system df: fix image-size calculations

Fix two bugs in `system df`:

1.  The total size was calculated incorrectly as it was creating the sum
    of all image sizes but did not consider that a) the same image may
    be listed more than once (i.e., for each repo-tag pair), and that
    b) images share layers.

    The total size is now calculated directly in `libimage` by taking
    multi-layer use into account.

2.  The reclaimable size was calculated incorrectly.  This number
    indicates which data we can actually remove which means the total
    size minus what containers use (i.e., the "unique" size of the image
    in use by containers).

NOTE: The c/storage version is pinned back to the previous commit as it
      is buggy.  c/common already requires the buggy version, so use a
      `replace` to force/pin.

Fixes: #16135
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

vendor/github.com/containers/common/libimage/disk_usage.go

@@ -28,26 +28,51 @@ type ImageDiskUsage struct {
 // DiskUsage calculates the disk usage for each image in the local containers
 // storage.  Note that a single image may yield multiple usage reports, one for
 // each repository tag.
-func (r *Runtime) DiskUsage(ctx context.Context) ([]ImageDiskUsage, error) {
+func (r *Runtime) DiskUsage(ctx context.Context) ([]ImageDiskUsage, int64, error) {
 	layerTree, err := r.layerTree()
 	if err != nil {
-		return nil, err
+		return nil, -1, err
 	}
 
 	images, err := r.ListImages(ctx, nil, nil)
 	if err != nil {
-		return nil, err
+		return nil, -1, err
 	}
 
+	var totalSize int64
+	visitedImages := make(map[string]bool)
+	visistedLayers := make(map[string]bool)
+
 	var allUsages []ImageDiskUsage
 	for _, image := range images {
 		usages, err := diskUsageForImage(ctx, image, layerTree)
 		if err != nil {
-			return nil, err
+			return nil, -1, err
 		}
 		allUsages = append(allUsages, usages...)
+
+		if _, ok := visitedImages[image.ID()]; ok {
+			// Do not count an image twice
+			continue
+		}
+		visitedImages[image.ID()] = true
+
+		size, err := image.Size()
+		if err != nil {
+			return nil, -1, err
+		}
+		for _, layer := range layerTree.layersOf(image) {
+			if _, ok := visistedLayers[layer.ID]; ok {
+				// Do not count a layer twice, so remove its
+				// size from the image size.
+				size -= layer.UncompressedSize
+				continue
+			}
+			visistedLayers[layer.ID] = true
+		}
+		totalSize += size
 	}
-	return allUsages, err
+	return allUsages, totalSize, err
 }
 
 // diskUsageForImage returns the disk-usage baseistics for the specified image.