xref: /openbmc/linux/fs/mpage.c (revision b593bce5)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * fs/mpage.c
4  *
5  * Copyright (C) 2002, Linus Torvalds.
6  *
7  * Contains functions related to preparing and submitting BIOs which contain
8  * multiple pagecache pages.
9  *
10  * 15May2002	Andrew Morton
11  *		Initial version
12  * 27Jun2002	axboe@suse.de
13  *		use bio_add_page() to build bio's just the right size
14  */
15 
16 #include <linux/kernel.h>
17 #include <linux/export.h>
18 #include <linux/mm.h>
19 #include <linux/kdev_t.h>
20 #include <linux/gfp.h>
21 #include <linux/bio.h>
22 #include <linux/fs.h>
23 #include <linux/buffer_head.h>
24 #include <linux/blkdev.h>
25 #include <linux/highmem.h>
26 #include <linux/prefetch.h>
27 #include <linux/mpage.h>
28 #include <linux/mm_inline.h>
29 #include <linux/writeback.h>
30 #include <linux/backing-dev.h>
31 #include <linux/pagevec.h>
32 #include <linux/cleancache.h>
33 #include "internal.h"
34 
35 /*
36  * I/O completion handler for multipage BIOs.
37  *
38  * The mpage code never puts partial pages into a BIO (except for end-of-file).
39  * If a page does not map to a contiguous run of blocks then it simply falls
40  * back to block_read_full_page().
41  *
42  * Why is this?  If a page's completion depends on a number of different BIOs
43  * which can complete in any order (or at the same time) then determining the
44  * status of that page is hard.  See end_buffer_async_read() for the details.
45  * There is no point in duplicating all that complexity.
46  */
47 static void mpage_end_io(struct bio *bio)
48 {
49 	struct bio_vec *bv;
50 	struct bvec_iter_all iter_all;
51 
52 	bio_for_each_segment_all(bv, bio, iter_all) {
53 		struct page *page = bv->bv_page;
54 		page_endio(page, bio_op(bio),
55 			   blk_status_to_errno(bio->bi_status));
56 	}
57 
58 	bio_put(bio);
59 }
60 
61 static struct bio *mpage_bio_submit(int op, int op_flags, struct bio *bio)
62 {
63 	bio->bi_end_io = mpage_end_io;
64 	bio_set_op_attrs(bio, op, op_flags);
65 	guard_bio_eod(op, bio);
66 	submit_bio(bio);
67 	return NULL;
68 }
69 
70 static struct bio *
71 mpage_alloc(struct block_device *bdev,
72 		sector_t first_sector, int nr_vecs,
73 		gfp_t gfp_flags)
74 {
75 	struct bio *bio;
76 
77 	/* Restrict the given (page cache) mask for slab allocations */
78 	gfp_flags &= GFP_KERNEL;
79 	bio = bio_alloc(gfp_flags, nr_vecs);
80 
81 	if (bio == NULL && (current->flags & PF_MEMALLOC)) {
82 		while (!bio && (nr_vecs /= 2))
83 			bio = bio_alloc(gfp_flags, nr_vecs);
84 	}
85 
86 	if (bio) {
87 		bio_set_dev(bio, bdev);
88 		bio->bi_iter.bi_sector = first_sector;
89 	}
90 	return bio;
91 }
92 
93 /*
94  * support function for mpage_readpages.  The fs supplied get_block might
95  * return an up to date buffer.  This is used to map that buffer into
96  * the page, which allows readpage to avoid triggering a duplicate call
97  * to get_block.
98  *
99  * The idea is to avoid adding buffers to pages that don't already have
100  * them.  So when the buffer is up to date and the page size == block size,
101  * this marks the page up to date instead of adding new buffers.
