written += n
		default:
			return written, true, err
		}
	}
	return written, true, nil
}

// copyFileRange performs one round of copy_file_range(2).
func copyFileRange(dst, src *FD, max int) (written int64, err error) {
	// The signature of copy_file_range(2) is:
	//
	// ssize_t copy_file_range(int fd_in, loff_t *off_in,
	//                         int fd_out, loff_t *off_out,

}

func (f *File) readFrom(r io.Reader) (written int64, handled bool, err error) {
	// Neither copy_file_range(2) nor splice(2) supports destinations opened with
	// O_APPEND, so don't bother to try zero-copy with these system calls.
	//
	// Visit https://man7.org/linux/man-pages/man2/copy_file_range.2.html#ERRORS and
	// https://man7.org/linux/man-pages/man2/splice.2.html#ERRORS for details.
	if f.appendMode {

	defer aa.Close()
	bb := NewFile(uintptr(bfd), b.Name())
	defer bb.Close()

	// This would fail on Linux in case the copy_file_range syscall was used because it doesn't
	// support destination files opened with O_APPEND, see
	// https://man7.org/linux/man-pages/man2/copy_file_range.2.html#ERRORS
	_, err = io.Copy(aa, bb)
	if err != nil {
		t.Fatal(err)
	}

	buf, err := ReadFile(aa.Name())
	if err != nil {

	// Now call ReadFrom (through io.Copy), which will hopefully call
	// poll.CopyFileRange.
	n, err := io.Copy(dst, realsrc)
	if err != nil {
		t.Fatal(err)
	}

	// If we didn't have a limit, we should have called poll.CopyFileRange
	// with the right file descriptor arguments.
	if limit > 0 && !hook.called {
		t.Fatal("never called poll.CopyFileRange")
	}
	if hook.called && hook.dstfd != int(dst.Fd()) {

// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package unix

import (
	"syscall"
	"unsafe"
)

func CopyFileRange(rfd int, roff *int64, wfd int, woff *int64, len int, flags int) (n int, err error) {
	r1, _, errno := syscall.Syscall6(copyFileRangeTrap,
		uintptr(rfd),
		uintptr(unsafe.Pointer(roff)),
		uintptr(wfd),

	if e1 != 0 {
		err = errnoErr(e1)
	}
	return
}

// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT

func CopyFileRange(rfd int, roff *int64, wfd int, woff *int64, len int, flags int) (n int, err error) {

//sys	ClockNanosleep(clockid int32, flags int, request *Timespec, remain *Timespec) (err error)
//sys	Close(fd int) (err error)
//sys	CloseRange(first uint, last uint, flags uint) (err error)
//sys	CopyFileRange(rfd int, roff *int64, wfd int, woff *int64, len int, flags int) (n int, err error)
//sys	DeleteModule(name string, flags int) (err error)
//sys	Dup(oldfd int) (fd int, err error)

func Dup2(oldfd, newfd int) error {