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Linux/fs/mpage.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  * fs/mpage.c
  4  *
  5  * Copyright (C) 2002, Linus Torvalds.
  6  *
  7  * Contains functions related to preparing and submitting BIOs which contain
  8  * multiple pagecache pages.
  9  *
 10  * 15May2002    Andrew Morton
 11  *              Initial version
 12  * 27Jun2002    axboe@suse.de
 13  *              use bio_add_page() to build bio's just the right size
 14  */
 15 
 16 #include <linux/kernel.h>
 17 #include <linux/export.h>
 18 #include <linux/mm.h>
 19 #include <linux/kdev_t.h>
 20 #include <linux/gfp.h>
 21 #include <linux/bio.h>
 22 #include <linux/fs.h>
 23 #include <linux/buffer_head.h>
 24 #include <linux/blkdev.h>
 25 #include <linux/highmem.h>
 26 #include <linux/prefetch.h>
 27 #include <linux/mpage.h>
 28 #include <linux/mm_inline.h>
 29 #include <linux/writeback.h>
 30 #include <linux/backing-dev.h>
 31 #include <linux/pagevec.h>
 32 #include <linux/cleancache.h>
 33 #include "internal.h"
 34 
 35 /*
 36  * I/O completion handler for multipage BIOs.
 37  *
 38  * The mpage code never puts partial pages into a BIO (except for end-of-file).
 39  * If a page does not map to a contiguous run of blocks then it simply falls
 40  * back to block_read_full_page().
 41  *
 42  * Why is this?  If a page's completion depends on a number of different BIOs
 43  * which can complete in any order (or at the same time) then determining the
 44  * status of that page is hard.  See end_buffer_async_read() for the details.
 45  * There is no point in duplicating all that complexity.
 46  */
 47 static void mpage_end_io(struct bio *bio)
 48 {
 49         struct bio_vec *bv;
 50         struct bvec_iter_all iter_all;
 51 
 52         bio_for_each_segment_all(bv, bio, iter_all) {
 53                 struct page *page = bv->bv_page;
 54                 page_endio(page, bio_op(bio),
 55                            blk_status_to_errno(bio->bi_status));
 56         }
 57 
 58         bio_put(bio);
 59 }
 60 
 61 static struct bio *mpage_bio_submit(int op, int op_flags, struct bio *bio)
 62 {
 63         bio->bi_end_io = mpage_end_io;
 64         bio_set_op_attrs(bio, op, op_flags);
 65         guard_bio_eod(bio);
 66         submit_bio(bio);
 67         return NULL;
 68 }
 69 
 70 static struct bio *
 71 mpage_alloc(struct block_device *bdev,
 72                 sector_t first_sector, int nr_vecs,
 73                 gfp_t gfp_flags)
 74 {
 75         struct bio *bio;
 76 
 77         /* Restrict the given (page cache) mask for slab allocations */
 78         gfp_flags &= GFP_KERNEL;
 79         bio = bio_alloc(gfp_flags, nr_vecs);
 80 
 81         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
 82                 while (!bio && (nr_vecs /= 2))
 83                         bio = bio_alloc(gfp_flags, nr_vecs);
 84         }
 85 
 86         if (bio) {
 87                 bio_set_dev(bio, bdev);
 88                 bio->bi_iter.bi_sector = first_sector;
 89         }
 90         return bio;
 91 }
 92 
 93 /*
 94  * support function for mpage_readpages.  The fs supplied get_block might
 95  * return an up to date buffer.  This is used to map that buffer into
 96  * the page, which allows readpage to avoid triggering a duplicate call
 97  * to get_block.
 98  *
 99  * The idea is to avoid adding buffers to pages that don't already have
100  * them.  So when the buffer is up to date and the page size == block size,
101  * this marks the page up to date instead of adding new buffers.
