summaryrefslogtreecommitdiff
path: root/src/core/transaction.c
blob: 88c064f096d08b9744d56f06ed45f77281608671 (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
/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

/***
  This file is part of systemd.

  Copyright 2010 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include <fcntl.h>
#include <unistd.h>

#include "alloc-util.h"
#include "bus-common-errors.h"
#include "bus-error.h"
#include "terminal-util.h"
#include "transaction.h"
#include "dbus-unit.h"

static void transaction_unlink_job(Transaction *tr, Job *j, bool delete_dependencies);

static void transaction_delete_job(Transaction *tr, Job *j, bool delete_dependencies) {
        assert(tr);
        assert(j);

        /* Deletes one job from the transaction */

        transaction_unlink_job(tr, j, delete_dependencies);

        job_free(j);
}

static void transaction_delete_unit(Transaction *tr, Unit *u) {
        Job *j;

        /* Deletes all jobs associated with a certain unit from the
         * transaction */

        while ((j = hashmap_get(tr->jobs, u)))
                transaction_delete_job(tr, j, true);
}

void transaction_abort(Transaction *tr) {
        Job *j;

        assert(tr);

        while ((j = hashmap_first(tr->jobs)))
                transaction_delete_job(tr, j, false);

        assert(hashmap_isempty(tr->jobs));
}

static void transaction_find_jobs_that_matter_to_anchor(Job *j, unsigned generation) {
        JobDependency *l;

        /* A recursive sweep through the graph that marks all units
         * that matter to the anchor job, i.e. are directly or
         * indirectly a dependency of the anchor job via paths that
         * are fully marked as mattering. */

        j->matters_to_anchor = true;
        j->generation = generation;

        LIST_FOREACH(subject, l, j->subject_list) {

                /* This link does not matter */
                if (!l->matters)
                        continue;

                /* This unit has already been marked */
                if (l->object->generation == generation)
                        continue;

                transaction_find_jobs_that_matter_to_anchor(l->object, generation);
        }
}

static void transaction_merge_and_delete_job(Transaction *tr, Job *j, Job *other, JobType t) {
        JobDependency *l, *last;

        assert(j);
        assert(other);
        assert(j->unit == other->unit);
        assert(!j->installed);

        /* Merges 'other' into 'j' and then deletes 'other'. */

        j->type = t;
        j->state = JOB_WAITING;
        j->irreversible = j->irreversible || other->irreversible;
        j->matters_to_anchor = j->matters_to_anchor || other->matters_to_anchor;

        /* Patch us in as new owner of the JobDependency objects */
        last = NULL;
        LIST_FOREACH(subject, l, other->subject_list) {
                assert(l->subject == other);
                l->subject = j;
                last = l;
        }

        /* Merge both lists */
        if (last) {
                last->subject_next = j->subject_list;
                if (j->subject_list)
                        j->subject_list->subject_prev = last;
                j->subject_list = other->subject_list;
        }

        /* Patch us in as new owner of the JobDependency objects */
        last = NULL;
        LIST_FOREACH(object, l, other->object_list) {
                assert(l->object == other);
                l->object = j;
                last = l;
        }

        /* Merge both lists */
        if (last) {
                last->object_next = j->object_list;
                if (j->object_list)
                        j->object_list->object_prev = last;
                j->object_list = other->object_list;
        }

        /* Kill the other job */
        other->subject_list = NULL;
        other->object_list = NULL;
        transaction_delete_job(tr, other, true);
}

_pure_ static bool job_is_conflicted_by(Job *j) {
        JobDependency *l;

        assert(j);

        /* Returns true if this job is pulled in by a least one
         * ConflictedBy dependency. */

        LIST_FOREACH(object, l, j->object_list)
                if (l->conflicts)
                        return true;

        return false;
}

static int delete_one_unmergeable_job(Transaction *tr, Job *j) {
        Job *k;

        assert(j);

        /* Tries to delete one item in the linked list
         * j->transaction_next->transaction_next->... that conflicts
         * with another one, in an attempt to make an inconsistent
         * transaction work. */

