From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753553AbZBQWbb (ORCPT ); Tue, 17 Feb 2009 17:31:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753803AbZBQWbB (ORCPT ); Tue, 17 Feb 2009 17:31:01 -0500 Received: from e32.co.us.ibm.com ([32.97.110.150]:50219 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753464AbZBQWa4 (ORCPT ); Tue, 17 Feb 2009 17:30:56 -0500 Subject: Re: What can OpenVZ do? From: Dave Hansen To: Ingo Molnar Cc: Andrew Morton , linux-api@vger.kernel.org, containers@lists.linux-foundation.org, hpa@zytor.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, viro@zeniv.linux.org.uk, mpm@selenic.com, tglx@linutronix.de, torvalds@linux-foundation.org, xemul@openvz.org, Nathan Lynch In-Reply-To: <20090217222319.GA10546@elte.hu> References: <1233076092-8660-1-git-send-email-orenl@cs.columbia.edu> <1234285547.30155.6.camel@nimitz> <20090211141434.dfa1d079.akpm@linux-foundation.org> <1234462282.30155.171.camel@nimitz> <1234467035.3243.538.camel@calx> <20090212114207.e1c2de82.akpm@linux-foundation.org> <1234475483.30155.194.camel@nimitz> <20090212141014.2cd3d54d.akpm@linux-foundation.org> <20090213105302.GC4608@elte.hu> <1234817490.30155.287.camel@nimitz> <20090217222319.GA10546@elte.hu> Content-Type: text/plain Date: Tue, 17 Feb 2009 14:30:49 -0800 Message-Id: <1234909849.4816.9.camel@nimitz> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2009-02-17 at 23:23 +0100, Ingo Molnar wrote: > * Dave Hansen wrote: > > On Fri, 2009-02-13 at 11:53 +0100, Ingo Molnar wrote: > > > In any case, by designing checkpointing to reuse the existing LSM > > > callbacks, we'd hit multiple birds with the same stone. (One of > > > which is the constant complaints about the runtime costs of the LSM > > > callbacks - with checkpointing we get an independent, non-security > > > user of the facility which is a nice touch.) > > > > There's a fundamental problem with using LSM that I'm seeing > > now that I look at using it for file descriptors. The LSM > > hooks are there to say, "No, you can't do this" and abort > > whatever kernel operation was going on. That's good for > > detecting when we do something that's "bad" for checkpointing. > > > > *But* it completely falls on its face when we want to find out > > when we are doing things that are *good*. For instance, let's > > say that we open a network socket. The LSM hook sees it and > > marks us as uncheckpointable. What about when we close it? > > We've become checkpointable again. But, there's no LSM hook > > for the close side because we don't currently have a need for > > it. > > Uncheckpointable should be a one-way flag anyway. We want this > to become usable, so uncheckpointable functionality should be as > painful as possible, to make sure it's getting fixed ... Again, as these patches stand, we don't support checkpointing when non-simple files are opened. Basically, if a open()/lseek() pair won't get you back where you were, we don't deal with them. init does non-checkpointable things. If the flag is a one-way trip, we'll never be able to checkpoint because we'll always inherit init's ! checkpointable flag. To fix this, we could start working on making sure we can checkpoint init, but that's practically worthless. -- Dave