Overlay size option: --overlay2=all:memory,size=1g

Implement #11504.

Add optional `size=` parameter to `--overlay2` flag: when it is set, overlay upper layer is mounted with given size flag.

Tested:

```
sudo bazel-bin/runsc/runsc_/runsc --overlay2=all:memory,size=1m run --bundle ~/bu cont-i

root@:/# dd if=/dev/urandom of=/x bs=1k count=1000
1000+0 records in
1000+0 records out
1024000 bytes (1.0 MB, 1000 KiB) copied, 0.0109061 s, 93.9 MB/s

root@:/# dd if=/dev/urandom of=/x bs=1k count=1100
dd: error writing '/x': No space left on device
1021+0 records in
1020+0 records out
1044480 bytes (1.0 MB, 1020 KiB) copied, 0.011396 s, 91.7 MB/s
```

```
  -overlay
        DEPRECATED: use --overlay2=all:memory to achieve the same effect
  -overlay2 value
        wrap mounts with overlayfs. Format is
        * 'none' to turn overlay mode off
        * {mount}:{medium}[size={size}], where
            'mount' can be 'root' or 'all'
            'medium' can be 'memory', 'self' or 'dir=/abs/dir/path' in which filestore will be created
            'size' optional parameter overrides default overlay upper layer size
         (default root:self)
  -panic-log string
        file path where panic reports and other Go's runtime messages are written.
```

FUTURE_COPYBARA_INTEGRATE_REVIEW=#11723 from stepancheg:overlay-size 32c91c3
PiperOrigin-RevId: 764885043

Author: stepancheg

g3doc/user_guide/filesystem.md

@@ -58,6 +58,9 @@ Self-backed rootfs overlay (`--overlay2=root:self`) is enabled by default in
 runsc for performance. If you need to propagate rootfs changes to the host
 filesystem, then disable it with `--overlay2=none`.
 
+Overlay has `size=` option which is passed as `size=` tmpfs mount option. For
+example, `--overlay2=root:memory,size=2g`.
+
 ## Directfs
 
 Directfs is a feature that allows the sandbox process to directly access the

runsc/boot/gofer_conf.go

@@ -124,19 +124,24 @@ func (l *GoferMountConfLowerType) Set(v string) error {
 
 // GoferMountConf describes how a gofer mount is configured in the sandbox.
 type GoferMountConf struct {
-	Upper GoferMountConfUpperType `json:"upper"`
 	Lower GoferMountConfLowerType `json:"lower"`
+	Upper GoferMountConfUpperType `json:"upper"`
+	Size  string                  `json:"size,omitempty"`
 }
 
 // String returns a human-readable string representing the gofer mount config.
 func (g GoferMountConf) String() string {
-	return fmt.Sprintf("%s:%s", g.Lower, g.Upper)
+	res := fmt.Sprintf("%s:%s", g.Lower, g.Upper)
+	if g.Size != "" {
+		res += ":size=" + g.Size
+	}
+	return res
 }
 
 // Set sets the value. Set(String()) should be idempotent.
 func (g *GoferMountConf) Set(v string) error {
 	parts := strings.Split(v, ":")
-	if len(parts) != 2 {
+	if len(parts) < 2 || len(parts) > 3 {
 		return fmt.Errorf("invalid gofer mount config format: %q", v)
 	}
 	if err := g.Lower.Set(parts[0]); err != nil {
@@ -145,8 +150,17 @@ func (g *GoferMountConf) Set(v string) error {
 	if err := g.Upper.Set(parts[1]); err != nil {
 		return err
 	}
+	g.Size = ""
+	if len(parts) >= 3 {
+		sizeArg := parts[2]
+		size, cut := strings.CutPrefix(sizeArg, "size=")
+		if !cut {
+			return fmt.Errorf("invalid gofer mount config format: %q", v)
+		}
+		g.Size = size
+	}
 	if !g.valid() {
-		return fmt.Errorf("invalid gofer mount config: %+v", g)
+		return fmt.Errorf("invalid gofer mount config: %q", v)
 	}
 	return nil
 }

