From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: What can OpenVZ do? Date: Tue, 17 Feb 2009 23:23:19 +0100 Message-ID: <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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1234817490.30155.287.camel@nimitz> Sender: owner-linux-mm@kvack.org To: Dave Hansen 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 List-Id: linux-api@vger.kernel.org * 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 ... > We have a couple of options: > > We can let uncheckpointable actions behave like security > violations and just abort the kernel calls. The problem with > this is that it makes it difficult to do *anything* unless > your application is 100% supported. Pretty inconvenient, > especially at first. Might be useful later on though. It still beats "no checkpointing support at all in the upstream kernel", by a wide merging. If an app fails, the more reasons to bring checkpointing support up to production quality? We dont want to make the 'interim' state _too_ convenient, because it will quickly turn into the status quo. Really, the LSM approach seems to be the right approach here. It keeps maintenance costs very low - there's no widespread BKL-style flaggery. Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org