Linux Audio

Check our new training course

Embedded Linux Audio

Check our new training course
with Creative Commons CC-BY-SA
lecture materials

Bootlin logo

Elixir Cross Referencer

Loading...
   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
/*
 * fs/dax.c - Direct Access filesystem code
 * Copyright (c) 2013-2014 Intel Corporation
 * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
 * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 */

#include <linux/atomic.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h>
#include <linux/dax.h>
#include <linux/fs.h>
#include <linux/genhd.h>
#include <linux/highmem.h>
#include <linux/memcontrol.h>
#include <linux/mm.h>
#include <linux/mutex.h>
#include <linux/pagevec.h>
#include <linux/pmem.h>
#include <linux/sched.h>
#include <linux/uio.h>
#include <linux/vmstat.h>
#include <linux/pfn_t.h>
#include <linux/sizes.h>

/*
 * We use lowest available bit in exceptional entry for locking, other two
 * bits to determine entry type. In total 3 special bits.
 */
#define RADIX_DAX_SHIFT	(RADIX_TREE_EXCEPTIONAL_SHIFT + 3)
#define RADIX_DAX_PTE (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 1))
#define RADIX_DAX_PMD (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 2))
#define RADIX_DAX_TYPE_MASK (RADIX_DAX_PTE | RADIX_DAX_PMD)
#define RADIX_DAX_TYPE(entry) ((unsigned long)entry & RADIX_DAX_TYPE_MASK)
#define RADIX_DAX_SECTOR(entry) (((unsigned long)entry >> RADIX_DAX_SHIFT))
#define RADIX_DAX_ENTRY(sector, pmd) ((void *)((unsigned long)sector << \
		RADIX_DAX_SHIFT | (pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE) | \
		RADIX_TREE_EXCEPTIONAL_ENTRY))

/* We choose 4096 entries - same as per-zone page wait tables */
#define DAX_WAIT_TABLE_BITS 12
#define DAX_WAIT_TABLE_ENTRIES (1 << DAX_WAIT_TABLE_BITS)

wait_queue_head_t wait_table[DAX_WAIT_TABLE_ENTRIES];

static int __init init_dax_wait_table(void)
{
	int i;

	for (i = 0; i < DAX_WAIT_TABLE_ENTRIES; i++)
		init_waitqueue_head(wait_table + i);
	return 0;
}
fs_initcall(init_dax_wait_table);

static wait_queue_head_t *dax_entry_waitqueue(struct address_space *mapping,
					      pgoff_t index)
{
	unsigned long hash = hash_long((unsigned long)mapping ^ index,
				       DAX_WAIT_TABLE_BITS);
	return wait_table + hash;
}

static long dax_map_atomic(struct block_device *bdev, struct blk_dax_ctl *dax)
{
	struct request_queue *q = bdev->bd_queue;
	long rc = -EIO;

	dax->addr = ERR_PTR(-EIO);
	if (blk_queue_enter(q, true) != 0)
		return rc;

	rc = bdev_direct_access(bdev, dax);
	if (rc < 0) {
		dax->addr = ERR_PTR(rc);
		blk_queue_exit(q);
		return rc;
	}
	return rc;
}

static void dax_unmap_atomic(struct block_device *bdev,
		const struct blk_dax_ctl *dax)
{
	if (IS_ERR(dax->addr))
		return;
	blk_queue_exit(bdev->bd_queue);
}

struct page *read_dax_sector(struct block_device *bdev, sector_t n)
{
	struct page *page = alloc_pages(GFP_KERNEL, 0);
	struct blk_dax_ctl dax = {
		.size = PAGE_SIZE,
		.sector = n & ~((((int) PAGE_SIZE) / 512) - 1),
	};
	long rc;

	if (!page)
		return ERR_PTR(-ENOMEM);

	rc = dax_map_atomic(bdev, &dax);
	if (rc < 0)
		return ERR_PTR(rc);
	memcpy_from_pmem(page_address(page), dax.addr, PAGE_SIZE);
	dax_unmap_atomic(bdev, &dax);
	return page;
}

static bool buffer_written(struct buffer_head *bh)
{
	return buffer_mapped(bh) && !buffer_unwritten(bh);
}

/*
 * When ext4 encounters a hole, it returns without modifying the buffer_head
 * which means that we can't trust b_size.  To cope with this, we set b_state
 * to 0 before calling get_block and, if any bit is set, we know we can trust
 * b_size.  Unfortunate, really, since ext4 knows precisely how long a hole is
 * and would save us time calling get_block repeatedly.
 */
static bool buffer_size_valid(struct buffer_head *bh)
{
	return bh->b_state != 0;
}


static sector_t to_sector(const struct buffer_head *bh,
		const struct inode *inode)
{
	sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);

	return sector;
}

static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
		      loff_t start, loff_t end, get_block_t get_block,
		      struct buffer_head *bh)
{
	loff_t pos = start, max = start, bh_max = start;
	bool hole = false;
	struct block_device *bdev = NULL;
	int rw = iov_iter_rw(iter), rc;
	long map_len = 0;
	struct blk_dax_ctl dax = {
		.addr = ERR_PTR(-EIO),
	};
	unsigned blkbits = inode->i_blkbits;
	sector_t file_blks = (i_size_read(inode) + (1 << blkbits) - 1)
								>> blkbits;

