File: syncoid

package info (click to toggle)
sanoid 2.0.3-4
  • links: PTS, VCS
  • area: main
  • in suites: bullseye, sid
  • size: 592 kB
  • sloc: perl: 2,550; sh: 367; makefile: 25
file content (1819 lines) | stat: -rwxr-xr-x 64,415 bytes parent folder | download
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
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
#!/usr/bin/perl

# this software is licensed for use under the Free Software Foundation's GPL v3.0 license, as retrieved
# from http://www.gnu.org/licenses/gpl-3.0.html on 2014-11-17.  A copy should also be available in this
# project's Git repository at https://github.com/jimsalterjrs/sanoid/blob/master/LICENSE.

$::VERSION = '2.0.3';

use strict;
use warnings;
use Data::Dumper;
use Getopt::Long qw(:config auto_version auto_help);
use Pod::Usage;
use Time::Local;
use Sys::Hostname;
use Capture::Tiny ':all';

my $mbuffer_size = "16M";

# Blank defaults to use ssh client's default
# TODO: Merge into a single "sshflags" option?
my %args = ('sshkey' => '', 'sshport' => '', 'sshcipher' => '', 'sshoption' => [], 'target-bwlimit' => '', 'source-bwlimit' => '');
GetOptions(\%args, "no-command-checks", "monitor-version", "compress=s", "dumpsnaps", "recursive|r", "sendoptions=s", "recvoptions=s",
                   "source-bwlimit=s", "target-bwlimit=s", "sshkey=s", "sshport=i", "sshcipher|c=s", "sshoption|o=s@",
                   "debug", "quiet", "no-stream", "no-sync-snap", "no-resume", "exclude=s@", "skip-parent", "identifier=s",
                   "no-clone-handling", "no-privilege-elevation", "force-delete", "no-clone-rollback", "no-rollback",
                   "create-bookmark",
                   "mbuffer-size=s" => \$mbuffer_size) or pod2usage(2);

my %compressargs = %{compressargset($args{'compress'} || 'default')}; # Can't be done with GetOptions arg, as default still needs to be set

my @sendoptions = ();
if (length $args{'sendoptions'}) {
	@sendoptions = parsespecialoptions($args{'sendoptions'});
	if (! defined($sendoptions[0])) {
		warn "invalid send options!";
		pod2usage(2);
		exit 127;
	}
}

my @recvoptions = ();
if (length $args{'recvoptions'}) {
	@recvoptions = parsespecialoptions($args{'recvoptions'});
	if (! defined($recvoptions[0])) {
		warn "invalid receive options!";
		pod2usage(2);
		exit 127;
	}
}


# TODO Expand to accept multiple sources?
if (scalar(@ARGV) != 2) {
	print("Source or target not found!\n");
	pod2usage(2);
	exit 127;
} else {
	$args{'source'} = $ARGV[0];
	$args{'target'} = $ARGV[1];
}

# Could possibly merge these into an options function
if (length $args{'source-bwlimit'}) {
	$args{'source-bwlimit'} = "-R $args{'source-bwlimit'}";
}
if (length $args{'target-bwlimit'}) {
	$args{'target-bwlimit'} = "-r $args{'target-bwlimit'}";
}
$args{'streamarg'} = (defined $args{'no-stream'} ? '-i' : '-I');

my $rawsourcefs = $args{'source'};
my $rawtargetfs = $args{'target'};
my $debug = $args{'debug'};
my $quiet = $args{'quiet'};
my $resume = !$args{'no-resume'};

# for compatibility reasons, older versions used hardcoded command paths
$ENV{'PATH'} = $ENV{'PATH'} . ":/bin:/usr/bin:/sbin";

my $zfscmd = 'zfs';
my $zpoolcmd = 'zpool';
my $sshcmd = 'ssh';
my $pscmd = 'ps';

my $pvcmd = 'pv';
my $mbuffercmd = 'mbuffer';
my $sudocmd = 'sudo';
my $mbufferoptions = "-q -s 128k -m $mbuffer_size 2>/dev/null";
# currently using POSIX compatible command to check for program existence because we aren't depending on perl
# being present on remote machines.
my $checkcmd = 'command -v';

if (length $args{'sshcipher'}) {
	$args{'sshcipher'} = "-c $args{'sshcipher'}";
}
if (length $args{'sshport'}) {
  $args{'sshport'} = "-p $args{'sshport'}";
}
if (length $args{'sshkey'}) {
	$args{'sshkey'} = "-i $args{'sshkey'}";
}
my $sshoptions = join " ", map { "-o " . $_ } @{$args{'sshoption'}}; # deref required

my $identifier = "";
if (length $args{'identifier'}) {
	if ($args{'identifier'} !~ /^[a-zA-Z0-9-_:.]+$/) {
		# invalid extra identifier
		print("CRITICAL: extra identifier contains invalid chars!\n");
		pod2usage(2);
		exit 127;
	}
	$identifier = "$args{'identifier'}_";
}

# figure out if source and/or target are remote.
$sshcmd = "$sshcmd $args{'sshcipher'} $sshoptions $args{'sshport'} $args{'sshkey'}";
if ($debug) { print "DEBUG: SSHCMD: $sshcmd\n"; }
my ($sourcehost,$sourcefs,$sourceisroot) = getssh($rawsourcefs);
my ($targethost,$targetfs,$targetisroot) = getssh($rawtargetfs);

my $sourcesudocmd = $sourceisroot ? '' : $sudocmd;
my $targetsudocmd = $targetisroot ? '' : $sudocmd;

# figure out whether compression, mbuffering, pv
# are available on source, target, local machines.
# warn user of anything missing, then continue with sync.
my %avail = checkcommands();

my %snaps;
my $exitcode = 0;

## break here to call replication individually so that we ##
## can loop across children separately, for recursive     ##
## replication                                            ##

if (!defined $args{'recursive'}) {
	syncdataset($sourcehost, $sourcefs, $targethost, $targetfs, undef);
} else {
	if ($debug) { print "DEBUG: recursive sync of $sourcefs.\n"; }
	my @datasets = getchilddatasets($sourcehost, $sourcefs, $sourceisroot);

	if (!@datasets) {
		warn "CRITICAL ERROR: no datasets found";
		@datasets = ();
		$exitcode = 2;
	}

	my @deferred;

	foreach my $datasetProperties(@datasets) {
		my $dataset = $datasetProperties->{'name'};
		my $origin = $datasetProperties->{'origin'};
		if ($origin eq "-" || defined $args{'no-clone-handling'}) {
			$origin = undef;
		} else {
			# check if clone source is replicated too
			my @values = split(/@/, $origin, 2);
			my $srcdataset = $values[0];

			my $found = 0;
			foreach my $datasetProperties(@datasets) {
				if ($datasetProperties->{'name'} eq $srcdataset) {
					$found = 1;
					last;
				}
			}

			if ($found == 0) {
				# clone source is not replicated, do a full replication
				$origin = undef;
			} else {
				# clone source is replicated, defer until all non clones are replicated
				push @deferred, $datasetProperties;
				next;
			}
		}

		$dataset =~ s/\Q$sourcefs\E//;
		chomp $dataset;
		my $childsourcefs = $sourcefs . $dataset;
		my $childtargetfs = $targetfs . $dataset;
		# print "syncdataset($sourcehost, $childsourcefs, $targethost, $childtargetfs); \n";
		syncdataset($sourcehost, $childsourcefs, $targethost, $childtargetfs, $origin);
	}

	# replicate cloned datasets and if this is the initial run, recreate them on the target
	foreach my $datasetProperties(@deferred) {
		my $dataset = $datasetProperties->{'name'};
		my $origin = $datasetProperties->{'origin'};

		$dataset =~ s/\Q$sourcefs\E//;
		chomp $dataset;
		my $childsourcefs = $sourcefs . $dataset;
		my $childtargetfs = $targetfs . $dataset;
		syncdataset($sourcehost, $childsourcefs, $targethost, $childtargetfs, $origin);
	}
}

# close SSH sockets for master connections as applicable
if ($sourcehost ne '') {
	open FH, "$sshcmd $sourcehost -O exit 2>&1 |";
	close FH;
}
if ($targethost ne '') {
	open FH, "$sshcmd $targethost -O exit 2>&1 |";
	close FH;
}

exit $exitcode;

##############################################################################
##############################################################################
##############################################################################
##############################################################################

sub getchilddatasets {
	my ($rhost,$fs,$isroot,%snaps) = @_;
	my $mysudocmd;
	my $fsescaped = escapeshellparam($fs);

	if ($isroot) { $mysudocmd = ''; } else { $mysudocmd = $sudocmd; }
	if ($rhost ne '') {
		$rhost = "$sshcmd $rhost";
		# double escaping needed
		$fsescaped = escapeshellparam($fsescaped);
	}

	my $getchildrencmd = "$rhost $mysudocmd $zfscmd list -o name,origin -t filesystem,volume -Hr $fsescaped |";
	if ($debug) { print "DEBUG: getting list of child datasets on $fs using $getchildrencmd...\n"; }
	if (! open FH, $getchildrencmd) {
		die "ERROR: list command failed!\n";
	}

	my @children;
	my $first = 1;

	DATASETS: while(<FH>) {
		chomp;

		if (defined $args{'skip-parent'} && $first eq 1) {
			# parent dataset is the first element
			$first = 0;
			next;
		}

		my ($dataset, $origin) = /^([^\t]+)\t([^\t]+)/;

		if (defined $args{'exclude'}) {
			my $excludes = $args{'exclude'};
			foreach (@$excludes) {
				if ($dataset =~ /$_/) {
					if ($debug) { print "DEBUG: excluded $dataset because of $_\n"; }
					next DATASETS;
				}
			}
		}

		my %properties;
		$properties{'name'} = $dataset;
		$properties{'origin'} = $origin;

		push @children, \%properties;
	}
	close FH;

	return @children;
}

sub syncdataset {

	my ($sourcehost, $sourcefs, $targethost, $targetfs, $origin, $skipsnapshot) = @_;

	my $stdout;
	my $exit;

	my $sourcefsescaped = escapeshellparam($sourcefs);
	my $targetfsescaped = escapeshellparam($targetfs);

