I tried to install cdemu and couldn't start cdemud. After all the depmod and modprobe vhba, I finally got this message:
FATAL: Error inserting vhba (/lib64/modules/3.1.0-sabayon/block/vhba.ko): Invalid module format
My linux version:
Linux dev00 3.0.0-sabayon #1 SMP Tue Oct 25 17:37:15 UTC 2011 x86_64 Intel(R) Core(TM)2 Duo CPU T9550 @ 2.66GHz GenuineIntel GNU/Linux
emerge, on the other hand, complains about some conflict with udev, so installing from there doesn't seem to be an option.