Podman manifest inspect doesn't work with existing images

[fatherlinux]

/kind bug

Description

Podman manifest inspect only works with manifests created with podman, not with manifests that are created with docker and other tools. This can be tested by trying any image on a registry server.

Steps to reproduce the issue:

Any of these three commands will fail:

podman manifest inspect docker.io/library/busybox

podman manifest inspect registry.access.redhat.com/ubi8/ubi-minimal

podman manifest inspect registry.access.redhat.com/ubi8/ubi

Describe the results you received:

All three of the above command will fail with the following error:

Error: error inspect manifest registry.access.redhat.com/ubi8/ubi: loading manifest "registry.access.redhat.com/ubi8/ubi": unable to load manifest list: unsupported format "application/vnd.docker.distribution.manifest.v2+json": manifest type not supported

Describe the results you expected:
I would expect the "podman manifest inspect" command to work with pre-existing images, just like it works with manifests created by podman. Here's an example of this command functioning with a manifest created by podman:

[root@fedora ~]# podman manifest create mylist:v1.11
74ad8d03f4ed4802b3f9f3a715e5c75c17b574dc5c65370667de4ba0b89d78e1
[root@fedora ~]# podman manifest inspect mylist:v1.11
{
"schemaVersion": 2,
"mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
"manifests": null
}

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

Output of podman version:

Version:      2.0.6
API Version:  1
Go Version:   go1.14.6
Built:        Tue Sep  1 15:26:51 2020
OS/Arch:      linux/amd64

Output of podman info --debug:

host:
  arch: amd64
  buildahVersion: 1.15.1
  cgroupVersion: v2
  conmon:
    package: conmon-2.0.19-1.fc32.x86_64
    path: /usr/bin/conmon
    version: 'conmon version 2.0.19, commit: 5dce9767526ed27f177a8fa3f281889ad509fea7'
  cpus: 1
  distribution:
    distribution: fedora
    version: "32"
  eventLogger: file
  hostname: fedora.dc2.crunchtools.com
  idMappings:
    gidmap: null
    uidmap: null
  kernel: 5.6.6-300.fc32.x86_64
  linkmode: dynamic
  memFree: 892121088
  memTotal: 2075738112
  ociRuntime:
    name: crun
    package: crun-0.14.1-4.fc32.x86_64
    path: /usr/bin/crun
    version: |-
      crun version 0.14.1
      commit: 598ea5e192ca12d4f6378217d3ab1415efeddefa
      spec: 1.0.0
      +SYSTEMD +SELINUX +APPARMOR +CAP +SECCOMP +EBPF +YAJL
  os: linux
  remoteSocket:
    path: /run/podman/podman.sock
  rootless: false
  slirp4netns:
    executable: ""
    package: ""
    version: ""
  swapFree: 2147479552
  swapTotal: 2147479552
  uptime: 1h 57m 55.39s (Approximately 0.04 days)
registries:
  search:
  - registry.fedoraproject.org
  - registry.access.redhat.com
  - registry.centos.org
  - docker.io
store:
  configFile: /etc/containers/storage.conf
  containerStore:
    number: 0
    paused: 0
    running: 0
    stopped: 0
  graphDriverName: overlay
  graphOptions:
    overlay.mountopt: nodev,metacopy=on
  graphRoot: /var/lib/containers/storage
  graphStatus:
    Backing Filesystem: xfs
    Native Overlay Diff: "false"
    Supports d_type: "true"
    Using metacopy: "true"
  imageStore:
    number: 3
  runRoot: /var/run/containers/storage
  volumePath: /var/lib/containers/storage/volumes
version:
  APIVersion: 1
  Built: 1598988411
  BuiltTime: Tue Sep  1 15:26:51 2020
  GitCommit: ""
  GoVersion: go1.14.6
  OsArch: linux/amd64
  Version: 2.0.6

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

podman-2.0.6-1.fc32.x86_64

Have you tested with the latest version of Podman and have you checked the Podman Troubleshooting Guide?

Yes, this is the latest version on Fedora.

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

Probably does not apply to this problem, but on x86 in a Fedora based KVM virtual machine, running on RHEL

[QiWang19]

I'll take a look.