xdp

Package github.com/asavie/xdp allows one to use XDP sockets from the Go programming language.

Here is a minimal example of a program which receives network frames, modifies their destination MAC address in-place to broadcast address and transmits them back out the same network link:

package main

import (
	"os"
	"os/signal"
	"syscall"

	"github.com/asavie/xdp"
	"github.com/vishvananda/netlink"
)

func main() {
	const NetworkDevice = "enp3s0"
	const QueueID = 0

	link, err := netlink.LinkByName(NetworkDevice)
	if err != nil {
		panic(err)
	}

	xsk, err := xdp.NewSocket(link.Attrs().Index, QueueID)
	defer xsk.Close()
	if err != nil {
		panic(err)
	}
	
	// removing the XDP program on interrupt
	c := make(chan os.Signal)
	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
	go func() {
		<-c
		xsk.Close()
		os.Exit(1)
	}()

	for {
		xsk.Fill(xsk.GetDescs(xsk.NumFreeFillSlots()))
		numRx, _, err := xsk.Poll(-1)
		if err != nil {
			panic(err)
		}
		rxDescs := xsk.Receive(numRx)
		for i := 0; i < len(rxDescs); i++ {
			// Set destination MAC address to
			// ff:ff:ff:ff:ff:ff
			frame := xsk.GetFrame(rxDescs[i])
			for i := 0; i < 6; i++ {
				frame[i] = byte(0xff)
			}
		}
		xsk.Transmit(rxDescs)
	}
}

Performance

examples/sendudp

With the default UDP payload size of 1400 bytes, running on Linux kernel 5.1.20, on a tg3 (so no native XDP support) gigabit NIC, sendudp.go does around 980 Mb/s, so practically line rate.

examples/senddnsqueries

TL;DR: in the same environment, sending a pre-generated DNS query using an ordinary UDP socket yields around 30 MiB/s whereas sending it using the senddnsqueries.go example program yields around 77 MiB/s.

Connecting a PC with Intel Core i7-7700 CPU running Linux kernel 5.0.17 and igb driver to a laptop with Intel Core i7-5600U CPU running Linux kernel 5.0.9 with e1000e with a cat 5E gigabit ethernet cable and using the following program

package main

import (
	"net"

	"github.com/miekg/dns"
)

func main() {
	query := new(dns.Msg)
	query.SetQuestion(dns.Fqdn("asavie.com"), dns.TypeA)
	payload, err := query.Pack()
	if err != nil {
		panic(err)
	}

	conn, err := net.ListenPacket("udp", ":0")
	if err != nil {
		panic(err)
	}
	defer conn.Close()

	dst, err := net.ResolveUDPAddr("udp", "192.168.111.10:53")
	if err != nil {
		panic(err)
	}

	for {
		_, err = conn.WriteTo(payload, dst)
		if err != nil {
			panic(err)
		}
	}
}

which uses an ordinary UDP socket to send a pre-generated DNS query from PC to laptop as quickly as possible - I get about 30 MiB/s at laptop side.

Using the senddnsqueries.go example program - I get about 77 MiB/s at laptop side.