write support for preallocated blocks
[linux-2.6] / 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 int mpage_end_io_read(struct bio *bio, unsigned int bytes_done, 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         if (bio->bi_size)
48                 return 1;
49
50         do {
51                 struct page *page = bvec->bv_page;
52
53                 if (--bvec >= bio->bi_io_vec)
54                         prefetchw(&bvec->bv_page->flags);
55
56                 if (uptodate) {
57                         SetPageUptodate(page);
58                 } else {
59                         ClearPageUptodate(page);
60                         SetPageError(page);
61                 }
62                 unlock_page(page);
63         } while (bvec >= bio->bi_io_vec);
64         bio_put(bio);
65         return 0;
66 }
67
68 static int mpage_end_io_write(struct bio *bio, unsigned int bytes_done, int err)
69 {
70         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
71         struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
72
73         if (bio->bi_size)
74                 return 1;
75
76         do {
77                 struct page *page = bvec->bv_page;
78
79                 if (--bvec >= bio->bi_io_vec)
80                         prefetchw(&bvec->bv_page->flags);
81
82                 if (!uptodate){
83                         SetPageError(page);
84                         if (page->mapping)
85                                 set_bit(AS_EIO, &page->mapping->flags);
86                 }
87                 end_page_writeback(page);
88         } while (bvec >= bio->bi_io_vec);
89         bio_put(bio);
90         return 0;
91 }
92
93 static struct bio *mpage_bio_submit(int rw, struct bio *bio)
94 {
95         bio->bi_end_io = mpage_end_io_read;
96         if (rw == WRITE)
97                 bio->bi_end_io = mpage_end_io_write;
98         submit_bio(rw, bio);
99         return NULL;
100 }
101
102 static struct bio *
103 mpage_alloc(struct block_device *bdev,
104                 sector_t first_sector, int nr_vecs,
105                 gfp_t gfp_flags)
106 {
107         struct bio *bio;
108
109         bio = bio_alloc(gfp_flags, nr_vecs);
110
111         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
112                 while (!bio && (nr_vecs /= 2))
113                         bio = bio_alloc(gfp_flags, nr_vecs);
114         }
115
116         if (bio) {
117                 bio->bi_bdev = bdev;
118                 bio->bi_sector = first_sector;
119         }
120         return bio;
121 }
122
123 /*
124  * support function for mpage_readpages.  The fs supplied get_block might
125  * return an up to date buffer.  This is used to map that buffer into
126  * the page, which allows readpage to avoid triggering a duplicate call
127  * to get_block.
128  *
129  * The idea is to avoid adding buffers to pages that don't already have
130  * them.  So when the buffer is up to date and the page size == block size,
131  * this marks the page up to date instead of adding new buffers.
132  */
133 static void 
134 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block) 
135 {
136         struct inode *inode = page->mapping->host;
137         struct buffer_head *page_bh, *head;
138         int block = 0;
139
140         if (!page_has_buffers(page)) {
141                 /*
142                  * don't make any buffers if there is only one buffer on
143                  * the page and the page just needs to be set up to date
144                  */
145                 if (inode->i_blkbits == PAGE_CACHE_SHIFT && 
146                     buffer_uptodate(bh)) {
147                         SetPageUptodate(page);    
148                         return;
149                 }
150                 create_empty_buffers(page, 1 << inode->i_blkbits, 0);
151         }
152         head = page_buffers(page);
153         page_bh = head;
154         do {
155                 if (block == page_block) {
156                         page_bh->b_state = bh->b_state;
157                         page_bh->b_bdev = bh->b_bdev;
158                         page_bh->b_blocknr = bh->b_blocknr;
159                         break;
160                 }
161                 page_bh = page_bh->b_this_page;
162                 block++;
163         } while (page_bh != head);
164 }
165
166 /*
167  * This is the worker routine which does all the work of mapping the disk
168  * blocks and constructs largest possible bios, submits them for IO if the
169  * blocks are not contiguous on the disk.
170  *
171  * We pass a buffer_head back and forth and use its buffer_mapped() flag to
172  * represent the validity of its disk mapping and to decide when to do the next
173  * get_block() call.
