Have host look for CPU controller of cgroupsv2 location.

Make the host class look under '/sys/fs/cgroup/cgroup.controllers' for support of the cpu controller. The host will try searching through cgroupsv1 first, just like up until now, and in the case that fails, it will try cgroupsv2 then. The host will not support the feature if both checks fail.

This new check needs to be mocked by all tests that focus on this piece of code, as it touches a system file that requires privileges. For such thing, the CGroupsFixture is defined to easily add suck mocking to all test cases that require so.

I also removed old mocking at test_driver.py in favor of the fixture from above.

Partial-Bug: #2008102
Change-Id: I99b57c27c8a4425389bec2b7f05af660bab85610

1 files changed, 71 insertions, 0 deletions

diff --git a/nova/tests/fixtures/nova.py b/nova/tests/fixtures/nova.py
index 5fd893e7dc..abfc3ecc6c 100644
--- a/nova/tests/fixtures/nova.py
+++ b/nova/tests/fixtures/nova.py
@@ -1318,6 +1318,77 @@ class PrivsepFixture(fixtures.Fixture):
             nova.privsep.sys_admin_pctxt, 'client_mode', False))
 
 
+class CGroupsFixture(fixtures.Fixture):
+    """Mocks checks made for available subsystems on the host's control group.
+
+    The fixture mocks all calls made on the host to verify the capabilities
+    provided by its kernel. Through this, one can simulate the underlying
+    system hosts work on top of and have tests react to expected outcomes from
+    such.
+
+    Use sample:
+    >>> cgroups = self.useFixture(CGroupsFixture())
+    >>> cgroups = self.useFixture(CGroupsFixture(version=2))
+    >>> cgroups = self.useFixture(CGroupsFixture())
+    ... cgroups.version = 2
+
+    :attr version: Arranges mocks to simulate the host interact with nova
+                   following the given version of cgroups.
+                   Available values are:
+                        - 0: All checks related to cgroups will return False.
+                        - 1: Checks related to cgroups v1 will return True.
+                        - 2: Checks related to cgroups v2 will return True.
+                   Defaults to 1.
+    """
+
+    def __init__(self, version=1):
+        self._cpuv1 = None
+        self._cpuv2 = None
+
+        self._version = version
+
+    @property
+    def version(self):
+        return self._version
+
+    @version.setter
+    def version(self, value):
+        self._version = value
+        self._update_mocks()
+
+    def setUp(self):
+        super().setUp()
+        self._cpuv1 = self.useFixture(fixtures.MockPatch(
+            'nova.virt.libvirt.host.Host._has_cgroupsv1_cpu_controller')).mock
+        self._cpuv2 = self.useFixture(fixtures.MockPatch(
+            'nova.virt.libvirt.host.Host._has_cgroupsv2_cpu_controller')).mock
+        self._update_mocks()
+
+    def _update_mocks(self):
+        if not self._cpuv1:
+            return
+
+        if not self._cpuv2:
+            return
+
+        if self.version == 0:
+            self._cpuv1.return_value = False
+            self._cpuv2.return_value = False
+            return
+
+        if self.version == 1:
+            self._cpuv1.return_value = True
+            self._cpuv2.return_value = False
+            return
+
+        if self.version == 2:
+            self._cpuv1.return_value = False
+            self._cpuv2.return_value = True
+            return
+
+        raise ValueError(f"Unknown cgroups version: '{self.version}'.")
+
+
 class NoopQuotaDriverFixture(fixtures.Fixture):
     """A fixture to run tests using the NoopQuotaDriver.