        /* We rely here on the fact that if a merged with b does not
         * merge with c, either a or b merge with c neither */
        LIST_FOREACH(transaction, j, j)
                LIST_FOREACH(transaction, k, j->transaction_next) {
                        Job *d;

                        /* Is this one mergeable? Then skip it */
                        if (job_type_is_mergeable(j->type, k->type))
                                continue;

                        /* Ok, we found two that conflict, let's see if we can
                         * drop one of them */
                        if (!j->matters_to_anchor && !k->matters_to_anchor) {

                                /* Both jobs don't matter, so let's
                                 * find the one that is smarter to
                                 * remove. Let's think positive and
                                 * rather remove stops then starts --
                                 * except if something is being
                                 * stopped because it is conflicted by
                                 * another unit in which case we
                                 * rather remove the start. */

                                log_unit_debug(j->unit,
                                               "Looking at job %s/%s conflicted_by=%s",
                                               j->unit->id, job_type_to_string(j->type),
                                               yes_no(j->type == JOB_STOP && job_is_conflicted_by(j)));
                                log_unit_debug(k->unit,
                                               "Looking at job %s/%s conflicted_by=%s",
                                               k->unit->id, job_type_to_string(k->type),
                                               yes_no(k->type == JOB_STOP && job_is_conflicted_by(k)));

                                if (j->type == JOB_STOP) {

                                        if (job_is_conflicted_by(j))
                                                d = k;
                                        else
                                                d = j;

                                } else if (k->type == JOB_STOP) {

                                        if (job_is_conflicted_by(k))
                                                d = j;
                                        else
                                                d = k;
                                } else
                                        d = j;

                        } else if (!j->matters_to_anchor)
                                d = j;
                        else if (!k->matters_to_anchor)
                                d = k;
                        else
                                return -ENOEXEC;

                        /* Ok, we can drop one, so let's do so. */
                        log_unit_debug(d->unit,
                                       "Fixing conflicting jobs %s/%s,%s/%s by deleting job %s/%s",
                                       j->unit->id, job_type_to_string(j->type),
                                       k->unit->id, job_type_to_string(k->type),
                                       d->unit->id, job_type_to_string(d->type));
                        transaction_delete_job(tr, d, true);
                        return 0;
                }

        return -EINVAL;
}

static int transaction_merge_jobs(Transaction *tr, sd_bus_error *e) {
        Job *j;
        Iterator i;
        int r;

        assert(tr);

        /* First step, check whether any of the jobs for one specific
         * task conflict. If so, try to drop one of them. */
        HASHMAP_FOREACH(j, tr->jobs, i) {
                JobType t;
                Job *k;

                t = j->type;
                LIST_FOREACH(transaction, k, j->transaction_next) {
                        if (job_type_merge_and_collapse(&t, k->type, j->unit) >= 0)
                                continue;

                        /* OK, we could not merge all jobs for this
                         * action. Let's see if we can get rid of one
                         * of them */

                        r = delete_one_unmergeable_job(tr, j);
                        if (r >= 0)
                                /* Ok, we managed to drop one, now
                                 * let's ask our callers to call us
                                 * again after garbage collecting */
                                return -EAGAIN;

                        /* We couldn't merge anything. Failure */
                        return sd_bus_error_setf(e, BUS_ERROR_TRANSACTION_JOBS_CONFLICTING,
                                                 "Transaction contains conflicting jobs '%s' and '%s' for %s. "
                                                 "Probably contradicting requirement dependencies configured.",
                                                 job_type_to_string(t),
                                                 job_type_to_string(k->type),
                                                 k->unit->id);
                }
        }

        /* Second step, merge the jobs. */
        HASHMAP_FOREACH(j, tr->jobs, i) {
                JobType t = j->type;
                Job *k;

