This post tries to brief about how android shutdown / poweroff sequence is with respect to the android open source code. We tried to take logs for reference to identify source code and below is the related logcat messages,
ShutdownThread: Notifying thread to start shutdown longPressBehavior=1
ShutdownThread: Sending shutdown broadcast...
SyncManager: Writing sync state before shutdown...
EntropyMixer: Writing entropy...
MyPppoeService: onReceive :android.intent.action.ACTION_SHUTDOWN
ShutdownThread: Shutting down activity manager...
AppOps : Writing app ops before shutdown...
UsageStatsService: User[0] Flushing usage stats to disk
BatteryStats: Writing battery stats before shutdown...
ProcessStatsService: Writing process stats before shutdown...
ProcessStatsService: Prepared write state in 3ms
ShutdownThread: Shutting down package manager...
ShutdownThread: Disabling Bluetooth...
ShutdownThread: not disable Bluetooth for BT wakeup
ShutdownThread: Waiting for NFC, Bluetooth and Radio...
ShutdownThread: Bluetooth turned off.
ShutdownThread: NFC, Radio and Bluetooth shutdown complete.
ShutdownThread: Shutting down MountService
MountService: Shutting down
VoldConnector: SND -> {7 volume shutdown}
VoldConnector: RCV <- {651 emulated 5}
VoldConnector: RCV <- {651 emulated 0}
VoldConnector: RCV <- {651 emulated 8}
VoldConnector: RCV <- {659 emulated}
VoldConnector: RCV <- {200 7 Command succeeded}
VoldConnector: NDC Command {7 volume shutdown} took too long (567ms)
ShutdownThread: Result code 0 from MountService.shutdown
MountService: Volume emulated broadcasting ejecting to UserHandle{0}
MountService: Volume emulated broadcasting unmounted to UserHandle{0}
MountService: Volume emulated broadcasting bad_removal to UserHandle{0}
ProductTestReciver: onReceive...action:android.intent.action.MEDIA_UNMOUNTED
ProductTestService: handleMessage { when=-1ms what=4098 target=net.amtc.service.stb.producttest.ProductTestService$1 }
MediaScannerReceiver: action: android.intent.action.MEDIA_UNMOUNTED path: /storage/emulated/0
ExternalStorage: After updating volumes, found 0 active roots
ShutdownThread: Performing low-level shutdown..-Above logs shows that it ShutdownThread starts the actual shutting down process, The source code reference for the ShutdownThread is as below,
frameworks/base/services/core/java/com/android/server/power/
├── Notifier.java
├── PowerManagerService.java
├── ScreenOnBlocker.java
├── ShutdownThread.java
├── SuspendBlocker.java
└── WirelessChargerDetector.javaThe power off button is mapped to string as below,
$ vim frameworks/base/core/res/res/values/strings.xml<!-- Button to turn off the phone, within the Phone Options dialog -->
<string name="power_off">Power off</string>$ vim frameworks/base/core/java/android/os/PowerManager.java/**
* Turn off the device.
*
* @param confirm If true, shows a shutdown confirmation dialog.
* @param reason code to pass to android_reboot() (e.g. "userrequested"), or null.
* @param wait If true, this call waits for the shutdown to complete and does not return.
*
* @hide
*/
public void shutdown(boolean confirm, String reason, boolean wait) {
try {
mService.shutdown(confirm, reason, wait);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}$ vim frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java /**
* Shuts down the device.
*
* @param confirm If true, shows a shutdown confirmation dialog.
* @param wait If true, this call waits for the shutdown to complete and does not return.
*/
@Override // Binder call
public void shutdown(boolean confirm, String reason, boolean wait) {
mContext.enforceCallingOrSelfPermission(android.Manifest.permission.REBOOT, null);
final long ident = Binder.clearCallingIdentity();
try {
shutdownOrRebootInternal(HALT_MODE_SHUTDOWN, confirm, reason, wait);
} finally {
Binder.restoreCallingIdentity(ident);
}
} private void shutdownOrRebootInternal(final @HaltMode int haltMode, final boolean confirm,
final String reason, boolean wait) {
if (mHandler == null || !mSystemReady) {
if (RescueParty.isAttemptingFactoryReset()) {
// If we're stuck in a really low-level reboot loop, and a
// rescue party is trying to prompt the user for a factory data
// reset, we must GET TO DA CHOPPA!
