> 1) An option to make an event run only once, the eventhandler list
>    entries are marked as dead just prior to being run and will be
>    removed from the eventhandler list at the end of the run.  This
>    behaviour can be enabled by setting a flag on the eventhandler list
>    (EHL_ONCE).
> 
> 2) Provide a mask function - a masking function can be associated with
>    a eventhandler list, this function takes the argument pointer that
>    will be given to the functions on the eventhandler list, if the
>    mask function returns 1 the eventhandler list function will be
>    executed, otherwise the function will be skipped.

i don't think it's worth to have these functionalities.
registered functions can do them by itself.

> Below are the diffs (eventq.diff), eventhandler.h (goes in sys/sys)
> and subr_eventhandler.c (goes in sys/kern)

can you provide diffs without whitespace changes?

i don't think this vararg trick is a good idea...

YAMAMOTO Takashi