builder: check if patch was already applied before applying patch

[dongsupark]

Check if patch was already applied before applying patch. This will allow builder to work even if the kernel already includes the patch.

[alban]

So you rely on the fact that set -e at the beginning of the script does not apply inside the function?

LGTM if CircleCI is green.

[dongsupark]

Ah, I missed something. Force-pushed with set +e and patch -f.

[dongsupark]

Added a kernel config 4.12 to make CI work again. Now the CI passed.

[alban]

The PR itself is good, however I see that CircleCI (build 106) builds the following versions:

11825624 /tmp/circle-artifacts.jOtleV1/stage1-kvm-1.26.0-linux-4.12.4.aci
10565012 /tmp/circle-artifacts.jOtleV1/stage1-kvm-1.26.0-linux-4.1.38.aci
10938884 /tmp/circle-artifacts.jOtleV1/stage1-kvm-1.26.0-linux-4.4.45.aci
11063794 /tmp/circle-artifacts.jOtleV1/stage1-kvm-1.26.0-linux-4.8.13.aci
11285604 /tmp/circle-artifacts.jOtleV1/stage1-kvm-1.26.0-linux-4.9.9.aci

And the previous build generated the following artifacts:

$ curl -sSL 'https://circleci.com/api/v1.1/project/github/kinvolk/stage1-builder/latest/artifacts?branch=master&filter=successful' \
>   | jq -r .[].path \
>   | sed -e 's/.*\/\([^/]*\)\.aci$/\1/'
stage1-kvm-1.26.0-linux-4.1.38
stage1-kvm-1.26.0-linux-4.10.6
stage1-kvm-1.26.0-linux-4.11.5
stage1-kvm-1.26.0-linux-4.4.45
stage1-kvm-1.26.0-linux-4.8.13
stage1-kvm-1.26.0-linux-4.9.6
stage1-kvm-1.26.0-linux-4.9.9

So kernel 4.9.6 was previously built but not anymore. This is a problem because tcptracer-bpf and gobpf rely on it. See the following links:

• kernel versions for tcptracer-bpf
• kernel versions for gobpf
• discovery URL
• ac-discovery meta tags

So, merging this PR would break tcptracer-bpf and gobpf. @schu used to trigger parametric CircleCI builds manually to avoid this issue. But I think it is wrong that tcptracer-bpf and gobpf always use the last version of the stage1-builder builds. We should use something like this:

rkt image fetch --insecure-options=image kinvolk.io/aci/rkt/stage1-kvm:1.23.0,kernelversion=4.9.6,stage1builderversion=1.0

(specifying 3 versions instead of 2: the rkt version, the kernel version, and a version of the stage1builder, so downstream projects would not break on every stage1-builder PR)

And instead of picking the latest CircleCI artifacts, tcptracer-bpf and gobpf should stick to a specific CircleCI build.

[dongsupark]

@alban Thanks for the explanation. I'm fine with not merging it until we had a new versioning policy.

[schu]

Nitpick: we try to follow https://google.github.io/styleguide/shell.xml, i.e.

• use local variables in functions
• prefer [[ over [

Also, shellcheck complains about a couple of things (e.g. missing " quotes; not all from your change).

I'll try to get back to issue with build images / assets later this week.

[dongsupark]

@schu Pushed a new commit to fix shell style issues.