PowerManagerService.lowLevelReboot(reason);
} else {
throw new IllegalStateException("Too early to call shutdown() or reboot()");
}
}
Runnable runnable = new Runnable() {
@Override
public void run() {
synchronized (this) {
if (haltMode == HALT_MODE_REBOOT_SAFE_MODE) {
ShutdownThread.rebootSafeMode(getUiContext(), confirm);
} else if (haltMode == HALT_MODE_REBOOT) {
ShutdownThread.reboot(getUiContext(), reason, confirm);
} else {
ShutdownThread.shutdown(getUiContext(), reason, confirm);
}
}
}
};
// ShutdownThread must run on a looper capable of displaying the UI.
Message msg = Message.obtain(UiThread.getHandler(), runnable);
msg.setAsynchronous(true);
UiThread.getHandler().sendMessage(msg);
// PowerManager.reboot() is documented not to return so just wait for the inevitable.
if (wait) {
synchronized (runnable) {
while (true) {
try {
runnable.wait();
} catch (InterruptedException e) {
}
}
}
}
}This calls the ShutdownThread.shutdown() function as,
$ vim 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);
}
}Above function at the end starts the shutdown sequence by calling function beginShutdownSequence(context),
// static instance of this thread
private static final ShutdownThread sInstance = new ShutdownThread();
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();
}The above call “sInstance.start” starts the shutdown thread,
/**
* 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 &lt;= 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);
}As we can see the last function called is “rebootOrShutdown” with a message as “Remaining work will be done by init, including vold shutdown”
/**
* 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 &gt; 0 &amp;&amp; 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);
}Above function call to “PowerManagerService.lowLevelShutdown(reason)” starts the shutdown procedure at very low / system level as,
$ vim 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 above “SystemProperties.set(“sys.powerctl”, “shutdown,” + reason)” is called is same as when we type command “setprop sys.powerctl shutdown”
$ vim system/core/init/init.cppvoid property_changed(const std::string&; name, const std::string&; value) {
// If the property is sys.powerctl, we bypass the event queue and immediately handle it.
// This is to ensure that init will always and immediately shutdown/reboot, regardless of
// if there are other pending events to process or if init is waiting on an exec service or
// waiting on a property.
// In non-thermal-shutdown case, 'shutdown' trigger will be fired to let device specific
// commands to be executed.
if (name == "sys.powerctl") {
// Despite the above comment, we can't call HandlePowerctlMessage() in this function,
// because it modifies the contents of the action queue, which can cause the action queue
// to get into a bad state if this function is called from a command being executed by the
// action queue. Instead we set this flag and ensure that shutdown happens before the next
// command is run in the main init loop.
// TODO: once property service is removed from init, this will never happen from a builtin,
// but rather from a callback from the property service socket, in which case this hack can
// go away.
shutdown_command = value;
do_shutdown = true;
}
if (property_triggers_enabled) ActionManager::GetInstance().QueuePropertyChange(name, value);
if (waiting_for_prop) {
if (wait_prop_name == name && wait_prop_value == value) {
LOG(INFO) << "Wait for property '" << wait_prop_name << "=" << wait_prop_value
<< "' took " << *waiting_for_prop;
ResetWaitForProp();
}
}
} while (true) {
// By default, sleep until something happens.
auto epoll_timeout = std::optional<std::chrono::milliseconds>{};
if (do_shutdown && !shutting_down) {
do_shutdown = false;
if (HandlePowerctlMessage(shutdown_command)) {
shutting_down = true;
}
}$ vim system/core/init/reboot.cppbool HandlePowerctlMessage(const std::string& command) {
if (cmd_params.size() > 3) {
command_invalid = true;
} else if (cmd_params[0] == "shutdown") {
cmd = ANDROID_RB_POWEROFF;
if (cmd_params.size() == 2) {
if (cmd_params[1] == "userrequested") {
// The shutdown reason is PowerManager.SHUTDOWN_USER_REQUESTED.
// Run fsck once the file system is remounted in read-only mode.
run_fsck = true;
} else if (cmd_params[1] == "thermal") {
// Turn off sources of heat immediately.