102  */
103 static void
104 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
105 {
106 	struct inode *inode = page->mapping->host;
107 	struct buffer_head *page_bh, *head;
108 	int block = 0;
109 
110 	if (!page_has_buffers(page)) {
111 		/*
112 		 * don't make any buffers if there is only one buffer on
113 		 * the page and the page just needs to be set up to date
114 		 */
115 		if (inode->i_blkbits == PAGE_SHIFT &&
116 		    buffer_uptodate(bh)) {
117 			SetPageUptodate(page);
118 			return;
119 		}
120 		create_empty_buffers(page, i_blocksize(inode), 0);
121 	}
122 	head = page_buffers(page);
123 	page_bh = head;
124 	do {
125 		if (block == page_block) {
126 			page_bh->b_state = bh->b_state;
127 			page_bh->b_bdev = bh->b_bdev;
128 			page_bh->b_blocknr = bh->b_blocknr;
129 			break;
130 		}
131 		page_bh = page_bh->b_this_page;
132 		block++;
133 	} while (page_bh != head);
134 }
135 
136 struct mpage_readpage_args {
137 	struct bio *bio;
138 	struct page *page;
139 	unsigned int nr_pages;
140 	bool is_readahead;
141 	sector_t last_block_in_bio;
142 	struct buffer_head map_bh;
143 	unsigned long first_logical_block;
144 	get_block_t *get_block;
145 };
146 
147 /*
148  * This is the worker routine which does all the work of mapping the disk
149  * blocks and constructs largest possible bios, submits them for IO if the
150  * blocks are not contiguous on the disk.
151  *
152  * We pass a buffer_head back and forth and use its buffer_mapped() flag to
153  * represent the validity of its disk mapping and to decide when to do the next
154  * get_block() call.
155  */
156 static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
157 {
158 	struct page *page = args->page;
159 	struct inode *inode = page->mapping->host;
160 	const unsigned blkbits = inode->i_blkbits;
161 	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
162 	const unsigned blocksize = 1 << blkbits;
163 	struct buffer_head *map_bh = &args->map_bh;
164 	sector_t block_in_file;
165 	sector_t last_block;
166 	sector_t last_block_in_file;
167 	sector_t blocks[MAX_BUF_PER_PAGE];
168 	unsigned page_block;
169 	unsigned first_hole = blocks_per_page;
170 	struct block_device *bdev = NULL;
171 	int length;
172 	int fully_mapped = 1;
173 	int op_flags;
174 	unsigned nblocks;
175 	unsigned relative_block;
176 	gfp_t gfp;
177 
178 	if (args->is_readahead) {
179 		op_flags = REQ_RAHEAD;
180 		gfp = readahead_gfp_mask(page->mapping);
181 	} else {
182 		op_flags = 0;
183 		gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
184 	}
185 
186 	if (page_has_buffers(page))
187 		goto confused;
188 
189 	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
190 	last_block = block_in_file + args->nr_pages * blocks_per_page;
191 	last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
192 	if (last_block > last_block_in_file)
193 		last_block = last_block_in_file;
194 	page_block = 0;
195 
196 	/*
197 	 * Map blocks using the result from the previous get_blocks call first.
198 	 */
199 	nblocks = map_bh->b_size >> blkbits;
200 	if (buffer_mapped(map_bh) &&
201 			block_in_file > args->first_logical_block &&
202 			block_in_file < (args->first_logical_block + nblocks)) {
203 		unsigned map_offset = block_in_file - args->first_logical_block;
204 		unsigned last = nblocks - map_offset;
205 
206 		for (relative_block = 0; ; relative_block++) {
207 			if (relative_block == last) {
208 				clear_buffer_mapped(map_bh);
209 				break;
210 			}
211 			if (page_block == blocks_per_page)
212 				break;
213 			blocks[page_block] = map_bh->b_blocknr + map_offset +
214 						relative_block;
215 			page_block++;
216 			block_in_file++;
217 		}
218 		bdev = map_bh->b_bdev;
219 	}
220 
221 	/*
222 	 * Then do more get_blocks calls until we are done with this page.
