Improve general quality of libcontainer

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)

system/pty_linux.go

@@ -0,0 +1,31 @@
+package system
+
+import (
+	"fmt"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+// Unlockpt unlocks the slave pseudoterminal device corresponding to the master pseudoterminal referred to by f.
+// Unlockpt should be called before opening the slave side of a pseudoterminal.
+func Unlockpt(f *os.File) error {
+	var u int
+	return Ioctl(f.Fd(), syscall.TIOCSPTLCK, uintptr(unsafe.Pointer(&u)))
+}
+
+// Ptsname retrieves the name of the first available pts for the given master.
+func Ptsname(f *os.File) (string, error) {
+	var n int
+
+	if err := Ioctl(f.Fd(), syscall.TIOCGPTN, uintptr(unsafe.Pointer(&n))); err != nil {
+		return "", err
+	}
+	return fmt.Sprintf("/dev/pts/%d", n), nil
+}
+
+// OpenPtmx opens /dev/ptmx, i.e. the PTY master.
+func OpenPtmx() (*os.File, error) {
+	// O_NOCTTY and O_CLOEXEC are not present in os package so we use the syscall's one for all.
+	return os.OpenFile("/dev/ptmx", syscall.O_RDONLY|syscall.O_NOCTTY|syscall.O_CLOEXEC, 0)
+}