summaryrefslogtreecommitdiffstats
path: root/drivers/dma-buf/dma-buf.c
blob: 9ad6397aaa97e10b580a23b54836162e765ae7ff (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Framework for buffer objects that can be shared across devices/subsystems.
 *
 * Copyright(C) 2011 Linaro Limited. All rights reserved.
 * Author: Sumit Semwal <sumit.semwal@ti.com>
 *
 * Many thanks to linaro-mm-sig list, and specially
 * Arnd Bergmann <arnd@arndb.de>, Rob Clark <rob@ti.com> and
 * Daniel Vetter <daniel@ffwll.ch> for their support in creation and
 * refining of this idea.
 */

#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/dma-buf.h>
#include <linux/dma-fence.h>
#include <linux/anon_inodes.h>
#include <linux/export.h>
#include <linux/debugfs.h>
#include <linux/module.h>
#include <linux/seq_file.h>
#include <linux/poll.h>
#include <linux/dma-resv.h>
#include <linux/mm.h>
#include <linux/mount.h>
#include <linux/pseudo_fs.h>

#include <uapi/linux/dma-buf.h>
#include <uapi/linux/magic.h>

static inline int is_dma_buf_file(struct file *);

struct dma_buf_list {
	struct list_head head;
	struct mutex lock;
};

static struct dma_buf_list db_list;

static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen)
{
	struct dma_buf *dmabuf;
	char name[DMA_BUF_NAME_LEN];
	size_t ret = 0;

	dmabuf = dentry->d_fsdata;
	spin_lock(&dmabuf->name_lock);
	if (dmabuf->name)
		ret = strlcpy(name, dmabuf->name, DMA_BUF_NAME_LEN);
	spin_unlock(&dmabuf->name_lock);

	return dynamic_dname(dentry, buffer, buflen, "/%s:%s",
			     dentry->d_name.name, ret > 0 ? name : "");
}

static void dma_buf_release(struct dentry *dentry)
{
	struct dma_buf *dmabuf;

	dmabuf = dentry->d_fsdata;
	if (unlikely(!dmabuf))
		return;

	BUG_ON(dmabuf->vmapping_counter);

	/*
	 * Any fences that a dma-buf poll can wait on should be signaled
	 * before releasing dma-buf. This is the responsibility of each
	 * driver that uses the reservation objects.
	 *
	 * If you hit this BUG() it means someone dropped their ref to the
	 * dma-buf while still having pending operation to the buffer.
	 */
	BUG_ON(dmabuf->cb_shared.active || dmabuf->cb_excl.active);

	dmabuf->ops->release(dmabuf);

	if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
		dma_resv_fini(dmabuf->resv);

	module_put(dmabuf->owner);
	kfree(dmabuf->name);
	kfree(dmabuf);
}

static int dma_buf_file_release(struct inode *inode, struct file *file)
{
	struct dma_buf *dmabuf;

	if (!is_dma_buf_file(file))
		return -EINVAL;

	dmabuf = file->private_data;

	mutex_lock(&db_list.lock);
	list_del(&dmabuf->list_node);
	mutex_unlock(&db_list.lock);

	return 0;
}

static const struct dentry_operations dma_buf_dentry_ops = {
	.d_dname = dmabuffs_dname,
	.d_release = dma_buf_release,
};

static struct vfsmount *dma_buf_mnt;

static int dma_buf_fs_init_context(struct fs_context *fc)
{
	struct pseudo_fs_context *ctx;

	ctx = init_pseudo(fc, DMA_BUF_MAGIC);
	if (!ctx)
		return -ENOMEM;
	ctx->dops = &dma_buf_dentry_ops;
	return 0;
}

static struct file_system_type dma_buf_fs_type = {
	.name = "dmabuf",
	.init_fs_context = dma_buf_fs_init_context,
	.kill_sb = kill_anon_super,
};

static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
{
	struct dma_buf *dmabuf;

	if (!is_dma_buf_file(file))
		return -EINVAL;

	dmabuf = file->private_data;

	/* check if buffer supports mmap */
	if (!dmabuf->ops->mmap)
		return -EINVAL;

	/* check for overflowing the buffer's size */
	if (vma->vm_pgoff + vma_pages(vma) >
	    dmabuf->size >> PAGE_SHIFT)
		return -EINVAL;

	return dmabuf->ops->mmap(dmabuf, vma);
}

static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
{
	struct dma_buf *dmabuf;
	loff_t base;

	if (!is_dma_buf_file(file))
		return -EBADF;

	dmabuf = file->private_data;

	/* only support discovering the end of the buffer,
	   but also allow SEEK_SET to maintain the idiomatic
	   SEEK_END(0), SEEK_CUR(0) pattern */
	if (whence == SEEK_END)
		base = dmabuf->size;
	else if (whence == SEEK_SET)
		base = 0;
	else
		return -EINVAL;

	if (offset != 0)
		return -EINVAL;

	return base + offset;
}

/**
 * DOC: implicit fence polling
 *
 * To support cross-device and cross-driver synchronization of buffer access
 * implicit fences (represented internally in the kernel with &struct dma_fence)
 * can be attached to a &dma_buf. The glue for that and a few related things are
 * provided in the &dma_resv structure.
 *
 * Userspace can query the state of these implicitly tracked fences using poll()
 * and related system calls:
 *
 * - Checking for EPOLLIN, i.e. read access, can be use to query the state of the
 *   most recent write or exclusive fence.
 *
 * - Checking for EPOLLOUT, i.e. write access, can be used to query the state of
 *   all attached fences, shared and exclusive ones.
 *
 * Note that this only signals the completion of the respective fences, i.e. the
 * DMA transfers are complete. Cache flushing and any other necessary
 * preparations before CPU access can begin still need to happen.
 */

static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
{
	struct dma_buf_poll_cb_t *dcb = (struct dma_buf_poll_cb_t *)cb;
	unsigned long flags;

