xref: /openbmc/linux/fs/mpage.c (revision 14b9f27886ce69c5f11445d107dd020f6fc5754b)
1 /*
2  * fs/mpage.c
3  *
4  * Copyright (C) 2002, Linus Torvalds.
5  *
6  * Contains functions related to preparing and submitting BIOs which contain
7  * multiple pagecache pages.
8  *
9  * 15May2002	Andrew Morton
10  *		Initial version
11  * 27Jun2002	axboe@suse.de
12  *		use bio_add_page() to build bio's just the right size
13  */
14 
15 #include <linux/kernel.h>
16 #include <linux/module.h>
17 #include <linux/mm.h>
18 #include <linux/kdev_t.h>
19 #include <linux/gfp.h>
20 #include <linux/bio.h>
21 #include <linux/fs.h>
22 #include <linux/buffer_head.h>
23 #include <linux/blkdev.h>
24 #include <linux/highmem.h>
25 #include <linux/prefetch.h>
26 #include <linux/mpage.h>
27 #include <linux/writeback.h>
28 #include <linux/backing-dev.h>
29 #include <linux/pagevec.h>
30 #include <linux/cleancache.h>
31 
32 /*
33  * I/O completion handler for multipage BIOs.
34  *
35  * The mpage code never puts partial pages into a BIO (except for end-of-file).
36  * If a page does not map to a contiguous run of blocks then it simply falls
37  * back to block_read_full_page().
38  *
39  * Why is this?  If a page's completion depends on a number of different BIOs
40  * which can complete in any order (or at the same time) then determining the
41  * status of that page is hard.  See end_buffer_async_read() for the details.
42  * There is no point in duplicating all that complexity.
43  */
44 static void mpage_end_io(struct bio *bio, int err)
45 {
46 	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
47 	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
48 
49 	do {
50 		struct page *page = bvec->bv_page;
51 
52 		if (--bvec >= bio->bi_io_vec)
53 			prefetchw(&bvec->bv_page->flags);
54 		if (bio_data_dir(bio) == READ) {
55 			if (uptodate) {
56 				SetPageUptodate(page);
57 			} else {
58 				ClearPageUptodate(page);
59 				SetPageError(page);
60 			}
61 			unlock_page(page);
62 		} else { /* bio_data_dir(bio) == WRITE */
63 			if (!uptodate) {
64 				SetPageError(page);
65 				if (page->mapping)
66 					set_bit(AS_EIO, &page->mapping->flags);
67 			}
68 			end_page_writeback(page);
69 		}
70 	} while (bvec >= bio->bi_io_vec);
71 	bio_put(bio);
72 }
73 
74 static struct bio *mpage_bio_submit(int rw, struct bio *bio)
75 {
76 	bio->bi_end_io = mpage_end_io;
77 	submit_bio(rw, bio);
78 	return NULL;
79 }
80 
81 static struct bio *
82 mpage_alloc(struct block_device *bdev,
83 		sector_t first_sector, int nr_vecs,
84 		gfp_t gfp_flags)
85 {
86 	struct bio *bio;
87 
88 	bio = bio_alloc(gfp_flags, nr_vecs);
89 
90 	if (bio == NULL && (current->flags & PF_MEMALLOC)) {
91 		while (!bio && (nr_vecs /= 2))
92 			bio = bio_alloc(gfp_flags, nr_vecs);
93 	}
94 
95 	if (bio) {
96 		bio->bi_bdev = bdev;
97 		bio->bi_sector = first_sector;
98 	}
99 	return bio;
100 }
101 
102 /*
103  * support function for mpage_readpages.  The fs supplied get_block might
104  * return an up to date buffer.  This is used to map that buffer into
105  * the page, which allows readpage to avoid triggering a duplicate call
106  * to get_block.
107  *
108  * The idea is to avoid adding buffers to pages that don't already have
109  * them.  So when the buffer is up to date and the page size == block size,
110  * this marks the page up to date instead of adding new buffers.
