qemu: Refactor qemuDomainHotplugVcpus

Refactor the code flow so that 'exit_monitor:' can be removed.

This patch also moves the auditing and setting of the new vCPU count
right to the place where the hotplug happens, since it's possible that
the hotplug succeeds and adds a cpu while other stuff fails.

Lastly, failures of qemuMonitorGetCPUInfo are now reported rather than
ignored. The function retuns 0 if it "successfully" detected 0 threads.

src/qemu/qemu_driver.c

@@ -4698,41 +4698,46 @@ qemuDomainHotplugAddVcpu(virQEMUDriverPtr driver,
 {
     qemuDomainObjPrivatePtr priv = vm->privateData;
     int ret = -1;
+    int rc;
     int oldvcpus = virDomainDefGetVcpus(vm->def);
-    int vcpus = oldvcpus;
     pid_t *cpupids = NULL;
-    int ncpupids;
+    int ncpupids = 0;
     virCgroupPtr cgroup_vcpu = NULL;
     char *mem_mask = NULL;
     virDomainNumatuneMemMode mem_mode;
 
     qemuDomainObjEnterMonitor(driver, vm);
 
-    if (qemuMonitorSetCPU(priv->mon, vcpu, true) < 0)
-        goto exit_monitor;
-
-    vcpus++;
+    rc = qemuMonitorSetCPU(priv->mon, vcpu, true);
 
-    /* After hotplugging the CPUs we need to re-detect threads corresponding
-     * to the virtual CPUs. Some older versions don't provide the thread ID
-     * or don't have the "info cpus" command (and they don't support multiple
-     * CPUs anyways), so errors in the re-detection will not be treated
-     * fatal */
-    if ((ncpupids = qemuMonitorGetCPUInfo(priv->mon, &cpupids)) <= 0) {
-        virResetLastError();
-        ret = 0;
-        goto exit_monitor;
-    }
+    if (rc == 0)
+        ncpupids = qemuMonitorGetCPUInfo(priv->mon, &cpupids);
 
     if (qemuDomainObjExitMonitor(driver, vm) < 0)
         goto cleanup;
 
-    if (ncpupids != vcpus) {
+    virDomainAuditVcpu(vm, oldvcpus, oldvcpus + 1, "update", rc == 0);
+
+    if (rc < 0)
+        goto cleanup;
+
+    ignore_value(virDomainDefSetVcpus(vm->def, oldvcpus + 1));
+
+    if (ncpupids < 0)
+        goto cleanup;
+
+    /* failure to re-detect vCPU pids after hotplug due to lack of support was
+     * historically deemed not fatal. We need to skip the rest of the steps though. */
+    if (ncpupids == 0) {
+        ret = 0;
+        goto cleanup;
+    }
+
+    if (ncpupids != oldvcpus + 1) {
         virReportError(VIR_ERR_INTERNAL_ERROR,
                        _("got wrong number of vCPU pids from QEMU monitor. "
                          "got %d, wanted %d"),
-                       ncpupids, vcpus);
-        vcpus = oldvcpus;
+                       ncpupids, oldvcpus + 1);
         goto cleanup;
     }
 
@@ -4781,17 +4786,8 @@ qemuDomainHotplugAddVcpu(virQEMUDriverPtr driver,
  cleanup:
     VIR_FREE(cpupids);
     VIR_FREE(mem_mask);
-    if (virDomainObjIsActive(vm) &&
-        virDomainDefSetVcpus(vm->def, vcpus) < 0)
-        ret = -1;
-    virDomainAuditVcpu(vm, oldvcpus, vcpus, "update", ret == 0);
-    if (cgroup_vcpu)
-        virCgroupFree(&cgroup_vcpu);
+    virCgroupFree(&cgroup_vcpu);
     return ret;
-
- exit_monitor:
-    ignore_value(qemuDomainObjExitMonitor(driver, vm));
-    goto cleanup;
 }