summaryrefslogtreecommitdiffstats
path: root/builtin/fsmonitor--daemon.c
blob: 1593713f4cb29fe8e608f4c3c7502fa5a624d1f9 (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
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
#include "builtin.h"
#include "abspath.h"
#include "config.h"
#include "dir.h"
#include "environment.h"
#include "gettext.h"
#include "parse-options.h"
#include "fsmonitor-ll.h"
#include "fsmonitor-ipc.h"
#include "fsmonitor-settings.h"
#include "compat/fsmonitor/fsm-health.h"
#include "compat/fsmonitor/fsm-listen.h"
#include "fsmonitor--daemon.h"
#include "repository.h"
#include "simple-ipc.h"
#include "khash.h"
#include "run-command.h"
#include "trace.h"
#include "trace2.h"

static const char * const builtin_fsmonitor__daemon_usage[] = {
	N_("git fsmonitor--daemon start [<options>]"),
	N_("git fsmonitor--daemon run [<options>]"),
	"git fsmonitor--daemon stop",
	"git fsmonitor--daemon status",
	NULL
};

#ifdef HAVE_FSMONITOR_DAEMON_BACKEND
/*
 * Global state loaded from config.
 */
#define FSMONITOR__IPC_THREADS "fsmonitor.ipcthreads"
static int fsmonitor__ipc_threads = 8;

#define FSMONITOR__START_TIMEOUT "fsmonitor.starttimeout"
static int fsmonitor__start_timeout_sec = 60;

#define FSMONITOR__ANNOUNCE_STARTUP "fsmonitor.announcestartup"
static int fsmonitor__announce_startup = 0;

static int fsmonitor_config(const char *var, const char *value,
			    const struct config_context *ctx, void *cb)
{
	if (!strcmp(var, FSMONITOR__IPC_THREADS)) {
		int i = git_config_int(var, value, ctx->kvi);
		if (i < 1)
			return error(_("value of '%s' out of range: %d"),
				     FSMONITOR__IPC_THREADS, i);
		fsmonitor__ipc_threads = i;
		return 0;
	}

	if (!strcmp(var, FSMONITOR__START_TIMEOUT)) {
		int i = git_config_int(var, value, ctx->kvi);
		if (i < 0)
			return error(_("value of '%s' out of range: %d"),
				     FSMONITOR__START_TIMEOUT, i);
		fsmonitor__start_timeout_sec = i;
		return 0;
	}

	if (!strcmp(var, FSMONITOR__ANNOUNCE_STARTUP)) {
		int is_bool;
		int i = git_config_bool_or_int(var, value, ctx->kvi, &is_bool);
		if (i < 0)
			return error(_("value of '%s' not bool or int: %d"),
				     var, i);
		fsmonitor__announce_startup = i;
		return 0;
	}

	return git_default_config(var, value, ctx, cb);
}

/*
 * Acting as a CLIENT.
 *
 * Send a "quit" command to the `git-fsmonitor--daemon` (if running)
 * and wait for it to shutdown.
 */
static int do_as_client__send_stop(void)
{
	struct strbuf answer = STRBUF_INIT;
	int ret;

	ret = fsmonitor_ipc__send_command("quit", &answer);

	/* The quit command does not return any response data. */
	strbuf_release(&answer);

	if (ret)
		return ret;

	trace2_region_enter("fsm_client", "polling-for-daemon-exit", NULL);
	while (fsmonitor_ipc__get_state() == IPC_STATE__LISTENING)
		sleep_millisec(50);
	trace2_region_leave("fsm_client", "polling-for-daemon-exit", NULL);

	return 0;
}

static int do_as_client__status(void)
{
	enum ipc_active_state state = fsmonitor_ipc__get_state();

	switch (state) {
	case IPC_STATE__LISTENING:
		printf(_("fsmonitor-daemon is watching '%s'\n"),
		       the_repository->worktree);
		return 0;

	default:
		printf(_("fsmonitor-daemon is not watching '%s'\n"),
		       the_repository->worktree);
		return 1;
	}
}

enum fsmonitor_cookie_item_result {
	FCIR_ERROR = -1, /* could not create cookie file ? */
	FCIR_INIT,
	FCIR_SEEN,
	FCIR_ABORT,
};

struct fsmonitor_cookie_item {
	struct hashmap_entry entry;
	char *name;
	enum fsmonitor_cookie_item_result result;
};

static int cookies_cmp(const void *data UNUSED,
		       const struct hashmap_entry *he1,
		       const struct hashmap_entry *he2, const void *keydata)
{
	const struct fsmonitor_cookie_item *a =
		container_of(he1, const struct fsmonitor_cookie_item, entry);
	const struct fsmonitor_cookie_item *b =
		container_of(he2, const struct fsmonitor_cookie_item, entry);

	return strcmp(a->name, keydata ? keydata : b->name);
}

static enum fsmonitor_cookie_item_result with_lock__wait_for_cookie(
	struct fsmonitor_daemon_state *state)
{
	/* assert current thread holding state->main_lock */

	int fd;
	struct fsmonitor_cookie_item *cookie;
	struct strbuf cookie_pathname = STRBUF_INIT;
	struct strbuf cookie_filename = STRBUF_INIT;
	enum fsmonitor_cookie_item_result result;
	int my_cookie_seq;

	CALLOC_ARRAY(cookie, 1);

	my_cookie_seq = state->cookie_seq++;

	strbuf_addf(&cookie_filename, "%i-%i", getpid(), my_cookie_seq);

	strbuf_addbuf(&cookie_pathname, &state->path_cookie_prefix);
	strbuf_addbuf(&cookie_pathname, &cookie_filename);

	cookie->name = strbuf_detach(&cookie_filename, NULL);
	cookie->result = FCIR_INIT;
	hashmap_entry_init(&cookie->entry, strhash(cookie->name));

	hashmap_add(&state->cookies, &cookie->entry);

	trace_printf_key(&trace_fsmonitor, "cookie-wait: '%s' '%s'",
			 cookie->name, cookie_pathname.buf);

	/*
	 * Create the cookie file on disk and then wait for a notification
	 * that the listener thread has seen it.
	 */
	fd = open(cookie_pathname.buf, O_WRONLY | O_CREAT | O_EXCL, 0600);
	if (fd < 0) {
		error_errno(_("could not create fsmonitor cookie '%s'"),
			    cookie->name);

		cookie->result = FCIR_ERROR;
		goto done;
	}

	/*
	 * Technically, close() and unlink() can fail, but we don't
	 * care here.  We only created the file to trigger a watch
	 * event from the FS to know that when we're up to date.
	 */
	close(fd);
	unlink(cookie_pathname.buf);

