Dynamips links can now ride the kernel datapath like Docker, QEMU and IOU:
each Ethernet slot/port gets a persistent TAP anchor (gd{id}e{slot}p{port}),
created through uBridge's tap module, and the Dynamips hypervisor opens it
with nio create_tap — the hypervisor holds the fd, exactly QEMU's shape.
Links attach the anchor to their per-link kernel bridge; the legacy UDP
tunnel remains the relay datapath for every other port.
Anchor lifecycle: born at node start (tap module probed with one
create/delete cycle, sweep of stale devices, ownership handed to the server
user, born down); a kernel link opens the anchor in the hypervisor, binds
the slot/port and enslaves it; removing the link releases the fd again
(nio delete) and detaches. A link bound while the router is stopped is
wired by the next start (deferred wiring). Node close follows QEMU's stop
order — the hypervisor's TAP NIOs go before tap delete, since it is
Dynamips, not uBridge, that holds the fds.
Stop is not close: vm stop only halts the emulated router, so the
hypervisor, the TAP fds, the bindings and the per-link bridges all survive
a stop/start untouched (attach skips ports that still hold their TAP NIO).
Port selection follows the adapter registry: ETHERNET_ADAPTERS and
ETHERNET_WICS name the models whose ports carry Ethernet frames (WIC-1ENET
included, at its Dynamips port number); serial, ATM and POS ports never
anchor, and a kernel link there errors with the relay-datapath message
instead of half-wiring. Adapters hot-added to a running router (OIR) get
their anchors at once.
The compute NIO routes accept nio_bridge alongside nio_udp (the same
widening QEMU needed), carry the endpoint's suspend flag on update (it is
the anchor's admin state on a kernel link), skip the hypervisor delete for
a kernel NIO (its TAP NIO was already released by the slot removal), and
the close path leaves NIOBridge instances to _stop_ubridge.
