summaryrefslogtreecommitdiff
path: root/nova/quota.py
blob: 98cf7fe9dd29bc264568680fc1074a0f4fa30c1a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# All Rights Reserved.
#
#    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
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    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.

"""Quotas for instances, and floating ips."""

import datetime

from oslo.config import cfg
import six

from nova import db
from nova import exception
from nova.i18n import _
from nova import objects
from nova.openstack.common import importutils
from nova.openstack.common import log as logging
from nova.openstack.common import timeutils

LOG = logging.getLogger(__name__)

quota_opts = [
    cfg.IntOpt('quota_instances',
               default=10,
               help='Number of instances allowed per project'),
    cfg.IntOpt('quota_cores',
               default=20,
               help='Number of instance cores allowed per project'),
    cfg.IntOpt('quota_ram',
               default=50 * 1024,
               help='Megabytes of instance RAM allowed per project'),
    cfg.IntOpt('quota_floating_ips',
               default=10,
               help='Number of floating IPs allowed per project'),
    cfg.IntOpt('quota_fixed_ips',
               default=-1,
               help=('Number of fixed IPs allowed per project (this should be '
                     'at least the number of instances allowed)')),
    cfg.IntOpt('quota_metadata_items',
               default=128,
               help='Number of metadata items allowed per instance'),
    cfg.IntOpt('quota_injected_files',
               default=5,
               help='Number of injected files allowed'),
    cfg.IntOpt('quota_injected_file_content_bytes',
               default=10 * 1024,
               help='Number of bytes allowed per injected file'),
    cfg.IntOpt('quota_injected_file_path_length',
               default=255,
               deprecated_name='quota_injected_file_path_bytes',
               help='Length of injected file path'),
    # TODO(lyj): quota_injected_file_path_bytes is deprecated in Juno, and will
    #            be removed in K.
    cfg.IntOpt('quota_security_groups',
               default=10,
               help='Number of security groups per project'),
    cfg.IntOpt('quota_security_group_rules',
               default=20,
               help='Number of security rules per security group'),
    cfg.IntOpt('quota_key_pairs',
               default=100,
               help='Number of key pairs per user'),
    cfg.IntOpt('reservation_expire',
               default=86400,
               help='Number of seconds until a reservation expires'),
    cfg.IntOpt('until_refresh',
               default=0,
               help='Count of reservations until usage is refreshed'),
    cfg.IntOpt('max_age',
               default=0,
               help='Number of seconds between subsequent usage refreshes'),
    cfg.StrOpt('quota_driver',
               default='nova.quota.DbQuotaDriver',
               help='Default driver to use for quota checks'),
    ]

CONF = cfg.CONF
CONF.register_opts(quota_opts)


class DbQuotaDriver(object):
    """Driver to perform necessary checks to enforce quotas and obtain
    quota information.  The default driver utilizes the local
    database.
    """
    UNLIMITED_VALUE = -1

    def get_by_project_and_user(self, context, project_id, user_id, resource):
        """Get a specific quota by project and user."""

        return db.quota_get(context, project_id, resource, user_id=user_id)

    def get_by_project(self, context, project_id, resource):
        """Get a specific quota by project."""

        return db.quota_get(context, project_id, resource)

    def get_by_class(self, context, quota_class, resource):
        """Get a specific quota by quota class."""

        return db.quota_class_get(context, quota_class, resource)

    def get_defaults(self, context, resources):
        """Given a list of resources, retrieve the default quotas.
        Use the class quotas named `_DEFAULT_QUOTA_NAME` as default quotas,
        if it exists.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        """

        quotas = {}
        default_quotas = db.quota_class_get_default(context)
        for resource in resources.values():
            quotas[resource.name] = default_quotas.get(resource.name,
                                                       resource.default)

        return quotas

    def get_class_quotas(self, context, resources, quota_class,
                         defaults=True):
        """Given a list of resources, retrieve the quotas for the given
        quota class.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param quota_class: The name of the quota class to return
                            quotas for.
        :param defaults: If True, the default value will be reported
                         if there is no specific value for the
                         resource.
        """

        quotas = {}
        class_quotas = db.quota_class_get_all_by_name(context, quota_class)
        for resource in resources.values():
            if defaults or resource.name in class_quotas:
                quotas[resource.name] = class_quotas.get(resource.name,
                                                         resource.default)

        return quotas

    def _process_quotas(self, context, resources, project_id, quotas,
                        quota_class=None, defaults=True, usages=None,
                        remains=False):
        modified_quotas = {}
        # Get the quotas for the appropriate class.  If the project ID
        # matches the one in the context, we use the quota_class from
        # the context, otherwise, we use the provided quota_class (if
        # any)
        if project_id == context.project_id:
            quota_class = context.quota_class
        if quota_class:
            class_quotas = db.quota_class_get_all_by_name(context, quota_class)
        else:
            class_quotas = {}

        default_quotas = self.get_defaults(context, resources)

        for resource in resources.values():
            # Omit default/quota class values
            if not defaults and resource.name not in quotas:
                continue

            limit = quotas.get(resource.name, class_quotas.get(
                        resource.name, default_quotas[resource.name]))
            modified_quotas[resource.name] = dict(limit=limit)

