readme: guest to host networking

README.adoc

@@ -1553,6 +1553,42 @@ Seems possible! Lets do it:
 * http://gem5.org/wiki/images/b/b8/Summit2017_wa_devlib.pdf
 * http://gem5.org/WA-gem5
 
+=== Guest host networking
+
+==== Host to guest
+
+Guest, BusyBox `nc` enabled with `CONFIG_NC=y`:
+
+....
+nc -l -p 45455
+....
+
+Host, `nc` from the `netcat-openbsd` package:
+
+....
+echo asdf | nc localhost 45455
+....
+
+Then `asdf` appears on the guest.
+
+Only this specific port works by default since we have forwarded it on the QEMU command line.
+
+We us this exact procedure to connect to <<gdbserver>>.
+
+==== Guest to host
+
+TODO. There is `guestfwd`, which sounds analogous to `hostwfd` used in the other sense, but I was not able to get it working, e.g.:
+
+....
+-netdev user,hostfwd=tcp::45455-:45455,guestfwd=tcp::45456-,id=net0 \
+....
+
+gives:
+
+....
+Could not open guest forwarding device 'guestfwd.tcp.45456'
+....
+
 === QEMU user mode
 
 This has nothing to do with the Linux kernel, but it is cool:
@@ -2766,7 +2802,7 @@ Build time: 2 hours.
 
 TODO specs, SHA.
 
-===== Benchmark internets
+===== Benchmark Internets
 
 ====== 38Mbps