	# if no rollbacks are allowed, disable forced receive
	my $forcedrecv = "-F";
	if (defined $args{'no-rollback'}) {
		$forcedrecv = "";
	}

	if ($debug) { print "DEBUG: syncing source $sourcefs to target $targetfs.\n"; }

	my $sync = getzfsvalue($sourcehost,$sourcefs,$sourceisroot,'syncoid:sync');

	if (!defined $sync) {
		# zfs already printed the corresponding error
		if ($exitcode < 2) { $exitcode = 2; }
		return 0;
	}

	if ($sync eq 'true' || $sync eq '-' || $sync eq '') {
		# empty is handled the same as unset (aka: '-')
		# definitely sync this dataset - if a host is called 'true' or '-', then you're special
	} elsif ($sync eq 'false') {
		if (!$quiet) { print "INFO: Skipping dataset (syncoid:sync=false): $sourcefs...\n"; }
		return 0;
	} else {
		my $hostid = hostname();
		my @hosts = split(/,/,$sync);
		if (!(grep $hostid eq $_, @hosts)) {
			if (!$quiet) { print "INFO: Skipping dataset (syncoid:sync doesn't include $hostid): $sourcefs...\n"; }
			return 0;
		}
	}

	# make sure target is not currently in receive.
	if (iszfsbusy($targethost,$targetfs,$targetisroot)) {
		warn "Cannot sync now: $targetfs is already target of a zfs receive process.\n";
		if ($exitcode < 1) { $exitcode = 1; }
		return 0;
	}

	# does the target filesystem exist yet?
	my $targetexists = targetexists($targethost,$targetfs,$targetisroot);

	my $receiveextraargs = "";
	my $receivetoken;
	if ($resume) {
		# save state of interrupted receive stream
		$receiveextraargs = "-s";

		if ($targetexists) {
			# check remote dataset for receive resume token (interrupted receive)
			$receivetoken = getreceivetoken($targethost,$targetfs,$targetisroot);

			if ($debug && defined($receivetoken)) {
				print "DEBUG: got receive resume token: $receivetoken: \n";
			}
		}
	}

	my $newsyncsnap;

	# skip snapshot checking/creation in case of resumed receive
	if (!defined($receivetoken)) {
		# build hashes of the snaps on the source and target filesystems.

		%snaps = getsnaps('source',$sourcehost,$sourcefs,$sourceisroot);

		if ($targetexists) {
		    my %targetsnaps = getsnaps('target',$targethost,$targetfs,$targetisroot);
		    my %sourcesnaps = %snaps;
		    %snaps = (%sourcesnaps, %targetsnaps);
		}

		if (defined $args{'dumpsnaps'}) {
		    print "merged snapshot list of $targetfs: \n";
		    dumphash(\%snaps);
		    print "\n\n\n";
		}

		if (!defined $args{'no-sync-snap'} && !defined $skipsnapshot) {
			# create a new syncoid snapshot on the source filesystem.
			$newsyncsnap = newsyncsnap($sourcehost,$sourcefs,$sourceisroot);
			if (!$newsyncsnap) {
				# we already whined about the error
				return 0;
			}
		} else {
			# we don't want sync snapshots created, so use the newest snapshot we can find.
			$newsyncsnap = getnewestsnapshot($sourcehost,$sourcefs,$sourceisroot);
			if ($newsyncsnap eq 0) {
				warn "CRITICAL: no snapshots exist on source $sourcefs, and you asked for --no-sync-snap.\n";
				if ($exitcode < 1) { $exitcode = 1; }
				return 0;
			}
		}
	}
	my $newsyncsnapescaped = escapeshellparam($newsyncsnap);

	# there is currently (2014-09-01) a bug in ZFS on Linux
	# that causes readonly to always show on if it's EVER
	# been turned on... even when it's off... unless and
	# until the filesystem is zfs umounted and zfs remounted.
	# we're going to do the right thing anyway.
		# dyking this functionality out for the time being due to buggy mount/unmount behavior
		# with ZFS on Linux (possibly OpenZFS in general) when setting/unsetting readonly.
	#my $originaltargetreadonly;

	my $sendoptions = getoptionsline(\@sendoptions, ('D','L','P','R','c','e','h','p','v','w'));
	my $recvoptions = getoptionsline(\@recvoptions, ('h','o','x','u','v'));

	# sync 'em up.
	if (! $targetexists) {
		# do an initial sync from the oldest source snapshot
		# THEN do an -I to the newest
		if ($debug) {
			if (!defined ($args{'no-stream'}) ) {
				print "DEBUG: target $targetfs does not exist.  Finding oldest available snapshot on source $sourcefs ...\n";
			} else {
				print "DEBUG: target $targetfs does not exist, and --no-stream selected.  Finding newest available snapshot on source $sourcefs ...\n";
			}
		}
		my $oldestsnap = getoldestsnapshot(\%snaps);
		if (! $oldestsnap) {
			if (defined ($args{'no-sync-snap'}) ) {
				# we already whined about the missing snapshots
				return 0;
			}

			# getoldestsnapshot() returned false, so use new sync snapshot
			if ($debug) { print "DEBUG: getoldestsnapshot() returned false, so using $newsyncsnap.\n"; }
			$oldestsnap = $newsyncsnap;
		}

		# if --no-stream is specified, our full needs to be the newest snapshot, not the oldest.
		if (defined $args{'no-stream'}) {
			if (defined ($args{'no-sync-snap'}) ) {
				$oldestsnap = getnewestsnapshot(\%snaps);
			} else {
				$oldestsnap = $newsyncsnap;
			}
		}
		my $oldestsnapescaped = escapeshellparam($oldestsnap);

		my $sendcmd = "$sourcesudocmd $zfscmd send $sendoptions $sourcefsescaped\@$oldestsnapescaped";
		my $recvcmd = "$targetsudocmd $zfscmd receive $recvoptions $receiveextraargs $forcedrecv $targetfsescaped";

		my $pvsize;
		if (defined $origin) {
			my $originescaped = escapeshellparam($origin);
			$sendcmd = "$sourcesudocmd $zfscmd send $sendoptions -i $originescaped $sourcefsescaped\@$oldestsnapescaped";
			my $streamargBackup = $args{'streamarg'};
			$args{'streamarg'} = "-i";
			$pvsize = getsendsize($sourcehost,$origin,"$sourcefs\@$oldestsnap",$sourceisroot);
			$args{'streamarg'} = $streamargBackup;
		} else {
			$pvsize = getsendsize($sourcehost,"$sourcefs\@$oldestsnap",0,$sourceisroot);
		}

		my $disp_pvsize = readablebytes($pvsize);
		if ($pvsize == 0) { $disp_pvsize = 'UNKNOWN'; }
		my $synccmd = buildsynccmd($sendcmd,$recvcmd,$pvsize,$sourceisroot,$targetisroot);
		if (!$quiet) {
			if (defined $origin) {
				print "INFO: Clone is recreated on target $targetfs based on $origin\n";
			}
			if (!defined ($args{'no-stream'}) ) {
				print "INFO: Sending oldest full snapshot $sourcefs\@$oldestsnap (~ $disp_pvsize) to new target filesystem:\n";
			} else {
				print "INFO: --no-stream selected; sending newest full snapshot $sourcefs\@$oldestsnap (~ $disp_pvsize) to new target filesystem:\n";
			}
		}
		if ($debug) { print "DEBUG: $synccmd\n"; }

		# make sure target is (still) not currently in receive.
		if (iszfsbusy($targethost,$targetfs,$targetisroot)) {
			warn "Cannot sync now: $targetfs is already target of a zfs receive process.\n";
			if ($exitcode < 1) { $exitcode = 1; }
			return 0;
		}
		system($synccmd) == 0 or do {
			if (defined $origin) {
				print "INFO: clone creation failed, trying ordinary replication as fallback\n";
				syncdataset($sourcehost, $sourcefs, $targethost, $targetfs, undef, 1);
				return 0;
			}

			warn "CRITICAL ERROR: $synccmd failed: $?";
			if ($exitcode < 2) { $exitcode = 2; }
			return 0;
		};

		# now do an -I to the new sync snapshot, assuming there were any snapshots
		# other than the new sync snapshot to begin with, of course - and that we
		# aren't invoked with --no-stream, in which case a full of the newest snap
		# available was all we needed to do
		if (!defined ($args{'no-stream'}) && ($oldestsnap ne $newsyncsnap) ) {

			# get current readonly status of target, then set it to on during sync
				# dyking this functionality out for the time being due to buggy mount/unmount behavior
				# with ZFS on Linux (possibly OpenZFS in general) when setting/unsetting readonly.
			# $originaltargetreadonly = getzfsvalue($targethost,$targetfs,$targetisroot,'readonly');
			# setzfsvalue($targethost,$targetfs,$targetisroot,'readonly','on');

			$sendcmd = "$sourcesudocmd $zfscmd send $sendoptions $args{'streamarg'} $sourcefsescaped\@$oldestsnapescaped $sourcefsescaped\@$newsyncsnapescaped";
			$pvsize = getsendsize($sourcehost,"$sourcefs\@$oldestsnap","$sourcefs\@$newsyncsnap",$sourceisroot);
			$disp_pvsize = readablebytes($pvsize);
			if ($pvsize == 0) { $disp_pvsize = "UNKNOWN"; }
			$synccmd = buildsynccmd($sendcmd,$recvcmd,$pvsize,$sourceisroot,$targetisroot);

