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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 : 3 : static void mpage_end_io(struct bio *bio)
48 : : {
49 : : struct bio_vec *bv;
50 : : struct bvec_iter_all iter_all;
51 : :
52 : 3 : bio_for_each_segment_all(bv, bio, iter_all) {
53 : 3 : struct page *page = bv->bv_page;
54 : 3 : page_endio(page, bio_op(bio),
55 : : blk_status_to_errno(bio->bi_status));
56 : : }
57 : :
58 : 3 : bio_put(bio);
59 : 3 : }
60 : :
61 : : static struct bio *mpage_bio_submit(int op, int op_flags, struct bio *bio)
62 : : {
63 : 3 : bio->bi_end_io = mpage_end_io;
64 : 2 : bio_set_op_attrs(bio, op, op_flags);
65 : 3 : guard_bio_eod(bio);
66 : 3 : submit_bio(bio);
67 : : return NULL;
68 : : }
69 : :
70 : : static struct bio *
71 : 3 : 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 : 3 : gfp_flags &= GFP_KERNEL;
79 : 3 : bio = bio_alloc(gfp_flags, nr_vecs);
80 : :
81 : 3 : if (bio == NULL && (current->flags & PF_MEMALLOC)) {
82 : 0 : while (!bio && (nr_vecs /= 2))
83 : 0 : bio = bio_alloc(gfp_flags, nr_vecs);
84 : : }
85 : :
86 : 3 : if (bio) {
87 : 3 : bio_set_dev(bio, bdev);
88 : 3 : bio->bi_iter.bi_sector = first_sector;
89 : : }
90 : 3 : 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 : 0 : map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
105 : : {
106 : 0 : struct inode *inode = page->mapping->host;
107 : : struct buffer_head *page_bh, *head;
108 : : int block = 0;
109 : :
110 : 0 : 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 : 0 : if (inode->i_blkbits == PAGE_SHIFT &&
116 : : buffer_uptodate(bh)) {
117 : : SetPageUptodate(page);
118 : 0 : return;
119 : : }
120 : 0 : create_empty_buffers(page, i_blocksize(inode), 0);
121 : : }
122 : 0 : head = page_buffers(page);
123 : : page_bh = head;
124 : : do {
125 : 0 : if (block == page_block) {
126 : 0 : page_bh->b_state = bh->b_state;
127 : 0 : page_bh->b_bdev = bh->b_bdev;
128 : 0 : page_bh->b_blocknr = bh->b_blocknr;
129 : 0 : break;
130 : : }
131 : 0 : page_bh = page_bh->b_this_page;
132 : 0 : block++;
133 : 0 : } 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 : 3 : static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
157 : : {
158 : 3 : struct page *page = args->page;
159 : 3 : struct inode *inode = page->mapping->host;
160 : 3 : const unsigned blkbits = inode->i_blkbits;
161 : 3 : const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
162 : 3 : const unsigned blocksize = 1 << blkbits;
163 : 3 : 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 : 3 : 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 : 3 : if (page_has_buffers(page))
187 : : goto confused;
188 : :
189 : 3 : block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
190 : 3 : last_block = block_in_file + args->nr_pages * blocks_per_page;
191 : 3 : last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
192 : 3 : 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 : 3 : nblocks = map_bh->b_size >> blkbits;
200 : 3 : if (buffer_mapped(map_bh) &&
201 : 3 : block_in_file > args->first_logical_block &&
202 : 3 : block_in_file < (args->first_logical_block + nblocks)) {
203 : 3 : unsigned map_offset = block_in_file - args->first_logical_block;
204 : 3 : unsigned last = nblocks - map_offset;
205 : :
206 : 3 : for (relative_block = 0; ; relative_block++) {
207 : 3 : if (relative_block == last) {
208 : : clear_buffer_mapped(map_bh);
209 : : break;
210 : : }
211 : 3 : if (page_block == blocks_per_page)
212 : : break;
213 : 3 : blocks[page_block] = map_bh->b_blocknr + map_offset +
214 : : relative_block;
215 : 3 : page_block++;
216 : 3 : block_in_file++;
217 : 3 : }
218 : 3 : bdev = map_bh->b_bdev;
219 : : }
220 : :
221 : : /*
222 : : * Then do more get_blocks calls until we are done with this page.
