dax: New fault locking
[sfrench/cifs-2.6.git] / fs / dax.c
1 /*
2  * fs/dax.c - Direct Access filesystem code
3  * Copyright (c) 2013-2014 Intel Corporation
4  * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
5  * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
6  *
7  * This program is free software; you can redistribute it and/or modify it
8  * under the terms and conditions of the GNU General Public License,
9  * version 2, as published by the Free Software Foundation.
10  *
11  * This program is distributed in the hope it will be useful, but WITHOUT
12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
14  * more details.
15  */
16
17 #include <linux/atomic.h>
18 #include <linux/blkdev.h>
19 #include <linux/buffer_head.h>
20 #include <linux/dax.h>
21 #include <linux/fs.h>
22 #include <linux/genhd.h>
23 #include <linux/highmem.h>
24 #include <linux/memcontrol.h>
25 #include <linux/mm.h>
26 #include <linux/mutex.h>
27 #include <linux/pagevec.h>
28 #include <linux/pmem.h>
29 #include <linux/sched.h>
30 #include <linux/uio.h>
31 #include <linux/vmstat.h>
32 #include <linux/pfn_t.h>
33 #include <linux/sizes.h>
34
35 /*
36  * We use lowest available bit in exceptional entry for locking, other two
37  * bits to determine entry type. In total 3 special bits.
38  */
39 #define RADIX_DAX_SHIFT (RADIX_TREE_EXCEPTIONAL_SHIFT + 3)
40 #define RADIX_DAX_PTE (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 1))
41 #define RADIX_DAX_PMD (1 << (RADIX_TREE_EXCEPTIONAL_SHIFT + 2))
42 #define RADIX_DAX_TYPE_MASK (RADIX_DAX_PTE | RADIX_DAX_PMD)
43 #define RADIX_DAX_TYPE(entry) ((unsigned long)entry & RADIX_DAX_TYPE_MASK)
44 #define RADIX_DAX_SECTOR(entry) (((unsigned long)entry >> RADIX_DAX_SHIFT))
45 #define RADIX_DAX_ENTRY(sector, pmd) ((void *)((unsigned long)sector << \
46                 RADIX_DAX_SHIFT | (pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE) | \
47                 RADIX_TREE_EXCEPTIONAL_ENTRY))
48
49 /* We choose 4096 entries - same as per-zone page wait tables */
50 #define DAX_WAIT_TABLE_BITS 12
51 #define DAX_WAIT_TABLE_ENTRIES (1 << DAX_WAIT_TABLE_BITS)
52
53 wait_queue_head_t wait_table[DAX_WAIT_TABLE_ENTRIES];
54
55 static int __init init_dax_wait_table(void)
56 {
57         int i;
58
59         for (i = 0; i < DAX_WAIT_TABLE_ENTRIES; i++)
60                 init_waitqueue_head(wait_table + i);
61         return 0;
62 }
63 fs_initcall(init_dax_wait_table);
64
65 static wait_queue_head_t *dax_entry_waitqueue(struct address_space *mapping,
66                                               pgoff_t index)
67 {
68         unsigned long hash = hash_long((unsigned long)mapping ^ index,
69                                        DAX_WAIT_TABLE_BITS);
70         return wait_table + hash;
71 }
72
73 static long dax_map_atomic(struct block_device *bdev, struct blk_dax_ctl *dax)
74 {
75         struct request_queue *q = bdev->bd_queue;
76         long rc = -EIO;
77
78         dax->addr = (void __pmem *) ERR_PTR(-EIO);
79         if (blk_queue_enter(q, true) != 0)
80                 return rc;
81
82         rc = bdev_direct_access(bdev, dax);
83         if (rc < 0) {
84                 dax->addr = (void __pmem *) ERR_PTR(rc);
85                 blk_queue_exit(q);
86                 return rc;
87         }
88         return rc;
89 }
90
91 static void dax_unmap_atomic(struct block_device *bdev,
92                 const struct blk_dax_ctl *dax)
93 {
94         if (IS_ERR(dax->addr))
95                 return;
96         blk_queue_exit(bdev->bd_queue);
97 }
98
99 struct page *read_dax_sector(struct block_device *bdev, sector_t n)
100 {
101         struct page *page = alloc_pages(GFP_KERNEL, 0);
102         struct blk_dax_ctl dax = {
103                 .size = PAGE_SIZE,
104                 .sector = n & ~((((int) PAGE_SIZE) / 512) - 1),
105         };
106         long rc;
107
108         if (!page)
109                 return ERR_PTR(-ENOMEM);
110
111         rc = dax_map_atomic(bdev, &dax);
112         if (rc < 0)
113                 return ERR_PTR(rc);
114         memcpy_from_pmem(page_address(page), dax.addr, PAGE_SIZE);
115         dax_unmap_atomic(bdev, &dax);
116         return page;
117 }
118
119 static bool buffer_written(struct buffer_head *bh)
120 {
121         return buffer_mapped(bh) && !buffer_unwritten(bh);
122 }
123
124 /*
125  * When ext4 encounters a hole, it returns without modifying the buffer_head
126  * which means that we can't trust b_size.  To cope with this, we set b_state
127  * to 0 before calling get_block and, if any bit is set, we know we can trust
128  * b_size.  Unfortunate, really, since ext4 knows precisely how long a hole is
129  * and would save us time calling get_block repeatedly.
