image list: speed up

Listing images has shown increasing performance penalties with an
increasing number of images.  Unless `--all` is specified, Podman
will filter intermediate images.  Determining intermediate images
has been done by finding (and comparing!) parent images which is
expensive.  We had to query the storage many times which turned it
into a bottleneck.

Instead, create a layer tree and assign one or more images to nodes that
match the images' top layer.  Determining the children of an image is
now exponentially faster as we already know the child images from the
layer graph and the images using the same top layer, which may also be
considered child images based on their history.

On my system with 510 images, a rootful image list drops from 6 secs
down to 0.3 secs.

Also use the tree to compute parent nodes, and to filter intermediate
images for pruning.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

4 files changed, 261 insertions, 125 deletions

diff --git a/libpod/image/filters.go b/libpod/image/filters.go
index 9738a7d5e..db647954f 100644
--- a/libpod/image/filters.go
+++ b/libpod/image/filters.go
@@ -29,6 +29,26 @@ func CreatedBeforeFilter(createTime time.Time) ResultFilter {
 	}
 }
 
+// IntermediateFilter returns filter for intermediate images (i.e., images
+// with children and no tags).
+func (ir *Runtime) IntermediateFilter(ctx context.Context, images []*Image) (ResultFilter, error) {
+	tree, err := ir.layerTree()
+	if err != nil {
+		return nil, err
+	}
+	return func(i *Image) bool {
+		if len(i.Names()) > 0 {
+			return true
+		}
+		children, err := tree.children(ctx, i, false)
+		if err != nil {
+			logrus.Error(err.Error())
+			return false
+		}
+		return len(children) == 0
+	}, nil
+}
+
 // CreatedAfterFilter allows you to filter on images created after
 // the given time.Time
 func CreatedAfterFilter(createTime time.Time) ResultFilter {
diff --git a/libpod/image/image.go b/libpod/image/image.go
index 8b2aa318f..ad9cec87f 100644
--- a/libpod/image/image.go
+++ b/libpod/image/image.go
@@ -856,26 +856,6 @@ func (i *Image) Dangling() bool {
 	return len(i.Names()) == 0
 }
 
-// Intermediate returns true if the image is cache or intermediate image.
-// Cache image has parent and child.
-func (i *Image) Intermediate(ctx context.Context) (bool, error) {
-	parent, err := i.IsParent(ctx)
-	if err != nil {
-		return false, err
-	}
-	if !parent {
-		return false, nil
-	}
-	img, err := i.GetParent(ctx)
-	if err != nil {
-		return false, err
-	}
-	if img != nil {
-		return true, nil
-	}
-	return false, nil
-}
-
 // User returns the image's user
 func (i *Image) User(ctx context.Context) (string, error) {
 	imgInspect, err := i.inspect(ctx, false)
@@ -1214,7 +1194,7 @@ func splitString(input string) string {
 // the parent of any other layer in store. Double check that image with that
 // layer exists as well.
 func (i *Image) IsParent(ctx context.Context) (bool, error) {
-	children, err := i.getChildren(ctx, 1)
+	children, err := i.getChildren(ctx, false)
 	if err != nil {
 		if errors.Cause(err) == ErrImageIsBareList {
 			return false, nil
@@ -1289,63 +1269,16 @@ func areParentAndChild(parent, child *imgspecv1.Image) bool {
 
