Date: Thu, 2 Feb 2017 08:29:20 +0000 From: <Hartmut.Brandt@dlr.de> To: <glebius@FreeBSD.org> Cc: <src-committers@freebsd.org>, <svn-src-all@freebsd.org>, <svn-src-head@freebsd.org> Subject: RE: svn commit: r313043 - head/sys/kern Message-ID: <611243783F62AF48AFB07BC25FA4B1061CED9FD9@DLREXMBX01.intra.dlr.de> In-Reply-To: <20170201180816.GF3334@FreeBSD.org> References: <201702011312.v11DC7WJ085025@repo.freebsd.org> <20170201180816.GF3334@FreeBSD.org>
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To be honest - I feared that when I saw your messages regarding this. Here =
is my original message from july. Attached is also a small test program.
Hi,
I'm trying to use asio (that's boost::asio without boost) to handle listeni=
ng sockets asynchronuosly. This appears not to work. There are also some re=
ports on the net about this problem. I was able to reproduce the problem wi=
th a small C-programm that does the same steps as asio. The relevant sequen=
ce of system calls is:
kqueue() =3D 3 (0x3)
socket(PF_INET,SOCK_STREAM,6) =3D 4 (0x4)
setsockopt(0x4,0xffff,0x800,0x7fffffffea2c,0x4) =3D 0 (0x0)
kevent(3,{ 4,EVFILT_READ,EV_ADD|EV_CLEAR,0x0,0x0,0x0 4,EVFILT_WRITE,EV_ADD|=
EV_CLEAR,0x0,0x0,0x0 },2,0x0,0,0x0) =3D 0 (0x0)
setsockopt(0x4,0xffff,0x4,0x7fffffffea2c,0x4) =3D 0 (0x0)
bind(4,{ AF_INET 0.0.0.0:8080 },16) =3D 0 (0x0)
listen(0x4,0x80) =3D 0 (0x0)
ioctl(4,FIONBIO,0xffffea2c) =3D 0 (0x0)
kevent(3,{ 4,EVFILT_READ,EV_ADD|EV_CLEAR,0x0,0x0,0x0 4,EVFILT_WRITE,EV_ADD|=
EV_CLEAR,0x0,0x0,0x0 },2,0x0,0,0x0) =3D 0 (0x0)
kevent(3,0x0,0,0x7fffffffe5a0,32,0x0) ERR#4 'Interrupted system call'
The problem here is that asio registers each file descriptor with EVFILT_RE=
AD and EVFILT_WRITE as soon as it is opened (first kevent call).=20
After bringing the socket into the listening state and when async_accept() =
is called it registers the socket a second time. According to the man page =
this is perfectly legal and can be used to modify the registration.
With this sequence of calls kevent() does not return when a connection is e=
stablished successfully.
I tracked down the problem and the reason is in soo_kqfilter(). This is cal=
led for the first EVFILT_READ registration and decides based on the SO_ACCE=
PTCONN flag which filter operations to use solisten_filtops or soread_filto=
ps. In this case it chooses soread_filtops.
The second EVFILT_READ registration does not call soo_kqfilter() again, but=
just updates the filter from the data and fflags field so the listening so=
cket ends up with the wrong filter operations.
-----Original Message-----
From: Gleb Smirnoff [mailto:glebius@FreeBSD.org]=20
Sent: Wednesday, February 01, 2017 7:08 PM
To: Hartmut Brandt
Cc: src-committers@freebsd.org; svn-src-all@freebsd.org; svn-src-head@freeb=
sd.org
Subject: Re: svn commit: r313043 - head/sys/kern
On Wed, Feb 01, 2017 at 01:12:07PM +0000, Hartmut Brandt wrote:
H> Author: harti
H> Date: Wed Feb 1 13:12:07 2017
H> New Revision: 313043
H> URL: https://svnweb.freebsd.org/changeset/base/313043
H>=20
H> Log:
H> Merge filt_soread and filt_solisten and decide what to do when checkin=
g
H> for EVFILT_READ at the point of the check not when the event is regist=
ers.
H> This fixes a problem with asio when accepting a connection.
H> =20
H> Reviewed by: kib@, Scott Mitchell
This goes into opposite direction with what I am doing:
https://reviews.freebsd.org/D9356
Can you please explain the problem with asio when accepting a connection?
--=20
Totus tuus, Glebius.
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