                /* Merge all transaction jobs for j->unit */
                LIST_FOREACH(transaction, k, j->transaction_next)
                        assert_se(job_type_merge_and_collapse(&t, k->type, j->unit) == 0);

                while ((k = j->transaction_next)) {
                        if (tr->anchor_job == k) {
                                transaction_merge_and_delete_job(tr, k, j, t);
                                j = k;
                        } else
                                transaction_merge_and_delete_job(tr, j, k, t);
                }

                assert(!j->transaction_next);
                assert(!j->transaction_prev);
        }

        return 0;
}

static void transaction_drop_redundant(Transaction *tr) {
        Job *j;
        Iterator i;

        /* Goes through the transaction and removes all jobs of the units
         * whose jobs are all noops. If not all of a unit's jobs are
         * redundant, they are kept. */

        assert(tr);

rescan:
        HASHMAP_FOREACH(j, tr->jobs, i) {
                Job *k;

                LIST_FOREACH(transaction, k, j) {

                        if (tr->anchor_job == k ||
                            !job_type_is_redundant(k->type, unit_active_state(k->unit)) ||
                            (k->unit->job && job_type_is_conflicting(k->type, k->unit->job->type)))
                                goto next_unit;
                }

                /* log_debug("Found redundant job %s/%s, dropping.", j->unit->id, job_type_to_string(j->type)); */
                transaction_delete_job(tr, j, false);
                goto rescan;
        next_unit:;
        }
}

_pure_ static bool unit_matters_to_anchor(Unit *u, Job *j) {
        assert(u);
        assert(!j->transaction_prev);

        /* Checks whether at least one of the jobs for this unit
         * matters to the anchor. */

        LIST_FOREACH(transaction, j, j)
                if (j->matters_to_anchor)
                        return true;

        return false;
}

static int transaction_verify_order_one(Transaction *tr, Job *j, Job *from, unsigned generation, sd_bus_error *e) {
        Iterator i;
        Unit *u;
        int r;

        assert(tr);
        assert(j);
        assert(!j->transaction_prev);

        /* Does a recursive sweep through the ordering graph, looking
         * for a cycle. If we find a cycle we try to break it. */

        /* Have we seen this before? */
        if (j->generation == generation) {
                Job *k, *delete;

                /* If the marker is NULL we have been here already and
                 * decided the job was loop-free from here. Hence
                 * shortcut things and return right-away. */
                if (!j->marker)
                        return 0;

                /* So, the marker is not NULL and we already have been
                 * here. We have a cycle. Let's try to break it. We go
                 * backwards in our path and try to find a suitable
                 * job to remove. We use the marker to find our way
                 * back, since smart how we are we stored our way back
                 * in there. */
                log_unit_warning(j->unit,
                                 "Found ordering cycle on %s/%s",
                                 j->unit->id, job_type_to_string(j->type));

                delete = NULL;
                for (k = from; k; k = ((k->generation == generation && k->marker != k) ? k->marker : NULL)) {

                        /* logging for j not k here here to provide consistent narrative */
                        log_unit_warning(j->unit,
                                         "Found dependency on %s/%s",
                                         k->unit->id, job_type_to_string(k->type));

                        if (!delete && hashmap_get(tr->jobs, k->unit) && !unit_matters_to_anchor(k->unit, k))
                                /* Ok, we can drop this one, so let's
                                 * do so. */
                                delete = k;

                        /* Check if this in fact was the beginning of
                         * the cycle */
                        if (k == j)
                                break;
                }


                if (delete) {
                        /* logging for j not k here here to provide consistent narrative */
                        log_unit_warning(j->unit,
                                         "Breaking ordering cycle by deleting job %s/%s",
                                         delete->unit->id, job_type_to_string(delete->type));
                        log_unit_error(delete->unit,
                                       "Job %s/%s deleted to break ordering cycle starting with %s/%s",
                                       delete->unit->id, job_type_to_string(delete->type),
                                       j->unit->id, job_type_to_string(j->type));
                        unit_status_printf(delete->unit, ANSI_HIGHLIGHT_RED " SKIP " ANSI_NORMAL,
                                           "Ordering cycle found, skipping %s");
                        transaction_delete_unit(tr, delete->unit);
                        return -EAGAIN;
                }

                log_error("Unable to break cycle");

                return sd_bus_error_setf(e, BUS_ERROR_TRANSACTION_ORDER_IS_CYCLIC,
                                         "Transaction order is cyclic. See system logs for details.");
        }

