Port forwarding to a running QEMU VM

If you are running a QEMU VM with -qmp (QEMU Machine Protocol), then you can add port-forwarding to it while running as follows:

echo '{ "execute": "qmp_capabilities" }
{ "execute": "human-monitor-command", "arguments": { "command-line": "hostfwd_add tcp::2222-:22" } }' \
  | socat - UNIX-CONNECT:/path/to/qmp.sock