Android Shutdown Sequence: PowerOff Source Code Explained

frameworks/base/services/core/java/com/android/server/power/ShutdownThread.java

 /**
     * Request a clean shutdown, waiting for subsystems to clean up their
     * state etc.  Must be called from a Looper thread in which its UI
     * is shown.
     *
     * @param context Context used to display the shutdown progress dialog. This must be a context
     *                suitable for displaying UI (aka Themable).
     * @param reason code to pass to android_reboot() (e.g. "userrequested"), or null.
     * @param confirm true if user confirmation is needed before shutting down.
     */
    public static void shutdown(final Context context, String reason, boolean confirm) {
        mReboot = false;
        mRebootSafeMode = false;
        mReason = reason;
        shutdownInner(context, confirm);
    }

private static void shutdownInner(final Context context, boolean confirm) {
        // ShutdownThread is called from many places, so best to verify here that the context passed
        // in is themed.
        context.assertRuntimeOverlayThemable();

        // ensure that only one thread is trying to power down.
        // any additional calls are just returned
        synchronized (sIsStartedGuard) {
            if (sIsStarted) {
                Log.d(TAG, "Request to shutdown already running, returning.");
                return;
            }
        }

        final int longPressBehavior = context.getResources().getInteger(
                        com.android.internal.R.integer.config_longPressOnPowerBehavior);
        final int resourceId = mRebootSafeMode
                ? com.android.internal.R.string.reboot_safemode_confirm
                : (longPressBehavior == 2
                        ? com.android.internal.R.string.shutdown_confirm_question
                        : com.android.internal.R.string.shutdown_confirm);

        Log.d(TAG, "Notifying thread to start shutdown longPressBehavior=" + longPressBehavior);

        if (confirm) {
            final CloseDialogReceiver closer = new CloseDialogReceiver(context);
            if (sConfirmDialog != null) {
                sConfirmDialog.dismiss();
            }
            sConfirmDialog = new AlertDialog.Builder(context)
                    .setTitle(mRebootSafeMode
                            ? com.android.internal.R.string.reboot_safemode_title
                            : com.android.internal.R.string.power_off)
                    .setMessage(resourceId)
                    .setPositiveButton(com.android.internal.R.string.yes, new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int which) {
                            beginShutdownSequence(context);
                        }
                    })
                    .setNegativeButton(com.android.internal.R.string.no, null)
                    .create();
            closer.dialog = sConfirmDialog;
            sConfirmDialog.setOnDismissListener(closer);
            sConfirmDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG);
            sConfirmDialog.show();
        } else {
            beginShutdownSequence(context);
        }
    }

As you can now see, above code prints the log message

ShutdownThread: Notifying thread to start shutdown longPressBehavior=1

in logcat as we seen earlier at the beginning of the post. Now we will continue with the actual function getting called next is beginShutdownSequence

 private static void beginShutdownSequence(Context context) {
        synchronized (sIsStartedGuard) {
            if (sIsStarted) {
                Log.d(TAG, "Shutdown sequence already running, returning.");
                return;
            }
            sIsStarted = true;
        }
        sInstance.mProgressDialog = showShutdownDialog(context);
        sInstance.mContext = context;
        sInstance.mPowerManager = (PowerManager)context.getSystemService(Context.POWER_SERVICE);

        // make sure we never fall asleep again
        sInstance.mCpuWakeLock = null;
        try {
            sInstance.mCpuWakeLock = sInstance.mPowerManager.newWakeLock(
                    PowerManager.PARTIAL_WAKE_LOCK, TAG + "-cpu");
            sInstance.mCpuWakeLock.setReferenceCounted(false);
            sInstance.mCpuWakeLock.acquire();
        } catch (SecurityException e) {
            Log.w(TAG, "No permission to acquire wake lock", e);
            sInstance.mCpuWakeLock = null;
        }

        // also make sure the screen stays on for better user experience
        sInstance.mScreenWakeLock = null;
        if (sInstance.mPowerManager.isScreenOn()) {
            try {
                sInstance.mScreenWakeLock = sInstance.mPowerManager.newWakeLock(
                        PowerManager.FULL_WAKE_LOCK, TAG + "-screen");
                sInstance.mScreenWakeLock.setReferenceCounted(false);
                sInstance.mScreenWakeLock.acquire();
            } catch (SecurityException e) {
                Log.w(TAG, "No permission to acquire wake lock", e);
                sInstance.mScreenWakeLock = null;
            }
        }

        if (SecurityLog.isLoggingEnabled()) {
            SecurityLog.writeEvent(SecurityLog.TAG_OS_SHUTDOWN);
        }