130  */
131 static bool buffer_size_valid(struct buffer_head *bh)
132 {
133         return bh->b_state != 0;
134 }
135
136
137 static sector_t to_sector(const struct buffer_head *bh,
138                 const struct inode *inode)
139 {
140         sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
141
142         return sector;
143 }
144
145 static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
146                       loff_t start, loff_t end, get_block_t get_block,
147                       struct buffer_head *bh)
148 {
149         loff_t pos = start, max = start, bh_max = start;
150         bool hole = false, need_wmb = false;
151         struct block_device *bdev = NULL;
152         int rw = iov_iter_rw(iter), rc;
153         long map_len = 0;
154         struct blk_dax_ctl dax = {
155                 .addr = (void __pmem *) ERR_PTR(-EIO),
156         };
157         unsigned blkbits = inode->i_blkbits;
158         sector_t file_blks = (i_size_read(inode) + (1 << blkbits) - 1)
159                                                                 >> blkbits;
160
161         if (rw == READ)
162                 end = min(end, i_size_read(inode));
163
164         while (pos < end) {
165                 size_t len;
166                 if (pos == max) {
167                         long page = pos >> PAGE_SHIFT;
168                         sector_t block = page << (PAGE_SHIFT - blkbits);
169                         unsigned first = pos - (block << blkbits);
170                         long size;
171
172                         if (pos == bh_max) {
173                                 bh->b_size = PAGE_ALIGN(end - pos);
174                                 bh->b_state = 0;
175                                 rc = get_block(inode, block, bh, rw == WRITE);
176                                 if (rc)
177                                         break;
178                                 if (!buffer_size_valid(bh))
179                                         bh->b_size = 1 << blkbits;
180                                 bh_max = pos - first + bh->b_size;
181                                 bdev = bh->b_bdev;
182                                 /*
183                                  * We allow uninitialized buffers for writes
184                                  * beyond EOF as those cannot race with faults
185                                  */
186                                 WARN_ON_ONCE(
187                                         (buffer_new(bh) && block < file_blks) ||
188                                         (rw == WRITE && buffer_unwritten(bh)));
189                         } else {
190                                 unsigned done = bh->b_size -
191                                                 (bh_max - (pos - first));
192                                 bh->b_blocknr += done >> blkbits;
193                                 bh->b_size -= done;
194                         }
195
196                         hole = rw == READ && !buffer_written(bh);
197                         if (hole) {
198                                 size = bh->b_size - first;
199                         } else {
200                                 dax_unmap_atomic(bdev, &dax);
201                                 dax.sector = to_sector(bh, inode);
202                                 dax.size = bh->b_size;
203                                 map_len = dax_map_atomic(bdev, &dax);
204                                 if (map_len < 0) {
205                                         rc = map_len;
206                                         break;
207                                 }
208                                 dax.addr += first;
209                                 size = map_len - first;
210                         }
211                         max = min(pos + size, end);
212                 }
213
214                 if (iov_iter_rw(iter) == WRITE) {
215                         len = copy_from_iter_pmem(dax.addr, max - pos, iter);
216                         need_wmb = true;
217                 } else if (!hole)
218                         len = copy_to_iter((void __force *) dax.addr, max - pos,
219                                         iter);
220                 else
221                         len = iov_iter_zero(max - pos, iter);
222
223                 if (!len) {
224                         rc = -EFAULT;
225                         break;
226                 }
227
228                 pos += len;
229                 if (!IS_ERR(dax.addr))
230                         dax.addr += len;
231         }
232
233         if (need_wmb)
234                 wmb_pmem();
235         dax_unmap_atomic(bdev, &dax);
236
237         return (pos == start) ? rc : pos - start;
238 }
239
240 /**
241  * dax_do_io - Perform I/O to a DAX file
242  * @iocb: The control block for this I/O
243  * @inode: The file which the I/O is directed at
244  * @iter: The addresses to do I/O from or to
245  * @pos: The file offset where the I/O starts
246  * @get_block: The filesystem method used to translate file offsets to blocks
247  * @end_io: A filesystem callback for I/O completion
248  * @flags: See below
249  *
250  * This function uses the same locking scheme as do_blockdev_direct_IO:
251  * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
252  * caller for writes.  For reads, we take and release the i_mutex ourselves.
253  * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
254  * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
255  * is in progress.
256  */
257 ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
258                   struct iov_iter *iter, loff_t pos, get_block_t get_block,
259                   dio_iodone_t end_io, int flags)
260 {
261         struct buffer_head bh;
262         ssize_t retval = -EINVAL;
263         loff_t end = pos + iov_iter_count(iter);
264
265         memset(&bh, 0, sizeof(bh));
266         bh.b_bdev = inode->i_sb->s_bdev;
267
268         if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
269                 inode_lock(inode);
270
271         /* Protects against truncate */
272         if (!(flags & DIO_SKIP_DIO_COUNT))
273                 inode_dio_begin(inode);
274
275         retval = dax_io(inode, iter, pos, end, get_block, &bh);
276
277         if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
278                 inode_unlock(inode);
279
280         if (end_io) {
281                 int err;
282
283                 err = end_io(iocb, pos, retval, bh.b_private);
284                 if (err)
285                         retval = err;
286         }
287
288         if (!(flags & DIO_SKIP_DIO_COUNT))
289                 inode_dio_end(inode);
290         return retval;
291 }
292 EXPORT_SYMBOL_GPL(dax_do_io);
293
294 /*
295  * DAX radix tree locking
296  */
297 struct exceptional_entry_key {
298         struct address_space *mapping;
299         unsigned long index;
300 };
301
302 struct wait_exceptional_entry_queue {
303         wait_queue_t wait;
304         struct exceptional_entry_key key;
305 };
306
307 static int wake_exceptional_entry_func(wait_queue_t *wait, unsigned int mode,
308                                        int sync, void *keyp)
309 {
310         struct exceptional_entry_key *key = keyp;
311         struct wait_exceptional_entry_queue *ewait =
312                 container_of(wait, struct wait_exceptional_entry_queue, wait);
313
314         if (key->mapping != ewait->key.mapping ||
315             key->index != ewait->key.index)
316                 return 0;
317         return autoremove_wake_function(wait, mode, sync, NULL);
318 }
319
320 /*
321  * Check whether the given slot is locked. The function must be called with
322  * mapping->tree_lock held
323  */
324 static inline int slot_locked(struct address_space *mapping, void **slot)
325 {
326         unsigned long entry = (unsigned long)
327                 radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
328         return entry & RADIX_DAX_ENTRY_LOCK;
329 }
330
331 /*
332  * Mark the given slot is locked. The function must be called with
333  * mapping->tree_lock held
334  */
335 static inline void *lock_slot(struct address_space *mapping, void **slot)
336 {
337         unsigned long entry = (unsigned long)
338                 radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
339
340         entry |= RADIX_DAX_ENTRY_LOCK;
341         radix_tree_replace_slot(slot, (void *)entry);
342         return (void *)entry;
343 }
344
345 /*
346  * Mark the given slot is unlocked. The function must be called with
347  * mapping->tree_lock held
348  */
349 static inline void *unlock_slot(struct address_space *mapping, void **slot)
350 {
351         unsigned long entry = (unsigned long)
352                 radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
353
354         entry &= ~(unsigned long)RADIX_DAX_ENTRY_LOCK;
355         radix_tree_replace_slot(slot, (void *)entry);
356         return (void *)entry;
357 }
358
359 /*
360  * Lookup entry in radix tree, wait for it to become unlocked if it is
361  * exceptional entry and return it. The caller must call
362  * put_unlocked_mapping_entry() when he decided not to lock the entry or
363  * put_locked_mapping_entry() when he locked the entry and now wants to
364  * unlock it.