            # Include usages if desired.  This is optional because one
            # internal consumer of this interface wants to access the
            # usages directly from inside a transaction.
            if usages:
                usage = usages.get(resource.name, {})
                modified_quotas[resource.name].update(
                    in_use=usage.get('in_use', 0),
                    reserved=usage.get('reserved', 0),
                    )
            # Initialize remains quotas.
            if remains:
                modified_quotas[resource.name].update(remains=limit)

        if remains:
            all_quotas = db.quota_get_all(context, project_id)
            for quota in all_quotas:
                if quota.resource in modified_quotas:
                    modified_quotas[quota.resource]['remains'] -= \
                            quota.hard_limit

        return modified_quotas

    def get_user_quotas(self, context, resources, project_id, user_id,
                        quota_class=None, defaults=True,
                        usages=True, project_quotas=None,
                        user_quotas=None):
        """Given a list of resources, retrieve the quotas for the given
        user and project.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param project_id: The ID of the project to return quotas for.
        :param user_id: The ID of the user to return quotas for.
        :param quota_class: If project_id != context.project_id, the
                            quota class cannot be determined.  This
                            parameter allows it to be specified.  It
                            will be ignored if project_id ==
                            context.project_id.
        :param defaults: If True, the quota class value (or the
                         default value, if there is no value from the
                         quota class) will be reported if there is no
                         specific value for the resource.
        :param usages: If True, the current in_use and reserved counts
                       will also be returned.
        :param project_quotas: Quotas dictionary for the specified project.
        :param user_quotas: Quotas dictionary for the specified project
                            and user.
        """
        user_quotas = user_quotas or db.quota_get_all_by_project_and_user(
            context, project_id, user_id)
        # Use the project quota for default user quota.
        proj_quotas = project_quotas or db.quota_get_all_by_project(
            context, project_id)
        for key, value in proj_quotas.iteritems():
            if key not in user_quotas.keys():
                user_quotas[key] = value
        user_usages = None
        if usages:
            user_usages = db.quota_usage_get_all_by_project_and_user(context,
                                                         project_id,
                                                         user_id)
        return self._process_quotas(context, resources, project_id,
                                    user_quotas, quota_class,
                                    defaults=defaults, usages=user_usages)

    def get_project_quotas(self, context, resources, project_id,
                           quota_class=None, defaults=True,
                           usages=True, remains=False, project_quotas=None):
        """Given a list of resources, retrieve the quotas for the given
        project.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param project_id: The ID of the project to return quotas for.
        :param quota_class: If project_id != context.project_id, the
                            quota class cannot be determined.  This
                            parameter allows it to be specified.  It
                            will be ignored if project_id ==
                            context.project_id.
        :param defaults: If True, the quota class value (or the
                         default value, if there is no value from the
                         quota class) will be reported if there is no
                         specific value for the resource.
        :param usages: If True, the current in_use and reserved counts
                       will also be returned.
        :param remains: If True, the current remains of the project will
                        will be returned.
        :param project_quotas: Quotas dictionary for the specified project.
        """
        project_quotas = project_quotas or db.quota_get_all_by_project(
            context, project_id)
        project_usages = None
        if usages:
            project_usages = db.quota_usage_get_all_by_project(context,
                                                               project_id)
        return self._process_quotas(context, resources, project_id,
                                    project_quotas, quota_class,
                                    defaults=defaults, usages=project_usages,
                                    remains=remains)

    def _is_unlimited_value(self, v):
        """A helper method to check for unlimited value.
        """

        return v <= self.UNLIMITED_VALUE

    def _sum_quota_values(self, v1, v2):
        """A helper method that handles unlimited values when performing
        sum operation.
        """

        if self._is_unlimited_value(v1) or self._is_unlimited_value(v2):
            return self.UNLIMITED_VALUE
        return v1 + v2

    def _sub_quota_values(self, v1, v2):
        """A helper method that handles unlimited values when performing
        subtraction operation.
        """

        if self._is_unlimited_value(v1) or self._is_unlimited_value(v2):
            return self.UNLIMITED_VALUE
        return v1 - v2

    def get_settable_quotas(self, context, resources, project_id,
                            user_id=None):
        """Given a list of resources, retrieve the range of settable quotas for
        the given user or project.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param project_id: The ID of the project to return quotas for.
        :param user_id: The ID of the user to return quotas for.
        """

        settable_quotas = {}
        db_proj_quotas = db.quota_get_all_by_project(context, project_id)
        project_quotas = self.get_project_quotas(context, resources,
                                                 project_id, remains=True,
                                                 project_quotas=db_proj_quotas)
        if user_id:
            setted_quotas = db.quota_get_all_by_project_and_user(context,
                                                     project_id,
                                                     user_id)
            user_quotas = self.get_user_quotas(context, resources,
                                               project_id, user_id,
                                               project_quotas=db_proj_quotas,
                                               user_quotas=setted_quotas)
            for key, value in user_quotas.items():
                maximum = \
                    self._sum_quota_values(project_quotas[key]['remains'],
                                           setted_quotas.get(key, 0))
                minimum = value['in_use'] + value['reserved']
                settable_quotas[key] = {'minimum': minimum, 'maximum': maximum}
        else:
            for key, value in project_quotas.items():
                minimum = \
                    max(int(self._sub_quota_values(value['limit'],
                                                   value['remains'])),
                        int(value['in_use'] + value['reserved']))
                settable_quotas[key] = {'minimum': minimum, 'maximum': -1}
        return settable_quotas

    def _get_quotas(self, context, resources, keys, has_sync, project_id=None,
                    user_id=None, project_quotas=None):
        """A helper method which retrieves the quotas for the specific
        resources identified by keys, and which apply to the current
        context.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param keys: A list of the desired quotas to retrieve.
        :param has_sync: If True, indicates that the resource must
                         have a sync function; if False, indicates
                         that the resource must NOT have a sync
                         function.
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        :param user_id: Specify the user_id if current context
                        is admin and admin wants to impact on
                        common user.
        :param project_quotas: Quotas dictionary for the specified project.
        """

