*: console rewrite

This implements {createTTY, detach} and all of the combinations and
negations of the two that were previously implemented. There are some
valid questions about out-of-OCI-scope topics like !createTTY and how
things should be handled (why do we dup the current stdio to the
process, and how is that not a security issue). However, these will be
dealt with in a separate patchset.

In order to allow for late console setup, split setupRootfs into the
"preparation" section where all of the mounts are created and the
"finalize" section where we pivot_root and set things as ro. In between
the two we can set up all of the console mountpoints and symlinks we
need.

We use two-stage synchronisation to ensures that when the syscalls are
reordered in a suboptimal way, an out-of-place read() on the parentPipe
will not gobble the ancilliary information.

This patch is part of the console rewrite patchset.

Signed-off-by: Aleksa Sarai <asarai@suse.de>

tty.go

@@ -7,11 +7,26 @@ import (
 	"io"
 	"os"
 	"sync"
+	"syscall"
 
 	"github.com/docker/docker/pkg/term"
 	"github.com/opencontainers/runc/libcontainer"
 )
 
+type tty struct {
+	console   libcontainer.Console
+	state     *term.State
+	closers   []io.Closer
+	postStart []io.Closer
+	wg        sync.WaitGroup
+}
+
+func (t *tty) copyIO(w io.Writer, r io.ReadCloser) {
+	defer t.wg.Done()
+	io.Copy(w, r)
+	r.Close()
+}
+
 // setup standard pipes so that the TTY of the calling runc process
 // is not inherited by the container.
 func createStdioPipes(p *libcontainer.Process, rootuid, rootgid int) (*tty, error) {
@@ -46,45 +61,43 @@ func createStdioPipes(p *libcontainer.Process, rootuid, rootgid int) (*tty, erro
 	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, rootgid int, consolePath string) (*tty, error) {
-	if consolePath != "" {
-		if err := p.ConsoleFromPath(consolePath); err != nil {
-			return nil, err
+func dupStdio(process *libcontainer.Process, rootuid, rootgid int) error {
+	process.Stdin = os.Stdin
+	process.Stdout = os.Stdout
+	process.Stderr = os.Stderr
+	for _, fd := range []uintptr{
+		os.Stdin.Fd(),
+		os.Stdout.Fd(),
+		os.Stderr.Fd(),
+	} {
+		if err := syscall.Fchown(int(fd), rootuid, rootgid); err != nil {
+			return err
 		}
-		return &tty{}, nil
 	}
-	console, err := p.NewConsole(rootuid, rootgid)
-	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)
-	}
-	return &tty{
-		console: console,
-		state:   state,
-		closers: []io.Closer{
-			console,
-		},
-	}, nil
+	return nil
 }
 
-type tty struct {
-	console   libcontainer.Console
-	state     *term.State
-	closers   []io.Closer
-	postStart []io.Closer
-	wg        sync.WaitGroup
+func (t *tty) recvtty(process *libcontainer.Process, detach bool) error {
+	console, err := process.GetConsole()
+	if err != nil {
+		return err
+	}
+
+	if !detach {
+		go io.Copy(console, os.Stdin)
+		t.wg.Add(1)
+		go t.copyIO(os.Stdout, console)
+
+		state, err := term.SetRawTerminal(os.Stdin.Fd())
+		if err != nil {
+			return fmt.Errorf("failed to set the terminal from the stdin: %v", err)
+		}
+		t.state = state
+	}
+
+	t.console = console
+	t.closers = []io.Closer{console}
+	return nil
 }
 
 // ClosePostStart closes any fds that are provided to the container and dup2'd