Don't lock while creating ID-mapped layer when --userns keep-id is used

[dkleissa]

Feature request description

This request is related to existing discussion in containers/podman#16541 where the --userns keep-id option is used with podman run.

Depending on the image, there can be a very long delay while the ID-mapped layer is created while using the --userns keep-id option. While it is understood that this is unavoidable with rootless podman, during this time all commands to podman hang.

The fact that podman completely hangs during this time is confusing and can cause other operations to fail. Is it possible to not lock out podman commands during this operation?

Suggest potential solution

Ideally, using podman run with the --userns keep-id option does not cause all other podman commands to hang until the operation completes.

Have you considered any alternatives?

No response

Additional context

No response