Bootlin logo

Elixir Cross Referencer

   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
// SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright (C) 2016 Oracle.  All Rights Reserved.
 * Author: Darrick J. Wong <darrick.wong@oracle.com>
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_defer.h"
#include "xfs_da_format.h"
#include "xfs_da_btree.h"
#include "xfs_inode.h"
#include "xfs_trans.h"
#include "xfs_inode_item.h"
#include "xfs_bmap.h"
#include "xfs_bmap_util.h"
#include "xfs_error.h"
#include "xfs_dir2.h"
#include "xfs_dir2_priv.h"
#include "xfs_ioctl.h"
#include "xfs_trace.h"
#include "xfs_log.h"
#include "xfs_icache.h"
#include "xfs_pnfs.h"
#include "xfs_btree.h"
#include "xfs_refcount_btree.h"
#include "xfs_refcount.h"
#include "xfs_bmap_btree.h"
#include "xfs_trans_space.h"
#include "xfs_bit.h"
#include "xfs_alloc.h"
#include "xfs_quota_defs.h"
#include "xfs_quota.h"
#include "xfs_reflink.h"
#include "xfs_iomap.h"
#include "xfs_rmap_btree.h"
#include "xfs_sb.h"
#include "xfs_ag_resv.h"

/*
 * Copy on Write of Shared Blocks
 *
 * XFS must preserve "the usual" file semantics even when two files share
 * the same physical blocks.  This means that a write to one file must not
 * alter the blocks in a different file; the way that we'll do that is
 * through the use of a copy-on-write mechanism.  At a high level, that
 * means that when we want to write to a shared block, we allocate a new
 * block, write the data to the new block, and if that succeeds we map the
 * new block into the file.
 *
 * XFS provides a "delayed allocation" mechanism that defers the allocation
 * of disk blocks to dirty-but-not-yet-mapped file blocks as long as
 * possible.  This reduces fragmentation by enabling the filesystem to ask
 * for bigger chunks less often, which is exactly what we want for CoW.
 *
 * The delalloc mechanism begins when the kernel wants to make a block
 * writable (write_begin or page_mkwrite).  If the offset is not mapped, we
 * create a delalloc mapping, which is a regular in-core extent, but without
 * a real startblock.  (For delalloc mappings, the startblock encodes both
 * a flag that this is a delalloc mapping, and a worst-case estimate of how
 * many blocks might be required to put the mapping into the BMBT.)  delalloc
 * mappings are a reservation against the free space in the filesystem;
 * adjacent mappings can also be combined into fewer larger mappings.
 *
 * As an optimization, the CoW extent size hint (cowextsz) creates
 * outsized aligned delalloc reservations in the hope of landing out of
 * order nearby CoW writes in a single extent on disk, thereby reducing
 * fragmentation and improving future performance.
 *
 * D: --RRRRRRSSSRRRRRRRR--- (data fork)
 * C: ------DDDDDDD--------- (CoW fork)
 *
 * When dirty pages are being written out (typically in writepage), the
 * delalloc reservations are converted into unwritten mappings by
 * allocating blocks and replacing the delalloc mapping with real ones.
 * A delalloc mapping can be replaced by several unwritten ones if the
 * free space is fragmented.
 *
 * D: --RRRRRRSSSRRRRRRRR---
 * C: ------UUUUUUU---------
 *
 * We want to adapt the delalloc mechanism for copy-on-write, since the
 * write paths are similar.  The first two steps (creating the reservation
 * and allocating the blocks) are exactly the same as delalloc except that
 * the mappings must be stored in a separate CoW fork because we do not want
 * to disturb the mapping in the data fork until we're sure that the write
 * succeeded.  IO completion in this case is the process of removing the old
 * mapping from the data fork and moving the new mapping from the CoW fork to
 * the data fork.  This will be discussed shortly.
 *
 * For now, unaligned directio writes will be bounced back to the page cache.
 * Block-aligned directio writes will use the same mechanism as buffered
 * writes.
 *
 * Just prior to submitting the actual disk write requests, we convert
 * the extents representing the range of the file actually being written
 * (as opposed to extra pieces created for the cowextsize hint) to real
 * extents.  This will become important in the next step:
 *
 * D: --RRRRRRSSSRRRRRRRR---
 * C: ------UUrrUUU---------
 *
 * CoW remapping must be done after the data block write completes,
 * because we don't want to destroy the old data fork map until we're sure
 * the new block has been written.  Since the new mappings are kept in a
 * separate fork, we can simply iterate these mappings to find the ones
 * that cover the file blocks that we just CoW'd.  For each extent, simply
 * unmap the corresponding range in the data fork, map the new range into
 * the data fork, and remove the extent from the CoW fork.  Because of
 * the presence of the cowextsize hint, however, we must be careful
 * only to remap the blocks that we've actually written out --  we must
 * never remap delalloc reservations nor CoW staging blocks that have
 * yet to be written.  This corresponds exactly to the real extents in
 * the CoW fork:
 *
 * D: --RRRRRRrrSRRRRRRRR---
 * C: ------UU--UUU---------
 *
 * Since the remapping operation can be applied to an arbitrary file
 * range, we record the need for the remap step as a flag in the ioend
 * instead of declaring a new IO type.  This is required for direct io
 * because we only have ioend for the whole dio, and we have to be able to
 * remember the presence of unwritten blocks and CoW blocks with a single
 * ioend structure.  Better yet, the more ground we can cover with one
 * ioend, the better.
 */

/*
 * Given an AG extent, find the lowest-numbered run of shared blocks
 * within that range and return the range in fbno/flen.  If
 * find_end_of_shared is true, return the longest contiguous extent of
 * shared blocks.  If there are no shared extents, fbno and flen will
 * be set to NULLAGBLOCK and 0, respectively.
 */
int
xfs_reflink_find_shared(
	struct xfs_mount	*mp,
	struct xfs_trans	*tp,
	xfs_agnumber_t		agno,
	xfs_agblock_t		agbno,
	xfs_extlen_t		aglen,
	xfs_agblock_t		*fbno,
	xfs_extlen_t		*flen,
	bool			find_end_of_shared)
{
	struct xfs_buf		*agbp;
	struct xfs_btree_cur	*cur;
	int			error;

	error = xfs_alloc_read_agf(mp, tp, agno, 0, &agbp);
	if (error)
		return error;
	if (!agbp)
		return -ENOMEM;

	cur = xfs_refcountbt_init_cursor(mp, tp, agbp, agno);

	error = xfs_refcount_find_shared(cur, agbno, aglen, fbno, flen,
			find_end_of_shared);

	xfs_btree_del_cursor(cur, error);

	xfs_trans_brelse(tp, agbp);
	return error;
}

/*
 * Trim the mapping to the next block where there's a change in the
 * shared/unshared status.  More specifically, this means that we
 * find the lowest-numbered extent of shared blocks that coincides with
 * the given block mapping.  If the shared extent overlaps the start of
 * the mapping, trim the mapping to the end of the shared extent.  If
 * the shared region intersects the mapping, trim the mapping to the
 * start of the shared extent.  If there are no shared regions that
 * overlap, just return the original extent.
 */
int
xfs_reflink_trim_around_shared(
	struct xfs_inode	*ip,
	struct xfs_bmbt_irec	*irec,
	bool			*shared)
{
	xfs_agnumber_t		agno;
	xfs_agblock_t		agbno;
	xfs_extlen_t		aglen;
	xfs_agblock_t		fbno;
	xfs_extlen_t		flen;
	int			error = 0;