	/*
	 * Technically, this is an infinite wait (well, unless another
	 * thread sends us an abort).  I'd like to change this to
	 * use `pthread_cond_timedwait()` and return an error/timeout
	 * and let the caller do the trivial response thing, but we
	 * don't have that routine in our thread-utils.
	 *
	 * After extensive beta testing I'm not really worried about
	 * this.  Also note that the above open() and unlink() calls
	 * will cause at least two FS events on that path, so the odds
	 * of getting stuck are pretty slim.
	 */
	while (cookie->result == FCIR_INIT)
		pthread_cond_wait(&state->cookies_cond,
				  &state->main_lock);

done:
	hashmap_remove(&state->cookies, &cookie->entry, NULL);

	result = cookie->result;

	free(cookie->name);
	free(cookie);
	strbuf_release(&cookie_pathname);

	return result;
}

/*
 * Mark these cookies as _SEEN and wake up the corresponding client threads.
 */
static void with_lock__mark_cookies_seen(struct fsmonitor_daemon_state *state,
					 const struct string_list *cookie_names)
{
	/* assert current thread holding state->main_lock */

	int k;
	int nr_seen = 0;

	for (k = 0; k < cookie_names->nr; k++) {
		struct fsmonitor_cookie_item key;
		struct fsmonitor_cookie_item *cookie;

		key.name = cookie_names->items[k].string;
		hashmap_entry_init(&key.entry, strhash(key.name));

		cookie = hashmap_get_entry(&state->cookies, &key, entry, NULL);
		if (cookie) {
			trace_printf_key(&trace_fsmonitor, "cookie-seen: '%s'",
					 cookie->name);
			cookie->result = FCIR_SEEN;
			nr_seen++;
		}
	}

	if (nr_seen)
		pthread_cond_broadcast(&state->cookies_cond);
}

/*
 * Set _ABORT on all pending cookies and wake up all client threads.
 */
static void with_lock__abort_all_cookies(struct fsmonitor_daemon_state *state)
{
	/* assert current thread holding state->main_lock */

	struct hashmap_iter iter;
	struct fsmonitor_cookie_item *cookie;
	int nr_aborted = 0;

	hashmap_for_each_entry(&state->cookies, &iter, cookie, entry) {
		trace_printf_key(&trace_fsmonitor, "cookie-abort: '%s'",
				 cookie->name);
		cookie->result = FCIR_ABORT;
		nr_aborted++;
	}

	if (nr_aborted)
		pthread_cond_broadcast(&state->cookies_cond);
}

/*
 * Requests to and from a FSMonitor Protocol V2 provider use an opaque
 * "token" as a virtual timestamp.  Clients can request a summary of all
 * created/deleted/modified files relative to a token.  In the response,
 * clients receive a new token for the next (relative) request.
 *
 *
 * Token Format
 * ============
 *
 * The contents of the token are private and provider-specific.
 *
 * For the built-in fsmonitor--daemon, we define a token as follows:
 *
 *     "builtin" ":" <token_id> ":" <sequence_nr>
 *
 * The "builtin" prefix is used as a namespace to avoid conflicts
 * with other providers (such as Watchman).
 *
 * The <token_id> is an arbitrary OPAQUE string, such as a GUID,
 * UUID, or {timestamp,pid}.  It is used to group all filesystem
 * events that happened while the daemon was monitoring (and in-sync
 * with the filesystem).
 *
 *     Unlike FSMonitor Protocol V1, it is not defined as a timestamp
 *     and does not define less-than/greater-than relationships.
 *     (There are too many race conditions to rely on file system
 *     event timestamps.)
 *
 * The <sequence_nr> is a simple integer incremented whenever the
 * daemon needs to make its state public.  For example, if 1000 file
 * system events come in, but no clients have requested the data,
 * the daemon can continue to accumulate file changes in the same
 * bin and does not need to advance the sequence number.  However,
 * as soon as a client does arrive, the daemon needs to start a new
 * bin and increment the sequence number.
 *
 *     The sequence number serves as the boundary between 2 sets
 *     of bins -- the older ones that the client has already seen
 *     and the newer ones that it hasn't.
 *
 * When a new <token_id> is created, the <sequence_nr> is reset to
 * zero.
 *
 *
 * About Token Ids
 * ===============
 *
 * A new token_id is created:
 *
 * [1] each time the daemon is started.
 *
 * [2] any time that the daemon must re-sync with the filesystem
 *     (such as when the kernel drops or we miss events on a very
 *     active volume).
 *
 * [3] in response to a client "flush" command (for dropped event
 *     testing).
 *
 * When a new token_id is created, the daemon is free to discard all
 * cached filesystem events associated with any previous token_ids.
 * Events associated with a non-current token_id will never be sent
 * to a client.  A token_id change implicitly means that the daemon
 * has gap in its event history.
 *
 * Therefore, clients that present a token with a stale (non-current)
 * token_id will always be given a trivial response.
 */
struct fsmonitor_token_data {
	struct strbuf token_id;
	struct fsmonitor_batch *batch_head;
	struct fsmonitor_batch *batch_tail;
	uint64_t client_ref_count;
};

struct fsmonitor_batch {
	struct fsmonitor_batch *next;
	uint64_t batch_seq_nr;
	const char **interned_paths;
	size_t nr, alloc;
	time_t pinned_time;
};

static struct fsmonitor_token_data *fsmonitor_new_token_data(void)
{
	static int test_env_value = -1;
	static uint64_t flush_count = 0;
	struct fsmonitor_token_data *token;
	struct fsmonitor_batch *batch;

	CALLOC_ARRAY(token, 1);
	batch = fsmonitor_batch__new();

	strbuf_init(&token->token_id, 0);
	token->batch_head = batch;
	token->batch_tail = batch;
	token->client_ref_count = 0;

	if (test_env_value < 0)
		test_env_value = git_env_bool("GIT_TEST_FSMONITOR_TOKEN", 0);

	if (!test_env_value) {
		struct timeval tv;
		struct tm tm;
		time_t secs;

		gettimeofday(&tv, NULL);
		secs = tv.tv_sec;
		gmtime_r(&secs, &tm);

		strbuf_addf(&token->token_id,
			    "%"PRIu64".%d.%4d%02d%02dT%02d%02d%02d.%06ldZ",
			    flush_count++,
			    getpid(),
			    tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
			    tm.tm_hour, tm.tm_min, tm.tm_sec,
			    (long)tv.tv_usec);
	} else {
		strbuf_addf(&token->token_id, "test_%08x", test_env_value++);
	}

