Re: [PATCH 3/3] eventfd: add internal reference counting to fix notifier race conditions

Rusty Russell
2009-06-24T03:26:04Z

On Tue, 23 Jun 2009 03:33:22 am Davide Libenzi wrote:
> What you're doing there, is setting up a kernel-to-kernel (since
> userspace only role is to create the eventfd) communication, using a file*
> as accessory. That IMO is plain wrong.

The most sensible is that userspace can use these fds; an in-kernel variant is
possible too, but not primary IMHO.

It's nice that userspace create the fds; it can then use the same fd for
multiple event sources.

But I didn't see anything wrong with the way eventfd used to work: you have a
kvm ioctl to say "attach this eventfd to this guest notification" and that does
the eventfd_fget. A detach ioctl does the fput (as does release of the kvm
fd).

If they close the eventfd and don't do the detach ioctl, it's their problem.

Rusty.