365  *
366  * The function must be called with mapping->tree_lock held.
367  */
368 static void *get_unlocked_mapping_entry(struct address_space *mapping,
369                                         pgoff_t index, void ***slotp)
370 {
371         void *ret, **slot;
372         struct wait_exceptional_entry_queue ewait;
373         wait_queue_head_t *wq = dax_entry_waitqueue(mapping, index);
374
375         init_wait(&ewait.wait);
376         ewait.wait.func = wake_exceptional_entry_func;
377         ewait.key.mapping = mapping;
378         ewait.key.index = index;
379
380         for (;;) {
381                 ret = __radix_tree_lookup(&mapping->page_tree, index, NULL,
382                                           &slot);
383                 if (!ret || !radix_tree_exceptional_entry(ret) ||
384                     !slot_locked(mapping, slot)) {
385                         if (slotp)
386                                 *slotp = slot;
387                         return ret;
388                 }
389                 prepare_to_wait_exclusive(wq, &ewait.wait,
390                                           TASK_UNINTERRUPTIBLE);
391                 spin_unlock_irq(&mapping->tree_lock);
392                 schedule();
393                 finish_wait(wq, &ewait.wait);
394                 spin_lock_irq(&mapping->tree_lock);
395         }
396 }
397
398 /*
399  * Find radix tree entry at given index. If it points to a page, return with
400  * the page locked. If it points to the exceptional entry, return with the
401  * radix tree entry locked. If the radix tree doesn't contain given index,
402  * create empty exceptional entry for the index and return with it locked.
403  *
404  * Note: Unlike filemap_fault() we don't honor FAULT_FLAG_RETRY flags. For
405  * persistent memory the benefit is doubtful. We can add that later if we can
406  * show it helps.
407  */
408 static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index)
409 {
410         void *ret, **slot;
411
412 restart:
413         spin_lock_irq(&mapping->tree_lock);
414         ret = get_unlocked_mapping_entry(mapping, index, &slot);
415         /* No entry for given index? Make sure radix tree is big enough. */
416         if (!ret) {
417                 int err;
418
419                 spin_unlock_irq(&mapping->tree_lock);
420                 err = radix_tree_preload(
421                                 mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM);
422                 if (err)
423                         return ERR_PTR(err);
424                 ret = (void *)(RADIX_TREE_EXCEPTIONAL_ENTRY |
425                                RADIX_DAX_ENTRY_LOCK);
426                 spin_lock_irq(&mapping->tree_lock);
427                 err = radix_tree_insert(&mapping->page_tree, index, ret);
428                 radix_tree_preload_end();
429                 if (err) {
430                         spin_unlock_irq(&mapping->tree_lock);
431                         /* Someone already created the entry? */
432                         if (err == -EEXIST)
433                                 goto restart;
434                         return ERR_PTR(err);
435                 }
436                 /* Good, we have inserted empty locked entry into the tree. */
437                 mapping->nrexceptional++;
438                 spin_unlock_irq(&mapping->tree_lock);
439                 return ret;
440         }
441         /* Normal page in radix tree? */
442         if (!radix_tree_exceptional_entry(ret)) {
443                 struct page *page = ret;
444
445                 get_page(page);
446                 spin_unlock_irq(&mapping->tree_lock);
447                 lock_page(page);
448                 /* Page got truncated? Retry... */
449                 if (unlikely(page->mapping != mapping)) {
450                         unlock_page(page);
451                         put_page(page);
452                         goto restart;
453                 }
454                 return page;
455         }
456         ret = lock_slot(mapping, slot);
457         spin_unlock_irq(&mapping->tree_lock);
458         return ret;
459 }
460
461 void dax_wake_mapping_entry_waiter(struct address_space *mapping,
462                                    pgoff_t index, bool wake_all)
463 {
464         wait_queue_head_t *wq = dax_entry_waitqueue(mapping, index);
465
466         /*
467          * Checking for locked entry and prepare_to_wait_exclusive() happens
468          * under mapping->tree_lock, ditto for entry handling in our callers.
469          * So at this point all tasks that could have seen our entry locked
470          * must be in the waitqueue and the following check will see them.
471          */
472         if (waitqueue_active(wq)) {
473                 struct exceptional_entry_key key;
474
475                 key.mapping = mapping;
476                 key.index = index;
477                 __wake_up(wq, TASK_NORMAL, wake_all ? 0 : 1, &key);
478         }
479 }
480
481 static void unlock_mapping_entry(struct address_space *mapping, pgoff_t index)
482 {
483         void *ret, **slot;
484
485         spin_lock_irq(&mapping->tree_lock);
486         ret = __radix_tree_lookup(&mapping->page_tree, index, NULL, &slot);
487         if (WARN_ON_ONCE(!ret || !radix_tree_exceptional_entry(ret) ||
488                          !slot_locked(mapping, slot))) {
489                 spin_unlock_irq(&mapping->tree_lock);
490                 return;
491         }
492         unlock_slot(mapping, slot);
493         spin_unlock_irq(&mapping->tree_lock);
494         dax_wake_mapping_entry_waiter(mapping, index, false);
495 }
496
497 static void put_locked_mapping_entry(struct address_space *mapping,
498                                      pgoff_t index, void *entry)
499 {
500         if (!radix_tree_exceptional_entry(entry)) {
501                 unlock_page(entry);
502                 put_page(entry);
503         } else {
504                 unlock_mapping_entry(mapping, index);
505         }
506 }
507
508 /*
509  * Called when we are done with radix tree entry we looked up via
510  * get_unlocked_mapping_entry() and which we didn't lock in the end.
