pre-fill the tx ring with bogus empty packets

outside.go

@@ -455,11 +455,11 @@ func newPacket(data []byte, incoming bool, fp *firewall.Packet) error {
 		return ErrPacketTooShort
 	}
 
-	version := int((data[0] >> 4) & 0x0f)
-	switch version {
-	case ipv4.Version:
+	//version := int((data[0] >> 4) & 0x0f)
+	switch data[0] & 0xf0 {
+	case ipv4.Version << 4:
 		return parseV4(data, incoming, fp)
-	case ipv6.Version:
+	case ipv6.Version << 4:
 		return parseV6(data, incoming, fp)
 	}
 	return ErrUnknownIPVersion

overlay/tun_linux.go

@@ -806,8 +806,11 @@ func (t *tun) WriteMany(x []*packet.OutPacket, q int) (int, error) {
 }
 
 func (t *tun) RecycleRxSeg(pkt TunPacket, kick bool, q int) error {
+	if pkt.GetPayload() == nil {
+		return nil
+	}
 	vpkt := pkt.(*vhostnet.VirtIOPacket)
-	err := t.vdev[q].ReceiveQueue.OfferDescriptorChains(vpkt.Chains, kick)
+	err := t.vdev[q].ReceiveQueue.OfferDescriptorChains([]uint16{vpkt.Chain}, kick)
 	vpkt.Reset() //intentionally ignoring err!
 	return err
 }

overlay/vhostnet/device.go

@@ -123,6 +123,9 @@ func NewDevice(options ...Option) (*Device, error) {
 	if err = dev.refillReceiveQueue(); err != nil {
 		return nil, fmt.Errorf("refill receive queue: %w", err)
 	}
+	if err = dev.prefillTxQueue(); err != nil {
+		return nil, fmt.Errorf("refill tx queue: %w", err)
+	}
 
 	dev.initialized = true
 
@@ -150,6 +153,27 @@ func (dev *Device) refillReceiveQueue() error {
 	}
 }
 
+func (dev *Device) prefillTxQueue() error {
+	for {
+		dt := dev.TransmitQueue.DescriptorTable()
+		for {
+			x, _, err := dt.CreateDescriptorForOutputs()
+			if err != nil {
+				if errors.Is(err, virtqueue.ErrNotEnoughFreeDescriptors) {
+					// Queue is full, job is done.
+					return nil
+				}
+				return err
+			}
+			err = dev.TransmitQueue.OfferDescriptorChains([]uint16{x}, false)
+			if err != nil {
+				return err
+			}
+		}
+
+	}
+}
+
 // Close cleans up the vhost networking device within the kernel and releases
 // all resources used for it.
 // The implementation will try to release as many resources as possible and
@@ -211,15 +235,16 @@ func createQueue(controlFD int, queueIndex int, queueSize int, itemSize int) (*v
 func (dev *Device) GetPacketForTx() (uint16, []byte, error) {
 	var err error
 	var idx uint16
-	if !dev.fullTable {
-		idx, err = dev.TransmitQueue.DescriptorTable().CreateDescriptorForOutputs()
-		if err == virtqueue.ErrNotEnoughFreeDescriptors {
-			dev.fullTable = true
-			idx, err = dev.TransmitQueue.TakeSingleIndex(context.TODO())
-		}
-	} else {
-		idx, err = dev.TransmitQueue.TakeSingleIndex(context.TODO())
-	}
+	//if !dev.fullTable {
+	//	idx, err = dev.TransmitQueue.DescriptorTable().CreateDescriptorForOutputs()
+	//	if err == virtqueue.ErrNotEnoughFreeDescriptors {
+	//		dev.fullTable = true
+	//		idx, err = dev.TransmitQueue.TakeSingleIndex(context.TODO())
+	//	}
+	//} else {
+	//	idx, err = dev.TransmitQueue.TakeSingleIndex(context.TODO())
+	//}
+	idx, err = dev.TransmitQueue.TakeSingleIndex(context.TODO())
 	if err != nil {
 		return 0, nil, fmt.Errorf("transmit queue: %w", err)
 	}
@@ -304,26 +329,26 @@ func (dev *Device) ProcessRxChain(pkt *VirtIOPacket, chain virtqueue.UsedElement
 
 	//shift the buffer out of out:
 	pkt.payload = buf[virtio.NetHdrSize:chain.Length]
-	pkt.Chains = append(pkt.Chains, idx)
+	pkt.Chain = idx
 	return 1, nil
 }
 
 type VirtIOPacket struct {
 	payload []byte
 	//header  virtio.NetHdr
-	Chains []uint16
+	Chain uint16
 }
 
 func NewVIO() *VirtIOPacket {
 	out := new(VirtIOPacket)
 	out.payload = nil
-	out.Chains = make([]uint16, 0, 8)
+	out.Chain = 0
 	return out
 }
 
 func (v *VirtIOPacket) Reset() {
 	v.payload = nil
-	v.Chains = v.Chains[:0]
+	v.Chain = 0
 }
 
 func (v *VirtIOPacket) GetPayload() []byte {

overlay/virtqueue/descriptor_table.go

@@ -168,12 +168,12 @@ func (dt *DescriptorTable) releaseBuffers() error {
 	return nil
 }
 
