Android 6.0 Reboot 流程源代码分析
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Shutdown 跟 reboot流程很类似,所以这里以reboot分析:
reboot的类型:
1、手动长按power键选择reboot;
2、adb reboot;
3、手动长按power键11s触发reboot;
4、BUG_ON(1),触发kernel panic流程reboot;
上面1、2的本质上代码跑的是一样的,下面主要分析第1类正常的关键源码流程。
关机流程总图:
一、首先看Android 层.
1、长按power键选择reboot必定走以下接口:
下面开始进入reboot 前的准备工作,大致分为发起有序shutdown广播、执行Activity、安装包管理、无线相关、挂载服务等组件的shutdown工作.
ShutdownThread.javapublic void run() {//SHUTDOWN有序广播结果接受 BroadcastReceiver br = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { actionDone(); } };...//发送SHUTDOWN有序广播,注意是同步的,如果被阻塞将会block住main thread. Intent intent = new Intent(Intent.ACTION_SHUTDOWN); intent.addFlags(Intent.FLAG_RECEIVER_FOREGROUND); mContext.sendOrderedBroadcastAsUser(intent, UserHandle.ALL, null, br, mHandler, 0, null, null);//等待有序广播全部处理完成,也就是等上面的br.onReveive回调. synchronized (mActionDoneSync) { while (!mActionDone) {... try { mActionDoneSync.wait(Math.min(delay, PHONE_STATE_POLL_SLEEP_MSEC)); } catch (InterruptedException e) { } } }...//ActivityManagerService执行shutdown操作,写一些相关状态(比如battery)记录到文件. final IActivityManager am = ActivityManagerNative.asInterface(ServiceManager.checkService("activity")); if (am != null) { try { am.shutdown(MAX_BROADCAST_TIME); } catch (RemoteException e) { } }...//安装包管理服务执行shutdonw,将当前的packageName写入data/system目录文件中. final PackageManagerService pm = (PackageManagerService) ServiceManager.getService("package"); if (pm != null) { pm.shutdown(); }....//无线相关执行shutdown,比如nfc、电话服务相关等. shutdownRadios(MAX_RADIO_WAIT_TIME);....//挂载服务卸载完成回调 IMountShutdownObserver observer = new IMountShutdownObserver.Stub() { public void onShutDownComplete(int statusCode) throws RemoteException { actionDone(); } };//执行文件系统挂载服务卸载 synchronized (mActionDoneSync) { try { final IMountService mount = IMountService.Stub.asInterface( ServiceManager.checkService("mount")); mount.shutdown(observer); } catch (Exception e) { Log.e(TAG, "Exception during MountService shutdown", e); }// 等待卸载完成,也就是等上面的 observer.onShutDownComplete执行完 while (!mActionDone) { .... try { mActionDoneSync.wait(Math.min(delay, PHONE_STATE_POLL_SLEEP_MSEC)); } catch (InterruptedException e) { } } }....//准备工作完成,进入正式reboot流程 rebootOrShutdown(mContext, mReboot, mRebootReason); }
继续分析准备工作后的reboot流程,主要要干的事情就是把shutdown或者reboot的command从java层传到native层的reboot接口.
