Android(安卓)关机（reboot）流程

Base On Android 4.2

recovery 和 reboot流程

part 1. reboot recovery流程。 1,RecoverySystem.java中 private static File RECOVERY_DIR = new File("/cache/recovery");
private static File COMMAND_FILE = new File(RECOVERY_DIR, "command"); pm.reboot("recovery"); =》PowerManager.java public void reboot(String reason) { try {
mService .reboot(false, reason, true);
} catch (RemoteException e) {
}
} mService就是PowerManagerService.java的实例因为 public final class PowerManagerService extends IPowerManager.Stub
=>PowerManagerService.java reboot(){ shutdownOrRebootInternal(false, confirm, reason, wait); }
private void shutdownOrRebootInternal(final boolean shutdown, final boolean confirm,
final String reason, boolean wait) { ShutdownThread.reboot(mContext, reason, confirm); }
=> ShutdownThread.java
public static void reboot(final Context context, String reason, boolean confirm) {
mReboot = true;
mRebootSafeMode = false;
mRebootReason = reason;
shutdownInner(context, confirm);
}
shutdownInner
-》 beginShutdownSequence 拿两个wake_lock让系统不待机，让屏幕常亮然后 sInstance.start();这个ShutdwonThread的实例start.即调用其的run方法
在run方法中，关掉am,radio....之后，调用 rebootOrShutdown -》 public static void rebootOrShutdown(boolean reboot, String reason)
-》 PowerManagerService.lowLevelReboot(reason); 又调回PowerManagerService了。
->PowerManagerService中 lowLevelReboot（） SystemProperties.set("sys.powerctl", "reboot," + reason); //就传给Kernel进入reboot了
=》那么接下来，走到哪里去了？参考： “ KK 以后 Google 将关机/重启的最后转移到了init 进程上执行。其他Process 通过system property sys.powerctl 通知init 执行。
sys.powerctl 的配置在init.rc 当中，可以参考 on property:sys.powerctl=*
powerctl ${sys.powerctl}

然后执行system/core/init/builtins.c#do_powerctl 函数，call android_reboot 重启或者关机。为何工厂模式下无法adb reboot ? 正常情况下adb reboot 可以重启，其关键就是因为mediatek/config/{platform}factory_init.rc 中没有定义
on property:sys.powerctl=*
powerctl ${sys.powerctl}

如果要添加此功能，只有在factory_init.rc 中添加这两行即可 ” 继续跟
=》在init.rc中和一个相关的on 触发器 396 on property:sys.powerctl=*
397 powerctl ${sys.powerctl}
=》会调用 builtins.c 的，参考间reboot,recovery int do_powerctl(int nargs, char **args)
=> return android_reboot(cmd, 0, reboot_target); cmd =ANDROID_RB_RESTART2 //在android_reboot.h中#define ANDROID_RB_RESTART2 0xDEAD0003 reboot_target =第二个参考recovery
=》 /system/core/libcutils/android_reboot.c 中的执行android_reboot();
case ANDROID_RB_RESTART2:
121 ret = __reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
122 LINUX_REBOOT_CMD_RESTART2, arg); //arg= recovery
=> 这个在bionic/libc/include/sys/reboot.h中定义的。说明这是一个标准的系统调用 extern int __reboot(int, int, int, void *);
具体位于bionic/libc/arch-arm/syscalls/__reboot.S 1 /* autogenerated by gensyscalls.py */
2 #include <asm/unistd.h>
3 #include <linux/err.h>
4 #include <machine/asm.h>
5
6 ENTRY(__reboot)
7 mov ip, r7
8 ldr r7, =__NR_reboot
9 swi #0
10 mov r7, ip
11 cmn r0, #(MAX_ERRNO + 1)
12 bxls lr
13 neg r0, r0
14 b __set_errno
15 END(__reboot)

=》最后会进入Kernel kernel/sys.c 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); //buffer= arg= recovery
break;
=>machine_restart()
=>arch/arm/kernel/process.c void machine_restart(char *cmd)
{
local_irq_disable();
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(reboot_mode, cmd);

/* Give a grace period for failure to restart of 1s */
mdelay(1000); // 1s之内没有restart完成就reboot失败。

/* Whoops - the platform was unable to reboot. Tell the user! */
printk("Reboot failed -- System halted\n");
local_irq_disable();
while (1);
}
=》 void (*arm_pm_restart)(char str, const char *cmd) = arm_machine_restart; =》 void arm_machine_restart(char mode, const char *cmd) { ... aml_write_reg32(P_AO_RTI_STATUS_REG1, reboot_reason); //这一个标志寄存器 ...
arch_reset(mode, cmd); // mode = 'h' cmd = "recovery" }
差不多了，尝试就如此吧。
那么有必要了解这个寄存器P_AO_RTI_STATUS_REG1在下次启动的时候，uboot是什么时候读。这就可以实现一些关机之后的状态保存。

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