OpenStack Networking (Neutron)
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
from neutron_lib.db import api as db_api
from import base as service_base
from oslo_log import log as logging
import sqlalchemy
from sqlalchemy.orm import exc
from sqlalchemy.orm import session as se
import webob.exc
from neutron._i18n import _
from neutron.db import _resource_extend as resource_extend
from neutron.db import standard_attr
LOG = logging.getLogger(__name__)
class RevisionPlugin(service_base.ServicePluginBase):
"""Plugin to populate revision numbers into standard attr resources."""
supported_extension_aliases = ['standard-attr-revisions',
def __init__(self):
super(RevisionPlugin, self).__init__()
db_api.sqla_listen(se.Session, 'before_flush', self.bump_revisions)
db_api.sqla_listen(se.Session, 'after_commit',
db_api.sqla_listen(se.Session, 'after_rollback',
def bump_revisions(self, session, context, instances):
# bump revision number for any updated objects in the session
for obj in session.dirty:
if isinstance(obj, standard_attr.HasStandardAttributes):
self._bump_obj_revision(session, obj)
# see if any created/updated/deleted objects bump the revision
# of another object
objects_with_related_revisions = [
o for o in session.deleted | session.dirty |
if getattr(o, 'revises_on_change', ())
for obj in objects_with_related_revisions:
self._bump_related_revisions(session, obj)
def _bump_related_revisions(self, session, obj):
for revises_col in getattr(obj, 'revises_on_change', ()):
related_obj = self._find_related_obj(session, obj, revises_col)
if not related_obj:
LOG.warning("Could not find related %(col)s for "
"resource %(obj)s to bump revision.",
{'obj': obj, 'col': revises_col})
# if related object revises others, bump those as well
self._bump_related_revisions(session, related_obj)
# no need to bump revisions on related objects being deleted
if related_obj not in session.deleted:
self._bump_obj_revision(session, related_obj)
except exc.ObjectDeletedError:
# object was in session but another writer deleted it
def get_plugin_type(self):
return "revision_plugin"
def get_plugin_description(self):
return "Adds revision numbers to resources."
def extend_resource_dict_revision(resource_res, resource_db):
resource_res['revision_number'] = resource_db.revision_number
def _find_related_obj(self, session, obj, relationship_col):
"""Gets a related object off of a relationship.
Raises a runtime error if the relationship isn't configured correctly
for revision bumping.
# first check to see if it's directly attached to the object already
related_obj = getattr(obj, relationship_col)
if related_obj:
return related_obj
for rel in sqlalchemy.inspect(obj).mapper.relationships:
if rel.key != relationship_col:
if not rel.load_on_pending:
raise RuntimeError(_("revises_on_change relationships must "
"have load_on_pending set to True to "
"bump parent revisions on create: %s"),
def _clear_rev_bumped_flags(self, session):
"""This clears all flags on commit/rollback to enable rev bumps."""
for inst in session:
setattr(inst, '_rev_bumped', False)
def _bump_obj_revision(self, session, obj):
"""Increment object revision in compare and swap fashion.
Before the increment, this checks and enforces any revision number
if getattr(obj, '_rev_bumped', False):
# we've already bumped the revision of this object in this txn
instance, match = self._get_constrained_instance_match(session)
if instance and instance == obj:
# one last check before bumping revision
setattr(obj, '_rev_bumped', True)
def _find_instance_by_column_value(self, session, model, column, value):
"""Lookup object in session or from DB based on a column's value."""
for session_obj in session:
if not isinstance(session_obj, model):
if getattr(session_obj, column) == value:
return session_obj
# object isn't in session so we have to query for it
related_obj = (session.query(model).filter_by(**{column: value}).
return related_obj
def _get_constrained_instance_match(self, session):
"""Returns instance and constraint of if-match criterion if present.
Checks the context associated with the session for compare-and-swap
update revision number constraints. If one is found, this returns the
instance that is constrained as well as the requested revision number
to match.
context ='using_context')
criteria = context.get_transaction_constraint() if context else None
if not criteria:
return None, None
match = criteria.if_revision_match
mmap = standard_attr.get_standard_attr_resource_model_map()
model = mmap.get(criteria.resource)
if not model:
msg = _("Revision matching not supported for this resource")
raise exc.BadRequest(resource=criteria.resource, msg=msg)
instance = self._find_instance_by_column_value(
session, model, 'id', criteria.resource_id)
return instance, match
def _enforce_if_match_constraints(self, session):
"""Check for if-match constraints and raise exception if violated.
We determine the collection being modified and look for any
objects of the collection type in the dirty/deleted items in
the session. If they don't match the revision_number constraint
supplied, we throw an exception.
We are protected from a concurrent update because if we match
revision number here and another update commits to the database
first, the compare and swap of revision_number will fail and a
StaleDataError (or deadlock in galera multi-writer) will be raised,
at which point this will be retried and fail to match.
instance, match = self._get_constrained_instance_match(session)
if not instance or getattr(instance, '_rev_bumped', False):
# no constraints present or constrain satisfied in this transaction
if instance.revision_number != match:
raise RevisionNumberConstraintFailed(match,
class RevisionNumberConstraintFailed(webob.exc.HTTPPreconditionFailed):
def __init__(self, expected, current):
detail = (_("Constrained to %(exp)s, but current revision is %(cur)s")
% {'exp': expected, 'cur': current})
super(RevisionNumberConstraintFailed, self).__init__(detail=detail)