fs/mpage.c

   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/export.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/mm_inline.h>
  28 #include <linux/writeback.h>
  29 #include <linux/backing-dev.h>
  30 #include <linux/pagevec.h>
  31 #include <linux/cleancache.h>
  32 #include "internal.h"
  33
  34 /*
  35  * I/O completion handler for multipage BIOs.
  36  *
  37  * The mpage code never puts partial pages into a BIO (except for end-of-file).
  38  * If a page does not map to a contiguous run of blocks then it simply falls
  39  * back to block_read_full_page().
  40  *
  41  * Why is this?  If a page's completion depends on a number of different BIOs
  42  * which can complete in any order (or at the same time) then determining the
  43  * status of that page is hard.  See end_buffer_async_read() for the details.
  44  * There is no point in duplicating all that complexity.
  45  */
  46 static void mpage_end_io(struct bio *bio)
  47 {
  48         struct bio_vec *bv;
  49         int i;
  50
  51         bio_for_each_segment_all(bv, bio, i) {
  52                 struct page *page = bv->bv_page;
  53                 page_endio(page, op_is_write(bio_op(bio)), bio->bi_error);
  54         }
  55
  56         bio_put(bio);
  57 }
  58
  59 static struct bio *mpage_bio_submit(int op, int op_flags, struct bio *bio)
  60 {
  61         bio->bi_end_io = mpage_end_io;
  62         bio_set_op_attrs(bio, op, op_flags);
  63         guard_bio_eod(op, bio);
  64         submit_bio(bio);
  65         return NULL;
  66 }
  67
  68 static struct bio *
  69 mpage_alloc(struct block_device *bdev,
  70                 sector_t first_sector, int nr_vecs,
  71                 gfp_t gfp_flags)
  72 {
  73         struct bio *bio;
  74
  75         /* Restrict the given (page cache) mask for slab allocations */
  76         gfp_flags &= GFP_KERNEL;
  77         bio = bio_alloc(gfp_flags, nr_vecs);
  78
  79         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
  80                 while (!bio && (nr_vecs /= 2))
  81                         bio = bio_alloc(gfp_flags, nr_vecs);
  82         }
  83
  84         if (bio) {
  85                 bio->bi_bdev = bdev;
  86                 bio->bi_iter.bi_sector = first_sector;
  87         }
  88         return bio;
  89 }
  90
  91 /*
  92  * support function for mpage_readpages.  The fs supplied get_block might
  93  * return an up to date buffer.  This is used to map that buffer into
  94  * the page, which allows readpage to avoid triggering a duplicate call
  95  * to get_block.
  96  *
  97  * The idea is to avoid adding buffers to pages that don't already have
  98  * them.  So when the buffer is up to date and the page size == block size,
  99  * this marks the page up to date instead of adding new buffers.
 100  */
 101 static void
 102 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
 103 {
 104         struct inode *inode = page->mapping->host;
 105         struct buffer_head *page_bh, *head;
 106         int block = 0;
 107
 108         if (!page_has_buffers(page)) {
 109                 /*
 110                  * don't make any buffers if there is only one buffer on
 111                  * the page and the page just needs to be set up to date
 112                  */
 113                 if (inode->i_blkbits == PAGE_SHIFT &&
 114                     buffer_uptodate(bh)) {
 115                         SetPageUptodate(page);
 116                         return;
 117                 }
 118                 create_empty_buffers(page, 1 << inode->i_blkbits, 0);
 119         }
 120         head = page_buffers(page);
 121         page_bh = head;
 122         do {
 123                 if (block == page_block) {
 124                         page_bh->b_state = bh->b_state;
 125                         page_bh->b_bdev = bh->b_bdev;
 126                         page_bh->b_blocknr = bh->b_blocknr;
 127                         break;
 128                 }
 129                 page_bh = page_bh->b_this_page;
 130                 block++;
 131         } while (page_bh != head);
 132 }
 133
 134 /*
 135  * This is the worker routine which does all the work of mapping the disk
 136  * blocks and constructs largest possible bios, submits them for IO if the
 137  * blocks are not contiguous on the disk.
 138  *
 139  * We pass a buffer_head back and forth and use its buffer_mapped() flag to
 140  * represent the validity of its disk mapping and to decide when to do the next
 141  * get_block() call.
