Date: Wed, 7 Aug 2013 12:13:28 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-arch@freebsd.org Cc: arch@freebsd.org, John-Mark Gurney <jmg@funkthat.com> Subject: Re: EVFILT_PROC always returns an EV_EOF event Message-ID: <201308071213.28577.jhb@freebsd.org> In-Reply-To: <201307261618.19408.jhb@freebsd.org> References: <201307251537.04491.jhb@freebsd.org> <20130726185232.GR26412@funkthat.com> <201307261618.19408.jhb@freebsd.org>
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On Friday, July 26, 2013 4:18:19 pm John Baldwin wrote: > On Friday, July 26, 2013 2:52:32 pm John-Mark Gurney wrote: > > John Baldwin wrote this message on Thu, Jul 25, 2013 at 15:37 -0400: > > > A co-worker ran into this undocumented behavior today. If you register an > > > EVFILT_PROC event but do not set NOTE_EXIT, you can still get an event with > > > fflags set to 0 but EV_EOF set. This is not documented in the manpage, and > > > it seems inconsistent to me. If the caller hasn't set NOTE_EXIT, then > > > presumably they do not wish to know about NOTE_EXIT events. > > > > This is probably to let the consumer know that the process no longer > > exists and that there will be no more events delivered for this process.. > > This allows the process to clean up in this case.. If you look at the > > code in filt_proc in kern_event.c, you'll also see that is forces > > _ONESHOT to be set, meaning that the knote will be deleted... > > > > It is someone documented: > > EV_EOF Filters may set this flag to indicate filter-specific EOF > > condition. > > > > But I do agree that the documentation could be better... > > > > I don't have a strong opinion on which behavior is best. I do think > > that delivering the EOF is best, since on an fd, you get _EOF when the > > socket closes, even though you didn't ask for it.. it's implicit.. > > Well, processes aren't fd's. Also, why have both NOTE_EXIT and EV_EOF for > the same thing? Also, the doc says "may" for EV_EOF, meaning it's not > guaranteed (and can not be there if there isn't a filter-specific EOF > condition). > > It seems to me that the code used EV_ONESHOT as a workaround to cleanup the > knote since it couldn't do it safely in filt_proc(), but I'm curious what > other folks think? > > I tried my test on OS X and it does not return the spurious EV_EOF event if > you don't register for NOTE_EXIT. Given this last, I'm inclined to commit my change so we are consistent with the other kqueue implementation in the wild. -- John Baldwin
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