223 	 */
224 	map_bh->b_page = page;
225 	while (page_block < blocks_per_page) {
226 		map_bh->b_state = 0;
227 		map_bh->b_size = 0;
228 
229 		if (block_in_file < last_block) {
230 			map_bh->b_size = (last_block-block_in_file) << blkbits;
231 			if (args->get_block(inode, block_in_file, map_bh, 0))
232 				goto confused;
233 			args->first_logical_block = block_in_file;
234 		}
235 
236 		if (!buffer_mapped(map_bh)) {
237 			fully_mapped = 0;
238 			if (first_hole == blocks_per_page)
239 				first_hole = page_block;
240 			page_block++;
241 			block_in_file++;
242 			continue;
243 		}
244 
245 		/* some filesystems will copy data into the page during
246 		 * the get_block call, in which case we don't want to
247 		 * read it again.  map_buffer_to_page copies the data
248 		 * we just collected from get_block into the page's buffers
249 		 * so readpage doesn't have to repeat the get_block call
250 		 */
251 		if (buffer_uptodate(map_bh)) {
252 			map_buffer_to_page(page, map_bh, page_block);
253 			goto confused;
254 		}
255 
256 		if (first_hole != blocks_per_page)
257 			goto confused;		/* hole -> non-hole */
258 
259 		/* Contiguous blocks? */
260 		if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
261 			goto confused;
262 		nblocks = map_bh->b_size >> blkbits;
263 		for (relative_block = 0; ; relative_block++) {
264 			if (relative_block == nblocks) {
265 				clear_buffer_mapped(map_bh);
266 				break;
267 			} else if (page_block == blocks_per_page)
268 				break;
269 			blocks[page_block] = map_bh->b_blocknr+relative_block;
270 			page_block++;
271 			block_in_file++;
272 		}
273 		bdev = map_bh->b_bdev;
274 	}
275 
276 	if (first_hole != blocks_per_page) {
277 		zero_user_segment(page, first_hole << blkbits, PAGE_SIZE);
278 		if (first_hole == 0) {
279 			SetPageUptodate(page);
280 			unlock_page(page);
281 			goto out;
282 		}
283 	} else if (fully_mapped) {
284 		SetPageMappedToDisk(page);
285 	}
286 
287 	if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
288 	    cleancache_get_page(page) == 0) {
289 		SetPageUptodate(page);
290 		goto confused;
291 	}
292 
293 	/*
294 	 * This page will go to BIO.  Do we need to send this BIO off first?
295 	 */
296 	if (args->bio && (args->last_block_in_bio != blocks[0] - 1))
297 		args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
298 
299 alloc_new:
300 	if (args->bio == NULL) {
301 		if (first_hole == blocks_per_page) {
302 			if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
303 								page))
304 				goto out;
305 		}
306 		args->bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
307 					min_t(int, args->nr_pages,
308 					      BIO_MAX_PAGES),
309 					gfp);
310 		if (args->bio == NULL)
311 			goto confused;
312 	}
313 
314 	length = first_hole << blkbits;
315 	if (bio_add_page(args->bio, page, length, 0) < length) {
316 		args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
317 		goto alloc_new;
318 	}
319 
320 	relative_block = block_in_file - args->first_logical_block;
321 	nblocks = map_bh->b_size >> blkbits;
322 	if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
323 	    (first_hole != blocks_per_page))
324 		args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
325 	else
326 		args->last_block_in_bio = blocks[blocks_per_page - 1];
327 out:
328 	return args->bio;
329 
330 confused:
331 	if (args->bio)
332 		args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
333 	if (!PageUptodate(page))
334 		block_read_full_page(page, args->get_block);
335 	else
336 		unlock_page(page);
337 	goto out;
338 }
339 
340 /**
341  * mpage_readpages - populate an address space with some pages & start reads against them
342  * @mapping: the address_space
343  * @pages: The address of a list_head which contains the target pages.  These
344  *   pages have their ->index populated and are otherwise uninitialised.
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  * @nr_pages: The number of pages at *@pages
348  * @get_block: The filesystem's block mapper function.
349  *
350  * This function walks the pages and the blocks within each page, building and
351  * emitting large BIOs.
352  *
353  * If anything unusual happens, such as:
354  *
355  * - encountering a page which has buffers
356  * - encountering a page which has a non-hole after a hole
357  * - encountering a page with non-contiguous blocks
358  *
359  * then this code just gives up and calls the buffer_head-based read function.
360  * It does handle a page which has holes at the end - that is a common case:
361  * the end-of-file on blocksize < PAGE_SIZE setups.
362  *
363  * BH_Boundary explanation:
364  *
365  * There is a problem.  The mpage read code assembles several pages, gets all
366  * their disk mappings, and then submits them all.  That's fine, but obtaining
367  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
368  *
369  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
370  * submitted in the following order:
371  *
372  * 	12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
373  *
374  * because the indirect block has to be read to get the mappings of blocks
375  * 13,14,15,16.  Obviously, this impacts performance.
