linux/fs/mpage.c
<<
>>
Prefs
   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/writeback.h>
  28#include <linux/backing-dev.h>
  29#include <linux/pagevec.h>
  30#include <linux/cleancache.h>
  31
  32/*
  33 * I/O completion handler for multipage BIOs.
  34 *
  35 * The mpage code never puts partial pages into a BIO (except for end-of-file).
  36 * If a page does not map to a contiguous run of blocks then it simply falls
  37 * back to block_read_full_page().
  38 *
  39 * Why is this?  If a page's completion depends on a number of different BIOs
  40 * which can complete in any order (or at the same time) then determining the
  41 * status of that page is hard.  See end_buffer_async_read() for the details.
  42 * There is no point in duplicating all that complexity.
  43 */
  44static void mpage_end_io(struct bio *bio, int err)
  45{
  46        const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  47        struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
  48
  49        do {
  50                struct page *page = bvec->bv_page;
  51
  52                if (--bvec >= bio->bi_io_vec)
  53                        prefetchw(&bvec->bv_page->flags);
  54                if (bio_data_dir(bio) == READ) {
  55                        if (uptodate) {
  56                                SetPageUptodate(page);
  57                        } else {
  58                                ClearPageUptodate(page);
  59                                SetPageError(page);
  60                        }
  61                        unlock_page(page);
  62                } else { /* bio_data_dir(bio) == WRITE */
  63                        if (!uptodate) {
  64                                SetPageError(page);
  65                                if (page->mapping)
  66                                        set_bit(AS_EIO, &page->mapping->flags);
  67                        }
  68                        end_page_writeback(page);
  69                }
  70        } while (bvec >= bio->bi_io_vec);
  71        bio_put(bio);
  72}
  73
  74static struct bio *mpage_bio_submit(int rw, struct bio *bio)
  75{
  76        bio->bi_end_io = mpage_end_io;
  77        submit_bio(rw, bio);
  78        return NULL;
  79}
  80
  81static struct bio *
  82mpage_alloc(struct block_device *bdev,
  83                sector_t first_sector, int nr_vecs,
  84                gfp_t gfp_flags)
  85{
  86        struct bio *bio;
  87
  88        bio = bio_alloc(gfp_flags, nr_vecs);
  89
  90        if (bio == NULL && (current->flags & PF_MEMALLOC)) {
  91                while (!bio && (nr_vecs /= 2))
  92                        bio = bio_alloc(gfp_flags, nr_vecs);
  93        }
  94
  95        if (bio) {
  96                bio->bi_bdev = bdev;
  97                bio->bi_sector = first_sector;
  98        }
  99        return bio;
 100}
 101
 102/*
 103 * support function for mpage_readpages.  The fs supplied get_block might
 104 * return an up to date buffer.  This is used to map that buffer into
 105 * the page, which allows readpage to avoid triggering a duplicate call
 106 * to get_block.
 107 *
 108 * The idea is to avoid adding buffers to pages that don't already have
 109 * them.  So when the buffer is up to date and the page size == block size,
 110 * this marks the page up to date instead of adding new buffers.
 111 */
 112static void 
 113map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block) 
 114{
 115        struct inode *inode = page->mapping->host;
 116        struct buffer_head *page_bh, *head;
 117        int block = 0;
 118
 119        if (!page_has_buffers(page)) {
 120                /*
 121                 * don't make any buffers if there is only one buffer on
 122                 * the page and the page just needs to be set up to date
 123                 */
 124                if (inode->i_blkbits == PAGE_CACHE_SHIFT && 
 125                    buffer_uptodate(bh)) {
 126                        SetPageUptodate(page);    
 127                        return;
 128                }
 129                create_empty_buffers(page, 1 << inode->i_blkbits, 0);
 130        }
 131        head = page_buffers(page);
 132        page_bh = head;
 133        do {
 134                if (block == page_block) {
 135                        page_bh->b_state = bh->b_state;
 136                        page_bh->b_bdev = bh->b_bdev;
 137                        page_bh->b_blocknr = bh->b_blocknr;
 138                        break;
 139                }
 140                page_bh = page_bh->b_this_page;
 141                block++;
 142        } while (page_bh != head);
 143}
 144
 145/*
 146 * This is the worker routine which does all the work of mapping the disk
 147 * blocks and constructs largest possible bios, submits them for IO if the
 148 * blocks are not contiguous on the disk.
