github.com/tumi8/quic-go@v0.37.4-tum/sys_conn_df_linux.go (about)

     1  //go:build linux
     2  
     3  package quic
     4  
     5  import (
     6  	"errors"
     7  	"log"
     8  	"os"
     9  	"strconv"
    10  	"syscall"
    11  	"unsafe"
    12  
    13  	"golang.org/x/sys/unix"
    14  
    15  	"github.com/tumi8/quic-go/noninternal/utils"
    16  )
    17  
    18  func setDF(rawConn syscall.RawConn) (bool, error) {
    19  	// Enabling IP_MTU_DISCOVER will force the kernel to return "sendto: message too long"
    20  	// and the datagram will not be fragmented
    21  	var errDFIPv4, errDFIPv6 error
    22  	if err := rawConn.Control(func(fd uintptr) {
    23  		errDFIPv4 = unix.SetsockoptInt(int(fd), unix.IPPROTO_IP, unix.IP_MTU_DISCOVER, unix.IP_PMTUDISC_DO)
    24  		errDFIPv6 = unix.SetsockoptInt(int(fd), unix.IPPROTO_IPV6, unix.IPV6_MTU_DISCOVER, unix.IPV6_PMTUDISC_DO)
    25  	}); err != nil {
    26  		return false, err
    27  	}
    28  	switch {
    29  	case errDFIPv4 == nil && errDFIPv6 == nil:
    30  		utils.DefaultLogger.Debugf("Setting DF for IPv4 and IPv6.")
    31  	case errDFIPv4 == nil && errDFIPv6 != nil:
    32  		utils.DefaultLogger.Debugf("Setting DF for IPv4.")
    33  	case errDFIPv4 != nil && errDFIPv6 == nil:
    34  		utils.DefaultLogger.Debugf("Setting DF for IPv6.")
    35  	case errDFIPv4 != nil && errDFIPv6 != nil:
    36  		return false, errors.New("setting DF failed for both IPv4 and IPv6")
    37  	}
    38  	return true, nil
    39  }
    40  
    41  func maybeSetGSO(rawConn syscall.RawConn) bool {
    42  	enable, _ := strconv.ParseBool(os.Getenv("QUIC_GO_ENABLE_GSO"))
    43  	if !enable {
    44  		return false
    45  	}
    46  
    47  	var setErr error
    48  	if err := rawConn.Control(func(fd uintptr) {
    49  		setErr = unix.SetsockoptInt(int(fd), syscall.IPPROTO_UDP, unix.UDP_SEGMENT, 1)
    50  	}); err != nil {
    51  		setErr = err
    52  	}
    53  	if setErr != nil {
    54  		log.Println("failed to enable GSO")
    55  		return false
    56  	}
    57  	return true
    58  }
    59  
    60  func isSendMsgSizeErr(err error) bool {
    61  	// https://man7.org/linux/man-pages/man7/udp.7.html
    62  	return errors.Is(err, unix.EMSGSIZE)
    63  }
    64  
    65  func isRecvMsgSizeErr(err error) bool { return false }
    66  
    67  func appendUDPSegmentSizeMsg(b []byte, size uint16) []byte {
    68  	startLen := len(b)
    69  	const dataLen = 2 // payload is a uint16
    70  	b = append(b, make([]byte, unix.CmsgSpace(dataLen))...)
    71  	h := (*unix.Cmsghdr)(unsafe.Pointer(&b[startLen]))
    72  	h.Level = syscall.IPPROTO_UDP
    73  	h.Type = unix.UDP_SEGMENT
    74  	h.SetLen(unix.CmsgLen(dataLen))
    75  
    76  	// UnixRights uses the private `data` method, but I *think* this achieves the same goal.
    77  	offset := startLen + unix.CmsgSpace(0)
    78  	*(*uint16)(unsafe.Pointer(&b[offset])) = size
    79  	return b
    80  }