102  */
103 static void 
104 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block) 
105 {
106         struct inode *inode = page->mapping->host;
107         struct buffer_head *page_bh, *head;
108         int block = 0;
109 
110         if (!page_has_buffers(page)) {
111                 /*
112                  * don't make any buffers if there is only one buffer on
113                  * the page and the page just needs to be set up to date
114                  */
115                 if (inode->i_blkbits == PAGE_SHIFT &&
116                     buffer_uptodate(bh)) {
117                         SetPageUptodate(page);    
118                         return;
119                 }
120                 create_empty_buffers(page, i_blocksize(inode), 0);
121         }
122         head = page_buffers(page);
123         page_bh = head;
124         do {
125                 if (block == page_block) {
126                         page_bh->b_state = bh->b_state;
127                         page_bh->b_bdev = bh->b_bdev;
128                         page_bh->b_blocknr = bh->b_blocknr;
129                         break;
130                 }
131                 page_bh = page_bh->b_this_page;
132                 block++;
133         } while (page_bh != head);
134 }
135 
136 struct mpage_readpage_args {
137         struct bio *bio;
138         struct page *page;
139         unsigned int nr_pages;
140         bool is_readahead;
141         sector_t last_block_in_bio;
142         struct buffer_head map_bh;
143         unsigned long first_logical_block;
144         get_block_t *get_block;
145 };
146 
147 /*
148  * This is the worker routine which does all the work of mapping the disk
149  * blocks and constructs largest possible bios, submits them for IO if the
150  * blocks are not contiguous on the disk.
151  *
152  * We pass a buffer_head back and forth and use its buffer_mapped() flag to
153  * represent the validity of its disk mapping and to decide when to do the next
154  * get_block() call.
155  */
156 static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
157 {
158         struct page *page = args->page;
159         struct inode *inode = page->mapping->host;
160         const unsigned blkbits = inode->i_blkbits;
161         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
162         const unsigned blocksize = 1 << blkbits;
163         struct buffer_head *map_bh = &args->map_bh;
164         sector_t block_in_file;
165         sector_t last_block;
166         sector_t last_block_in_file;
167         sector_t blocks[MAX_BUF_PER_PAGE];
168         unsigned page_block;
169         unsigned first_hole = blocks_per_page;
170         struct block_device *bdev = NULL;
171         int length;
172         int fully_mapped = 1;
173         int op_flags;
174         unsigned nblocks;
175         unsigned relative_block;
176         gfp_t gfp;
177 
178         if (args->is_readahead) {
179                 op_flags = REQ_RAHEAD;
180                 gfp = readahead_gfp_mask(page->mapping);
181         } else {
182                 op_flags = 0;
183                 gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
184         }
185 
186         if (page_has_buffers(page))
187                 goto confused;
188 
189         block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
190         last_block = block_in_file + args->nr_pages * blocks_per_page;
191         last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
192         if (last_block > last_block_in_file)
193                 last_block = last_block_in_file;
194         page_block = 0;
195 
196         /*
197          * Map blocks using the result from the previous get_blocks call first.
198          */
199         nblocks = map_bh->b_size >> blkbits;
200         if (buffer_mapped(map_bh) &&
201                         block_in_file > args->first_logical_block &&
202                         block_in_file < (args->first_logical_block + nblocks)) {
203                 unsigned map_offset = block_in_file - args->first_logical_block;
204                 unsigned last = nblocks - map_offset;
205 
206                 for (relative_block = 0; ; relative_block++) {
207                         if (relative_block == last) {
208                                 clear_buffer_mapped(map_bh);
209                                 break;
210                         }
211                         if (page_block == blocks_per_page)
212                                 break;
213                         blocks[page_block] = map_bh->b_blocknr + map_offset +
214                                                 relative_block;
215                         page_block++;
216                         block_in_file++;
217                 }
218                 bdev = map_bh->b_bdev;
219         }
220 
221         /*
222          * Then do more get_blocks calls until we are done with this page.