runsc/boot/gofer_conf_test.go

@@ -171,7 +171,32 @@ func TestGoferConfFlags(t *testing.T) {
 	}
 	for i := range want {
 		if want[i] != got[i] {
-			t.Errorf("gofer conf is incorrect: want = %d, got = %d", want[i], got[i])
+			t.Errorf("gofer conf is incorrect: want = %s, got = %s", want[i], got[i])
 		}
 	}
 }
+
+func TestGoferMountConfSetGet(t *testing.T) {
+	t.Run("Without size", func(t *testing.T) {
+		conf := GoferMountConf{}
+		err := conf.Set("lisafs:anon")
+		if err != nil {
+			t.Fatalf("Expect success: %v", err)
+		}
+		s := conf.String()
+		if s != "lisafs:anon" {
+			t.Fatalf("Expected lisafs:anon, got %s", s)
+		}
+	})
+	t.Run("With size", func(t *testing.T) {
+		conf := GoferMountConf{}
+		err := conf.Set("lisafs:anon:size=1719")
+		if err != nil {
+			t.Fatalf("Expect success: %v", err)
+		}
+		s := conf.String()
+		if s != "lisafs:anon:size=1719" {
+			t.Fatalf("Expected lisafs:anon:size=1719, got %s", s)
+		}
+	})
+}

runsc/boot/mount_hints.go

@@ -238,6 +238,9 @@ func (p *PodMountHints) FindMount(mountSrc string) *MountHint {
 type RootfsHint struct {
 	Mount   specs.Mount
 	Overlay config.OverlayMedium
+	// Size of overlay tmpfs. Passed as `size={Size}` to tmpfs mount.
+	// Use default if unspecified.
+	Size string
 }
 
 func (r *RootfsHint) setSource(val string) error {
@@ -258,6 +261,30 @@ func (r *RootfsHint) setType(val string) error {
 	return nil
 }
 
+func (r *RootfsHint) setOption(key, val string) error {
+	switch key {
+	case "size":
+		r.Size = val
+	default:
+		return fmt.Errorf("invalid rootfs option: %s=%s", key, val)
+	}
+	return nil
+}
+
+func (r *RootfsHint) setOptions(val string) error {
+	for _, option := range strings.Split(val, ",") {
+		parts := strings.SplitN(option, "=", 2)
+		if len(parts) != 2 {
+			return fmt.Errorf("rootfs options must be key=value: %s", option)
+		}
+		key, val := parts[0], parts[1]
+		if err := r.setOption(key, val); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 func (r *RootfsHint) setField(key, val string) error {
 	switch key {
 	case "source":
@@ -266,6 +293,8 @@ func (r *RootfsHint) setField(key, val string) error {
 		return r.setType(val)
 	case "overlay":
 		return r.Overlay.Set(val)
+	case "options":
+		return r.setOptions(val)
 	default:
 		return fmt.Errorf("invalid rootfs annotation: %s=%s", key, val)
 	}

runsc/boot/mount_hints_test.go

@@ -258,6 +258,7 @@ func TestRootfsHintHappy(t *testing.T) {
 			RootfsPrefix + "source":  imagePath,
 			RootfsPrefix + "type":    erofs.Name,
 			RootfsPrefix + "overlay": config.MemoryOverlay.String(),
+			RootfsPrefix + "options": "size=100m",
 		},
 	}
 	hint, err := NewRootfsHint(spec)
@@ -275,6 +276,9 @@ func TestRootfsHintHappy(t *testing.T) {
 	if hint.Overlay != config.MemoryOverlay {
 		t.Errorf("rootfs overlay, want: %q, got: %q", config.MemoryOverlay, hint.Overlay)
 	}
+	if hint.Size != "100m" {
+		t.Errorf("rootfs size, want: 100m, got: %q", hint.Size)
+	}
 }
 
