XI2 = moving target?

Peter Hutterer peter.hutterer at who-t.net
Sun Jul 26 01:41:37 PDT 2009

On Sat, Jul 25, 2009 at 08:29:40PM -0400, Jim Gettys wrote:
> I guess I'm still confused...
> So they'd show up as different devices with time; each time you get 
> notification that the keysym mapping for the keycodes have changed.
> Why is there a problem?

It makes things overly complicated.

We use a number of shortcuts to simplify the keycode handling. One is that
we don't actually use the keycode range as an actual range but rather use
the keycodes in a way similar to keysyms. If you're using the evdev driver,
each keycode is already defined to a specific symbol with hardware-specific
quirks being done in the kernel or in HAL (possibly udev now, I still
haven't looked into that).

You could free the keycodes completely but then you'd have to have a Kcgst
mapping for xkeyboard-config for every single device. Which means that the
maintainance of xkeyboard-config becomes a nightmare, together with the
myriads of things that can go wrong when users select the wrong keyboard

By having a standardised set of keycodes this becomes much easier.
In fact these days it is irrelevant what you select as your keyboard model
in the evdev ruleset - they all map to the evdev model (there are a few
exceptions that do require separate models). So the XKB configuration mostly
deals with the actual layouts, taking one layer of complexity out.

You could treat the keycode range as intended in the original X protocol,
but then you'd have to have a model for every keyboard, remote, magic other
device ever manufactured. We sort-of do that (look at the xorg/xfree86
ruleset) but it's not pretty.

So by upping the keycode range to 32 bits we enable a larger standardised
set of keycodes without the nightmare of maintaining loads of different
keyboard models and requiring the user to configure them correctly.

Note that a keycode still doesn't stand for a symbol. KEY_Q is still an 'a'
if you have an azerty group.


> Alan Cox wrote:
> >> Ergo my question on whether anyone has ever actually seen in captivity a 
> >> keyboard with more than 248 keys...
> > 
> > I'm not sure that is a useful question.
> > 
> > I have a collection of keyboards and remotes. All of them have different
> > functions above 255 which could be remapped. All of them are hot
> > pluggable.
> > 
> > Trying to manage a mapping of all the devices randomly on the fly plugged
> > into a system and map them into a tiny space is rather more difficult
> > than you make out.
> > 
> > If you had to map a set of devices, once, to a fixed mapping it wouldn't
> > be a big deal, but the world has moved on from that.
> > 
> > Alan

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