From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262539AbUCOKdJ (ORCPT ); Mon, 15 Mar 2004 05:33:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262537AbUCOKdJ (ORCPT ); Mon, 15 Mar 2004 05:33:09 -0500 Received: from moutng.kundenserver.de ([212.227.126.176]:30933 "EHLO moutng.kundenserver.de") by vger.kernel.org with ESMTP id S262539AbUCOKdF (ORCPT ); Mon, 15 Mar 2004 05:33:05 -0500 Date: Mon, 15 Mar 2004 11:33:00 +0100 (MET) From: Armin Schindler To: Manfred Spraul cc: Marcelo Tosatti , Linux Kernel Mailinglist Subject: Re: [PATCH 2.4] sys_select() return error on bad file In-Reply-To: <4054A213.6010402@colorfullife.com> Message-ID: Organization: Cytronics & Melware MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Provags-ID: kundenserver.de abuse@kundenserver.de auth:4f0aeee4703bc17a8237042c4702a75a Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 14 Mar 2004, Manfred Spraul wrote: > Marcelo wrote: > > >> > >> Anyway, I don't see how your proposal would do better performance? > >> My patch just adds a new variable on the stack, which should not make any > >> difference in performance. And later, it is the same if the new or another > >> variable gets changed or checked. > > > >Curiosity: Does SuS/POSIX define behaviour for "all fds are closed" ? > > > > > I'd interpret SuS that a closed fd is ready for reading and writing: > From the select page: > <<< > A descriptor shall be considered ready for reading when a call to an > input function with O_NONBLOCK clear would not block, whether or not the > function would transfer data successfully. (The function might return > data, an end-of-file indication, or an error other than one indicating > that it is blocked, and in each of these cases the descriptor shall be > considered ready for reading.) > <<< > read(fd,,) will return immediately with EBADF, thus the fd is ready. > > But that's a grey area, especially if you close the fd during the select > call. For example HP UX just kills the current process if an fd that is > polled is closed by overwriting it with dup2. I didn't test select, but > I'd expect a similar behavior. > > Armin: did you compare the Linux behavior with other unices? Are there > other unices that return EBADF for select() if all fds are closed? No, I didn't compare yet, but I could not find any definition on that. It really seems to be a "grey area". > Attached is an untested proposal, against 2.6, but I'm not sure if it's > really a good idea to change the current code - it might break existing > apps. This patch should also work on 2.4 and looks good to me, if "ready" should be returned instead of EBADF. I don't think this would break existing apps. Without such a patch, the app would sleep forever unless a signal arrives. If any app depends on that behavior, I think it is bad coded. Armin