 // TestRootfsHintErrors tests that proper errors will be returned when parsing

runsc/boot/vfs.go

@@ -586,6 +586,12 @@ func (c *containerMounter) configureOverlay(ctx context.Context, conf *config.Co
 	// filesystem specific options.
 	upperOpts := *lowerOpts
 	upperOpts.GetFilesystemOptions = vfs.GetFilesystemOptions{InternalMount: true}
+	if mountConf.Size != "" {
+		if upperOpts.GetFilesystemOptions.Data != "" {
+			upperOpts.GetFilesystemOptions.Data += ","
+		}
+		upperOpts.GetFilesystemOptions.Data += "size=" + mountConf.Size
+	}
 
 	overlayOpts := *lowerOpts
 	overlayOpts.GetFilesystemOptions = vfs.GetFilesystemOptions{InternalMount: true}

runsc/config/config.go

@@ -909,24 +909,42 @@ type Overlay2 struct {
 	rootMount bool
 	subMounts bool
 	medium    OverlayMedium
+	// Size of overlay upper layer.
+	// Passed as is to tmpfs mount, as `size={size}`.
+	// Empty means use default.
+	// Size is applied to each overlay independently and not shared by overlays.
+	size 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: SelfOverlay}
 }
 
+func setOverlay2Err(v string) error {
+	return fmt.Errorf("expected format is --overlay2={mount}:{medium}[,size={size}], got %q", v)
+}
+
+// `--overlay2=...` param `size=`.
+const overlay2SizeEq = "size="
+
 // 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.size = ""
 		return nil
 	}
-	vs := strings.Split(v, ":")
+	parts := strings.Split(v, ",")
+	if len(parts) < 1 {
+		return setOverlay2Err(v)
+	}
+
+	vs := strings.Split(parts[0], ":")
 	if len(vs) != 2 {
-		return fmt.Errorf("expected format is --overlay2={mount}:{medium}, got %q", v)
+		return setOverlay2Err(v)
 	}
 
 	switch mount := vs[0]; mount {
@@ -939,7 +957,25 @@ func (o *Overlay2) Set(v string) error {
 		return fmt.Errorf("unexpected mount specifier for --overlay2: %q", mount)
 	}
 
-	return o.medium.Set(vs[1])
+	err := o.medium.Set(vs[1])
+	if err != nil {
+		return err
+	}
+
+	if len(parts) == 1 {
+		o.size = ""
+	} else if len(parts) == 2 {
+		sizeArg := parts[1]
+		size, cut := strings.CutPrefix(sizeArg, overlay2SizeEq)
+		if !cut {
+			return setOverlay2Err(v)
+		}
+		o.size = size
+	} else {
+		return setOverlay2Err(v)
+	}
+
+	return nil
 }
 
 // Get implements flag.Value.
@@ -961,7 +997,13 @@ func (o Overlay2) String() string {
 	default:
 		panic("invalid state of subMounts = true and rootMount = false")
 	}
-	return res + ":" + o.medium.String()
+
+	var sizeSuffix string
+	if o.size != "" {
+		sizeSuffix = fmt.Sprintf(",%s%s", overlay2SizeEq, o.size)
+	}
+
+	return res + ":" + o.medium.String() + sizeSuffix
 }
 
 // Enabled returns true if the overlay option is enabled for any mounts.
@@ -977,6 +1019,13 @@ func (o *Overlay2) RootOverlayMedium() OverlayMedium {
 	return o.medium
 }
 
+func (o *Overlay2) RootOverlaySize() string {
+	if !o.rootMount {
+		return ""
+	}
+	return o.size
+}
+
 // SubMountOverlayMedium returns the overlay medium config of submounts.
 func (o *Overlay2) SubMountOverlayMedium() OverlayMedium {
 	if !o.subMounts {
@@ -985,6 +1034,13 @@ func (o *Overlay2) SubMountOverlayMedium() OverlayMedium {
 	return o.medium
 }
 
