Don't require reboot if setting fan control

Signed-off-by: Christina Ying Wang <christina@balena.io>

src/config/backends/backend.ts

@@ -41,6 +41,12 @@ export abstract class ConfigBackend {
 	// Example an empty string should return null.
 	public abstract createConfigVarName(configName: string): string | null;
 
+	// Is a reboot required for the given config options?
+	// eslint-disable-next-line @typescript-eslint/no-unused-vars
+	public async isRebootRequired(_opts: ConfigOptions): Promise<boolean> {
+		return true;
+	}
+
 	// Allow a chosen config backend to be initialised
 	public async initialise(): Promise<ConfigBackend> {
 		return this;

src/config/backends/power-fan.ts

@@ -1,6 +1,7 @@
 import { isRight } from 'fp-ts/lib/Either';
 import Reporter from 'io-ts-reporters';
 import * as t from 'io-ts';
+import * as _ from 'lodash';
 
 import { ConfigBackend } from './backend';
 import type { ConfigOptions } from './backend';
@@ -145,6 +146,16 @@ export class PowerFanConfig extends ConfigBackend {
 		return PowerFanConfig.CONFIGS.has(PowerFanConfig.stripPrefix(envVar));
 	}
 
+	public async isRebootRequired(opts: ConfigOptions): Promise<boolean> {
+		const supportedOpts = _.pickBy(
+			_.mapKeys(opts, (_value, key) => PowerFanConfig.stripPrefix(key)),
+			(_value, key) => this.isSupportedConfig(key),
+		);
+		const current = await this.getBootConfig();
+		// A reboot is only required if the power mode is changing
+		return current.power_mode !== supportedOpts.power_mode;
+	}
+
 	public processConfigVarName(envVar: string): string {
 		return PowerFanConfig.stripPrefix(envVar).toLowerCase();
 	}

src/device-config.ts

@@ -529,18 +529,21 @@ async function getBackendSteps(
 	const { deviceType } = await config.getMany(['deviceType']);
 
 	// Check for required bootConfig changes
+	let rebootRequired = false;
 	for (const backend of backends) {
 		if (changeRequired(backend, current, target, deviceType)) {
 			steps.push({
 				action: 'setBootConfig',
 				target,
 			});
+			rebootRequired =
+				(await backend.isRebootRequired(target)) || rebootRequired;
 		}
 	}
 
 	return [
-		// All backend steps require a reboot
-		...(steps.length > 0
+		// All backend steps require a reboot except fan control
+		...(steps.length > 0 && rebootRequired
 			? [{ action: 'setRebootBreadcrumb' } as ConfigStep]
 			: []),
 		...steps,