模拟U盘

参考：http://hi.baidu.com/deep_pro/item/370abc23dbd8ea0d76272c32
        http://blog.youkuaiyun.com/sanlinux/article/details/5884660     

http://blog.youkuaiyun.com/wenxy1/article/details/6915140

insmod g_file_storage.ko file=/dev/mmcblk0p1 removable=1 stall=0