add QUIC_GO_DISABLE_GSO env to disable GSO

sys_conn_helper_linux.go

@@ -7,12 +7,22 @@ import (
 	"errors"
 	"net/netip"
 	"os"
+	"strconv"
 	"syscall"
 	"unsafe"
 
 	"golang.org/x/sys/unix"
 )
 
+var gsoDisabled bool
+
+func init() {
+	disabled, err := strconv.ParseBool(os.Getenv("QUIC_GO_DISABLE_GSO"))
+	if err == nil {
+		gsoDisabled = disabled
+	}
+}
+
 const (
 	msgTypeIPTOS = unix.IP_TOS
 	ipv4PKTINFO  = unix.IP_PKTINFO
@@ -55,6 +65,9 @@ func parseIPv4PktInfo(body []byte) (ip netip.Addr, ifIndex uint32, ok bool) {
 // isGSOSupported tests if the kernel supports GSO.
 // Sending with GSO might still fail later on, if the interface doesn't support it (see isGSOError).
 func isGSOSupported(conn syscall.RawConn) bool {
+	if gsoDisabled {
+		return false
+	}
 	var serr error
 	if err := conn.Control(func(fd uintptr) {
 		_, serr = unix.GetsockoptInt(int(fd), unix.IPPROTO_UDP, unix.UDP_SEGMENT)