Re: [RFC container/storage] OCI image OverlayFS integration proposal

[Filip Schauer <f.schauer@proxmox.com>]

On 14/07/2026 16:11, Jörg Behrmann wrote:
> Hi!
>
> I usually only watch from the sidelines, but this just tumbled through my mail
> client while I was waiting for a build to finish. I've not read the whole
> proposel, so excuse me if this comment is silly…
>
> On Tue, Jul 14, 2026 at 03:19:09PM +0200, Filip Schauer wrote:
>> Directory structure of the content type:
>> ```
>> oci/
>> +-- layers/
>> |   +-- sha256-111.../
>> |   +-- sha256-222.../
>> |   `-- by-blob-id/
>> |       +-- sha256-abc...
>> |       `-- sha256-def...
>> `-- images/
>>      +-- sha256-9f86d081...
>>      `-- sha256-2c26b46b...
>> ```
>>
> This looks a bit like composefs. I grepped through your proposal and didn't see
> it mentioned.
>
> - The original C project https://github.com/composefs/composefs
> - The Rust rewrite https://github.com/composefs/composefs-rs
>
> RH built this because of their bootc plans. I'm not a fan of that and also not
> much a fan of OCI containers themselves, but I know the people working on it and
> they are nice and the project does have some cool uses.
>
> There's a talk from last year's All Systems Go at [1] and you can find the
> slides at [2]. The above reminded me particularly of slide 13 and later.
>
> I hope this isn't too far off from what you want to do.
>
> best regards,
> Jörg Behrmann
>
> [1] https://media.ccc.de/v/all-systems-go-2025-362-uki-composefs-and-remote-attestation-for-bootable-containers
> [2] https://cfp.all-systems-go.io/media/all-systems-go-2025/submissions/TNKPQS/resources/2025_All_Systems_Go_-_UKI_composefs_and_r9Z95aW.pdf

Hello,

thanks for pointing this out, composefs certainly looks interesting.

As I understand it, composefs deduplicates at the individual file level,
while my proposal deduplicates at the layer level.

composefs is not yet packaged in Debian stable. That said, it might be
something to keep in mind for a potential future extension.
For the initial version however, I would rather keep things simple and
stay aligned with the layer model defined by the OCI spec.