インスタンスの起動時にアクセスが拒否されましたエラー（「バッキングファイルを開けませんでした」）
Debianテストで利用可能なパッケージからインストールされたOpenStackの操作（バスター）。インスタンスを起動しようとすると、nova-compute.logに次のメッセージを表示してビルドした後、失敗します。
バッキングファイルを開けませんでした： '/ var/lib/nova/instances/_base/affe96668a4c64ef380ff1c71b4caec17039080e'を開けませんでした：アクセスが拒否されました
そのファイルには次の権限があります。
$ namei -l /var/lib/nova/instances/_base/affe96668a4c64ef380ff1c71b4caec17039080e
f: /var/lib/nova/instances/_base/affe96668a4c64ef380ff1c71b4caec17039080e
drwxr-xr-x root root /
drwxr-xr-x root root var
drwxr-xr-x root root lib
drwxr-xr-x nova nova nova
drwxr-xr-x nova nova instances
drwxr-xr-x nova nova _base
-rw-r--r-- libvirt-qemu libvirt-qemu affe96668a4c64ef380ff1c71b4caec17039080e
関連する問題を見つけました（ https://bugs.launchpad.net/openstack-helm/+bug/1714421 ）が、そのためのパッチ（/ etcにユーザーとグループを設定する） /libvirt/qemu.conf）は機能しません。
私の知る限り、QEMUプロセスはrootとして実行されるため、どのユーザーが実際にアクセス許可を拒否されているのかわかりません。
あるいは、openstackまたはlibvirtのどの部分がそのファイルを作成し、「libvirt-qemu」をユーザーおよびグループとして設定しますか？
Nova-compute.logの関連部分：
2018-03-02T05:15:27.083155Z qemu-system-x86_64: -drive file=/var/lib/nova/instances/9ac0d3ec-35ad-4420-ae20-f6c0c9845f05/disk,format=qcow2,if=none,id=drive-virtio-disk0,cache=none: Could not open backing file: Could not open '/var/lib/nova/instances/_base/affe96668a4c64ef380ff1c71b4caec17039080e': Permission denied
2018-03-01 23:15:27.373 2376 ERROR nova.virt.libvirt.driver [req-3cb9fbc5-8f4e-4244-8b14-b52ac1f0494b a6f48b630f634371ba94558f3ba576b8 5f46526ffab3410a9cf71b37fa242e11 - default default] [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] Failed to start libvirt guest: libvirtError: internal error: process exited while connecting to monitor: outputs=1,bus=pci.0,addr=0x2 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6 -msg timestamp=on
2018-03-02T05:15:27.083155Z qemu-system-x86_64: -drive file=/var/lib/nova/instances/9ac0d3ec-35ad-4420-ae20-f6c0c9845f05/disk,format=qcow2,if=none,id=drive-virtio-disk0,cache=none: Could not open backing file: Could not open '/var/lib/nova/instances/_base/affe96668a4c64ef380ff1c71b4caec17039080e': Permission denied
2018-03-01 23:15:27.374 2376 INFO os_vif [req-3cb9fbc5-8f4e-4244-8b14-b52ac1f0494b a6f48b630f634371ba94558f3ba576b8 5f46526ffab3410a9cf71b37fa242e11 - default default] Successfully unplugged vif VIFBridge(active=False,address=fa:16:3e:b4:ed:53,bridge_name='brq03b5dd02-ac',has_traffic_filtering=True,id=042a5f68-01bb-453e-bb2a-2d798b7691d5,network=Network(03b5dd02-ac2f-49f0-b1ff-fa26059f352c),plugin='linux_bridge',port_profile=<?>,preserve_on_delete=False,vif_name='tap042a5f68-01')
2018-03-01 23:15:27.434 2376 INFO nova.virt.libvirt.driver [req-3cb9fbc5-8f4e-4244-8b14-b52ac1f0494b a6f48b630f634371ba94558f3ba576b8 5f46526ffab3410a9cf71b37fa242e11 - default default] [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] Deleting instance files /var/lib/nova/instances/9ac0d3ec-35ad-4420-ae20-f6c0c9845f05_del
2018-03-01 23:15:27.436 2376 INFO nova.virt.libvirt.driver [req-3cb9fbc5-8f4e-4244-8b14-b52ac1f0494b a6f48b630f634371ba94558f3ba576b8 5f46526ffab3410a9cf71b37fa242e11 - default default] [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] Deletion of /var/lib/nova/instances/9ac0d3ec-35ad-4420-ae20-f6c0c9845f05_del complete
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [req-3cb9fbc5-8f4e-4244-8b14-b52ac1f0494b a6f48b630f634371ba94558f3ba576b8 5f46526ffab3410a9cf71b37fa242e11 - default default] [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] Instance failed to spawn: libvirtError: internal error: process exited while connecting to monitor: outputs=1,bus=pci.0,addr=0x2 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6 -msg timestamp=on
2018-03-02T05:15:27.083155Z qemu-system-x86_64: -drive file=/var/lib/nova/instances/9ac0d3ec-35ad-4420-ae20-f6c0c9845f05/disk,format=qcow2,if=none,id=drive-virtio-disk0,cache=none: Could not open backing file: Could not open '/var/lib/nova/instances/_base/affe96668a4c64ef380ff1c71b4caec17039080e': Permission denied
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] Traceback (most recent call last):
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 2192, in _build_resources
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] yield resources
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 2007, in _build_and_run_instance
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] block_device_info=block_device_info)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 2814, in spawn
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] destroy_disks_on_failure=True)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 5294, in _create_domain_and_network
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] destroy_disks_on_failure)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 220, in __exit__
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] self.force_reraise()
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 196, in force_reraise
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] six.reraise(self.type_, self.value, self.tb)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 5264, in _create_domain_and_network
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] post_xml_callback=post_xml_callback)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py", line 5182, in _create_domain
