Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758965AbYJJNJH (ORCPT ); Fri, 10 Oct 2008 09:09:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755767AbYJJNIz (ORCPT ); Fri, 10 Oct 2008 09:08:55 -0400 Received: from mail-in-17.arcor-online.net ([151.189.21.57]:34512 "EHLO mail-in-17.arcor-online.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754150AbYJJNIz (ORCPT ); Fri, 10 Oct 2008 09:08:55 -0400 Date: Fri, 10 Oct 2008 15:19:31 +0200 (CEST) From: Bodo Eggert <7eggert@gmx.de> To: mtk.manpages@gmail.com cc: 7eggert@gmx.de, "H. Peter Anvin" , Ulrich Drepper , Al Viro , LKML Subject: Re: dup2() vs dup3() inconsistency when In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=us-ascii X-be10.7eggert.dyndns.org-MailScanner-Information: See www.mailscanner.info for information X-be10.7eggert.dyndns.org-MailScanner: Found to be clean X-be10.7eggert.dyndns.org-MailScanner-From: 7eggert@gmx.de Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2006 Lines: 49 On Fri, 10 Oct 2008, Michael Kerrisk wrote: > On Fri, Oct 10, 2008 at 1:42 PM, Bodo Eggert <7eggert@gmx.de> wrote: > > Michael Kerrisk wrote: > > > >> Well, as long as we are fixing the dup3() interface in the way that Al > >> and Ulrich have suggested, what about another fix: > >> > >> give an error if newfd is already open, thus forcing the user to do an > >> explicit close > >> > >> ? > >> > >> This silent close in dup2() is an implementation blemish. Why not eliminate > >> it? > > > > I think it might be usefull: > > Thread B does some logging to fd 42 > > Thread A switches the logfile by creating a new file, writing a header and > > then does dup3(fd, 42, O_WRONLY|O_APPEND|O_CLOEXEC); close(fd); > > I don't know the details of the kernel locks here, so perhaps this is > a naive question: but, as things stand is there not the potential for > some nasty race if one thread is writing to fd 42 at the same time as > another thread does a dup2(fd, 42)? I strongly hope there would not be any ... > > (Off cause this is not yet implemented, O_RDONLY would give some problems, > > O_CLOEXEC alone might be better done while open()ing the file, ... but you > > get the idea.) > > > > > > BTW: I think dup3(fd, -1, flags) should use the file descriptor dup() would > > return. Or should there be a dupf(fd, flags) syscall instead? > > If one did this, maybe it would be better to have an extra flag that > said: "use the first free file descriptor >= newfd", thus giving the > more general functionality like fcntl(F_DUPFD). I think you are right. I thought about something similar, too, but was distracted enough to not think about the connection. -- Funny quotes: 10. Nothing is fool proof to a talented fool. -- 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/