Easier handling for disabled qvm-services

[marmarek]

How to file a helpful issue

The problem you're addressing (if any)

Right now, enabling qvm-service creates a /run/qubes-service/(service-name) file, which then can be used for ConditionPathExists=... in a systemd unit file. Disabling a service that is normally enabled prevents creating such file (or rather - removes the file that was created for default-enabled services). But explicitly disabled service is not easily distinguishable from not set service. This means services that each service that should be enabled by default, but can be disabled via qvm-service needs the file first to be created (for example in qubes-sysinit.sh) and then removed. The need to modify qubes-sysinit.sh makes it harder to use this method in other packages, and also doesn't scale well.

The solution you'd like

For disabled services, not only remove relevant /run/qubes-service file, but also create negated one. For example /run/qubes-service/no-(service-name), or maybe /run/qubes-service-disable/(service-name). Then, a systemd unit can have a ConditionPathExists=!/run/... and no qubes-sysinit.sh modification is needed.

The value to a user, and who that user might be

More flexible qvm-service framework.

Completion criteria checklist

(This section is for developer use only. Please do not modify it.)

• Decide on specific path
• Extend qubes-sysinit.sh to create relevant negated files
• Update documentation (https://www.qubes-os.org/doc/qubes-service/, https://dev.qubes-os.org/projects/core-admin/en/latest/qubes-features.html#services)