android系统reboot

这里所说的reboot指的是软件重启，并非断电重启。我们知道android系统的几个功能，比如：回复出厂设置、OTA升级等都需要重启系统，而且重启后要进入recovery模式，有的手机还带有重启进入fastboot或者其他模式。这些在软重启中式怎么做到的呢？

经过一段查找找到了这个文件：\frameworks\base\core\java\android\os\RecoverySystem.java

我们来看这个文件里面有一个类public class RecoverySystem  我们来看这个类的说明

/**
 * RecoverySystem contains methods for interacting with the Android
 * recovery system (the separate partition that can be used to install
 * system updates, wipe user data, etc.)
 */

这个类里面完成了android系统的回复包括安装系统更新，删除用户数据等。

下面我们来看这个类里面的几个 函数

 /**
     * Reboots the device in order to install the given update
     * package.
     * 重启系统来安装升级包
     * Requires the {@link android.Manifest.permission#REBOOT} permission.
     *
     * @param context      the Context to use
     * @param packageFile  the update package to install.  Must be on
     * a partition mountable by recovery.  (The set of partitions
     * known to recovery may vary from device to device.  Generally,
     * /cache and /data are safe.)
     *
     * @throws IOException  if writing the recovery command file
     * fails, or if the reboot itself fails.
     */
    public static void installPackage(Context context, File packageFile)
        throws IOException {
        String filename = packageFile.getCanonicalPath();
        Log.w(TAG, "!!! REBOOTING TO INSTALL " + filename + " !!!");
        String arg = "--update_package=" + filename;
        bootCommand(context, arg);
    }

    /**
     * Reboots the device and wipes the user data partition.  This is
     * sometimes called a "factory reset", which is something of a
     * misnomer because the system partition is not restored to its
     * factory state.
     * 重启系统删除用户数据，这个通常被回复出厂设置调用
     * Requires the {@link android.Manifest.permission#REBOOT} permission.
     *
     * @param context  the Context to use
     *
     * @throws IOException  if writing the recovery command file
     * fails, or if the reboot itself fails.
     */
    public static void rebootWipeUserData(Context context) throws IOException {
        final ConditionVariable condition = new ConditionVariable();

        Intent intent = new Intent("android.intent.action.MASTER_CLEAR_NOTIFICATION");
        context.sendOrderedBroadcast(intent, android.Manifest.permission.MASTER_CLEAR,
                new BroadcastReceiver() {
                    @Override
                    public void onReceive(Context context, Intent intent) {
                        condition.open();
                    }
                }, null, 0, null, null);

        // Block until the ordered broadcast has completed.
        condition.block();

        bootCommand(context, "--wipe_data");
    }
    /**
     * Reboot into the recovery system to wipe the /cache partition.
     * 重启系统来删除 /cache目录文件
     * @throws IOException if something goes wrong.
     */
    public static void rebootWipeCache(Context context) throws IOException {
        bootCommand(context, "--wipe_cache");
    }

这几个函数功能的注释写的很清楚，android系统做 wipe_data、wipe_cache、OTA升级就是调用的这三个函数。具体在哪调用的我们不一一列举了，简单说一下，比如rebootWipeUserData是在回复出厂设置时候调用的，代码在\frameworks\base\services\java\com\android\server\MasterClearReceiver.java中。

我们仔细研究着几个 函数发现，要实现不同的重启模式就是要bootCommand()这个函数传送不同的参数，android重启就是由这个函数来实现的，

我们就来看

   /**
     * Reboot into the recovery system with the supplied argument.
     * @param arg to pass to the recovery utility.
     * @throws IOException if something goes wrong.
     */
    private static void bootCommand(Context context, String arg) throws IOException {
        RECOVERY_DIR.mkdirs();  // 创建recovery的目录
        COMMAND_FILE.delete();  // 清空recovery命令文件
        /*
        *这两个文件都在/cache目录中，他俩的定义是
        * private static File RECOVERY_DIR = new File("/cache/recovery");
        * private static File COMMAND_FILE = new File(RECOVERY_DIR, "command");
        */
        LOG_FILE.delete();

