From owner-freebsd-bugs@FreeBSD.ORG  Fri Feb  4 21:21:00 2005
Return-Path: <owner-freebsd-bugs@FreeBSD.ORG>
Delivered-To: freebsd-bugs@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 5B38E16A4CE
	for <freebsd-bugs@freebsd.org>; Fri,  4 Feb 2005 21:21:00 +0000 (GMT)
Received: from rosebud.otenet.gr (rosebud.otenet.gr [195.170.0.26])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 9907A43D45
	for <freebsd-bugs@freebsd.org>; Fri,  4 Feb 2005 21:20:57 +0000 (GMT)
	(envelope-from keramida@ceid.upatras.gr)
Received: from gothmog.gr (patr530-a208.otenet.gr [212.205.215.208])
	j14LJq2W032490;	Fri, 4 Feb 2005 23:19:53 +0200
Received: from gothmog.gr (gothmog [127.0.0.1])
	by gothmog.gr (8.13.1/8.13.1) with ESMTP id j14LJnB9001311;
	Fri, 4 Feb 2005 23:19:49 +0200 (EET)
	(envelope-from keramida@ceid.upatras.gr)
Received: (from giorgos@localhost)
	by gothmog.gr (8.13.1/8.13.1/Submit) id j14LJnNm001310;
	Fri, 4 Feb 2005 23:19:49 +0200 (EET)
	(envelope-from keramida@ceid.upatras.gr)
Date: Fri, 4 Feb 2005 23:19:49 +0200
From: Giorgos Keramidas <keramida@ceid.upatras.gr>
To: Mario Hoerich <lists@MHoerich.de>
Message-ID: <20050204211949.GC1041@gothmog.gr>
References: <200502040930.j149UQDc043307@freefall.freebsd.org>
	<20050204201622.GA29998@Pandora.MHoerich.de>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20050204201622.GA29998@Pandora.MHoerich.de>
cc: freebsd-bugs@freebsd.org
cc: Fergus Cameron <fergus@cobbled.net>
Subject: Re: bin/77031: [patch] comm(1) unable to handle lines greater than
	LINE_MAX (2048)
X-BeenThere: freebsd-bugs@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Bug reports <freebsd-bugs.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-bugs>,
	<mailto:freebsd-bugs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-bugs>
List-Post: <mailto:freebsd-bugs@freebsd.org>
List-Help: <mailto:freebsd-bugs-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-bugs>,
	<mailto:freebsd-bugs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 04 Feb 2005 21:21:00 -0000

On 2005-02-04 21:16, Mario Hoerich <lists@MHoerich.de> wrote:
> # Fergus Cameron:
> >  	http://people.freebsd.org/~keramida/fergus/comm.c-diff
>
> Now to your patch. What I've noticed while doing a preliminary
> review (bit short on time right now) was:
>
>	file1 = file( argv[0] ) ;
> 	file2 = file( argv[1] ) ;
>
> 	if( file1 == file2 )
> 		errx(EXIT_FAILURE, "cannot match file against self");
>
> You sure this is guaranteed to trigger? I'm not standard-
> savvy enough to know for sure, but it seems like a potential
> problem. Anyone with a definitive answer?

It is not guaranteed by any standard that I know of.  A small sample
program like the following shows it is, in fact, not going to work on
FreeBSD:

% #include <err.h>
% #include <stdio.h>
%
% int
% main(int argc, char *argv[0])
% {
%         FILE *fp, *fp2;
%
%         if (argc != 2)
%                 errx(1, "usage: foo FILENAME");
%         fp = fopen(argv[1], "r");
%         if (fp == NULL)
%                 err(1, "fopen: %s", argv[1]);
%         fp2 = fopen(argv[1], "r");
%         if (fp2 == NULL) {
%                 fclose(fp);
%                 err(1, "fopen: %s", argv[1]);
%         }
%         printf("%p\n%p\n", fp, fp2);
%         fclose(fp);
%         fclose(fp2);
%         return (0);
% }

This will not print the same pointer value for fp and fp2, regardless of
the fopen() calls being passed the same filename as their first
argument:

% $ ./foo foo
% 0x28148880
% 0x281488d8

FWIW, a good way to find if two files are, indeed, pointers to the same
i-node (i.e. hard links to the same disk file) is to compare the device
major/minor numbers *AND* the i-node number.