Event handling

Functions to handle events and fetch the current state of the event. More...

Functions
int	libevdev_next_event (struct libevdev *dev, unsigned int flags, struct input_event *ev)
	Get the next event from the device. More...
int	libevdev_has_event_pending (struct libevdev *dev)
	Check if there are events waiting for us. More...

Detailed Description

Functions to handle events and fetch the current state of the event.

Generally, libevdev updates its internal state as the event is processed and forwarded to the caller. Thus, the libevdev state of the device should always be identical to the caller's state. It may however lag behind the actual state of the device.

Function Documentation

int libevdev_has_event_pending

(

struct libevdev *

dev

)

Check if there are events waiting for us.

This does not read an event off the fd and may not access the fd at all. If there are events queued internally this function will return non-zero. If the internal queue is empty, this function will poll the file descriptor for data.

This is a convenience function for simple processes, most complex programs are expected to use select(2) or poll(2) on the file descriptor. The kernel guarantees that if data is available, it is a multiple of sizeof(struct input_event), and thus calling libevdev_next_event() when select(2) or poll(2) return is safe. You do not need libevdev_has_event_pending() if you're using select(2) or poll(2).

Parameters

dev	The evdev device, already initialized with libevdev_set_fd()

Returns

On failure, a negative errno is returned.

Return values

0	No event is currently available
1	One or more events are available on the fd

Note

This function is signal-safe.

int libevdev_next_event	(	struct libevdev *	dev,
		unsigned int	flags,
		struct input_event *	ev
	)

Get the next event from the device.

This function operates in two different modes: normal mode or sync mode.

In normal mode, this function returns 0 and returns the event in the parameter ev. If no events are available at this time, it returns -EAGAIN and ev is undefined.

If a SYN_DROPPED is read from the device, this function returns 1. The caller should now call this function with the LIBEVDEV_READ_SYNC flag set, to get the set of events that make up the device state delta. This function returns 1 for each event part of that delta, until it returns -EAGAIN once all events have been synced.

If a device needs to be synced by the caller but the caller does not call with the LIBEVDEV_READ_SYNC flag set, all events from the diff are dropped and event processing continues as normal.

Parameters

dev	The evdev device, already initialized with libevdev_set_fd()
flags	Set of flags to determine behaviour. If LIBEVDEV_READ_NORMAL is set, the next event is read in normal mode. If LIBEVDEV_READ_SYNC is set, the next event is read in sync mode.
ev	On success, set to the current event.

Returns

On failure, a negative errno is returned.

Return values

0	One or more events where read of the device
-EAGAIN	No events are currently available on the device
1	A SYN_DROPPED event was received, or a synced event was returned.

Note

This function is signal-safe.