        FileWriter command = new FileWriter(COMMAND_FILE);//穿件新的命令文件
        try {
            command.write(arg); //将命令写入命令文件，给recovery模式使用
            command.write("\n");
        } finally {
            command.close();
        }

        // Having written the command file, go ahead and reboot
        PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
        pm.reboot("recovery");  //重启系统

        throw new IOException("Reboot failed (no permissions?)");
    }

这里首先要说明/cache目录和命令文件这两个东西，他们是主系统和recovery模式之间交流的桥梁，主系统把要做的事情写入到这两个中，然后recovery会读取这两个文件，再做相应的处理，这一点在我的另一篇文章中做了更详细的说明 http://blog.csdn.net/dkleikesa/article/details/9706137

从这个函数就可以看出了，到了这里上面的三个功能最终合并成了一个--进入recovery模式，于是我们就来看 pm.reboot("recovery");

在\frameworks\base\core\java\android\os\PowerManager.java

public void reboot(String reason)
    {
        try {
            mService.reboot(reason);
        } catch (RemoteException e) {
        }
    }

这里mService的定义

   public PowerManager(IPowerManager service, Handler handler)
    {
        mService = service;
        mHandler = handler;
    }

是在构造函数里传进来的，我们继续来看这个参数的传送在\frameworks\base\core\java\android\app\ContextImpl.java中有这么一段

        registerService(POWER_SERVICE, new ServiceFetcher() {
                public Object createService(ContextImpl ctx) {
                    IBinder b = ServiceManager.getService(POWER_SERVICE);
                    IPowerManager service = IPowerManager.Stub.asInterface(b);
                    return new PowerManager(service, ctx.mMainThread.getHandler());
                }});

可以知道 b = ServiceManager.getService(POWER_SERVICE);得到了PowerManagerService这个服务，service = IPowerManager.Stub.asInterface(b);然后将这个sevice的指针传给PowerManager()的构造函数。也就是说 这里的mService就是 PowerManagerService这个服务，因此这里的reboot也就是PowerManagerService的reboot 我们来看它的代码在：\frameworks\base\services\java\com\android\server\PowerManagerService.java中

    /**
     * Reboot the device immediately, passing 'reason' (may be null)
     * to the underlying __reboot system call.  Should not return.
     */
    public void reboot(String reason)
    {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.REBOOT, null);

        if (mHandler == null || !ActivityManagerNative.isSystemReady()) {
            throw new IllegalStateException("Too early to call reboot()");
        }
    //建立一个 shutdown线程来执行整个关机过程
        final String finalReason = reason;
        Runnable runnable = new Runnable() {
            public void run() {
                synchronized (this) {
                    ShutdownThread.reboot(mContext, finalReason, false);
                }

            }
        };
        // ShutdownThread must run on a looper capable of displaying the UI.
        //关机时的UI显示
        mHandler.post(runnable);

        // PowerManager.reboot() is documented not to return so just wait for the inevitable.
        synchronized (runnable) {
            while (true) {
                try {
                    runnable.wait();
                } catch (InterruptedException e) {
                }
            }
        }
    }

下面我们就来看shutdown线程的 reboot函数：\frameworks\base\core\java\com\android\internal\app\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.
     * @param reason code to pass to the kernel (e.g. "recovery"), or null.
     * @param confirm true if user confirmation is needed before shutting down.
     */
    public static void reboot(final Context context, String reason, boolean confirm) {
        mReboot = true; //吧reboot设置为true
        mRebootReason = reason;
        shutdown(context, confirm);//关机之前的 系统清理，保存好所有的数据
    }