	if (rw == READ)
		end = min(end, i_size_read(inode));

	while (pos < end) {
		size_t len;
		if (pos == max) {
			long page = pos >> PAGE_SHIFT;
			sector_t block = page << (PAGE_SHIFT - blkbits);
			unsigned first = pos - (block << blkbits);
			long size;

			if (pos == bh_max) {
				bh->b_size = PAGE_ALIGN(end - pos);
				bh->b_state = 0;
				rc = get_block(inode, block, bh, rw == WRITE);
				if (rc)
					break;
				if (!buffer_size_valid(bh))
					bh->b_size = 1 << blkbits;
				bh_max = pos - first + bh->b_size;
				bdev = bh->b_bdev;
				/*
				 * We allow uninitialized buffers for writes
				 * beyond EOF as those cannot race with faults
				 */
				WARN_ON_ONCE(
					(buffer_new(bh) && block < file_blks) ||
					(rw == WRITE && buffer_unwritten(bh)));
			} else {
				unsigned done = bh->b_size -
						(bh_max - (pos - first));
				bh->b_blocknr += done >> blkbits;
				bh->b_size -= done;
			}

			hole = rw == READ && !buffer_written(bh);
			if (hole) {
				size = bh->b_size - first;
			} else {
				dax_unmap_atomic(bdev, &dax);
				dax.sector = to_sector(bh, inode);
				dax.size = bh->b_size;
				map_len = dax_map_atomic(bdev, &dax);
				if (map_len < 0) {
					rc = map_len;
					break;
				}
				dax.addr += first;
				size = map_len - first;
			}
			/*
			 * pos + size is one past the last offset for IO,
			 * so pos + size can overflow loff_t at extreme offsets.
			 * Cast to u64 to catch this and get the true minimum.
			 */
			max = min_t(u64, pos + size, end);
		}

		if (iov_iter_rw(iter) == WRITE) {
			len = copy_from_iter_pmem(dax.addr, max - pos, iter);
		} else if (!hole)
			len = copy_to_iter((void __force *) dax.addr, max - pos,
					iter);
		else
			len = iov_iter_zero(max - pos, iter);

		if (!len) {
			rc = -EFAULT;
			break;
		}

		pos += len;
		if (!IS_ERR(dax.addr))
			dax.addr += len;
	}

	dax_unmap_atomic(bdev, &dax);

	return (pos == start) ? rc : pos - start;
}

/**
 * dax_do_io - Perform I/O to a DAX file
 * @iocb: The control block for this I/O
 * @inode: The file which the I/O is directed at
 * @iter: The addresses to do I/O from or to
 * @get_block: The filesystem method used to translate file offsets to blocks
 * @end_io: A filesystem callback for I/O completion
 * @flags: See below
 *
 * This function uses the same locking scheme as do_blockdev_direct_IO:
 * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
 * caller for writes.  For reads, we take and release the i_mutex ourselves.
 * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
 * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
 * is in progress.
 */
ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
		  struct iov_iter *iter, get_block_t get_block,
		  dio_iodone_t end_io, int flags)
{
	struct buffer_head bh;
	ssize_t retval = -EINVAL;
	loff_t pos = iocb->ki_pos;
	loff_t end = pos + iov_iter_count(iter);

	memset(&bh, 0, sizeof(bh));
	bh.b_bdev = inode->i_sb->s_bdev;

	if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
		inode_lock(inode);

	/* Protects against truncate */
	if (!(flags & DIO_SKIP_DIO_COUNT))
		inode_dio_begin(inode);

	retval = dax_io(inode, iter, pos, end, get_block, &bh);

	if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
		inode_unlock(inode);

	if (end_io) {
		int err;

		err = end_io(iocb, pos, retval, bh.b_private);
		if (err)
			retval = err;
	}

	if (!(flags & DIO_SKIP_DIO_COUNT))
		inode_dio_end(inode);
	return retval;
}
EXPORT_SYMBOL_GPL(dax_do_io);

/*
 * DAX radix tree locking
 */
struct exceptional_entry_key {
	struct address_space *mapping;
	unsigned long index;
};

struct wait_exceptional_entry_queue {
	wait_queue_t wait;
	struct exceptional_entry_key key;
};

static int wake_exceptional_entry_func(wait_queue_t *wait, unsigned int mode,
				       int sync, void *keyp)
{
	struct exceptional_entry_key *key = keyp;
	struct wait_exceptional_entry_queue *ewait =
		container_of(wait, struct wait_exceptional_entry_queue, wait);

	if (key->mapping != ewait->key.mapping ||
	    key->index != ewait->key.index)
		return 0;
	return autoremove_wake_function(wait, mode, sync, NULL);
}

/*
 * Check whether the given slot is locked. The function must be called with
 * mapping->tree_lock held
 */
static inline int slot_locked(struct address_space *mapping, void **slot)
{
	unsigned long entry = (unsigned long)
		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
	return entry & RADIX_DAX_ENTRY_LOCK;
}