111  */
112 static void
113 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
114 {
115 	struct inode *inode = page->mapping->host;
116 	struct buffer_head *page_bh, *head;
117 	int block = 0;
118 
119 	if (!page_has_buffers(page)) {
120 		/*
121 		 * don't make any buffers if there is only one buffer on
122 		 * the page and the page just needs to be set up to date
123 		 */
124 		if (inode->i_blkbits == PAGE_CACHE_SHIFT &&
125 		    buffer_uptodate(bh)) {
126 			SetPageUptodate(page);
127 			return;
128 		}
129 		create_empty_buffers(page, 1 << inode->i_blkbits, 0);
130 	}
131 	head = page_buffers(page);
132 	page_bh = head;
133 	do {
134 		if (block == page_block) {
135 			page_bh->b_state = bh->b_state;
136 			page_bh->b_bdev = bh->b_bdev;
137 			page_bh->b_blocknr = bh->b_blocknr;
138 			break;
139 		}
140 		page_bh = page_bh->b_this_page;
141 		block++;
142 	} while (page_bh != head);
143 }
144 
145 /*
146  * This is the worker routine which does all the work of mapping the disk
147  * blocks and constructs largest possible bios, submits them for IO if the
148  * blocks are not contiguous on the disk.
149  *
150  * We pass a buffer_head back and forth and use its buffer_mapped() flag to
151  * represent the validity of its disk mapping and to decide when to do the next
152  * get_block() call.
153  */
154 static struct bio *
155 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
156 		sector_t *last_block_in_bio, struct buffer_head *map_bh,
157 		unsigned long *first_logical_block, get_block_t get_block)
158 {
159 	struct inode *inode = page->mapping->host;
160 	const unsigned blkbits = inode->i_blkbits;
161 	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
162 	const unsigned blocksize = 1 << blkbits;
163 	sector_t block_in_file;
164 	sector_t last_block;
165 	sector_t last_block_in_file;
166 	sector_t blocks[MAX_BUF_PER_PAGE];
167 	unsigned page_block;
168 	unsigned first_hole = blocks_per_page;
169 	struct block_device *bdev = NULL;
170 	int length;
171 	int fully_mapped = 1;
172 	unsigned nblocks;
173 	unsigned relative_block;
174 
175 	if (page_has_buffers(page))
176 		goto confused;
177 
178 	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
179 	last_block = block_in_file + nr_pages * blocks_per_page;
180 	last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
181 	if (last_block > last_block_in_file)
182 		last_block = last_block_in_file;
183 	page_block = 0;
184 
185 	/*
186 	 * Map blocks using the result from the previous get_blocks call first.
187 	 */
188 	nblocks = map_bh->b_size >> blkbits;
189 	if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
190 			block_in_file < (*first_logical_block + nblocks)) {
191 		unsigned map_offset = block_in_file - *first_logical_block;
192 		unsigned last = nblocks - map_offset;
193 
194 		for (relative_block = 0; ; relative_block++) {
195 			if (relative_block == last) {
196 				clear_buffer_mapped(map_bh);
197 				break;
198 			}
199 			if (page_block == blocks_per_page)
200 				break;
201 			blocks[page_block] = map_bh->b_blocknr + map_offset +
202 						relative_block;
203 			page_block++;
204 			block_in_file++;
205 		}
206 		bdev = map_bh->b_bdev;
207 	}
208 
209 	/*
210 	 * Then do more get_blocks calls until we are done with this page.
