* Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> 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 from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
