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>
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.
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
17 #include <linux/atomic.h>
18 #include <linux/blkdev.h>
19 #include <linux/buffer_head.h>
20 #include <linux/dax.h>
22 #include <linux/genhd.h>
23 #include <linux/highmem.h>
24 #include <linux/memcontrol.h>
26 #include <linux/mutex.h>
27 #include <linux/pmem.h>
28 #include <linux/sched.h>
29 #include <linux/uio.h>
30 #include <linux/vmstat.h>
31 #include <linux/pfn_t.h>
32 #include <linux/sizes.h>
34 static long dax_map_atomic(struct block_device *bdev, struct blk_dax_ctl *dax)
36 struct request_queue *q = bdev->bd_queue;
39 dax->addr = (void __pmem *) ERR_PTR(-EIO);
40 if (blk_queue_enter(q, true) != 0)
43 rc = bdev_direct_access(bdev, dax);
45 dax->addr = (void __pmem *) ERR_PTR(rc);
52 static void dax_unmap_atomic(struct block_device *bdev,
53 const struct blk_dax_ctl *dax)
55 if (IS_ERR(dax->addr))
57 blk_queue_exit(bdev->bd_queue);
61 * dax_clear_blocks() is called from within transaction context from XFS,
62 * and hence this means the stack from this point must follow GFP_NOFS
63 * semantics for all operations.
65 int dax_clear_blocks(struct inode *inode, sector_t block, long _size)
67 struct block_device *bdev = inode->i_sb->s_bdev;
68 struct blk_dax_ctl dax = {
69 .sector = block << (inode->i_blkbits - 9),
77 count = dax_map_atomic(bdev, &dax);
80 sz = min_t(long, count, SZ_128K);
81 clear_pmem(dax.addr, sz);
83 dax.sector += sz / 512;
84 dax_unmap_atomic(bdev, &dax);
91 EXPORT_SYMBOL_GPL(dax_clear_blocks);
93 /* the clear_pmem() calls are ordered by a wmb_pmem() in the caller */
94 static void dax_new_buf(void __pmem *addr, unsigned size, unsigned first,
95 loff_t pos, loff_t end)
97 loff_t final = end - pos + first; /* The final byte of the buffer */
100 clear_pmem(addr, first);
102 clear_pmem(addr + final, size - final);
105 static bool buffer_written(struct buffer_head *bh)
107 return buffer_mapped(bh) && !buffer_unwritten(bh);
111 * When ext4 encounters a hole, it returns without modifying the buffer_head
112 * which means that we can't trust b_size. To cope with this, we set b_state
113 * to 0 before calling get_block and, if any bit is set, we know we can trust
114 * b_size. Unfortunate, really, since ext4 knows precisely how long a hole is
115 * and would save us time calling get_block repeatedly.
117 static bool buffer_size_valid(struct buffer_head *bh)
119 return bh->b_state != 0;
123 static sector_t to_sector(const struct buffer_head *bh,
124 const struct inode *inode)
126 sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
131 static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
132 loff_t start, loff_t end, get_block_t get_block,
133 struct buffer_head *bh)
135 loff_t pos = start, max = start, bh_max = start;
136 bool hole = false, need_wmb = false;
137 struct block_device *bdev = NULL;
138 int rw = iov_iter_rw(iter), rc;
140 struct blk_dax_ctl dax = {
141 .addr = (void __pmem *) ERR_PTR(-EIO),
145 end = min(end, i_size_read(inode));
150 unsigned blkbits = inode->i_blkbits;
151 long page = pos >> PAGE_SHIFT;
152 sector_t block = page << (PAGE_SHIFT - blkbits);
153 unsigned first = pos - (block << blkbits);
157 bh->b_size = PAGE_ALIGN(end - pos);
159 rc = get_block(inode, block, bh, rw == WRITE);
162 if (!buffer_size_valid(bh))
163 bh->b_size = 1 << blkbits;
164 bh_max = pos - first + bh->b_size;
167 unsigned done = bh->b_size -
168 (bh_max - (pos - first));
169 bh->b_blocknr += done >> blkbits;
173 hole = rw == READ && !buffer_written(bh);
175 size = bh->b_size - first;
177 dax_unmap_atomic(bdev, &dax);
178 dax.sector = to_sector(bh, inode);
179 dax.size = bh->b_size;
180 map_len = dax_map_atomic(bdev, &dax);
185 if (buffer_unwritten(bh) || buffer_new(bh)) {
186 dax_new_buf(dax.addr, map_len, first,
191 size = map_len - first;
193 max = min(pos + size, end);
196 if (iov_iter_rw(iter) == WRITE) {
197 len = copy_from_iter_pmem(dax.addr, max - pos, iter);
200 len = copy_to_iter((void __force *) dax.addr, max - pos,
203 len = iov_iter_zero(max - pos, iter);
211 if (!IS_ERR(dax.addr))
217 dax_unmap_atomic(bdev, &dax);
219 return (pos == start) ? rc : pos - start;
223 * dax_do_io - Perform I/O to a DAX file
224 * @iocb: The control block for this I/O
225 * @inode: The file which the I/O is directed at
226 * @iter: The addresses to do I/O from or to
227 * @pos: The file offset where the I/O starts
228 * @get_block: The filesystem method used to translate file offsets to blocks
229 * @end_io: A filesystem callback for I/O completion
232 * This function uses the same locking scheme as do_blockdev_direct_IO:
233 * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
234 * caller for writes. For reads, we take and release the i_mutex ourselves.