	/* Holes, unwritten, and delalloc extents cannot be shared */
	if (!xfs_is_reflink_inode(ip) || !xfs_bmap_is_real_extent(irec)) {
		*shared = false;
		return 0;
	}

	trace_xfs_reflink_trim_around_shared(ip, irec);

	agno = XFS_FSB_TO_AGNO(ip->i_mount, irec->br_startblock);
	agbno = XFS_FSB_TO_AGBNO(ip->i_mount, irec->br_startblock);
	aglen = irec->br_blockcount;

	error = xfs_reflink_find_shared(ip->i_mount, NULL, agno, agbno,
			aglen, &fbno, &flen, true);
	if (error)
		return error;

	*shared = false;
	if (fbno == NULLAGBLOCK) {
		/* No shared blocks at all. */
		return 0;
	} else if (fbno == agbno) {
		/*
		 * The start of this extent is shared.  Truncate the
		 * mapping at the end of the shared region so that a
		 * subsequent iteration starts at the start of the
		 * unshared region.
		 */
		irec->br_blockcount = flen;
		*shared = true;
		return 0;
	} else {
		/*
		 * There's a shared extent midway through this extent.
		 * Truncate the mapping at the start of the shared
		 * extent so that a subsequent iteration starts at the
		 * start of the shared region.
		 */
		irec->br_blockcount = fbno - agbno;
		return 0;
	}
}

/*
 * Trim the passed in imap to the next shared/unshared extent boundary, and
 * if imap->br_startoff points to a shared extent reserve space for it in the
 * COW fork.
 *
 * Note that imap will always contain the block numbers for the existing blocks
 * in the data fork, as the upper layers need them for read-modify-write
 * operations.
 */
int
xfs_reflink_reserve_cow(
	struct xfs_inode	*ip,
	struct xfs_bmbt_irec	*imap)
{
	struct xfs_ifork	*ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
	struct xfs_bmbt_irec	got;
	int			error = 0;
	bool			eof = false;
	struct xfs_iext_cursor	icur;
	bool			shared;

	/*
	 * Search the COW fork extent list first.  This serves two purposes:
	 * first this implement the speculative preallocation using cowextisze,
	 * so that we also unshared block adjacent to shared blocks instead
	 * of just the shared blocks themselves.  Second the lookup in the
	 * extent list is generally faster than going out to the shared extent
	 * tree.
	 */

	if (!xfs_iext_lookup_extent(ip, ifp, imap->br_startoff, &icur, &got))
		eof = true;
	if (!eof && got.br_startoff <= imap->br_startoff) {
		trace_xfs_reflink_cow_found(ip, imap);
		xfs_trim_extent(imap, got.br_startoff, got.br_blockcount);
		return 0;
	}

	/* Trim the mapping to the nearest shared extent boundary. */
	error = xfs_reflink_trim_around_shared(ip, imap, &shared);
	if (error)
		return error;

	/* Not shared?  Just report the (potentially capped) extent. */
	if (!shared)
		return 0;

	/*
	 * Fork all the shared blocks from our write offset until the end of
	 * the extent.
	 */
	error = xfs_qm_dqattach_locked(ip, false);
	if (error)
		return error;

	error = xfs_bmapi_reserve_delalloc(ip, XFS_COW_FORK, imap->br_startoff,
			imap->br_blockcount, 0, &got, &icur, eof);
	if (error == -ENOSPC || error == -EDQUOT)
		trace_xfs_reflink_cow_enospc(ip, imap);
	if (error)
		return error;

	xfs_trim_extent(imap, got.br_startoff, got.br_blockcount);
	trace_xfs_reflink_cow_alloc(ip, &got);
	return 0;
}

/* Convert part of an unwritten CoW extent to a real one. */
STATIC int
xfs_reflink_convert_cow_extent(
	struct xfs_inode		*ip,
	struct xfs_bmbt_irec		*imap,
	xfs_fileoff_t			offset_fsb,
	xfs_filblks_t			count_fsb)
{
	int				nimaps = 1;

	if (imap->br_state == XFS_EXT_NORM)
		return 0;

	xfs_trim_extent(imap, offset_fsb, count_fsb);
	trace_xfs_reflink_convert_cow(ip, imap);
	if (imap->br_blockcount == 0)
		return 0;
	return xfs_bmapi_write(NULL, ip, imap->br_startoff, imap->br_blockcount,
			XFS_BMAPI_COWFORK | XFS_BMAPI_CONVERT, 0, imap,
			&nimaps);
}

/* Convert all of the unwritten CoW extents in a file's range to real ones. */
int
xfs_reflink_convert_cow(
	struct xfs_inode	*ip,
	xfs_off_t		offset,
	xfs_off_t		count)
{
	struct xfs_mount	*mp = ip->i_mount;
	xfs_fileoff_t		offset_fsb = XFS_B_TO_FSBT(mp, offset);
	xfs_fileoff_t		end_fsb = XFS_B_TO_FSB(mp, offset + count);
	xfs_filblks_t		count_fsb = end_fsb - offset_fsb;
	struct xfs_bmbt_irec	imap;
	int			nimaps = 1, error = 0;

	ASSERT(count != 0);

	xfs_ilock(ip, XFS_ILOCK_EXCL);
	error = xfs_bmapi_write(NULL, ip, offset_fsb, count_fsb,
			XFS_BMAPI_COWFORK | XFS_BMAPI_CONVERT |
			XFS_BMAPI_CONVERT_ONLY, 0, &imap, &nimaps);
	xfs_iunlock(ip, XFS_ILOCK_EXCL);
	return error;
}

/*
 * Find the extent that maps the given range in the COW fork. Even if the extent
 * is not shared we might have a preallocation for it in the COW fork. If so we
 * use it that rather than trigger a new allocation.
 */
static int
xfs_find_trim_cow_extent(
	struct xfs_inode	*ip,
	struct xfs_bmbt_irec	*imap,
	bool			*shared,
	bool			*found)
{
	xfs_fileoff_t		offset_fsb = imap->br_startoff;
	xfs_filblks_t		count_fsb = imap->br_blockcount;
	struct xfs_iext_cursor	icur;
	struct xfs_bmbt_irec	got;

	*found = false;

	/*
	 * If we don't find an overlapping extent, trim the range we need to
	 * allocate to fit the hole we found.
	 */
	if (!xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, &got))
		got.br_startoff = offset_fsb + count_fsb;
	if (got.br_startoff > offset_fsb) {
		xfs_trim_extent(imap, imap->br_startoff,
				got.br_startoff - imap->br_startoff);
		return xfs_reflink_trim_around_shared(ip, imap, shared);
	}

