Hey again, On Tue, Mar 01, 2022 at 04:42:47PM +0100, Jason A. Donenfeld wrote: > For (B), it's a little bit trickier. But I think our options follow the > same rubric. We can expose a generation counter in the vDSO, with > semantics akin to the extern integer I described above. Or we could > expose that counter in a file that userspace could poll() on and receive > notifications that way. Or perhaps a third way. I'm all ears here. > Alex's team from Amazon last year proposed something similar to the vDSO > idea, except using mmap on a sysfs file, though from what I can tell, > that wound up being kind of complicated. Due to the fact that we're > _already_ racy, I think I'm most inclined at this point toward the > poll() approach for the same reasons as I prefer a notifier_block. But > on userspace I could be convinced otherwise, and I'd be interested in > totally different ideas here too. I implemented the poll() case here in 15 lines of code and found it remarkably simple to do: https://lore.kernel.org/lkml/20220302143331.654426-1-Jason@xxxxxxxxx/ This is just a PoC/RFC for the sake of having something tangible to look at for this thread. It is notable to me, though, that implementing this was so minimal. Regards, Jason
