android L 关机流程图

下面是简单的流程图，从Java到kernel层。

ShutdownThread.java文件

stop playing music，因为后面可能要playing shutdown music.

代码如下：（我在Android6.0上沒有看到調用requestAudioFocus的代碼）

    private static void beginShutdownSequence(Context context) {

      ....

            //acquire audio focus to make the other apps to stop playing muisc

            mAudioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);

            mAudioManager.requestAudioFocus(null,

                    AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN);

show system dialog to indicate phone is shutting down，如果没有关机动画的话，要show一个关机提示出来。

代码如下：

 1     if (!checkAnimationFileExist()) {

 2         // throw up an indeterminate system dialog to indicate radio is

 3         // shutting down.

 4         ProgressDialog pd = new ProgressDialog(context);

 5         pd.setTitle(context.getText(com.android.internal.R.string.power_off));

 6         pd.setMessage(context.getText(com.android.internal.R.string.shutdown_progress));

 7         pd.setIndeterminate(true);

 8         pd.setCancelable(false);

 9         pd.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG);

10

11         pd.show();

12     }

Hold the wakelock,make sure we never fall asleep again，抓锁防止机器关机过程中休眠

代码如下：

1     sInstance.mCpuWakeLock = sInstance.mPowerManager.newWakeLock(

2             PowerManager.PARTIAL_WAKE_LOCK, TAG + "-cpu");//这个只是锁住cpu不进入休眠，但screen是off的，需full锁来保证screen常亮

3     sInstance.mCpuWakeLock.setReferenceCounted(false);

4     sInstance.mCpuWakeLock.acquire();

make sure the screen stays on,再抓一个full锁，防止屏幕半暗

代码如下：

1     sInstance.mScreenWakeLock = sInstance.mPowerManager.newWakeLock(

2             PowerManager.FULL_WAKE_LOCK, TAG + "-screen");//保持srceen常亮

3     sInstance.mScreenWakeLock.setReferenceCounted(false);

4     sInstance.mScreenWakeLock.acquire();

sending shutdown broadcast，发出广播，通知各app该保存数据赶紧的，我要关机了

代码如下：

1     Intent intent = new Intent(Intent.ACTION_SHUTDOWN);

2     intent.addFlags(Intent.FLAG_RECEIVER_FOREGROUND);

3     mContext.sendOrderedBroadcastAsUser(intent,//发广播

4             UserHandle.ALL, null, br, mHandler, 0, null, null);

shutdown activity manager，关闭activity manager，即关闭AppOpsService，UsageStatsService，BatteryStatsService

注意：Android L 与KK在关闭UsageStatsService上有所区别

代码如下：

[ActivityManagerService.java]

1     final IActivityManager am =

2                 ActivityManagerNative.asInterface(ServiceManager.checkService("activity"));

3             if (am != null) {

4                 try {

5                     am.shutdown(MAX_BROADCAST_TIME);

6                 } catch (RemoteException e) {

7                 }

8             }

shutdown package manager，保存app使用时间到 disk里，这是android L新增的功能。

代码如下：

[PackageManagerService.java]

1     final PackageManagerService pm = (PackageManagerService)

2         ServiceManager.getService("package");

3     if (pm != null) {

4         pm.shutdown();

5     }

show shutdown animation，播放关机动画了

代码如下：

 1     private static void showShutdownAnimation() {

 2         /*

 3          * When boot completed, "service.bootanim.exit" property is set to 1.

 4          * Bootanimation checks this property to stop showing the boot animation.

 5          * Since we use the same code for shutdown animation, we

 6          * need to reset this property to 0. If this is not set to 0 then shutdown

 7          * will stop and exit after displaying the first frame of the animation

 8          */

 9         SystemProperties.set("service.bootanim.exit", "0");

10

11         SystemProperties.set("ctl.start", "bootanim");//也是用bootanim进程，跟开关动画一样的方式。

12     }

shutdown radio[NFC,BT,MODEM],注意这里关闭modem这块与andorid KK的不一样。

代码如下：

shutdownRadios(MAX_RADIO_WAIT_TIME);

shutdown MountService,特别这里会导致关机失败。

代码如下：

 1     // Set initial variables and time out time.