        /* Make the marker point to where we come from, so that we can
         * find our way backwards if we want to break a cycle. We use
         * a special marker for the beginning: we point to
         * ourselves. */
        j->marker = from ? from : j;
        j->generation = generation;

        /* We assume that the dependencies are bidirectional, and
         * hence can ignore UNIT_AFTER */
        SET_FOREACH(u, j->unit->dependencies[UNIT_BEFORE], i) {
                Job *o;

                /* Is there a job for this unit? */
                o = hashmap_get(tr->jobs, u);
                if (!o) {
                        /* Ok, there is no job for this in the
                         * transaction, but maybe there is already one
                         * running? */
                        o = u->job;
                        if (!o)
                                continue;
                }

                r = transaction_verify_order_one(tr, o, j, generation, e);
                if (r < 0)
                        return r;
        }

        /* Ok, let's backtrack, and remember that this entry is not on
         * our path anymore. */
        j->marker = NULL;

        return 0;
}

static int transaction_verify_order(Transaction *tr, unsigned *generation, sd_bus_error *e) {
        Job *j;
        int r;
        Iterator i;
        unsigned g;

        assert(tr);
        assert(generation);

        /* Check if the ordering graph is cyclic. If it is, try to fix
         * that up by dropping one of the jobs. */

        g = (*generation)++;

        HASHMAP_FOREACH(j, tr->jobs, i) {
                r = transaction_verify_order_one(tr, j, NULL, g, e);
                if (r < 0)
                        return r;
        }

        return 0;
}

static void transaction_collect_garbage(Transaction *tr) {
        Iterator i;
        Job *j;

        assert(tr);

        /* Drop jobs that are not required by any other job */

rescan:
        HASHMAP_FOREACH(j, tr->jobs, i) {
                if (tr->anchor_job == j || j->object_list) {
                        /* log_debug("Keeping job %s/%s because of %s/%s", */
                        /*           j->unit->id, job_type_to_string(j->type), */
                        /*           j->object_list->subject ? j->object_list->subject->unit->id : "root", */
                        /*           j->object_list->subject ? job_type_to_string(j->object_list->subject->type) : "root"); */
                        continue;
                }

                /* log_debug("Garbage collecting job %s/%s", j->unit->id, job_type_to_string(j->type)); */
                transaction_delete_job(tr, j, true);
                goto rescan;
        }
}

static int transaction_is_destructive(Transaction *tr, JobMode mode, sd_bus_error *e) {
        Iterator i;
        Job *j;

        assert(tr);

        /* Checks whether applying this transaction means that
         * existing jobs would be replaced */

        HASHMAP_FOREACH(j, tr->jobs, i) {

                /* Assume merged */
                assert(!j->transaction_prev);
                assert(!j->transaction_next);

                if (j->unit->job && (mode == JOB_FAIL || j->unit->job->irreversible) &&
                    job_type_is_conflicting(j->unit->job->type, j->type))
                        return sd_bus_error_setf(e, BUS_ERROR_TRANSACTION_IS_DESTRUCTIVE,
                                                 "Transaction is destructive.");
        }

        return 0;
}

static void transaction_minimize_impact(Transaction *tr) {
        Job *j;
        Iterator i;

        assert(tr);

        /* Drops all unnecessary jobs that reverse already active jobs
         * or that stop a running service. */

rescan:
        HASHMAP_FOREACH(j, tr->jobs, i) {
                LIST_FOREACH(transaction, j, j) {
                        bool stops_running_service, changes_existing_job;

                        /* If it matters, we shouldn't drop it */
                        if (j->matters_to_anchor)
                                continue;

                        /* Would this stop a running service?
                         * Would this change an existing job?
                         * If so, let's drop this entry */

                        stops_running_service =
                                j->type == JOB_STOP && UNIT_IS_ACTIVE_OR_ACTIVATING(unit_active_state(j->unit));

                        changes_existing_job =
                                j->unit->job &&
                                job_type_is_conflicting(j->type, j->unit->job->type);