 149 *
 150 * We pass a buffer_head back and forth and use its buffer_mapped() flag to
 151 * represent the validity of its disk mapping and to decide when to do the next
 152 * get_block() call.
 153 */
 154static struct bio *
 155do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 156                sector_t *last_block_in_bio, struct buffer_head *map_bh,
 157                unsigned long *first_logical_block, get_block_t get_block)
 158{
 159        struct inode *inode = page->mapping->host;
 160        const unsigned blkbits = inode->i_blkbits;
 161        const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
 162        const unsigned blocksize = 1 << blkbits;
 163        sector_t block_in_file;
 164        sector_t last_block;
 165        sector_t last_block_in_file;
 166        sector_t blocks[MAX_BUF_PER_PAGE];
 167        unsigned page_block;
 168        unsigned first_hole = blocks_per_page;
 169        struct block_device *bdev = NULL;
 170        int length;
 171        int fully_mapped = 1;
 172        unsigned nblocks;
 173        unsigned relative_block;
 174
 175        if (page_has_buffers(page))
 176                goto confused;
 177
 178        block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
 179        last_block = block_in_file + nr_pages * blocks_per_page;
 180        last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
 181        if (last_block > last_block_in_file)
 182                last_block = last_block_in_file;
 183        page_block = 0;
 184
 185        /*
 186         * Map blocks using the result from the previous get_blocks call first.
 187         */
 188        nblocks = map_bh->b_size >> blkbits;
 189        if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
 190                        block_in_file < (*first_logical_block + nblocks)) {
 191                unsigned map_offset = block_in_file - *first_logical_block;
 192                unsigned last = nblocks - map_offset;
 193
 194                for (relative_block = 0; ; relative_block++) {
 195                        if (relative_block == last) {
 196                                clear_buffer_mapped(map_bh);
 197                                break;
 198                        }
 199                        if (page_block == blocks_per_page)
 200                                break;
 201                        blocks[page_block] = map_bh->b_blocknr + map_offset +
 202                                                relative_block;
 203                        page_block++;
 204                        block_in_file++;
 205                }
 206                bdev = map_bh->b_bdev;
 207        }
 208
 209        /*
 210         * Then do more get_blocks calls until we are done with this page.
 211         */
 212        map_bh->b_page = page;
 213        while (page_block < blocks_per_page) {
 214                map_bh->b_state = 0;
 215                map_bh->b_size = 0;
 216
 217                if (block_in_file < last_block) {
 218                        map_bh->b_size = (last_block-block_in_file) << blkbits;
 219                        if (get_block(inode, block_in_file, map_bh, 0))
 220                                goto confused;
 221                        *first_logical_block = block_in_file;
 222                }
 223
 224                if (!buffer_mapped(map_bh)) {
 225                        fully_mapped = 0;
 226                        if (first_hole == blocks_per_page)
 227                                first_hole = page_block;
 228                        page_block++;
 229                        block_in_file++;
 230                        continue;
 231                }
 232
 233                /* some filesystems will copy data into the page during
 234                 * the get_block call, in which case we don't want to
 235                 * read it again.  map_buffer_to_page copies the data
 236                 * we just collected from get_block into the page's buffers
 237                 * so readpage doesn't have to repeat the get_block call
 238                 */
 239                if (buffer_uptodate(map_bh)) {
 240                        map_buffer_to_page(page, map_bh, page_block);
 241                        goto confused;
 242                }
 243        
 244                if (first_hole != blocks_per_page)
 245                        goto confused;          /* hole -> non-hole */
 246
 247                /* Contiguous blocks? */
 248                if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
 249                        goto confused;
 250                nblocks = map_bh->b_size >> blkbits;
 251                for (relative_block = 0; ; relative_block++) {
 252                        if (relative_block == nblocks) {
 253                                clear_buffer_mapped(map_bh);
 254                                break;
 255                        } else if (page_block == blocks_per_page)
 256                                break;
 257                        blocks[page_block] = map_bh->b_blocknr+relative_block;
 258                        page_block++;
 259                        block_in_file++;
 260                }
 261                bdev = map_bh->b_bdev;
 262        }
 263
 264        if (first_hole != blocks_per_page) {
 265                zero_user_segment(page, first_hole << blkbits, PAGE_CACHE_SIZE);
 266                if (first_hole == 0) {
 267                        SetPageUptodate(page);
 268                        unlock_page(page);
 269                        goto out;
 270                }
 271        } else if (fully_mapped) {
 272                SetPageMappedToDisk(page);
 273        }
 274
 275        if (fully_mapped && blocks_per_page == 1 && !PageUptodate(page) &&
 276            cleancache_get_page(page) == 0) {
 277                SetPageUptodate(page);
 278                goto confused;
 279        }
 280
 281        /*
 282         * This page will go to BIO.  Do we need to send this BIO off first?
