Simplify namespaces with only nsinit

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

libcontainer/nsinit/exec.go

@@ -0,0 +1,80 @@
+package main
+
+import (
+	"github.com/dotcloud/docker/pkg/libcontainer"
+	"github.com/dotcloud/docker/pkg/system"
+	"github.com/dotcloud/docker/pkg/term"
+	"io"
+	"log"
+	"os"
+	"os/exec"
+	"syscall"
+)
+
+func execCommand(container *libcontainer.Container) (pid int, err error) {
+	master, console, err := createMasterAndConsole()
+	if err != nil {
+		return -1, err
+	}
+
+	// we need CLONE_VFORK so we can wait on the child
+	flag := uintptr(getNamespaceFlags(container.Namespaces) | CLONE_VFORK)
+
+	command := exec.Command("nsinit", console)
+	command.SysProcAttr = &syscall.SysProcAttr{
+		Cloneflags: flag,
+	}
+
+	if err := command.Start(); err != nil {
+		return -1, err
+	}
+	pid = command.Process.Pid
+
+	go func() {
+		if _, err := io.Copy(os.Stdout, master); err != nil {
+			log.Println(err)
+		}
+	}()
+
+	go func() {
+		if _, err := io.Copy(master, os.Stdin); err != nil {
+			log.Println(err)
+		}
+	}()
+
+	ws, err := term.GetWinsize(os.Stdin.Fd())
+	if err != nil {
+		return -1, err
+	}
+	if err := term.SetWinsize(master.Fd(), ws); err != nil {
+		return -1, err
+	}
+	state, err := term.SetRawTerminal(os.Stdin.Fd())
+	if err != nil {
+		command.Process.Kill()
+		return -1, err
+	}
+	defer term.RestoreTerminal(os.Stdin.Fd(), state)
+
+	if err := command.Wait(); err != nil {
+		return pid, err
+	}
+	return pid, nil
+}
+
+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 := system.Ptsname(master)
+	if err != nil {
+		return nil, "", err
+	}
+
+	if err := system.Unlockpt(master); err != nil {
+		return nil, "", err
+	}
+	return master, console, nil
+}