fix trailing whitespace

[invirt/packages/invirt-xen-config.git] / vif-invirtroute

diff --git a/vif-invirtroute b/vif-invirtroute
index 49a7e4c..4872758 100755 (executable)
--- a/vif-invirtroute
+++ b/vif-invirtroute
@@ -54,6 +54,27 @@ if [  ${vif_type} != "ioemu"  -o  x${qemu_online} = xyes ] ; then
     # If we've been given a list of IP addresses, then add routes from dom0 to
     # the guest using those addresses.
        for addr in ${ip} ; do
+           # 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.
+
            if [ $ipcmd == "add" ]; then
                case $dev in
                    vif*)