f_dfu_snippet2.c

static int handle_dnload(struct usb_gadget *gadget, u16 len)
{
	struct usb_composite_dev *cdev = get_gadget_data(gadget);
	struct usb_request *req = cdev->req;
	struct f_dfu *f_dfu = req->context;

	if (len == 0)
		f_dfu->dfu_state = DFU_STATE_dfuMANIFEST_SYNC;

	req->complete = dnload_request_complete;

	return len;
}

static int state_dfu_idle(struct f_dfu *f_dfu,
			  const struct usb_ctrlrequest *ctrl,
			  struct usb_gadget *gadget,
			  struct usb_request *req)
{
	u16 w_value = le16_to_cpu(ctrl->wValue);
	u16 len = le16_to_cpu(ctrl->wLength);
	int value = 0;

	switch (ctrl->bRequest) {
	case USB_REQ_DFU_DNLOAD:
		if (len == 0) {
			f_dfu->dfu_state = DFU_STATE_dfuERROR;
			value = RET_STALL;
			break;
		}
		f_dfu->dfu_state = DFU_STATE_dfuDNLOAD_SYNC;
		f_dfu->blk_seq_num = w_value;
		value = handle_dnload(gadget, len);
		break;
	…
	}

	return value;
}