511  */
512 static void put_unlocked_mapping_entry(struct address_space *mapping,
513                                        pgoff_t index, void *entry)
514 {
515         if (!radix_tree_exceptional_entry(entry))
516                 return;
517
518         /* We have to wake up next waiter for the radix tree entry lock */
519         dax_wake_mapping_entry_waiter(mapping, index, false);
520 }
521
522 /*
523  * Delete exceptional DAX entry at @index from @mapping. Wait for radix tree
524  * entry to get unlocked before deleting it.
525  */
526 int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
527 {
528         void *entry;
529
530         spin_lock_irq(&mapping->tree_lock);
531         entry = get_unlocked_mapping_entry(mapping, index, NULL);
532         /*
533          * This gets called from truncate / punch_hole path. As such, the caller
534          * must hold locks protecting against concurrent modifications of the
535          * radix tree (usually fs-private i_mmap_sem for writing). Since the
536          * caller has seen exceptional entry for this index, we better find it
537          * at that index as well...
538          */
539         if (WARN_ON_ONCE(!entry || !radix_tree_exceptional_entry(entry))) {
540                 spin_unlock_irq(&mapping->tree_lock);
541                 return 0;
542         }
543         radix_tree_delete(&mapping->page_tree, index);
544         mapping->nrexceptional--;
545         spin_unlock_irq(&mapping->tree_lock);
546         dax_wake_mapping_entry_waiter(mapping, index, true);
547
548         return 1;
549 }
550
551 /*
552  * The user has performed a load from a hole in the file.  Allocating
553  * a new page in the file would cause excessive storage usage for
554  * workloads with sparse files.  We allocate a page cache page instead.
555  * We'll kick it out of the page cache if it's ever written to,
556  * otherwise it will simply fall out of the page cache under memory
557  * pressure without ever having been dirtied.
558  */
559 static int dax_load_hole(struct address_space *mapping, void *entry,
560                          struct vm_fault *vmf)
561 {
562         struct page *page;
563
564         /* Hole page already exists? Return it...  */
565         if (!radix_tree_exceptional_entry(entry)) {
566                 vmf->page = entry;
567                 return VM_FAULT_LOCKED;
568         }
569
570         /* This will replace locked radix tree entry with a hole page */
571         page = find_or_create_page(mapping, vmf->pgoff,
572                                    vmf->gfp_mask | __GFP_ZERO);
573         if (!page) {
574                 put_locked_mapping_entry(mapping, vmf->pgoff, entry);
575                 return VM_FAULT_OOM;
576         }
577         vmf->page = page;
578         return VM_FAULT_LOCKED;
579 }
580
581 static int copy_user_bh(struct page *to, struct inode *inode,
582                 struct buffer_head *bh, unsigned long vaddr)
583 {
584         struct blk_dax_ctl dax = {
585                 .sector = to_sector(bh, inode),
586                 .size = bh->b_size,
587         };
588         struct block_device *bdev = bh->b_bdev;
589         void *vto;
590
591         if (dax_map_atomic(bdev, &dax) < 0)
592                 return PTR_ERR(dax.addr);
593         vto = kmap_atomic(to);
594         copy_user_page(vto, (void __force *)dax.addr, vaddr, to);
595         kunmap_atomic(vto);
596         dax_unmap_atomic(bdev, &dax);
597         return 0;
598 }
599
600 #define DAX_PMD_INDEX(page_index) (page_index & (PMD_MASK >> PAGE_SHIFT))
601
602 static void *dax_insert_mapping_entry(struct address_space *mapping,
603                                       struct vm_fault *vmf,
604                                       void *entry, sector_t sector)
605 {
606         struct radix_tree_root *page_tree = &mapping->page_tree;
607         int error = 0;
608         bool hole_fill = false;
609         void *new_entry;
610         pgoff_t index = vmf->pgoff;
611
612         if (vmf->flags & FAULT_FLAG_WRITE)
613                 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
614
615         /* Replacing hole page with block mapping? */
616         if (!radix_tree_exceptional_entry(entry)) {
617                 hole_fill = true;
618                 /*
619                  * Unmap the page now before we remove it from page cache below.
620                  * The page is locked so it cannot be faulted in again.
621                  */
622                 unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
623                                     PAGE_SIZE, 0);
624                 error = radix_tree_preload(vmf->gfp_mask & ~__GFP_HIGHMEM);
625                 if (error)
626                         return ERR_PTR(error);
627         }
628
629         spin_lock_irq(&mapping->tree_lock);
630         new_entry = (void *)((unsigned long)RADIX_DAX_ENTRY(sector, false) |
631                        RADIX_DAX_ENTRY_LOCK);
632         if (hole_fill) {
633                 __delete_from_page_cache(entry, NULL);
634                 /* Drop pagecache reference */
635                 put_page(entry);
636                 error = radix_tree_insert(page_tree, index, new_entry);
637                 if (error) {
638                         new_entry = ERR_PTR(error);
639                         goto unlock;
640                 }
641                 mapping->nrexceptional++;
642         } else {
643                 void **slot;
644                 void *ret;
645
646                 ret = __radix_tree_lookup(page_tree, index, NULL, &slot);
647                 WARN_ON_ONCE(ret != entry);
648                 radix_tree_replace_slot(slot, new_entry);
649         }
650         if (vmf->flags & FAULT_FLAG_WRITE)
651                 radix_tree_tag_set(page_tree, index, PAGECACHE_TAG_DIRTY);
652  unlock:
653         spin_unlock_irq(&mapping->tree_lock);
654         if (hole_fill) {
655                 radix_tree_preload_end();
656                 /*
657                  * We don't need hole page anymore, it has been replaced with
658                  * locked radix tree entry now.
