container/libcontainer: simplify for cgroup v2

In case of cgroup v2, there are no separate per-subsystem mount points,
and so it does not make sense to have a subsystem to mountpoint map.

Yet for the unification of code between v1 and v2, we still use this
map, although a single element is enough.

For cgroup v2, the key is "", the value is the mount point (or the path
to a specific cgroup).

This commit
 - simplifes GetCgroupSubsystems for cgroup v2 (trivial) case;
 - modifies GetCgroupPath() methods to use "" as the key for cgroup v2;
 - fixes NewCgroupManager() to use "" as the key for cgroup v2 case.

Signed-off-by: Kir Kolyshkin <[email protected]>

Author: kolyshkin

container/containerd/handler.go

@@ -22,6 +22,7 @@ import (
 	"time"
 
 	"github.com/containerd/containerd/errdefs"
+	"github.com/opencontainers/runc/libcontainer/cgroups"
 	"golang.org/x/net/context"
 
 	specs "github.com/opencontainers/runtime-spec/specs-go"
@@ -216,7 +217,11 @@ func (h *containerdContainerHandler) ListContainers(listType container.ListType)
 }
 
 func (h *containerdContainerHandler) GetCgroupPath(resource string) (string, error) {
-	path, ok := h.cgroupPaths[resource]
+	var res string
+	if !cgroups.IsCgroup2UnifiedMode() {
+		res = resource
+	}
+	path, ok := h.cgroupPaths[res]
 	if !ok {
 		return "", fmt.Errorf("could not find path for resource %q for container %q", resource, h.reference.Name)
 	}

container/crio/handler.go

@@ -328,7 +328,11 @@ func (h *crioContainerHandler) ListContainers(listType container.ListType) ([]in
 }
 
 func (h *crioContainerHandler) GetCgroupPath(resource string) (string, error) {
-	path, ok := h.cgroupPaths[resource]
+	var res string
+	if !cgroups.IsCgroup2UnifiedMode() {
+		res = resource
+	}
+	path, ok := h.cgroupPaths[res]
 	if !ok {
 		return "", fmt.Errorf("could not find path for resource %q for container %q", resource, h.reference.Name)
 	}

container/docker/handler.go

@@ -31,6 +31,7 @@ import (
 	"github.com/google/cadvisor/fs"
 	info "github.com/google/cadvisor/info/v1"
 	"github.com/google/cadvisor/zfs"
+	"github.com/opencontainers/runc/libcontainer/cgroups"
 
 	dockercontainer "github.com/docker/docker/api/types/container"
 	docker "github.com/docker/docker/client"
@@ -484,7 +485,11 @@ func (h *dockerContainerHandler) ListContainers(listType container.ListType) ([]
 }
 
 func (h *dockerContainerHandler) GetCgroupPath(resource string) (string, error) {
-	path, ok := h.cgroupPaths[resource]
+	var res string
+	if !cgroups.IsCgroup2UnifiedMode() {
+		res = resource
+	}
+	path, ok := h.cgroupPaths[res]
 	if !ok {
 		return "", fmt.Errorf("could not find path for resource %q for container %q", resource, h.reference.Name)
 	}

container/libcontainer/helpers.go

@@ -36,7 +36,13 @@ import (
 // The incudeMetrics arguments specifies which metrics are requested,
 // and is used to filter out some cgroups and their mounts. If nil,
 // all supported cgroup subsystems are included.
+//
+// For cgroup v2, includedMetrics argument is unused, the only map key is ""
+// (empty string), and the value is the unified cgroup mount point.
 func GetCgroupSubsystems(includedMetrics container.MetricSet) (map[string]string, error) {
+	if cgroups.IsCgroup2UnifiedMode() {
+		return map[string]string{"": fs2.UnifiedMountpoint}, nil
+	}
 	// Get all cgroup mounts.
 	allCgroups, err := cgroups.GetCgroupMounts(true)
 	if err != nil {
@@ -152,7 +158,7 @@ func diskStatsCopy(blkioStats []cgroups.BlkioStatEntry) (stat []info.PerDiskStat
 
 func NewCgroupManager(name string, paths map[string]string) (cgroups.Manager, error) {
 	if cgroups.IsCgroup2UnifiedMode() {
-		path := paths["cpu"]
+		path := paths[""]
 		return fs2.NewManager(nil, path, false)
 	}
 

container/raw/handler.go

@@ -24,6 +24,7 @@ import (
 	"github.com/google/cadvisor/fs"
 	info "github.com/google/cadvisor/info/v1"
 	"github.com/google/cadvisor/machine"
+	"github.com/opencontainers/runc/libcontainer/cgroups"
 
 	"k8s.io/klog/v2"
 )
@@ -244,7 +245,11 @@ func (h *rawContainerHandler) GetStats() (*info.ContainerStats, error) {
 }
 
 func (h *rawContainerHandler) GetCgroupPath(resource string) (string, error) {
-	path, ok := h.cgroupPaths[resource]
+	var res string
+	if !cgroups.IsCgroup2UnifiedMode() {
+		res = resource
+	}
+	path, ok := h.cgroupPaths[res]
 	if !ok {
 		return "", fmt.Errorf("could not find path for resource %q for container %q", resource, h.name)
 	}