From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755541AbYHKXX0 (ORCPT ); Mon, 11 Aug 2008 19:23:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752243AbYHKXXS (ORCPT ); Mon, 11 Aug 2008 19:23:18 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:49892 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751826AbYHKXXR (ORCPT ); Mon, 11 Aug 2008 19:23:17 -0400 Subject: Re: checkpoint/restart ABI From: Dave Hansen To: Jonathan Corbet Cc: Arnd Bergmann , "Serge E. Hallyn" , containers@lists.linux-foundation.org, Theodore Tso , linux-kernel@vger.kernel.org In-Reply-To: <20080811171433.2ce81f28@bike.lwn.net> References: <20080807224033.FFB3A2C1@kernel> <200808111853.13854.arnd@arndb.de> <1218484114.5598.43.camel@nimitz> <200808112347.50245.arnd@arndb.de> <20080811171433.2ce81f28@bike.lwn.net> Content-Type: text/plain Date: Mon, 11 Aug 2008 16:23:14 -0700 Message-Id: <1218496994.5598.50.camel@nimitz> Mime-Version: 1.0 X-Mailer: Evolution 2.22.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2008-08-11 at 17:14 -0600, Jonathan Corbet wrote: > On Mon, 11 Aug 2008 23:47:49 +0200 > Arnd Bergmann wrote: > > > The other problem that you really need to solve is interface > > stability. What you are creating is a binary representation > > of many kernel internal data structures, so in our common > > rules, you have to make sure that you remain forward and > > backward compatible. Simply saying that you need to run > > an identical kernel when restarting from a checkpoint is not > > enough IMHO. > > OTOH, making one of these checkpoint files go into any 2.6.x kernel > seems like a very high bar, to the point, perhaps, of killing this > feature entirely. The OpenVZ dudes like refer to something that Andrew Morton said about this (paraphrasing...): if we need cross-version restore support, we can count on userspace to do the conversion. You can almost think of it like the crashdump processing utility that we have. Instead of worrying about having the kernel *always* produce the same crashdump with the same gunk in it, we make userspace do all the parsing and interpretation. It also makes it quite possible for a distribution to make a change (say because of a security fix) in the kernel that changes the checkpoint format, then to quickly code up the necessary bits for the conversion program. -- Dave