/*
 * Mark the given slot is locked. The function must be called with
 * mapping->tree_lock held
 */
static inline void *lock_slot(struct address_space *mapping, void **slot)
{
	unsigned long entry = (unsigned long)
		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);

	entry |= RADIX_DAX_ENTRY_LOCK;
	radix_tree_replace_slot(slot, (void *)entry);
	return (void *)entry;
}

/*
 * Mark the given slot is unlocked. The function must be called with
 * mapping->tree_lock held
 */
static inline void *unlock_slot(struct address_space *mapping, void **slot)
{
	unsigned long entry = (unsigned long)
		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);

	entry &= ~(unsigned long)RADIX_DAX_ENTRY_LOCK;
	radix_tree_replace_slot(slot, (void *)entry);
	return (void *)entry;
}

/*
 * Lookup entry in radix tree, wait for it to become unlocked if it is
 * exceptional entry and return it. The caller must call
 * put_unlocked_mapping_entry() when he decided not to lock the entry or
 * put_locked_mapping_entry() when he locked the entry and now wants to
 * unlock it.
 *
 * The function must be called with mapping->tree_lock held.
 */
static void *get_unlocked_mapping_entry(struct address_space *mapping,
					pgoff_t index, void ***slotp)
{
	void *ret, **slot;
	struct wait_exceptional_entry_queue ewait;
	wait_queue_head_t *wq = dax_entry_waitqueue(mapping, index);

	init_wait(&ewait.wait);
	ewait.wait.func = wake_exceptional_entry_func;
	ewait.key.mapping = mapping;
	ewait.key.index = index;

	for (;;) {
		ret = __radix_tree_lookup(&mapping->page_tree, index, NULL,
					  &slot);
		if (!ret || !radix_tree_exceptional_entry(ret) ||
		    !slot_locked(mapping, slot)) {
			if (slotp)
				*slotp = slot;
			return ret;
		}
		prepare_to_wait_exclusive(wq, &ewait.wait,
					  TASK_UNINTERRUPTIBLE);
		spin_unlock_irq(&mapping->tree_lock);
		schedule();
		finish_wait(wq, &ewait.wait);
		spin_lock_irq(&mapping->tree_lock);
	}
}

/*
 * Find radix tree entry at given index. If it points to a page, return with
 * the page locked. If it points to the exceptional entry, return with the
 * radix tree entry locked. If the radix tree doesn't contain given index,
 * create empty exceptional entry for the index and return with it locked.
 *
 * Note: Unlike filemap_fault() we don't honor FAULT_FLAG_RETRY flags. For
 * persistent memory the benefit is doubtful. We can add that later if we can
 * show it helps.
 */
static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index)
{
	void *ret, **slot;

restart:
	spin_lock_irq(&mapping->tree_lock);
	ret = get_unlocked_mapping_entry(mapping, index, &slot);
	/* No entry for given index? Make sure radix tree is big enough. */
	if (!ret) {
		int err;

		spin_unlock_irq(&mapping->tree_lock);
		err = radix_tree_preload(
				mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM);
		if (err)
			return ERR_PTR(err);
		ret = (void *)(RADIX_TREE_EXCEPTIONAL_ENTRY |
			       RADIX_DAX_ENTRY_LOCK);
		spin_lock_irq(&mapping->tree_lock);
		err = radix_tree_insert(&mapping->page_tree, index, ret);
		radix_tree_preload_end();
		if (err) {
			spin_unlock_irq(&mapping->tree_lock);
			/* Someone already created the entry? */
			if (err == -EEXIST)
				goto restart;
			return ERR_PTR(err);
		}
		/* Good, we have inserted empty locked entry into the tree. */
		mapping->nrexceptional++;
		spin_unlock_irq(&mapping->tree_lock);
		return ret;
	}
	/* Normal page in radix tree? */
	if (!radix_tree_exceptional_entry(ret)) {
		struct page *page = ret;

		get_page(page);
		spin_unlock_irq(&mapping->tree_lock);
		lock_page(page);
		/* Page got truncated? Retry... */
		if (unlikely(page->mapping != mapping)) {
			unlock_page(page);
			put_page(page);
			goto restart;
		}
		return page;
	}
	ret = lock_slot(mapping, slot);
	spin_unlock_irq(&mapping->tree_lock);
	return ret;
}

void dax_wake_mapping_entry_waiter(struct address_space *mapping,
				   pgoff_t index, bool wake_all)
{
	wait_queue_head_t *wq = dax_entry_waitqueue(mapping, index);

