add method for trunk driver to check if vlan segment is present for current physnet

Author: Milan Fencik

python/neutron-understack/neutron_understack/trunk.py

@@ -171,7 +171,11 @@ def _handle_segment_allocation(
             subport_network_id = utils.fetch_subport_network_id(
                 subport_id=subport["port_id"]
             )
-            network_segment = utils.allocate_dynamic_segment(
+            current_segment = utils.network_segment_by_physnet(
+                network_id=subport_network_id,
+                physnet=vlan_group_name,
+            )
+            network_segment = current_segment or utils.allocate_dynamic_segment(
                 network_id=subport_network_id,
                 physnet=vlan_group_name,
             )

python/neutron-understack/neutron_understack/utils.py

@@ -77,6 +77,26 @@ def network_segment_by_id(id: str) -> NetworkSegment:
     return NetworkSegment.get_object(context, id=id)
 
 
+def network_segment_by_physnet(network_id: str, physnet: str) -> NetworkSegment | None:
+    """Fetches vlan network segments for network in particular physnet.
+
+    We return first segment on purpose, there shouldn't be more, but if
+    that is the case, it may be intended for some reason and we don't want
+    to halt the code.
+    """
+    context = n_context.get_admin_context()
+
+    segments = NetworkSegment.get_objects(
+        context,
+        network_id=network_id,
+        physical_network=physnet,
+        network_type=constants.TYPE_VLAN,
+    )
+    if not segments:
+        return
+    return segments[0]
+
+
 def release_dynamic_segment(segment_id: str) -> None:
     context = n_context.get_admin_context()
     core_plugin = directory.get_plugin()  # Get the core plugin