Look for the switch path in the DB when doing the initial mapping to

devices (for creating the stack object). We were using the older
mapping code (that computes on the fly) in the snmpit front end, but
now we use the DB in both the front end, and from the stack later.

tbsetup/snmpit_test/snmpit_lib.pm

 #!/usr/bin/perl -w
 #
 # EMULAB-LGPL
-# Copyright (c) 2000-2011 University of Utah and the Flux Group.
+# Copyright (c) 2000-2012 University of Utah and the Flux Group.
 # All rights reserved.
 #
 
@@ -1207,12 +1207,18 @@ sub mapVlansToSwitches(@)
     #
     foreach my $vlan_id (@vlan_ids) {
 	my @ports   = uniq_ports(getVlanPorts($vlan_id),
-			   getExperimentVlanPorts($vlan_id));
-	my @devices = mapPortsToSwitches(@ports);
+				 getExperimentVlanPorts($vlan_id));
+	my %map     = mapPortsToDevices(@ports);
+
+	#
+	# We want to use the DB path if it exists.
+	#
+	my @trunks = getTrunksForVlan($vlan_id, keys(%map));
 
 	# And update the total set of switches.
-	foreach my $device (@devices) {
-	    $switches{$device} = 1;
+	foreach my $trunk (@trunks) {
+	    my ($src,$dst) = @$trunk;
+	    $switches{$src} = $switches{$dst} = 1;
 	}
     }
     my @sorted = sort {tbsort($a,$b)} keys %switches;
@@ -1236,11 +1242,17 @@ sub mapStaleVlansToSwitches(@)
 	# this. 
 	#
 	my @ports   = getExperimentVlanPorts($vlan_id);
-	my @devices = mapPortsToSwitches(@ports);
+	my %map     = mapPortsToDevices(@ports);
+
+	#
+	# We want to use the DB path if it exists.
+	#
+	my @trunks = getExperimentTrunksForVlan($vlan_id, keys(%map));
 
 	# And update the total set of switches.
-	foreach my $device (@devices) {
-	    $switches{$device} = 1;
+	foreach my $trunk (@trunks) {
+	    my ($src,$dst) = @$trunk;
+	    $switches{$src} = $switches{$dst} = 1;
 	}
     }
     my @sorted = sort {tbsort($a,$b)} keys %switches;
@@ -1271,6 +1283,12 @@ sub mapPortsToSwitches(@)
     # its trunks.
     #
     my @trunks = getTrunksFromSwitches(\%trunks, keys %devices);
+
+    #
+    # Now form a spanning tree to ensure there are no loops.
+    #
+    @trunks = SpanningTree(\@trunks);
+    
     foreach my $trunk (@trunks) {
 	my ($src,$dst) = @$trunk;
 	$devices{$src} = $devices{$dst} = 1;