From owner-freebsd-threads@FreeBSD.ORG  Thu Dec 29 05:30:09 2005
Return-Path: <owner-freebsd-threads@FreeBSD.ORG>
X-Original-To: freebsd-threads@hub.freebsd.org
Delivered-To: freebsd-threads@hub.freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id AA6F016A420
	for <freebsd-threads@hub.freebsd.org>;
	Thu, 29 Dec 2005 05:30:09 +0000 (GMT)
	(envelope-from gnats@FreeBSD.org)
Received: from freefall.freebsd.org (freefall.freebsd.org [216.136.204.21])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 4430243D5D
	for <freebsd-threads@hub.freebsd.org>;
	Thu, 29 Dec 2005 05:30:09 +0000 (GMT)
	(envelope-from gnats@FreeBSD.org)
Received: from freefall.freebsd.org (gnats@localhost [127.0.0.1])
	by freefall.freebsd.org (8.13.4/8.13.4) with ESMTP id jBT5U81N071115
	for <freebsd-threads@freefall.freebsd.org>;
	Thu, 29 Dec 2005 05:30:08 GMT
	(envelope-from gnats@freefall.freebsd.org)
Received: (from gnats@localhost)
	by freefall.freebsd.org (8.13.4/8.13.4/Submit) id jBT5U8qX071114;
	Thu, 29 Dec 2005 05:30:08 GMT (envelope-from gnats)
Date: Thu, 29 Dec 2005 05:30:08 GMT
Message-Id: <200512290530.jBT5U8qX071114@freefall.freebsd.org>
To: freebsd-threads@FreeBSD.org
From: David Xu <davidxu@freebsd.org>
Cc: 
Subject: Re: threads/79887: [patch] freopen() isn't thread-safe
X-BeenThere: freebsd-threads@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
Reply-To: David Xu <davidxu@freebsd.org>
List-Id: Threading on FreeBSD <freebsd-threads.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-threads>, 
	<mailto:freebsd-threads-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-threads>
List-Post: <mailto:freebsd-threads@freebsd.org>
List-Help: <mailto:freebsd-threads-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-threads>,
	<mailto:freebsd-threads-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 29 Dec 2005 05:30:09 -0000

The following reply was made to PR threads/79887; it has been noted by GNATS.

From: David Xu <davidxu@freebsd.org>
To: Dmitrij Tejblum <tejblum@yandex-team.ru>
Cc: bug-followup@freebsd.org
Subject: Re: threads/79887: [patch] freopen() isn't thread-safe
Date: Thu, 29 Dec 2005 13:26:03 +0800

 Dmitrij Tejblum wrote:
 > 
 > David Xu wrote:
 > 
 >> Indeed, this a bug, but the patch you provided breaks the samentic the
 >> FILE structure was designed for, here you conditionally call
 >> fp->_close(), this is incorrect, because the hook may be an external
 >> function, it should always be called to notify external code.
 > 
 > 
 > I only assume that
 > 1) _file and _close fields are internal to stdio, i.e. only stdio code 
 > manipulate with them directly
 > 2) If _file != -1, then the FILE is associated with the file descriptor, 
 > fp->_close == __sclose (because the only code that can set fp_close to 
 > something different is funopen, and it set _file to -1) and __sclose 
 > just close the _fp->_file
 > If so, we know that dup2() will close the descriptor too, dup2() is 
 > required to do it.
 > 
 I think we allow _close and others to be changed by user code unless
 someone can clarify that this is not allowed now, otherwise your
 assumption is false.
 
 
 >> I think the right fix is to fix those code which is still using
 >> STDERR_FILENO, or don't do following hack in freopen.c:
 >>     if (wantfd >= 0 && f != wantfd) {
 >>            if (_dup2(f, wantfd) >= 0) {
 >>                      (void)_close(f);
 >>                      f = wantfd;
 >>            }
 >>     }
 >> This is not required by standard.
 > 
 > 
 > Well, I tried to keep existing behaviour, and I think that the hack is 
 > indeed a good idea even though it is not required.