174  */
175 static struct bio *
176 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
177                 sector_t *last_block_in_bio, struct buffer_head *map_bh,
178                 unsigned long *first_logical_block, get_block_t get_block)
179 {
180         struct inode *inode = page->mapping->host;
181         const unsigned blkbits = inode->i_blkbits;
182         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
183         const unsigned blocksize = 1 << blkbits;
184         sector_t block_in_file;
185         sector_t last_block;
186         sector_t last_block_in_file;
187         sector_t blocks[MAX_BUF_PER_PAGE];
188         unsigned page_block;
189         unsigned first_hole = blocks_per_page;
190         struct block_device *bdev = NULL;
191         int length;
192         int fully_mapped = 1;
193         unsigned nblocks;
194         unsigned relative_block;
195
196         if (page_has_buffers(page))
197                 goto confused;
198
199         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
200         last_block = block_in_file + nr_pages * blocks_per_page;
201         last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
202         if (last_block > last_block_in_file)
203                 last_block = last_block_in_file;
204         page_block = 0;
205
206         /*
207          * Map blocks using the result from the previous get_blocks call first.
208          */
209         nblocks = map_bh->b_size >> blkbits;
210         if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
211                         block_in_file < (*first_logical_block + nblocks)) {
212                 unsigned map_offset = block_in_file - *first_logical_block;
213                 unsigned last = nblocks - map_offset;
214
215                 for (relative_block = 0; ; relative_block++) {
216                         if (relative_block == last) {
217                                 clear_buffer_mapped(map_bh);
218                                 break;
219                         }
220                         if (page_block == blocks_per_page)
221                                 break;
222                         blocks[page_block] = map_bh->b_blocknr + map_offset +
223                                                 relative_block;
224                         page_block++;
225                         block_in_file++;
226                 }
227                 bdev = map_bh->b_bdev;
228         }
229
230         /*
231          * Then do more get_blocks calls until we are done with this page.
232          */
233         map_bh->b_page = page;
234         while (page_block < blocks_per_page) {
235                 map_bh->b_state = 0;
236                 map_bh->b_size = 0;
237
238                 if (block_in_file < last_block) {
239                         map_bh->b_size = (last_block-block_in_file) << blkbits;
240                         if (get_block(inode, block_in_file, map_bh, 0))
241                                 goto confused;
242                         *first_logical_block = block_in_file;
243                 }
244
245                 if (!buffer_mapped(map_bh)) {
246                         fully_mapped = 0;
247                         if (first_hole == blocks_per_page)
248                                 first_hole = page_block;
249                         page_block++;
250                         block_in_file++;
251                         clear_buffer_mapped(map_bh);
252                         continue;
253                 }
254
255                 /* some filesystems will copy data into the page during
256                  * the get_block call, in which case we don't want to
257                  * read it again.  map_buffer_to_page copies the data
258                  * we just collected from get_block into the page's buffers
259                  * so readpage doesn't have to repeat the get_block call
260                  */
261                 if (buffer_uptodate(map_bh)) {
262                         map_buffer_to_page(page, map_bh, page_block);
263                         goto confused;
264                 }
265         
266                 if (first_hole != blocks_per_page)
267                         goto confused;          /* hole -> non-hole */
268
269                 /* Contiguous blocks? */
270                 if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
271                         goto confused;
272                 nblocks = map_bh->b_size >> blkbits;
273                 for (relative_block = 0; ; relative_block++) {
274                         if (relative_block == nblocks) {
275                                 clear_buffer_mapped(map_bh);
276                                 break;
277                         } else if (page_block == blocks_per_page)
278                                 break;
279                         blocks[page_block] = map_bh->b_blocknr+relative_block;
280                         page_block++;
281                         block_in_file++;
282                 }
283                 bdev = map_bh->b_bdev;
284         }
285
286         if (first_hole != blocks_per_page) {
287                 zero_user_page(page, first_hole << blkbits,
288                                 PAGE_CACHE_SIZE - (first_hole << blkbits),
289                                 KM_USER0);
290                 if (first_hole == 0) {
291                         SetPageUptodate(page);
292                         unlock_page(page);
293                         goto out;
294                 }
295         } else if (fully_mapped) {
296                 SetPageMappedToDisk(page);
297         }
298
299         /*
300          * This page will go to BIO.  Do we need to send this BIO off first?
301          */
302         if (bio && (*last_block_in_bio != blocks[0] - 1))
303                 bio = mpage_bio_submit(READ, bio);
304
305 alloc_new:
306         if (bio == NULL) {
307                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
308                                 min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
309                                 GFP_KERNEL);
310                 if (bio == NULL)
311                         goto confused;
312         }
313
314         length = first_hole << blkbits;
315         if (bio_add_page(bio, page, length, 0) < length) {
316                 bio = mpage_bio_submit(READ, bio);
317                 goto alloc_new;
318         }
319
320         if (buffer_boundary(map_bh) || (first_hole != blocks_per_page))
321                 bio = mpage_bio_submit(READ, bio);
322         else
323                 *last_block_in_bio = blocks[blocks_per_page - 1];
324 out:
325         return bio;
326
327 confused:
328         if (bio)
329                 bio = mpage_bio_submit(READ, bio);
330         if (!PageUptodate(page))
331                 block_read_full_page(page, get_block);
332         else
333                 unlock_page(page);
334         goto out;
335 }
336
337 /**
338  * mpage_readpages - populate an address space with some pages, and
339  *                       start reads against them.
