conn: disable GRO/GSO on Android

We're already getting weird reports about performance drops. Android
kernels are known to be wild, so let's not play games.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Author: zx2c4

conn/bind_std.go

@@ -175,7 +175,7 @@ again:
 	var fns []ReceiveFunc
 	if v4conn != nil {
 		s.ipv4TxOffload, s.ipv4RxOffload = supportsUDPOffload(v4conn)
-		if runtime.GOOS == "linux" || runtime.GOOS == "android" {
+		if runtime.GOOS == "linux" {
 			v4pc = ipv4.NewPacketConn(v4conn)
 			s.ipv4PC = v4pc
 		}
@@ -184,7 +184,7 @@ again:
 	}
 	if v6conn != nil {
 		s.ipv6TxOffload, s.ipv6RxOffload = supportsUDPOffload(v6conn)
-		if runtime.GOOS == "linux" || runtime.GOOS == "android" {
+		if runtime.GOOS == "linux" {
 			v6pc = ipv6.NewPacketConn(v6conn)
 			s.ipv6PC = v6pc
 		}
@@ -238,7 +238,7 @@ func (s *StdNetBind) receiveIP(
 	}
 	defer s.putMessages(msgs)
 	var numMsgs int
-	if runtime.GOOS == "linux" || runtime.GOOS == "android" {
+	if runtime.GOOS == "linux" {
 		if rxOffload {
 			readAt := len(*msgs) - (IdealBatchSize / udpSegmentMaxDatagrams)
 			numMsgs, err = br.ReadBatch((*msgs)[readAt:], 0)
@@ -292,7 +292,7 @@ func (s *StdNetBind) makeReceiveIPv6(pc *ipv6.PacketConn, conn *net.UDPConn, rxO
 // TODO: When all Binds handle IdealBatchSize, remove this dynamic function and
 // rename the IdealBatchSize constant to BatchSize.
 func (s *StdNetBind) BatchSize() int {
-	if runtime.GOOS == "linux" || runtime.GOOS == "android" {
+	if runtime.GOOS == "linux" {
 		return IdealBatchSize
 	}
 	return 1
@@ -415,7 +415,7 @@ func (s *StdNetBind) send(conn *net.UDPConn, pc batchWriter, msgs []ipv6.Message
 		err   error
 		start int
 	)
-	if runtime.GOOS == "linux" || runtime.GOOS == "android" {
+	if runtime.GOOS == "linux" {
 		for {
 			n, err = pc.WriteBatch(msgs[start:], 0)
 			if err != nil || n == len(msgs[start:]) {

conn/features_default.go

@@ -1,5 +1,4 @@
-//go:build !linux
-// +build !linux
+//go:build !linux || android
 
 /* SPDX-License-Identifier: MIT
  *

conn/features_linux.go

@@ -1,3 +1,5 @@
+//go:build linux && !android
+
 /* SPDX-License-Identifier: MIT
  *
  * Copyright (C) 2017-2025 WireGuard LLC. All Rights Reserved.
@@ -7,6 +9,7 @@ package conn
 
 import (
 	"net"
+	"runtime"
 
 	"golang.org/x/sys/unix"
 )

conn/gso_default.go

@@ -1,4 +1,4 @@
-//go:build !linux
+//go:build !linux || android
 
 /* SPDX-License-Identifier: MIT
  *

conn/gso_linux.go

@@ -1,4 +1,4 @@
-//go:build linux
+//go:build linux && !android
 
 /* SPDX-License-Identifier: MIT
  *

device/queueconstants_android.go

@@ -14,6 +14,6 @@ const (
 	QueueOutboundSize          = 1024
 	QueueInboundSize           = 1024
 	QueueHandshakeSize         = 1024
-	MaxSegmentSize             = (1 << 16) - 1 // largest possible UDP datagram
+	MaxSegmentSize             = 2200
 	PreallocatedBuffersPerPool = 4096
 )