 2     mActionDone = false;

 3     final long endShutTime = SystemClock.elapsedRealtime() + MAX_SHUTDOWN_WAIT_TIME;

 4     synchronized (mActionDoneSync) {

 5         try {

 6             final IMountService mount = IMountService.Stub.asInterface(

 7                     ServiceManager.checkService("mount"));

 8             if (mount != null) {

 9                 mount.shutdown(observer);

10             } else {

11                 Log.w(TAG, "MountService unavailable for shutdown");

12             }

13         } catch (Exception e) {

14             Log.e(TAG, "Exception during MountService shutdown", e);

15         }

16         while (!mActionDone) {

17             long delay = endShutTime - SystemClock.elapsedRealtime();

18             if (delay <= 0) {

19                 Log.w(TAG, "Shutdown wait timed out");

20                 break;

21             }

22             try {

23                 mActionDoneSync.wait(delay);

24             } catch (InterruptedException e) {

25             }

26         }

27     }

走完上层关机流程，下面就要执行关机动作了。

代码如下：

 1     public static void rebootOrShutdown(boolean reboot, String reason) {

 2         deviceRebootOrShutdown(reboot, reason);

 3         if (reboot) {

 4             Log.i(TAG, "Rebooting, reason: " + reason);

 5             PowerManagerService.lowLevelReboot(reason);//重启, 其中reason字符串可以爲空、“bootloader”、“recovery”, 在手機下次啓動中LK會根據這些值使手機進入不同的模式

 6             Log.e(TAG, "Reboot failed, will attempt shutdown instead");

 7         } else if (SHUTDOWN_VIBRATE_MS > 0) {

 8             // vibrate before shutting down

 9             Vibrator vibrator = new SystemVibrator();

10             try {

11                 vibrator.vibrate(SHUTDOWN_VIBRATE_MS, VIBRATION_ATTRIBUTES);

12             } catch (Exception e) {

13                 // Failure to vibrate shouldn't interrupt shutdown.  Just log it.

14                 Log.w(TAG, "Failed to vibrate during shutdown.", e);

15             }

16

17             // vibrator is asynchronous so we need to wait to avoid shutting down too soon.

18             try {

19                 Thread.sleep(SHUTDOWN_VIBRATE_MS);

20             } catch (InterruptedException unused) {

21             }

22         }

23

24         // Shutdown power

25         Log.i(TAG, "Performing low-level shutdown...");

26         PowerManagerService.lowLevelShutdown();//关机

27     }

从代码上看始终会走到lowLevelShutdown()，但如果是重启就不会，lowLevelReboot()就停止了。

lowLevelShutdown()与lowLevelReboot()都在PowerManagerService.java实现，其实都只是设置一个属性：SystemProperties.set("sys.powerctl", "xxx");

正是这个动作触发关机流程往下走，这涉及到init进程的4大功能，请参考我的另一篇文章Android的init进程

sys.powerctl属性触发开关在init.rc定义

    on property:sys.powerctl=*

        powerctl ${sys.powerctl}

我们来解读这句话，on property:sys.powerctl=*表示当属性sys.powerctl设置为任何值是都会跑到这里，触发动作是powerctl ${sys.powerctl},这个动作的意思是调用powerctl指令，并把sys.powerctl的值传给它。powerctl指令在init 进程会执行。

从下面的表可知，powerctl对应的操作是do_powerctl

[system/core/init/keywords.h]

KEYWORD(powerctl,    COMMAND, 1, do_powerctl)

do_powerctl的实现

代码如下：

[system/core/init/builtins.c]

 1 int do_powerctl(int nargs, char **args)

 2 {

 3     char command[PROP_VALUE_MAX];

 4     int res;

 5     int len = 0;

 6     int cmd = 0;

 7     const char *reboot_target;

