Re: [Qemu-devel] [PATCH for-3.2 v10 3/3] qmp hmp: Make system_wakeup check wake-up support and run state

[Daniel Henrique Barboza <danielhb413@gmail.com>]

On 11/29/18 4:55 PM, Markus Armbruster wrote:
> One more thing...
>
> Markus Armbruster <armbru@redhat.com> writes:
>
>> Daniel Henrique Barboza <danielhb413@gmail.com> writes:
>>
>>> The qmp/hmp command 'system_wakeup' is simply a direct call to
>>> 'qemu_system_wakeup_request' from vl.c. This function verifies if
>>> runstate is SUSPENDED and if the wake up reason is valid before
>>> proceeding. However, no error or warning is thrown if any of those
>>> pre-requirements isn't met. There is no way for the caller to
>>> differentiate between a successful wakeup or an error state caused
>>> when trying to wake up a guest that wasn't suspended.
>>>
>>> This means that system_wakeup is silently failing, which can be
>>> considered a bug. Adding error handling isn't an API break in this
>>> case - applications that didn't check the result will remain broken,
>>> the ones that check it will have a chance to deal with it.
>>>
>>> Adding to that, the commit before previous created a new QMP API called
>>> query-current-machine, with a new flag called wakeup-suspend-support,
>>> that indicates if the guest has the capability of waking up from suspended
>>> state. Although such guest will never reach SUSPENDED state and erroring
>>> it out in this scenario would suffice, it is more informative for the user
>>> to differentiate between a failure because the guest isn't suspended versus
>>> a failure because the guest does not have support for wake up at all.
>>>
>>> All this considered, this patch changes qmp_system_wakeup to check if
>>> the guest is capable of waking up from suspend, and if it is suspended.
>>> After this patch, this is the output of system_wakeup in a guest that
>>> does not have wake-up from suspend support (ppc64):
>>>
>>> (qemu) system_wakeup
>>> wake-up from suspend is not supported by this guest
>>> (qemu)
>>>
>>> And this is the output of system_wakeup in a x86 guest that has the
>>> support but isn't suspended:
>>>
>>> (qemu) system_wakeup
>>> Unable to wake up: guest is not in suspended state
>>> (qemu)
>>>
>>> Reported-by: Balamuruhan S <bala24@linux.vnet.ibm.com>
>>> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
>>> ---
>>>   hmp.c                   |  5 ++++-
>>>   hw/acpi/core.c          |  4 +++-
>>>   hw/char/serial.c        |  3 ++-
>>>   hw/input/ps2.c          |  9 ++++++---
>>>   hw/timer/mc146818rtc.c  |  3 ++-
>>>   include/sysemu/sysemu.h |  3 ++-
>>>   migration/migration.c   |  7 +++++--
>>>   qapi/misc.json          |  8 +++++++-
>>>   qmp.c                   | 13 ++++++++++++-
>>>   vl.c                    |  6 ++++--
>>>   10 files changed, 47 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/hmp.c b/hmp.c
>>> index 7828f93a39..0f5d943413 100644
>>> --- a/hmp.c
>>> +++ b/hmp.c
>>> @@ -1220,7 +1220,10 @@ void hmp_cont(Monitor *mon, const QDict *qdict)
>>>   
>>>   void hmp_system_wakeup(Monitor *mon, const QDict *qdict)
>>>   {
>>> -    qmp_system_wakeup(NULL);
>>> +    Error *err = NULL;
>>> +
>>> +    qmp_system_wakeup(&err);
>>> +    hmp_handle_error(mon, &err);
>>>   }
>>>   
>>>   void hmp_nmi(Monitor *mon, const QDict *qdict)
>>> diff --git a/hw/acpi/core.c b/hw/acpi/core.c
>>> index 52e18d7810..a7073dd435 100644
>>> --- a/hw/acpi/core.c
>>> +++ b/hw/acpi/core.c
>>> @@ -514,7 +514,9 @@ static uint32_t acpi_pm_tmr_get(ACPIREGS *ar)
>>>   static void acpi_pm_tmr_timer(void *opaque)
>>>   {
>>>       ACPIREGS *ar = opaque;
>>> -    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_PMTIMER);
>>> +    Error *err = NULL;
>>> +
>>> +    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_PMTIMER, &err);
>>>       ar->tmr.update_sci(ar);
>>>   }
> Leaks the error object when qemu_system_wakeup_request() fails.
>
> If it cannot fail here, pass &error_abort.
>
> If it can fail, but you want to ignore failure, pass NULL.

Good point. I'll simply pass NULL to all callers that didn't care
for the error prior to this change.



Thanks,


Daniel


>
> More of the same elsewhere.
>
> [...]