	spin_lock_irqsave(&dcb->poll->lock, flags);
	wake_up_locked_poll(dcb->poll, dcb->active);
	dcb->active = 0;
	spin_unlock_irqrestore(&dcb->poll->lock, flags);
}

static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
{
	struct dma_buf *dmabuf;
	struct dma_resv *resv;
	struct dma_resv_list *fobj;
	struct dma_fence *fence_excl;
	__poll_t events;
	unsigned shared_count, seq;

	dmabuf = file->private_data;
	if (!dmabuf || !dmabuf->resv)
		return EPOLLERR;

	resv = dmabuf->resv;

	poll_wait(file, &dmabuf->poll, poll);

	events = poll_requested_events(poll) & (EPOLLIN | EPOLLOUT);
	if (!events)
		return 0;

retry:
	seq = read_seqcount_begin(&resv->seq);
	rcu_read_lock();

	fobj = rcu_dereference(resv->fence);
	if (fobj)
		shared_count = fobj->shared_count;
	else
		shared_count = 0;
	fence_excl = rcu_dereference(resv->fence_excl);
	if (read_seqcount_retry(&resv->seq, seq)) {
		rcu_read_unlock();
		goto retry;
	}

	if (fence_excl && (!(events & EPOLLOUT) || shared_count == 0)) {
		struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_excl;
		__poll_t pevents = EPOLLIN;

		if (shared_count == 0)
			pevents |= EPOLLOUT;

		spin_lock_irq(&dmabuf->poll.lock);
		if (dcb->active) {
			dcb->active |= pevents;
			events &= ~pevents;
		} else
			dcb->active = pevents;
		spin_unlock_irq(&dmabuf->poll.lock);

		if (events & pevents) {
			if (!dma_fence_get_rcu(fence_excl)) {
				/* force a recheck */
				events &= ~pevents;
				dma_buf_poll_cb(NULL, &dcb->cb);
			} else if (!dma_fence_add_callback(fence_excl, &dcb->cb,
							   dma_buf_poll_cb)) {
				events &= ~pevents;
				dma_fence_put(fence_excl);
			} else {
				/*
				 * No callback queued, wake up any additional
				 * waiters.
				 */
				dma_fence_put(fence_excl);
				dma_buf_poll_cb(NULL, &dcb->cb);
			}
		}
	}

	if ((events & EPOLLOUT) && shared_count > 0) {
		struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_shared;
		int i;

		/* Only queue a new callback if no event has fired yet */
		spin_lock_irq(&dmabuf->poll.lock);
		if (dcb->active)
			events &= ~EPOLLOUT;
		else
			dcb->active = EPOLLOUT;
		spin_unlock_irq(&dmabuf->poll.lock);

		if (!(events & EPOLLOUT))
			goto out;

		for (i = 0; i < shared_count; ++i) {
			struct dma_fence *fence = rcu_dereference(fobj->shared[i]);

			if (!dma_fence_get_rcu(fence)) {
				/*
				 * fence refcount dropped to zero, this means
				 * that fobj has been freed
				 *
				 * call dma_buf_poll_cb and force a recheck!
				 */
				events &= ~EPOLLOUT;
				dma_buf_poll_cb(NULL, &dcb->cb);
				break;
			}
			if (!dma_fence_add_callback(fence, &dcb->cb,
						    dma_buf_poll_cb)) {
				dma_fence_put(fence);
				events &= ~EPOLLOUT;
				break;
			}
			dma_fence_put(fence);
		}

		/* No callback queued, wake up any additional waiters. */
		if (i == shared_count)
			dma_buf_poll_cb(NULL, &dcb->cb);
	}

out:
	rcu_read_unlock();
	return events;
}

/**
 * dma_buf_set_name - Set a name to a specific dma_buf to track the usage.
 * The name of the dma-buf buffer can only be set when the dma-buf is not
 * attached to any devices. It could theoritically support changing the
 * name of the dma-buf if the same piece of memory is used for multiple
 * purpose between different devices.
 *
 * @dmabuf: [in]     dmabuf buffer that will be renamed.
 * @buf:    [in]     A piece of userspace memory that contains the name of
 *                   the dma-buf.
 *
 * Returns 0 on success. If the dma-buf buffer is already attached to
 * devices, return -EBUSY.
 *
 */
static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
{
	char *name = strndup_user(buf, DMA_BUF_NAME_LEN);
	long ret = 0;

	if (IS_ERR(name))
		return PTR_ERR(name);

	dma_resv_lock(dmabuf->resv, NULL);
	if (!list_empty(&dmabuf->attachments)) {
		ret = -EBUSY;
		kfree(name);
		goto out_unlock;
	}
	spin_lock(&dmabuf->name_lock);
	kfree(dmabuf->name);
	dmabuf->name = name;
	spin_unlock(&dmabuf->name_lock);

out_unlock:
	dma_resv_unlock(dmabuf->resv);
	return ret;
}

static long dma_buf_ioctl(struct file *file,
			  unsigned int cmd, unsigned long arg)
{
	struct dma_buf *dmabuf;
	struct dma_buf_sync sync;
	enum dma_data_direction direction;
	int ret;

	dmabuf = file->private_data;

	switch (cmd) {
	case DMA_BUF_IOCTL_SYNC:
		if (copy_from_user(&sync, (void __user *) arg, sizeof(sync)))
			return -EFAULT;

		if (sync.flags & ~DMA_BUF_SYNC_VALID_FLAGS_MASK)
			return -EINVAL;

		switch (sync.flags & DMA_BUF_SYNC_RW) {
		case DMA_BUF_SYNC_READ:
			direction = DMA_FROM_DEVICE;
			break;
		case DMA_BUF_SYNC_WRITE:
			direction = DMA_TO_DEVICE;
			break;
		case DMA_BUF_SYNC_RW:
			direction = DMA_BIDIRECTIONAL;
			break;
		default:
			return -EINVAL;
		}

