[$] BPF and io_uring, two different ways

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