211 	 */
212 	map_bh->b_page = page;
213 	while (page_block < blocks_per_page) {
214 		map_bh->b_state = 0;
215 		map_bh->b_size = 0;
216 
217 		if (block_in_file < last_block) {
218 			map_bh->b_size = (last_block-block_in_file) << blkbits;
219 			if (get_block(inode, block_in_file, map_bh, 0))
220 				goto confused;
221 			*first_logical_block = block_in_file;
222 		}
223 
224 		if (!buffer_mapped(map_bh)) {
225 			fully_mapped = 0;
226 			if (first_hole == blocks_per_page)
227 				first_hole = page_block;
228 			page_block++;
229 			block_in_file++;
230 			continue;
231 		}
232 
233 		/* some filesystems will copy data into the page during
234 		 * the get_block call, in which case we don't want to
235 		 * read it again.  map_buffer_to_page copies the data
236 		 * we just collected from get_block into the page's buffers
237 		 * so readpage doesn't have to repeat the get_block call
238 		 */
239 		if (buffer_uptodate(map_bh)) {
240 			map_buffer_to_page(page, map_bh, page_block);
241 			goto confused;
242 		}
243 
244 		if (first_hole != blocks_per_page)
245 			goto confused;		/* hole -> non-hole */
246 
247 		/* Contiguous blocks? */
248 		if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
249 			goto confused;
250 		nblocks = map_bh->b_size >> blkbits;
251 		for (relative_block = 0; ; relative_block++) {
252 			if (relative_block == nblocks) {
253 				clear_buffer_mapped(map_bh);
254 				break;
255 			} else if (page_block == blocks_per_page)
256 				break;
257 			blocks[page_block] = map_bh->b_blocknr+relative_block;
258 			page_block++;
259 			block_in_file++;
260 		}
261 		bdev = map_bh->b_bdev;
262 	}
263 
264 	if (first_hole != blocks_per_page) {
265 		zero_user_segment(page, first_hole << blkbits, PAGE_CACHE_SIZE);
266 		if (first_hole == 0) {
267 			SetPageUptodate(page);
268 			unlock_page(page);
269 			goto out;
270 		}
271 	} else if (fully_mapped) {
272 		SetPageMappedToDisk(page);
273 	}
274 
275 	if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
276 	    cleancache_get_page(page) == 0) {
277 		SetPageUptodate(page);
278 		goto confused;
279 	}
280 
281 	/*
282 	 * This page will go to BIO.  Do we need to send this BIO off first?
283 	 */
284 	if (bio && (*last_block_in_bio != blocks[0] - 1))
285 		bio = mpage_bio_submit(READ, bio);
286 
287 alloc_new:
288 	if (bio == NULL) {
289 		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
290 			  	min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
291 				GFP_KERNEL);
292 		if (bio == NULL)
293 			goto confused;
294 	}
295 
296 	length = first_hole << blkbits;
297 	if (bio_add_page(bio, page, length, 0) < length) {
298 		bio = mpage_bio_submit(READ, bio);
299 		goto alloc_new;
300 	}
301 
302 	relative_block = block_in_file - *first_logical_block;
303 	nblocks = map_bh->b_size >> blkbits;
304 	if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
305 	    (first_hole != blocks_per_page))
306 		bio = mpage_bio_submit(READ, bio);
307 	else
308 		*last_block_in_bio = blocks[blocks_per_page - 1];
309 out:
310 	return bio;
311 
312 confused:
313 	if (bio)
314 		bio = mpage_bio_submit(READ, bio);
315 	if (!PageUptodate(page))
316 	        block_read_full_page(page, get_block);
317 	else
318 		unlock_page(page);
319 	goto out;
320 }
321 
322 /**
323  * mpage_readpages - populate an address space with some pages & start reads against them
324  * @mapping: the address_space
325  * @pages: The address of a list_head which contains the target pages.  These
326  *   pages have their ->index populated and are otherwise uninitialised.
327  *   The page at @pages->prev has the lowest file offset, and reads should be
328  *   issued in @pages->prev to @pages->next order.
329  * @nr_pages: The number of pages at *@pages
330  * @get_block: The filesystem's block mapper function.
331  *
332  * This function walks the pages and the blocks within each page, building and
333  * emitting large BIOs.
334  *
335  * If anything unusual happens, such as:
336  *
337  * - encountering a page which has buffers
338  * - encountering a page which has a non-hole after a hole
339  * - encountering a page with non-contiguous blocks
340  *
341  * then this code just gives up and calls the buffer_head-based read function.
342  * It does handle a page which has holes at the end - that is a common case:
343  * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
344  *
345  * BH_Boundary explanation:
346  *
347  * There is a problem.  The mpage read code assembles several pages, gets all
348  * their disk mappings, and then submits them all.  That's fine, but obtaining
349  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
350  *
351  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
352  * submitted in the following order:
353  * 	12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
354  *
355  * because the indirect block has to be read to get the mappings of blocks
356  * 13,14,15,16.  Obviously, this impacts performance.
357  *
358  * So what we do it to allow the filesystem's get_block() function to set
359  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
360  * after this one will require I/O against a block which is probably close to
361  * this one.  So you should push what I/O you have currently accumulated.
