bpf: create samples/bpf/tcp_bpf.readme

This file describes how to run the tcp_*_kern.o tcp_bpf (or socket_ops)

programs. These programs attach to a cgroupv2. The following commands create

a cgroupv2 and attach a bash shell to the group.

  mkdir -p /tmp/cgroupv2

  mount -t cgroup2 none /tmp/cgroupv2

  mkdir -p /tmp/cgroupv2/foo

  bash

  echo $$ >> /tmp/cgroupv2/foo/cgroup.procs

Anything that runs under this shell belongs to the foo cgroupv2 To load

(attach) one of the tcp_*_kern.o programs:

  ./load_sock_ops -l /tmp/cgroupv2/foo tcp_basertt_kern.o

If the "-l" flag is used, the load_sock_ops program will continue to run

printing the BPF log buffer. The tcp_*_kern.o programs use special print

functions to print logging information (if enabled by the ifdef).

If using netperf/netserver to create traffic, you need to run them under the

cgroupv2 to which the BPF programs are attached (i.e. under bash shell

attached to the cgroupv2).

To remove (unattach) a socket_ops BPF program from a cgroupv2:

  ./load_sock_ops -r /tmp/cgroupv2/foo