Introduction
The X servers provided in Fedora 9 and later use HAL to retrieve the list of input devices. Whenever the X server is started, it asks HAL for the list of input devices and adds each of them with the respective driver. Whenever a new input device is plugged in or an existing input device is removed, HAL notifies the X server about the presence or removal of this device. Because of this notification system, some devices configured in the xorg.conf are ignored by the X server (all devices using the 'mouse', 'kbd' or 'vmmouse' driver).
In addition to signaling the presence of the new device, HAL also provides the X server with a number of options for each device. Most notably, this includes the driver the server should load and the device file to open. It also allows for additional, user-specific configuration options.
Device configuration
Fedora provides a list of default configurations in /usr/share/hal/fdi/policies/10osvendor/10-x11-input.fdi and some driver-specific configurations in e.g. /usr/share/hal/fdi/policies/20thirdparty/10-synaptics.fdi. Do not edit these files directly, as they will be overwritten in the next update. Instead, copy the file into /etc/hal/fdi/policy first and then edit as appropriate.
For example, the fdi for a synaptics touchpad may look like this:
<?xml version="1.0" encoding="ISO-8859-1"?>
<deviceinfo version="0.2">
<device>
<match key="info.capabilities" contains="input.touchpad">
<merge key="input.x11_driver" type="string">synaptics</merge>
<merge key="input.x11_options.TapButton1" type="string">1</merge>
</match>
</device>
</deviceinfo>
The above XML file defines the following: If the device is a touchpad (HAL assigns this capability automatically), then load the synaptics X11 driver for this device. The key input.x11_driver is interpreted by the server. The second merge command states that the option TapButton1 with a value of '1' should be passed to the driver. Any input.x11_options key is interpreted by the driver and is equivalent to the traditional form of Option "Option name" "Option value" in the xorg.conf. The man page of the respective driver lists the available options. Note that any input.x11_options key must have the type 'string' even if it denotes a number. Other types will be ignored by the server.
Merge commands are additive. For example, the fdi file provided by the xorg-x11-drv-synaptics package supplies the input.x11_driver key. User-specific configuration does not need to specify this key again and instead should only provide local configuration options (such as the TapButton1 setting above).
To remove an existing key, the following syntax may be used:
<?xml version="1.0" encoding="ISO-8859-1"?>
<deviceinfo version="0.2">
<device>
<match key="input.product" contains="Random String">
<remove key="input.x11_driver"></remove>
</match>
</device>
</deviceinfo>
This snipped removes the input.x11_driver key from all devices that include the string "Random String". As said above, input.x11_driver is a special key and removing it prevents the X server from adding this device. The same syntax may be used to remove other options.
Reviewing configuration changes
In the extreme case, a misconfiguration of input drivers may result in an X server with no input devices. It is advisable that changes to the fdi files are reviewed before restarting the server to ensure that at least some devices are available.
After editing the fdi files, the HAL daemon can be restarted with service haldaemon restart. Once the restart is successful, lshal may be used to list all devices and their configurations.
As a general rule, at least one keyboard device should have input.x11_driver set to 'evdev' to allow keyboard input if all other configurations fail.
Disabling the use of HAL
Some users wish to disable the use of HAL. The X server provides two options to achieve this:
- Option "AutoAddDevices" "false"
If this option is disabled, then no devices will be added from HAL events. Note that if this option is disabled, AllowEmptyInput is automatically disabled too unless explicitly enabled the user.
- Option "AllowEmptyInput" "false"
If AllowEmptyInput is false, the server checks the xorg.conf for core devices (Option "CorePointer" and Option "CoreKeyboard"). If none are present and referenced in the ServerLayout section, the server automatically adds the first mouse and keyboard device in the xorg.conf or (if neither are present) the hard-coded default input devices. Disabling AllowEmptyInput also forces the server to honor devices using the 'mouse', 'kbd' and 'vmmouse' drivers (these devices are ignored by default).
In most cases, simply disabling AutoAddDevices is the correct way to disable the use of HAL. Note that if AllowEmptyInput is off and AutoAddDevices is on, then devices may be added multiple times (once as specified in the xorg.conf, and once as listed by HAL). This leads to duplicate button presses and triplicate key presses.