                        if (!stops_running_service && !changes_existing_job)
                                continue;

                        if (stops_running_service)
                                log_unit_debug(j->unit,
                                               "%s/%s would stop a running service.",
                                               j->unit->id, job_type_to_string(j->type));

                        if (changes_existing_job)
                                log_unit_debug(j->unit,
                                               "%s/%s would change existing job.",
                                               j->unit->id, job_type_to_string(j->type));

                        /* Ok, let's get rid of this */
                        log_unit_debug(j->unit,
                                       "Deleting %s/%s to minimize impact.",
                                       j->unit->id, job_type_to_string(j->type));

                        transaction_delete_job(tr, j, true);
                        goto rescan;
                }
        }
}

static int transaction_apply(Transaction *tr, Manager *m, JobMode mode) {
        Iterator i;
        Job *j;
        int r;

        /* Moves the transaction jobs to the set of active jobs */

        if (mode == JOB_ISOLATE || mode == JOB_FLUSH) {

                /* When isolating first kill all installed jobs which
                 * aren't part of the new transaction */
                HASHMAP_FOREACH(j, m->jobs, i) {
                        assert(j->installed);

                        if (hashmap_get(tr->jobs, j->unit))
                                continue;

                        /* Not invalidating recursively. Avoids triggering
                         * OnFailure= actions of dependent jobs. Also avoids
                         * invalidating our iterator. */
                        job_finish_and_invalidate(j, JOB_CANCELED, false);
                }
        }

        HASHMAP_FOREACH(j, tr->jobs, i) {
                /* Assume merged */
                assert(!j->transaction_prev);
                assert(!j->transaction_next);

                r = hashmap_put(m->jobs, UINT32_TO_PTR(j->id), j);
                if (r < 0)
                        goto rollback;
        }

        while ((j = hashmap_steal_first(tr->jobs))) {
                Job *installed_job;

                /* Clean the job dependencies */
                transaction_unlink_job(tr, j, false);

                installed_job = job_install(j);
                if (installed_job != j) {
                        /* j has been merged into a previously installed job */
                        if (tr->anchor_job == j)
                                tr->anchor_job = installed_job;
                        hashmap_remove(m->jobs, UINT32_TO_PTR(j->id));
                        job_free(j);
                        j = installed_job;
                }

                job_add_to_run_queue(j);
                job_add_to_dbus_queue(j);
                job_start_timer(j);
                job_shutdown_magic(j);
        }

        return 0;

rollback:

        HASHMAP_FOREACH(j, tr->jobs, i)
                hashmap_remove(m->jobs, UINT32_TO_PTR(j->id));

        return r;
}

int transaction_activate(Transaction *tr, Manager *m, JobMode mode, sd_bus_error *e) {
        Iterator i;
        Job *j;
        int r;
        unsigned generation = 1;

        assert(tr);

        /* This applies the changes recorded in tr->jobs to
         * the actual list of jobs, if possible. */

        /* Reset the generation counter of all installed jobs. The detection of cycles
         * looks at installed jobs. If they had a non-zero generation from some previous
         * walk of the graph, the algorithm would break. */
        HASHMAP_FOREACH(j, m->jobs, i)
                j->generation = 0;

        /* First step: figure out which jobs matter */
        transaction_find_jobs_that_matter_to_anchor(tr->anchor_job, generation++);

        /* Second step: Try not to stop any running services if
         * we don't have to. Don't try to reverse running
         * jobs if we don't have to. */
        if (mode == JOB_FAIL)
                transaction_minimize_impact(tr);

        /* Third step: Drop redundant jobs */
        transaction_drop_redundant(tr);

        for (;;) {
                /* Fourth step: Let's remove unneeded jobs that might
                 * be lurking. */
                if (mode != JOB_ISOLATE)
                        transaction_collect_garbage(tr);

                /* Fifth step: verify order makes sense and correct
                 * cycles if necessary and possible */
                r = transaction_verify_order(tr, &generation, e);
                if (r >= 0)
                        break;

                if (r != -EAGAIN) {
                        log_warning("Requested transaction contains an unfixable cyclic ordering dependency: %s", bus_error_message(e, r));
                        return r;
                }

