Android 用 libusb 操作 USB 設備，無須 root

基本思路：

利用 Android （3.1版本以上）的 USB HOST API 獲得 USB 設備的 FileDescriptor，然後libusb 使用 FileDescriptor 打開 USB 設備，當然 libusb 需要做少量修改，後面有代碼。

總體的效果就是，用戶插入USB 設備，或者啓動 Android 系統，你的 App 會根據事先設定的 device filter 自動啓動。如果是第一次啓動，會詢問用戶是否授權使用該USB設備。

關鍵代碼（如何使用libusb，請參考官方文檔）：
獲取 FileDescriptor

    // get FileDescriptor by Android USB Host API
    UsbManager manager = (UsbManager) mContext.getSystemService(Context.USB_SERVICE);
    final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION";
    HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
    Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();
     
    PendingIntent mPermissionIntent = PendingIntent.getBroadcast(mContext, 0,
                                                                 new Intent(ACTION_USB_PERMISSION), 0);
    IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
    mContext.registerReceiver(mUsbReceiver, filter);
     
    int fd = -1;
    while(deviceIterator.hasNext()){
        UsbDevice device = deviceIterator.next();
        Log.i(TAG, device.getDeviceName() + " " + Integer.toHexString(device.getVendorId()) +
                   " " + Integer.toHexString(device.getProductId()));
     
        manager.requestPermission(device, mPermissionIntent);
        UsbDeviceConnection connection = manager.openDevice(device);
        if(connection != null){
           fd = connection.getFileDescriptor();
        } else
           Log.e(TAG, "UsbManager openDevice failed");
        break;
    }

接着修改 libusb，我用的是libusbx-1.0.17，主要工作是增加一個 libusb_open_fd 函數，替代原來的 libusb_open，將上一步的 fd 傳入即可。
libusbx\libusb\core.c 中在 libusb_open 後面增加 libusb_open_fd 函數

    int LIBUSB_CALL libusb_open_fd(libusb_device *dev, libusb_device_handle **handle, int fd)
    {
    struct libusb_context *ctx = DEVICE_CTX(dev);
    struct libusb_device_handle *_handle;
    size_t priv_size = usbi_backend->device_handle_priv_size;
    int r;
    usbi_dbg("open %d.%d", dev->bus_number, dev->device_address);
     
    _handle = malloc(sizeof(*_handle) + priv_size);
    if (!_handle)
    return LIBUSB_ERROR_NO_MEM;
     
    r = usbi_mutex_init(&_handle->lock, NULL);
    if (r) {
    free(_handle);
    return LIBUSB_ERROR_OTHER;
    }
     
    _handle->dev = libusb_ref_device(dev);
    _handle->claimed_interfaces = 0;
    memset(&_handle->os_priv, 0, priv_size);
     
    r = usbi_backend->open_fd(_handle, fd);
    if (r < 0) {
    usbi_dbg("open %d.%d returns %d", dev->bus_number, dev->device_address, r);
    libusb_unref_device(dev);
    usbi_mutex_destroy(&_handle->lock);
    free(_handle);
    return r;
    }
     
    usbi_mutex_lock(&ctx->open_devs_lock);
    list_add(&_handle->list, &ctx->open_devs);
    usbi_mutex_unlock(&ctx->open_devs_lock);
    *handle = _handle;
     
    /* At this point, we want to interrupt any existing event handlers so
     * that they realise the addition of the new device's poll fd. One
     * example when this is desirable is if the user is running a separate
     * dedicated libusb events handling thread, which is running with a long
     * or infinite timeout. We want to interrupt that iteration of the loop,
     * so that it picks up the new fd, and then continues. */
    usbi_fd_notification(ctx);
     
    return 0;
    }

在libusbx\libusb\libusb.h中找到libusb_open函數的聲明，在其下面添加libusb_open_fd聲明：

int LIBUSB_CALL libusb_open_fd(libusb_device *dev, libusb_device_handle **handle, int fd);

在libusbx\libusb\libusbi.h中找到結構體usbi_os_backend，在其內部成員open下面添加

int (*open_fd)(struct libusb_device_handle *handle, int fd);

libusbx\libusb\os\linux_usbfs.c 中在 op_open 後面增加 op_open_fd 函數

    static int op_open_fd(struct libusb_device_handle *handle, int fd) {
    struct linux_device_handle_priv *hpriv = _device_handle_priv(handle);
     
    hpriv->fd = fd;
     
    return usbi_add_pollfd(HANDLE_CTX(handle), hpriv->fd, POLLOUT);
    }

libusbx\libusb\os\linux_usbfs.c 中在 結構體 linux_usbfs_backend 中 .open = op_open 一行後面增加一行

        .open_fd = op_open_fd,

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原文鏈接：https://blog.csdn.net/hubbybob1/article/details/52101356