rkt, config: Add loading configuration from user directory

[krnowak]

Fixes #1568.

This is rather a complete fix code-wise, though untested. Still need to update the documentation where necessary and probably add some functional tests.

[alban]

• tests
• documentation
• changelog

Do we have a test that fetch images from several different users? E.g. 1 image fetched by 1 user, and deleted by another user, etc.

[krnowak]

The local configuration directory path is passed down to stage1. Should user config be passed there as well? This would allow us to override networking configuration. Not sure about the overriding semantics, that would be up to the stage1 implementation to decide I guess.

[alban]

Non-root users can run rkt fetch but not rkt run so they cannot do anything with stage1. So I don't think stage1 needs to have access to user config.

[jonboulle]

So I don't think stage1 needs to have access to user config.

hmm? what about for the aforementioned network example?

[krnowak]

Non-root users can run rkt fetch but not rkt run so they cannot do anything with stage1. So I don't think stage1 needs to have access to user config.

I think that the problem here is that you think of --user-config's value as a config provided by non-root user, which is not a point. It is just a name (I'd like to hear suggestions for better names, though, that would convey that it is going to override local config, like local config is overriding system config). You could use --user-config flag as a root like sudo rkt --user-config=${HOME}/test-cfg run coreos.com/etcd:v2.0.10.

[jonboulle]

Right. We need this for #1992

[krnowak]

ping @robszumski about possible better name for the --user-config flag.

[alban]

• back quotes around --user-config
• link to the pull request
• link to the doc. "See rkt's Global Options documentation.
• why is it useful from a user perspective? E.g. fetching as user while keeping credentials in the user directory. Or using networking plugins installed in a different directory. (Is it correct?)

[robszumski]

--user-config sounds ok because it matches the existing flags. Ideally it would indicate that it was a directory, so something like --user-config-dir, but its fine as is.

[krnowak]

Do we have a test that fetch images from several different users? E.g. 1 image fetched by 1 user, and deleted by another user, etc.

How about this test - https://github.com/coreos/rkt/blob/master/tests/rkt_non_root_test.go#L91 Is root there somehow special or can be treated as any other users in this case?

[alban]

@krnowak ok. So the test already exists :)

[krnowak]

Updated, for now I decided not to forward the user config path to stage1. This needs a bit more work.

[iaguis]

s/Can be useful/It can be useful/

s/in the globally/in a globally/

[iaguis]

LGTM after the nits

[krnowak]

About config for stage1 - #2013.