A correctness read-through of the five delivered datapath documents, plus
the two code comments that carried the same stale vocabulary.
Datapath selection: the VendorDockerVM selector is `console_type=docker_exec`
alone (`GNS3_SKIP_INIT` and friends are behavior knobs of the chosen class);
the cross-compute and anchor-less fallbacks are named for what they are; the
Ethernet-switch endpoint is the documented exception to the anchoring rule,
and the IOL runner container is called out as the Docker node that does not
anchor on a veth.
Filter vocabulary: the stateful eBPF program evaluates four modes
(nth → quota → window → flow), GNS3 exposes three of them, and window_drop
joins the kernel-only list; the correl suffixes gate on the `rate` token as
the extension-build marker.
group_fwd_mask: the 0xfffd port mask is applied inside uBridge's `brctl addif`
itself, not as a separate command — the link-creation sequences and the
operation tables no longer show an arrow the server never sends. Same class
of fix for `link set up` on the IOL anchor (addif already brought it up; the
command only pushes a suspended anchor back down) and for the QEMU carrier
replication (QMP `set_link`, gated by `replicate_network_connection_state`).
Lifecycles and stop orders re-worded around the invariant rather than the
node type: the fd holder must release before the devices are deleted, which
is QEMU's process-first order, IOU's uBridge-first order and Dynamips'
hypervisor-NIO-first order. Deferred wiring for a stopped endpoint is
documented as the common path it is, and the Dynamips "stop is not a close"
note now says what recovery from a dead hypervisor actually requires.
Dynamips specifics: a c7200 needs an adapter in slot 1 (slot 0 is the fixed
I/O slot), the tap-fd direction is stated correctly (writes inject into the
kernel, reads return what the kernel transmits), and the anchor registry is
name-keyed against the controller's port matrix by convention, not derivation.
IOL port bridge naming: `bridge{bay}` on unit 0, `bridge{bay}_{unit}`
elsewhere; the leg swap happens on link delete/re-create or a datapath
switch, while suspend is an in-place NIO update and a project reopen is a
fresh build.
Verified and Roadmap sections: the in-repo e2e suite is distinguished from
the isolated-instance development harness (IOU), assertions are stated with
their bounds and capability gates, and the roadmap entries collapse into the
one remaining project — VXLAN/GENEVE for cross-compute links.
Code comments: `flow` added to the documented mode order in the eBPF apply
path, and the `nio_bridge` module docstring corrected on which filter types
run on the kernel datapath (bpf via cls_bpf, frequency_drop/quota/window_drop
via the eBPF classifier — neither is relay-only any more).
The dynamips doc gets the full suite: anatomy (anchors reached by the
hypervisors' TAP fds, uBridge's AF_PACKET-tap / tc-qdisc sidebands), a
one-way copy-numbered relay comparison (six kernel/user crossings per
way against the kernel datapath's two TAP-fd legs), a staged walkthrough
(reserved-range diamond, egress clsact chain, capture/markers observation
sideband, copies 1-2) and a control sequence of real commands in real
order (hypervisor fd first, capture before markers, carrier last; router
handlers, not computes, as the per-node participants).
The four sibling frame paths are unified on the same form: netem qdisc
node labels, one capture/markers node outside the stages with AF_PACKET
tap edges anchored at ingress and post-chain egress, copy numbering
wherever the trace crosses the kernel/user boundary (qemu's two TAP-fd
legs, iol-docker's six socket/TAP legs), stage subgraphs with role-noted
titles everywhere (iol-docker restructured from its flat chain, iou's
chA/tapA variants folded into the canonical shapes).
The documentation skill records the rules as v3.1.0: four diagram kinds
(anatomy / comparison / control sequence / walkthrough), one step per
node, dashed sidebands per role with meaningful direction, numbered
crossings when copies are the point, glossary before the first diagram.
