Add null io option

This adds null IO option for efficient handling of IO.
It provides a container directly with `/dev/null` and does not require
any io.Copy within the shim whenever a user does not want the IO of the
container.

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

cmd/stress/main.go

@@ -1,10 +1,8 @@
 package main
 
 import (
-	"bytes"
 	"context"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"os/signal"
 	"runtime"
@@ -205,7 +203,7 @@ func (w *worker) runContainer(ctx context.Context, id string) error {
 	}
 	defer c.Delete(ctx, containerd.WithSnapshotCleanup)
 
-	task, err := c.NewTask(ctx, containerd.NewIO(bytes.NewBuffer(nil), ioutil.Discard, ioutil.Discard))
+	task, err := c.NewTask(ctx, containerd.NullIO)
 	if err != nil {
 		return err
 	}

container_test.go

@@ -19,8 +19,7 @@ import (
 )
 
 func empty() IOCreation {
-	null := ioutil.Discard
-	return NewIO(bytes.NewBuffer(nil), null, null)
+	return NullIO
 }
 
 func TestContainerList(t *testing.T) {

io.go

@@ -126,6 +126,11 @@ func StdioTerminal(id string) (*IO, error) {
 	return NewIOWithTerminal(os.Stdin, os.Stdout, os.Stderr, true)(id)
 }
 
+// NullIO redirects the container's IO into /dev/null
+func NullIO(id string) (*IO, error) {
+	return &IO{}, nil
+}
+
 // FIFOSet is a set of fifos for use with tasks
 type FIFOSet struct {
 	// Dir is the directory holding the task fifos

linux/shim/exec.go

@@ -133,7 +133,6 @@ func (e *execProcess) Stdio() stdio {
 func (e *execProcess) Start(ctx context.Context) (err error) {
 	var (
 		socket  *runc.Socket
-		io      runc.IO
 		pidfile = filepath.Join(e.path, fmt.Sprintf("%s.pid", e.id))
 	)
 	if e.stdio.terminal {
@@ -141,15 +140,18 @@ func (e *execProcess) Start(ctx context.Context) (err error) {
 			return errors.Wrap(err, "failed to create runc console socket")
 		}
 		defer socket.Close()
+	} else if e.stdio.isNull() {
+		if e.io, err = runc.NewNullIO(); err != nil {
+			return errors.Wrap(err, "creating new NULL IO")
+		}
 	} else {
-		if io, err = runc.NewPipeIO(); err != nil {
+		if e.io, err = runc.NewPipeIO(); err != nil {
 			return errors.Wrap(err, "failed to create runc io pipes")
 		}
-		e.io = io
 	}
 	opts := &runc.ExecOpts{
 		PidFile: pidfile,
-		IO:      io,
+		IO:      e.io,
 		Detach:  true,
 	}
 	if socket != nil {
@@ -175,8 +177,8 @@ func (e *execProcess) Start(ctx context.Context) (err error) {
 		if e.console, err = e.parent.platform.copyConsole(ctx, console, e.stdio.stdin, e.stdio.stdout, e.stdio.stderr, &e.WaitGroup, &copyWaitGroup); err != nil {
 			return errors.Wrap(err, "failed to start console copy")
 		}
-	} else {
-		if err := copyPipes(ctx, io, e.stdio.stdin, e.stdio.stdout, e.stdio.stderr, &e.WaitGroup, &copyWaitGroup); err != nil {
+	} else if !e.stdio.isNull() {
+		if err := copyPipes(ctx, e.io, e.stdio.stdin, e.stdio.stdout, e.stdio.stderr, &e.WaitGroup, &copyWaitGroup); err != nil {
 			return errors.Wrap(err, "failed to start io pipe copy")
 		}
 	}

linux/shim/init.go

@@ -117,18 +117,20 @@ func newInitProcess(context context.Context, plat platform, path, namespace, wor
 	var (
 		err    error
 		socket *runc.Socket
-		io     runc.IO
 	)
 	if r.Terminal {
 		if socket, err = runc.NewTempConsoleSocket(); err != nil {
 			return nil, errors.Wrap(err, "failed to create OCI runtime console socket")
 		}
 		defer socket.Close()
+	} else if hasNoIO(r) {
+		if p.io, err = runc.NewNullIO(); err != nil {
+			return nil, errors.Wrap(err, "creating new NULL IO")
+		}
 	} else {
-		if io, err = runc.NewPipeIO(); err != nil {
+		if p.io, err = runc.NewPipeIO(); err != nil {
 			return nil, errors.Wrap(err, "failed to create OCI runtime io pipes")
 		}
-		p.io = io
 	}
 	pidFile := filepath.Join(path, "init.pid")
 	if r.Checkpoint != "" {
@@ -139,7 +141,7 @@ func newInitProcess(context context.Context, plat platform, path, namespace, wor
 				ParentPath: r.ParentCheckpoint,
 			},
 			PidFile:     pidFile,
-			IO:          io,
+			IO:          p.io,
 			NoPivot:     options.NoPivotRoot,
 			Detach:      true,
 			NoSubreaper: true,
@@ -150,7 +152,7 @@ func newInitProcess(context context.Context, plat platform, path, namespace, wor
 	} else {
 		opts := &runc.CreateOpts{
 			PidFile:      pidFile,
-			IO:           io,
+			IO:           p.io,
 			NoPivot:      options.NoPivotRoot,
 			NoNewKeyring: options.NoNewKeyring,
 		}
@@ -180,8 +182,8 @@ func newInitProcess(context context.Context, plat platform, path, namespace, wor
 			return nil, errors.Wrap(err, "failed to start console copy")
 		}
 		p.console = console
-	} else {
-		if err := copyPipes(context, io, r.Stdin, r.Stdout, r.Stderr, &p.WaitGroup, &copyWaitGroup); err != nil {
+	} else if !hasNoIO(r) {
+		if err := copyPipes(context, p.io, r.Stdin, r.Stdout, r.Stderr, &p.WaitGroup, &copyWaitGroup); err != nil {
 			return nil, errors.Wrap(err, "failed to start io pipe copy")
 		}
 	}
@@ -427,3 +429,7 @@ func checkKillError(err error) error {
 	}
 	return errors.Wrapf(err, "unknown error after kill")
 }
+
+func hasNoIO(r *shimapi.CreateTaskRequest) bool {
+	return r.Stdin == "" && r.Stdout == "" && r.Stderr == ""
+}

linux/shim/process.go

@@ -17,6 +17,10 @@ type stdio struct {
 	terminal bool
 }
 
+func (s stdio) isNull() bool {
+	return s.stdin == "" && s.stdout == "" && s.stderr == ""
+}
+
 type process interface {
 	// ID returns the id for the process
 	ID() string