340  *
341  * @mapping: the address_space
342  * @pages: The address of a list_head which contains the target pages.  These
343  *   pages have their ->index populated and are otherwise uninitialised.
344  *
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  *
348  * @nr_pages: The number of pages at *@pages
349  * @get_block: The filesystem's block mapper function.
350  *
351  * This function walks the pages and the blocks within each page, building and
352  * emitting large BIOs.
353  *
354  * If anything unusual happens, such as:
355  *
356  * - encountering a page which has buffers
357  * - encountering a page which has a non-hole after a hole
358  * - encountering a page with non-contiguous blocks
359  *
360  * then this code just gives up and calls the buffer_head-based read function.
361  * It does handle a page which has holes at the end - that is a common case:
362  * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
363  *
364  * BH_Boundary explanation:
365  *
366  * There is a problem.  The mpage read code assembles several pages, gets all
367  * their disk mappings, and then submits them all.  That's fine, but obtaining
368  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
369  *
370  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
371  * submitted in the following order:
372  *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
373  * because the indirect block has to be read to get the mappings of blocks
374  * 13,14,15,16.  Obviously, this impacts performance.
375  *
376  * So what we do it to allow the filesystem's get_block() function to set
377  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
378  * after this one will require I/O against a block which is probably close to
379  * this one.  So you should push what I/O you have currently accumulated.
380  *
381  * This all causes the disk requests to be issued in the correct order.
382  */
383 int
384 mpage_readpages(struct address_space *mapping, struct list_head *pages,
385                                 unsigned nr_pages, get_block_t get_block)
386 {
387         struct bio *bio = NULL;
388         unsigned page_idx;
389         sector_t last_block_in_bio = 0;
390         struct pagevec lru_pvec;
391         struct buffer_head map_bh;
392         unsigned long first_logical_block = 0;
393
394         clear_buffer_mapped(&map_bh);
395         pagevec_init(&lru_pvec, 0);
396         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
397                 struct page *page = list_entry(pages->prev, struct page, lru);
398
399                 prefetchw(&page->flags);
400                 list_del(&page->lru);
401                 if (!add_to_page_cache(page, mapping,
402                                         page->index, GFP_KERNEL)) {
403                         bio = do_mpage_readpage(bio, page,
404                                         nr_pages - page_idx,
405                                         &last_block_in_bio, &map_bh,
406                                         &first_logical_block,
407                                         get_block);
408                         if (!pagevec_add(&lru_pvec, page))
409                                 __pagevec_lru_add(&lru_pvec);
410                 } else {
411                         page_cache_release(page);
412                 }
413         }
414         pagevec_lru_add(&lru_pvec);
415         BUG_ON(!list_empty(pages));
416         if (bio)
417                 mpage_bio_submit(READ, bio);
418         return 0;
419 }
420 EXPORT_SYMBOL(mpage_readpages);
421
422 /*
423  * This isn't called much at all
424  */
425 int mpage_readpage(struct page *page, get_block_t get_block)
426 {
427         struct bio *bio = NULL;
428         sector_t last_block_in_bio = 0;
429         struct buffer_head map_bh;
430         unsigned long first_logical_block = 0;
431
432         clear_buffer_mapped(&map_bh);
433         bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
434                         &map_bh, &first_logical_block, get_block);
435         if (bio)
436                 mpage_bio_submit(READ, bio);
437         return 0;
438 }
439 EXPORT_SYMBOL(mpage_readpage);
440
441 /*
442  * Writing is not so simple.
443  *
444  * If the page has buffers then they will be used for obtaining the disk
445  * mapping.  We only support pages which are fully mapped-and-dirty, with a
446  * special case for pages which are unmapped at the end: end-of-file.
447  *
448  * If the page has no buffers (preferred) then the page is mapped here.
449  *
450  * If all blocks are found to be contiguous then the page can go into the
451  * BIO.  Otherwise fall back to the mapping's writepage().
452  * 
453  * FIXME: This code wants an estimate of how many pages are still to be
454  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
455  * just allocate full-size (16-page) BIOs.
