Detecting the used keyboard driver

Marvin Raaijmakers marvin.nospam at
Sun May 3 11:00:28 PDT 2009

Yes I know the kernel keycode to X keycode translation is fixed for
each keyboard driver. But the problem is that the evdev driver (in the
X server) does another translation than the kbd driver. You stated:
 "As long as the kernel keycode is KEY_BATTERY, the X keycode will
depend only on whether kbd or evdev is in use."
And now we've come to the main question in my first mail: how can i
detect whether the X server uses the evdev or kbd driver?

On Thu, Apr 30, 2009 at 8:20 PM, Matthew Garrett <mjg59 at> wrote:
> On Thu, Apr 30, 2009 at 08:09:01PM +0200, Marvin Raaijmakers wrote:
>> Well a scancode is for the kernel like what a X keycode is to the X
>> server, and a kernel keycode is for the kernel what a key symbol is to
>> the X server. So when you change the kernel keycode of a key, then the
>> X server will receive another kernel keycode from the kernel and as a
>> result the key will have another X keycode. So an X keycode is not
>> fixed for a specific key. Furthermore some keys will not have a kernel
>> keycode by default and such keys won't work under X (because the X
>> server doesn't receive anything about these keys from the kernel).
>> Believe me I've thought about this ;)
> For a given kernel keycode and a given X keyboard driver, the X keycode
> will always be the same. If you're setting the scancode to the canonical
> kernel keycode that'll be a meaningful transformation. So you could just
> add those X keycodes to the pc105 keymap, since they're already present
> in the evdev keymap and so will already produce the correct keysyms with
> the evdev driver. For example:
> Scancode e007 will be the battery key scancode on a Dell. This will map
> to kernel keycode 236 (KEY_BATTERY). kbd will read this as e044 and
> translate it into X keycode 204. evdev will read this as 236 and (I
> /think/ - I can't remember if the +8 mapping is still relevant for
> evdev) translate it into X keycode 244.
> As long as the kernel keycode is KEY_BATTERY, the X keycode will depend
> only on whether kbd or evdev is in use. evdev will always use the evdev
> keymap and that already maps all of the Linux keycodes to appropriate X
> keysyms. The keymap typically used for the old driver is pc105, and I
> suspect that it doesn't have these mappings. They'd be easy to add and
> it's the appropriate place to put them.
> --
> Matthew Garrett | mjg59 at

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