235 * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
236 * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
239 ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
240 struct iov_iter *iter, loff_t pos, get_block_t get_block,
241 dio_iodone_t end_io, int flags)
243 struct buffer_head bh;
244 ssize_t retval = -EINVAL;
245 loff_t end = pos + iov_iter_count(iter);
247 memset(&bh, 0, sizeof(bh));
249 if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ) {
250 struct address_space *mapping = inode->i_mapping;
251 mutex_lock(&inode->i_mutex);
252 retval = filemap_write_and_wait_range(mapping, pos, end - 1);
254 mutex_unlock(&inode->i_mutex);
259 /* Protects against truncate */
260 if (!(flags & DIO_SKIP_DIO_COUNT))
261 inode_dio_begin(inode);
263 retval = dax_io(inode, iter, pos, end, get_block, &bh);
265 if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ)
266 mutex_unlock(&inode->i_mutex);
268 if ((retval > 0) && end_io)
269 end_io(iocb, pos, retval, bh.b_private);
271 if (!(flags & DIO_SKIP_DIO_COUNT))
272 inode_dio_end(inode);
276 EXPORT_SYMBOL_GPL(dax_do_io);
279 * The user has performed a load from a hole in the file. Allocating
280 * a new page in the file would cause excessive storage usage for
281 * workloads with sparse files. We allocate a page cache page instead.
282 * We'll kick it out of the page cache if it's ever written to,
283 * otherwise it will simply fall out of the page cache under memory
284 * pressure without ever having been dirtied.
286 static int dax_load_hole(struct address_space *mapping, struct page *page,
287 struct vm_fault *vmf)
290 struct inode *inode = mapping->host;
292 page = find_or_create_page(mapping, vmf->pgoff,
293 GFP_KERNEL | __GFP_ZERO);
296 /* Recheck i_size under page lock to avoid truncate race */
297 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
298 if (vmf->pgoff >= size) {
300 page_cache_release(page);
301 return VM_FAULT_SIGBUS;
305 return VM_FAULT_LOCKED;
308 static int copy_user_bh(struct page *to, struct inode *inode,
309 struct buffer_head *bh, unsigned long vaddr)
311 struct blk_dax_ctl dax = {
312 .sector = to_sector(bh, inode),
315 struct block_device *bdev = bh->b_bdev;
318 if (dax_map_atomic(bdev, &dax) < 0)
319 return PTR_ERR(dax.addr);
320 vto = kmap_atomic(to);
321 copy_user_page(vto, (void __force *)dax.addr, vaddr, to);
323 dax_unmap_atomic(bdev, &dax);
327 static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
328 struct vm_area_struct *vma, struct vm_fault *vmf)
330 unsigned long vaddr = (unsigned long)vmf->virtual_address;
331 struct address_space *mapping = inode->i_mapping;
332 struct block_device *bdev = bh->b_bdev;
333 struct blk_dax_ctl dax = {
334 .sector = to_sector(bh, inode),
340 i_mmap_lock_read(mapping);
343 * Check truncate didn't happen while we were allocating a block.
344 * If it did, this block may or may not be still allocated to the
345 * file. We can't tell the filesystem to free it because we can't
346 * take i_mutex here. In the worst case, the file still has blocks
347 * allocated past the end of the file.
