tillOffset int64           // Affects the length of data requested in disk.ReadFile depending on Read()'s offset
	buf        []byte          // Holds bit-rot verified data
}

func (b *wholeBitrotReader) ReadAt(buf []byte, offset int64) (n int, err error) {
	if b.buf == nil {
		b.buf = make([]byte, b.tillOffset-offset)
		if _, err := b.disk.ReadFile(context.TODO(), b.volume, b.filePath, offset, b.buf, b.verifier); err != nil {

	if src != nil {
		switch s := src.(type) {
		case string:
			return []byte(s), nil
		case []byte:
			return s, nil
		case *bytes.Buffer:
			// is io.Reader, but src is already available in []byte form
			if s != nil {
				return s.Bytes(), nil
			}
		case io.Reader:
			return io.ReadAll(s)
		}
		return nil, errors.New("invalid source")
	}
	return os.ReadFile(filename)
}

// A Mode value is a set of flags (or 0).

	}

	// This code assumes that d.r strips supported whitespace ('\r' and '\n').

	// Refill buffer.
	for d.nbuf < 4 && d.readErr == nil {
		nn := len(p) / 3 * 4
		if nn < 4 {
			nn = 4
		}
		if nn > len(d.buf) {
			nn = len(d.buf)
		}
		nn, d.readErr = d.r.Read(d.buf[d.nbuf:nn])
		d.nbuf += nn
	}

	if d.nbuf < 4 {
		if d.enc.padChar == NoPadding && d.nbuf > 0 {

}

// NewFile creates a new [File] for accessing a Plan 9 binary in an underlying reader.
// The Plan 9 binary is expected to start at position 0 in the ReaderAt.
func NewFile(r io.ReaderAt) (*File, error) {
	sr := io.NewSectionReader(r, 0, 1<<63-1)
	// Read and decode Plan 9 magic
	var magic [4]byte
	if _, err := r.ReadAt(magic[:], 0); err != nil {
		return nil, err
	}
	_, err := parseMagic(magic[:])

	return fs.ReadFile(fsOnly{fsys}, name)
}

func (fsys MapFS) Stat(name string) (fs.FileInfo, error) {
	return fs.Stat(fsOnly{fsys}, name)
}

func (fsys MapFS) ReadDir(name string) ([]fs.DirEntry, error) {
	return fs.ReadDir(fsOnly{fsys}, name)
}

func (fsys MapFS) Glob(pattern string) ([]string, error) {
	return fs.Glob(fsOnly{fsys}, pattern)
}

type noSub struct {
	MapFS
}

	// Prefer to use ReadDir instead of Readdir,
	// because the former doesn't require calling
	// Stat on every entry of a directory on Unix.
	var dirs anyDirs
	var err error
	if d, ok := f.(fs.ReadDirFile); ok {
		var list dirEntryDirs
		list, err = d.ReadDir(-1)
		dirs = list
	} else {
		var list fileInfoDirs
		list, err = f.Readdir(-1)
		dirs = list
	}

	if err != nil {

	if file == nil {
		return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist}
	}
	if file.IsDir() {
		return &openDir{file, f.readDir(name), 0}, nil
	}
	return &openFile{file, 0}, nil
}

// ReadDir reads and returns the entire named directory.
func (f FS) ReadDir(name string) ([]fs.DirEntry, error) {
	file, err := f.Open(name)
	if err != nil {
		return nil, err
	}
	dir, ok := file.(*openDir)

func (f *File) Readdir(n int) ([]FileInfo, error) {
	if f == nil {
		return nil, ErrInvalid
	}
	_, _, infos, err := f.readdir(n, readdirFileInfo)
	if infos == nil {
		// Readdir has historically always returned a non-nil empty slice, never nil,
		// even on error (except misuse with nil receiver above).
		// Keep it that way to avoid breaking overly sensitive callers.
		infos = []FileInfo{}
	}
	return infos, err
}

			case LDRB_EQ, LDRSB_EQ:
				if _, err := text.ReadAt(buf[:1], int64(addr)); err != nil {
					break
				}
				args[1] = fmt.Sprintf("$%#x", buf[0])

			case LDRH_EQ, LDRSH_EQ:
				if _, err := text.ReadAt(buf[:2], int64(addr)); err != nil {
					break
				}
				args[1] = fmt.Sprintf("$%#x", binary.LittleEndian.Uint16(buf))

			case LDR_EQ:
				if _, err := text.ReadAt(buf[:4], int64(addr)); err != nil {
					break
				}

        then:
        reader.hasOutput(1, StdOut)
        !reader.hasOutput(1, StdErr)
        !reader.hasOutput(2, StdErr)

        cleanup:
        reader.close()
    }

    def "can open empty reader"() {
        // neither file
        expect:
        output.reader().close() // no exception
    }

    def "exception if no output file"() {
        when: