Date: Sat, 01 Apr 2006 20:35:35 +0200 From: =?UTF-8?B?VsOhY2xhdiBIYWlzbWFu?= <V.Haisman@sh.cvut.cz> To: Dan Nelson <dnelson@allantgroup.com> Cc: hackers@freebsd.org Subject: Re: kqueue oddity Message-ID: <442EC7F7.3000608@sh.cvut.cz> In-Reply-To: <20060401180311.GA83967@dan.emsphone.com> References: <442E9354.5010700@sh.cvut.cz> <20060401180311.GA83967@dan.emsphone.com>
next in thread | previous in thread | raw e-mail | index | archive | help
[-- Attachment #1 --]
Dan Nelson wrote:
> In the last episode (Apr 01), Vclav Haisman said:
>> Hi,
>> I have a little problem with kqueue/kevent. I am getting somewhat
>> strange events from kevent(). The struct kevent's contents looks like this:
>>
>> kevent {.ident = 1, .filter = 0xfffffffe, .flags = 0x0001,
>> .fflags = 0x00000000, .data = 0x000084c6}
>>
>> .ident == 1 is stdout.
>> .filter == 0x fffffffe is -2 is EVFILT_WRITE which makes sense for stdout.
>> .fflags is empty, nothing out of ordinary for EVFILT_WRITE.
>> And here comes the oddity: .flags == 0x0001 means EV_ADD which totally
>> doesn't make sense to me and neither does according to man kqueue. The
>> code that exhibits this behaviour is io_loop_handler_run() in
>> ioloop-kqueue.c of Dovecot IMAP server.
>
> It's a kqueue bug, but a minor one. The problem is that the same
> "flags" field is used to pass "actions" from the client, and return
> status from the kernel. When you call kqueue with EV_ADD, the kernel
> never clears the flags when creating the internal object, so it's
> always visible when events fire. This can get annoying when trussing
> kqueue-using programs because very single event has the EV_ADD flag :)
> Apply the following diff to have the kernel strip EV_ADD:
>
> Index: kern_event.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/kern/kern_event.c,v
> retrieving revision 1.79.2.9
> diff -u -p -r1.79.2.9 kern_event.c
> --- kern_event.c 29 Jun 2005 18:08:31 -0000 1.79.2.9
> +++ kern_event.c 7 Jul 2005 18:51:29 -0000
> @@ -864,6 +864,7 @@ findkn:
> kev->fflags = 0;
> kev->data = 0;
> kn->kn_kevent = *kev;
> + kn->kn_kevent.flags &= ~EV_ADD;
> kn->kn_status = KN_INFLUX|KN_DETACHED;
>
> error = knote_attach(kn, kq);
>
>
Thanks. Why isn't this fix applied? From the patch's time stamp it seems
like it is known for quite some time now.
Vaclav Haisman
[-- Attachment #2 --]
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.2.2 (MingW32)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org
iQEVAwUBRC7H/m56zbtzMDG0AQLoUggAhwf/2GwWw5sU/icVfYzbJdioeAqqlhPj
Wmlu11C0ooYi2+bdPxdgTqEZcvVEmT5H9WLnWpQgySY7zv7eCt4KilbD9XwjIc6R
LIZeYB3eq8b4dw8EttxiuFDNqR1O8OqOVJyfLEzwTHLf27+dOEB9mhjbaePzeEvR
643fGTjY84IDjPGF/doQ4nsYW9qfoGTRwkegHqeKZPWdpM/dmpZaOAD8s+vwWyxB
n3dxQHeREnbF7TnWtUom7QKrclP9fsiq7IJIzdhg6km/ydHotMT3ZeKuJ0xRgnMc
K1ORJVSnwCU/MaEOZzo52dBV5FRt48MhXt4csUWLbDbb1kMK2Q+pug==
=9Poo
-----END PGP SIGNATURE-----
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?442EC7F7.3000608>