                /* Let's see if the resulting transaction ordering
                 * graph is still cyclic... */
        }

        for (;;) {
                /* Sixth step: let's drop unmergeable entries if
                 * necessary and possible, merge entries we can
                 * merge */
                r = transaction_merge_jobs(tr, e);
                if (r >= 0)
                        break;

                if (r != -EAGAIN) {
                        log_warning("Requested transaction contains unmergeable jobs: %s", bus_error_message(e, r));
                        return r;
                }

                /* Seventh step: an entry got dropped, let's garbage
                 * collect its dependencies. */
                if (mode != JOB_ISOLATE)
                        transaction_collect_garbage(tr);

                /* Let's see if the resulting transaction still has
                 * unmergeable entries ... */
        }

        /* Eights step: Drop redundant jobs again, if the merging now allows us to drop more. */
        transaction_drop_redundant(tr);

        /* Ninth step: check whether we can actually apply this */
        r = transaction_is_destructive(tr, mode, e);
        if (r < 0) {
                log_notice("Requested transaction contradicts existing jobs: %s", bus_error_message(e, r));
                return r;
        }

        /* Tenth step: apply changes */
        r = transaction_apply(tr, m, mode);
        if (r < 0)
                return log_warning_errno(r, "Failed to apply transaction: %m");

        assert(hashmap_isempty(tr->jobs));

        if (!hashmap_isempty(m->jobs)) {
                /* Are there any jobs now? Then make sure we have the
                 * idle pipe around. We don't really care too much
                 * whether this works or not, as the idle pipe is a
                 * feature for cosmetics, not actually useful for
                 * anything beyond that. */

                if (m->idle_pipe[0] < 0 && m->idle_pipe[1] < 0 &&
                    m->idle_pipe[2] < 0 && m->idle_pipe[3] < 0) {
                        (void) pipe2(m->idle_pipe, O_NONBLOCK|O_CLOEXEC);
                        (void) pipe2(m->idle_pipe + 2, O_NONBLOCK|O_CLOEXEC);
                }
        }

        return 0;
}

static Job* transaction_add_one_job(Transaction *tr, JobType type, Unit *unit, bool *is_new) {
        Job *j, *f;

        assert(tr);
        assert(unit);

        /* Looks for an existing prospective job and returns that. If
         * it doesn't exist it is created and added to the prospective
         * jobs list. */

        f = hashmap_get(tr->jobs, unit);

        LIST_FOREACH(transaction, j, f) {
                assert(j->unit == unit);

                if (j->type == type) {
                        if (is_new)
                                *is_new = false;
                        return j;
                }
        }

        j = job_new(unit, type);
        if (!j)
                return NULL;

        j->generation = 0;
        j->marker = NULL;
        j->matters_to_anchor = false;
        j->irreversible = tr->irreversible;

        LIST_PREPEND(transaction, f, j);

        if (hashmap_replace(tr->jobs, unit, f) < 0) {
                LIST_REMOVE(transaction, f, j);
                job_free(j);
                return NULL;
        }

        if (is_new)
                *is_new = true;

        /* log_debug("Added job %s/%s to transaction.", unit->id, job_type_to_string(type)); */

        return j;
}

static void transaction_unlink_job(Transaction *tr, Job *j, bool delete_dependencies) {
        assert(tr);
        assert(j);

        if (j->transaction_prev)
                j->transaction_prev->transaction_next = j->transaction_next;
        else if (j->transaction_next)
                hashmap_replace(tr->jobs, j->unit, j->transaction_next);
        else
                hashmap_remove_value(tr->jobs, j->unit, j);

        if (j->transaction_next)
                j->transaction_next->transaction_prev = j->transaction_prev;

        j->transaction_prev = j->transaction_next = NULL;

        while (j->subject_list)
                job_dependency_free(j->subject_list);

        while (j->object_list) {
                Job *other = j->object_list->matters ? j->object_list->subject : NULL;

