這裏所說的reboot指的是軟件重啓，並非斷電重啓。我們知道android系統的幾個功能，比如：回覆出廠設置、OTA升級等都需要重啓系統，而且重啓後要進入recovery模式，有的手機還帶有重啓進入fastboot或者其他模式。這些在軟重啓中式怎麼做到的呢？
經過一段查找找到了這個文件：\frameworks\base\core\java\android\os\RecoverySystem.java
我們來看這個文件裏面有一個類public class RecoverySystem 我們來看這個類的說明
/**
* 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.)
*/這個類裏面完成了android系統的回覆包括安裝系統更新，刪除用戶數據等。
下面我們來看這個類裏面的幾個 函數
/**
* Reboots the device in order to install the given update
* package.
* 重啓系統來安裝升級包
* 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.
* 重啓系統刪除用戶數據，這個通常被回覆出廠設置調用
* 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.
* 重啓系統來刪除 /cache目錄文件
* @throws IOException if something goes wrong.
*/
public static void rebootWipeCache(Context context) throws IOException {
bootCommand(context, "--wipe_cache");
}我們仔細研究着幾個 函數發現，要實現不同的重啓模式就是要bootCommand()這個函數傳送不同的參數，android重啓就是由這個函數來實現的，
我們就來看
/**
* 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(); // 創建recovery的目錄
COMMAND_FILE.delete(); // 清空recovery命令文件
/*
*這兩個文件都在/cache目錄中，他倆的定義是
* 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); //將命令寫入命令文件，給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"); //重啓系統
throw new IOException("Reboot failed (no permissions?)");
}從這個函數就可以看出了，到了這裏上面的三個功能最終合併成了一個--進入recovery模式，於是我們就來看 pm.reboot("recovery");
在\frameworks\base\core\java\android\os\PowerManager.java
public void reboot(String reason)
{
try {
mService.reboot(reason);
} catch (RemoteException e) {
}
}
public PowerManager(IPowerManager service, Handler handler)
{
mService = service;
mHandler = handler;
} 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());
}}); /**
* 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()");
}
//建立一個 shutdown線程來執行整個關機過程
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.
//關機時的UI顯示
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) {
}
}
}
}
下面我們就來看shutdown線程的 reboot函數：\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設置爲true
mRebootReason = reason;
shutdown(context, confirm);//關機之前的 系統清理，保存好所有的數據
}
/**
* 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);
} /**
* 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);//關機震動一下，如果是reboot就不震動
} 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();
}
/**
* 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);
}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);
}
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,//我們的參數要執行這一句
LINUX_REBOOT_CMD_RESTART2, arg);
break;
default:
ret = -1;
}
return ret;
}剩下的我們是要看__reboot(）這個函數了，這個函數其實是一個系統調用，調用的linux內核reboot函數它的實現在\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)
系統調用的原理這裏就不多講了，可以百度一下很容易找到，最終得到的reboot函數在\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;
/**
* 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);
}
void machine_restart(char *cmd)
{
machine_shutdown();
arm_pm_restart(reboot_mode, cmd);
}
也就是這個函數指針指向了arm_machine_restart，它的代碼在本文件中
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);
}
好了下面來看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 */
}
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();
}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));
}
過了這個函數，下面執行__raw_writew(wcr_enable, wdog_base); 這個是打開看門狗，可以知道系統重啓最後就是利用看門狗，產生復位信號，來重啓的。
到了這裏reboot的流程就走完了，下一步就是正常啓動了，詳細的啓動過程參見我的另一篇文章 http://blog.csdn.net/dkleikesa/article/details/9792747
下面來說明一個小技巧，如果要重啓進入各個模式，是可以由命令來實現的，也就是"reboot recovery"進入recovery模式 “reboot fastboot”是進入fastboot模式