Boots into initramfs then switch_root

initramfs/rootfs-extra/init

@@ -1,24 +1,114 @@
 #!/bin/sh
+set -eu
 
-mount -t devtmpfs devtmpfs /dev
-mount -t proc proc /proc
-mount -t sysfs sysfs /sys
+log() {
+    echo "[init] $*" >&2
+}
 
-# Spin the fan
-echo 100 > /sys/class/hwmon/hwmon0/pwm1
+panic() {
+    echo "initramfs panic: $*" >&2
+    exec sh
+}
+
+mount_or_panic() {
+    mount "$@" || panic "mount failed: $*"
+}
+
+mount_retry() {
+    dev="$1"
+    target="$2"
+    fstype="$3"
+    opts="$4"
+
+    i=0
+    while :; do
+        if mount -o "$opts" -t "$fstype" "$dev" "$target"; then
+            return 0
+        fi
+
+        i=$((i + 1))
+        [ "$i" -ge 50 ] && panic "Timed out mounting $dev on $target"
+        sleep 0.2
+    done
+}
+
+wait_for_path() {
+    path="$1"
+    i=0
+    while [ ! -e "$path" ]; do
+        i=$((i + 1))
+        [ "$i" -ge 50 ] && panic "Timed out waiting for $path"
+        sleep 0.2
+    done
+}
+
+mkdir -p /dev /proc /sys /run
+mount_or_panic -t devtmpfs devtmpfs /dev
+mount_or_panic -t proc proc /proc
+mount_or_panic -t sysfs sysfs /sys
+mount_or_panic -t tmpfs tmpfs /run
+
+echo 1 > /proc/sys/kernel/printk
 
-# Optional but nice
 mkdir -p /dev/pts
-mount -t devpts devpts /dev/pts
+mount_or_panic -t devpts devpts /dev/pts
 
-echo "Booting kernel took $(cut -d' ' -f1 /proc/uptime) seconds."
-echo "Dropping to shell on ttyS0..."
+# Optional early fan kick. Do not fail boot if this path is not ready yet.
+if [ -w /sys/class/hwmon/hwmon0/pwm1 ]; then
+    echo 100 > /sys/class/hwmon/hwmon0/pwm1 || true
+fi
 
-. /etc/build-info
+log "Booting kernel took $(cut -d' ' -f1 /proc/uptime) seconds."
 
-while true; do
-    setsid cttyhack /bin/sh
-    echo "Shell exited. Starting another one..."
+. /etc/build-info || panic "failed to source /etc/build-info"
+
+ROOT_DEV=""
+DATA_DEV=""
+
+for arg in $(cat /proc/cmdline); do
+    case "$arg" in
+        root=*)
+            ROOT_DEV="${arg#root=}"
+            ;;
+        data=*)
+            DATA_DEV="${arg#data=}"
+            ;;
+    esac
 done
 
-exec poweroff -f
+[ -n "$ROOT_DEV" ] || {
+    log "No root= specified in cmdline"
+    exec sh
+}
+
+[ -n "$DATA_DEV" ] || {
+    log "No data= specified in cmdline"
+    exec sh
+}
+
+wait_for_path "$DATA_DEV"
+
+e2fsck -p "$DATA_DEV" || {
+    echo "Auto fsck failed, forcing repair"
+    e2fsck -y "$DATA_DEV" || panic "fsck failed on $DATA_DEV"
+}
+
+mkdir -p /newroot
+mount_retry "$ROOT_DEV" /newroot ext4 ro
+mount_retry "$DATA_DEV" /newroot/data ext4 rw
+
+mount_or_panic --bind /newroot/data/var /newroot/var
+
+mount_or_panic -t overlay overlay \
+    -o lowerdir=/newroot/etc,upperdir=/newroot/data/etc-overlay/upper,workdir=/newroot/data/etc-overlay/work \
+    /newroot/etc
+
+mount_or_panic --move /dev /newroot/dev
+mount_or_panic --move /proc /newroot/proc
+mount_or_panic --move /sys /newroot/sys
+mount_or_panic --move /run /newroot/run
+
+log "Switching root to $ROOT_DEV"
+exec switch_root /newroot /sbin/init
+
+panic "switch_root returned unexpectedly"