Refactor and improve libcontainer and driver

Remove logging for now because it is complicating things
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

system/calls_linux.go

@@ -1,6 +1,7 @@
 package system
 
 import (
+	"os/exec"
 	"syscall"
 )
 
@@ -16,6 +17,14 @@ func Exec(cmd string, args []string, env []string) error {
 	return syscall.Exec(cmd, args, env)
 }
 
+func Execv(cmd string, args []string, env []string) error {
+	name, err := exec.LookPath(cmd)
+	if err != nil {
+		return err
+	}
+	return Exec(name, args, env)
+}
+
 func Fork() (int, error) {
 	syscall.ForkLock.Lock()
 	pid, _, err := syscall.Syscall(syscall.SYS_FORK, 0, 0, 0)

system/pty_linux.go

@@ -24,8 +24,35 @@ func Ptsname(f *os.File) (string, error) {
 	return fmt.Sprintf("/dev/pts/%d", n), nil
 }
 
+// CreateMasterAndConsole will open /dev/ptmx on the host and retreive the
+// pts name for use as the pty slave inside the container
+func CreateMasterAndConsole() (*os.File, string, error) {
+	master, err := os.OpenFile("/dev/ptmx", syscall.O_RDWR|syscall.O_NOCTTY|syscall.O_CLOEXEC, 0)
+	if err != nil {
+		return nil, "", err
+	}
+	console, err := Ptsname(master)
+	if err != nil {
+		return nil, "", err
+	}
+	if err := Unlockpt(master); err != nil {
+		return nil, "", err
+	}
+	return master, console, 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)
 }
+
+// OpenTerminal is a clone of os.OpenFile without the O_CLOEXEC
+// used to open the pty slave inside the container namespace
+func OpenTerminal(name string, flag int) (*os.File, error) {
+	r, e := syscall.Open(name, flag, 0)
+	if e != nil {
+		return nil, &os.PathError{"open", name, e}
+	}
+	return os.NewFile(uintptr(r), name), nil
+}