Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/davej/cpufreq
[linux-3.10.git] / fs / mpage.c
1 /*
2  * fs/mpage.c
3  *
4  * Copyright (C) 2002, Linus Torvalds.
5  *
6  * Contains functions related to preparing and submitting BIOs which contain
7  * multiple pagecache pages.
8  *
9  * 15May2002    Andrew Morton
10  *              Initial version
11  * 27Jun2002    axboe@suse.de
12  *              use bio_add_page() to build bio's just the right size
13  */
14
15 #include <linux/kernel.h>
16 #include <linux/module.h>
17 #include <linux/mm.h>
18 #include <linux/kdev_t.h>
19 #include <linux/gfp.h>
20 #include <linux/bio.h>
21 #include <linux/fs.h>
22 #include <linux/buffer_head.h>
23 #include <linux/blkdev.h>
24 #include <linux/highmem.h>
25 #include <linux/prefetch.h>
26 #include <linux/mpage.h>
27 #include <linux/writeback.h>
28 #include <linux/backing-dev.h>
29 #include <linux/pagevec.h>
30
31 /*
32  * I/O completion handler for multipage BIOs.
33  *
34  * The mpage code never puts partial pages into a BIO (except for end-of-file).
35  * If a page does not map to a contiguous run of blocks then it simply falls
36  * back to block_read_full_page().
37  *
38  * Why is this?  If a page's completion depends on a number of different BIOs
39  * which can complete in any order (or at the same time) then determining the
40  * status of that page is hard.  See end_buffer_async_read() for the details.
41  * There is no point in duplicating all that complexity.
42  */
43 static void mpage_end_io_read(struct bio *bio, int err)
44 {
45         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
46         struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
47
48         do {
49                 struct page *page = bvec->bv_page;
50
51                 if (--bvec >= bio->bi_io_vec)
52                         prefetchw(&bvec->bv_page->flags);
53
54                 if (uptodate) {
55                         SetPageUptodate(page);
56                 } else {
57                         ClearPageUptodate(page);
58                         SetPageError(page);
59                 }
60                 unlock_page(page);
61         } while (bvec >= bio->bi_io_vec);
62         bio_put(bio);
63 }
64
65 static void mpage_end_io_write(struct bio *bio, int err)
66 {
67         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
68         struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
69
70         do {
71                 struct page *page = bvec->bv_page;
72
73                 if (--bvec >= bio->bi_io_vec)
74                         prefetchw(&bvec->bv_page->flags);
75
76                 if (!uptodate){
77                         SetPageError(page);
78                         if (page->mapping)
79                                 set_bit(AS_EIO, &page->mapping->flags);
80                 }
81                 end_page_writeback(page);
82         } while (bvec >= bio->bi_io_vec);
83         bio_put(bio);
84 }
85
86 static struct bio *mpage_bio_submit(int rw, struct bio *bio)
87 {
88         bio->bi_end_io = mpage_end_io_read;
89         if (rw == WRITE)
90                 bio->bi_end_io = mpage_end_io_write;
91         submit_bio(rw, bio);
92         return NULL;
93 }
94
95 static struct bio *
96 mpage_alloc(struct block_device *bdev,
97                 sector_t first_sector, int nr_vecs,
98                 gfp_t gfp_flags)
99 {
100         struct bio *bio;
101
102         bio = bio_alloc(gfp_flags, nr_vecs);
103
104         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
105                 while (!bio && (nr_vecs /= 2))
106                         bio = bio_alloc(gfp_flags, nr_vecs);
107         }
108
109         if (bio) {
110                 bio->bi_bdev = bdev;
111                 bio->bi_sector = first_sector;
112         }
113         return bio;
114 }
115
116 /*
117  * support function for mpage_readpages.  The fs supplied get_block might
118  * return an up to date buffer.  This is used to map that buffer into
119  * the page, which allows readpage to avoid triggering a duplicate call
120  * to get_block.
121  *
122  * The idea is to avoid adding buffers to pages that don't already have
123  * them.  So when the buffer is up to date and the page size == block size,
124  * this marks the page up to date instead of adding new buffers.
125  */
126 static void 
127 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block) 
128 {
129         struct inode *inode = page->mapping->host;
130         struct buffer_head *page_bh, *head;
131         int block = 0;
132
133         if (!page_has_buffers(page)) {
134                 /*
135                  * don't make any buffers if there is only one buffer on
136                  * the page and the page just needs to be set up to date
137                  */
138                 if (inode->i_blkbits == PAGE_CACHE_SHIFT && 
139                     buffer_uptodate(bh)) {
140                         SetPageUptodate(page);    
141                         return;
142                 }
143                 create_empty_buffers(page, 1 << inode->i_blkbits, 0);
144         }
145         head = page_buffers(page);
146         page_bh = head;
147         do {
148                 if (block == page_block) {
149                         page_bh->b_state = bh->b_state;
150                         page_bh->b_bdev = bh->b_bdev;
151                         page_bh->b_blocknr = bh->b_blocknr;
152                         break;
153                 }
154                 page_bh = page_bh->b_this_page;
155                 block++;
156         } while (page_bh != head);
157 }
158
159 /*
160  * This is the worker routine which does all the work of mapping the disk
161  * blocks and constructs largest possible bios, submits them for IO if the
162  * blocks are not contiguous on the disk.
163  *
164  * We pass a buffer_head back and forth and use its buffer_mapped() flag to
165  * represent the validity of its disk mapping and to decide when to do the next
166  * get_block() call.
167  */
168 static struct bio *
169 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
170                 sector_t *last_block_in_bio, struct buffer_head *map_bh,
171                 unsigned long *first_logical_block, get_block_t get_block)
172 {
173         struct inode *inode = page->mapping->host;
174         const unsigned blkbits = inode->i_blkbits;
175         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
176         const unsigned blocksize = 1 << blkbits;
177         sector_t block_in_file;
178         sector_t last_block;
179         sector_t last_block_in_file;
180         sector_t blocks[MAX_BUF_PER_PAGE];
181         unsigned page_block;
182         unsigned first_hole = blocks_per_page;
183         struct block_device *bdev = NULL;
184         int length;
185         int fully_mapped = 1;
186         unsigned nblocks;
187         unsigned relative_block;
188
189         if (page_has_buffers(page))
190                 goto confused;
191
192         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
193         last_block = block_in_file + nr_pages * blocks_per_page;
194         last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
195         if (last_block > last_block_in_file)
196                 last_block = last_block_in_file;
197         page_block = 0;
198
199         /*
200          * Map blocks using the result from the previous get_blocks call first.
201          */
202         nblocks = map_bh->b_size >> blkbits;
203         if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
204                         block_in_file < (*first_logical_block + nblocks)) {
205                 unsigned map_offset = block_in_file - *first_logical_block;
206                 unsigned last = nblocks - map_offset;
207
208                 for (relative_block = 0; ; relative_block++) {
209                         if (relative_block == last) {
210                                 clear_buffer_mapped(map_bh);
211                                 break;
212                         }
213                         if (page_block == blocks_per_page)
214                                 break;
215                         blocks[page_block] = map_bh->b_blocknr + map_offset +
216                                                 relative_block;
217                         page_block++;
218                         block_in_file++;
219                 }
220                 bdev = map_bh->b_bdev;
221         }
222
223         /*
224          * Then do more get_blocks calls until we are done with this page.
225          */
226         map_bh->b_page = page;
227         while (page_block < blocks_per_page) {
228                 map_bh->b_state = 0;
229                 map_bh->b_size = 0;
230
231                 if (block_in_file < last_block) {
232                         map_bh->b_size = (last_block-block_in_file) << blkbits;
233                         if (get_block(inode, block_in_file, map_bh, 0))
234                                 goto confused;
235                         *first_logical_block = block_in_file;
236                 }
237
238                 if (!buffer_mapped(map_bh)) {
239                         fully_mapped = 0;
240                         if (first_hole == blocks_per_page)
241                                 first_hole = page_block;
242                         page_block++;
243                         block_in_file++;
244                         continue;
245                 }
246
247                 /* some filesystems will copy data into the page during
248                  * the get_block call, in which case we don't want to
249                  * read it again.  map_buffer_to_page copies the data
250                  * we just collected from get_block into the page's buffers
251                  * so readpage doesn't have to repeat the get_block call
252                  */
253                 if (buffer_uptodate(map_bh)) {
254                         map_buffer_to_page(page, map_bh, page_block);
255                         goto confused;
256                 }
257         
258                 if (first_hole != blocks_per_page)
259                         goto confused;          /* hole -> non-hole */
260
261                 /* Contiguous blocks? */
262                 if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
263                         goto confused;
264                 nblocks = map_bh->b_size >> blkbits;
265                 for (relative_block = 0; ; relative_block++) {
266                         if (relative_block == nblocks) {
267                                 clear_buffer_mapped(map_bh);
268                                 break;
269                         } else if (page_block == blocks_per_page)
270                                 break;
271                         blocks[page_block] = map_bh->b_blocknr+relative_block;
272                         page_block++;
273                         block_in_file++;
274                 }
275                 bdev = map_bh->b_bdev;
276         }
277
278         if (first_hole != blocks_per_page) {
279                 zero_user_segment(page, first_hole << blkbits, PAGE_CACHE_SIZE);
280                 if (first_hole == 0) {
281                         SetPageUptodate(page);
282                         unlock_page(page);
283                         goto out;
284                 }
285         } else if (fully_mapped) {
286                 SetPageMappedToDisk(page);
287         }
288
289         /*
290          * This page will go to BIO.  Do we need to send this BIO off first?
291          */
292         if (bio && (*last_block_in_bio != blocks[0] - 1))
293                 bio = mpage_bio_submit(READ, bio);
294
295 alloc_new:
296         if (bio == NULL) {
297                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
298                                 min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
299                                 GFP_KERNEL);
300                 if (bio == NULL)
301                         goto confused;
302         }
303
304         length = first_hole << blkbits;
305         if (bio_add_page(bio, page, length, 0) < length) {
306                 bio = mpage_bio_submit(READ, bio);
307                 goto alloc_new;
308         }
309
310         relative_block = block_in_file - *first_logical_block;
311         nblocks = map_bh->b_size >> blkbits;
312         if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
313             (first_hole != blocks_per_page))
314                 bio = mpage_bio_submit(READ, bio);
315         else
316                 *last_block_in_bio = blocks[blocks_per_page - 1];
317 out:
318         return bio;
319
320 confused:
321         if (bio)
322                 bio = mpage_bio_submit(READ, bio);
323         if (!PageUptodate(page))
324                 block_read_full_page(page, get_block);
325         else
326                 unlock_page(page);
327         goto out;
328 }
329
330 /**
331  * mpage_readpages - populate an address space with some pages & start reads against them
332  * @mapping: the address_space
333  * @pages: The address of a list_head which contains the target pages.  These
334  *   pages have their ->index populated and are otherwise uninitialised.
335  *   The page at @pages->prev has the lowest file offset, and reads should be
336  *   issued in @pages->prev to @pages->next order.
337  * @nr_pages: The number of pages at *@pages
338  * @get_block: The filesystem's block mapper function.
339  *
340  * This function walks the pages and the blocks within each page, building and
341  * emitting large BIOs.
342  *
343  * If anything unusual happens, such as:
344  *
345  * - encountering a page which has buffers
346  * - encountering a page which has a non-hole after a hole
347  * - encountering a page with non-contiguous blocks
348  *
349  * then this code just gives up and calls the buffer_head-based read function.
350  * It does handle a page which has holes at the end - that is a common case:
351  * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
352  *
353  * BH_Boundary explanation:
354  *
355  * There is a problem.  The mpage read code assembles several pages, gets all
356  * their disk mappings, and then submits them all.  That's fine, but obtaining
357  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
358  *
359  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
360  * submitted in the following order:
361  *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
362  *
363  * because the indirect block has to be read to get the mappings of blocks
364  * 13,14,15,16.  Obviously, this impacts performance.
365  *
366  * So what we do it to allow the filesystem's get_block() function to set
367  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
368  * after this one will require I/O against a block which is probably close to
369  * this one.  So you should push what I/O you have currently accumulated.
370  *
371  * This all causes the disk requests to be issued in the correct order.
372  */
373 int
374 mpage_readpages(struct address_space *mapping, struct list_head *pages,
375                                 unsigned nr_pages, get_block_t get_block)
376 {
377         struct bio *bio = NULL;
378         unsigned page_idx;
379         sector_t last_block_in_bio = 0;
380         struct buffer_head map_bh;
381         unsigned long first_logical_block = 0;
382
383         map_bh.b_state = 0;
384         map_bh.b_size = 0;
385         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
386                 struct page *page = list_entry(pages->prev, struct page, lru);
387
388                 prefetchw(&page->flags);
389                 list_del(&page->lru);
390                 if (!add_to_page_cache_lru(page, mapping,
391                                         page->index, GFP_KERNEL)) {
392                         bio = do_mpage_readpage(bio, page,
393                                         nr_pages - page_idx,
394                                         &last_block_in_bio, &map_bh,
395                                         &first_logical_block,
396                                         get_block);
397                 }
398                 page_cache_release(page);
399         }
400         BUG_ON(!list_empty(pages));
401         if (bio)
402                 mpage_bio_submit(READ, bio);
403         return 0;
404 }
405 EXPORT_SYMBOL(mpage_readpages);
406
407 /*
408  * This isn't called much at all
409  */
410 int mpage_readpage(struct page *page, get_block_t get_block)
411 {
412         struct bio *bio = NULL;
413         sector_t last_block_in_bio = 0;
414         struct buffer_head map_bh;
415         unsigned long first_logical_block = 0;
416
417         map_bh.b_state = 0;
418         map_bh.b_size = 0;
419         bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
420                         &map_bh, &first_logical_block, get_block);
421         if (bio)
422                 mpage_bio_submit(READ, bio);
423         return 0;
424 }
425 EXPORT_SYMBOL(mpage_readpage);
426
427 /*
428  * Writing is not so simple.
429  *
430  * If the page has buffers then they will be used for obtaining the disk
431  * mapping.  We only support pages which are fully mapped-and-dirty, with a
432  * special case for pages which are unmapped at the end: end-of-file.
433  *
434  * If the page has no buffers (preferred) then the page is mapped here.
435  *
436  * If all blocks are found to be contiguous then the page can go into the
437  * BIO.  Otherwise fall back to the mapping's writepage().
438  * 
439  * FIXME: This code wants an estimate of how many pages are still to be
440  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
441  * just allocate full-size (16-page) BIOs.
442  */
443
444 struct mpage_data {
445         struct bio *bio;
446         sector_t last_block_in_bio;
447         get_block_t *get_block;
448         unsigned use_writepage;
449 };
450
451 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
452                       void *data)
453 {
454         struct mpage_data *mpd = data;
455         struct bio *bio = mpd->bio;
456         struct address_space *mapping = page->mapping;
457         struct inode *inode = page->mapping->host;
458         const unsigned blkbits = inode->i_blkbits;
459         unsigned long end_index;
460         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
461         sector_t last_block;
462         sector_t block_in_file;
463         sector_t blocks[MAX_BUF_PER_PAGE];
464         unsigned page_block;
465         unsigned first_unmapped = blocks_per_page;
466         struct block_device *bdev = NULL;
467         int boundary = 0;
468         sector_t boundary_block = 0;
469         struct block_device *boundary_bdev = NULL;
470         int length;
471         struct buffer_head map_bh;
472         loff_t i_size = i_size_read(inode);
473         int ret = 0;
474
475         if (page_has_buffers(page)) {
476                 struct buffer_head *head = page_buffers(page);
477                 struct buffer_head *bh = head;
478
479                 /* If they're all mapped and dirty, do it */
480                 page_block = 0;
481                 do {
482                         BUG_ON(buffer_locked(bh));
483                         if (!buffer_mapped(bh)) {
484                                 /*
485                                  * unmapped dirty buffers are created by
486                                  * __set_page_dirty_buffers -> mmapped data
487                                  */
488                                 if (buffer_dirty(bh))
489                                         goto confused;
490                                 if (first_unmapped == blocks_per_page)
491                                         first_unmapped = page_block;
492                                 continue;
493                         }
494
495                         if (first_unmapped != blocks_per_page)
496                                 goto confused;  /* hole -> non-hole */
497
498                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
499                                 goto confused;
500                         if (page_block) {
501                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
502                                         goto confused;
503                         }
504                         blocks[page_block++] = bh->b_blocknr;
505                         boundary = buffer_boundary(bh);
506                         if (boundary) {
507                                 boundary_block = bh->b_blocknr;
508                                 boundary_bdev = bh->b_bdev;
509                         }
510                         bdev = bh->b_bdev;
511                 } while ((bh = bh->b_this_page) != head);
512
513                 if (first_unmapped)
514                         goto page_is_mapped;
515
516                 /*
517                  * Page has buffers, but they are all unmapped. The page was
518                  * created by pagein or read over a hole which was handled by
519                  * block_read_full_page().  If this address_space is also
520                  * using mpage_readpages then this can rarely happen.
521                  */
522                 goto confused;
523         }
524
525         /*
526          * The page has no buffers: map it to disk
527          */
528         BUG_ON(!PageUptodate(page));
529         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
530         last_block = (i_size - 1) >> blkbits;
531         map_bh.b_page = page;
532         for (page_block = 0; page_block < blocks_per_page; ) {
533
534                 map_bh.b_state = 0;
535                 map_bh.b_size = 1 << blkbits;
536                 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
537                         goto confused;
538                 if (buffer_new(&map_bh))
539                         unmap_underlying_metadata(map_bh.b_bdev,
540                                                 map_bh.b_blocknr);
541                 if (buffer_boundary(&map_bh)) {
542                         boundary_block = map_bh.b_blocknr;
543                         boundary_bdev = map_bh.b_bdev;
544                 }
545                 if (page_block) {
546                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
547                                 goto confused;
548                 }
549                 blocks[page_block++] = map_bh.b_blocknr;
550                 boundary = buffer_boundary(&map_bh);
551                 bdev = map_bh.b_bdev;
552                 if (block_in_file == last_block)
553                         break;
554                 block_in_file++;
555         }
556         BUG_ON(page_block == 0);
557
558         first_unmapped = page_block;
559
560 page_is_mapped:
561         end_index = i_size >> PAGE_CACHE_SHIFT;
562         if (page->index >= end_index) {
563                 /*
564                  * The page straddles i_size.  It must be zeroed out on each
565                  * and every writepage invocation because it may be mmapped.
566                  * "A file is mapped in multiples of the page size.  For a file
567                  * that is not a multiple of the page size, the remaining memory
568                  * is zeroed when mapped, and writes to that region are not
569                  * written out to the file."
570                  */
571                 unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
572
573                 if (page->index > end_index || !offset)
574                         goto confused;
575                 zero_user_segment(page, offset, PAGE_CACHE_SIZE);
576         }
577
578         /*
579          * This page will go to BIO.  Do we need to send this BIO off first?
580          */
581         if (bio && mpd->last_block_in_bio != blocks[0] - 1)
582                 bio = mpage_bio_submit(WRITE, bio);
583
584 alloc_new:
585         if (bio == NULL) {
586                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
587                                 bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
588                 if (bio == NULL)
589                         goto confused;
590         }
591
592         /*
593          * Must try to add the page before marking the buffer clean or
594          * the confused fail path above (OOM) will be very confused when
595          * it finds all bh marked clean (i.e. it will not write anything)
596          */
597         length = first_unmapped << blkbits;
598         if (bio_add_page(bio, page, length, 0) < length) {
599                 bio = mpage_bio_submit(WRITE, bio);
600                 goto alloc_new;
601         }
602
603         /*
604          * OK, we have our BIO, so we can now mark the buffers clean.  Make
605          * sure to only clean buffers which we know we'll be writing.
606          */
607         if (page_has_buffers(page)) {
608                 struct buffer_head *head = page_buffers(page);
609                 struct buffer_head *bh = head;
610                 unsigned buffer_counter = 0;
611
612                 do {
613                         if (buffer_counter++ == first_unmapped)
614                                 break;
615                         clear_buffer_dirty(bh);
616                         bh = bh->b_this_page;
617                 } while (bh != head);
618
619                 /*
620                  * we cannot drop the bh if the page is not uptodate
621                  * or a concurrent readpage would fail to serialize with the bh
622                  * and it would read from disk before we reach the platter.
623                  */
624                 if (buffer_heads_over_limit && PageUptodate(page))
625                         try_to_free_buffers(page);
626         }
627
628         BUG_ON(PageWriteback(page));
629         set_page_writeback(page);
630         unlock_page(page);
631         if (boundary || (first_unmapped != blocks_per_page)) {
632                 bio = mpage_bio_submit(WRITE, bio);
633                 if (boundary_block) {
634                         write_boundary_block(boundary_bdev,
635                                         boundary_block, 1 << blkbits);
636                 }
637         } else {
638                 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
639         }
640         goto out;
641
642 confused:
643         if (bio)
644                 bio = mpage_bio_submit(WRITE, bio);
645
646         if (mpd->use_writepage) {
647                 ret = mapping->a_ops->writepage(page, wbc);
648         } else {
649                 ret = -EAGAIN;
650                 goto out;
651         }
652         /*
653          * The caller has a ref on the inode, so *mapping is stable
654          */
655         mapping_set_error(mapping, ret);
656 out:
657         mpd->bio = bio;
658         return ret;
659 }
660
661 /**
662  * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
663  * @mapping: address space structure to write
664  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
665  * @get_block: the filesystem's block mapper function.
666  *             If this is NULL then use a_ops->writepage.  Otherwise, go
667  *             direct-to-BIO.
668  *
669  * This is a library function, which implements the writepages()
670  * address_space_operation.
671  *
672  * If a page is already under I/O, generic_writepages() skips it, even
673  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
674  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
675  * and msync() need to guarantee that all the data which was dirty at the time
676  * the call was made get new I/O started against them.  If wbc->sync_mode is
677  * WB_SYNC_ALL then we were called for data integrity and we must wait for
678  * existing IO to complete.
679  */
680 int
681 mpage_writepages(struct address_space *mapping,
682                 struct writeback_control *wbc, get_block_t get_block)
683 {
684         int ret;
685
686         if (!get_block)
687                 ret = generic_writepages(mapping, wbc);
688         else {
689                 struct mpage_data mpd = {
690                         .bio = NULL,
691                         .last_block_in_bio = 0,
692                         .get_block = get_block,
693                         .use_writepage = 1,
694                 };
695
696                 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
697                 if (mpd.bio)
698                         mpage_bio_submit(WRITE, mpd.bio);
699         }
700         return ret;
701 }
702 EXPORT_SYMBOL(mpage_writepages);
703
704 int mpage_writepage(struct page *page, get_block_t get_block,
705         struct writeback_control *wbc)
706 {
707         struct mpage_data mpd = {
708                 .bio = NULL,
709                 .last_block_in_bio = 0,
710                 .get_block = get_block,
711                 .use_writepage = 0,
712         };
713         int ret = __mpage_writepage(page, wbc, &mpd);
714         if (mpd.bio)
715                 mpage_bio_submit(WRITE, mpd.bio);
716         return ret;
717 }
718 EXPORT_SYMBOL(mpage_writepage);