362  *
363  * This all causes the disk requests to be issued in the correct order.
364  */
365 int
366 mpage_readpages(struct address_space *mapping, struct list_head *pages,
367 				unsigned nr_pages, get_block_t get_block)
368 {
369 	struct bio *bio = NULL;
370 	unsigned page_idx;
371 	sector_t last_block_in_bio = 0;
372 	struct buffer_head map_bh;
373 	unsigned long first_logical_block = 0;
374 	struct blk_plug plug;
375 
376 	blk_start_plug(&plug);
377 
378 	map_bh.b_state = 0;
379 	map_bh.b_size = 0;
380 	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
381 		struct page *page = list_entry(pages->prev, struct page, lru);
382 
383 		prefetchw(&page->flags);
384 		list_del(&page->lru);
385 		if (!add_to_page_cache_lru(page, mapping,
386 					page->index, GFP_KERNEL)) {
387 			bio = do_mpage_readpage(bio, page,
388 					nr_pages - page_idx,
389 					&last_block_in_bio, &map_bh,
390 					&first_logical_block,
391 					get_block);
392 		}
393 		page_cache_release(page);
394 	}
395 	BUG_ON(!list_empty(pages));
396 	if (bio)
397 		mpage_bio_submit(READ, bio);
398 	blk_finish_plug(&plug);
399 	return 0;
400 }
401 EXPORT_SYMBOL(mpage_readpages);
402 
403 /*
404  * This isn't called much at all
405  */
406 int mpage_readpage(struct page *page, get_block_t get_block)
407 {
408 	struct bio *bio = NULL;
409 	sector_t last_block_in_bio = 0;
410 	struct buffer_head map_bh;
411 	unsigned long first_logical_block = 0;
412 
413 	map_bh.b_state = 0;
414 	map_bh.b_size = 0;
415 	bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
416 			&map_bh, &first_logical_block, get_block);
417 	if (bio)
418 		mpage_bio_submit(READ, bio);
419 	return 0;
420 }
421 EXPORT_SYMBOL(mpage_readpage);
422 
423 /*
424  * Writing is not so simple.
425  *
426  * If the page has buffers then they will be used for obtaining the disk
427  * mapping.  We only support pages which are fully mapped-and-dirty, with a
428  * special case for pages which are unmapped at the end: end-of-file.
429  *
430  * If the page has no buffers (preferred) then the page is mapped here.
431  *
432  * If all blocks are found to be contiguous then the page can go into the
433  * BIO.  Otherwise fall back to the mapping's writepage().
434  *
435  * FIXME: This code wants an estimate of how many pages are still to be
436  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
437  * just allocate full-size (16-page) BIOs.
438  */
439 
440 struct mpage_data {
441 	struct bio *bio;
442 	sector_t last_block_in_bio;
443 	get_block_t *get_block;
444 	unsigned use_writepage;
445 };
446 
447 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
448 		      void *data)
449 {
450 	struct mpage_data *mpd = data;
451 	struct bio *bio = mpd->bio;
452 	struct address_space *mapping = page->mapping;
453 	struct inode *inode = page->mapping->host;
454 	const unsigned blkbits = inode->i_blkbits;
455 	unsigned long end_index;
456 	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
457 	sector_t last_block;
458 	sector_t block_in_file;
459 	sector_t blocks[MAX_BUF_PER_PAGE];
460 	unsigned page_block;
461 	unsigned first_unmapped = blocks_per_page;
462 	struct block_device *bdev = NULL;
463 	int boundary = 0;
464 	sector_t boundary_block = 0;
465 	struct block_device *boundary_bdev = NULL;
466 	int length;
467 	struct buffer_head map_bh;
468 	loff_t i_size = i_size_read(inode);
469 	int ret = 0;
470 
471 	if (page_has_buffers(page)) {
472 		struct buffer_head *head = page_buffers(page);
473 		struct buffer_head *bh = head;
474 
475 		/* If they're all mapped and dirty, do it */
476 		page_block = 0;
477 		do {
478 			BUG_ON(buffer_locked(bh));
479 			if (!buffer_mapped(bh)) {
480 				/*
481 				 * unmapped dirty buffers are created by
482 				 * __set_page_dirty_buffers -> mmapped data
483 				 */