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] guest.launch(pause=pause)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/guest.py", line 144, in launch
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] self._encoded_xml, errors='ignore')
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 220, in __exit__
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] self.force_reraise()
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 196, in force_reraise
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] six.reraise(self.type_, self.value, self.tb)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/guest.py", line 139, in launch
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] return self._domain.createWithFlags(flags)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/eventlet/tpool.py", line 186, in doit
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] result = proxy_call(self._autowrap, f, *args, **kwargs)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/eventlet/tpool.py", line 144, in proxy_call
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] rv = execute(f, *args, **kwargs)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/eventlet/tpool.py", line 125, in execute
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] six.reraise(c, e, tb)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/eventlet/tpool.py", line 83, in tworker
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] rv = meth(*args, **kwargs)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] File "/usr/lib/python2.7/dist-packages/libvirt.py", line 1099, in createWithFlags
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] if ret == -1: raise libvirtError ('virDomainCreateWithFlags() failed', dom=self)
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] libvirtError: internal error: process exited while connecting to monitor: outputs=1,bus=pci.0,addr=0x2 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6 -msg timestamp=on
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] 2018-03-02T05:15:27.083155Z qemu-system-x86_64: -drive file=/var/lib/nova/instances/9ac0d3ec-35ad-4420-ae20-f6c0c9845f05/disk,format=qcow2,if=none,id=drive-virtio-disk0,cache=none: Could not open backing file: Could not open '/var/lib/nova/instances/_base/affe96668a4c64ef380ff1c71b4caec17039080e': Permission denied
2018-03-01 23:15:27.813 2376 ERROR nova.compute.manager [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05]
2018-03-01 23:15:27.815 2376 INFO nova.compute.manager [req-3cb9fbc5-8f4e-4244-8b14-b52ac1f0494b a6f48b630f634371ba94558f3ba576b8 5f46526ffab3410a9cf71b37fa242e11 - default default] [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] Terminating instance
2018-03-01 23:15:27.822 2376 INFO nova.virt.libvirt.driver [-] [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] Instance destroyed successfully.
2018-03-01 23:15:27.824 2376 INFO os_vif [req-3cb9fbc5-8f4e-4244-8b14-b52ac1f0494b a6f48b630f634371ba94558f3ba576b8 5f46526ffab3410a9cf71b37fa242e11 - default default] Successfully unplugged vif VIFBridge(active=False,address=fa:16:3e:b4:ed:53,bridge_name='brq03b5dd02-ac',has_traffic_filtering=True,id=042a5f68-01bb-453e-bb2a-2d798b7691d5,network=Network(03b5dd02-ac2f-49f0-b1ff-fa26059f352c),plugin='linux_bridge',port_profile=<?>,preserve_on_delete=False,vif_name='tap042a5f68-01')
2018-03-01 23:15:28.107 2376 INFO nova.virt.libvirt.driver [req-3cb9fbc5-8f4e-4244-8b14-b52ac1f0494b a6f48b630f634371ba94558f3ba576b8 5f46526ffab3410a9cf71b37fa242e11 - default default] [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] Deletion of /var/lib/nova/instances/9ac0d3ec-35ad-4420-ae20-f6c0c9845f05_del complete
2018-03-01 23:15:28.501 2376 INFO nova.compute.manager [req-3cb9fbc5-8f4e-4244-8b14-b52ac1f0494b a6f48b630f634371ba94558f3ba576b8 5f46526ffab3410a9cf71b37fa242e11 - default default] [instance: 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05] Took 0.68 seconds to destroy the instance on the hypervisor.
2018-03-01 23:15:29.721 2376 WARNING nova.scheduler.client.report [req-3cb9fbc5-8f4e-4244-8b14-b52ac1f0494b a6f48b630f634371ba94558f3ba576b8 5f46526ffab3410a9cf71b37fa242e11 - default default] Unable to delete allocation for instance 9ac0d3ec-35ad-4420-ae20-f6c0c9845f05: (500 {"computeFault": {"message": "The server has either erred or is incapable of performing the requested operation.", "code": 500}})
2018-03-01 23:15:29.721 2376 WARNING nova.compute.manager [req-3cb9fbc5-8f4e-4244-8b14-b52ac1f0494b a6f48b630f634371ba94558f3ba576b8 5f46526ffab3410a9cf71b37fa242e11 - default default] 6 consecutive build failures
必要に応じて追加のログを投稿できます。
これは、debian libvirtパッケージに含まれているlibvirtのAppArmorプロファイルにnovaのインスタンスディレクトリ（/ var/lib/nova/instances）へのアクセスが含まれておらず、openstackパッケージにapparmorプロファイルがないために発生します。
このエラーは、/etc/apparmor.d/usr.lib.libvirt.virt-aa-helperに次の行を追加することで修正されました。
/var/lib/nova/instances/_base/ r,
/var/lib/nova/instances/_base/* r,
/var/lib/nova/instances/** rw,
と実行中：
Sudo apparmor_parser -r /etc/apparmor.d/usr.lib.libvirt.virt-aa-helper
user = "root" group = "root"
etc/libvirt/qemu.confでこの行のコメントを外してみてください