        # Filter resources
        if has_sync:
            sync_filt = lambda x: hasattr(x, 'sync')
        else:
            sync_filt = lambda x: not hasattr(x, 'sync')
        desired = set(keys)
        sub_resources = dict((k, v) for k, v in resources.items()
                             if k in desired and sync_filt(v))

        # Make sure we accounted for all of them...
        if len(keys) != len(sub_resources):
            unknown = desired - set(sub_resources.keys())
            raise exception.QuotaResourceUnknown(unknown=sorted(unknown))

        if user_id:
            # Grab and return the quotas (without usages)
            quotas = self.get_user_quotas(context, sub_resources,
                                          project_id, user_id,
                                          context.quota_class, usages=False,
                                          project_quotas=project_quotas)
        else:
            # Grab and return the quotas (without usages)
            quotas = self.get_project_quotas(context, sub_resources,
                                             project_id,
                                             context.quota_class,
                                             usages=False,
                                             project_quotas=project_quotas)

        return dict((k, v['limit']) for k, v in quotas.items())

    def limit_check(self, context, resources, values, project_id=None,
                    user_id=None):
        """Check simple quota limits.

        For limits--those quotas for which there is no usage
        synchronization function--this method checks that a set of
        proposed values are permitted by the limit restriction.

        This method will raise a QuotaResourceUnknown exception if a
        given resource is unknown or if it is not a simple limit
        resource.

        If any of the proposed values is over the defined quota, an
        OverQuota exception will be raised with the sorted list of the
        resources which are too high.  Otherwise, the method returns
        nothing.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param values: A dictionary of the values to check against the
                       quota.
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        :param user_id: Specify the user_id if current context
                        is admin and admin wants to impact on
                        common user.
        """

        # Ensure no value is less than zero
        unders = [key for key, val in values.items() if val < 0]
        if unders:
            raise exception.InvalidQuotaValue(unders=sorted(unders))

        # If project_id is None, then we use the project_id in context
        if project_id is None:
            project_id = context.project_id
        # If user id is None, then we use the user_id in context
        if user_id is None:
            user_id = context.user_id

        # Get the applicable quotas
        project_quotas = db.quota_get_all_by_project(context, project_id)
        quotas = self._get_quotas(context, resources, values.keys(),
                                  has_sync=False, project_id=project_id,
                                  project_quotas=project_quotas)
        user_quotas = self._get_quotas(context, resources, values.keys(),
                                       has_sync=False, project_id=project_id,
                                       user_id=user_id,
                                       project_quotas=project_quotas)

        # Check the quotas and construct a list of the resources that
        # would be put over limit by the desired values
        overs = [key for key, val in values.items()
                 if quotas[key] >= 0 and quotas[key] < val or
                 (user_quotas[key] >= 0 and user_quotas[key] < val)]
        if overs:
            headroom = {}
            # Check project_quotas:
            for key in quotas:
                if quotas[key] >= 0 and quotas[key] < val:
                    headroom[key] = quotas[key]
            # Check user quotas:
            for key in user_quotas:
                if (user_quotas[key] >= 0 and user_quotas[key] < val and
                        headroom.get(key) > user_quotas[key]):
                    headroom[key] = user_quotas[key]

            raise exception.OverQuota(overs=sorted(overs), quotas=quotas,
                                      usages={}, headroom=headroom)

    def reserve(self, context, resources, deltas, expire=None,
                project_id=None, user_id=None):
        """Check quotas and reserve resources.

        For counting quotas--those quotas for which there is a usage
        synchronization function--this method checks quotas against
        current usage and the desired deltas.

        This method will raise a QuotaResourceUnknown exception if a
        given resource is unknown or if it does not have a usage
        synchronization function.

        If any of the proposed values is over the defined quota, an
        OverQuota exception will be raised with the sorted list of the
        resources which are too high.  Otherwise, the method returns a
        list of reservation UUIDs which were created.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param deltas: A dictionary of the proposed delta changes.
        :param expire: An optional parameter specifying an expiration
                       time for the reservations.  If it is a simple
                       number, it is interpreted as a number of
                       seconds and added to the current time; if it is
                       a datetime.timedelta object, it will also be
                       added to the current time.  A datetime.datetime
                       object will be interpreted as the absolute
                       expiration time.  If None is specified, the
                       default expiration time set by
                       --default-reservation-expire will be used (this
                       value will be treated as a number of seconds).
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        :param user_id: Specify the user_id if current context
                        is admin and admin wants to impact on
                        common user.
        """

        # Set up the reservation expiration
        if expire is None:
            expire = CONF.reservation_expire
        if isinstance(expire, (int, long)):
            expire = datetime.timedelta(seconds=expire)
        if isinstance(expire, datetime.timedelta):
            expire = timeutils.utcnow() + expire
        if not isinstance(expire, datetime.datetime):
            raise exception.InvalidReservationExpiration(expire=expire)

