A cross-platform user library to access USB devices
Version 1.0.16, LIBUSB_API_VERSION >= 0x01000102, has added support for hotplug events on some platforms (you should test if your platform supports hotplug notification by calling libusb_has_capability() with parameter LIBUSB_CAP_HAS_HOTPLUG).
This interface allows you to request notification for the arrival and departure of matching USB devices.
To receive hotplug notification you register a callback by calling libusb_hotplug_register_callback(). This function will optionally return a handle that can be passed to libusb_hotplug_deregister_callback().
A callback function must return an int (0 or 1) indicating whether the callback is expecting additional events. Returning 0 will rearm the callback and 1 will cause the callback to be deregistered. Note that when callbacks are called from libusb_hotplug_register_callback() because of the LIBUSB_HOTPLUG_ENUMERATE flag, the callback return value is ignored, iow you cannot cause a callback to be deregistered by returning 1 when it is called from libusb_hotplug_register_callback().
Callbacks for a particular context are automatically deregistered by libusb_exit().
As of 1.0.16 there are two supported hotplug events:
A hotplug event can listen for either or both of these events.
Note: If you receive notification that a device has left and you have any a libusb_device_handles for the device it is up to you to call libusb_close() on each handle to free up any remaining resources associated with the device. Once a device has left any libusb_device_handle associated with the device are invalid and will remain so even if the device comes back.
When handling a LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED event it is considered safe to call any libusb function that takes a libusb_device. On the other hand, when handling a LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT event the only safe function is libusb_get_device_descriptor().
The following code provides an example of the usage of the hotplug interface: