added contrib/Dokerfile.armv7 to build docker on ARMv7 with the original...

[umiddelb]

.../unpatched sources

Hi,

I've modified the existing Dockerfile in order to build docker successfully for ARMv7 on ARMv7 (since this commit with the original sources :). If you find it useful you may add this to the contrib directory (other docker users would appreciate this as well. I'll try to keep at least the release versions in sync.

Regards
Uli Middelberg uli@middelberg.de

[jessfraz]

Can you please sign your commits following these rules:

https://github.com/docker/docker/blob/master/CONTRIBUTING.md#sign-your-work

The easiest way to do this is to amend the last commit:

git commit --amend -s --no-edit && git push -f

[tiborvass]

@umiddelb Thanks very much for your contribution, however we wouldn't like to duplicate Dockerfiles just to add a few arch specific variations.

I believe @duglin has some ideas on how to parameterize Dockerfiles in a way that could be used for having docker build on ARMv7.

I'm gonna close this PR for now, if anyone finds a better way please comment below and we could reopen it. Again, we DO WANT this!

[umiddelb]

@duglin
Fine, let's discuss. I see tree different kinds of changes:

• Changes related to the ARMv7 platform, e.g. FROM ...
• Changes related to vanilla ubuntu_core taken as baseimage, e.g. RUN apt-get update ...
• Changes making the build process run in a smarter way, e.g. RUN dpkg-divert --local --rename ...

[duglin]

ping @brahmaroutu

[duglin]

@umiddelb as mentioned, there is work going on to add more flexibility to Dockerfile processing. @brahmaroutu is working on adding if-statement support - a first pass can be seen here: https://github.com/brahmaroutu/docker/tree/ifdef_commands hopefully a PR will be created for soon, but some other pieces of work need to come first - like: #9176 .

[umiddelb]

@brahmaroutu
Do you have written down your ideas in a 'design document' explaining how the if-statement support will look like?
Will you equip the docker binary with some predefined primitives?
How can I interact inside the Dockerfile with the operation system and the environment variables?

[brahmaroutu]

@umiddelb As pointed out by @duglin once the build supports environment variables and the ifdef capability in the docker file we can pretty much have good control on Dockerfile. Please checkout also
https://github.com/brahmaroutu/docker/compare/gccgo_x86 where the Dockerfile and the Makefile would demo how we have gc or gccgo builds. We can invoke the build using a command like "make binary gccgo=true" for example. Please review and let me know. Also please follow #9207