	*shared = true;
	if (isnullstartblock(got.br_startblock)) {
		xfs_trim_extent(imap, got.br_startoff, got.br_blockcount);
		return 0;
	}

	/* real extent found - no need to allocate */
	xfs_trim_extent(&got, offset_fsb, count_fsb);
	*imap = got;
	*found = true;
	return 0;
}

/* Allocate all CoW reservations covering a range of blocks in a file. */
int
xfs_reflink_allocate_cow(
	struct xfs_inode	*ip,
	struct xfs_bmbt_irec	*imap,
	bool			*shared,
	uint			*lockmode)
{
	struct xfs_mount	*mp = ip->i_mount;
	xfs_fileoff_t		offset_fsb = imap->br_startoff;
	xfs_filblks_t		count_fsb = imap->br_blockcount;
	struct xfs_trans	*tp;
	int			nimaps, error = 0;
	bool			found;
	xfs_filblks_t		resaligned;
	xfs_extlen_t		resblks = 0;

	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
	ASSERT(xfs_is_reflink_inode(ip));

	error = xfs_find_trim_cow_extent(ip, imap, shared, &found);
	if (error || !*shared)
		return error;
	if (found)
		goto convert;

	resaligned = xfs_aligned_fsb_count(imap->br_startoff,
		imap->br_blockcount, xfs_get_cowextsz_hint(ip));
	resblks = XFS_DIOSTRAT_SPACE_RES(mp, resaligned);

	xfs_iunlock(ip, *lockmode);
	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0, 0, &tp);
	*lockmode = XFS_ILOCK_EXCL;
	xfs_ilock(ip, *lockmode);

	if (error)
		return error;

	error = xfs_qm_dqattach_locked(ip, false);
	if (error)
		goto out_trans_cancel;

	/*
	 * Check for an overlapping extent again now that we dropped the ilock.
	 */
	error = xfs_find_trim_cow_extent(ip, imap, shared, &found);
	if (error || !*shared)
		goto out_trans_cancel;
	if (found) {
		xfs_trans_cancel(tp);
		goto convert;
	}

	error = xfs_trans_reserve_quota_nblks(tp, ip, resblks, 0,
			XFS_QMOPT_RES_REGBLKS);
	if (error)
		goto out_trans_cancel;

	xfs_trans_ijoin(tp, ip, 0);

	/* Allocate the entire reservation as unwritten blocks. */
	nimaps = 1;
	error = xfs_bmapi_write(tp, ip, imap->br_startoff, imap->br_blockcount,
			XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC,
			resblks, imap, &nimaps);
	if (error)
		goto out_unreserve;

	xfs_inode_set_cowblocks_tag(ip);
	error = xfs_trans_commit(tp);
	if (error)
		return error;

	/*
	 * Allocation succeeded but the requested range was not even partially
	 * satisfied?  Bail out!
	 */
	if (nimaps == 0)
		return -ENOSPC;
convert:
	return xfs_reflink_convert_cow_extent(ip, imap, offset_fsb, count_fsb);

out_unreserve:
	xfs_trans_unreserve_quota_nblks(tp, ip, (long)resblks, 0,
			XFS_QMOPT_RES_REGBLKS);
out_trans_cancel:
	xfs_trans_cancel(tp);
	return error;
}

/*
 * Cancel CoW reservations for some block range of an inode.
 *
 * If cancel_real is true this function cancels all COW fork extents for the
 * inode; if cancel_real is false, real extents are not cleared.
 *
 * Caller must have already joined the inode to the current transaction. The
 * inode will be joined to the transaction returned to the caller.
 */
int
xfs_reflink_cancel_cow_blocks(
	struct xfs_inode		*ip,
	struct xfs_trans		**tpp,
	xfs_fileoff_t			offset_fsb,
	xfs_fileoff_t			end_fsb,
	bool				cancel_real)
{
	struct xfs_ifork		*ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
	struct xfs_bmbt_irec		got, del;
	struct xfs_iext_cursor		icur;
	int				error = 0;

	if (!xfs_inode_has_cow_data(ip))
		return 0;
	if (!xfs_iext_lookup_extent_before(ip, ifp, &end_fsb, &icur, &got))
		return 0;

	/* Walk backwards until we're out of the I/O range... */
	while (got.br_startoff + got.br_blockcount > offset_fsb) {
		del = got;
		xfs_trim_extent(&del, offset_fsb, end_fsb - offset_fsb);

		/* Extent delete may have bumped ext forward */
		if (!del.br_blockcount) {
			xfs_iext_prev(ifp, &icur);
			goto next_extent;
		}

		trace_xfs_reflink_cancel_cow(ip, &del);

		if (isnullstartblock(del.br_startblock)) {
			error = xfs_bmap_del_extent_delay(ip, XFS_COW_FORK,
					&icur, &got, &del);
			if (error)
				break;
		} else if (del.br_state == XFS_EXT_UNWRITTEN || cancel_real) {
			ASSERT((*tpp)->t_firstblock == NULLFSBLOCK);

			/* Free the CoW orphan record. */
			error = xfs_refcount_free_cow_extent(*tpp,
					del.br_startblock, del.br_blockcount);
			if (error)
				break;

			xfs_bmap_add_free(*tpp, del.br_startblock,
					  del.br_blockcount, NULL);

			/* Roll the transaction */
			error = xfs_defer_finish(tpp);
			if (error)
				break;

			/* Remove the mapping from the CoW fork. */
			xfs_bmap_del_extent_cow(ip, &icur, &got, &del);

			/* Remove the quota reservation */
			error = xfs_trans_reserve_quota_nblks(NULL, ip,
					-(long)del.br_blockcount, 0,
					XFS_QMOPT_RES_REGBLKS);
			if (error)
				break;
		} else {
			/* Didn't do anything, push cursor back. */
			xfs_iext_prev(ifp, &icur);
		}
next_extent:
		if (!xfs_iext_get_extent(ifp, &icur, &got))
			break;
	}

	/* clear tag if cow fork is emptied */
	if (!ifp->if_bytes)
		xfs_inode_clear_cowblocks_tag(ip);
	return error;
}

/*
 * Cancel CoW reservations for some byte range of an inode.
 *
 * If cancel_real is true this function cancels all COW fork extents for the
 * inode; if cancel_real is false, real extents are not cleared.
 */
int
xfs_reflink_cancel_cow_range(
	struct xfs_inode	*ip,
	xfs_off_t		offset,
	xfs_off_t		count,
	bool			cancel_real)
{
	struct xfs_trans	*tp;
	xfs_fileoff_t		offset_fsb;
	xfs_fileoff_t		end_fsb;
	int			error;

	trace_xfs_reflink_cancel_cow_range(ip, offset, count);
	ASSERT(xfs_is_reflink_inode(ip));

	offset_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
	if (count == NULLFILEOFF)
		end_fsb = NULLFILEOFF;
	else
		end_fsb = XFS_B_TO_FSB(ip->i_mount, offset + count);

