Unexport fields of config.Overlay2.

Users/callers of config.Overlay2 relied on its internal functioning/layout.
The stable contract is at the --overlay2 flag level. So changed callers to use
that contract instead via Overlay2.Set().

Unexported fields to encapsulate the type correctly.

PiperOrigin-RevId: 530818635

runsc/cli/main.go

@@ -233,8 +233,7 @@ func Main() {
 	log.Infof("\t\tPlatform: %v", conf.Platform)
 	log.Infof("\t\tFileAccess: %v", conf.FileAccess)
 	log.Infof("\t\tDirectfs: %t", conf.DirectFS)
-	overlay2 := conf.GetOverlay2()
-	log.Infof("\t\tOverlay: Root=%t, SubMounts=%t, Medium=%q", overlay2.RootMount, overlay2.SubMounts, overlay2.Medium)
+	log.Infof("\t\tOverlay: %s", conf.GetOverlay2())
 	log.Infof("\t\tNetwork: %v, logging: %t", conf.Network, conf.LogPackets)
 	log.Infof("\t\tStrace: %t, max size: %d, syscalls: %s", conf.Strace, conf.StraceLogSize, conf.StraceSyscalls)
 	log.Infof("\t\tIOURING: %t", conf.IOUring)

runsc/cmd/do.go

@@ -149,9 +149,9 @@ func (c *Do) Execute(_ context.Context, f *flag.FlagSet, args ...any) subcommand
 	// If c.overlay is set, then enable overlay.
 	conf.Overlay = false // conf.Overlay is deprecated.
 	if c.overlay {
-		conf.Overlay2 = config.Overlay2{RootMount: true, SubMounts: true, Medium: "memory"}
+		conf.Overlay2.Set("all:memory")
 	} else {
-		conf.Overlay2 = config.Overlay2{RootMount: false, SubMounts: false, Medium: ""}
+		conf.Overlay2.Set("none")
 	}
 	absRoot, err := resolvePath(c.root)
 	if err != nil {

runsc/config/config.go

@@ -360,7 +360,7 @@ func (c *Config) GetOverlay2() Overlay2 {
 			panic(fmt.Sprintf("Overlay2 cannot be set when --overlay=true"))
 		}
 		// Using a deprecated flag, honor it to avoid breaking users.
-		return Overlay2{RootMount: true, SubMounts: true, Medium: "memory"}
+		return Overlay2{rootMount: true, subMounts: true, medium: "memory"}
 	}
 	return c.Overlay2
 }
@@ -692,22 +692,22 @@ func (g HostFifo) AllowOpen() bool {
 // Overlay2 holds the configuration for setting up overlay filesystems for the
 // container.
 type Overlay2 struct {
-	RootMount bool
-	SubMounts bool
-	Medium    string
+	rootMount bool
+	subMounts bool
+	medium    string
 }
 
 func defaultOverlay2() *Overlay2 {
 	// Rootfs overlay is enabled by default and backed by a file in rootfs itself.
-	return &Overlay2{RootMount: true, SubMounts: false, Medium: "self"}
+	return &Overlay2{rootMount: true, subMounts: false, medium: "self"}
 }
 
 // Set implements flag.Value.
 func (o *Overlay2) Set(v string) error {
 	if v == "none" {
-		o.RootMount = false
-		o.SubMounts = false
-		o.Medium = ""
+		o.rootMount = false
+		o.subMounts = false
+		o.medium = ""
 		return nil
 	}
 	vs := strings.Split(v, ":")
@@ -717,22 +717,22 @@ func (o *Overlay2) Set(v string) error {
 
 	switch mount := vs[0]; mount {
 	case "root":
-		o.RootMount = true
+		o.rootMount = true
 	case "all":
-		o.RootMount = true
-		o.SubMounts = true
+		o.rootMount = true
+		o.subMounts = true
 	default:
 		return fmt.Errorf("unexpected mount specifier for --overlay2: %q", mount)
 	}
 
-	o.Medium = vs[1]
-	switch o.Medium {
+	o.medium = vs[1]
+	switch o.medium {
 	case "memory", "self": // OK
 	default:
-		if !strings.HasPrefix(o.Medium, "dir=") {
-			return fmt.Errorf("unexpected medium specifier for --overlay2: %q", o.Medium)
+		if !strings.HasPrefix(o.medium, "dir=") {
+			return fmt.Errorf("unexpected medium specifier for --overlay2: %q", o.medium)
 		}
-		if hostFileDir := strings.TrimPrefix(o.Medium, "dir="); !filepath.IsAbs(hostFileDir) {
+		if hostFileDir := strings.TrimPrefix(o.medium, "dir="); !filepath.IsAbs(hostFileDir) {
 			return fmt.Errorf("overlay host file directory should be an absolute path, got %q", hostFileDir)
 		}
 	}
@@ -746,36 +746,46 @@ func (o *Overlay2) Get() any {
 