		if (sync.flags & DMA_BUF_SYNC_END)
			ret = dma_buf_end_cpu_access(dmabuf, direction);
		else
			ret = dma_buf_begin_cpu_access(dmabuf, direction);

		return ret;

	case DMA_BUF_SET_NAME_A:
	case DMA_BUF_SET_NAME_B:
		return dma_buf_set_name(dmabuf, (const char __user *)arg);

	default:
		return -ENOTTY;
	}
}

static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file)
{
	struct dma_buf *dmabuf = file->private_data;

	seq_printf(m, "size:\t%zu\n", dmabuf->size);
	/* Don't count the temporary reference taken inside procfs seq_show */
	seq_printf(m, "count:\t%ld\n", file_count(dmabuf->file) - 1);
	seq_printf(m, "exp_name:\t%s\n", dmabuf->exp_name);
	spin_lock(&dmabuf->name_lock);
	if (dmabuf->name)
		seq_printf(m, "name:\t%s\n", dmabuf->name);
	spin_unlock(&dmabuf->name_lock);
}

static const struct file_operations dma_buf_fops = {
	.release	= dma_buf_file_release,
	.mmap		= dma_buf_mmap_internal,
	.llseek		= dma_buf_llseek,
	.poll		= dma_buf_poll,
	.unlocked_ioctl	= dma_buf_ioctl,
	.compat_ioctl	= compat_ptr_ioctl,
	.show_fdinfo	= dma_buf_show_fdinfo,
};

/*
 * is_dma_buf_file - Check if struct file* is associated with dma_buf
 */
static inline int is_dma_buf_file(struct file *file)
{
	return file->f_op == &dma_buf_fops;
}

static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags)
{
	struct file *file;
	struct inode *inode = alloc_anon_inode(dma_buf_mnt->mnt_sb);

	if (IS_ERR(inode))
		return ERR_CAST(inode);

	inode->i_size = dmabuf->size;
	inode_set_bytes(inode, dmabuf->size);

	file = alloc_file_pseudo(inode, dma_buf_mnt, "dmabuf",
				 flags, &dma_buf_fops);
	if (IS_ERR(file))
		goto err_alloc_file;
	file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
	file->private_data = dmabuf;
	file->f_path.dentry->d_fsdata = dmabuf;

	return file;

err_alloc_file:
	iput(inode);
	return file;
}

/**
 * DOC: dma buf device access
 *
 * For device DMA access to a shared DMA buffer the usual sequence of operations
 * is fairly simple:
 *
 * 1. The exporter defines his exporter instance using
 *    DEFINE_DMA_BUF_EXPORT_INFO() and calls dma_buf_export() to wrap a private
 *    buffer object into a &dma_buf. It then exports that &dma_buf to userspace
 *    as a file descriptor by calling dma_buf_fd().
 *
 * 2. Userspace passes this file-descriptors to all drivers it wants this buffer
 *    to share with: First the filedescriptor is converted to a &dma_buf using
 *    dma_buf_get(). Then the buffer is attached to the device using
 *    dma_buf_attach().
 *
 *    Up to this stage the exporter is still free to migrate or reallocate the
 *    backing storage.
 *
 * 3. Once the buffer is attached to all devices userspace can initiate DMA
 *    access to the shared buffer. In the kernel this is done by calling
 *    dma_buf_map_attachment() and dma_buf_unmap_attachment().
 *
 * 4. Once a driver is done with a shared buffer it needs to call
 *    dma_buf_detach() (after cleaning up any mappings) and then release the
 *    reference acquired with dma_buf_get by calling dma_buf_put().
 *
 * For the detailed semantics exporters are expected to implement see
 * &dma_buf_ops.
 */

/**
 * dma_buf_export - Creates a new dma_buf, and associates an anon file
 * with this buffer, so it can be exported.
 * Also connect the allocator specific data and ops to the buffer.
 * Additionally, provide a name string for exporter; useful in debugging.
 *
 * @exp_info:	[in]	holds all the export related information provided
 *			by the exporter. see &struct dma_buf_export_info
 *			for further details.
 *
 * Returns, on success, a newly created dma_buf object, which wraps the
 * supplied private data and operations for dma_buf_ops. On either missing
 * ops, or error in allocating struct dma_buf, will return negative error.
 *
 * For most cases the easiest way to create @exp_info is through the
 * %DEFINE_DMA_BUF_EXPORT_INFO macro.
 */
struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
{
	struct dma_buf *dmabuf;
	struct dma_resv *resv = exp_info->resv;
	struct file *file;
	size_t alloc_size = sizeof(struct dma_buf);
	int ret;

	if (!exp_info->resv)
		alloc_size += sizeof(struct dma_resv);
	else
		/* prevent &dma_buf[1] == dma_buf->resv */
		alloc_size += 1;

	if (WARN_ON(!exp_info->priv
			  || !exp_info->ops
			  || !exp_info->ops->map_dma_buf
			  || !exp_info->ops->unmap_dma_buf
			  || !exp_info->ops->release)) {
		return ERR_PTR(-EINVAL);
	}

	if (WARN_ON(exp_info->ops->cache_sgt_mapping &&
		    (exp_info->ops->pin || exp_info->ops->unpin)))
		return ERR_PTR(-EINVAL);

	if (WARN_ON(!exp_info->ops->pin != !exp_info->ops->unpin))
		return ERR_PTR(-EINVAL);

	if (!try_module_get(exp_info->owner))
		return ERR_PTR(-ENOENT);

	dmabuf = kzalloc(alloc_size, GFP_KERNEL);
	if (!dmabuf) {
		ret = -ENOMEM;
		goto err_module;
	}

