bpf-sockmap uses BPF_PROG_TYPE_SK_SKB BPF programs to create a simple telnet echo server. It is heavily inspired by the Cloudflare blog.
Vagrant can be used to spin up a virtual environment to test the BPF programs. The environment depends on VirtualBox but other providers exist.
$ vagrant plugin install vagrant-reload
$ vagrant box list | grep ubuntu/bionic64 || vagrant box add ubuntu/bionic64
$ vagrant up
$ vagrant ssh
# we are assuming commands are run from within the vagrant vm from here
$ cd /vagrant
$ make build
$ make run
...
2019/04/03 00:53:12 listening on address: 0.0.0.0:12345
# in another terminal watch debug output
$ sudo cat /sys/kernel/debug/tracing/trace_pipe
# in yet another terminal start a telnet session
$ telnet 127.0.0.1 12345
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
Hello!
Hello!
Bye
Bye
^]q
telnet> q
Connection closed.
The generated object file can be inspected using llvm-objdump
llvm-objdump -S ./bpf/bpf_sockmap.o