	/* Start a rolling transaction to remove the mappings */
	error = xfs_trans_alloc(ip->i_mount, &M_RES(ip->i_mount)->tr_write,
			0, 0, XFS_TRANS_NOFS, &tp);
	if (error)
		goto out;

	xfs_ilock(ip, XFS_ILOCK_EXCL);
	xfs_trans_ijoin(tp, ip, 0);

	/* Scrape out the old CoW reservations */
	error = xfs_reflink_cancel_cow_blocks(ip, &tp, offset_fsb, end_fsb,
			cancel_real);
	if (error)
		goto out_cancel;

	error = xfs_trans_commit(tp);

	xfs_iunlock(ip, XFS_ILOCK_EXCL);
	return error;

out_cancel:
	xfs_trans_cancel(tp);
	xfs_iunlock(ip, XFS_ILOCK_EXCL);
out:
	trace_xfs_reflink_cancel_cow_range_error(ip, error, _RET_IP_);
	return error;
}

/*
 * Remap parts of a file's data fork after a successful CoW.
 */
int
xfs_reflink_end_cow(
	struct xfs_inode		*ip,
	xfs_off_t			offset,
	xfs_off_t			count)
{
	struct xfs_ifork		*ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
	struct xfs_bmbt_irec		got, del;
	struct xfs_trans		*tp;
	xfs_fileoff_t			offset_fsb;
	xfs_fileoff_t			end_fsb;
	int				error;
	unsigned int			resblks;
	xfs_filblks_t			rlen;
	struct xfs_iext_cursor		icur;

	trace_xfs_reflink_end_cow(ip, offset, count);

	/* No COW extents?  That's easy! */
	if (ifp->if_bytes == 0)
		return 0;

	offset_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
	end_fsb = XFS_B_TO_FSB(ip->i_mount, offset + count);

	/*
	 * Start a rolling transaction to switch the mappings.  We're
	 * unlikely ever to have to remap 16T worth of single-block
	 * extents, so just cap the worst case extent count to 2^32-1.
	 * Stick a warning in just in case, and avoid 64-bit division.
	 */
	BUILD_BUG_ON(MAX_RW_COUNT > UINT_MAX);
	if (end_fsb - offset_fsb > UINT_MAX) {
		error = -EFSCORRUPTED;
		xfs_force_shutdown(ip->i_mount, SHUTDOWN_CORRUPT_INCORE);
		ASSERT(0);
		goto out;
	}
	resblks = XFS_NEXTENTADD_SPACE_RES(ip->i_mount,
			(unsigned int)(end_fsb - offset_fsb),
			XFS_DATA_FORK);
	error = xfs_trans_alloc(ip->i_mount, &M_RES(ip->i_mount)->tr_write,
			resblks, 0, XFS_TRANS_RESERVE | XFS_TRANS_NOFS, &tp);
	if (error)
		goto out;

	xfs_ilock(ip, XFS_ILOCK_EXCL);
	xfs_trans_ijoin(tp, ip, 0);

	/*
	 * In case of racing, overlapping AIO writes no COW extents might be
	 * left by the time I/O completes for the loser of the race.  In that
	 * case we are done.
	 */
	if (!xfs_iext_lookup_extent_before(ip, ifp, &end_fsb, &icur, &got))
		goto out_cancel;

	/* Walk backwards until we're out of the I/O range... */
	while (got.br_startoff + got.br_blockcount > offset_fsb) {
		del = got;
		xfs_trim_extent(&del, offset_fsb, end_fsb - offset_fsb);

		/* Extent delete may have bumped ext forward */
		if (!del.br_blockcount)
			goto prev_extent;

		/*
		 * Only remap real extent that contain data.  With AIO
		 * speculatively preallocations can leak into the range we
		 * are called upon, and we need to skip them.
		 */
		if (!xfs_bmap_is_real_extent(&got))
			goto prev_extent;

		/* Unmap the old blocks in the data fork. */
		ASSERT(tp->t_firstblock == NULLFSBLOCK);
		rlen = del.br_blockcount;
		error = __xfs_bunmapi(tp, ip, del.br_startoff, &rlen, 0, 1);
		if (error)
			goto out_cancel;

		/* Trim the extent to whatever got unmapped. */
		if (rlen) {
			xfs_trim_extent(&del, del.br_startoff + rlen,
				del.br_blockcount - rlen);
		}
		trace_xfs_reflink_cow_remap(ip, &del);

		/* Free the CoW orphan record. */
		error = xfs_refcount_free_cow_extent(tp, del.br_startblock,
				del.br_blockcount);
		if (error)
			goto out_cancel;

		/* Map the new blocks into the data fork. */
		error = xfs_bmap_map_extent(tp, ip, &del);
		if (error)
			goto out_cancel;

		/* Charge this new data fork mapping to the on-disk quota. */
		xfs_trans_mod_dquot_byino(tp, ip, XFS_TRANS_DQ_DELBCOUNT,
				(long)del.br_blockcount);

		/* Remove the mapping from the CoW fork. */
		xfs_bmap_del_extent_cow(ip, &icur, &got, &del);

		error = xfs_defer_finish(&tp);
		if (error)
			goto out_cancel;
		if (!xfs_iext_get_extent(ifp, &icur, &got))
			break;
		continue;
prev_extent:
		if (!xfs_iext_prev_extent(ifp, &icur, &got))
			break;
	}

	error = xfs_trans_commit(tp);
	xfs_iunlock(ip, XFS_ILOCK_EXCL);
	if (error)
		goto out;
	return 0;

out_cancel:
	xfs_trans_cancel(tp);
	xfs_iunlock(ip, XFS_ILOCK_EXCL);
out:
	trace_xfs_reflink_end_cow_error(ip, error, _RET_IP_);
	return error;
}

/*
 * Free leftover CoW reservations that didn't get cleaned out.
 */
int
xfs_reflink_recover_cow(
	struct xfs_mount	*mp)
{
	xfs_agnumber_t		agno;
	int			error = 0;

	if (!xfs_sb_version_hasreflink(&mp->m_sb))
		return 0;

	for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
		error = xfs_refcount_recover_cow_leftovers(mp, agno);
		if (error)
			break;
	}