                job_dependency_free(j->object_list);

                if (other && delete_dependencies) {
                        log_unit_debug(other->unit,
                                       "Deleting job %s/%s as dependency of job %s/%s",
                                       other->unit->id, job_type_to_string(other->type),
                                       j->unit->id, job_type_to_string(j->type));
                        transaction_delete_job(tr, other, delete_dependencies);
                }
        }
}

int transaction_add_job_and_dependencies(
                Transaction *tr,
                JobType type,
                Unit *unit,
                Job *by,
                bool matters,
                bool conflicts,
                bool ignore_requirements,
                bool ignore_order,
                sd_bus_error *e) {
        Job *ret;
        Iterator i;
        Unit *dep;
        int r;
        bool is_new;

        assert(tr);
        assert(type < _JOB_TYPE_MAX);
        assert(type < _JOB_TYPE_MAX_IN_TRANSACTION);
        assert(unit);

        /* Before adding jobs for this unit, let's ensure that its state has been loaded
         * This matters when jobs are spawned as part of coldplugging itself (see e. g. path_coldplug()).
         * This way, we "recursively" coldplug units, ensuring that we do not look at state of
         * not-yet-coldplugged units. */
        if (unit->manager->n_reloading > 0)
                unit_coldplug(unit);

        /* log_debug("Pulling in %s/%s from %s/%s", */
        /*           unit->id, job_type_to_string(type), */
        /*           by ? by->unit->id : "NA", */
        /*           by ? job_type_to_string(by->type) : "NA"); */

        if (!IN_SET(unit->load_state, UNIT_LOADED, UNIT_ERROR, UNIT_NOT_FOUND, UNIT_MASKED))
                return sd_bus_error_setf(e, BUS_ERROR_LOAD_FAILED, "Unit %s is not loaded properly.", unit->id);

        if (type != JOB_STOP) {
                r = bus_unit_check_load_state(unit, e);
                if (r < 0)
                        return r;
        }

        if (!unit_job_is_applicable(unit, type))
                return sd_bus_error_setf(e, BUS_ERROR_JOB_TYPE_NOT_APPLICABLE,
                                         "Job type %s is not applicable for unit %s.",
                                         job_type_to_string(type), unit->id);


        /* First add the job. */
        ret = transaction_add_one_job(tr, type, unit, &is_new);
        if (!ret)
                return -ENOMEM;

        ret->ignore_order = ret->ignore_order || ignore_order;

        /* Then, add a link to the job. */
        if (by) {
                if (!job_dependency_new(by, ret, matters, conflicts))
                        return -ENOMEM;
        } else {
                /* If the job has no parent job, it is the anchor job. */
                assert(!tr->anchor_job);
                tr->anchor_job = ret;
        }

        if (is_new && !ignore_requirements && type != JOB_NOP) {
                Set *following;

                /* If we are following some other unit, make sure we
                 * add all dependencies of everybody following. */
                if (unit_following_set(ret->unit, &following) > 0) {
                        SET_FOREACH(dep, following, i) {
                                r = transaction_add_job_and_dependencies(tr, type, dep, ret, false, false, false, ignore_order, e);
                                if (r < 0) {
                                        log_unit_warning(dep, "Cannot add dependency job for, ignoring: %s", bus_error_message(e, r));
                                        sd_bus_error_free(e);
                                }
                        }

                        set_free(following);
                }

                /* Finally, recursively add in all dependencies. */
                if (type == JOB_START || type == JOB_RESTART) {
                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_REQUIRES], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_START, dep, ret, true, false, false, ignore_order, e);
                                if (r < 0) {
                                        if (r != -EBADR)
                                                goto fail;

                                        sd_bus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_BINDS_TO], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_START, dep, ret, true, false, false, ignore_order, e);
                                if (r < 0) {
                                        if (r != -EBADR)
                                                goto fail;

