vdsm hook howto

Hi,

1) is it enough to add a hook.py in /usr/libexec/vdsm/hooks/before_vm_start directory , and then shuftdown and reboot a guest to
see this hook.py invoked ?

2) when running manually my hook.py, I got followinfg error :
ImportError: No module named hooking

Do I have to install anything to solve this issue ?

Thanks for help.

Regards,