Address nits from self-review

pkg/rootless/portdriver.go

@@ -6,6 +6,7 @@ package rootless
 import (
 	"io"
 	"path"
+	"strings"
 
 	"github.com/rootless-containers/rootlesskit/pkg/port"
 	portbuiltin "github.com/rootless-containers/rootlesskit/pkg/port/builtin"
@@ -13,6 +14,15 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
+type logrusDebugWriter struct {
+}
+
+func (w *logrusDebugWriter) Write(p []byte) (int, error) {
+	s := strings.TrimSuffix(string(p), "\n")
+	logrus.Debug(s)
+	return len(p), nil
+}
+
 type portDriver interface {
 	NewParentDriver() (port.ParentDriver, error)
 	NewChildDriver() port.ChildDriver
@@ -74,7 +84,9 @@ func (s *slirp4netnsDriver) APISocketPath() string {
 	return ""
 }
 
-func getDriver(driverName string, logWriter io.Writer) portDriver {
+func getDriver(driverName string) portDriver {
+	logWriter := &logrusDebugWriter{}
+
 	if driverName == "slirp4netns" {
 		return &slirp4netnsDriver{logWriter: logWriter}
 	}

pkg/rootless/rootless.go

@@ -42,9 +42,8 @@ func Rootless(stateDir string, enableIPv6 bool) error {
 
 	hasFD := os.Getenv(pipeFD) != ""
 	hasChildEnv := os.Getenv(childEnv) != ""
-	driverName := strings.ToLower(os.Getenv(portDriverEnv))
 	rootlessDir := filepath.Join(stateDir, "rootless")
-	driver := getDriver(driverName, &logrusDebugWriter{})
+	driver := getDriver(strings.ToLower(os.Getenv(portDriverEnv)))
 
 	if hasFD {
 		logrus.Debug("Running rootless child")
@@ -166,7 +165,7 @@ func createParentOpt(driver portDriver, stateDir string, enableIPv6 bool) (*pare
 	mtu := 0
 	if val := os.Getenv(mtuEnv); val != "" {
 		if v, err := strconv.ParseInt(val, 10, 0); err != nil {
-			logrus.Warn("Failed to parse rootless mtu; using default")
+			logrus.Warn("Failed to parse rootless mtu value; using default")
 		} else {
 			mtu = int(v)
 		}
@@ -217,15 +216,6 @@ func createParentOpt(driver portDriver, stateDir string, enableIPv6 bool) (*pare
 	return opt, nil
 }
 
-type logrusDebugWriter struct {
-}
-
-func (w *logrusDebugWriter) Write(p []byte) (int, error) {
-	s := strings.TrimSuffix(string(p), "\n")
-	logrus.Debug(s)
-	return len(p), nil
-}
-
 func createChildOpt(driver portDriver) (*child.Opt, error) {
 	opt := &child.Opt{}
 	opt.TargetCmd = os.Args