summaryrefslogtreecommitdiff
path: root/fs/fuse/dax.c
blob: 713818d74de6cfcf93d079eee7e726c3660c2fbe (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
// SPDX-License-Identifier: GPL-2.0
/*
 * dax: direct host memory access
 * Copyright (C) 2020 Red Hat, Inc.
 */

#include "fuse_i.h"

#include <linux/delay.h>
#include <linux/dax.h>
#include <linux/uio.h>
#include <linux/pagemap.h>
#include <linux/pfn_t.h>
#include <linux/iomap.h>
#include <linux/interval_tree.h>

/*
 * Default memory range size.  A power of 2 so it agrees with common FUSE_INIT
 * map_alignment values 4KB and 64KB.
 */
#define FUSE_DAX_SHIFT	21
#define FUSE_DAX_SZ	(1 << FUSE_DAX_SHIFT)
#define FUSE_DAX_PAGES	(FUSE_DAX_SZ / PAGE_SIZE)

/* Number of ranges reclaimer will try to free in one invocation */
#define FUSE_DAX_RECLAIM_CHUNK		(10)

/*
 * Dax memory reclaim threshold in percetage of total ranges. When free
 * number of free ranges drops below this threshold, reclaim can trigger
 * Default is 20%
 */
#define FUSE_DAX_RECLAIM_THRESHOLD	(20)

/** Translation information for file offsets to DAX window offsets */
struct fuse_dax_mapping {
	/* Pointer to inode where this memory range is mapped */
	struct inode *inode;

	/* Will connect in fcd->free_ranges to keep track of free memory */
	struct list_head list;

	/* For interval tree in file/inode */
	struct interval_tree_node itn;

	/* Will connect in fc->busy_ranges to keep track busy memory */
	struct list_head busy_list;

	/** Position in DAX window */
	u64 window_offset;

	/** Length of mapping, in bytes */
	loff_t length;

	/* Is this mapping read-only or read-write */
	bool writable;

	/* reference count when the mapping is used by dax iomap. */
	refcount_t refcnt;
};

/* Per-inode dax map */
struct fuse_inode_dax {
	/* Semaphore to protect modifications to the dmap tree */
	struct rw_semaphore sem;

	/* Sorted rb tree of struct fuse_dax_mapping elements */
	struct rb_root_cached tree;
	unsigned long nr;
};

struct fuse_conn_dax {
	/* DAX device */
	struct dax_device *dev;

	/* Lock protecting accessess to  members of this structure */
	spinlock_t lock;

	/* List of memory ranges which are busy */
	unsigned long nr_busy_ranges;
	struct list_head busy_ranges;

	/* Worker to free up memory ranges */
	struct delayed_work free_work;

	/* Wait queue for a dax range to become free */
	wait_queue_head_t range_waitq;

	/* DAX Window Free Ranges */
	long nr_free_ranges;
	struct list_head free_ranges;

	unsigned long nr_ranges;
};

static inline struct fuse_dax_mapping *
node_to_dmap(struct interval_tree_node *node)
{
	if (!node)
		return NULL;

	return container_of(node, struct fuse_dax_mapping, itn);
}

static struct fuse_dax_mapping *
alloc_dax_mapping_reclaim(struct fuse_conn_dax *fcd, struct inode *inode);

static void
__kick_dmap_free_worker(struct fuse_conn_dax *fcd, unsigned long delay_ms)
{
	unsigned long free_threshold;

	/* If number of free ranges are below threshold, start reclaim */
	free_threshold = max_t(unsigned long, fcd->nr_ranges * FUSE_DAX_RECLAIM_THRESHOLD / 100,
			     1);
	if (fcd->nr_free_ranges < free_threshold)
		queue_delayed_work(system_long_wq, &fcd->free_work,
				   msecs_to_jiffies(delay_ms));
}

static void kick_dmap_free_worker(struct fuse_conn_dax *fcd,
				  unsigned long delay_ms)
{
	spin_lock(&fcd->lock);
	__kick_dmap_free_worker(fcd, delay_ms);
	spin_unlock(&fcd->lock);
}

static struct fuse_dax_mapping *alloc_dax_mapping(struct fuse_conn_dax *fcd)
{
	struct fuse_dax_mapping *dmap;

	spin_lock(&fcd->lock);
	dmap = list_first_entry_or_null(&fcd->free_ranges,
					struct fuse_dax_mapping, list);
	if (dmap) {
		list_del_init(&dmap->list);
		WARN_ON(fcd->nr_free_ranges <= 0);
		fcd->nr_free_ranges--;
	}
	spin_unlock(&fcd->lock);

	kick_dmap_free_worker(fcd, 0);
	return dmap;
}

/* This assumes fcd->lock is held */
static void __dmap_remove_busy_list(struct fuse_conn_dax *fcd,
				    struct fuse_dax_mapping *dmap)
{
	list_del_init(&dmap->busy_list);
	WARN_ON(fcd->nr_busy_ranges == 0);
	fcd->nr_busy_ranges--;
}

static void dmap_remove_busy_list(struct fuse_conn_dax *fcd,
				  struct fuse_dax_mapping *dmap)
{
	spin_lock(&fcd->lock);
	__dmap_remove_busy_list(fcd, dmap);
	spin_unlock(&fcd->lock);
}

