Set content labels based on content type

[dmcgowan]

This change gives control of the content labeling process for children to the client. This allows the client to control the names associated with the labels and filter out labels.

Includes and replaces changes from #4332

This newer approach avoids the additional label mutation pass after unpack. This prevents the process for removing previously set labels and better ensures the content gets garbage collected if the client ends the operation before the removal.

Comment from #4332

Fixes: #4304

This commit adds a flag through Pull API for allowing GC to clean layer contents up after unpacking these contents completed.

This patch takes an approach to directly delete GC labels pointing to layers from the manifest blob. This will result in other snapshotters cannot reuse these contents on the next pull. But this patch mainly focuses on CRI use-cases where single snapshotter is usually used throughout the node lifecycle so this shouldn't be a matter.

Could I get comments on this approach towards unpacked contents deduplication?
What I currently concern is whether is it OK to clean layers up immediately after the unpack because other services in containerd will also be inaccessible to that contents.

Related also to: #4249

[theopenlab-ci]

Build succeeded.

• containerd-build-arm64 : FAILURE in 2m 11s (non-voting)

[ktock]

LGTM

nit:
Converters add GC labels by their own so we can't dedupe old images that require manifest conversions. But they are special cases so I think we can make follow-up PRs for covering them as well (if needed).

containerd/remotes/docker/converter.go

Lines 78 to 81 in ec05460

	labels := map[string]string{}
	for i, c := range append([]ocispec.Descriptor{manifest.Config}, manifest.Layers...) {
	labels[fmt.Sprintf("containerd.io/gc.ref.content.%d", i)] = c.Digest.String()
	}

containerd/remotes/docker/schema1/converter.go

Lines 211 to 215 in ec05460

	labels := map[string]string{}
	labels["containerd.io/gc.ref.content.0"] = manifest.Config.Digest.String()
	for i, ch := range manifest.Layers {
	labels[fmt.Sprintf("containerd.io/gc.ref.content.%d", i+1)] = ch.Digest.String()
	}

[ktock]

And thanks a lot for this patch!

[crosbymichael]

LGTM

[fuweid]

LGTM

[AkihiroSuda]

@ktock Do you want to open a follow-up PR?

[ktock]

Yes, I'm willing to work on the following-up PRs and update on cri-plugin's side to enable this dedupe functionality. (update on cri plugin might be the first)