223 : : */
224 : 3 : map_bh->b_page = page;
225 : 3 : while (page_block < blocks_per_page) {
226 : 3 : map_bh->b_state = 0;
227 : 3 : map_bh->b_size = 0;
228 : :
229 : 3 : if (block_in_file < last_block) {
230 : 3 : map_bh->b_size = (last_block-block_in_file) << blkbits;
231 : 3 : if (args->get_block(inode, block_in_file, map_bh, 0))
232 : : goto confused;
233 : 3 : args->first_logical_block = block_in_file;
234 : : }
235 : :
236 : 3 : if (!buffer_mapped(map_bh)) {
237 : : fully_mapped = 0;
238 : 0 : if (first_hole == blocks_per_page)
239 : : first_hole = page_block;
240 : 0 : page_block++;
241 : 0 : block_in_file++;
242 : 0 : 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 : 3 : if (buffer_uptodate(map_bh)) {
252 : 0 : map_buffer_to_page(page, map_bh, page_block);
253 : 0 : goto confused;
254 : : }
255 : :
256 : 3 : if (first_hole != blocks_per_page)
257 : : goto confused; /* hole -> non-hole */
258 : :
259 : : /* Contiguous blocks? */
260 : 3 : if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
261 : : goto confused;
262 : 3 : nblocks = map_bh->b_size >> blkbits;
263 : 3 : for (relative_block = 0; ; relative_block++) {
264 : 3 : if (relative_block == nblocks) {
265 : : clear_buffer_mapped(map_bh);
266 : : break;
267 : 3 : } else if (page_block == blocks_per_page)
268 : : break;
269 : 3 : blocks[page_block] = map_bh->b_blocknr+relative_block;
270 : 3 : page_block++;
271 : 3 : block_in_file++;
272 : 3 : }
273 : 3 : bdev = map_bh->b_bdev;
274 : : }
275 : :
276 : 3 : if (first_hole != blocks_per_page) {
277 : 0 : zero_user_segment(page, first_hole << blkbits, PAGE_SIZE);
278 : 0 : if (first_hole == 0) {
279 : : SetPageUptodate(page);
280 : 0 : unlock_page(page);
281 : 0 : goto out;
282 : : }
283 : 3 : } else if (fully_mapped) {
284 : : SetPageMappedToDisk(page);
285 : : }
286 : :
287 : 3 : if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
288 : 3 : 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 : 3 : if (args->bio && (args->last_block_in_bio != blocks[0] - 1))
297 : 2 : args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
298 : :
299 : : alloc_new:
300 : 3 : if (args->bio == NULL) {
301 : 3 : if (first_hole == blocks_per_page) {
302 : 3 : if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
303 : : page))
304 : : goto out;
305 : : }
306 : 3 : args->bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
307 : 3 : min_t(int, args->nr_pages,
308 : : BIO_MAX_PAGES),
309 : : gfp);
310 : 3 : if (args->bio == NULL)
311 : : goto confused;
312 : : }
313 : :
314 : 3 : length = first_hole << blkbits;
315 : 3 : if (bio_add_page(args->bio, page, length, 0) < length) {
316 : 0 : args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
317 : 0 : goto alloc_new;
318 : : }
319 : :
320 : 3 : relative_block = block_in_file - args->first_logical_block;
321 : 3 : nblocks = map_bh->b_size >> blkbits;
322 : 3 : if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
323 : : (first_hole != blocks_per_page))
324 : 0 : args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
325 : : else
326 : 3 : args->last_block_in_bio = blocks[blocks_per_page - 1];
327 : : out:
328 : 3 : return args->bio;
329 : :
330 : : confused:
331 : 0 : if (args->bio)
332 : 0 : args->bio = mpage_bio_submit(REQ_OP_READ, op_flags, args->bio);
333 : 0 : if (!PageUptodate(page))
334 : 0 : block_read_full_page(page, args->get_block);
335 : : else
336 : 0 : 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 : 3 : mpage_readpages(struct address_space *mapping, struct list_head *pages,
386 : : unsigned nr_pages, get_block_t get_block)
387 : : {
388 : 3 : struct mpage_readpage_args args = {
389 : : .get_block = get_block,
390 : : .is_readahead = true,
391 : : };
