Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756176AbXJATFN (ORCPT ); Mon, 1 Oct 2007 15:05:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752091AbXJATFB (ORCPT ); Mon, 1 Oct 2007 15:05:01 -0400 Received: from x35.xmailserver.org ([64.71.152.41]:60422 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752181AbXJATFA (ORCPT ); Mon, 1 Oct 2007 15:05:00 -0400 X-AuthUser: davidel@xmailserver.org Date: Mon, 1 Oct 2007 12:04:58 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Denys Vlasenko cc: Al Viro , Ulrich Drepper , Linux Kernel Mailing List , Andrew Morton Subject: Re: F_DUPFD_CLOEXEC implementation In-Reply-To: <200710011949.03482.vda.linux@googlemail.com> Message-ID: References: <200709281734.l8SHYTmd027235@devserv.devel.redhat.com> <200710011107.15846.vda.linux@googlemail.com> <20071001181648.GB8181@ftp.linux.org.uk> <200710011949.03482.vda.linux@googlemail.com> X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1688 Lines: 49 On Mon, 1 Oct 2007, Denys Vlasenko wrote: > On Monday 01 October 2007 19:16, Al Viro wrote: > > * it's on a bunch of cyclic lists. Have its neighbor > > go away while you are doing all that crap => boom > > * there's that thing call current position... It gets buggered. > > * overwriting it while another task might be in the middle of > > syscall involving it => boom > > Hm, I suspected that it's herecy. Any idea how to do it cleanly? > > > * non-cooperative tasks reading *in* *parallel* from the same > > opened file are going to have a lot more serious problems than agreeing > > on O_NONBLOCK anyway, so I really don't understand what the hell is that for. > > They don't even need to read in parallel, just having shared fd is enough. > Think about pipes, sockets and terminals. A real-world scenario: > > * a process started from shell (interactive or shell script) > * it sets O_NONBLOCK and does a read from fd 0... > * it gets killed (kill -9, whatever) > * shell suddenly has it's fd 0 in O_NONBLOCK mode > * shell and all subsequent commands started from it unexpectedly have > O_NONBLOCKed stdin. I told you how in the previous email. You cannot use the: 1) set O_NONBLOCK 2) read/write 3) unset O_NONBLOCK in a racy-free fashion, w/out wrapping it with a lock (thing that we don't want to do). PS: send/recv are socket functions, and you really don't want to overload them for other fds. - Davide - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/