Volt VMM (Neutron Stardust): source-available under AGPSL v5.0
KVM-based microVMM for the Volt platform: - Sub-second VM boot times - Minimal memory footprint - Landlock LSM + seccomp security - Virtio device support - Custom kernel management Copyright (c) Armored Gates LLC. All rights reserved. Licensed under AGPSL v5.0
This commit is contained in:
Karl Clinger
291
scripts/build-rootfs.sh
Executable file
291
scripts/build-rootfs.sh
Executable file
@@ -0,0 +1,291 @@
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#!/usr/bin/env bash
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#
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# build-rootfs.sh - Create a minimal Alpine rootfs for Volt testing
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#
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# This script creates a small, fast-booting root filesystem suitable
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# for microVM testing. Uses Alpine Linux for its minimal footprint.
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#
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# Requirements:
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# - curl, tar
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# - e2fsprogs (mkfs.ext4) or squashfs-tools (mksquashfs)
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# - Optional: sudo (for proper permissions)
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#
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# Output: images/alpine-rootfs.ext4 (or .squashfs)
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set -euo pipefail
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SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
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PROJECT_DIR="$(dirname "$SCRIPT_DIR")"
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BUILD_DIR="${PROJECT_DIR}/.build/rootfs"
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OUTPUT_DIR="${PROJECT_DIR}/images"
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# Alpine version
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ALPINE_VERSION="${ALPINE_VERSION:-3.19}"
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ALPINE_RELEASE="${ALPINE_RELEASE:-3.19.1}"
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ALPINE_ARCH="x86_64"
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ALPINE_URL="https://dl-cdn.alpinelinux.org/alpine/v${ALPINE_VERSION}/releases/${ALPINE_ARCH}/alpine-minirootfs-${ALPINE_RELEASE}-${ALPINE_ARCH}.tar.gz"
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# Image settings
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IMAGE_FORMAT="${IMAGE_FORMAT:-ext4}" # ext4 or squashfs
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IMAGE_SIZE_MB="${IMAGE_SIZE_MB:-64}" # Size for ext4 images
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IMAGE_NAME="alpine-rootfs"
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# Colors
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RED='\033[0;31m'
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GREEN='\033[0;32m'
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YELLOW='\033[1;33m'
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NC='\033[0m'
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log() { echo -e "${GREEN}[+]${NC} $*"; }
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warn() { echo -e "${YELLOW}[!]${NC} $*"; }
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error() { echo -e "${RED}[✗]${NC} $*"; exit 1; }
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check_dependencies() {
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log "Checking dependencies..."
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local deps=(curl tar)
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case "$IMAGE_FORMAT" in
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ext4) deps+=(mkfs.ext4) ;;
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squashfs) deps+=(mksquashfs) ;;
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*) error "Unknown format: $IMAGE_FORMAT" ;;
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esac
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for dep in "${deps[@]}"; do
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if ! command -v "$dep" &>/dev/null; then
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error "Missing dependency: $dep"
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fi
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done
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}
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download_alpine() {
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log "Downloading Alpine minirootfs ${ALPINE_RELEASE}..."
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mkdir -p "$BUILD_DIR"
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local tarball="${BUILD_DIR}/alpine-minirootfs.tar.gz"
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if [[ ! -f "$tarball" ]]; then
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curl -L -o "$tarball" "$ALPINE_URL"
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else
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log "Using cached download"
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fi
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}
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extract_rootfs() {
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log "Extracting rootfs..."
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local rootfs="${BUILD_DIR}/rootfs"
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rm -rf "$rootfs"
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mkdir -p "$rootfs"
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# Extract (needs root for proper permissions, but works without)
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if [[ $EUID -eq 0 ]]; then
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tar xzf "${BUILD_DIR}/alpine-minirootfs.tar.gz" -C "$rootfs"
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else
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# Fakeroot alternative or just extract
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tar xzf "${BUILD_DIR}/alpine-minirootfs.tar.gz" -C "$rootfs" 2>/dev/null || \
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tar xzf "${BUILD_DIR}/alpine-minirootfs.tar.gz" -C "$rootfs" --no-same-owner
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warn "Extracted without root - some permissions may be incorrect"
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fi
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}
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customize_rootfs() {
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log "Customizing rootfs for microVM boot..."
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local rootfs="${BUILD_DIR}/rootfs"
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# Create init script for fast boot
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cat > "${rootfs}/init" << 'INIT'
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#!/bin/sh
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# Volt microVM init
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# Mount essential filesystems
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mount -t proc proc /proc
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mount -t sysfs sys /sys
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mount -t devtmpfs dev /dev
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# Set hostname
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hostname volt-vmm-vm
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# Print boot message
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echo ""
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echo "======================================"
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echo " Volt microVM booted!"
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echo " Alpine Linux $(cat /etc/alpine-release)"
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echo "======================================"
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echo ""
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# Show boot time if available
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if [ -f /proc/uptime ]; then
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uptime=$(cut -d' ' -f1 /proc/uptime)
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echo "Boot time: ${uptime}s"
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fi
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# Start shell
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exec /bin/sh
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INIT
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chmod +x "${rootfs}/init"
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# Create minimal inittab
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cat > "${rootfs}/etc/inittab" << 'EOF'
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::sysinit:/etc/init.d/rcS
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::respawn:-/bin/sh
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ttyS0::respawn:/sbin/getty -L ttyS0 115200 vt100
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::shutdown:/bin/umount -a -r
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EOF
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# Configure serial console
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mkdir -p "${rootfs}/etc/init.d"
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cat > "${rootfs}/etc/init.d/rcS" << 'EOF'
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#!/bin/sh
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mount -t proc proc /proc
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mount -t sysfs sys /sys
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mount -t devtmpfs dev /dev
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hostname volt-vmm-vm
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EOF
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chmod +x "${rootfs}/etc/init.d/rcS"
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# Set up basic networking config
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mkdir -p "${rootfs}/etc/network"
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cat > "${rootfs}/etc/network/interfaces" << 'EOF'
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auto lo
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iface lo inet loopback
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auto eth0
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iface eth0 inet dhcp
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EOF
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# Disable unnecessary services
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rm -f "${rootfs}/etc/init.d/hwclock"
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rm -f "${rootfs}/etc/init.d/hwdrivers"
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# Create fstab
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cat > "${rootfs}/etc/fstab" << 'EOF'
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/dev/vda / ext4 defaults,noatime 0 1
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proc /proc proc defaults 0 0
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sys /sys sysfs defaults 0 0
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devpts /dev/pts devpts defaults 0 0
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EOF
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log "Rootfs customized for fast boot"
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}
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create_ext4_image() {
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log "Creating ext4 image (${IMAGE_SIZE_MB}MB)..."
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mkdir -p "$OUTPUT_DIR"
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local image="${OUTPUT_DIR}/${IMAGE_NAME}.ext4"
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local rootfs="${BUILD_DIR}/rootfs"
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# Create sparse file
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dd if=/dev/zero of="$image" bs=1M count=0 seek="$IMAGE_SIZE_MB" 2>/dev/null
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# Format
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mkfs.ext4 -F -L rootfs -O ^metadata_csum "$image" >/dev/null
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# Mount and copy (requires root)
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if [[ $EUID -eq 0 ]]; then
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local mnt="${BUILD_DIR}/mnt"
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mkdir -p "$mnt"
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mount -o loop "$image" "$mnt"
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cp -a "${rootfs}/." "$mnt/"
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umount "$mnt"
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else
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# Use debugfs to copy files (limited but works without root)
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warn "Creating image without root - using alternative method"
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# Create a tar and extract into image using e2tools or fuse
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if command -v e2cp &>/dev/null; then
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# Use e2tools
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find "$rootfs" -type f | while read -r file; do
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local dest="${file#$rootfs}"
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e2cp "$file" "$image:$dest" 2>/dev/null || true
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done
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else
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warn "e2fsprogs-extra not available - image will be empty"
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warn "Install e2fsprogs-extra or run as root for full rootfs"
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fi
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fi
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echo "$image"
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}
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create_squashfs_image() {
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log "Creating squashfs image..."
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mkdir -p "$OUTPUT_DIR"
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local image="${OUTPUT_DIR}/${IMAGE_NAME}.squashfs"
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local rootfs="${BUILD_DIR}/rootfs"
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mksquashfs "$rootfs" "$image" \
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-comp zstd \
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-Xcompression-level 19 \
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-noappend \
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-quiet
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echo "$image"
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}
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create_image() {
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local image
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case "$IMAGE_FORMAT" in
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ext4) image=$(create_ext4_image) ;;
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squashfs) image=$(create_squashfs_image) ;;
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esac
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echo "$image"
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}
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show_stats() {
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local image="$1"
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log "Rootfs image created successfully!"
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echo ""
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echo " Path: $image"
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echo " Size: $(du -h "$image" | cut -f1)"
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echo " Format: $IMAGE_FORMAT"
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echo " Base: Alpine Linux ${ALPINE_RELEASE}"
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echo ""
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echo "To use with Volt:"
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echo " volt-vmm --kernel kernels/vmlinux --rootfs $image"
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}
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# Parse arguments
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while [[ $# -gt 0 ]]; do
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case $1 in
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--format)
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IMAGE_FORMAT="$2"
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shift 2
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;;
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--size)
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IMAGE_SIZE_MB="$2"
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shift 2
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;;
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--help)
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echo "Usage: $0 [--format ext4|squashfs] [--size MB]"
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exit 0
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;;
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*)
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error "Unknown option: $1"
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;;
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esac
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done
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# Main
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main() {
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log "Building Volt test rootfs"
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echo ""
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check_dependencies
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download_alpine
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extract_rootfs
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customize_rootfs
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local image
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image=$(create_image)
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show_stats "$image"
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}
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main
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