silly opinionated tweak

overlay/tio/tio_gso_linux.go

@@ -358,7 +358,8 @@ func (r *Offload) WriteGSO(hdr []byte, transportHdr []byte, pays [][]byte, proto
 	if gsoType != unix.VIRTIO_NET_HDR_GSO_NONE {
 		gsoSize = uint16(segSize)
 	}
-	vhdr := virtio.NewHeader(
+	virtio.EncodeHeader(
+		r.gsoHdrBuf[:],
 		unix.VIRTIO_NET_HDR_F_NEEDS_CSUM,   /*flags*/
 		gsoType,                            /*gsoType*/
 		uint16(len(hdr)+len(transportHdr)), /*hdrLen*/
@@ -366,7 +367,6 @@ func (r *Offload) WriteGSO(hdr []byte, transportHdr []byte, pays [][]byte, proto
 		uint16(len(hdr)),                   /*csumStart*/
 		csumOff,                            /*csumOffset*/
 	)
-	vhdr.Encode(r.gsoHdrBuf[:])
 
 	_, err := r.rawWrite(r.gsoIovs)
 	return err

overlay/tio/virtio/header_linux.go

@@ -46,15 +46,19 @@ func (h *Hdr) Decode(b []byte) {
 	h.CsumOffset = binary.NativeEndian.Uint16(b[8:10])
 }
 
+func EncodeHeader(b []byte, flags, gsoType uint8, hdrLen, gsoSize, csumStart, csumOffset uint16) {
+	b[0] = flags
+	b[1] = gsoType
+	binary.NativeEndian.PutUint16(b[2:4], hdrLen)
+	binary.NativeEndian.PutUint16(b[4:6], gsoSize)
+	binary.NativeEndian.PutUint16(b[6:8], csumStart)
+	binary.NativeEndian.PutUint16(b[8:10], csumOffset)
+}
+
 // Encode is the inverse of Decode: writes the virtio_net_hdr fields into b
 // (must be at least Size bytes). Used to emit a TSO superpacket on egress.
 func (h *Hdr) Encode(b []byte) {
-	b[0] = h.Flags
-	b[1] = h.gsoType
-	binary.NativeEndian.PutUint16(b[2:4], h.HdrLen)
-	binary.NativeEndian.PutUint16(b[4:6], h.GSOSize)
-	binary.NativeEndian.PutUint16(b[6:8], h.CsumStart)
-	binary.NativeEndian.PutUint16(b[8:10], h.CsumOffset)
+	EncodeHeader(b, h.Flags, h.gsoType, h.HdrLen, h.GSOSize, h.CsumStart, h.CsumOffset)
 }
 
 // GSOType returns gsoType with the ECN-flag masked out