Define generic directory heirarchy for content addressable objects

[stevvooe]

#38, #23 and #94 outlined support for transporting content addressable OCI image objects in a tar layer. Tar may not be a desirable transport in all cases. We need to ensure that we have a generic layout that can work in several situations:

1. Directory layout works in zipfile.
2. Directory layout works on most filesystems.
3. Works over ssh or other path oriented platforms.

A CAS image layout has the following properties:

1. Only objects are files and directories.
2. Metadata is not preserved.
3. Atomic assembly may be undefined (writes).

This issue can be closed when we are confident that the image layout specification is sufficiently generic:

• Confirm that current image layout doesn't require backwards compatible changes to support this. (pre-1.0)
• Confirm shipping of content over the following:
  • Plain old directory on windows and unix platform
  • Translating between zip and tar is lossless.
• Consider directory layout as a possible caching target

My guess is that we already meet much of this criteria. Footwork will be in cross-platform confirmation.

[vbatts]

What issues with the image-layout are you thinking regarding zip files Or
ar or etc?

On Wed, Jun 15, 2016, 18:59 Stephen Day notifications@github.com wrote:

#38 #38, #23
#23 and #94
#94 outlined support
for transporting content addressable OCI image objects in a tar layer. Tar
may not be a desirable transport in all cases. We need to ensure that we
have a generic layout that can work in several situations:

1. Directory layout works in zipfile.
2. Directory layout works on most filesystems.
3. Works over ssh or other path oriented platforms.

A CAS image layout has the following properties:

1. Only objects are files and directories.
2. Metadata is not preserved.
3. Atomic assembly may be undefined (writes).

This issue can be closed when we are confident that the image layout
specification is sufficiently generic:

• Confirm that current image layout doesn't require backwards
  compatible changes to support this.
• Confirm shipping of content over the following:
  • Plain old directory on windows and unix platform
  • Translating between zip and tar is lossless.
• Consider directory layout as a possible caching target

My guess is that we already meet much of this criteria. Footwork will be
in cross-platform confirmation.

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[stevvooe]

What issues with the image-layout are you thinking regarding zip files Or
ar or etc?

My guess is that there are none. We don't require metadata, links or any other special features.

I hadn't consider ar.

[wking]

On Wed, Jun 15, 2016 at 03:59:11PM -0700, Stephen Day wrote:

#38, #23 and #94 outlined support for transporting content
addressable OCI image objects in a tar layer. Tar may not be a
desirable transport in all cases. We need to ensure that we have a
generic layout that can work in several situations:

1. Directory layout works in zipfile.
2. Directory layout works on most filesystems.
3. Works over ssh or other path oriented platforms.

#94 does not single out tar and explicily mentions zip, NFS, HTTP,
FTP, and rsync 1. I don't see any problems to be solved by this
issue, but it would be nice to replace image/walker with a generic CAS
API so we could more cleanly plug in backends for these various
transport mechanisms and file formats.

[philips]

In the OCI f2f we discussed that if you want to share blobs/ between multiple layouts that is totally reasonable. I will close this out for now.

🎤 💧