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#!/bin/sh
# SPDX-FileCopyrightText: Copyright (C) 2025 Bruce Ashfield
#
# SPDX-License-Identifier: GPL-2.0-only
#
# vcontainer-preinit.sh
# Minimal init for initramfs - mounts rootfs and does switch_root
#
# This script runs from the initramfs and:
# 1. Mounts essential filesystems
# 2. Finds and mounts the rootfs.img (squashfs, read-only)
# 3. Creates overlayfs with tmpfs for writes
# 4. Executes switch_root to the overlay root filesystem
#
# The real init (/init or /sbin/init on rootfs) then continues boot
# Mount essential filesystems first (needed to check cmdline)
mount -t proc proc /proc
mount -t sysfs sysfs /sys
mount -t devtmpfs devtmpfs /dev
# Check for quiet mode (interactive)
QUIET=0
for param in $(cat /proc/cmdline 2>/dev/null); do
case "$param" in
docker_interactive=1) QUIET=1 ;;
esac
done
log() {
[ "$QUIET" = "0" ] && echo "$@"
}
log "=== vcontainer preinit (squashfs) ==="
# Wait for block devices to appear
log "Waiting for block devices..."
sleep 2
# Show available block devices
log "Block devices:"
[ "$QUIET" = "0" ] && ls -la /dev/vd* 2>/dev/null || log "No virtio block devices found"
# The rootfs.img is always the first virtio-blk device (/dev/vda)
# Additional devices (input, state) come after
ROOTFS_DEV="/dev/vda"
if [ ! -b "$ROOTFS_DEV" ]; then
echo "ERROR: Rootfs device $ROOTFS_DEV not found!"
echo "Available devices:"
ls -la /dev/
sleep 10
reboot -f
fi
# Create mount points for overlay setup
mkdir -p /mnt/lower # squashfs (read-only)
mkdir -p /mnt/upper # tmpfs for overlay upper
mkdir -p /mnt/work # tmpfs for overlay work
mkdir -p /mnt/root # final overlayfs mount
# Mount squashfs read-only
log "Mounting squashfs rootfs from $ROOTFS_DEV..."
if ! mount -t squashfs -o ro "$ROOTFS_DEV" /mnt/lower; then
# Fallback to ext4 for backwards compatibility
log "squashfs mount failed, trying ext4..."
if ! mount -t ext4 -o ro "$ROOTFS_DEV" /mnt/lower; then
echo "ERROR: Failed to mount rootfs (tried squashfs and ext4)!"
sleep 10
reboot -f
fi
# ext4 fallback - just use it directly without overlay
log "Using ext4 rootfs directly (no overlay)"
mount --move /mnt/lower /mnt/root
else
log "Squashfs mounted successfully"
# Create tmpfs for overlay upper/work directories
# Size is generous since container operations need temp space
log "Creating tmpfs overlay..."
mount -t tmpfs -o size=1G tmpfs /mnt/upper
mkdir -p /mnt/upper/upper
mkdir -p /mnt/upper/work
# Create overlayfs combining squashfs (lower) + tmpfs (upper)
log "Mounting overlayfs..."
if ! mount -t overlay overlay -o lowerdir=/mnt/lower,upperdir=/mnt/upper/upper,workdir=/mnt/upper/work /mnt/root; then
echo "ERROR: Failed to mount overlayfs!"
sleep 10
reboot -f
fi
log "Overlayfs mounted successfully"
fi
if [ "$QUIET" = "0" ]; then
echo "Contents:"
ls -la /mnt/root/
fi
# Verify init exists on rootfs
if [ ! -x /mnt/root/init ] && [ ! -x /mnt/root/sbin/init ]; then
echo "ERROR: No init found on rootfs!"
sleep 10
reboot -f
fi
# Move filesystems to new root before switch_root
# This way they persist across switch_root and the new init doesn't need to remount
mkdir -p /mnt/root/proc /mnt/root/sys /mnt/root/dev
mount --move /proc /mnt/root/proc
mount --move /sys /mnt/root/sys
mount --move /dev /mnt/root/dev
# Switch to real root
# switch_root will:
# 1. Mount the new root
# 2. chroot into it
# 3. Execute the new init
# 4. Delete everything in the old initramfs
log "Switching to real root..."
if [ -x /mnt/root/init ]; then
exec switch_root /mnt/root /init
elif [ -x /mnt/root/sbin/init ]; then
exec switch_root /mnt/root /sbin/init
fi
# If we get here, switch_root failed
echo "ERROR: switch_root failed!"
sleep 10
reboot -f
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