fix(instances): enabling vCPU hot plug keeps the current vCPU count

Enabling hot plug on a stopped VM wrote every vCPU up to the maximum as
enabled, so a VM with 2 of 4 vCPUs booted with 4. The current vCPUs stay
enabled now; libvirt adds the rest as disabled hotpluggable vCPUs.

README.md

@@ -534,6 +534,7 @@ A rollback leaves the clone on a detached HEAD at the restored commit; the updat
 - A VM that vanishes from its compute keeps its owners for `INSTANCE_OWNERSHIP_RETENTION_DAYS` (30) in case the same UUID comes back; superusers list and remove these records on the "Removed VMs" admin page.
 - The log rotates (10 MB × 5) in `data/webvirtcloud.log`.
 - A disk can be grown while its VM runs or is paused, not only when it is shut off.
+- Enabling vCPU hot plug keeps the VM's current vCPU count (it enabled all of them up to the maximum).
 - A host's CPU graph shows the average since its previous point (normally 5 s) instead of a 1 s sample taken while a worker waits.
 - A VM's stats are polled every 5 s like the host graph, the first point as soon as the tab opens; each point is the average since the previous one, disk rates in MB/s (they were MiB/s labelled Mb/s); a counter the host does not report shows a gap instead of 0.
 - An ISO uploads to an SSH compute about 3.5 times faster (SFTP writes no longer wait for each 32 KiB); a failed write still fails the upload.

instances/test_live_xml_effects.py

@@ -278,3 +278,17 @@ class LiveXmlEffectsTestCase(SimpleTestCase):
 
     def test_edits_of_a_paused_vm(self):
         self.check(running=True, paused=True)
+
+    def test_enabling_vcpu_hotplug_keeps_the_current_vcpus(self):
+        try:
+            dom, vm = self.vm(running=False)
+            vm.resize_cpu("2", "4")
+            vm.set_vcpu_hotplug(True)
+            after = self.persistent(dom)
+            self.assertEqual((after.findtext("vcpu"), first(after, "vcpu/@current")), ("4", "2"))
+            self.assertEqual(after.xpath("vcpus/vcpu/@enabled"), ["yes", "yes", "no", "no"])
+            self.assertEqual(after.xpath("vcpus/vcpu/@hotpluggable"), ["no", "yes", "yes", "yes"])
+            dom.create()
+            self.assertEqual(dom.vcpusFlags(libvirt.VIR_DOMAIN_AFFECT_LIVE), 2)
+        finally:
+            livetest.cleanup(self.conn)

vrtManager/instance.py

@@ -1105,8 +1105,9 @@ class wvmInstance(wvmConnect):
         self.instance.setVcpu(str(cpu_id), enabled)
 
     def set_vcpu_hotplug(self, status, vcpus_hotplug=0):
-        """vcpus_hotplug = 0 make all vpus hotpluggable"""
-        vcpus_hotplug = int(self.get_vcpu()) if vcpus_hotplug == 0 else vcpus_hotplug
+        """vcpus_hotplug: the vCPUs enabled at boot, 0 keeps the current ones;
+        libvirt adds the rest up to the maximum as disabled hotpluggable vCPUs"""
+        vcpus_hotplug = self.get_cur_vcpu() if vcpus_hotplug == 0 else vcpus_hotplug
         if self.get_status() == 5:  # shutoff
             if status:
                 xml = """ <vcpus>"""

vrtManager/test_device_edits.py

@@ -1,7 +1,8 @@
 """Device edits of a VM: each definition is changed as it describes the
 device, every NIC type can be a boot device, posted values stay values, and
 definition changes go through _defineXML. An active VM's memory is resized
-by balloon, a stopped one's in its definition."""
+by balloon, a stopped one's in its definition. Enabling vCPU hot plug keeps
+the vCPUs enabled at boot."""
 
 import unittest
 from unittest.mock import MagicMock
@@ -65,6 +66,15 @@ class DetachDiskTestCase(unittest.TestCase):
         p.instance.detachDeviceFlags.assert_not_called()
 
 
+class VcpuHotplugTestCase(unittest.TestCase):
+    def test_enabling_hotplug_keeps_the_current_vcpus_enabled(self):
+        p = proxy(active=False)
+        p.instance.info.return_value = [5]
+        p._XMLDesc = lambda flags: "<domain><vcpu current='2'>4</vcpu></domain>"
+        p.set_vcpu_hotplug(True)
+        self.assertEqual(defined(p).xpath("vcpus/vcpu/@enabled"), ["yes", "yes"])
+
+
 class DeviceEditsTestCase(unittest.TestCase):
     def test_a_block_volume_is_attached_by_its_device_path(self):
         p = proxy(active=False)