 283         */
 284        if (bio && (*last_block_in_bio != blocks[0] - 1))
 285                bio = mpage_bio_submit(READ, bio);
 286
 287alloc_new:
 288        if (bio == NULL) {
 289                bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 290                                min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
 291                                GFP_KERNEL);
 292                if (bio == NULL)
 293                        goto confused;
 294        }
 295
 296        length = first_hole << blkbits;
 297        if (bio_add_page(bio, page, length, 0) < length) {
 298                bio = mpage_bio_submit(READ, bio);
 299                goto alloc_new;
 300        }
 301
 302        relative_block = block_in_file - *first_logical_block;
 303        nblocks = map_bh->b_size >> blkbits;
 304        if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
 305            (first_hole != blocks_per_page))
 306                bio = mpage_bio_submit(READ, bio);
 307        else
 308                *last_block_in_bio = blocks[blocks_per_page - 1];
 309out:
 310        return bio;
 311
 312confused:
 313        if (bio)
 314                bio = mpage_bio_submit(READ, bio);
 315        if (!PageUptodate(page))
 316                block_read_full_page(page, get_block);
 317        else
 318                unlock_page(page);
 319        goto out;
 320}
 321
 322/**
 323 * mpage_readpages - populate an address space with some pages & start reads against them
 324 * @mapping: the address_space
 325 * @pages: The address of a list_head which contains the target pages.  These
 326 *   pages have their ->index populated and are otherwise uninitialised.
 327 *   The page at @pages->prev has the lowest file offset, and reads should be
 328 *   issued in @pages->prev to @pages->next order.
 329 * @nr_pages: The number of pages at *@pages
 330 * @get_block: The filesystem's block mapper function.
 331 *
 332 * This function walks the pages and the blocks within each page, building and
 333 * emitting large BIOs.
 334 *
 335 * If anything unusual happens, such as:
 336 *
 337 * - encountering a page which has buffers
 338 * - encountering a page which has a non-hole after a hole
 339 * - encountering a page with non-contiguous blocks
 340 *
 341 * then this code just gives up and calls the buffer_head-based read function.
 342 * It does handle a page which has holes at the end - that is a common case:
 343 * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
 344 *
 345 * BH_Boundary explanation:
 346 *
 347 * There is a problem.  The mpage read code assembles several pages, gets all
 348 * their disk mappings, and then submits them all.  That's fine, but obtaining
 349 * the disk mappings may require I/O.  Reads of indirect blocks, for example.
 350 *
 351 * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
 352 * submitted in the following order:
 353 *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
 354 *
 355 * because the indirect block has to be read to get the mappings of blocks
 356 * 13,14,15,16.  Obviously, this impacts performance.
 357 *
 358 * So what we do it to allow the filesystem's get_block() function to set
 359 * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
 360 * after this one will require I/O against a block which is probably close to
 361 * this one.  So you should push what I/O you have currently accumulated.
 362 *
 363 * This all causes the disk requests to be issued in the correct order.