223          */
224         map_bh->b_page = page;
225         while (page_block < blocks_per_page) {
226                 map_bh->b_state = 0;
227                 map_bh->b_size = 0;
228 
229                 if (block_in_file < last_block) {
230                         map_bh->b_size = (last_block-block_in_file) << blkbits;
231                         if (args->get_block(inode, block_in_file, map_bh, 0))
232                                 goto confused;
233                         args->first_logical_block = block_in_file;
234                 }
235 
236                 if (!buffer_mapped(map_bh)) {
237                         fully_mapped = 0;
238                         if (first_hole == blocks_per_page)
239                                 first_hole = page_block;
240                         page_block++;
241                         block_in_file++;
242                         continue;
243                 }
244 
245                 /* some filesystems will copy data into the page during
246                  * the get_block call, in which case we don't want to
247                  * read it again.  map_buffer_to_page copies the data
248                  * we just collected from get_block into the page's buffers
249                  * so readpage doesn't have to repeat the get_block call
250                  */
251                 if (buffer_uptodate(map_bh)) {
252                         map_buffer_to_page(page, map_bh, page_block);
253                         goto confused;
254                 }
255         
256                 if (first_hole != blocks_per_page)
257                         goto confused;          /* hole -> non-hole */
258 
259                 /* Contiguous blocks? */
260                 if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
261                         goto confused;
262                 nblocks = map_bh->b_size >> blkbits;
263                 for (relative_block = 0; ; relative_block++) {
264                         if (relative_block == nblocks) {
265                                 clear_buffer_mapped(map_bh);
266                                 break;
267                         } else if (page_block == blocks_per_page)
268                                 break;
269                         blocks[page_block] = map_bh->b_blocknr+relative_block;
270                         page_block++;
271                         block_in_file++;
272                 }
273                 bdev = map_bh->b_bdev;
274         }
275 
276         if (first_hole != blocks_per_page) {
277                 zero_user_segment(page, first_hole << blkbits, PAGE_SIZE);
278                 if (first_hole == 0) {
279                         SetPageUptodate(page);
280                         unlock_page(page);
281                         goto out;
282                 }
283         } else if (fully_mapped) {
284                 SetPageMappedToDisk(page);
285         }
286 
287         if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
288             cleancache_get_page(page) == 0) {
289                 SetPageUptodate(page);
290                 goto confused;
291         }
292 
293         /*
294          * This page will go to BIO.  Do we need to send this BIO off first?
295          */
296         if (args->bio && (args->last_block_in_bio != blocks[0] - 1))
297                 args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
298 
299 alloc_new:
300         if (args->bio == NULL) {
301                 if (first_hole == blocks_per_page) {
302                         if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
303                                                                 page))
304                                 goto out;
305                 }
306                 args->bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
307                                         min_t(int, args->nr_pages,
308                                               BIO_MAX_PAGES),
309                                         gfp);
310                 if (args->bio == NULL)
311                         goto confused;
312         }
313 
314         length = first_hole << blkbits;
315         if (bio_add_page(args->bio, page, length, 0) < length) {
316                 args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
317                 goto alloc_new;
318         }
319 
320         relative_block = block_in_file - args->first_logical_block;
321         nblocks = map_bh->b_size >> blkbits;
322         if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
323             (first_hole != blocks_per_page))
324                 args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
325         else
326                 args->last_block_in_bio = blocks[blocks_per_page - 1];
327 out:
328         return args->bio;
329 
330 confused:
331         if (args->bio)
332                 args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
333         if (!PageUptodate(page))
334                 block_read_full_page(page, args->get_block);
335         else
336                 unlock_page(page);
337         goto out;
338 }
339 
340 /**
341  * mpage_readpages - populate an address space with some pages & start reads against them
342  * @mapping: the address_space
343  * @pages: The address of a list_head which contains the target pages.  These
344  *   pages have their ->index populated and are otherwise uninitialised.
345  *   The page at @pages->prev has the lowest file offset, and reads should be
346  *   issued in @pages->prev to @pages->next order.
347  * @nr_pages: The number of pages at *@pages
348  * @get_block: The filesystem's block mapper function.
349  *
350  * This function walks the pages and the blocks within each page, building and
351  * emitting large BIOs.
352  *
353  * If anything unusual happens, such as:
354  *
355  * - encountering a page which has buffers
356  * - encountering a page which has a non-hole after a hole
357  * - encountering a page with non-contiguous blocks
358  *
359  * then this code just gives up and calls the buffer_head-based read function.
360  * It does handle a page which has holes at the end - that is a common case:
361  * the end-of-file on blocksize < PAGE_SIZE setups.
362  *
363  * BH_Boundary explanation:
364  *
365  * There is a problem.  The mpage read code assembles several pages, gets all
366  * their disk mappings, and then submits them all.  That's fine, but obtaining
367  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
368  *
369  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
370  * submitted in the following order:
371  *
372  *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
373  *
374  * because the indirect block has to be read to get the mappings of blocks
375  * 13,14,15,16.  Obviously, this impacts performance.
