From 73c6306075ada9c4cfbf5da57c57c2bb15e29497 Mon Sep 17 00:00:00 2001
From: Kyle Harding <kyle@balena.io>
Date: Thu, 12 Oct 2023 15:46:26 -0400
Subject: [PATCH] Use kernel command line to initialize network

Change-type: patch
Signed-off-by: Kyle Harding <kyle@balena.io>
---
 README.md         |  2 --
 overlay/sbin/init | 22 -----------------
 start.sh          | 60 +++++++++++++++++++++++++++++++----------------
 3 files changed, 40 insertions(+), 44 deletions(-)

diff --git a/README.md b/README.md
index 35ebc26..09fb14d 100644
--- a/README.md
+++ b/README.md
@@ -50,9 +50,7 @@ Guest containers based on Alpine, Debian, and Ubuntu have been tested and must h
 available from a shell.
 
 - `sh`
-- `ip` via `iproute2`
 - `mount`
-- `awk`
 
 Distroless containers are not expected to work as the kernel init binary is a shell script.
 
diff --git a/overlay/sbin/init b/overlay/sbin/init
index 401d521..b06d13e 100644
--- a/overlay/sbin/init
+++ b/overlay/sbin/init
@@ -24,28 +24,6 @@ if ! mountpoint -q /run; then
   mount -t tmpfs none /run
 fi
 
-# rngd -b
-
-# The IP is assigned by converting the last 4 hexa groups of the MAC into decimals.
-# https://github.com/firecracker-microvm/firecracker/blob/main/resources/overlay/usr/local/bin/fcnet-setup.sh
-for dev in $(ip link list | awk /'^[0-9]+:/ {print $2}' | sed 's/://'); do
-    dev="$(basename "$dev")"
-    case $dev in
-    *lo) continue ;;
-    esac
-    for octet in $(
-        ip link show dev "$dev" |
-            awk '/link\/ether/ {print $2}' |
-            awk -F: '{print $3" "$4" "$5" "$6}'
-    ); do
-        ip=$ip$(printf "%d" 0x"$octet").
-    done
-    ip=${ip%?}
-    ip addr add "$ip/30" dev "$dev"
-    ip link set "$dev" up
-    ip route add default via "${ip%?}1" dev "$dev"
-done
-
 set +a
 # shellcheck disable=SC1091
 . /etc/profile || true
diff --git a/start.sh b/start.sh
index 34b4072..721db9c 100644
--- a/start.sh
+++ b/start.sh
@@ -99,7 +99,8 @@ generate_config() {
     jq ".\"machine-config\".mem_size_mib = ${MEM_SIZE_MIB}" "${_dst_config}" >"${_dst_config}".tmp
     mv "${_dst_config}".tmp "${_dst_config}"
 
-    jq ".\"network-interfaces\"[0].iface_id = \"${GUEST_IFACE}\"" "${_dst_config}" >"${_dst_config}".tmp
+    # It doesn't seem to matter what we call this interface, it always shows up as 'eth0' in the guest
+    jq ".\"network-interfaces\"[0].iface_id = \"net0\"" "${_dst_config}" >"${_dst_config}".tmp
     mv "${_dst_config}".tmp "${_dst_config}"
 
     jq ".\"network-interfaces\"[0].guest_mac = \"${GUEST_MAC}\"" "${_dst_config}" >"${_dst_config}".tmp
@@ -153,6 +154,23 @@ normalize_cidr() {
     echo "${_address}/${_short_netmask}"
 }
 
+network_config() {
+    local _client_ip="${1}"
+    local _server_ip=""
+    local _gw_ip="${2}"
+    local _netmask
+    local _hostname="${3:-${HOSTNAME}}"
+    local _device="${4:-eth0}"
+    local _autoconf=off
+
+    # normalize addresses to remove cidr suffix
+    _client_ip="$(ipcalc -nb "${_client_ip}" | awk '/^Address:/ {print $2}')"
+    _gw_ip="$(ipcalc -nb "${_gw_ip}" | awk '/^Address:/ {print $2}')"
+    _netmask="$(ipcalc -nb "${_client_ip}" | awk '/^Netmask:/ {print $2}')"
+
+    echo "ip=${_client_ip}:${_server_ip}:${_gw_ip}:${_netmask}:${_hostname}:${_device}:${_autoconf}"
+}
+
 ip_to_mac() {
     # shellcheck disable=SC2183,SC2046
     printf '52:54:%02X:%02X:%02X:%02X\n' $(echo "${1}" | tr '.' ' ')
@@ -226,22 +244,10 @@ if [ -z "${DATAFS_SIZE:-}" ]; then
     DATAFS_SIZE=$(df -Ph . | tail -1 | awk '{print $4}')
 fi
 
