From owner-freebsd-hackers@FreeBSD.ORG  Sat Jul  4 22:48:47 2009
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id CBB3E1065673
	for <freebsd-hackers@freebsd.org>; Sat,  4 Jul 2009 22:48:47 +0000 (UTC)
	(envelope-from a_best01@uni-muenster.de)
Received: from zivm-out3.uni-muenster.de (ZIVM-OUT3.UNI-MUENSTER.DE
	[128.176.192.18])
	by mx1.freebsd.org (Postfix) with ESMTP id 635418FC1B
	for <freebsd-hackers@freebsd.org>; Sat,  4 Jul 2009 22:48:46 +0000 (UTC)
	(envelope-from a_best01@uni-muenster.de)
X-IronPort-AV: E=Sophos;i="4.42,349,1243807200"; 
   d="scan'208";a="7589543"
Received: from zivmaildisp2.uni-muenster.de (HELO
	ZIVMAILUSER01.UNI-MUENSTER.DE) ([128.176.188.143])
	by zivm-relay3.uni-muenster.de with ESMTP; 05 Jul 2009 00:48:45 +0200
Received: by ZIVMAILUSER01.UNI-MUENSTER.DE (Postfix, from userid 149459)
	id 7F3531B0764; Sun,  5 Jul 2009 00:48:45 +0200 (CEST)
Date: Sun, 05 Jul 2009 00:48:45 +0200 (CEST)
From: Alexander Best <alexbestms@math.uni-muenster.de>
Sender: <a_best01@uni-muenster.de>
Organization: Westfaelische Wilhelms-Universitaet Muenster
To: <freebsd-hackers@FreeBSD.org>
Message-ID: <permail-20090704224845f0889e84000046f1-a_best01@message-id.uni-muenster.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: 
Subject: mmap/munmap with zero length
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, 
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sat, 04 Jul 2009 22:48:48 -0000

i'm wondering why mmap and munmap behave differently when it comes to a length
argument of zero. allocating memory with mmap for a zero length file returns a
valid pointer to the mapped region.

munmap however isn't able to remove a mapping with no length.

wouldn't it be better to either forbid this in mmap or to allow it in munmap?

cheers.
alex