knotes

[Matthew Fleming]

I am trying to understand the knote system (on 6.1) and I am having some
troubles.

Specifically, I am confused by the uses of KN_DETACHED and EV_ONESHOT.
>From what I can determine from the comments and code, knotes have a
filterops member, kn_fop.  This among other things has a callback to
handle when a note is attached and detached.

But e.g. in knlist_clear(), when knlist_remove_kq() removes a knote from
the list, it sets KN_DETACHED but does not call the kn_fop->f_detach
routine.  Then, in the killkn case, KN_DETACHED is set (again).
Otherwise, EV_ONESHOT is set, presumably so that kqueue_scan() will run
on the knote.  However, kqueue_scan() won't call kn_fop->f_detach either
because KN_DETACHED is already set.

It seems that in knlist_cleardel(), the killkn case should be calling
kn_fop->f_detach before knote_drop().  It also seems that the !killkn
case should not have KN_DETACHED set, which means that
knlist_remove_kq() can't set it.  Alternatively, knlist_remove_kq()
should be calling kn_fop->f_detach itself before setting KN_DETACHED.
But in that case I'm not sure I see why there needs to be a use of
EV_ONESHOT.

So am I reading this wrong, understanding it wrong, or is there a bug in
the code?

Thanks,
matthew