sysfs: Makes ReadFS and AdaptFS embeddable (#1607)

Signed-off-by: Adrian Cole <[email protected]>

Author: codefromthecrypt

Diff for: cmd/wazero/wazero.go

@@ -419,9 +419,9 @@ func validateMounts(mounts sliceFlag, stdErr logging.Writer) (rc int, rootPath s
 			fmt.Fprintf(stdErr, "invalid mount: path %q is not a directory\n", dir)
 		}
 
-		root := sysfs.NewDirFS(dir)
+		root := sysfs.DirFS(dir)
 		if readOnly {
-			root = sysfs.NewReadFS(root)
+			root = &sysfs.ReadFS{FS: root}
 		}
 
 		config = config.(sysfs.FSConfig).WithSysFSMount(root, guestPath)

Diff for: config_test.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/tetratelabs/wazero/api"
+	experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
 	"github.com/tetratelabs/wazero/internal/fstest"
 	"github.com/tetratelabs/wazero/internal/platform"
 	internalsys "github.com/tetratelabs/wazero/internal/sys"
@@ -325,7 +326,7 @@ func TestModuleConfig_toSysContext(t *testing.T) {
 				config := base.WithFS(testFS)
 				return config, func(t *testing.T, sys *internalsys.Context) {
 					rootfs := sys.FS().RootFS()
-					require.Equal(t, sysfs.Adapt(testFS), rootfs)
+					require.Equal(t, &sysfs.AdaptFS{FS: testFS}, rootfs)
 				}
 			},
 		},
@@ -336,7 +337,7 @@ func TestModuleConfig_toSysContext(t *testing.T) {
 				config := base.WithFS(testFS).WithFS(testFS2)
 				return config, func(t *testing.T, sys *internalsys.Context) {
 					rootfs := sys.FS().RootFS()
-					require.Equal(t, sysfs.Adapt(testFS2), rootfs)
+					require.Equal(t, &sysfs.AdaptFS{FS: testFS2}, rootfs)
 				}
 			},
 		},
@@ -346,7 +347,7 @@ func TestModuleConfig_toSysContext(t *testing.T) {
 				config := base.WithFS(nil)
 				return config, func(t *testing.T, sys *internalsys.Context) {
 					rootfs := sys.FS().RootFS()
-					require.Equal(t, sysfs.Adapt(nil), rootfs)
+					require.Equal(t, experimentalsys.UnimplementedFS{}, rootfs)
 				}
 			},
 		},

Diff for: experimental/sys/unimplemented.go

@@ -10,16 +10,6 @@ import (
 // This should be embedded to have forward compatible implementations.
 type UnimplementedFS struct{}
 
-// String implements fmt.Stringer
-func (UnimplementedFS) String() string {
-	return "Unimplemented:/"
-}
-
-// Open implements the same method as documented on fs.FS
-func (UnimplementedFS) Open(name string) (fs.File, error) {
-	return nil, &fs.PathError{Op: "open", Path: name, Err: ENOSYS}
-}
-
 // OpenFile implements FS.OpenFile
 func (UnimplementedFS) OpenFile(path string, flag Oflag, perm fs.FileMode) (File, Errno) {
 	return nil, ENOSYS
@@ -80,11 +70,6 @@ func (UnimplementedFS) Utimens(path string, atim, mtim int64) Errno {
 	return ENOSYS
 }
 
-// Truncate implements FS.Truncate
-func (UnimplementedFS) Truncate(string, int64) Errno {
-	return ENOSYS
-}
-
 // UnimplementedFile is a File that returns ENOSYS for all functions,
 // except where no-op are otherwise documented.
 //

Diff for: experimental/sysfs/config_example_test.go

@@ -10,31 +10,31 @@ import (
 
 var moduleConfig wazero.ModuleConfig
 
-// This example shows how to configure a sysfs.NewDirFS
-func ExampleNewDirFS() {
-	root := sysfs.NewDirFS(".")
+// This example shows how to adapt a fs.FS to a sys.FS
+func ExampleAdaptFS() {
+	m := fstest.MapFS{
+		"a/b.txt": &fstest.MapFile{Mode: 0o666},
+		".":       &fstest.MapFile{Mode: 0o777 | fs.ModeDir},
+	}
+	root := &sysfs.AdaptFS{FS: m}
 
 	moduleConfig = wazero.NewModuleConfig().
 		WithFSConfig(wazero.NewFSConfig().(sysfs.FSConfig).WithSysFSMount(root, "/"))
 }
 