这里要进一步执行的话靠的是mReboot=true;这一句，具体的执行过程在ShutdownThread:run()函数中

    /**
     * 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() {
       。。。。。。。。。。。。。
       。。。。。。。。。。。。。

        rebootOrShutdown(mReboot, mRebootReason);
    }

继续看:\frameworks\base\core\java\com\android\internal\app\ShutdownThread.java

    /**
     * Do not call this directly. Use {@link #reboot(Context, String, boolean)}
     * or {@link #shutdown(Context, boolean)} instead.
     *
     * @param reboot true to reboot or false to shutdown
     * @param reason reason for reboot
     */
    public static void rebootOrShutdown(boolean reboot, String reason) {
        if (reboot) {
            Log.i(TAG, "Rebooting, reason: " + reason);
            try {
                Power.reboot(reason);
            } catch (Exception e) {
                Log.e(TAG, "Reboot failed, will attempt shutdown instead", e);
            }
        } else if (SHUTDOWN_VIBRATE_MS > 0) {
            // vibrate before shutting down
            Vibrator vibrator = new Vibrator();
            try {
                vibrator.vibrate(SHUTDOWN_VIBRATE_MS);//关机震动一下，如果是reboot就不震动
            } 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...");
        Power.shutdown();
    }

这里最终调用的是Power.reboot(reason);代码在\frameworks\base\core\java\android\os\Power.java

    /**
     * Reboot the device.
     * @param reason code to pass to the kernel (e.g. "recovery"), or null.
     *
     * @throws IOException if reboot fails for some reason (eg, lack of
     *         permission)
     */
    public static void reboot(String reason) throws IOException
    {
        rebootNative(reason);
    }

这里到了jni层 代码在\frameworks\base\core\jni\android_os_Power.cpp

static void android_os_Power_reboot(JNIEnv *env, jobject clazz, jstring reason)
{
    if (reason == NULL) {
        android_reboot(ANDROID_RB_RESTART, 0, 0);
    } else {
        const char *chars = env->GetStringUTFChars(reason, NULL);
        android_reboot(ANDROID_RB_RESTART2, 0, (char *) chars);
        env->ReleaseStringUTFChars(reason, chars);  // In case it fails.
    }
    jniThrowIOException(env, errno);
}

继续看这里调用的android_reboot()在：\system\core\libcutils\android_reboot.c

int android_reboot(int cmd, int flags, char *arg)
{
    int ret;

    if (!(flags & ANDROID_RB_FLAG_NO_SYNC))
        sync();

    if (!(flags & ANDROID_RB_FLAG_NO_REMOUNT_RO))
        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 = __reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,//我们的参数要执行这一句
                           LINUX_REBOOT_CMD_RESTART2, arg);
            break;

        default:
            ret = -1;
    }

    return ret;
}

剩下的我们是要看__reboot(）这个函数了，这个函数其实是一个系统调用，调用的linux内核reboot函数它的实现在\android40\bionic\libc\arch-arm\syscalls\__reboot.S

ENTRY(__reboot)
    .save   {r4, r7}
    stmfd   sp!, {r4, r7}
    ldr     r7, =__NR_reboot
    swi     #0
    ldmfd   sp!, {r4, r7}
    movs    r0, r0
    bxpl    lr
    b       __set_syscall_errno
END(__reboot)

这里__NR_reboot 定义为88 也就是说它是linux系统调用列表里的第88个函数，这样我们就可以去kernel里找这个函数的定义了

系统调用的原理这里就不多讲了，可以百度一下很容易找到，最终得到的reboot函数在\kernel_imx\kernel\sys.c中

SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
		void __user *, arg)
{
	char buffer[256];
	int ret = 0;

	/* We only trust the superuser with rebooting the system. */
	if (!capable(CAP_SYS_BOOT))
		return -EPERM;

	/* For safety, we require "magic" arguments. */
	if (magic1 != LINUX_REBOOT_MAGIC1 ||
	    (magic2 != LINUX_REBOOT_MAGIC2 &&
	                magic2 != LINUX_REBOOT_MAGIC2A &&
			magic2 != LINUX_REBOOT_MAGIC2B &&
	                magic2 != LINUX_REBOOT_MAGIC2C))
		return -EINVAL;

	/* Instead of trying to make the power_off code look like
	 * halt when pm_power_off is not set do it the easy way.
	 */
	if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !pm_power_off)
		cmd = LINUX_REBOOT_CMD_HALT;

	mutex_lock(&reboot_mutex);
	switch (cmd) {
	case LINUX_REBOOT_CMD_RESTART:
		kernel_restart(NULL);
		break;

	case LINUX_REBOOT_CMD_CAD_ON:
		C_A_D = 1;
		break;

	case LINUX_REBOOT_CMD_CAD_OFF:
		C_A_D = 0;
		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:
		if (strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1) < 0) {
			ret = -EFAULT;
			break;
		}
		buffer[sizeof(buffer) - 1] = '\0';

		kernel_restart(buffer);
		break;

#ifdef CONFIG_KEXEC
	case LINUX_REBOOT_CMD_KEXEC:
		ret = kernel_kexec();
		break;
#endif

#ifdef CONFIG_HIBERNATION
	case LINUX_REBOOT_CMD_SW_SUSPEND:
		ret = hibernate();
		break;
#endif

	default:
		ret = -EINVAL;
		break;
	}
	mutex_unlock(&reboot_mutex);
	return ret;

这里下一步调用的是kernel_restart()代码在本文件中

/**
 *	kernel_restart - reboot the system
 *	@cmd: pointer to buffer containing command to execute for restart
 *		or %NULL
 *
 *	Shutdown everything and perform a clean reboot.
 *	This is not safe to call in interrupt context.
 */
void kernel_restart(char *cmd)
{
	kernel_restart_prepare(cmd);
	if (!cmd)
		printk(KERN_EMERG "Restarting system.\n");
	else
		printk(KERN_EMERG "Restarting system with command '%s'.\n", cmd);
	kmsg_dump(KMSG_DUMP_RESTART);
	machine_restart(cmd);
}

下一步调用machine_restart()代码在\kernel_imx\arch\arm\kernel\process.c中

void machine_restart(char *cmd)
{
	machine_shutdown();
	arm_pm_restart(reboot_mode, cmd);
}

下一步看arm_pm_restart(reboot_mode, cmd);，在本文件中有这个的定义void (*arm_pm_restart)(char str, const char *cmd) = arm_machine_restart;

也就是这个函数指针指向了arm_machine_restart，它的代码在本文件中

void arm_machine_restart(char mode, const char *cmd)
{

	//ar_mode(mode,cmd); 	//lijianzhang
	/* Flush the console to make sure all the relevant messages make it
	 * out to the console drivers */
	arm_machine_flush_console();

	/* Disable interrupts first */
	local_irq_disable();
	local_fiq_disable();

	/*
	 * Tell the mm system that we are going to reboot -
	 * we may need it to insert some 1:1 mappings so that
	 * soft boot works.
	 */
	setup_mm_for_reboot(mode);

	/* Clean and invalidate caches */
	flush_cache_all();

	/* Turn off caching */
	cpu_proc_fin();

	/* Push out any further dirty data, and ensure cache is empty */
	flush_cache_all();

	/*
	 * Now call the architecture specific reboot code.
	 */
	arch_reset(mode, cmd);

	/*
	 * Whoops - the architecture was unable to reboot.
	 * Tell the user!
	 */
	mdelay(1000);
	printk("Reboot failed -- System halted\n");
	while (1);
}

这里执行reboot的函数是arch_reset(mode, cmd)，在执行arch_reset的代码都是关闭系统和cpu一些东西，其中包括了mmu，关闭了mmu以后，访问寄存器必须直接使用寄存器地址，ioremap这个函数就不能再使用了，同样的，由于mmu关闭了 ，这个函数下面就是printk是打印不出来的，字符过多还会报出内核错误，因此这里虽然写了printk 可以打印出reboot错误，其实也是打不出来的，这点gun官网上也有说明，网上有人修改了内核，在关闭mmu以后将printk缓存替换成物理地址，这样才能正常使用。

