Question

我正在编写一个简单的库，该库使用libusb连接到我的自定义硬件，该硬件每50毫秒将信号发送到主机设备一次。它旨在提供一个简单的抽象层，以使用户完全不会被libusb所困扰。我需要将指向非静态类成员函数的指针传递给libusb_fill_bulk_transfer。即我需要为MyDevice的每个实例提供一个单独的回调，而又不向用户暴露libusb逻辑。

基本设计是：

初始化库

int mylib_init(){
  libusb_init(&context);
}

找到所有兼容的设备

int mylib_get_valid_devices(vector devs){
 //...
 libusb_device **devs1;
 int countAll = libusb_get_device_list(context, &devs1);
 //... fill devs
}
int mylib_print_device_info(MyDevice* dev);

连接到用户喜欢的设备

int mylib_init_device(MyDevice* dev){
   libusb_open(dev->device, &dev->dev_handle);
   // check for kernel driver & remove if needed
   libusb_claim_interface(dev->dev_handle, 0);
   //...
}

设置回调，以将数据传入连接设备的所有实例

int mylib_start_transmission_async(MyDevice* dev, MyLibCallbackIn user_cb, unsigned char* buffer_in, int bufferSize){
   libusb_control_transfer(dev->dev_handle, p1, p2, p3, p4, p5, p6, p7);
   // .. rest of libusb_control_transfer -s

   //start device:
   int actual;
   unsigned char startSig = 0b00110111;
   libusb_bulk_transfer(dev->dev_handle, (1 | LIBUSB_ENDPOINT_OUT), &tosend, 1, &actual, 100);

   dev->user_callback = user_cb;
   dev->buffer_in = buffer_in; 
   dev->bufferSize = bufferSize;

   //setup transfer
   dev->transfer_in = libusb_alloc_transfer(0);
   libusb_fill_bulk_transfer(dev->transfer_in, dev->dev_handle, LIBUSB_ENDPOINT_IN, dev->buffer_in,dev->bufferSize, cb_in, NULL, 0);
   libusb_submit_transfer(dev->transfer_in); 

}

完成后断开连接

int mylib_disconnect_device(MyDevice* device);
退出lib

int mylib_exit();

MyDevice定义为：

typedef int (*MyLibdCallbackIn)(unsigned char* buffer, int length);

class MyDevice{

  unsigned char* buffer_in;
  unsigned char* buffer_out;

  libusb_device* device = nullptr;
  libusb_device_handle* dev_handle = nullptr;

  struct libusb_transfer* transfer_in = nullptr;
  struct libusb_transfer* transfer_out = nullptr;

//this obviously wouldn't work because libusb doesn't accept it as a param:
  void LIBUSB_CALL cb_in(struct libusb_transfer* transfer); 
  MyLibCallbackIn user_callback;

  void run();
  //...

}

和cb_in定义为：

void LIBUSB_CALL MyDevice::cb_in(libusb_transfer* transfer){
  int r = libusb_submit_transfer(this->transfer_in);
  callback_in(transfer->buffer, transfered);

}

由于函数指针类型不兼容，我无法将MyDevice::cb_in传递给libusb_fill_bulk_transfer。同时，我不希望我的用户必须编写以libusb_transfer*作为参数（暴露于libusb）的回调函数直接传递给libusb_fill_bulk_transfer。

编辑：我尝试过

void LIBUSB_CALL callback_wrapper(struct libusb_transfer* transfer){
  MyDevice* dev = reinterpret_cast<MyDevice*>(transfer->user_data);
  dev->cb_in(transfer);
}

但出现Sementation fault (Core dumped)错误

Answer 1

根据Max Langhof和Sam Varshavchik的评论，解决方案是将MyDevice的实例传递给libusb_fill_bulk_transfer。因此：

int mylib_start_transmission_async(MyDevice* dev, MyLibCallbackIn user_cb, unsigned char* buffer_in, int bufferSize){

   //...
   // setup transfer:
   dev->transfer_in = libusb_alloc_transfer(0);
   libusb_fill_bulk_transfer(dev->transfer_in, dev->dev_handle, LIBUSB_ENDPOINT_IN, dev->buffer_in,dev->bufferSize, cb_in, dev, 0);
   libusb_submit_transfer(dev->transfer_in);                                                                               ^^^

}

，然后像在Edit中一样使用callback_wrapper。谢谢！

如何将成员函数指针传递给libusb？

1 个答案: