zosbuilder/scripts/build-boot.sh

#!/bin/bash
set -e

BOOT_ROOT="/build/boot"
OUTPUT_DIR="/build/output"
CONFIG_DIR="/build/configs"

echo "[+] Building minimal boot initramfs..."
echo "    Target: ~10-20MB embedded in kernel"
echo "    Purpose: Boot + network + mount Alpine runtime"

# Clean and create boot root
rm -rf "$BOOT_ROOT"
mkdir -p "$BOOT_ROOT"

echo "[+] Installing minimal boot packages..."

# Set up APK for boot root
mkdir -p "$BOOT_ROOT/etc/apk"
cp /etc/apk/repositories "$BOOT_ROOT/etc/apk/"

# Copy APK keys
if [ -d /etc/apk/keys ]; then
    mkdir -p "$BOOT_ROOT/etc/apk/keys"
    cp /etc/apk/keys/* "$BOOT_ROOT/etc/apk/keys/"
fi

# Create APK database
mkdir -p "$BOOT_ROOT/lib/apk/db"
mkdir -p "$BOOT_ROOT/var/cache/apk"

# Install absolute minimal packages
echo "  Installing boot packages from packages-boot.txt..."
apk --root "$BOOT_ROOT" --clean-protected --update-cache --initdb add alpine-baselayout busybox apk-tools musl

# Install additional boot packages
while read -r package; do
    # Skip comments and empty lines
    case "$package" in
        \#*|"") continue ;;
    esac
    
    echo "    Installing: $package"
    if apk --root "$BOOT_ROOT" add --no-cache "$package"; then
        echo "      Success: $package"
    else
        echo "      Warning: Failed to install $package"
    fi
done < "$CONFIG_DIR/packages-boot.txt"

echo "[+] Installing minimal ethernet drivers..."
# Install essential ethernet firmware and drivers using our minimal script
INITRAMFS_ROOT="$BOOT_ROOT" /build/scripts/install-firmware-minimal.sh

echo "[+] Setting up boot filesystem structure..."

# Create essential directories
mkdir -p "$BOOT_ROOT"/{dev,proc,sys,mnt,tmp,var/run,var/log}
mkdir -p "$BOOT_ROOT"/{root,home,opt}
mkdir -p "$BOOT_ROOT"/mnt/{alpine,debug}

# Create device nodes
echo "  Creating device nodes..."
[ ! -e "$BOOT_ROOT/dev/console" ] && mknod "$BOOT_ROOT/dev/console" c 5 1
[ ! -e "$BOOT_ROOT/dev/null" ] && mknod "$BOOT_ROOT/dev/null" c 1 3
[ ! -e "$BOOT_ROOT/dev/zero" ] && mknod "$BOOT_ROOT/dev/zero" c 1 5

# Set proper permissions
chmod 666 "$BOOT_ROOT/dev/null" "$BOOT_ROOT/dev/zero"
chmod 600 "$BOOT_ROOT/dev/console"

echo "[+] Creating boot init script..."
# Create minimal init script for mounting Alpine runtime
cat > "$BOOT_ROOT/init" << 'EOF'
#!/bin/bash
# Minimal boot init - establish network and mount Alpine runtime

echo "[BOOT] Zero-OS minimal boot starting..."

# Mount essential filesystems
mount -t proc proc /proc
mount -t sysfs sysfs /sys
mount -t devtmpfs devtmpfs /dev

# Load essential modules
echo "[BOOT] Loading ethernet drivers..."
modprobe -a e1000 e1000e igb ixgbe r8169 8139too bnx2 tg3 2>/dev/null || true

# Start eudev for hardware detection
echo "[BOOT] Starting hardware detection..."
/sbin/udevd --daemon
udevadm trigger
udevadm settle

# Network configuration
echo "[BOOT] Configuring network..."
for iface in $(ls /sys/class/net/ | grep -v lo); do
    echo "  Bringing up interface: $iface"
    ip link set "$iface" up
    # Try DHCP with timeout
    timeout 30 dhcpcd "$iface" && break
done

# Mount Alpine runtime system
echo "[BOOT] Mounting Alpine runtime system..."

# Check for VirtioFS mount (development)
if [ -d /sys/fs/virtio_fs ]; then
    echo "  Attempting VirtioFS mount..."
    mount -t virtiofs alpine-root /mnt/alpine && ALPINE_MOUNTED=true
fi

# If VirtioFS failed, try network mount (production)
if [ "$ALPINE_MOUNTED" != "true" ]; then
    echo "  VirtioFS not available, attempting network mount..."
    # Add network mounting logic here (NFS, HTTP, etc.)
    echo "  Network mount not implemented yet"
fi

# Switch to Alpine runtime if mounted
if [ "$ALPINE_MOUNTED" = "true" ]; then
    echo "[BOOT] Switching to Alpine runtime system..."
    
    # Move boot mounts to Alpine
    mount --move /proc /mnt/alpine/proc
    mount --move /sys /mnt/alpine/sys
    mount --move /dev /mnt/alpine/dev
    
    # Switch root to Alpine
    exec switch_root /mnt/alpine /sbin/zinit
else
    echo "[BOOT] Failed to mount Alpine runtime - dropping to shell"
    exec /bin/sh
fi
EOF

chmod +x "$BOOT_ROOT/init"

echo "[+] Setting up symlinks..."
cd "$BOOT_ROOT"

# Standard symlinks
ln -sf usr/lib lib || true
ln -sf usr/lib lib64 || true

# Fixed run symlink (not circular)
mkdir -p run
cd var
ln -sf ../run run || true
cd ..

echo "[+] Cleaning up boot initramfs..."
# Remove unnecessary files
rm -rf var/cache/apk/*
rm -rf usr/share/doc usr/share/man usr/share/info 2>/dev/null || true

# Aggressive cleanup for embedded
find . -name "*.a" -delete 2>/dev/null || true
find . -name "*.la" -delete 2>/dev/null || true

echo "[+] Creating boot initramfs archive..."
cd "$BOOT_ROOT"

# Create cpio archive
find . | cpio -H newc -o > "$OUTPUT_DIR/boot-initramfs.cpio"

if [ -f "$OUTPUT_DIR/boot-initramfs.cpio" ]; then
    size=$(stat -c%s "$OUTPUT_DIR/boot-initramfs.cpio")
    size_mb=$((size / 1024 / 1024))
    echo "[+] Boot initramfs created: $OUTPUT_DIR/boot-initramfs.cpio (${size_mb}MB)"
else
    echo "[-] Error: Failed to create boot initramfs"
    exit 1
fi

echo "[+] Minimal boot initramfs build complete"
echo "    Size: ${size_mb}MB (target: ~10-20MB)"
echo "    Contains: Boot + network + minimal drivers"
echo "    Purpose: Mount and switch to Alpine runtime"