From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Subject: Re: What can OpenVZ do? Date: Tue, 17 Feb 2009 14:30:49 -0800 Message-ID: <1234909849.4816.9.camel@nimitz> 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> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20090217222319.GA10546-X9Un+BFzKDI@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Ingo Molnar Cc: Andrew Morton , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org, mpm-VDJrAJ4Gl5ZBDgjK7y7TUQ@public.gmane.org, tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org, torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, Nathan Lynch List-Id: linux-api@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 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html