如何默认打开user 版本的USB debug 选项， 默认打开adb 连接
 
user usb debug root adb 连接
 

【方法】
1. 在android 4.0 之前，这个设置是在frameworks/base/service/..../SystemServer.java 里面设置会根据system property 的persist.service.adb.enable 来设置。您可以看到类似如代码：
        // make sure the ADB_ENABLED setting value matches the secure property value
        Settings.Secure.putInt(mContentResolver, Settings.Secure.ADB_ENABLED,
                "1".equals(SystemProperties.get("persist.service.adb.enable")) ? 1 : 0);

        // register observer to listen for settings changes
        mContentResolver.registerContentObserver(Settings.Secure.getUriFor(Settings.Secure.ADB_ENABLED),
                false, new AdbSettingsObserver());
    
 而这个persist.service.adb.enable 默认是放在在default.prop 中，在编译的时候在build/core/main.mk 中确认, 
 ifeq (true,$(strip $(enable_target_debugging)))
   # Target is more debuggable and adbd is on by default
   ADDITIONAL_DEFAULT_PROPERTIES += ro.debuggable=1 persist.service.adb.enable=1
   # Include the debugging/testing OTA keys in this build.
   INCLUDE_TEST_OTA_KEYS := true
 else # !enable_target_debugging
   # Target is less debuggable and adbd is off by default
   ADDITIONAL_DEFAULT_PROPERTIES += ro.debuggable=0 persist.service.adb.enable=0 
 endif # !enable_target_debugging
 您需要将: ADDITIONAL_DEFAULT_PROPERTIES += ro.debuggable=0 persist.service.adb.enable=0  改成
 ADDITIONAL_DEFAULT_PROPERTIES += ro.debuggable=1 persist.service.adb.enable=1 
    
2. 在android 4.0 之后，因为adb 的控制，统一使用了persist.sys.usb.config 来控制，于是对应的设置点也改到了frameworks/base/service/...../usb/UsbDeviceManager.java 中，您也可以看到类似的代码如：
public  UsbHandler(Looper looper) {
        // persist.sys.usb.config should never be unset.  But if it is, set it to "adb"
        // so we have a chance of debugging what happened.
         mDefaultFunctions = SystemProperties.get("persist.sys.usb.config", "adb");
        // sanity check the sys.usb.config system property
        // this may be necessary if we crashed while switching USB configurations
        String config = SystemProperties.get("sys.usb.config", "none");
        if (!config.equals(mDefaultFunctions)) {
            Slog.w(TAG, "resetting config to persistent property: " + mDefaultFunctions);
            SystemProperties.set("sys.usb.config", mDefaultFunctions);
        }
        mCurrentFunctions = mDefaultFunctions;
        String state = FileUtils.readTextFile(new File(STATE_PATH), 0, null).trim();
        updateState(state);
        mAdbEnabled = containsFunction(mCurrentFunctions, UsbManager.USB_FUNCTION_ADB);

public void  systemReady() {
 // make sure the ADB_ENABLED setting value matches the current state
    Settings.Secure.putInt(mContentResolver, Settings.Secure.ADB_ENABLED, mAdbEnabled ? 1 : 0);
 
而这个persist.sys.usb.config 中adb 的配置是在alps/build/tools/post_process_props.py 中根据ro.debuggable = 1 or 0 来设置，1 就是开启adb, 0 即关闭adb debug. 而这个ro.debuggable 也是在alps/build/core/main.mk 中设置，和2.3 修改类似

不过您这样打开之后，对于user 版本adb shell 开启的还是shell 权限，而不是root 权限，如果您需要root 权限，需要再改一下system/core/adb/adb.c 里面的should_drop_privileges() 这个函数，在#ifndef ALLOW_ADBD_ROOT 时return 0; 而不是return 1; 即可。

博客来源：http://blog.csdn.net/pfgmylove/article/details/16985159