SWUpdate Update Flow¶

SWUpdatePlugin (plugin id swupdate) delegates the actual firmware install to systemd, and only supervises it.

When the OTA state machine enters its installing state, install_update starts a fresh transient unit, swupdate@<timestamp>.service, by calling StartUnit on the system D-Bus. It then returns without waiting for the unit to finish.

A separate task, monitor_update, polls the unit's ActiveState and SubState once per second until it reaches a terminal state, then drives the OTA state machine to update_successful or a failure state. On success, reboot_system starts systemd-reboot.service to boot into the new firmware.

Design notes¶

• A transient unit per install. Each attempt uses a uniquely named instance of the swupdate@.service template, isolating its systemd state and leaving a per-attempt journal.
• A separate monitor task. StartUnit only confirms that systemd accepted the request, so completion is observed asynchronously by monitor_update after install_update returns.
• Reboot only on success. A failed install leaves the current, working firmware in place; only update_successful triggers the reboot.

Relationship to the OTA state machine¶

install_update and monitor_update implement, for systemd, the generic transitions Py ToloMEO's OTA state machine defines. See the OTA State Machine reference for the states and transitions, and OTA Mechanism for how the FSM, checkpointing, and plugin hooks fit together across any OTAPlugin.