	dmabuf->priv = exp_info->priv;
	dmabuf->ops = exp_info->ops;
	dmabuf->size = exp_info->size;
	dmabuf->exp_name = exp_info->exp_name;
	dmabuf->owner = exp_info->owner;
	spin_lock_init(&dmabuf->name_lock);
	init_waitqueue_head(&dmabuf->poll);
	dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll;
	dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0;

	if (!resv) {
		resv = (struct dma_resv *)&dmabuf[1];
		dma_resv_init(resv);
	}
	dmabuf->resv = resv;

	file = dma_buf_getfile(dmabuf, exp_info->flags);
	if (IS_ERR(file)) {
		ret = PTR_ERR(file);
		goto err_dmabuf;
	}

	file->f_mode |= FMODE_LSEEK;
	dmabuf->file = file;

	mutex_init(&dmabuf->lock);
	INIT_LIST_HEAD(&dmabuf->attachments);

	mutex_lock(&db_list.lock);
	list_add(&dmabuf->list_node, &db_list.head);
	mutex_unlock(&db_list.lock);

	return dmabuf;

err_dmabuf:
	kfree(dmabuf);
err_module:
	module_put(exp_info->owner);
	return ERR_PTR(ret);
}
EXPORT_SYMBOL_GPL(dma_buf_export);

/**
 * dma_buf_fd - returns a file descriptor for the given dma_buf
 * @dmabuf:	[in]	pointer to dma_buf for which fd is required.
 * @flags:      [in]    flags to give to fd
 *
 * On success, returns an associated 'fd'. Else, returns error.
 */
int dma_buf_fd(struct dma_buf *dmabuf, int flags)
{
	int fd;

	if (!dmabuf || !dmabuf->file)
		return -EINVAL;

	fd = get_unused_fd_flags(flags);
	if (fd < 0)
		return fd;

	fd_install(fd, dmabuf->file);

	return fd;
}
EXPORT_SYMBOL_GPL(dma_buf_fd);

/**
 * dma_buf_get - returns the dma_buf structure related to an fd
 * @fd:	[in]	fd associated with the dma_buf to be returned
 *
 * On success, returns the dma_buf structure associated with an fd; uses
 * file's refcounting done by fget to increase refcount. returns ERR_PTR
 * otherwise.
 */
struct dma_buf *dma_buf_get(int fd)
{
	struct file *file;

	file = fget(fd);

	if (!file)
		return ERR_PTR(-EBADF);

	if (!is_dma_buf_file(file)) {
		fput(file);
		return ERR_PTR(-EINVAL);
	}

	return file->private_data;
}
EXPORT_SYMBOL_GPL(dma_buf_get);

/**
 * dma_buf_put - decreases refcount of the buffer
 * @dmabuf:	[in]	buffer to reduce refcount of
 *
 * Uses file's refcounting done implicitly by fput().
 *
 * If, as a result of this call, the refcount becomes 0, the 'release' file
 * operation related to this fd is called. It calls &dma_buf_ops.release vfunc
 * in turn, and frees the memory allocated for dmabuf when exported.
 */
void dma_buf_put(struct dma_buf *dmabuf)
{
	if (WARN_ON(!dmabuf || !dmabuf->file))
		return;

	fput(dmabuf->file);
}
EXPORT_SYMBOL_GPL(dma_buf_put);

/**
 * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list; optionally,
 * calls attach() of dma_buf_ops to allow device-specific attach functionality
 * @dmabuf:		[in]	buffer to attach device to.
 * @dev:		[in]	device to be attached.
 * @importer_ops:	[in]	importer operations for the attachment
 * @importer_priv:	[in]	importer private pointer for the attachment
 *
 * Returns struct dma_buf_attachment pointer for this attachment. Attachments
 * must be cleaned up by calling dma_buf_detach().
 *
 * Returns:
 *
 * A pointer to newly created &dma_buf_attachment on success, or a negative
 * error code wrapped into a pointer on failure.
 *
 * Note that this can fail if the backing storage of @dmabuf is in a place not
 * accessible to @dev, and cannot be moved to a more suitable place. This is
 * indicated with the error code -EBUSY.
 */
struct dma_buf_attachment *
dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
		       const struct dma_buf_attach_ops *importer_ops,
		       void *importer_priv)
{
	struct dma_buf_attachment *attach;
	int ret;

	if (WARN_ON(!dmabuf || !dev))
		return ERR_PTR(-EINVAL);

	if (WARN_ON(importer_ops && !importer_ops->move_notify))
		return ERR_PTR(-EINVAL);

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

	attach->dev = dev;
	attach->dmabuf = dmabuf;
	if (importer_ops)
		attach->peer2peer = importer_ops->allow_peer2peer;
	attach->importer_ops = importer_ops;
	attach->importer_priv = importer_priv;

	if (dmabuf->ops->attach) {
		ret = dmabuf->ops->attach(dmabuf, attach);
		if (ret)
			goto err_attach;
	}
	dma_resv_lock(dmabuf->resv, NULL);
	list_add(&attach->node, &dmabuf->attachments);
	dma_resv_unlock(dmabuf->resv);

	/* When either the importer or the exporter can't handle dynamic
	 * mappings we cache the mapping here to avoid issues with the
	 * reservation object lock.
	 */
	if (dma_buf_attachment_is_dynamic(attach) !=
	    dma_buf_is_dynamic(dmabuf)) {
		struct sg_table *sgt;

		if (dma_buf_is_dynamic(attach->dmabuf)) {
			dma_resv_lock(attach->dmabuf->resv, NULL);
			ret = dma_buf_pin(attach);
			if (ret)
				goto err_unlock;
		}

		sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
		if (!sgt)
			sgt = ERR_PTR(-ENOMEM);
		if (IS_ERR(sgt)) {
			ret = PTR_ERR(sgt);
			goto err_unpin;
		}
		if (dma_buf_is_dynamic(attach->dmabuf))
			dma_resv_unlock(attach->dmabuf->resv);
		attach->sgt = sgt;
		attach->dir = DMA_BIDIRECTIONAL;
	}

	return attach;

err_attach:
	kfree(attach);
	return ERR_PTR(ret);

err_unpin:
	if (dma_buf_is_dynamic(attach->dmabuf))
		dma_buf_unpin(attach);

err_unlock:
	if (dma_buf_is_dynamic(attach->dmabuf))
		dma_resv_unlock(attach->dmabuf->resv);

	dma_buf_detach(dmabuf, attach);
	return ERR_PTR(ret);
}
EXPORT_SYMBOL_GPL(dma_buf_dynamic_attach);

