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slightly nicer contract?

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This commit is contained in:
JackDoan
2026-04-28 16:50:50 -05:00
parent f5db77f214
commit c62f27d4b4
3 changed files with 20 additions and 26 deletions
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35
overlay/tio/tio_gso_linux.go
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@@ -291,33 +291,18 @@ func (r *Offload) rawWrite(iovs []unix.Iovec) (int, error) {
// Write calls.
func (r *Offload) GSOSupported() bool { return true }
// WriteGSO emits a TCP TSO superpacket in a single writev. hdr is the
// IPv4/IPv6 + TCP header prefix (already finalized — total length, IP csum,
// and TCP pseudo-header partial set by the caller). pays are payload
// fragments whose concatenation forms the full coalesced payload; each
// slice is read-only and must stay valid until return. gsoSize is the MSS;
// every segment except possibly the last is exactly gsoSize bytes.
// csumStart is the byte offset where the TCP header begins within hdr.
func (r *Offload) WriteGSO(hdr []byte, pays [][]byte, gsoSize uint16, csumStart uint16) error {
if len(hdr) == 0 || len(pays) == 0 {
func (r *Offload) WriteGSO(hdr []byte, transportHdr []byte, pays [][]byte) error {
if len(hdr) == 0 || len(pays) == 0 || len(transportHdr) == 0 {
return nil
}
// Build the virtio_net_hdr. When pays total to <= gsoSize the kernel
// would produce a single segment; keep NEEDS_CSUM semantics but skip
// the GSO type so the kernel doesn't spuriously mark this as TSO.
vhdr := VirtioNetHdr{
Flags: unix.VIRTIO_NET_HDR_F_NEEDS_CSUM,
HdrLen: uint16(len(hdr)),
HdrLen: uint16(len(hdr) + len(transportHdr)),
GSOSize: uint16(len(pays[0])),
CsumStart: csumStart,
CsumStart: uint16(len(hdr)),
CsumOffset: 16, // TCP checksum field lives 16 bytes into the TCP header
}
var totalPay int
for _, p := range pays {
totalPay += len(p)
}
if totalPay > int(gsoSize) {
if len(pays) > 1 {
ipVer := hdr[0] >> 4
if ipVer == 6 {
vhdr.GSOType = unix.VIRTIO_NET_HDR_GSO_TCPV6
@@ -333,9 +318,9 @@ func (r *Offload) WriteGSO(hdr []byte, pays [][]byte, gsoSize uint16, csumStart
}
vhdr.encode(r.gsoHdrBuf[:])
// Build the iovec array: [virtio_hdr, hdr, pays...]. r.gsoIovs[0] is
// Build the iovec array: [virtio_hdr, hdr, transportHdr, pays...]. r.gsoIovs[0] is
// wired to gsoHdrBuf at construction and never changes.
need := 2 + len(pays)
need := 3 + len(pays)
if cap(r.gsoIovs) < need {
grown := make([]unix.Iovec, need)
grown[0] = r.gsoIovs[0]
@@ -345,9 +330,11 @@ func (r *Offload) WriteGSO(hdr []byte, pays [][]byte, gsoSize uint16, csumStart
}
r.gsoIovs[1].Base = &hdr[0]
r.gsoIovs[1].SetLen(len(hdr))
r.gsoIovs[2].Base = &transportHdr[0]
r.gsoIovs[2].SetLen(len(transportHdr))
for i, p := range pays {
r.gsoIovs[2+i].Base = &p[0]
r.gsoIovs[2+i].SetLen(len(p))
r.gsoIovs[3+i].Base = &p[0]
r.gsoIovs[3+i].SetLen(len(p))
}
_, err := r.rawWrite(r.gsoIovs)