[$] Generalized events notification and security policies

Interfaces for the reporting of events to user space from the kernel havebeen a recurring topic on the kernel mailing lists for almost as long asthe kernel has existed; LWN covered one 15years ago, for example. Numerous special-purpose event-reporting APIsexist, but there are none that are designed to be a single place toobtain any type of event. David Howells is the latest to attempt to changethat situation with anew notification interface that, naturally, uses a ring buffer totransfer events to user space without the need to make system calls. TheAPI itself (which hasn't changed greatly since it was posted in 2018) is not hugely controversial,but the associated security model has inspired a few heated discussions.