-func (dt *DescriptorTable) CreateDescriptorForOutputs() (uint16, error) {
+func (dt *DescriptorTable) CreateDescriptorForOutputs() (uint16, uint32, error) {
 	//todo just fill the damn table
 	// Do we still have enough free descriptors?
 
 	if 1 > dt.freeNum {
-		return 0, ErrNotEnoughFreeDescriptors
+		return 0, 0, ErrNotEnoughFreeDescriptors
 	}
 
 	// Above validation ensured that there is at least one free descriptor, so
@@ -216,7 +216,7 @@ func (dt *DescriptorTable) CreateDescriptorForOutputs() (uint16, error) {
 		dt.descriptors[dt.freeHeadIndex].next = next
 	}
 
-	return head, nil
+	return head, desc.length, nil
 }
 
 func (dt *DescriptorTable) createDescriptorForInputs() (uint16, error) {

overlay/virtqueue/split_virtqueue.go

@@ -301,7 +301,6 @@ func (sq *SplitQueue) BlockAndGetHeadsCapped(ctx context.Context, maxToTake int)
 // and any further calls to [SplitQueue.OfferDescriptorChain] will stall.
 
 func (sq *SplitQueue) OfferInDescriptorChains() (uint16, error) {
-	// Create a descriptor chain for the given buffers.
 	var (
 		head uint16
 		err  error
@@ -350,18 +349,6 @@ func (sq *SplitQueue) SetDescSize(head uint16, sz int) {
 	sq.descriptorTable.descriptors[int(head)].length = uint32(sz)
 }
 
-func (sq *SplitQueue) OfferDescriptor(chain uint16, kick bool) error {
-	// Make the descriptor chain available to the device.
-	sq.availableRing.offerSingle(chain)
-
-	// Notify the device to make it process the updated available ring.
-	if kick {
-		return sq.Kick()
-	}
-
-	return nil
-}
-
 func (sq *SplitQueue) OfferDescriptorChains(chains []uint16, kick bool) error {
 	// Make the descriptor chain available to the device.
 	sq.availableRing.offer(chains)

overlay/virtqueue/used_ring.go

@@ -153,11 +153,7 @@ func (r *UsedRing) takeOne() (UsedElement, bool) {
 }
 
 // InitOfferSingle is only used to pre-fill the used queue at startup, and should not be used if the device is running!
-func (r *UsedRing) InitOfferSingle(x uint16, size int) {
-	//always called under lock
-	//r.mu.Lock()
-	//defer r.mu.Unlock()
-
+func (r *UsedRing) InitOfferSingle(x uint16, size uint32) {
 	offset := 0
 	// Add descriptor chain heads to the ring.
 
@@ -166,10 +162,8 @@ func (r *UsedRing) InitOfferSingle(x uint16, size int) {
 	// size) is always a power of 2 and smaller than the highest possible
 	// 16-bit value.
 	insertIndex := int(*r.ringIndex+uint16(offset)) % len(r.ring)
-	r.ring[insertIndex] = UsedElement{
-		DescriptorIndex: uint32(x),
-		Length:          uint32(size),
-	}
+	r.ring[insertIndex].DescriptorIndex = uint32(x)
+	r.ring[insertIndex].Length = size
 
 	// Increase the ring index by the number of descriptor chains added to the ring.
 	*r.ringIndex += 1

packet/packet.go

@@ -87,17 +87,15 @@ func (p *UDPPacket) updateCtrl(ctrlLen int) {
 	if len(p.Control) == 0 {
 		return
 	}
-	cmsgs, err := unix.ParseSocketControlMessage(p.Control)
+	header, data, _ /*remain*/, err := unix.ParseOneSocketControlMessage(p.Control)
 	if err != nil {
 		return // oh well
 	}
 
-	for _, c := range cmsgs {
-		if c.Header.Level == unix.SOL_UDP && c.Header.Type == unix.UDP_GRO && len(c.Data) >= 2 {
-			p.wasSegmented = true
-			p.SegSize = int(binary.LittleEndian.Uint16(c.Data[:2]))
-			return
-		}
+	if header.Level == unix.SOL_UDP && header.Type == unix.UDP_GRO && len(data) >= 2 {
+		p.wasSegmented = true
+		p.SegSize = int(binary.LittleEndian.Uint16(data[:2]))
+		return
 	}
 }