UNIQUE SIZE column of docker system df -v should sum to total image occupancy

[exposedcranium]

Description

NOTE: I am listing this as a bug as I believe UNIQUE SIZE must sum to the total image occupancy as reported by docker system df.

The output of docker system df -v is not as useful as it could be. As it currently stands, many images may "pretend" to be completely shared (UNIQUE SIZE of 0B) as the top-level layer is a nop.

This yields the degenerative case where a docker image whose last build step is something like an ENV will always show a unique size of 0B.

A quick fix for this would be to show untagged/intermediate layers (such as in docker images -a).

A better fix would be to improve this view to show layer hierarchies and sharing relationships. This is an important debug tool for registry optimisation, but it still isn't present in the CLI.

Reproduce

docker system df -v

Expected behavior

No response

docker version

Client: Docker Engine - Community
 Version:           23.0.4
 API version:       1.42
 Go version:        go1.19.8
 Git commit:        f480fb1
 Built:             Fri Apr 14 10:32:03 2023
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          23.0.4
  API version:      1.42 (minimum version 1.12)
  Go version:       go1.19.8
  Git commit:       cbce331
  Built:            Fri Apr 14 10:32:03 2023
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.20
  GitCommit:        2806fc1057397dbaeefbea0e4e17bddfbd388f38
 runc:
  Version:          1.1.5
  GitCommit:        v1.1.5-0-gf19387a
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

docker info

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.10.4
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.17.2
    Path:     /usr/libexec/docker/cli-plugins/docker-compose

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 76
 Server Version: 23.0.4
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 2806fc1057397dbaeefbea0e4e17bddfbd388f38
 runc version: v1.1.5-0-gf19387a
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: builtin
  cgroupns
 Kernel Version: 5.15.0-86-generic
 Operating System: Ubuntu 22.04.2 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 32
 Total Memory: 117.1GiB
 Name: at-gitlab-runner
 ID: bba78f4a-9d21-41c7-96d6-02cd5f124b16
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

Additional Info

No response