376  *
377  * So what we do it to allow the filesystem's get_block() function to set
378  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
379  * after this one will require I/O against a block which is probably close to
380  * this one.  So you should push what I/O you have currently accumulated.
381  *
382  * This all causes the disk requests to be issued in the correct order.
383  */
384 int
385 mpage_readpages(struct address_space *mapping, struct list_head *pages,
386                                 unsigned nr_pages, get_block_t get_block)
387 {
388         struct mpage_readpage_args args = {
389                 .get_block = get_block,
390                 .is_readahead = true,
391         };
392         unsigned page_idx;
393 
394         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
395                 struct page *page = lru_to_page(pages);
396 
397                 prefetchw(&page->flags);
398                 list_del(&page->lru);
399                 if (!add_to_page_cache_lru(page, mapping,
400                                         page->index,
401                                         readahead_gfp_mask(mapping))) {
402                         args.page = page;
403                         args.nr_pages = nr_pages - page_idx;
404                         args.bio = do_mpage_readpage(&args);
405                 }
406                 put_page(page);
407         }
408         BUG_ON(!list_empty(pages));
409         if (args.bio)
410                 mpage_bio_submit(REQ_OP_READ, REQ_RAHEAD, args.bio);
411         return 0;
412 }
413 EXPORT_SYMBOL(mpage_readpages);
414 
415 /*
416  * This isn't called much at all
417  */
418 int mpage_readpage(struct page *page, get_block_t get_block)
419 {
420         struct mpage_readpage_args args = {
421                 .page = page,
422                 .nr_pages = 1,
423                 .get_block = get_block,
424         };
425 
426         args.bio = do_mpage_readpage(&args);
427         if (args.bio)
428                 mpage_bio_submit(REQ_OP_READ, 0, args.bio);
429         return 0;
430 }
431 EXPORT_SYMBOL(mpage_readpage);
432 
433 /*
434  * Writing is not so simple.
435  *
436  * If the page has buffers then they will be used for obtaining the disk
437  * mapping.  We only support pages which are fully mapped-and-dirty, with a
438  * special case for pages which are unmapped at the end: end-of-file.
439  *
440  * If the page has no buffers (preferred) then the page is mapped here.
441  *
442  * If all blocks are found to be contiguous then the page can go into the
443  * BIO.  Otherwise fall back to the mapping's writepage().
444  * 
445  * FIXME: This code wants an estimate of how many pages are still to be
446  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
447  * just allocate full-size (16-page) BIOs.
448  */
449 
450 struct mpage_data {
451         struct bio *bio;
452         sector_t last_block_in_bio;
453         get_block_t *get_block;
454         unsigned use_writepage;
455 };
456 
457 /*
458  * We have our BIO, so we can now mark the buffers clean.  Make
459  * sure to only clean buffers which we know we'll be writing.
460  */
461 static void clean_buffers(struct page *page, unsigned first_unmapped)
462 {
463         unsigned buffer_counter = 0;
464         struct buffer_head *bh, *head;
465         if (!page_has_buffers(page))
466                 return;
467         head = page_buffers(page);
468         bh = head;
469 
470         do {
471                 if (buffer_counter++ == first_unmapped)
472                         break;
473                 clear_buffer_dirty(bh);
474                 bh = bh->b_this_page;
475         } while (bh != head);
476 
477         /*
478          * we cannot drop the bh if the page is not uptodate or a concurrent
479          * readpage would fail to serialize with the bh and it would read from
480          * disk before we reach the platter.
481          */
482         if (buffer_heads_over_limit && PageUptodate(page))
483                 try_to_free_buffers(page);
484 }
485 
486 /*
487  * For situations where we want to clean all buffers attached to a page.
488  * We don't need to calculate how many buffers are attached to the page,
489  * we just need to specify a number larger than the maximum number of buffers.
