containerd/save: Export only present platform manifests

[vvoland]

Follow-up to:

• emptyfs: Use newer image layout #31

Changing load to import all platforms breaks the use case:

dockef pull busybox
docker save busybox > busybox.tar

# after docker image prune -a, or other daemon
docker load <busybox.tar

Because exporting the image (even with platform matcher) does export the whole manifest list referencing other platforms blobs (even if we don't have them).

Perhaps that's something that could be worked on upstream - for example adding the flag for Import to ignore importing the missing blobs? On the other hand the solution in this PR seems a bit better to me - because it feels wrong for the manifest in the archive to reference data it doesn't contain.

Signed-off-by: Paweł Gronowski pawel.gronowski@docker.com

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[rumpl]

nit: we don't really nee the is parameter, we can use cs.client.ImageService() directly

[vvoland]

done

[vvoland]

Rebased on the c8d branch

[thaJeztah]

For upstreaming;

• should include c8d/push: Push lazy blobs with distribution source labels #74
• possibly (could be separate) c8d/push: Fetch missing resources that can't be mounted #80