QEMU is the guest side of every adapter TAP, and uBridge's tap delete
refuses a device another process holds open ('Device or resource busy') —
a best-effort delete whose failure is suppressed. QEMU's stop did the
delete first and stopped the process after, so every node stop or project
delete leaked the persistent TAPs: found by inspecting the host after a
project delete (16 taps left behind, carrier down, no holder), and the
held-tap behaviour reproduced against uBridge directly.
Stop the QEMU process first, then remove the TAPs and the per-link kernel
bridges — process side first, then the devices, the same lesson as IOU's
reverse stop order. Verified live: node stop and project delete now leave
no taps and no processes behind, while a restart recreates the TAPs.
The adapter anchor naming also goes through the shared
utils.kernel_anchor helper, like the other node types.
_console_options() fell through the "none" branch and returned None, so
_build_command() blew up on `command.extend(None)`: a QEMU node with
console_type "none" -- offered by the GUI, and what API/MCP-driven labs use
to skip the console entirely -- failed to start with a 500 and a traceback.
Return an empty list, exactly like _aux_options() already does, and cover it
with a test that builds the command line for a headless node. Verified on a
live instance: such a node now starts (204) with `console: null` and no
-serial device in the QEMU command line.
QEMU had no host-side interface at all: every adapter was a local UDP tunnel
into uBridge (-netdev socket plus two UDP ports per adapter), so a link could
only ever be a userspace relay. Each adapter now owns a persistent TAP
(gq{node_id[:8]}e{adapter}p{port}), created by uBridge before QEMU is launched
and handed to this user, and the netdev is that TAP -- the anchor role Docker's
veth host end plays. Links attach to it:
* kernel link (NIOBridge): brctl create/up/addif enslaves the TAP into the
per-link bridge and capture, markers and tc filters are installed on it,
verbatim through the shared KernelDatapathMixin -- a TAP and a veth host end
are interchangeable there (an egress qdisc on either impairs traffic entering
the node, and PACKET_OUTGOING on either is the node receiving);
* relay link: bridge add_nio_ethernet plus add_nio_udp -- AF_PACKET, never the
TAP NIO, which would take the fd QEMU itself holds.
The netdev type is fixed at launch, so this is all-or-nothing per VM: on the
TAP datapath every link type attaches to (or detaches from) a running VM,
including switching a link between the two datapaths. Stop un-persists the
TAPs (QEMU's open fd keeps each device alive until it exits) and removes the
per-link bridges; start sweeps leftovers first. A uBridge without the tap
module keeps the previous socket-netdev datapath, so an unupgraded install is
unaffected -- such a node simply cannot carry kernel links.