 // String implements flag.Value.
 func (o Overlay2) String() string {
-	if !o.RootMount && !o.SubMounts {
+	if !o.rootMount && !o.subMounts {
 		return "none"
 	}
 	res := ""
 	switch {
-	case o.RootMount && o.SubMounts:
+	case o.rootMount && o.subMounts:
 		res = "all"
-	case o.RootMount:
+	case o.rootMount:
 		res = "root"
 	default:
 		panic("invalid state of subMounts = true and rootMount = false")
 	}
 
-	return res + ":" + o.Medium
+	return res + ":" + o.medium
 }
 
 // Enabled returns true if the overlay option is enabled for any mounts.
 func (o *Overlay2) Enabled() bool {
-	return o.RootMount || o.SubMounts
+	return o.rootMount || o.subMounts
+}
+
+// RootEnabled returns true if the overlay is enabled for the root mount.
+func (o *Overlay2) RootEnabled() bool {
+	return o.rootMount
+}
+
+// SubMountEnabled returns true if the overlay is enabled for submounts.
+func (o *Overlay2) SubMountEnabled() bool {
+	return o.subMounts
 }
 
 // IsBackedByMemory indicates whether the overlay is backed by app memory.
 func (o *Overlay2) IsBackedByMemory() bool {
-	return o.Enabled() && o.Medium == "memory"
+	return o.Enabled() && o.medium == "memory"
 }
 
 // IsBackedBySelf indicates whether the overlaid mounts are backed by
 // themselves.
 func (o *Overlay2) IsBackedBySelf() bool {
-	return o.Enabled() && o.Medium == "self"
+	return o.Enabled() && o.medium == "self"
 }
 
 // HostFileDir indicates the directory in which the overlay-backing host file
@@ -783,10 +793,10 @@ func (o *Overlay2) IsBackedBySelf() bool {
 //
 // Precondition: o.IsBackedByHostFile() && !o.IsBackedBySelf().
 func (o *Overlay2) HostFileDir() string {
-	if !strings.HasPrefix(o.Medium, "dir=") {
-		panic(fmt.Sprintf("Overlay2.Medium = %q does not have dir= prefix when overlay is backed by a host file", o.Medium))
+	if !strings.HasPrefix(o.medium, "dir=") {
+		panic(fmt.Sprintf("Overlay2.Medium = %q does not have dir= prefix when overlay is backed by a host file", o.medium))
 	}
-	hostFileDir := strings.TrimPrefix(o.Medium, "dir=")
+	hostFileDir := strings.TrimPrefix(o.medium, "dir=")
 	if !filepath.IsAbs(hostFileDir) {
 		panic(fmt.Sprintf("overlay host file directory should be an absolute path, got %q", hostFileDir))
 	}

runsc/config/config_test.go

@@ -477,7 +477,7 @@ func TestOverrideAllowlist(t *testing.T) {
 func TestBundles(t *testing.T) {
 	noChange := func(t *testing.T, old, new *Config) {
 		t.Helper()
-		if diff := cmp.Diff(old, new, cmp.AllowUnexported(Config{})); diff != "" {
+		if diff := cmp.Diff(old, new, cmp.AllowUnexported(Config{}, Overlay2{})); diff != "" {
 			t.Errorf("different configs:\n%+v\nvs\n%+v\nDiff:\n%s", old, new, diff)
 		}
 	}

runsc/container/container.go

@@ -871,7 +871,7 @@ func (c *Container) createOverlayFilestores(mountHints *boot.PodMountHints) ([]*
 	var overlayMediums []boot.OverlayMedium
 
 	// Handle root mount first.
-	shouldOverlay := c.OverlayConf.RootMount && !c.Spec.Root.Readonly
+	shouldOverlay := c.OverlayConf.RootEnabled() && !c.Spec.Root.Readonly
 	filestore, medium, err := c.createOverlayFilestore(c.Spec.Root.Path, shouldOverlay, nil /* hint */)
 	if err != nil {
 		return nil, nil, err
@@ -887,7 +887,7 @@ func (c *Container) createOverlayFilestores(mountHints *boot.PodMountHints) ([]*
 			continue
 		}
 		hint := mountHints.FindMount(&c.Spec.Mounts[i])
-		shouldOverlay := c.OverlayConf.SubMounts && !specutils.IsReadonlyMount(c.Spec.Mounts[i].Options)
+		shouldOverlay := c.OverlayConf.SubMountEnabled() && !specutils.IsReadonlyMount(c.Spec.Mounts[i].Options)
 		filestore, medium, err := c.createOverlayFilestore(c.Spec.Mounts[i].Source, shouldOverlay, hint)
 		if err != nil {
 			return nil, nil, err