/* This assumes fcd->lock is held */
static void __dmap_add_to_free_pool(struct fuse_conn_dax *fcd,
				struct fuse_dax_mapping *dmap)
{
	list_add_tail(&dmap->list, &fcd->free_ranges);
	fcd->nr_free_ranges++;
	wake_up(&fcd->range_waitq);
}

static void dmap_add_to_free_pool(struct fuse_conn_dax *fcd,
				struct fuse_dax_mapping *dmap)
{
	/* Return fuse_dax_mapping to free list */
	spin_lock(&fcd->lock);
	__dmap_add_to_free_pool(fcd, dmap);
	spin_unlock(&fcd->lock);
}

static int fuse_setup_one_mapping(struct inode *inode, unsigned long start_idx,
				  struct fuse_dax_mapping *dmap, bool writable,
				  bool upgrade)
{
	struct fuse_mount *fm = get_fuse_mount(inode);
	struct fuse_conn_dax *fcd = fm->fc->dax;
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_setupmapping_in inarg;
	loff_t offset = start_idx << FUSE_DAX_SHIFT;
	FUSE_ARGS(args);
	ssize_t err;

	WARN_ON(fcd->nr_free_ranges < 0);

	/* Ask fuse daemon to setup mapping */
	memset(&inarg, 0, sizeof(inarg));
	inarg.foffset = offset;
	inarg.fh = -1;
	inarg.moffset = dmap->window_offset;
	inarg.len = FUSE_DAX_SZ;
	inarg.flags |= FUSE_SETUPMAPPING_FLAG_READ;
	if (writable)
		inarg.flags |= FUSE_SETUPMAPPING_FLAG_WRITE;
	args.opcode = FUSE_SETUPMAPPING;
	args.nodeid = fi->nodeid;
	args.in_numargs = 1;
	args.in_args[0].size = sizeof(inarg);
	args.in_args[0].value = &inarg;
	err = fuse_simple_request(fm, &args);
	if (err < 0)
		return err;
	dmap->writable = writable;
	if (!upgrade) {
		/*
		 * We don't take a reference on inode. inode is valid right now
		 * and when inode is going away, cleanup logic should first
		 * cleanup dmap entries.
		 */
		dmap->inode = inode;
		dmap->itn.start = dmap->itn.last = start_idx;
		/* Protected by fi->dax->sem */
		interval_tree_insert(&dmap->itn, &fi->dax->tree);
		fi->dax->nr++;
		spin_lock(&fcd->lock);
		list_add_tail(&dmap->busy_list, &fcd->busy_ranges);
		fcd->nr_busy_ranges++;
		spin_unlock(&fcd->lock);
	}
	return 0;
}

static int fuse_send_removemapping(struct inode *inode,
				   struct fuse_removemapping_in *inargp,
				   struct fuse_removemapping_one *remove_one)
{
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_mount *fm = get_fuse_mount(inode);
	FUSE_ARGS(args);

	args.opcode = FUSE_REMOVEMAPPING;
	args.nodeid = fi->nodeid;
	args.in_numargs = 2;
	args.in_args[0].size = sizeof(*inargp);
	args.in_args[0].value = inargp;
	args.in_args[1].size = inargp->count * sizeof(*remove_one);
	args.in_args[1].value = remove_one;
	return fuse_simple_request(fm, &args);
}

static int dmap_removemapping_list(struct inode *inode, unsigned int num,
				   struct list_head *to_remove)
{
	struct fuse_removemapping_one *remove_one, *ptr;
	struct fuse_removemapping_in inarg;
	struct fuse_dax_mapping *dmap;
	int ret, i = 0, nr_alloc;

	nr_alloc = min_t(unsigned int, num, FUSE_REMOVEMAPPING_MAX_ENTRY);
	remove_one = kmalloc_array(nr_alloc, sizeof(*remove_one), GFP_NOFS);
	if (!remove_one)
		return -ENOMEM;

	ptr = remove_one;
	list_for_each_entry(dmap, to_remove, list) {
		ptr->moffset = dmap->window_offset;
		ptr->len = dmap->length;
		ptr++;
		i++;
		num--;
		if (i >= nr_alloc || num == 0) {
			memset(&inarg, 0, sizeof(inarg));
			inarg.count = i;
			ret = fuse_send_removemapping(inode, &inarg,
						      remove_one);
			if (ret)
				goto out;
			ptr = remove_one;
			i = 0;
		}
	}
out:
	kfree(remove_one);
	return ret;
}

/*
 * Cleanup dmap entry and add back to free list. This should be called with
 * fcd->lock held.
 */
static void dmap_reinit_add_to_free_pool(struct fuse_conn_dax *fcd,
					    struct fuse_dax_mapping *dmap)
{
	pr_debug("fuse: freeing memory range start_idx=0x%lx end_idx=0x%lx window_offset=0x%llx length=0x%llx\n",
		 dmap->itn.start, dmap->itn.last, dmap->window_offset,
		 dmap->length);
	__dmap_remove_busy_list(fcd, dmap);
	dmap->inode = NULL;
	dmap->itn.start = dmap->itn.last = 0;
	__dmap_add_to_free_pool(fcd, dmap);
}

/*
 * Free inode dmap entries whose range falls inside [start, end].
 * Does not take any locks. At this point of time it should only be
 * called from evict_inode() path where we know all dmap entries can be
 * reclaimed.
 */
static void inode_reclaim_dmap_range(struct fuse_conn_dax *fcd,
				     struct inode *inode,
				     loff_t start, loff_t end)
{
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_dax_mapping *dmap, *n;
	int err, num = 0;
	LIST_HEAD(to_remove);
	unsigned long start_idx = start >> FUSE_DAX_SHIFT;
	unsigned long end_idx = end >> FUSE_DAX_SHIFT;
	struct interval_tree_node *node;

	while (1) {
		node = interval_tree_iter_first(&fi->dax->tree, start_idx,
						end_idx);
		if (!node)
			break;
		dmap = node_to_dmap(node);
		/* inode is going away. There should not be any users of dmap */
		WARN_ON(refcount_read(&dmap->refcnt) > 1);
		interval_tree_remove(&dmap->itn, &fi->dax->tree);
		num++;
		list_add(&dmap->list, &to_remove);
	}