659                  */
660                 if (mapping->a_ops->freepage)
661                         mapping->a_ops->freepage(entry);
662                 unlock_page(entry);
663                 put_page(entry);
664         }
665         return new_entry;
666 }
667
668 static int dax_writeback_one(struct block_device *bdev,
669                 struct address_space *mapping, pgoff_t index, void *entry)
670 {
671         struct radix_tree_root *page_tree = &mapping->page_tree;
672         int type = RADIX_DAX_TYPE(entry);
673         struct radix_tree_node *node;
674         struct blk_dax_ctl dax;
675         void **slot;
676         int ret = 0;
677
678         spin_lock_irq(&mapping->tree_lock);
679         /*
680          * Regular page slots are stabilized by the page lock even
681          * without the tree itself locked.  These unlocked entries
682          * need verification under the tree lock.
683          */
684         if (!__radix_tree_lookup(page_tree, index, &node, &slot))
685                 goto unlock;
686         if (*slot != entry)
687                 goto unlock;
688
689         /* another fsync thread may have already written back this entry */
690         if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
691                 goto unlock;
692
693         if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD)) {
694                 ret = -EIO;
695                 goto unlock;
696         }
697
698         dax.sector = RADIX_DAX_SECTOR(entry);
699         dax.size = (type == RADIX_DAX_PMD ? PMD_SIZE : PAGE_SIZE);
700         spin_unlock_irq(&mapping->tree_lock);
701
702         /*
703          * We cannot hold tree_lock while calling dax_map_atomic() because it
704          * eventually calls cond_resched().
705          */
706         ret = dax_map_atomic(bdev, &dax);
707         if (ret < 0)
708                 return ret;
709
710         if (WARN_ON_ONCE(ret < dax.size)) {
711                 ret = -EIO;
712                 goto unmap;
713         }
714
715         wb_cache_pmem(dax.addr, dax.size);
716
717         spin_lock_irq(&mapping->tree_lock);
718         radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
719         spin_unlock_irq(&mapping->tree_lock);
720  unmap:
721         dax_unmap_atomic(bdev, &dax);
722         return ret;
723
724  unlock:
725         spin_unlock_irq(&mapping->tree_lock);
726         return ret;
727 }
728
729 /*
730  * Flush the mapping to the persistent domain within the byte range of [start,
731  * end]. This is required by data integrity operations to ensure file data is
732  * on persistent storage prior to completion of the operation.
733  */
734 int dax_writeback_mapping_range(struct address_space *mapping,
735                 struct block_device *bdev, struct writeback_control *wbc)
736 {
737         struct inode *inode = mapping->host;
738         pgoff_t start_index, end_index, pmd_index;
739         pgoff_t indices[PAGEVEC_SIZE];
740         struct pagevec pvec;
741         bool done = false;
742         int i, ret = 0;
743         void *entry;
744
745         if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
746                 return -EIO;
747
748         if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL)
749                 return 0;
750
751         start_index = wbc->range_start >> PAGE_SHIFT;
752         end_index = wbc->range_end >> PAGE_SHIFT;
753         pmd_index = DAX_PMD_INDEX(start_index);
754
755         rcu_read_lock();
756         entry = radix_tree_lookup(&mapping->page_tree, pmd_index);
757         rcu_read_unlock();
758
759         /* see if the start of our range is covered by a PMD entry */
760         if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
761                 start_index = pmd_index;
762
763         tag_pages_for_writeback(mapping, start_index, end_index);
764
765         pagevec_init(&pvec, 0);
766         while (!done) {
767                 pvec.nr = find_get_entries_tag(mapping, start_index,
768                                 PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
769                                 pvec.pages, indices);
770
771                 if (pvec.nr == 0)
772                         break;
773
774                 for (i = 0; i < pvec.nr; i++) {
775                         if (indices[i] > end_index) {
776                                 done = true;
777                                 break;
778                         }
779
780                         ret = dax_writeback_one(bdev, mapping, indices[i],
781                                         pvec.pages[i]);
782                         if (ret < 0)
783                                 return ret;
784                 }
785         }
786         wmb_pmem();
787         return 0;
788 }
789 EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
790
791 static int dax_insert_mapping(struct address_space *mapping,
792                         struct buffer_head *bh, void **entryp,
793                         struct vm_area_struct *vma, struct vm_fault *vmf)
794 {
795         unsigned long vaddr = (unsigned long)vmf->virtual_address;
796         struct block_device *bdev = bh->b_bdev;
797         struct blk_dax_ctl dax = {
798                 .sector = to_sector(bh, mapping->host),
799                 .size = bh->b_size,
800         };
801         int error;
802         void *ret;
803         void *entry = *entryp;
804
805         i_mmap_lock_read(mapping);
806
807         if (dax_map_atomic(bdev, &dax) < 0) {
808                 error = PTR_ERR(dax.addr);
809                 goto out;
810         }
811         dax_unmap_atomic(bdev, &dax);
812
813         ret = dax_insert_mapping_entry(mapping, vmf, entry, dax.sector);
814         if (IS_ERR(ret)) {
815                 error = PTR_ERR(ret);
816                 goto out;
817         }
818         *entryp = ret;
819
820         error = vm_insert_mixed(vma, vaddr, dax.pfn);
821  out:
822         i_mmap_unlock_read(mapping);
823         return error;
824 }
825
826 /**
827  * __dax_fault - handle a page fault on a DAX file
828  * @vma: The virtual memory area where the fault occurred
829  * @vmf: The description of the fault
830  * @get_block: The filesystem method used to translate file offsets to blocks
831  *
832  * When a page fault occurs, filesystems may call this helper in their
833  * fault handler for DAX files. __dax_fault() assumes the caller has done all
834  * the necessary locking for the page fault to proceed successfully.
835  */
836 int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
837                         get_block_t get_block)
838 {
839         struct file *file = vma->vm_file;
840         struct address_space *mapping = file->f_mapping;
841         struct inode *inode = mapping->host;
842         void *entry;
843         struct buffer_head bh;
844         unsigned long vaddr = (unsigned long)vmf->virtual_address;
845         unsigned blkbits = inode->i_blkbits;
846         sector_t block;
847         pgoff_t size;
848         int error;
849         int major = 0;
850
851         /*
852          * Check whether offset isn't beyond end of file now. Caller is supposed
853          * to hold locks serializing us with truncate / punch hole so this is
854          * a reliable test.
