[$] Magic kernel functions for BPF

When programs written in BPF (the kernel's hot-loadable virtual-machine
bytecode) call kernel functions (kfuncs), it may be useful
for those functions to have additional information about the context in which
those BPF programs are executing. Rather than requiring it to supply
that information, it would be convenient to let the BPF verifier pass that
information to the called function automatically. That is already possible, but

a recent patch set from Ihor Solodrai would make it more ergonomic.
It allows kernel
developers to specify that a kfunc should be passed additional
parameters inferred by the verifier, invisibly to the BPF program. The
discussion included concerns that Solodrai's implementation was unnecessarily
complex, however.