484 				if (buffer_dirty(bh))
485 					goto confused;
486 				if (first_unmapped == blocks_per_page)
487 					first_unmapped = page_block;
488 				continue;
489 			}
490 
491 			if (first_unmapped != blocks_per_page)
492 				goto confused;	/* hole -> non-hole */
493 
494 			if (!buffer_dirty(bh) || !buffer_uptodate(bh))
495 				goto confused;
496 			if (page_block) {
497 				if (bh->b_blocknr != blocks[page_block-1] + 1)
498 					goto confused;
499 			}
500 			blocks[page_block++] = bh->b_blocknr;
501 			boundary = buffer_boundary(bh);
502 			if (boundary) {
503 				boundary_block = bh->b_blocknr;
504 				boundary_bdev = bh->b_bdev;
505 			}
506 			bdev = bh->b_bdev;
507 		} while ((bh = bh->b_this_page) != head);
508 
509 		if (first_unmapped)
510 			goto page_is_mapped;
511 
512 		/*
513 		 * Page has buffers, but they are all unmapped. The page was
514 		 * created by pagein or read over a hole which was handled by
515 		 * block_read_full_page().  If this address_space is also
516 		 * using mpage_readpages then this can rarely happen.
517 		 */
518 		goto confused;
519 	}
520 
521 	/*
522 	 * The page has no buffers: map it to disk
523 	 */
524 	BUG_ON(!PageUptodate(page));
525 	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
526 	last_block = (i_size - 1) >> blkbits;
527 	map_bh.b_page = page;
528 	for (page_block = 0; page_block < blocks_per_page; ) {
529 
530 		map_bh.b_state = 0;
531 		map_bh.b_size = 1 << blkbits;
532 		if (mpd->get_block(inode, block_in_file, &map_bh, 1))
533 			goto confused;
534 		if (buffer_new(&map_bh))
535 			unmap_underlying_metadata(map_bh.b_bdev,
536 						map_bh.b_blocknr);
537 		if (buffer_boundary(&map_bh)) {
538 			boundary_block = map_bh.b_blocknr;
539 			boundary_bdev = map_bh.b_bdev;
540 		}
541 		if (page_block) {
542 			if (map_bh.b_blocknr != blocks[page_block-1] + 1)
543 				goto confused;
544 		}
545 		blocks[page_block++] = map_bh.b_blocknr;
546 		boundary = buffer_boundary(&map_bh);
547 		bdev = map_bh.b_bdev;
548 		if (block_in_file == last_block)
549 			break;
550 		block_in_file++;
551 	}
552 	BUG_ON(page_block == 0);
553 
554 	first_unmapped = page_block;
555 
556 page_is_mapped:
557 	end_index = i_size >> PAGE_CACHE_SHIFT;
558 	if (page->index >= end_index) {
559 		/*
560 		 * The page straddles i_size.  It must be zeroed out on each
561 		 * and every writepage invocation because it may be mmapped.
562 		 * "A file is mapped in multiples of the page size.  For a file
563 		 * that is not a multiple of the page size, the remaining memory
564 		 * is zeroed when mapped, and writes to that region are not
565 		 * written out to the file."
566 		 */
567 		unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
568 
569 		if (page->index > end_index || !offset)
570 			goto confused;
571 		zero_user_segment(page, offset, PAGE_CACHE_SIZE);
572 	}
573 
574 	/*
575 	 * This page will go to BIO.  Do we need to send this BIO off first?
576 	 */
577 	if (bio && mpd->last_block_in_bio != blocks[0] - 1)
578 		bio = mpage_bio_submit(WRITE, bio);
579 
580 alloc_new:
581 	if (bio == NULL) {
582 		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
583 				bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
584 		if (bio == NULL)
585 			goto confused;
586 	}
587 
588 	/*
589 	 * Must try to add the page before marking the buffer clean or
590 	 * the confused fail path above (OOM) will be very confused when
591 	 * it finds all bh marked clean (i.e. it will not write anything)
592 	 */
593 	length = first_unmapped << blkbits;
594 	if (bio_add_page(bio, page, length, 0) < length) {
595 		bio = mpage_bio_submit(WRITE, bio);
596 		goto alloc_new;
597 	}
598 
599 	/*
600 	 * OK, we have our BIO, so we can now mark the buffers clean.  Make
601 	 * sure to only clean buffers which we know we'll be writing.