349 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
350 if (unlikely(vmf->pgoff >= size)) {
355 if (dax_map_atomic(bdev, &dax) < 0) {
356 error = PTR_ERR(dax.addr);
360 if (buffer_unwritten(bh) || buffer_new(bh)) {
361 clear_pmem(dax.addr, PAGE_SIZE);
364 dax_unmap_atomic(bdev, &dax);
366 error = vm_insert_mixed(vma, vaddr, dax.pfn);
369 i_mmap_unlock_read(mapping);
375 * __dax_fault - handle a page fault on a DAX file
376 * @vma: The virtual memory area where the fault occurred
377 * @vmf: The description of the fault
378 * @get_block: The filesystem method used to translate file offsets to blocks
379 * @complete_unwritten: The filesystem method used to convert unwritten blocks
380 * to written so the data written to them is exposed. This is required for
381 * required by write faults for filesystems that will return unwritten
382 * extent mappings from @get_block, but it is optional for reads as
383 * dax_insert_mapping() will always zero unwritten blocks. If the fs does
384 * not support unwritten extents, the it should pass NULL.
386 * When a page fault occurs, filesystems may call this helper in their
387 * fault handler for DAX files. __dax_fault() assumes the caller has done all
388 * the necessary locking for the page fault to proceed successfully.
390 int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
391 get_block_t get_block, dax_iodone_t complete_unwritten)
393 struct file *file = vma->vm_file;
394 struct address_space *mapping = file->f_mapping;
395 struct inode *inode = mapping->host;
397 struct buffer_head bh;
398 unsigned long vaddr = (unsigned long)vmf->virtual_address;
399 unsigned blkbits = inode->i_blkbits;
405 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
406 if (vmf->pgoff >= size)
407 return VM_FAULT_SIGBUS;
409 memset(&bh, 0, sizeof(bh));
410 block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
411 bh.b_size = PAGE_SIZE;
414 page = find_get_page(mapping, vmf->pgoff);
416 if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
417 page_cache_release(page);
418 return VM_FAULT_RETRY;
420 if (unlikely(page->mapping != mapping)) {
422 page_cache_release(page);
425 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
426 if (unlikely(vmf->pgoff >= size)) {
428 * We have a struct page covering a hole in the file
429 * from a read fault and we've raced with a truncate
436 error = get_block(inode, block, &bh, 0);
437 if (!error && (bh.b_size < PAGE_SIZE))
438 error = -EIO; /* fs corruption? */
442 if (!buffer_mapped(&bh) && !buffer_unwritten(&bh) && !vmf->cow_page) {
443 if (vmf->flags & FAULT_FLAG_WRITE) {
444 error = get_block(inode, block, &bh, 1);
445 count_vm_event(PGMAJFAULT);
446 mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
447 major = VM_FAULT_MAJOR;
448 if (!error && (bh.b_size < PAGE_SIZE))
453 return dax_load_hole(mapping, page, vmf);
458 struct page *new_page = vmf->cow_page;
459 if (buffer_written(&bh))
460 error = copy_user_bh(new_page, inode, &bh, vaddr);
462 clear_user_highpage(new_page, vaddr);
467 i_mmap_lock_read(mapping);
468 /* Check we didn't race with truncate */
469 size = (i_size_read(inode) + PAGE_SIZE - 1) >>
471 if (vmf->pgoff >= size) {
472 i_mmap_unlock_read(mapping);
477 return VM_FAULT_LOCKED;
480 /* Check we didn't race with a read fault installing a new page */
482 page = find_lock_page(mapping, vmf->pgoff);
485 unmap_mapping_range(mapping, vmf->pgoff << PAGE_SHIFT,
487 delete_from_page_cache(page);
489 page_cache_release(page);
493 * If we successfully insert the new mapping over an unwritten extent,
494 * we need to ensure we convert the unwritten extent. If there is an
495 * error inserting the mapping, the filesystem needs to leave it as
496 * unwritten to prevent exposure of the stale underlying data to
497 * userspace, but we still need to call the completion function so
498 * the private resources on the mapping buffer can be released. We
499 * indicate what the callback should do via the uptodate variable, same
500 * as for normal BH based IO completions.
502 error = dax_insert_mapping(inode, &bh, vma, vmf);
503 if (buffer_unwritten(&bh)) {
504 if (complete_unwritten)
505 complete_unwritten(&bh, !error);
507 WARN_ON_ONCE(!(vmf->flags & FAULT_FLAG_WRITE));
511 if (error == -ENOMEM)
512 return VM_FAULT_OOM | major;
513 /* -EBUSY is fine, somebody else faulted on the same PTE */
514 if ((error < 0) && (error != -EBUSY))
515 return VM_FAULT_SIGBUS | major;
516 return VM_FAULT_NOPAGE | major;
521 page_cache_release(page);
525 EXPORT_SYMBOL(__dax_fault);
528 * dax_fault - handle a page fault on a DAX file
529 * @vma: The virtual memory area where the fault occurred
530 * @vmf: The description of the fault
531 * @get_block: The filesystem method used to translate file offsets to blocks
533 * When a page fault occurs, filesystems may call this helper in their
534 * fault handler for DAX files.