	/*
	 * Checking for locked entry and prepare_to_wait_exclusive() happens
	 * under mapping->tree_lock, ditto for entry handling in our callers.
	 * So at this point all tasks that could have seen our entry locked
	 * must be in the waitqueue and the following check will see them.
	 */
	if (waitqueue_active(wq)) {
		struct exceptional_entry_key key;

		key.mapping = mapping;
		key.index = index;
		__wake_up(wq, TASK_NORMAL, wake_all ? 0 : 1, &key);
	}
}

void dax_unlock_mapping_entry(struct address_space *mapping, pgoff_t index)
{
	void *ret, **slot;

	spin_lock_irq(&mapping->tree_lock);
	ret = __radix_tree_lookup(&mapping->page_tree, index, NULL, &slot);
	if (WARN_ON_ONCE(!ret || !radix_tree_exceptional_entry(ret) ||
			 !slot_locked(mapping, slot))) {
		spin_unlock_irq(&mapping->tree_lock);
		return;
	}
	unlock_slot(mapping, slot);
	spin_unlock_irq(&mapping->tree_lock);
	dax_wake_mapping_entry_waiter(mapping, index, false);
}

static void put_locked_mapping_entry(struct address_space *mapping,
				     pgoff_t index, void *entry)
{
	if (!radix_tree_exceptional_entry(entry)) {
		unlock_page(entry);
		put_page(entry);
	} else {
		dax_unlock_mapping_entry(mapping, index);
	}
}

/*
 * Called when we are done with radix tree entry we looked up via
 * get_unlocked_mapping_entry() and which we didn't lock in the end.
 */
static void put_unlocked_mapping_entry(struct address_space *mapping,
				       pgoff_t index, void *entry)
{
	if (!radix_tree_exceptional_entry(entry))
		return;

	/* We have to wake up next waiter for the radix tree entry lock */
	dax_wake_mapping_entry_waiter(mapping, index, false);
}

/*
 * Delete exceptional DAX entry at @index from @mapping. Wait for radix tree
 * entry to get unlocked before deleting it.
 */
int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
{
	void *entry;

	spin_lock_irq(&mapping->tree_lock);
	entry = get_unlocked_mapping_entry(mapping, index, NULL);
	/*
	 * This gets called from truncate / punch_hole path. As such, the caller
	 * must hold locks protecting against concurrent modifications of the
	 * radix tree (usually fs-private i_mmap_sem for writing). Since the
	 * caller has seen exceptional entry for this index, we better find it
	 * at that index as well...
	 */
	if (WARN_ON_ONCE(!entry || !radix_tree_exceptional_entry(entry))) {
		spin_unlock_irq(&mapping->tree_lock);
		return 0;
	}
	radix_tree_delete(&mapping->page_tree, index);
	mapping->nrexceptional--;
	spin_unlock_irq(&mapping->tree_lock);
	dax_wake_mapping_entry_waiter(mapping, index, true);

	return 1;
}

/*
 * The user has performed a load from a hole in the file.  Allocating
 * a new page in the file would cause excessive storage usage for
 * workloads with sparse files.  We allocate a page cache page instead.
 * We'll kick it out of the page cache if it's ever written to,
 * otherwise it will simply fall out of the page cache under memory
 * pressure without ever having been dirtied.
 */
static int dax_load_hole(struct address_space *mapping, void *entry,
			 struct vm_fault *vmf)
{
	struct page *page;

	/* Hole page already exists? Return it...  */
	if (!radix_tree_exceptional_entry(entry)) {
		vmf->page = entry;
		return VM_FAULT_LOCKED;
	}

	/* This will replace locked radix tree entry with a hole page */
	page = find_or_create_page(mapping, vmf->pgoff,
				   vmf->gfp_mask | __GFP_ZERO);
	if (!page) {
		put_locked_mapping_entry(mapping, vmf->pgoff, entry);
		return VM_FAULT_OOM;
	}
	vmf->page = page;
	return VM_FAULT_LOCKED;
}

static int copy_user_bh(struct page *to, struct inode *inode,
		struct buffer_head *bh, unsigned long vaddr)
{
	struct blk_dax_ctl dax = {
		.sector = to_sector(bh, inode),
		.size = bh->b_size,
	};
	struct block_device *bdev = bh->b_bdev;
	void *vto;

	if (dax_map_atomic(bdev, &dax) < 0)
		return PTR_ERR(dax.addr);
	vto = kmap_atomic(to);
	copy_user_page(vto, (void __force *)dax.addr, vaddr, to);
	kunmap_atomic(vto);
	dax_unmap_atomic(bdev, &dax);
	return 0;
}

#define DAX_PMD_INDEX(page_index) (page_index & (PMD_MASK >> PAGE_SHIFT))

static void *dax_insert_mapping_entry(struct address_space *mapping,
				      struct vm_fault *vmf,
				      void *entry, sector_t sector)
{
	struct radix_tree_root *page_tree = &mapping->page_tree;
	int error = 0;
	bool hole_fill = false;
	void *new_entry;
	pgoff_t index = vmf->pgoff;

	if (vmf->flags & FAULT_FLAG_WRITE)
		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);

