Re: [Qemu-devel] [PATCH v9 1/3] qmp: query-current-machine with wakeup-suspend-support

[Markus Armbruster]

Daniel Henrique Barboza <address@hidden> writes:

> When issuing the qmp/hmp 'system_wakeup' command, what happens in a
> nutshell is:
>
> - qmp_system_wakeup_request set runstate to RUNNING, sets a wakeup_reason
> and notify the event
> - in the main_loop, all vcpus are paused, a system reset is issued, all
> subscribers of wakeup_notifiers receives a notification, vcpus are then
> resumed and the wake up QAPI event is fired
>
> Note that this procedure alone doesn't ensure that the guest will awake
> from SUSPENDED state - the subscribers of the wake up event must take
> action to resume the guest, otherwise the guest will simply reboot. At
> this moment, only the ACPI machines via acpi_pm1_cnt_init has wake-up
> from suspend support.
>
> However, only the presence of 'system_wakeup' is required for QGA to
> support 'guest-suspend-ram' and 'guest-suspend-hybrid' at this moment.
> This means that the user/management will expect to suspend the guest using
> one of those suspend commands and then resume execution using system_wakeup,
> regardless of the support offered in system_wakeup in the first place.
>
> This patch creates a new API called query-current-machine [1], that holds
> a new flag called 'wakeup-suspend-support' that indicates if the guest
> supports wake up from suspend via system_wakeup. The machine is considered
> to implement wake-up support if a call to a new 'qemu_register_wakeup_support'
> is made during its init, as it is now being done inside acpi_pm1_cnt_init.
> This allows for any other machine type to declare wake-up support regardless
> of ACPI state or wakeup_notifiers subscription, making easier for
> newer implementations that might have its own mechanisms in the future.
>
> This is the expected output of query-current-machine when running a x86
> guest:
>
> {"execute" : "query-current-machine"}
> {"return": {"wakeup-suspend-support": true}}
>
> Running the same x86 guest, but with the --no-acpi option:
>
> {"execute" : "query-current-machine"}
> {"return": {"wakeup-suspend-support": false}}
>
> This is the output when running a pseries guest:
>
> {"execute" : "query-current-machine"}
> {"return": {"wakeup-suspend-support": false}}
>
> With this extra tool, management can avoid situations where a guest
> that does not have proper suspend/wake capabilities ends up in
> inconsistent state (e.g.
> https://github.com/open-power-host-os/qemu/issues/31).
>
> [1] the decision of creating the query-current-machine API is based
> on discussions in the QEMU mailing list where it was decided that
> query-target wasn't a proper place to store the wake-up flag, neither
> was query-machines because this isn't a static property of the
> machine object. This new API can then be used to store other
> dynamic machine properties that are scattered around the code
> ATM. More info at:
> https://lists.gnu.org/archive/html/qemu-devel/2018-05/msg04235.html
>
> Reported-by: Balamuruhan S <address@hidden>
> Signed-off-by: Daniel Henrique Barboza <address@hidden>
> ---
>  hw/acpi/core.c          |  1 +
>  include/sysemu/sysemu.h |  1 +
>  qapi/misc.json          | 24 ++++++++++++++++++++++++
>  vl.c                    | 19 +++++++++++++++++++
>  4 files changed, 45 insertions(+)
>
> diff --git a/hw/acpi/core.c b/hw/acpi/core.c
> index b8d39012cd..2dea893245 100644
> --- a/hw/acpi/core.c
> +++ b/hw/acpi/core.c
> @@ -617,6 +617,7 @@ void acpi_pm1_cnt_init(ACPIREGS *ar, MemoryRegion *parent,
>      ar->pm1.cnt.s4_val = s4_val;
>      ar->wakeup.notify = acpi_notify_wakeup;
>      qemu_register_wakeup_notifier(&ar->wakeup);
> +    qemu_register_wakeup_support();
>      memory_region_init_io(&ar->pm1.cnt.io, memory_region_owner(parent),
>                            &acpi_pm_cnt_ops, ar, "acpi-cnt", 2);
>      memory_region_add_subregion(parent, 4, &ar->pm1.cnt.io);

We might've discussed this before, not sure...  There's a second
qemu_register_wakeup_notifier() in xen-hvm.c.  By not adding
qemu_register_wakeup_support() there, you implicitly state that it
doesn't provide wakeup support.  I have no idea whether that's true.  If
it is, then I think the commit message should explain it.  We might even
want a comment.  Please advise.

> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> index 8d6095d98b..0446adacc6 100644
> --- a/include/sysemu/sysemu.h
> +++ b/include/sysemu/sysemu.h
> @@ -77,6 +77,7 @@ void qemu_register_suspend_notifier(Notifier *notifier);
>  void qemu_system_wakeup_request(WakeupReason reason);
>  void qemu_system_wakeup_enable(WakeupReason reason, bool enabled);
>  void qemu_register_wakeup_notifier(Notifier *notifier);
> +void qemu_register_wakeup_support(void);
>  void qemu_system_shutdown_request(ShutdownCause reason);
>  void qemu_system_powerdown_request(void);
>  void qemu_register_powerdown_notifier(Notifier *notifier);
> diff --git a/qapi/misc.json b/qapi/misc.json
> index d450cfef21..b616d385a4 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -2003,6 +2003,30 @@
>  ##
>  { 'command': 'query-machines', 'returns': ['MachineInfo'] }
>  
> +##
> +# @CurrentMachineParams:
> +#
> +# Information describing the running machine parameters.
> +#
> +# @wakeup-suspend-support: true if the target supports wake up from

s/target/machine/

> +#                          suspend
> +#
> +# Since: 3.1.0
> +##
> +{ 'struct': 'CurrentMachineParams',
> +  'data': { 'wakeup-suspend-support': 'bool'} }
> +
> +##
> +# @query-current-machine:
> +#
> +# Return a list of parameters of the running machine.

"a list of" suggests it returns a QAPI list.  Let's say "Return
information on the current virtual machine".

> +#
> +# Returns: CurrentMachineParams
> +#
> +# Since: 3.1.0
> +##
> +{ 'command': 'query-current-machine', 'returns': 'CurrentMachineParams' }
> +
>  ##
>  # @CpuDefinitionInfo:
>  #
> diff --git a/vl.c b/vl.c
> index 5ba06adf78..f78947f69c 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -184,6 +184,7 @@ bool boot_strict;
>  uint8_t *boot_splash_filedata;
>  size_t boot_splash_filedata_size;
>  uint8_t qemu_extra_params_fw[2];
> +bool wakeup_suspend_enabled;
>  
>  int icount_align_option;
>  
> @@ -1753,6 +1754,24 @@ void qemu_register_wakeup_notifier(Notifier *notifier)
>      notifier_list_add(&wakeup_notifiers, notifier);
>  }
>  
> +void qemu_register_wakeup_support(void)
> +{
> +    wakeup_suspend_enabled = true;
> +}
> +
> +static bool qemu_wakeup_suspend_enabled(void)
> +{
> +    return wakeup_suspend_enabled;
> +}
> +
> +CurrentMachineParams *qmp_query_current_machine(Error **errp)
> +{
> +    CurrentMachineParams *params = g_malloc0(sizeof(*params));
> +    params->wakeup_suspend_support = qemu_wakeup_suspend_enabled();
> +
> +    return params;
> +}
> +
>  void qemu_system_killed(int signal, pid_t pid)
>  {
>      shutdown_signal = signal;