CRI: "Fix" imageFSPath behavior

Currently it didn't take into account that certain snapshots can explicitly
have their root directories placed at a different location. This changes
it to use the RootPath method of the snapshotter if it implements it.

Without this change, cadvisor is not able to get filesystem usage
information, which prevents the kubelet from doing image garbage
collection and enforcing ephemeral storage limits.

Signed-off-by: Danny Canter <danny@dcantah.dev>
(cherry picked from commit 6aeec45)
Signed-off-by: Kern Walster <walster@amazon.com>

pkg/cri/cri.go

@@ -50,6 +50,7 @@ func init() {
 			plugin.ServicePlugin,
 			plugin.NRIApiPlugin,
 			plugin.WarningPlugin,
+			plugin.SnapshotPlugin,
 		},
 		InitFn: initCRIService,
 	})

pkg/cri/server/service.go

@@ -17,7 +17,9 @@
 package server
 
 import (
+	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -126,6 +128,11 @@ type criService struct {
 func NewCRIService(config criconfig.Config, client *containerd.Client, nri *nri.API, warn warning.Service) (CRIService, error) {
 	var err error
 	labels := label.NewStore()
+
+	if client.SnapshotService(config.ContainerdConfig.Snapshotter) == nil {
+		return nil, fmt.Errorf("failed to find snapshotter %q", config.ContainerdConfig.Snapshotter)
+	}
+
 	c := &criService{
 		config:                      config,
 		client:                      client,
@@ -149,7 +156,11 @@ func NewCRIService(config criconfig.Config, client *containerd.Client, nri *nri.
 		return nil, fmt.Errorf("failed to find snapshotter %q", c.config.ContainerdConfig.Snapshotter)
 	}
 
-	c.imageFSPath = imageFSPath(config.ContainerdRootDir, config.ContainerdConfig.Snapshotter)
+	c.imageFSPath = imageFSPath(
+		config.ContainerdRootDir,
+		config.ContainerdConfig.Snapshotter,
+		client,
+	)
 	logrus.Infof("Get image filesystem path %q", c.imageFSPath)
 
 	if err := c.initPlatform(); err != nil {
@@ -341,8 +352,40 @@ func (c *criService) register(s *grpc.Server) error {
 
 // imageFSPath returns containerd image filesystem path.
 // Note that if containerd changes directory layout, we also needs to change this.
-func imageFSPath(rootDir, snapshotter string) string {
-	return filepath.Join(rootDir, fmt.Sprintf("%s.%s", plugin.SnapshotPlugin, snapshotter))
+func imageFSPath(rootDir, snapshotter string, client *containerd.Client) string {
+	introspection := func() (string, error) {
+		filters := []string{fmt.Sprintf("type==%s, id==%s", plugin.SnapshotPlugin, snapshotter)}
+		in := client.IntrospectionService()
+
+		resp, err := in.Plugins(context.Background(), filters)
+		if err != nil {
+			return "", err
+		}
+
+		if len(resp.Plugins) <= 0 {
+			return "", fmt.Errorf("inspection service could not find snapshotter %s plugin", snapshotter)
+		}
+
+		sn := resp.Plugins[0]
+		if root, ok := sn.Exports[plugin.SnapshotterRootDir]; ok {
+			return root, nil
+		}
+		return "", errors.New("snapshotter does not export root path")
+	}
+
+	var imageFSPath string
+	path, err := introspection()
+	if err != nil {
+		logrus.WithError(err).WithField("snapshotter", snapshotter).Warn("snapshotter doesn't export root path")
+		imageFSPath = filepath.Join(
+			rootDir,
+			plugin.SnapshotPlugin.String()+"."+snapshotter,
+		)
+	} else {
+		imageFSPath = path
+	}
+
+	return imageFSPath
 }
 
 func loadOCISpec(filename string) (*oci.Spec, error) {