vinput: A collection of virtual input device drivers for Linux

Prerequisite

The following package must be installed before building vinput.

In order to compile the kernel driver successfully, package versions of currently used kernel, kernel-devel and kernel-headers need to be matched.

$ sudo apt install linux-headers-$(uname -r)

Build and Run

After running make, you should be able to generate the following files:

• vinput.ko - virtual input device layer
• vkbd.ko - virtual keyboard
• vmouse.ko - virtual mouse
• vts.ko - virtual multitouch screen inputs

The module can be loaded to Linux kernel by runnning the command:

$ sudo insmod vinput.ko
$ sudo insmod vkbd.ko

Kernel API

vinput is a API to allow easy development of virtual input drivers.

The drivers needs to export a vinput_device function that contains the virtual device name and vinput_ops structure that describes:

• the init function: init
• the input event injection function: send
• the readback function: read

Then using vinput_register_device and vinput_unregister_device will add a new device to the list of support virtual input devices.

int init(struct vinput *);

This function is passed a struct vinput already initialized with an allocated struct input_dev. The init function is responsible for initializing the capabilities of the input device and register it.

int send(struct vinput *, char *, int);

This function will receive a user string to interpret and inject the event using the input_report_XXXX or input_event call. The string is already copied from user.

int read(struct vinput *, char *, int);

This function is used for debugging and should fill the buffer parameter with the last event sent in the virtual input device format. The buffer will then be copied to user.

Userland API

vinput devices are created and destroyed using sysfs. event injection is done through a /dev node.

The device name will be used by the userland to export a new virtual input device.

To create a vinputX sysfs entry and /dev node.

$ echo "vkbd" | sudo tee /sys/class/vinput/export

To unexport the device, just echo its id in unexport:

$ echo "0" | sudo tee /sys/class/vinput/unexport

vkbd

This is the virtual keyboard. It supports all KEY_MAX keycodes. The injection format is the KEY_CODE such as defined in linux/input.h. A positive value means KEY_PRESS while a negative value is a KEY_RELEASE. The keyboard supports repetition when the key stays pressed for too long.

Simulate a key press on "g" (KEY_G = 34)

$ echo "+34" | sudo tee /dev/vinput0

Simulate a key release on "g" (KEY_G = 34)

$ echo "-34" | sudo tee /dev/vinput0

License

vinput is released under the GNU General Public License. Use of this source code is governed by the GPL License version 2 that can be found in the LICENSE file.

Related Projects

• virtual_touchscreen: A simple evdev linux device driver and GUI program to simulate multitouch touchscreen.
• mqtt2js: Linux virtual joystick controlled by MQTT
• VirtualMouse: Virtual mouse drivers for linux.