Do not set file descriptor into blocking mode

(*os.File).Fd() implicitly sets file descriptor into blocking mode [1], [2]
We avoid that by calling (*os.File).SyscallConn instead.
This method was added in go1.12 (released on 2019-02-25)

[1]: https://pkg.go.dev/os#File.Fd
[2]: https://cs.opensource.google/go/go/+/refs/tags/go1.20.3:src/os/file_unix.go;l=80-87

ioctl_inner.go

@@ -10,7 +10,7 @@ const (
 	TIOCSWINSZ = syscall.TIOCSWINSZ
 )
 
-func ioctl(fd, cmd, ptr uintptr) error {
+func ioctl_inner(fd, cmd, ptr uintptr) error {
 	_, _, e := syscall.Syscall(syscall.SYS_IOCTL, fd, cmd, ptr)
 	if e != 0 {
 		return e

ioctl_outer.go

@@ -0,0 +1,24 @@
+//go:build !windows
+// +build !windows
+
+//
+package pty
+
+import "os"
+
+func ioctl(f *os.File, cmd, ptr uintptr) error {
+	sc, e := f.SyscallConn()
+	if e != nil {
+		return ioctl_inner(f.Fd(), cmd, ptr) // fall back to blocking io (old behavior)
+	}
+
+	ch := make(chan error, 1)
+	defer close(ch)
+
+	e = sc.Control(func(fd uintptr) { ch <- ioctl_inner(fd, cmd, ptr) })
+	if e != nil {
+		return e
+	}
+	e = <-ch
+	return e
+}

ioctl_solaris.go

@@ -40,7 +40,7 @@ type strioctl struct {
 // Defined in asm_solaris_amd64.s.
 func sysvicall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err syscall.Errno)
 
-func ioctl(fd, cmd, ptr uintptr) error {
+func ioctl_inner(fd, cmd, ptr uintptr) error {
 	if _, _, errno := sysvicall6(uintptr(unsafe.Pointer(&procioctl)), 3, fd, cmd, ptr, 0, 0, 0); errno != 0 {
 		return errno
 	}

ioctl_unsupported.go

@@ -8,6 +8,6 @@ const (
 	TIOCSWINSZ = 0
 )
 
-func ioctl(fd, cmd, ptr uintptr) error {
+func ioctl_inner(fd, cmd, ptr uintptr) error {
 	return ErrUnsupported
 }

pty_darwin.go

@@ -46,7 +46,7 @@ func open() (pty, tty *os.File, err error) {
 func ptsname(f *os.File) (string, error) {
 	n := make([]byte, _IOC_PARM_LEN(syscall.TIOCPTYGNAME))
 
-	err := ioctl(f.Fd(), syscall.TIOCPTYGNAME, uintptr(unsafe.Pointer(&n[0])))
+	err := ioctl(f, syscall.TIOCPTYGNAME, uintptr(unsafe.Pointer(&n[0])))
 	if err != nil {
 		return "", err
 	}
@@ -60,9 +60,9 @@ func ptsname(f *os.File) (string, error) {
 }
 
 func grantpt(f *os.File) error {
-	return ioctl(f.Fd(), syscall.TIOCPTYGRANT, 0)
+	return ioctl(f, syscall.TIOCPTYGRANT, 0)
 }
 
 func unlockpt(f *os.File) error {
-	return ioctl(f.Fd(), syscall.TIOCPTYUNLK, 0)
+	return ioctl(f, syscall.TIOCPTYUNLK, 0)
 }

pty_dragonfly.go

@@ -45,17 +45,17 @@ func open() (pty, tty *os.File, err error) {
 }
 
 func grantpt(f *os.File) error {
-	_, err := isptmaster(f.Fd())
+	_, err := isptmaster(f)
 	return err
 }
 
 func unlockpt(f *os.File) error {
-	_, err := isptmaster(f.Fd())
+	_, err := isptmaster(f)
 	return err
 }
 
-func isptmaster(fd uintptr) (bool, error) {
-	err := ioctl(fd, syscall.TIOCISPTMASTER, 0)
+func isptmaster(f *os.File) (bool, error) {
+	err := ioctl(f, syscall.TIOCISPTMASTER, 0)
 	return err == nil, err
 }
 
@@ -68,7 +68,7 @@ func ptsname(f *os.File) (string, error) {
 	name := make([]byte, _C_SPECNAMELEN)
 	fa := fiodgnameArg{Name: (*byte)(unsafe.Pointer(&name[0])), Len: _C_SPECNAMELEN, Pad_cgo_0: [4]byte{0, 0, 0, 0}}
 