 142  */
 143 static struct bio *
 144 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 145                 sector_t *last_block_in_bio, struct buffer_head *map_bh,
 146                 unsigned long *first_logical_block, get_block_t get_block,
 147                 gfp_t gfp)
 148 {
 149         struct inode *inode = page->mapping->host;
 150         const unsigned blkbits = inode->i_blkbits;
 151         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
 152         const unsigned blocksize = 1 << blkbits;
 153         sector_t block_in_file;
 154         sector_t last_block;
 155         sector_t last_block_in_file;
 156         sector_t blocks[MAX_BUF_PER_PAGE];
 157         unsigned page_block;
 158         unsigned first_hole = blocks_per_page;
 159         struct block_device *bdev = NULL;
 160         int length;
 161         int fully_mapped = 1;
 162         unsigned nblocks;
 163         unsigned relative_block;
 164
 165         if (page_has_buffers(page))
 166                 goto confused;
 167
 168         block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
 169         last_block = block_in_file + nr_pages * blocks_per_page;
 170         last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
 171         if (last_block > last_block_in_file)
 172                 last_block = last_block_in_file;
 173         page_block = 0;
 174
 175         /*
 176          * Map blocks using the result from the previous get_blocks call first.
 177          */
 178         nblocks = map_bh->b_size >> blkbits;
 179         if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
 180                         block_in_file < (*first_logical_block + nblocks)) {
 181                 unsigned map_offset = block_in_file - *first_logical_block;
 182                 unsigned last = nblocks - map_offset;
 183
 184                 for (relative_block = 0; ; relative_block++) {
 185                         if (relative_block == last) {
 186                                 clear_buffer_mapped(map_bh);
 187                                 break;
 188                         }
 189                         if (page_block == blocks_per_page)
 190                                 break;
 191                         blocks[page_block] = map_bh->b_blocknr + map_offset +
 192                                                 relative_block;
 193                         page_block++;
 194                         block_in_file++;
 195                 }
 196                 bdev = map_bh->b_bdev;
 197         }
 198
 199         /*
 200          * Then do more get_blocks calls until we are done with this page.
 201          */
 202         map_bh->b_page = page;
 203         while (page_block < blocks_per_page) {
 204                 map_bh->b_state = 0;
 205                 map_bh->b_size = 0;
 206
 207                 if (block_in_file < last_block) {
 208                         map_bh->b_size = (last_block-block_in_file) << blkbits;
 209                         if (get_block(inode, block_in_file, map_bh, 0))
 210                                 goto confused;
 211                         *first_logical_block = block_in_file;
 212                 }
 213
 214                 if (!buffer_mapped(map_bh)) {
 215                         fully_mapped = 0;
 216                         if (first_hole == blocks_per_page)
 217                                 first_hole = page_block;
 218                         page_block++;
 219                         block_in_file++;
 220                         continue;
 221                 }
 222
 223                 /* some filesystems will copy data into the page during
 224                  * the get_block call, in which case we don't want to
 225                  * read it again.  map_buffer_to_page copies the data
 226                  * we just collected from get_block into the page's buffers
 227                  * so readpage doesn't have to repeat the get_block call
 228                  */
 229                 if (buffer_uptodate(map_bh)) {
 230                         map_buffer_to_page(page, map_bh, page_block);
 231                         goto confused;
 232                 }
 233
 234                 if (first_hole != blocks_per_page)
 235                         goto confused;          /* hole -> non-hole */
 236
 237                 /* Contiguous blocks? */
 238                 if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
 239                         goto confused;
 240                 nblocks = map_bh->b_size >> blkbits;
 241                 for (relative_block = 0; ; relative_block++) {
 242                         if (relative_block == nblocks) {
 243                                 clear_buffer_mapped(map_bh);
 244                                 break;
 245                         } else if (page_block == blocks_per_page)
 246                                 break;
 247                         blocks[page_block] = map_bh->b_blocknr+relative_block;
 248                         page_block++;
 249                         block_in_file++;
 250                 }
 251                 bdev = map_bh->b_bdev;
 252         }
 253
 254         if (first_hole != blocks_per_page) {
 255                 zero_user_segment(page, first_hole << blkbits, PAGE_SIZE);
 256                 if (first_hole == 0) {
 257                         SetPageUptodate(page);
 258                         unlock_page(page);
 259                         goto out;
 260                 }
 261         } else if (fully_mapped) {
 262                 SetPageMappedToDisk(page);
 263         }
 264
 265         if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
 266             cleancache_get_page(page) == 0) {
 267                 SetPageUptodate(page);
 268                 goto confused;
 269         }
 270
 271         /*
 272          * This page will go to BIO.  Do we need to send this BIO off first?