+func (o *Overlay2) SubMountOverlaySize() string {
+	if !o.subMounts {
+		return ""
+	}
+	return o.size
+}
+
 // Medium returns the overlay medium config.
 func (o Overlay2) Medium() OverlayMedium {
 	return o.medium

runsc/config/config_test.go

@@ -231,6 +231,11 @@ func TestInvalidFlags(t *testing.T) {
 			value: "root:dir=tmp",
 			error: "overlay host file directory should be an absolute path, got \"tmp\"",
 		},
+		{
+			name:  "overlay2",
+			value: "root:memory,sz=sdg",
+			error: "expected format is --overlay2",
+		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			testFlags := flag.NewFlagSet("test", flag.ContinueOnError)
@@ -781,3 +786,32 @@ root = "%s"
 	}
 
 }
+
+func TestParseSerializeOverlay2(t *testing.T) {
+	t.Run("Without size", func(t *testing.T) {
+		o := Overlay2{}
+		err := o.Set("all:memory")
+		if err != nil {
+			t.Fatalf("Set failed: %v", err)
+		}
+		if o.RootOverlaySize() != "" || o.SubMountOverlaySize() != "" {
+			t.Fatalf("Size mismatch, expecting empty, got %q, %q", o.RootOverlaySize(), o.SubMountOverlaySize())
+		}
+		if o.String() != "all:memory" {
+			t.Fatalf("String mismatch, expecting all:memory, got %q", o.String())
+		}
+	})
+	t.Run("With size", func(t *testing.T) {
+		o := Overlay2{}
+		err := o.Set("root:memory,size=1g")
+		if err != nil {
+			t.Fatalf("Set failed: %v", err)
+		}
+		if o.RootOverlaySize() != "1g" || o.SubMountOverlaySize() != "" {
+			t.Fatalf("Size mismatch, expecting 1g, empty, got %q, %q", o.RootOverlaySize(), o.SubMountOverlaySize())
+		}
+		if o.String() != "root:memory,size=1g" {
+			t.Fatalf("String mismatch, expecting ll:memory,size=1g, got %q", o.String())
+		}
+	})
+}

runsc/config/flags.go

@@ -119,7 +119,12 @@ func RegisterFlags(flagSet *flag.FlagSet) {
 	flagSet.Var(fileAccessTypePtr(FileAccessExclusive), "file-access", "specifies which filesystem validation to use for the root mount: exclusive (default), shared.")
 	flagSet.Var(fileAccessTypePtr(FileAccessShared), "file-access-mounts", "specifies which filesystem validation to use for volumes other than the root mount: shared (default), exclusive.")
 	flagSet.Bool("overlay", false, "DEPRECATED: use --overlay2=all:memory to achieve the same effect")
-	flagSet.Var(defaultOverlay2(), flagOverlay2, "wrap mounts with overlayfs. Format is {mount}:{medium}, where 'mount' can be 'root' or 'all' and medium can be 'memory', 'self' or 'dir=/abs/dir/path' in which filestore will be created. 'none' will turn overlay mode off.")
+	flagSet.Var(defaultOverlay2(), flagOverlay2, "wrap mounts with overlayfs. Format is\n"+
+		"* 'none' to turn overlay mode off\n"+
+		"* {mount}:{medium}[,size={size}], where\n"+
+		"    'mount' can be 'root' or 'all'\n"+
+		"    'medium' can be 'memory', 'self' or 'dir=/abs/dir/path' in which filestore will be created\n"+
+		"    'size' optional parameter overrides default overlay upper layer size\n")
 	flagSet.Bool("fsgofer-host-uds", false, "DEPRECATED: use host-uds=all")
 	flagSet.Var(hostUDSPtr(HostUDSNone), flagHostUDS, "controls permission to access host Unix-domain sockets. Values: none|open|create|all, default: none")
 	flagSet.Var(hostFifoPtr(HostFifoNone), "host-fifo", "controls permission to access host FIFOs (or named pipes). Values: none|open, default: none")