I know what BPF is. You are missing the point. I have enough work to not want to have to learn what new little specific twist SystemD that goes the other direction of everyone else has made in its latest release. While is the 'old ways' are HEAVILY documented on thousands of sites and new feature X has barely a half-page documentation.

I've spent a whole week trying to figure out why I had filesystem permission issue on chmod syscall and not on fchmodat. The culprit was SystemD trying to be clever with namespacing which could have been fine if the reported error was semantically correct. It gets in the way provokes untrackable issues.

And yes, namespace is a kernel tool. But it's SystemD that sets it up ...

Edit: tipo and clarification