Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751137AbVLGPfL (ORCPT ); Wed, 7 Dec 2005 10:35:11 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751140AbVLGPfL (ORCPT ); Wed, 7 Dec 2005 10:35:11 -0500 Received: from mx1.redhat.com ([66.187.233.31]:55739 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S1751137AbVLGPfK (ORCPT ); Wed, 7 Dec 2005 10:35:10 -0500 Message-ID: <4397011E.9010703@redhat.com> Date: Wed, 07 Dec 2005 10:34:54 -0500 From: Peter Staubach User-Agent: Mozilla Thunderbird 1.0.7-1.4.1 (X11/20050929) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Trond Myklebust CC: Kenny Simpson , linux-kernel@vger.kernel.org Subject: Re: another nfs puzzle References: <20051206220448.82860.qmail@web34109.mail.mud.yahoo.com> <4396EB2F.3060404@redhat.com> <1133964667.27373.13.camel@lade.trondhjem.org> <4396EF50.30201@redhat.com> <1133966063.27373.29.camel@lade.trondhjem.org> In-Reply-To: <1133966063.27373.29.camel@lade.trondhjem.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1318 Lines: 33 Trond Myklebust wrote: >>Yup, same problem. Why is this allowed? Does it really work correctly? >> >> > >Assuming that the processes have _some_ method of synchronisation, then >I cannot see why it shouldn't be workable. Come to think of it, it might >even be possible to use O_DIRECT to provide that synchronisation (use >O_DIRECT to set a "lock" on the page, then modify it using mmap). > >Whether or not there are people out there that actually _want_ to do >this is a different matter. > Mixing O_DIRECT i/o and cached i/o is probably a recipe for disaster, unless the cooperating programs are very careful and very aware of how the particular file system in the particular kernel implements direct i/o and caching, including cache validation. This seems like a dangerous enough area that denying mmap on a file which has been opened with O_DIRECT by any process and denying open(O_DIRECT) on a file which has been mmap'd would be a good thing. These things are easy enough to keep track of, so it shouldn't be too hard to implement. Thanx... ps - 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/