I'm using a Verdex XL6P motherboard connected to a Console-VX, making available the USB host. To the USB host I've connected a Option's iCon 225 dongle.

I'm following instructions here: http://www.pharscape.org/icon225.html which instructs me to install ozerocdoff (udev) and the hso driver kernel module. "bitbake udev" seems to have gotten ozerocdoff working, but I'm having trouble with the hso driver kernel module.

When running the Makefile for hso it gives me this:
make -C /lib/modules/2.6.21/build M=/media/hdd/ftw/hso_26-v1.9 MODVERDIR=/media/hdd/ftw/hso_26-v1.9/tmp/.tmp_versions modules
make: *** /lib/modules/2.6.21/build: No such file or directory.  Stop.
make: *** [modules] Error 2

The equivalent /lib/modules/2.6.21/build on my Ubuntu laptop points to kernel headers, so I guess this is what I need for the gumstix too. I can't find any linux-headers bitbake recipe either.

How can I get the hso driver kernel module to compile?