support cgroup2

* only shim v2 runc v2 ("io.containerd.runc.v2") is supported
* only PID metrics is implemented. Others should be implemented in separate PRs.
* lots of code duplication in v1 metrics and v2 metrics. Dedupe should be separate PR.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

runtime/opts/opts_linux.go

@@ -20,11 +20,22 @@ import (
 	"context"
 
 	"github.com/containerd/cgroups"
+	cgroupsv2 "github.com/containerd/cgroups/v2"
 	"github.com/containerd/containerd/namespaces"
 )
 
 // WithNamespaceCgroupDeletion removes the cgroup directory that was created for the namespace
 func WithNamespaceCgroupDeletion(ctx context.Context, i *namespaces.DeleteInfo) error {
+	if cgroups.Mode() == cgroups.Unified {
+		cg, err := cgroupsv2.LoadManager("/sys/fs/cgroup", i.Name)
+		if err != nil {
+			if err == cgroupsv2.ErrCgroupDeleted {
+				return nil
+			}
+			return err
+		}
+		return cg.Delete()
+	}
 	cg, err := cgroups.Load(cgroups.V1, cgroups.StaticPath(i.Name))
 	if err != nil {
 		if err == cgroups.ErrCgroupDeleted {