Device hotplug event notification

This page details how to use the libusb hotplug interface, where available. More...

Macros
#define	LIBUSB_HOTPLUG_NO_FLAGS   0
	Convenience macro when not using any flags.
#define	LIBUSB_HOTPLUG_MATCH_ANY   -1
	Wildcard matching for hotplug events.

Typedefs
typedef int	libusb_hotplug_callback_handle
	Callback handle. More...
typedef int(*	libusb_hotplug_callback_fn) (libusb_context *ctx, libusb_device *device, libusb_hotplug_event event, void *user_data)
	Hotplug callback function type. More...

Enumerations
enum	libusb_hotplug_event { LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED = (1 << 0) , LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT = (1 << 1) }
	Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102. More...
enum	libusb_hotplug_flag { LIBUSB_HOTPLUG_ENUMERATE = (1 << 0) }
	Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102. More...

Functions
int	libusb_hotplug_register_callback (libusb_context *ctx, int events, int flags, int vendor_id, int product_id, int dev_class, libusb_hotplug_callback_fn cb_fn, void *user_data, libusb_hotplug_callback_handle *callback_handle)
	Register a hotplug callback function. More...
void	libusb_hotplug_deregister_callback (libusb_context *ctx, libusb_hotplug_callback_handle callback_handle)
	Deregisters a hotplug callback. More...
void *	libusb_hotplug_get_user_data (libusb_context *ctx, libusb_hotplug_callback_handle callback_handle)
	Gets the user_data associated with a hotplug callback. More...

Detailed Description

This page details how to use the libusb hotplug interface, where available.

Be mindful that not all platforms currently implement hotplug notification and that you should first call on libusb_has_capability() with parameter LIBUSB_CAP_HAS_HOTPLUG to confirm that hotplug support is available.

Typedef Documentation

libusb_hotplug_callback_handle

typedef int libusb_hotplug_callback_handle

Callback handle.

Callbacks handles are generated by libusb_hotplug_register_callback() and can be used to deregister callbacks. Callback handles are unique per libusb_context and it is safe to call libusb_hotplug_deregister_callback() on an already deregistered callback.

Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102

For more information, see Device hotplug event notification.

libusb_hotplug_callback_fn

typedef int( * libusb_hotplug_callback_fn) (libusb_context *ctx, libusb_device *device, libusb_hotplug_event event, void *user_data)

Hotplug callback function type.

When requesting hotplug event notifications, you pass a pointer to a callback function of this type.

This callback may be called by an internal event thread and as such it is recommended the callback do minimal processing before returning.

libusb will call this function later, when a matching event had happened on a matching device. See Device hotplug event notification for more information.

It is safe to call either libusb_hotplug_register_callback() or libusb_hotplug_deregister_callback() from within a callback function.

Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102

Parameters

ctx	context of this notification
device	libusb_device this event occurred on
event	event that occurred
user_data	user data provided when this callback was registered

Returns

bool whether this callback is finished processing events. returning 1 will cause this callback to be deregistered

Enumeration Type Documentation

libusb_hotplug_event

enum libusb_hotplug_event

Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102.

Hotplug events

Enumerator
LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED	A device has been plugged in and is ready to use.
LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT	A device has left and is no longer available. It is the user's responsibility to call libusb_close on any handle associated with a disconnected device. It is safe to call libusb_get_device_descriptor on a device that has left

libusb_hotplug_flag

enum libusb_hotplug_flag

Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102.

Hotplug flags

Enumerator
LIBUSB_HOTPLUG_ENUMERATE	Arm the callback and fire it for all matching currently attached devices.

Function Documentation

libusb_hotplug_register_callback()

int libusb_hotplug_register_callback	(	libusb_context *	ctx,
		int	events,
		int	flags,
		int	vendor_id,
		int	product_id,
		int	dev_class,
		libusb_hotplug_callback_fn	cb_fn,
		void *	user_data,
		libusb_hotplug_callback_handle *	callback_handle
	)

Register a hotplug callback function.

Register a callback with the libusb_context. The callback will fire when a matching event occurs on a matching device. The callback is armed until either it is deregistered with libusb_hotplug_deregister_callback() or the supplied callback returns 1 to indicate it is finished processing events.

If the LIBUSB_HOTPLUG_ENUMERATE is passed the callback will be called with a LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED for all devices already plugged into the machine. Note that libusb modifies its internal device list from a separate thread, while calling hotplug callbacks from libusb_handle_events(), so it is possible for a device to already be present on, or removed from, its internal device list, while the hotplug callbacks still need to be dispatched. This means that when using LIBUSB_HOTPLUG_ENUMERATE, your callback may be called twice for the arrival of the same device, once from libusb_hotplug_register_callback() and once from libusb_handle_events(); and/or your callback may be called for the removal of a device for which an arrived call was never made.

Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102

Parameters

[in]	ctx	context to register this callback with
[in]	events	bitwise or of hotplug events that will trigger this callback. See libusb_hotplug_event
[in]	flags	bitwise or of hotplug flags that affect registration. See libusb_hotplug_flag
[in]	vendor_id	the vendor id to match or LIBUSB_HOTPLUG_MATCH_ANY
[in]	product_id	the product id to match or LIBUSB_HOTPLUG_MATCH_ANY
[in]	dev_class	the device class to match or LIBUSB_HOTPLUG_MATCH_ANY
[in]	cb_fn	the function to be invoked on a matching event/device
[in]	user_data	user data to pass to the callback function
[out]	callback_handle	pointer to store the handle of the allocated callback (can be NULL)

Returns

LIBUSB_SUCCESS on success LIBUSB_ERROR code on failure

libusb_hotplug_deregister_callback()

void libusb_hotplug_deregister_callback	(	libusb_context *	ctx,
		libusb_hotplug_callback_handle	callback_handle
	)

Deregisters a hotplug callback.

Deregister a callback from a libusb_context. This function is safe to call from within a hotplug callback.

Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102

Parameters

[in]	ctx	context this callback is registered with
[in]	callback_handle	the handle of the callback to deregister

libusb_hotplug_get_user_data()

void* libusb_hotplug_get_user_data	(	libusb_context *	ctx,
		libusb_hotplug_callback_handle	callback_handle
	)

Gets the user_data associated with a hotplug callback.

Since version v1.0.24 LIBUSB_API_VERSION >= 0x01000108

Parameters

[in]	ctx	context this callback is registered with
[in]	callback_handle	the handle of the callback to get the user_data of