456  */
457 struct mpage_data {
458         struct bio *bio;
459         sector_t last_block_in_bio;
460         get_block_t *get_block;
461         unsigned use_writepage;
462 };
463
464 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
465                              void *data)
466 {
467         struct mpage_data *mpd = data;
468         struct bio *bio = mpd->bio;
469         struct address_space *mapping = page->mapping;
470         struct inode *inode = page->mapping->host;
471         const unsigned blkbits = inode->i_blkbits;
472         unsigned long end_index;
473         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
474         sector_t last_block;
475         sector_t block_in_file;
476         sector_t blocks[MAX_BUF_PER_PAGE];
477         unsigned page_block;
478         unsigned first_unmapped = blocks_per_page;
479         struct block_device *bdev = NULL;
480         int boundary = 0;
481         sector_t boundary_block = 0;
482         struct block_device *boundary_bdev = NULL;
483         int length;
484         struct buffer_head map_bh;
485         loff_t i_size = i_size_read(inode);
486         int ret = 0;
487
488         if (page_has_buffers(page)) {
489                 struct buffer_head *head = page_buffers(page);
490                 struct buffer_head *bh = head;
491
492                 /* If they're all mapped and dirty, do it */
493                 page_block = 0;
494                 do {
495                         BUG_ON(buffer_locked(bh));
496                         if (!buffer_mapped(bh)) {
497                                 /*
498                                  * unmapped dirty buffers are created by
499                                  * __set_page_dirty_buffers -> mmapped data
500                                  */
501                                 if (buffer_dirty(bh))
502                                         goto confused;
503                                 if (first_unmapped == blocks_per_page)
504                                         first_unmapped = page_block;
505                                 continue;
506                         }
507
508                         if (first_unmapped != blocks_per_page)
509                                 goto confused;  /* hole -> non-hole */
510
511                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
512                                 goto confused;
513                         if (page_block) {
514                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
515                                         goto confused;
516                         }
517                         blocks[page_block++] = bh->b_blocknr;
518                         boundary = buffer_boundary(bh);
519                         if (boundary) {
520                                 boundary_block = bh->b_blocknr;
521                                 boundary_bdev = bh->b_bdev;
522                         }
523                         bdev = bh->b_bdev;
524                 } while ((bh = bh->b_this_page) != head);
525
526                 if (first_unmapped)
527                         goto page_is_mapped;
528
529                 /*
530                  * Page has buffers, but they are all unmapped. The page was
531                  * created by pagein or read over a hole which was handled by
532                  * block_read_full_page().  If this address_space is also
533                  * using mpage_readpages then this can rarely happen.
534                  */
535                 goto confused;
536         }
537
538         /*
539          * The page has no buffers: map it to disk
540          */
541         BUG_ON(!PageUptodate(page));
542         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
543         last_block = (i_size - 1) >> blkbits;
544         map_bh.b_page = page;
545         for (page_block = 0; page_block < blocks_per_page; ) {
546
547                 map_bh.b_state = 0;
548                 map_bh.b_size = 1 << blkbits;
549                 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
550                         goto confused;
551                 if (buffer_new(&map_bh))
552                         unmap_underlying_metadata(map_bh.b_bdev,
553                                                 map_bh.b_blocknr);
554                 if (buffer_boundary(&map_bh)) {
555                         boundary_block = map_bh.b_blocknr;
556                         boundary_bdev = map_bh.b_bdev;
557                 }
558                 if (page_block) {
559                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
560                                 goto confused;
561                 }
562                 blocks[page_block++] = map_bh.b_blocknr;
563                 boundary = buffer_boundary(&map_bh);
564                 bdev = map_bh.b_bdev;
565                 if (block_in_file == last_block)
566                         break;
567                 block_in_file++;
568         }
569         BUG_ON(page_block == 0);
570
571         first_unmapped = page_block;
572
573 page_is_mapped:
574         end_index = i_size >> PAGE_CACHE_SHIFT;
575         if (page->index >= end_index) {
576                 /*
577                  * The page straddles i_size.  It must be zeroed out on each
578                  * and every writepage invokation because it may be mmapped.
579                  * "A file is mapped in multiples of the page size.  For a file
580                  * that is not a multiple of the page size, the remaining memory
581                  * is zeroed when mapped, and writes to that region are not
582                  * written out to the file."
583                  */
584                 unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
585
586                 if (page->index > end_index || !offset)
587                         goto confused;
588                 zero_user_page(page, offset, PAGE_CACHE_SIZE - offset,
589                                 KM_USER0);
590         }
591
592         /*
593          * This page will go to BIO.  Do we need to send this BIO off first?