	return error;
}

/*
 * Reflinking (Block) Ranges of Two Files Together
 *
 * First, ensure that the reflink flag is set on both inodes.  The flag is an
 * optimization to avoid unnecessary refcount btree lookups in the write path.
 *
 * Now we can iteratively remap the range of extents (and holes) in src to the
 * corresponding ranges in dest.  Let drange and srange denote the ranges of
 * logical blocks in dest and src touched by the reflink operation.
 *
 * While the length of drange is greater than zero,
 *    - Read src's bmbt at the start of srange ("imap")
 *    - If imap doesn't exist, make imap appear to start at the end of srange
 *      with zero length.
 *    - If imap starts before srange, advance imap to start at srange.
 *    - If imap goes beyond srange, truncate imap to end at the end of srange.
 *    - Punch (imap start - srange start + imap len) blocks from dest at
 *      offset (drange start).
 *    - If imap points to a real range of pblks,
 *         > Increase the refcount of the imap's pblks
 *         > Map imap's pblks into dest at the offset
 *           (drange start + imap start - srange start)
 *    - Advance drange and srange by (imap start - srange start + imap len)
 *
 * Finally, if the reflink made dest longer, update both the in-core and
 * on-disk file sizes.
 *
 * ASCII Art Demonstration:
 *
 * Let's say we want to reflink this source file:
 *
 * ----SSSSSSS-SSSSS----SSSSSS (src file)
 *   <-------------------->
 *
 * into this destination file:
 *
 * --DDDDDDDDDDDDDDDDDDD--DDD (dest file)
 *        <-------------------->
 * '-' means a hole, and 'S' and 'D' are written blocks in the src and dest.
 * Observe that the range has different logical offsets in either file.
 *
 * Consider that the first extent in the source file doesn't line up with our
 * reflink range.  Unmapping  and remapping are separate operations, so we can
 * unmap more blocks from the destination file than we remap.
 *
 * ----SSSSSSS-SSSSS----SSSSSS
 *   <------->
 * --DDDDD---------DDDDD--DDD
 *        <------->
 *
 * Now remap the source extent into the destination file:
 *
 * ----SSSSSSS-SSSSS----SSSSSS
 *   <------->
 * --DDDDD--SSSSSSSDDDDD--DDD
 *        <------->
 *
 * Do likewise with the second hole and extent in our range.  Holes in the
 * unmap range don't affect our operation.
 *
 * ----SSSSSSS-SSSSS----SSSSSS
 *            <---->
 * --DDDDD--SSSSSSS-SSSSS-DDD
 *                 <---->
 *
 * Finally, unmap and remap part of the third extent.  This will increase the
 * size of the destination file.
 *
 * ----SSSSSSS-SSSSS----SSSSSS
 *                  <----->
 * --DDDDD--SSSSSSS-SSSSS----SSS
 *                       <----->
 *
 * Once we update the destination file's i_size, we're done.
 */

/*
 * Ensure the reflink bit is set in both inodes.
 */
STATIC int
xfs_reflink_set_inode_flag(
	struct xfs_inode	*src,
	struct xfs_inode	*dest)
{
	struct xfs_mount	*mp = src->i_mount;
	int			error;
	struct xfs_trans	*tp;

	if (xfs_is_reflink_inode(src) && xfs_is_reflink_inode(dest))
		return 0;

	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ichange, 0, 0, 0, &tp);
	if (error)
		goto out_error;

	/* Lock both files against IO */
	if (src->i_ino == dest->i_ino)
		xfs_ilock(src, XFS_ILOCK_EXCL);
	else
		xfs_lock_two_inodes(src, XFS_ILOCK_EXCL, dest, XFS_ILOCK_EXCL);

	if (!xfs_is_reflink_inode(src)) {
		trace_xfs_reflink_set_inode_flag(src);
		xfs_trans_ijoin(tp, src, XFS_ILOCK_EXCL);
		src->i_d.di_flags2 |= XFS_DIFLAG2_REFLINK;
		xfs_trans_log_inode(tp, src, XFS_ILOG_CORE);
		xfs_ifork_init_cow(src);
	} else
		xfs_iunlock(src, XFS_ILOCK_EXCL);

	if (src->i_ino == dest->i_ino)
		goto commit_flags;

	if (!xfs_is_reflink_inode(dest)) {
		trace_xfs_reflink_set_inode_flag(dest);
		xfs_trans_ijoin(tp, dest, XFS_ILOCK_EXCL);
		dest->i_d.di_flags2 |= XFS_DIFLAG2_REFLINK;
		xfs_trans_log_inode(tp, dest, XFS_ILOG_CORE);
		xfs_ifork_init_cow(dest);
	} else
		xfs_iunlock(dest, XFS_ILOCK_EXCL);

commit_flags:
	error = xfs_trans_commit(tp);
	if (error)
		goto out_error;
	return error;

out_error:
	trace_xfs_reflink_set_inode_flag_error(dest, error, _RET_IP_);
	return error;
}

/*
 * Update destination inode size & cowextsize hint, if necessary.
 */
int
xfs_reflink_update_dest(
	struct xfs_inode	*dest,
	xfs_off_t		newlen,
	xfs_extlen_t		cowextsize,
	unsigned int		remap_flags)
{
	struct xfs_mount	*mp = dest->i_mount;
	struct xfs_trans	*tp;
	int			error;

	if (newlen <= i_size_read(VFS_I(dest)) && cowextsize == 0)
		return 0;

	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ichange, 0, 0, 0, &tp);
	if (error)
		goto out_error;

	xfs_ilock(dest, XFS_ILOCK_EXCL);
	xfs_trans_ijoin(tp, dest, XFS_ILOCK_EXCL);

	if (newlen > i_size_read(VFS_I(dest))) {
		trace_xfs_reflink_update_inode_size(dest, newlen);
		i_size_write(VFS_I(dest), newlen);
		dest->i_d.di_size = newlen;
	}

	if (cowextsize) {
		dest->i_d.di_cowextsize = cowextsize;
		dest->i_d.di_flags2 |= XFS_DIFLAG2_COWEXTSIZE;
	}

	xfs_trans_log_inode(tp, dest, XFS_ILOG_CORE);

	error = xfs_trans_commit(tp);
	if (error)
		goto out_error;
	return error;

out_error:
	trace_xfs_reflink_update_inode_size_error(dest, error, _RET_IP_);
	return error;
}

/*
 * Do we have enough reserve in this AG to handle a reflink?  The refcount
 * btree already reserved all the space it needs, but the rmap btree can grow
 * infinitely, so we won't allow more reflinks when the AG is down to the
 * btree reserves.
 */
static int
xfs_reflink_ag_has_free_space(
	struct xfs_mount	*mp,
	xfs_agnumber_t		agno)
{
	struct xfs_perag	*pag;
	int			error = 0;

	if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
		return 0;

	pag = xfs_perag_get(mp, agno);
	if (xfs_ag_resv_critical(pag, XFS_AG_RESV_RMAPBT) ||
	    xfs_ag_resv_critical(pag, XFS_AG_RESV_METADATA))
		error = -ENOSPC;
	xfs_perag_put(pag);
	return error;
}

/*
 * Unmap a range of blocks from a file, then map other blocks into the hole.
 * The range to unmap is (destoff : destoff + srcioff + irec->br_blockcount).
 * The extent irec is mapped into dest at irec->br_startoff.
 */
STATIC int
xfs_reflink_remap_extent(
	struct xfs_inode	*ip,
	struct xfs_bmbt_irec	*irec,
	xfs_fileoff_t		destoff,
	xfs_off_t		new_isize)
{
	struct xfs_mount	*mp = ip->i_mount;
	bool			real_extent = xfs_bmap_is_real_extent(irec);
	struct xfs_trans	*tp;
	unsigned int		resblks;
	struct xfs_bmbt_irec	uirec;
	xfs_filblks_t		rlen;
	xfs_filblks_t		unmap_len;
	xfs_off_t		newlen;
	int			error;

	unmap_len = irec->br_startoff + irec->br_blockcount - destoff;
	trace_xfs_reflink_punch_range(ip, destoff, unmap_len);