A Linux bridge standing in for a cable does not forward the IEEE 802.1D
reserved range (01:80:c2:00:00:00-0f) by default, so LACP/LLDP/802.1X never
crossed a kernel-datapath link while the UDP relay carried them fine. uBridge
now opens every enslave'd port's IFLA_BRPORT_GROUP_FWD_MASK to 0xfffd at
brctl addif time (branch feature/bridge-tap-l2only, commits 0284500/03a18f1/
cf4e494), which the six kernel-datapath feature docs now document as a
section: STP, LACP, 802.1X and LLDP/DCBX cross; 802.3x PAUSE / PFC stays
dropped — br_handle_frame()'s case 0x01 discards it unconditionally, no mask
can enable it, and PFC labs must use a relay link. The full contract, kernel
references and requirements live in the new design spec, marked landed.
The feature doc covers the architecture (one irreducible userspace hop
on the unix-socket leg; the link segment kernelized through the port
bridge's swappable TAP leg), the capability gate, the anchor lifecycle,
the swap flow, the inherited capture/markers/filters, the relay
fallback and the live verification — including the ensure-then-add
lesson (tap create is strictly create-only).
The other datapath docs' roadmaps catch up: the IOL runner container
has landed (and the ethernet-switch doc's stale 'cascade deferred'
exclusion from d2f8aba58 is corrected while there); the docker doc's
adapter table no longer rejects IOLDockerVM.
The Ethernet switch's kernel fast path: instead of a link crossing the
switch's per-port uBridge relay, the switch absorbs the peer's anchor into
its own kernel bridge. The peer's interface (Docker veth host end, QEMU
TAP, IOU port TAP, Dynamips port TAP) becomes the switch port, and frames
cross anchor -> switch bridge -> switch ports entirely in the kernel.
Wire format: the switch end receives nio_anchor ('join this interface to
my own bridge' — the mirror of nio_bridge), the peer end nio_bridge with a
null bridge ('your anchor is bridged elsewhere': carrier, markers and
impairments only — never bridge membership, and never a bridge delete, on
an interface this node does not own). Anchor names come from the shared
naming contract (utils.kernel_anchor), a pure function of node type, id,
adapter and port — the controller computes the peer's anchor while the
node may be stopped, which is what makes links to stopped nodes wireable.
Stopped peers defer the join; after any node of a link starts
(UDPLink.node_started) the controller re-pushes the switch NIO, and the
switch completes — or repairs, when a peer restart replaced its interface
under the same name — the join against the kernel's actual membership
instead of assuming it.
VLAN changes now edit membership in place: only the ports whose mode/VLAN
actually changed are touched, each losing exactly the previous mode's
entries the new mode does not want (the dot1q admits-all entry is one
range operation in both directions), and no port ever leaves the bridge to
change its VLANs. This replaces the old 'reset by re-enslaving' shortcut
(delif+addif on every wired port, added when the ports were the switch's
own TAPs): on absorbed anchors, re-enslaving an interface owned by another
node is where live testing watched links die — anchors occasionally lost
their bridge membership right after a ports_mapping update (later updates
then failed with delif EINVAL), reproducibly with qemu, IOU and Dynamips
peers and never with Docker's veths.
Eligibility: the switch side needs no capability of its own (its bridge
exists by construction); the peer must be able to anchor. Switch-to-switch
cascades stay on the relay — a kernel interface belongs to one bridge, and
joining two bridges needs a veth pair, deferred.
Verified live on a real server: qemu peers through four VLAN cycles with
both anchors enslaved throughout; a mixed switch (2 IOU + 2 Dynamips, four
kernel ports); Docker peers with real ICMP isolating and recovering (with
both anchors still enslaved); VPCS relay ports likewise in place.
New features/dynamips-kernel-datapath.md: the anchor model (persistent TAP
per Ethernet port, the hypervisor opens it with nio create_tap), port
selection via the adapter registry, the anchor lifecycle with QEMU's stop
order and the stop-is-not-close semantics, link operations, capture/
markers/filters, the relay fallback, the live e2e results, configuration
and the roadmap (Ethernet switch next). The IOU and QEMU roadmaps note
that Dynamips has landed.
