Add charm config option for force_raw_images

Since Ocata, backing images are by default converted into raw format
but since Pike a problem with O_DIRECT calls and ZFS backend storage
has presented - i.e., Pike on LXD with ZFS backend storage will result
in an error about image conversion. This config option allows
that default to be changed so that Pike on LXD with ZFS will lauch
instances succesfully.

Closes-Bug: 1710994

Change-Id: Ieba15b44b4b56a356d58c4504dd259fc80e7575d

config.yaml

@@ -273,6 +273,14 @@ options:
       Tell Nova which libvirt image backend to use. Supported backends are rbd,
       lvm and qcow2. If no backend is specified, the Nova default (qcow2) is
       used. Note that rbd imagebackend is only supported with >= Juno.
+  force-raw-images:
+    type: boolean
+    default: True
+    description: |
+      Force conversion of backing images to raw format. Note that the conversion
+      process in Pike uses O_DIRECT calls - certain file systems do not support this,
+      for example ZFS; e.g. if using the LXD provider with ZFS backend, this option
+      should be set to False.
   rbd-pool:
     type: string
     default: 'nova'

hooks/nova_compute_context.py

@@ -244,6 +244,8 @@ class NovaComputeLibvirtContext(context.OSContextGenerator):
         if config('libvirt-image-backend'):
             ctxt['libvirt_images_type'] = config('libvirt-image-backend')
 
+        ctxt['force_raw_images'] = config('force-raw-images')
+
         return ctxt
 
 

templates/ocata/nova.conf

@@ -20,6 +20,7 @@ api_paste_config=/etc/nova/api-paste.ini
 enabled_apis=osapi_compute,metadata
 auth_strategy=keystone
 my_ip = {{ host_ip }}
+force_raw_images = {{ force_raw_images }}
 
 {% if arch == 'aarch64' -%}
 libvirt_use_virtio_for_bridges=False

unit_tests/test_nova_compute_contexts.py

@@ -225,6 +225,7 @@ class NovaComputeContextTests(CharmTestCase):
              'kvm_hugepages': 0,
              'listen_tls': 0,
              'host_uuid': self.host_uuid,
+             'force_raw_images': True,
              'reserved_host_memory': 512}, libvirt())
 
     def test_libvirt_bin_context_no_migration(self):
@@ -241,6 +242,7 @@ class NovaComputeContextTests(CharmTestCase):
              'kvm_hugepages': 0,
              'listen_tls': 0,
              'host_uuid': self.host_uuid,
+             'force_raw_images': True,
              'reserved_host_memory': 512}, libvirt())
 
     def test_libvirt_bin_context_migration_tcp_listen(self):
@@ -258,6 +260,7 @@ class NovaComputeContextTests(CharmTestCase):
              'listen_tls': 0,
              'host_uuid': self.host_uuid,
              'live_migration_uri': 'qemu+ssh://%s/system',
+             'force_raw_images': True,
              'reserved_host_memory': 512}, libvirt())
 
     def test_libvirt_disk_cachemodes(self):
@@ -275,6 +278,7 @@ class NovaComputeContextTests(CharmTestCase):
              'kvm_hugepages': 0,
              'listen_tls': 0,
              'host_uuid': self.host_uuid,
+             'force_raw_images': True,
              'reserved_host_memory': 512}, libvirt())
 
     def test_libvirt_hugepages(self):
@@ -293,6 +297,25 @@ class NovaComputeContextTests(CharmTestCase):
              'kvm_hugepages': 1,
              'listen_tls': 0,
              'host_uuid': self.host_uuid,
+             'force_raw_images': True,
+             'reserved_host_memory': 512}, libvirt())
+
+    def test_libvirt_context_libvirtd_force_raw_images(self):
+        self.lsb_release.return_value = {'DISTRIB_CODENAME': 'zesty'}
+        self.os_release.return_value = 'ocata'
+        self.kv.return_value = FakeUnitdata(**{'host_uuid': self.host_uuid})
+        self.test_config.set('force-raw-images', False)
+        libvirt = context.NovaComputeLibvirtContext()
+
+        self.assertEqual(
+            {'libvirtd_opts': '',
+             'libvirt_user': 'libvirt',
+             'arch': platform.machine(),
+             'ksm': 'AUTO',
+             'kvm_hugepages': 0,
+             'listen_tls': 0,
+             'host_uuid': self.host_uuid,
+             'force_raw_images': False,
              'reserved_host_memory': 512}, libvirt())
 
     def test_lxd_live_migration_opts_xenial(self):
@@ -396,6 +419,7 @@ class NovaComputeContextTests(CharmTestCase):
              'host_uuid': self.host_uuid,
              'reserved_host_memory': 1024,
              'vcpu_pin_set': '^0^2',
+             'force_raw_images': True,
              'pci_passthrough_whitelist': 'mypcidevices'}, libvirt())
 
     def test_ksm_configs(self):