GSO/GRO offloads, with TCP+ECN and UDP support

overlay/tio/tun_linux_offload.go

@@ -0,0 +1,51 @@
+//go:build linux && !android && !e2e_testing
+// +build linux,!android,!e2e_testing
+
+package tio
+
+import (
+	"fmt"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/slackhq/nebula/overlay/tio/virtio"
+)
+
+// protoFromGSOType maps a virtio_net_hdr GSOType to the GSOProto value the
+// segment-time helpers use. Returns an error for GSO_NONE or any unknown
+// value — the caller should only invoke this on a confirmed superpacket.
+func protoFromGSOType(t uint8) (GSOProto, error) {
+	switch t {
+	case unix.VIRTIO_NET_HDR_GSO_TCPV4, unix.VIRTIO_NET_HDR_GSO_TCPV6:
+		return GSOProtoTCP, nil
+	case unix.VIRTIO_NET_HDR_GSO_UDP_L4:
+		return GSOProtoUDP, nil
+	default:
+		return 0, fmt.Errorf("unsupported virtio gso type: %d", t)
+	}
+}
+
+// SegmentSuperpacket invokes fn once per segment of pkt. For non-GSO pkts
+// fn is called once with pkt.Bytes (no segmentation, no copy). For GSO/USO
+// superpackets fn is called once per segment with a slice of pkt.Bytes
+// holding that segment's plaintext (a freshly-patched L3+L4 header sliced
+// in front of the original payload chunk). The slide is destructive: pkt is
+// consumed by this call and its bytes are in an undefined state when
+// SegmentSuperpacket returns. Callers must not retain pkt or any earlier
+// seg slice past fn's return for that segment. The scratch parameter is
+// unused on the destructive path and kept only for cross-platform
+// signature compatibility. Aborts and returns the first error from fn or
+// from per-segment construction.
+func SegmentSuperpacket(pkt Packet, fn func(seg []byte) error) error {
+	if !pkt.GSO.IsSuperpacket() {
+		return fn(pkt.Bytes)
+	}
+	switch pkt.GSO.Proto {
+	case GSOProtoTCP:
+		return virtio.SegmentTCP(pkt.Bytes, pkt.GSO.HdrLen, pkt.GSO.CsumStart, pkt.GSO.Size, fn)
+	case GSOProtoUDP:
+		return virtio.SegmentUDP(pkt.Bytes, pkt.GSO.HdrLen, pkt.GSO.CsumStart, pkt.GSO.Size, fn)
+	default:
+		return fmt.Errorf("unsupported gso proto: %d", pkt.GSO.Proto)
+	}
+}