init: disable all userland processes started from init

In order to make the system easier to understand.

These include:

* networking
* klogd and syslogd. TODO what are those for? I could not see anything useful that they do.

Also get rid of the useless S20random thing while we are at it.

README.adoc

@@ -846,7 +846,9 @@ But TODO I don't think you can see where you are in the kernel source code and l
 
 Step debug userland processes to understand how they are talking to the kernel.
 
-In guest:
+First ensure that <<networking>> is enabled.
+
+Then in guest:
 
 ....
 /gdbserver.sh /myinsmod.out /hello.ko
@@ -1138,16 +1140,38 @@ Finally, the docs are lying, arguments with dots that come after `-` are still t
 ./run -e 'init=/init_env_poweroff.sh - /poweroff.out'
 ....
 
-=== Disable networking
+=== Networking
 
-The default BusyBox init scripts enable networking, and there is a 15 second timeout in case your network is down or if your kernel / emulator setup does not support it.
+We disable networking by default because it starts an userland process, and we want to keep the number of userland processes to a minimum to make the system more understandable.
 
-We have hacked it up so that you can disable networking with:
+To enable it run:
 
 ....
-./run -f 'lkmc_nonet=y'
+/sbin/ifup -a
 ....
 
+To disable it, run:
+
+....
+/sbin/ifdown -a
+....
+
+To test it out, try:
+
+....
+wget google.com
+....
+
+BusyBox' `ping` does not work with hostnames even when networking is working fine:
+
+....
+ping google.com
+....
+
+TODO why: https://unix.stackexchange.com/questions/124283/busybox-ping-ip-works-but-hostname-nslookup-fails-with-bad-address
+
+To enable networking by default, use the methods documented at <<automatic-startup-commands>>
+
 == KVM
 
 You can make QEMU or gem5 <<gem5-vs-qemu-performance,run faster>> by passing enabling KVM with:
@@ -1864,6 +1888,8 @@ Even mor awesome than `chroot` be to `pivot_root`, but I couldn't get that worki
 
 === Guest host networking
 
+First ensure that networking is enabled before trying out anything in this section: <<networking>>
+
 ==== Host to guest networking
 
 Guest, BusyBox `nc` enabled with `CONFIG_NC=y`:

rootfs_overlay/etc/init.d/S40network

@@ -1,44 +0,0 @@
-#!/bin/sh
-
-# Copied from: package/ifupdown-scripts/S40network at
-# 8ce27bb9fee80a406a4199657ef90e3c315e7457
-#
-# We then just added this line to turn it off at runtime.
-#
-# We also considered copying the file at build to / and then
-# sourcing it from S98 to be a bit DRYer, but it wouldn't work
-# very well if some S50 requires networking to work.
-#
-# This became necessary nitially when aarch64 qemu and gem5
-# started using the same Buildroot output directory.
-[ -n "$lkmc_nonet" ] && exit 0
-
-#
-# Start the network....
-#
-
-# Debian ifupdown needs the /run/network lock directory
-mkdir -p /run/network
-
-case "$1" in
-  start)
-	printf "Starting network: "
-	/sbin/ifup -a
-	[ $? = 0 ] && echo "OK" || echo "FAIL"
-	;;
-  stop)
-	printf "Stopping network: "
-	/sbin/ifdown -a
-	[ $? = 0 ] && echo "OK" || echo "FAIL"
-	;;
-  restart|reload)
-	"$0" stop
-	"$0" start
-	;;
-  *)
-	echo "Usage: $0 {start|stop|restart}"
-	exit 1
-esac
-
-exit $?
-

rootfs_overlay/rand_check_poweroff.sh

@@ -3,16 +3,8 @@ set -ex
 /rand_check.out
 
 # Check if network is being replayed.
-#
-# TODO; requires internet to be up, which is done by inittab.
-# We could do this with a /etc/init.d/SXX file,
-# but how to both check that into git, and make it optional?
-#
 # https://superuser.com/questions/635020/how-to-know-current-time-from-internet-from-command-line-in-linux
-# Raw IP because was failing with hostname:
-# https://unix.stackexchange.com/questions/124283/busybox-ping-ip-works-but-hostname-nslookup-fails-with-bad-address
 # https://tf.nist.gov/tf-cgi/servers.cgi
-#
 #echo | nc 129.6.15.28 13
 
 # busybox's poweroff panics, TODO why. Likely tries to kill shell.

rootfs_post_build_script

@@ -9,3 +9,10 @@ mkdir -p \
   "${target_dir}/mnt/9p" \
   "${target_dir}/mnt/out" \
 ;
+# Maybe there is a cleaner way to get rid of those files,
+# like disabling some Buildroot packages, but no patience.
+rm -rf \
+  "${target_dir}/etc/init.d/S01logging" \
+  "${target_dir}/etc/init.d/S20urandom" \
+  "${target_dir}/etc/init.d/S40network" \
+;

run

@@ -108,9 +108,6 @@ if "$nographic" && [ "$arch" = x86_64 ]; then
   extra_append="$extra_append console=ttyS0"
   extra_flags_qemu="$extra_flags_qemu -nographic"
 fi
-if "$gem5"; then
-  extra_append_after_dash="${extra_append_after_dash} lkmc_nonet=y"
-fi
 if [ -n "$extra_append_after_dash" ]; then
   extra_append="${extra_append} - ${extra_append_after_dash}"
 fi

run-usage.adoc

@@ -23,7 +23,7 @@
                               add a dash `-` separator, and place the options after the dash.
                               Intended for custom options understood by our `init` scripts,
                               most of which are prefixed by `lkmc_`, e.g.:
-                              `./run -f 'lkmc_eval="wget google.com" lkmc_nonet=y'`
+                              `./run -f 'lkmc_eval="wget google.com" lkmc_lala=y'`
                               Mnenomic: comes after `-e`.
 |`-G` |                     | Pass extra options to the gem5 executable.
                               Only useful if `-g` is given.