			# make sure target is (still) not currently in receive.
			if (iszfsbusy($targethost,$targetfs,$targetisroot)) {
				warn "Cannot sync now: $targetfs is already target of a zfs receive process.\n";
				if ($exitcode < 1) { $exitcode = 1; }
				return 0;
			}

			if (!$quiet) { print "INFO: Updating new target filesystem with incremental $sourcefs\@$oldestsnap ... $newsyncsnap (~ $disp_pvsize):\n"; }
			if ($debug) { print "DEBUG: $synccmd\n"; }

			if ($oldestsnap ne $newsyncsnap) {
				my $ret = system($synccmd);
				if ($ret != 0) {
					warn "CRITICAL ERROR: $synccmd failed: $?";
					if ($exitcode < 1) { $exitcode = 1; }
					return 0;
				}
			} else {
				if (!$quiet) { print "INFO: no incremental sync needed; $oldestsnap is already the newest available snapshot.\n"; }
			}

			# restore original readonly value to target after sync complete
				# dyking this functionality out for the time being due to buggy mount/unmount behavior
				# with ZFS on Linux (possibly OpenZFS in general) when setting/unsetting readonly.
			# setzfsvalue($targethost,$targetfs,$targetisroot,'readonly',$originaltargetreadonly);
		}
	} else {
		# resume interrupted receive if there is a valid resume $token
		# and because this will ony resume the receive to the next
		# snapshot, do a normal sync after that
		if (defined($receivetoken)) {
			$sendoptions = getoptionsline(\@sendoptions, ('P','e','v','w'));
			my $sendcmd = "$sourcesudocmd $zfscmd send $sendoptions -t $receivetoken";
			my $recvcmd = "$targetsudocmd $zfscmd receive $recvoptions $receiveextraargs $forcedrecv $targetfsescaped 2>&1";
			my $pvsize = getsendsize($sourcehost,"","",$sourceisroot,$receivetoken);
			my $disp_pvsize = readablebytes($pvsize);
			if ($pvsize == 0) { $disp_pvsize = "UNKNOWN"; }
			my $synccmd = buildsynccmd($sendcmd,$recvcmd,$pvsize,$sourceisroot,$targetisroot);

			if (!$quiet) { print "Resuming interrupted zfs send/receive from $sourcefs to $targetfs (~ $disp_pvsize remaining):\n"; }
			if ($debug) { print "DEBUG: $synccmd\n"; }

			if ($pvsize == 0) {
				# we need to capture the error of zfs send, this will render pv useless but in this case
				# it doesn't matter because we don't know the estimated send size (probably because
				# the initial snapshot used for resumed send doesn't exist anymore)
				($stdout, $exit) = tee_stderr {
					system("$synccmd")
				};
			} else {
				($stdout, $exit) = tee_stdout {
					system("$synccmd")
				};
			}

			$exit == 0 or do {
				if ($stdout =~ /\Qused in the initial send no longer exists\E/) {
					if (!$quiet) { print "WARN: resetting partially receive state because the snapshot source no longer exists\n"; }
					resetreceivestate($targethost,$targetfs,$targetisroot);
					# do an normal sync cycle
					return syncdataset($sourcehost, $sourcefs, $targethost, $targetfs, $origin);
				} else {
					warn "CRITICAL ERROR: $synccmd failed: $?";
					if ($exitcode < 2) { $exitcode = 2; }
					return 0;
				}
			};

			# a resumed transfer will only be done to the next snapshot,
			# so do an normal sync cycle
			return syncdataset($sourcehost, $sourcefs, $targethost, $targetfs, undef);
		}

		# find most recent matching snapshot and do an -I
		# to the new snapshot

		# get current readonly status of target, then set it to on during sync
			# dyking this functionality out for the time being due to buggy mount/unmount behavior
			# with ZFS on Linux (possibly OpenZFS in general) when setting/unsetting readonly.
		# $originaltargetreadonly = getzfsvalue($targethost,$targetfs,$targetisroot,'readonly');
		# setzfsvalue($targethost,$targetfs,$targetisroot,'readonly','on');

		my $targetsize = getzfsvalue($targethost,$targetfs,$targetisroot,'-p used');

		my $bookmark = 0;
		my $bookmarkcreation = 0;

		my $matchingsnap = getmatchingsnapshot($sourcefs, $targetfs, \%snaps);
		if (! $matchingsnap) {
			# no matching snapshots, check for bookmarks as fallback
			my %bookmarks = getbookmarks($sourcehost,$sourcefs,$sourceisroot);

			# check for matching guid of source bookmark and target snapshot (oldest first)
			foreach my $snap ( sort { $snaps{'target'}{$b}{'creation'}<=>$snaps{'target'}{$a}{'creation'} } keys %{ $snaps{'target'} }) {
				my $guid = $snaps{'target'}{$snap}{'guid'};

				if (defined $bookmarks{$guid}) {
					# found a match
					$bookmark = $bookmarks{$guid}{'name'};
					$bookmarkcreation = $bookmarks{$guid}{'creation'};
					$matchingsnap = $snap;
					last;
				}
			}

			if (! $bookmark) {
				if ($args{'force-delete'}) {
					if (!$quiet) { print "Removing $targetfs because no matching snapshots were found\n"; }

					my $rcommand = '';
					my $mysudocmd = '';
					my $targetfsescaped = escapeshellparam($targetfs);

					if ($targethost ne '') { $rcommand = "$sshcmd $targethost"; }
					if (!$targetisroot) { $mysudocmd = $sudocmd; }

					my $prunecmd = "$mysudocmd $zfscmd destroy -r $targetfsescaped; ";
					if ($targethost ne '') {
						$prunecmd = escapeshellparam($prunecmd);
					}

					my $ret = system("$rcommand $prunecmd");
					if ($ret != 0) {
						warn "WARNING: $rcommand $prunecmd failed: $?";
					} else {
						# redo sync and skip snapshot creation (already taken)
						return syncdataset($sourcehost, $sourcefs, $targethost, $targetfs, undef, 1);
					}
				}

				# if we got this far, we failed to find a matching snapshot/bookmark.
				if ($exitcode < 2) { $exitcode = 2; }

				print "\n";
				print "CRITICAL ERROR: Target $targetfs exists but has no snapshots matching with $sourcefs!\n";
				print "                Replication to target would require destroying existing\n";
				print "                target. Cowardly refusing to destroy your existing target.\n\n";

				# experience tells me we need a mollyguard for people who try to
				# zfs create targetpool/targetsnap ; syncoid sourcepool/sourcesnap targetpool/targetsnap ...

				if ( $targetsize < (64*1024*1024) ) {
					print "          NOTE: Target $targetfs dataset is < 64MB used - did you mistakenly run\n";
					print "                \`zfs create $args{'target'}\` on the target? ZFS initial\n";
					print "                replication must be to a NON EXISTENT DATASET, which will\n";
					print "                then be CREATED BY the initial replication process.\n\n";
				}

				# return false now in case more child datasets need replication.
				return 0;
			}
		}

		# make sure target is (still) not currently in receive.
		if (iszfsbusy($targethost,$targetfs,$targetisroot)) {
			warn "Cannot sync now: $targetfs is already target of a zfs receive process.\n";
			if ($exitcode < 1) { $exitcode = 1; }
			return 0;
		}

		if ($matchingsnap eq $newsyncsnap) {
			# barf some text but don't touch the filesystem
			if (!$quiet) { print "INFO: no snapshots on source newer than $newsyncsnap on target. Nothing to do, not syncing.\n"; }
			return 0;
		} else {
			my $matchingsnapescaped = escapeshellparam($matchingsnap);
			# rollback target to matchingsnap
			if (!defined $args{'no-rollback'}) {
				my $rollbacktype = "-R";
				if (defined $args{'no-clone-rollback'}) {
					$rollbacktype = "-r";
				}
				if ($debug) { print "DEBUG: rolling back target to $targetfs\@$matchingsnap...\n"; }
				if ($targethost ne '') {
					if ($debug) { print "$sshcmd $targethost $targetsudocmd $zfscmd rollback $rollbacktype $targetfsescaped\@$matchingsnapescaped\n"; }
					system ("$sshcmd $targethost " . escapeshellparam("$targetsudocmd $zfscmd rollback $rollbacktype $targetfsescaped\@$matchingsnapescaped"));
				} else {
					if ($debug) { print "$targetsudocmd $zfscmd rollback $rollbacktype $targetfsescaped\@$matchingsnapescaped\n"; }
					system ("$targetsudocmd $zfscmd rollback $rollbacktype $targetfsescaped\@$matchingsnapescaped");
				}
			}

			my $nextsnapshot = 0;

			if ($bookmark) {
				my $bookmarkescaped = escapeshellparam($bookmark);

				if (!defined $args{'no-stream'}) {
					# if intermediate snapshots are needed we need to find the next oldest snapshot,
					# do an replication to it and replicate as always from oldest to newest
					# because bookmark sends doesn't support intermediates directly
					foreach my $snap ( sort { $snaps{'source'}{$a}{'creation'}<=>$snaps{'source'}{$b}{'creation'} } keys %{ $snaps{'source'} }) {
						if ($snaps{'source'}{$snap}{'creation'} >= $bookmarkcreation) {
							$nextsnapshot = $snap;
							last;
						}
					}
				}