        // start the thread that initiates shutdown
        sInstance.mHandler = new Handler() {
        };
        sInstance.start();
    }

/**
     * Makes sure we handle the shutdown gracefully.
     * Shuts off power regardless of radio state if the allotted time has passed.
     */
    public void run() {
        TimingsTraceLog shutdownTimingLog = newTimingsLog();
        shutdownTimingLog.traceBegin("SystemServerShutdown");
        metricShutdownStart();
        metricStarted(METRIC_SYSTEM_SERVER);

        BroadcastReceiver br = new BroadcastReceiver() {
            @Override public void onReceive(Context context, Intent intent) {
                // We don't allow apps to cancel this, so ignore the result.
                actionDone();
            }
        };

        /*
         * Write a system property in case the system_server reboots before we
         * get to the actual hardware restart. If that happens, we'll retry at
         * the beginning of the SystemServer startup.
         */
        {
            String reason = (mReboot ? "1" : "0") + (mReason != null ? mReason : "");
            SystemProperties.set(SHUTDOWN_ACTION_PROPERTY, reason);
        }

        /*
         * If we are rebooting into safe mode, write a system property
         * indicating so.
         */
        if (mRebootSafeMode) {
            SystemProperties.set(REBOOT_SAFEMODE_PROPERTY, "1");
        }

        metricStarted(METRIC_SEND_BROADCAST);
        shutdownTimingLog.traceBegin("SendShutdownBroadcast");
        Log.i(TAG, "Sending shutdown broadcast...");

        // First send the high-level shut down broadcast.
        mActionDone = false;
        Intent intent = new Intent(Intent.ACTION_SHUTDOWN);
        intent.addFlags(Intent.FLAG_RECEIVER_FOREGROUND | Intent.FLAG_RECEIVER_REGISTERED_ONLY);
        mContext.sendOrderedBroadcastAsUser(intent,
                UserHandle.ALL, null, br, mHandler, 0, null, null);

        final long endTime = SystemClock.elapsedRealtime() + MAX_BROADCAST_TIME;
        synchronized (mActionDoneSync) {
            while (!mActionDone) {
                long delay = endTime - SystemClock.elapsedRealtime();
                if (delay <= 0) {
                    Log.w(TAG, "Shutdown broadcast timed out");
                    break;
                } else if (mRebootHasProgressBar) {
                    int status = (int)((MAX_BROADCAST_TIME - delay) * 1.0 *
                            BROADCAST_STOP_PERCENT / MAX_BROADCAST_TIME);
                    sInstance.setRebootProgress(status, null);
                }
                try {
                    mActionDoneSync.wait(Math.min(delay, ACTION_DONE_POLL_WAIT_MS));
                } catch (InterruptedException e) {
                }
            }
        }
        if (mRebootHasProgressBar) {
            sInstance.setRebootProgress(BROADCAST_STOP_PERCENT, null);
        }
        shutdownTimingLog.traceEnd(); // SendShutdownBroadcast
        metricEnded(METRIC_SEND_BROADCAST);

        Log.i(TAG, "Shutting down activity manager...");
        shutdownTimingLog.traceBegin("ShutdownActivityManager");
        metricStarted(METRIC_AM);

        final IActivityManager am =
                IActivityManager.Stub.asInterface(ServiceManager.checkService("activity"));
        if (am != null) {
            try {
                am.shutdown(MAX_BROADCAST_TIME);
            } catch (RemoteException e) {
            }
        }

        if (mRebootHasProgressBar) {
          sInstance.setRebootProgress(ACTIVITY_MANAGER_STOP_PERCENT, null);
        }
        shutdownTimingLog.traceEnd();// ShutdownActivityManager
        metricEnded(METRIC_AM);

        Log.i(TAG, "Shutting down package manager...");
        shutdownTimingLog.traceBegin("ShutdownPackageManager");
        metricStarted(METRIC_PM);

        final PackageManagerService pm = (PackageManagerService)
            ServiceManager.getService("package");
        if (pm != null) {
            pm.shutdown();
        }
        if (mRebootHasProgressBar) {
            sInstance.setRebootProgress(PACKAGE_MANAGER_STOP_PERCENT, null);
        }
        shutdownTimingLog.traceEnd(); // ShutdownPackageManager
        metricEnded(METRIC_PM);