392 : : unsigned page_idx;
393 : :
394 : 3 : for (page_idx = 0; page_idx < nr_pages; page_idx++) {
395 : 3 : struct page *page = lru_to_page(pages);
396 : :
397 : 3 : prefetchw(&page->flags);
398 : : list_del(&page->lru);
399 : 3 : if (!add_to_page_cache_lru(page, mapping,
400 : : page->index,
401 : : readahead_gfp_mask(mapping))) {
402 : 3 : args.page = page;
403 : 3 : args.nr_pages = nr_pages - page_idx;
404 : 3 : args.bio = do_mpage_readpage(&args);
405 : : }
406 : 3 : put_page(page);
407 : : }
408 : 3 : BUG_ON(!list_empty(pages));
409 : 3 : if (args.bio)
410 : : mpage_bio_submit(REQ_OP_READ, REQ_RAHEAD, args.bio);
411 : 3 : return 0;
412 : : }
413 : : EXPORT_SYMBOL(mpage_readpages);
414 : :
415 : : /*
416 : : * This isn't called much at all
417 : : */
418 : 0 : int mpage_readpage(struct page *page, get_block_t get_block)
419 : : {
420 : 0 : struct mpage_readpage_args args = {
421 : : .page = page,
422 : : .nr_pages = 1,
423 : : .get_block = get_block,
424 : : };
425 : :
426 : 0 : args.bio = do_mpage_readpage(&args);
427 : 0 : if (args.bio)
428 : : mpage_bio_submit(REQ_OP_READ, 0, args.bio);
429 : 0 : 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 : 0 : static void clean_buffers(struct page *page, unsigned first_unmapped)
462 : : {
463 : : unsigned buffer_counter = 0;
464 : : struct buffer_head *bh, *head;
465 : 0 : if (!page_has_buffers(page))
466 : 0 : return;
467 : 0 : head = page_buffers(page);
468 : : bh = head;
469 : :
470 : : do {
471 : 0 : if (buffer_counter++ == first_unmapped)
472 : : break;
473 : : clear_buffer_dirty(bh);
474 : 0 : bh = bh->b_this_page;
475 : 0 : } 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 : 0 : if (buffer_heads_over_limit && PageUptodate(page))
483 : 0 : 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 : 0 : void clean_page_buffers(struct page *page)
492 : : {
493 : 0 : clean_buffers(page, ~0U);
494 : 0 : }
495 : :
496 : 0 : static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
497 : : void *data)
498 : : {
499 : : struct mpage_data *mpd = data;
500 : 0 : struct bio *bio = mpd->bio;
501 : 0 : struct address_space *mapping = page->mapping;
502 : 0 : struct inode *inode = page->mapping->host;
503 : 0 : const unsigned blkbits = inode->i_blkbits;
504 : : unsigned long end_index;
505 : 0 : 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 : 0 : if (page_has_buffers(page)) {
522 : 0 : 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 : 0 : BUG_ON(buffer_locked(bh));
529 : 0 : if (!buffer_mapped(bh)) {
530 : : /*
531 : : * unmapped dirty buffers are created by
532 : : * __set_page_dirty_buffers -> mmapped data
533 : : */
534 : 0 : if (buffer_dirty(bh))
535 : : goto confused;
536 : 0 : if (first_unmapped == blocks_per_page)
537 : : first_unmapped = page_block;
538 : 0 : continue;
539 : : }
540 : :
541 : 0 : if (first_unmapped != blocks_per_page)
542 : : goto confused; /* hole -> non-hole */
543 : :
544 : 0 : if (!buffer_dirty(bh) || !buffer_uptodate(bh))
545 : : goto confused;
546 : 0 : if (page_block) {
547 : 0 : if (bh->b_blocknr != blocks[page_block-1] + 1)
548 : : goto confused;
549 : : }
550 : 0 : blocks[page_block++] = bh->b_blocknr;
551 : : boundary = buffer_boundary(bh);
552 : 0 : if (boundary) {
553 : 0 : boundary_block = bh->b_blocknr;
554 : 0 : boundary_bdev = bh->b_bdev;
555 : : }
556 : 0 : bdev = bh->b_bdev;
557 : 0 : } while ((bh = bh->b_this_page) != head);
558 : :
559 : 0 : 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 : 0 : BUG_ON(!PageUptodate(page));
575 : 0 : block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
576 : 0 : last_block = (i_size - 1) >> blkbits;
577 : 0 : map_bh.b_page = page;
578 : 0 : for (page_block = 0; page_block < blocks_per_page; ) {
