Extend the docker and IOU relay negative controls with the filters the
relay itself supports (delay, frequency_drop, bpf), asserted through real
ICMP — the first live coverage of the relay filter path:
* bridge engine (docker): delay 100 grows the RTT by ~200 ms and comes
back on clear; frequency_drop 2 kills the round trips (the filter counts
every packet crossing the bridge, both directions sharing one counter,
so on an alternating ping stream one whole direction dies; verified
against uBridge directly), frequency_drop -1 blackholes, and bpf drops
by libpcap expression ('icmp', then 'greater 150' discriminating by
frame size).
* iol_bridge engine (IOU): the same delay and frequency_drop effects
through the port's iol_bridge filter list, plus the available_filters
spot check.
Docker 33 s, IOU 168 s, both green.
The Verified section only described the /tmp driver with a fake IOU
image; the repository suite now carries the same scenario with real
routers on a real L3 image.
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.
The tool descriptions have always advertised kernel_datapath as a
requestable field, but the handler's whitelist did not contain it: asking
for it was rejected as an invalid field, so the MCP clients could not see
which links run on kernel interfaces at all.
Also record what seeding a netem experiment on IOU costs: IOL emits its own
CDP/keepalive frames and they draw from the netem RNG stream, so a
seeded run only reproduces after `no cdp run` (verified bit-identical pcaps).
* docs/features/iou-kernel-datapath.md: architecture (one irreducible
userspace hop on the fabric leg, kernel link segment), datapath
selection, the anchor lifecycle with the reverse-of-QEMU stop order,
capture/markers/filters, relay fallback, and the verified numbers (an
isolated server with two IOU nodes behind a fake ELF image, the test
playing the IOL fabric: 64/64 kernel, 62/62 relay).
* docs/design/ubridge-iol-tap-anchor-spec.md: delivered — implemented on
the ubridge fork's feature/iol-tap-anchor branch (both commands, the
listener hardening, plus releasing every port NIO on iol_bridge delete
even when the bridge was not running), with the implementation notes
that came back (208 vs the older 214 for a missing bridge; one perror
line per frame dropped on a down anchor).
* The Docker/QEMU feature docs point at it from their roadmaps.