	/*
	 * We created a new <token_id> and are starting a new series
	 * of tokens with a zero <seq_nr>.
	 *
	 * Since clients cannot guess our new (non test) <token_id>
	 * they will always receive a trivial response (because of the
	 * mismatch on the <token_id>).  The trivial response will
	 * tell them our new <token_id> so that subsequent requests
	 * will be relative to our new series.  (And when sending that
	 * response, we pin the current head of the batch list.)
	 *
	 * Even if the client correctly guesses the <token_id>, their
	 * request of "builtin:<token_id>:0" asks for all changes MORE
	 * RECENT than batch/bin 0.
	 *
	 * This implies that it is a waste to accumulate paths in the
	 * initial batch/bin (because they will never be transmitted).
	 *
	 * So the daemon could be running for days and watching the
	 * file system, but doesn't need to actually accumulate any
	 * paths UNTIL we need to set a reference point for a later
	 * relative request.
	 *
	 * However, it is very useful for testing to always have a
	 * reference point set.  Pin batch 0 to force early file system
	 * events to accumulate.
	 */
	if (test_env_value)
		batch->pinned_time = time(NULL);

	return token;
}

struct fsmonitor_batch *fsmonitor_batch__new(void)
{
	struct fsmonitor_batch *batch;

	CALLOC_ARRAY(batch, 1);

	return batch;
}

void fsmonitor_batch__free_list(struct fsmonitor_batch *batch)
{
	while (batch) {
		struct fsmonitor_batch *next = batch->next;

		/*
		 * The actual strings within the array of this batch
		 * are interned, so we don't own them.  We only own
		 * the array.
		 */
		free(batch->interned_paths);
		free(batch);

		batch = next;
	}
}

void fsmonitor_batch__add_path(struct fsmonitor_batch *batch,
			       const char *path)
{
	const char *interned_path = strintern(path);

	trace_printf_key(&trace_fsmonitor, "event: %s", interned_path);

	ALLOC_GROW(batch->interned_paths, batch->nr + 1, batch->alloc);
	batch->interned_paths[batch->nr++] = interned_path;
}

static void fsmonitor_batch__combine(struct fsmonitor_batch *batch_dest,
				     const struct fsmonitor_batch *batch_src)
{
	size_t k;

	ALLOC_GROW(batch_dest->interned_paths,
		   batch_dest->nr + batch_src->nr + 1,
		   batch_dest->alloc);

	for (k = 0; k < batch_src->nr; k++)
		batch_dest->interned_paths[batch_dest->nr++] =
			batch_src->interned_paths[k];
}

/*
 * To keep the batch list from growing unbounded in response to filesystem
 * activity, we try to truncate old batches from the end of the list as
 * they become irrelevant.
 *
 * We assume that the .git/index will be updated with the most recent token
 * any time the index is updated.  And future commands will only ask for
 * recent changes *since* that new token.  So as tokens advance into the
 * future, older batch items will never be requested/needed.  So we can
 * truncate them without loss of functionality.
 *
 * However, multiple commands may be talking to the daemon concurrently
 * or perform a slow command, so a little "token skew" is possible.
 * Therefore, we want this to be a little bit lazy and have a generous
 * delay.
 *
 * The current reader thread walked backwards in time from `token->batch_head`
 * back to `batch_marker` somewhere in the middle of the batch list.
 *
 * Let's walk backwards in time from that marker an arbitrary delay
 * and truncate the list there.  Note that these timestamps are completely
 * artificial (based on when we pinned the batch item) and not on any
 * filesystem activity.
 *
 * Return the obsolete portion of the list after we have removed it from
 * the official list so that the caller can free it after leaving the lock.
 */
#define MY_TIME_DELAY_SECONDS (5 * 60) /* seconds */

static struct fsmonitor_batch *with_lock__truncate_old_batches(
	struct fsmonitor_daemon_state *state,
	const struct fsmonitor_batch *batch_marker)
{
	/* assert current thread holding state->main_lock */

	const struct fsmonitor_batch *batch;
	struct fsmonitor_batch *remainder;

	if (!batch_marker)
		return NULL;

	trace_printf_key(&trace_fsmonitor, "Truncate: mark (%"PRIu64",%"PRIu64")",
			 batch_marker->batch_seq_nr,
			 (uint64_t)batch_marker->pinned_time);

	for (batch = batch_marker; batch; batch = batch->next) {
		time_t t;

		if (!batch->pinned_time) /* an overflow batch */
			continue;

		t = batch->pinned_time + MY_TIME_DELAY_SECONDS;
		if (t > batch_marker->pinned_time) /* too close to marker */
			continue;

		goto truncate_past_here;
	}

	return NULL;

truncate_past_here:
	state->current_token_data->batch_tail = (struct fsmonitor_batch *)batch;

	remainder = ((struct fsmonitor_batch *)batch)->next;
	((struct fsmonitor_batch *)batch)->next = NULL;

	return remainder;
}

static void fsmonitor_free_token_data(struct fsmonitor_token_data *token)
{
	if (!token)
		return;

	assert(token->client_ref_count == 0);

	strbuf_release(&token->token_id);

	fsmonitor_batch__free_list(token->batch_head);

	free(token);
}

/*
 * Flush all of our cached data about the filesystem.  Call this if we
 * lose sync with the filesystem and miss some notification events.
 *
 * [1] If we are missing events, then we no longer have a complete
 *     history of the directory (relative to our current start token).
 *     We should create a new token and start fresh (as if we just
 *     booted up).
 *
 * [2] Some of those lost events may have been for cookie files.  We
 *     should assume the worst and abort them rather letting them starve.
 *
 * If there are no concurrent threads reading the current token data
 * series, we can free it now.  Otherwise, let the last reader free
 * it.
 *
 * Either way, the old token data series is no longer associated with
 * our state data.
 */
static void with_lock__do_force_resync(struct fsmonitor_daemon_state *state)
{
	/* assert current thread holding state->main_lock */

	struct fsmonitor_token_data *free_me = NULL;
	struct fsmonitor_token_data *new_one = NULL;

	new_one = fsmonitor_new_token_data();

	if (state->current_token_data->client_ref_count == 0)
		free_me = state->current_token_data;
	state->current_token_data = new_one;

	fsmonitor_free_token_data(free_me);

	with_lock__abort_all_cookies(state);
}

void fsmonitor_force_resync(struct fsmonitor_daemon_state *state)
{
	pthread_mutex_lock(&state->main_lock);
	with_lock__do_force_resync(state);
	pthread_mutex_unlock(&state->main_lock);
}

