ignition: add support for ignition config file

it adds support to pass an ignition config file to vfkit that handles the provisioning process.
Vfkit start a small server, listening to a unix socket to feed the config file, and create a virtio-vsock device using port 1024. This will be used by Ignition that read its configuration using an HTTP GET over a vsock connection on port 1024.
Server code taken from https://github.com/containers/podman/blob/6487940534c1065d6c7753e3b6dfbe253666537d/pkg/machine/applehv/ignition.go

cmd/vfkit/main.go

@@ -20,7 +20,11 @@ limitations under the License.
 package main
 
 import (
+	"bytes"
 	"fmt"
+	"io"
+	"net"
+	"net/http"
 	"os"
 	"os/signal"
 	"runtime"
@@ -33,6 +37,7 @@ import (
 	"github.com/crc-org/vfkit/pkg/rest"
 	restvf "github.com/crc-org/vfkit/pkg/rest/vf"
 	"github.com/crc-org/vfkit/pkg/vf"
+	"github.com/sirupsen/logrus"
 	log "github.com/sirupsen/logrus"
 )
 
@@ -86,6 +91,10 @@ func newVMConfiguration(opts *cmdline.Options) (*config.VirtualMachine, error) {
 		return nil, err
 	}
 
+	if err := vmConfig.AddIgnitionFileFromCmdLine(opts.IgnitionPath); err != nil {
+		return nil, err
+	}
+
 	return vmConfig, nil
 }
 
@@ -137,6 +146,15 @@ func runVFKit(vmConfig *config.VirtualMachine, opts *cmdline.Options) error {
 }
 
 func runVirtualMachine(vmConfig *config.VirtualMachine, vm *vf.VirtualMachine) error {
+	if vm.Config().Ignition.SocketPath != "" {
+		go func() {
+			if err := startServer(vmConfig.Ignition.ConfigPath, vmConfig.Ignition.SocketPath); err != nil {
+				logrus.Error(err)
+			}
+			logrus.Debug("ignition vsock server exited")
+		}()
+	}
+
 	if err := vm.Start(); err != nil {
 		return err
 	}
@@ -198,3 +216,37 @@ func runVirtualMachine(vmConfig *config.VirtualMachine, vm *vf.VirtualMachine) e
 
 	return <-errCh
 }
+
+func startServer(ignitionFile string, ignitionSocketPath string) error {
+	file, err := os.Open(ignitionFile)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	buf := new(bytes.Buffer)
+	_, err = io.Copy(buf, file)
+	if err != nil {
+		return err
+	}
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		_, err := w.Write(buf.Bytes())
+		if err != nil {
+			logrus.Errorf("failed to serve ignition file: %v", err)
+		}
+	})
+
+	listener, err := net.Listen("unix", ignitionSocketPath)
+	if err != nil {
+		return err
+	}
+	logrus.Debugf("ignition socket device: %s", ignitionSocketPath)
+	defer func() {
+		if err := listener.Close(); err != nil {
+			logrus.Error(err)
+		}
+	}()
+	return http.Serve(listener, mux)
+}

pkg/cmdline/cmdline.go

@@ -23,6 +23,8 @@ type Options struct {
 	LogLevel string
 
 	UseGUI bool
+
+	IgnitionPath string
 }
 
 const DefaultRestfulURI = "none://"
@@ -50,4 +52,6 @@ func AddFlags(cmd *cobra.Command, opts *Options) {
 	cmd.Flags().StringVar(&opts.LogLevel, "log-level", "", "set log level")
 	cmd.Flags().StringVar(&opts.RestfulURI, "restful-uri", DefaultRestfulURI, "URI address for RESTful services")
 
+	cmd.Flags().StringVar(&opts.IgnitionPath, "ignition", "", "path to the ignition file")
+
 }

pkg/config/config.go

@@ -16,6 +16,7 @@ import (
 	"math"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"strconv"
 	"strings"
 
@@ -30,6 +31,7 @@ type VirtualMachine struct {
 	Bootloader Bootloader     `json:"bootloader"`
 	Devices    []VirtioDevice `json:"devices,omitempty"`
 	Timesync   *TimeSync      `json:"timesync,omitempty"`
+	Ignition   Ignition       `json:"ignition,omitempty"`
 }
 
 // TimeSync enables synchronization of the host time to the linux guest after the host was suspended.
@@ -38,6 +40,11 @@ type TimeSync struct {
 	VsockPort uint32 `json:"vsockPort"`
 }
 
+type Ignition struct {
+	ConfigPath string
+	SocketPath string
+}
+
 // The VMComponent interface represents a VM element (device, bootloader, ...)
 // which can be converted from/to commandline parameters
 type VMComponent interface {
@@ -96,6 +103,10 @@ func (vm *VirtualMachine) ToCmdLine() ([]string, error) {
 		args = append(args, devArgs...)
 	}
 
+	if vm.Ignition.ConfigPath != "" {
+		args = append(args, "--ignition", vm.Ignition.ConfigPath)
+	}
+
 	return args, nil
 }
 
@@ -191,6 +202,39 @@ func (vm *VirtualMachine) TimeSync() *TimeSync {
 	return vm.Timesync
 }
 
+func IgnitionNew(configPath string, socketPath string) (Ignition, error) {
+	if configPath == "" || socketPath == "" {
+		return Ignition{}, fmt.Errorf("config path and socket path cannot be empty")
+	}
+	return Ignition{
+		ConfigPath: configPath,
+		SocketPath: socketPath,
+	}, nil
+}
+
+func (vm *VirtualMachine) AddIgnitionFileFromCmdLine(cmdlineOpts string) error {
+	if cmdlineOpts == "" {
+		return nil
+	}
+	opts := strings.Split(cmdlineOpts, ",")
+	if len(opts) != 1 {
+		return fmt.Errorf("ignition only accept one option in command line argument")
+	}
+
+	socketPath := filepath.Join(os.TempDir(), "ignition.sock")
+	dev, err := VirtioVsockNew(1024, socketPath, true)
+	if err != nil {
+		return err
+	}
+	vm.Devices = append(vm.Devices, dev)
+	ignition, err := IgnitionNew(opts[0], socketPath)
+	if err != nil {
+		return err
+	}
+	vm.Ignition = ignition
+	return nil
+}
+
 func TimeSyncNew(vsockPort uint) (VMComponent, error) {
 
 	if vsockPort > math.MaxUint32 {