95 lines
2.4 KiB
Python
95 lines
2.4 KiB
Python
"""Build and persist Firecracker configuration for one VM."""
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from __future__ import annotations
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import json
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import math
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import os
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import tempfile
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from collections.abc import Mapping
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from ipaddress import IPv4Address, IPv4Network
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from pathlib import Path
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from typing import Any
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from ..config import Settings
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from ..domain import VmRecord
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def vcpu_count(cpu: float) -> int:
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"""Firecracker accepts whole vCPUs; fractional capacity rounds up for now."""
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return max(1, math.ceil(cpu))
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def boot_ip_argument(
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guest_ip: IPv4Address,
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gateway: IPv4Address,
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network: IPv4Network,
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) -> str:
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return f"ip={guest_ip}::{gateway}:{network.netmask}::eth0:off"
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def build_config(
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settings: Settings,
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vm: VmRecord,
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kernel: Path,
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rootfs: Path,
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) -> dict[str, Any]:
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boot_args = " ".join(
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(
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"console=ttyS0",
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"reboot=k",
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"panic=1",
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"pci=off",
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boot_ip_argument(IPv4Address(vm.guest_ip), settings.gateway, settings.network),
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)
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)
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return {
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"boot-source": {
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"kernel_image_path": str(kernel),
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"boot_args": boot_args,
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},
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"drives": [
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{
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"drive_id": "rootfs",
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"path_on_host": str(rootfs),
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"is_root_device": True,
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"is_read_only": False,
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}
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],
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"machine-config": {
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"vcpu_count": vcpu_count(vm.cpu),
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"mem_size_mib": vm.ram_mib,
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},
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"network-interfaces": [
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{
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"iface_id": "eth0",
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"guest_mac": vm.mac,
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"host_dev_name": vm.tap,
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}
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],
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}
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def write_config(path: Path, config: Mapping[str, Any]) -> None:
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"""Atomically publish a rendered Firecracker configuration file."""
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path.parent.mkdir(parents=True, exist_ok=True)
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descriptor, temporary_name = tempfile.mkstemp(
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prefix=f".{path.name}.",
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suffix=".tmp",
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dir=path.parent,
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)
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try:
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with os.fdopen(descriptor, "w", encoding="utf-8") as temporary_file:
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json.dump(config, temporary_file, indent=2)
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temporary_file.write("\n")
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temporary_file.flush()
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os.fsync(temporary_file.fileno())
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os.replace(temporary_name, path)
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finally:
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try:
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os.unlink(temporary_name)
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except FileNotFoundError:
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pass
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