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rauc / meta-rauc

Yocto/Open Embedded meta layer for RAUC, the embedded Linux update framework
MIT License
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rauc: rauc-mark-good: disable implicit dependencies #307

Closed js731ca closed 4 months ago

js731ca commented 5 months ago

Having implicit dependencies enabled would lead to ordering cycles when enabling 'boot assessment', through systemd-boot-check-no-failures [1], which is a service that forces the multi-user.target to be reached before the boot-complete.target.

The ordering cycle in this case would be: boot-complete -requires-> systemd-boot-check-no-failures systemd-boot-check-no-failures -after-> multi-user rauc-mark-good -after-> boot-complete boot-complete -after-> multi-user multi-user -after-> rauc-mark-good

circle

Which systemd would break by simply not running rauc-mark-good.

The solution is to disable implicit dependencies that would otherwise add an 'After=rauc-mark-good.service' to the multi-user.target via the [Install] section.

Link: https://www.freedesktop.org/software/systemd/man/latest/systemd-boot-check-no-failures.html

ejoerns commented 4 months ago

Having implicit dependencies enabled would lead to ordering cycles when enabling 'boot assessment', through systemd-boot-check-no-failures [1], which is a service that forces the multi-user.target to be reached before the boot-complete.target.

Even if not using the example systemd-boot-check-no-failures directly, it is probably a good blueprint to order multi-user.target before boot-complete.target, yes.

@js731ca thank you for diving into this.

The solution is to disable implicit dependencies that would otherwise add an 'After=rauc-mark-good.service' to the multi-user.target via the [Install] section.

I had to look this up, so for reference: this addresses systemd behavior that's described in https://www.freedesktop.org/software/systemd/man/latest/systemd.target.html#Default%20Dependencies

Setting DefaultDependencies=no sounds reasonable to me. An alternative would be not to use WantedBy=multi-user.target for installation. But I actually don't know a better option, yet.

@michaelolbrich maybe?

js731ca commented 4 months ago

Setting DefaultDependencies=no sounds reasonable to me. An alternative would be not to use WantedBy=multi-user.target for installation. But I actually don't know a better option, yet.

@michaelolbrich maybe?

Btw: what also worked was using [Install] WantedBy=basic.target, since the service "just needs to be queued $somehow"... but the DefaultDependencies seemed cleaner to me

michaelolbrich commented 4 months ago

This looks like the correct solution to me. And the equivalent service from systemd (systemd-bless-boot.service) contains DefaultDependencies=no as well.