	/* Replacing hole page with block mapping? */
	if (!radix_tree_exceptional_entry(entry)) {
		hole_fill = true;
		/*
		 * Unmap the page now before we remove it from page cache below.
		 * The page is locked so it cannot be faulted in again.
		 */
		unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
				    PAGE_SIZE, 0);
		error = radix_tree_preload(vmf->gfp_mask & ~__GFP_HIGHMEM);
		if (error)
			return ERR_PTR(error);
	}

	spin_lock_irq(&mapping->tree_lock);
	new_entry = (void *)((unsigned long)RADIX_DAX_ENTRY(sector, false) |
		       RADIX_DAX_ENTRY_LOCK);
	if (hole_fill) {
		__delete_from_page_cache(entry, NULL);
		/* Drop pagecache reference */
		put_page(entry);
		error = radix_tree_insert(page_tree, index, new_entry);
		if (error) {
			new_entry = ERR_PTR(error);
			goto unlock;
		}
		mapping->nrexceptional++;
	} else {
		void **slot;
		void *ret;

		ret = __radix_tree_lookup(page_tree, index, NULL, &slot);
		WARN_ON_ONCE(ret != entry);
		radix_tree_replace_slot(slot, new_entry);
	}
	if (vmf->flags & FAULT_FLAG_WRITE)
		radix_tree_tag_set(page_tree, index, PAGECACHE_TAG_DIRTY);
 unlock:
	spin_unlock_irq(&mapping->tree_lock);
	if (hole_fill) {
		radix_tree_preload_end();
		/*
		 * We don't need hole page anymore, it has been replaced with
		 * locked radix tree entry now.
		 */
		if (mapping->a_ops->freepage)
			mapping->a_ops->freepage(entry);
		unlock_page(entry);
		put_page(entry);
	}
	return new_entry;
}

static int dax_writeback_one(struct block_device *bdev,
		struct address_space *mapping, pgoff_t index, void *entry)
{
	struct radix_tree_root *page_tree = &mapping->page_tree;
	int type = RADIX_DAX_TYPE(entry);
	struct radix_tree_node *node;
	struct blk_dax_ctl dax;
	void **slot;
	int ret = 0;

	spin_lock_irq(&mapping->tree_lock);
	/*
	 * Regular page slots are stabilized by the page lock even
	 * without the tree itself locked.  These unlocked entries
	 * need verification under the tree lock.
	 */
	if (!__radix_tree_lookup(page_tree, index, &node, &slot))
		goto unlock;
	if (*slot != entry)
		goto unlock;

	/* another fsync thread may have already written back this entry */
	if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
		goto unlock;

	if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD)) {
		ret = -EIO;
		goto unlock;
	}

	dax.sector = RADIX_DAX_SECTOR(entry);
	dax.size = (type == RADIX_DAX_PMD ? PMD_SIZE : PAGE_SIZE);
	spin_unlock_irq(&mapping->tree_lock);

	/*
	 * We cannot hold tree_lock while calling dax_map_atomic() because it
	 * eventually calls cond_resched().
	 */
	ret = dax_map_atomic(bdev, &dax);
	if (ret < 0)
		return ret;

	if (WARN_ON_ONCE(ret < dax.size)) {
		ret = -EIO;
		goto unmap;
	}

	wb_cache_pmem(dax.addr, dax.size);

	spin_lock_irq(&mapping->tree_lock);
	radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
	spin_unlock_irq(&mapping->tree_lock);
 unmap:
	dax_unmap_atomic(bdev, &dax);
	return ret;

 unlock:
	spin_unlock_irq(&mapping->tree_lock);
	return ret;
}

/*
 * Flush the mapping to the persistent domain within the byte range of [start,
 * end]. This is required by data integrity operations to ensure file data is
 * on persistent storage prior to completion of the operation.
 */
int dax_writeback_mapping_range(struct address_space *mapping,
		struct block_device *bdev, struct writeback_control *wbc)
{
	struct inode *inode = mapping->host;
	pgoff_t start_index, end_index, pmd_index;
	pgoff_t indices[PAGEVEC_SIZE];
	struct pagevec pvec;
	bool done = false;
	int i, ret = 0;
	void *entry;

	if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
		return -EIO;

	if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL)
		return 0;

	start_index = wbc->range_start >> PAGE_SHIFT;
	end_index = wbc->range_end >> PAGE_SHIFT;
	pmd_index = DAX_PMD_INDEX(start_index);

	rcu_read_lock();
	entry = radix_tree_lookup(&mapping->page_tree, pmd_index);
	rcu_read_unlock();

	/* see if the start of our range is covered by a PMD entry */
	if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
		start_index = pmd_index;

	tag_pages_for_writeback(mapping, start_index, end_index);

	pagevec_init(&pvec, 0);
	while (!done) {
		pvec.nr = find_get_entries_tag(mapping, start_index,
				PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
				pvec.pages, indices);

		if (pvec.nr == 0)
			break;

		for (i = 0; i < pvec.nr; i++) {
			if (indices[i] > end_index) {
				done = true;
				break;
			}

			ret = dax_writeback_one(bdev, mapping, indices[i],
					pvec.pages[i]);
			if (ret < 0)
				return ret;
		}
	}
	return 0;
}
EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);

static int dax_insert_mapping(struct address_space *mapping,
			struct buffer_head *bh, void **entryp,
			struct vm_area_struct *vma, struct vm_fault *vmf)
{
	unsigned long vaddr = (unsigned long)vmf->virtual_address;
	struct block_device *bdev = bh->b_bdev;
	struct blk_dax_ctl dax = {
		.sector = to_sector(bh, mapping->host),
		.size = bh->b_size,
	};
	void *ret;
	void *entry = *entryp;