490  */
491 void clean_page_buffers(struct page *page)
492 {
493         clean_buffers(page, ~0U);
494 }
495 
496 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
497                       void *data)
498 {
499         struct mpage_data *mpd = data;
500         struct bio *bio = mpd->bio;
501         struct address_space *mapping = page->mapping;
502         struct inode *inode = page->mapping->host;
503         const unsigned blkbits = inode->i_blkbits;
504         unsigned long end_index;
505         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
506         sector_t last_block;
507         sector_t block_in_file;
508         sector_t blocks[MAX_BUF_PER_PAGE];
509         unsigned page_block;
510         unsigned first_unmapped = blocks_per_page;
511         struct block_device *bdev = NULL;
512         int boundary = 0;
513         sector_t boundary_block = 0;
514         struct block_device *boundary_bdev = NULL;
515         int length;
516         struct buffer_head map_bh;
517         loff_t i_size = i_size_read(inode);
518         int ret = 0;
519         int op_flags = wbc_to_write_flags(wbc);
520 
521         if (page_has_buffers(page)) {
522                 struct buffer_head *head = page_buffers(page);
523                 struct buffer_head *bh = head;
524 
525                 /* If they're all mapped and dirty, do it */
526                 page_block = 0;
527                 do {
528                         BUG_ON(buffer_locked(bh));
529                         if (!buffer_mapped(bh)) {
530                                 /*
531                                  * unmapped dirty buffers are created by
532                                  * __set_page_dirty_buffers -> mmapped data
533                                  */
534                                 if (buffer_dirty(bh))
535                                         goto confused;
536                                 if (first_unmapped == blocks_per_page)
537                                         first_unmapped = page_block;
538                                 continue;
539                         }
540 
541                         if (first_unmapped != blocks_per_page)
542                                 goto confused;  /* hole -> non-hole */
543 
544                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
545                                 goto confused;
546                         if (page_block) {
547                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
548                                         goto confused;
549                         }
550                         blocks[page_block++] = bh->b_blocknr;
551                         boundary = buffer_boundary(bh);
552                         if (boundary) {
553                                 boundary_block = bh->b_blocknr;
554                                 boundary_bdev = bh->b_bdev;
555                         }
556                         bdev = bh->b_bdev;
557                 } while ((bh = bh->b_this_page) != head);
558 
559                 if (first_unmapped)
560                         goto page_is_mapped;
561 
562                 /*
563                  * Page has buffers, but they are all unmapped. The page was
564                  * created by pagein or read over a hole which was handled by
565                  * block_read_full_page().  If this address_space is also
566                  * using mpage_readpages then this can rarely happen.
567                  */
568                 goto confused;
569         }
570 
571         /*
572          * The page has no buffers: map it to disk
573          */
574         BUG_ON(!PageUptodate(page));
575         block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
576         last_block = (i_size - 1) >> blkbits;
577         map_bh.b_page = page;
578         for (page_block = 0; page_block < blocks_per_page; ) {
579 
580                 map_bh.b_state = 0;
581                 map_bh.b_size = 1 << blkbits;
582                 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
583                         goto confused;
584                 if (buffer_new(&map_bh))
585                         clean_bdev_bh_alias(&map_bh);
586                 if (buffer_boundary(&map_bh)) {
587                         boundary_block = map_bh.b_blocknr;
588                         boundary_bdev = map_bh.b_bdev;
589                 }
590                 if (page_block) {
591                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
592                                 goto confused;
593                 }
594                 blocks[page_block++] = map_bh.b_blocknr;
595                 boundary = buffer_boundary(&map_bh);
596                 bdev = map_bh.b_bdev;
597                 if (block_in_file == last_block)
598                         break;
599                 block_in_file++;
600         }
601         BUG_ON(page_block == 0);
602 
603         first_unmapped = page_block;
604 
605 page_is_mapped:
606         end_index = i_size >> PAGE_SHIFT;
607         if (page->index >= end_index) {
608                 /*
609                  * The page straddles i_size.  It must be zeroed out on each
610                  * and every writepage invocation because it may be mmapped.
611                  * "A file is mapped in multiples of the page size.  For a file
612                  * that is not a multiple of the page size, the remaining memory
613                  * is zeroed when mapped, and writes to that region are not
614                  * written out to the file."
615                  */
616                 unsigned offset = i_size & (PAGE_SIZE - 1);
617 
618                 if (page->index > end_index || !offset)
619                         goto confused;
620                 zero_user_segment(page, offset, PAGE_SIZE);
621         }
622 
623         /*
624          * This page will go to BIO.  Do we need to send this BIO off first?
