[Request]: add `container export` for running containers.

[saehejkang]

Feature or enhancement request details

Using container export on a running container produces the following error:

% container export -o liveexport-test-run-1.tar liveexport-test-run
Error: failed to export container (cause: "invalidState: "container is not stopped"")

The export function should also work for running containers.

Relates To

#1399

Code of Conduct

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[saehejkang]

currently working on this

[jglogan]

@saehejkang you mentioned that you'd like to learn more about containerization?

If you implement apple/containerization#660, we should be able to get guaranteed-correct --live snapshots for both container export and container commit.

[saehejkang]

you mentioned that you'd like to learn more about containerization?

Yep! I can work on that issue before doing container export and container commit.

[dcantah]

Thinking more on this, what is the rationale for --live? Today we don't have commit at all right? I'd think it'd be much easier to just freeze the cgroup for the container (so nothing can write to the block dev anyways) than freeze the blockdev itself.

[saehejkang]

Today we don't have commit at all right?

Yes there is no commit command at the moment.