/*
 * Format an opaque token string to send to the client.
 */
static void with_lock__format_response_token(
	struct strbuf *response_token,
	const struct strbuf *response_token_id,
	const struct fsmonitor_batch *batch)
{
	/* assert current thread holding state->main_lock */

	strbuf_reset(response_token);
	strbuf_addf(response_token, "builtin:%s:%"PRIu64,
		    response_token_id->buf, batch->batch_seq_nr);
}

/*
 * Parse an opaque token from the client.
 * Returns -1 on error.
 */
static int fsmonitor_parse_client_token(const char *buf_token,
					struct strbuf *requested_token_id,
					uint64_t *seq_nr)
{
	const char *p;
	char *p_end;

	strbuf_reset(requested_token_id);
	*seq_nr = 0;

	if (!skip_prefix(buf_token, "builtin:", &p))
		return -1;

	while (*p && *p != ':')
		strbuf_addch(requested_token_id, *p++);
	if (!*p++)
		return -1;

	*seq_nr = (uint64_t)strtoumax(p, &p_end, 10);
	if (*p_end)
		return -1;

	return 0;
}

KHASH_INIT(str, const char *, int, 0, kh_str_hash_func, kh_str_hash_equal)

static int do_handle_client(struct fsmonitor_daemon_state *state,
			    const char *command,
			    ipc_server_reply_cb *reply,
			    struct ipc_server_reply_data *reply_data)
{
	struct fsmonitor_token_data *token_data = NULL;
	struct strbuf response_token = STRBUF_INIT;
	struct strbuf requested_token_id = STRBUF_INIT;
	struct strbuf payload = STRBUF_INIT;
	uint64_t requested_oldest_seq_nr = 0;
	uint64_t total_response_len = 0;
	const char *p;
	const struct fsmonitor_batch *batch_head;
	const struct fsmonitor_batch *batch;
	struct fsmonitor_batch *remainder = NULL;
	intmax_t count = 0, duplicates = 0;
	kh_str_t *shown;
	int hash_ret;
	int do_trivial = 0;
	int do_flush = 0;
	int do_cookie = 0;
	enum fsmonitor_cookie_item_result cookie_result;

	/*
	 * We expect `command` to be of the form:
	 *
	 * <command> := quit NUL
	 *            | flush NUL
	 *            | <V1-time-since-epoch-ns> NUL
	 *            | <V2-opaque-fsmonitor-token> NUL
	 */

	if (!strcmp(command, "quit")) {
		/*
		 * A client has requested over the socket/pipe that the
		 * daemon shutdown.
		 *
		 * Tell the IPC thread pool to shutdown (which completes
		 * the await in the main thread (which can stop the
		 * fsmonitor listener thread)).
		 *
		 * There is no reply to the client.
		 */
		return SIMPLE_IPC_QUIT;

	} else if (!strcmp(command, "flush")) {
		/*
		 * Flush all of our cached data and generate a new token
		 * just like if we lost sync with the filesystem.
		 *
		 * Then send a trivial response using the new token.
		 */
		do_flush = 1;
		do_trivial = 1;

	} else if (!skip_prefix(command, "builtin:", &p)) {
		/* assume V1 timestamp or garbage */

		char *p_end;

		strtoumax(command, &p_end, 10);
		trace_printf_key(&trace_fsmonitor,
				 ((*p_end) ?
				  "fsmonitor: invalid command line '%s'" :
				  "fsmonitor: unsupported V1 protocol '%s'"),
				 command);
		do_trivial = 1;
		do_cookie = 1;

	} else {
		/* We have "builtin:*" */
		if (fsmonitor_parse_client_token(command, &requested_token_id,
						 &requested_oldest_seq_nr)) {
			trace_printf_key(&trace_fsmonitor,
					 "fsmonitor: invalid V2 protocol token '%s'",
					 command);
			do_trivial = 1;
			do_cookie = 1;

		} else {
			/*
			 * We have a V2 valid token:
			 *     "builtin:<token_id>:<seq_nr>"
			 */
			do_cookie = 1;
		}
	}

	pthread_mutex_lock(&state->main_lock);

	if (!state->current_token_data)
		BUG("fsmonitor state does not have a current token");

	/*
	 * Write a cookie file inside the directory being watched in
	 * an effort to flush out existing filesystem events that we
	 * actually care about.  Suspend this client thread until we
	 * see the filesystem events for this cookie file.
	 *
	 * Creating the cookie lets us guarantee that our FS listener
	 * thread has drained the kernel queue and we are caught up
	 * with the kernel.
	 *
	 * If we cannot create the cookie (or otherwise guarantee that
	 * we are caught up), we send a trivial response.  We have to
	 * assume that there might be some very, very recent activity
	 * on the FS still in flight.
	 */
	if (do_cookie) {
		cookie_result = with_lock__wait_for_cookie(state);
		if (cookie_result != FCIR_SEEN) {
			error(_("fsmonitor: cookie_result '%d' != SEEN"),
			      cookie_result);
			do_trivial = 1;
		}
	}

	if (do_flush)
		with_lock__do_force_resync(state);

	/*
	 * We mark the current head of the batch list as "pinned" so
	 * that the listener thread will treat this item as read-only
	 * (and prevent any more paths from being added to it) from
	 * now on.
	 */
	token_data = state->current_token_data;
	batch_head = token_data->batch_head;
	((struct fsmonitor_batch *)batch_head)->pinned_time = time(NULL);

	/*
	 * FSMonitor Protocol V2 requires that we send a response header
	 * with a "new current token" and then all of the paths that changed
	 * since the "requested token".  We send the seq_nr of the just-pinned
	 * head batch so that future requests from a client will be relative
	 * to it.
	 */
	with_lock__format_response_token(&response_token,
					 &token_data->token_id, batch_head);

	reply(reply_data, response_token.buf, response_token.len + 1);
	total_response_len += response_token.len + 1;

	trace2_data_string("fsmonitor", the_repository, "response/token",
			   response_token.buf);
	trace_printf_key(&trace_fsmonitor, "response token: %s",
			 response_token.buf);

	if (!do_trivial) {
		if (strcmp(requested_token_id.buf, token_data->token_id.buf)) {
			/*
			 * The client last spoke to a different daemon
			 * instance -OR- the daemon had to resync with
			 * the filesystem (and lost events), so reject.
			 */
			trace2_data_string("fsmonitor", the_repository,
					   "response/token", "different");
			do_trivial = 1;

