Here's the error I get:
make: *** [rioio.lo] Error 1
make: *** Waiting for unfinished jobs....
In file included from ../include/usbdevfs.h:42,
../include/usbdrv.h:66: error: redefinition of `struct usb_device_descriptor'
rio.c: In function `get_flist_riohd':
rio.c:400: warning: use of cast expressions as lvalues is deprecated
make: *** [rio.lo] Error 1
make: Leaving directory `/var/tmp/portage/rioutil-1.4.7/work/rioutil-1.4.7/librioutil'
make: *** [all-recursive] Error 1
I'm running on Gentoo-Linux. Kernel 2.6.9. gcc 3.4.3
I eventually got it to work. I just have to use libusb instead of usbdevfs. I have a gentoo ebuild, if anyone needs it.