/**
 * dma_buf_attach - Wrapper for dma_buf_dynamic_attach
 * @dmabuf:	[in]	buffer to attach device to.
 * @dev:	[in]	device to be attached.
 *
 * Wrapper to call dma_buf_dynamic_attach() for drivers which still use a static
 * mapping.
 */
struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
					  struct device *dev)
{
	return dma_buf_dynamic_attach(dmabuf, dev, NULL, NULL);
}
EXPORT_SYMBOL_GPL(dma_buf_attach);

/**
 * dma_buf_detach - Remove the given attachment from dmabuf's attachments list;
 * optionally calls detach() of dma_buf_ops for device-specific detach
 * @dmabuf:	[in]	buffer to detach from.
 * @attach:	[in]	attachment to be detached; is free'd after this call.
 *
 * Clean up a device attachment obtained by calling dma_buf_attach().
 */
void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
{
	if (WARN_ON(!dmabuf || !attach))
		return;

	if (attach->sgt) {
		if (dma_buf_is_dynamic(attach->dmabuf))
			dma_resv_lock(attach->dmabuf->resv, NULL);

		dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);

		if (dma_buf_is_dynamic(attach->dmabuf)) {
			dma_buf_unpin(attach);
			dma_resv_unlock(attach->dmabuf->resv);
		}
	}

	dma_resv_lock(dmabuf->resv, NULL);
	list_del(&attach->node);
	dma_resv_unlock(dmabuf->resv);
	if (dmabuf->ops->detach)
		dmabuf->ops->detach(dmabuf, attach);

	kfree(attach);
}
EXPORT_SYMBOL_GPL(dma_buf_detach);

/**
 * dma_buf_pin - Lock down the DMA-buf
 *
 * @attach:	[in]	attachment which should be pinned
 *
 * Returns:
 * 0 on success, negative error code on failure.
 */
int dma_buf_pin(struct dma_buf_attachment *attach)
{
	struct dma_buf *dmabuf = attach->dmabuf;
	int ret = 0;

	dma_resv_assert_held(dmabuf->resv);

	if (dmabuf->ops->pin)
		ret = dmabuf->ops->pin(attach);

	return ret;
}
EXPORT_SYMBOL_GPL(dma_buf_pin);

/**
 * dma_buf_unpin - Remove lock from DMA-buf
 *
 * @attach:	[in]	attachment which should be unpinned
 */
void dma_buf_unpin(struct dma_buf_attachment *attach)
{
	struct dma_buf *dmabuf = attach->dmabuf;

	dma_resv_assert_held(dmabuf->resv);

	if (dmabuf->ops->unpin)
		dmabuf->ops->unpin(attach);
}
EXPORT_SYMBOL_GPL(dma_buf_unpin);

/**
 * dma_buf_map_attachment - Returns the scatterlist table of the attachment;
 * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
 * dma_buf_ops.
 * @attach:	[in]	attachment whose scatterlist is to be returned
 * @direction:	[in]	direction of DMA transfer
 *
 * Returns sg_table containing the scatterlist to be returned; returns ERR_PTR
 * on error. May return -EINTR if it is interrupted by a signal.
 *
 * On success, the DMA addresses and lengths in the returned scatterlist are
 * PAGE_SIZE aligned.
 *
 * A mapping must be unmapped by using dma_buf_unmap_attachment(). Note that
 * the underlying backing storage is pinned for as long as a mapping exists,
 * therefore users/importers should not hold onto a mapping for undue amounts of
 * time.
 */
struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
					enum dma_data_direction direction)
{
	struct sg_table *sg_table;
	int r;

	might_sleep();

	if (WARN_ON(!attach || !attach->dmabuf))
		return ERR_PTR(-EINVAL);

	if (dma_buf_attachment_is_dynamic(attach))
		dma_resv_assert_held(attach->dmabuf->resv);

	if (attach->sgt) {
		/*
		 * Two mappings with different directions for the same
		 * attachment are not allowed.
		 */
		if (attach->dir != direction &&
		    attach->dir != DMA_BIDIRECTIONAL)
			return ERR_PTR(-EBUSY);

		return attach->sgt;
	}

	if (dma_buf_is_dynamic(attach->dmabuf)) {
		dma_resv_assert_held(attach->dmabuf->resv);
		if (!IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) {
			r = dma_buf_pin(attach);
			if (r)
				return ERR_PTR(r);
		}
	}

	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
	if (!sg_table)
		sg_table = ERR_PTR(-ENOMEM);

	if (IS_ERR(sg_table) && dma_buf_is_dynamic(attach->dmabuf) &&
	     !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
		dma_buf_unpin(attach);

	if (!IS_ERR(sg_table) && attach->dmabuf->ops->cache_sgt_mapping) {
		attach->sgt = sg_table;
		attach->dir = direction;
	}

#ifdef CONFIG_DMA_API_DEBUG
	if (!IS_ERR(sg_table)) {
		struct scatterlist *sg;
		u64 addr;
		int len;
		int i;

		for_each_sgtable_dma_sg(sg_table, sg, i) {
			addr = sg_dma_address(sg);
			len = sg_dma_len(sg);
			if (!PAGE_ALIGNED(addr) || !PAGE_ALIGNED(len)) {
				pr_debug("%s: addr %llx or len %x is not page aligned!\n",
					 __func__, addr, len);
			}
		}
	}
#endif /* CONFIG_DMA_API_DEBUG */

	return sg_table;
}
EXPORT_SYMBOL_GPL(dma_buf_map_attachment);