-// This example shows how to configure a sysfs.NewReadFS
-func ExampleNewReadFS() {
-	root := sysfs.NewDirFS(".")
-	readOnly := sysfs.NewReadFS(root)
+// This example shows how to configure a sysfs.DirFS
+func ExampleDirFS() {
+	root := sysfs.DirFS(".")
 
 	moduleConfig = wazero.NewModuleConfig().
-		WithFSConfig(wazero.NewFSConfig().(sysfs.FSConfig).WithSysFSMount(readOnly, "/"))
+		WithFSConfig(wazero.NewFSConfig().(sysfs.FSConfig).WithSysFSMount(root, "/"))
 }
 
-// This example shows how to adapt a fs.FS as a sys.FS
-func ExampleAdapt() {
-	m := fstest.MapFS{
-		"a/b.txt": &fstest.MapFile{Mode: 0o666},
-		".":       &fstest.MapFile{Mode: 0o777 | fs.ModeDir},
-	}
-	root := sysfs.Adapt(m)
+// This example shows how to configure a sysfs.ReadFS
+func ExampleReadFS() {
+	root := sysfs.DirFS(".")
+	readOnly := &sysfs.ReadFS{FS: root}
 
 	moduleConfig = wazero.NewModuleConfig().
-		WithFSConfig(wazero.NewFSConfig().(sysfs.FSConfig).WithSysFSMount(root, "/"))
+		WithFSConfig(wazero.NewFSConfig().(sysfs.FSConfig).WithSysFSMount(readOnly, "/"))
 }

Diff for: experimental/sysfs/sysfs.go

@@ -8,32 +8,29 @@
 package sysfs
 
 import (
-	"io/fs"
-
 	experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
 	"github.com/tetratelabs/wazero/internal/sysfs"
 )
 
-// Adapt adapts the input to sys.FS unless it is already one. Use NewDirFS
-// instead of os.DirFS as it handles interop issues such as windows support.
+// AdaptFS adapts the input to sys.FS. Use DirFS instead of adapting an
+// os.DirFS as it handles interop issues such as windows support.
 //
-// Note: This performs no flag verification on OpenFile. fs.FS cannot read
-// flags as there is no parameter to pass them through with. Moreover, fs.FS
+// Note: This performs no flag verification on OpenFile. sys.FS cannot read
+// flags as there is no parameter to pass them through with. Moreover, sys.FS
 // documentation does not require the file to be present. In summary, we can't
 // enforce flag behavior.
-func Adapt(fs fs.FS) experimentalsys.FS {
-	return sysfs.Adapt(fs)
+type AdaptFS = sysfs.AdaptFS
+
+// DirFS is like os.DirFS except it returns sys.FS, which has more features.
+func DirFS(dir string) experimentalsys.FS {
+	return sysfs.DirFS(dir)
 }
 
-// NewReadFS is used to mask an existing sys.FS for reads. Notably, this allows
+// ReadFS is used to mask an existing sys.FS for reads. Notably, this allows
 // the CLI to do read-only mounts of directories the host user can write, but
 // doesn't want the guest wasm to. For example, Python libraries shouldn't be
 // written to at runtime by the python wasm file.
-func NewReadFS(fs experimentalsys.FS) experimentalsys.FS {
-	return sysfs.NewReadFS(fs)
-}
-
-// NewDirFS is like os.DirFS except it returns sys.FS, which has more features.
-func NewDirFS(dir string) experimentalsys.FS {
-	return sysfs.NewDirFS(dir)
-}
+//
+// Note: This implements read-only by returning sys.EROFS or sys.EBADF,
+// depending on the operation that require write access.
+type ReadFS = sysfs.ReadFS

Diff for: fsconfig.go

@@ -165,17 +165,21 @@ func (c *fsConfig) clone() *fsConfig {
 
 // WithDirMount implements FSConfig.WithDirMount
 func (c *fsConfig) WithDirMount(dir, guestPath string) FSConfig {
-	return c.WithSysFSMount(sysfs.NewDirFS(dir), guestPath)
+	return c.WithSysFSMount(sysfs.DirFS(dir), guestPath)
 }
 
 // WithReadOnlyDirMount implements FSConfig.WithReadOnlyDirMount
 func (c *fsConfig) WithReadOnlyDirMount(dir, guestPath string) FSConfig {
-	return c.WithSysFSMount(sysfs.NewReadFS(sysfs.NewDirFS(dir)), guestPath)
+	return c.WithSysFSMount(&sysfs.ReadFS{FS: sysfs.DirFS(dir)}, guestPath)
 }
 
