When checking IsDangling make sure image is not in manifest list

Currently when we run podman image prune or podman images --filter
dangling

It is pruning images that are in a local manifest. These images are
not dangling because they are currently in use by a named manifest list.

You can create this situation simply by doing

echo "from scratch" > /tmp/Containerfile
id=$(podman build /tmp)
podman manifest create test $id
podman image prune --force
podman image exists $id

Will return an error since the image was pruned.  Now the local manifest
test is broken.

Signed-off-by: Daniel J Walsh <[email protected]>

Author: rhatdan

libimage/history.go

@@ -25,7 +25,7 @@ func (i *Image) History(ctx context.Context) ([]ImageHistory, error) {
 		return nil, err
 	}
 
-	layerTree, err := i.runtime.newFreshLayerTree()
+	layerTree, err := i.runtime.newFreshLayerTree(ctx)
 	if err != nil {
 		return nil, err
 	}

libimage/image.go

@@ -206,7 +206,7 @@ func (i *Image) isDangling(ctx context.Context, tree *layerTree) (bool, error) {
 	if err != nil {
 		return false, err
 	}
-	return len(children) == 0, nil
+	return (len(children) == 0 && !tree.manifestListDigests[i.Digest()]), nil
 }
 
 // IsIntermediate returns true if the image is an intermediate image, that is
@@ -258,7 +258,7 @@ func (i *Image) TopLayer() string {
 
 // Parent returns the parent image or nil if there is none
 func (i *Image) Parent(ctx context.Context) (*Image, error) {
-	tree, err := i.runtime.newFreshLayerTree()
+	tree, err := i.runtime.newFreshLayerTree(ctx)
 	if err != nil {
 		return nil, err
 	}
@@ -292,7 +292,7 @@ func (i *Image) Children(ctx context.Context) ([]*Image, error) {
 // created for this invocation only.
 func (i *Image) getChildren(ctx context.Context, all bool, tree *layerTree) ([]*Image, error) {
 	if tree == nil {
-		t, err := i.runtime.newFreshLayerTree()
+		t, err := i.runtime.newFreshLayerTree(ctx)
 		if err != nil {
 			return nil, err
 		}

libimage/image_tree.go

@@ -3,6 +3,7 @@
 package libimage
 
 import (
+	"context"
 	"fmt"
 	"strings"
 
@@ -13,7 +14,7 @@ import (
 // Tree generates a tree for the specified image and its layers.  Use
 // `traverseChildren` to traverse the layers of all children.  By default, only
 // layers of the image are printed.
-func (i *Image) Tree(traverseChildren bool) (string, error) {
+func (i *Image) Tree(ctx context.Context, traverseChildren bool) (string, error) {
 	// NOTE: a string builder prevents us from copying to much data around
 	// and compile the string when and where needed.
 	sb := &strings.Builder{}
@@ -37,7 +38,7 @@ func (i *Image) Tree(traverseChildren bool) (string, error) {
 		fmt.Fprintf(sb, "No Image Layers")
 	}
 
-	layerTree, err := i.runtime.newFreshLayerTree()
+	layerTree, err := i.runtime.newFreshLayerTree(ctx)
 	if err != nil {
 		return "", err
 	}

libimage/layer_tree.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/containers/storage"
 	storageTypes "github.com/containers/storage/types"
+	digest "github.com/opencontainers/go-digest"
 	ociv1 "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/sirupsen/logrus"
 )
@@ -22,6 +23,10 @@ type layerTree struct {
 	// emptyImages do not have any top-layer so we cannot create a
 	// *layerNode for them.
 	emptyImages []*Image
+	// manifestList keep track of images based on their digest.
+	// Library will use this map when checking if a image is dangling.
+	// If an image is used in a manifestList it is NOT dangling
+	manifestListDigests map[digest.Digest]bool
 }
 
 // node returns a layerNode for the specified layerID.
@@ -90,20 +95,21 @@ func (l *layerNode) repoTags() ([]string, error) {
 }
 
 // newFreshLayerTree extracts a layerTree from consistent layers and images in the local storage.
-func (r *Runtime) newFreshLayerTree() (*layerTree, error) {
+func (r *Runtime) newFreshLayerTree(ctx context.Context) (*layerTree, error) {
 	images, layers, err := r.getImagesAndLayers()
 	if err != nil {
 		return nil, err
 	}
-	return r.newLayerTreeFromData(images, layers)
+	return r.newLayerTreeFromData(ctx, images, layers)
 }
 
 // newLayerTreeFromData extracts a layerTree from the given the layers and images.
 // The caller is responsible for (layers, images) being consistent.
-func (r *Runtime) newLayerTreeFromData(images []*Image, layers []storage.Layer) (*layerTree, error) {
+func (r *Runtime) newLayerTreeFromData(ctx context.Context, images []*Image, layers []storage.Layer) (*layerTree, error) {
 	tree := layerTree{
-		nodes:    make(map[string]*layerNode),
-		ociCache: make(map[string]*ociv1.Image),
+		nodes:               make(map[string]*layerNode),
+		ociCache:            make(map[string]*ociv1.Image),
+		manifestListDigests: make(map[digest.Digest]bool),
 	}
 
 	// First build a tree purely based on layer information.
@@ -124,6 +130,18 @@ func (r *Runtime) newLayerTreeFromData(images []*Image, layers []storage.Layer)
 		topLayer := img.TopLayer()
 		if topLayer == "" {
 			tree.emptyImages = append(tree.emptyImages, img)
+			// When img is a manifest list, cache the lists of
+			// digests refereenced in manifest list. Digests can
+			// be used to check for dangling images.
+			if manifestList, _ := img.IsManifestList(ctx); manifestList {
+				mlist, err := img.ToManifestList()
+				if err != nil {
+					return nil, err
+				}
+				for _, digest := range mlist.list.Instances() {
+					tree.manifestListDigests[digest] = true
+				}
+			}
 			continue
 		}
 		node, exists := tree.nodes[topLayer]

libimage/runtime.go

@@ -634,7 +634,7 @@ func (r *Runtime) ListImages(ctx context.Context, options *ListImagesOptions) ([
 
 	var tree *layerTree
 	if needsLayerTree {
-		tree, err = r.newLayerTreeFromData(images, snapshot.Layers)
+		tree, err = r.newLayerTreeFromData(ctx, images, snapshot.Layers)
 		if err != nil {
 			return nil, err
 		}