- multi_coalesce/batch: the ordering contract now states what Flush
actually guarantees -- per-flow DATA order -- and names the two
shapes later data may legally overtake (pure ACKs by design, and
unparseable in-flow shapes as an accepted tradeoff).
- validVnetHdr claimed DATA_VALID makes the stack skip L4 checksum
verification; the tun write path ignores that bit entirely. What the
header buys is the absence of NEEDS_CSUM.
- tun_darwin Write said "only valid for single threaded use"; it is
concurrency-safe and concurrent callers exist.
- udp_coalesce eviction comment said "Seal it" but never sets sealed.
- recordCapability: note the gauges are process-global while the state
is per-socket (last writer wins).
- drop a stale tunReadBufSize reference.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014ugV2edVqoz3tBvq9J6yWp
Every non-coalesceable in-flow packet evicted the flow's open slot, so
a bidirectional connection's inbound data run was broken by each peer
ACK interleaved into it, largely defeating coalescing on concurrent
upload+download. A bare acknowledgment (zero payload, nothing beyond
ACK|PSH|ECE) carries no ordering obligation toward the flow's data --
delivered late it is just a stale ACK the receiver ignores -- so it
can ride the lane as a passthrough without the evict, same as kernel
GRO, which doesn't flush held data on pure ACKs. SYN/FIN/RST/CWR keep
sealing.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014ugV2edVqoz3tBvq9J6yWp
A slot that stays single-segment is byte-identical to the packet it
was seeded from, but flushSlot re-emitted it via WriteGSO with a
seeded pseudo-sum, forcing the kernel to software-checksum up to
~1400B that arrived with a perfectly valid checksum. Keep the borrowed
seed packet on the slot (valid until Flush per the Commit contract)
and emit it through the plain DATA_VALID path when numSeg is still 1
at flush time. appendPayload and mergeSlots only touch hdrBuf once
numSeg >= 2, so the raw bytes are pristine whenever the fast path
fires. This is every non-coalesced TCP/UDP packet: request/response
flows, many-flow fan-in, and each run's leftover tail.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014ugV2edVqoz3tBvq9J6yWp
pseudoSumIPv4/IPv6, foldOnceNoInvert, ipv4HdrChecksum (batch) and
foldComplement (tio/virtio) feed the virtio NEEDS_CSUM contract; a wrong
seed means every coalesced packet is silently dropped by the receiver
with nothing failing on our side. Check them against an independent
reference built from explicit RFC pseudo-header bytes -- deliberately
not the production checksum code -- including the carry/fold edge cases
and an end-to-end seed -> kernel-completion -> receiver-accepts
property.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
The Warn("==== end of batch ====") delimiter (and the `logged` flag that
fed it) was left over from debugging the cross-slot gap logging.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
SendBatch.Reserve duplicated Arena's grow-on-demand logic byte for byte.
Use an Arena for the slot backing so the borrow/grow/recycle semantics
live in one place.
Multi-disciplinary correctness review of the batched tun / GSO-GRO / sendmmsg
rework. Each fix has a regression test; the merged tree builds on
linux/darwin/openbsd/windows/freebsd/netbsd, vets clean, passes the unit and
e2e suites, and is -race clean.
Critical:
- C1 zero-length inner UDP datagram no longer panics the process (remote DoS):
the UDP coalescer routes payLen==0 to passthrough instead of seeding a GSO
slot, and WriteGSO skips empty payload iovecs as defense in depth.
- C2 segmenter no longer corrupts inner headers when gsoSize < headerLen: the
L3+L4 header is snapshotted once and each segment stamped from the copy,
replacing the destructive overlapping in-place slide (SegmentTCP + SegmentUDP).
High:
- H1 applyOuterECN updates the IPv4 header checksum (RFC 1624 incremental) when
folding outer CE into the inner ToS, so passthrough packets are no longer
dropped by the peer stack.
- H2 the GRO reject path caps the borrowed RX segment ([:n:n]) so a reject can
no longer overrun into the next coalesced segment's Nebula header. Note:
oversized ICMPv6 rejects that need >16B beyond the segment are now refused
rather than sent under GRO (safe; see TOFIX.md for the scratch-buffer follow-up).
- H3 WriteBatch falls back to per-packet WriteTo for a chunk when writeSockaddr
fails, so one bad-family destination costs only its own packet, not the batch.
- H4 UserDevice.Readers returns N distinct queue wrappers with private buffers
(sharing the pipes) so concurrent readers no longer race/overwrite borrowed
packet bytes.
- H5 Poll.Close / Offload.Close no longer null t.fd (matching master's
tunFile.Close), removing the data race with a concurrent readOne load.
Medium/Low:
- M1 the UDP GSO 127-segment gate moved from kernel >=5.5 to >=6.9 (the real
UDP_MAX_SEGMENTS 64->128 threshold), avoiding EINVAL + per-packet fallback on
5.5-6.8 kernels.
- M2 NewMultiQueueReader replays the offload mask newTun actually negotiated
instead of the TSO-only mask, so adding a queue no longer disables USO
device-wide; the advertised USO capability derives from the same mask.
- M3 the shutdown eventfd is closed in pollQueueSet.Close / offloadQueueSet.Close
(double-close guarded), fixing the per-lifecycle fd leak.
- M4 dual-stack ECN selects the cmsg by address family, not socket family: RX
parseRecvCmsg reads both IP_TOS and IPV6_TCLASS; TX writeEntryCmsg stamps
IP_TOS for v4/v4-mapped dests and IPV6_TCLASS for v6 (on-host verified).
- L1 newPoll no longer closes the fd on failure (matching newOffload), removing
the double-close on QueueSet.Add error.
JackDoan