Commit script to setup gre tunnels; sadly they do not work,

using the same routing trick we us on the openvz image. But
lets save it in case we figure it out.

clientside/tmcc/linux/xen/emulab-tun.pl

+#!/usr/bin/perl -w
+#
+# Copyright (c) 2000-2013 University of Utah and the Flux Group.
+# 
+# {{{EMULAB-LICENSE
+# 
+# This file is part of the Emulab network testbed software.
+# 
+# This file is free software: you can redistribute it and/or modify it
+# under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or (at
+# your option) any later version.
+# 
+# This file is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public
+# License for more details.
+# 
+# You should have received a copy of the GNU Affero General Public License
+# along with this file.  If not, see <http://www.gnu.org/licenses/>.
+# 
+# }}}
+#
+use strict;
+use Getopt::Std;
+use English;
+use Data::Dumper;
+
+#
+# Invoked by xmcreate script to configure a tunnel interface.
+#
+# NOTE: vmid should be an integer ID.
+#
+sub usage()
+{
+    print "Usage: emulab-tun ".
+	"vmid inetip basetable routetable (online|offline)\n";
+    exit(1);
+}
+
+#
+# Turn off line buffering on output
+#
+$| = 1;
+
+# Drag in path stuff so we can find emulab stuff.
+BEGIN { require "/etc/emulab/paths.pm"; import emulabpaths; }
+
+#
+# Load the OS independent support library. It will load the OS dependent
+# library and initialize itself. 
+# 
+use libsetup;
+use libtmcc;
+use libutil;
+use libtestbed;
+use libvnode;
+
+#
+# Configure.
+#
+my $IPTABLES	= "/sbin/iptables";
+my $IPBIN	= "/sbin/ip";
+my $IFCONFIG    = "/sbin/ifconfig";
+
+usage()
+    if (@ARGV < 6);
+
+my $vmid       = shift(@ARGV);
+my $inetip     = shift(@ARGV);
+my $mac        = shift(@ARGV);
+my $bridge     = shift(@ARGV);
+my $basetable  = shift(@ARGV);
+my $routetable = shift(@ARGV);
+
+# The caller (xmcreate) puts this into the environment.
+my $vif         = $ENV{'vif'};
+my $XENBUS_PATH = $ENV{'XENBUS_PATH'};
+my $vifname     = `xenstore-read "$XENBUS_PATH/vifname"`;
+chomp($vifname);
+
+#
+# Set up ip rules and routes for tunnels.
+#
+sub Online()
+{
+    mysystem2("$IPBIN link set $vif name $vifname");
+    if ($?) {
+	return -1;
+    }
+    $vif = $vifname;
+    mysystem2("$IFCONFIG $vif 0 up");
+    mysystem2("echo 1 > /proc/sys/net/ipv4/conf/$vif/forwarding");
+    mysystem2("echo 1 > /proc/sys/net/ipv4/conf/$vif/proxy_arp");
+    mysystem2("$IPBIN link set $vif mtu 1472");
+    
+    #
+    # Insert the ip *rule* for the routetable that directs the traffic
+    # through the iproute inserted into this table in libvnode_xen.
+    #
+    mysystem2("$IPBIN rule add unicast iif $vif table $routetable");
+    if ($?) {
+	return -1;
+    }
+
+    #
+    # And this is the route that goes in the basetable that we attached
+    # to the gre in libvnode_xen. This sends all packets coming out of
+    # the physical gre, down the veth. onlink very important; it says
+    # to "pretend that the nexthop is directly attached to this link, even
+    # if it does not match any interface prefix."
+    #
+    mysystem2("$IPBIN route replace default ".
+	      "via $inetip dev $vif onlink table $basetable");
+    if ($?) {
+	return -1;
+    }
+    # Ug, tell xen hotplug that we really did what was needed.
+    mysystem2("xenstore-write '$XENBUS_PATH/hotplug-status' connected");
+    return 0;
+}
+
+sub Offline()
+{
+    mysystem2("$IPBIN rule del unicast iif $vif table $routetable");
+    
+    mysystem2("$IPBIN route delete default ".
+	      "via $inetip dev $vif onlink table $basetable");
+    return 0;
+}
+
+if (@ARGV) {
+    my $rval = 0;
+    my $op   = shift(@ARGV);
+    if ($op eq "online") {
+	$rval = Online();
+    }
+    elsif ($op eq "offline") {
+	$rval = Offline();
+    }
+    exit($rval);
+}
+exit(0);