runsc/container/container_test.go

@@ -417,7 +417,7 @@ func configs(t *testing.T, noOverlay bool) map[string]*config.Config {
 	cs := make(map[string]*config.Config)
 	for _, p := range ps {
 		c := testutil.TestConfig(t)
-		c.Overlay2 = config.Overlay2{RootMount: false, SubMounts: false, Medium: ""}
+		c.Overlay2.Set("none")
 		c.Platform = p
 		cs[p] = c
 	}
@@ -427,7 +427,7 @@ func configs(t *testing.T, noOverlay bool) map[string]*config.Config {
 		for _, p := range ps {
 			c := testutil.TestConfig(t)
 			c.Platform = p
-			c.Overlay2 = config.Overlay2{RootMount: true, SubMounts: true, Medium: "memory"}
+			c.Overlay2.Set("all:memory")
 			cs[p+"-overlay"] = c
 		}
 	}
@@ -622,12 +622,14 @@ func TestExePath(t *testing.T) {
 		t.Fatalf("error making directory: %v", err)
 	}
 
+	defaultConf := testutil.TestConfig(t)
+	defaultConf.Overlay2.Set("none")
+	overlayConf := testutil.TestConfig(t)
+	overlayConf.Overlay2.Set("all:memory")
 	configs := map[string]*config.Config{
-		"default": testutil.TestConfig(t),
-		"overlay": testutil.TestConfig(t),
+		"default": defaultConf,
+		"overlay": overlayConf,
 	}
-	configs["default"].Overlay2 = config.Overlay2{RootMount: false, SubMounts: false, Medium: ""}
-	configs["overlay"].Overlay2 = config.Overlay2{RootMount: true, SubMounts: true, Medium: "memory"}
 
 	for name, conf := range configs {
 		t.Run(name, func(t *testing.T) {

runsc/container/multi_container_test.go

@@ -1086,7 +1086,7 @@ func TestMultiContainerDifferentFilesystems(t *testing.T) {
 
 	// Make sure overlay is enabled, and none of the root filesystems are
 	// read-only, otherwise we won't be able to create the file.
-	conf.Overlay2 = config.Overlay2{RootMount: true, SubMounts: true, Medium: "memory"}
+	conf.Overlay2.Set("all:memory")
 	specs, ids := createSpecs(cmdRoot, cmd, cmd)
 	for _, s := range specs {
 		s.Root.Readonly = false
@@ -2231,10 +2231,7 @@ func TestMultiContainerOverlayLeaks(t *testing.T) {
 	conf.RootDir = rootDir
 
 	// Configure root overlay backed by rootfs itself.
-	conf.Overlay2 = config.Overlay2{
-		RootMount: true,
-		Medium:    "self",
-	}
+	conf.Overlay2.Set("root:self")
 
 	// Root container will just sleep.
 	sleep := []string{"sleep", "100"}
@@ -2336,10 +2333,7 @@ func TestMultiContainerMemoryLeakStress(t *testing.T) {
 
 	// Configure root overlay (backed by memory) so that containers can create
 	// files in the root directory.
-	conf.Overlay2 = config.Overlay2{
-		RootMount: true,
-		Medium:    "memory",
-	}
+	conf.Overlay2.Set("root:memory")
 
 	// Root container will just sleep.
 	sleep := []string{"sleep", "1000"}

runsc/container/shared_volume_test.go

@@ -33,7 +33,7 @@ import (
 // into and out of the sandbox.
 func TestSharedVolume(t *testing.T) {
 	conf := testutil.TestConfig(t)
-	conf.Overlay2 = config.Overlay2{RootMount: false, SubMounts: false, Medium: ""}
+	conf.Overlay2.Set("none")
 	conf.FileAccess = config.FileAccessShared
 
 	// Main process just sleeps. We will use "exec" to probe the state of
@@ -182,7 +182,7 @@ func checkFile(conf *config.Config, c *Container, filename string, want []byte)
 // is reflected inside.
 func TestSharedVolumeFile(t *testing.T) {
 	conf := testutil.TestConfig(t)
-	conf.Overlay2 = config.Overlay2{RootMount: false, SubMounts: false, Medium: ""}
+	conf.Overlay2.Set("none")
 	conf.FileAccess = config.FileAccessShared
 
 	// Main process just sleeps. We will use "exec" to probe the state of
@@ -266,11 +266,7 @@ func TestSharedVolumeFile(t *testing.T) {
 // wrapped in an overlay are not visible externally.
 func TestSharedVolumeOverlay(t *testing.T) {
 	conf := testutil.TestConfig(t)
-	conf.Overlay2 = config.Overlay2{
-		RootMount: true,
-		SubMounts: true,
-		Medium:    "dir=/tmp",
-	}
+	conf.Overlay2.Set("all:dir=/tmp")
 
 	// File that will be used to check consistency inside/outside sandbox.
 	// Note that TmpDir() is set up as a shared volume by NewSpecWithArgs(). So