BAM! a hit from my spice-weasel. Now TX is zero-copy, at the expense of my sanity!

packet/outpacket.go

@@ -1,7 +1,15 @@
 package packet
 
+import (
+	"github.com/slackhq/nebula/util/virtio"
+	"golang.org/x/sys/unix"
+)
+
 type OutPacket struct {
-	Segments [][]byte
+	Segments        [][]byte
+	SegmentPayloads [][]byte
+	SegmentHeaders  [][]byte
+	SegmentIDs      []uint16
 	//todo virtio header?
 	SegSize      int
 	SegCounter   int
@@ -13,11 +21,45 @@ type OutPacket struct {
 
 func NewOut() *OutPacket {
 	out := new(OutPacket)
-	const numSegments = 64
-	out.Segments = make([][]byte, numSegments)
-	for i := 0; i < numSegments; i++ { //todo this is dumb
-		out.Segments[i] = make([]byte, Size)
-	}
+	out.Segments = make([][]byte, 0, 64)
+	out.SegmentHeaders = make([][]byte, 0, 64)
+	out.SegmentPayloads = make([][]byte, 0, 64)
+	out.SegmentIDs = make([]uint16, 0, 64)
 	out.Scratch = make([]byte, Size)
 	return out
 }
+
+func (pkt *OutPacket) Reset() {
+	pkt.Segments = pkt.Segments[:0]
+	pkt.SegmentPayloads = pkt.SegmentPayloads[:0]
+	pkt.SegmentHeaders = pkt.SegmentHeaders[:0]
+	pkt.SegmentIDs = pkt.SegmentIDs[:0]
+	pkt.SegSize = 0
+	pkt.Valid = false
+	pkt.wasSegmented = false
+}
+
+func (pkt *OutPacket) UseSegment(segID uint16, seg []byte) int {
+	pkt.Valid = true
+	pkt.SegmentIDs = append(pkt.SegmentIDs, segID)
+	pkt.Segments = append(pkt.Segments, seg) //todo do we need this?
+
+	vhdr := virtio.NetHdr{ //todo
+		Flags:      unix.VIRTIO_NET_HDR_F_DATA_VALID,
+		GSOType:    unix.VIRTIO_NET_HDR_GSO_NONE,
+		HdrLen:     0,
+		GSOSize:    0,
+		CsumStart:  0,
+		CsumOffset: 0,
+		NumBuffers: 0,
+	}
+
+	hdr := seg[0 : virtio.NetHdrSize+14]
+	_ = vhdr.Encode(hdr)
+	hdr[virtio.NetHdrSize+14-2] = 0x86
+	hdr[virtio.NetHdrSize+14-1] = 0xdd //todo ipv6 ethertype
+
+	pkt.SegmentHeaders = append(pkt.SegmentHeaders, hdr)
+	pkt.SegmentPayloads = append(pkt.SegmentPayloads, seg[virtio.NetHdrSize+14:])
+	return len(pkt.SegmentIDs) - 1
+}

packet/virtio.go

@@ -9,13 +9,13 @@ type VirtIOPacket struct {
 	Header    virtio.NetHdr
 	Chains    []uint16
 	ChainRefs [][]byte
-	// RecycleDescriptorChains(chains []uint16, kick bool) error
+	// OfferDescriptorChains(chains []uint16, kick bool) error
 	Recycler func([]uint16, bool) error
 }
 
 func NewVIO() *VirtIOPacket {
 	out := new(VirtIOPacket)
-	out.Payload = make([]byte, Size)
+	out.Payload = nil
 	out.ChainRefs = make([][]byte, 0, 4)
 	out.Chains = make([]uint16, 0, 8)
 	return out
@@ -37,3 +37,13 @@ func (v *VirtIOPacket) Recycle(lastOne bool) error {
 	v.Reset()
 	return nil
 }
+
+type VirtIOTXPacket struct {
+	VirtIOPacket
+}
+
+func NewVIOTX(isV4 bool) *VirtIOTXPacket {
+	out := new(VirtIOTXPacket)
+	out.VirtIOPacket = *NewVIO()
+	return out
+}