594          */
595         if (bio && mpd->last_block_in_bio != blocks[0] - 1)
596                 bio = mpage_bio_submit(WRITE, bio);
597
598 alloc_new:
599         if (bio == NULL) {
600                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
601                                 bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
602                 if (bio == NULL)
603                         goto confused;
604         }
605
606         /*
607          * Must try to add the page before marking the buffer clean or
608          * the confused fail path above (OOM) will be very confused when
609          * it finds all bh marked clean (i.e. it will not write anything)
610          */
611         length = first_unmapped << blkbits;
612         if (bio_add_page(bio, page, length, 0) < length) {
613                 bio = mpage_bio_submit(WRITE, bio);
614                 goto alloc_new;
615         }
616
617         /*
618          * OK, we have our BIO, so we can now mark the buffers clean.  Make
619          * sure to only clean buffers which we know we'll be writing.
620          */
621         if (page_has_buffers(page)) {
622                 struct buffer_head *head = page_buffers(page);
623                 struct buffer_head *bh = head;
624                 unsigned buffer_counter = 0;
625
626                 do {
627                         if (buffer_counter++ == first_unmapped)
628                                 break;
629                         clear_buffer_dirty(bh);
630                         bh = bh->b_this_page;
631                 } while (bh != head);
632
633                 /*
634                  * we cannot drop the bh if the page is not uptodate
635                  * or a concurrent readpage would fail to serialize with the bh
636                  * and it would read from disk before we reach the platter.
637                  */
638                 if (buffer_heads_over_limit && PageUptodate(page))
639                         try_to_free_buffers(page);
640         }
641
642         BUG_ON(PageWriteback(page));
643         set_page_writeback(page);
644         unlock_page(page);
645         if (boundary || (first_unmapped != blocks_per_page)) {
646                 bio = mpage_bio_submit(WRITE, bio);
647                 if (boundary_block) {
648                         write_boundary_block(boundary_bdev,
649                                         boundary_block, 1 << blkbits);
650                 }
651         } else {
652                 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
653         }
654         goto out;
655
656 confused:
657         if (bio)
658                 bio = mpage_bio_submit(WRITE, bio);
659
660         if (mpd->use_writepage) {
661                 ret = mapping->a_ops->writepage(page, wbc);
662         } else {
663                 ret = -EAGAIN;
664                 goto out;
665         }
666         /*
667          * The caller has a ref on the inode, so *mapping is stable
668          */
669         mapping_set_error(mapping, ret);
670 out:
671         mpd->bio = bio;
672         return ret;
673 }
674
675 /**
676  * mpage_writepages - walk the list of dirty pages of the given
677  * address space and writepage() all of them.
678  * 
679  * @mapping: address space structure to write
680  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
681  * @get_block: the filesystem's block mapper function.
682  *             If this is NULL then use a_ops->writepage.  Otherwise, go
683  *             direct-to-BIO.
684  *
685  * This is a library function, which implements the writepages()
686  * address_space_operation.
687  *
688  * If a page is already under I/O, generic_writepages() skips it, even
689  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
690  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
691  * and msync() need to guarantee that all the data which was dirty at the time
692  * the call was made get new I/O started against them.  If wbc->sync_mode is
693  * WB_SYNC_ALL then we were called for data integrity and we must wait for
694  * existing IO to complete.
695  */
696 int
697 mpage_writepages(struct address_space *mapping,
698                 struct writeback_control *wbc, get_block_t get_block)
699 {
700         int ret;
701
702         if (!get_block)
703                 ret = generic_writepages(mapping, wbc);
704         else {
705                 struct mpage_data mpd = {
706                         .bio = NULL,
707                         .last_block_in_bio = 0,
708                         .get_block = get_block,
709                         .use_writepage = 1,
710                 };
711
712                 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
713                 if (mpd.bio)
714                         mpage_bio_submit(WRITE, mpd.bio);
715         }
716         return ret;
717 }
718 EXPORT_SYMBOL(mpage_writepages);
719
720 int mpage_writepage(struct page *page, get_block_t get_block,
721         struct writeback_control *wbc)
722 {
723         struct mpage_data mpd = {
724                 .bio = NULL,
725                 .last_block_in_bio = 0,
726                 .get_block = get_block,
727                 .use_writepage = 0,
728         };
729         int ret = __mpage_writepage(page, wbc, &mpd);
730         if (mpd.bio)
731                 mpage_bio_submit(WRITE, mpd.bio);
732         return ret;
733 }
734 EXPORT_SYMBOL(mpage_writepage);