 273          */
 274         if (bio && (*last_block_in_bio != blocks[0] - 1))
 275                 bio = mpage_bio_submit(REQ_OP_READ, 0, bio);
 276
 277 alloc_new:
 278         if (bio == NULL) {
 279                 if (first_hole == blocks_per_page) {
 280                         if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
 281                                                                 page))
 282                                 goto out;
 283                 }
 284                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 285                                 min_t(int, nr_pages, BIO_MAX_PAGES), gfp);
 286                 if (bio == NULL)
 287                         goto confused;
 288         }
 289
 290         length = first_hole << blkbits;
 291         if (bio_add_page(bio, page, length, 0) < length) {
 292                 bio = mpage_bio_submit(REQ_OP_READ, 0, bio);
 293                 goto alloc_new;
 294         }
 295
 296         relative_block = block_in_file - *first_logical_block;
 297         nblocks = map_bh->b_size >> blkbits;
 298         if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
 299             (first_hole != blocks_per_page))
 300                 bio = mpage_bio_submit(REQ_OP_READ, 0, bio);
 301         else
 302                 *last_block_in_bio = blocks[blocks_per_page - 1];
 303 out:
 304         return bio;
 305
 306 confused:
 307         if (bio)
 308                 bio = mpage_bio_submit(REQ_OP_READ, 0, bio);
 309         if (!PageUptodate(page))
 310                 block_read_full_page(page, get_block);
 311         else
 312                 unlock_page(page);
 313         goto out;
 314 }
 315
 316 /**
 317  * mpage_readpages - populate an address space with some pages & start reads against them
 318  * @mapping: the address_space
 319  * @pages: The address of a list_head which contains the target pages.  These
 320  *   pages have their ->index populated and are otherwise uninitialised.
 321  *   The page at @pages->prev has the lowest file offset, and reads should be
 322  *   issued in @pages->prev to @pages->next order.
 323  * @nr_pages: The number of pages at *@pages
 324  * @get_block: The filesystem's block mapper function.
 325  *
 326  * This function walks the pages and the blocks within each page, building and
 327  * emitting large BIOs.
 328  *
 329  * If anything unusual happens, such as:
 330  *
 331  * - encountering a page which has buffers
 332  * - encountering a page which has a non-hole after a hole
 333  * - encountering a page with non-contiguous blocks
 334  *
 335  * then this code just gives up and calls the buffer_head-based read function.
 336  * It does handle a page which has holes at the end - that is a common case:
 337  * the end-of-file on blocksize < PAGE_SIZE setups.
 338  *
 339  * BH_Boundary explanation:
 340  *
 341  * There is a problem.  The mpage read code assembles several pages, gets all
 342  * their disk mappings, and then submits them all.  That's fine, but obtaining
 343  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
 344  *
 345  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
 346  * submitted in the following order:
 347  *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
 348  *
 349  * because the indirect block has to be read to get the mappings of blocks
 350  * 13,14,15,16.  Obviously, this impacts performance.
 351  *
 352  * So what we do it to allow the filesystem's get_block() function to set
 353  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
 354  * after this one will require I/O against a block which is probably close to
 355  * this one.  So you should push what I/O you have currently accumulated.
 356  *
 357  * This all causes the disk requests to be issued in the correct order.