855          */
856         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
857         if (vmf->pgoff >= size)
858                 return VM_FAULT_SIGBUS;
859
860         memset(&bh, 0, sizeof(bh));
861         block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
862         bh.b_bdev = inode->i_sb->s_bdev;
863         bh.b_size = PAGE_SIZE;
864
865         entry = grab_mapping_entry(mapping, vmf->pgoff);
866         if (IS_ERR(entry)) {
867                 error = PTR_ERR(entry);
868                 goto out;
869         }
870
871         error = get_block(inode, block, &bh, 0);
872         if (!error && (bh.b_size < PAGE_SIZE))
873                 error = -EIO;           /* fs corruption? */
874         if (error)
875                 goto unlock_entry;
876
877         if (vmf->cow_page) {
878                 struct page *new_page = vmf->cow_page;
879                 if (buffer_written(&bh))
880                         error = copy_user_bh(new_page, inode, &bh, vaddr);
881                 else
882                         clear_user_highpage(new_page, vaddr);
883                 if (error)
884                         goto unlock_entry;
885                 if (!radix_tree_exceptional_entry(entry)) {
886                         vmf->page = entry;
887                 } else {
888                         unlock_mapping_entry(mapping, vmf->pgoff);
889                         i_mmap_lock_read(mapping);
890                         vmf->page = NULL;
891                 }
892                 return VM_FAULT_LOCKED;
893         }
894
895         if (!buffer_mapped(&bh)) {
896                 if (vmf->flags & FAULT_FLAG_WRITE) {
897                         error = get_block(inode, block, &bh, 1);
898                         count_vm_event(PGMAJFAULT);
899                         mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
900                         major = VM_FAULT_MAJOR;
901                         if (!error && (bh.b_size < PAGE_SIZE))
902                                 error = -EIO;
903                         if (error)
904                                 goto unlock_entry;
905                 } else {
906                         return dax_load_hole(mapping, entry, vmf);
907                 }
908         }
909
910         /* Filesystem should not return unwritten buffers to us! */
911         WARN_ON_ONCE(buffer_unwritten(&bh) || buffer_new(&bh));
912         error = dax_insert_mapping(mapping, &bh, &entry, vma, vmf);
913  unlock_entry:
914         put_locked_mapping_entry(mapping, vmf->pgoff, entry);
915  out:
916         if (error == -ENOMEM)
917                 return VM_FAULT_OOM | major;
918         /* -EBUSY is fine, somebody else faulted on the same PTE */
919         if ((error < 0) && (error != -EBUSY))
920                 return VM_FAULT_SIGBUS | major;
921         return VM_FAULT_NOPAGE | major;
922 }
923 EXPORT_SYMBOL(__dax_fault);
924
925 /**
926  * dax_fault - handle a page fault on a DAX file
927  * @vma: The virtual memory area where the fault occurred
928  * @vmf: The description of the fault
929  * @get_block: The filesystem method used to translate file offsets to blocks
930  *
931  * When a page fault occurs, filesystems may call this helper in their
932  * fault handler for DAX files.
933  */
934 int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
935               get_block_t get_block)
936 {
937         int result;
938         struct super_block *sb = file_inode(vma->vm_file)->i_sb;
939
940         if (vmf->flags & FAULT_FLAG_WRITE) {
941                 sb_start_pagefault(sb);
942                 file_update_time(vma->vm_file);
943         }
944         result = __dax_fault(vma, vmf, get_block);
945         if (vmf->flags & FAULT_FLAG_WRITE)
946                 sb_end_pagefault(sb);
947
948         return result;
949 }
950 EXPORT_SYMBOL_GPL(dax_fault);
951
952 #if defined(CONFIG_TRANSPARENT_HUGEPAGE)
953 /*
954  * The 'colour' (ie low bits) within a PMD of a page offset.  This comes up
955  * more often than one might expect in the below function.
956  */
957 #define PG_PMD_COLOUR   ((PMD_SIZE >> PAGE_SHIFT) - 1)
958
959 static void __dax_dbg(struct buffer_head *bh, unsigned long address,
960                 const char *reason, const char *fn)
961 {
962         if (bh) {
963                 char bname[BDEVNAME_SIZE];
964                 bdevname(bh->b_bdev, bname);
965                 pr_debug("%s: %s addr: %lx dev %s state %lx start %lld "
966                         "length %zd fallback: %s\n", fn, current->comm,
967                         address, bname, bh->b_state, (u64)bh->b_blocknr,
968                         bh->b_size, reason);
969         } else {
970                 pr_debug("%s: %s addr: %lx fallback: %s\n", fn,
971                         current->comm, address, reason);
972         }
973 }
974
975 #define dax_pmd_dbg(bh, address, reason)        __dax_dbg(bh, address, reason, "dax_pmd")
976
977 int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
978                 pmd_t *pmd, unsigned int flags, get_block_t get_block)
979 {
980         struct file *file = vma->vm_file;
981         struct address_space *mapping = file->f_mapping;
982         struct inode *inode = mapping->host;
983         struct buffer_head bh;
984         unsigned blkbits = inode->i_blkbits;
985         unsigned long pmd_addr = address & PMD_MASK;
986         bool write = flags & FAULT_FLAG_WRITE;
987         struct block_device *bdev;
988         pgoff_t size, pgoff;
989         sector_t block;
990         int result = 0;
991         bool alloc = false;
992
993         /* dax pmd mappings require pfn_t_devmap() */
994         if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
995                 return VM_FAULT_FALLBACK;
996
997         /* Fall back to PTEs if we're going to COW */
998         if (write && !(vma->vm_flags & VM_SHARED)) {
999                 split_huge_pmd(vma, pmd, address);
1000                 dax_pmd_dbg(NULL, address, "cow write");
1001                 return VM_FAULT_FALLBACK;
1002         }
1003         /* If the PMD would extend outside the VMA */
1004         if (pmd_addr < vma->vm_start) {
1005                 dax_pmd_dbg(NULL, address, "vma start unaligned");
1006                 return VM_FAULT_FALLBACK;
1007         }
1008         if ((pmd_addr + PMD_SIZE) > vma->vm_end) {
1009                 dax_pmd_dbg(NULL, address, "vma end unaligned");
1010                 return VM_FAULT_FALLBACK;
1011         }
1012
1013         pgoff = linear_page_index(vma, pmd_addr);
1014         size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
1015         if (pgoff >= size)
1016                 return VM_FAULT_SIGBUS;
1017         /* If the PMD would cover blocks out of the file */
1018         if ((pgoff | PG_PMD_COLOUR) >= size) {
1019                 dax_pmd_dbg(NULL, address,
1020                                 "offset + huge page size > file size");
1021                 return VM_FAULT_FALLBACK;
1022         }
1023
1024         memset(&bh, 0, sizeof(bh));
1025         bh.b_bdev = inode->i_sb->s_bdev;
1026         block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
1027
1028         bh.b_size = PMD_SIZE;
1029
1030         if (get_block(inode, block, &bh, 0) != 0)
1031                 return VM_FAULT_SIGBUS;
1032
1033         if (!buffer_mapped(&bh) && write) {
1034                 if (get_block(inode, block, &bh, 1) != 0)
1035                         return VM_FAULT_SIGBUS;
1036                 alloc = true;
1037                 WARN_ON_ONCE(buffer_unwritten(&bh) || buffer_new(&bh));
1038         }
1039
1040         bdev = bh.b_bdev;
1041
1042         /*
1043          * If the filesystem isn't willing to tell us the length of a hole,
1044          * just fall back to PTEs.  Calling get_block 512 times in a loop
1045          * would be silly.
