Added --export command

[craigloewen-msft]

I made a PR to add the --export command to nerdctl.

I did it to solve issues like #1854 and since I saw it had support from the maintainers.

I also looked at this PR for inspiration: https://github.com/containerd/nerdctl/pull/2161/files

Please let me know if you want any changes or if it looks good!

[craigloewen-msft]

@AkihiroSuda is this change good to go? Anything else I can do to help merge this in? :)

[AkihiroSuda]

Not compilable 😞

https://github.com/containerd/nerdctl/actions/runs/16174086400/job/45654760202?pr=4405

# github.com/containerd/nerdctl/v2/pkg/cmd/container
Error: pkg/cmd/container/export.go:69:38: undefined: containerutil.MountSnapshotForContainer

[craigloewen-msft]

Not compilable 😞

https://github.com/containerd/nerdctl/actions/runs/16174086400/job/45654760202?pr=4405

# github.com/containerd/nerdctl/v2/pkg/cmd/container
Error: pkg/cmd/container/export.go:69:38: undefined: containerutil.MountSnapshotForContainer

Fixed the build!

[craigloewen-msft]

@AkihiroSuda I fixed the PR!
Looks like all the linting succeeds now, it's using the correct WriteDiff function and the only failing tests seem to be from other causes.

[apostasie]

@craigloewen-msft
TestExportRunningContainer is failing.
https://github.com/containerd/nerdctl/actions/runs/16451175448/job/46496554366?pr=4405#step:9:42466

[craigloewen-msft]

@apostasie thank you for the spot. Seems like somehow it's failing on Windows? Would need to dig into that further but for now I have to pause for a little to prioritize my other work.

[craigloewen-msft]

Errors seem to be an access denied error and a can't access the file since it's already in use. Maybe my use of the snapshotter here is bad??

[craigloewen-msft]

I did investigation and docker just bans the exports of Windows containers. I think we should follow suite. @AkihiroSuda does this seem good to you? If so I can just add in an error saying export is not allowed on Windows.

[AkihiroSuda]

I did investigation and docker just bans the exports of Windows containers. I think we should follow suite

👍

[craigloewen-msft]

It seems like it passes all the tests now! I looked at the failures and they seem to be related to other issues. Is this ready to merge? Anything else I can fix?

[AkihiroSuda]

Please squash the commits

[craigloewen-msft]

Please squash the commits

Do you want me to squash all the commits on my fork? I could do that but it would break my GitHub history. Can you just squash it when you merge it in here using the 'squash commits' tool in the GitHub PR review?

If not, I'm happy to squash my commits and force a push to my main branch.

[AkihiroSuda]

Do you want me to squash all the commits on my fork?

Yes.

I could do that but it would break my GitHub history.

You can back up the history in your repo using git tags

Can you just squash it when you merge it in here using the 'squash commits' tool in the GitHub PR review?

We have been expecting contributors to tidy up the commit messages, so the "squash commits" button does not work for us.

CI is also failing
https://github.com/containerd/nerdctl/actions/runs/16732676050/job/47364238814?pr=4405

FAIL - does not have a valid DCO

[craigloewen-msft]

Tests all pass! The only failure is due to some other test failing.

Seems like we should be good to merge now :)

[AkihiroSuda]

Thanks