android L adb获取root原理

下面的方法就是判断要不要打开root，先上代码

static int should_drop_privileges() {
#ifndef ALLOW_ADBD_ROOT
    return 1;                     //如果没定义AllOW_ADVD_ROOT,则return1，不能root
#else /* ALLOW_ADBD_ROOT */    
    int secure = 0;
    char value[PROPERTY_VALUE_MAX];

   /* run adbd in secure mode if ro.secure is set and
    ** we are not in the emulator
    */
    property_get("ro.kernel.qemu", value, "");          //这个属性不知道是什么，一般不存在
    if (strcmp(value, "1") != 0) {
        property_get("ro.secure", value, "1");            //如果ro.secure是1，不打开root，但如果ro.debuggable是1，且service.adb.root是1，则可以打开root
        if (strcmp(value, "1") == 0) {
            // don't run as root if ro.secure is set...
            secure = 1;

            // ... except we allow running as root in userdebug builds if the
            // service.adb.root property has been set by the "adb root" command
            property_get("ro.debuggable", value, "");
            if (strcmp(value, "1") == 0) {
                property_get("service.adb.root", value, "");
                if (strcmp(value, "1") == 0) {
                    secure = 0;
                }
            }
        }
    }
    return secure;
#endif /* ALLOW_ADBD_ROOT */
}

所以根据上面的代码，可以设置属性ro.secure为0，则打开了root！！！！