Move STDIO initialization to libcontainer.Process

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

libcontainer/process.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"math"
 	"os"
+	"syscall"
 )
 
 type processOperations interface {
@@ -78,6 +79,54 @@ func (p Process) Signal(sig os.Signal) error {
 	return p.ops.signal(sig)
 }
 
+// IO holds the process's STDIO
+type IO struct {
+	Stdin  io.WriteCloser
+	Stdout io.ReadCloser
+	Stderr io.ReadCloser
+}
+
+// InitializeIO creates pipes for use with the process's STDIO
+// and returns the opposite side for each
+func (p *Process) InitializeIO(rootuid int) (i *IO, err error) {
+	var fds []uintptr
+	i = &IO{}
+	// cleanup in case of an error
+	defer func() {
+		if err != nil {
+			for _, fd := range fds {
+				syscall.Close(int(fd))
+			}
+		}
+	}()
+	// STDIN
+	r, w, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+	fds = append(fds, r.Fd(), w.Fd())
+	p.Stdin, i.Stdin = r, w
+	// STDOUT
+	if r, w, err = os.Pipe(); err != nil {
+		return nil, err
+	}
+	fds = append(fds, r.Fd(), w.Fd())
+	p.Stdout, i.Stdout = w, r
+	// STDERR
+	if r, w, err = os.Pipe(); err != nil {
+		return nil, err
+	}
+	fds = append(fds, r.Fd(), w.Fd())
+	p.Stderr, i.Stderr = w, r
+	// change ownership of the pipes incase we are in a user namespace
+	for _, fd := range fds {
+		if err := syscall.Fchown(int(fd), rootuid, rootuid); err != nil {
+			return nil, err
+		}
+	}
+	return i, nil
+}
+
 // NewConsole creates new console for process and returns it
 func (p *Process) NewConsole(rootuid int) (Console, error) {
 	console, err := NewConsole(rootuid, rootuid)