added virtio post

1 files changed, 90 insertions, 0 deletions

diff --git a/content/2021-12-02-toying-with-virtio/build_initramfs.sh b/content/2021-12-02-toying-with-virtio/build_initramfs.sh
new file mode 100755
index 0000000..c30fa5e
--- /dev/null
+++ b/content/2021-12-02-toying-with-virtio/build_initramfs.sh
@@ -0,0 +1,90 @@
+#!/bin/bash
+
+set -e
+
+BUSYBOX=busybox-1.34.1
+INITRAMFS=$PWD/initramfs.cpio.gz
+
+## Build busybox (static).
+
+test -f $BUSYBOX.tar.bz2 || wget -nc https://busybox.net/downloads/$BUSYBOX.tar.bz2
+test -d $BUSYBOX || tar xf $BUSYBOX.tar.bz2
+
+cd $BUSYBOX
+make defconfig
+sed -i 's/[# ]*CONFIG_STATIC[ =].*/CONFIG_STATIC=y/' .config
+make -j$(nproc) busybox
+make install
+
+## Create initramfs.
+
+cd _install
+
+# 1. Create initramfs folder structure.
+
+mkdir -p bin sbin etc/init.d proc sys usr/bin usr/sbin dev mnt
+
+# 2. Prepare init.
+
+# By default, initramfs executes /init.
+# Optionally change with rdinit= kernel parameter.
+ln -sfn sbin/init init
+
+cat <<EOF > etc/inittab
+# Initialization after boot.
+::sysinit:/etc/init.d/rcS
+
+# Shell on console after user presses key.
+::askfirst:/bin/cttyhack /bin/sh -l
+
+# Spawn getty on first virtio console.
+::respawn:/sbin/getty hvc0 9600 vt100
+EOF
+
+cat <<EOF > etc/init.d/rcS
+#!/bin/sh
+
+# Mount devtmpfs, which automatically populates /dev with devices nodes.
+# So no mknod for our experiments :}
+mount -t devtmpfs none /dev
+
+# Mount procfs and sysfs.
+mount -t proc none /proc
+mount -t sysfs none /sys
+
+# Set hostname.
+hostname virtio-box
+EOF
+chmod +x etc/init.d/rcS
+
+cat <<EOF > etc/profile
+export PS1="\[\e[31m\e[1m\]\u@\h\[\e[0m\] \w # "
+EOF
+
+# 3. Create minimal passwd db with 'root' user and password '1234'.
+#    Mainly used for login on virtual console in this experiments.
+echo "root:x:0:0:root:/:/bin/sh" > etc/passwd
+echo "root:$(openssl passwd -crypt 1234):0::::::" > etc/shadow
+
+# 4. Create minimal setup for basic networking.
+
+# Virtul DNS from qemu user network.
+echo "nameserver 10.0.2.3" > etc/resolv.conf
+
+# Assign static IP address, bring-up interface and define default route.
+cat <<EOF >> etc/init.d/rcS
+# Assign static IP address to eth0 interface.
+ip addr add 10.0.2.15/24 dev eth0
+
+# Bring up eth0 interface.
+ip link set dev eth0 up
+
+# Add default route via the host (qemu user networking exposes host at this
+# address by default).
+ip route add default via 10.0.2.2
+EOF
+
+# 5. Created cpio compressed initramfs.
+find . -print0                      \
+    | cpio --null -ov --format=newc \
+    | gzip -9 > $INITRAMFS