 // WithFSMount implements FSConfig.WithFSMount
 func (c *fsConfig) WithFSMount(fs fs.FS, guestPath string) FSConfig {
-	return c.WithSysFSMount(sysfs.Adapt(fs), guestPath)
+	var adapted experimentalsys.FS
+	if fs != nil {
+		adapted = &sysfs.AdaptFS{FS: fs}
+	}
+	return c.WithSysFSMount(adapted, guestPath)
 }
 
 // WithSysFSMount implements sysfs.FSConfig
@@ -188,7 +192,7 @@ func (c *fsConfig) WithSysFSMount(fs experimentalsys.FS, guestPath string) FSCon
 	if i, ok := ret.guestPathToFS[cleaned]; ok {
 		ret.fs[i] = fs
 		ret.guestPaths[i] = guestPath
-	} else {
+	} else if fs != nil {
 		ret.guestPathToFS[cleaned] = len(ret.fs)
 		ret.fs = append(ret.fs, fs)
 		ret.guestPaths = append(ret.guestPaths, guestPath)

Diff for: fsconfig_test.go

@@ -29,13 +29,13 @@ func TestFSConfig(t *testing.T) {
 		{
 			name:               "WithFSMount",
 			input:              base.WithFSMount(testFS, "/"),
-			expectedFS:         []sys.FS{sysfs.Adapt(testFS)},
+			expectedFS:         []sys.FS{&sysfs.AdaptFS{FS: testFS}},
 			expectedGuestPaths: []string{"/"},
 		},
 		{
 			name:               "WithFSMount overwrites",
 			input:              base.WithFSMount(testFS, "/").WithFSMount(testFS2, "/"),
-			expectedFS:         []sys.FS{sysfs.Adapt(testFS2)},
+			expectedFS:         []sys.FS{&sysfs.AdaptFS{FS: testFS2}},
 			expectedGuestPaths: []string{"/"},
 		},
 		{
@@ -45,13 +45,13 @@ func TestFSConfig(t *testing.T) {
 		{
 			name:               "WithDirMount overwrites",
 			input:              base.WithFSMount(testFS, "/").WithDirMount(".", "/"),
-			expectedFS:         []sys.FS{sysfs.NewDirFS(".")},
+			expectedFS:         []sys.FS{sysfs.DirFS(".")},
 			expectedGuestPaths: []string{"/"},
 		},
 		{
 			name:               "multiple",
 			input:              base.WithReadOnlyDirMount(".", "/").WithDirMount("/tmp", "/tmp"),
-			expectedFS:         []sys.FS{sysfs.NewReadFS(sysfs.NewDirFS(".")), sysfs.NewDirFS("/tmp")},
+			expectedFS:         []sys.FS{&sysfs.ReadFS{FS: sysfs.DirFS(".")}, sysfs.DirFS("/tmp")},
 			expectedGuestPaths: []string{"/", "/tmp"},
 		},
 	}

Diff for: imports/wasi_snapshot_preview1/fs_test.go

@@ -242,9 +242,9 @@ func Test_fdFdstatGet(t *testing.T) {
 	// replace stdin with a fake TTY file.
 	// TODO: Make this easier once we have in-memory sys.File
 	stdin, _ := fsc.LookupFile(sys.FdStdin)
-	stdinFile, errno := sysfs.Adapt(&gofstest.MapFS{"stdin": &gofstest.MapFile{
+	stdinFile, errno := (&sysfs.AdaptFS{FS: &gofstest.MapFS{"stdin": &gofstest.MapFile{
 		Mode: fs.ModeDevice | fs.ModeCharDevice | 0o600,
-	}}).OpenFile("stdin", 0, 0)
+	}}}).OpenFile("stdin", 0, 0)
 	require.EqualErrno(t, 0, errno)
 
 	stdin.File = stdinFile
@@ -3648,8 +3648,8 @@ func Test_pathLink(t *testing.T) {
 
 func Test_pathOpen(t *testing.T) {
 	dir := t.TempDir() // open before loop to ensure no locking problems.
-	writeFS := sysfs.NewDirFS(dir)
-	readFS := sysfs.NewReadFS(writeFS)
+	writeFS := sysfs.DirFS(dir)
+	readFS := &sysfs.ReadFS{FS: writeFS}
 
 	fileName := "file"
 	fileContents := []byte("012")

Diff for: internal/sys/fs_test.go

@@ -24,7 +24,7 @@ func TestNewFSContext(t *testing.T) {
 	embedFS, err := fs.Sub(testdata, "testdata")
 	require.NoError(t, err)
 
-	dirfs := sysfs.NewDirFS(".")
+	dirfs := sysfs.DirFS(".")
 
