nova.virt.block_device.DriverBlockDevice cannot save to DB if bdm passed in was not already an object

[Matt Riedemann]

This code doesn't work:

https://github.com/openstack/nova/blob/master/nova/virt/block_device.py#L128-L131

That will create a BlockDeviceMapping object to be wrapped in the DriverBlockDevice object (if a BDM object was not passed in). The problem is on self._bdm_obj.save() will fail with something like this:

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    Traceback (most recent call last):
      File "nova/tests/unit/virt/test_block_device.py", line 909, in test_blank_attach_volume_cinder_cross_az_attach_false
        self.virt_driver)
      File "nova/virt/block_device.py", line 456, in attach
        self.save()
      File "nova/virt/block_device.py", line 363, in save
        super(DriverVolumeBlockDevice, self).save()
      File "nova/virt/block_device.py", line 176, in save
        self._bdm_obj.save()
      File "/home/mriedem/git/nova/.tox/py27/local/lib/python2.7/site-packages/oslo_versionedobjects/base.py", line 203, in wrapper
        objtype=self.obj_name())
    oslo_versionedobjects.exception.OrphanedObjectError: Cannot call save on orphaned BlockDeviceMapping object

That's because the BDM object that was created doesn't have a context set on it.

And we can't pass context to self._bdm_obj.save() because we removed that here: https://review.openstack.org/#/c/164268/

We've apparently never had a problem with this in runtime because we must always be constructing the DriverBlockDevice with a real BDM object in the compute code, we just weren't doing it properly in the tests - and the tests mock out nova.objects.BlockDeviceMapping.save() so we never knew it was a problem.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/260685

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/260685
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=215f403ad3b7705a28075217b97a0f6f6e658204
Submitter: Jenkins
Branch: master

commit 215f403ad3b7705a28075217b97a0f6f6e658204
Author: Matt Riedemann <email address hidden>
Date: Mon Dec 21 13:48:36 2015 -0800

    DriverBlockDevice must receive a BDM object, not a dict

    Commit 7a54543a81cbb8d20e6df29e7f4468a436dae212
    made it such that a BlockDeviceMapping object has to be
    constructed with a request context in order to call the
    remotable save() method on it.

    We must be already passing BDM objects when constructing
    DriverBlockDevices otherwise calling self._bdm_obj.save()
    would fail with an OrphanedObjectError. So the only places
    that were still using bdm dicts were unit tests, and those
    worked because objects.BlockDeviceMapping.save() is being
    mocked out.

    This removes the false sense of ability to construct a
    DriverBlocKDevice without a BDM object and cleans up the
    unit tests to reflect that reality.

    Closes-Bug: #1524035

    Change-Id: Ie745fc4d36ceb3e0aae1b14d5d56b2b83bbb192c

[Thierry Carrez (ttx)]

This issue was fixed in the openstack/nova 13.0.0.0b2 development milestone.