 364 */
 365int
 366mpage_readpages(struct address_space *mapping, struct list_head *pages,
 367                                unsigned nr_pages, get_block_t get_block)
 368{
 369        struct bio *bio = NULL;
 370        unsigned page_idx;
 371        sector_t last_block_in_bio = 0;
 372        struct buffer_head map_bh;
 373        unsigned long first_logical_block = 0;
 374
 375        map_bh.b_state = 0;
 376        map_bh.b_size = 0;
 377        for (page_idx = 0; page_idx < nr_pages; page_idx++) {
 378                struct page *page = list_entry(pages->prev, struct page, lru);
 379
 380                prefetchw(&page->flags);
 381                list_del(&page->lru);
 382                if (!add_to_page_cache_lru(page, mapping,
 383                                        page->index, GFP_KERNEL)) {
 384                        bio = do_mpage_readpage(bio, page,
 385                                        nr_pages - page_idx,
 386                                        &last_block_in_bio, &map_bh,
 387                                        &first_logical_block,
 388                                        get_block);
 389                }
 390                page_cache_release(page);
 391        }
 392        BUG_ON(!list_empty(pages));
 393        if (bio)
 394                mpage_bio_submit(READ, bio);
 395        return 0;
 396}
 397EXPORT_SYMBOL(mpage_readpages);
 398
 399/*
 400 * This isn't called much at all
 401 */
 402int mpage_readpage(struct page *page, get_block_t get_block)
 403{
 404        struct bio *bio = NULL;
 405        sector_t last_block_in_bio = 0;
 406        struct buffer_head map_bh;
 407        unsigned long first_logical_block = 0;
 408
 409        map_bh.b_state = 0;
 410        map_bh.b_size = 0;
 411        bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
 412                        &map_bh, &first_logical_block, get_block);
 413        if (bio)
 414                mpage_bio_submit(READ, bio);
 415        return 0;
 416}
 417EXPORT_SYMBOL(mpage_readpage);
 418
 419/*
 420 * Writing is not so simple.
 421 *
 422 * If the page has buffers then they will be used for obtaining the disk
 423 * mapping.  We only support pages which are fully mapped-and-dirty, with a
 424 * special case for pages which are unmapped at the end: end-of-file.
 425 *
 426 * If the page has no buffers (preferred) then the page is mapped here.
 427 *
 428 * If all blocks are found to be contiguous then the page can go into the
 429 * BIO.  Otherwise fall back to the mapping's writepage().
 430 * 
 431 * FIXME: This code wants an estimate of how many pages are still to be
 432 * written, so it can intelligently allocate a suitably-sized BIO.  For now,
 433 * just allocate full-size (16-page) BIOs.
 434 */
 435
 436struct mpage_data {
 437        struct bio *bio;
 438        sector_t last_block_in_bio;
 439        get_block_t *get_block;
 440        unsigned use_writepage;
 441};
 442
 443static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
 444                      void *data)
 445{
 446        struct mpage_data *mpd = data;
 447        struct bio *bio = mpd->bio;
 448        struct address_space *mapping = page->mapping;
 449        struct inode *inode = page->mapping->host;
 450        const unsigned blkbits = inode->i_blkbits;
 451        unsigned long end_index;
 452        const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
 453        sector_t last_block;
 454        sector_t block_in_file;
 455        sector_t blocks[MAX_BUF_PER_PAGE];
 456        unsigned page_block;
 457        unsigned first_unmapped = blocks_per_page;
 458        struct block_device *bdev = NULL;
 459        int boundary = 0;
 460        sector_t boundary_block = 0;
 461        struct block_device *boundary_bdev = NULL;
 462        int length;
 463        struct buffer_head map_bh;
 464        loff_t i_size = i_size_read(inode);
 465        int ret = 0;
 466
 467        if (page_has_buffers(page)) {
 468                struct buffer_head *head = page_buffers(page);
 469                struct buffer_head *bh = head;
 470
 471                /* If they're all mapped and dirty, do it */
 472                page_block = 0;
 473                do {
 474                        BUG_ON(buffer_locked(bh));
 475                        if (!buffer_mapped(bh)) {
 476                                /*
 477                                 * unmapped dirty buffers are created by
 478                                 * __set_page_dirty_buffers -> mmapped data
 479                                 */
 480                                if (buffer_dirty(bh))
 481                                        goto confused;
 482                                if (first_unmapped == blocks_per_page)
 483                                        first_unmapped = page_block;
 484                                continue;
 485                        }
 486
 487                        if (first_unmapped != blocks_per_page)
 488                                goto confused;  /* hole -> non-hole */
 489
 490                        if (!buffer_dirty(bh) || !buffer_uptodate(bh))
 491                                goto confused;
 492                        if (page_block) {
 493                                if (bh->b_blocknr != blocks[page_block-1] + 1)
 494                                        goto confused;
 495                        }
 496                        blocks[page_block++] = bh->b_blocknr;
 497                        boundary = buffer_boundary(bh);
 498                        if (boundary) {
 499                                boundary_block = bh->b_blocknr;
 500                                boundary_bdev = bh->b_bdev;
 501                        }
 502                        bdev = bh->b_bdev;
 503                } while ((bh = bh->b_this_page) != head);
 504
 505                if (first_unmapped)
 506                        goto page_is_mapped;
 507
 508                /*
 509                 * Page has buffers, but they are all unmapped. The page was
 510                 * created by pagein or read over a hole which was handled by
 511                 * block_read_full_page().  If this address_space is also
 512                 * using mpage_readpages then this can rarely happen.