TurnOffBacklight();
// run_fsck is false to avoid delay
cmd = ANDROID_RB_THERMOFF;
}
}
}
LOG(INFO) &lt;&lt; "Clear action queue and start shutdown trigger";
ActionManager::GetInstance().ClearQueue();
// Queue shutdown trigger first
ActionManager::GetInstance().QueueEventTrigger("shutdown");
// Queue built-in shutdown_done
auto shutdown_handler = [cmd, command, reboot_target, run_fsck](const BuiltinArguments&amp;) {
DoReboot(cmd, command, reboot_target, run_fsck);
return Success();
};
ActionManager::GetInstance().QueueBuiltinAction(shutdown_handler, "shutdown_done");
}bool HandlePowerctlMessage(const std::string& command) {
if (cmd_params.size() > 3) {
command_invalid = true;
} else if (cmd_params[0] == "shutdown") {
cmd = ANDROID_RB_POWEROFF;
if (cmd_params.size() == 2) {
if (cmd_params[1] == "userrequested") {
// The shutdown reason is PowerManager.SHUTDOWN_USER_REQUESTED.
// Run fsck once the file system is remounted in read-only mode.
run_fsck = true;
} else if (cmd_params[1] == "thermal") {
// Turn off sources of heat immediately.
TurnOffBacklight();
// run_fsck is false to avoid delay
cmd = ANDROID_RB_THERMOFF;
}
}
}
LOG(INFO) << "Clear action queue and start shutdown trigger";
ActionManager::GetInstance().ClearQueue();
// Queue shutdown trigger first
ActionManager::GetInstance().QueueEventTrigger("shutdown");
// Queue built-in shutdown_done
auto shutdown_handler = [cmd, command, reboot_target, run_fsck](const BuiltinArguments&) {
DoReboot(cmd, command, reboot_target, run_fsck);
return Success();
};
ActionManager::GetInstance().QueueBuiltinAction(shutdown_handler, "shutdown_done");
}The above function calls “DoReboot”
//* Reboot / shutdown the system.
// cmd ANDROID_RB_* as defined in android_reboot.h
// reason Reason string like "reboot", "shutdown,userrequested"
// rebootTarget Reboot target string like "bootloader". Otherwise, it should be an
// empty string.
// runFsck Whether to run fsck after umount is done.
//
static void DoReboot(unsigned int cmd, const std::string& reason, const std::string& rebootTarget,
bool runFsck) {
Timer t;
LOG(INFO) << "Reboot start, reason: " << reason << ", rebootTarget: " << rebootTarget;
// Ensure last reboot reason is reduced to canonical
// alias reported in bootloader or system boot reason.
size_t skip = 0;
std::vector<std::string> reasons = Split(reason, ",");
if (reasons.size() >= 2 && reasons[0] == "reboot" &&
(reasons[1] == "recovery" || reasons[1] == "bootloader" || reasons[1] == "cold" ||
reasons[1] == "hard" || reasons[1] == "warm")) {
skip = strlen("reboot,");
}
property_set(LAST_REBOOT_REASON_PROPERTY, reason.c_str() + skip);
sync();
bool is_thermal_shutdown = cmd == ANDROID_RB_THERMOFF;
auto shutdown_timeout = 0ms;
if (!SHUTDOWN_ZERO_TIMEOUT) {
constexpr unsigned int shutdown_timeout_default = 6;
constexpr unsigned int max_thermal_shutdown_timeout = 3;
auto shutdown_timeout_final = android::base::GetUintProperty("ro.build.shutdown_timeout",
shutdown_timeout_default);
if (is_thermal_shutdown && shutdown_timeout_final > max_thermal_shutdown_timeout) {
shutdown_timeout_final = max_thermal_shutdown_timeout;
}
shutdown_timeout = std::chrono::seconds(shutdown_timeout_final);
}
LOG(INFO) << "Shutdown timeout: " << shutdown_timeout.count() << " ms";
// keep debugging tools until non critical ones are all gone.
const std::set<std::string> kill_after_apps{"tombstoned", "logd", "adbd"};
// watchdogd is a vendor specific component but should be alive to complete shutdown safely.
const std::set<std::string> to_starts{"watchdogd"};
for (const auto& s : ServiceList::GetInstance()) {
if (kill_after_apps.count(s->name())) {
s->SetShutdownCritical();
} else if (to_starts.count(s->name())) {
if (auto result = s->Start(); !result) {
LOG(ERROR) << "Could not start shutdown 'to_start' service '" << s->name()
<< "': " << result.error();
}
s->SetShutdownCritical();
} else if (s->IsShutdownCritical()) {
// Start shutdown critical service if not started.
