// to close the wrong file descriptor.
type file struct {
	pfd        poll.FD
	name       string
	dirinfo    atomic.Pointer[dirInfo] // nil unless directory being read
	appendMode bool                    // whether file is opened for appending
}

// Fd returns the Windows handle referencing the open file.
// If f is closed, the file descriptor becomes invalid.

//
// If file was opened with the O_APPEND flag, WriteAt returns an error.
func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
	if err := f.checkValid("write"); err != nil {
		return 0, err
	}
	if f.appendMode {
		return 0, errWriteAtInAppendMode
	}

	if off < 0 {
		return 0, &PathError{Op: "writeat", Path: f.name, Err: errors.New("negative offset")}
	}

	for len(b) > 0 {
		m, e := f.pwrite(b, off)

// to close the wrong file descriptor.
type file struct {
	fdmu       poll.FDMutex
	fd         int
	name       string
	dirinfo    atomic.Pointer[dirInfo] // nil unless directory being read
	appendMode bool                    // whether file is opened for appending
}

// Fd returns the integer Plan 9 file descriptor referencing the open file.
// If f is closed, the file descriptor becomes invalid.