From owner-freebsd-hackers@freebsd.org  Mon Jan  8 18:42:42 2018
Return-Path: <owner-freebsd-hackers@freebsd.org>
Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id 66FBAE7DC79
 for <freebsd-hackers@mailman.ysv.freebsd.org>;
 Mon,  8 Jan 2018 18:42:42 +0000 (UTC)
 (envelope-from kostikbel@gmail.com)
Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id D3D0E6C1F5;
 Mon,  8 Jan 2018 18:42:41 +0000 (UTC)
 (envelope-from kostikbel@gmail.com)
Received: from tom.home (kib@localhost [127.0.0.1])
 by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id w08IgXqF005789
 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO);
 Mon, 8 Jan 2018 20:42:36 +0200 (EET)
 (envelope-from kostikbel@gmail.com)
DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua w08IgXqF005789
Received: (from kostik@localhost)
 by tom.home (8.15.2/8.15.2/Submit) id w08IgX58005788;
 Mon, 8 Jan 2018 20:42:33 +0200 (EET)
 (envelope-from kostikbel@gmail.com)
X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com
 using -f
Date: Mon, 8 Jan 2018 20:42:33 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Conrad Meyer <cem@freebsd.org>
Cc: Andrew Duane <aduane@juniper.net>,
 Freebsd hackers list <freebsd-hackers@freebsd.org>
Subject: Re: Is it considered to be ok to not check the return code of
 close(2) in base?
Message-ID: <20180108184233.GL1684@kib.kiev.ua>
References: <201801081655.w08GtO3D022568@pdx.rh.CN85.dnsmgr.net>
 <df6f98a5-76db-d6d8-6321-d35b59eeec22@vangyzen.net>
 <SN1PR0501MB212559C6D852EBEEA3A89C7CCE130@SN1PR0501MB2125.namprd05.prod.outlook.com>
 <CAG6CVpXq5rx6HW=UuHD29D7EZPr0z7LfZ4Rox1j6u=qMyGvpnQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAG6CVpXq5rx6HW=UuHD29D7EZPr0z7LfZ4Rox1j6u=qMyGvpnQ@mail.gmail.com>
User-Agent: Mutt/1.9.2 (2017-12-15)
X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00,
 DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no
 autolearn_force=no version=3.4.1
X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.25
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
 <freebsd-hackers.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/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: <https://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, 
 <mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 08 Jan 2018 18:42:42 -0000

On Mon, Jan 08, 2018 at 10:13:19AM -0800, Conrad Meyer wrote:
> On Mon, Jan 8, 2018 at 10:05 AM, Andrew Duane <aduane@juniper.net> wrote:
> > Of course, my OCD will kick in and say this would need to be something like:
> >
> > #ifdef DEBUG_CLOSE
> > #define close(f)        do {if (close(f) < 0) assert(errno != EBADF); } while (0)
> > #endif
> >
> > Have to watch those macro replacements like "if (need_to_close) close(f);". And the close succeeding :-)
> 
> Of course, this has turned into nerd sniping.  But I'll take my turn.
> 
> Better to use the GCC "statement expression" extension so that the
> return value of "close()" can still be used by callers naive to the
> macro.
> 
> #define close(f)    ({ int __ret;  __ret = (close)(f);  if (__ret < 0)
> assert(errno != EBADF);  __ret; })
You can create a dso which interposes close(3), calls original close()
resolved by dlsym(RTLD_NEXT), and checks for the error, for use with
LD_PRELOAD environment variable. No need to vandali^H^H^H^hack on either
kernel nor userland code.