qemu: Don't fail to shutdown domains with unresponsive agent

Currently, qemuDomainShutdownFlags() chooses the agent method of
shutdown whenever the agent is configured. However, this
assumption is not enough as the guest agent may be unresponsive
at the moment. So unless guest agent method has been explicitly
requested, we should fall back to the ACPI method.

src/qemu/qemu_driver.c

@@ -1702,40 +1702,40 @@ static int qemuDomainShutdownFlags(virDomainPtr dom, unsigned int flags) {
     virDomainObjPtr vm;
     int ret = -1;
     qemuDomainObjPrivatePtr priv;
-    bool useAgent = false;
+    bool useAgent = false, agentRequested, acpiRequested;
 
     virCheckFlags(VIR_DOMAIN_SHUTDOWN_ACPI_POWER_BTN |
                   VIR_DOMAIN_SHUTDOWN_GUEST_AGENT, -1);
 
-    /* At most one of these two flags should be set.  */
-    if ((flags & VIR_DOMAIN_SHUTDOWN_ACPI_POWER_BTN) &&
-        (flags & VIR_DOMAIN_SHUTDOWN_GUEST_AGENT)) {
-        virReportInvalidArg(flags, "%s",
-                            _("flags for acpi power button and guest agent are mutually exclusive"));
-        return -1;
-    }
-
     if (!(vm = qemuDomObjFromDomain(dom)))
         goto cleanup;
 
     priv = vm->privateData;
+    agentRequested = flags & VIR_DOMAIN_SHUTDOWN_GUEST_AGENT;
+    acpiRequested  = flags & VIR_DOMAIN_SHUTDOWN_ACPI_POWER_BTN;
 
-    if ((flags & VIR_DOMAIN_SHUTDOWN_GUEST_AGENT) ||
-        (!(flags & VIR_DOMAIN_SHUTDOWN_ACPI_POWER_BTN) &&
-         priv->agent))
+    /* Prefer agent unless we were requested to not to. */
+    if (agentRequested || (!flags && priv->agent))
         useAgent = true;
 
-    if (useAgent) {
-        if (priv->agentError) {
+    if (priv->agentError) {
+        if (agentRequested && !acpiRequested) {
             virReportError(VIR_ERR_AGENT_UNRESPONSIVE, "%s",
                            _("QEMU guest agent is not "
                              "available due to an error"));
             goto cleanup;
+        } else {
+            useAgent = false;
         }
-        if (!priv->agent) {
+    }
+
+    if (!priv->agent) {
+        if (agentRequested && !acpiRequested) {
             virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED, "%s",
                            _("QEMU guest agent is not configured"));
             goto cleanup;
+        } else {
+            useAgent = false;
         }
     }
 
@@ -1752,7 +1752,13 @@ static int qemuDomainShutdownFlags(virDomainPtr dom, unsigned int flags) {
         qemuDomainObjEnterAgent(vm);
         ret = qemuAgentShutdown(priv->agent, QEMU_AGENT_SHUTDOWN_POWERDOWN);
         qemuDomainObjExitAgent(vm);
-    } else {
+    }
+
+    /* If we are not enforced to use just an agent, try ACPI
+     * shutdown as well in case agent did not succeed.
+     */
+    if (!useAgent ||
+        (ret < 0 && (acpiRequested || !flags))) {
         qemuDomainSetFakeReboot(driver, vm, false);
 
         qemuDomainObjEnterMonitor(driver, vm);