376  *
377  * So what we do it to allow the filesystem's get_block() function to set
378  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
379  * after this one will require I/O against a block which is probably close to
380  * this one.  So you should push what I/O you have currently accumulated.
381  *
382  * This all causes the disk requests to be issued in the correct order.
383  */
384 int
385 mpage_readpages(struct address_space *mapping, struct list_head *pages,
386 				unsigned nr_pages, get_block_t get_block)
387 {
388 	struct mpage_readpage_args args = {
389 		.get_block = get_block,
390 		.is_readahead = true,
391 	};
392 	unsigned page_idx;
393 
394 	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
395 		struct page *page = lru_to_page(pages);
396 
397 		prefetchw(&page->flags);
398 		list_del(&page->lru);
399 		if (!add_to_page_cache_lru(page, mapping,
400 					page->index,
401 					readahead_gfp_mask(mapping))) {
402 			args.page = page;
403 			args.nr_pages = nr_pages - page_idx;
404 			args.bio = do_mpage_readpage(&args);
405 		}
406 		put_page(page);
407 	}
408 	BUG_ON(!list_empty(pages));
409 	if (args.bio)
410 		mpage_bio_submit(REQ_OP_READ, REQ_RAHEAD, args.bio);
411 	return 0;
412 }
413 EXPORT_SYMBOL(mpage_readpages);
414 
415 /*
416  * This isn't called much at all
417  */
418 int mpage_readpage(struct page *page, get_block_t get_block)
419 {
420 	struct mpage_readpage_args args = {
421 		.page = page,
422 		.nr_pages = 1,
423 		.get_block = get_block,
424 	};
425 
426 	args.bio = do_mpage_readpage(&args);
427 	if (args.bio)
428 		mpage_bio_submit(REQ_OP_READ, 0, args.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 
450 struct mpage_data {
451 	struct bio *bio;
452 	sector_t last_block_in_bio;
453 	get_block_t *get_block;
454 	unsigned use_writepage;
455 };
456 
457 /*
458  * We have our BIO, so we can now mark the buffers clean.  Make
459  * sure to only clean buffers which we know we'll be writing.
460  */
461 static void clean_buffers(struct page *page, unsigned first_unmapped)
462 {
463 	unsigned buffer_counter = 0;
464 	struct buffer_head *bh, *head;
465 	if (!page_has_buffers(page))
466 		return;
467 	head = page_buffers(page);
468 	bh = head;
469 
470 	do {
471 		if (buffer_counter++ == first_unmapped)
472 			break;
473 		clear_buffer_dirty(bh);
474 		bh = bh->b_this_page;
475 	} while (bh != head);
476 
477 	/*
478 	 * we cannot drop the bh if the page is not uptodate or a concurrent
479 	 * readpage would fail to serialize with the bh and it would read from
480 	 * disk before we reach the platter.
481 	 */
482 	if (buffer_heads_over_limit && PageUptodate(page))
483 		try_to_free_buffers(page);
484 }
485 
486 /*
487  * For situations where we want to clean all buffers attached to a page.
488  * We don't need to calculate how many buffers are attached to the page,
489  * we just need to specify a number larger than the maximum number of buffers.
