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overlay: Extend documentation comment for layout#1933

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overlay: Extend documentation comment for layout#1933
cgwalters wants to merge 1 commit intocontainers:mainfrom
cgwalters:doc-architecture

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@cgwalters
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@cgwalters cgwalters commented May 30, 2024

Let's expand the existing doc comment, as it's really
useful to understand the implementation in order to
debug or improve things.

We also clearly say first that these are implementation details.

Signed-off-by: Colin Walters walters@verbum.org

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BTW, feel free to (please do) just force push updates to this PR to add/fix things.

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Just some quick comments because I glanced at the PR list…

One vague thought: that there are two very different audiences who might read this: support investigators who need to understand some specific broken filesystem state, and developers who need to understand all possible combinations and rules and invariants.

Comment thread docs/containers-storage-architecture.md Outdated
Comment thread docs/containers-storage-architecture.md Outdated
## DESCRIPTION
The *containers/storage* library manages the following object types:

- layer: A filesystem tree, along with metadata
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… organized in, and optimized for, a tree of parent/child links, where a single “layer” may either serve as a complete filesystem tree, or a difference from the parent.

Comment thread docs/containers-storage-architecture.md Outdated
Comment on lines +15 to +16
- image: A reference to a layer, along with metadata
- container: A layer whose parent is an image
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These feel a bit too reductionist to me.

The important thing about images is that, unlike, layers, users frequently with deal with them directly; that they have human-usable names; and that they are nevertheless deduplicated.

The important thing about containers is… ? That the top layer is read-write? That a lot of the metadata is actually not in c/storage but in Podman’s / CRI-O’s data? Also, technically the parent of the container’s layer is still a layer.

Comment thread docs/containers-storage-architecture.md Outdated
- image: A reference to a layer, along with metadata
- container: A layer whose parent is an image

## Layer storage
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Discusssion of graph drivers?

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Would make sense to add in theory but I personally don't care much since I think we're in a place where there is only the overlay driver that matters, right?

Comment thread docs/containers-storage-architecture.md Outdated
Comment thread docs/containers-storage-architecture.md Outdated
Comment thread docs/containers-storage-architecture.md Outdated
Comment thread docs/containers-storage-architecture.md Outdated
Let's expand the existing doc comment, as it's really
useful to understand the implementation in order to
debug or improve things.

We also clearly say first that these are implementation details.

Signed-off-by: Colin Walters <walters@verbum.org>
@cgwalters cgwalters changed the title docs: Add containers-storage-architecture.md overlay: Extend documentation comment for layout May 31, 2024
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rhatdan commented Jun 5, 2024

@giuseppe PTAL

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rhatdan commented Jun 5, 2024

/approve

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openshift-ci Bot commented Jun 5, 2024

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cgwalters, rhatdan

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@openshift-ci openshift-ci Bot added the approved label Jun 5, 2024
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rhatdan commented Jun 5, 2024

LGTM

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rhatdan commented Jun 20, 2024

@giuseppe @saschagrunert @mtrmac PTAL

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This one isn't urgent, I think we can just leave it as draft and I may circle back to it later. No need for others to dive in for review now, we have more important things.

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Hi, and thank you for your contribution!

We’ve recently migrated this repository into a new monorepo: containers/container-libs along with other repositories

As part of this migration, this repository is no longer accepting new Pull-Requests and therefore this Pull-Request is being closed.

Thank you very much for your contribution. We would appreciate your continued help in migrating this PR to the new container-libs repository. Please let us know if you are facing any issues.

You can read more about the migration and the reasoning behind it in our blog post: Upcoming migration of three containers repositories to monorepo.

Thanks again for your work and for supporting the containers ecosystem!

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4 participants