				# bookmark stream size can't be determined
				my $pvsize = 0;
				my $disp_pvsize = "UNKNOWN";

				$sendoptions = getoptionsline(\@sendoptions, ('L','c','e','w'));
				if ($nextsnapshot) {
					my $nextsnapshotescaped = escapeshellparam($nextsnapshot);
					my $sendcmd = "$sourcesudocmd $zfscmd send $sendoptions -i $sourcefsescaped#$bookmarkescaped $sourcefsescaped\@$nextsnapshotescaped";
					my $recvcmd = "$targetsudocmd $zfscmd receive $recvoptions $receiveextraargs $forcedrecv $targetfsescaped 2>&1";
					my $synccmd = buildsynccmd($sendcmd,$recvcmd,$pvsize,$sourceisroot,$targetisroot);

					if (!$quiet) { print "Sending incremental $sourcefs#$bookmarkescaped ... $nextsnapshot (~ $disp_pvsize):\n"; }
					if ($debug) { print "DEBUG: $synccmd\n"; }

					($stdout, $exit) = tee_stdout {
						system("$synccmd")
					};

					$exit == 0 or do {
						if (!$resume && $stdout =~ /\Qcontains partially-complete state\E/) {
							if (!$quiet) { print "WARN: resetting partially receive state\n"; }
							resetreceivestate($targethost,$targetfs,$targetisroot);
							system("$synccmd") == 0 or do {
								warn "CRITICAL ERROR: $synccmd failed: $?";
								if ($exitcode < 2) { $exitcode = 2; }
								return 0;
							}
						} else {
							warn "CRITICAL ERROR: $synccmd failed: $?";
							if ($exitcode < 2) { $exitcode = 2; }
							return 0;
						}
					};

					$matchingsnap = $nextsnapshot;
					$matchingsnapescaped = escapeshellparam($matchingsnap);
				} else {
					my $sendcmd = "$sourcesudocmd $zfscmd send $sendoptions -i $sourcefsescaped#$bookmarkescaped $sourcefsescaped\@$newsyncsnapescaped";
					my $recvcmd = "$targetsudocmd $zfscmd receive $recvoptions $receiveextraargs $forcedrecv $targetfsescaped 2>&1";
					my $synccmd = buildsynccmd($sendcmd,$recvcmd,$pvsize,$sourceisroot,$targetisroot);

					if (!$quiet) { print "Sending incremental $sourcefs#$bookmarkescaped ... $newsyncsnap (~ $disp_pvsize):\n"; }
					if ($debug) { print "DEBUG: $synccmd\n"; }

					($stdout, $exit) = tee_stdout {
						system("$synccmd")
					};

					$exit == 0 or do {
						if (!$resume && $stdout =~ /\Qcontains partially-complete state\E/) {
							if (!$quiet) { print "WARN: resetting partially receive state\n"; }
							resetreceivestate($targethost,$targetfs,$targetisroot);
							system("$synccmd") == 0 or do {
								warn "CRITICAL ERROR: $synccmd failed: $?";
								if ($exitcode < 2) { $exitcode = 2; }
								return 0;
							}
						} else {
							warn "CRITICAL ERROR: $synccmd failed: $?";
							if ($exitcode < 2) { $exitcode = 2; }
							return 0;
						}
					};
				}
			}

			# do a normal replication if bookmarks aren't used or if previous
			# bookmark replication was only done to the next oldest snapshot
			if (!$bookmark || $nextsnapshot) {
				if ($matchingsnap eq $newsyncsnap) {
					# edge case: bookmark replication used the latest snapshot
					return 0;
				}

				$sendoptions = getoptionsline(\@sendoptions, ('D','L','P','R','c','e','h','p','v','w'));
				my $sendcmd = "$sourcesudocmd $zfscmd send $sendoptions $args{'streamarg'} $sourcefsescaped\@$matchingsnapescaped $sourcefsescaped\@$newsyncsnapescaped";
				my $recvcmd = "$targetsudocmd $zfscmd receive $recvoptions $receiveextraargs $forcedrecv $targetfsescaped 2>&1";
				my $pvsize = getsendsize($sourcehost,"$sourcefs\@$matchingsnap","$sourcefs\@$newsyncsnap",$sourceisroot);
				my $disp_pvsize = readablebytes($pvsize);
				if ($pvsize == 0) { $disp_pvsize = "UNKNOWN"; }
				my $synccmd = buildsynccmd($sendcmd,$recvcmd,$pvsize,$sourceisroot,$targetisroot);

				if (!$quiet) { print "Sending incremental $sourcefs\@$matchingsnap ... $newsyncsnap (~ $disp_pvsize):\n"; }
				if ($debug) { print "DEBUG: $synccmd\n"; }

				($stdout, $exit) = tee_stdout {
					system("$synccmd")
				};

				$exit == 0 or do {
					# FreeBSD reports "dataset is busy" instead of "contains partially-complete state"
					if (!$resume && ($stdout =~ /\Qcontains partially-complete state\E/ || $stdout =~ /\Qdataset is busy\E/)) {
						if (!$quiet) { print "WARN: resetting partially receive state\n"; }
						resetreceivestate($targethost,$targetfs,$targetisroot);
						system("$synccmd") == 0 or do {
							warn "CRITICAL ERROR: $synccmd failed: $?";
							if ($exitcode < 2) { $exitcode = 2; }
							return 0;
						}
					} else {
						warn "CRITICAL ERROR: $synccmd failed: $?";
						if ($exitcode < 2) { $exitcode = 2; }
						return 0;
					}
				};
			}

			# restore original readonly value to target after sync complete
				# dyking this functionality out for the time being due to buggy mount/unmount behavior
				# with ZFS on Linux (possibly OpenZFS in general) when setting/unsetting readonly.
			#setzfsvalue($targethost,$targetfs,$targetisroot,'readonly',$originaltargetreadonly);
		}
	}

	if (defined $args{'no-sync-snap'}) {
		if (defined $args{'create-bookmark'}) {
			my $bookmarkcmd;
			if ($sourcehost ne '') {
				$bookmarkcmd = "$sshcmd $sourcehost " . escapeshellparam("$sourcesudocmd $zfscmd bookmark $sourcefsescaped\@$newsyncsnapescaped $sourcefsescaped\#$newsyncsnapescaped");
			} else {
				$bookmarkcmd = "$sourcesudocmd $zfscmd bookmark $sourcefsescaped\@$newsyncsnapescaped $sourcefsescaped\#$newsyncsnapescaped";
			}
			if ($debug) { print "DEBUG: $bookmarkcmd\n"; }
			system($bookmarkcmd) == 0 or do {
				# fallback: assume nameing conflict and try again with guid based suffix
				my $guid = $snaps{'source'}{$newsyncsnap}{'guid'};
				$guid = substr($guid, 0, 6);

				if (!$quiet) { print "INFO: bookmark creation failed, retrying with guid based suffix ($guid)...\n"; }

				if ($sourcehost ne '') {
					$bookmarkcmd = "$sshcmd $sourcehost " . escapeshellparam("$sourcesudocmd $zfscmd bookmark $sourcefsescaped\@$newsyncsnapescaped $sourcefsescaped\#$newsyncsnapescaped$guid");
				} else {
					$bookmarkcmd = "$sourcesudocmd $zfscmd bookmark $sourcefsescaped\@$newsyncsnapescaped $sourcefsescaped\#$newsyncsnapescaped$guid";
				}
				if ($debug) { print "DEBUG: $bookmarkcmd\n"; }
				system($bookmarkcmd) == 0 or do {
					warn "CRITICAL ERROR: $bookmarkcmd failed: $?";
					if ($exitcode < 2) { $exitcode = 2; }
					return 0;
				}
			};
		}
	} else {
		# prune obsolete sync snaps on source and target (only if this run created ones).
		pruneoldsyncsnaps($sourcehost,$sourcefs,$newsyncsnap,$sourceisroot,keys %{ $snaps{'source'}});
		pruneoldsyncsnaps($targethost,$targetfs,$newsyncsnap,$targetisroot,keys %{ $snaps{'target'}});
	}

} # end syncdataset()

sub compressargset {
	my ($value) = @_;
	my $DEFAULT_COMPRESSION = 'lzo';
	my %COMPRESS_ARGS = (
		'none' => {
			rawcmd      => '',
			args        => '',
			decomrawcmd => '',
			decomargs   => '',
		},
		'gzip' => {
			rawcmd      => 'gzip',
			args        => '-3',
			decomrawcmd => 'zcat',
			decomargs   => '',
		},
		'pigz-fast' => {
			rawcmd      => 'pigz',
			args        => '-3',
			decomrawcmd => 'pigz',
			decomargs   => '-dc',
		},
		'pigz-slow' => {
			rawcmd      => 'pigz',
			args        => '-9',
			decomrawcmd => 'pigz',
			decomargs   => '-dc',
		},
		'zstd-fast' => {
			rawcmd      => 'zstd',
			args        => '-3',
			decomrawcmd => 'zstd',
			decomargs   => '-dc',
		},
		'zstd-slow' => {
			rawcmd      => 'zstd',
			args        => '-19',
			decomrawcmd => 'zstd',
			decomargs   => '-dc',
		},
		'xz' => {
			rawcmd      => 'xz',
			args        => '',
			decomrawcmd => 'xz',
			decomargs   => '-d',
		},
		'lzo' => {
			rawcmd      => 'lzop',
			args        => '',
			decomrawcmd => 'lzop',
			decomargs   => '-dfc',
		},
		'lz4' => {
			rawcmd      => 'lz4',
			args        => '',
			decomrawcmd => 'lz4',
			decomargs   => '-dc',
		},
	);

	if ($value eq 'default') {
		$value = $DEFAULT_COMPRESSION;
	} elsif (!(grep $value eq $_, ('gzip', 'pigz-fast', 'pigz-slow', 'zstd-fast', 'zstd-slow', 'lz4', 'xz', 'lzo', 'default', 'none'))) {
		warn "Unrecognised compression value $value, defaulting to $DEFAULT_COMPRESSION";
		$value = $DEFAULT_COMPRESSION;
	}

	my %comargs = %{$COMPRESS_ARGS{$value}}; # copy
	$comargs{'compress'} = $value;
	$comargs{'cmd'}      = "$comargs{'rawcmd'} $comargs{'args'}";
	$comargs{'decomcmd'} = "$comargs{'decomrawcmd'} $comargs{'decomargs'}";
	return \%comargs;
}

sub checkcommands {
	# make sure compression, mbuffer, and pv are available on
	# source, target, and local hosts as appropriate.