public static void rebootOrShutdown(final Context context, boolean reboot, String reason) {//如果是重启的话就执行lowLevelReboot,否则就执行lowLevelShutdown接口 if (reboot) { PowerManagerService.lowLevelReboot(reason); } else if (SHUTDOWN_VIBRATE_MS > 0 && context != null) {//如果是关机命令,则会振动500ms提示 Vibrator vibrator = new SystemVibrator(context); try { vibrator.vibrate(SHUTDOWN_VIBRATE_MS, VIBRATION_ATTRIBUTES); } catch (Exception e) { }//等500ms待vib完成再进入shutdown. try { Thread.sleep(SHUTDOWN_VIBRATE_MS); } catch (InterruptedException unused) { } } PowerManagerService.lowLevelShutdown(); }public static void lowLevelReboot(String reason) {...//使用属性服务传入cmd触发reboot的 Action SystemProperties.set("sys.powerctl", "reboot," + reason);//等待20s,也就是说20s内需要关机完成 try { Thread.sleep(20 * 1000L); } catch (InterruptedException e) { Thread.currentThread().interrupt(); }//下面这条log很关机,如果这条log打出来了,就说明关机失败了,需要找原因了... Slog.wtf(TAG, "Unexpected return from lowLevelReboot!");}//如果执行的是shutdown则走执行下面的cmdpublic static void lowLevelShutdown() { SystemProperties.set("sys.powerctl", "shutdown");}
Java层关机流程分析到此结束,进入native层,我们知道,属性服务贯穿整个Android系统可以很方便的触发各种Action、启动服务等,那么这里的SystemProperties.set(“sys.powerctl”, “reboot,” + reason)到底干了什么事情呢?这个需要从init.rc找答案(属性服务触发实现机制暂不讨论)。搜索sys.powerctl关键字:
./rootdir/init.rc:544:on property:sys.powerctl=*./rootdir/init.rc:545: powerctl ${sys.powerctl}
这是一个on 的action,意思是当sys.powerctl的值改变时,执行powerctl命令,参数就是${sys.powerctl},此处就是上面的reboot,那么具体是什么呢?搜索powerctl会发现:
./init/keywords.h:17:int do_powerctl(int nargs, char **args);./init/keywords.h:79: KEYWORD(powerctl, COMMAND, 1, do_powerctl)
很显然其实就是代表的do_powerctl函数!简单来说就是执行SystemProperties.set(“sys.powerctl”, “reboot,” + reason) 函数的时候其实就是会最终下面的函数:
int do_powerctl(int nargs, char **args){ char command[PROP_VALUE_MAX];.... res = expand_props(command, args[1], sizeof(command));.... if (strncmp(command, "shutdown", 8) == 0) { cmd = ANDROID_RB_POWEROFF; len = 8; } else if (strncmp(command, "reboot", 6) == 0) { cmd = ANDROID_RB_RESTART2; len = 6; } else { ERROR("powerctl: unrecognized command '%s'\n", command); return -EINVAL; }...//很简单,就是解析出要下发哪一个cmd,这里显然就是ANDROID_RB_RESTART2了,接着//调用android层最后一个函数接口 return android_reboot(cmd, 0, reboot_target);}int android_reboot(int cmd, int flags UNUSED, const char *arg){ int ret;// 将缓冲区数据写回磁盘,保证数据同步. sync();//把filesystem置为read only,不允许proc再往里面写东西. remount_ro();//下面就是reboot的system call进入内核空间了: switch (cmd) { case ANDROID_RB_RESTART: ret = reboot(RB_AUTOBOOT); break; case ANDROID_RB_POWEROFF: ret = reboot(RB_POWER_OFF); break; case ANDROID_RB_RESTART2: ret = syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, LINUX_REBOOT_CMD_RESTART2, arg); break; default: ret = -1; } return ret;}
二、Android层关机流程分析完成,进入内核层分析,执行系统调用后进入kernel层系统调用入口:(系统调用是用户程序请求内核服务的标准形式,这里我们不去关注其具体实现)
SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd, void __user *, arg){....//忽略前头一堆各种检查细节,关注reboot流程主线.//互斥锁,保证当前就一个CPU在执行此路径. mutex_lock(&reboot_mutex); switch (cmd) { case LINUX_REBOOT_CMD_RESTART: kernel_restart(NULL); break;.... case LINUX_REBOOT_CMD_HALT: kernel_halt(); do_exit(0); panic("cannot halt"); case LINUX_REBOOT_CMD_POWER_OFF: kernel_power_off(); do_exit(0); break; case LINUX_REBOOT_CMD_RESTART2: ret = strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1); if (ret < 0) { ret = -EFAULT; break; } buffer[sizeof(buffer) - 1] = '\0';//进入内核restart入口函数 kernel_restart(buffer); break;... mutex_unlock(&reboot_mutex); return ret;}
kernel_restart 函数要干的事情主要分为几部分:
void kernel_restart(char *cmd){//kernel关机准备工作. kernel_restart_prepare(cmd);//挂起其他cpu的工作,只留下当前cpu干活 migrate_to_reboot_cpu();//核心设备执行shutdown,比如PM,irq,usb等. syscore_shutdown(); if (!cmd) pr_emerg("Restarting system\n"); else pr_emerg("Restarting system with command '%s'\n", cmd); kmsg_dump(KMSG_DUMP_RESTART);//执行各个体系结构相关的关机、restart操作实现 machine_restart(cmd);}
kernel_restart_prepare 分析,主要干了两件事情:发通知给感兴趣的dev + 执行dev卸载
void kernel_restart_prepare(char *cmd){//发cmd给通知链中对SYS_RESTART感兴趣的设备,执行nofifier回调. blocking_notifier_call_chain(&reboot_notifier_list, SYS_RESTART, cmd); system_state = SYSTEM_RESTART;//用户模式 disable ? usermodehelper_disable();//设备卸载 device_shutdown();}
这里需要重点分析下device_shutdown函数,如果该函数stuck,会导致无法关机.
