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Re: [Qemu-devel] [PATCH v6 1/2] qmp: adding 'wakeup-suspend-support' in

From: Daniel Henrique Barboza
Subject: Re: [Qemu-devel] [PATCH v6 1/2] qmp: adding 'wakeup-suspend-support' in query-target
Date: Thu, 17 May 2018 09:35:01 -0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0

On 05/17/2018 05:44 AM, Markus Armbruster wrote:
Daniel Henrique Barboza <address@hidden> writes:

On 05/15/2018 12:45 PM, 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 there are only two subscribers of the wake up event: one
in hw/acpi/core.c and another one in hw/i386/xen/xen-hvm.c. This means
that system_wakeup does not work as intended with other architectures.

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 adds a new flag called 'wakeup-suspend-support' in TargetInfo
that allows the caller to query if the guest supports wake up from
suspend via system_wakeup. It goes over the subscribers of the wake up
event and, if it's empty, it assumes that the guest does not support
wake up from suspend (and thus, pm-suspend itself).

This is the expected output of query-target when running a x86 guest:

{"execute" : "query-target"}
{"return": {"arch": "x86_64", "wakeup-suspend-support": true}}

This is the output when running a pseries guest:

{"execute" : "query-target"}
{"return": {"arch": "ppc64", "wakeup-suspend-support": false}}

Given that the TargetInfo structure is read-only, adding a new flag to
it is backwards compatible. There is no need to deprecate the old
TargetInfo format.

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.

Reported-by: Balamuruhan S <address@hidden>
Signed-off-by: Daniel Henrique Barboza <address@hidden>
   arch_init.c             |  1 +
   include/sysemu/sysemu.h |  1 +
   qapi/misc.json          |  4 +++-
   vl.c                    | 21 +++++++++++++++++++++
   4 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/arch_init.c b/arch_init.c
index 9597218ced..67bdf27528 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -115,6 +115,7 @@ TargetInfo *qmp_query_target(Error **errp)
         info->arch = qapi_enum_parse(&SysEmuTarget_lookup,
+    info->wakeup_suspend_support = !qemu_wakeup_notifier_is_empty();
Huh?  Hmm, see "hack" below.

         return info;
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 544ab77a2b..fbe2a3373e 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -69,6 +69,7 @@ typedef enum WakeupReason {
   void qemu_system_reset_request(ShutdownCause reason);
   void qemu_system_suspend_request(void);
   void qemu_register_suspend_notifier(Notifier *notifier);
+bool qemu_wakeup_notifier_is_empty(void);
   void qemu_system_wakeup_request(WakeupReason reason);
   void qemu_system_wakeup_enable(WakeupReason reason, bool enabled);
   void qemu_register_wakeup_notifier(Notifier *notifier);
diff --git a/qapi/misc.json b/qapi/misc.json
index f5988cc0b5..a385d897ae 100644
--- a/qapi/misc.json
+++ b/qapi/misc.json
@@ -2484,11 +2484,13 @@
   # Information describing the QEMU target.
   # @arch: the target architecture
+# @wakeup-suspend-support: true if the target supports wake up from
+#                          suspend (since 2.13)
   # Since: 1.2.0
   { 'struct': 'TargetInfo',
-  'data': { 'arch': 'SysEmuTarget' } }
+  'data': { 'arch': 'SysEmuTarget', 'wakeup-suspend-support': 'bool' } }
   # @query-target:
Does the documentation of system_wakeup need fixing?

     # @system_wakeup:
     # Wakeup guest from suspend.  Does nothing in case the guest isn't 
     # Since:  1.1
     # Returns:  nothing.
     # Example:
     # -> { "execute": "system_wakeup" }
     # <- { "return": {} }
     { 'command': 'system_wakeup' }

I figure we better explain right here what the command does, both for
wakeup-suspend-support: false and true.
Hmm, I've re-sent a patch that changes a bit the behavior of system_wakeup
yesterday. The command should now fail with an error if the VM isn't in
SUSPENDED state. However, I failed to update this documentation
in that patch.

What if I resend that system_wakeup patch with the updated
documentation such

    # @system_wakeup:
    # Wakeup guest from suspend.  Throws an error in case the guest isn't 
    # Since:  1.1
    # Returns:  nothing if succeed

And then I believe we don't need to update this doc again - if the
guest isn't suspended,
  system_wakeup will still fire up an error.
What about a guest that is suspended under a QEMU that isn't capable of
waking it?

Shouldn't system_wakeup's documentation point to query-target's

Fair enough.

In fact, I could have added that patch in this series too since it
kind of relates with these
changes as well. Let me know if you think it helps and I'll respin it
together with this
Respinning in a single series is the simplest way to ensure the patches
get committed in a sane order.  I'd appreciate that.

I'll respin all together.




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