 8

 9     res = expand_props(command, args[1], sizeof(command));  //args中存放的是: shutdown 或者 reboot 或者 reboot,bootloader 或者 reboot,recovery

10     if (res) {

11         ERROR("powerctl: cannot expand '%s'\n", args[1]);

12         return -EINVAL;

13     }

14

15     if (strncmp(command, "shutdown", 8) == 0) {

16         cmd = ANDROID_RB_POWEROFF;

17         len = 8;

18     } else if (strncmp(command, "reboot", 6) == 0) {

19         cmd = ANDROID_RB_RESTART2;

20         len = 6;

21     } else {

22         ERROR("powerctl: unrecognized command '%s'\n", command);

23         return -EINVAL;

24     }

25

26     if (command[len] == ',') {

27         char prop_value[PROP_VALUE_MAX] = {0};

28         reboot_target = &command[len + 1];  // 存放reboot的reason，也就是下次手機重啓將要進入的模式

29

30         if ((property_get("init.svc.recovery", prop_value) == 0) &&

31             (strncmp(reboot_target, "keys", 4) == 0)) {

32             ERROR("powerctl: permission denied\n");

33             return -EINVAL;

34         }

35     } else if (command[len] == '\0') {  // 如果reason爲空，對於reboot來說，下次手機會正常啓機

36         reboot_target = "";

37     } else {

38         ERROR("powerctl: unrecognized reboot target '%s'\n", &command[len]);

39         return -EINVAL;

40     }

41

42     return android_reboot(cmd, 0, reboot_target);

43 }

它调用android_reboot()函数，实现如下：

[system/core/libcutils/android_reboot.c]

 1 int android_reboot(int cmd, int flags UNUSED, const char *arg)

 2 {

 3     int ret;

 4

 5     sync();

 6     remount_ro();

 7

 8     switch (cmd) {

 9         case ANDROID_RB_RESTART:

10             ret = reboot(RB_AUTOBOOT);

11             break;

12

13         case ANDROID_RB_POWEROFF:

14             ret = reboot(RB_POWER_OFF);

15             break;

16

17         case ANDROID_RB_RESTART2:  // arg中存放的是reboot的reason，如bootloader、recovery

18             ret = syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,

19                            LINUX_REBOOT_CMD_RESTART2, arg);

20             break;

21

22         default:

23             ret = -1;

24     }

25

26     return ret;

27 }

从这里看出它的主要工作：

sync() 回写block设备的内容，这是阻塞型操作。

remount_ro() 把block设备remount成ro，这里有个关键LOG：SysRq : Emergency Remount R/O，这是在logkit所能看到的最后一句LOG，因为remount成ro了，后面的LOG要通过last kmsg技术导出来。

reboot()或者syscall(__NR_reboot....，这点与android KK不同，这边直接用syscall功能，KK则通过汇编。

后面syscall(__NR_reboot...知道，直接调用了linux的__NR_reboot系统调用，这个系统调用会跑哪里？后面会讲。

reboot()这个函数实现如下：

[bionic/libc/bionic/reboot.cpp]

1     int reboot(int mode) {

2       return __reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, mode, NULL);

3     }

调用了__reboot,它在汇编实现　如下：

[bionic/libc/arch-arm/syscalls/__reboot.S]

 1     ENTRY(__reboot)

 2         mov     ip, r7

 3         ldr     r7, =__NR_reboot      //也跑到__NR_reboot系统调用

 4         swi     #0

 5         mov     r7, ip

 6         cmn     r0, #(MAX_ERRNO + 1)

 7         bxls    lr

 8         neg     r0, r0

 9         b       __set_errno_internal

10     END(__reboot)

__NR_reboot对应的内核入口在哪里？

如下：

[bionic/libc/kernel/uapi/asm-generic/unistd.h]

    #define __NR_reboot 142

它在内核入口如下：

注：bionic/libc/kernel/uapi/asm-generic/unistd.h与kernel/include/uapi/asm-generic/unistd.h是对应的，方便以后代码追踪

[kernel/include/uapi/asm-generic/unistd.h]

1     #define __NR_reboot 142

2     __SYSCALL(__NR_reboot, sys_reboot)

__NR_reboot 映射到 sys_reboot

grep 下sys_reboot　找不到，其实在这里

用SYSCALL_DEFINE定义

[kernel/kernel/reboot.c]

 1 /*

 2  * Reboot system call: for obvious reasons only root may call it,

 3  * and even root needs to set up some magic numbers in the registers

 4  * so that some mistake won't make this reboot the whole machine.