/**
 * dma_buf_unmap_attachment - unmaps and decreases usecount of the buffer;might
 * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
 * dma_buf_ops.
 * @attach:	[in]	attachment to unmap buffer from
 * @sg_table:	[in]	scatterlist info of the buffer to unmap
 * @direction:  [in]    direction of DMA transfer
 *
 * This unmaps a DMA mapping for @attached obtained by dma_buf_map_attachment().
 */
void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
				struct sg_table *sg_table,
				enum dma_data_direction direction)
{
	might_sleep();

	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
		return;

	if (dma_buf_attachment_is_dynamic(attach))
		dma_resv_assert_held(attach->dmabuf->resv);

	if (attach->sgt == sg_table)
		return;

	if (dma_buf_is_dynamic(attach->dmabuf))
		dma_resv_assert_held(attach->dmabuf->resv);

	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);

	if (dma_buf_is_dynamic(attach->dmabuf) &&
	    !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
		dma_buf_unpin(attach);
}
EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);

/**
 * dma_buf_move_notify - notify attachments that DMA-buf is moving
 *
 * @dmabuf:	[in]	buffer which is moving
 *
 * Informs all attachmenst that they need to destroy and recreated all their
 * mappings.
 */
void dma_buf_move_notify(struct dma_buf *dmabuf)
{
	struct dma_buf_attachment *attach;

	dma_resv_assert_held(dmabuf->resv);

	list_for_each_entry(attach, &dmabuf->attachments, node)
		if (attach->importer_ops)
			attach->importer_ops->move_notify(attach);
}
EXPORT_SYMBOL_GPL(dma_buf_move_notify);

/**
 * DOC: cpu access
 *
 * There are mutliple reasons for supporting CPU access to a dma buffer object:
 *
 * - Fallback operations in the kernel, for example when a device is connected
 *   over USB and the kernel needs to shuffle the data around first before
 *   sending it away. Cache coherency is handled by braketing any transactions
 *   with calls to dma_buf_begin_cpu_access() and dma_buf_end_cpu_access()
 *   access.
 *
 *   Since for most kernel internal dma-buf accesses need the entire buffer, a
 *   vmap interface is introduced. Note that on very old 32-bit architectures
 *   vmalloc space might be limited and result in vmap calls failing.
 *
 *   Interfaces::
 *      void \*dma_buf_vmap(struct dma_buf \*dmabuf)
 *      void dma_buf_vunmap(struct dma_buf \*dmabuf, void \*vaddr)
 *
 *   The vmap call can fail if there is no vmap support in the exporter, or if
 *   it runs out of vmalloc space. Fallback to kmap should be implemented. Note
 *   that the dma-buf layer keeps a reference count for all vmap access and
 *   calls down into the exporter's vmap function only when no vmapping exists,
 *   and only unmaps it once. Protection against concurrent vmap/vunmap calls is
 *   provided by taking the dma_buf->lock mutex.
 *
 * - For full compatibility on the importer side with existing userspace
 *   interfaces, which might already support mmap'ing buffers. This is needed in
 *   many processing pipelines (e.g. feeding a software rendered image into a
 *   hardware pipeline, thumbnail creation, snapshots, ...). Also, Android's ION
 *   framework already supported this and for DMA buffer file descriptors to
 *   replace ION buffers mmap support was needed.
 *
 *   There is no special interfaces, userspace simply calls mmap on the dma-buf
 *   fd. But like for CPU access there's a need to braket the actual access,
 *   which is handled by the ioctl (DMA_BUF_IOCTL_SYNC). Note that
 *   DMA_BUF_IOCTL_SYNC can fail with -EAGAIN or -EINTR, in which case it must
 *   be restarted.
 *
 *   Some systems might need some sort of cache coherency management e.g. when
 *   CPU and GPU domains are being accessed through dma-buf at the same time.
 *   To circumvent this problem there are begin/end coherency markers, that
 *   forward directly to existing dma-buf device drivers vfunc hooks. Userspace
 *   can make use of those markers through the DMA_BUF_IOCTL_SYNC ioctl. The
 *   sequence would be used like following:
 *
 *     - mmap dma-buf fd
 *     - for each drawing/upload cycle in CPU 1. SYNC_START ioctl, 2. read/write
 *       to mmap area 3. SYNC_END ioctl. This can be repeated as often as you
 *       want (with the new data being consumed by say the GPU or the scanout
 *       device)
 *     - munmap once you don't need the buffer any more
 *
 *    For correctness and optimal performance, it is always required to use
 *    SYNC_START and SYNC_END before and after, respectively, when accessing the
 *    mapped address. Userspace cannot rely on coherent access, even when there
 *    are systems where it just works without calling these ioctls.
 *
 * - And as a CPU fallback in userspace processing pipelines.
 *
 *   Similar to the motivation for kernel cpu access it is again important that
 *   the userspace code of a given importing subsystem can use the same
 *   interfaces with a imported dma-buf buffer object as with a native buffer
 *   object. This is especially important for drm where the userspace part of
 *   contemporary OpenGL, X, and other drivers is huge, and reworking them to
 *   use a different way to mmap a buffer rather invasive.
 *
 *   The assumption in the current dma-buf interfaces is that redirecting the
 *   initial mmap is all that's needed. A survey of some of the existing
 *   subsystems shows that no driver seems to do any nefarious thing like
 *   syncing up with outstanding asynchronous processing on the device or
 *   allocating special resources at fault time. So hopefully this is good
 *   enough, since adding interfaces to intercept pagefaults and allow pte
 *   shootdowns would increase the complexity quite a bit.
 *
 *   Interface::
 *      int dma_buf_mmap(struct dma_buf \*, struct vm_area_struct \*,
 *		       unsigned long);
 *
 *   If the importing subsystem simply provides a special-purpose mmap call to
 *   set up a mapping in userspace, calling do_mmap with dma_buf->file will
 *   equally achieve that for a dma-buf object.
 */

static int __dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
				      enum dma_data_direction direction)
{
	bool write = (direction == DMA_BIDIRECTIONAL ||
		      direction == DMA_TO_DEVICE);
	struct dma_resv *resv = dmabuf->resv;
	long ret;

