Android 关机umount

Java layer

• Helper Java Power class : framework/base/core/java/android/os/power.java
  

  public class Power
  {
      // can't instantiate this class
      private Power()
      {
      }
  
      /**
       * Wake lock that ensures that the CPU is running.  The screen might
       * not be on.
       */
      public static final int PARTIAL_WAKE_LOCK = 1;
  
      /**
       * Wake lock that ensures that the screen is on.
       */
      public static final int FULL_WAKE_LOCK = 2;
  
      public static native void acquireWakeLock(int lock, String id);
      public static native void releaseWakeLock(String id);
  
      /**
       * Brightness value for fully off
       */
      public static final int BRIGHTNESS_OFF = 0;
  
      /**
       * Brightness value for dim backlight
       */
      public static final int BRIGHTNESS_DIM = 20;
  
      /**
       * Brightness value for fully on
       */
      public static final int BRIGHTNESS_ON = 255;
  
      /**
       * Brightness value to use when battery is low
       */
      public static final int BRIGHTNESS_LOW_BATTERY = 10;
  
      /**
       * Threshold for BRIGHTNESS_LOW_BATTERY (percentage)
       * Screen will stay dim if battery level is <= LOW_BATTERY_THRESHOLD
       */
      public static final int LOW_BATTERY_THRESHOLD = 10;
  
      /**
       * Turn the screen on or off
       *
       * @param on Whether you want the screen on or off
       */
      public static native int setScreenState(boolean on);
  
      public static native int setLastUserActivityTimeout(long ms);
  
      /**
       * Low-level function turn the device off immediately, without trying
       * to be clean.  Most people should use
       * {@link android.internal.app.ShutdownThread} for a clean shutdown.
       *
       * @deprecated
       * @hide
       */
      @Deprecated
      public static native void 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)
  static JNINativeMethod method_table[] = {
      { "acquireWakeLock", "(ILjava/lang/String;)V", (void*)acquireWakeLock },
      { "releaseWakeLock", "(Ljava/lang/String;)V", (void*)releaseWakeLock },
      { "setLastUserActivityTimeout", "(J)I", (void*)setLastUserActivityTimeout },
      { "setScreenState", "(Z)I", (void*)setScreenState },
      { "shutdown", "()V", (void*)android_os_Power_shutdown },
      { "rebootNative", "(Ljava/lang/String;)V", (void*)android_os_Power_reboot },
  };
  
  */ public static void reboot(String reason) throws IOException { rebootNative(reason); } private static native void
  rebootNative(String reason) throws IOException ;}
  
  
  
  

JNI layer

• frameworks/base/core/jni/android_os_Power.cpp
  

  static JNINativeMethod method_table[] = {
      { "acquireWakeLock", "(ILjava/lang/String;)V", (void*)acquireWakeLock },
      { "releaseWakeLock", "(Ljava/lang/String;)V", (void*)releaseWakeLock },
      { "setLastUserActivityTimeout", "(J)I", (void*)setLastUserActivityTimeout },
      { "setScreenState", "(Z)I", (void*)setScreenState },
      { "shutdown", "()V", (void*)android_os_Power_shutdown },
      { "rebootNative", "(Ljava/lang/String;)V", (void*)android_os_Power_reboot },
  };
  
  static void android_os_Power_shutdown(JNIEnv *env, jobject clazz)
  {
      android_reboot(ANDROID_RB_POWEROFF, 0, 0);
  }
  
  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);
  }
  
  

System lib cutils/android_reboot.h

• system/core/libcutils/android_reboot.c
  • android_reboot()
    

    int android_reboot(int cmd, int flags, char *arg)
    {
        int ret;
    	
    	//Gozone start BID 11184 chenglong: for reboot status capture
    	save_reboot_log(cmd, flags, arg);
    	//Gozone end BID 11184
    
        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,
                               LINUX_REBOOT_CMD_RESTART2, arg);
                break;
    
            default:
                ret = -1;
        }
    
        return ret;
    }

    
    
    
  • remount_ro_done()
    check to see if /proc/mounts contains any writable file systems; return TRUE
    

    static int remount_ro_done(void)
    {
        FILE *f;
        char mount_dev[256];
        char mount_dir[256];
        char mount_type[256];
        char mount_opts[256];
        int mount_freq;
        int mount_passno;
        int match;
        int found_rw_fs = 0;
    
        f = fopen("/proc/mounts", "r");
        if (! f) {
            /* If we can't read /proc/mounts, just give up */
            return 1;
        }
    
        do {
            match = fscanf(f, "%255s %255s %255s %255s %d %d\n",
                           mount_dev, mount_dir, mount_type,
                           mount_opts, &mount_freq, &mount_passno);
            mount_dev[255] = 0;
            mount_dir[255] = 0;
            mount_type[255] = 0;
            mount_opts[255] = 0;
            if ((match == 6) && !strncmp(mount_dev, "/dev/block", 10) && strstr(mount_opts, "rw")) {
                found_rw_fs = 1;
                break;
            }
        } while (match != EOF);
    
        fclose(f);
    
        return !found_rw_fs;
    }

    典型的，／ｐｒｏｃ／ｍｏｕｎｔｓ　内容示例如下:
    

    root@android:/proc # cat mounts
    cat mounts
    rootfs / rootfs ro,relatime 0 0
    tmpfs /dev tmpfs rw,nosuid,relatime,mode=755 0 0
    devpts /dev/pts devpts rw,relatime,mode=600 0 0
    proc /proc proc rw,relatime 0 0
    sysfs /sys sysfs rw,relatime 0 0
    none /acct cgroup rw,relatime,cpuacct 0 0
    tmpfs /mnt/asec tmpfs rw,relatime,mode=755,gid=1000 0 0
    tmpfs /mnt/obb tmpfs rw,relatime,mode=755,gid=1000 0 0
    none /dev/cpuctl cgroup rw,relatime,cpu 0 0
    /dev/block/platform/sdhci.1/by-name/system /system ext4 rw,relatime,user_xattr,barrier=1,data=ordered 0 0
    /dev/block/platform/sdhci.1/by-name/userdata /data ext4 rw,nosuid,nodev,noatime,user_xattr,barrier=1,data=ordered 0 0
    /dev/block/platform/sdhci.1/by-name/cache /cache ext4 rw,nosuid,noatime,user_xattr,barrier=1,data=ordered 0 0
    /sys/kernel/debug /sys/kernel/debug debugfs rw,relatime 0 0
    /dev/block/vold/179:27 /mnt/sdcard vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0002,dmask=0002,
    allow_utime=0020,codepage=cp437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro 0 0
    /dev/block/vold/179:27 /mnt/secure/asec vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0002,dmask=
    0002,allow_utime=0020,codepage=cp437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro 0 0
    tmpfs /mnt/sdcard/.android_secure tmpfs ro,relatime,size=0k,mode=000 0 0
    root@android:/proc #

    
    
    
  • remount_ro()
    

    static void remount_ro(void)
    {
        int fd, cnt = 0;
    
        /* Trigger the remount of the filesystems as read-only,
         * which also marks them clean.
         */
        fd = open("/proc/sysrq-trigger", O_WRONLY);
        if (fd < 0) {
            return;
        }
        write(fd, "u", 1);
        close(fd);
    
    
        /* Now poll /proc/mounts till it's done */
        while (!remount_ro_done() && (cnt < 50)) {
            usleep(100000);
            cnt++;
        }
    
        return;