cgroupv2: move sanity path check to common code

The fs2 cgroup driver has a sanity check for path.
Since systemd driver is relying on the same path,
it makes sense to move this check to the common code.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/fs2/fs2.go

@@ -30,11 +30,7 @@ func NewManager(config *configs.Cgroup, dirPath string, rootless bool) (cgroups.
 	if config == nil {
 		config = &configs.Cgroup{}
 	}
-	if dirPath != "" {
+	if dirPath == "" {
-		if filepath.Clean(dirPath) != dirPath || !filepath.IsAbs(dirPath) {
-			return nil, errors.Errorf("invalid dir path %q", dirPath)
-		}
-	} else {
 		var err error
 		dirPath, err = defaultDirPath(config)
 		if err != nil {

libcontainer/factory_linux.go

@@ -51,16 +51,22 @@ func InitArgs(args ...string) func(*LinuxFactory) error {
 }
 
 func getUnifiedPath(paths map[string]string) string {
-	unifiedPath := ""
+	path := ""
 	for k, v := range paths {
-		if unifiedPath == "" {
+		if path == "" {
-			unifiedPath = v
+			path = v
-		} else if v != unifiedPath {
+		} else if v != path {
-			panic(errors.Errorf("expected %q path to be unified path %q, got %q", k, unifiedPath, v))
+			panic(errors.Errorf("expected %q path to be unified path %q, got %q", k, path, v))
 		}
 	}
 	// can be empty
-	return unifiedPath
+	if path != "" {
+		if filepath.Clean(path) != path || !filepath.IsAbs(path) {
+			panic(errors.Errorf("invalid dir path %q", path))
+		}
+	}
+
+	return path
 }
 
 func systemdCgroupV2(l *LinuxFactory, rootless bool) error {