490  */
491 void clean_page_buffers(struct page *page)
492 {
493 	clean_buffers(page, ~0U);
494 }
495 
496 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
497 		      void *data)
498 {
499 	struct mpage_data *mpd = data;
500 	struct bio *bio = mpd->bio;
501 	struct address_space *mapping = page->mapping;
502 	struct inode *inode = page->mapping->host;
503 	const unsigned blkbits = inode->i_blkbits;
504 	unsigned long end_index;
505 	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
506 	sector_t last_block;
507 	sector_t block_in_file;
508 	sector_t blocks[MAX_BUF_PER_PAGE];
509 	unsigned page_block;
510 	unsigned first_unmapped = blocks_per_page;
511 	struct block_device *bdev = NULL;
512 	int boundary = 0;
513 	sector_t boundary_block = 0;
514 	struct block_device *boundary_bdev = NULL;
515 	int length;
516 	struct buffer_head map_bh;
517 	loff_t i_size = i_size_read(inode);
518 	int ret = 0;
519 	int op_flags = wbc_to_write_flags(wbc);
520 
521 	if (page_has_buffers(page)) {
522 		struct buffer_head *head = page_buffers(page);
523 		struct buffer_head *bh = head;
524 
525 		/* If they're all mapped and dirty, do it */
526 		page_block = 0;
527 		do {
528 			BUG_ON(buffer_locked(bh));
529 			if (!buffer_mapped(bh)) {
530 				/*
531 				 * unmapped dirty buffers are created by
532 				 * __set_page_dirty_buffers -> mmapped data
533 				 */
534 				if (buffer_dirty(bh))
535 					goto confused;
536 				if (first_unmapped == blocks_per_page)
537 					first_unmapped = page_block;
538 				continue;
539 			}
540 
541 			if (first_unmapped != blocks_per_page)
542 				goto confused;	/* hole -> non-hole */
543 
544 			if (!buffer_dirty(bh) || !buffer_uptodate(bh))
545 				goto confused;
546 			if (page_block) {
547 				if (bh->b_blocknr != blocks[page_block-1] + 1)
548 					goto confused;
549 			}
550 			blocks[page_block++] = bh->b_blocknr;
551 			boundary = buffer_boundary(bh);
552 			if (boundary) {
553 				boundary_block = bh->b_blocknr;
554 				boundary_bdev = bh->b_bdev;
555 			}
556 			bdev = bh->b_bdev;
557 		} while ((bh = bh->b_this_page) != head);
558 
559 		if (first_unmapped)
560 			goto page_is_mapped;
561 
562 		/*
563 		 * Page has buffers, but they are all unmapped. The page was
564 		 * created by pagein or read over a hole which was handled by
565 		 * block_read_full_page().  If this address_space is also
566 		 * using mpage_readpages then this can rarely happen.
567 		 */
568 		goto confused;
569 	}
570 
571 	/*
572 	 * The page has no buffers: map it to disk
573 	 */
574 	BUG_ON(!PageUptodate(page));
575 	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
576 	last_block = (i_size - 1) >> blkbits;
577 	map_bh.b_page = page;
578 	for (page_block = 0; page_block < blocks_per_page; ) {
579 
580 		map_bh.b_state = 0;
581 		map_bh.b_size = 1 << blkbits;
582 		if (mpd->get_block(inode, block_in_file, &map_bh, 1))
583 			goto confused;
584 		if (buffer_new(&map_bh))
585 			clean_bdev_bh_alias(&map_bh);
586 		if (buffer_boundary(&map_bh)) {
587 			boundary_block = map_bh.b_blocknr;
588 			boundary_bdev = map_bh.b_bdev;
589 		}
590 		if (page_block) {
591 			if (map_bh.b_blocknr != blocks[page_block-1] + 1)
592 				goto confused;
593 		}
594 		blocks[page_block++] = map_bh.b_blocknr;
595 		boundary = buffer_boundary(&map_bh);
596 		bdev = map_bh.b_bdev;
597 		if (block_in_file == last_block)
598 			break;
599 		block_in_file++;
600 	}
601 	BUG_ON(page_block == 0);
602 
603 	first_unmapped = page_block;
604 
605 page_is_mapped:
606 	end_index = i_size >> PAGE_SHIFT;
607 	if (page->index >= end_index) {
608 		/*
609 		 * The page straddles i_size.  It must be zeroed out on each
610 		 * and every writepage invocation because it may be mmapped.
611 		 * "A file is mapped in multiples of the page size.  For a file
612 		 * that is not a multiple of the page size, the remaining memory
613 		 * is zeroed when mapped, and writes to that region are not
614 		 * written out to the file."
615 		 */
616 		unsigned offset = i_size & (PAGE_SIZE - 1);
617 
618 		if (page->index > end_index || !offset)
619 			goto confused;
620 		zero_user_segment(page, offset, PAGE_SIZE);
621 	}
622 
623 	/*
624 	 * This page will go to BIO.  Do we need to send this BIO off first?
