Android(安卓)关机、重启、recovery流程分析

以Android5.1的代码来分析。

应用层和框架层实现

上层应用可以通过PowerManager来实现关机、重启、进recovery等功能。比如RecoverySystem 中就是使用PM使系统进入recovery模式：

源码路径：frameworks/base/core/java/android/os/RecoverySystem.java

    private static void bootCommand(Context context, String... args) throws IOException {        ......        // Having written the command file, go ahead and reboot        PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);        pm.reboot(PowerManager.REBOOT_RECOVERY);       ......    }

PowerManager会通过aidl与PowerManagerService交互，reboot带reason参数，像重启、关机、恢复出厂设置等等；

源码路径：frameworks/base/core/java/android/os/IPowerManager.aidl

reboot在aidl中的定义

interface IPowerManager{    // WARNING: The first five methods must remain the first five methods because their    // transaction numbers must not change unless IPowerManager.cpp is also updated.    void acquireWakeLock(IBinder lock, int flags, String tag, String packageName, in WorkSource ws,            String historyTag);    void acquireWakeLockWithUid(IBinder lock, int flags, String tag, String packageName,            int uidtoblame);    void releaseWakeLock(IBinder lock, int flags);    void updateWakeLockUids(IBinder lock, in int[] uids);    ......    void reboot(boolean confirm, String reason, boolean wait);    void shutdown(boolean confirm, boolean wait);    void crash(String message);    void setStayOnSetting(int val);    void boostScreenBrightness(long time);    // temporarily overrides the screen brightness settings to allow the user to    // see the effect of a settings change without applying it immediately    void setTemporaryScreenBrightnessSettingOverride(int brightness);    void setTemporaryScreenAutoBrightnessAdjustmentSettingOverride(float adj);    // sets the attention light (used by phone app only)    void setAttentionLight(boolean on, int color);}

PMS中reboot调用shutdownOrRebootInternal

源码路径：frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java

        @Override // Binder call        public void reboot(boolean confirm, String reason, boolean wait) {            ......            final long ident = Binder.clearCallingIdentity();            try {                shutdownOrRebootInternal(false, confirm, reason, wait);            } finally {                Binder.restoreCallingIdentity(ident);            }        }

    public static void lowLevelShutdown() {        SystemProperties.set("sys.powerctl", "shutdown");    }

    public static void lowLevelReboot(String reason) {        if (reason == null) {            reason = "";        }        long duration;        if (reason.equals(PowerManager.REBOOT_RECOVERY)) {            SystemProperties.set("ctl.start", "pre-recovery");            duration = 300 * 1000L;        } else {            SystemProperties.set("sys.powerctl", "reboot," + reason);            duration = 20 * 1000L;        }        try {            Thread.sleep(duration);        } catch (InterruptedException e) {            Thread.currentThread().interrupt();        }    }

shutdownOrRebootInternal根据reason来决定是调用ShutdownThread的reboot或者shutdown:

  private void shutdownOrRebootInternal(final boolean shutdown, final boolean confirm,            final String reason, boolean wait) {        ......        Runnable runnable = new Runnable() {            @Override            public void run() {                synchronized (this) {                    if (shutdown) {                        ShutdownThread.shutdown(mContext, confirm);                    } else {                        ShutdownThread.reboot(mContext, reason, confirm);                    }                ......

不管是关机还是重启都是走shutdownInner 源码路径：frameworks/base/services/core/java/com/android/server/power/ShutdownThread.java

    public static void reboot(final Context context, String reason, boolean confirm) {        mReboot = true;        mRebootSafeMode = false;        mRebootReason = reason;        shutdownInner(context, confirm);    }    ......    public static void shutdown(final Context context, boolean confirm) {        mReboot = false;        mRebootSafeMode = false;        shutdownInner(context, confirm);    }    ......    static void shutdownInner(final Context context, boolean confirm) {    ......            beginShutdownSequence(context);        }    }

看一下beginShutdownSequence

    private static void beginShutdownSequence(Context context) {       ......        // start the thread that initiates shutdown        sInstance.mHandler = new Handler() {        };        sInstance.start();    }

已经start了，我们就去run里面瞧一瞧干了什么事，就对“REBOOT_SAFEMODE_PROPERTY”设置了1或者0，然后调用rebootOrShutdown。

   /**     * Makes sure we handle the shutdown gracefully.     * Shuts off power regardless of radio and bluetooth state if the alloted time has passed.     */    public void run() {        ....//关机或者重启前的一些处理            String reason = (mReboot ? "1" : "0") + (mRebootReason != null ? mRebootReason : "");            SystemProperties.set(SHUTDOWN_ACTION_PROPERTY, reason);......        if (mRebootSafeMode) {            SystemProperties.set(REBOOT_SAFEMODE_PROPERTY, "1");        }        ......        rebootOrShutdown(mReboot, mRebootReason);    }

rebootOrShutdown中会调用PMS的lowLevelReboot或者lowLevelShutdown，这两个函数在上面有展示

    public static void rebootOrShutdown(boolean reboot, String reason) {        if (reboot) {            Log.i(TAG, "Rebooting, reason: " + reason);            PowerManagerService.lowLevelReboot(reason);//重启            Log.e(TAG, "Reboot failed, will attempt shutdown instead");        } else if (SHUTDOWN_VIBRATE_MS > 0) {      ....//关机震动相关处理        // Shutdown power        Log.i(TAG, "Performing low-level shutdown...");        PowerManagerService.lowLevelShutdown();//关机    }

