From owner-freebsd-hackers@FreeBSD.ORG Mon Oct 24 00:10:39 2011 Return-Path: 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 183E6106564A for ; Mon, 24 Oct 2011 00:10:39 +0000 (UTC) (envelope-from dan@dan.emsphone.com) Received: from email2.allantgroup.com (email2.emsphone.com [199.67.51.116]) by mx1.freebsd.org (Postfix) with ESMTP id 90F508FC15 for ; Mon, 24 Oct 2011 00:10:38 +0000 (UTC) Received: from dan.emsphone.com (dan.emsphone.com [199.67.51.101]) by email2.allantgroup.com (8.14.4/8.14.4) with ESMTP id p9O0AZXG055258 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Sun, 23 Oct 2011 19:10:35 -0500 (CDT) (envelope-from dan@dan.emsphone.com) Received: from dan.emsphone.com (smmsp@localhost [127.0.0.1]) by dan.emsphone.com (8.14.5/8.14.5) with ESMTP id p9O0AY6P079535 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Sun, 23 Oct 2011 19:10:34 -0500 (CDT) (envelope-from dan@dan.emsphone.com) Received: (from dan@localhost) by dan.emsphone.com (8.14.5/8.14.5/Submit) id p9O0AYul079534; Sun, 23 Oct 2011 19:10:34 -0500 (CDT) (envelope-from dan) Date: Sun, 23 Oct 2011 19:10:34 -0500 From: Dan Nelson To: "Christopher J. Ruwe" Message-ID: <20111024001034.GE93709@dan.emsphone.com> References: <20111023235231.71f73ea3@dijkstra> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111023235231.71f73ea3@dijkstra> X-OS: FreeBSD 8.2-STABLE User-Agent: Mutt/1.5.21 (2010-09-15) X-Virus-Scanned: clamav-milter 0.97.2 at email2.allantgroup.com X-Virus-Status: Clean X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.6 (email2.allantgroup.com [199.67.51.78]); Sun, 23 Oct 2011 19:10:35 -0500 (CDT) X-Scanned-By: MIMEDefang 2.68 on 199.67.51.78 Cc: freebsd-hackers@freebsd.org Subject: Re: _SC_GETPW_R_SIZE_MAX undefined in sysconf.c, what is correct value? X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 24 Oct 2011 00:10:39 -0000 In the last episode (Oct 23), Christopher J. Ruwe said: > I need to get the maximum size of an pwd-entry to determine the correct > buffersize for calling getpwnam_r("uname",&pwd, buf, bufsize, &pwdp). I > would like to use sysconf(_SC_GETPW_R_SIZE_MAX) to determine bufsize, > which unfornutately fails (returns -1). Currently, I used 16384, which > seems to be too much, bit works for the time being. > > From recent mails I get that _SC_GETPW_R_SIZE_MAX is not available on > FreeBSD, e.g., > http://lists.freebsd.org/pipermail/freebsd-ports-bugs/2009-September/173081.html > and http://www.redhat.com/archives/libvir-list/2011-May/msg01013.html. > This assertion seems to be backed by /usr/srclib/libc/gen/sysconf.c, line > 374. > > From Stevens & Rago, Adavanced Programming in the UNIX Environment, I can > get that FreeBSD supports all possible members in the passwd structure, > but where can I determine the maximum size of these so that I can > calculate the ax size of the pwd struct therefrom? Does anybody know or > know where to look what maximum size a pwd-entry can have? > > Knowing the maximum size a pwd structure can have, it seems like to be an > idea to define the correct value in sysconf.c. As that is not done though > suggested in the code, are there any obstacles in defining that value so > nobody has done that so far? >From looking at the libc/gen/getpwent.c file, it looks like a maximum size might be 1MB. The wrapper functions that convert getpw*_r functions into ones that simply return a pointer to malloced data all use the getpw() helper function, which starts with a 1k buffer and keeps doubling its size until the data fits or it hits PWD_STORAGE_MAX (1MB). PWD_STORAGE_MAX is only checked within that getpw() function, though, so it's possible that an nss library might return an even longer string to a get*_r call. It's up to you to decide what your own limit is :) -- Dan Nelson dnelson@allantgroup.com