libevdev  1.5.7
A wrapper library for evdev devices
Functions
uinput device creation

Creation of uinput devices based on existing libevdev devices. More...

Functions

int libevdev_uinput_create_from_device (const struct libevdev *dev, int uinput_fd, struct libevdev_uinput **uinput_dev)
 Create a uinput device based on the given libevdev device. More...
 
void libevdev_uinput_destroy (struct libevdev_uinput *uinput_dev)
 Destroy a previously created uinput device and free associated memory. More...
 
int libevdev_uinput_get_fd (const struct libevdev_uinput *uinput_dev)
 Return the file descriptor used to create this uinput device. More...
 
const char * libevdev_uinput_get_syspath (struct libevdev_uinput *uinput_dev)
 Return the syspath representing this uinput device. More...
 
const char * libevdev_uinput_get_devnode (struct libevdev_uinput *uinput_dev)
 Return the device node representing this uinput device. More...
 
int libevdev_uinput_write_event (const struct libevdev_uinput *uinput_dev, unsigned int type, unsigned int code, int value)
 Post an event through the uinput device. More...
 

Detailed Description

Creation of uinput devices based on existing libevdev devices.

These functions help to create uinput devices that emulate libevdev devices. In the simplest form it serves to duplicate an existing device:

int err;
int fd, new_fd, uifd;
struct libevdev *dev;
struct libevdev_uinput *uidev;
struct input_event ev[2];
fd = open("/dev/input/event0", O_RDONLY);
if (fd < 0)
return err;
err = libevdev_new_from_fd(fd, &dev);
if (err != 0)
return err;
uifd = open("/dev/uinput", O_RDWR);
if (uifd < 0)
return -errno;
err = libevdev_uinput_create_from_device(dev, uifd, &uidev);
if (err != 0)
return err;
// post a REL_X event
err = libevdev_uinput_write_event(uidev, EV_REL, REL_X, -1);
if (err != 0)
return err;
libevdev_uinput_write_event(uidev, EV_SYN, SYN_REPORT, 0);
if (err != 0)
return err;
close(uifd);
close(fd);

Alternatively, a device can be constructed from scratch:

int err;
struct libevdev *dev;
struct libevdev_uinput *uidev;
dev = libevdev_new();
libevdev_set_name(dev, "test device");
libevdev_enable_event_code(dev, EV_REL, REL_X, NULL);
libevdev_enable_event_code(dev, EV_REL, REL_Y, NULL);
libevdev_enable_event_code(dev, EV_KEY, BTN_LEFT, NULL);
libevdev_enable_event_code(dev, EV_KEY, BTN_MIDDLE, NULL);
libevdev_enable_event_code(dev, EV_KEY, BTN_RIGHT, NULL);
&uidev);
if (err != 0)
return err;
// ... do something ...

Function Documentation

◆ libevdev_uinput_create_from_device()

int libevdev_uinput_create_from_device ( const struct libevdev *  dev,
int  uinput_fd,
struct libevdev_uinput **  uinput_dev 
)

Create a uinput device based on the given libevdev device.

The uinput device will be an exact copy of the libevdev device, minus the bits that uinput doesn't allow to be set.

If uinput_fd is LIBEVDEV_UINPUT_OPEN_MANAGED, libevdev_uinput_create_from_device() will open /dev/uinput in read/write mode and manage the file descriptor. Otherwise, uinput_fd must be opened by the caller and opened with the appropriate permissions.

The device's lifetime is tied to the uinput file descriptor, closing it will destroy the uinput device. You should call libevdev_uinput_destroy() before closing the file descriptor to free allocated resources. A file descriptor can only create one uinput device at a time; the second device will fail with -EINVAL.

You don't need to keep the file descriptor variable around, libevdev_uinput_get_fd() will return it when needed.

Note
Due to limitations in the uinput kernel module, REP_DELAY and REP_PERIOD will default to the kernel defaults, not to the ones set in the source device.
Parameters
devThe device to duplicate
uinput_fdLIBEVDEV_UINPUT_OPEN_MANAGED or a file descriptor to /dev/uinput,
[out]uinput_devThe newly created libevdev device.
Returns
0 on success or a negative errno on failure. On failure, the value of uinput_dev is unmodified.
See also
libevdev_uinput_destroy

◆ libevdev_uinput_destroy()

void libevdev_uinput_destroy ( struct libevdev_uinput *  uinput_dev)

Destroy a previously created uinput device and free associated memory.

If the device was opened with LIBEVDEV_UINPUT_OPEN_MANAGED, libevdev_uinput_destroy() also closes the file descriptor. Otherwise, the fd is left as-is and must be closed by the caller.

Parameters
uinput_devA previously created uinput device.

◆ libevdev_uinput_get_devnode()

const char* libevdev_uinput_get_devnode ( struct libevdev_uinput *  uinput_dev)

Return the device node representing this uinput device.

This relies on libevdev_uinput_get_syspath() to provide a valid syspath. See libevdev_uinput_get_syspath() for more details.

Note
This function may return NULL. libevdev may have to guess the syspath and the device node. See libevdev_uinput_get_syspath() for details.
Parameters
uinput_devA previously created uinput device.
Returns
The device node for this device, in the form of /dev/input/eventN
See also
libevdev_uinput_get_syspath

◆ libevdev_uinput_get_fd()

int libevdev_uinput_get_fd ( const struct libevdev_uinput *  uinput_dev)

Return the file descriptor used to create this uinput device.

This is the fd pointing to /dev/uinput. This file descriptor may be used to write events that are emitted by the uinput device. Closing this file descriptor will destroy the uinput device, you should call libevdev_uinput_destroy() first to free allocated resources.

Parameters
uinput_devA previously created uinput device.
Returns
The file descriptor used to create this device

◆ libevdev_uinput_get_syspath()

const char* libevdev_uinput_get_syspath ( struct libevdev_uinput *  uinput_dev)

Return the syspath representing this uinput device.

If the UI_GET_SYSNAME ioctl not available, libevdev makes an educated guess. The UI_GET_SYSNAME ioctl is available since Linux 3.15.

The syspath returned is the one of the input node itself (e.g. /sys/devices/virtual/input/input123), not the syspath of the device node returned with libevdev_uinput_get_devnode().

Note
This function may return NULL if UI_GET_SYSNAME is not available. In that case, libevdev uses ctime and the device name to guess devices. To avoid false positives, wait at least wait at least 1.5s between creating devices that have the same name.
Parameters
uinput_devA previously created uinput device.
Returns
The syspath for this device, including the preceding /sys
See also
libevdev_uinput_get_devnode

◆ libevdev_uinput_write_event()

int libevdev_uinput_write_event ( const struct libevdev_uinput *  uinput_dev,
unsigned int  type,
unsigned int  code,
int  value 
)

Post an event through the uinput device.

It is the caller's responsibility that any event sequence is terminated with an EV_SYN/SYN_REPORT/0 event. Otherwise, listeners on the device node will not see the events until the next EV_SYN event is posted.

Parameters
uinput_devA previously created uinput device.
typeEvent type (EV_ABS, EV_REL, etc.)
codeEvent code (ABS_X, REL_Y, etc.)
valueThe event value
Returns
0 on success or a negative errno on error