-if [ -z "${KERNEL_BOOT_ARGS:-}" ]; then
-    KERNEL_BOOT_ARGS="console=ttyS0 reboot=k panic=1 pci=off random.trust_cpu=on"
-
-    if [ "$(uname -m)" = "aarch64" ]; then
-        KERNEL_BOOT_ARGS="keep_bootcon ${KERNEL_BOOT_ARGS}"
-    fi
-fi
-
 if [ -z "${HOST_IFACE:-}" ]; then
     HOST_IFACE="$(ip route | awk '/default/ {print $5}')"
 fi
 
-if [ -z "${GUEST_IFACE:-}" ]; then
-    GUEST_IFACE="net0"
-fi
-
 if [ -z "${TAP_IP:-}" ]; then
     # generate random number between 1 and 254
     TAP_IP=10.$((1 + RANDOM % 254)).$((1 + RANDOM % 254)).1/30
@@ -249,27 +255,41 @@ fi
 
 TAP_IP="$(normalize_cidr "${TAP_IP}")"
 
+if [ -z "${GUEST_IP:-}" ]; then
+    # the default guest IP is the TAP IP + 1
+    GUEST_IP="$(echo "${TAP_IP}" | awk -F'[./]' '{print $1"."$2"."$3"."$4+1}')"
+fi
+
 if [ -z "${TAP_DEVICE:-}" ]; then
     # must be less than 16 characters
     TAP_DEVICE="$(echo "${TAP_IP}" | awk -F'[./]' '{print "tap-"$1"-"$2"-"$3}')"
 fi
 
 if [ -z "${GUEST_MAC:-}" ]; then
-    # Guest MAC is '52:54' followed by the first 3 octets of the TAP IP,
-    # followed by the last octet of the TAP IP incremented by 1.
-    GUEST_MAC="$(ip_to_mac "$(echo "${TAP_IP}" | awk -F'[./]' '{print $1"."$2"."$3"."$4+1}')")"
+    # guest MAC is '52:54' followed by the hex encoded guest IP octets
+    GUEST_MAC="$(ip_to_mac "${GUEST_IP}")"
 fi
 
-echo "VCPUs: ${VCPU_COUNT}"
+if [ -z "${KERNEL_BOOT_ARGS:-}" ]; then
+    KERNEL_BOOT_ARGS="console=ttyS0 reboot=k panic=1 pci=off random.trust_cpu=on"
+
+    if [ "$(uname -m)" = "aarch64" ]; then
+        KERNEL_BOOT_ARGS="keep_bootcon ${KERNEL_BOOT_ARGS}"
+    fi
+fi
+
+KERNEL_BOOT_ARGS="${KERNEL_BOOT_ARGS} $(network_config "${GUEST_IP}" "${TAP_IP}" "$(hostname)" eth0)"
+
+echo "Virtual CPUs: ${VCPU_COUNT}"
 echo "Memory: ${MEM_SIZE_MIB}M"
 echo "Root Drive (vda): ${ROOTFS_SIZE}"
 echo "Data Drive (vdb): ${DATAFS_SIZE}"
-echo "Kernel boot args: ${KERNEL_BOOT_ARGS}"
 echo "Host Interface: ${HOST_IFACE}"
-echo "Guest Interface: ${GUEST_IFACE}"
-echo "TAP Device ID: ${TAP_DEVICE}"
+echo "TAP Device: ${TAP_DEVICE}"
 echo "TAP IP Address: ${TAP_IP}"
+echo "Guest IP Address: ${GUEST_IP}"
 echo "Guest MAC Address: ${GUEST_MAC}"
+echo "Kernel Boot Args: ${KERNEL_BOOT_ARGS}"
 
 trap cleanup EXIT