        // Shutdown radios.
        shutdownTimingLog.traceBegin("ShutdownRadios");
        metricStarted(METRIC_RADIOS);
        shutdownRadios(MAX_RADIO_WAIT_TIME);
        if (mRebootHasProgressBar) {
            sInstance.setRebootProgress(RADIO_STOP_PERCENT, null);
        }
        shutdownTimingLog.traceEnd(); // ShutdownRadios
        metricEnded(METRIC_RADIOS);

        if (mRebootHasProgressBar) {
            sInstance.setRebootProgress(MOUNT_SERVICE_STOP_PERCENT, null);

            // If it's to reboot to install an update and uncrypt hasn't been
            // done yet, trigger it now.
            uncrypt();
        }

        shutdownTimingLog.traceEnd(); // SystemServerShutdown
        metricEnded(METRIC_SYSTEM_SERVER);
        saveMetrics(mReboot, mReason);
        // Remaining work will be done by init, including vold shutdown
        rebootOrShutdown(mContext, mReboot, mReason);
    }

/**
     * Do not call this directly. Use {@link #reboot(Context, String, boolean)}
     * or {@link #shutdown(Context, String, boolean)} instead.
     *
     * @param context Context used to vibrate or null without vibration
     * @param reboot true to reboot or false to shutdown
     * @param reason reason for reboot/shutdown
     */
    public static void rebootOrShutdown(final Context context, boolean reboot, String reason) {
        if (reboot) {
            Log.i(TAG, "Rebooting, reason: " + reason);
            PowerManagerService.lowLevelReboot(reason);
            Log.e(TAG, "Reboot failed, will attempt shutdown instead");
            reason = null;
        } else if (SHUTDOWN_VIBRATE_MS > 0 && context != null) {
            // vibrate before shutting down
            Vibrator vibrator = new SystemVibrator(context);
            try {
                vibrator.vibrate(SHUTDOWN_VIBRATE_MS, VIBRATION_ATTRIBUTES);
            } catch (Exception e) {
                // Failure to vibrate shouldn't interrupt shutdown.  Just log it.
                Log.w(TAG, "Failed to vibrate during shutdown.", e);
            }

            // vibrator is asynchronous so we need to wait to avoid shutting down too soon.
            try {
                Thread.sleep(SHUTDOWN_VIBRATE_MS);
            } catch (InterruptedException unused) {
            }
        }
        // Shutdown power
        Log.i(TAG, "Performing low-level shutdown...");
        PowerManagerService.lowLevelShutdown(reason);
    }

From now, actual low level shutdown gets started, and it calls above code

// Shutdown power
    Log.i(TAG, "Performing low-level shutdown...");
    PowerManagerService.lowLevelShutdown(reason);

frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java

/**
     * Low-level function turn the device off immediately, without trying
     * to be clean.  Most people should use {@link ShutdownThread} for a clean shutdown.
     *
     * @param reason code to pass to android_reboot() (e.g. "userrequested"), or null.
     */
    public static void lowLevelShutdown(String reason) {
        if (reason == null) {
            reason = "";
        }
        SystemProperties.set("sys.powerctl", "shutdown," + reason);
    }

Actual Action Taken by Android when it calls “setprop sys.powerctl shutdown” as can be seen above..

int android_reboot(int cmd, int flags UNUSED, const char *arg)
{
        case ANDROID_RB_POWEROFF:
            ret = reboot(RB_POWER_OFF);
            break;
}

int reboot(int mode) {
  return __reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, mode, NULL);
}

ENTRY(__reboot)
    mov     ip, r7
    ldr     r7, =__NR_reboot
    swi     #0
    mov     r7, ip
    cmn     r0, #(MAX_ERRNO + 1)
    bxls    lr
    neg     r0, r0
    b       __set_errno_internal
END(__reboot)

#define __NR_reboot 142

common/include/uapi/asm-generic/unistd.h:#define __NR_reboot 142
common/include/uapi/asm-generic/unistd.h:__SYSCALL(__NR_reboot, sys_reboot)

SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
                void __user *, arg)
{
        case LINUX_REBOOT_CMD_POWER_OFF:
                kernel_power_off();
                do_exit(0);
                break;
}

void kernel_power_off(void)
{
        kernel_shutdown_prepare(SYSTEM_POWER_OFF);
        if (pm_power_off_prepare)
                pm_power_off_prepare();
        migrate_to_reboot_cpu();
        syscore_shutdown();
        pr_emerg("Power down\n");
        kmsg_dump(KMSG_DUMP_POWEROFF);
        machine_power_off();
}
EXPORT_SYMBOL_GPL(kernel_power_off);

void machine_power_off(void)
{
local_irq_disable();
smp_send_stop();
if (pm_power_off)
            pm_power_off();
}