add better generate

Signed-off-by: Jess Frazelle <acidburn@microsoft.com>

container/rootfs.go

@@ -0,0 +1,43 @@
+package container
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"github.com/docker/docker/pkg/archive"
+)
+
+const (
+	// DefaultTarballPath holds the default path for the embedded tarball.
+	DefaultTarballPath = "image.tar"
+)
+
+// UnpackRootfs unpacks the embedded tarball to the rootfs.
+func (c *Container) UnpackRootfs(rootfsDir string, asset func(string) ([]byte, error)) error {
+	// Make the rootfs directory.
+	if err := os.MkdirAll(rootfsDir, 0755); err != nil {
+		return err
+	}
+
+	// Get the embedded tarball.
+	data, err := asset(DefaultTarballPath)
+	if err != nil {
+		return fmt.Errorf("getting bindata asset image.tar failed: %v", err)
+	}
+
+	// Unpack the tarball.
+	r := bytes.NewReader(data)
+	if err := archive.Untar(r, rootfsDir, &archive.TarOptions{NoLchown: true}); err != nil {
+		return err
+	}
+
+	// Write a resolv.conf.
+	if err := ioutil.WriteFile(filepath.Join(rootfsDir, "etc", "resolv.conf"), []byte("nameserver 8.8.8.8\nnameserver 8.8.4.4"), 0755); err != nil {
+		return err
+	}
+
+	return nil
+}