From owner-freebsd-net@FreeBSD.ORG  Tue Apr 15 23:55:21 2014
Return-Path: <owner-freebsd-net@FreeBSD.ORG>
Delivered-To: FreeBSD-net@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115])
 (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id BBC615E6
 for <FreeBSD-net@freebsd.org>; Tue, 15 Apr 2014 23:55:21 +0000 (UTC)
Received: from raven.bwct.de (raven.bwct.de [85.159.14.73])
 (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
 (Client CN "raven.bwct.de", Issuer "BWCT" (not verified))
 by mx1.freebsd.org (Postfix) with ESMTPS id 4F9DC1CE5
 for <FreeBSD-net@freebsd.org>; Tue, 15 Apr 2014 23:55:16 +0000 (UTC)
Received: from mail.cicely.de ([10.1.1.37])
 by raven.bwct.de (8.13.4/8.13.4) with ESMTP id s3FNsZSb002212
 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=FAIL)
 for <FreeBSD-net@freebsd.org>; Wed, 16 Apr 2014 01:54:51 +0200 (CEST)
 (envelope-from ticso@cicely7.cicely.de)
Received: from cicely7.cicely.de (cicely7.cicely.de [10.1.1.9])
 by mail.cicely.de (8.14.5/8.14.4) with ESMTP id s3FNsJ3m013200
 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO);
 Wed, 16 Apr 2014 01:54:20 +0200 (CEST)
 (envelope-from ticso@cicely7.cicely.de)
Received: from cicely7.cicely.de (localhost [127.0.0.1])
 by cicely7.cicely.de (8.14.2/8.14.2) with ESMTP id s3FNsJEJ032326;
 Wed, 16 Apr 2014 01:54:19 +0200 (CEST)
 (envelope-from ticso@cicely7.cicely.de)
Received: (from ticso@localhost)
 by cicely7.cicely.de (8.14.2/8.14.2/Submit) id s3FNsJsf032325;
 Wed, 16 Apr 2014 01:54:19 +0200 (CEST) (envelope-from ticso)
Date: Wed, 16 Apr 2014 01:54:19 +0200
From: Bernd Walter <ticso@cicely7.cicely.de>
To: FreeBSD-net@freebsd.org
Subject: SCTP stream socket read(2) can block a process
Message-ID: <20140415235419.GG30429@cicely7.cicely.de>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
X-Operating-System: FreeBSD cicely7.cicely.de 7.0-STABLE i386
User-Agent: Mutt/1.5.11
X-Spam-Status: No, score=-2.9 required=5.0 tests=ALL_TRUSTED=-1, BAYES_00=-1.9,
 T_RP_MATCHES_RCVD=-0.01 autolearn=unavailable version=3.3.0
X-Spam-Checker-Version: SpamAssassin 3.3.0 (2010-01-18) on spamd.cicely.de
Cc: Bernd Walter <ticso@cicely7.cicely.de>
X-BeenThere: freebsd-net@freebsd.org
X-Mailman-Version: 2.1.17
Precedence: list
Reply-To: ticso@cicely.de
List-Id: Networking and TCP/IP with FreeBSD <freebsd-net.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-net>,
 <mailto:freebsd-net-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-net/>
List-Post: <mailto:freebsd-net@freebsd.org>
List-Help: <mailto:freebsd-net-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
 <mailto:freebsd-net-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 15 Apr 2014 23:55:21 -0000

When using SCTP in TCP like stream style.
socket(2)
connect(2)
write(2) request
read(2) answer

When the other side disconnects the association (e.g. process restarted)
after the write and before read call the read never returns.
With TCP stream sockets the read would return with an error instead.
SCTP are not TCP, but the other side can't associate back in on such
a connect(2) socket, so returning would be expected.
I've switched to nonblocking with timeout in the meantime - I wanted
to have a response timeout anyway.
In my test case the other side was a one2many socket on the same host.

-- 
B.Walter <bernd@bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.