system df: fix image-size calculations

Fix the image-size calculations of system-df, where the shared size is
the actual shared size with other images (including children) and the
(total) size is the sum of the shared and unique size [1].

To calculate parent/child relations, make use of the recently added
layer tree which allows for quick (and cached!) calculations.

Break calculating image disk usages into the image runtime to a) access
the layer tree, and b) make the code easier to maintain and extend.

[1] https://docs.docker.com/engine/reference/commandline/system_df/

Fixes: #7406
Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

2 files changed, 141 insertions, 55 deletions

diff --git a/libpod/image/df.go b/libpod/image/df.go
new file mode 100644
index 000000000..84cf7af9e
--- /dev/null
+++ b/libpod/image/df.go
@@ -0,0 +1,126 @@
+package image
+
+import (
+	"context"
+	"time"
+
+	"github.com/containers/image/v5/docker/reference"
+)
+
+// DiskUsageStat gives disk-usage statistics for a specific image.
+type DiskUsageStat struct {
+	// ID of the image.
+	ID string
+	// Repository of the first recorded name of the image.
+	Repository string
+	// Tag of the first recorded name of the image.
+	Tag string
+	// Created is the creation time of the image.
+	Created time.Time
+	// SharedSize is the amount of space shared with another image.
+	SharedSize uint64
+	// UniqueSize is the amount of space used only by this image.
+	UniqueSize uint64
+	// Size is the total size of the image (i.e., the sum of the shared and
+	// unique size).
+	Size uint64
+	// Number of containers using the image.
+	Containers int
+}
+
+// DiskUsage returns disk-usage statistics for the specified slice of images.
+func (ir *Runtime) DiskUsage(ctx context.Context, images []*Image) ([]DiskUsageStat, error) {
+	stats := make([]DiskUsageStat, len(images))
+
+	// Build a layerTree to quickly compute (and cache!) parent/child
+	// relations.
+	tree, err := ir.layerTree()
+	if err != nil {
+		return nil, err
+	}
+
+	// Calculate the stats for each image.
+	for i, img := range images {
+		stat, err := diskUsageForImage(ctx, img, tree)
+		if err != nil {
+			return nil, err
+		}
+		stats[i] = *stat
+	}
+
+	return stats, nil
+}
+
+// diskUsageForImage returns the disk-usage statistics for the spcified image.
+func diskUsageForImage(ctx context.Context, image *Image, tree *layerTree) (*DiskUsageStat, error) {
+	stat := DiskUsageStat{
+		ID:      image.ID(),
+		Created: image.Created(),
+	}
+
+	// Repository and tag.
+	var name, repository, tag string
+	for _, n := range image.Names() {
+		if len(n) > 0 {
+			name = n
+			break
+		}
+	}
+	if len(name) > 0 {
+		named, err := reference.ParseNormalizedNamed(name)
+		if err != nil {
+			return nil, err
+		}
+		repository = named.Name()
+		if tagged, isTagged := named.(reference.NamedTagged); isTagged {
+			tag = tagged.Tag()
+		}
+	} else {
+		repository = "<none>"
+		tag = "<none>"
+	}
+	stat.Repository = repository
+	stat.Tag = tag
+
+	// Shared, unique and total size.
+	parent, err := tree.parent(ctx, image)
+	if err != nil {
+		return nil, err
+	}
+	childIDs, err := tree.children(ctx, image, false)
+	if err != nil {
+		return nil, err
+	}
+	// Optimistically set unique size to the full size of the image.
+	size, err := image.Size(ctx)
+	if err != nil {
+		return nil, err
+	}
+	stat.UniqueSize = *size
+
+	if len(childIDs) > 0 {
+		// If we have children, we share everything.
+		stat.SharedSize = stat.UniqueSize
+		stat.UniqueSize = 0
+	} else if parent != nil {
+		// If we have no children but a parent, remove the parent
+		// (shared) size from the unique one.
+		size, err := parent.Size(ctx)
+		if err != nil {
+			return nil, err
+		}
+		stat.UniqueSize -= *size
+		stat.SharedSize = *size
+	}
+
+	stat.Size = stat.SharedSize + stat.UniqueSize
+
+	// Number of containers using the image.
+	containers, err := image.Containers()
+	if err != nil {
+		return nil, err
+	}
+	stat.Containers = len(containers)
+
+	return &stat, nil
+}
diff --git a/pkg/domain/infra/abi/system.go b/pkg/domain/infra/abi/system.go
index 914a7681d..57c098166 100644
--- a/pkg/domain/infra/abi/system.go
+++ b/pkg/domain/infra/abi/system.go
@@ -17,7 +17,6 @@ import (
 	"github.com/containers/podman/v2/pkg/rootless"
 	"github.com/containers/podman/v2/pkg/util"
 	"github.com/containers/podman/v2/utils"
-	"github.com/docker/distribution/reference"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
@@ -199,71 +198,32 @@ func (ic *ContainerEngine) SystemDf(ctx context.Context, options entities.System
 		dfImages = []*entities.SystemDfImageReport{}
 	)
 
-	// Get Images and iterate them
+	// Compute disk-usage stats for all local images.
 	imgs, err := ic.Libpod.ImageRuntime().GetImages()
 	if err != nil {
 		return nil, err
 	}
-	for _, i := range imgs {
-		var sharedSize uint64
-		cons, err := i.Containers()
-		if err != nil {
-			return nil, err
-		}
-		imageSize, err := i.Size(ctx)
-		if err != nil {
-			return nil, err
-		}
-		uniqueSize := *imageSize
 
-		parent, err := i.GetParent(ctx)
-		if err != nil {
-			return nil, err
-		}
-		if parent != nil {
-			parentSize, err := parent.Size(ctx)
-			if err != nil {
-				return nil, err
-			}
-			uniqueSize = *parentSize - *imageSize
-			sharedSize = *imageSize - uniqueSize
-		}
-		var name, repository, tag string
-		for _, n := range i.Names() {
-			if len(n) > 0 {
-				name = n
-				break
-			}
-		}
-
-		if len(name) > 0 {
-			named, err := reference.ParseNormalizedNamed(name)
-			if err != nil {
-				return nil, err
-			}
-			repository = named.Name()
-			if tagged, isTagged := named.(reference.NamedTagged); isTagged {
-				tag = tagged.Tag()
-			}
-		} else {
-			repository = "<none>"
-			tag = "<none>"
-		}
+	imageStats, err := ic.Libpod.ImageRuntime().DiskUsage(ctx, imgs)
+	if err != nil {
+		return nil, err
+	}
 
+	for _, stat := range imageStats {
 		report := entities.SystemDfImageReport{
-			Repository: repository,
-			Tag:        tag,
-			ImageID:    i.ID(),
-			Created:    i.Created(),
-			Size:       int64(*imageSize),
-			SharedSize: int64(sharedSize),
-			UniqueSize: int64(uniqueSize),
-			Containers: len(cons),
+			Repository: stat.Repository,
+			Tag:        stat.Tag,
+			ImageID:    stat.ID,
+			Created:    stat.Created,
+			Size:       int64(stat.Size),
+			SharedSize: int64(stat.SharedSize),
+			UniqueSize: int64(stat.UniqueSize),
+			Containers: stat.Containers,
 		}
 		dfImages = append(dfImages, &report)
 	}
 
-	//	GetContainers and iterate them
+	// Get Containers and iterate them
 	cons, err := ic.Libpod.GetAllContainers()
 	if err != nil {
 		return nil, err