        # If project_id is None, then we use the project_id in context
        if project_id is None:
            project_id = context.project_id
        # If user_id is None, then we use the project_id in context
        if user_id is None:
            user_id = context.user_id

        # Get the applicable quotas.
        # NOTE(Vek): We're not worried about races at this point.
        #            Yes, the admin may be in the process of reducing
        #            quotas, but that's a pretty rare thing.
        project_quotas = db.quota_get_all_by_project(context, project_id)
        quotas = self._get_quotas(context, resources, deltas.keys(),
                                  has_sync=True, project_id=project_id,
                                  project_quotas=project_quotas)
        user_quotas = self._get_quotas(context, resources, deltas.keys(),
                                       has_sync=True, project_id=project_id,
                                       user_id=user_id,
                                       project_quotas=project_quotas)

        # NOTE(Vek): Most of the work here has to be done in the DB
        #            API, because we have to do it in a transaction,
        #            which means access to the session.  Since the
        #            session isn't available outside the DBAPI, we
        #            have to do the work there.
        return db.quota_reserve(context, resources, quotas, user_quotas,
                                deltas, expire,
                                CONF.until_refresh, CONF.max_age,
                                project_id=project_id, user_id=user_id)

    def commit(self, context, reservations, project_id=None, user_id=None):
        """Commit reservations.

        :param context: The request context, for access checks.
        :param reservations: A list of the reservation UUIDs, as
                             returned by the reserve() method.
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        :param user_id: Specify the user_id if current context
                        is admin and admin wants to impact on
                        common user.
        """
        # If project_id is None, then we use the project_id in context
        if project_id is None:
            project_id = context.project_id
        # If user_id is None, then we use the user_id in context
        if user_id is None:
            user_id = context.user_id

        db.reservation_commit(context, reservations, project_id=project_id,
                              user_id=user_id)

    def rollback(self, context, reservations, project_id=None, user_id=None):
        """Roll back reservations.

        :param context: The request context, for access checks.
        :param reservations: A list of the reservation UUIDs, as
                             returned by the reserve() method.
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        :param user_id: Specify the user_id if current context
                        is admin and admin wants to impact on
                        common user.
        """
        # If project_id is None, then we use the project_id in context
        if project_id is None:
            project_id = context.project_id
        # If user_id is None, then we use the user_id in context
        if user_id is None:
            user_id = context.user_id

        db.reservation_rollback(context, reservations, project_id=project_id,
                                user_id=user_id)

    def usage_reset(self, context, resources):
        """Reset the usage records for a particular user on a list of
        resources.  This will force that user's usage records to be
        refreshed the next time a reservation is made.

        Note: this does not affect the currently outstanding
        reservations the user has; those reservations must be
        committed or rolled back (or expired).

        :param context: The request context, for access checks.
        :param resources: A list of the resource names for which the
                          usage must be reset.
        """

        # We need an elevated context for the calls to
        # quota_usage_update()
        elevated = context.elevated()

        for resource in resources:
            try:
                # Reset the usage to -1, which will force it to be
                # refreshed
                db.quota_usage_update(elevated, context.project_id,
                                      context.user_id,
                                      resource, in_use=-1)
            except exception.QuotaUsageNotFound:
                # That means it'll be refreshed anyway
                pass

    def destroy_all_by_project_and_user(self, context, project_id, user_id):
        """Destroy all quotas, usages, and reservations associated with a
        project and user.

        :param context: The request context, for access checks.
        :param project_id: The ID of the project being deleted.
        :param user_id: The ID of the user being deleted.
        """

        db.quota_destroy_all_by_project_and_user(context, project_id, user_id)

    def destroy_all_by_project(self, context, project_id):
        """Destroy all quotas, usages, and reservations associated with a
        project.

        :param context: The request context, for access checks.
        :param project_id: The ID of the project being deleted.
        """

        db.quota_destroy_all_by_project(context, project_id)

    def expire(self, context):
        """Expire reservations.

        Explores all currently existing reservations and rolls back
        any that have expired.

        :param context: The request context, for access checks.
        """

        db.reservation_expire(context)


class NoopQuotaDriver(object):
    """Driver that turns quotas calls into no-ops and pretends that quotas
    for all resources are unlimited.  This can be used if you do not
    wish to have any quota checking.  For instance, with nova compute
    cells, the parent cell should do quota checking, but the child cell
    should not.
    """

    def get_by_project_and_user(self, context, project_id, user_id, resource):
        """Get a specific quota by project and user."""
        # Unlimited
        return -1

    def get_by_project(self, context, project_id, resource):
        """Get a specific quota by project."""
        # Unlimited
        return -1

    def get_by_class(self, context, quota_class, resource):
        """Get a specific quota by quota class."""
        # Unlimited
        return -1

    def get_defaults(self, context, resources):
        """Given a list of resources, retrieve the default quotas.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        """
        quotas = {}
        for resource in resources.values():
            quotas[resource.name] = -1
        return quotas

