Allow overriding libvirt/num_pcie_ports

Especially with arm64/aarch64, the default value limits the number of
volume attachments to two usually. And when more than two volumes are to
be attached, it will fail with "No more available PCI slots". There is
no one-size-fits-all value here so let operators override the default
value.

Closes-Bug: #1944214
Change-Id: I9b9565873cbaeb575704b94a25d0a8556ab96292

config.yaml

@@ -294,6 +294,15 @@ options:
       preemption and avoiding packet drops. Only works with Rocky and later,
       since QEMU 2.7.0 and libvirt 2.3.0. Default value 256. Authorized
       values [256, 512, 1024].
+  num-pcie-ports:
+    type: int
+    default:
+    description: |
+      Sets libvirt/num_pcie_ports option in nova.conf to assign more
+      PCIe ports available for a VM. The default value relies on libvirt
+      calculating amount of ports. The maximum value can be set is "28".
+      .
+      This option is only available from the Rocky release and later.
   worker-multiplier:
     type: float
     default:

hooks/nova_compute_context.py

@@ -298,6 +298,9 @@ class NovaComputeLibvirtContext(context.OSContextGenerator):
             ctxt['virtio_net_rx_queue_size'] = (
                 config('virtio-net-rx-queue-size'))
 
+        if config('num-pcie-ports'):
+            ctxt['num_pcie_ports'] = config('num-pcie-ports')
+
         ctxt['reserved_host_memory'] = config('reserved-host-memory')
 
         db = kv()

templates/rocky/nova.conf

@@ -305,6 +305,9 @@ tx_queue_size = {{ virtio_net_tx_queue_size }}
 {% if virtio_net_rx_queue_size -%}
 rx_queue_size = {{ virtio_net_rx_queue_size }}
 {% endif %}
+{% if num_pcie_ports -%}
+num_pcie_ports = {{ num_pcie_ports }}
+{% endif %}
 
 {% if virt_type == 'lxd' -%}
 [lxd]

templates/stein/nova.conf

@@ -318,6 +318,9 @@ tx_queue_size = {{ virtio_net_tx_queue_size }}
 {% if virtio_net_rx_queue_size -%}
 rx_queue_size = {{ virtio_net_rx_queue_size }}
 {% endif %}
+{% if num_pcie_ports -%}
+num_pcie_ports = {{ num_pcie_ports }}
+{% endif %}
 
 {% if virt_type == 'lxd' -%}
 [lxd]

templates/train/nova.conf

@@ -325,6 +325,9 @@ tx_queue_size = {{ virtio_net_tx_queue_size }}
 {% if virtio_net_rx_queue_size -%}
 rx_queue_size = {{ virtio_net_rx_queue_size }}
 {% endif %}
+{% if num_pcie_ports -%}
+num_pcie_ports = {{ num_pcie_ports }}
+{% endif %}
 
 {% if virt_type == 'lxd' -%}
 [lxd]

unit_tests/test_nova_compute_contexts.py

@@ -738,6 +738,7 @@ class NovaComputeContextTests(CharmTestCase):
         self.test_config.set('pci-passthrough-whitelist', 'mypcidevices')
         self.test_config.set('virtio-net-tx-queue-size', 512)
         self.test_config.set('virtio-net-rx-queue-size', 1024)
+        self.test_config.set('num-pcie-ports', 15)
         self.test_config.set('cpu-shared-set', "4-12,^8,15")
         self.test_config.set('cpu-dedicated-set', "0-3,^10,33")
         libvirt = context.NovaComputeLibvirtContext()
@@ -758,6 +759,7 @@ class NovaComputeContextTests(CharmTestCase):
              'pci_passthrough_whitelist': 'mypcidevices',
              'virtio_net_tx_queue_size': 512,
              'virtio_net_rx_queue_size': 1024,
+             'num_pcie_ports': 15,
              'default_ephemeral_format': 'ext4',
              'cpu_shared_set': "4-12,^8,15",
              'cpu_dedicated_set': "0-3,^10,33"}, libvirt())