drivers: Add VirtioFS support for vfkit and krunkit

Add --virtio-fs flag for specifying one or more shared directories
separated by comma. The shared directories are be mounted in the guest
using virtio-fs.

Testing with krunkit shows that virtio-fs mount is 10 times faster
compared with 9p mount.

Usage:

   --virtio-fs HOST_PATH:MOUNT_TAG[,HOST_PATH:MOUNT_TAG,...]

Example:

    minikube start --vrtio-fs /Users/joe/models:my-models

Using a new flag since none of the mount options matches virtio-fs
usage, and it will be too confusing to use using mount options.

In krunkit and vfkit, every virtio-fs shared directory will be added as:

    --device virtio-fs,sharedDir=/host-path,mountTag=mount-tag

In the guest the shared directory will be mounted using:

    sudo mount -t virtiofs my-models /mnt/my-models

This change only adds the options and configure vfkit and krunkit. The
next step is connecting to the guest and mounting the shared
directories.

More work is needed to add VirtioFS to qemu. I'm starting with fkit and
krunkit since they have identical interface (krunkit was designed as
drop-in replacement for vfkit).

Author: nirs

cmd/minikube/cmd/start_flags.go

@@ -145,6 +145,7 @@ const (
 	staticIP                = "static-ip"
 	gpus                    = "gpus"
 	autoPauseInterval       = "auto-pause-interval"
+	virtioFS                = "virtio-fs"
 )
 
 var (
@@ -209,6 +210,7 @@ func initMinikubeFlags() {
 	startCmd.Flags().String(staticIP, "", "Set a static IP for the minikube cluster, the IP must be: private, IPv4, and the last octet must be between 2 and 254, for example 192.168.200.200 (Docker and Podman drivers only)")
 	startCmd.Flags().StringP(gpus, "g", "", "Allow pods to use your GPUs. Options include: [all,nvidia,amd] (Docker driver with Docker container-runtime only)")
 	startCmd.Flags().Duration(autoPauseInterval, time.Minute*1, "Duration of inactivity before the minikube VM is paused (default 1m0s)")
+	startCmd.Flags().StringSlice(virtioFS, nil, "virtio-fs shared directories '/host-path:mount-tag,...' (vfkkit and krunkit drivers only)")
 }
 
 // initKubernetesFlags inits the commandline flags for Kubernetes related options
@@ -650,6 +652,7 @@ func generateNewConfigFromFlags(cmd *cobra.Command, k8sVersion string, rtime str
 		MultiNodeRequested: viper.GetInt(nodes) > 1 || viper.GetBool(ha),
 		GPUs:               viper.GetString(gpus),
 		AutoPauseInterval:  viper.GetDuration(autoPauseInterval),
+		VirtioFS:           viper.GetStringSlice(virtioFS),
 	}
 	cc.VerifyComponents = interpretWaitFlag(*cmd)
 	if viper.GetBool(createMount) && driver.IsKIC(drvName) {
@@ -880,6 +883,7 @@ func updateExistingConfigFromFlags(cmd *cobra.Command, existing *config.ClusterC
 	updateStringFromFlag(cmd, &cc.SocketVMnetClientPath, socketVMnetClientPath)
 	updateStringFromFlag(cmd, &cc.SocketVMnetPath, socketVMnetPath)
 	updateDurationFromFlag(cmd, &cc.AutoPauseInterval, autoPauseInterval)
+	updateStringSliceFromFlag(cmd, &cc.VirtioFS, virtioFS)
 
 	if cmd.Flags().Changed(kubernetesVersion) {
 		kubeVer, err := getKubernetesVersion(existing)

pkg/drivers/krunkit/krunkit.go

@@ -71,6 +71,7 @@ type Driver struct {
 	CPU            int
 	Memory         int
 	ExtraDisks     int
+	VirtioFS       []string
 	MACAddress     string
 	VmnetHelper    vmnet.Helper
 }
@@ -231,6 +232,15 @@ func (d *Driver) startKrunkit(socketPath string) error {
 			"--device", fmt.Sprintf("virtio-blk,path=%s", pkgdrivers.ExtraDiskPath(d.BaseDriver, i)))
 	}
 
