feat(wireguard): WIREGUARD_GSO option to disable TUN vnet hdr batching (#3424)

internal/wireguard/log_test.go

@@ -1,6 +1,7 @@
 package wireguard
 
 import (
+	"errors"
 	"testing"
 
 	"go.uber.org/mock/gomock"
@@ -13,7 +14,7 @@ func Test_makeDeviceLogger(t *testing.T) {
 
 	logger := NewMockLogger(ctrl)
 
-	deviceLogger := makeDeviceLogger(logger)
+	deviceLogger := makeDeviceLogger(logger, false)
 
 	logger.EXPECT().Debugf("test %d", 1)
 	deviceLogger.Verbosef("test %d", 1)
@@ -21,3 +22,23 @@ func Test_makeDeviceLogger(t *testing.T) {
 	logger.EXPECT().Errorf("test %d", 2)
 	deviceLogger.Errorf("test %d", 2)
 }
+
+func Test_makeDeviceLogger_gso_suggestion(t *testing.T) {
+	t.Parallel()
+
+	ctrl := gomock.NewController(t)
+
+	logger := NewMockLogger(ctrl)
+
+	deviceLogger := makeDeviceLogger(logger, true)
+
+	const format = "Failed to write packets to TUN device: %v"
+	writeError := errors.New("write /dev/net/tun: invalid argument")
+	logger.EXPECT().Errorf(format, writeError).Times(2)
+	logger.EXPECT().Warn("The kernel seems to reject GRO-coalesced writes to " +
+		"the TUN device; consider setting WIREGUARD_GSO=off").Times(1)
+
+	deviceLogger.Errorf(format, writeError)
+	// The suggestion is only logged once for repeated errors.
+	deviceLogger.Errorf(format, writeError)
+}