This adds support for epoll manipulation through io_uring, in particular epoll_ctl(2). Patch 1 is just a prep patch, patch 2 adds non-block support for epoll, and patch 3 wires it up for io_uring. Patch 2 isn't the prettiest thing in the world, but we need to do nonblock grabbing of the mutexes and be able to back out safely. Please review, thanks. -- Jens Axboe