 5  * You can also set the meaning of the ctrl-alt-del-key here.

 6  *

 7  * reboot doesn't sync: do that yourself before calling this.

 8  */

 9 SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,

10         void __user *, arg)

11 {

12     struct pid_namespace *pid_ns = task_active_pid_ns(current);

13     char buffer[256];

14     int ret = 0;

15

16     /* We only trust the superuser with rebooting the system. */

17     if (!ns_capable(pid_ns->user_ns, CAP_SYS_BOOT))

18         return -EPERM;

19

20     /* For safety, we require "magic" arguments. */

21     if (magic1 != LINUX_REBOOT_MAGIC1 ||

22             (magic2 != LINUX_REBOOT_MAGIC2 &&

23             magic2 != LINUX_REBOOT_MAGIC2A &&

24             magic2 != LINUX_REBOOT_MAGIC2B &&

25             magic2 != LINUX_REBOOT_MAGIC2C))

26         return -EINVAL;

27

28     /*

29      * If pid namespaces are enabled and the current task is in a child

30      * pid_namespace, the command is handled by reboot_pid_ns() which will

31      * call do_exit().

32      */

33     ret = reboot_pid_ns(pid_ns, cmd);

34     if (ret)

35         return ret;

36

37     /* Instead of trying to make the power_off code look like

38      * halt when pm_power_off is not set do it the easy way.

39      */

40     if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !pm_power_off)

41         cmd = LINUX_REBOOT_CMD_HALT;

42

43     mutex_lock(&reboot_mutex);

44     switch (cmd) {

45     case LINUX_REBOOT_CMD_RESTART:

46         kernel_restart(NULL);

47         break;

48

49     case LINUX_REBOOT_CMD_CAD_ON:

50         C_A_D = 1;

51         break;

52

53     case LINUX_REBOOT_CMD_CAD_OFF:

54         C_A_D = 0;

55         break;

56

57     case LINUX_REBOOT_CMD_HALT:

58         kernel_halt();

59         do_exit(0);

60         panic("cannot halt");

61

62     case LINUX_REBOOT_CMD_POWER_OFF:

63         kernel_power_off();

64         do_exit(0);

65         break;

66

67     case LINUX_REBOOT_CMD_RESTART2:

68         ret = strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1);

69         if (ret < 0) {

70             ret = -EFAULT;

71             break;

72         }

73         buffer[sizeof(buffer) - 1] = '\0';

74

75         kernel_restart(buffer);

76         break;

77

78 #ifdef CONFIG_KEXEC

79     case LINUX_REBOOT_CMD_KEXEC:

80         ret = kernel_kexec();

81         break;

82 #endif

83

84 #ifdef CONFIG_HIBERNATION

85     case LINUX_REBOOT_CMD_SW_SUSPEND:

86         ret = hibernate();

87         break;

88 #endif

89

90     default:

91         ret = -EINVAL;

92         break;

93     }

94     mutex_unlock(&reboot_mutex);

95     return ret;

96 }

有很多分支，我们只关心kernel_power_off()和kernel_restart()两函数就行

如下：

kernel_power_off：

 1     void kernel_power_off(void)

 2     {

 3         kernel_shutdown_prepare(SYSTEM_POWER_OFF);//关闭外设

 4         if (pm_power_off_prepare)

 5             pm_power_off_prepare();

 6         migrate_to_reboot_cpu();   // 比如執行reboot命令的進程運行在CPU1上，而將來CPU1會先於CPU0被停止，故需要將當前進程轉移至CPU0上