	/* Nothing to remove */
	if (list_empty(&to_remove))
		return;

	WARN_ON(fi->dax->nr < num);
	fi->dax->nr -= num;
	err = dmap_removemapping_list(inode, num, &to_remove);
	if (err && err != -ENOTCONN) {
		pr_warn("Failed to removemappings. start=0x%llx end=0x%llx\n",
			start, end);
	}
	spin_lock(&fcd->lock);
	list_for_each_entry_safe(dmap, n, &to_remove, list) {
		list_del_init(&dmap->list);
		dmap_reinit_add_to_free_pool(fcd, dmap);
	}
	spin_unlock(&fcd->lock);
}

static int dmap_removemapping_one(struct inode *inode,
				  struct fuse_dax_mapping *dmap)
{
	struct fuse_removemapping_one forget_one;
	struct fuse_removemapping_in inarg;

	memset(&inarg, 0, sizeof(inarg));
	inarg.count = 1;
	memset(&forget_one, 0, sizeof(forget_one));
	forget_one.moffset = dmap->window_offset;
	forget_one.len = dmap->length;

	return fuse_send_removemapping(inode, &inarg, &forget_one);
}

/*
 * It is called from evict_inode() and by that time inode is going away. So
 * this function does not take any locks like fi->dax->sem for traversing
 * that fuse inode interval tree. If that lock is taken then lock validator
 * complains of deadlock situation w.r.t fs_reclaim lock.
 */
void fuse_dax_inode_cleanup(struct inode *inode)
{
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_inode *fi = get_fuse_inode(inode);

	/*
	 * fuse_evict_inode() has already called truncate_inode_pages_final()
	 * before we arrive here. So we should not have to worry about any
	 * pages/exception entries still associated with inode.
	 */
	inode_reclaim_dmap_range(fc->dax, inode, 0, -1);
	WARN_ON(fi->dax->nr);
}

static void fuse_fill_iomap_hole(struct iomap *iomap, loff_t length)
{
	iomap->addr = IOMAP_NULL_ADDR;
	iomap->length = length;
	iomap->type = IOMAP_HOLE;
}

static void fuse_fill_iomap(struct inode *inode, loff_t pos, loff_t length,
			    struct iomap *iomap, struct fuse_dax_mapping *dmap,
			    unsigned int flags)
{
	loff_t offset, len;
	loff_t i_size = i_size_read(inode);

	offset = pos - (dmap->itn.start << FUSE_DAX_SHIFT);
	len = min(length, dmap->length - offset);

	/* If length is beyond end of file, truncate further */
	if (pos + len > i_size)
		len = i_size - pos;

	if (len > 0) {
		iomap->addr = dmap->window_offset + offset;
		iomap->length = len;
		if (flags & IOMAP_FAULT)
			iomap->length = ALIGN(len, PAGE_SIZE);
		iomap->type = IOMAP_MAPPED;
		/*
		 * increace refcnt so that reclaim code knows this dmap is in
		 * use. This assumes fi->dax->sem mutex is held either
		 * shared/exclusive.
		 */
		refcount_inc(&dmap->refcnt);

		/* iomap->private should be NULL */
		WARN_ON_ONCE(iomap->private);
		iomap->private = dmap;
	} else {
		/* Mapping beyond end of file is hole */
		fuse_fill_iomap_hole(iomap, length);
	}
}

static int fuse_setup_new_dax_mapping(struct inode *inode, loff_t pos,
				      loff_t length, unsigned int flags,
				      struct iomap *iomap)
{
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_conn_dax *fcd = fc->dax;
	struct fuse_dax_mapping *dmap, *alloc_dmap = NULL;
	int ret;
	bool writable = flags & IOMAP_WRITE;
	unsigned long start_idx = pos >> FUSE_DAX_SHIFT;
	struct interval_tree_node *node;

	/*
	 * Can't do inline reclaim in fault path. We call
	 * dax_layout_busy_page() before we free a range. And
	 * fuse_wait_dax_page() drops mapping->invalidate_lock and requires it.
	 * In fault path we enter with mapping->invalidate_lock held and can't
	 * drop it. Also in fault path we hold mapping->invalidate_lock shared
	 * and not exclusive, so that creates further issues with
	 * fuse_wait_dax_page().  Hence return -EAGAIN and fuse_dax_fault()
	 * will wait for a memory range to become free and retry.
	 */
	if (flags & IOMAP_FAULT) {
		alloc_dmap = alloc_dax_mapping(fcd);
		if (!alloc_dmap)
			return -EAGAIN;
	} else {
		alloc_dmap = alloc_dax_mapping_reclaim(fcd, inode);
		if (IS_ERR(alloc_dmap))
			return PTR_ERR(alloc_dmap);
	}

	/* If we are here, we should have memory allocated */
	if (WARN_ON(!alloc_dmap))
		return -EIO;

	/*
	 * Take write lock so that only one caller can try to setup mapping
	 * and other waits.
	 */
	down_write(&fi->dax->sem);
	/*
	 * We dropped lock. Check again if somebody else setup
	 * mapping already.
	 */
	node = interval_tree_iter_first(&fi->dax->tree, start_idx, start_idx);
	if (node) {
		dmap = node_to_dmap(node);
		fuse_fill_iomap(inode, pos, length, iomap, dmap, flags);
		dmap_add_to_free_pool(fcd, alloc_dmap);
		up_write(&fi->dax->sem);
		return 0;
	}

