banger/interactive.sh

#!/usr/bin/env bash
set -euo pipefail

log() {
  printf '[interactive] %s\n' "$*"
}

usage() {
  cat <<'EOF'
Usage: ./interactive.sh <base-rootfs> [--out <path>] [--size <size>]

Creates a writable copy of the base rootfs and boots a VM so you can
customize it manually over SSH. No automatic package/config changes
are applied.
EOF
}

parse_size() {
  local raw="$1"
  if [[ "$raw" =~ ^([0-9]+)([KMG])?$ ]]; then
    local num="${BASH_REMATCH[1]}"
    local unit="${BASH_REMATCH[2]}"
    case "$unit" in
      K) echo $((num * 1024)) ;;
      M|"") echo $((num * 1024 * 1024)) ;;
      G) echo $((num * 1024 * 1024 * 1024)) ;;
    esac
    return 0
  fi
  return 1
}

DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
source "$DIR/dns.sh"
STATE="$DIR/state"
VM_ROOT="$STATE/vms"
mkdir -p "$VM_ROOT"

FC_BIN="$DIR/firecracker"
KERNEL="$DIR/wtf/root/boot/vmlinux-6.8.0-94-generic"
INITRD="$DIR/wtf/root/boot/initrd.img-6.8.0-94-generic"
SSH_KEY="$DIR/id_ed25519"

BR_DEV="br-fc"
BR_IP="172.16.0.1"
CIDR="24"
DNS_SERVER="1.1.1.1"

BASE_ROOTFS=""
OUT_ROOTFS=""
SIZE_SPEC=""
while [[ $# -gt 0 ]]; do
  case "$1" in
    --out)
      OUT_ROOTFS="${2:-}"
      shift 2
      ;;
    --size)
      SIZE_SPEC="${2:-}"
      shift 2
      ;;
    -h|--help)
      usage
      exit 0
      ;;
    *)
      if [[ -z "$BASE_ROOTFS" ]]; then
        BASE_ROOTFS="$1"
        shift
      else
        log "unknown option: $1"
        usage
        exit 1
      fi
      ;;
  esac
done

if [[ -z "$BASE_ROOTFS" ]]; then
  usage
  exit 1
fi
if [[ ! -f "$BASE_ROOTFS" ]]; then
  log "base rootfs not found: $BASE_ROOTFS"
  exit 1
fi
if [[ ! -f "$KERNEL" ]]; then
  log "kernel not found: $KERNEL"
  exit 1
fi
if [[ ! -f "$INITRD" ]]; then
  log "initrd not found: $INITRD"
  exit 1
fi

if [[ -z "$OUT_ROOTFS" ]]; then
  base_dir="$(dirname "$BASE_ROOTFS")"
  base_name="$(basename "$BASE_ROOTFS")"
  OUT_ROOTFS="${base_dir}/rw-${base_name}"
fi
if [[ -e "$OUT_ROOTFS" ]]; then
  log "output rootfs already exists: $OUT_ROOTFS"
  exit 1
fi

log "copying base rootfs to $OUT_ROOTFS"
cp --reflink=auto "$BASE_ROOTFS" "$OUT_ROOTFS"

if [[ -n "$SIZE_SPEC" ]]; then
  SIZE_BYTES="$(parse_size "$SIZE_SPEC")"
  BASE_BYTES="$(stat -c%s "$BASE_ROOTFS")"
  if [[ -z "$SIZE_BYTES" || "$SIZE_BYTES" -lt "$BASE_BYTES" ]]; then
    log "size must be >= base image size"
    exit 1
  fi
  log "resizing rootfs to $SIZE_SPEC"
  truncate -s "$SIZE_BYTES" "$OUT_ROOTFS"
  e2fsck -p -f "$OUT_ROOTFS" >/dev/null
  resize2fs "$OUT_ROOTFS" >/dev/null
fi

VM_ID="$(head -c 32 /dev/urandom | xxd -p -c 256)"
VM_TAG="${VM_ID:0:8}"
VM_NAME="interactive-${VM_TAG}"
VM_DIR="$VM_ROOT/$VM_ID"
mkdir -p "$VM_DIR"

API_SOCK="${XDG_RUNTIME_DIR:-/run/user/$(id -u)}/banger/fc-$VM_TAG.sock"
LOG_FILE="$VM_DIR/firecracker.log"
TAP_DEV="tap-fc-$VM_TAG"
DNS_NAME=""

# Allocate guest IP
NEXT_IP_FILE="$STATE/next_ip"
NEXT_IP="$(cat "$NEXT_IP_FILE" 2>/dev/null || echo 2)"
GUEST_IP="172.16.0.$NEXT_IP"
echo "$((NEXT_IP + 1))" > "$NEXT_IP_FILE"

sudo -v

cleanup() {
  sudo kill "${FC_PID:-}" 2>/dev/null || true
  sudo ip link del "$TAP_DEV" 2>/dev/null || true
  rm -f "$API_SOCK"
  banger_dns_remove_record_name "${DNS_NAME:-}"
  rm -rf "$VM_DIR"
}
trap cleanup EXIT

sudo mkdir -p "$(dirname "$API_SOCK")"
sudo chown "$(id -u):$(id -g)" "$(dirname "$API_SOCK")"