-	err := ioctl(f.Fd(), ioctl_FIODNAME, uintptr(unsafe.Pointer(&fa)))
+	err := ioctl(f, ioctl_FIODNAME, uintptr(unsafe.Pointer(&fa)))
 	if err != nil {
 		return "", err
 	}

pty_freebsd.go

@@ -44,8 +44,8 @@ func open() (pty, tty *os.File, err error) {
 	return p, t, nil
 }
 
-func isptmaster(fd uintptr) (bool, error) {
-	err := ioctl(fd, syscall.TIOCPTMASTER, 0)
+func isptmaster(f *os.File) (bool, error) {
+	err := ioctl(f, syscall.TIOCPTMASTER, 0)
 	return err == nil, err
 }
 
@@ -55,7 +55,7 @@ var (
 )
 
 func ptsname(f *os.File) (string, error) {
-	master, err := isptmaster(f.Fd())
+	master, err := isptmaster(f)
 	if err != nil {
 		return "", err
 	}
@@ -68,7 +68,7 @@ func ptsname(f *os.File) (string, error) {
 		buf = make([]byte, n)
 		arg = fiodgnameArg{Len: n, Buf: (*byte)(unsafe.Pointer(&buf[0]))}
 	)
-	if err := ioctl(f.Fd(), ioctlFIODGNAME, uintptr(unsafe.Pointer(&arg))); err != nil {
+	if err := ioctl(f, ioctlFIODGNAME, uintptr(unsafe.Pointer(&arg))); err != nil {
 		return "", err
 	}
 

pty_linux.go

@@ -40,7 +40,7 @@ func open() (pty, tty *os.File, err error) {
 
 func ptsname(f *os.File) (string, error) {
 	var n _C_uint
-	err := ioctl(f.Fd(), syscall.TIOCGPTN, uintptr(unsafe.Pointer(&n))) //nolint:gosec // Expected unsafe pointer for Syscall call.
+	err := ioctl(f, syscall.TIOCGPTN, uintptr(unsafe.Pointer(&n))) //nolint:gosec // Expected unsafe pointer for Syscall call.
 	if err != nil {
 		return "", err
 	}
@@ -50,5 +50,5 @@ func ptsname(f *os.File) (string, error) {
 func unlockpt(f *os.File) error {
 	var u _C_int
 	// use TIOCSPTLCK with a pointer to zero to clear the lock
-	return ioctl(f.Fd(), syscall.TIOCSPTLCK, uintptr(unsafe.Pointer(&u))) //nolint:gosec // Expected unsafe pointer for Syscall call.
+	return ioctl(f, syscall.TIOCSPTLCK, uintptr(unsafe.Pointer(&u))) //nolint:gosec // Expected unsafe pointer for Syscall call.
 }

pty_netbsd.go

@@ -47,7 +47,7 @@ func ptsname(f *os.File) (string, error) {
 	 * ioctl(fd, TIOCPTSNAME, &pm) == -1 ? NULL : pm.sn;
 	 */
 	var ptm ptmget
-	if err := ioctl(f.Fd(), uintptr(ioctl_TIOCPTSNAME), uintptr(unsafe.Pointer(&ptm))); err != nil {
+	if err := ioctl(f, uintptr(ioctl_TIOCPTSNAME), uintptr(unsafe.Pointer(&ptm))); err != nil {
 		return "", err
 	}
 	name := make([]byte, len(ptm.Sn))
@@ -65,5 +65,5 @@ func grantpt(f *os.File) error {
 	 * from grantpt(3): Calling grantpt() is equivalent to:
 	 * ioctl(fd, TIOCGRANTPT, 0);
 	 */
-	return ioctl(f.Fd(), uintptr(ioctl_TIOCGRANTPT), 0)
+	return ioctl(f, uintptr(ioctl_TIOCGRANTPT), 0)
 }

pty_openbsd.go

@@ -36,7 +36,7 @@ func open() (pty, tty *os.File, err error) {
 	defer p.Close()
 
 	var ptm ptmget
-	if err := ioctl(p.Fd(), uintptr(ioctl_PTMGET), uintptr(unsafe.Pointer(&ptm))); err != nil {
+	if err := ioctl(p, uintptr(ioctl_PTMGET), uintptr(unsafe.Pointer(&ptm))); err != nil {
 		return nil, nil, err
 	}
 