    def get_class_quotas(self, context, resources, quota_class,
                         defaults=True):
        """Given a list of resources, retrieve the quotas for the given
        quota class.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param quota_class: The name of the quota class to return
                            quotas for.
        :param defaults: If True, the default value will be reported
                         if there is no specific value for the
                         resource.
        """
        quotas = {}
        for resource in resources.values():
            quotas[resource.name] = -1
        return quotas

    def _get_noop_quotas(self, resources, usages=None, remains=False):
        quotas = {}
        for resource in resources.values():
            quotas[resource.name] = {}
            quotas[resource.name]['limit'] = -1
            if usages:
                quotas[resource.name]['in_use'] = -1
                quotas[resource.name]['reserved'] = -1
            if remains:
                quotas[resource.name]['remains'] = -1
        return quotas

    def get_user_quotas(self, context, resources, project_id, user_id,
                        quota_class=None, defaults=True,
                        usages=True):
        """Given a list of resources, retrieve the quotas for the given
        user and project.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param project_id: The ID of the project to return quotas for.
        :param user_id: The ID of the user to return quotas for.
        :param quota_class: If project_id != context.project_id, the
                            quota class cannot be determined.  This
                            parameter allows it to be specified.  It
                            will be ignored if project_id ==
                            context.project_id.
        :param defaults: If True, the quota class value (or the
                         default value, if there is no value from the
                         quota class) will be reported if there is no
                         specific value for the resource.
        :param usages: If True, the current in_use and reserved counts
                       will also be returned.
        """
        return self._get_noop_quotas(resources, usages=usages)

    def get_project_quotas(self, context, resources, project_id,
                           quota_class=None, defaults=True,
                           usages=True, remains=False):
        """Given a list of resources, retrieve the quotas for the given
        project.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param project_id: The ID of the project to return quotas for.
        :param quota_class: If project_id != context.project_id, the
                            quota class cannot be determined.  This
                            parameter allows it to be specified.  It
                            will be ignored if project_id ==
                            context.project_id.
        :param defaults: If True, the quota class value (or the
                         default value, if there is no value from the
                         quota class) will be reported if there is no
                         specific value for the resource.
        :param usages: If True, the current in_use and reserved counts
                       will also be returned.
        :param remains: If True, the current remains of the project will
                        will be returned.
        """
        return self._get_noop_quotas(resources, usages=usages, remains=remains)

    def get_settable_quotas(self, context, resources, project_id,
                            user_id=None):
        """Given a list of resources, retrieve the range of settable quotas for
        the given user or project.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param project_id: The ID of the project to return quotas for.
        :param user_id: The ID of the user to return quotas for.
        """
        quotas = {}
        for resource in resources.values():
            quotas[resource.name].update(minimum=0, maximum=-1)
        return quotas

    def limit_check(self, context, resources, values, project_id=None,
                    user_id=None):
        """Check simple quota limits.

        For limits--those quotas for which there is no usage
        synchronization function--this method checks that a set of
        proposed values are permitted by the limit restriction.

        This method will raise a QuotaResourceUnknown exception if a
        given resource is unknown or if it is not a simple limit
        resource.

        If any of the proposed values is over the defined quota, an
        OverQuota exception will be raised with the sorted list of the
        resources which are too high.  Otherwise, the method returns
        nothing.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param values: A dictionary of the values to check against the
                       quota.
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        :param user_id: Specify the user_id if current context
                        is admin and admin wants to impact on
                        common user.
        """
        pass

    def reserve(self, context, resources, deltas, expire=None,
                project_id=None, user_id=None):
        """Check quotas and reserve resources.

        For counting quotas--those quotas for which there is a usage
        synchronization function--this method checks quotas against
        current usage and the desired deltas.

        This method will raise a QuotaResourceUnknown exception if a
        given resource is unknown or if it does not have a usage
        synchronization function.

        If any of the proposed values is over the defined quota, an
        OverQuota exception will be raised with the sorted list of the
        resources which are too high.  Otherwise, the method returns a
        list of reservation UUIDs which were created.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param deltas: A dictionary of the proposed delta changes.
        :param expire: An optional parameter specifying an expiration
                       time for the reservations.  If it is a simple
                       number, it is interpreted as a number of
                       seconds and added to the current time; if it is
                       a datetime.timedelta object, it will also be
                       added to the current time.  A datetime.datetime
                       object will be interpreted as the absolute
                       expiration time.  If None is specified, the
                       default expiration time set by
                       --default-reservation-expire will be used (this
                       value will be treated as a number of seconds).
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        :param user_id: Specify the user_id if current context
                        is admin and admin wants to impact on
                        common user.
        """
        return []

    def commit(self, context, reservations, project_id=None, user_id=None):
        """Commit reservations.

        :param context: The request context, for access checks.
        :param reservations: A list of the reservation UUIDs, as
                             returned by the reserve() method.
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        :param user_id: Specify the user_id if current context
                        is admin and admin wants to impact on
                        common user.
        """
        pass

    def rollback(self, context, reservations, project_id=None, user_id=None):
        """Roll back reservations.

        :param context: The request context, for access checks.
        :param reservations: A list of the reservation UUIDs, as
                             returned by the reserve() method.
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        :param user_id: Specify the user_id if current context
                        is admin and admin wants to impact on
                        common user.
        """
        pass

    def usage_reset(self, context, resources):
        """Reset the usage records for a particular user on a list of
        resources.  This will force that user's usage records to be
        refreshed the next time a reservation is made.