void device_shutdown(void){ struct device *dev, *parent;//自旋锁,关抢断. spin_lock(&devices_kset->list_lock); /* * Walk the devices list backward, shutting down each in turn. * Beware that device unplug events may also start pulling * devices offline, even as the system is shutting down. */ while (!list_empty(&devices_kset->list)) {//从device链表使用“内核中经典大法-从实例找容器方式” 遍历各个dev dev = list_entry(devices_kset->list.prev, struct device, kobj.entry); /* * hold reference count of device's parent to * prevent it from being freed because parent's * lock is to be held *///激活parent dev和dev,这get,put名字起的容易让人误解,汗.. parent = get_device(dev->parent); get_device(dev); /* * Make sure the device is off the kset list, in the * event that dev->*->shutdown() doesn't remove it. *///把dev从kobj.entry容器中删除 list_del_init(&dev->kobj.entry); spin_unlock(&devices_kset->list_lock); /* hold lock to avoid race with probe/release */ if (parent) device_lock(parent); device_lock(dev);//阻止任何的runtime相关的dev挂起 /* Don't allow any more runtime suspends */ pm_runtime_get_noresume(dev);//这个pm runtime相关函数很复杂,暂时没看懂要干什么,汗.. pm_runtime_barrier(dev);//执行各个对关机感兴趣dev的shutdown回调函数 if (dev->bus && dev->bus->shutdown) { if (initcall_debug) dev_info(dev, "shutdown\n"); dev->bus->shutdown(dev); } else if (dev->driver && dev->driver->shutdown) { if (initcall_debug) dev_info(dev, "shutdown\n"); dev->driver->shutdown(dev); } device_unlock(dev); if (parent) device_unlock(parent);//告诉dev,你现在可以挂起了. put_device(dev); put_device(parent); spin_lock(&devices_kset->list_lock); } spin_unlock(&devices_kset->list_lock);}
下面进入执行真正的关机操作:
void machine_restart(char *cmd){//关闭中断 local_irq_disable();//停掉别的cpu,只留下当前执行的cpu(smp:多对称处理器结构<symmetrical multi-processing="">) smp_send_stop(); /* Flush the console to make sure all the relevant messages make it * out to the console drivers */ arm_machine_flush_console();//arm_pm_restart 是函数指针,指向各个体系结构和芯片厂商具体的restart入口,传参给pmic执行restart或者shutdwon的动作。//比如高通8937项目对于的就是:do_msm_restart,mtk 6580对应的就是:psci_sys_reset//(还需要打log确认),如果没有定义则跑默认的kernel restart接口. if (arm_pm_restart) arm_pm_restart(reboot_mode, cmd); else do_kernel_restart(cmd);//等1s时间,若1s后打印出下面的log就说明shutdwon失败了,正常情况就已经断电关机了. mdelay(1000); /* Whoops - the platform was unable to reboot. Tell the user! */ printk("Reboot failed -- System halted\n"); local_irq_disable();//如果跑到这里就说明关机失败了. while (1);}</symmetrical>
Android reboot 流程整体比较简单,到此分析完.
文章转载自:https://www.2cto.com/kf/201609/550976.html
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