Newtype OverlayMedium

runsc/boot/mount_hints_test.go

@@ -257,7 +257,7 @@ func TestRootfsHintHappy(t *testing.T) {
 		Annotations: map[string]string{
 			RootfsPrefix + "source":  imagePath,
 			RootfsPrefix + "type":    erofs.Name,
-			RootfsPrefix + "overlay": config.MemoryOverlay.String(),
+			RootfsPrefix + "overlay": config.OverlayMediumMemory().String(),
 		},
 	}
 	hint, err := NewRootfsHint(spec)
@@ -272,7 +272,7 @@ func TestRootfsHintHappy(t *testing.T) {
 	if hint.Mount.Type != erofs.Name {
 		t.Errorf("rootfs type, want: %q, got: %q", erofs.Name, hint.Mount.Type)
 	}
-	if hint.Overlay != config.MemoryOverlay {
+	if hint.Overlay.MediumType() != config.MemoryOverlay {
 		t.Errorf("rootfs overlay, want: %q, got: %q", config.MemoryOverlay, hint.Overlay)
 	}
 }
@@ -317,23 +317,23 @@ func TestRootfsHintErrors(t *testing.T) {
 				RootfsPrefix + "invalid": "invalid",
 				RootfsPrefix + "source":  imagePath,
 				RootfsPrefix + "type":    erofs.Name,
-				RootfsPrefix + "overlay": config.MemoryOverlay.String(),
+				RootfsPrefix + "overlay": config.OverlayMediumMemory().String(),
 			},
 			error: "invalid rootfs annotation",
 		},
 		{
 			name: "missing source",
 			annotations: map[string]string{
 				RootfsPrefix + "type":    erofs.Name,
-				RootfsPrefix + "overlay": config.MemoryOverlay.String(),
+				RootfsPrefix + "overlay": config.OverlayMediumMemory().String(),
 			},
 			error: "rootfs annotations missing required field",
 		},
 		{
 			name: "missing type",
 			annotations: map[string]string{
 				RootfsPrefix + "source":  imagePath,
-				RootfsPrefix + "overlay": config.MemoryOverlay.String(),
+				RootfsPrefix + "overlay": config.OverlayMediumMemory().String(),
 			},
 			error: "rootfs annotations missing required field",
 		},

runsc/config/config.go

@@ -493,7 +493,7 @@ 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: OverlayMediumMemory()}
 	}
 	return c.Overlay2
 }
@@ -844,49 +844,82 @@ func (g HostFifo) AllowOpen() bool {
 	return g&HostFifoOpen != 0
 }
 
-// OverlayMedium describes how overlay medium is configured.
-type OverlayMedium string
+// OverlayMediumType describes types of overlay medium.
+type OverlayMediumType string
 
 const (
 	// NoOverlay indicates that no overlay will be applied.
-	NoOverlay = OverlayMedium("")
+	NoOverlay = OverlayMediumType("")
 
 	// MemoryOverlay indicates that the overlay is backed by app memory.
-	MemoryOverlay = OverlayMedium("memory")
+	MemoryOverlay = OverlayMediumType("memory")
 
 	// SelfOverlay indicates that the overlaid mount is backed by itself.
-	SelfOverlay = OverlayMedium("self")
+	SelfOverlay = OverlayMediumType("self")
+
+	AnonOverlay = OverlayMediumType("dir")
 
-	// AnonOverlayPrefix is the prefix that users should specify in the
+	// anonOverlayPrefix is the prefix that users should specify in the
 	// config for the anonymous overlay.
-	AnonOverlayPrefix = "dir="
+	anonOverlayPrefix = "dir="
 )
 