536 int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
537 get_block_t get_block, dax_iodone_t complete_unwritten)
540 struct super_block *sb = file_inode(vma->vm_file)->i_sb;
542 if (vmf->flags & FAULT_FLAG_WRITE) {
543 sb_start_pagefault(sb);
544 file_update_time(vma->vm_file);
546 result = __dax_fault(vma, vmf, get_block, complete_unwritten);
547 if (vmf->flags & FAULT_FLAG_WRITE)
548 sb_end_pagefault(sb);
552 EXPORT_SYMBOL_GPL(dax_fault);
554 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
556 * The 'colour' (ie low bits) within a PMD of a page offset. This comes up
557 * more often than one might expect in the below function.
559 #define PG_PMD_COLOUR ((PMD_SIZE >> PAGE_SHIFT) - 1)
561 int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
562 pmd_t *pmd, unsigned int flags, get_block_t get_block,
563 dax_iodone_t complete_unwritten)
565 struct file *file = vma->vm_file;
566 struct address_space *mapping = file->f_mapping;
567 struct inode *inode = mapping->host;
568 struct buffer_head bh;
569 unsigned blkbits = inode->i_blkbits;
570 unsigned long pmd_addr = address & PMD_MASK;
571 bool write = flags & FAULT_FLAG_WRITE;
572 struct block_device *bdev;
577 /* dax pmd mappings are broken wrt gup and fork */
578 if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
579 return VM_FAULT_FALLBACK;
581 /* Fall back to PTEs if we're going to COW */
582 if (write && !(vma->vm_flags & VM_SHARED)) {
583 split_huge_pmd(vma, pmd, address);
584 return VM_FAULT_FALLBACK;
586 /* If the PMD would extend outside the VMA */
587 if (pmd_addr < vma->vm_start)
588 return VM_FAULT_FALLBACK;
589 if ((pmd_addr + PMD_SIZE) > vma->vm_end)
590 return VM_FAULT_FALLBACK;
592 pgoff = linear_page_index(vma, pmd_addr);
593 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
595 return VM_FAULT_SIGBUS;
596 /* If the PMD would cover blocks out of the file */
597 if ((pgoff | PG_PMD_COLOUR) >= size)
598 return VM_FAULT_FALLBACK;
600 memset(&bh, 0, sizeof(bh));
601 block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
603 bh.b_size = PMD_SIZE;
604 if (get_block(inode, block, &bh, write) != 0)
605 return VM_FAULT_SIGBUS;
607 i_mmap_lock_read(mapping);
610 * If the filesystem isn't willing to tell us the length of a hole,
611 * just fall back to PTEs. Calling get_block 512 times in a loop
614 if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
618 * If we allocated new storage, make sure no process has any
619 * zero pages covering this hole
621 if (buffer_new(&bh)) {
622 i_mmap_unlock_read(mapping);
623 unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0);
624 i_mmap_lock_read(mapping);
628 * If a truncate happened while we were allocating blocks, we may
629 * leave blocks allocated to the file that are beyond EOF. We can't
630 * take i_mutex here, so just leave them hanging; they'll be freed
631 * when the file is deleted.
633 size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
635 result = VM_FAULT_SIGBUS;
638 if ((pgoff | PG_PMD_COLOUR) >= size)
641 if (!write && !buffer_mapped(&bh) && buffer_uptodate(&bh)) {
644 struct page *zero_page = get_huge_zero_page();
646 if (unlikely(!zero_page))
649 ptl = pmd_lock(vma->vm_mm, pmd);
650 if (!pmd_none(*pmd)) {
655 entry = mk_pmd(zero_page, vma->vm_page_prot);
656 entry = pmd_mkhuge(entry);
657 set_pmd_at(vma->vm_mm, pmd_addr, pmd, entry);
658 result = VM_FAULT_NOPAGE;
661 struct blk_dax_ctl dax = {
662 .sector = to_sector(&bh, inode),
665 long length = dax_map_atomic(bdev, &dax);
668 result = VM_FAULT_SIGBUS;
671 if (length < PMD_SIZE
672 || (pfn_t_to_pfn(dax.pfn) & PG_PMD_COLOUR)) {
673 dax_unmap_atomic(bdev, &dax);
678 * TODO: teach vmf_insert_pfn_pmd() to support
679 * 'pte_special' for pmds
681 if (pfn_t_has_page(dax.pfn)) {
682 dax_unmap_atomic(bdev, &dax);
686 if (buffer_unwritten(&bh) || buffer_new(&bh)) {
687 clear_pmem(dax.addr, PMD_SIZE);
689 count_vm_event(PGMAJFAULT);
690 mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
691 result |= VM_FAULT_MAJOR;
693 dax_unmap_atomic(bdev, &dax);
695 result |= vmf_insert_pfn_pmd(vma, address, pmd,
700 i_mmap_unlock_read(mapping);
702 if (buffer_unwritten(&bh))
703 complete_unwritten(&bh, !(result & VM_FAULT_ERROR));
708 count_vm_event(THP_FAULT_FALLBACK);
709 result = VM_FAULT_FALLBACK;
712 EXPORT_SYMBOL_GPL(__dax_pmd_fault);
715 * dax_pmd_fault - handle a PMD fault on a DAX file
716 * @vma: The virtual memory area where the fault occurred
717 * @vmf: The description of the fault
718 * @get_block: The filesystem method used to translate file offsets to blocks
720 * When a page fault occurs, filesystems may call this helper in their
721 * pmd_fault handler for DAX files.
