From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760258AbYDCSed (ORCPT ); Thu, 3 Apr 2008 14:34:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756177AbYDCSeP (ORCPT ); Thu, 3 Apr 2008 14:34:15 -0400 Received: from emh04.mail.saunalahti.fi ([62.142.5.110]:37219 "EHLO emh04.mail.saunalahti.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755902AbYDCSeN (ORCPT ); Thu, 3 Apr 2008 14:34:13 -0400 Date: Thu, 3 Apr 2008 21:34:09 +0300 (EEST) From: Kai Makisara X-X-Sender: makisara@kai.makisara.local To: Robert Hancock cc: Carlo Nyto , linux-kernel@vger.kernel.org Subject: Re: Slow tape drive timeout In-Reply-To: <47F45B39.7080305@shaw.ca> Message-ID: References: <47F45B39.7080305@shaw.ca> User-Agent: Alpine 1.10 (LSU 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Antivirus: VAMS Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2 Apr 2008, Robert Hancock wrote: > Kai Makisara wrote: > > On Tue, 1 Apr 2008, Carlo Nyto wrote: > > > > > I am experiencing a two minute timeout open()ing a tape device when > > > there is no tape in the drive. > > > > > > open() with O_NONBLOCK succeeds immediately, however. > > > > > This is how open() is supposed to work according to standards (e.g., SUS) if > > O_NONBLOCK is supported. (Well, actually open() should wait indefinitely but > > the non-linux systems I tested had a timeout.) The linux st driver was > > changed to comply with standards at 2.5.3. I.e., the 2.4 kernels did return > > immediately but the 2.6 kernels have always waited. > > ... > Why is accessing the tape drive with no tape in it causing a timeout in the > first place? I should think that would fail immediately with some "medium not > present" error from the drive. Unless the drive has no mechanism to detect it, > but that seems really retarded.. > It does not seem retarded to me. If a program wants to just wait until the tape drive becomes ready (e.g., loads the tape), it can use the blocking open. This is simple. If a program wants to test the status, it uses non-blocking open. The behavior mandated by the standards provides alternatives. If O_NONBLOCK is not supported, the user program must implement the waiting logic if the program just wants to wait until the drive is ready before starting i/o. -- Kai