	if (dax_map_atomic(bdev, &dax) < 0)
		return PTR_ERR(dax.addr);
	dax_unmap_atomic(bdev, &dax);

	ret = dax_insert_mapping_entry(mapping, vmf, entry, dax.sector);
	if (IS_ERR(ret))
		return PTR_ERR(ret);
	*entryp = ret;

	return vm_insert_mixed(vma, vaddr, dax.pfn);
}

/**
 * dax_fault - handle a page fault on a DAX file
 * @vma: The virtual memory area where the fault occurred
 * @vmf: The description of the fault
 * @get_block: The filesystem method used to translate file offsets to blocks
 *
 * When a page fault occurs, filesystems may call this helper in their
 * fault handler for DAX files. dax_fault() assumes the caller has done all
 * the necessary locking for the page fault to proceed successfully.
 */
int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
			get_block_t get_block)
{
	struct file *file = vma->vm_file;
	struct address_space *mapping = file->f_mapping;
	struct inode *inode = mapping->host;
	void *entry;
	struct buffer_head bh;
	unsigned long vaddr = (unsigned long)vmf->virtual_address;
	unsigned blkbits = inode->i_blkbits;
	sector_t block;
	pgoff_t size;
	int error;
	int major = 0;

	/*
	 * Check whether offset isn't beyond end of file now. Caller is supposed
	 * to hold locks serializing us with truncate / punch hole so this is
	 * a reliable test.
	 */
	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
	if (vmf->pgoff >= size)
		return VM_FAULT_SIGBUS;

	memset(&bh, 0, sizeof(bh));
	block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
	bh.b_bdev = inode->i_sb->s_bdev;
	bh.b_size = PAGE_SIZE;

	entry = grab_mapping_entry(mapping, vmf->pgoff);
	if (IS_ERR(entry)) {
		error = PTR_ERR(entry);
		goto out;
	}

	error = get_block(inode, block, &bh, 0);
	if (!error && (bh.b_size < PAGE_SIZE))
		error = -EIO;		/* fs corruption? */
	if (error)
		goto unlock_entry;

	if (vmf->cow_page) {
		struct page *new_page = vmf->cow_page;
		if (buffer_written(&bh))
			error = copy_user_bh(new_page, inode, &bh, vaddr);
		else
			clear_user_highpage(new_page, vaddr);
		if (error)
			goto unlock_entry;
		if (!radix_tree_exceptional_entry(entry)) {
			vmf->page = entry;
			return VM_FAULT_LOCKED;
		}
		vmf->entry = entry;
		return VM_FAULT_DAX_LOCKED;
	}

	if (!buffer_mapped(&bh)) {
		if (vmf->flags & FAULT_FLAG_WRITE) {
			error = get_block(inode, block, &bh, 1);
			count_vm_event(PGMAJFAULT);
			mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
			major = VM_FAULT_MAJOR;
			if (!error && (bh.b_size < PAGE_SIZE))
				error = -EIO;
			if (error)
				goto unlock_entry;
		} else {
			return dax_load_hole(mapping, entry, vmf);
		}
	}

	/* Filesystem should not return unwritten buffers to us! */
	WARN_ON_ONCE(buffer_unwritten(&bh) || buffer_new(&bh));
	error = dax_insert_mapping(mapping, &bh, &entry, vma, vmf);
 unlock_entry:
	put_locked_mapping_entry(mapping, vmf->pgoff, entry);
 out:
	if (error == -ENOMEM)
		return VM_FAULT_OOM | major;
	/* -EBUSY is fine, somebody else faulted on the same PTE */
	if ((error < 0) && (error != -EBUSY))
		return VM_FAULT_SIGBUS | major;
	return VM_FAULT_NOPAGE | major;
}
EXPORT_SYMBOL_GPL(dax_fault);

#if defined(CONFIG_TRANSPARENT_HUGEPAGE)
/*
 * The 'colour' (ie low bits) within a PMD of a page offset.  This comes up
 * more often than one might expect in the below function.
 */
#define PG_PMD_COLOUR	((PMD_SIZE >> PAGE_SHIFT) - 1)

static void __dax_dbg(struct buffer_head *bh, unsigned long address,
		const char *reason, const char *fn)
{
	if (bh) {
		char bname[BDEVNAME_SIZE];
		bdevname(bh->b_bdev, bname);
		pr_debug("%s: %s addr: %lx dev %s state %lx start %lld "
			"length %zd fallback: %s\n", fn, current->comm,
			address, bname, bh->b_state, (u64)bh->b_blocknr,
			bh->b_size, reason);
	} else {
		pr_debug("%s: %s addr: %lx fallback: %s\n", fn,
			current->comm, address, reason);
	}
}

#define dax_pmd_dbg(bh, address, reason)	__dax_dbg(bh, address, reason, "dax_pmd")