+// OverlayMedium describes how overlay medium is configured.
+type OverlayMedium struct {
+	medium OverlayMediumType
+	// Set iff medium is AnonOverlay.
+	dir string
+}
+
+func OverlayMediumNoOverlay() OverlayMedium {
+	return OverlayMedium{medium: NoOverlay}
+}
+
+func OverlayMediumMemory() OverlayMedium {
+	return OverlayMedium{medium: MemoryOverlay}
+}
+
 // String returns a human-readable string representing the overlay medium config.
 func (m OverlayMedium) String() string {
-	return string(m)
+	switch m.medium {
+	case NoOverlay, MemoryOverlay, SelfOverlay:
+		return string(m.medium)
+	case AnonOverlay:
+		return fmt.Sprintf("%s=%s", AnonOverlay, m.dir)
+	default:
+		panic(fmt.Sprintf("Invalid overlay medium %q", m.medium))
+	}
 }
 
 // Set sets the value. Set(String()) should be idempotent.
 func (m *OverlayMedium) Set(v string) error {
-	switch OverlayMedium(v) {
-	case NoOverlay, MemoryOverlay, SelfOverlay: // OK
+	switch OverlayMediumType(v) {
+	case NoOverlay, MemoryOverlay, SelfOverlay:
+		{
+			*m = OverlayMedium{medium: OverlayMediumType(v), dir: ""}
+			return nil
+		}
 	default:
-		if !strings.HasPrefix(v, AnonOverlayPrefix) {
+		if !strings.HasPrefix(v, anonOverlayPrefix) {
 			return fmt.Errorf("unexpected medium: %q", v)
 		}
-		if hostFileDir := strings.TrimPrefix(v, AnonOverlayPrefix); !filepath.IsAbs(hostFileDir) {
+		hostFileDir := strings.TrimPrefix(v, anonOverlayPrefix)
+		if !filepath.IsAbs(hostFileDir) {
 			return fmt.Errorf("overlay host file directory should be an absolute path, got %q", hostFileDir)
 		}
+		*m = OverlayMedium{medium: OverlayMediumType(v), dir: hostFileDir}
 	}
-	*m = OverlayMedium(v)
 	return nil
 }
 
+func (m OverlayMedium) MediumType() OverlayMediumType {
+	return m.medium
+}
+
 // IsBackedByAnon indicates whether the overlaid mount is backed by a host file
 // in an anonymous directory.
 func (m OverlayMedium) IsBackedByAnon() bool {
-	return strings.HasPrefix(string(m), AnonOverlayPrefix)
+	return m.medium == AnonOverlay
 }
 
 // HostFileDir indicates the directory in which the overlay-backing host file
@@ -895,9 +928,9 @@ func (m OverlayMedium) IsBackedByAnon() bool {
 // Precondition: m.IsBackedByAnon().
 func (m OverlayMedium) HostFileDir() string {
 	if !m.IsBackedByAnon() {
-		panic(fmt.Sprintf("anonymous overlay medium = %q does not have %v prefix", m, AnonOverlayPrefix))
+		panic(fmt.Sprintf("anonymous overlay medium = %q does not have %v prefix", m, anonOverlayPrefix))
 	}
-	return strings.TrimPrefix(string(m), AnonOverlayPrefix)
+	return m.dir
 }
 
 // Overlay2 holds the configuration for setting up overlay filesystems for the
@@ -910,15 +943,15 @@ type Overlay2 struct {
 
 func defaultOverlay2() *Overlay2 {
 	// Rootfs overlay is enabled by default and backed by a file in rootfs itself.
-	return &Overlay2{rootMount: true, subMounts: false, medium: SelfOverlay}
+	return &Overlay2{rootMount: true, subMounts: false, medium: OverlayMedium{medium: SelfOverlay}}
 }
 
 // Set implements flag.Value. Set(String()) should be idempotent.
 func (o *Overlay2) Set(v string) error {
 	if v == "none" {
 		o.rootMount = false
 		o.subMounts = false
-		o.medium = NoOverlay
+		o.medium = OverlayMediumNoOverlay()
 		return nil
 	}
 	vs := strings.Split(v, ":")
@@ -963,21 +996,21 @@ func (o Overlay2) String() string {
 
 // Enabled returns true if the overlay option is enabled for any mounts.
 func (o *Overlay2) Enabled() bool {
-	return o.medium != NoOverlay
+	return o.medium.medium != NoOverlay
 }
 
