replay guys.

Scandalously, replay/ is not covered by MAINTAINERS.
scripts/get_maintainers.pl blames it on Pavel Dovgalyuk (cc'ed), and git
shows recent activity.  Pavel, please post a suitable patch to
MAINTAINERS, and please help us figure out what to do about replaying
reset here.

> See also https://bugzilla.redhat.com/1384007
>
> Signed-off-by: Eric Blake <eblake@redhat.com>