Podman behavior with shared volumes : copying files from mounted path

[pycloux]

/kind bug

Description

I don't know if this is "on purpose" but the behavior with named volumes is different between Docker and Podman.
If you mount an "empty" volume into a docker container to a new path (say "/opt/test") and then mount the same volume to another container to a "non-empty" path, then the content of the "non-empty" path will be copied on to the volume.
With Podman, the volume will remain "empty" as soon as it was mounted to one container.
Docker is more permissive and will allow the data to be copied if the volume is empty (even if it was mounted previously).

Steps to reproduce the issue:

1. create a new volume

$ podman volume create volume-test

2. create a container with the volume mapped to an empty location

$ podman run --rm -ti --name=centos-test -v volume-test:/opt/test centos:7

3. create a container with the volume mapped to a location with some pre-existing content:

$ podman run --rm -ti --name=centos-test -v volume-test:/var centos:7

Describe the results you received:

When running ls on the volume, that is to say either:

• ls /opt/test in the first container
• ls /var in the second container

The folder is empty.

Describe the results you expected:

With Docker, the folder would contain the content copied from the /var directory of the centos:7 container.

Additional information you deem important (e.g. issue happens only occasionally):

None

Output of podman version:

Version:      3.3.1
API Version:  3.3.1
Go Version:   go1.16.7
Built:        Wed Nov 10 01:48:06 2021
OS/Arch:      linux/amd64

Output of podman info --debug:

host:
  arch: amd64
  buildahVersion: 1.22.3
  cgroupControllers: []
  cgroupManager: cgroupfs
  cgroupVersion: v1
  conmon:
    package: conmon-2.0.29-1.module+el8.5.0+710+4c471e88.x86_64
    path: /usr/bin/conmon
    version: 'conmon version 2.0.29, commit: 7a80c42d2005a1f098cd800cd1db2b7a4ba8a8ae'
  cpus: 2
  distribution:
    distribution: '"rocky"'
    version: "8.4"
  eventLogger: file
  hostname: localhost.localdomain
  idMappings:
    gidmap:
    - container_id: 0
      host_id: 1000
      size: 1
    - container_id: 1
      host_id: 100000
      size: 65536
    uidmap:
    - container_id: 0
      host_id: 1000
      size: 1
    - container_id: 1
      host_id: 100000
      size: 65536
  kernel: 4.18.0-305.3.1.el8_4.x86_64
  linkmode: dynamic
  memFree: 7776194560
  memTotal: 8347975680
  ociRuntime:
    name: runc
    package: runc-1.0.2-1.module+el8.5.0+710+4c471e88.x86_64
    path: /usr/bin/runc
    version: |-
      runc version 1.0.2
      spec: 1.0.2-dev
      go: go1.16.7
      libseccomp: 2.5.1
  os: linux
  remoteSocket:
    path: /run/user/1000/podman/podman.sock
  security:
    apparmorEnabled: false
    capabilities: CAP_NET_RAW,CAP_CHOWN,CAP_DAC_OVERRIDE,CAP_FOWNER,CAP_FSETID,CAP_KILL,CAP_NET_BIND_SERVICE,CAP_SETFCAP,CAP_SETGID,CAP_SETPCAP,CAP_SETUID,CAP_SYS_CHROOT
    rootless: true
    seccompEnabled: true
    seccompProfilePath: /usr/share/containers/seccomp.json
    selinuxEnabled: true
  serviceIsRemote: false
  slirp4netns:
    executable: /usr/bin/slirp4netns
    package: slirp4netns-1.1.8-1.module+el8.5.0+710+4c471e88.x86_64
    version: |-
      slirp4netns version 1.1.8
      commit: d361001f495417b880f20329121e3aa431a8f90f
      libslirp: 4.4.0
      SLIRP_CONFIG_VERSION_MAX: 3
      libseccomp: 2.5.1
  swapFree: 2147479552
  swapTotal: 2147479552
  uptime: 1h 55m 35.28s (Approximately 0.04 days)
registries:
  search:
  - registry.fedoraproject.org
  - registry.access.redhat.com
  - registry.centos.org
  - docker.io
store:
  configFile: /home/vagrant/.config/containers/storage.conf
  containerStore:
    number: 0
    paused: 0
    running: 0
    stopped: 0
  graphDriverName: overlay
  graphOptions:
    overlay.mount_program:
      Executable: /usr/bin/fuse-overlayfs
      Package: fuse-overlayfs-1.7.1-1.module+el8.5.0+710+4c471e88.x86_64
      Version: |-
        fusermount3 version: 3.2.1
        fuse-overlayfs: version 1.7.1
        FUSE library version 3.2.1
        using FUSE kernel interface version 7.26
  graphRoot: /home/vagrant/.local/share/containers/storage
  graphStatus:
    Backing Filesystem: xfs
    Native Overlay Diff: "false"
    Supports d_type: "true"
    Using metacopy: "false"
  imageStore:
    number: 2
  runRoot: /run/user/1000/containers
  volumePath: /home/vagrant/.local/share/containers/storage/volumes
version:
  APIVersion: 3.3.1
  Built: 1636508886
  BuiltTime: Wed Nov 10 01:48:06 2021
  GitCommit: ""
  GoVersion: go1.16.7
  OsArch: linux/amd64
  Version: 3.3.1

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

podman-3.3.1-9.module+el8.5.0+710+4c471e88.x86_64

Have you tested with the latest version of Podman and have you checked the Podman Troubleshooting Guide? (https://github.com/containers/podman/blob/master/troubleshooting.md)

Podman troubleshooting guide : YES

Podman lastest release (3.4.0) : NO

Additional environment details (AWS, VirtualBox, physical, etc.):

Running in Vagrant with Virtualbox provider.