 // GetParent returns the image ID of the parent. Return nil if a parent is not found.
 func (i *Image) GetParent(ctx context.Context) (*Image, error) {
-	var childLayer *storage.Layer
-	images, err := i.imageruntime.GetImages()
+	tree, err := i.imageruntime.layerTree()
 	if err != nil {
 		return nil, err
 	}
-	if i.TopLayer() != "" {
-		if childLayer, err = i.imageruntime.store.Layer(i.TopLayer()); err != nil {
-			return nil, err
-		}
-	}
-	// fetch the configuration for the child image
-	child, err := i.ociv1Image(ctx)
-	if err != nil {
-		if errors.Cause(err) == ErrImageIsBareList {
-			return nil, nil
-		}
-		return nil, err
-	}
-	for _, img := range images {
-		if img.ID() == i.ID() {
-			continue
-		}
-		candidateLayer := img.TopLayer()
-		// as a child, our top layer, if we have one, is either the
-		// candidate parent's layer, or one that's derived from it, so
-		// skip over any candidate image where we know that isn't the
-		// case
-		if childLayer != nil {
-			// The child has at least one layer, so a parent would
-			// have a top layer that's either the same as the child's
-			// top layer or the top layer's recorded parent layer,
-			// which could be an empty value.
-			if candidateLayer != childLayer.Parent && candidateLayer != childLayer.ID {
-				continue
-			}
-		} else {
-			// The child has no layers, but the candidate does.
-			if candidateLayer != "" {
-				continue
-			}
-		}
-		// fetch the configuration for the candidate image
-		candidate, err := img.ociv1Image(ctx)
-		if err != nil {
-			return nil, err
-		}
-		// compare them
-		if areParentAndChild(candidate, child) {
-			return img, nil
-		}
-	}
-	return nil, nil
+	return tree.parent(ctx, i)
 }
 
 // GetChildren returns a list of the imageIDs that depend on the image
 func (i *Image) GetChildren(ctx context.Context) ([]string, error) {
-	children, err := i.getChildren(ctx, 0)
+	children, err := i.getChildren(ctx, true)
 	if err != nil {
 		if errors.Cause(err) == ErrImageIsBareList {
 			return nil, nil
@@ -1355,62 +1288,15 @@ func (i *Image) GetChildren(ctx context.Context) ([]string, error) {
 	return children, nil
 }
 
-// getChildren returns a list of at most "max" imageIDs that depend on the image
-func (i *Image) getChildren(ctx context.Context, max int) ([]string, error) {
-	var children []string
-
-	if _, err := i.toImageRef(ctx); err != nil {
-		return nil, nil
-	}
-
-	images, err := i.imageruntime.GetImages()
-	if err != nil {
-		return nil, err
-	}
-
-	// fetch the configuration for the parent image
-	parent, err := i.ociv1Image(ctx)
+// getChildren returns a list of imageIDs that depend on the image. If all is
+// false, only the first child image is returned.
+func (i *Image) getChildren(ctx context.Context, all bool) ([]string, error) {
+	tree, err := i.imageruntime.layerTree()
 	if err != nil {
 		return nil, err
 	}
-	parentLayer := i.TopLayer()
 
-	for _, img := range images {
-		if img.ID() == i.ID() {
-			continue
-		}
-		if img.TopLayer() == "" {
-			if parentLayer != "" {
-				// this image has no layers, but we do, so
-				// it can't be derived from this one
-				continue
-			}
-		} else {
-			candidateLayer, err := img.Layer()
-			if err != nil {
-				return nil, err
-			}
-			// if this image's top layer is not our top layer, and is not
-			// based on our top layer, we can skip it
-			if candidateLayer.Parent != parentLayer && candidateLayer.ID != parentLayer {
-				continue
-			}
-		}
-		// fetch the configuration for the candidate image
-		candidate, err := img.ociv1Image(ctx)
-		if err != nil {
-			return nil, err
-		}
-		// compare them
-		if areParentAndChild(parent, candidate) {
-			children = append(children, img.ID())
-		}
-		// if we're not building an exhaustive list, maybe we're done?
-		if max > 0 && len(children) >= max {
-			break
-		}
-	}
-	return children, nil
+	return tree.children(ctx, i, all)
 }
 
 // InputIsID returns a bool if the user input for an image
@@ -1667,6 +1553,7 @@ type LayerInfo struct {
 
 // GetLayersMapWithImageInfo returns map of image-layers, with associated information like RepoTags, parent and list of child layers.
 func GetLayersMapWithImageInfo(imageruntime *Runtime) (map[string]*LayerInfo, error) {
+	// TODO: evaluate if we can reuse `layerTree` here.
 
