Wait for pipes to write all data before exit

Add a waitgroup to wait for the io.Copy of stdout/err to finish before
existing runc.  The problem happens more in exec because it is really
fast and the pipe has data buffered but not yet read after the process
has already exited.

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

tty.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"sync"
 
 	"github.com/docker/docker/pkg/term"
 	"github.com/opencontainers/runc/libcontainer"
@@ -35,15 +36,32 @@ func createStdioPipes(p *libcontainer.Process, rootuid int) (*tty, error) {
 			i.Stderr,
 		},
 	}
+	// add the process's io to the post start closers if they support close
+	for _, cc := range []interface{}{
+		p.Stdin,
+		p.Stdout,
+		p.Stderr,
+	} {
+		if c, ok := cc.(io.Closer); ok {
+			t.postStart = append(t.postStart, c)
+		}
+	}
 	go func() {
 		io.Copy(i.Stdin, os.Stdin)
 		i.Stdin.Close()
 	}()
-	go io.Copy(os.Stdout, i.Stdout)
-	go io.Copy(os.Stderr, i.Stderr)
+	t.wg.Add(2)
+	go t.copyIO(os.Stdout, i.Stdout)
+	go t.copyIO(os.Stderr, i.Stderr)
 	return t, nil
 }
 
+func (t *tty) copyIO(w io.Writer, r io.ReadCloser) {
+	defer t.wg.Done()
+	io.Copy(w, r)
+	r.Close()
+}
+
 func createTty(p *libcontainer.Process, rootuid int, consolePath string) (*tty, error) {
 	if consolePath != "" {
 		if err := p.ConsoleFromPath(consolePath); err != nil {
@@ -62,23 +80,41 @@ func createTty(p *libcontainer.Process, rootuid int, consolePath string) (*tty,
 	if err != nil {
 		return nil, fmt.Errorf("failed to set the terminal from the stdin: %v", err)
 	}
-	t := &tty{
+	return &tty{
 		console: console,
 		state:   state,
 		closers: []io.Closer{
 			console,
 		},
-	}
-	return t, nil
+	}, nil
 }
 
 type tty struct {
-	console libcontainer.Console
-	state   *term.State
-	closers []io.Closer
+	console   libcontainer.Console
+	state     *term.State
+	closers   []io.Closer
+	postStart []io.Closer
+	wg        sync.WaitGroup
 }
 
+// ClosePostStart closes any fds that are provided to the container and dup2'd
+// so that we no longer have copy in our process.
+func (t *tty) ClosePostStart() error {
+	for _, c := range t.postStart {
+		c.Close()
+	}
+	return nil
+}
+
+// Close closes all open fds for the tty and/or restores the orignal
+// stdin state to what it was prior to the container execution
 func (t *tty) Close() error {
+	// ensure that our side of the fds are always closed
+	for _, c := range t.postStart {
+		c.Close()
+	}
+	// wait for the copy routines to finish before closing the fds
+	t.wg.Wait()
 	for _, c := range t.closers {
 		c.Close()
 	}