WIP: Bug 1885365: update.go: use systemd presets to enable/disable units

[yuqi-zhang]

Change unit enable/disable to write a mco systemd preset file, so
that we can properly handle units not targetting multi-user.target.wants.
The code is essentially copied from Ignition/units and emulates
Ignition behaviour for this.

[openshift-ci-robot]

@yuqi-zhang: This pull request references Bugzilla bug 1885365, which is valid. The bug has been moved to the POST state. The bug has been updated to refer to the pull request using the external bug tracker.

3 validation(s) were run on this bug

• bug is open, matching expected state (open)
• bug target release (4.7.0) matches configured target release for branch (4.7.0)
• bug is in the state NEW, which is one of the valid states (NEW, ASSIGNED, ON_DEV, POST, POST)

In response to this:

WIP: Bug 1885365: update.go: use systemd presets to enable/disable units

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[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[openshift-ci-robot]

@yuqi-zhang: The following tests failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
ci/prow/unit	248d6d3	link	/test unit
ci/prow/okd-images	248d6d3	link	/test okd-images
ci/prow/okd-e2e-aws	248d6d3	link	/test okd-e2e-aws
ci/prow/images	248d6d3	link	/test images
ci/prow/e2e-aws-workers-rhel7	248d6d3	link	/test e2e-aws-workers-rhel7
ci/prow/e2e-aws	248d6d3	link	/test e2e-aws
ci/prow/e2e-ovn-step-registry	248d6d3	link	/test e2e-ovn-step-registry
ci/prow/e2e-metal-ipi	248d6d3	link	/test e2e-metal-ipi
ci/prow/e2e-gcp-op	248d6d3	link	/test e2e-gcp-op
ci/prow/e2e-upgrade	248d6d3	link	/test e2e-upgrade

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[yuqi-zhang]

I think I should perhaps just shell out directly to systemctl enable/disable, Benjamin noted that presets are really just used for defaults on firstboot.

[bgilbert]

The officially recommended approach for programmatic enable/disable operations at runtime is to use the systemd D-Bus API, but I don't know if that's feasible here.

[cgwalters]

I think I should perhaps just shell out directly to systemctl enable/disable, Benjamin noted that presets are really just used for defaults on firstboot.

Yeah, I think so. It'd be a lot simpler of a patch too.

[yuqi-zhang]

closing in favour of #2145

[openshift-ci-robot]

@yuqi-zhang: This pull request references Bugzilla bug 1885365. The bug has been updated to no longer refer to the pull request using the external bug tracker.

In response to this:

WIP: Bug 1885365: update.go: use systemd presets to enable/disable units

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.