REST API /system/df UsageData.RefCount on volumes is always 1

[benoitf]

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

/kind bug

Description

In order to see who is using a volume, I'm using the RefCount attribute of UsageData field

But even if you create a volume without using it, it returns 1.
And if you create multiple containers using that volume, it's still using 1

Steps to reproduce the issue:

1. Create a volume without using it

$ dummyVolume=$(podman volume create)

Use REST api to see refCount

$ curl --silent --unix-socket /Users/benoitf/.local/share/containers/podman/machine/podman-machine-default/podman.sock "http:/v1.41/system/df" | jq --arg volumeName $dummyVolume '.Volumes[] | select(.Name == ($volumeName))'
{
  "Driver": "",
  "Labels": {},
  "Mountpoint": "",
  "Name": "413f47a2d1656a4ec6e876543dc8a0caa5256c670a425638eff7be9730da0229",
  "Options": null,
  "Scope": "local",
  "UsageData": {
    "RefCount": 1,
    "Size": 0
  }
}

It's already invalid

3. Now, try to start containers using that volume

$ podman run -d --mount "type=volume,src=$dummyVolume,target=/foo" docker.io/library/httpd
$ podman run -d --mount "type=volume,src=$dummyVolume,target=/foo" docker.io/library/httpd

4. Rest API is still invalid

$ curl --silent --unix-socket /Users/benoitf/.local/share/containers/podman/machine/podman-machine-default/podman.sock "http:/v1.41/system/df" | jq --arg volumeName $dummyVolume '.Volumes[] | select(.Name == ($volumeName))'
{
  "Driver": "",
  "Labels": {},
  "Mountpoint": "",
  "Name": "413f47a2d1656a4ec6e876543dc8a0caa5256c670a425638eff7be9730da0229",
  "Options": null,
  "Scope": "local",
  "UsageData": {
    "RefCount": 1,
    "Size": 0
  }
}

And we still have our container using it

$ podman inspect 18e7216f21ab0eddb5fab99c388ba04030809b6870cd0c595e7bc84008c7fb3d | jq '.[0].Mounts'
[
  {
    "Type": "volume",
    "Name": "413f47a2d1656a4ec6e876543dc8a0caa5256c670a425638eff7be9730da0229",
    "Source": "/var/home/core/.local/share/containers/storage/volumes/413f47a2d1656a4ec6e876543dc8a0caa5256c670a425638eff7be9730da0229/_data",
    "Destination": "/foo",
    "Driver": "local",
    "Mode": "",
    "Options": [
      "nosuid",
      "nodev",
      "rbind"
    ],
    "RW": true,
    "Propagation": "rprivate"
  }
]

Describe the results you received:
RefCount = 1

Describe the results you expected:
Valid RefCount

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

Output of podman version:

4.2.1

Output of podman info:

(paste your output here)

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

(paste your output here)

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

Yes/No

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

[benoitf]

Implementation is bogus:

podman/pkg/api/handlers/compat/system.go

Line 79 in 29d7ab3

RefCount: 1,

[vrothberg]

Thanks for reaching out, @benoitf!

@mheon PTAL

[mheon]

We can get an array of containers referencing a volume via VolumeInUse() from the state. Get the length of the array, and we have the refcount. I can take this.