io: stop screwing with \n in console output

The default terminal setting for a new pty on Linux (unix98) has +ONLCR,
resulting in '\n' writes by a container process to be converted to
'\r\n' reads by the managing process. This is quite unexpected, To fix it, make
the terminal sane after opening it by setting -ONLCR.

this patch fix method comes from: eea28f480d
thanks @cyphar Aleksa Sarai <asarai@suse.de>

Signed-off-by: Wang Long <long.wanglong@huawei.com>

cmd/containerd-shim/console.go

@@ -16,6 +16,9 @@ func newConsole(uid, gid int) (*os.File, string, error) {
 	if err != nil {
 		return nil, "", err
 	}
+	if err = saneTerminal(master); err != nil {
+		return nil, "", err
+	}
 	console, err := ptsname(master)
 	if err != nil {
 		return nil, "", err
@@ -32,6 +35,29 @@ func newConsole(uid, gid int) (*os.File, string, error) {
 	return master, console, nil
 }
 
+// saneTerminal sets the necessary tty_ioctl(4)s to ensure that a pty pair
+// created by us acts normally. In particular, a not-very-well-known default of
+// Linux unix98 ptys is that they have +onlcr by default. While this isn't a
+// problem for terminal emulators, because we relay data from the terminal we
+// also relay that funky line discipline.
+func saneTerminal(terminal *os.File) error {
+	// Go doesn't have a wrapper for any of the termios ioctls.
+	var termios syscall.Termios
+
+	if err := ioctl(terminal.Fd(), syscall.TCGETS, uintptr(unsafe.Pointer(&termios))); err != nil {
+		return fmt.Errorf("ioctl(tty, tcgets): %s", err.Error())
+	}
+
+	// Set -onlcr so we don't have to deal with \r.
+	termios.Oflag &^= syscall.ONLCR
+
+	if err := ioctl(terminal.Fd(), syscall.TCSETS, uintptr(unsafe.Pointer(&termios))); err != nil {
+		return fmt.Errorf("ioctl(tty, tcsets): %s", err.Error())
+	}
+
+	return nil
+}
+
 func ioctl(fd uintptr, flag, data uintptr) error {
 	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, fd, flag, data); err != 0 {
 		return err