	/* Wait on any implicit rendering fences */
	ret = dma_resv_wait_timeout_rcu(resv, write, true,
						  MAX_SCHEDULE_TIMEOUT);
	if (ret < 0)
		return ret;

	return 0;
}

/**
 * dma_buf_begin_cpu_access - Must be called before accessing a dma_buf from the
 * cpu in the kernel context. Calls begin_cpu_access to allow exporter-specific
 * preparations. Coherency is only guaranteed in the specified range for the
 * specified access direction.
 * @dmabuf:	[in]	buffer to prepare cpu access for.
 * @direction:	[in]	length of range for cpu access.
 *
 * After the cpu access is complete the caller should call
 * dma_buf_end_cpu_access(). Only when cpu access is braketed by both calls is
 * it guaranteed to be coherent with other DMA access.
 *
 * Can return negative error values, returns 0 on success.
 */
int dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
			     enum dma_data_direction direction)
{
	int ret = 0;

	if (WARN_ON(!dmabuf))
		return -EINVAL;

	if (dmabuf->ops->begin_cpu_access)
		ret = dmabuf->ops->begin_cpu_access(dmabuf, direction);

	/* Ensure that all fences are waited upon - but we first allow
	 * the native handler the chance to do so more efficiently if it
	 * chooses. A double invocation here will be reasonably cheap no-op.
	 */
	if (ret == 0)
		ret = __dma_buf_begin_cpu_access(dmabuf, direction);

	return ret;
}
EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access);

/**
 * dma_buf_end_cpu_access - Must be called after accessing a dma_buf from the
 * cpu in the kernel context. Calls end_cpu_access to allow exporter-specific
 * actions. Coherency is only guaranteed in the specified range for the
 * specified access direction.
 * @dmabuf:	[in]	buffer to complete cpu access for.
 * @direction:	[in]	length of range for cpu access.
 *
 * This terminates CPU access started with dma_buf_begin_cpu_access().
 *
 * Can return negative error values, returns 0 on success.
 */
int dma_buf_end_cpu_access(struct dma_buf *dmabuf,
			   enum dma_data_direction direction)
{
	int ret = 0;

	WARN_ON(!dmabuf);

	if (dmabuf->ops->end_cpu_access)
		ret = dmabuf->ops->end_cpu_access(dmabuf, direction);

	return ret;
}
EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);


/**
 * dma_buf_mmap - Setup up a userspace mmap with the given vma
 * @dmabuf:	[in]	buffer that should back the vma
 * @vma:	[in]	vma for the mmap
 * @pgoff:	[in]	offset in pages where this mmap should start within the
 *			dma-buf buffer.
 *
 * This function adjusts the passed in vma so that it points at the file of the
 * dma_buf operation. It also adjusts the starting pgoff and does bounds
 * checking on the size of the vma. Then it calls the exporters mmap function to
 * set up the mapping.
 *
 * Can return negative error values, returns 0 on success.
 */
int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
		 unsigned long pgoff)
{
	if (WARN_ON(!dmabuf || !vma))
		return -EINVAL;

	/* check if buffer supports mmap */
	if (!dmabuf->ops->mmap)
		return -EINVAL;

	/* check for offset overflow */
	if (pgoff + vma_pages(vma) < pgoff)
		return -EOVERFLOW;

	/* check for overflowing the buffer's size */
	if (pgoff + vma_pages(vma) >
	    dmabuf->size >> PAGE_SHIFT)
		return -EINVAL;

	/* readjust the vma */
	vma_set_file(vma, dmabuf->file);
	vma->vm_pgoff = pgoff;

	return dmabuf->ops->mmap(dmabuf, vma);
}
EXPORT_SYMBOL_GPL(dma_buf_mmap);

/**
 * dma_buf_vmap - Create virtual mapping for the buffer object into kernel
 * address space. Same restrictions as for vmap and friends apply.
 * @dmabuf:	[in]	buffer to vmap
 * @map:	[out]	returns the vmap pointer
 *
 * This call may fail due to lack of virtual mapping address space.
 * These calls are optional in drivers. The intended use for them
 * is for mapping objects linear in kernel space for high use objects.
 * Please attempt to use kmap/kunmap before thinking about these interfaces.
 *
 * Returns 0 on success, or a negative errno code otherwise.
 */
int dma_buf_vmap(struct dma_buf *dmabuf, struct dma_buf_map *map)
{
	struct dma_buf_map ptr;
	int ret = 0;

	dma_buf_map_clear(map);

	if (WARN_ON(!dmabuf))
		return -EINVAL;

	if (!dmabuf->ops->vmap)
		return -EINVAL;

	mutex_lock(&dmabuf->lock);
	if (dmabuf->vmapping_counter) {
		dmabuf->vmapping_counter++;
		BUG_ON(dma_buf_map_is_null(&dmabuf->vmap_ptr));
		*map = dmabuf->vmap_ptr;
		goto out_unlock;
	}

	BUG_ON(dma_buf_map_is_set(&dmabuf->vmap_ptr));

	ret = dmabuf->ops->vmap(dmabuf, &ptr);
	if (WARN_ON_ONCE(ret))
		goto out_unlock;

	dmabuf->vmap_ptr = ptr;
	dmabuf->vmapping_counter = 1;

	*map = dmabuf->vmap_ptr;

out_unlock:
	mutex_unlock(&dmabuf->lock);
	return ret;
}
EXPORT_SYMBOL_GPL(dma_buf_vmap);

