Add --console to specify path to use from runc

This flag allows systems that are running runc to allocate tty's that
they own and provide to the container.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

exec.go

@@ -15,6 +15,13 @@ import (
 var execCommand = cli.Command{
 	Name:  "exec",
 	Usage: "execute new process inside the container",
+	Flags: []cli.Flag{
+		cli.StringFlag{
+			Name:  "console",
+			Value: "",
+			Usage: "specify the pty slave path for use with the container",
+		},
+	},
 	Action: func(context *cli.Context) {
 		config, err := loadProcessConfig(context.Args().First())
 		if err != nil {
@@ -45,7 +52,7 @@ func execProcess(context *cli.Context, config *specs.Process) (int, error) {
 	if err != nil {
 		return -1, err
 	}
-	tty, err := newTty(config.Terminal, process, rootuid)
+	tty, err := newTty(config.Terminal, process, rootuid, context.String("console"))
 	if err != nil {
 		return -1, err
 	}

restore.go

@@ -114,7 +114,7 @@ func restoreContainer(context *cli.Context, spec *specs.LinuxSpec, config *confi
 		Stdout: os.Stdout,
 		Stderr: os.Stderr,
 	}
-	tty, err := newTty(spec.Process.Terminal, process, rootuid)
+	tty, err := newTty(spec.Process.Terminal, process, rootuid, "")
 	if err != nil {
 		return -1, err
 	}

start.go

@@ -26,6 +26,11 @@ var startCommand = cli.Command{
 			Value: "",
 			Usage: "path to the root of the bundle directory",
 		},
+		cli.StringFlag{
+			Name:  "console",
+			Value: "",
+			Usage: "specify the pty slave path for use with the container",
+		},
 	},
 	Action: func(context *cli.Context) {
 		bundle := context.String("bundle")
@@ -44,9 +49,10 @@ var startCommand = cli.Command{
 			setupSdNotify(spec, rspec, notifySocket)
 		}
 
-		listenFds := os.Getenv("LISTEN_FDS")
-		listenPid := os.Getenv("LISTEN_PID")
-
+		var (
+			listenFds = os.Getenv("LISTEN_FDS")
+			listenPid = os.Getenv("LISTEN_PID")
+		)
 		if listenFds != "" && listenPid == strconv.Itoa(os.Getpid()) {
 			setupSocketActivation(spec, listenFds)
 		}
@@ -114,7 +120,7 @@ func startContainer(context *cli.Context, spec *specs.LinuxSpec, rspec *specs.Li
 			process.ExtraFiles = append(process.ExtraFiles, os.NewFile(uintptr(i), ""))
 		}
 	}
-	tty, err := newTty(spec.Process.Terminal, process, rootuid)
+	tty, err := newTty(spec.Process.Terminal, process, rootuid, context.String("console"))
 	if err != nil {
 		return -1, err
 	}

tty.go

@@ -14,9 +14,9 @@ import (
 // newTty creates a new tty for use with the container.  If a tty is not to be
 // created for the process, pipes are created so that the TTY of the parent
 // process are not inherited by the container.
-func newTty(create bool, p *libcontainer.Process, rootuid int) (*tty, error) {
+func newTty(create bool, p *libcontainer.Process, rootuid int, console string) (*tty, error) {
 	if create {
-		return createTty(p, rootuid)
+		return createTty(p, rootuid, console)
 	}
 	return createStdioPipes(p, rootuid)
 }
@@ -41,13 +41,20 @@ func createStdioPipes(p *libcontainer.Process, rootuid int) (*tty, error) {
 	return t, nil
 }
 
-func createTty(p *libcontainer.Process, rootuid int) (*tty, error) {
+func createTty(p *libcontainer.Process, rootuid int, consolePath string) (*tty, error) {
+	if consolePath != "" {
+		if err := p.ConsoleFromPath(consolePath); err != nil {
+			return nil, err
+		}
+		return &tty{}, nil
+	}
 	console, err := p.NewConsole(rootuid)
 	if err != nil {
 		return nil, err
 	}
 	go io.Copy(console, os.Stdin)
 	go io.Copy(os.Stdout, console)
+
 	state, err := term.SetRawTerminal(os.Stdin.Fd())
 	if err != nil {
 		return nil, fmt.Errorf("failed to set the terminal from the stdin: %v", err)