pty_solaris.go

@@ -65,7 +65,7 @@ func open() (pty, tty *os.File, err error) {
 }
 
 func ptsname(f *os.File) (string, error) {
-	dev, err := ptsdev(f.Fd())
+	dev, err := ptsdev(f)
 	if err != nil {
 		return "", err
 	}
@@ -84,12 +84,12 @@ func unlockpt(f *os.File) error {
 		icLen:     0,
 		icDP:      nil,
 	}
-	return ioctl(f.Fd(), I_STR, uintptr(unsafe.Pointer(&istr)))
+	return ioctl(f, I_STR, uintptr(unsafe.Pointer(&istr)))
 }
 
 func minor(x uint64) uint64 { return x & 0377 }
 
-func ptsdev(fd uintptr) (uint64, error) {
+func ptsdev(f *os.File) (uint64, error) {
 	istr := strioctl{
 		icCmd:     ISPTM,
 		icTimeout: 0,
@@ -97,14 +97,33 @@ func ptsdev(fd uintptr) (uint64, error) {
 		icDP:      nil,
 	}
 
-	if err := ioctl(fd, I_STR, uintptr(unsafe.Pointer(&istr))); err != nil {
+	if err := ioctl(f, I_STR, uintptr(unsafe.Pointer(&istr))); err != nil {
 		return 0, err
 	}
-	var status syscall.Stat_t
-	if err := syscall.Fstat(int(fd), &status); err != nil {
+	var errors = make(chan error, 1)
+	var results = make(chan uint64, 1)
+	defer close(errors)
+	defer close(results)
+
+	var err error
+	var sc syscall.RawConn
+	sc, err = f.SyscallConn()
+	if err != nil {
 		return 0, err
 	}
-	return uint64(minor(status.Rdev)), nil
+	err = sc.Control(func(fd uintptr) {
+		var status syscall.Stat_t
+		if err := syscall.Fstat(int(fd), &status); err != nil {
+			results <- 0
+			errors <- err
+		}
+		results <- uint64(minor(status.Rdev))
+		errors <- nil
+	})
+	if err != nil {
+		return 0, err
+	}
+	return <-results, <-errors
 }
 
 type ptOwn struct {
@@ -113,7 +132,7 @@ type ptOwn struct {
 }
 
 func grantpt(f *os.File) error {
-	if _, err := ptsdev(f.Fd()); err != nil {
+	if _, err := ptsdev(f); err != nil {
 		return err
 	}
 	pto := ptOwn{
@@ -127,7 +146,7 @@ func grantpt(f *os.File) error {
 		icLen:     int32(unsafe.Sizeof(strioctl{})),
 		icDP:      unsafe.Pointer(&pto),
 	}
-	if err := ioctl(f.Fd(), I_STR, uintptr(unsafe.Pointer(&istr))); err != nil {
+	if err := ioctl(f, I_STR, uintptr(unsafe.Pointer(&istr))); err != nil {
 		return errors.New("access denied")
 	}
 	return nil
@@ -145,8 +164,8 @@ func streamsPush(f *os.File, mod string) error {
 	// but since we are not using libc or XPG4.2, we should not be
 	// double-pushing modules
 
-	if err := ioctl(f.Fd(), I_FIND, uintptr(unsafe.Pointer(&buf[0]))); err != nil {
+	if err := ioctl(f, I_FIND, uintptr(unsafe.Pointer(&buf[0]))); err != nil {
 		return nil
 	}
-	return ioctl(f.Fd(), I_PUSH, uintptr(unsafe.Pointer(&buf[0])))
+	return ioctl(f, I_PUSH, uintptr(unsafe.Pointer(&buf[0])))
 }

winsize_unix.go

@@ -20,7 +20,7 @@ type Winsize struct {
 // Setsize resizes t to s.
 func Setsize(t *os.File, ws *Winsize) error {
 	//nolint:gosec // Expected unsafe pointer for Syscall call.
-	return ioctl(t.Fd(), syscall.TIOCSWINSZ, uintptr(unsafe.Pointer(ws)))
+	return ioctl(t, syscall.TIOCSWINSZ, uintptr(unsafe.Pointer(ws)))
 }
 
 // GetsizeFull returns the full terminal size description.
@@ -28,7 +28,7 @@ func GetsizeFull(t *os.File) (size *Winsize, err error) {
 	var ws Winsize
 
 	//nolint:gosec // Expected unsafe pointer for Syscall call.
-	if err := ioctl(t.Fd(), syscall.TIOCGWINSZ, uintptr(unsafe.Pointer(&ws))); err != nil {
+	if err := ioctl(t, syscall.TIOCGWINSZ, uintptr(unsafe.Pointer(&ws))); err != nil {
 		return nil, err
 	}
 	return &ws, nil