A cross-platform user library to access USB devices
Macros | Typedefs | Enumerations | Functions
Device hotplug event notification

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

Macros

#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_flag { LIBUSB_HOTPLUG_NO_FLAGS = 0, LIBUSB_HOTPLUG_ENUMERATE = 1<<0 }
 Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102. More...
 
enum  libusb_hotplug_event { LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED = 0x01, LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT = 0x02 }
 Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102. More...
 

Functions

int libusb_hotplug_register_callback (libusb_context *ctx, libusb_hotplug_event events, libusb_hotplug_flag flags, int vendor_id, int product_id, int dev_class, libusb_hotplug_callback_fn cb_fn, void *user_data, libusb_hotplug_callback_handle *handle)
 Register a hotplug callback function. More...
 
void libusb_hotplug_deregister_callback (libusb_context *ctx, libusb_hotplug_callback_handle handle)
 Deregisters 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

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 deregisted callback.

Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102

For more information, see Device hotplug event notification.

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
ctxcontext of this notification
devicelibusb_device this event occurred on
eventevent that occurred
user_datauser 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

Since version 1.0.16, LIBUSB_API_VERSION >= 0x01000102.

Flags for hotplug events

Enumerator
LIBUSB_HOTPLUG_NO_FLAGS 

Default value when not using any flags.

LIBUSB_HOTPLUG_ENUMERATE 

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

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

Function Documentation

int libusb_hotplug_register_callback ( libusb_context ctx,
libusb_hotplug_event  events,
libusb_hotplug_flag  flags,
int  vendor_id,
int  product_id,
int  dev_class,
libusb_hotplug_callback_fn  cb_fn,
void *  user_data,
libusb_hotplug_callback_handle 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]ctxcontext to register this callback with
[in]eventsbitwise or of events that will trigger this callback. See libusb_hotplug_event
[in]flagshotplug callback flags. See libusb_hotplug_flag
[in]vendor_idthe vendor id to match or LIBUSB_HOTPLUG_MATCH_ANY
[in]product_idthe product id to match or LIBUSB_HOTPLUG_MATCH_ANY
[in]dev_classthe device class to match or LIBUSB_HOTPLUG_MATCH_ANY
[in]cb_fnthe function to be invoked on a matching event/device
[in]user_datauser data to pass to the callback function
[out]handlepointer to store the handle of the allocated callback (can be NULL)
Returns
LIBUSB_SUCCESS on success LIBUSB_ERROR code on failure
void libusb_hotplug_deregister_callback ( libusb_context ctx,
libusb_hotplug_callback_handle  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]ctxcontext this callback is registered with
[in]handlethe handle of the callback to deregister