625          */
626         if (bio && mpd->last_block_in_bio != blocks[0] - 1)
627                 bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
628 
629 alloc_new:
630         if (bio == NULL) {
631                 if (first_unmapped == blocks_per_page) {
632                         if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
633                                                                 page, wbc))
634                                 goto out;
635                 }
636                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
637                                 BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH);
638                 if (bio == NULL)
639                         goto confused;
640 
641                 wbc_init_bio(wbc, bio);
642                 bio->bi_write_hint = inode->i_write_hint;
643         }
644 
645         /*
646          * Must try to add the page before marking the buffer clean or
647          * the confused fail path above (OOM) will be very confused when
648          * it finds all bh marked clean (i.e. it will not write anything)
649          */
650         wbc_account_cgroup_owner(wbc, page, PAGE_SIZE);
651         length = first_unmapped << blkbits;
652         if (bio_add_page(bio, page, length, 0) < length) {
653                 bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
654                 goto alloc_new;
655         }
656 
657         clean_buffers(page, first_unmapped);
658 
659         BUG_ON(PageWriteback(page));
660         set_page_writeback(page);
661         unlock_page(page);
662         if (boundary || (first_unmapped != blocks_per_page)) {
663                 bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
664                 if (boundary_block) {
665                         write_boundary_block(boundary_bdev,
666                                         boundary_block, 1 << blkbits);
667                 }
668         } else {
669                 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
670         }
671         goto out;
672 
673 confused:
674         if (bio)
675                 bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
676 
677         if (mpd->use_writepage) {
678                 ret = mapping->a_ops->writepage(page, wbc);
679         } else {
680                 ret = -EAGAIN;
681                 goto out;
682         }
683         /*
684          * The caller has a ref on the inode, so *mapping is stable
685          */
686         mapping_set_error(mapping, ret);
687 out:
688         mpd->bio = bio;
689         return ret;
690 }
691 
692 /**
693  * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
694  * @mapping: address space structure to write
695  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
696  * @get_block: the filesystem's block mapper function.
697  *             If this is NULL then use a_ops->writepage.  Otherwise, go
698  *             direct-to-BIO.
699  *
700  * This is a library function, which implements the writepages()
701  * address_space_operation.
702  *
703  * If a page is already under I/O, generic_writepages() skips it, even
704  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
705  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
706  * and msync() need to guarantee that all the data which was dirty at the time
707  * the call was made get new I/O started against them.  If wbc->sync_mode is
708  * WB_SYNC_ALL then we were called for data integrity and we must wait for
709  * existing IO to complete.
710  */
711 int
712 mpage_writepages(struct address_space *mapping,
713                 struct writeback_control *wbc, get_block_t get_block)
714 {
715         struct blk_plug plug;
716         int ret;
717 
718         blk_start_plug(&plug);
719 
720         if (!get_block)
721                 ret = generic_writepages(mapping, wbc);
722         else {
723                 struct mpage_data mpd = {
724                         .bio = NULL,
725                         .last_block_in_bio = 0,
726                         .get_block = get_block,
727                         .use_writepage = 1,
728                 };
729 
730                 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
731                 if (mpd.bio) {
732                         int op_flags = (wbc->sync_mode == WB_SYNC_ALL ?
733                                   REQ_SYNC : 0);
734                         mpage_bio_submit(REQ_OP_WRITE, op_flags, mpd.bio);
735                 }
736         }
737         blk_finish_plug(&plug);
738         return ret;
739 }
740 EXPORT_SYMBOL(mpage_writepages);
741 
742 int mpage_writepage(struct page *page, get_block_t get_block,
743         struct writeback_control *wbc)
744 {
745         struct mpage_data mpd = {
746                 .bio = NULL,
747                 .last_block_in_bio = 0,
748                 .get_block = get_block,
749                 .use_writepage = 0,
750         };
751         int ret = __mpage_writepage(page, wbc, &mpd);
752         if (mpd.bio) {
753                 int op_flags = (wbc->sync_mode == WB_SYNC_ALL ?
754                           REQ_SYNC : 0);
755                 mpage_bio_submit(REQ_OP_WRITE, op_flags, mpd.bio);
756         }
757         return ret;
758 }
759 EXPORT_SYMBOL(mpage_writepage);
760 

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