From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: [PATCH] Add facility to collect stderr of async subprocess Date: Tue, 07 Apr 2015 17:47:20 -0700 Organization: UCLA Computer Science Department Message-ID: <55247A98.5020302@cs.ucla.edu> References: <87d24d3uwz.fsf-ueno@gnu.org> <83pp87y6iu.fsf@gnu.org> <83mw3bxz9f.fsf@gnu.org> <83k2yfx8zi.fsf@gnu.org> <83egomxog1.fsf@gnu.org> <83ego5tjgt.fsf@gnu.org> <877ftno4fr.fsf-ueno@gnu.org> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1428454066 27818 80.91.229.3 (8 Apr 2015 00:47:46 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 8 Apr 2015 00:47:46 +0000 (UTC) Cc: emacs-devel@gnu.org To: Daiki Ueno Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Wed Apr 08 02:47:38 2015 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Yfe9Z-0004c8-SG for ged-emacs-devel@m.gmane.org; Wed, 08 Apr 2015 02:47:38 +0200 Original-Received: from localhost ([::1]:49772 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yfe9Z-00052i-6a for ged-emacs-devel@m.gmane.org; Tue, 07 Apr 2015 20:47:37 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:44534) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yfe9W-00052Z-3u for emacs-devel@gnu.org; Tue, 07 Apr 2015 20:47:34 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Yfe9S-0004ub-If for emacs-devel@gnu.org; Tue, 07 Apr 2015 20:47:34 -0400 Original-Received: from smtp.cs.ucla.edu ([131.179.128.62]:44025) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yfe9S-0004t9-Cp; Tue, 07 Apr 2015 20:47:30 -0400 Original-Received: from localhost (localhost.localdomain [127.0.0.1]) by smtp.cs.ucla.edu (Postfix) with ESMTP id DEE08A60009; Tue, 7 Apr 2015 17:47:21 -0700 (PDT) X-Virus-Scanned: amavisd-new at smtp.cs.ucla.edu Original-Received: from smtp.cs.ucla.edu ([127.0.0.1]) by localhost (smtp.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id XM5U5GpSliUJ; Tue, 7 Apr 2015 17:47:21 -0700 (PDT) Original-Received: from Penguin.CS.UCLA.EDU (Penguin.CS.UCLA.EDU [131.179.64.200]) by smtp.cs.ucla.edu (Postfix) with ESMTPSA id F33F3A60008; Tue, 7 Apr 2015 17:47:20 -0700 (PDT) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 In-Reply-To: <877ftno4fr.fsf-ueno@gnu.org> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6.x X-Received-From: 131.179.128.62 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:185121 Archived-At: I took a quick look, and in the ordinary POSIXish code there's a race condition between the calls to pipe2 and the calls to fcntl with FD_CLOEXEC. If some other thread forks and execs a process after pipe2 but before fcntl, that process will have access to the pipe ends and this could cause problems. Instead, please call pipe2 (.., O_BINARY | O_CLOEXEC) so that the other process won't see the pipe end. Any child process that needs to have the pipe end survive an exec should then call fcntl (pipe_end, F_SETFD, 0) before execing. This is how the existing Emacs code works. So, there should be no need to call fcntl (inchannel, F_SETFD, FD_CLOEXEC) and likewise for outchannel.