+static int open_device(am7xxx_context *ctx,
+                      unsigned int device_index,
+                      libusb_device *usb_dev,
+                      am7xxx_device **dev)
+{
+       int ret;
+       int current_configuration;
+
+       *dev = find_device(ctx, device_index);
+       if (*dev == NULL) {
+               ret = -ENODEV;
+               goto out;
+       }
+
+       /* the usb device has already been opened */
+       if ((*dev)->usb_device) {
+               debug(ctx, "(*dev)->usb_device already set\n");
+               ret = 1;
+               goto out;
+       }
+
+       ret = libusb_open(usb_dev, &((*dev)->usb_device));
+       if (ret < 0) {
+               debug(ctx, "libusb_open failed: %s\n", libusb_error_name(ret));
+               goto out;
+       }
+
+       /* XXX, the device is now open, if any of the calls below fail we need
+        * to close it again before bailing out.
+        */
+
+       current_configuration = -1;
+       ret = libusb_get_configuration((*dev)->usb_device,
+                                      ¤t_configuration);
+       if (ret < 0) {
+               debug(ctx, "libusb_get_configuration failed: %s\n",
+                     libusb_error_name(ret));
+               goto out_libusb_close;
+       }
+
+       if (current_configuration != (*dev)->desc->configuration) {
+               /*
+                * In principle, before setting a new configuration, kernel
+                * drivers should be detached from _all_ interfaces; for
+                * example calling something like the following "invented"
+                * function _before_ setting the new configuration:
+                *
+                *   libusb_detach_all_kernel_drivers((*dev)->usb_device);
+                *
+                * However, in practice, this is not necessary for most
+                * devices as they have only one configuration.
+                *
+                * When a device only has one configuration:
+                *
+                *   - if there was a kernel driver bound to the device, it
+                *     had already set the configuration and the call below
+                *     will be skipped;
+                *
+                *   - if no kernel driver was bound to the device, the call
+                *     below will suceed.
+                */
+               ret = libusb_set_configuration((*dev)->usb_device,
+                                              (*dev)->desc->configuration);
+               if (ret < 0) {
+                       debug(ctx, "libusb_set_configuration failed: %s\n",
+                             libusb_error_name(ret));
+                       debug(ctx, "Cannot set configuration %hhu\n",
+                             (*dev)->desc->configuration);
+                       goto out_libusb_close;
+               }
+       }
+
+       libusb_set_auto_detach_kernel_driver((*dev)->usb_device, 1);
+
+       ret = libusb_claim_interface((*dev)->usb_device,
+                                    (*dev)->desc->interface_number);
+       if (ret < 0) {
+               debug(ctx, "libusb_claim_interface failed: %s\n",
+                     libusb_error_name(ret));
+               debug(ctx, "Cannot claim interface %hhu\n",
+                     (*dev)->desc->interface_number);
+               goto out_libusb_close;
+       }
+
+       /* Checking that the configuration has not changed, as suggested in
+        * http://libusb.sourceforge.net/api-1.0/caveats.html
+        */
+       current_configuration = -1;
+       ret = libusb_get_configuration((*dev)->usb_device,
+                                      ¤t_configuration);
+       if (ret < 0) {
+               debug(ctx, "libusb_get_configuration after claim failed: %s\n",
+                     libusb_error_name(ret));
+               goto out_libusb_release_interface;
+       }
+
+       if (current_configuration != (*dev)->desc->configuration) {
+               debug(ctx, "libusb configuration changed (expected: %hhu, current: %hhu\n",
+                     (*dev)->desc->configuration, current_configuration);
+               ret = -EINVAL;
+               goto out_libusb_release_interface;
+       }
+out:
+       return ret;
+
+out_libusb_release_interface:
+       libusb_release_interface((*dev)->usb_device,
+                                (*dev)->desc->interface_number);
+out_libusb_close:
+       libusb_close((*dev)->usb_device);
+       (*dev)->usb_device = NULL;
+       return ret;
+}
+