	/* Setup one mapping */
	ret = fuse_setup_one_mapping(inode, pos >> FUSE_DAX_SHIFT, alloc_dmap,
				     writable, false);
	if (ret < 0) {
		dmap_add_to_free_pool(fcd, alloc_dmap);
		up_write(&fi->dax->sem);
		return ret;
	}
	fuse_fill_iomap(inode, pos, length, iomap, alloc_dmap, flags);
	up_write(&fi->dax->sem);
	return 0;
}

static int fuse_upgrade_dax_mapping(struct inode *inode, loff_t pos,
				    loff_t length, unsigned int flags,
				    struct iomap *iomap)
{
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_dax_mapping *dmap;
	int ret;
	unsigned long idx = pos >> FUSE_DAX_SHIFT;
	struct interval_tree_node *node;

	/*
	 * Take exclusive lock so that only one caller can try to setup
	 * mapping and others wait.
	 */
	down_write(&fi->dax->sem);
	node = interval_tree_iter_first(&fi->dax->tree, idx, idx);

	/* We are holding either inode lock or invalidate_lock, and that should
	 * ensure that dmap can't be truncated. We are holding a reference
	 * on dmap and that should make sure it can't be reclaimed. So dmap
	 * should still be there in tree despite the fact we dropped and
	 * re-acquired the fi->dax->sem lock.
	 */
	ret = -EIO;
	if (WARN_ON(!node))
		goto out_err;

	dmap = node_to_dmap(node);

	/* We took an extra reference on dmap to make sure its not reclaimd.
	 * Now we hold fi->dax->sem lock and that reference is not needed
	 * anymore. Drop it.
	 */
	if (refcount_dec_and_test(&dmap->refcnt)) {
		/* refcount should not hit 0. This object only goes
		 * away when fuse connection goes away
		 */
		WARN_ON_ONCE(1);
	}

	/* Maybe another thread already upgraded mapping while we were not
	 * holding lock.
	 */
	if (dmap->writable) {
		ret = 0;
		goto out_fill_iomap;
	}

	ret = fuse_setup_one_mapping(inode, pos >> FUSE_DAX_SHIFT, dmap, true,
				     true);
	if (ret < 0)
		goto out_err;
out_fill_iomap:
	fuse_fill_iomap(inode, pos, length, iomap, dmap, flags);
out_err:
	up_write(&fi->dax->sem);
	return ret;
}

/* This is just for DAX and the mapping is ephemeral, do not use it for other
 * purposes since there is no block device with a permanent mapping.
 */
static int fuse_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
			    unsigned int flags, struct iomap *iomap,
			    struct iomap *srcmap)
{
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_dax_mapping *dmap;
	bool writable = flags & IOMAP_WRITE;
	unsigned long start_idx = pos >> FUSE_DAX_SHIFT;
	struct interval_tree_node *node;

	/* We don't support FIEMAP */
	if (WARN_ON(flags & IOMAP_REPORT))
		return -EIO;

	iomap->offset = pos;
	iomap->flags = 0;
	iomap->bdev = NULL;
	iomap->dax_dev = fc->dax->dev;

	/*
	 * Both read/write and mmap path can race here. So we need something
	 * to make sure if we are setting up mapping, then other path waits
	 *
	 * For now, use a semaphore for this. It probably needs to be
	 * optimized later.
	 */
	down_read(&fi->dax->sem);
	node = interval_tree_iter_first(&fi->dax->tree, start_idx, start_idx);
	if (node) {
		dmap = node_to_dmap(node);
		if (writable && !dmap->writable) {
			/* Upgrade read-only mapping to read-write. This will
			 * require exclusive fi->dax->sem lock as we don't want
			 * two threads to be trying to this simultaneously
			 * for same dmap. So drop shared lock and acquire
			 * exclusive lock.
			 *
			 * Before dropping fi->dax->sem lock, take reference
			 * on dmap so that its not freed by range reclaim.
			 */
			refcount_inc(&dmap->refcnt);
			up_read(&fi->dax->sem);
			pr_debug("%s: Upgrading mapping at offset 0x%llx length 0x%llx\n",
				 __func__, pos, length);
			return fuse_upgrade_dax_mapping(inode, pos, length,
							flags, iomap);
		} else {
			fuse_fill_iomap(inode, pos, length, iomap, dmap, flags);
			up_read(&fi->dax->sem);
			return 0;
		}
	} else {
		up_read(&fi->dax->sem);
		pr_debug("%s: no mapping at offset 0x%llx length 0x%llx\n",
				__func__, pos, length);
		if (pos >= i_size_read(inode))
			goto iomap_hole;

		return fuse_setup_new_dax_mapping(inode, pos, length, flags,
						  iomap);
	}

	/*
	 * If read beyond end of file happens, fs code seems to return
	 * it as hole
	 */
iomap_hole:
	fuse_fill_iomap_hole(iomap, length);
	pr_debug("%s returning hole mapping. pos=0x%llx length_asked=0x%llx length_returned=0x%llx\n",
		 __func__, pos, length, iomap->length);
	return 0;
}

static int fuse_iomap_end(struct inode *inode, loff_t pos, loff_t length,
			  ssize_t written, unsigned int flags,
			  struct iomap *iomap)
{
	struct fuse_dax_mapping *dmap = iomap->private;

	if (dmap) {
		if (refcount_dec_and_test(&dmap->refcnt)) {
			/* refcount should not hit 0. This object only goes
			 * away when fuse connection goes away
			 */
			WARN_ON_ONCE(1);
		}
	}

