Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756014AbZCTVcT (ORCPT ); Fri, 20 Mar 2009 17:32:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751703AbZCTVcI (ORCPT ); Fri, 20 Mar 2009 17:32:08 -0400 Received: from brinza.cc.columbia.edu ([128.59.29.8]:34090 "EHLO brinza.cc.columbia.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751060AbZCTVcH (ORCPT ); Fri, 20 Mar 2009 17:32:07 -0400 Message-ID: <49C40AEE.6040309@cs.columbia.edu> Date: Fri, 20 Mar 2009 17:30:22 -0400 From: Oren Laadan Organization: Columbia University User-Agent: Thunderbird 2.0.0.21 (X11/20090318) MIME-Version: 1.0 To: Dave Hansen CC: Christoph Hellwig , Alexey Dobriyan , containers , Ingo Molnar , "linux-kernel@vger.kernel.org" Subject: Re: [RFC][PATCH 5/8] add f_op for checkpointability References: <20090227203425.F3B51176@kernel> <20090227203431.D1E697CB@kernel> <20090228205329.GB4254@infradead.org> <1236013556.26788.466.camel@nimitz> <20090303131528.GB10931@infradead.org> <1237583604.8286.294.camel@nimitz> In-Reply-To: <1237583604.8286.294.camel@nimitz> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-No-Spam-Score: Local Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1986 Lines: 48 Dave Hansen wrote: > On Tue, 2009-03-03 at 08:15 -0500, Christoph Hellwig wrote: >> On Mon, Mar 02, 2009 at 09:05:56AM -0800, Dave Hansen wrote: >>> On Sat, 2009-02-28 at 15:53 -0500, Christoph Hellwig wrote: >>>> Also the double-use of the op seem not very nice to me. Is there any >>>> real life use case were you would have the operation on a file but >>>> sometimes not allow checkpoiting? >>> I'm still reaching here... >>> >>> I was thinking of /proc. Opening your own /proc/$$/* would certainly be >>> considered OK. But, doing it for some other process not in your pid >>> namespace would not be OK and would not be checkpointable. >>> >>> I know we're not quite in real-life territory here, yet, but I'm still >>> thinking. >> That mighr be a good enough excuse, I was just wondering what the use >> case was. > > I just thought of another one: unlinked files and directories. They're > a pain to checkpoint and won't be supported for a while. Holding open > an unlinked file would make a process uncheckpointable for a bit. Actually, unlinked directories are the easiest to restore: you recreate it, open it, and then immediately delete them. This works, because an unlinked directory does not hold any data except for its existence. For unlinked files, in physical file systems (non pseudo), for many apps they are small in size, so a first approximation would be to save the contents of that file with the checkpoint image, and on restart recreate the file, put the contents, open it, and then unlink it again. Oren. > > -- Dave > > _______________________________________________ > Containers mailing list > Containers@lists.linux-foundation.org > https://lists.linux-foundation.org/mailman/listinfo/containers > -- 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/