	my %avail;
	my $sourcessh;
	my $targetssh;

	# if --nocommandchecks then assume everything's available and return
	if ($args{'nocommandchecks'}) {
		if ($debug) { print "DEBUG: not checking for command availability due to --nocommandchecks switch.\n"; }
		$avail{'compress'} = 1;
		$avail{'localpv'} = 1;
		$avail{'localmbuffer'} = 1;
		$avail{'sourcembuffer'} = 1;
		$avail{'targetmbuffer'} = 1;
		$avail{'sourceresume'} = 1;
		$avail{'targetresume'} = 1;
		return %avail;
	}

	if (!defined $sourcehost) { $sourcehost = ''; }
	if (!defined $targethost) { $targethost = ''; }

	if ($sourcehost ne '') { $sourcessh = "$sshcmd $sourcehost"; } else { $sourcessh = ''; }
	if ($targethost ne '') { $targetssh = "$sshcmd $targethost"; } else { $targetssh = ''; }

	# if raw compress command is null, we must have specified no compression. otherwise,
	# make sure that compression is available everywhere we need it
	if ($compressargs{'compress'} eq 'none') {
		if ($debug) { print "DEBUG: compression forced off from command line arguments.\n"; }
	} else {
		if ($debug) { print "DEBUG: checking availability of $compressargs{'rawcmd'} on source...\n"; }
		$avail{'sourcecompress'} = `$sourcessh $checkcmd $compressargs{'rawcmd'} 2>/dev/null`;
		if ($debug) { print "DEBUG: checking availability of $compressargs{'rawcmd'} on target...\n"; }
		$avail{'targetcompress'} = `$targetssh $checkcmd $compressargs{'rawcmd'} 2>/dev/null`;
		if ($debug) { print "DEBUG: checking availability of $compressargs{'rawcmd'} on local machine...\n"; }
		$avail{'localcompress'} = `$checkcmd $compressargs{'rawcmd'} 2>/dev/null`;
	}

	my ($s,$t);
	if ($sourcehost eq '') {
		$s = '[local machine]'
	} else {
		$s = $sourcehost;
		$s =~ s/^\S*\@//;
		$s = "ssh:$s";
	}
	if ($targethost eq '') {
		$t = '[local machine]'
	} else {
		$t = $targethost;
		$t =~ s/^\S*\@//;
		$t = "ssh:$t";
	}

	if (!defined $avail{'sourcecompress'}) { $avail{'sourcecompress'} = ''; }
	if (!defined $avail{'targetcompress'}) { $avail{'targetcompress'} = ''; }
	if (!defined $avail{'localcompress'}) { $avail{'localcompress'} = ''; }
	if (!defined $avail{'sourcembuffer'}) { $avail{'sourcembuffer'} = ''; }
	if (!defined $avail{'targetmbuffer'}) { $avail{'targetmbuffer'} = ''; }


	if ($avail{'sourcecompress'} eq '') {
		if ($compressargs{'rawcmd'} ne '') {
			print "WARN: $compressargs{'rawcmd'} not available on source $s- sync will continue without compression.\n";
		}
		$avail{'compress'} = 0;
	}
	if ($avail{'targetcompress'} eq '') {
		if ($compressargs{'rawcmd'} ne '') {
			print "WARN: $compressargs{'rawcmd'} not available on target $t - sync will continue without compression.\n";
		}
		$avail{'compress'} = 0;
	}
	if ($avail{'targetcompress'} ne '' && $avail{'sourcecompress'} ne '') {
		# compression available - unless source and target are both remote, which we'll check
		# for in the next block and respond to accordingly.
		$avail{'compress'} = 1;
	}

	# corner case - if source AND target are BOTH remote, we have to check for local compress too
	if ($sourcehost ne '' && $targethost ne '' && $avail{'localcompress'} eq '') {
		if ($compressargs{'rawcmd'} ne '') {
			print "WARN: $compressargs{'rawcmd'} not available on local machine - sync will continue without compression.\n";
		}
		$avail{'compress'} = 0;
	}

	if ($debug) { print "DEBUG: checking availability of $mbuffercmd on source...\n"; }
	$avail{'sourcembuffer'} = `$sourcessh $checkcmd $mbuffercmd 2>/dev/null`;
	if ($avail{'sourcembuffer'} eq '') {
		if (!$quiet) { print "WARN: $mbuffercmd not available on source $s - sync will continue without source buffering.\n"; }
		$avail{'sourcembuffer'} = 0;
	} else {
		$avail{'sourcembuffer'} = 1;
	}

	if ($debug) { print "DEBUG: checking availability of $mbuffercmd on target...\n"; }
	$avail{'targetmbuffer'} = `$targetssh $checkcmd $mbuffercmd 2>/dev/null`;
	if ($avail{'targetmbuffer'} eq '') {
		if (!$quiet) { print "WARN: $mbuffercmd not available on target $t - sync will continue without target buffering.\n"; }
		$avail{'targetmbuffer'} = 0;
	} else {
		$avail{'targetmbuffer'} = 1;
	}

	# if we're doing remote source AND remote target, check for local mbuffer as well
	if ($sourcehost ne '' && $targethost ne '') {
		if ($debug) { print "DEBUG: checking availability of $mbuffercmd on local machine...\n"; }
		$avail{'localmbuffer'} = `$checkcmd $mbuffercmd 2>/dev/null`;
		if ($avail{'localmbuffer'} eq '') {
			$avail{'localmbuffer'} = 0;
			if (!$quiet) { print "WARN: $mbuffercmd not available on local machine - sync will continue without local buffering.\n"; }
		}
	}

	if ($debug) { print "DEBUG: checking availability of $pvcmd on local machine...\n"; }
	$avail{'localpv'} = `$checkcmd $pvcmd 2>/dev/null`;
	if ($avail{'localpv'} eq '') {
		if (!$quiet) { print "WARN: $pvcmd not available on local machine - sync will continue without progress bar.\n"; }
		$avail{'localpv'} = 0;
	} else {
		$avail{'localpv'} = 1;
	}

	# check for ZFS resume feature support
	if ($resume) {
		my @parts = split ('/', $sourcefs);
		my $srcpool = $parts[0];
		@parts = split ('/', $targetfs);
		my $dstpool = $parts[0];

		$srcpool = escapeshellparam($srcpool);
		$dstpool = escapeshellparam($dstpool);

		if ($sourcehost ne '') {
			# double escaping needed
			$srcpool = escapeshellparam($srcpool);
		}

		if ($targethost ne '') {
			# double escaping needed
			$dstpool = escapeshellparam($dstpool);
		}

		my $resumechkcmd = "$zpoolcmd get -o value -H feature\@extensible_dataset";

		if ($debug) { print "DEBUG: checking availability of zfs resume feature on source...\n"; }
		$avail{'sourceresume'} = system("$sourcessh $resumechkcmd $srcpool 2>/dev/null | grep '\\(active\\|enabled\\)' >/dev/null 2>&1");
		$avail{'sourceresume'} = $avail{'sourceresume'} == 0 ? 1 : 0;

		if ($debug) { print "DEBUG: checking availability of zfs resume feature on target...\n"; }
		$avail{'targetresume'} = system("$targetssh $resumechkcmd $dstpool 2>/dev/null | grep '\\(active\\|enabled\\)' >/dev/null 2>&1");
		$avail{'targetresume'} = $avail{'targetresume'} == 0 ? 1 : 0;

		if ($avail{'sourceresume'} == 0 || $avail{'targetresume'} == 0) {
			# disable resume
			$resume = '';

			my @hosts = ();
			if ($avail{'sourceresume'} == 0) {
				push @hosts, 'source';
			}
			if ($avail{'targetresume'} == 0) {
				push @hosts, 'target';
			}
			my $affected = join(" and ", @hosts);
			print "WARN: ZFS resume feature not available on $affected machine - sync will continue without resume support.\n";
		}
	} else {
		$avail{'sourceresume'} = 0;
		$avail{'targetresume'} = 0;
	}

	return %avail;
}

sub iszfsbusy {
	my ($rhost,$fs,$isroot) = @_;
	if ($rhost ne '') { $rhost = "$sshcmd $rhost"; }
	if ($debug) { print "DEBUG: checking to see if $fs on $rhost is already in zfs receive using $rhost $pscmd -Ao args= ...\n"; }

	open PL, "$rhost $pscmd -Ao args= |";
	my @processes = <PL>;
	close PL;

	foreach my $process (@processes) {
		# if ($debug) { print "DEBUG: checking process $process...\n"; }
		if ($process =~ /zfs *(receive|recv).*\Q$fs\E/) {
			# there's already a zfs receive process for our target filesystem - return true
			if ($debug) { print "DEBUG: process $process matches target $fs!\n"; }
			return 1;
		}
	}

