On Tue, 2009-02-17 at 23:23 +0100, Ingo Molnar wrote: > * 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 ... 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@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