 // RootOverlayMedium returns the overlay medium config of the root mount.
 func (o *Overlay2) RootOverlayMedium() OverlayMedium {
 	if !o.rootMount {
-		return NoOverlay
+		return OverlayMediumNoOverlay()
 	}
 	return o.medium
 }
 
 // SubMountOverlayMedium returns the overlay medium config of submounts.
 func (o *Overlay2) SubMountOverlayMedium() OverlayMedium {
 	if !o.subMounts {
-		return NoOverlay
+		return OverlayMediumNoOverlay()
 	}
 	return o.medium
 }

runsc/config/flags.go

@@ -193,7 +193,7 @@ func checkOverlay2(name string, value string) error {
 	if err := o.Set(value); err != nil {
 		return fmt.Errorf("invalid overlay2 annotation: %w", err)
 	}
-	switch o.medium {
+	switch o.medium.MediumType() {
 	case NoOverlay, MemoryOverlay, SelfOverlay:
 		return nil
 	default:

runsc/container/container.go

@@ -911,7 +911,7 @@ func createGoferConf(overlayMedium config.OverlayMedium, mountType string, mount
 	default:
 		return boot.GoferMountConf{}, fmt.Errorf("unsupported mount type %q in mount hint", mountType)
 	}
-	switch overlayMedium {
+	switch overlayMedium.MediumType() {
 	case config.NoOverlay:
 		return boot.GoferMountConf{Lower: lower, Upper: boot.NoOverlay}, nil
 	case config.MemoryOverlay:
@@ -947,7 +947,7 @@ func (c *Container) initGoferConfs(ovlConf config.Overlay2, mountHints *boot.Pod
 		}
 	}
 	if c.Spec.Root.Readonly {
-		overlayMedium = config.NoOverlay
+		overlayMedium = config.OverlayMediumNoOverlay()
 	}
 	goferConf, err := createGoferConf(overlayMedium, mountType, c.Spec.Root.Path)
 	if err != nil {
@@ -963,12 +963,12 @@ func (c *Container) initGoferConfs(ovlConf config.Overlay2, mountHints *boot.Pod
 		overlayMedium = ovlConf.SubMountOverlayMedium()
 		mountType = boot.Bind
 		if specutils.IsReadonlyMount(c.Spec.Mounts[i].Options) {
-			overlayMedium = config.NoOverlay
+			overlayMedium = config.OverlayMediumNoOverlay()
 		}
 		if hint := mountHints.FindMount(c.Spec.Mounts[i].Source); hint != nil {
 			// Note that we want overlayMedium=self even if this is a read-only mount so that
 			// the shared mount is created correctly. Future containers may mount this writably.
-			overlayMedium = config.SelfOverlay
+			overlayMedium = config.OverlayMediumNoOverlay()
 			if !specutils.IsGoferMount(hint.Mount) {
 				mountType = hint.Mount.Type
 			}

runsc/container/container_test.go

@@ -3486,7 +3486,7 @@ func TestRootfsEROFS(t *testing.T) {
 	spec.Annotations[boot.RootfsPrefix+"source"] = rootfsImage
 	// Disable the overlay, as we want to be sure that rootfs will always be
 	// shown as EROFS in mountinfo.
-	spec.Annotations[boot.RootfsPrefix+"overlay"] = config.NoOverlay.String()
+	spec.Annotations[boot.RootfsPrefix+"overlay"] = config.OverlayMediumNoOverlay().String()
 
 	conf := testutil.TestConfig(t)
 
@@ -3563,7 +3563,7 @@ func TestCheckpointRestoreEROFS(t *testing.T) {
 				// a writeable and savable overlay for rootfs, which allows the sentry to
 				// create the mount point for the bind mount of the temporary directory shared
 				// between host and test container.
-				spec.Annotations[boot.RootfsPrefix+"overlay"] = config.MemoryOverlay.String()
+				spec.Annotations[boot.RootfsPrefix+"overlay"] = config.OverlayMediumMemory().String()
 				return spec
 			})
 		})