625 	 */
626 	if (bio && mpd->last_block_in_bio != blocks[0] - 1)
627 		bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
628 
629 alloc_new:
630 	if (bio == NULL) {
631 		if (first_unmapped == blocks_per_page) {
632 			if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
633 								page, wbc))
634 				goto out;
635 		}
636 		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
637 				BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH);
638 		if (bio == NULL)
639 			goto confused;
640 
641 		wbc_init_bio(wbc, bio);
642 		bio->bi_write_hint = inode->i_write_hint;
643 	}
644 
645 	/*
646 	 * Must try to add the page before marking the buffer clean or
647 	 * the confused fail path above (OOM) will be very confused when
648 	 * it finds all bh marked clean (i.e. it will not write anything)
649 	 */
650 	wbc_account_cgroup_owner(wbc, page, PAGE_SIZE);
651 	length = first_unmapped << blkbits;
652 	if (bio_add_page(bio, page, length, 0) < length) {
653 		bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
654 		goto alloc_new;
655 	}
656 
657 	clean_buffers(page, first_unmapped);
658 
659 	BUG_ON(PageWriteback(page));
660 	set_page_writeback(page);
661 	unlock_page(page);
662 	if (boundary || (first_unmapped != blocks_per_page)) {
663 		bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
664 		if (boundary_block) {
665 			write_boundary_block(boundary_bdev,
666 					boundary_block, 1 << blkbits);
667 		}
668 	} else {
669 		mpd->last_block_in_bio = blocks[blocks_per_page - 1];
670 	}
671 	goto out;
672 
673 confused:
674 	if (bio)
675 		bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
676 
677 	if (mpd->use_writepage) {
678 		ret = mapping->a_ops->writepage(page, wbc);
679 	} else {
680 		ret = -EAGAIN;
681 		goto out;
682 	}
683 	/*
684 	 * The caller has a ref on the inode, so *mapping is stable
685 	 */
686 	mapping_set_error(mapping, ret);
687 out:
688 	mpd->bio = bio;
689 	return ret;
690 }
691 
692 /**
693  * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
694  * @mapping: address space structure to write
695  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
696  * @get_block: the filesystem's block mapper function.
697  *             If this is NULL then use a_ops->writepage.  Otherwise, go
698  *             direct-to-BIO.
699  *
700  * This is a library function, which implements the writepages()
701  * address_space_operation.
702  *
703  * If a page is already under I/O, generic_writepages() skips it, even
704  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
705  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
706  * and msync() need to guarantee that all the data which was dirty at the time
707  * the call was made get new I/O started against them.  If wbc->sync_mode is
708  * WB_SYNC_ALL then we were called for data integrity and we must wait for
709  * existing IO to complete.
710  */
711 int
712 mpage_writepages(struct address_space *mapping,
713 		struct writeback_control *wbc, get_block_t get_block)
714 {
715 	struct blk_plug plug;
716 	int ret;
717 
718 	blk_start_plug(&plug);
719 
720 	if (!get_block)
721 		ret = generic_writepages(mapping, wbc);
722 	else {
723 		struct mpage_data mpd = {
724 			.bio = NULL,
725 			.last_block_in_bio = 0,
726 			.get_block = get_block,
727 			.use_writepage = 1,
728 		};
729 
730 		ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
731 		if (mpd.bio) {
732 			int op_flags = (wbc->sync_mode == WB_SYNC_ALL ?
733 				  REQ_SYNC : 0);
734 			mpage_bio_submit(REQ_OP_WRITE, op_flags, mpd.bio);
735 		}
736 	}
737 	blk_finish_plug(&plug);
738 	return ret;
739 }
740 EXPORT_SYMBOL(mpage_writepages);
741 
742 int mpage_writepage(struct page *page, get_block_t get_block,
743 	struct writeback_control *wbc)
744 {
745 	struct mpage_data mpd = {
746 		.bio = NULL,
747 		.last_block_in_bio = 0,
748 		.get_block = get_block,
749 		.use_writepage = 0,
750 	};
751 	int ret = __mpage_writepage(page, wbc, &mpd);
752 	if (mpd.bio) {
753 		int op_flags = (wbc->sync_mode == WB_SYNC_ALL ?
754 			  REQ_SYNC : 0);
755 		mpage_bio_submit(REQ_OP_WRITE, op_flags, mpd.bio);
756 	}
757 	return ret;
758 }
759 EXPORT_SYMBOL(mpage_writepage);
760