 	// Test various usual configuration for the file system.
 	tests := []struct {
@@ -33,21 +33,21 @@ func TestNewFSContext(t *testing.T) {
 	}{
 		{
 			name: "embed.FS",
-			fs:   sysfs.Adapt(embedFS),
+			fs:   &sysfs.AdaptFS{FS: embedFS},
 		},
 		{
-			name: "NewDirFS",
+			name: "DirFS",
 			// Don't use "testdata" because it may not be present in
 			// cross-architecture (a.k.a. scratch) build containers.
 			fs: dirfs,
 		},
 		{
-			name: "NewReadFS",
-			fs:   sysfs.NewReadFS(dirfs),
+			name: "ReadFS",
+			fs:   &sysfs.ReadFS{FS: dirfs},
 		},
 		{
 			name: "fstest.MapFS",
-			fs:   sysfs.Adapt(gofstest.MapFS{}),
+			fs:   &sysfs.AdaptFS{FS: gofstest.MapFS{}},
 		},
 	}
 
@@ -96,7 +96,7 @@ func TestNewFSContext(t *testing.T) {
 func TestFSContext_CloseFile(t *testing.T) {
 	embedFS, err := fs.Sub(testdata, "testdata")
 	require.NoError(t, err)
-	testFS := sysfs.Adapt(embedFS)
+	testFS := &sysfs.AdaptFS{FS: embedFS}
 
 	c := Context{}
 	err = c.InitFSContext(nil, nil, nil, []sys.FS{testFS}, []string{"/"}, nil)
@@ -154,7 +154,7 @@ func TestFSContext_noPreopens(t *testing.T) {
 }
 
 func TestContext_Close(t *testing.T) {
-	testFS := sysfs.Adapt(testfs.FS{"foo": &testfs.File{}})
+	testFS := &sysfs.AdaptFS{FS: testfs.FS{"foo": &testfs.File{}}}
 
 	c := Context{}
 	err := c.InitFSContext(nil, nil, nil, []sys.FS{testFS}, []string{"/"}, nil)
@@ -181,7 +181,7 @@ func TestContext_Close(t *testing.T) {
 func TestContext_Close_Error(t *testing.T) {
 	file := &testfs.File{CloseErr: errors.New("error closing")}
 
-	testFS := sysfs.Adapt(testfs.FS{"foo": file})
+	testFS := &sysfs.AdaptFS{FS: testfs.FS{"foo": file}}
 
 	c := Context{}
 	err := c.InitFSContext(nil, nil, nil, []sys.FS{testFS}, []string{"/"}, nil)
@@ -201,7 +201,7 @@ func TestContext_Close_Error(t *testing.T) {
 
 func TestFSContext_Renumber(t *testing.T) {
 	tmpDir := t.TempDir()
-	dirFS := sysfs.NewDirFS(tmpDir)
+	dirFS := sysfs.DirFS(tmpDir)
 
 	const dirName = "dir"
 	errno := dirFS.Mkdir(dirName, 0o700)
@@ -252,7 +252,7 @@ func TestFSContext_Renumber(t *testing.T) {
 
 func TestDirentCache_Read(t *testing.T) {
 	c := Context{}
-	err := c.InitFSContext(nil, nil, nil, []sys.FS{sysfs.Adapt(fstest.FS)}, []string{"/"}, nil)
+	err := c.InitFSContext(nil, nil, nil, []sys.FS{&sysfs.AdaptFS{FS: fstest.FS}}, []string{"/"}, nil)
 	require.NoError(t, err)
 	fsc := c.fsc
 	defer fsc.Close()
@@ -430,7 +430,7 @@ func TestDirentCache_ReadNewFile(t *testing.T) {
 	tmpDir := t.TempDir()
 
 	c := Context{}
-	err := c.InitFSContext(nil, nil, nil, []sys.FS{sysfs.NewDirFS(tmpDir)}, []string{"/"}, nil)
+	err := c.InitFSContext(nil, nil, nil, []sys.FS{sysfs.DirFS(tmpDir)}, []string{"/"}, nil)
 	require.NoError(t, err)
 	fsc := c.fsc
 	defer fsc.Close()

Diff for: internal/sys/sys_test.go

@@ -20,7 +20,7 @@ func TestContext_WalltimeNanos(t *testing.T) {
 }
 
 func TestDefaultSysContext(t *testing.T) {
-	testFS := sysfs.Adapt(fstest.FS)
+	testFS := &sysfs.AdaptFS{FS: fstest.FS}
 
 	sysCtx, err := NewContext(0, nil, nil, nil, nil, nil, nil, nil, 0, nil, 0, nil, nil, []experimentalsys.FS{testFS}, []string{"/"}, nil)
 	require.NoError(t, err)