再回过头去看PowerManagerService里面的lowLevelShutdown，发现关机、重启、recovery等是通过设置Properties来实现控制的:SystemProperties.set("sys.powerctl"......

native实现

Android系统开始会执行init，而init会去解析执行init.rc中的内容。其中就有对于Properties “sys.powerctl ”的处理（当“sys.powerctl 发生改变时触发进行powerctl 操作）。位于源码：system/core/rootdir/init.rc

on property:sys.powerctl=*    powerctl ${sys.powerctl}

而powerctl 是init的内嵌命令,在init源码中：源码路径：system/core/init/builtins.c

int do_powerctl(int nargs, char **args){......    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;    }    if (command[len] == ',') {        reboot_target = &command[len + 1];    } else if (command[len] == '\0') {        reboot_target = "";    } else {        ERROR("powerctl: unrecognized reboot target '%s'\n", &command[len]);        return -EINVAL;    }    return android_reboot(cmd, 0, reboot_target);}

android_reboot系统调用reboot，如果是recovery、wipe data等操作还需要额外写参数到misc分区，以便开机时区分正常进Android系统还是recovery、efex。

源码路径：system/core/libcutils/android_reboot.c

int android_reboot(int cmd, int flags UNUSED, char *arg){    int ret;    sync();    remount_ro();    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);            write_misc(arg);            ret = reboot(RB_AUTOBOOT);            break;        default:            ret = -1;    }    return ret;}

write_misc源码路径：system/core/libcutils/misc_rw.c有兴趣的可以研究一下。

static const char *MISC_DEVICE = "/dev/block/by-name/misc";/* Bootloader Message */struct bootloader_message {    char command[32];    char status[32];    char recovery[1024];};....../* force the next boot to recovery/efex */int write_misc(char *reason) {    struct bootloader_message boot, temp;    memset(&boot, 0, sizeof(boot));    if (!strcmp("recovery", reason)) {        reason = "boot-recovery";    }    strcpy(boot.command, reason);    if (set_bootloader_message_block(&boot, MISC_DEVICE) )        return -1;    //read for compare    memset(&temp, 0, sizeof(temp));    if (get_bootloader_message_block(&temp, MISC_DEVICE))        return -1;    if( memcmp(&boot, &temp, sizeof(boot)) )        return -1;    return 0;}static int set_bootloader_message_block(const struct bootloader_message *in,                                        const char* device) {    FILE* f = fopen(device, "wb");    if (f == NULL) {        LOGE("Can't open %s\n(%s)\n", device, strerror(errno));        return -1;    }    int count = fwrite(in, sizeof(*in), 1, f);    if (count != 1) {        LOGE("Failed writing %s\n(%s)\n", device, strerror(errno));        return -1;    }    sync();    if (fclose(f) != 0) {        LOGE("Failed closing %s\n(%s)\n", device, strerror(errno));        return -1;    }    return 0;}

那么问题来了，开机时怎么判断是该正常开机、还是进入recovery呢？一般是在u-boot中读取misc分区的数据，然后进行解析后对boot env "bootcmd"进行参数配置，这样就可以引导进入不同的系统了。例如全志平台u-boot： board/sunxi/common/board_common.c

int update_bootcmd(void){......misc_message = (struct bootloader_message *)misc_args;memset(misc_args, 0x0, 2048);memset(misc_fill, 0xff, 2048);mode = detect_other_boot_mode();switch(mode){......case ANDROID_NULL_MODE:{......else{misc_offset = sunxi_partition_get_offset_byname("misc");......printf("misc partition found\n");//read misc partition datasunxi_flash_read(misc_offset, 2048/512, misc_args);......else if(!strcmp(misc_message->command, "boot-recovery"))......puts("Recovery detected, will boot recovery\n");sunxi_str_replace(boot_commond, "boot_normal", "boot_recovery");}/* android recovery will clean the misc */}else if(!strcmp(misc_message->command, "bootloader")){puts("Fastboot detected, will boot fastboot\n");sunxi_str_replace(boot_commond, "boot_normal", "boot_fastboot");if(misc_offset)sunxi_flash_write(misc_offset, 2048/512, misc_fill);}else if(!strcmp(misc_message->command, "usb-recovery")){puts("Recovery detected, will usb recovery\n");sunxi_str_replace(boot_commond, "boot_normal", "boot_recovery");}else if(!strcmp(misc_message->command ,"debug_mode")){puts("debug_mode detected ,will enter debug_mode");if(0 == debug_mode_set()){debug_mode_update_info();}sunxi_flash_write(misc_offset,2048/512,misc_fill);......setenv("bootcmd", boot_commond);printf("to be run cmd=%s\n", boot_commond);return 0;}

boot_recovery的evn：

"boot_recovery=sunxi_flash read 4007f800 recovery;boota 4007f800\0"

boot_recovery将recovery加载到内存中并引导，然后就这样就进入recovery中了。

以Android5.1的代码来分析。

应用层和框架层实现

reboot在aidl中的定义

PMS中reboot调用shutdownOrRebootInternal

native实现

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