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