[$] One more pidfdfs surprise
The "pidfdfs" virtual filesystem was added to the 6.9 kernel release as a
way to export better information about running processes to user space. It
replaced a previous implementation in a way that was, on its surface, fully
compatible while adding a number of new capabilities. This transition,
which was intended to be entirely invisible to existing applications,
already ran into trouble in March, when a
misunderstanding with SELinux caused systems with pidfdfs to fail to boot
properly. That problem was quickly fixed, but it turns out that there was
one more surprise in store, showing just how hard ABI compatibility can be
at times.