if (auto result = s->Start(); !result) {
LOG(ERROR) << "Could not start shutdown critical service '" << s->name()
<< "': " << result.error();
}
}
}
// remaining operations (specifically fsck) may take a substantial duration
if (cmd == ANDROID_RB_POWEROFF || is_thermal_shutdown) {
TurnOffBacklight();
}
Service* bootAnim = ServiceList::GetInstance().FindService("bootanim");
Service* surfaceFlinger = ServiceList::GetInstance().FindService("surfaceflinger");
if (bootAnim != nullptr && surfaceFlinger != nullptr && surfaceFlinger->IsRunning()) {
bool do_shutdown_animation = GetBoolProperty("ro.init.shutdown_animation", false);
if (do_shutdown_animation) {
property_set("service.bootanim.exit", "0");
// Could be in the middle of animation. Stop and start so that it can pick
// up the right mode.
bootAnim->Stop();
}
for (const auto& service : ServiceList::GetInstance()) {
if (service->classnames().count("animation") == 0) {
continue;
}
// start all animation classes if stopped.
if (do_shutdown_animation) {
service->Start().IgnoreError();
}
service->SetShutdownCritical(); // will not check animation class separately
}
if (do_shutdown_animation) {
bootAnim->Start().IgnoreError();
surfaceFlinger->SetShutdownCritical();
bootAnim->SetShutdownCritical();
}
}
// optional shutdown step
// 1. terminate all services except shutdown critical ones. wait for delay to finish
if (shutdown_timeout > 0ms) {
LOG(INFO) << "terminating init services";
// Ask all services to terminate except shutdown critical ones.
for (const auto& s : ServiceList::GetInstance().services_in_shutdown_order()) {
if (!s->IsShutdownCritical()) s->Terminate();
}
int service_count = 0;
// Only wait up to half of timeout here
auto termination_wait_timeout = shutdown_timeout / 2;
while (t.duration() < termination_wait_timeout) {
ReapAnyOutstandingChildren();
service_count = 0;
for (const auto& s : ServiceList::GetInstance()) {
// Count the number of services running except shutdown critical.
// Exclude the console as it will ignore the SIGTERM signal
// and not exit.
// Note: SVC_CONSOLE actually means "requires console" but
// it is only used by the shell.
if (!s->IsShutdownCritical() && s->pid() != 0 && (s->flags() & SVC_CONSOLE) == 0) {
service_count++;
}
}
if (service_count == 0) {
// All terminable services terminated. We can exit early.
break;
}
// Wait a bit before recounting the number or running services.
std::this_thread::sleep_for(50ms);
}
LOG(INFO) << "Terminating running services took " << t
<< " with remaining services:" << service_count;
}
// minimum safety steps before restarting
// 2. kill all services except ones that are necessary for the shutdown sequence.
for (const auto& s : ServiceList::GetInstance().services_in_shutdown_order()) {
if (!s->IsShutdownCritical()) s->Stop();
}
SubcontextTerminate();
ReapAnyOutstandingChildren();
// 3. send volume shutdown to vold
Service* voldService = ServiceList::GetInstance().FindService("vold");
if (voldService != nullptr && voldService->IsRunning()) {
ShutdownVold();
voldService->Stop();
} else {
LOG(INFO) << "vold not running, skipping vold shutdown";
}
// logcat stopped here
for (const auto& s : ServiceList::GetInstance().services_in_shutdown_order()) {
if (kill_after_apps.count(s->name())) s->Stop();
}
// 4. sync, try umount, and optionally run fsck for user shutdown
{
Timer sync_timer;
LOG(INFO) << "sync() before umount...";
sync();
LOG(INFO) << "sync() before umount took" << sync_timer;
}
// 5. drop caches and disable zram backing device, if exist
KillZramBackingDevice();
UmountStat stat = TryUmountAndFsck(runFsck, shutdown_timeout - t.duration());
// Follow what linux shutdown is doing: one more sync with little bit delay
{
Timer sync_timer;
LOG(INFO) << "sync() after umount...";
sync();
LOG(INFO) << "sync() after umount took" << sync_timer;
}
if (!is_thermal_shutdown) std::this_thread::sleep_for(100ms);
LogShutdownTime(stat, &t);
// Reboot regardless of umount status. If umount fails, fsck after reboot will fix it.
