[libvirt] [PATCH v4 3/3] qemuDomainPMSuspendForDuration: check for wake-up support

[Daniel Henrique Barboza]

If the current QEMU guest can't wake up from suspend properly,
and we are able to determine that, avoid suspending the guest
at all. To be able to determine this support, QEMU needs to
implement the 'query-current-machine' QMP call. This is reflected
by the QEMU_CAPS_QUERY_CURRENT_MACHINE cap.

If the cap is enabled, a new function qemuDomainProbeQMPCurrentMachine
is called. This is wrapper for qemuMonitorGetCurrentMachineInfo,
where the 'wakeup-suspend-support' flag is retrieved from
'query-current-machine'. If wakeupSuspendSupport is true,
proceed with the regular flow of qemuDomainPMSuspendForDuration.

The absence of QEMU_CAPS_QUERY_CURRENT_MACHINE indicates that
we're dealing with a QEMU version older than 4.0 (which implements
the required QMP API). In this case, proceed as usual with the
suspend logic of qemuDomainPMSuspendForDuration, since we can't
assume whether the guest has support or not.

Fixes: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1759509
Reported-by: Balamuruhan S <bala24 at linux.vnet.ibm.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413 at gmail.com>
---
 src/qemu/qemu_driver.c | 54 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 31d8647eee..d584f6ae66 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -19145,6 +19145,35 @@ qemuDomainGetCPUStats(virDomainPtr domain,
     return ret;
 }
 
+static int
+qemuDomainProbeQMPCurrentMachine(virQEMUDriverPtr driver,
+                                 virDomainObjPtr vm,
+                                 bool *enabled)
+{
+    qemuMonitorCurrentMachineInfo info = { 0 };
+    qemuDomainObjPrivatePtr priv;
+    int ret = -1;
+
+    *enabled = false;
+    priv = vm->privateData;
+
+    qemuDomainObjEnterMonitor(driver, vm);
+
+    if (qemuMonitorGetCurrentMachineInfo(priv->mon, &info) < 0)
+        goto cleanup;
+
+    ret = 0;
+
+    if (info.wakeupSuspendSupport)
+        *enabled = true;
+
+ cleanup:
+    if (qemuDomainObjExitMonitor(driver, vm) < 0)
+        ret = -1;
+
+    return ret;
+}
+
 static int
 qemuDomainPMSuspendForDuration(virDomainPtr dom,
                                unsigned int target,
@@ -19152,6 +19181,7 @@ qemuDomainPMSuspendForDuration(virDomainPtr dom,
                                unsigned int flags)
 {
     virQEMUDriverPtr driver = dom->conn->privateData;
+    qemuDomainObjPrivatePtr priv;
     virDomainObjPtr vm;
     qemuAgentPtr agent;
     int ret = -1;
@@ -19185,6 +19215,30 @@ qemuDomainPMSuspendForDuration(virDomainPtr dom,
     if (virDomainObjCheckActive(vm) < 0)
         goto endjob;
 
+    /*
+     * The case we want to handle here is when QEMU has the API (i.e.
+     * QEMU_CAPS_QUERY_CURRENT_MACHINE is set). Otherwise, do not interfere
+     * with the suspend process. This means that existing running domains,
+     * that don't know about this cap, will keep their old behavior of
+     * suspending 'in the dark'.
+     */
+    priv = vm->privateData;
+    if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_QUERY_CURRENT_MACHINE)) {
+        bool enabled;
+
+        if (qemuDomainProbeQMPCurrentMachine(driver, vm, &enabled) < 0) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("Error executing query-current-machine call"));
+            goto endjob;
+        }
+
+        if (!enabled) {
+            virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
+                          _("Domain does not have suspend support"));
+            goto endjob;
+        }
+    }
+
     if (vm->def->pm.s3 || vm->def->pm.s4) {
         if (vm->def->pm.s3 == VIR_TRISTATE_BOOL_NO &&
             (target == VIR_NODE_SUSPEND_TARGET_MEM ||
-- 
2.20.1