723 int dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
724 pmd_t *pmd, unsigned int flags, get_block_t get_block,
725 dax_iodone_t complete_unwritten)
728 struct super_block *sb = file_inode(vma->vm_file)->i_sb;
730 if (flags & FAULT_FLAG_WRITE) {
731 sb_start_pagefault(sb);
732 file_update_time(vma->vm_file);
734 result = __dax_pmd_fault(vma, address, pmd, flags, get_block,
736 if (flags & FAULT_FLAG_WRITE)
737 sb_end_pagefault(sb);
741 EXPORT_SYMBOL_GPL(dax_pmd_fault);
742 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
745 * dax_pfn_mkwrite - handle first write to DAX page
746 * @vma: The virtual memory area where the fault occurred
747 * @vmf: The description of the fault
750 int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
752 struct super_block *sb = file_inode(vma->vm_file)->i_sb;
754 sb_start_pagefault(sb);
755 file_update_time(vma->vm_file);
756 sb_end_pagefault(sb);
757 return VM_FAULT_NOPAGE;
759 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
762 * dax_zero_page_range - zero a range within a page of a DAX file
763 * @inode: The file being truncated
764 * @from: The file offset that is being truncated to
765 * @length: The number of bytes to zero
766 * @get_block: The filesystem method used to translate file offsets to blocks
768 * This function can be called by a filesystem when it is zeroing part of a
769 * page in a DAX file. This is intended for hole-punch operations. If
770 * you are truncating a file, the helper function dax_truncate_page() may be
773 * We work in terms of PAGE_CACHE_SIZE here for commonality with
774 * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
775 * took care of disposing of the unnecessary blocks. Even if the filesystem
776 * block size is smaller than PAGE_SIZE, we have to zero the rest of the page
777 * since the file might be mmapped.
779 int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
780 get_block_t get_block)
782 struct buffer_head bh;
783 pgoff_t index = from >> PAGE_CACHE_SHIFT;
784 unsigned offset = from & (PAGE_CACHE_SIZE-1);
787 /* Block boundary? Nothing to do */
790 BUG_ON((offset + length) > PAGE_CACHE_SIZE);
792 memset(&bh, 0, sizeof(bh));
793 bh.b_size = PAGE_CACHE_SIZE;
794 err = get_block(inode, index, &bh, 0);
797 if (buffer_written(&bh)) {
798 struct block_device *bdev = bh.b_bdev;
799 struct blk_dax_ctl dax = {
800 .sector = to_sector(&bh, inode),
801 .size = PAGE_CACHE_SIZE,
804 if (dax_map_atomic(bdev, &dax) < 0)
805 return PTR_ERR(dax.addr);
806 clear_pmem(dax.addr + offset, length);
808 dax_unmap_atomic(bdev, &dax);
813 EXPORT_SYMBOL_GPL(dax_zero_page_range);
816 * dax_truncate_page - handle a partial page being truncated in a DAX file
817 * @inode: The file being truncated
818 * @from: The file offset that is being truncated to
819 * @get_block: The filesystem method used to translate file offsets to blocks
821 * Similar to block_truncate_page(), this function can be called by a
822 * filesystem when it is truncating a DAX file to handle the partial page.
824 * We work in terms of PAGE_CACHE_SIZE here for commonality with
825 * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
826 * took care of disposing of the unnecessary blocks. Even if the filesystem
827 * block size is smaller than PAGE_SIZE, we have to zero the rest of the page
828 * since the file might be mmapped.
830 int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
832 unsigned length = PAGE_CACHE_ALIGN(from) - from;
833 return dax_zero_page_range(inode, from, length, get_block);
835 EXPORT_SYMBOL_GPL(dax_truncate_page);