xref: /openbmc/linux/fs/mpage.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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);
735