def _create_uuid(context, bdm_id):
# NOTE(mdbooth): This method is only required until uuid is made
# non-nullable in a future release.
# NOTE(mdbooth): We wrap this method in a retry loop because it can
# fail (safely) on multi-master galera if concurrent updates happen on
# different masters. It will never fail on single-master. We can only
# ever need one retry.
uuid = uuidutils.generate_uuid()
values = {'uuid': uuid}
compare = db_models.BlockDeviceMapping(id=bdm_id, uuid=None)
# NOTE(mdbooth): We explicitly use an independent transaction context
# here so as not to fail if:
# 1. We retry.
# 2. We're in a read transaction.This is an edge case of what's
# normally a read operation. Forcing everything (transitively)
# which reads a BDM to be in a write transaction for a narrow
# temporary edge case is undesirable.
tctxt = db_api.get_context_manager(context).writer.independent
with tctxt.using(context):
query = context.session.query(db_models.BlockDeviceMapping).\
filter_by(id=bdm_id)
try:
query.update_on_match(compare, 'id', values)
except update_match.NoRowsMatched:
# We can only get here if we raced, and another writer already
# gave this bdm a uuid
result = query.one()
uuid = result['uuid']
assert (uuid is not None)
return uuid
def _create_legacy_bdm(context, deleted=False):
# Create a BDM with no uuid
values = {'instance_uuid': uuids.instance_uuid}
bdm_ref = db_models.BlockDeviceMapping()
bdm_ref.update(values)
bdm_ref.save(context.session)
if deleted:
bdm_ref.soft_delete(context.session)
return bdm_ref