libvirt: Add announce-self post live-migration workaround

NOTE(melwitt): This is the combination of two commits, the workaround
config option and a followup change to add a note that enabling the
workaround will cause the guest domain to be considered tainted by
libvirt.

This patch adds a workaround that can be enabled
to send an announce_self QEMU monitor command
post live-migration to send out RARP frames
that was lost due to port binding or flows not
being installed.

Please note that this makes marks the domain
in libvirt as tainted.

See previous information about this issue in
the [1] bug.

[1] https://bugs.launchpad.net/nova/+bug/1815989

Related-Bug: 1815989

Update announce self workaround opt description

This updates the announce self workaround config opt
description to include info about instance being set
as tainted by libvirt.

Change-Id: I8140c8fe592dd54fc09a9510723892806db49a56
(cherry picked from commit 2aa1ed5810)

Change-Id: I7a6a6fe5f5b23e76948b59a85ca9be075a1c2d6d
(cherry picked from commit d44e24efe2)

nova/conf/workarounds.py

@@ -358,6 +358,19 @@ backend.
 Related options:
 
 * :oslo.config:option:`DEFAULT.vif_plugging_timeout`
+"""),
+    cfg.BoolOpt('enable_qemu_monitor_announce_self',
+                default=False,
+                help="""
+If it is set to True the libvirt driver will  try as a best effort to send
+the announce-self command to the QEMU monitor so that it generates RARP frames
+to update network switches in the post live migration phase on the destination.
+
+Please note that this causes the domain to be considered tainted by libvirt.
+
+Related options:
+
+* :oslo.config:option:`DEFAULT.compute_driver` (libvirt)
 """),
 ]
 

nova/virt/libvirt/driver.py

@@ -10510,6 +10510,26 @@ class LibvirtDriver(driver.ComputeDriver):
         """
         self.unplug_vifs(instance, network_info)
 
+    def _qemu_monitor_announce_self(self, instance):
+        """Send announce_self command to QEMU monitor.
+
+        This is to trigger generation of broadcast RARP frames to
+        update network switches. This is best effort.
+        """
+        if not CONF.workarounds.enable_qemu_monitor_announce_self:
+            return
+
+        LOG.info('Sending announce-self command to QEMU monitor',
+                 instance=instance)
+
+        try:
+            guest = self._host.get_guest(instance)
+            guest.announce_self()
+        except Exception:
+            LOG.warning('Failed to send announce-self command to QEMU monitor',
+                        instance=instance)
+            LOG.exception()
+
     def post_live_migration_at_destination(self, context,
                                            instance,
                                            network_info,
@@ -10525,6 +10545,7 @@ class LibvirtDriver(driver.ComputeDriver):
         :param block_migration: if true, post operation of block_migration.
         """
         self._reattach_instance_vifs(context, instance, network_info)
+        self._qemu_monitor_announce_self(instance)
 
     def _get_instance_disk_info_from_config(self, guest_config,
                                             block_device_info):

nova/virt/libvirt/guest.py

@@ -48,6 +48,12 @@ if ty.TYPE_CHECKING:
 else:
     libvirt = None
 
+try:
+    import libvirtmod_qemu
+except ImportError:
+    libvirtmod_qemu = None
+
+
 LOG = logging.getLogger(__name__)
 
 VIR_DOMAIN_NOSTATE = 0
@@ -632,6 +638,10 @@ class Guest(object):
         """Switch running live migration to post-copy mode"""
         self._domain.migrateStartPostCopy()
 
+    def announce_self(self):
+        libvirtmod_qemu.virDomainQemuMonitorCommand(
+            self._domain._o, 'announce_self', 1)
+
     def get_job_info(self):
         """Get job info for the domain
 

releasenotes/notes/announce-self-post-live-migration-936721b1ab887514.yaml

@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    Added a new configuration option ``[workarounds]/enable_qemu_monitor_announce_self``
+    that when enabled causes the Libvirt driver to send a announce_self QEMU
+    monitor command post live-migration. Please see `bug 1815989 <https://bugs.launchpad.net/nova/+bug/1815989>`_
+    for more details. Please note that this causes the domain to be considered
+    tainted by libvirt.