oci/*: major split ups

[cyphar]

In preparation for migrating most of oci/* to image-tools or some such
repo, we need to split up several packages so that they are less of a
conglomeration and more of a useful set of packages that implement the minimal
functionality so other packages can build on top of them.

This changeset also includes quite a few refactorings to make certain
interfaces more generic, in anticipation for the requirements that
image-tools needs to fulfill using these libraries.

Things that need to be done:

• Split conversion (image -> runtime) from generation (image).
• Refactor GC by implementing a generic Walk utility.
• Split out gc and walk from oci/cas.

Possibilities:

• Instead of implementing all of the wrappers around cas.Engine as functions that take it as an argument, implement some wrapping structure that provides extra methods (but still provides the old ones) -- like a derived type.

• Split oci/cas/dir.go into some sort of "drivers"-style code so that multiple drivers can more easily be added later. To be honest, this isn't something we need right now -- and the code is already separate enough that you could split it by just moving the file (even the tests would continue to work).

Signed-off-by: Aleksa Sarai asarai@suse.de

[wking]

On Sat, Feb 18, 2017 at 01:01:00PM -0800, Aleksa Sarai wrote: * oci: oci/generate -> oci/spec/generate

I know runtime-tools uses ‘Spec’ for the config Go type, but I'd recommend using ‘config’ instead of ‘spec’. Lots of things are spec'ed, but what you're generating here is an image-spec configuration. For more on this, see opencontainers/runtime-tools#266.

[wking]

On Sat, Feb 18, 2017 at 01:01:00PM -0800, Aleksa Sarai wrote: * .: remove LICENSE

From the commit message for e764c54:

It confuses GitHub's automated license detection.

Because the content you have there is the boilerplate, not the license itself. More on this exact issue in licensee/licensee#103. What you should have there is the Apache license itself (for an example, see opencontainers/project-template).

The header in every file describing the license is sufficient.

I don't think that's true. From the Apache license itself [1]:

4. Redistribution. You may reproduce and distribute copies of the Work or Derivative Works thereof in any medium, with or without modifications, and in Source or Object form, provided that You meet the following conditions: a. You must give any other recipients of the Work or Derivative Works a copy of this License; and

[1]: https://www.apache.org/licenses/LICENSE-2.0.html

[cyphar]

@wking I already have a full copy of the license in COPYING. Not to mention that the header itself tells you where you can get a copy of the license. This is really not the point of this PR. It'd be great if you didn't derail a PR like this with license discussion.

[wking]

On Sun, Feb 19, 2017 at 01:04:55PM -0800, Aleksa Sarai wrote: @wking I already have a full copy of the license in COPYING.

That should be all you need then. No need to have a separate LICENSE with just the boilerplate. Removing it (like you're doing in this PR) should un-confuse Licensee by avoiding licensee/licensee#103.

This is _really_ not the point of this PR.

I'd missed the presense of a separate COPYING (sorry about that). Maybe pull e764c54 into its own PR? I think the change it's making is good, although I'd prefer the commit message to be closer to: LICENSE: Remove boilerplate file (full license still in COPYING) It confuses GitHub's automated license detection (licensee/licensee#103). And with the full license in COPYING, there's no reason to have a separate file with just the boilerplate.

[cyphar]

LGTM