	# no zfs receive processes for our target filesystem found - return false
	return 0;
}

sub setzfsvalue {
	my ($rhost,$fs,$isroot,$property,$value) = @_;

	my $fsescaped = escapeshellparam($fs);

	if ($rhost ne '') {
		$rhost = "$sshcmd $rhost";
		# double escaping needed
		$fsescaped = escapeshellparam($fsescaped);
	}

	if ($debug) { print "DEBUG: setting $property to $value on $fs...\n"; }
	my $mysudocmd;
	if ($isroot) { $mysudocmd = ''; } else { $mysudocmd = $sudocmd; }
	if ($debug) { print "$rhost $mysudocmd $zfscmd set $property=$value $fsescaped\n"; }
	system("$rhost $mysudocmd $zfscmd set $property=$value $fsescaped") == 0
		or warn "WARNING: $rhost $mysudocmd $zfscmd set $property=$value $fsescaped died: $?, proceeding anyway.\n";
	return;
}

sub getzfsvalue {
	my ($rhost,$fs,$isroot,$property) = @_;

	my $fsescaped = escapeshellparam($fs);

	if ($rhost ne '') {
		$rhost = "$sshcmd $rhost";
		# double escaping needed
		$fsescaped = escapeshellparam($fsescaped);
	}

	if ($debug) { print "DEBUG: getting current value of $property on $fs...\n"; }
	my $mysudocmd;
	if ($isroot) { $mysudocmd = ''; } else { $mysudocmd = $sudocmd; }
	if ($debug) { print "$rhost $mysudocmd $zfscmd get -H $property $fsescaped\n"; }
	open FH, "$rhost $mysudocmd $zfscmd get -H $property $fsescaped |";
	my $value = <FH>;
	close FH;

	if (!defined $value) {
		return undef;
	}

	my @values = split(/\t/,$value);
	$value = $values[2];
	return $value;
}

sub readablebytes {
	my $bytes = shift;
	my $disp;

	if ($bytes > 1024*1024*1024) {
		$disp = sprintf("%.1f",$bytes/1024/1024/1024) . ' GB';
	} elsif ($bytes > 1024*1024) {
		$disp = sprintf("%.1f",$bytes/1024/1024) . ' MB';
	} else {
		$disp = sprintf("%d",$bytes/1024) . ' KB';
	}
	return $disp;
}

sub getoldestsnapshot {
	my $snaps = shift;
	foreach my $snap ( sort { $snaps{'source'}{$a}{'creation'}<=>$snaps{'source'}{$b}{'creation'} } keys %{ $snaps{'source'} }) {
		# return on first snap found - it's the oldest
		return $snap;
	}
	# must not have had any snapshots on source - luckily, we already made one, amirite?
	if (defined ($args{'no-sync-snap'}) ) {
		# well, actually we set --no-sync-snap, so no we *didn't* already make one. Whoops.
		warn "CRIT: --no-sync-snap is set, and getoldestsnapshot() could not find any snapshots on source!\n";
	}
	return 0;
}

sub getnewestsnapshot {
	my $snaps = shift;
	foreach my $snap ( sort { $snaps{'source'}{$b}{'creation'}<=>$snaps{'source'}{$a}{'creation'} } keys %{ $snaps{'source'} }) {
		# return on first snap found - it's the newest
		if (!$quiet) { print "NEWEST SNAPSHOT: $snap\n"; }
		return $snap;
	}
	# must not have had any snapshots on source - looks like we'd better create one!
	if (defined ($args{'no-sync-snap'}) ) {
		if (!defined ($args{'recursive'}) ) {
			# well, actually we set --no-sync-snap and we're not recursive, so no we *can't* make one. Whoops.
			die "CRIT: --no-sync-snap is set, and getnewestsnapshot() could not find any snapshots on source!\n";
		}
		# fixme: we need to output WHAT the current dataset IS if we encounter this WARN condition.
		#        we also probably need an argument to mute this WARN, for people who deliberately exclude
		#        datasets from recursive replication this way.
		warn "WARN: --no-sync-snap is set, and getnewestsnapshot() could not find any snapshots on source for current dataset. Continuing.\n";
		if ($exitcode < 2) { $exitcode = 2; }
	}
	return 0;
}

sub buildsynccmd {
	my ($sendcmd,$recvcmd,$pvsize,$sourceisroot,$targetisroot) = @_;
	# here's where it gets fun: figuring out when to compress and decompress.
	# to make this work for all possible combinations, you may have to decompress
	# AND recompress across the pipe viewer. FUN.
	my $synccmd;

	if ($sourcehost eq '' && $targethost eq '') {
		# both sides local. don't compress. do mbuffer, once, on the source side.
		# $synccmd = "$sendcmd | $mbuffercmd | $pvcmd | $recvcmd";
		$synccmd = "$sendcmd |";
		# avoid confusion - accept either source-bwlimit or target-bwlimit as the bandwidth limiting option here
		my $bwlimit = '';
		if (length $args{'source-bwlimit'}) {
			$bwlimit = $args{'source-bwlimit'};
		} elsif (length $args{'target-bwlimit'}) {
			$bwlimit = $args{'target-bwlimit'};
		}

		if ($avail{'sourcembuffer'}) { $synccmd .= " $mbuffercmd $bwlimit $mbufferoptions |"; }
		if ($avail{'localpv'} && !$quiet) { $synccmd .= " $pvcmd -s $pvsize |"; }
		$synccmd .= " $recvcmd";
	} elsif ($sourcehost eq '') {
		# local source, remote target.
		#$synccmd = "$sendcmd | $pvcmd | $compressargs{'cmd'} | $mbuffercmd | $sshcmd $targethost '$compressargs{'decomcmd'} | $mbuffercmd | $recvcmd'";
		$synccmd = "$sendcmd |";
		if ($avail{'localpv'} && !$quiet) { $synccmd .= " $pvcmd -s $pvsize |"; }
		if ($avail{'compress'}) { $synccmd .= " $compressargs{'cmd'} |"; }
		if ($avail{'sourcembuffer'}) { $synccmd .= " $mbuffercmd $args{'source-bwlimit'} $mbufferoptions |"; }
		$synccmd .= " $sshcmd $targethost ";

		my $remotecmd = "";
		if ($avail{'targetmbuffer'}) { $remotecmd .= " $mbuffercmd $args{'target-bwlimit'} $mbufferoptions |"; }
		if ($avail{'compress'}) { $remotecmd .= " $compressargs{'decomcmd'} |"; }
		$remotecmd .= " $recvcmd";

		$synccmd .= escapeshellparam($remotecmd);
	} elsif ($targethost eq '') {
		# remote source, local target.
		#$synccmd = "$sshcmd $sourcehost '$sendcmd | $compressargs{'cmd'} | $mbuffercmd' | $compressargs{'decomcmd'} | $mbuffercmd | $pvcmd | $recvcmd";

		my $remotecmd = $sendcmd;
		if ($avail{'compress'}) { $remotecmd .= " | $compressargs{'cmd'}"; }
		if ($avail{'sourcembuffer'}) { $remotecmd .= " | $mbuffercmd $args{'source-bwlimit'} $mbufferoptions"; }

		$synccmd = "$sshcmd $sourcehost " . escapeshellparam($remotecmd);
		$synccmd .= " | ";
		if ($avail{'targetmbuffer'}) { $synccmd .= "$mbuffercmd $args{'target-bwlimit'} $mbufferoptions | "; }
		if ($avail{'compress'}) { $synccmd .= "$compressargs{'decomcmd'} | "; }
		if ($avail{'localpv'} && !$quiet) { $synccmd .= "$pvcmd -s $pvsize | "; }
		$synccmd .= "$recvcmd";
	} else {
		#remote source, remote target... weird, but whatever, I'm not here to judge you.
		#$synccmd = "$sshcmd $sourcehost '$sendcmd | $compressargs{'cmd'} | $mbuffercmd' | $compressargs{'decomcmd'} | $pvcmd | $compressargs{'cmd'} | $mbuffercmd | $sshcmd $targethost '$compressargs{'decomcmd'} | $mbuffercmd | $recvcmd'";

		my $remotecmd = $sendcmd;
		if ($avail{'compress'}) { $remotecmd .= " | $compressargs{'cmd'}"; }
		if ($avail{'sourcembuffer'}) { $remotecmd .= " | $mbuffercmd $args{'source-bwlimit'} $mbufferoptions"; }

		$synccmd = "$sshcmd $sourcehost " . escapeshellparam($remotecmd);
		$synccmd .= " | ";

		if ($avail{'compress'}) { $synccmd .= "$compressargs{'decomcmd'} | "; }
		if ($avail{'localpv'} && !$quiet) { $synccmd .= "$pvcmd -s $pvsize | "; }
		if ($avail{'compress'}) { $synccmd .= "$compressargs{'cmd'} | "; }
		if ($avail{'localmbuffer'}) { $synccmd .= "$mbuffercmd $mbufferoptions | "; }
		$synccmd .= "$sshcmd $targethost ";

		$remotecmd = "";
		if ($avail{'targetmbuffer'}) { $remotecmd .= " $mbuffercmd $args{'target-bwlimit'} $mbufferoptions |"; }
		if ($avail{'compress'}) { $remotecmd .= " $compressargs{'decomcmd'} |"; }
		$remotecmd .= " $recvcmd";

		$synccmd .= escapeshellparam($remotecmd);
	}
	return $synccmd;
}

sub pruneoldsyncsnaps {
	my ($rhost,$fs,$newsyncsnap,$isroot,@snaps) = @_;

	my $fsescaped = escapeshellparam($fs);

	if ($rhost ne '') { $rhost = "$sshcmd $rhost"; }

	my $hostid = hostname();

	my $mysudocmd;
	if ($isroot) { $mysudocmd=''; } else { $mysudocmd = $sudocmd; }

	my @prunesnaps;

	# only prune snaps beginning with syncoid and our own hostname
	foreach my $snap(@snaps) {
		if ($snap =~ /^syncoid_\Q$identifier$hostid\E/) {
			# no matter what, we categorically refuse to
			# prune the new sync snap we created for this run
			if ($snap ne $newsyncsnap) {
				push (@prunesnaps,$snap);
			}
		}
	}

