fs: convert core functions to zero_user_page
[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 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 static struct bio *
458 __mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
459         sector_t *last_block_in_bio, int *ret, struct writeback_control *wbc,
460         writepage_t writepage_fn)
461 {
462         struct address_space *mapping = page->mapping;
463         struct inode *inode = page->mapping->host;
464         const unsigned blkbits = inode->i_blkbits;
465         unsigned long end_index;
466         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
467         sector_t last_block;
468         sector_t block_in_file;
469         sector_t blocks[MAX_BUF_PER_PAGE];
470         unsigned page_block;
471         unsigned first_unmapped = blocks_per_page;
472         struct block_device *bdev = NULL;
473         int boundary = 0;
474         sector_t boundary_block = 0;
475         struct block_device *boundary_bdev = NULL;
476         int length;
477         struct buffer_head map_bh;
478         loff_t i_size = i_size_read(inode);
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 (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 && *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                 *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 (writepage_fn) {
653                 *ret = (*writepage_fn)(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         return bio;
664 }
665
666 /**
667  * mpage_writepages - walk the list of dirty pages of the given
668  * address space and writepage() all of them.
669  * 
670  * @mapping: address space structure to write
671  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
672  * @get_block: the filesystem's block mapper function.
673  *             If this is NULL then use a_ops->writepage.  Otherwise, go
674  *             direct-to-BIO.
675  *
676  * This is a library function, which implements the writepages()
677  * address_space_operation.
678  *
679  * If a page is already under I/O, generic_writepages() skips it, even
680  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
681  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
682  * and msync() need to guarantee that all the data which was dirty at the time
683  * the call was made get new I/O started against them.  If wbc->sync_mode is
684  * WB_SYNC_ALL then we were called for data integrity and we must wait for
685  * existing IO to complete.
686  *
687  * If you fix this you should check generic_writepages() also!
688  */
689 int
690 mpage_writepages(struct address_space *mapping,
691                 struct writeback_control *wbc, get_block_t get_block)
692 {
693         struct backing_dev_info *bdi = mapping->backing_dev_info;
694         struct bio *bio = NULL;
695         sector_t last_block_in_bio = 0;
696         int ret = 0;
697         int done = 0;
698         int (*writepage)(struct page *page, struct writeback_control *wbc);
699         struct pagevec pvec;
700         int nr_pages;
701         pgoff_t index;
702         pgoff_t end;            /* Inclusive */
703         int scanned = 0;
704         int range_whole = 0;
705
706         if (wbc->nonblocking && bdi_write_congested(bdi)) {
707                 wbc->encountered_congestion = 1;
708                 return 0;
709         }
710
711         writepage = NULL;
712         if (get_block == NULL)
713                 writepage = mapping->a_ops->writepage;
714
715         pagevec_init(&pvec, 0);
716         if (wbc->range_cyclic) {
717                 index = mapping->writeback_index; /* Start from prev offset */
718                 end = -1;
719         } else {
720                 index = wbc->range_start >> PAGE_CACHE_SHIFT;
721                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
722                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
723                         range_whole = 1;
724                 scanned = 1;
725         }
726 retry:
727         while (!done && (index <= end) &&
728                         (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
729                         PAGECACHE_TAG_DIRTY,
730                         min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
731                 unsigned i;
732
733                 scanned = 1;
734                 for (i = 0; i < nr_pages; i++) {
735                         struct page *page = pvec.pages[i];
736
737                         /*
738                          * At this point we hold neither mapping->tree_lock nor
739                          * lock on the page itself: the page may be truncated or
740                          * invalidated (changing page->mapping to NULL), or even
741                          * swizzled back from swapper_space to tmpfs file
742                          * mapping
743                          */
744
745                         lock_page(page);
746
747                         if (unlikely(page->mapping != mapping)) {
748                                 unlock_page(page);
749                                 continue;
750                         }
751
752                         if (!wbc->range_cyclic && page->index > end) {
753                                 done = 1;
754                                 unlock_page(page);
755                                 continue;
756                         }
757
758                         if (wbc->sync_mode != WB_SYNC_NONE)
759                                 wait_on_page_writeback(page);
760
761                         if (PageWriteback(page) ||
762                                         !clear_page_dirty_for_io(page)) {
763                                 unlock_page(page);
764                                 continue;
765                         }
766
767                         if (writepage) {
768                                 ret = (*writepage)(page, wbc);
769                                 mapping_set_error(mapping, ret);
770                         } else {
771                                 bio = __mpage_writepage(bio, page, get_block,
772                                                 &last_block_in_bio, &ret, wbc,
773                                                 page->mapping->a_ops->writepage);
774                         }
775                         if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE))
776                                 unlock_page(page);
777                         if (ret || (--(wbc->nr_to_write) <= 0))
778                                 done = 1;
779                         if (wbc->nonblocking && bdi_write_congested(bdi)) {
780                                 wbc->encountered_congestion = 1;
781                                 done = 1;
782                         }
783                 }
784                 pagevec_release(&pvec);
785                 cond_resched();
786         }
787         if (!scanned && !done) {
788                 /*
789                  * We hit the last page and there is more work to be done: wrap
790                  * back to the start of the file
791                  */
792                 scanned = 1;
793                 index = 0;
794                 goto retry;
795         }
796         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
797                 mapping->writeback_index = index;
798         if (bio)
799                 mpage_bio_submit(WRITE, bio);
800         return ret;
801 }
802 EXPORT_SYMBOL(mpage_writepages);
803
804 int mpage_writepage(struct page *page, get_block_t get_block,
805         struct writeback_control *wbc)
806 {
807         int ret = 0;
808         struct bio *bio;
809         sector_t last_block_in_bio = 0;
810
811         bio = __mpage_writepage(NULL, page, get_block,
812                         &last_block_in_bio, &ret, wbc, NULL);
813         if (bio)
814                 mpage_bio_submit(WRITE, bio);
815
816         return ret;
817 }
818 EXPORT_SYMBOL(mpage_writepage);