Add syncpipe for passing context

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

pkg/libcontainer/nsinit/exec.go

@@ -3,7 +3,6 @@
 package nsinit
 
 import (
-	"encoding/json"
 	"fmt"
 	"github.com/dotcloud/docker/pkg/libcontainer"
 	"github.com/dotcloud/docker/pkg/libcontainer/network"
@@ -28,11 +27,10 @@ func Exec(container *libcontainer.Container, stdin io.Reader, stdout, stderr io.
 
 	// create a pipe so that we can syncronize with the namespaced process and
 	// pass the veth name to the child
-	r, w, err := os.Pipe()
+	syncPipe, err := NewSyncPipe()
 	if err != nil {
 		return -1, err
 	}
-	system.UsetCloseOnExec(r.Fd())
 
 	if container.Tty {
 		log.Printf("setting up master and console")
@@ -42,8 +40,7 @@ func Exec(container *libcontainer.Container, stdin io.Reader, stdout, stderr io.
 		}
 	}
 
-	command := CreateCommand(container, console, logFile, r.Fd(), args)
-
+	command := CreateCommand(container, console, logFile, syncPipe.child.Fd(), args)
 	if container.Tty {
 		log.Printf("starting copy for tty")
 		go io.Copy(stdout, master)
@@ -79,15 +76,14 @@ func Exec(container *libcontainer.Container, stdin io.Reader, stdout, stderr io.
 		command.Process.Kill()
 		return -1, err
 	}
-	if err := InitializeNetworking(container, command.Process.Pid, w); err != nil {
+	if err := InitializeNetworking(container, command.Process.Pid, syncPipe); err != nil {
 		command.Process.Kill()
 		return -1, err
 	}
 
 	// Sync with child
 	log.Printf("closing sync pipes")
-	w.Close()
-	r.Close()
+	syncPipe.Close()
 
 	log.Printf("waiting on process")
 	if err := command.Wait(); err != nil {
@@ -109,7 +105,7 @@ func SetupCgroups(container *libcontainer.Container, nspid int) error {
 	return nil
 }
 
-func InitializeNetworking(container *libcontainer.Container, nspid int, pipe io.Writer) error {
+func InitializeNetworking(container *libcontainer.Container, nspid int, pipe *SyncPipe) error {
 	if container.Network != nil {
 		log.Printf("creating host network configuration type %s", container.Network.Type)
 		strategy, err := network.GetStrategy(container.Network.Type)
@@ -121,24 +117,13 @@ func InitializeNetworking(container *libcontainer.Container, nspid int, pipe io.
 			return err
 		}
 		log.Printf("sending %v as network context", networkContext)
-		if err := SendContext(pipe, networkContext); err != nil {
+		if err := pipe.SendToChild(networkContext); err != nil {
 			return err
 		}
 	}
 	return nil
 }
 
-// SendContext writes the veth pair name to the child's stdin then closes the
-// pipe so that the child stops waiting for more data
-func SendContext(pipe io.Writer, context libcontainer.Context) error {
-	data, err := json.Marshal(context)
-	if err != nil {
-		return err
-	}
-	pipe.Write(data)
-	return nil
-}
-
 // SetupWindow gets the parent window size and sets the master
 // pty to the current size and set the parents mode to RAW
 func SetupWindow(master, parent *os.File) (*term.State, error) {

pkg/libcontainer/nsinit/init.go

@@ -3,14 +3,11 @@
 package nsinit
 
 import (
-	"encoding/json"
 	"fmt"
 	"github.com/dotcloud/docker/pkg/libcontainer"
 	"github.com/dotcloud/docker/pkg/libcontainer/capabilities"
 	"github.com/dotcloud/docker/pkg/libcontainer/network"
 	"github.com/dotcloud/docker/pkg/system"
-	"io"
-	"io/ioutil"
 	"log"
 	"os"
 	"os/exec"
@@ -20,7 +17,7 @@ import (
 
 // Init is the init process that first runs inside a new namespace to setup mounts, users, networking,
 // and other options required for the new container.
-func Init(container *libcontainer.Container, uncleanRootfs, console string, pipe io.ReadCloser, args []string) error {
+func Init(container *libcontainer.Container, uncleanRootfs, console string, syncPipe *SyncPipe, args []string) error {
 	rootfs, err := resolveRootfs(uncleanRootfs)
 	if err != nil {
 		return err
@@ -28,16 +25,18 @@ func Init(container *libcontainer.Container, uncleanRootfs, console string, pipe
 	log.Printf("initializing namespace at %s", rootfs)
 