/**
 * dax_pmd_fault - handle a PMD fault on a DAX file
 * @vma: The virtual memory area where the fault occurred
 * @vmf: The description of the fault
 * @get_block: The filesystem method used to translate file offsets to blocks
 *
 * When a page fault occurs, filesystems may call this helper in their
 * pmd_fault handler for DAX files.
 */
int dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
		pmd_t *pmd, unsigned int flags, get_block_t get_block)
{
	struct file *file = vma->vm_file;
	struct address_space *mapping = file->f_mapping;
	struct inode *inode = mapping->host;
	struct buffer_head bh;
	unsigned blkbits = inode->i_blkbits;
	unsigned long pmd_addr = address & PMD_MASK;
	bool write = flags & FAULT_FLAG_WRITE;
	struct block_device *bdev;
	pgoff_t size, pgoff;
	sector_t block;
	int result = 0;
	bool alloc = false;

	/* dax pmd mappings require pfn_t_devmap() */
	if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
		return VM_FAULT_FALLBACK;

	/* Fall back to PTEs if we're going to COW */
	if (write && !(vma->vm_flags & VM_SHARED)) {
		split_huge_pmd(vma, pmd, address);
		dax_pmd_dbg(NULL, address, "cow write");
		return VM_FAULT_FALLBACK;
	}
	/* If the PMD would extend outside the VMA */
	if (pmd_addr < vma->vm_start) {
		dax_pmd_dbg(NULL, address, "vma start unaligned");
		return VM_FAULT_FALLBACK;
	}
	if ((pmd_addr + PMD_SIZE) > vma->vm_end) {
		dax_pmd_dbg(NULL, address, "vma end unaligned");
		return VM_FAULT_FALLBACK;
	}

	pgoff = linear_page_index(vma, pmd_addr);
	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
	if (pgoff >= size)
		return VM_FAULT_SIGBUS;
	/* If the PMD would cover blocks out of the file */
	if ((pgoff | PG_PMD_COLOUR) >= size) {
		dax_pmd_dbg(NULL, address,
				"offset + huge page size > file size");
		return VM_FAULT_FALLBACK;
	}

	memset(&bh, 0, sizeof(bh));
	bh.b_bdev = inode->i_sb->s_bdev;
	block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);

	bh.b_size = PMD_SIZE;

	if (get_block(inode, block, &bh, 0) != 0)
		return VM_FAULT_SIGBUS;

	if (!buffer_mapped(&bh) && write) {
		if (get_block(inode, block, &bh, 1) != 0)
			return VM_FAULT_SIGBUS;
		alloc = true;
		WARN_ON_ONCE(buffer_unwritten(&bh) || buffer_new(&bh));
	}

	bdev = bh.b_bdev;

	/*
	 * If the filesystem isn't willing to tell us the length of a hole,
	 * just fall back to PTEs.  Calling get_block 512 times in a loop
	 * would be silly.
	 */
	if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE) {
		dax_pmd_dbg(&bh, address, "allocated block too small");
		return VM_FAULT_FALLBACK;
	}

	/*
	 * If we allocated new storage, make sure no process has any
	 * zero pages covering this hole
	 */
	if (alloc) {
		loff_t lstart = pgoff << PAGE_SHIFT;
		loff_t lend = lstart + PMD_SIZE - 1; /* inclusive */

		truncate_pagecache_range(inode, lstart, lend);
	}

	if (!write && !buffer_mapped(&bh)) {
		spinlock_t *ptl;
		pmd_t entry;
		struct page *zero_page = get_huge_zero_page();

		if (unlikely(!zero_page)) {
			dax_pmd_dbg(&bh, address, "no zero page");
			goto fallback;
		}

		ptl = pmd_lock(vma->vm_mm, pmd);
		if (!pmd_none(*pmd)) {
			spin_unlock(ptl);
			dax_pmd_dbg(&bh, address, "pmd already present");
			goto fallback;
		}

		dev_dbg(part_to_dev(bdev->bd_part),
				"%s: %s addr: %lx pfn: <zero> sect: %llx\n",
				__func__, current->comm, address,
				(unsigned long long) to_sector(&bh, inode));

		entry = mk_pmd(zero_page, vma->vm_page_prot);
		entry = pmd_mkhuge(entry);
		set_pmd_at(vma->vm_mm, pmd_addr, pmd, entry);
		result = VM_FAULT_NOPAGE;
		spin_unlock(ptl);
	} else {
		struct blk_dax_ctl dax = {
			.sector = to_sector(&bh, inode),
			.size = PMD_SIZE,
		};
		long length = dax_map_atomic(bdev, &dax);

		if (length < 0) {
			dax_pmd_dbg(&bh, address, "dax-error fallback");
			goto fallback;
		}
		if (length < PMD_SIZE) {
			dax_pmd_dbg(&bh, address, "dax-length too small");
			dax_unmap_atomic(bdev, &dax);
			goto fallback;
		}
		if (pfn_t_to_pfn(dax.pfn) & PG_PMD_COLOUR) {
			dax_pmd_dbg(&bh, address, "pfn unaligned");
			dax_unmap_atomic(bdev, &dax);
			goto fallback;
		}

		if (!pfn_t_devmap(dax.pfn)) {
			dax_unmap_atomic(bdev, &dax);
			dax_pmd_dbg(&bh, address, "pfn not in memmap");
			goto fallback;
		}
		dax_unmap_atomic(bdev, &dax);