 358  */
 359 int
 360 mpage_readpages(struct address_space *mapping, struct list_head *pages,
 361                                 unsigned nr_pages, get_block_t get_block)
 362 {
 363         struct bio *bio = NULL;
 364         unsigned page_idx;
 365         sector_t last_block_in_bio = 0;
 366         struct buffer_head map_bh;
 367         unsigned long first_logical_block = 0;
 368         gfp_t gfp = readahead_gfp_mask(mapping);
 369
 370         map_bh.b_state = 0;
 371         map_bh.b_size = 0;
 372         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
 373                 struct page *page = lru_to_page(pages);
 374
 375                 prefetchw(&page->flags);
 376                 list_del(&page->lru);
 377                 if (!add_to_page_cache_lru(page, mapping,
 378                                         page->index,
 379                                         gfp)) {
 380                         bio = do_mpage_readpage(bio, page,
 381                                         nr_pages - page_idx,
 382                                         &last_block_in_bio, &map_bh,
 383                                         &first_logical_block,
 384                                         get_block, gfp);
 385                 }
 386                 put_page(page);
 387         }
 388         BUG_ON(!list_empty(pages));
 389         if (bio)
 390                 mpage_bio_submit(REQ_OP_READ, 0, bio);
 391         return 0;
 392 }
 393 EXPORT_SYMBOL(mpage_readpages);
 394
 395 /*
 396  * This isn't called much at all
 397  */
 398 int mpage_readpage(struct page *page, get_block_t get_block)
 399 {
 400         struct bio *bio = NULL;
 401         sector_t last_block_in_bio = 0;
 402         struct buffer_head map_bh;
 403         unsigned long first_logical_block = 0;
 404         gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
 405
 406         map_bh.b_state = 0;
 407         map_bh.b_size = 0;
 408         bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
 409                         &map_bh, &first_logical_block, get_block, gfp);
 410         if (bio)
 411                 mpage_bio_submit(REQ_OP_READ, 0, bio);
 412         return 0;
 413 }
 414 EXPORT_SYMBOL(mpage_readpage);
 415
 416 /*
 417  * Writing is not so simple.
 418  *
 419  * If the page has buffers then they will be used for obtaining the disk
 420  * mapping.  We only support pages which are fully mapped-and-dirty, with a
 421  * special case for pages which are unmapped at the end: end-of-file.
 422  *
 423  * If the page has no buffers (preferred) then the page is mapped here.
 424  *
 425  * If all blocks are found to be contiguous then the page can go into the
 426  * BIO.  Otherwise fall back to the mapping's writepage().
 427  *
 428  * FIXME: This code wants an estimate of how many pages are still to be
 429  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
 430  * just allocate full-size (16-page) BIOs.
 431  */
 432
 433 struct mpage_data {
 434         struct bio *bio;
 435         sector_t last_block_in_bio;
 436         get_block_t *get_block;
 437         unsigned use_writepage;
 438 };
 439
 440 /*
 441  * We have our BIO, so we can now mark the buffers clean.  Make
 442  * sure to only clean buffers which we know we'll be writing.
 443  */
 444 static void clean_buffers(struct page *page, unsigned first_unmapped)
 445 {
 446         unsigned buffer_counter = 0;
 447         struct buffer_head *bh, *head;
 448         if (!page_has_buffers(page))
 449                 return;
 450         head = page_buffers(page);
 451         bh = head;
 452
 453         do {
 454                 if (buffer_counter++ == first_unmapped)
 455                         break;
 456                 clear_buffer_dirty(bh);
 457                 bh = bh->b_this_page;
 458         } while (bh != head);
 459
 460         /*
 461          * we cannot drop the bh if the page is not uptodate or a concurrent
 462          * readpage would fail to serialize with the bh and it would read from
 463          * disk before we reach the platter.
