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Linux/fs/dax.c

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

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