		} else if (requested_oldest_seq_nr <
			   token_data->batch_tail->batch_seq_nr) {
			/*
			 * The client wants older events than we have for
			 * this token_id.  This means that the end of our
			 * batch list was truncated and we cannot give the
			 * client a complete snapshot relative to their
			 * request.
			 */
			trace_printf_key(&trace_fsmonitor,
					 "client requested truncated data");
			do_trivial = 1;
		}
	}

	if (do_trivial) {
		pthread_mutex_unlock(&state->main_lock);

		reply(reply_data, "/", 2);

		trace2_data_intmax("fsmonitor", the_repository,
				   "response/trivial", 1);

		goto cleanup;
	}

	/*
	 * We're going to hold onto a pointer to the current
	 * token-data while we walk the list of batches of files.
	 * During this time, we will NOT be under the lock.
	 * So we ref-count it.
	 *
	 * This allows the listener thread to continue prepending
	 * new batches of items to the token-data (which we'll ignore).
	 *
	 * AND it allows the listener thread to do a token-reset
	 * (and install a new `current_token_data`).
	 */
	token_data->client_ref_count++;

	pthread_mutex_unlock(&state->main_lock);

	/*
	 * The client request is relative to the token that they sent,
	 * so walk the batch list backwards from the current head back
	 * to the batch (sequence number) they named.
	 *
	 * We use khash to de-dup the list of pathnames.
	 *
	 * NEEDSWORK: each batch contains a list of interned strings,
	 * so we only need to do pointer comparisons here to build the
	 * hash table.  Currently, we're still comparing the string
	 * values.
	 */
	shown = kh_init_str();
	for (batch = batch_head;
	     batch && batch->batch_seq_nr > requested_oldest_seq_nr;
	     batch = batch->next) {
		size_t k;

		for (k = 0; k < batch->nr; k++) {
			const char *s = batch->interned_paths[k];
			size_t s_len;

			if (kh_get_str(shown, s) != kh_end(shown))
				duplicates++;
			else {
				kh_put_str(shown, s, &hash_ret);

				trace_printf_key(&trace_fsmonitor,
						 "send[%"PRIuMAX"]: %s",
						 count, s);

				/* Each path gets written with a trailing NUL */
				s_len = strlen(s) + 1;

				if (payload.len + s_len >=
				    LARGE_PACKET_DATA_MAX) {
					reply(reply_data, payload.buf,
					      payload.len);
					total_response_len += payload.len;
					strbuf_reset(&payload);
				}

				strbuf_add(&payload, s, s_len);
				count++;
			}
		}
	}

	if (payload.len) {
		reply(reply_data, payload.buf, payload.len);
		total_response_len += payload.len;
	}

	kh_release_str(shown);

	pthread_mutex_lock(&state->main_lock);

	if (token_data->client_ref_count > 0)
		token_data->client_ref_count--;

	if (token_data->client_ref_count == 0) {
		if (token_data != state->current_token_data) {
			/*
			 * The listener thread did a token-reset while we were
			 * walking the batch list.  Therefore, this token is
			 * stale and can be discarded completely.  If we are
			 * the last reader thread using this token, we own
			 * that work.
			 */
			fsmonitor_free_token_data(token_data);
		} else if (batch) {
			/*
			 * We are holding the lock and are the only
			 * reader of the ref-counted portion of the
			 * list, so we get the honor of seeing if the
			 * list can be truncated to save memory.
			 *
			 * The main loop did not walk to the end of the
			 * list, so this batch is the first item in the
			 * batch-list that is older than the requested
			 * end-point sequence number.  See if the tail
			 * end of the list is obsolete.
			 */
			remainder = with_lock__truncate_old_batches(state,
								    batch);
		}
	}

	pthread_mutex_unlock(&state->main_lock);

	if (remainder)
		fsmonitor_batch__free_list(remainder);

	trace2_data_intmax("fsmonitor", the_repository, "response/length", total_response_len);
	trace2_data_intmax("fsmonitor", the_repository, "response/count/files", count);
	trace2_data_intmax("fsmonitor", the_repository, "response/count/duplicates", duplicates);

cleanup:
	strbuf_release(&response_token);
	strbuf_release(&requested_token_id);
	strbuf_release(&payload);

	return 0;
}

static ipc_server_application_cb handle_client;

static int handle_client(void *data,
			 const char *command, size_t command_len,
			 ipc_server_reply_cb *reply,
			 struct ipc_server_reply_data *reply_data)
{
	struct fsmonitor_daemon_state *state = data;
	int result;

	/*
	 * The Simple IPC API now supports {char*, len} arguments, but
	 * FSMonitor always uses proper null-terminated strings, so
	 * we can ignore the command_len argument.  (Trust, but verify.)
	 */
	if (command_len != strlen(command))
		BUG("FSMonitor assumes text messages");

	trace_printf_key(&trace_fsmonitor, "requested token: %s", command);

	trace2_region_enter("fsmonitor", "handle_client", the_repository);
	trace2_data_string("fsmonitor", the_repository, "request", command);

	result = do_handle_client(state, command, reply, reply_data);

	trace2_region_leave("fsmonitor", "handle_client", the_repository);

	return result;
}

#define FSMONITOR_DIR           "fsmonitor--daemon"
#define FSMONITOR_COOKIE_DIR    "cookies"
#define FSMONITOR_COOKIE_PREFIX (FSMONITOR_DIR "/" FSMONITOR_COOKIE_DIR "/")

enum fsmonitor_path_type fsmonitor_classify_path_workdir_relative(
	const char *rel)
{
	if (fspathncmp(rel, ".git", 4))
		return IS_WORKDIR_PATH;
	rel += 4;

	if (!*rel)
		return IS_DOT_GIT;
	if (*rel != '/')
		return IS_WORKDIR_PATH; /* e.g. .gitignore */
	rel++;