 464          */
 465         if (buffer_heads_over_limit && PageUptodate(page))
 466                 try_to_free_buffers(page);
 467 }
 468
 469 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
 470                       void *data)
 471 {
 472         struct mpage_data *mpd = data;
 473         struct bio *bio = mpd->bio;
 474         struct address_space *mapping = page->mapping;
 475         struct inode *inode = page->mapping->host;
 476         const unsigned blkbits = inode->i_blkbits;
 477         unsigned long end_index;
 478         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
 479         sector_t last_block;
 480         sector_t block_in_file;
 481         sector_t blocks[MAX_BUF_PER_PAGE];
 482         unsigned page_block;
 483         unsigned first_unmapped = blocks_per_page;
 484         struct block_device *bdev = NULL;
 485         int boundary = 0;
 486         sector_t boundary_block = 0;
 487         struct block_device *boundary_bdev = NULL;
 488         int length;
 489         struct buffer_head map_bh;
 490         loff_t i_size = i_size_read(inode);
 491         int ret = 0;
 492         int op_flags = (wbc->sync_mode == WB_SYNC_ALL ?  WRITE_SYNC : 0);
 493
 494         if (page_has_buffers(page)) {
 495                 struct buffer_head *head = page_buffers(page);
 496                 struct buffer_head *bh = head;
 497
 498                 /* If they're all mapped and dirty, do it */
 499                 page_block = 0;
 500                 do {
 501                         BUG_ON(buffer_locked(bh));
 502                         if (!buffer_mapped(bh)) {
 503                                 /*
 504                                  * unmapped dirty buffers are created by
 505                                  * __set_page_dirty_buffers -> mmapped data
 506                                  */
 507                                 if (buffer_dirty(bh))
 508                                         goto confused;
 509                                 if (first_unmapped == blocks_per_page)
 510                                         first_unmapped = page_block;
 511                                 continue;
 512                         }
 513
 514                         if (first_unmapped != blocks_per_page)
 515                                 goto confused;  /* hole -> non-hole */
 516
 517                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
 518                                 goto confused;
 519                         if (page_block) {
 520                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
 521                                         goto confused;
 522                         }
 523                         blocks[page_block++] = bh->b_blocknr;
 524                         boundary = buffer_boundary(bh);
 525                         if (boundary) {
 526                                 boundary_block = bh->b_blocknr;
 527                                 boundary_bdev = bh->b_bdev;
 528                         }
 529                         bdev = bh->b_bdev;
 530                 } while ((bh = bh->b_this_page) != head);
 531
 532                 if (first_unmapped)
 533                         goto page_is_mapped;
 534
 535                 /*
 536                  * Page has buffers, but they are all unmapped. The page was
 537                  * created by pagein or read over a hole which was handled by
 538                  * block_read_full_page().  If this address_space is also
 539                  * using mpage_readpages then this can rarely happen.
 540                  */
 541                 goto confused;
 542         }
 543
 544         /*
 545          * The page has no buffers: map it to disk
 546          */
 547         BUG_ON(!PageUptodate(page));
 548         block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
 549         last_block = (i_size - 1) >> blkbits;
 550         map_bh.b_page = page;
 551         for (page_block = 0; page_block < blocks_per_page; ) {
 552
 553                 map_bh.b_state = 0;
 554                 map_bh.b_size = 1 << blkbits;
 555                 if (mpd->get_block(inode, block_in_file, &map_bh, 1))
 556                         goto confused;
 557                 if (buffer_new(&map_bh))
 558                         unmap_underlying_metadata(map_bh.b_bdev,
 559                                                 map_bh.b_blocknr);
 560                 if (buffer_boundary(&map_bh)) {
 561                         boundary_block = map_bh.b_blocknr;
 562                         boundary_bdev = map_bh.b_bdev;
 563                 }
 564                 if (page_block) {
 565                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
 566                                 goto confused;
 567                 }
 568                 blocks[page_block++] = map_bh.b_blocknr;
 569                 boundary = buffer_boundary(&map_bh);
 570                 bdev = map_bh.b_bdev;
 571                 if (block_in_file == last_block)
 572                         break;
 573                 block_in_file++;
 574         }
 575         BUG_ON(page_block == 0);
 576
 577         first_unmapped = page_block;
 578
 579 page_is_mapped:
 580         end_index = i_size >> PAGE_SHIFT;
 581         if (page->index >= end_index) {
 582                 /*
 583                  * The page straddles i_size.  It must be zeroed out on each
 584                  * and every writepage invocation because it may be mmapped.
 585                  * "A file is mapped in multiples of the page size.  For a file
 586                  * that is not a multiple of the page size, the remaining memory
 587                  * is zeroed when mapped, and writes to that region are not
 588                  * written out to the file."
 589                  */
 590                 unsigned offset = i_size & (PAGE_SIZE - 1);
 591
 592                 if (page->index > end_index || !offset)
 593                         goto confused;
 594                 zero_user_segment(page, offset, PAGE_SIZE);
 595         }
 596
 597         /*
 598          * This page will go to BIO.  Do we need to send this BIO off first?
