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

internal/wireguard/log.go

@@ -1,6 +1,10 @@
 package wireguard
 
 import (
+	"fmt"
+	"strings"
+	"sync"
+
 	"golang.zx2c4.com/wireguard/device"
 )
 
@@ -10,6 +14,7 @@ type Logger interface {
 	Debug(s string)
 	Debugf(format string, args ...interface{})
 	Info(s string)
+	Warn(s string)
 	Error(s string)
 	Erroer
 }
@@ -18,9 +23,28 @@ type Erroer interface {
 	Errorf(format string, args ...any)
 }
 
-func makeDeviceLogger(logger Logger) (deviceLogger *device.Logger) {
+func makeDeviceLogger(logger Logger, gso bool) (deviceLogger *device.Logger) {
+	errorf := logger.Errorf
+	if gso {
+		// Kernels advertising IFF_VNET_HDR support but rejecting
+		// GRO-coalesced writes make wireguard-go log this error for
+		// each failed write batch, see
+		// https://github.com/tailscale/tailscale/issues/13041
+		var suggestOnce sync.Once
+		errorf = func(format string, args ...any) {
+			logger.Errorf(format, args...)
+			message := fmt.Sprintf(format, args...)
+			if strings.Contains(message, "Failed to write packets to TUN device") &&
+				strings.Contains(message, "invalid argument") {
+				suggestOnce.Do(func() {
+					logger.Warn("The kernel seems to reject GRO-coalesced writes to " +
+						"the TUN device; consider setting WIREGUARD_GSO=off")
+				})
+			}
+		}
+	}
 	return &device.Logger{
 		Verbosef: logger.Debugf,
-		Errorf:   logger.Errorf,
+		Errorf:   errorf,
 	}
 }