Containers should be pruned before pods

[QuLogic]

Is this a BUG REPORT or FEATURE REQUEST? (leave only one on its own line)

/kind bug

Description

Say we're running through a Podman tutorial and want to clean up afterwards. Using podman system prune fails because pods are deleted before containers.

Steps to reproduce the issue:

1. podman run -dt --pod new:nginx -p 32597:80 quay.io/libpod/alpine_nginx:latest
2. podman pod stop nginx
3. podman system prune

Describe the results you received:

WARNING! This will remove:
        - all stopped containers
        - all stopped pods
        - all dangling images
        - all build cache
Are you sure you want to continue? [y/N] y
Deleted Pods
Error: pod 764aea25e5feca61a840898c78445f990358495c39cd2ba26b893ae1f048b4d0 contains containers and cannot be removed: container already exists

Describe the results you expected:
Pruning should remove the stopped containers in a fully stopped pod before removing the pod. If only parts of a pod are stopped, then it should skip deleting the pod entirely.

The error message is also a bit weird; I'm not creating a new container so it should not "already" exist.

Output of podman version:

Version:            1.6.1
RemoteAPI Version:  1
Go Version:         go1.12.9
OS/Arch:            linux/amd64

Output of podman info --debug:

debug:
  compiler: gc
  git commit: ""
  go version: go1.12.9
  podman version: 1.6.1
host:
  BuildahVersion: 1.11.2
  CgroupVersion: v1
  Conmon:
    package: conmon-2.0.1-1.fc30.x86_64
    path: /usr/bin/conmon
    version: 'conmon version 2.0.1, commit: 4346fbe0b2634b05857973bdf663598081240374'
  Distribution:
    distribution: fedora
    version: "30"
  MemFree: 249163776
  MemTotal: 4042072064
  OCIRuntime:
    package: runc-1.0.0-95.rc9.gitc1485a1.fc30.x86_64
    path: /usr/bin/runc
    version: |-
      runc version 1.0.0-rc9+dev
      commit: 0840802d505e28d3adcbc7a275cbeadbdf64ddec
      spec: 1.0.1-dev
  SwapFree: 4001206272
  SwapTotal: 4278185984
  arch: amd64
  cpus: 4
  eventlogger: journald
  hostname: TerraNova
  kernel: 5.2.17-200.fc30.x86_64
  os: linux
  rootless: true
  slirp4netns:
    Executable: /usr/bin/slirp4netns
    Package: slirp4netns-0.4.0-4.git19d199a.fc30.x86_64
    Version: |-
      slirp4netns version 0.4.0-beta.2
      commit: 19d199a6ca424fcf9516320a327cedad85cf4dfb
  uptime: 72h 3m 4.52s (Approximately 3.00 days)
registries:
  blocked: null
  insecure: null
  search:
  - docker.io
  - registry.fedoraproject.org
  - quay.io
  - registry.access.redhat.com
  - registry.centos.org
store:
  ConfigFile: ~/.config/containers/storage.conf
  ContainerStore:
    number: 2
  GraphDriverName: overlay
  GraphOptions:
    overlay.mount_program:
      Executable: /usr/bin/fuse-overlayfs
      Package: fuse-overlayfs-0.6.4-2.fc30.x86_64
      Version: |-
        fusermount3 version: 3.6.2
        fuse-overlayfs: version 0.6.4
        FUSE library version 3.6.2
        using FUSE kernel interface version 7.29
  GraphRoot: ~/.local/share/containers/storage
  GraphStatus:
    Backing Filesystem: extfs
    Native Overlay Diff: "false"
    Supports d_type: "true"
    Using metacopy: "false"
  ImageStore:
    number: 4
  RunRoot: /run/user/$ID
  VolumePath: ~/.local/share/containers/storage/volumes

Package info (e.g. output of rpm -q podman or apt list podman):

podman-1.6.1-2.fc30.x86_64

[QuLogic]

Note: I need to podman rm the stopped nginx container for podman system prune to work on the pod. It does not appear necessary to remove the infra container explicitly.

[rhatdan]

@QiWang19 PTAL

[QiWang19]

Note: I need to podman rm the stopped nginx container for podman system prune to work on the pod. It does not appear necessary to remove the infra container explicitly.

we can't prune containers before pod because the pod may have infra container. https://github.com/containers/libpod/blob/04e8bf3dba50e079278ac33b43ecc2ebb8f4a156/cmd/podman/system_prune.go#L81

After looking through the tutorial I think the stopped nginx container is not the infra container, it's a container created by podman run -dt.
I open a PR may be can fix this issue.