+ # When PVHVM is enabled, Xen plugs two interfaces into
+ # HVMs - an emulated tap device and a paravirt vif device.
+ # vif-invirtroute (and vif-route, for that matter!) will
+ # fail when the second one is brought up, because the
+ # second invocation of 'ip route add' is identical to the
+ # first (same source and destination IPs) and the kernel
+ # rejects the new route.
+ #
+ # We work around this by adding the routes with different metrics.
+ # This should work because:
+ #
+ # 1) In the case of a pv-aware guest, the kernel will
+ # unplug the tap interface, which will bring down the tap
+ # interface's route, leaving only the one via the vif (and
+ # so the metric shouldn't matter, because it's the only
+ # route)
+ #
+ # 2) In the case of a non-pv-aware guest, the tap route
+ # (with metric 1) should take precedence over the vif
+ # route and carry all the traffic.