Linux源代码阅读：Linux/drivers/usb/gadget/dummy_hcd.c

这个文件共2062行，是内核目前最适合拿来做样板的代码了。
参见：http://lxr.linux.no/source/drivers/usb/gadget/dummy_hcd.c

 /*
  * This exposes a device side "USB gadget" API, driven by requests to a
  * Linux-USB host controller driver.  USB traffic is simulated; there's
  * no need for USB hardware.  Use this with two other drivers:
  *
  *  - Gadget driver, responding to requests (slave);
  *  - Host-side device driver, as already familiar in Linux.
  *
  * Having this all in one kernel can help some stages of development,
  * bypassing some hardware (and driver) issues.  UML could help too.
  */

这段注释说得很清楚，这是用来模拟USB传输的一个驱动，它同时起Host Controler和模拟Gadget设备的作用。
至于Gadget，它是用在一些嵌入式设备的OTG控制器上的。

今天晚了，明天继续