	if (!fspathncmp(rel, FSMONITOR_COOKIE_PREFIX,
			strlen(FSMONITOR_COOKIE_PREFIX)))
		return IS_INSIDE_DOT_GIT_WITH_COOKIE_PREFIX;

	return IS_INSIDE_DOT_GIT;
}

enum fsmonitor_path_type fsmonitor_classify_path_gitdir_relative(
	const char *rel)
{
	if (!fspathncmp(rel, FSMONITOR_COOKIE_PREFIX,
			strlen(FSMONITOR_COOKIE_PREFIX)))
		return IS_INSIDE_GITDIR_WITH_COOKIE_PREFIX;

	return IS_INSIDE_GITDIR;
}

static enum fsmonitor_path_type try_classify_workdir_abs_path(
	struct fsmonitor_daemon_state *state,
	const char *path)
{
	const char *rel;

	if (fspathncmp(path, state->path_worktree_watch.buf,
		       state->path_worktree_watch.len))
		return IS_OUTSIDE_CONE;

	rel = path + state->path_worktree_watch.len;

	if (!*rel)
		return IS_WORKDIR_PATH; /* it is the root dir exactly */
	if (*rel != '/')
		return IS_OUTSIDE_CONE;
	rel++;

	return fsmonitor_classify_path_workdir_relative(rel);
}

enum fsmonitor_path_type fsmonitor_classify_path_absolute(
	struct fsmonitor_daemon_state *state,
	const char *path)
{
	const char *rel;
	enum fsmonitor_path_type t;

	t = try_classify_workdir_abs_path(state, path);
	if (state->nr_paths_watching == 1)
		return t;
	if (t != IS_OUTSIDE_CONE)
		return t;

	if (fspathncmp(path, state->path_gitdir_watch.buf,
		       state->path_gitdir_watch.len))
		return IS_OUTSIDE_CONE;

	rel = path + state->path_gitdir_watch.len;

	if (!*rel)
		return IS_GITDIR; /* it is the <gitdir> exactly */
	if (*rel != '/')
		return IS_OUTSIDE_CONE;
	rel++;

	return fsmonitor_classify_path_gitdir_relative(rel);
}

/*
 * We try to combine small batches at the front of the batch-list to avoid
 * having a long list.  This hopefully makes it a little easier when we want
 * to truncate and maintain the list.  However, we don't want the paths array
 * to just keep growing and growing with realloc, so we insert an arbitrary
 * limit.
 */
#define MY_COMBINE_LIMIT (1024)

void fsmonitor_publish(struct fsmonitor_daemon_state *state,
		       struct fsmonitor_batch *batch,
		       const struct string_list *cookie_names)
{
	if (!batch && !cookie_names->nr)
		return;

	pthread_mutex_lock(&state->main_lock);

	if (batch) {
		struct fsmonitor_batch *head;

		head = state->current_token_data->batch_head;
		if (!head) {
			BUG("token does not have batch");
		} else if (head->pinned_time) {
			/*
			 * We cannot alter the current batch list
			 * because:
			 *
			 * [a] it is being transmitted to at least one
			 * client and the handle_client() thread has a
			 * ref-count, but not a lock on the batch list
			 * starting with this item.
			 *
			 * [b] it has been transmitted in the past to
			 * at least one client such that future
			 * requests are relative to this head batch.
			 *
			 * So, we can only prepend a new batch onto
			 * the front of the list.
			 */
			batch->batch_seq_nr = head->batch_seq_nr + 1;
			batch->next = head;
			state->current_token_data->batch_head = batch;
		} else if (!head->batch_seq_nr) {
			/*
			 * Batch 0 is unpinned.  See the note in
			 * `fsmonitor_new_token_data()` about why we
			 * don't need to accumulate these paths.
			 */
			fsmonitor_batch__free_list(batch);
		} else if (head->nr + batch->nr > MY_COMBINE_LIMIT) {
			/*
			 * The head batch in the list has never been
			 * transmitted to a client, but folding the
			 * contents of the new batch onto it would
			 * exceed our arbitrary limit, so just prepend
			 * the new batch onto the list.
			 */
			batch->batch_seq_nr = head->batch_seq_nr + 1;
			batch->next = head;
			state->current_token_data->batch_head = batch;
		} else {
			/*
			 * We are free to add the paths in the given
			 * batch onto the end of the current head batch.
			 */
			fsmonitor_batch__combine(head, batch);
			fsmonitor_batch__free_list(batch);
		}
	}

	if (cookie_names->nr)
		with_lock__mark_cookies_seen(state, cookie_names);

	pthread_mutex_unlock(&state->main_lock);
}

static void *fsm_health__thread_proc(void *_state)
{
	struct fsmonitor_daemon_state *state = _state;

	trace2_thread_start("fsm-health");

	fsm_health__loop(state);

	trace2_thread_exit();
	return NULL;
}

static void *fsm_listen__thread_proc(void *_state)
{
	struct fsmonitor_daemon_state *state = _state;

	trace2_thread_start("fsm-listen");

	trace_printf_key(&trace_fsmonitor, "Watching: worktree '%s'",
			 state->path_worktree_watch.buf);
	if (state->nr_paths_watching > 1)
		trace_printf_key(&trace_fsmonitor, "Watching: gitdir '%s'",
				 state->path_gitdir_watch.buf);

	fsm_listen__loop(state);

	pthread_mutex_lock(&state->main_lock);
	if (state->current_token_data &&
	    state->current_token_data->client_ref_count == 0)
		fsmonitor_free_token_data(state->current_token_data);
	state->current_token_data = NULL;
	pthread_mutex_unlock(&state->main_lock);

	trace2_thread_exit();
	return NULL;
}

static int fsmonitor_run_daemon_1(struct fsmonitor_daemon_state *state)
{
	struct ipc_server_opts ipc_opts = {
		.nr_threads = fsmonitor__ipc_threads,

		/*
		 * We know that there are no other active threads yet,
		 * so we can let the IPC layer temporarily chdir() if
		 * it needs to when creating the server side of the
		 * Unix domain socket.
		 */
		.uds_disallow_chdir = 0
	};
	int health_started = 0;
	int listener_started = 0;
	int err = 0;

	/*
	 * Start the IPC thread pool before the we've started the file
	 * system event listener thread so that we have the IPC handle
	 * before we need it.
	 */
	if (ipc_server_run_async(&state->ipc_server_data,
				 state->path_ipc.buf, &ipc_opts,
				 handle_client, state))
		return error_errno(
			_("could not start IPC thread pool on '%s'"),
			state->path_ipc.buf);

