Keep IsCgroup2UnifiedMode funcs

Signed-off-by: Lokesh Mandvekar <lsm5@redhat.com>

Author: lsm5

common/pkg/cgroups/cgroups_linux.go

@@ -13,6 +13,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"sync"
 	"syscall"
 	"time"
 
@@ -29,7 +30,13 @@ import (
 var (
 	// ErrCgroupDeleted means the cgroup was deleted.
 	ErrCgroupDeleted = errors.New("cgroup deleted")
-	ErrStatCgroup    = errors.New("no cgroup available for gathering user statistics")
+	// ErrCgroupV1Rootless means the cgroup v1 were attempted to be used in rootless environment.
+	ErrCgroupV1Rootless = errors.New("no support for CGroups V1 in rootless environments")
+	ErrStatCgroup       = errors.New("no cgroup available for gathering user statistics")
+
+	isUnifiedOnce sync.Once
+	isUnified     bool
+	isUnifiedErr  error
 )
 
 // CgroupControl controls a cgroup hierarchy.
@@ -600,6 +607,19 @@ func SystemCPUUsage() (uint64, error) {
 	return total, nil
 }
 
+// IsCgroup2UnifiedMode returns whether we are running in cgroup 2 cgroup2 mode.
+func IsCgroup2UnifiedMode() (bool, error) {
+	isUnifiedOnce.Do(func() {
+		var st syscall.Statfs_t
+		if err := syscall.Statfs("/sys/fs/cgroup", &st); err != nil {
+			isUnified, isUnifiedErr = false, err
+		} else {
+			isUnified, isUnifiedErr = st.Type == unix.CGROUP2_SUPER_MAGIC, nil
+		}
+	})
+	return isUnified, isUnifiedErr
+}
+
 // UserConnection returns an user connection to D-BUS.
 func UserConnection(uid int) (*systemdDbus.Conn, error) {
 	return systemdDbus.NewConnection(func() (*dbus.Conn, error) {

common/pkg/cgroups/cgroups_unsupported.go

@@ -2,6 +2,11 @@
 
 package cgroups
 
+// IsCgroup2UnifiedMode returns whether we are running in cgroup 2 cgroup2 mode.
+func IsCgroup2UnifiedMode() (bool, error) {
+	return false, nil
+}
+
 // UserOwnsCurrentSystemdCgroup checks whether the current EUID owns the
 // current cgroup.
 func UserOwnsCurrentSystemdCgroup() (bool, error) {