metrics: rename pids_v2 to pids

dicussed in #3726

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

metrics/cgroups/v2/cgroups.go

@@ -23,43 +23,18 @@ import (
 
 	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/events"
-	"github.com/containerd/containerd/platforms"
-	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/runtime"
 	"github.com/containerd/containerd/runtime/v1/linux"
 	metrics "github.com/docker/go-metrics"
 )
 
-// Config for the cgroups monitor
-type Config struct {
-	NoPrometheus bool `toml:"no_prometheus"`
-}
-
-func init() {
-	plugin.Register(&plugin.Registration{
-		Type:   plugin.TaskMonitorPlugin,
-		ID:     "cgroups-v2",
-		InitFn: New,
-		Config: &Config{},
-	})
-}
-
-// New returns a new cgroups monitor
-func New(ic *plugin.InitContext) (interface{}, error) {
-	var ns *metrics.Namespace
-	config := ic.Config.(*Config)
-	if !config.NoPrometheus {
-		ns = metrics.NewNamespace("container", "", nil)
-	}
+// NewTaskMonitor returns a new cgroups monitor
+func NewTaskMonitor(ctx context.Context, publisher events.Publisher, ns *metrics.Namespace) (runtime.TaskMonitor, error) {
 	collector := newCollector(ns)
-	if ns != nil {
-		metrics.Register(ns)
-	}
-	ic.Meta.Platforms = append(ic.Meta.Platforms, platforms.DefaultSpec())
 	return &cgroupsMonitor{
 		collector: collector,
-		context:   ic.Context,
-		publisher: ic.Events,
+		context:   ctx,
+		publisher: publisher,
 	}, nil
 }