 599          */
 600         if (bio && mpd->last_block_in_bio != blocks[0] - 1)
 601                 bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
 602
 603 alloc_new:
 604         if (bio == NULL) {
 605                 if (first_unmapped == blocks_per_page) {
 606                         if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
 607                                                                 page, wbc)) {
 608                                 clean_buffers(page, first_unmapped);
 609                                 goto out;
 610                         }
 611                 }
 612                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 613                                 BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH);
 614                 if (bio == NULL)
 615                         goto confused;
 616
 617                 wbc_init_bio(wbc, bio);
 618         }
 619
 620         /*
 621          * Must try to add the page before marking the buffer clean or
 622          * the confused fail path above (OOM) will be very confused when
 623          * it finds all bh marked clean (i.e. it will not write anything)
 624          */
 625         wbc_account_io(wbc, page, PAGE_SIZE);
 626         length = first_unmapped << blkbits;
 627         if (bio_add_page(bio, page, length, 0) < length) {
 628                 bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
 629                 goto alloc_new;
 630         }
 631
 632         clean_buffers(page, first_unmapped);
 633
 634         BUG_ON(PageWriteback(page));
 635         set_page_writeback(page);
 636         unlock_page(page);
 637         if (boundary || (first_unmapped != blocks_per_page)) {
 638                 bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
 639                 if (boundary_block) {
 640                         write_boundary_block(boundary_bdev,
 641                                         boundary_block, 1 << blkbits);
 642                 }
 643         } else {
 644                 mpd->last_block_in_bio = blocks[blocks_per_page - 1];
 645         }
 646         goto out;
 647
 648 confused:
 649         if (bio)
 650                 bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
 651
 652         if (mpd->use_writepage) {
 653                 ret = mapping->a_ops->writepage(page, wbc);
 654         } else {
 655                 ret = -EAGAIN;
 656                 goto out;
 657         }
 658         /*
 659          * The caller has a ref on the inode, so *mapping is stable
 660          */
 661         mapping_set_error(mapping, ret);
 662 out:
 663         mpd->bio = bio;
 664         return ret;
 665 }
 666
 667 /**
 668  * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
 669  * @mapping: address space structure to write
 670  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 671  * @get_block: the filesystem's block mapper function.
 672  *             If this is NULL then use a_ops->writepage.  Otherwise, go
 673  *             direct-to-BIO.
 674  *
 675  * This is a library function, which implements the writepages()
 676  * address_space_operation.
 677  *
 678  * If a page is already under I/O, generic_writepages() skips it, even
 679  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 680  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 681  * and msync() need to guarantee that all the data which was dirty at the time
 682  * the call was made get new I/O started against them.  If wbc->sync_mode is
 683  * WB_SYNC_ALL then we were called for data integrity and we must wait for
 684  * existing IO to complete.
 685  */
 686 int
 687 mpage_writepages(struct address_space *mapping,
 688                 struct writeback_control *wbc, get_block_t get_block)
 689 {
 690         struct blk_plug plug;
 691         int ret;
 692
 693         blk_start_plug(&plug);
 694
 695         if (!get_block)
 696                 ret = generic_writepages(mapping, wbc);
 697         else {
 698                 struct mpage_data mpd = {
 699                         .bio = NULL,
 700                         .last_block_in_bio = 0,
 701                         .get_block = get_block,
 702                         .use_writepage = 1,
 703                 };
 704
 705                 ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
 706                 if (mpd.bio) {
 707                         int op_flags = (wbc->sync_mode == WB_SYNC_ALL ?
 708                                   WRITE_SYNC : 0);
 709                         mpage_bio_submit(REQ_OP_WRITE, op_flags, mpd.bio);
 710                 }
 711         }
 712         blk_finish_plug(&plug);
 713         return ret;
 714 }
 715 EXPORT_SYMBOL(mpage_writepages);
 716
 717 int mpage_writepage(struct page *page, get_block_t get_block,
 718         struct writeback_control *wbc)
 719 {
 720         struct mpage_data mpd = {
 721                 .bio = NULL,
 722                 .last_block_in_bio = 0,
 723                 .get_block = get_block,
 724                 .use_writepage = 0,
 725         };
 726         int ret = __mpage_writepage(page, wbc, &mpd);
 727         if (mpd.bio) {
 728                 int op_flags = (wbc->sync_mode == WB_SYNC_ALL ?
 729                           WRITE_SYNC : 0);
 730                 mpage_bio_submit(REQ_OP_WRITE, op_flags, mpd.bio);
 731         }
 732         return ret;
 733 }
 734 EXPORT_SYMBOL(mpage_writepage);