1046          */
1047         if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE) {
1048                 dax_pmd_dbg(&bh, address, "allocated block too small");
1049                 return VM_FAULT_FALLBACK;
1050         }
1051
1052         /*
1053          * If we allocated new storage, make sure no process has any
1054          * zero pages covering this hole
1055          */
1056         if (alloc) {
1057                 loff_t lstart = pgoff << PAGE_SHIFT;
1058                 loff_t lend = lstart + PMD_SIZE - 1; /* inclusive */
1059
1060                 truncate_pagecache_range(inode, lstart, lend);
1061         }
1062
1063         i_mmap_lock_read(mapping);
1064
1065         if (!write && !buffer_mapped(&bh)) {
1066                 spinlock_t *ptl;
1067                 pmd_t entry;
1068                 struct page *zero_page = get_huge_zero_page();
1069
1070                 if (unlikely(!zero_page)) {
1071                         dax_pmd_dbg(&bh, address, "no zero page");
1072                         goto fallback;
1073                 }
1074
1075                 ptl = pmd_lock(vma->vm_mm, pmd);
1076                 if (!pmd_none(*pmd)) {
1077                         spin_unlock(ptl);
1078                         dax_pmd_dbg(&bh, address, "pmd already present");
1079                         goto fallback;
1080                 }
1081
1082                 dev_dbg(part_to_dev(bdev->bd_part),
1083                                 "%s: %s addr: %lx pfn: <zero> sect: %llx\n",
1084                                 __func__, current->comm, address,
1085                                 (unsigned long long) to_sector(&bh, inode));
1086
1087                 entry = mk_pmd(zero_page, vma->vm_page_prot);
1088                 entry = pmd_mkhuge(entry);
1089                 set_pmd_at(vma->vm_mm, pmd_addr, pmd, entry);
1090                 result = VM_FAULT_NOPAGE;
1091                 spin_unlock(ptl);
1092         } else {
1093                 struct blk_dax_ctl dax = {
1094                         .sector = to_sector(&bh, inode),
1095                         .size = PMD_SIZE,
1096                 };
1097                 long length = dax_map_atomic(bdev, &dax);
1098
1099                 if (length < 0) {
1100                         dax_pmd_dbg(&bh, address, "dax-error fallback");
1101                         goto fallback;
1102                 }
1103                 if (length < PMD_SIZE) {
1104                         dax_pmd_dbg(&bh, address, "dax-length too small");
1105                         dax_unmap_atomic(bdev, &dax);
1106                         goto fallback;
1107                 }
1108                 if (pfn_t_to_pfn(dax.pfn) & PG_PMD_COLOUR) {
1109                         dax_pmd_dbg(&bh, address, "pfn unaligned");
1110                         dax_unmap_atomic(bdev, &dax);
1111                         goto fallback;
1112                 }
1113
1114                 if (!pfn_t_devmap(dax.pfn)) {
1115                         dax_unmap_atomic(bdev, &dax);
1116                         dax_pmd_dbg(&bh, address, "pfn not in memmap");
1117                         goto fallback;
1118                 }
1119                 dax_unmap_atomic(bdev, &dax);
1120
1121                 /*
1122                  * For PTE faults we insert a radix tree entry for reads, and
1123                  * leave it clean.  Then on the first write we dirty the radix
1124                  * tree entry via the dax_pfn_mkwrite() path.  This sequence
1125                  * allows the dax_pfn_mkwrite() call to be simpler and avoid a
1126                  * call into get_block() to translate the pgoff to a sector in
1127                  * order to be able to create a new radix tree entry.
1128                  *
1129                  * The PMD path doesn't have an equivalent to
1130                  * dax_pfn_mkwrite(), though, so for a read followed by a
1131                  * write we traverse all the way through __dax_pmd_fault()
1132                  * twice.  This means we can just skip inserting a radix tree
1133                  * entry completely on the initial read and just wait until
1134                  * the write to insert a dirty entry.
1135                  */
1136                 if (write) {
1137                         /*
1138                          * We should insert radix-tree entry and dirty it here.
1139                          * For now this is broken...
