check root cpu.stat instead of kernel version for cgroup v2

pkg/kubelet/kubelet_linux.go

@@ -0,0 +1,51 @@
+//go:build linux
+
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package kubelet
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	v1 "k8s.io/api/core/v1"
+	"k8s.io/kubernetes/pkg/kubelet/cm"
+	"k8s.io/kubernetes/pkg/kubelet/cm/util"
+	"k8s.io/kubernetes/pkg/kubelet/events"
+	"k8s.io/kubernetes/pkg/kubelet/metrics"
+)
+
+func (kl *Kubelet) cgroupVersionCheck() error {
+	cgroupVersion := kl.containerManager.GetNodeConfig().CgroupVersion
+	metrics.CgroupVersion.Set(float64(cgroupVersion))
+	switch cgroupVersion {
+	case 1:
+		kl.recorder.Eventf(kl.nodeRef, v1.EventTypeWarning, events.CgroupV1, cm.CgroupV1MaintenanceModeWarning)
+		return errors.New(cm.CgroupV1MaintenanceModeWarning)
+	case 2:
+		cpustat := filepath.Join(util.CgroupRoot, "cpu.stat")
+		if _, err := os.Stat(cpustat); os.IsNotExist(err) {
+			// if `/sys/fs/cgroup/cpu.stat` does not exist, log a warning
+			return errors.New(cm.CgroupV2KernelWarning)
+		}
+	default:
+		return fmt.Errorf("unsupported cgroup version: %d", cgroupVersion)
+	}
+	return nil
+}