Squash image layers.

[lingdie]

What is the problem you're trying to solve

After committing a container, the commit image will continuously grow larger. Squashing the commit image layers can effectively reduce the size of the commit image.

Describe the solution you'd like

example commands:

# squash last 2 layers.
nerdctl squash docker.io/library/busybox:latest --from-layer 2 --tag docker.io/library/busybox:squash

Additional context

ref: https://github.com/goldmann/docker-squash

[lingdie]

I am interested in implementing this feature, but I might need your help. I have encountered the first problem.

After reading the commit code, I understood how to add a new layer to the image, but how do I merge the layers?

[lingdie]

I believe the implementation should avoid directly manipulating the fs corresponding to the layer.

Instead, the layers cloud be applied to the snapshot, and then the snapshot cloud be converted into a layer. Can the existing SDK achieve this logic?

[lingdie]

Here is my simple implementation. I would be happy to submit a pull request if there are plans to implement this feature.

https://github.com/lingdie/squash/blob/main/pkg/squash/runtime.go

[AkihiroSuda]

Thanks, feel free to submit a PR, but probably this command should be under nerdctl image and marked as an experimental feature
https://github.com/containerd/nerdctl/blob/main/docs/experimental.md?plain=1

nerdctl/pkg/cmd/image/convert.go

Line 214 in b030e1d

if options.EstargzExternalToc && !options.GOptions.Experimental {

[AkihiroSuda]

Also consider consolidating this to nerdctl image convert