 	// Memory allocated to store map of layers with key LayerID.
 	// Map will build dependency chain with ParentID and ChildID(s)
diff --git a/libpod/image/layer_tree.go b/libpod/image/layer_tree.go
new file mode 100644
index 000000000..3699655fd
--- /dev/null
+++ b/libpod/image/layer_tree.go
@@ -0,0 +1,222 @@
+package image
+
+import (
+	"context"
+
+	ociv1 "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/pkg/errors"
+)
+
+// layerTree is an internal representation of local layers.
+type layerTree struct {
+	// nodes is the actual layer tree with layer IDs being keys.
+	nodes map[string]*layerNode
+	// ociCache is a cache for Image.ID -> OCI Image. Translations are done
+	// on-demand.
+	ociCache map[string]*ociv1.Image
+}
+
+// node returns a layerNode for the specified layerID.
+func (t *layerTree) node(layerID string) *layerNode {
+	node, exists := t.nodes[layerID]
+	if !exists {
+		node = &layerNode{}
+		t.nodes[layerID] = node
+	}
+	return node
+}
+
+// toOCI returns an OCI image for the specified image.
+func (t *layerTree) toOCI(ctx context.Context, i *Image) (*ociv1.Image, error) {
+	var err error
+	oci, exists := t.ociCache[i.ID()]
+	if !exists {
+		oci, err = i.ociv1Image(ctx)
+		t.ociCache[i.ID()] = oci
+	}
+	return oci, err
+}
+
+// layerNode is a node in a layerTree.  It's ID is the key in a layerTree.
+type layerNode struct {
+	children []*layerNode
+	images   []*Image
+	parent   *layerNode
+}
+
+// layerTree extracts a layerTree from the layers in the local storage and
+// relates them to the specified images.
+func (ir *Runtime) layerTree() (*layerTree, error) {
+	layers, err := ir.store.Layers()
+	if err != nil {
+		return nil, err
+	}
+
+	images, err := ir.GetImages()
+	if err != nil {
+		return nil, err
+	}
+
+	tree := layerTree{
+		nodes:    make(map[string]*layerNode),
+		ociCache: make(map[string]*ociv1.Image),
+	}
+
+	// First build a tree purely based on layer information.
+	for _, layer := range layers {
+		node := tree.node(layer.ID)
+		if layer.Parent == "" {
+			continue
+		}
+		parent := tree.node(layer.Parent)
+		node.parent = parent
+		parent.children = append(parent.children, node)
+	}
+
+	// Now assign the images to each (top) layer.
+	for i := range images {
+		img := images[i] // do not leak loop variable outside the scope
+		topLayer := img.TopLayer()
+		if topLayer == "" {
+			continue
+		}
+		node, exists := tree.nodes[topLayer]
+		if !exists {
+			return nil, errors.Errorf("top layer %s of image %s not found in layer tree", img.TopLayer(), img.ID())
+		}
+		node.images = append(node.images, img)
+	}
+
+	return &tree, nil
+}
+
+// children returns the image IDs of children . Child images are images
+// with either the same top layer as parent or parent being the true parent
+// layer.  Furthermore, the history of the parent and child images must match
+// with the parent having one history item less.
+// If all is true, all images are returned.  Otherwise, the first image is
+// returned.
+func (t *layerTree) children(ctx context.Context, parent *Image, all bool) ([]string, error) {
+	if parent.TopLayer() == "" {
+		return nil, nil
+	}
+
+	var children []string
+
+	parentNode, exists := t.nodes[parent.TopLayer()]
+	if !exists {
+		return nil, errors.Errorf("layer not found in layer tree: %q", parent.TopLayer())
+	}
+
+	parentID := parent.ID()
+	parentOCI, err := t.toOCI(ctx, parent)
+	if err != nil {
+		return nil, err
+	}
+
+	// checkParent returns true if child and parent are in such a relation.