好了下面来看arch_reset(mode, cmd); \kernel_imx\arch\arm\plat-mxc\system.c

/*
 * Reset the system. It is called by machine_restart().
 */
void arch_reset(char mode, const char *cmd)
{
	unsigned int wcr_enable;

	arch_reset_special_mode(mode, cmd);

#ifdef CONFIG_ARCH_MX6
	/* wait for reset to assert... */
	#ifdef CONFIG_MX6_INTER_LDO_BYPASS
	wcr_enable = 0x14; /*reset system by extern pmic*/
	#else
	wcr_enable = (1 << 2);
	#endif

	__raw_writew(wcr_enable, wdog_base);
	 /*errata TKT039676, SRS bit may be missed when
	SRC sample it, need to write the wdog controller
	twice to avoid it */
	__raw_writew(wcr_enable, wdog_base/*MX6Q_WDOG1_BASE_ADDR*/);

	/* wait for reset to assert... */
	mdelay(500);

	printk(KERN_ERR "Watchdog reset failed to assert reset\n");

	return;
#endif

#ifdef CONFIG_MACH_MX51_EFIKAMX
	if (machine_is_mx51_efikamx()) {
		mx51_efikamx_reset();
		return;
	}
#endif

	if (cpu_is_mx1()) {
		wcr_enable = (1 << 0);
	} else {
		struct clk *clk;

		clk = clk_get_sys("imx2-wdt.0", NULL);
		if (!IS_ERR(clk))
			clk_enable(clk);
		wcr_enable = (1 << 2);
	}

	/* Assert SRS signal */
	__raw_writew(wcr_enable, wdog_base);

	/* wait for reset to assert... */
	mdelay(500);

	printk(KERN_ERR "Watchdog reset failed to assert reset\n");

	/* delay to allow the serial port to show the message */
	mdelay(50);

	/* we'll take a jump through zero as a poor second */
}

好了这里看arch_reset_special_mode(mode, cmd); 这个函数就是进入各个模式，与uboot通信的地方,来看代码

static void arch_reset_special_mode(char mode, const char *cmd)
{
	if (strcmp(cmd, "download") == 0)
		do_switch_mfgmode();
	else if (strcmp(cmd, "recovery") == 0)
		do_switch_recovery();
	else if (strcmp(cmd, "fastboot") == 0)
		do_switch_fastboot();
	else if (strcmp(cmd, "bootloader") == 0)
		do_switch_bootloader();
}

这里可以看到内核支持4个模式，每个模式都有相应的函数，我们来贴一个recovery的，在\kernel_imx\arch\arm\mach-mx6\system.c

void do_switch_recovery(void)
{
	u32 reg;

	reg = __raw_readl((SRC_BASE_ADDR + SRC_GPR10));
	reg |= ANDROID_RECOVERY_BOOT;
	__raw_writel(reg, (SRC_BASE_ADDR + SRC_GPR10));
}

原理是把一个寄存器的值的一位置高，这个寄存器在复位过程中是不会被清零的，重启以后，uboot可以检测这一位来确定启动的模式，
过了这个函数，下面执行__raw_writew(wcr_enable, wdog_base); 这个是打开看门狗，可以知道系统重启最后就是利用看门狗，产生复位信号，来重启的。

到了这里reboot的流程就走完了，下一步就是正常启动了，详细的启动过程参见我的另一篇文章 http://blog.csdn.net/dkleikesa/article/details/9792747

下面来说明一个小技巧，如果要重启进入各个模式，是可以由命令来实现的，也就是"reboot recovery"进入recovery模式 “reboot fastboot”是进入fastboot模式