Re: spapr watchdog vs watchdog_perform_action() / QMP watchdog-set-action

[Markus Armbruster]

Peter Maydell <peter.maydell@linaro.org> writes:

> Hi; one of the "bitesized tasks" we have listed is to convert
> watchdog timers which directly call qemu_system_reset_request() on
> watchdog timeout to call watchdog_perform_action() instead. This
> means they honour the QMP commands that let the user specifiy
> the behaviour on watchdog expiry:
> https://www.qemu.org/docs/master/interop/qemu-qmp-ref.html#qapidoc-141
> https://www.qemu.org/docs/master/interop/qemu-qmp-ref.html#qapidoc-129
> (choices include reset, power off the system, do nothing, etc).
>
> There are only a few remaining watchdogs that don't use the
> watchdog_perform_action() function. In most cases the change
> is obvious and easy: just make them do that instead of calling
> qemu_system_reset_request(SHUTDOWN_CAUSE_GUEST_RESET).
>
> However, the hw/watchdog/spapr_watchdog.c case is trickier. As
> far as I can tell from the sources, this is a watchdog set up via
> a hypercall, and the guest makes a choice of "power off, restart,
> or dump and restart" for its on-expiry action.
>
> What should this watchdog's interaction with the watchdog-set-action
> QMP command be? If the user says "do X" and the guest says "do Y",
> which do we do? (With the current code, we always honour what
> the guest asks for and ignore what the user asks for.)

Gut reaction: when the user says "do X", the guest should not get a say.
But one of the values of X could be "whatever the guest says".

> (The bitesized task for watchdog_perform_action() is
> https://gitlab.com/qemu-project/qemu/-/issues/2124 . For the
> purposes of this email thread I'm only after a concrete decision
> about what we think the right thing is, not for any code. Then
> I can write that up in the bug for potential new contributors.)
>
> thanks
> -- PMM