        Note: this does not affect the currently outstanding
        reservations the user has; those reservations must be
        committed or rolled back (or expired).

        :param context: The request context, for access checks.
        :param resources: A list of the resource names for which the
                          usage must be reset.
        """
        pass

    def destroy_all_by_project_and_user(self, context, project_id, user_id):
        """Destroy all quotas, usages, and reservations associated with a
        project and user.

        :param context: The request context, for access checks.
        :param project_id: The ID of the project being deleted.
        :param user_id: The ID of the user being deleted.
        """
        pass

    def destroy_all_by_project(self, context, project_id):
        """Destroy all quotas, usages, and reservations associated with a
        project.

        :param context: The request context, for access checks.
        :param project_id: The ID of the project being deleted.
        """
        pass

    def expire(self, context):
        """Expire reservations.

        Explores all currently existing reservations and rolls back
        any that have expired.

        :param context: The request context, for access checks.
        """
        pass


class BaseResource(object):
    """Describe a single resource for quota checking."""

    def __init__(self, name, flag=None):
        """Initializes a Resource.

        :param name: The name of the resource, i.e., "instances".
        :param flag: The name of the flag or configuration option
                     which specifies the default value of the quota
                     for this resource.
        """

        self.name = name
        self.flag = flag

    def quota(self, driver, context, **kwargs):
        """Given a driver and context, obtain the quota for this
        resource.

        :param driver: A quota driver.
        :param context: The request context.
        :param project_id: The project to obtain the quota value for.
                           If not provided, it is taken from the
                           context.  If it is given as None, no
                           project-specific quota will be searched
                           for.
        :param quota_class: The quota class corresponding to the
                            project, or for which the quota is to be
                            looked up.  If not provided, it is taken
                            from the context.  If it is given as None,
                            no quota class-specific quota will be
                            searched for.  Note that the quota class
                            defaults to the value in the context,
                            which may not correspond to the project if
                            project_id is not the same as the one in
                            the context.
        """

        # Get the project ID
        project_id = kwargs.get('project_id', context.project_id)

        # Ditto for the quota class
        quota_class = kwargs.get('quota_class', context.quota_class)

        # Look up the quota for the project
        if project_id:
            try:
                return driver.get_by_project(context, project_id, self.name)
            except exception.ProjectQuotaNotFound:
                pass

        # Try for the quota class
        if quota_class:
            try:
                return driver.get_by_class(context, quota_class, self.name)
            except exception.QuotaClassNotFound:
                pass

        # OK, return the default
        return self.default

    @property
    def default(self):
        """Return the default value of the quota."""

        return CONF[self.flag] if self.flag else -1


class ReservableResource(BaseResource):
    """Describe a reservable resource."""

    def __init__(self, name, sync, flag=None):
        """Initializes a ReservableResource.

        Reservable resources are those resources which directly
        correspond to objects in the database, i.e., instances,
        cores, etc.

        Usage synchronization function must be associated with each
        object. This function will be called to determine the current
        counts of one or more resources. This association is done in
        database backend.

        The usage synchronization function will be passed three
        arguments: an admin context, the project ID, and an opaque
        session object, which should in turn be passed to the
        underlying database function.  Synchronization functions
        should return a dictionary mapping resource names to the
        current in_use count for those resources; more than one
        resource and resource count may be returned.  Note that
        synchronization functions may be associated with more than one
        ReservableResource.

        :param name: The name of the resource, i.e., "volumes".
        :param sync: A dbapi methods name which returns a dictionary
                     to resynchronize the in_use count for one or more
                     resources, as described above.
        :param flag: The name of the flag or configuration option
                     which specifies the default value of the quota
                     for this resource.
        """
        super(ReservableResource, self).__init__(name, flag=flag)
        self.sync = sync


class AbsoluteResource(BaseResource):
    """Describe a non-reservable resource."""

    pass


class CountableResource(AbsoluteResource):
    """Describe a resource where the counts aren't based solely on the
    project ID.
    """

    def __init__(self, name, count, flag=None):
        """Initializes a CountableResource.

        Countable resources are those resources which directly
        correspond to objects in the database, i.e., instances, cores,
        etc., but for which a count by project ID is inappropriate.  A
        CountableResource must be constructed with a counting
        function, which will be called to determine the current counts
        of the resource.

        The counting function will be passed the context, along with
        the extra positional and keyword arguments that are passed to
        Quota.count().  It should return an integer specifying the
        count.

        Note that this counting is not performed in a transaction-safe
        manner.  This resource class is a temporary measure to provide
        required functionality, until a better approach to solving
        this problem can be evolved.