	/* No reflinking if we're low on space */
	if (real_extent) {
		error = xfs_reflink_ag_has_free_space(mp,
				XFS_FSB_TO_AGNO(mp, irec->br_startblock));
		if (error)
			goto out;
	}

	/* Start a rolling transaction to switch the mappings */
	resblks = XFS_EXTENTADD_SPACE_RES(ip->i_mount, XFS_DATA_FORK);
	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0, 0, &tp);
	if (error)
		goto out;

	xfs_ilock(ip, XFS_ILOCK_EXCL);
	xfs_trans_ijoin(tp, ip, 0);

	/* If we're not just clearing space, then do we have enough quota? */
	if (real_extent) {
		error = xfs_trans_reserve_quota_nblks(tp, ip,
				irec->br_blockcount, 0, XFS_QMOPT_RES_REGBLKS);
		if (error)
			goto out_cancel;
	}

	trace_xfs_reflink_remap(ip, irec->br_startoff,
				irec->br_blockcount, irec->br_startblock);

	/* Unmap the old blocks in the data fork. */
	rlen = unmap_len;
	while (rlen) {
		ASSERT(tp->t_firstblock == NULLFSBLOCK);
		error = __xfs_bunmapi(tp, ip, destoff, &rlen, 0, 1);
		if (error)
			goto out_cancel;

		/*
		 * Trim the extent to whatever got unmapped.
		 * Remember, bunmapi works backwards.
		 */
		uirec.br_startblock = irec->br_startblock + rlen;
		uirec.br_startoff = irec->br_startoff + rlen;
		uirec.br_blockcount = unmap_len - rlen;
		unmap_len = rlen;

		/* If this isn't a real mapping, we're done. */
		if (!real_extent || uirec.br_blockcount == 0)
			goto next_extent;

		trace_xfs_reflink_remap(ip, uirec.br_startoff,
				uirec.br_blockcount, uirec.br_startblock);

		/* Update the refcount tree */
		error = xfs_refcount_increase_extent(tp, &uirec);
		if (error)
			goto out_cancel;

		/* Map the new blocks into the data fork. */
		error = xfs_bmap_map_extent(tp, ip, &uirec);
		if (error)
			goto out_cancel;

		/* Update quota accounting. */
		xfs_trans_mod_dquot_byino(tp, ip, XFS_TRANS_DQ_BCOUNT,
				uirec.br_blockcount);

		/* Update dest isize if needed. */
		newlen = XFS_FSB_TO_B(mp,
				uirec.br_startoff + uirec.br_blockcount);
		newlen = min_t(xfs_off_t, newlen, new_isize);
		if (newlen > i_size_read(VFS_I(ip))) {
			trace_xfs_reflink_update_inode_size(ip, newlen);
			i_size_write(VFS_I(ip), newlen);
			ip->i_d.di_size = newlen;
			xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
		}

next_extent:
		/* Process all the deferred stuff. */
		error = xfs_defer_finish(&tp);
		if (error)
			goto out_cancel;
	}

	error = xfs_trans_commit(tp);
	xfs_iunlock(ip, XFS_ILOCK_EXCL);
	if (error)
		goto out;
	return 0;

out_cancel:
	xfs_trans_cancel(tp);
	xfs_iunlock(ip, XFS_ILOCK_EXCL);
out:
	trace_xfs_reflink_remap_extent_error(ip, error, _RET_IP_);
	return error;
}

/*
 * Iteratively remap one file's extents (and holes) to another's.
 */
int
xfs_reflink_remap_blocks(
	struct xfs_inode	*src,
	loff_t			pos_in,
	struct xfs_inode	*dest,
	loff_t			pos_out,
	loff_t			remap_len,
	loff_t			*remapped)
{
	struct xfs_bmbt_irec	imap;
	xfs_fileoff_t		srcoff;
	xfs_fileoff_t		destoff;
	xfs_filblks_t		len;
	xfs_filblks_t		range_len;
	xfs_filblks_t		remapped_len = 0;
	xfs_off_t		new_isize = pos_out + remap_len;
	int			nimaps;
	int			error = 0;

	destoff = XFS_B_TO_FSBT(src->i_mount, pos_out);
	srcoff = XFS_B_TO_FSBT(src->i_mount, pos_in);
	len = XFS_B_TO_FSB(src->i_mount, remap_len);

	/* drange = (destoff, destoff + len); srange = (srcoff, srcoff + len) */
	while (len) {
		uint		lock_mode;

		trace_xfs_reflink_remap_blocks_loop(src, srcoff, len,
				dest, destoff);

		/* Read extent from the source file */
		nimaps = 1;
		lock_mode = xfs_ilock_data_map_shared(src);
		error = xfs_bmapi_read(src, srcoff, len, &imap, &nimaps, 0);
		xfs_iunlock(src, lock_mode);
		if (error)
			break;
		ASSERT(nimaps == 1);

		trace_xfs_reflink_remap_imap(src, srcoff, len, XFS_IO_OVERWRITE,
				&imap);

		/* Translate imap into the destination file. */
		range_len = imap.br_startoff + imap.br_blockcount - srcoff;
		imap.br_startoff += destoff - srcoff;

		/* Clear dest from destoff to the end of imap and map it in. */
		error = xfs_reflink_remap_extent(dest, &imap, destoff,
				new_isize);
		if (error)
			break;

		if (fatal_signal_pending(current)) {
			error = -EINTR;
			break;
		}

		/* Advance drange/srange */
		srcoff += range_len;
		destoff += range_len;
		len -= range_len;
		remapped_len += range_len;
	}

	if (error)
		trace_xfs_reflink_remap_blocks_error(dest, error, _RET_IP_);
	*remapped = min_t(loff_t, remap_len,
			  XFS_FSB_TO_B(src->i_mount, remapped_len));
	return error;
}

/*
 * Grab the exclusive iolock for a data copy from src to dest, making
 * sure to abide vfs locking order (lowest pointer value goes first) and
 * breaking the pnfs layout leases on dest before proceeding.  The loop
 * is needed because we cannot call the blocking break_layout() with the
 * src iolock held, and therefore have to back out both locks.
 */
static int
xfs_iolock_two_inodes_and_break_layout(
	struct inode		*src,
	struct inode		*dest)
{
	int			error;

retry:
	if (src < dest) {
		inode_lock_shared(src);
		inode_lock_nested(dest, I_MUTEX_NONDIR2);
	} else {
		/* src >= dest */
		inode_lock(dest);
	}

	error = break_layout(dest, false);
	if (error == -EWOULDBLOCK) {
		inode_unlock(dest);
		if (src < dest)
			inode_unlock_shared(src);
		error = break_layout(dest, true);
		if (error)
			return error;
		goto retry;
	}
	if (error) {
		inode_unlock(dest);
		if (src < dest)
			inode_unlock_shared(src);
		return error;
	}
	if (src > dest)
		inode_lock_shared_nested(src, I_MUTEX_NONDIR2);
	return 0;
}

