在 libusb_fill_interrupt_transfer 回调中使用 "user_data" 时出错

Error when using "user_data" in libusb_fill_interrupt_transfer callback

我正在使用 libusb-1.0 将 BLE 加密狗与 RCU 配对。

为此,我成功向dongle接口写入配对请求。 为了收听加密狗响应,我使用函数 libusb_fill_interrupt_transfer 并传递一个回调,该回调将在收到响应时执行。 此函数接受一个参数,如文档 (void *user_data) 中所述,可在回调中使用。但是当我尝试使用这个参数时,我得到一个编译错误。

undeclared (first use in this function)

继上一个函数的调用和我的回调声明之后:

libusb_fill_interrupt_transfer(pairing->transfer, dctx->devh, 0x84, pairing->buffer,
    sizeof(pairing->buffer), cb_aknowledgement, pairing, 0);

static void cb_aknowledgement(struct libusb_transfer *transfer)
{
    if (pairing->transfer->status != LIBUSB_TRANSFER_COMPLETED) {
        printf( "img transfer status %d?\n", pairing->transfer->status);
        libusb_free_transfer(pairing->transfer);
        pairing->transfer = NULL;
        return;
    }

    if(pairing->buffer[0]!=0x05 || pairing->buffer[1]!=0x21)
    {
        printf( "wrong command recieved\n");
        libusb_free_transfer(pairing->transfer);
        pairing->transfer = NULL;
        return;
    }

    printf("I've read data  \n");
    printf("USB Report Id           =  0x%x \n",pairing->buffer[0]);
    printf("Command                 =  0x%x \n",pairing->buffer[1]);
    printf("Acknowledgement type    =  0x%x \n",pairing->buffer[2]);
    return ;
}

问题是:如何使用作为参数传递给回调的 user_data

使用transfer->user_data。来自 libusb_transfer structure doc :

Data Fields
void * user_data
User context data to pass to the callback function.

我不知道 pairing 的类型是什么,但它看起来像这样:

int main() {
   ...
   struct pairing_type_s *pairing = pairing_init();
   ...
   libusb_fill_interrupt_transfer(pairing->transfer, dctx->devh, 0x84, pairing->buffer,
    sizeof(pairing->buffer), cb_aknowledgement, pairing, 0);
    ...
}

// Then later:

static void cb_aknowledgement(struct libusb_transfer *transfer)
{
     assert(transfer != NULL);
     struct pairing_type_s *pairing = transfer->user_data;
     assert(pairing != NULL);
     // use pairing like a pro
     ...
}

但你也可以更专业,如果你确保你总是用 pairing->transfercb_aknowledgement 调用 libusb_fill_interrupt_transfer 并使用 container_of 宏:

int main() {
   ...
   struct pairing_type_s *pairing = pairing_init();
   ...
   libusb_fill_interrupt_transfer(pairing->transfer, dctx->devh, 0x84, pairing->buffer,
    sizeof(pairing->buffer), cb_aknowledgement, NULL, 0);
    ...
}

// Then later:

static void cb_aknowledgement(struct libusb_transfer *transfer)
{
     assert(transfer != NULL);
     struct pairing_type_s *pairing = container_of(transfer, struct pairing_type_s, transfer);
     assert(pairing != NULL);
     // use pairing like a pro
     ...
}

但在这种情况下我更喜欢第一种方法,因为它更易读且更不会出错。