libvirt-evdev

The purpose of libvirt-evdev service is to provide means to use libvirt evdev passthrough for hot pluggable input devices.

Example configuration

This service is intended to be used in configuration like in the following diagram:

                           +---------------------+
                           |        Screen       |
                           +---------------------+
                           | HDMI1  HDMI2  HDMI3 |
                           +---^------^------^---+
                               |      |      |
            +--------------+   |      |      |   +--------------+
            |   Main PC    |   |      |      |   |   Other PC   |
    evdev   +--------------+   |      |      |   +--------------+
+----------->   Guest      +---+      |      +---+              |
|passthrough|--------------+          |          |              |
+-----------+   Host       +----------+          |              |
            +-------^------+                     +-------^------+
                    |                                    |
                    |              +------+              |
                    |              | USB  |              |
                    +--------------+SWITCH+--------------+
                                   +-^--^-+
                                     |  |
                            +--------+  +--------+
                            |                    |
                      +-----+------+       +-----+-----+
                      |  Keyboard  |       |   Mouse   |
                      +------------+       +-----------+

In such configuration there are two PCs - main and other. Both PCs uses one set of keyboard and mouse which could be unplugged/hotplugged using USB switch. There two OSes running on main PC - Host and Guest. Guest uses evdev passthrough input from Host.

Primary problem

Due to fact the keyboard and mouse is shared by two PCs, evdev passthrough stops working after keyboard/mouse is unplugged and replugged using USB switch.

Primary solution

• using uinput module (CONFIG_INPUT_UINPUT) create two set of keyboard/mouse input devices - one for Host and one for Guest,
• provide mode selector (SCROLL_LOCK key) which selects which OS receives input events,
• replicate uinput events form real input devices to uinput devices selected by mode selector,
• passthrough uinput device to Guest.

Secondary problem

Sine Guest is configured to be started during boot of main PC, this service is intended to be started during boot and before libvirtd.service to ensure that uinput devices are created before Guest is started. The problem shows up when this service is started with keyboard/mouse connected to the other PC. There are not device based on which uninput devices could be created, thus this service will fail following by libvrtd.service and Guest is not started.

Secondary solution

• when service is started with keyboard/mouse connected to the main PC, save input devices' capabilities in /var/lib/libvirt-evdev/,
• when service is started with keyboard/mouse connected to the other PC, create proper uinput devices based on previously saved capabilities.

Extras

Configuration File

Simple toml file (libvirt-evdev.toml) with definition of input devices, screens and USB switch parameters.

Screen Input Switch

This service provide Screen Input switch using DDC/CI control (https://github.com/ddccontrol/ddccontrol)

Installation

Very basic install script provided (install.sh) which creates mandatory directories and copies files.

TODO

• improve exception handling
• verify correctness of aysncio usage
• remove dependency to ddccontrol and implement DDC/CI using python-smbus