root/fs/mpage.c

DEFINITIONS

1. mpage_end_io
2. mpage_bio_submit
3. mpage_alloc
4. map_buffer_to_page
5. do_mpage_readpage
6. mpage_readpages
7. mpage_readpage
8. clean_buffers
9. clean_page_buffers
10. __mpage_writepage
11. mpage_writepages
12. mpage_writepage

   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(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);