RebootSystem(cmd, rebootTarget);
abort();
}$ vim system/core/init/reboot_utils.cppvoid __attribute__((noreturn)) RebootSystem(unsigned int cmd, const std::string&amp; rebootTarget) {
LOG(INFO) << "Reboot ending, jumping to kernel";
if (!IsRebootCapable()) {
// On systems where init does not have the capability of rebooting the
// device, just exit cleanly.
exit(0);
}
switch (cmd) {
case ANDROID_RB_POWEROFF:
reboot(RB_POWER_OFF);
break;
case ANDROID_RB_RESTART2:
syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
LINUX_REBOOT_CMD_RESTART2, rebootTarget.c_str());
break;
case ANDROID_RB_THERMOFF:
reboot(RB_POWER_OFF);
break;
}
// In normal case, reboot should not return.
PLOG(ERROR) << "reboot call returned";
abort();
}$ vim bionic/libc/bionic/reboot.cpp#include <unistd.h>
#include <sys/reboot.h>
extern "C" int __reboot(int, int, int, void*);
int reboot(int mode) {
return __reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, mode, nullptr);
}$ vim bionic/libc/arch-arm/syscalls/__reboot.S#include <private/bionic_asm.h>
ENTRY(__reboot)
mov ip, r7
.cfi_register r7, ip
ldr r7, =__NR_reboot
swi #0
mov r7, ip
.cfi_restore r7
cmn r0, #(MAX_ERRNO + 1)
bxls lr
neg r0, r0
b __set_errno_internal
END(__reboot)As we can see, reboot is a 142 number system call,
$ vim bionic/libc/kernel/uapi/asm-generic/unistd.h #define __NR_reboot 142Below code is from kernel source code,
common/include/uapi/asm-generic/unistd.h:#define __NR_reboot 142
common/include/uapi/asm-generic/unistd.h:__SYSCALL(__NR_reboot, sys_reboot)This system call is defined in kernel_source/kernel/reboot.c as below,
/*
* Reboot system call: for obvious reasons only root may call it,
* and even root needs to set up some magic numbers in the registers
* so that some mistake won't make this reboot the whole machine.
* You can also set the meaning of the ctrl-alt-del-key here.
*
* reboot doesn't sync: do that yourself before calling this.
*/
SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
void __user *, arg)
{
switch (cmd) {
case LINUX_REBOOT_CMD_POWER_OFF:
kernel_power_off();
do_exit(0);
break;
}
}
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[bash]
/**
* kernel_power_off - power_off the system
*
* Shutdown everything and perform a clean system power_off.
*/
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);As we can see in above “machine_power_off” is the function which will actually interface the hardware architecture specific code with the kernel core code, [ For arm64 the code is in arch/arm64/kernel/process. where as for 32 bit ARM platforms its in arch/arm/kernel/reboot.c]
/*
* Power-off simply requires that the secondary CPUs stop performing any
* activity (executing tasks, handling interrupts). smp_send_stop()
* achieves this. When the system power is turned off, it will take all CPUs
* with it.
*/
void machine_power_off(void)
{
local_irq_disable();
smp_send_stop();
if (pm_power_off)
pm_power_off();
}same file has definition of pm_power_off as,
/*
* Function pointers to optional machine specific functions
*/
void (*pm_power_off)(void);
EXPORT_SYMBOL_GPL(pm_power_off);Now, if we take Qualcomm MSM hardware as an example, this pm_power_off has been initialised in drivers/power/reset/msm-poweroff.c as,
static void do_msm_poweroff(void)
{
/* TODO: Add poweroff capability */
}
static int msm_restart_probe(struct platform_device *pdev)
{
pm_power_off = do_msm_poweroff;
return 0;
}
static const struct of_device_id of_msm_restart_match[] = {
{ .compatible = "qcom,pshold", },
{},
};
MODULE_DEVICE_TABLE(of, of_msm_restart_match);
static struct platform_driver msm_restart_driver = {
.probe = msm_restart_probe,
.driver = {
.name = "msm-restart",
.of_match_table = of_match_ptr(of_msm_restart_match),
},
};
static int __init msm_restart_init(void)
{
return platform_driver_register(&msm_restart_driver);
}
device_initcall(msm_restart_init);