        :param name: The name of the resource, i.e., "instances".
        :param count: A callable which returns the count of the
                      resource.  The arguments passed are as described
                      above.
        :param flag: The name of the flag or configuration option
                     which specifies the default value of the quota
                     for this resource.
        """

        super(CountableResource, self).__init__(name, flag=flag)
        self.count = count


class QuotaEngine(object):
    """Represent the set of recognized quotas."""

    def __init__(self, quota_driver_class=None):
        """Initialize a Quota object."""
        self._resources = {}
        self._driver_cls = quota_driver_class
        self.__driver = None

    @property
    def _driver(self):
        if self.__driver:
            return self.__driver
        if not self._driver_cls:
            self._driver_cls = CONF.quota_driver
        if isinstance(self._driver_cls, six.string_types):
            self._driver_cls = importutils.import_object(self._driver_cls)
        self.__driver = self._driver_cls
        return self.__driver

    def __contains__(self, resource):
        return resource in self._resources

    def register_resource(self, resource):
        """Register a resource."""

        self._resources[resource.name] = resource

    def register_resources(self, resources):
        """Register a list of resources."""

        for resource in resources:
            self.register_resource(resource)

    def get_by_project_and_user(self, context, project_id, user_id, resource):
        """Get a specific quota by project and user."""

        return self._driver.get_by_project_and_user(context, project_id,
                                                    user_id, resource)

    def get_by_project(self, context, project_id, resource):
        """Get a specific quota by project."""

        return self._driver.get_by_project(context, project_id, resource)

    def get_by_class(self, context, quota_class, resource):
        """Get a specific quota by quota class."""

        return self._driver.get_by_class(context, quota_class, resource)

    def get_defaults(self, context):
        """Retrieve the default quotas.

        :param context: The request context, for access checks.
        """

        return self._driver.get_defaults(context, self._resources)

    def get_class_quotas(self, context, quota_class, defaults=True):
        """Retrieve the quotas for the given quota class.

        :param context: The request context, for access checks.
        :param quota_class: The name of the quota class to return
                            quotas for.
        :param defaults: If True, the default value will be reported
                         if there is no specific value for the
                         resource.
        """

        return self._driver.get_class_quotas(context, self._resources,
                                             quota_class, defaults=defaults)

    def get_user_quotas(self, context, project_id, user_id, quota_class=None,
                        defaults=True, usages=True):
        """Retrieve the quotas for the given user and project.

        :param context: The request context, for access checks.
        :param project_id: The ID of the project to return quotas for.
        :param user_id: The ID of the user to return quotas for.
        :param quota_class: If project_id != context.project_id, the
                            quota class cannot be determined.  This
                            parameter allows it to be specified.
        :param defaults: If True, the quota class value (or the
                         default value, if there is no value from the
                         quota class) will be reported if there is no
                         specific value for the resource.
        :param usages: If True, the current in_use and reserved counts
                       will also be returned.
        """

        return self._driver.get_user_quotas(context, self._resources,
                                            project_id, user_id,
                                            quota_class=quota_class,
                                            defaults=defaults,
                                            usages=usages)

    def get_project_quotas(self, context, project_id, quota_class=None,
                           defaults=True, usages=True, remains=False):
        """Retrieve the quotas for the given project.

        :param context: The request context, for access checks.
        :param project_id: The ID of the project to return quotas for.
        :param quota_class: If project_id != context.project_id, the
                            quota class cannot be determined.  This
                            parameter allows it to be specified.
        :param defaults: If True, the quota class value (or the
                         default value, if there is no value from the
                         quota class) will be reported if there is no
                         specific value for the resource.
        :param usages: If True, the current in_use and reserved counts
                       will also be returned.
        :param remains: If True, the current remains of the project will
                        will be returned.
        """

        return self._driver.get_project_quotas(context, self._resources,
                                              project_id,
                                              quota_class=quota_class,
                                              defaults=defaults,
                                              usages=usages,
                                              remains=remains)

    def get_settable_quotas(self, context, project_id, user_id=None):
        """Given a list of resources, retrieve the range of settable quotas for
        the given user or project.

        :param context: The request context, for access checks.
        :param resources: A dictionary of the registered resources.
        :param project_id: The ID of the project to return quotas for.
        :param user_id: The ID of the user to return quotas for.
        """

        return self._driver.get_settable_quotas(context, self._resources,
                                                project_id,
                                                user_id=user_id)

    def count(self, context, resource, *args, **kwargs):
        """Count a resource.

        For countable resources, invokes the count() function and
        returns its result.  Arguments following the context and
        resource are passed directly to the count function declared by
        the resource.

        :param context: The request context, for access checks.
        :param resource: The name of the resource, as a string.
        """

        # Get the resource
        res = self._resources.get(resource)
        if not res or not hasattr(res, 'count'):
            raise exception.QuotaResourceUnknown(unknown=[resource])

        return res.count(context, *args, **kwargs)

    def limit_check(self, context, project_id=None, user_id=None, **values):
        """Check simple quota limits.

        For limits--those quotas for which there is no usage
        synchronization function--this method checks that a set of
        proposed values are permitted by the limit restriction.  The
        values to check are given as keyword arguments, where the key
        identifies the specific quota limit to check, and the value is
        the proposed value.

        This method will raise a QuotaResourceUnknown exception if a
        given resource is unknown or if it is not a simple limit
        resource.

        If any of the proposed values is over the defined quota, an
        OverQuota exception will be raised with the sorted list of the
        resources which are too high.  Otherwise, the method returns
        nothing.

        :param context: The request context, for access checks.
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        :param user_id: Specify the user_id if current context
                        is admin and admin wants to impact on
                        common user.
        """

        return self._driver.limit_check(context, self._resources, values,
                                        project_id=project_id, user_id=user_id)

    def reserve(self, context, expire=None, project_id=None, user_id=None,
                **deltas):
        """Check quotas and reserve resources.

        For counting quotas--those quotas for which there is a usage
        synchronization function--this method checks quotas against
        current usage and the desired deltas.  The deltas are given as
        keyword arguments, and current usage and other reservations
        are factored into the quota check.

