The kernel's correlated-random generator (get_crandom, sch_netem.c) truncates
instead of wrapping, starving both edges of the stationary distribution: an
event threshold below the correlation value is almost never reached. Measured
with stock iproute2 on this kernel — uBridge's netlink encoding is identical:
loss 1% + correl 25% drops nothing over 2000 pings (expected ~2%), 10%/25%
measures ~1.8% one way, only the 50% symmetry point survives. duplicate and
reorder correl share the same comparison structure and collapse the same way;
gemodel is immune (Markov chain over plain uniform draws) and is the honest
tool for bursty loss at a chosen mean rate.
Documented in the packet-filters correlation-bias bullet, and surfaced in the
two machine-facing descriptions (MCP link_update packet_loss note, controller
filter schema) so agents and clients stop walking into the trap.
The persistent-TAP lifecycle — probe, sweep, create, register, delete —
was implemented four times, once per node type, and the copies had drifted
(probe mechanism, _tap_datapath reset, keep-vs-recreate policy). The
mechanical half moves into KernelDatapathMixin:
- _probe_persistent_taps(probe_name): the scratch-TAP probe, returning the
refusal for the caller's own warning (QEMU, Dynamips);
- _create_anchor_taps(ports, set_owner, keep_existing): sweep + create +
optional ownership handover + carrier down + registry, with the ports
enumerated by the node type and named through the new _tap_name hook;
- _delete_anchor_taps(): the suppressed tap sweep + per-link bridge
cleanup + registry clear.
Each node type keeps what its fd holder dictates: the release step before
the tap sweep (the QEMU process, the IOL bridge, the hypervisor's NIO
bindings, the container port bridges), its probe policy, and its registry
lifetime. QEMU's now-unconditional registry clear aligns it with the other
three; everything else is behavior-preserving.
Compute:
- Track the anchor that owns uBridge's single AF_PACKET capture slot: a
second kernel port's capture is refused with a clear error (its flag
rolled back), a failed start no longer wedges the port, and only the
owning port's stop issues the process-wide `capture stop_kernel`
(docker/qemu/iou/dynamips/switch, via the mixin's slot helpers).
- Unwind failed starts instead of leaking uBridge and the anchor TAPs:
QEMU's stop body runs under try/finally, QEMU and IOU start the datapath
inside the launch try, Dynamips undoes a half-attached port (the retry
used to be short-circuited into a silent black hole), and Docker deletes
the veth pair when the namespace move fails.
- Restore the relay filter guard on IOU (kernel-only filters raise
NodeError, an uncompilable BPF line degrades to a warning), validate the
eBPF/quota/window/bpf filter shapes before touching the bridge (short or
non-numeric values surfaced as 500s after partial state), and refuse a
second NIO on an occupied Docker/QEMU port (the guard IOU and Dynamips
already had).
- Probe fixes: `_probe_bridge_tap` survives a failing uBridge start, and
the probe caches key on ctime too, so a chmod/setcap remedy re-probes.
Controller:
- Parse GNS3_UNIX_SOCKET_NIO like the compute does (line-anchored, truthy
value) and mirror the compute's class selection in kernel_anchor_type.
- Read partial capability reports defensively; make BridgeNIO.bridge
required-but-nullable so an omitted key is a 422 rather than a KeyError.
- Strip the packet_loss correlation slot even when it is zero: the relay
filter takes exactly one argument and rejected `packet_loss 10 0`.
Ethernet switch: skip ports whose absorbed anchor does not exist yet (the
join is deferred by design) and roll the ports_mapping back when the VLAN
reconcile fails, so a retry still diffs against the old mapping.
Agent: reject device config entries without a device_name instead of
silently dropping them (a malformed batch used to execute partially while
reporting success).
Also split the netem builder to clear C901 and drop the two per-file ruff
ignores the PR had added, keeping the remove-only policy.
The rebase onto 65c858d45 brought upstream's UP032 enforcement; the
conflict resolution kept this branch's semantics on the overlapping
lines, so their .format() calls needed the conversion afterwards
(ruff check --fix, 41 sites) plus the formatter's rewrap (7 files).
Replicates the CI recipe locally: pip check, ruff check/format, mypy
2.3.1 (clean, 434 files), unit suite 2216 passed.
Upstream's mypy pass narrowed the filter copy to UDPNIO only (the
Ethernet/TAP members of the union have no filters field). BridgeNIO —
the kernel-datapath NIO — carries filters too, so on an IOU kernel link
every PUT of a link's filters cleared them and applied nothing: netem
never landed on the anchor (e2e test_iou_kernel_datapath caught it).
Narrow to (UDPNIO, BridgeNIO): still avoids attribute access on the
models without the field, keeps both filter-carrying types.
The rebase onto upstream 3.1 (mypy + ruff I001/F401 waves) left the tree
short of the newly enforced baselines in three ways:
* contextlib / UbridgeError imports dropped as false duplicates during
conflict resolution left NameErrors in iou_vm and qemu_vm (F821);
the Dynamips router grabbed the compute-level NIOTAP instead of the
hypervisor one, breaking TAP anchoring (test failure).
* unused imports (KERNEL_UNSUPPORTED_FILTERS, UbridgeError, List) and
unsorted blocks left behind where the stack's later commits moved the
last usage elsewhere — ruff I001/F401/RUF022 now enforce these.
* mypy, now baseline-free: cache dict annotations in tc_probe, the
locators candidate list, the resolved-params None branch in the MCP
runner, and validate_bpf_syntax keeps the upstream Dict[str, Any]
return (the strict Optional[str] was wrong for the "valid" bool entry).
The e2e raw-frame probe resolves its compiler via shutil.which (S607)
and zips with strict= (B905); the remaining subprocess call is S603 by
nature and gets a per-file ignore like other test files.
ruff check/format clean, mypy at upstream parity (no new errors),
full unit suite 2167 passed.