	# concatenate pruning commands to ten per line, to cut down
	# auth times for any remote hosts that must be operated via SSH
	my $counter;
	my $maxsnapspercmd = 10;
	my $prunecmd;
	foreach my $snap(@prunesnaps) {
		$counter ++;
		$prunecmd .= "$mysudocmd $zfscmd destroy $fsescaped\@$snap; ";
		if ($counter > $maxsnapspercmd) {
			$prunecmd =~ s/\; $//;
			if ($debug) { print "DEBUG: pruning up to $maxsnapspercmd obsolete sync snapshots...\n"; }
			if ($debug) { print "DEBUG: $rhost $prunecmd\n"; }
			if ($rhost ne '') {
				$prunecmd = escapeshellparam($prunecmd);
			}
			system("$rhost $prunecmd") == 0
				or warn "WARNING: $rhost $prunecmd failed: $?";
			$prunecmd = '';
			$counter = 0;
		}
	}
	# if we still have some prune commands stacked up after finishing
	# the loop, commit 'em now
	if ($counter) {
		$prunecmd =~ s/\; $//;
		if ($debug) { print "DEBUG: pruning up to $maxsnapspercmd obsolete sync snapshots...\n"; }
		if ($debug) { print "DEBUG: $rhost $prunecmd\n"; }
		if ($rhost ne '') {
			$prunecmd = escapeshellparam($prunecmd);
		}
		system("$rhost $prunecmd") == 0
			or warn "WARNING: $rhost $prunecmd failed: $?";
	}
	return;
}

sub getmatchingsnapshot {
	my ($sourcefs, $targetfs, $snaps) = @_;
	foreach my $snap ( sort { $snaps{'source'}{$b}{'creation'}<=>$snaps{'source'}{$a}{'creation'} } keys %{ $snaps{'source'} }) {
		if (defined $snaps{'target'}{$snap}) {
			if ($snaps{'source'}{$snap}{'guid'} == $snaps{'target'}{$snap}{'guid'}) {
				return $snap;
			}
		}
	}

	return 0;
}

sub newsyncsnap {
	my ($rhost,$fs,$isroot) = @_;
	my $fsescaped = escapeshellparam($fs);
	if ($rhost ne '') {
		$rhost = "$sshcmd $rhost";
		# double escaping needed
		$fsescaped = escapeshellparam($fsescaped);
	}
	my $mysudocmd;
	if ($isroot) { $mysudocmd = ''; } else { $mysudocmd = $sudocmd; }
	my $hostid = hostname();
	my %date = getdate();
	my $snapname = "syncoid\_$identifier$hostid\_$date{'stamp'}";
	my $snapcmd = "$rhost $mysudocmd $zfscmd snapshot $fsescaped\@$snapname\n";
	if ($debug) { print "DEBUG: creating sync snapshot using \"$snapcmd\"...\n"; }
	system($snapcmd) == 0 or do {
		warn "CRITICAL ERROR: $snapcmd failed: $?";
		if ($exitcode < 2) { $exitcode = 2; }
		return 0;
	};

	return $snapname;
}

sub targetexists {
	my ($rhost,$fs,$isroot) = @_;
	my $fsescaped = escapeshellparam($fs);
	if ($rhost ne '') {
		$rhost = "$sshcmd $rhost";
		# double escaping needed
		$fsescaped = escapeshellparam($fsescaped);
	}
	my $mysudocmd;
	if ($isroot) { $mysudocmd = ''; } else { $mysudocmd = $sudocmd; }
	my $checktargetcmd = "$rhost $mysudocmd $zfscmd get -H name $fsescaped";
	if ($debug) { print "DEBUG: checking to see if target filesystem exists using \"$checktargetcmd 2>&1 |\"...\n"; }
	open FH, "$checktargetcmd 2>&1 |";
	my $targetexists = <FH>;
	close FH;
	my $exit = $?;
	$targetexists = ( $targetexists =~ /^\Q$fs\E/ && $exit == 0 );
	return $targetexists;
}

sub getssh {
	my $fs = shift;

	my $rhost;
	my $isroot;
	my $socket;

	# if we got passed something with an @ in it, we assume it's an ssh connection, eg root@myotherbox
	if ($fs =~ /\@/) {
		$rhost = $fs;
		$fs =~ s/^\S*\@\S*://;
		$rhost =~ s/:\Q$fs\E$//;
		my $remoteuser = $rhost;
		 $remoteuser =~ s/\@.*$//;
		if ($remoteuser eq 'root' || $args{'no-privilege-elevation'}) { $isroot = 1; } else { $isroot = 0; }
		# now we need to establish a persistent master SSH connection
		$socket = "/tmp/syncoid-$remoteuser-$rhost-" . time();
		open FH, "$sshcmd -M -S $socket -o ControlPersist=1m $args{'sshport'} $rhost exit |";
		close FH;

		system("$sshcmd -S $socket $rhost echo -n") == 0 or do {
			my $code = $? >> 8;
			warn "CRITICAL ERROR: ssh connection echo test failed for $rhost with exit code $code";
			exit(2);
		};

		$rhost = "-S $socket $rhost";
	} else {
		my $localuid = $<;
		if ($localuid == 0 || $args{'no-privilege-elevation'}) { $isroot = 1; } else { $isroot = 0; }
	}
	# if ($isroot) { print "this user is root.\n"; } else { print "this user is not root.\n"; }
	return ($rhost,$fs,$isroot);
}

sub dumphash() {
	my $hash = shift;
	$Data::Dumper::Sortkeys = 1;
	print Dumper($hash);
}

sub getsnaps() {
	my ($type,$rhost,$fs,$isroot,%snaps) = @_;
	my $mysudocmd;
	my $fsescaped = escapeshellparam($fs);
	if ($isroot) { $mysudocmd = ''; } else { $mysudocmd = $sudocmd; }

	if ($rhost ne '') {
		$rhost = "$sshcmd $rhost";
		# double escaping needed
		$fsescaped = escapeshellparam($fsescaped);
	}

	my $getsnapcmd = "$rhost $mysudocmd $zfscmd get -Hpd 1 -t snapshot guid,creation $fsescaped |";
	if ($debug) { print "DEBUG: getting list of snapshots on $fs using $getsnapcmd...\n"; }
	open FH, $getsnapcmd;
	my @rawsnaps = <FH>;
	close FH or die "CRITICAL ERROR: snapshots couldn't be listed for $fs (exit code $?)";

	# this is a little obnoxious. get guid,creation returns guid,creation on two separate lines
	# as though each were an entirely separate get command.

	my %creationtimes=();

	foreach my $line (@rawsnaps) {
		# only import snap guids from the specified filesystem
		if ($line =~ /\Q$fs\E\@.*guid/) {
			chomp $line;
			my $guid = $line;
			$guid =~ s/^.*\tguid\t*(\d*).*/$1/;
			my $snap = $line;
			$snap =~ s/^.*\@(.*)\tguid.*$/$1/;
			$snaps{$type}{$snap}{'guid'}=$guid;
		}
	}

	foreach my $line (@rawsnaps) {
		# only import snap creations from the specified filesystem
		if ($line =~ /\Q$fs\E\@.*creation/) {
			chomp $line;
			my $creation = $line;
			$creation =~ s/^.*\tcreation\t*(\d*).*/$1/;
			my $snap = $line;
			$snap =~ s/^.*\@(.*)\tcreation.*$/$1/;

			# the accuracy of the creation timestamp is only for a second, but
			# snapshots in the same second are highly likely. The list command
			# has an ordered output so we append another three digit running number
			# to the creation timestamp and make sure those are ordered correctly
			# for snapshot with the same creation timestamp
			my $counter = 0;
			my $creationsuffix;
			while ($counter < 999) {
				$creationsuffix = sprintf("%s%03d", $creation, $counter);
				if (!defined $creationtimes{$creationsuffix}) {
					$creationtimes{$creationsuffix} = 1;
					last;
				}
				$counter += 1;
			}

			$snaps{$type}{$snap}{'creation'}=$creationsuffix;
		}
	}

	return %snaps;
}

sub getbookmarks() {
	my ($rhost,$fs,$isroot,%bookmarks) = @_;
	my $mysudocmd;
	my $fsescaped = escapeshellparam($fs);
	if ($isroot) { $mysudocmd = ''; } else { $mysudocmd = $sudocmd; }

	if ($rhost ne '') {
		$rhost = "$sshcmd $rhost";
		# double escaping needed
		$fsescaped = escapeshellparam($fsescaped);
	}

	my $error = 0;
	my $getbookmarkcmd = "$rhost $mysudocmd $zfscmd get -Hpd 1 -t bookmark guid,creation $fsescaped 2>&1 |";
	if ($debug) { print "DEBUG: getting list of bookmarks on $fs using $getbookmarkcmd...\n"; }
	open FH, $getbookmarkcmd;
	my @rawbookmarks = <FH>;
	close FH or $error = 1;

	if ($error == 1) {
		if ($rawbookmarks[0] =~ /invalid type/ or $rawbookmarks[0] =~ /operation not applicable to datasets of this type/) {
			# no support for zfs bookmarks, return empty hash
			return %bookmarks;
		}

		die "CRITICAL ERROR: bookmarks couldn't be listed for $fs (exit code $?)";
	}

	# this is a little obnoxious. get guid,creation returns guid,creation on two separate lines
	# as though each were an entirely separate get command.