/**
 * dma_buf_vunmap - Unmap a vmap obtained by dma_buf_vmap.
 * @dmabuf:	[in]	buffer to vunmap
 * @map:	[in]	vmap pointer to vunmap
 */
void dma_buf_vunmap(struct dma_buf *dmabuf, struct dma_buf_map *map)
{
	if (WARN_ON(!dmabuf))
		return;

	BUG_ON(dma_buf_map_is_null(&dmabuf->vmap_ptr));
	BUG_ON(dmabuf->vmapping_counter == 0);
	BUG_ON(!dma_buf_map_is_equal(&dmabuf->vmap_ptr, map));

	mutex_lock(&dmabuf->lock);
	if (--dmabuf->vmapping_counter == 0) {
		if (dmabuf->ops->vunmap)
			dmabuf->ops->vunmap(dmabuf, map);
		dma_buf_map_clear(&dmabuf->vmap_ptr);
	}
	mutex_unlock(&dmabuf->lock);
}
EXPORT_SYMBOL_GPL(dma_buf_vunmap);

#ifdef CONFIG_DEBUG_FS
static int dma_buf_debug_show(struct seq_file *s, void *unused)
{
	int ret;
	struct dma_buf *buf_obj;
	struct dma_buf_attachment *attach_obj;
	struct dma_resv *robj;
	struct dma_resv_list *fobj;
	struct dma_fence *fence;
	unsigned seq;
	int count = 0, attach_count, shared_count, i;
	size_t size = 0;

	ret = mutex_lock_interruptible(&db_list.lock);

	if (ret)
		return ret;

	seq_puts(s, "\nDma-buf Objects:\n");
	seq_printf(s, "%-8s\t%-8s\t%-8s\t%-8s\texp_name\t%-8s\n",
		   "size", "flags", "mode", "count", "ino");

	list_for_each_entry(buf_obj, &db_list.head, list_node) {

		ret = dma_resv_lock_interruptible(buf_obj->resv, NULL);
		if (ret)
			goto error_unlock;

		seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\t%08lu\t%s\n",
				buf_obj->size,
				buf_obj->file->f_flags, buf_obj->file->f_mode,
				file_count(buf_obj->file),
				buf_obj->exp_name,
				file_inode(buf_obj->file)->i_ino,
				buf_obj->name ?: "");

		robj = buf_obj->resv;
		while (true) {
			seq = read_seqcount_begin(&robj->seq);
			rcu_read_lock();
			fobj = rcu_dereference(robj->fence);
			shared_count = fobj ? fobj->shared_count : 0;
			fence = rcu_dereference(robj->fence_excl);
			if (!read_seqcount_retry(&robj->seq, seq))
				break;
			rcu_read_unlock();
		}

		if (fence)
			seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",
				   fence->ops->get_driver_name(fence),
				   fence->ops->get_timeline_name(fence),
				   dma_fence_is_signaled(fence) ? "" : "un");
		for (i = 0; i < shared_count; i++) {
			fence = rcu_dereference(fobj->shared[i]);
			if (!dma_fence_get_rcu(fence))
				continue;
			seq_printf(s, "\tShared fence: %s %s %ssignalled\n",
				   fence->ops->get_driver_name(fence),
				   fence->ops->get_timeline_name(fence),
				   dma_fence_is_signaled(fence) ? "" : "un");
			dma_fence_put(fence);
		}
		rcu_read_unlock();

		seq_puts(s, "\tAttached Devices:\n");
		attach_count = 0;

		list_for_each_entry(attach_obj, &buf_obj->attachments, node) {
			seq_printf(s, "\t%s\n", dev_name(attach_obj->dev));
			attach_count++;
		}
		dma_resv_unlock(buf_obj->resv);

		seq_printf(s, "Total %d devices attached\n\n",
				attach_count);

		count++;
		size += buf_obj->size;
	}

	seq_printf(s, "\nTotal %d objects, %zu bytes\n", count, size);

	mutex_unlock(&db_list.lock);
	return 0;

error_unlock:
	mutex_unlock(&db_list.lock);
	return ret;
}

DEFINE_SHOW_ATTRIBUTE(dma_buf_debug);

static struct dentry *dma_buf_debugfs_dir;

static int dma_buf_init_debugfs(void)
{
	struct dentry *d;
	int err = 0;

	d = debugfs_create_dir("dma_buf", NULL);
	if (IS_ERR(d))
		return PTR_ERR(d);

	dma_buf_debugfs_dir = d;

	d = debugfs_create_file("bufinfo", S_IRUGO, dma_buf_debugfs_dir,
				NULL, &dma_buf_debug_fops);
	if (IS_ERR(d)) {
		pr_debug("dma_buf: debugfs: failed to create node bufinfo\n");
		debugfs_remove_recursive(dma_buf_debugfs_dir);
		dma_buf_debugfs_dir = NULL;
		err = PTR_ERR(d);
	}

	return err;
}

static void dma_buf_uninit_debugfs(void)
{
	debugfs_remove_recursive(dma_buf_debugfs_dir);
}
#else
static inline int dma_buf_init_debugfs(void)
{
	return 0;
}
static inline void dma_buf_uninit_debugfs(void)
{
}
#endif

static int __init dma_buf_init(void)
{
	dma_buf_mnt = kern_mount(&dma_buf_fs_type);
	if (IS_ERR(dma_buf_mnt))
		return PTR_ERR(dma_buf_mnt);

	mutex_init(&db_list.lock);
	INIT_LIST_HEAD(&db_list.head);
	dma_buf_init_debugfs();
	return 0;
}
subsys_initcall(dma_buf_init);

static void __exit dma_buf_deinit(void)
{
	dma_buf_uninit_debugfs();
	kern_unmount(dma_buf_mnt);
}
__exitcall(dma_buf_deinit);