	/*
	 * Start the fsmonitor listener thread to collect filesystem
	 * events.
	 */
	if (pthread_create(&state->listener_thread, NULL,
			   fsm_listen__thread_proc, state)) {
		ipc_server_stop_async(state->ipc_server_data);
		err = error(_("could not start fsmonitor listener thread"));
		goto cleanup;
	}
	listener_started = 1;

	/*
	 * Start the health thread to watch over our process.
	 */
	if (pthread_create(&state->health_thread, NULL,
			   fsm_health__thread_proc, state)) {
		ipc_server_stop_async(state->ipc_server_data);
		err = error(_("could not start fsmonitor health thread"));
		goto cleanup;
	}
	health_started = 1;

	/*
	 * The daemon is now fully functional in background threads.
	 * Our primary thread should now just wait while the threads
	 * do all the work.
	 */
cleanup:
	/*
	 * Wait for the IPC thread pool to shutdown (whether by client
	 * request, from filesystem activity, or an error).
	 */
	ipc_server_await(state->ipc_server_data);

	/*
	 * The fsmonitor listener thread may have received a shutdown
	 * event from the IPC thread pool, but it doesn't hurt to tell
	 * it again.  And wait for it to shutdown.
	 */
	if (listener_started) {
		fsm_listen__stop_async(state);
		pthread_join(state->listener_thread, NULL);
	}

	if (health_started) {
		fsm_health__stop_async(state);
		pthread_join(state->health_thread, NULL);
	}

	if (err)
		return err;
	if (state->listen_error_code)
		return state->listen_error_code;
	if (state->health_error_code)
		return state->health_error_code;
	return 0;
}

static int fsmonitor_run_daemon(void)
{
	struct fsmonitor_daemon_state state;
	const char *home;
	int err;

	memset(&state, 0, sizeof(state));

	hashmap_init(&state.cookies, cookies_cmp, NULL, 0);
	pthread_mutex_init(&state.main_lock, NULL);
	pthread_cond_init(&state.cookies_cond, NULL);
	state.listen_error_code = 0;
	state.health_error_code = 0;
	state.current_token_data = fsmonitor_new_token_data();

	/* Prepare to (recursively) watch the <worktree-root> directory. */
	strbuf_init(&state.path_worktree_watch, 0);
	strbuf_addstr(&state.path_worktree_watch, absolute_path(get_git_work_tree()));
	state.nr_paths_watching = 1;

	strbuf_init(&state.alias.alias, 0);
	strbuf_init(&state.alias.points_to, 0);
	if ((err = fsmonitor__get_alias(state.path_worktree_watch.buf, &state.alias)))
		goto done;

	/*
	 * We create and delete cookie files somewhere inside the .git
	 * directory to help us keep sync with the file system.  If
	 * ".git" is not a directory, then <gitdir> is not inside the
	 * cone of <worktree-root>, so set up a second watch to watch
	 * the <gitdir> so that we get events for the cookie files.
	 */
	strbuf_init(&state.path_gitdir_watch, 0);
	strbuf_addbuf(&state.path_gitdir_watch, &state.path_worktree_watch);
	strbuf_addstr(&state.path_gitdir_watch, "/.git");
	if (!is_directory(state.path_gitdir_watch.buf)) {
		strbuf_reset(&state.path_gitdir_watch);
		strbuf_addstr(&state.path_gitdir_watch, absolute_path(get_git_dir()));
		state.nr_paths_watching = 2;
	}

	/*
	 * We will write filesystem syncing cookie files into
	 * <gitdir>/<fsmonitor-dir>/<cookie-dir>/<pid>-<seq>.
	 *
	 * The extra layers of subdirectories here keep us from
	 * changing the mtime on ".git/" or ".git/foo/" when we create
	 * or delete cookie files.
	 *
	 * There have been problems with some IDEs that do a
	 * non-recursive watch of the ".git/" directory and run a
	 * series of commands any time something happens.
	 *
	 * For example, if we place our cookie files directly in
	 * ".git/" or ".git/foo/" then a `git status` (or similar
	 * command) from the IDE will cause a cookie file to be
	 * created in one of those dirs.  This causes the mtime of
	 * those dirs to change.  This triggers the IDE's watch
	 * notification.  This triggers the IDE to run those commands
	 * again.  And the process repeats and the machine never goes
	 * idle.
	 *
	 * Adding the extra layers of subdirectories prevents the
	 * mtime of ".git/" and ".git/foo" from changing when a
	 * cookie file is created.
	 */
	strbuf_init(&state.path_cookie_prefix, 0);
	strbuf_addbuf(&state.path_cookie_prefix, &state.path_gitdir_watch);

	strbuf_addch(&state.path_cookie_prefix, '/');
	strbuf_addstr(&state.path_cookie_prefix, FSMONITOR_DIR);
	mkdir(state.path_cookie_prefix.buf, 0777);

	strbuf_addch(&state.path_cookie_prefix, '/');
	strbuf_addstr(&state.path_cookie_prefix, FSMONITOR_COOKIE_DIR);
	mkdir(state.path_cookie_prefix.buf, 0777);

	strbuf_addch(&state.path_cookie_prefix, '/');

	/*
	 * We create a named-pipe or unix domain socket inside of the
	 * ".git" directory.  (Well, on Windows, we base our named
	 * pipe in the NPFS on the absolute path of the git
	 * directory.)
	 */
	strbuf_init(&state.path_ipc, 0);
	strbuf_addstr(&state.path_ipc,
		absolute_path(fsmonitor_ipc__get_path(the_repository)));

	/*
	 * Confirm that we can create platform-specific resources for the
	 * filesystem listener before we bother starting all the threads.
	 */
	if (fsm_listen__ctor(&state)) {
		err = error(_("could not initialize listener thread"));
		goto done;
	}

	if (fsm_health__ctor(&state)) {
		err = error(_("could not initialize health thread"));
		goto done;
	}