 	// We always read this as it is a way to sync with the parent as well
-	context, err := GetContextFromParent(pipe)
+	context, err := syncPipe.ReadFromParent()
 	if err != nil {
+		syncPipe.Close()
 		return err
 	}
+	syncPipe.Close()
+	log.Printf("received context from parent %v", context)
+
 	if console != "" {
 		log.Printf("setting up console for %s", console)
 		// close pipes so that we can replace it with the pty
-		os.Stdin.Close()
-		os.Stdout.Close()
-		os.Stderr.Close()
+		closeStdPipes()
 		slave, err := openTerminal(console, syscall.O_RDWR)
 		if err != nil {
 			return fmt.Errorf("open terminal %s", err)
@@ -79,18 +78,27 @@ func Init(container *libcontainer.Container, uncleanRootfs, console string, pipe
 			return fmt.Errorf("chdir to %s %s", container.WorkingDir, err)
 		}
 	}
+	return execArgs(args, container.Env)
+}
+
+func execArgs(args []string, env []string) error {
 	name, err := exec.LookPath(args[0])
 	if err != nil {
 		return err
 	}
-
 	log.Printf("execing %s goodbye", name)
-	if err := system.Exec(name, args[0:], container.Env); err != nil {
+	if err := system.Exec(name, args[0:], env); err != nil {
 		return fmt.Errorf("exec %s", err)
 	}
 	panic("unreachable")
 }
 
+func closeStdPipes() {
+	os.Stdin.Close()
+	os.Stdout.Close()
+	os.Stderr.Close()
+}
+
 // resolveRootfs ensures that the current working directory is
 // not a symlink and returns the absolute path to the rootfs
 func resolveRootfs(uncleanRootfs string) (string, error) {
@@ -153,19 +161,3 @@ func setupNetwork(config *libcontainer.Network, context libcontainer.Context) er
 	}
 	return nil
 }
-
-func GetContextFromParent(pipe io.ReadCloser) (libcontainer.Context, error) {
-	defer pipe.Close()
-	data, err := ioutil.ReadAll(pipe)
-	if err != nil {
-		return nil, fmt.Errorf("error reading from stdin %s", err)
-	}
-	var context libcontainer.Context
-	if len(data) > 0 {
-		if err := json.Unmarshal(data, &context); err != nil {
-			return nil, err
-		}
-		log.Printf("received context %v", context)
-	}
-	return context, nil
-}

pkg/libcontainer/nsinit/nsinit/main.go

@@ -74,7 +74,11 @@ func main() {
 		if flag.NArg() < 2 {
 			log.Fatal(ErrWrongArguments)
 		}
-		if err := nsinit.Init(container, cwd, console, os.NewFile(uintptr(pipeFd), "pipe"), flag.Args()[1:]); err != nil {
+		syncPipe, err := nsinit.NewSyncPipeFromFd(0, uintptr(pipeFd))
+		if err != nil {
+			log.Fatal(err)
+		}
+		if err := nsinit.Init(container, cwd, console, syncPipe, flag.Args()[1:]); err != nil {
 			log.Fatal(err)
 		}
 	default:

pkg/libcontainer/nsinit/sync_pipe.go

@@ -0,0 +1,73 @@
+package nsinit
+
+import (
+	"encoding/json"
+	"fmt"
+	"github.com/dotcloud/docker/pkg/libcontainer"
+	"github.com/dotcloud/docker/pkg/system"
+	"io/ioutil"
+	"os"
+)
+
+// SyncPipe allows communication to and from the child processes
+// to it's parent and allows the two independent processes to
+// syncronize their state.
+type SyncPipe struct {
+	parent, child *os.File
+}
+
+func NewSyncPipe() (s *SyncPipe, err error) {
+	s = &SyncPipe{}
+	s.child, s.parent, err = os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+	system.UsetCloseOnExec(s.child.Fd())
+	return s, nil
+}
+
+func NewSyncPipeFromFd(parendFd, childFd uintptr) (*SyncPipe, error) {
+	s := &SyncPipe{}
+	if parendFd > 0 {
+		s.parent = os.NewFile(parendFd, "parendPipe")
+	} else if childFd > 0 {
+		s.child = os.NewFile(childFd, "childPipe")
+	} else {
+		return nil, fmt.Errorf("no valid sync pipe fd specified")
+	}
+	return s, nil
+}
+
+func (s *SyncPipe) SendToChild(context libcontainer.Context) error {
+	data, err := json.Marshal(context)
+	if err != nil {
+		return err
+	}
+	s.parent.Write(data)
+	return nil
+}
+
+func (s *SyncPipe) ReadFromParent() (libcontainer.Context, error) {
+	data, err := ioutil.ReadAll(s.child)
+	if err != nil {
+		return nil, fmt.Errorf("error reading from sync pipe %s", err)
+	}
+	var context libcontainer.Context
+	if len(data) > 0 {
+		if err := json.Unmarshal(data, &context); err != nil {
+			return nil, err
+		}
+	}
+	return context, nil
+
+}
+
+func (s *SyncPipe) Close() error {
+	if s.parent != nil {
+		s.parent.Close()
+	}
+	if s.child != nil {
+		s.child.Close()
+	}
+	return nil
+}