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Re: [Qemu-devel] [PATCH for-3.2 v10 3/3] qmp hmp: Make system_wakeup che

From: Daniel Henrique Barboza
Subject: Re: [Qemu-devel] [PATCH for-3.2 v10 3/3] qmp hmp: Make system_wakeup check wake-up support and run state
Date: Tue, 4 Dec 2018 16:36:56 -0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1

On 11/29/18 4:55 PM, Markus Armbruster wrote:
One more thing...

Markus Armbruster <address@hidden> writes:

Daniel Henrique Barboza <address@hidden> 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

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

Reported-by: Balamuruhan S <address@hidden>
Signed-off-by: Daniel Henrique Barboza <address@hidden>
  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);
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.



More of the same elsewhere.


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