[$] Generalized events notification and security policies

Interfaces for the reporting of events to user space from the kernel have
been a recurring topic on the kernel mailing lists for almost as long as
the kernel has existed; LWN covered one 15
years ago, for example. Numerous special-purpose event-reporting APIs
exist, but there are none that are designed to be a single place to
obtain any type of event. David Howells is the latest to attempt to change
that situation with a
new notification interface that, naturally, uses a ring buffer to
transfer events to user space without the need to make system calls. The
API 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.