b1c3e58905086eb920cafd4df806b7d70dd6ef36
[linux-2.6.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    akpm@zip.com.au
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/bio.h>
20 #include <linux/fs.h>
21 #include <linux/buffer_head.h>
22 #include <linux/blkdev.h>
23 #include <linux/highmem.h>
24 #include <linux/prefetch.h>
25 #include <linux/mpage.h>
26 #include <linux/writeback.h>
27 #include <linux/backing-dev.h>
28 #include <linux/pagevec.h>
29
30 /*
31  * I/O completion handler for multipage BIOs.
32  *
33  * The mpage code never puts partial pages into a BIO (except for end-of-file).
34  * If a page does not map to a contiguous run of blocks then it simply falls
35  * back to block_read_full_page().
36  *
37  * Why is this?  If a page's completion depends on a number of different BIOs
38  * which can complete in any order (or at the same time) then determining the
39  * status of that page is hard.  See end_buffer_async_read() for the details.
40  * There is no point in duplicating all that complexity.
41  */
42 static void mpage_end_io_read(struct bio *bio, int err)
43 {
44         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
45         struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
46
47         do {
48                 struct page *page = bvec->bv_page;
49
50                 if (--bvec >= bio->bi_io_vec)
51                         prefetchw(&bvec->bv_page->flags);
52
53                 if (uptodate) {
54                         SetPageUptodate(page);
55                 } else {
56                         ClearPageUptodate(page);
57                         SetPageError(page);
58                 }
59                 unlock_page(page);
60         } while (bvec >= bio->bi_io_vec);
61         bio_put(bio);
62 }
63
64 static void mpage_end_io_write(struct bio *bio, int err)
65 {
66         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
67         struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
68
69         do {
70                 struct page *page = bvec->bv_page;
71
72                 if (--bvec >= bio->bi_io_vec)
73                         prefetchw(&bvec->bv_page->flags);
74
75                 if (!uptodate){
76                         SetPageError(page);
77                         if (page->mapping)
78                                 set_bit(AS_EIO, &page->mapping->flags);
79                 }
80                 end_page_writeback(page);
81         } while (bvec >= bio->bi_io_vec);
82         bio_put(bio);
83 }
84
85 static struct bio *mpage_bio_submit(int rw, struct bio *bio)
86 {
87         bio->bi_end_io = mpage_end_io_read;
88         if (rw == WRITE)
89                 bio->bi_end_io = mpage_end_io_write;
90         submit_bio(rw, bio);
91         return NULL;
92 }
93
94 static struct bio *
95 mpage_alloc(struct block_device *bdev,
96                 sector_t first_sector, int nr_vecs,
97                 gfp_t gfp_flags)
98 {
99         struct bio *bio;
100
101         bio = bio_alloc(gfp_flags, nr_vecs);
102
103         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
104                 while (!bio && (nr_vecs /= 2))
105                         bio = bio_alloc(gfp_flags, nr_vecs);
106         }
107
108         if (bio) {
109                 bio->bi_bdev = bdev;
110                 bio->bi_sector = first_sector;
111         }
112         return bio;
113 }
114
115 /*
116  * support function for mpage_readpages.  The fs supplied get_block might
117  * return an up to date buffer.  This is used to map that buffer into
118  * the page, which allows readpage to avoid triggering a duplicate call
119  * to get_block.
120  *
121  * The idea is to avoid adding buffers to pages that don't already have
122  * them.  So when the buffer is up to date and the page size == block size,
123  * this marks the page up to date instead of adding new buffers.
124  */
125 static void 
126 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block) 
127 {
128         struct inode *inode = page->mapping->host;
129         struct buffer_head *page_bh, *head;
130         int block = 0;
131
132         if (!page_has_buffers(page)) {
133                 /*
134                  * don't make any buffers if there is only one buffer on
135                  * the page and the page just needs to be set up to date
136                  */
137                 if (inode->i_blkbits == PAGE_CACHE_SHIFT && 
138                     buffer_uptodate(bh)) {
139                         SetPageUptodate(page);    
140                         return;
141                 }
142                 create_empty_buffers(page, 1 << inode->i_blkbits, 0);
143         }
144         head = page_buffers(page);
145         page_bh = head;
146         do {
147                 if (block == page_block) {
148                         page_bh->b_state = bh->b_state;
149                         page_bh->b_bdev = bh->b_bdev;
150                         page_bh->b_blocknr = bh->b_blocknr;
151                         break;
152                 }
153                 page_bh = page_bh->b_this_page;
154                 block++;
155         } while (page_bh != head);
156 }
157
158 /*
159  * This is the worker routine which does all the work of mapping the disk
160  * blocks and constructs largest possible bios, submits them for IO if the
161  * blocks are not contiguous on the disk.
162  *
163  * We pass a buffer_head back and forth and use its buffer_mapped() flag to
164  * represent the validity of its disk mapping and to decide when to do the next
165  * get_block() call.
166  */
167 static struct bio *
168 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
169                 sector_t *last_block_in_bio, struct buffer_head *map_bh,
170                 unsigned long *first_logical_block, get_block_t get_block)
171 {
172         struct inode *inode = page->mapping->host;
173         const unsigned blkbits = inode->i_blkbits;
174         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
175         const unsigned blocksize = 1 << blkbits;
176         sector_t block_in_file;
177         sector_t last_block;
178         sector_t last_block_in_file;
179         sector_t blocks[MAX_BUF_PER_PAGE];
180         unsigned page_block;
181         unsigned first_hole = blocks_per_page;
182         struct block_device *bdev = NULL;
183         int length;
184         int fully_mapped = 1;
185         unsigned nblocks;
186         unsigned relative_block;
187
188         if (page_has_buffers(page))
189                 goto confused;
190
191         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
192         last_block = block_in_file + nr_pages * blocks_per_page;
193         last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
194         if (last_block > last_block_in_file)
195                 last_block = last_block_in_file;
196         page_block = 0;
197
198         /*
199          * Map blocks using the result from the previous get_blocks call first.
200          */
201         nblocks = map_bh->b_size >> blkbits;
202         if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
203                         block_in_file < (*first_logical_block + nblocks)) {
204                 unsigned map_offset = block_in_file - *first_logical_block;
205                 unsigned last = nblocks - map_offset;
206
207                 for (relative_block = 0; ; relative_block++) {
208                         if (relative_block == last) {
209                                 clear_buffer_mapped(map_bh);
210                                 break;
211                         }
212                         if (page_block == blocks_per_page)
213                                 break;
214                         blocks[page_block] = map_bh->b_blocknr + map_offset +
215                                                 relative_block;
216                         page_block++;
217                         block_in_file++;
218                 }
219                 bdev = map_bh->b_bdev;
220         }
221
222         /*
223          * Then do more get_blocks calls until we are done with this page.
224          */
225         map_bh->b_page = page;
226         while (page_block < blocks_per_page) {
227                 map_bh->b_state = 0;
228                 map_bh->b_size = 0;
229
230                 if (block_in_file < last_block) {
231                         map_bh->b_size = (last_block-block_in_file) << blkbits;
232                         if (get_block(inode, block_in_file, map_bh, 0))
233                                 goto confused;
234                         *first_logical_block = block_in_file;
235                 }
236
237                 if (!buffer_mapped(map_bh)) {
238                         fully_mapped = 0;
239                         if (first_hole == blocks_per_page)
240                                 first_hole = page_block;
241                         page_block++;
242                         block_in_file++;
243                         clear_buffer_mapped(map_bh);
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_page(page, first_hole << blkbits,
280                                 PAGE_CACHE_SIZE - (first_hole << blkbits),
281                                 KM_USER0);
282                 if (first_hole == 0) {
283                         SetPageUptodate(page);
284                         unlock_page(page);
285                         goto out;
286                 }
287         } else if (fully_mapped) {
288                 SetPageMappedToDisk(page);
289         }
290
291         /*
292          * This page will go to BIO.  Do we need to send this BIO off first?
293          */
294         if (bio && (*last_block_in_bio != blocks[0] - 1))
295                 bio = mpage_bio_submit(READ, bio);
296
297 alloc_new:
298         if (bio == NULL) {
299                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
300                                 min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
301                                 GFP_KERNEL);
302                 if (bio == NULL)
303                         goto confused;
304         }
305
306         length = first_hole << blkbits;
307         if (bio_add_page(bio, page, length, 0) < length) {
308                 bio = mpage_bio_submit(READ, bio);
309                 goto alloc_new;
310         }
311
312         if (buffer_boundary(map_bh) || (first_hole != blocks_per_page))
313                 bio = mpage_bio_submit(READ, bio);
314         else
315                 *last_block_in_bio = blocks[blocks_per_page - 1];
316 out:
317         return bio;
318
319 confused:
320         if (bio)
321                 bio = mpage_bio_submit(READ, bio);
322         if (!PageUptodate(page))
323                 block_read_full_page(page, get_block);
324         else
325                 unlock_page(page);
326         goto out;
327 }
328
329 /**
330  * mpage_readpages - populate an address space with some pages, and
331  *                       start reads against them.
332  *
333  * @mapping: the address_space
334  * @pages: The address of a list_head which contains the target pages.  These
335  *   pages have their ->index populated and are otherwise uninitialised.
336  *
337  *   The page at @pages->prev has the lowest file offset, and reads should be
338  *   issued in @pages->prev to @pages->next order.
339  *
340  * @nr_pages: The number of pages at *@pages
341  * @get_block: The filesystem's block mapper function.
342  *
343  * This function walks the pages and the blocks within each page, building and
344  * emitting large BIOs.
345  *
346  * If anything unusual happens, such as:
347  *
348  * - encountering a page which has buffers
349  * - encountering a page which has a non-hole after a hole
350  * - encountering a page with non-contiguous blocks
351  *
352  * then this code just gives up and calls the buffer_head-based read function.
353  * It does handle a page which has holes at the end - that is a common case:
354  * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
355  *
356  * BH_Boundary explanation:
357  *
358  * There is a problem.  The mpage read code assembles several pages, gets all
359  * their disk mappings, and then submits them all.  That's fine, but obtaining
360  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
361  *
362  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
363  * submitted in the following order:
364  *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
365  * because the indirect block has to be read to get the mappings of blocks
366  * 13,14,15,16.  Obviously, this impacts performance.
367  *
368  * So what we do it to allow the filesystem's get_block() function to set
369  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
370  * after this one will require I/O against a block which is probably close to
371  * this one.  So you should push what I/O you have currently accumulated.
372  *
373  * This all causes the disk requests to be issued in the correct order.
374  */
375 int
376 mpage_readpages(struct address_space *mapping, struct list_head *pages,
377                                 unsigned nr_pages, get_block_t get_block)
378 {
379         struct bio *bio = NULL;
380         unsigned page_idx;
381         sector_t last_block_in_bio = 0;
382         struct pagevec lru_pvec;
383         struct buffer_head map_bh;
384         unsigned long first_logical_block = 0;
385
386         clear_buffer_mapped(&map_bh);
387         pagevec_init(&lru_pvec, 0);
388         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
389                 struct page *page = list_entry(pages->prev, struct page, lru);
390
391                 prefetchw(&page->flags);
392                 list_del(&page->lru);
393                 if (!add_to_page_cache(page, mapping,
394                                         page->index, GFP_KERNEL)) {
395                         bio = do_mpage_readpage(bio, page,
396                                         nr_pages - page_idx,
397                                         &last_block_in_bio, &map_bh,
398                                         &first_logical_block,
399                                         get_block);
400                         if (!pagevec_add(&lru_pvec, page))
401                                 __pagevec_lru_add(&lru_pvec);
402                 } else {
403                         page_cache_release(page);
404                 }
405         }
406         pagevec_lru_add(&lru_pvec);
407         BUG_ON(!list_empty(pages));
408         if (bio)
409                 mpage_bio_submit(READ, bio);
410         return 0;
411 }
412 EXPORT_SYMBOL(mpage_readpages);
413
414 /*
415  * This isn't called much at all
416  */
417 int mpage_readpage(struct page *page, get_block_t get_block)
418 {
419         struct bio *bio = NULL;
420         sector_t last_block_in_bio = 0;
421         struct buffer_head map_bh;
422         unsigned long first_logical_block = 0;
423
424         clear_buffer_mapped(&map_bh);
425         bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
426                         &map_bh, &first_logical_block, get_block);
427         if (bio)
428                 mpage_bio_submit(READ, 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 struct mpage_data {
450         struct bio *bio;
451         sector_t last_block_in_bio;
452         get_block_t *get_block;
453         unsigned use_writepage;
454 };
455
456 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
457                              void *data)
458 {
459         struct mpage_data *mpd = data;
460         struct bio *bio = mpd->bio;
461         struct address_space *mapping = page->mapping;
462         struct inode *inode = page->mapping->host;
463         const unsigned blkbits = inode->i_blkbits;
464         unsigned long end_index;
465         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
466         sector_t last_block;
467         sector_t block_in_file;
468         sector_t blocks[MAX_BUF_PER_PAGE];
469         unsigned page_block;
470         unsigned first_unmapped = blocks_per_page;
471         struct block_device *bdev = NULL;
472         int boundary = 0;
473         sector_t boundary_block = 0;
474         struct block_device *boundary_bdev = NULL;
475         int length;
476         struct buffer_head map_bh;
477         loff_t i_size = i_size_read(inode);
478         int ret = 0;
479
480         if (page_has_buffers(page)) {
481                 struct buffer_head *head = page_buffers(page);
482                 struct buffer_head *bh = head;
483
484                 /* If they're all mapped and dirty, do it */
485                 page_block = 0;
486                 do {
487                         BUG_ON(buffer_locked(bh));
488                         if (!buffer_mapped(bh)) {
489                                 /*
490                                  * unmapped dirty buffers are created by
491                                  * __set_page_dirty_buffers -> mmapped data
492                                  */
493                                 if (buffer_dirty(bh))
494                                         goto confused;
495                                 if (first_unmapped == blocks_per_page)
496                                         first_unmapped = page_block;
497                                 continue;
498                         }
499
500                         if (first_unmapped != blocks_per_page)
501                                 goto confused;  /* hole -> non-hole */
502
503                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
504                                 goto confused;
505                         if (page_block) {
506                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
507                                         goto confused;
508                         }
509                         blocks[page_block++] = bh->b_blocknr;
510                         boundary = buffer_boundary(bh);
511                         if (boundary) {
512                                 boundary_block = bh->b_blocknr;
513                                 boundary_bdev = bh->b_bdev;
514                         }
515                         bdev = bh->b_bdev;
516                 } while ((bh = bh->b_this_page) != head);
517
518                 if (first_unmapped)
519                         goto page_is_mapped;
520
521                 /*
522                  * Page has buffers, but they are all unmapped. The page was
523                  * created by pagein or read over a hole which was handled by
524                  * block_read_full_page().  If this address_space is also
525                  * using mpage_readpages then this can rarely happen.
526                  */
527                 goto confused;
528         }
529
530         /*
531          * The page has no buffers: map it to disk
532          */
533         BUG_ON(!PageUptodate(page));
534         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
535         last_block = (i_size - 1) >> blkbits;
536         map_bh.b_page = page;
537         for (page_block = 0; page_block < blocks_per_page; ) {
538
539                 map_bh.b_state = 0;
540                 map_bh.b_size = 1 << blkbits;
541                 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
542                         goto confused;
543                 if (buffer_new(&map_bh))
544                         unmap_underlying_metadata(map_bh.b_bdev,
545                                                 map_bh.b_blocknr);
546                 if (buffer_boundary(&map_bh)) {
547                         boundary_block = map_bh.b_blocknr;
548                         boundary_bdev = map_bh.b_bdev;
549                 }
550                 if (page_block) {
551                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
552                                 goto confused;
553                 }
554                 blocks[page_block++] = map_bh.b_blocknr;
555                 boundary = buffer_boundary(&map_bh);
556                 bdev = map_bh.b_bdev;
557                 if (block_in_file == last_block)
558                         break;
559                 block_in_file++;
560         }
561         BUG_ON(page_block == 0);
562
563         first_unmapped = page_block;
564
565 page_is_mapped:
566         end_index = i_size >> PAGE_CACHE_SHIFT;
567         if (page->index >= end_index) {
568                 /*
569                  * The page straddles i_size.  It must be zeroed out on each
570                  * and every writepage invokation because it may be mmapped.
571                  * "A file is mapped in multiples of the page size.  For a file
572                  * that is not a multiple of the page size, the remaining memory
573                  * is zeroed when mapped, and writes to that region are not
574                  * written out to the file."
575                  */
576                 unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
577
578                 if (page->index > end_index || !offset)
579                         goto confused;
580                 zero_user_page(page, offset, PAGE_CACHE_SIZE - offset,
581                                 KM_USER0);
582         }
583
584         /*
585          * This page will go to BIO.  Do we need to send this BIO off first?
586          */
587         if (bio && mpd->last_block_in_bio != blocks[0] - 1)
588                 bio = mpage_bio_submit(WRITE, bio);
589
590 alloc_new:
591         if (bio == NULL) {
592                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
593                                 bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
594                 if (bio == NULL)
595                         goto confused;
596         }
597
598         /*
599          * Must try to add the page before marking the buffer clean or
600          * the confused fail path above (OOM) will be very confused when
601          * it finds all bh marked clean (i.e. it will not write anything)
602          */
603         length = first_unmapped << blkbits;
604         if (bio_add_page(bio, page, length, 0) < length) {
605                 bio = mpage_bio_submit(WRITE, bio);
606                 goto alloc_new;
607         }
608
609         /*
610          * OK, we have our BIO, so we can now mark the buffers clean.  Make
611          * sure to only clean buffers which we know we'll be writing.
612          */
613         if (page_has_buffers(page)) {
614                 struct buffer_head *head = page_buffers(page);
615                 struct buffer_head *bh = head;
616                 unsigned buffer_counter = 0;
617
618                 do {
619                         if (buffer_counter++ == first_unmapped)
620                                 break;
621                         clear_buffer_dirty(bh);
622                         bh = bh->b_this_page;
623                 } while (bh != head);
624
625                 /*
626                  * we cannot drop the bh if the page is not uptodate
627                  * or a concurrent readpage would fail to serialize with the bh
628                  * and it would read from disk before we reach the platter.
629                  */
630                 if (buffer_heads_over_limit && PageUptodate(page))
631                         try_to_free_buffers(page);
632         }
633
634         BUG_ON(PageWriteback(page));
635         set_page_writeback(page);
636         unlock_page(page);
637         if (boundary || (first_unmapped != blocks_per_page)) {
638                 bio = mpage_bio_submit(WRITE, bio);
639                 if (boundary_block) {
640                         write_boundary_block(boundary_bdev,
641                                         boundary_block, 1 << blkbits);
642                 }
643         } else {
644                 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
645         }
646         goto out;
647
648 confused:
649         if (bio)
650                 bio = mpage_bio_submit(WRITE, bio);
651
652         if (mpd->use_writepage) {
653                 ret = mapping->a_ops->writepage(page, wbc);
654         } else {
655                 ret = -EAGAIN;
656                 goto out;
657         }
658         /*
659          * The caller has a ref on the inode, so *mapping is stable
660          */
661         mapping_set_error(mapping, ret);
662 out:
663         mpd->bio = bio;
664         return ret;
665 }
666
667 /**
668  * mpage_writepages - walk the list of dirty pages of the given
669  * address space and writepage() all of them.
670  * 
671  * @mapping: address space structure to write
672  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
673  * @get_block: the filesystem's block mapper function.
674  *             If this is NULL then use a_ops->writepage.  Otherwise, go
675  *             direct-to-BIO.
676  *
677  * This is a library function, which implements the writepages()
678  * address_space_operation.
679  *
680  * If a page is already under I/O, generic_writepages() skips it, even
681  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
682  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
683  * and msync() need to guarantee that all the data which was dirty at the time
684  * the call was made get new I/O started against them.  If wbc->sync_mode is
685  * WB_SYNC_ALL then we were called for data integrity and we must wait for
686  * existing IO to complete.
687  */
688 int
689 mpage_writepages(struct address_space *mapping,
690                 struct writeback_control *wbc, get_block_t get_block)
691 {
692         int ret;
693
694         if (!get_block)
695                 ret = generic_writepages(mapping, wbc);
696         else {
697                 struct mpage_data mpd = {
698                         .bio = NULL,
699                         .last_block_in_bio = 0,
700                         .get_block = get_block,
701                         .use_writepage = 1,
702                 };
703
704                 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
705                 if (mpd.bio)
706                         mpage_bio_submit(WRITE, mpd.bio);
707         }
708         return ret;
709 }
710 EXPORT_SYMBOL(mpage_writepages);
711
712 int mpage_writepage(struct page *page, get_block_t get_block,
713         struct writeback_control *wbc)
714 {
715         struct mpage_data mpd = {
716                 .bio = NULL,
717                 .last_block_in_bio = 0,
718                 .get_block = get_block,
719                 .use_writepage = 0,
720         };
721         int ret = __mpage_writepage(page, wbc, &mpd);
722         if (mpd.bio)
723                 mpage_bio_submit(WRITE, mpd.bio);
724         return ret;
725 }
726 EXPORT_SYMBOL(mpage_writepage);