	/*
	 * CD out of the worktree root directory.
	 *
	 * The common Git startup mechanism causes our CWD to be the
	 * root of the worktree.  On Windows, this causes our process
	 * to hold a locked handle on the CWD.  This prevents the
	 * worktree from being moved or deleted while the daemon is
	 * running.
	 *
	 * We assume that our FS and IPC listener threads have either
	 * opened all of the handles that they need or will do
	 * everything using absolute paths.
	 */
	home = getenv("HOME");
	if (home && *home && chdir(home))
		die_errno(_("could not cd home '%s'"), home);

	err = fsmonitor_run_daemon_1(&state);

done:
	pthread_cond_destroy(&state.cookies_cond);
	pthread_mutex_destroy(&state.main_lock);
	fsm_listen__dtor(&state);
	fsm_health__dtor(&state);

	ipc_server_free(state.ipc_server_data);

	strbuf_release(&state.path_worktree_watch);
	strbuf_release(&state.path_gitdir_watch);
	strbuf_release(&state.path_cookie_prefix);
	strbuf_release(&state.path_ipc);
	strbuf_release(&state.alias.alias);
	strbuf_release(&state.alias.points_to);

	return err;
}

static int try_to_run_foreground_daemon(int detach_console MAYBE_UNUSED)
{
	/*
	 * Technically, we don't need to probe for an existing daemon
	 * process, since we could just call `fsmonitor_run_daemon()`
	 * and let it fail if the pipe/socket is busy.
	 *
	 * However, this method gives us a nicer error message for a
	 * common error case.
	 */
	if (fsmonitor_ipc__get_state() == IPC_STATE__LISTENING)
		die(_("fsmonitor--daemon is already running '%s'"),
		    the_repository->worktree);

	if (fsmonitor__announce_startup) {
		fprintf(stderr, _("running fsmonitor-daemon in '%s'\n"),
			the_repository->worktree);
		fflush(stderr);
	}

#ifdef GIT_WINDOWS_NATIVE
	if (detach_console)
		FreeConsole();
#endif

	return !!fsmonitor_run_daemon();
}

static start_bg_wait_cb bg_wait_cb;

static int bg_wait_cb(const struct child_process *cp UNUSED,
		      void *cb_data UNUSED)
{
	enum ipc_active_state s = fsmonitor_ipc__get_state();

	switch (s) {
	case IPC_STATE__LISTENING:
		/* child is "ready" */
		return 0;

	case IPC_STATE__NOT_LISTENING:
	case IPC_STATE__PATH_NOT_FOUND:
		/* give child more time */
		return 1;

	default:
	case IPC_STATE__INVALID_PATH:
	case IPC_STATE__OTHER_ERROR:
		/* all the time in world won't help */
		return -1;
	}
}

static int try_to_start_background_daemon(void)
{
	struct child_process cp = CHILD_PROCESS_INIT;
	enum start_bg_result sbgr;

	/*
	 * Before we try to create a background daemon process, see
	 * if a daemon process is already listening.  This makes it
	 * easier for us to report an already-listening error to the
	 * console, since our spawn/daemon can only report the success
	 * of creating the background process (and not whether it
	 * immediately exited).
	 */
	if (fsmonitor_ipc__get_state() == IPC_STATE__LISTENING)
		die(_("fsmonitor--daemon is already running '%s'"),
		    the_repository->worktree);

	if (fsmonitor__announce_startup) {
		fprintf(stderr, _("starting fsmonitor-daemon in '%s'\n"),
			the_repository->worktree);
		fflush(stderr);
	}

	cp.git_cmd = 1;

	strvec_push(&cp.args, "fsmonitor--daemon");
	strvec_push(&cp.args, "run");
	strvec_push(&cp.args, "--detach");
	strvec_pushf(&cp.args, "--ipc-threads=%d", fsmonitor__ipc_threads);

	cp.no_stdin = 1;
	cp.no_stdout = 1;
	cp.no_stderr = 1;

	sbgr = start_bg_command(&cp, bg_wait_cb, NULL,
				fsmonitor__start_timeout_sec);

	switch (sbgr) {
	case SBGR_READY:
		return 0;

	default:
	case SBGR_ERROR:
	case SBGR_CB_ERROR:
		return error(_("daemon failed to start"));

	case SBGR_TIMEOUT:
		return error(_("daemon not online yet"));

	case SBGR_DIED:
		return error(_("daemon terminated"));
	}
}

int cmd_fsmonitor__daemon(int argc, const char **argv, const char *prefix)
{
	const char *subcmd;
	enum fsmonitor_reason reason;
	int detach_console = 0;

	struct option options[] = {
		OPT_BOOL(0, "detach", &detach_console, N_("detach from console")),
		OPT_INTEGER(0, "ipc-threads",
			    &fsmonitor__ipc_threads,
			    N_("use <n> ipc worker threads")),
		OPT_INTEGER(0, "start-timeout",
			    &fsmonitor__start_timeout_sec,
			    N_("max seconds to wait for background daemon startup")),

		OPT_END()
	};

	git_config(fsmonitor_config, NULL);

	argc = parse_options(argc, argv, prefix, options,
			     builtin_fsmonitor__daemon_usage, 0);
	if (argc != 1)
		usage_with_options(builtin_fsmonitor__daemon_usage, options);
	subcmd = argv[0];

	if (fsmonitor__ipc_threads < 1)
		die(_("invalid 'ipc-threads' value (%d)"),
		    fsmonitor__ipc_threads);

	prepare_repo_settings(the_repository);
	/*
	 * If the repo is fsmonitor-compatible, explicitly set IPC-mode
	 * (without bothering to load the `core.fsmonitor` config settings).
	 *
	 * If the repo is not compatible, the repo-settings will be set to
	 * incompatible rather than IPC, so we can use one of the __get
	 * routines to detect the discrepancy.
	 */
	fsm_settings__set_ipc(the_repository);

	reason = fsm_settings__get_reason(the_repository);
	if (reason > FSMONITOR_REASON_OK)
		die("%s",
		    fsm_settings__get_incompatible_msg(the_repository,
						       reason));

	if (!strcmp(subcmd, "start"))
		return !!try_to_start_background_daemon();

	if (!strcmp(subcmd, "run"))
		return !!try_to_run_foreground_daemon(detach_console);

	if (!strcmp(subcmd, "stop"))
		return !!do_as_client__send_stop();

	if (!strcmp(subcmd, "status"))
		return !!do_as_client__status();

	die(_("Unhandled subcommand '%s'"), subcmd);
}

#else
int cmd_fsmonitor__daemon(int argc, const char **argv, const char *prefix UNUSED)
{
	struct option options[] = {
		OPT_END()
	};

	if (argc == 2 && !strcmp(argv[1], "-h"))
		usage_with_options(builtin_fsmonitor__daemon_usage, options);

	die(_("fsmonitor--daemon not supported on this platform"));
}
#endif