1 files changed, 76 insertions, 1 deletions
diff --git a/daemon/containerd/cache.go b/daemon/containerd/cache.go
index e066e8ae87..8bd01768f8 100644
--- a/daemon/containerd/cache.go
+++ b/daemon/containerd/cache.go
@@ -2,11 +2,86 @@ package containerd
 
 import (
 	"context"
+	"reflect"
+	"strings"
 
+	"github.com/docker/docker/api/types/container"
+	imagetype "github.com/docker/docker/api/types/image"
 	"github.com/docker/docker/builder"
+	"github.com/docker/docker/image"
 )
 
 // MakeImageCache creates a stateful image cache.
 func (i *ImageService) MakeImageCache(ctx context.Context, cacheFrom []string) (builder.ImageCache, error) {
-	panic("not implemented")
+	images := []*image.Image{}
+	for _, c := range cacheFrom {
+		im, err := i.GetImage(ctx, c, imagetype.GetImageOpts{})
+		if err != nil {
+			return nil, err
+		}
+		images = append(images, im)
+	}
+	return &imageCache{images: images, c: i}, nil
+}
+
+type imageCache struct {
+	images []*image.Image
+	c      *ImageService
+}
+
+func (ic *imageCache) GetCache(parentID string, cfg *container.Config) (imageID string, err error) {
+	ctx := context.TODO()
+	parent, err := ic.c.GetImage(ctx, parentID, imagetype.GetImageOpts{})
+	if err != nil {
+		return "", err
+	}
+
+	for _, localCachedImage := range ic.images {
+		if isMatch(localCachedImage, parent, cfg) {
+			return localCachedImage.ID().String(), nil
+		}
+	}
+
+	children, err := ic.c.Children(ctx, parent.ID())
+	if err != nil {
+		return "", err
+	}
+
+	for _, children := range children {
+		childImage, err := ic.c.GetImage(ctx, children.String(), imagetype.GetImageOpts{})
+		if err != nil {
+			return "", err
+		}
+
+		if isMatch(childImage, parent, cfg) {
+			return children.String(), nil
+		}
+	}
+
+	return "", nil
+}
+
+// isMatch checks whether a given target can be used as cache for the given
+// parent image/config combination.
+// A target can only be an immediate child of the given parent image. For
+// a parent image with `n` history entries, a valid target must have `n+1`
+// entries and the extra entry must match the provided config
+func isMatch(target, parent *image.Image, cfg *container.Config) bool {
+	if target == nil || parent == nil || cfg == nil {
+		return false
+	}
+
+	if len(target.History) != len(parent.History)+1 ||
+		len(target.RootFS.DiffIDs) != len(parent.RootFS.DiffIDs)+1 {
+		return false
+	}
+
+	for i := range parent.History {
+		if !reflect.DeepEqual(parent.History[i], target.History[i]) {
+			return false
+		}
+	}
+
+	childCreatedBy := target.History[len(target.History)-1].CreatedBy
+	return childCreatedBy == strings.Join(cfg.Cmd, " ")
 }