Add deadman: prime a forced reboot before risky PCIe ops#47
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The dpv1 wedge class that needs a power cycle is a driver/PCIe hang where the kernel and systemd stay alive and keep petting the hardware watchdog, so systemd's RuntimeWatchdog never fires, yet a clean reboot hangs on the stuck device. Arm schedules a sysrq-b (emergency_restart) as a cancellable transient systemd timer that survives the SSH session; disarm cancels it on clean completion. Complements systemd's watchdog, which still catches a full kernel lock.
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disarm now confirms the timer is inactive via systemctl is-active before reporting success, and raises DeadmanError otherwise, so a failed stop (auth/D-Bus) can no longer leave a healthy host to reboot. arm refuses to replace an already-armed timer, so concurrent callers cannot silently cancel each other's protection. A query that cannot confirm inactive is treated as still-armed.
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Rewrites the reboot-priming safety net for dpv1 board operations (rescan/flash/register-probe) that was never committed.
Mechanism
The wedge class that needed manual power cycles is a driver/PCIe hang where the kernel and systemd stay alive — they keep petting the hardware watchdog, so systemd's
RuntimeWatchdogSecnever fires, yetsystemctl reboothangs on the stuck device. Recovery issysrq-b(emergency_restart()), which resets past the wedged driver.armschedules the reset as a cancellable transientsystemd-runtimer (survives the controlling SSH session);disarmcancels it. A full kernel lock (systemd dead) is still caught by systemd's own hardware watchdog, so the two are complementary.dau-utils-deadman {arm,disarm,status}plus anarmed()context manager.Verified live on the dpv1 host: arm creates a pending timer, disarm removes it, no reboot triggered. Pure command-builders are unit-tested; sudo/systemd side effects are exercised only via
--dry-runin tests.