        This method will raise a QuotaResourceUnknown exception if a
        given resource is unknown or if it does not have a usage
        synchronization function.

        If any of the proposed values is over the defined quota, an
        OverQuota exception will be raised with the sorted list of the
        resources which are too high.  Otherwise, the method returns a
        list of reservation UUIDs which were created.

        :param context: The request context, for access checks.
        :param expire: An optional parameter specifying an expiration
                       time for the reservations.  If it is a simple
                       number, it is interpreted as a number of
                       seconds and added to the current time; if it is
                       a datetime.timedelta object, it will also be
                       added to the current time.  A datetime.datetime
                       object will be interpreted as the absolute
                       expiration time.  If None is specified, the
                       default expiration time set by
                       --default-reservation-expire will be used (this
                       value will be treated as a number of seconds).
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        """

        reservations = self._driver.reserve(context, self._resources, deltas,
                                            expire=expire,
                                            project_id=project_id,
                                            user_id=user_id)

        LOG.debug("Created reservations %s", reservations)

        return reservations

    def commit(self, context, reservations, project_id=None, user_id=None):
        """Commit reservations.

        :param context: The request context, for access checks.
        :param reservations: A list of the reservation UUIDs, as
                             returned by the reserve() method.
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        """

        try:
            self._driver.commit(context, reservations, project_id=project_id,
                                user_id=user_id)
        except Exception:
            # NOTE(Vek): Ignoring exceptions here is safe, because the
            # usage resynchronization and the reservation expiration
            # mechanisms will resolve the issue.  The exception is
            # logged, however, because this is less than optimal.
            LOG.exception(_("Failed to commit reservations %s"), reservations)
            return
        LOG.debug("Committed reservations %s", reservations)

    def rollback(self, context, reservations, project_id=None, user_id=None):
        """Roll back reservations.

        :param context: The request context, for access checks.
        :param reservations: A list of the reservation UUIDs, as
                             returned by the reserve() method.
        :param project_id: Specify the project_id if current context
                           is admin and admin wants to impact on
                           common user's tenant.
        """

        try:
            self._driver.rollback(context, reservations, project_id=project_id,
                                  user_id=user_id)
        except Exception:
            # NOTE(Vek): Ignoring exceptions here is safe, because the
            # usage resynchronization and the reservation expiration
            # mechanisms will resolve the issue.  The exception is
            # logged, however, because this is less than optimal.
            LOG.exception(_("Failed to roll back reservations %s"),
                          reservations)
            return
        LOG.debug("Rolled back reservations %s", reservations)

    def usage_reset(self, context, resources):
        """Reset the usage records for a particular user on a list of
        resources.  This will force that user's usage records to be
        refreshed the next time a reservation is made.

        Note: this does not affect the currently outstanding
        reservations the user has; those reservations must be
        committed or rolled back (or expired).

        :param context: The request context, for access checks.
        :param resources: A list of the resource names for which the
                          usage must be reset.
        """

        self._driver.usage_reset(context, resources)

    def destroy_all_by_project_and_user(self, context, project_id, user_id):
        """Destroy all quotas, usages, and reservations associated with a
        project and user.

        :param context: The request context, for access checks.
        :param project_id: The ID of the project being deleted.
        :param user_id: The ID of the user being deleted.
        """

        self._driver.destroy_all_by_project_and_user(context,
                                                     project_id, user_id)

    def destroy_all_by_project(self, context, project_id):
        """Destroy all quotas, usages, and reservations associated with a
        project.

        :param context: The request context, for access checks.
        :param project_id: The ID of the project being deleted.
        """

        self._driver.destroy_all_by_project(context, project_id)

    def expire(self, context):
        """Expire reservations.

        Explores all currently existing reservations and rolls back
        any that have expired.

        :param context: The request context, for access checks.
        """

        self._driver.expire(context)

    @property
    def resources(self):
        return sorted(self._resources.keys())


def _keypair_get_count_by_user(*args, **kwargs):
    """Helper method to avoid referencing objects.KeyPairList on import."""
    return objects.KeyPairList.get_count_by_user(*args, **kwargs)


QUOTAS = QuotaEngine()


resources = [
    ReservableResource('instances', '_sync_instances', 'quota_instances'),
    ReservableResource('cores', '_sync_instances', 'quota_cores'),
    ReservableResource('ram', '_sync_instances', 'quota_ram'),
    ReservableResource('security_groups', '_sync_security_groups',
                       'quota_security_groups'),
    ReservableResource('floating_ips', '_sync_floating_ips',
                       'quota_floating_ips'),
    ReservableResource('fixed_ips', '_sync_fixed_ips', 'quota_fixed_ips'),
    AbsoluteResource('metadata_items', 'quota_metadata_items'),
    AbsoluteResource('injected_files', 'quota_injected_files'),
    AbsoluteResource('injected_file_content_bytes',
                     'quota_injected_file_content_bytes'),
    AbsoluteResource('injected_file_path_bytes',
                     'quota_injected_file_path_length'),
    CountableResource('security_group_rules',
                      db.security_group_rule_count_by_group,
                      'quota_security_group_rules'),
    CountableResource('key_pairs', _keypair_get_count_by_user,
                      'quota_key_pairs'),
    ]


QUOTAS.register_resources(resources)