Re: [PATCH] mc146818rtc: add a way to generate RTC interrupts via QMP

[Markus Armbruster]

Daniil Tatianin <d-tatianin@yandex-team.ru> writes:

> This can be used to force-synchronize the time in guest after a long
> stop-cont pause, which can be useful for serverless-type workload.
>
> Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
> ---
>  hw/rtc/mc146818rtc.c         | 15 +++++++++++++++
>  include/hw/rtc/mc146818rtc.h |  1 +
>  qapi/misc-target.json        | 16 ++++++++++++++++
>  3 files changed, 32 insertions(+)
>
> diff --git a/hw/rtc/mc146818rtc.c b/hw/rtc/mc146818rtc.c
> index f4c1869232..6980a78d5f 100644
> --- a/hw/rtc/mc146818rtc.c
> +++ b/hw/rtc/mc146818rtc.c
> @@ -116,6 +116,21 @@ void qmp_rtc_reset_reinjection(Error **errp)
>      }
>  }
>  
> +void qmp_rtc_notify(Error **errp)
> +{
> +    MC146818RtcState *s;
> +
> +    /*
> +     * See:
> +     * https://www.kernel.org/doc/Documentation/virtual/kvm/timekeeping.txt
> +     */
> +    QLIST_FOREACH(s, &rtc_devices, link) {
> +        s->cmos_data[RTC_REG_B] |= REG_B_UIE;
> +        s->cmos_data[RTC_REG_C] |= REG_C_IRQF | REG_C_UF;
> +        qemu_irq_raise(s->irq);
> +    }
> +}
> +

Note for later: qmp_rtc_notify() works on all realized mc146818rtc
devices.  Other kinds of RTC devices are silently ignored.  Just like
qmp_rtc_reset_reinjection().

>  static bool rtc_policy_slew_deliver_irq(MC146818RtcState *s)
>  {
>      kvm_reset_irq_delivered();
> diff --git a/include/hw/rtc/mc146818rtc.h b/include/hw/rtc/mc146818rtc.h
> index 97cec0b3e8..5229dffbbd 100644
> --- a/include/hw/rtc/mc146818rtc.h
> +++ b/include/hw/rtc/mc146818rtc.h
> @@ -56,5 +56,6 @@ MC146818RtcState *mc146818_rtc_init(ISABus *bus, int 
> base_year,
>  void mc146818rtc_set_cmos_data(MC146818RtcState *s, int addr, int val);
>  int mc146818rtc_get_cmos_data(MC146818RtcState *s, int addr);
>  void qmp_rtc_reset_reinjection(Error **errp);
> +void qmp_rtc_notify(Error **errp);
>  
>  #endif /* HW_RTC_MC146818RTC_H */
> diff --git a/qapi/misc-target.json b/qapi/misc-target.json
> index 4e0a6492a9..20457b0acc 100644
> --- a/qapi/misc-target.json
> +++ b/qapi/misc-target.json
> @@ -19,6 +19,22 @@
   ##
   # @rtc-reset-reinjection:
   #
   # This command will reset the RTC interrupt reinjection backlog.  Can
   # be used if another mechanism to synchronize guest time is in effect,
   # for example QEMU guest agent's guest-set-time command.
   #
   # Since: 2.1
   #
   # Example:
   #
   #     -> { "execute": "rtc-reset-reinjection" }
   #     <- { "return": {} }
   ##
>  { 'command': 'rtc-reset-reinjection',
>    'if': 'TARGET_I386' }
>  
> +##
> +# @rtc-notify:
> +#
> +# Generate an RTC interrupt.

Our QMP command to generate NMIs is called inject-nmi.  Call this one
inject-rtc-irq for consistency?  rtc-inject-irq?

> +#
> +# Since: 9.1
> +#
> +# Example:
> +#
> +#     -> { "execute": "rtc-notify" }
> +#     <- { "return": {} }
> +#
> +##
> +{ 'command': 'rtc-notify',
> +  'if': 'TARGET_I386' }
> +

As noted above, both commands silently ignore RTCs other than
mc146818rtc.

They're only available with TARGET_I386.

As long as all machines available with TARGET_I386 can only ever contain
mc146818rtc RTCs, ignoring other RTCs is a non-problem in practice.

Feels a bit fragile to me.  Thoughts?

>  ##
>  # @SevState:
>  #