common/pkg/cgroups: remove IsCgroup2UnifiedMode

common/pkg/cgroupv2.Enabled provides the same functionality that podman
and buildah could call in main to check for Cgroups v2.

Keep IsCgroup2UnifiedMode in cgroups_unsupported.go for buildah cross
compiles.

Signed-off-by: Lokesh Mandvekar <[email protected]>

Author: lsm5

common/pkg/cgroups/cgroups_linux.go

@@ -13,7 +13,6 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
-	"sync"
 	"syscall"
 	"time"
 
@@ -31,10 +30,6 @@ var (
 	// ErrCgroupDeleted means the cgroup was deleted.
 	ErrCgroupDeleted = errors.New("cgroup deleted")
 	ErrStatCgroup    = errors.New("no cgroup available for gathering user statistics")
-
-	isUnifiedOnce sync.Once
-	isUnified     bool
-	isUnifiedErr  error
 )
 
 // CgroupControl controls a cgroup hierarchy.
@@ -605,19 +600,6 @@ 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

@@ -2,7 +2,7 @@
 
 package cgroups
 
-// IsCgroup2UnifiedMode returns whether we are running in cgroup 2 cgroup2 mode.
+// IsCgroup2UnifiedMode returns whether we are running in cgroup 2 unified mode.
 func IsCgroup2UnifiedMode() (bool, error) {
 	return false, nil
 }