		/*
		 * For PTE faults we insert a radix tree entry for reads, and
		 * leave it clean.  Then on the first write we dirty the radix
		 * tree entry via the dax_pfn_mkwrite() path.  This sequence
		 * allows the dax_pfn_mkwrite() call to be simpler and avoid a
		 * call into get_block() to translate the pgoff to a sector in
		 * order to be able to create a new radix tree entry.
		 *
		 * The PMD path doesn't have an equivalent to
		 * dax_pfn_mkwrite(), though, so for a read followed by a
		 * write we traverse all the way through dax_pmd_fault()
		 * twice.  This means we can just skip inserting a radix tree
		 * entry completely on the initial read and just wait until
		 * the write to insert a dirty entry.
		 */
		if (write) {
			/*
			 * We should insert radix-tree entry and dirty it here.
			 * For now this is broken...
			 */
		}

		dev_dbg(part_to_dev(bdev->bd_part),
				"%s: %s addr: %lx pfn: %lx sect: %llx\n",
				__func__, current->comm, address,
				pfn_t_to_pfn(dax.pfn),
				(unsigned long long) dax.sector);
		result |= vmf_insert_pfn_pmd(vma, address, pmd,
				dax.pfn, write);
	}

 out:
	return result;

 fallback:
	count_vm_event(THP_FAULT_FALLBACK);
	result = VM_FAULT_FALLBACK;
	goto out;
}
EXPORT_SYMBOL_GPL(dax_pmd_fault);
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

/**
 * dax_pfn_mkwrite - handle first write to DAX page
 * @vma: The virtual memory area where the fault occurred
 * @vmf: The description of the fault
 */
int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
{
	struct file *file = vma->vm_file;
	struct address_space *mapping = file->f_mapping;
	void *entry;
	pgoff_t index = vmf->pgoff;

	spin_lock_irq(&mapping->tree_lock);
	entry = get_unlocked_mapping_entry(mapping, index, NULL);
	if (!entry || !radix_tree_exceptional_entry(entry))
		goto out;
	radix_tree_tag_set(&mapping->page_tree, index, PAGECACHE_TAG_DIRTY);
	put_unlocked_mapping_entry(mapping, index, entry);
out:
	spin_unlock_irq(&mapping->tree_lock);
	return VM_FAULT_NOPAGE;
}
EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);

static bool dax_range_is_aligned(struct block_device *bdev,
				 unsigned int offset, unsigned int length)
{
	unsigned short sector_size = bdev_logical_block_size(bdev);

	if (!IS_ALIGNED(offset, sector_size))
		return false;
	if (!IS_ALIGNED(length, sector_size))
		return false;

	return true;
}

int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
		unsigned int offset, unsigned int length)
{
	struct blk_dax_ctl dax = {
		.sector		= sector,
		.size		= PAGE_SIZE,
	};

	if (dax_range_is_aligned(bdev, offset, length)) {
		sector_t start_sector = dax.sector + (offset >> 9);

		return blkdev_issue_zeroout(bdev, start_sector,
				length >> 9, GFP_NOFS, true);
	} else {
		if (dax_map_atomic(bdev, &dax) < 0)
			return PTR_ERR(dax.addr);
		clear_pmem(dax.addr + offset, length);
		dax_unmap_atomic(bdev, &dax);
	}
	return 0;
}
EXPORT_SYMBOL_GPL(__dax_zero_page_range);

/**
 * dax_zero_page_range - zero a range within a page of a DAX file
 * @inode: The file being truncated
 * @from: The file offset that is being truncated to
 * @length: The number of bytes to zero
 * @get_block: The filesystem method used to translate file offsets to blocks
 *
 * This function can be called by a filesystem when it is zeroing part of a
 * page in a DAX file.  This is intended for hole-punch operations.  If
 * you are truncating a file, the helper function dax_truncate_page() may be
 * more convenient.
 */
int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
							get_block_t get_block)
{
	struct buffer_head bh;
	pgoff_t index = from >> PAGE_SHIFT;
	unsigned offset = from & (PAGE_SIZE-1);
	int err;

	/* Block boundary? Nothing to do */
	if (!length)
		return 0;
	BUG_ON((offset + length) > PAGE_SIZE);

	memset(&bh, 0, sizeof(bh));
	bh.b_bdev = inode->i_sb->s_bdev;
	bh.b_size = PAGE_SIZE;
	err = get_block(inode, index, &bh, 0);
	if (err < 0 || !buffer_written(&bh))
		return err;

	return __dax_zero_page_range(bh.b_bdev, to_sector(&bh, inode),
			offset, length);
}
EXPORT_SYMBOL_GPL(dax_zero_page_range);

/**
 * dax_truncate_page - handle a partial page being truncated in a DAX file
 * @inode: The file being truncated
 * @from: The file offset that is being truncated to
 * @get_block: The filesystem method used to translate file offsets to blocks
 *
 * Similar to block_truncate_page(), this function can be called by a
 * filesystem when it is truncating a DAX file to handle the partial page.
 */
int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
{
	unsigned length = PAGE_ALIGN(from) - from;
	return dax_zero_page_range(inode, from, length, get_block);
}
EXPORT_SYMBOL_GPL(dax_truncate_page);