add pkg/chrootarchive and use it on the daemon

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)

chrootarchive/diff.go

@@ -0,0 +1,38 @@
+package chrootarchive
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"runtime"
+	"syscall"
+
+	"github.com/docker/docker/pkg/archive"
+	"github.com/docker/docker/pkg/reexec"
+)
+
+func applyLayer() {
+	runtime.LockOSThread()
+	flag.Parse()
+
+	if err := syscall.Chroot(flag.Arg(0)); err != nil {
+		fatal(err)
+	}
+	if err := syscall.Chdir("/"); err != nil {
+		fatal(err)
+	}
+	if err := archive.ApplyLayer("/", os.Stdin); err != nil {
+		fatal(err)
+	}
+	os.Exit(0)
+}
+
+func ApplyLayer(dest string, layer archive.ArchiveReader) error {
+	cmd := reexec.Command("docker-applyLayer", dest)
+	cmd.Stdin = layer
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("ApplyLayer %s %s", err, out)
+	}
+	return nil
+}