/* Unlock both inodes after they've been prepped for a range clone. */
void
xfs_reflink_remap_unlock(
	struct file		*file_in,
	struct file		*file_out)
{
	struct inode		*inode_in = file_inode(file_in);
	struct xfs_inode	*src = XFS_I(inode_in);
	struct inode		*inode_out = file_inode(file_out);
	struct xfs_inode	*dest = XFS_I(inode_out);
	bool			same_inode = (inode_in == inode_out);

	xfs_iunlock(dest, XFS_MMAPLOCK_EXCL);
	if (!same_inode)
		xfs_iunlock(src, XFS_MMAPLOCK_SHARED);
	inode_unlock(inode_out);
	if (!same_inode)
		inode_unlock_shared(inode_in);
}

/*
 * If we're reflinking to a point past the destination file's EOF, we must
 * zero any speculative post-EOF preallocations that sit between the old EOF
 * and the destination file offset.
 */
static int
xfs_reflink_zero_posteof(
	struct xfs_inode	*ip,
	loff_t			pos)
{
	loff_t			isize = i_size_read(VFS_I(ip));

	if (pos <= isize)
		return 0;

	trace_xfs_zero_eof(ip, isize, pos - isize);
	return iomap_zero_range(VFS_I(ip), isize, pos - isize, NULL,
			&xfs_iomap_ops);
}

/*
 * Prepare two files for range cloning.  Upon a successful return both inodes
 * will have the iolock and mmaplock held, the page cache of the out file will
 * be truncated, and any leases on the out file will have been broken.  This
 * function borrows heavily from xfs_file_aio_write_checks.
 *
 * The VFS allows partial EOF blocks to "match" for dedupe even though it hasn't
 * checked that the bytes beyond EOF physically match. Hence we cannot use the
 * EOF block in the source dedupe range because it's not a complete block match,
 * hence can introduce a corruption into the file that has it's block replaced.
 *
 * In similar fashion, the VFS file cloning also allows partial EOF blocks to be
 * "block aligned" for the purposes of cloning entire files.  However, if the
 * source file range includes the EOF block and it lands within the existing EOF
 * of the destination file, then we can expose stale data from beyond the source
 * file EOF in the destination file.
 *
 * XFS doesn't support partial block sharing, so in both cases we have check
 * these cases ourselves. For dedupe, we can simply round the length to dedupe
 * down to the previous whole block and ignore the partial EOF block. While this
 * means we can't dedupe the last block of a file, this is an acceptible
 * tradeoff for simplicity on implementation.
 *
 * For cloning, we want to share the partial EOF block if it is also the new EOF
 * block of the destination file. If the partial EOF block lies inside the
 * existing destination EOF, then we have to abort the clone to avoid exposing
 * stale data in the destination file. Hence we reject these clone attempts with
 * -EINVAL in this case.
 */
int
xfs_reflink_remap_prep(
	struct file		*file_in,
	loff_t			pos_in,
	struct file		*file_out,
	loff_t			pos_out,
	loff_t			*len,
	unsigned int		remap_flags)
{
	struct inode		*inode_in = file_inode(file_in);
	struct xfs_inode	*src = XFS_I(inode_in);
	struct inode		*inode_out = file_inode(file_out);
	struct xfs_inode	*dest = XFS_I(inode_out);
	bool			same_inode = (inode_in == inode_out);
	ssize_t			ret;

	/* Lock both files against IO */
	ret = xfs_iolock_two_inodes_and_break_layout(inode_in, inode_out);
	if (ret)
		return ret;
	if (same_inode)
		xfs_ilock(src, XFS_MMAPLOCK_EXCL);
	else
		xfs_lock_two_inodes(src, XFS_MMAPLOCK_SHARED, dest,
				XFS_MMAPLOCK_EXCL);

	/* Check file eligibility and prepare for block sharing. */
	ret = -EINVAL;
	/* Don't reflink realtime inodes */
	if (XFS_IS_REALTIME_INODE(src) || XFS_IS_REALTIME_INODE(dest))
		goto out_unlock;

	/* Don't share DAX file data for now. */
	if (IS_DAX(inode_in) || IS_DAX(inode_out))
		goto out_unlock;

	ret = generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
			len, remap_flags);
	if (ret < 0 || *len == 0)
		goto out_unlock;

	/* Attach dquots to dest inode before changing block map */
	ret = xfs_qm_dqattach(dest);
	if (ret)
		goto out_unlock;

	/*
	 * Zero existing post-eof speculative preallocations in the destination
	 * file.
	 */
	ret = xfs_reflink_zero_posteof(dest, pos_out);
	if (ret)
		goto out_unlock;

	/* Set flags and remap blocks. */
	ret = xfs_reflink_set_inode_flag(src, dest);
	if (ret)
		goto out_unlock;

	/*
	 * If pos_out > EOF, we may have dirtied blocks between EOF and
	 * pos_out. In that case, we need to extend the flush and unmap to cover
	 * from EOF to the end of the copy length.
	 */
	if (pos_out > XFS_ISIZE(dest)) {
		loff_t	flen = *len + (pos_out - XFS_ISIZE(dest));
		ret = xfs_flush_unmap_range(dest, XFS_ISIZE(dest), flen);
	} else {
		ret = xfs_flush_unmap_range(dest, pos_out, *len);
	}
	if (ret)
		goto out_unlock;

	return 1;
out_unlock:
	xfs_reflink_remap_unlock(file_in, file_out);
	return ret;
}

/*
 * The user wants to preemptively CoW all shared blocks in this file,
 * which enables us to turn off the reflink flag.  Iterate all
 * extents which are not prealloc/delalloc to see which ranges are
 * mentioned in the refcount tree, then read those blocks into the
 * pagecache, dirty them, fsync them back out, and then we can update
 * the inode flag.  What happens if we run out of memory? :)
 */
STATIC int
xfs_reflink_dirty_extents(
	struct xfs_inode	*ip,
	xfs_fileoff_t		fbno,
	xfs_filblks_t		end,
	xfs_off_t		isize)
{
	struct xfs_mount	*mp = ip->i_mount;
	xfs_agnumber_t		agno;
	xfs_agblock_t		agbno;
	xfs_extlen_t		aglen;
	xfs_agblock_t		rbno;
	xfs_extlen_t		rlen;
	xfs_off_t		fpos;
	xfs_off_t		flen;
	struct xfs_bmbt_irec	map[2];
	int			nmaps;
	int			error = 0;

	while (end - fbno > 0) {
		nmaps = 1;
		/*
		 * Look for extents in the file.  Skip holes, delalloc, or
		 * unwritten extents; they can't be reflinked.
		 */
		error = xfs_bmapi_read(ip, fbno, end - fbno, map, &nmaps, 0);
		if (error)
			goto out;
		if (nmaps == 0)
			break;
		if (!xfs_bmap_is_real_extent(&map[0]))
			goto next;

		map[1] = map[0];
		while (map[1].br_blockcount) {
			agno = XFS_FSB_TO_AGNO(mp, map[1].br_startblock);
			agbno = XFS_FSB_TO_AGBNO(mp, map[1].br_startblock);
			aglen = map[1].br_blockcount;

			error = xfs_reflink_find_shared(mp, NULL, agno, agbno,
					aglen, &rbno, &rlen, true);
			if (error)
				goto out;
			if (rbno == NULLAGBLOCK)
				break;

