[$] BPF and io_uring, two different ways

BPF allows programs uploaded from user space to be run, safely, within the
kernel. The io_uring subsystem, too, can be thought of as a way of loading
programs in the kernel, though the programs in question are mostly a
sequence of I/O-related system calls. It has sometimes seemed inevitable
that io_uring would, like many other parts of the kernel, gain BPF
capabilities as a way of providing more flexibility to user space. That
has not yet happened, but there are currently two patches sets under
consideration that take different approaches to the problem.