602 	 */
603 	if (page_has_buffers(page)) {
604 		struct buffer_head *head = page_buffers(page);
605 		struct buffer_head *bh = head;
606 		unsigned buffer_counter = 0;
607 
608 		do {
609 			if (buffer_counter++ == first_unmapped)
610 				break;
611 			clear_buffer_dirty(bh);
612 			bh = bh->b_this_page;
613 		} while (bh != head);
614 
615 		/*
616 		 * we cannot drop the bh if the page is not uptodate
617 		 * or a concurrent readpage would fail to serialize with the bh
618 		 * and it would read from disk before we reach the platter.
619 		 */
620 		if (buffer_heads_over_limit && PageUptodate(page))
621 			try_to_free_buffers(page);
622 	}
623 
624 	BUG_ON(PageWriteback(page));
625 	set_page_writeback(page);
626 	unlock_page(page);
627 	if (boundary || (first_unmapped != blocks_per_page)) {
628 		bio = mpage_bio_submit(WRITE, bio);
629 		if (boundary_block) {
630 			write_boundary_block(boundary_bdev,
631 					boundary_block, 1 << blkbits);
632 		}
633 	} else {
634 		mpd->last_block_in_bio = blocks[blocks_per_page - 1];
635 	}
636 	goto out;
637 
638 confused:
639 	if (bio)
640 		bio = mpage_bio_submit(WRITE, bio);
641 
642 	if (mpd->use_writepage) {
643 		ret = mapping->a_ops->writepage(page, wbc);
644 	} else {
645 		ret = -EAGAIN;
646 		goto out;
647 	}
648 	/*
649 	 * The caller has a ref on the inode, so *mapping is stable
650 	 */
651 	mapping_set_error(mapping, ret);
652 out:
653 	mpd->bio = bio;
654 	return ret;
655 }
656 
657 /**
658  * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
659  * @mapping: address space structure to write
660  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
661  * @get_block: the filesystem's block mapper function.
662  *             If this is NULL then use a_ops->writepage.  Otherwise, go
663  *             direct-to-BIO.
664  *
665  * This is a library function, which implements the writepages()
666  * address_space_operation.
667  *
668  * If a page is already under I/O, generic_writepages() skips it, even
669  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
670  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
671  * and msync() need to guarantee that all the data which was dirty at the time
672  * the call was made get new I/O started against them.  If wbc->sync_mode is
673  * WB_SYNC_ALL then we were called for data integrity and we must wait for
674  * existing IO to complete.
675  */
676 int
677 mpage_writepages(struct address_space *mapping,
678 		struct writeback_control *wbc, get_block_t get_block)
679 {
680 	struct blk_plug plug;
681 	int ret;
682 
683 	blk_start_plug(&plug);
684 
685 	if (!get_block)
686 		ret = generic_writepages(mapping, wbc);
687 	else {
688 		struct mpage_data mpd = {
689 			.bio = NULL,
690 			.last_block_in_bio = 0,
691 			.get_block = get_block,
692 			.use_writepage = 1,
693 		};
694 
695 		ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
696 		if (mpd.bio)
697 			mpage_bio_submit(WRITE, mpd.bio);
698 	}
699 	blk_finish_plug(&plug);
700 	return ret;
701 }
702 EXPORT_SYMBOL(mpage_writepages);
703 
704 int mpage_writepage(struct page *page, get_block_t get_block,
705 	struct writeback_control *wbc)
706 {
707 	struct mpage_data mpd = {
708 		.bio = NULL,
709 		.last_block_in_bio = 0,
710 		.get_block = get_block,
711 		.use_writepage = 0,
712 	};
713 	int ret = __mpage_writepage(page, wbc, &mpd);
714 	if (mpd.bio)
715 		mpage_bio_submit(WRITE, mpd.bio);
716 	return ret;
717 }
718 EXPORT_SYMBOL(mpage_writepage);
719