	/* DAX writes beyond end-of-file aren't handled using iomap, so the
	 * file size is unchanged and there is nothing to do here.
	 */
	return 0;
}

static const struct iomap_ops fuse_iomap_ops = {
	.iomap_begin = fuse_iomap_begin,
	.iomap_end = fuse_iomap_end,
};

static void fuse_wait_dax_page(struct inode *inode)
{
	filemap_invalidate_unlock(inode->i_mapping);
	schedule();
	filemap_invalidate_lock(inode->i_mapping);
}

/* Should be called with mapping->invalidate_lock held exclusively */
static int __fuse_dax_break_layouts(struct inode *inode, bool *retry,
				    loff_t start, loff_t end)
{
	struct page *page;

	page = dax_layout_busy_page_range(inode->i_mapping, start, end);
	if (!page)
		return 0;

	*retry = true;
	return ___wait_var_event(&page->_refcount,
			atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
			0, 0, fuse_wait_dax_page(inode));
}

/* dmap_end == 0 leads to unmapping of whole file */
int fuse_dax_break_layouts(struct inode *inode, u64 dmap_start,
				  u64 dmap_end)
{
	bool	retry;
	int	ret;

	do {
		retry = false;
		ret = __fuse_dax_break_layouts(inode, &retry, dmap_start,
					       dmap_end);
	} while (ret == 0 && retry);

	return ret;
}

ssize_t fuse_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
	struct inode *inode = file_inode(iocb->ki_filp);
	ssize_t ret;

	if (iocb->ki_flags & IOCB_NOWAIT) {
		if (!inode_trylock_shared(inode))
			return -EAGAIN;
	} else {
		inode_lock_shared(inode);
	}

	ret = dax_iomap_rw(iocb, to, &fuse_iomap_ops);
	inode_unlock_shared(inode);

	/* TODO file_accessed(iocb->f_filp) */
	return ret;
}

static bool file_extending_write(struct kiocb *iocb, struct iov_iter *from)
{
	struct inode *inode = file_inode(iocb->ki_filp);

	return (iov_iter_rw(from) == WRITE &&
		((iocb->ki_pos) >= i_size_read(inode) ||
		  (iocb->ki_pos + iov_iter_count(from) > i_size_read(inode))));
}

static ssize_t fuse_dax_direct_write(struct kiocb *iocb, struct iov_iter *from)
{
	struct inode *inode = file_inode(iocb->ki_filp);
	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(iocb);
	ssize_t ret;

	ret = fuse_direct_io(&io, from, &iocb->ki_pos, FUSE_DIO_WRITE);

	fuse_write_update_attr(inode, iocb->ki_pos, ret);
	return ret;
}

ssize_t fuse_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
	struct inode *inode = file_inode(iocb->ki_filp);
	ssize_t ret;

	if (iocb->ki_flags & IOCB_NOWAIT) {
		if (!inode_trylock(inode))
			return -EAGAIN;
	} else {
		inode_lock(inode);
	}

	ret = generic_write_checks(iocb, from);
	if (ret <= 0)
		goto out;

	ret = file_remove_privs(iocb->ki_filp);
	if (ret)
		goto out;
	/* TODO file_update_time() but we don't want metadata I/O */

	/* Do not use dax for file extending writes as write and on
	 * disk i_size increase are not atomic otherwise.
	 */
	if (file_extending_write(iocb, from))
		ret = fuse_dax_direct_write(iocb, from);
	else
		ret = dax_iomap_rw(iocb, from, &fuse_iomap_ops);

out:
	inode_unlock(inode);

	if (ret > 0)
		ret = generic_write_sync(iocb, ret);
	return ret;
}

static int fuse_dax_writepages(struct address_space *mapping,
			       struct writeback_control *wbc)
{

	struct inode *inode = mapping->host;
	struct fuse_conn *fc = get_fuse_conn(inode);

	return dax_writeback_mapping_range(mapping, fc->dax->dev, wbc);
}

static vm_fault_t __fuse_dax_fault(struct vm_fault *vmf,
				   enum page_entry_size pe_size, bool write)
{
	vm_fault_t ret;
	struct inode *inode = file_inode(vmf->vma->vm_file);
	struct super_block *sb = inode->i_sb;
	pfn_t pfn;
	int error = 0;
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_conn_dax *fcd = fc->dax;
	bool retry = false;

	if (write)
		sb_start_pagefault(sb);
retry:
	if (retry && !(fcd->nr_free_ranges > 0))
		wait_event(fcd->range_waitq, (fcd->nr_free_ranges > 0));

	/*
	 * We need to serialize against not only truncate but also against
	 * fuse dax memory range reclaim. While a range is being reclaimed,
	 * we do not want any read/write/mmap to make progress and try
	 * to populate page cache or access memory we are trying to free.
	 */
	filemap_invalidate_lock_shared(inode->i_mapping);
	ret = dax_iomap_fault(vmf, pe_size, &pfn, &error, &fuse_iomap_ops);
	if ((ret & VM_FAULT_ERROR) && error == -EAGAIN) {
		error = 0;
		retry = true;
		filemap_invalidate_unlock_shared(inode->i_mapping);
		goto retry;
	}

	if (ret & VM_FAULT_NEEDDSYNC)
		ret = dax_finish_sync_fault(vmf, pe_size, pfn);
	filemap_invalidate_unlock_shared(inode->i_mapping);

	if (write)
		sb_end_pagefault(sb);

	return ret;
}

static vm_fault_t fuse_dax_fault(struct vm_fault *vmf)
{
	return __fuse_dax_fault(vmf, PE_SIZE_PTE,
				vmf->flags & FAULT_FLAG_WRITE);
}

static vm_fault_t fuse_dax_huge_fault(struct vm_fault *vmf,
			       enum page_entry_size pe_size)
{
	return __fuse_dax_fault(vmf, pe_size, vmf->flags & FAULT_FLAG_WRITE);
}