1140                          */
1141                 }
1142
1143                 dev_dbg(part_to_dev(bdev->bd_part),
1144                                 "%s: %s addr: %lx pfn: %lx sect: %llx\n",
1145                                 __func__, current->comm, address,
1146                                 pfn_t_to_pfn(dax.pfn),
1147                                 (unsigned long long) dax.sector);
1148                 result |= vmf_insert_pfn_pmd(vma, address, pmd,
1149                                 dax.pfn, write);
1150         }
1151
1152  out:
1153         i_mmap_unlock_read(mapping);
1154
1155         return result;
1156
1157  fallback:
1158         count_vm_event(THP_FAULT_FALLBACK);
1159         result = VM_FAULT_FALLBACK;
1160         goto out;
1161 }
1162 EXPORT_SYMBOL_GPL(__dax_pmd_fault);
1163
1164 /**
1165  * dax_pmd_fault - handle a PMD fault on a DAX file
1166  * @vma: The virtual memory area where the fault occurred
1167  * @vmf: The description of the fault
1168  * @get_block: The filesystem method used to translate file offsets to blocks
1169  *
1170  * When a page fault occurs, filesystems may call this helper in their
1171  * pmd_fault handler for DAX files.
1172  */
1173 int dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
1174                         pmd_t *pmd, unsigned int flags, get_block_t get_block)
1175 {
1176         int result;
1177         struct super_block *sb = file_inode(vma->vm_file)->i_sb;
1178
1179         if (flags & FAULT_FLAG_WRITE) {
1180                 sb_start_pagefault(sb);
1181                 file_update_time(vma->vm_file);
1182         }
1183         result = __dax_pmd_fault(vma, address, pmd, flags, get_block);
1184         if (flags & FAULT_FLAG_WRITE)
1185                 sb_end_pagefault(sb);
1186
1187         return result;
1188 }
1189 EXPORT_SYMBOL_GPL(dax_pmd_fault);
1190 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
1191
1192 /**
1193  * dax_pfn_mkwrite - handle first write to DAX page
1194  * @vma: The virtual memory area where the fault occurred
1195  * @vmf: The description of the fault
1196  */
1197 int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
1198 {
1199         struct file *file = vma->vm_file;
1200         struct address_space *mapping = file->f_mapping;
1201         void *entry;
1202         pgoff_t index = vmf->pgoff;
1203
1204         spin_lock_irq(&mapping->tree_lock);
1205         entry = get_unlocked_mapping_entry(mapping, index, NULL);
1206         if (!entry || !radix_tree_exceptional_entry(entry))
1207                 goto out;
1208         radix_tree_tag_set(&mapping->page_tree, index, PAGECACHE_TAG_DIRTY);
1209         put_unlocked_mapping_entry(mapping, index, entry);
1210 out:
1211         spin_unlock_irq(&mapping->tree_lock);
1212         return VM_FAULT_NOPAGE;
1213 }
1214 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
1215
1216 static bool dax_range_is_aligned(struct block_device *bdev,
1217                                  unsigned int offset, unsigned int length)
1218 {
1219         unsigned short sector_size = bdev_logical_block_size(bdev);
1220
1221         if (!IS_ALIGNED(offset, sector_size))
1222                 return false;
1223         if (!IS_ALIGNED(length, sector_size))
1224                 return false;
1225
1226         return true;
1227 }
1228
1229 int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
1230                 unsigned int offset, unsigned int length)
1231 {
1232         struct blk_dax_ctl dax = {
1233                 .sector         = sector,
1234                 .size           = PAGE_SIZE,
1235         };
1236
1237         if (dax_range_is_aligned(bdev, offset, length)) {
1238                 sector_t start_sector = dax.sector + (offset >> 9);
1239
1240                 return blkdev_issue_zeroout(bdev, start_sector,
1241                                 length >> 9, GFP_NOFS, true);
1242         } else {
1243                 if (dax_map_atomic(bdev, &dax) < 0)
1244                         return PTR_ERR(dax.addr);
1245                 clear_pmem(dax.addr + offset, length);
1246                 wmb_pmem();
1247                 dax_unmap_atomic(bdev, &dax);
1248         }
1249         return 0;
1250 }
1251 EXPORT_SYMBOL_GPL(__dax_zero_page_range);
1252
1253 /**
1254  * dax_zero_page_range - zero a range within a page of a DAX file
1255  * @inode: The file being truncated
1256  * @from: The file offset that is being truncated to
1257  * @length: The number of bytes to zero
1258  * @get_block: The filesystem method used to translate file offsets to blocks
1259  *
1260  * This function can be called by a filesystem when it is zeroing part of a
1261  * page in a DAX file.  This is intended for hole-punch operations.  If
1262  * you are truncating a file, the helper function dax_truncate_page() may be
1263  * more convenient.
1264  */
1265 int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
1266                                                         get_block_t get_block)
1267 {
1268         struct buffer_head bh;
1269         pgoff_t index = from >> PAGE_SHIFT;
1270         unsigned offset = from & (PAGE_SIZE-1);
1271         int err;
1272
1273         /* Block boundary? Nothing to do */
1274         if (!length)
1275                 return 0;
1276         BUG_ON((offset + length) > PAGE_SIZE);
1277
1278         memset(&bh, 0, sizeof(bh));
1279         bh.b_bdev = inode->i_sb->s_bdev;
1280         bh.b_size = PAGE_SIZE;
1281         err = get_block(inode, index, &bh, 0);
1282         if (err < 0 || !buffer_written(&bh))
1283                 return err;
1284
1285         return __dax_zero_page_range(bh.b_bdev, to_sector(&bh, inode),
1286                         offset, length);
1287 }
1288 EXPORT_SYMBOL_GPL(dax_zero_page_range);
1289
1290 /**
1291  * dax_truncate_page - handle a partial page being truncated in a DAX file
1292  * @inode: The file being truncated
1293  * @from: The file offset that is being truncated to
1294  * @get_block: The filesystem method used to translate file offsets to blocks
1295  *
1296  * Similar to block_truncate_page(), this function can be called by a
1297  * filesystem when it is truncating a DAX file to handle the partial page.
1298  */
1299 int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
1300 {
1301         unsigned length = PAGE_ALIGN(from) - from;
1302         return dax_zero_page_range(inode, from, length, get_block);
1303 }
1304 EXPORT_SYMBOL_GPL(dax_truncate_page);