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

[Daniel Henrique Barboza]

On 10/11/18 4:38 AM, Markus Armbruster wrote:
> 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.

Not adding the wakeup notifier at xen-hvm.c was a mistake. I am under
the assumption that everyone that register a notifier is implementing
wakeup support, which seems reasonable to me (why else would you
want to listen to that event?). Simply put, I failed to check on all 
callers of
qemu_register_wakeup_notifier().

Thanks for noticing it.


> > 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/

ok!

> > +#                          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".

ok!

> > +#
> > +# 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;