static vm_fault_t fuse_dax_page_mkwrite(struct vm_fault *vmf)
{
	return __fuse_dax_fault(vmf, PE_SIZE_PTE, true);
}

static vm_fault_t fuse_dax_pfn_mkwrite(struct vm_fault *vmf)
{
	return __fuse_dax_fault(vmf, PE_SIZE_PTE, true);
}

static const struct vm_operations_struct fuse_dax_vm_ops = {
	.fault		= fuse_dax_fault,
	.huge_fault	= fuse_dax_huge_fault,
	.page_mkwrite	= fuse_dax_page_mkwrite,
	.pfn_mkwrite	= fuse_dax_pfn_mkwrite,
};

int fuse_dax_mmap(struct file *file, struct vm_area_struct *vma)
{
	file_accessed(file);
	vma->vm_ops = &fuse_dax_vm_ops;
	vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
	return 0;
}

static int dmap_writeback_invalidate(struct inode *inode,
				     struct fuse_dax_mapping *dmap)
{
	int ret;
	loff_t start_pos = dmap->itn.start << FUSE_DAX_SHIFT;
	loff_t end_pos = (start_pos + FUSE_DAX_SZ - 1);

	ret = filemap_fdatawrite_range(inode->i_mapping, start_pos, end_pos);
	if (ret) {
		pr_debug("fuse: filemap_fdatawrite_range() failed. err=%d start_pos=0x%llx, end_pos=0x%llx\n",
			 ret, start_pos, end_pos);
		return ret;
	}

	ret = invalidate_inode_pages2_range(inode->i_mapping,
					    start_pos >> PAGE_SHIFT,
					    end_pos >> PAGE_SHIFT);
	if (ret)
		pr_debug("fuse: invalidate_inode_pages2_range() failed err=%d\n",
			 ret);

	return ret;
}

static int reclaim_one_dmap_locked(struct inode *inode,
				   struct fuse_dax_mapping *dmap)
{
	int ret;
	struct fuse_inode *fi = get_fuse_inode(inode);

	/*
	 * igrab() was done to make sure inode won't go under us, and this
	 * further avoids the race with evict().
	 */
	ret = dmap_writeback_invalidate(inode, dmap);
	if (ret)
		return ret;

	/* Remove dax mapping from inode interval tree now */
	interval_tree_remove(&dmap->itn, &fi->dax->tree);
	fi->dax->nr--;

	/* It is possible that umount/shutdown has killed the fuse connection
	 * and worker thread is trying to reclaim memory in parallel.  Don't
	 * warn in that case.
	 */
	ret = dmap_removemapping_one(inode, dmap);
	if (ret && ret != -ENOTCONN) {
		pr_warn("Failed to remove mapping. offset=0x%llx len=0x%llx ret=%d\n",
			dmap->window_offset, dmap->length, ret);
	}
	return 0;
}

/* Find first mapped dmap for an inode and return file offset. Caller needs
 * to hold fi->dax->sem lock either shared or exclusive.
 */
static struct fuse_dax_mapping *inode_lookup_first_dmap(struct inode *inode)
{
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_dax_mapping *dmap;
	struct interval_tree_node *node;

	for (node = interval_tree_iter_first(&fi->dax->tree, 0, -1); node;
	     node = interval_tree_iter_next(node, 0, -1)) {
		dmap = node_to_dmap(node);
		/* still in use. */
		if (refcount_read(&dmap->refcnt) > 1)
			continue;

		return dmap;
	}

	return NULL;
}

/*
 * Find first mapping in the tree and free it and return it. Do not add
 * it back to free pool.
 */
static struct fuse_dax_mapping *
inode_inline_reclaim_one_dmap(struct fuse_conn_dax *fcd, struct inode *inode,
			      bool *retry)
{
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_dax_mapping *dmap;
	u64 dmap_start, dmap_end;
	unsigned long start_idx;
	int ret;
	struct interval_tree_node *node;

	filemap_invalidate_lock(inode->i_mapping);

	/* Lookup a dmap and corresponding file offset to reclaim. */
	down_read(&fi->dax->sem);
	dmap = inode_lookup_first_dmap(inode);
	if (dmap) {
		start_idx = dmap->itn.start;
		dmap_start = start_idx << FUSE_DAX_SHIFT;
		dmap_end = dmap_start + FUSE_DAX_SZ - 1;
	}
	up_read(&fi->dax->sem);

	if (!dmap)
		goto out_mmap_sem;
	/*
	 * Make sure there are no references to inode pages using
	 * get_user_pages()
	 */
	ret = fuse_dax_break_layouts(inode, dmap_start, dmap_end);
	if (ret) {
		pr_debug("fuse: fuse_dax_break_layouts() failed. err=%d\n",
			 ret);
		dmap = ERR_PTR(ret);
		goto out_mmap_sem;
	}

	down_write(&fi->dax->sem);
	node = interval_tree_iter_first(&fi->dax->tree, start_idx, start_idx);
	/* Range already got reclaimed by somebody else */
	if (!node) {
		if (retry)
			*retry = true;
		goto out_write_dmap_sem;
	}

	dmap = node_to_dmap(node);
	/* still in use. */
	if (refcount_read(&dmap->refcnt) > 1) {
		dmap = NULL;
		if (retry)
			*retry = true;
		goto out_write_dmap_sem;
	}

	ret = reclaim_one_dmap_locked(inode, dmap);
	if (ret < 0) {
		dmap = ERR_PTR(ret);
		goto out_write_dmap_sem;
	}

