c8d/commit: Use manifest digest for dangling image

Previously commit incorrectly used image config digest as an image id
for the new image which isn't consistent with the image target.
This changes it to use manifest digest.

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

daemon/containerd/image_commit.go

@@ -87,14 +87,14 @@ func (i *ImageService) CommitImage(ctx context.Context, cc backend.CommitConfig)
 	}
 
 	layers := append(manifest.Layers, diffLayerDesc)
-	commitManifestDesc, configDigest, err := writeContentsForImage(ctx, i.snapshotter, cs, imageConfig, layers)
+	commitManifestDesc, err := writeContentsForImage(ctx, i.snapshotter, cs, imageConfig, layers)
 	if err != nil {
 		return "", err
 	}
 
 	// image create
 	img := images.Image{
-		Name:      danglingImageName(configDigest.Digest()),
+		Name:      danglingImageName(commitManifestDesc.Digest),
 		Target:    commitManifestDesc,
 		CreatedAt: time.Now(),
 	}
@@ -156,10 +156,10 @@ func generateCommitImageConfig(ctx context.Context, container *containerapi.Conf
 }
 
 // writeContentsForImage will commit oci image config and manifest into containerd's content store.
-func writeContentsForImage(ctx context.Context, snName string, cs content.Store, newConfig ocispec.Image, layers []ocispec.Descriptor) (ocispec.Descriptor, image.ID, error) {
+func writeContentsForImage(ctx context.Context, snName string, cs content.Store, newConfig ocispec.Image, layers []ocispec.Descriptor) (ocispec.Descriptor, error) {
 	newConfigJSON, err := json.Marshal(newConfig)
 	if err != nil {
-		return ocispec.Descriptor{}, "", err
+		return ocispec.Descriptor{}, err
 	}
 
 	configDesc := ocispec.Descriptor{
@@ -184,7 +184,7 @@ func writeContentsForImage(ctx context.Context, snName string, cs content.Store,
 
 	newMfstJSON, err := json.MarshalIndent(newMfst, "", "    ")
 	if err != nil {
-		return ocispec.Descriptor{}, "", err
+		return ocispec.Descriptor{}, err
 	}
 
 	newMfstDesc := ocispec.Descriptor{
@@ -203,7 +203,7 @@ func writeContentsForImage(ctx context.Context, snName string, cs content.Store,
 
 	err = content.WriteBlob(ctx, cs, newMfstDesc.Digest.String(), bytes.NewReader(newMfstJSON), newMfstDesc, content.WithLabels(labels))
 	if err != nil {
-		return ocispec.Descriptor{}, "", err
+		return ocispec.Descriptor{}, err
 	}
 
 	// config should reference to snapshotter
@@ -212,10 +212,10 @@ func writeContentsForImage(ctx context.Context, snName string, cs content.Store,
 	})
 	err = content.WriteBlob(ctx, cs, configDesc.Digest.String(), bytes.NewReader(newConfigJSON), configDesc, labelOpt)
 	if err != nil {
-		return ocispec.Descriptor{}, "", err
+		return ocispec.Descriptor{}, err
 	}
 
-	return newMfstDesc, image.ID(configDesc.Digest), nil
+	return newMfstDesc, nil
 }
 
 // createDiff creates a layer diff into containerd's content store.