> Adding a subsystem such as metahook(9) (or whatever name you'd like,
> and regardless of underlying implementation :) will require some help
> to let it know when a file it keeps meta-data for is gone.
> 
> So... it might be a good time to add the fileop scope. See attached
> diffs for the backend (fileop.kauth.diff) and relevent triggers
> (fileop.kern.diff).
> 
> The fileop scope is notification only, so special care is taken in
> kauth_authorize_action() to ignore whatever return value the listeners
> return.

i don't think kauth is an appropriate framework for your purpose.
kern_subr.c "hooks", eventhandler, subr_callback.c are.
hook points should be somehow unified with VN_KNOTE, i guess.

YAMAMOTO Takashi