add mtu to libvirt xml for ethernet and bridge types

Where libvirt is creating the tap device e.g: OVS bridge
(hybrid=False). os-vif will just ensure that the OVS bridge exists. We
want libvirt to create the tap, configure the MTU and then plug the
tap into the right bridge.

- This change adds the mtu element to libvirt guest
  interface xml for vifs of type ethernet and bridge.
- This change adds a libvirt version check
  to enable setting the interface mtu on hosts with
  libvirt 3.3.0+

Conflicts:
        nova/virt/libvirt/vif.py

NOTE(lyarwood): This conflict is due to the removal of IVS plug/unplug
via dIcf948f6ee1c0da2327fb5eac61fec6e89ac30531 during Rocky, resulting
in the eventual master change having to reintroduce get_config_bridge
that is already present in stable/queens.

Change-Id: Iecc265fb25e88fa00a66f1fd38e215cad53e7669
Partial-bug: #1747496
(cherry picked from commit f02b3800051234ecc14f3117d5987b1a8ef75877)

3 files changed, 36 insertions, 0 deletions

diff --git a/nova/virt/libvirt/config.py b/nova/virt/libvirt/config.py
index 0c0e6ee0f9..6725ddcac7 100644
--- a/nova/virt/libvirt/config.py
+++ b/nova/virt/libvirt/config.py
@@ -1328,6 +1328,7 @@ class LibvirtConfigGuestInterface(LibvirtConfigGuestDevice):
         self.vif_outbound_average = None
         self.vlan = None
         self.device_addr = None
+        self.mtu = None
 
     def format_dom(self):
         dev = super(LibvirtConfigGuestInterface, self).format_dom()
@@ -1348,6 +1349,8 @@ class LibvirtConfigGuestInterface(LibvirtConfigGuestDevice):
         if self.net_type == "ethernet":
             if self.script is not None:
                 dev.append(etree.Element("script", path=self.script))
+            if self.mtu is not None:
+                dev.append(etree.Element("mtu", size=str(self.mtu)))
         elif self.net_type == "direct":
             dev.append(etree.Element("source", dev=self.source_dev,
                                      mode=self.source_mode))
@@ -1370,6 +1373,8 @@ class LibvirtConfigGuestInterface(LibvirtConfigGuestDevice):
             dev.append(etree.Element("source", bridge=self.source_dev))
             if self.script is not None:
                 dev.append(etree.Element("script", path=self.script))
+            if self.mtu is not None:
+                dev.append(etree.Element("mtu", size=str(self.mtu)))
         else:
             dev.append(etree.Element("source", bridge=self.source_dev))
 
@@ -1501,6 +1506,8 @@ class LibvirtConfigGuestInterface(LibvirtConfigGuestDevice):
             elif c.tag == 'address':
                 obj = LibvirtConfigGuestDeviceAddress.parse_dom(c)
                 self.device_addr = obj
+            elif c.tag == 'mtu':
+                self.mtu = int(c.get('size'))
 
     def add_filter_param(self, key, value):
         self.filterparams.append({'key': key, 'value': value})
diff --git a/nova/virt/libvirt/designer.py b/nova/virt/libvirt/designer.py
index 847faa6598..9448847937 100644
--- a/nova/virt/libvirt/designer.py
+++ b/nova/virt/libvirt/designer.py
@@ -158,6 +158,13 @@ def set_vif_host_backend_vhostuser_config(conf, mode, path):
     conf.vhostuser_path = path
 
 
+def set_vif_mtu_config(conf, mtu):
+    """Populate a LibvirtConfigGuestInterface instance
+    with network mtu.
+    """
+    conf.mtu = mtu
+
+
 def set_vif_bandwidth_config(conf, inst_type):
     """Config vif inbound/outbound bandwidth limit. parameters are
     set in instance_type_extra_specs table, key is in  the format
diff --git a/nova/virt/libvirt/vif.py b/nova/virt/libvirt/vif.py
index 6d5f2385e9..6b2ad06b33 100644
--- a/nova/virt/libvirt/vif.py
+++ b/nova/virt/libvirt/vif.py
@@ -48,6 +48,8 @@ CONF = nova.conf.CONF
 MIN_LIBVIRT_VHOSTUSER_MQ = (1, 2, 17)
 #  vlan tag for macvtap passthrough mode on SRIOV VFs
 MIN_LIBVIRT_MACVTAP_PASSTHROUGH_VLAN = (1, 3, 5)
+# setting interface mtu was intoduced in libvirt 3.3
+MIN_LIBVIRT_INTERFACE_MTU = (3, 3, 0)
 
 
 def is_vif_model_valid_for_virt(virt_type, vif_model):
@@ -237,8 +239,23 @@ class LibvirtGenericVIFDriver(object):
             conf.filtername = name
         designer.set_vif_bandwidth_config(conf, inst_type)
 
+        self._set_mtu_config(vif, host, conf)
+
         return conf
 
+    def _set_mtu_config(self, vif, host, conf):
+        """:param vif: nova.network.modle.vif
+           :param host: nova.virt.libvirt.host.Host
+           :param conf: nova.virt.libvirt.config.LibvirtConfigGuestInterface
+        """
+        network = vif.get('network')
+        if (network and network.get_meta("mtu") and
+                self._has_min_version_for_mtu(host)):
+            designer.set_vif_mtu_config(conf, network.get_meta("mtu"))
+
+    def _has_min_version_for_mtu(self, host):
+        return host.has_min_version(MIN_LIBVIRT_INTERFACE_MTU)
+
     def get_config_ivs_hybrid(self, instance, vif, image_meta,
                               inst_type, virt_type, host):
         newvif = copy.deepcopy(vif)
@@ -404,6 +421,8 @@ class LibvirtGenericVIFDriver(object):
         dev = self.get_vif_devname(vif)
         designer.set_vif_host_backend_ethernet_config(conf, dev, host)
 
+        self._set_mtu_config(vif, host, conf)
+
         return conf
 
     def _get_vhostuser_settings(self, vif):
@@ -530,6 +549,9 @@ class LibvirtGenericVIFDriver(object):
         func(instance, vif, conf, host)
 
         designer.set_vif_bandwidth_config(conf, inst_type)
+        if ('network' in vif and 'mtu' in vif.network and
+                self._has_min_version_for_mtu(host)):
+            designer.set_vif_mtu_config(conf, vif.network.mtu)
 
         return conf