# Host bridge
if ! ip link show "$BR_DEV" >/dev/null 2>&1; then
  log "creating host bridge $BR_DEV ($BR_IP/$CIDR)"
  sudo ip link add name "$BR_DEV" type bridge
  sudo ip addr add "${BR_IP}/${CIDR}" dev "$BR_DEV"
  sudo ip link set "$BR_DEV" up
else
  sudo ip link set "$BR_DEV" up
fi

log "creating tap device $TAP_DEV"
TAP_USER="${SUDO_UID:-$(id -u)}"
TAP_GROUP="${SUDO_GID:-$(id -g)}"
sudo ip tuntap add dev "$TAP_DEV" mode tap user "$TAP_USER" group "$TAP_GROUP"
sudo ip link set "$TAP_DEV" master "$BR_DEV"
sudo ip link set "$TAP_DEV" up
sudo ip link set "$BR_DEV" up

log "starting firecracker process"
rm -f "$API_SOCK"
nohup sudo -E "$FC_BIN" --api-sock "$API_SOCK" >"$LOG_FILE" 2>&1 &
FC_PID="$!"

log "waiting for firecracker api socket"
for _ in $(seq 1 200); do
  [[ -S "$API_SOCK" ]] && break
  sleep 0.02
done
[[ -S "$API_SOCK" ]] || { log "firecracker api socket not ready"; exit 1; }

log "configuring machine"
sudo -E curl --unix-socket "$API_SOCK" -X PUT http://localhost/machine-config \
  -H "Content-Type: application/json" \
  -d '{
    "vcpu_count": 2,
    "mem_size_mib": 1024,
    "smt": false
  }' >/dev/null

KCMD="console=ttyS0 reboot=k panic=1 pci=off root=/dev/vda rw ip=${GUEST_IP}::${BR_IP}:255.255.255.0:${VM_NAME}:eth0:off:${DNS_SERVER} hostname=${VM_NAME} systemd.mask=home.mount systemd.mask=var.mount"

sudo -E curl --unix-socket "$API_SOCK" -X PUT http://localhost/boot-source \
  -H "Content-Type: application/json" \
  -d "{
    \"kernel_image_path\": \"$KERNEL\",
    \"boot_args\": \"$KCMD\",
    \"initrd_path\": \"$INITRD\"
  }" >/dev/null

sudo -E curl --unix-socket "$API_SOCK" -X PUT http://localhost/drives/rootfs \
  -H "Content-Type: application/json" \
  -d "{
    \"drive_id\": \"rootfs\",
    \"path_on_host\": \"$OUT_ROOTFS\",
    \"is_root_device\": true,
    \"is_read_only\": false
  }" >/dev/null

sudo -E curl --unix-socket "$API_SOCK" -X PUT http://localhost/network-interfaces/eth0 \
  -H "Content-Type: application/json" \
  -d "{
    \"iface_id\": \"eth0\",
    \"host_dev_name\": \"$TAP_DEV\"
  }" >/dev/null

sudo -E curl --unix-socket "$API_SOCK" -X PUT http://localhost/actions \
  -H "Content-Type: application/json" \
  -d '{ "action_type": "InstanceStart" }' >/dev/null

SUDO_CHILD_PID="$(pgrep -n -f "$API_SOCK" || true)"
if [[ -n "$SUDO_CHILD_PID" ]]; then
  FC_PID="$SUDO_CHILD_PID"
fi

VM_CONFIG_JSON="$(sudo -E curl --unix-socket "$API_SOCK" -sS http://localhost/vm/config)"
CREATED_AT="$(date -Iseconds)"
DNS_NAME="$(banger_dns_name "$VM_NAME")"
banger_dns_write_record "$VM_NAME" "$GUEST_IP"
jq -n \
  --arg id "$VM_ID" \
  --arg name "$VM_NAME" \
  --arg pid "$FC_PID" \
  --arg created_at "$CREATED_AT" \
  --arg guest_ip "$GUEST_IP" \
  --arg tap "$TAP_DEV" \
  --arg api_sock "$API_SOCK" \
  --arg log "$LOG_FILE" \
  --arg rootfs "$OUT_ROOTFS" \
  --arg kernel "$KERNEL" \
  --arg dns_name "$DNS_NAME" \
  --argjson config "$VM_CONFIG_JSON" \
  '{meta:{id:$id,name:$name,pid:$pid,created_at:$created_at,guest_ip:$guest_ip,tap:$tap,api_sock:$api_sock,log:$log,rootfs:$rootfs,kernel:$kernel,dns_name:$dns_name},config:$config}' \
  > "$VM_DIR/vm.json"

log "enabling NAT for interactive session"
sudo -E ./nat.sh up "$VM_TAG" >/dev/null

log "waiting for SSH"
log "guest ip: $GUEST_IP"
log "ssh: ssh -i \"$SSH_KEY\" root@${GUEST_IP}"
for _ in $(seq 1 60); do
  if ssh -i "$SSH_KEY" -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null \
    "root@${GUEST_IP}" "true" >/dev/null 2>&1; then
    log "ssh ready"
    break
  fi
  sleep 1
done

log "output rootfs: $OUT_ROOTFS"
log "press Ctrl+C to stop and clean up"

while kill -0 "$FC_PID" >/dev/null 2>&1; do
  sleep 1
done