// Copyright 2019 psgo 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 cgroups

import (
	"sync"
	"syscall"
)

const (
	CgroupRoot        = "/sys/fs/cgroup"
	cgroup2SuperMagic = 0x63677270
)

var (
	isUnifiedOnce sync.Once
	isUnified     bool
	isUnifiedErr  error
)

// IsCgroup2UnifiedMode returns whether we are running in cgroup or cgroupv2 mode.
func IsCgroup2UnifiedMode() (bool, error) {
	isUnifiedOnce.Do(func() {
		var st syscall.Statfs_t
		if err := syscall.Statfs(CgroupRoot, &st); err != nil {
			isUnified, isUnifiedErr = false, err
		} else {
			isUnified, isUnifiedErr = st.Type == cgroup2SuperMagic, nil
		}
	})
	return isUnified, isUnifiedErr
}