	/* Clean up dmap. Do not add back to free list */
	dmap_remove_busy_list(fcd, dmap);
	dmap->inode = NULL;
	dmap->itn.start = dmap->itn.last = 0;

	pr_debug("fuse: %s: inline reclaimed memory range. inode=%p, window_offset=0x%llx, length=0x%llx\n",
		 __func__, inode, dmap->window_offset, dmap->length);

out_write_dmap_sem:
	up_write(&fi->dax->sem);
out_mmap_sem:
	filemap_invalidate_unlock(inode->i_mapping);
	return dmap;
}

static struct fuse_dax_mapping *
alloc_dax_mapping_reclaim(struct fuse_conn_dax *fcd, struct inode *inode)
{
	struct fuse_dax_mapping *dmap;
	struct fuse_inode *fi = get_fuse_inode(inode);

	while (1) {
		bool retry = false;

		dmap = alloc_dax_mapping(fcd);
		if (dmap)
			return dmap;

		dmap = inode_inline_reclaim_one_dmap(fcd, inode, &retry);
		/*
		 * Either we got a mapping or it is an error, return in both
		 * the cases.
		 */
		if (dmap)
			return dmap;

		/* If we could not reclaim a mapping because it
		 * had a reference or some other temporary failure,
		 * Try again. We want to give up inline reclaim only
		 * if there is no range assigned to this node. Otherwise
		 * if a deadlock is possible if we sleep with
		 * mapping->invalidate_lock held and worker to free memory
		 * can't make progress due to unavailability of
		 * mapping->invalidate_lock.  So sleep only if fi->dax->nr=0
		 */
		if (retry)
			continue;
		/*
		 * There are no mappings which can be reclaimed. Wait for one.
		 * We are not holding fi->dax->sem. So it is possible
		 * that range gets added now. But as we are not holding
		 * mapping->invalidate_lock, worker should still be able to
		 * free up a range and wake us up.
		 */
		if (!fi->dax->nr && !(fcd->nr_free_ranges > 0)) {
			if (wait_event_killable_exclusive(fcd->range_waitq,
					(fcd->nr_free_ranges > 0))) {
				return ERR_PTR(-EINTR);
			}
		}
	}
}

static int lookup_and_reclaim_dmap_locked(struct fuse_conn_dax *fcd,
					  struct inode *inode,
					  unsigned long start_idx)
{
	int ret;
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_dax_mapping *dmap;
	struct interval_tree_node *node;

	/* Find fuse dax mapping at file offset inode. */
	node = interval_tree_iter_first(&fi->dax->tree, start_idx, start_idx);

	/* Range already got cleaned up by somebody else */
	if (!node)
		return 0;
	dmap = node_to_dmap(node);

	/* still in use. */
	if (refcount_read(&dmap->refcnt) > 1)
		return 0;

	ret = reclaim_one_dmap_locked(inode, dmap);
	if (ret < 0)
		return ret;

	/* Cleanup dmap entry and add back to free list */
	spin_lock(&fcd->lock);
	dmap_reinit_add_to_free_pool(fcd, dmap);
	spin_unlock(&fcd->lock);
	return ret;
}

/*
 * Free a range of memory.
 * Locking:
 * 1. Take mapping->invalidate_lock to block dax faults.
 * 2. Take fi->dax->sem to protect interval tree and also to make sure
 *    read/write can not reuse a dmap which we might be freeing.
 */
static int lookup_and_reclaim_dmap(struct fuse_conn_dax *fcd,
				   struct inode *inode,
				   unsigned long start_idx,
				   unsigned long end_idx)
{
	int ret;
	struct fuse_inode *fi = get_fuse_inode(inode);
	loff_t dmap_start = start_idx << FUSE_DAX_SHIFT;
	loff_t dmap_end = (dmap_start + FUSE_DAX_SZ) - 1;

	filemap_invalidate_lock(inode->i_mapping);
	ret = fuse_dax_break_layouts(inode, dmap_start, dmap_end);
	if (ret) {
		pr_debug("virtio_fs: fuse_dax_break_layouts() failed. err=%d\n",
			 ret);
		goto out_mmap_sem;
	}

	down_write(&fi->dax->sem);
	ret = lookup_and_reclaim_dmap_locked(fcd, inode, start_idx);
	up_write(&fi->dax->sem);
out_mmap_sem:
	filemap_invalidate_unlock(inode->i_mapping);
	return ret;
}

static int try_to_free_dmap_chunks(struct fuse_conn_dax *fcd,
				   unsigned long nr_to_free)
{
	struct fuse_dax_mapping *dmap, *pos, *temp;
	int ret, nr_freed = 0;
	unsigned long start_idx = 0, end_idx = 0;
	struct inode *inode = NULL;

	/* Pick first busy range and free it for now*/
	while (1) {
		if (nr_freed >= nr_to_free)
			break;

		dmap = NULL;
		spin_lock(&fcd->lock);

		if (!fcd->nr_busy_ranges) {
			spin_unlock(&fcd->lock);
			return 0;
		}

		list_for_each_entry_safe(pos, temp, &fcd->busy_ranges,
						busy_list) {
			/* skip this range if it's in use. */
			if (refcount_read(&pos->refcnt) > 1)
				continue;

			inode = igrab(pos->inode);
			/*
			 * This inode is going away. That will free
			 * up all the ranges anyway, continue to
			 * next range.
			 */
			if (!inode)
				continue;
			/*
			 * Take this element off list and add it tail. If
			 * this element can't be freed, it will help with
			 * selecting new element in next iteration of loop.
			 */
			dmap = pos;
			list_move_tail(&dmap->busy_list, &fcd->busy_ranges);
			start_idx = end_idx = dmap->itn.start;
			break;
		}
		spin_unlock(&fcd->lock);
		if (!dmap)
			return 0;

		ret = lookup_and_reclaim_dmap(fcd, inode, start_idx, end_idx);
		iput(inode);
		if (ret)
			return ret;
		nr_freed++;
	}
	return 0;
}

static void fuse_dax_free_mem_worker(struct work_struct *work)
{
	int ret;
	struct fuse_conn_dax *fcd = container_of(work, struct fuse_conn_dax,
						 free_work.work);
	ret = try_to_free_dmap_chunks(fcd, FUSE_DAX_RECLAIM_CHUNK);
	if (ret) {
		pr_debug("fuse: try_to_free_dmap_chunks() failed with err=%d\n",
			 ret);
	}

