Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754927AbZCFPgF (ORCPT ); Fri, 6 Mar 2009 10:36:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754635AbZCFPfx (ORCPT ); Fri, 6 Mar 2009 10:35:53 -0500 Received: from e38.co.us.ibm.com ([32.97.110.159]:40139 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754208AbZCFPfx (ORCPT ); Fri, 6 Mar 2009 10:35:53 -0500 Date: Fri, 6 Mar 2009 09:35:49 -0600 From: "Serge E. Hallyn" To: Greg Kurz Cc: Alexey Dobriyan , Christoph Hellwig , "linux-kernel@vger.kernel.org" , containers , Ingo Molnar , Dave Hansen Subject: Re: [RFC][PATCH 00/11] track files for checkpointability Message-ID: <20090306153549.GA898@us.ibm.com> References: <20090305163857.0C18F3FD@kernel> <20090305174037.GA2274@x200.localdomain> <1236280567.22399.99.camel@nimitz> <20090305210840.GA2499@x200.localdomain> <1236288427.22399.122.camel@nimitz> <20090305220044.GA2819@x200.localdomain> <1236352121.5732.80.camel@bahia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1236352121.5732.80.camel@bahia> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1948 Lines: 44 Quoting Greg Kurz (gkurz@fr.ibm.com): > On Fri, 2009-03-06 at 01:00 +0300, Alexey Dobriyan wrote: > > On Thu, Mar 05, 2009 at 01:27:07PM -0800, Dave Hansen wrote: > > > > Imagine, unsupported file is opened between userspace checks > > > > for /proc/*/checkpointable and /proc/*/fdinfo/*/checkpointable > > > > and whatever, you stil have to do all the checks inside checkpoint(2). > > > > > > Alexey, we have two problems here. I completely agree that we have to > > > do complete and thorough checks of each file descriptor at > > > sys_checkpoint(). Any checks made at other times should not be trusted. > > > > > > The other side is what Ingo has been asking for. How do we *know* when > > > we are checkpointable *before* we call (and without calling) > > > > This "without calling checkpoint(2)" results in much complications > > as demonstrated. > > > > task_struct and file are not like other structures because they are exposed > > in /proc. For PROC_FS=n kernels, one can't even check. > > > > You can do checkpoint(2) without actual dump. You pass, you're most > > certainly checkpointable (with inevitable race condition in mind). > > > > Ahhh thank you very much Alexey ! I wanted to explain this to Dave a few > monthes ago but I failed... probably because of my poor English skills. > > https://lists.linux-foundation.org/pipermail/containers/2008-October/013549.html > > Why would we add checking all over the place when it MUST be done on the > sys_checkpoint() path ? The checkpoint(2) dry-run is definitely the way > to go. I'm sure Dave understood that this was possible :) But what you and Alexey are proposing does not and cannot fullfill Ingo's requirement. -serge -- 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/