libvirt: add version cap tied to gate CI testing

Limit the libvirt features that Nova will use in a default
configuration to only those which are tested in the CI gate.

The end user can override the limit if they wish to opt-in
to use of untested features via the 'version_cap' setting
in the 'libvirt' group.

Change-Id: Ib91164cc572b1dbde2a31beee5751c52b0445d3e

2 files changed, 28 insertions, 0 deletions

diff --git a/nova/tests/virt/libvirt/test_driver.py b/nova/tests/virt/libvirt/test_driver.py
index ccde7975ec..0280be9ff5 100644
--- a/nova/tests/virt/libvirt/test_driver.py
+++ b/nova/tests/virt/libvirt/test_driver.py
@@ -576,6 +576,21 @@ class LibvirtConnTestCase(test.TestCase,
         inst = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
         self.assertPublicAPISignatures(inst)
 
+    def test_min_version_cap(self):
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
+
+        with mock.patch.object(drvr._conn, 'getLibVersion') as mock_ver:
+            mock_ver.return_value = utils.convert_version_to_int((1, 5, 0))
+
+            self.flags(version_cap="2.0.0", group="libvirt")
+            self.assertTrue(drvr._has_min_version((1, 4, 0)))
+
+            self.flags(version_cap="1.3.0", group="libvirt")
+            self.assertFalse(drvr._has_min_version((1, 4, 0)))
+
+            self.flags(version_cap="", group="libvirt")
+            self.assertTrue(drvr._has_min_version((1, 4, 0)))
+
     def test_set_host_enabled_with_disable(self):
         # Tests disabling an enabled host.
         conn = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index 31712fdfd8..68889ccfa4 100644
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -106,6 +106,11 @@ libvirt = None
 LOG = logging.getLogger(__name__)
 
 libvirt_opts = [
+    cfg.StrOpt('version_cap',
+               default='1.2.2',  # Must always match the version in the gate
+               help='Limit use of features from newer libvirt versions. '
+                    'Defaults to the version that is used for automated '
+                    'testing of OpenStack.'),
     cfg.StrOpt('rescue_image_id',
                help='Rescue ami image. This will not be used if an image id '
                     'is provided by the user.'),
@@ -413,6 +418,14 @@ class LibvirtDriver(driver.ComputeDriver):
         try:
             if lv_ver is not None:
                 libvirt_version = conn.getLibVersion()
+
+                if CONF.libvirt.version_cap:
+                    libvirt_version_cap = utils.convert_version_to_int(
+                        utils.convert_version_to_tuple(
+                            CONF.libvirt.version_cap))
+                    if libvirt_version > libvirt_version_cap:
+                        libvirt_version = libvirt_version_cap
+
                 if libvirt_version < utils.convert_version_to_int(lv_ver):
                     return False