	/* If number of free ranges are still below threshold, requeue */
	kick_dmap_free_worker(fcd, 1);
}

static void fuse_free_dax_mem_ranges(struct list_head *mem_list)
{
	struct fuse_dax_mapping *range, *temp;

	/* Free All allocated elements */
	list_for_each_entry_safe(range, temp, mem_list, list) {
		list_del(&range->list);
		if (!list_empty(&range->busy_list))
			list_del(&range->busy_list);
		kfree(range);
	}
}

void fuse_dax_conn_free(struct fuse_conn *fc)
{
	if (fc->dax) {
		fuse_free_dax_mem_ranges(&fc->dax->free_ranges);
		kfree(fc->dax);
	}
}

static int fuse_dax_mem_range_init(struct fuse_conn_dax *fcd)
{
	long nr_pages, nr_ranges;
	struct fuse_dax_mapping *range;
	int ret, id;
	size_t dax_size = -1;
	unsigned long i;

	init_waitqueue_head(&fcd->range_waitq);
	INIT_LIST_HEAD(&fcd->free_ranges);
	INIT_LIST_HEAD(&fcd->busy_ranges);
	INIT_DELAYED_WORK(&fcd->free_work, fuse_dax_free_mem_worker);

	id = dax_read_lock();
	nr_pages = dax_direct_access(fcd->dev, 0, PHYS_PFN(dax_size), NULL,
				     NULL);
	dax_read_unlock(id);
	if (nr_pages < 0) {
		pr_debug("dax_direct_access() returned %ld\n", nr_pages);
		return nr_pages;
	}

	nr_ranges = nr_pages/FUSE_DAX_PAGES;
	pr_debug("%s: dax mapped %ld pages. nr_ranges=%ld\n",
		__func__, nr_pages, nr_ranges);

	for (i = 0; i < nr_ranges; i++) {
		range = kzalloc(sizeof(struct fuse_dax_mapping), GFP_KERNEL);
		ret = -ENOMEM;
		if (!range)
			goto out_err;

		/* TODO: This offset only works if virtio-fs driver is not
		 * having some memory hidden at the beginning. This needs
		 * better handling
		 */
		range->window_offset = i * FUSE_DAX_SZ;
		range->length = FUSE_DAX_SZ;
		INIT_LIST_HEAD(&range->busy_list);
		refcount_set(&range->refcnt, 1);
		list_add_tail(&range->list, &fcd->free_ranges);
	}

	fcd->nr_free_ranges = nr_ranges;
	fcd->nr_ranges = nr_ranges;
	return 0;
out_err:
	/* Free All allocated elements */
	fuse_free_dax_mem_ranges(&fcd->free_ranges);
	return ret;
}

int fuse_dax_conn_alloc(struct fuse_conn *fc, struct dax_device *dax_dev)
{
	struct fuse_conn_dax *fcd;
	int err;

	if (!dax_dev)
		return 0;

	fcd = kzalloc(sizeof(*fcd), GFP_KERNEL);
	if (!fcd)
		return -ENOMEM;

	spin_lock_init(&fcd->lock);
	fcd->dev = dax_dev;
	err = fuse_dax_mem_range_init(fcd);
	if (err) {
		kfree(fcd);
		return err;
	}

	fc->dax = fcd;
	return 0;
}

bool fuse_dax_inode_alloc(struct super_block *sb, struct fuse_inode *fi)
{
	struct fuse_conn *fc = get_fuse_conn_super(sb);

	fi->dax = NULL;
	if (fc->dax) {
		fi->dax = kzalloc(sizeof(*fi->dax), GFP_KERNEL_ACCOUNT);
		if (!fi->dax)
			return false;

		init_rwsem(&fi->dax->sem);
		fi->dax->tree = RB_ROOT_CACHED;
	}

	return true;
}

static const struct address_space_operations fuse_dax_file_aops  = {
	.writepages	= fuse_dax_writepages,
	.direct_IO	= noop_direct_IO,
	.set_page_dirty	= __set_page_dirty_no_writeback,
	.invalidatepage	= noop_invalidatepage,
};

void fuse_dax_inode_init(struct inode *inode)
{
	struct fuse_conn *fc = get_fuse_conn(inode);

	if (!fc->dax)
		return;

	inode->i_flags |= S_DAX;
	inode->i_data.a_ops = &fuse_dax_file_aops;
}

bool fuse_dax_check_alignment(struct fuse_conn *fc, unsigned int map_alignment)
{
	if (fc->dax && (map_alignment > FUSE_DAX_SHIFT)) {
		pr_warn("FUSE: map_alignment %u incompatible with dax mem range size %u\n",
			map_alignment, FUSE_DAX_SZ);
		return false;
	}
	return true;
}

void fuse_dax_cancel_work(struct fuse_conn *fc)
{
	struct fuse_conn_dax *fcd = fc->dax;

	if (fcd)
		cancel_delayed_work_sync(&fcd->free_work);

}
EXPORT_SYMBOL_GPL(fuse_dax_cancel_work);