correct location of evdev?

[Marc Weber]

Hi,

I'm keen on mpx.
I've sucessfully compiled xorg git sources now.
There hasn't been any big trouble, awesome!

However when starting xorgserver the server fails:

  (EE) XKB: Couldn't open rules file 
  /nix/store/smpg6lqc9irva4g1d918mzfwsjc925gi-xkeyboard-config-1.2/etc/X11/xkb/rules/evdev

  I've found an evdev file:
  /nix/store/smpg6lqc9irva4g1d918mzfwsjc925gi-xkeyboard-config-1.2/etc/X11/xkb/keycodes/evdev 

So can you tell me what's wrong here or where to lookup the information
about how to tell xkb where to find the correct evdev file?

Sincerly
Marc Weber