579 : :
580 : 0 : map_bh.b_state = 0;
581 : 0 : map_bh.b_size = 1 << blkbits;
582 : 0 : if (mpd->get_block(inode, block_in_file, &map_bh, 1))
583 : : goto confused;
584 : 0 : if (buffer_new(&map_bh))
585 : 0 : clean_bdev_bh_alias(&map_bh);
586 : 0 : if (buffer_boundary(&map_bh)) {
587 : 0 : boundary_block = map_bh.b_blocknr;
588 : 0 : boundary_bdev = map_bh.b_bdev;
589 : : }
590 : 0 : if (page_block) {
591 : 0 : if (map_bh.b_blocknr != blocks[page_block-1] + 1)
592 : : goto confused;
593 : : }
594 : 0 : blocks[page_block++] = map_bh.b_blocknr;
595 : : boundary = buffer_boundary(&map_bh);
596 : 0 : bdev = map_bh.b_bdev;
597 : 0 : if (block_in_file == last_block)
598 : : break;
599 : 0 : block_in_file++;
600 : : }
601 : 0 : BUG_ON(page_block == 0);
602 : :
603 : : first_unmapped = page_block;
604 : :
605 : : page_is_mapped:
606 : 0 : end_index = i_size >> PAGE_SHIFT;
607 : 0 : 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 : 0 : unsigned offset = i_size & (PAGE_SIZE - 1);
617 : :
618 : 0 : 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 : 0 : 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 : 0 : if (bio == NULL) {
631 : 0 : if (first_unmapped == blocks_per_page) {
632 : 0 : if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
633 : : page, wbc))
634 : : goto out;
635 : : }
636 : 0 : bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
637 : : BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH);
638 : 0 : if (bio == NULL)
639 : : goto confused;
640 : :
641 : : wbc_init_bio(wbc, bio);
642 : 0 : 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 : 0 : wbc_account_cgroup_owner(wbc, page, PAGE_SIZE);
651 : 0 : length = first_unmapped << blkbits;
652 : 0 : 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 : 0 : clean_buffers(page, first_unmapped);
658 : :
659 : 0 : BUG_ON(PageWriteback(page));
660 : : set_page_writeback(page);
661 : 0 : unlock_page(page);
662 : 0 : if (boundary || (first_unmapped != blocks_per_page)) {
663 : : bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
664 : 0 : if (boundary_block) {
665 : 0 : write_boundary_block(boundary_bdev,
666 : 0 : boundary_block, 1 << blkbits);
667 : : }
668 : : } else {
669 : 0 : mpd->last_block_in_bio = blocks[blocks_per_page - 1];
670 : : }
671 : : goto out;
672 : :
673 : : confused:
674 : 0 : if (bio)
675 : : bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
676 : :
677 : 0 : if (mpd->use_writepage) {
678 : 0 : 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 : 0 : mapping_set_error(mapping, ret);
687 : : out:
688 : 0 : mpd->bio = bio;
689 : 0 : 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 : 0 : 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 : 0 : blk_start_plug(&plug);
719 : :
720 : 0 : if (!get_block)
721 : 0 : ret = generic_writepages(mapping, wbc);
722 : : else {
723 : 0 : 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 : 0 : ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
731 : 0 : if (mpd.bio) {
732 : 0 : 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 : 0 : blk_finish_plug(&plug);
738 : 0 : return ret;
739 : : }
740 : : EXPORT_SYMBOL(mpage_writepages);
741 : :
742 : 0 : int mpage_writepage(struct page *page, get_block_t get_block,
743 : : struct writeback_control *wbc)
744 : : {
745 : 0 : struct mpage_data mpd = {
746 : : .bio = NULL,
747 : : .last_block_in_bio = 0,
748 : : .get_block = get_block,
749 : : .use_writepage = 0,
750 : : };
751 : 0 : int ret = __mpage_writepage(page, wbc, &mpd);
752 : 0 : if (mpd.bio) {
753 : 0 : 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 : 0 : return ret;
758 : : }
759 : : EXPORT_SYMBOL(mpage_writepage);
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