                                        sd_bus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_WANTS], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_START, dep, ret, false, false, false, ignore_order, e);
                                if (r < 0) {
                                        log_unit_full(dep,
                                                      r == -EADDRNOTAVAIL ? LOG_DEBUG : LOG_WARNING, r,
                                                      "Cannot add dependency job, ignoring: %s",
                                                      bus_error_message(e, r));
                                        sd_bus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_REQUISITE], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_VERIFY_ACTIVE, dep, ret, true, false, false, ignore_order, e);
                                if (r < 0) {
                                        if (r != -EBADR)
                                                goto fail;

                                        sd_bus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_CONFLICTS], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_STOP, dep, ret, true, true, false, ignore_order, e);
                                if (r < 0) {
                                        if (r != -EBADR)
                                                goto fail;

                                        sd_bus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_CONFLICTED_BY], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_STOP, dep, ret, false, false, false, ignore_order, e);
                                if (r < 0) {
                                        log_unit_warning(dep,
                                                         "Cannot add dependency job, ignoring: %s",
                                                         bus_error_message(e, r));
                                        sd_bus_error_free(e);
                                }
                        }

                }

                if (type == JOB_STOP || type == JOB_RESTART) {
                        static const UnitDependency propagate_deps[] = {
                                UNIT_REQUIRED_BY,
                                UNIT_REQUISITE_OF,
                                UNIT_BOUND_BY,
                                UNIT_CONSISTS_OF,
                        };

                        JobType ptype;
                        unsigned j;

                        /* We propagate STOP as STOP, but RESTART only
                         * as TRY_RESTART, in order not to start
                         * dependencies that are not around. */
                        ptype = type == JOB_RESTART ? JOB_TRY_RESTART : type;

                        for (j = 0; j < ELEMENTSOF(propagate_deps); j++)
                                SET_FOREACH(dep, ret->unit->dependencies[propagate_deps[j]], i) {
                                        JobType nt;

                                        nt = job_type_collapse(ptype, dep);
                                        if (nt == JOB_NOP)
                                                continue;

                                        r = transaction_add_job_and_dependencies(tr, nt, dep, ret, true, false, false, ignore_order, e);
                                        if (r < 0) {
                                                if (r != -EBADR)
                                                        goto fail;

                                                sd_bus_error_free(e);
                                        }
                                }
                }

                if (type == JOB_RELOAD) {

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_PROPAGATES_RELOAD_TO], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_RELOAD, dep, ret, false, false, false, ignore_order, e);
                                if (r < 0) {
                                        log_unit_warning(dep,
                                                         "Cannot add dependency reload job, ignoring: %s",
                                                         bus_error_message(e, r));
                                        sd_bus_error_free(e);
                                }
                        }
                }

                /* JOB_VERIFY_STARTED require no dependency handling */
        }

        return 0;

fail:
        return r;
}

int transaction_add_isolate_jobs(Transaction *tr, Manager *m) {
        Iterator i;
        Unit *u;
        char *k;
        int r;

        assert(tr);
        assert(m);

        HASHMAP_FOREACH_KEY(u, k, m->units, i) {

                /* ignore aliases */
                if (u->id != k)
                        continue;

                if (u->ignore_on_isolate)
                        continue;

                /* No need to stop inactive jobs */
                if (UNIT_IS_INACTIVE_OR_FAILED(unit_active_state(u)) && !u->job)
                        continue;

                /* Is there already something listed for this? */
                if (hashmap_get(tr->jobs, u))
                        continue;

                r = transaction_add_job_and_dependencies(tr, JOB_STOP, u, tr->anchor_job, true, false, false, false, NULL);
                if (r < 0)
                        log_unit_warning_errno(u, r, "Cannot add isolate job, ignoring: %m");
        }

        return 0;
}

Transaction *transaction_new(bool irreversible) {
        Transaction *tr;

        tr = new0(Transaction, 1);
        if (!tr)
                return NULL;

        tr->jobs = hashmap_new(NULL);
        if (!tr->jobs) {
                free(tr);
                return NULL;
        }

        tr->irreversible = irreversible;

        return tr;
}

void transaction_free(Transaction *tr) {
        assert(hashmap_isempty(tr->jobs));
        hashmap_free(tr->jobs);
        free(tr);
}