+	for _, s := range d.VirtioFS {
+		fs, err := pkgdrivers.ParseVirtioFS(s)
+		if err != nil {
+			return err
+		}
+		args = append(args,
+			"--device", fmt.Sprintf("virtio-fs,sharedDir=%s,mountTag=%s", fs.SharedDir, fs.MountTag))
+	}
+
 	log.Debugf("executing: krunkit %s", strings.Join(args, " "))
 	cmd := exec.Command(driverName, args...)
 

pkg/drivers/vfkit/vfkit.go

@@ -72,6 +72,7 @@ type Driver struct {
 	CPU            int
 	Memory         int
 	ExtraDisks     int
+	VirtioFS       []string
 	Network        string        // "", "nat", "vmnet-shared"
 	MACAddress     string        // For network=nat, network=""
 	VmnetHelper    *vmnet.Helper // For network=vmnet-shared
@@ -312,6 +313,15 @@ func (d *Driver) startVfkit(socketPath string) error {
 	startCmd = append(startCmd,
 		"--device", fmt.Sprintf("virtio-serial,logFilePath=%s", serialPath))
 
+	for _, s := range d.VirtioFS {
+		fs, err := pkgdrivers.ParseVirtioFS(s)
+		if err != nil {
+			return err
+		}
+		startCmd = append(startCmd,
+			"--device", fmt.Sprintf("virtio-fs,sharedDir=%s,mountTag=%s", fs.SharedDir, fs.MountTag))
+	}
+
 	log.Debugf("executing: vfkit %s", strings.Join(startCmd, " "))
 	os.Remove(d.sockfilePath())
 	cmd := exec.Command("vfkit", startCmd...)

pkg/drivers/virtiofs.go

@@ -0,0 +1,35 @@
+/*
+Copyright 2025 The Kubernetes Authors All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package drivers
+
+import (
+	"fmt"
+	"strings"
+)
+
+type VirtioFS struct {
+	SharedDir string
+	MountTag  string
+}
+
+func ParseVirtioFS(s string) (*VirtioFS, error) {
+	items := strings.SplitN(s, ":", 2)
+	if len(items) != 2 {
+		return nil, fmt.Errorf("invalid virtio-fs %q", s)
+	}
+	return &VirtioFS{SharedDir: items[0], MountTag: items[1]}, nil
+}

pkg/minikube/config/types.go

@@ -109,6 +109,7 @@ type ClusterConfig struct {
 	SSHAgentPID             int
 	GPUs                    string
 	AutoPauseInterval       time.Duration // Specifies interval of time to wait before checking if cluster should be paused
+	VirtioFS                []string
 }
 
 // KubernetesConfig contains the parameters used to configure the VM Kubernetes.

pkg/minikube/registry/drvs/krunkit/krunkit.go

@@ -76,6 +76,7 @@ func configure(cfg config.ClusterConfig, n config.Node) (interface{}, error) {
 		Memory:         cfg.Memory,
 		CPU:            cfg.CPUs,
 		ExtraDisks:     cfg.ExtraDisks,
+		VirtioFS:       cfg.VirtioFS,
 		VmnetHelper: vmnet.Helper{
 			MachineDir:  filepath.Join(storePath, "machines", machineName),
 			InterfaceID: u,

pkg/minikube/registry/drvs/vfkit/vfkit.go

@@ -99,6 +99,7 @@ func configure(cfg config.ClusterConfig, n config.Node) (interface{}, error) {
 		Memory:         cfg.Memory,
 		CPU:            cfg.CPUs,
 		ExtraDisks:     cfg.ExtraDisks,
+		VirtioFS:       cfg.VirtioFS,
 		Network:        cfg.Network,
 		MACAddress:     mac,
 		VmnetHelper:    helper,