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l2fwd.go
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l2fwd.go
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/*
l2fwd is a primitive layer 2 frame forwarder, it attaches to two given network
links and transmits any frames received on any of them on the other network
link with the given destination MAC address.
*/
package main
import (
"flag"
"fmt"
"log"
"net"
"os"
"time"
"github.com/asavie/xdp"
"github.com/vishvananda/netlink"
"golang.org/x/sys/unix"
)
func main() {
var inLinkName string
var inLinkDstStr string
var inLinkQueueId int
var outLinkName string
var outLinkDstStr string
var outLinkQueueId int
var verbose bool
flag.Usage = func() {
fmt.Fprintf(flag.CommandLine.Output(), "usage: %s -inlink <network link name> -outlink <network link name>\n", os.Args[0])
flag.PrintDefaults()
}
flag.StringVar(&inLinkName, "inlink", "", "Input network link name.")
flag.IntVar(&inLinkQueueId, "inlinkqueue", 0, "The queue ID to attach to on input link.")
flag.StringVar(&inLinkDstStr, "inlinkdst", "ff:ff:ff:ff:ff:ff", "Destination MAC address to forward frames to from 'in' interface.")
flag.StringVar(&outLinkName, "outlink", "", "Output network link name.")
flag.IntVar(&outLinkQueueId, "outlinkqueue", 0, "The queue ID to attach to on output link.")
flag.StringVar(&outLinkDstStr, "outlinkdst", "ff:ff:ff:ff:ff:ff", "Destination MAC address to forward frames to from 'out' interface.")
flag.BoolVar(&verbose, "verbose", false, "Output forwarding statistics.")
flag.Parse()
if inLinkName == "" || outLinkName == "" {
flag.Usage()
os.Exit(1)
}
inLinkDst, err := net.ParseMAC(inLinkDstStr)
if err != nil {
flag.Usage()
os.Exit(1)
}
outLinkDst, err := net.ParseMAC(outLinkDstStr)
if err != nil {
flag.Usage()
os.Exit(1)
}
inLink, err := netlink.LinkByName(inLinkName)
if err != nil {
log.Fatalf("failed to fetch info about link %s: %v", inLinkName, err)
}
outLink, err := netlink.LinkByName(outLinkName)
if err != nil {
log.Fatalf("failed to fetch info about link %s: %v", outLinkName, err)
}
forwardL2(verbose, inLink, inLinkQueueId, inLinkDst, outLink, outLinkQueueId, outLinkDst)
}
func forwardL2(verbose bool, inLink netlink.Link, inLinkQueueId int, inLinkDst net.HardwareAddr, outLink netlink.Link, outLinkQueueId int, outLinkDst net.HardwareAddr) {
log.Printf("opening XDP socket for %s...", inLink.Attrs().Name)
inXsk, err := xdp.NewSocket(inLink.Attrs().Index, inLinkQueueId)
if err != nil {
log.Fatalf("failed to open XDP socket for link %s: %v", inLink.Attrs().Name, err)
}
log.Printf("opening XDP socket for %s...", outLink.Attrs().Name)
outXsk, err := xdp.NewSocket(outLink.Attrs().Index, outLinkQueueId)
if err != nil {
log.Fatalf("failed to open XDP socket for link %s: %v", outLink.Attrs().Name, err)
}
log.Printf("starting L2 forwarder...")
numBytesTotal := uint64(0)
numFramesTotal := uint64(0)
if verbose {
go func() {
var numBytesPrev, numFramesPrev uint64
var numBytesNow, numFramesNow uint64
for {
numBytesPrev = numBytesNow
numFramesPrev = numFramesNow
time.Sleep(time.Duration(1) * time.Second)
numBytesNow = numBytesTotal
numFramesNow = numFramesTotal
pps := numFramesNow - numFramesPrev
bps := (numBytesNow - numBytesPrev) * 8
log.Printf("%9d pps / %6d Mbps", pps, bps/1000000)
}
}()
}
var fds [2]unix.PollFd
fds[0].Fd = int32(inXsk.FD())
fds[1].Fd = int32(outXsk.FD())
for {
inXsk.Fill(inXsk.GetDescs(inXsk.NumFreeFillSlots()))
outXsk.Fill(outXsk.GetDescs(outXsk.NumFreeFillSlots()))
fds[0].Events = unix.POLLIN
if inXsk.NumTransmitted() > 0 {
fds[0].Events |= unix.POLLOUT
}
fds[1].Events = unix.POLLIN
if outXsk.NumTransmitted() > 0 {
fds[1].Events |= unix.POLLOUT
}
fds[0].Revents = 0
fds[1].Revents = 0
_, err := unix.Poll(fds[:], -1)
if err != nil {
fmt.Fprintf(os.Stderr, "poll failed: %v\n", err)
os.Exit(1)
}
if (fds[0].Revents & unix.POLLIN) != 0 {
numBytes, numFrames := forwardFrames(inXsk, outXsk, inLinkDst)
numBytesTotal += numBytes
numFramesTotal += numFrames
}
if (fds[0].Revents & unix.POLLOUT) != 0 {
inXsk.Complete(inXsk.NumCompleted())
}
if (fds[1].Revents & unix.POLLIN) != 0 {
numBytes, numFrames := forwardFrames(outXsk, inXsk, outLinkDst)
numBytesTotal += numBytes
numFramesTotal += numFrames
}
if (fds[1].Revents & unix.POLLOUT) != 0 {
outXsk.Complete(outXsk.NumCompleted())
}
}
}
func forwardFrames(input *xdp.Socket, output *xdp.Socket, dstMac net.HardwareAddr) (numBytes uint64, numFrames uint64) {
inDescs := input.Receive(input.NumReceived())
replaceDstMac(input, inDescs, dstMac)
outDescs := output.GetDescs(output.NumFreeTxSlots())
if len(inDescs) > len(outDescs) {
inDescs = inDescs[:len(outDescs)]
}
numFrames = uint64(len(inDescs))
for i := 0; i < len(inDescs); i++ {
outFrame := output.GetFrame(outDescs[i])
inFrame := input.GetFrame(inDescs[i])
numBytes += uint64(len(inFrame))
outDescs[i].Len = uint32(copy(outFrame, inFrame))
}
outDescs = outDescs[:len(inDescs)]
output.Transmit(outDescs)
return
}
func replaceDstMac(xsk *xdp.Socket, descs []unix.XDPDesc, dstMac net.HardwareAddr) {
for _, d := range descs {
frame := xsk.GetFrame(d)
copy(frame, dstMac)
}
}