 7         syscore_shutdown();//关闭syscore

 8         printk(KERN_EMERG "Power down.\n");//关键打印

 9         kmsg_dump(KMSG_DUMP_POWEROFF);

10         machine_power_off();

11     }

kernel_restart:

 1     void kernel_restart(char *cmd)

 2     {

 3         kernel_restart_prepare(cmd);//关闭外设

 4         migrate_to_reboot_cpu();

 5         syscore_shutdown();//关闭syscore

 6         if (!cmd)

 7             printk(KERN_EMERG "Restarting system.\n");//关键打印

 8         else

 9             printk(KERN_EMERG "Restarting system with command '%s'.\n", cmd);

10         kmsg_dump(KMSG_DUMP_RESTART);

11         machine_restart(cmd);

12     }

都执行XX_prepare()函数

1     static void kernel_shutdown_prepare(enum system_states state)

2     {

3         blocking_notifier_call_chain(&reboot_notifier_list,

4             (state == SYSTEM_HALT)?SYS_HALT:SYS_POWER_OFF, NULL);

5         system_state = state;

6         usermodehelper_disable();

7         device_shutdown();

8     }

上面的第3行會遍歷reboot_notifier_list鏈表，向其中註冊的每一個notifier_block發送SYS_POWER_OFF事件。

在我們的驅動程序中可以調用如下函數將notifier_block註冊到系統中：

 1 /**

 2  *    register_reboot_notifier - Register function to be called at reboot time

 3  *    @nb: Info about notifier function to be called

 4  *

 5  *    Registers a function with the list of functions

 6  *    to be called at reboot time.

 7  *

 8  *    Currently always returns zero, as blocking_notifier_chain_register()

 9  *    always returns zero.

10  */

11 int register_reboot_notifier(struct notifier_block *nb)

12 {

13     return blocking_notifier_chain_register(&reboot_notifier_list, nb);

14 }

15 EXPORT_SYMBOL(register_reboot_notifier);

在第7行中調用了device_shutdown()函數，如下：

 1 /**

 2  * device_shutdown - call ->shutdown() on each device to shutdown.

 3  */

 4 void device_shutdown(void)

 5 {

 6     struct device *dev, *parent;

 7

 8     spin_lock(&devices_kset->list_lock);

 9     /*

10      * Walk the devices list backward, shutting down each in turn.

11      * Beware that device unplug events may also start pulling

12      * devices offline, even as the system is shutting down.

13      */

14     while (!list_empty(&devices_kset->list)) {

15         dev = list_entry(devices_kset->list.prev, struct device,

16                 kobj.entry);

17                 ......

18

19         if (dev->bus && dev->bus->shutdown) {   // 如 i2c_bus_type

20             if (initcall_debug)

21                 dev_info(dev, "shutdown\n");

22             dev->bus->shutdown(dev);

23         } else if (dev->driver && dev->driver->shutdown) {  // 如spi_bus_type、usb_bus_type

24             if (initcall_debug)

25                 dev_info(dev, "shutdown\n");

26             dev->driver->shutdown(dev);

27         }

28                 ......

29     }

30     spin_unlock(&devices_kset->list_lock);

31 }

32

kernel_restart_prepare:

1     void kernel_restart_prepare(char *cmd)

2     {

3         blocking_notifier_call_chain(&reboot_notifier_list, SYS_RESTART, cmd);

4         system_state = SYSTEM_RESTART;

5         usermodehelper_disable();

6         device_shutdown();

7     }

除了前面不同，都调用了device_shutdown()函数，关闭外设。

machine_power_off() machine_resestart()函数实现

machine_power_off:

1     void machine_power_off(void)

2     {

3         preempt_disable();

4         smp_send_stop();

5

6         if (pm_power_off)

7             pm_power_off();//关机

8     }

其中，第4行的smp_send_stop會將除CPU0之外的CPU全部stop。

machine_restart:

 1     void machine_restart(char *cmd)

 2     {

 3         preempt_disable();

 4         smp_send_stop();

 5

 6         /* Flush the console to make sure all the relevant messages make it

 7          * out to the console drivers */

 8         arm_machine_flush_console();

 9

10         arm_pm_restart(reboot_mode, cmd);//重启

11

12         /* Give a grace period for failure to restart of 1s */

13         mdelay(1000);

14

15         /* Whoops - the platform was unable to reboot. Tell the user! */

16         printk("Reboot failed -- System halted\n");

17         local_irq_disable();

18         while (1);

19     }

pm_power_offf()　arm_pm_restart()都是一个函数指针

赋值如下：

[kernel/drivers/power/reset/msm-poweroff.c]

1     pm_power_off = do_msm_poweroff;

2     arm_pm_restart = do_msm_restart;

高通平台的关机代码与之前有所不同，现在文件msm-poweroff.c以前是restart.c。

do_msm_poweroff()与do_msm_restart()实现如下：

do_msm_poweroff:

 1     static void do_msm_poweroff(void)

 2     {

 3     ....

 4         pr_notice("Powering off the SoC\n");//关键打印

 5     #ifdef CONFIG_MSM_DLOAD_MODE

 6         set_dload_mode(0);//关机，所以dloadmode是0

 7     #endif

 8         qpnp_pon_system_pwr_off(PON_POWER_OFF_SHUTDOWN);//配置PMIC,是关机

 9     .....

10         /* MSM initiated power off, lower ps_hold */

11         __raw_writel(0, msm_ps_hold);//拉　PS＿HOLD,执行关机动作。

12

13         mdelay(10000);

14         pr_err("Powering off has failed\n");

15         return;

16     }

do_msm_restart:

 1     static void msm_restart_prepare(const char *cmd)

 2     {

 3     #ifdef CONFIG_MSM_DLOAD_MODE

 4

 5         /* Write download mode flags if we're panic'ing

 6          * Write download mode flags if restart_mode says so

 7          * Kill download mode if master-kill switch is set

 8          */

 9

10         set_dload_mode(download_mode &&

11                 (in_panic || restart_mode == RESTART_DLOAD));//设置dload

12     #endif

13

14         /* Hard reset the PMIC unless memory contents must be maintained. */

15         if (get_dload_mode() || (cmd != NULL && cmd[0] != '\0'))

16             qpnp_pon_system_pwr_off(PON_POWER_OFF_WARM_RESET);//设置PIMC为热重启

17         else

18             qpnp_pon_system_pwr_off(PON_POWER_OFF_HARD_RESET);//设置PIMC为硬重启

19

20         if (cmd != NULL) {

21             if (!strncmp(cmd, "bootloader", 10)) {

22                 __raw_writel(0x77665500, restart_reason);//写一些东东到IMEM，用于bootloader,recovery等

23             } else if (!strncmp(cmd, "recovery", 8)) {

24                 __raw_writel(0x77665502, restart_reason);

25             } else if (!strcmp(cmd, "rtc")) {

26                 __raw_writel(0x77665503, restart_reason);

27             } else if (!strncmp(cmd, "oem-", 4)) {

28                 unsigned long code;

29                 int ret;

30                 ret = kstrtoul(cmd + 4, 16, &code);

31                 if (!ret)

32                     __raw_writel(0x6f656d00 | (code & 0xff),

33                              restart_reason);

34             } else if (!strncmp(cmd, "edl", 3)) {

35                 enable_emergency_dload_mode();

36             } else {

37                 __raw_writel(0x77665501, restart_reason);

38             }

39         }

40

41     .....

42

43     }

do_msm_poweroff()与do_msm_restart()都设置了dload,PMIC，唯一不同的是do_msm_restart()里多了一个__raw_writel的动作，即reason写入IMEM,目的在于重启进入sbl1时判断应该进入那种模式，如我们开发用的 bootloader模式，恢复出厂设置的recovery模式等。

完了

巴特西

android L 关机流程图

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