			/* Dirty the pages */
			xfs_iunlock(ip, XFS_ILOCK_EXCL);
			fpos = XFS_FSB_TO_B(mp, map[1].br_startoff +
					(rbno - agbno));
			flen = XFS_FSB_TO_B(mp, rlen);
			if (fpos + flen > isize)
				flen = isize - fpos;
			error = iomap_file_dirty(VFS_I(ip), fpos, flen,
					&xfs_iomap_ops);
			xfs_ilock(ip, XFS_ILOCK_EXCL);
			if (error)
				goto out;

			map[1].br_blockcount -= (rbno - agbno + rlen);
			map[1].br_startoff += (rbno - agbno + rlen);
			map[1].br_startblock += (rbno - agbno + rlen);
		}

next:
		fbno = map[0].br_startoff + map[0].br_blockcount;
	}
out:
	return error;
}

/* Does this inode need the reflink flag? */
int
xfs_reflink_inode_has_shared_extents(
	struct xfs_trans		*tp,
	struct xfs_inode		*ip,
	bool				*has_shared)
{
	struct xfs_bmbt_irec		got;
	struct xfs_mount		*mp = ip->i_mount;
	struct xfs_ifork		*ifp;
	xfs_agnumber_t			agno;
	xfs_agblock_t			agbno;
	xfs_extlen_t			aglen;
	xfs_agblock_t			rbno;
	xfs_extlen_t			rlen;
	struct xfs_iext_cursor		icur;
	bool				found;
	int				error;

	ifp = XFS_IFORK_PTR(ip, XFS_DATA_FORK);
	if (!(ifp->if_flags & XFS_IFEXTENTS)) {
		error = xfs_iread_extents(tp, ip, XFS_DATA_FORK);
		if (error)
			return error;
	}

	*has_shared = false;
	found = xfs_iext_lookup_extent(ip, ifp, 0, &icur, &got);
	while (found) {
		if (isnullstartblock(got.br_startblock) ||
		    got.br_state != XFS_EXT_NORM)
			goto next;
		agno = XFS_FSB_TO_AGNO(mp, got.br_startblock);
		agbno = XFS_FSB_TO_AGBNO(mp, got.br_startblock);
		aglen = got.br_blockcount;

		error = xfs_reflink_find_shared(mp, tp, agno, agbno, aglen,
				&rbno, &rlen, false);
		if (error)
			return error;
		/* Is there still a shared block here? */
		if (rbno != NULLAGBLOCK) {
			*has_shared = true;
			return 0;
		}
next:
		found = xfs_iext_next_extent(ifp, &icur, &got);
	}

	return 0;
}

/*
 * Clear the inode reflink flag if there are no shared extents.
 *
 * The caller is responsible for joining the inode to the transaction passed in.
 * The inode will be joined to the transaction that is returned to the caller.
 */
int
xfs_reflink_clear_inode_flag(
	struct xfs_inode	*ip,
	struct xfs_trans	**tpp)
{
	bool			needs_flag;
	int			error = 0;

	ASSERT(xfs_is_reflink_inode(ip));

	error = xfs_reflink_inode_has_shared_extents(*tpp, ip, &needs_flag);
	if (error || needs_flag)
		return error;

	/*
	 * We didn't find any shared blocks so turn off the reflink flag.
	 * First, get rid of any leftover CoW mappings.
	 */
	error = xfs_reflink_cancel_cow_blocks(ip, tpp, 0, NULLFILEOFF, true);
	if (error)
		return error;

	/* Clear the inode flag. */
	trace_xfs_reflink_unset_inode_flag(ip);
	ip->i_d.di_flags2 &= ~XFS_DIFLAG2_REFLINK;
	xfs_inode_clear_cowblocks_tag(ip);
	xfs_trans_log_inode(*tpp, ip, XFS_ILOG_CORE);

	return error;
}

/*
 * Clear the inode reflink flag if there are no shared extents and the size
 * hasn't changed.
 */
STATIC int
xfs_reflink_try_clear_inode_flag(
	struct xfs_inode	*ip)
{
	struct xfs_mount	*mp = ip->i_mount;
	struct xfs_trans	*tp;
	int			error = 0;

	/* Start a rolling transaction to remove the mappings */
	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0, 0, &tp);
	if (error)
		return error;

	xfs_ilock(ip, XFS_ILOCK_EXCL);
	xfs_trans_ijoin(tp, ip, 0);

	error = xfs_reflink_clear_inode_flag(ip, &tp);
	if (error)
		goto cancel;

	error = xfs_trans_commit(tp);
	if (error)
		goto out;

	xfs_iunlock(ip, XFS_ILOCK_EXCL);
	return 0;
cancel:
	xfs_trans_cancel(tp);
out:
	xfs_iunlock(ip, XFS_ILOCK_EXCL);
	return error;
}

/*
 * Pre-COW all shared blocks within a given byte range of a file and turn off
 * the reflink flag if we unshare all of the file's blocks.
 */
int
xfs_reflink_unshare(
	struct xfs_inode	*ip,
	xfs_off_t		offset,
	xfs_off_t		len)
{
	struct xfs_mount	*mp = ip->i_mount;
	xfs_fileoff_t		fbno;
	xfs_filblks_t		end;
	xfs_off_t		isize;
	int			error;

	if (!xfs_is_reflink_inode(ip))
		return 0;

	trace_xfs_reflink_unshare(ip, offset, len);

	inode_dio_wait(VFS_I(ip));

	/* Try to CoW the selected ranges */
	xfs_ilock(ip, XFS_ILOCK_EXCL);
	fbno = XFS_B_TO_FSBT(mp, offset);
	isize = i_size_read(VFS_I(ip));
	end = XFS_B_TO_FSB(mp, offset + len);
	error = xfs_reflink_dirty_extents(ip, fbno, end, isize);
	if (error)
		goto out_unlock;
	xfs_iunlock(ip, XFS_ILOCK_EXCL);

	/* Wait for the IO to finish */
	error = filemap_write_and_wait(VFS_I(ip)->i_mapping);
	if (error)
		goto out;

	/* Turn off the reflink flag if possible. */
	error = xfs_reflink_try_clear_inode_flag(ip);
	if (error)
		goto out;

	return 0;

out_unlock:
	xfs_iunlock(ip, XFS_ILOCK_EXCL);
out:
	trace_xfs_reflink_unshare_error(ip, error, _RET_IP_);
	return error;
}