	my $lastguid;

	foreach my $line (@rawbookmarks) {
		# only import bookmark guids, creation from the specified filesystem
		if ($line =~ /\Q$fs\E\#.*guid/) {
			chomp $line;
			$lastguid = $line;
			$lastguid =~ s/^.*\tguid\t*(\d*).*/$1/;
			my $bookmark = $line;
			$bookmark =~ s/^.*\#(.*)\tguid.*$/$1/;
			$bookmarks{$lastguid}{'name'}=$bookmark;
		} elsif ($line =~ /\Q$fs\E\#.*creation/) {
			chomp $line;
			my $creation = $line;
			$creation =~ s/^.*\tcreation\t*(\d*).*/$1/;
			my $bookmark = $line;
			$bookmark =~ s/^.*\#(.*)\tcreation.*$/$1/;
			$bookmarks{$lastguid}{'creation'}=$creation;
		}
	}

	return %bookmarks;
}

sub getsendsize {
	my ($sourcehost,$snap1,$snap2,$isroot,$receivetoken) = @_;

	my $snap1escaped = escapeshellparam($snap1);
	my $snap2escaped = escapeshellparam($snap2);

	my $mysudocmd;
	if ($isroot) { $mysudocmd = ''; } else { $mysudocmd = $sudocmd; }

	my $sourcessh;
	if ($sourcehost ne '') {
		$sourcessh = "$sshcmd $sourcehost";
		$snap1escaped = escapeshellparam($snap1escaped);
		$snap2escaped = escapeshellparam($snap2escaped);
	} else {
		$sourcessh = '';
	}

	my $snaps;
	if ($snap2) {
		# if we got a $snap2 argument, we want an incremental send estimate from $snap1 to $snap2.
		$snaps = "$args{'streamarg'} $snap1escaped $snap2escaped";
	} else {
		# if we didn't get a $snap2 arg, we want a full send estimate for $snap1.
		$snaps = "$snap1escaped";
	}

	# in case of a resumed receive, get the remaining
	# size based on the resume token
	if (defined($receivetoken)) {
		$snaps = "-t $receivetoken";
	}

	my $sendoptions;
	if (defined($receivetoken)) {
		$sendoptions = getoptionsline(\@sendoptions, ('e'));
	} else {
		$sendoptions = getoptionsline(\@sendoptions, ('D','L','R','c','e','h','p','v','w'));
	}
	my $getsendsizecmd = "$sourcessh $mysudocmd $zfscmd send $sendoptions -nP $snaps";
	if ($debug) { print "DEBUG: getting estimated transfer size from source $sourcehost using \"$getsendsizecmd 2>&1 |\"...\n"; }

	open FH, "$getsendsizecmd 2>&1 |";
	my @rawsize = <FH>;
	close FH;
	my $exit = $?;

	# process sendsize: last line of multi-line output is
	# size of proposed xfer in bytes, but we need to remove
	# human-readable crap from it
	my $sendsize = pop(@rawsize);
	# the output format is different in case of
	# a resumed receive
	if (defined($receivetoken)) {
		$sendsize =~ s/.*\t([0-9]+)$/$1/;
	} else {
		$sendsize =~ s/^size\t*//;
	}
	chomp $sendsize;

	# check for valid value
	if ($sendsize !~ /^\d+$/) {
		$sendsize = '';
	}

	# to avoid confusion with a zero size pv, give sendsize
	# a minimum 4K value - or if empty, make sure it reads UNKNOWN
	if ($debug) { print "DEBUG: sendsize = $sendsize\n"; }
	if ($sendsize eq '' || $exit != 0) {
		$sendsize = '0';
	} elsif ($sendsize < 4096) {
		$sendsize = 4096;
	}
	return $sendsize;
}

sub getdate {
	my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(time);
	$year += 1900;
	my %date;
	$date{'unix'} = (((((((($year - 1971) * 365) + $yday) * 24) + $hour) * 60) + $min) * 60) + $sec;
	$date{'year'} = $year;
	$date{'sec'} = sprintf ("%02u", $sec);
	$date{'min'} = sprintf ("%02u", $min);
	$date{'hour'} = sprintf ("%02u", $hour);
	$date{'mday'} = sprintf ("%02u", $mday);
	$date{'mon'} = sprintf ("%02u", ($mon + 1));
	$date{'stamp'} = "$date{'year'}-$date{'mon'}-$date{'mday'}:$date{'hour'}:$date{'min'}:$date{'sec'}";
	return %date;
}

sub escapeshellparam {
	my ($par) = @_;
	# avoid use of uninitialized string in regex
	if (length($par)) {
		# "escape" all single quotes
		$par =~ s/'/'"'"'/g;
	} else {
		# avoid use of uninitialized string in concatenation below
		$par = '';
	}
	# single-quote entire string
	return "'$par'";
}

sub getreceivetoken() {
	my ($rhost,$fs,$isroot) = @_;
	my $token = getzfsvalue($rhost,$fs,$isroot,"receive_resume_token");

	if (defined $token && $token ne '-' && $token ne '') {
		return $token;
	}

	if ($debug) {
        print "DEBUG: no receive token found \n";
    }

	return
}

sub parsespecialoptions {
	my ($line) = @_;

	my @options = ();

	my @values = split(/ /, $line);

	my $optionValue = 0;
	my $lastOption;

	foreach my $value (@values) {
		if ($optionValue ne 0) {
			my %item = (
				"option"  => $lastOption,
				"line" => "-$lastOption $value",
			);

			push @options, \%item;
			$optionValue = 0;
			next;
		}

		for my $char (split //, $value) {
			if ($optionValue ne 0) {
				return undef;
			}

			if ($char eq 'o' || $char eq 'x') {
				$lastOption = $char;
				$optionValue = 1;
			} else {
				my %item = (
					"option"  => $char,
					"line" => "-$char",
				);

				push @options, \%item;
			}
		}
	}

	return @options;
}

sub getoptionsline {
	my ($options_ref, @allowed) = @_;

	my $line = '';

	foreach my $value (@{ $options_ref }) {
		if (@allowed) {
			if (!grep( /^$$value{'option'}$/, @allowed) ) {
				next;
			}
		}

		$line = "$line$$value{'line'} ";
	}

	return $line;
}

sub resetreceivestate {
	my ($rhost,$fs,$isroot) = @_;

	my $fsescaped = escapeshellparam($fs);

	if ($rhost ne '') {
		$rhost = "$sshcmd $rhost";
		# double escaping needed
		$fsescaped = escapeshellparam($fsescaped);
	}

	if ($debug) { print "DEBUG: reset partial receive state of $fs...\n"; }
	my $mysudocmd;
	if ($isroot) { $mysudocmd = ''; } else { $mysudocmd = $sudocmd; }
	my $resetcmd = "$rhost $mysudocmd $zfscmd receive -A $fsescaped";
	if ($debug) { print "$resetcmd\n"; }
	system("$resetcmd") == 0
		or die "CRITICAL ERROR: $resetcmd failed: $?";
}

__END__

=head1 NAME

syncoid - ZFS snapshot replication tool

=head1 SYNOPSIS

 syncoid [options]... SOURCE TARGET
 or   syncoid [options]... SOURCE USER@HOST:TARGET
 or   syncoid [options]... USER@HOST:SOURCE TARGET
 or   syncoid [options]... USER@HOST:SOURCE USER@HOST:TARGET

 SOURCE                Source ZFS dataset. Can be either local or remote
 TARGET                Target ZFS dataset. Can be either local or remote

Options:

  --compress=FORMAT     Compresses data during transfer. Currently accepted options are gzip, pigz-fast, pigz-slow, zstd-fast, zstd-slow, lz4, xz, lzo (default) & none
  --identifier=EXTRA    Extra identifier which is included in the snapshot name. Can be used for replicating to multiple targets.
  --recursive|r         Also transfers child datasets
  --skip-parent         Skips syncing of the parent dataset. Does nothing without '--recursive' option.
  --source-bwlimit=<limit k|m|g|t>  Bandwidth limit in bytes/kbytes/etc per second on the source transfer
  --target-bwlimit=<limit k|m|g|t>  Bandwidth limit in bytes/kbytes/etc per second on the target transfer
  --mbuffer-size=VALUE  Specify the mbuffer size (default: 16M), please refer to mbuffer(1) manual page.
  --no-stream           Replicates using newest snapshot instead of intermediates
  --no-sync-snap        Does not create new snapshot, only transfers existing
  --create-bookmark     Creates a zfs bookmark for the newest snapshot on the source after replication succeeds (only works with --no-sync-snap)
  --no-clone-rollback   Does not rollback clones on target
  --no-rollback         Does not rollback clones or snapshots on target (it probably requires a readonly target)
  --exclude=REGEX       Exclude specific datasets which match the given regular expression. Can be specified multiple times
  --sendoptions=OPTIONS Use advanced options for zfs send (the arguments are filterd as needed), e.g. syncoid --sendoptions="Lc e" sets zfs send -L -c -e ...
  --recvoptions=OPTIONS Use advanced options for zfs receive (the arguments are filterd as needed), e.g. syncoid --recvoptions="ux recordsize o compression=lz4" sets zfs receive -u -x recordsize -o compression=lz4 ...
  --sshkey=FILE         Specifies a ssh key to use to connect
  --sshport=PORT        Connects to remote on a particular port
  --sshcipher|c=CIPHER  Passes CIPHER to ssh to use a particular cipher set
  --sshoption|o=OPTION  Passes OPTION to ssh for remote usage. Can be specified multiple times

  --help                Prints this helptext
  --version             Prints the version number
  --debug               Prints out a lot of additional information during a syncoid run
  --monitor-version     Currently does nothing
  --quiet               Suppresses non-error output
  --dumpsnaps           Dumps a list of snapshots during the run
  --no-command-checks   Do not check command existence before attempting transfer. Not recommended
  --no-resume           Don't use the ZFS resume feature if available
  --no-clone-handling   Don't try to recreate clones on target
  --no-privilege-elevation  Bypass the root check, for use with ZFS permission delegation

  --force-delete        Remove target datasets recursively, if there are no matching snapshots/bookmarks