banger/run.sh

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

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

log "starting"

DIR="$(pwd)"
STATE="$DIR/state"
mkdir -p "$STATE"

FC_BIN="$DIR/firecracker"
KERNEL="$DIR/vmlinux"
ROOTFS="$DIR/rootfs.ext4"
SSH_KEY="$DIR/id_ed25519"

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

VM_ID="$(date +%s)-$$"
VM_TAG="${VM_ID##*-}"
VM_DIR="$STATE/vm-$VM_ID"
mkdir -p "$VM_DIR"

API_SOCK="$VM_DIR/firecracker.sock"
LOG_FILE="$VM_DIR/firecracker.log"
TAP_DEV="tap-fc-$VM_TAG"

# 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"

log "vm id: $VM_ID"
log "allocated guest ip: $GUEST_IP"

sudo -v

FC_USE_SUDO="${FC_USE_SUDO:-1}"
FC_RUN=("$FC_BIN")
CURL_CMD=(curl)
if [[ "$FC_USE_SUDO" == "1" ]]; then
  log "running firecracker with sudo (FC_USE_SUDO=1)"
  FC_RUN=(sudo -E "$FC_BIN")
  CURL_CMD=(sudo -E curl)
fi

if command -v setcap >/dev/null 2>&1; then
  if ! getcap "$FC_BIN" 2>/dev/null | rg -q "cap_net_admin"; then
    log "granting cap_net_admin to firecracker binary"
    sudo setcap cap_net_admin+ep "$FC_BIN"
  fi
else
  log "setcap not available; firecracker may need root to open TAP"
fi

# 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
  log "host bridge $BR_DEV already exists"
  # Ensure existing bridge is up in case it was left down.
  sudo ip link set "$BR_DEV" up
fi

# Per-VM TAP
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

# Start Firecracker
log "starting firecracker process"
rm -f "$API_SOCK"
nohup "${FC_RUN[@]}" --api-sock "$API_SOCK" >"$LOG_FILE" 2>&1 &
FC_PID="$!"
log "firecracker pid: $FC_PID"

# Wait for API socket
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 "api socket ready"

if [[ "$FC_USE_SUDO" == "1" ]]; then
  SUDO_CHILD_PID="$(pgrep -n -f "$API_SOCK" || true)"
  if [[ -n "$SUDO_CHILD_PID" ]]; then
    FC_PID="$SUDO_CHILD_PID"
    log "firecracker child pid: $FC_PID"
  fi
fi
echo "$FC_PID" > "$VM_DIR/pid"

# Machine config
log "configuring machine"
"${CURL_CMD[@]}" --unix-socket "$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

# Boot source
log "configuring boot source"
KCMD="console=ttyS0 reboot=k panic=1 pci=off root=/dev/vda rw ip=${GUEST_IP}::${BR_IP}:255.255.255.0::eth0:off"

"${CURL_CMD[@]}" --unix-socket "$API_SOCK" -X PUT http://localhost/boot-source \
  -H "Content-Type: application/json" \
  -d "{
    \"kernel_image_path\": \"$KERNEL\",
    \"boot_args\": \"$KCMD\"
  }" >/dev/null

# Root filesystem
log "attaching root filesystem"
"${CURL_CMD[@]}" --unix-socket "$API_SOCK" -X PUT http://localhost/drives/rootfs \
  -H "Content-Type: application/json" \
  -d "{
    \"drive_id\": \"rootfs\",
    \"path_on_host\": \"$ROOTFS\",
    \"is_root_device\": true,
    \"is_read_only\": false
  }" >/dev/null

# Network interface
log "configuring network interface"
"${CURL_CMD[@]}" --unix-socket "$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

# Start VM
log "starting virtual machine"
"${CURL_CMD[@]}" --unix-socket "$API_SOCK" -X PUT http://localhost/actions \
  -H "Content-Type: application/json" \
  -d '{ "action_type": "InstanceStart" }' >/dev/null

cat > "$VM_DIR/info" <<EOF
vm_id=$VM_ID
pid=$FC_PID
guest_ip=$GUEST_IP
tap=$TAP_DEV
api_sock=$API_SOCK
log=$LOG_FILE
EOF

log "vm started successfully"
log "guest ip: $GUEST_IP"
log "ssh: ssh -i \"$SSH_KEY\" root@$GUEST_IP"
log "logs: $LOG_FILE"