+	checkParent := func(child *Image) (bool, error) {
+		if parentID == child.ID() {
+			return false, nil
+		}
+		childOCI, err := t.toOCI(ctx, child)
+		if err != nil {
+			return false, err
+		}
+		// History check.
+		return areParentAndChild(parentOCI, childOCI), nil
+	}
+
+	// addChildrenFrom adds child images of parent to children.  Returns
+	// true if any image is a child of parent.
+	addChildrenFromNode := func(node *layerNode) (bool, error) {
+		foundChildren := false
+		for _, childImage := range node.images {
+			isChild, err := checkParent(childImage)
+			if err != nil {
+				return foundChildren, err
+			}
+			if isChild {
+				foundChildren = true
+				children = append(children, childImage.ID())
+				if all {
+					return foundChildren, nil
+				}
+			}
+		}
+		return foundChildren, nil
+	}
+
+	// First check images where parent's top layer is also the parent
+	// layer.
+	for _, childNode := range parentNode.children {
+		found, err := addChildrenFromNode(childNode)
+		if err != nil {
+			return nil, err
+		}
+		if found && all {
+			return children, nil
+		}
+	}
+
+	// Now check images with the same top layer.
+	if _, err := addChildrenFromNode(parentNode); err != nil {
+		return nil, err
+	}
+
+	return children, nil
+}
+
+// parent returns the parent image or nil if no parent image could be found.
+func (t *layerTree) parent(ctx context.Context, child *Image) (*Image, error) {
+	if child.TopLayer() == "" {
+		return nil, nil
+	}
+
+	node, exists := t.nodes[child.TopLayer()]
+	if !exists {
+		return nil, errors.Errorf("layer not found in layer tree: %q", child.TopLayer())
+	}
+
+	childOCI, err := t.toOCI(ctx, child)
+	if err != nil {
+		return nil, err
+	}
+
+	// Check images from the parent node (i.e., parent layer) and images
+	// with the same layer (i.e., same top layer).
+	childID := child.ID()
+	images := node.images
+	if node.parent != nil {
+		images = append(images, node.parent.images...)
+	}
+	for _, parent := range images {
+		if parent.ID() == childID {
+			continue
+		}
+		parentOCI, err := t.toOCI(ctx, parent)
+		if err != nil {
+			return nil, err
+		}
+		// History check.
+		if areParentAndChild(parentOCI, childOCI) {
+			return parent, nil
+		}
+	}
+
+	return nil, nil
+}
+
+// hasChildrenAndParent returns true if the specified image has children and a
+// parent.
+func (t *layerTree) hasChildrenAndParent(ctx context.Context, i *Image) (bool, error) {
+	children, err := t.children(ctx, i, false)
+	if err != nil {
+		return false, err
+	}
+	if len(children) == 0 {
+		return false, nil
+	}
+	parent, err := t.parent(ctx, i)
+	return parent != nil, err
+}
diff --git a/libpod/image/prune.go b/libpod/image/prune.go
index 8c9267650..5a9ca5d8e 100644
--- a/libpod/image/prune.go
+++ b/libpod/image/prune.go
@@ -66,6 +66,12 @@ func (ir *Runtime) GetPruneImages(ctx context.Context, all bool, filterFuncs []I
 	if err != nil {
 		return nil, err
 	}
+
+	tree, err := ir.layerTree()
+	if err != nil {
+		return nil, err
+	}
+
 	for _, i := range allImages {
 		// filter the images based on this.
 		for _, filterFunc := range filterFuncs {
@@ -85,8 +91,9 @@ func (ir *Runtime) GetPruneImages(ctx context.Context, all bool, filterFuncs []I
 			}
 		}
 
-		//skip the cache or intermediate images
-		intermediate, err := i.Intermediate(ctx)
+		// skip the cache (i.e., with parent) and intermediate (i.e.,
+		// with children) images
+		intermediate, err := tree.hasChildrenAndParent(ctx, i)
 		if err != nil {
 			return nil, err
 		}