 513                 */
 514                goto confused;
 515        }
 516
 517        /*
 518         * The page has no buffers: map it to disk
 519         */
 520        BUG_ON(!PageUptodate(page));
 521        block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
 522        last_block = (i_size - 1) >> blkbits;
 523        map_bh.b_page = page;
 524        for (page_block = 0; page_block < blocks_per_page; ) {
 525
 526                map_bh.b_state = 0;
 527                map_bh.b_size = 1 << blkbits;
 528                if (mpd->get_block(inode, block_in_file, &map_bh, 1))
 529                        goto confused;
 530                if (buffer_new(&map_bh))
 531                        unmap_underlying_metadata(map_bh.b_bdev,
 532                                                map_bh.b_blocknr);
 533                if (buffer_boundary(&map_bh)) {
 534                        boundary_block = map_bh.b_blocknr;
 535                        boundary_bdev = map_bh.b_bdev;
 536                }
 537                if (page_block) {
 538                        if (map_bh.b_blocknr != blocks[page_block-1] + 1)
 539                                goto confused;
 540                }
 541                blocks[page_block++] = map_bh.b_blocknr;
 542                boundary = buffer_boundary(&map_bh);
 543                bdev = map_bh.b_bdev;
 544                if (block_in_file == last_block)
 545                        break;
 546                block_in_file++;
 547        }
 548        BUG_ON(page_block == 0);
 549
 550        first_unmapped = page_block;
 551
 552page_is_mapped:
 553        end_index = i_size >> PAGE_CACHE_SHIFT;
 554        if (page->index >= end_index) {
 555                /*
 556                 * The page straddles i_size.  It must be zeroed out on each
 557                 * and every writepage invocation because it may be mmapped.
 558                 * "A file is mapped in multiples of the page size.  For a file
 559                 * that is not a multiple of the page size, the remaining memory
 560                 * is zeroed when mapped, and writes to that region are not
 561                 * written out to the file."
 562                 */
 563                unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
 564
 565                if (page->index > end_index || !offset)
 566                        goto confused;
 567                zero_user_segment(page, offset, PAGE_CACHE_SIZE);
 568        }
 569
 570        /*
 571         * This page will go to BIO.  Do we need to send this BIO off first?
 572         */
 573        if (bio && mpd->last_block_in_bio != blocks[0] - 1)
 574                bio = mpage_bio_submit(WRITE, bio);
 575
 576alloc_new:
 577        if (bio == NULL) {
 578                bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 579                                bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
 580                if (bio == NULL)
 581                        goto confused;
 582        }
 583
 584        /*
 585         * Must try to add the page before marking the buffer clean or
 586         * the confused fail path above (OOM) will be very confused when
 587         * it finds all bh marked clean (i.e. it will not write anything)
 588         */
 589        length = first_unmapped << blkbits;
 590        if (bio_add_page(bio, page, length, 0) < length) {
 591                bio = mpage_bio_submit(WRITE, bio);
 592                goto alloc_new;
 593        }
 594
 595        /*
 596         * OK, we have our BIO, so we can now mark the buffers clean.  Make
 597         * sure to only clean buffers which we know we'll be writing.
 598         */
 599        if (page_has_buffers(page)) {
 600                struct buffer_head *head = page_buffers(page);
 601                struct buffer_head *bh = head;
 602                unsigned buffer_counter = 0;
 603
 604                do {
 605                        if (buffer_counter++ == first_unmapped)
 606                                break;
 607                        clear_buffer_dirty(bh);
 608                        bh = bh->b_this_page;
 609                } while (bh != head);
 610
 611                /*
 612                 * we cannot drop the bh if the page is not uptodate
 613                 * or a concurrent readpage would fail to serialize with the bh
 614                 * and it would read from disk before we reach the platter.
 615                 */
 616                if (buffer_heads_over_limit && PageUptodate(page))
 617                        try_to_free_buffers(page);
 618        }
 619
 620        BUG_ON(PageWriteback(page));
 621        set_page_writeback(page);
 622        unlock_page(page);
 623        if (boundary || (first_unmapped != blocks_per_page)) {
 624                bio = mpage_bio_submit(WRITE, bio);
 625                if (boundary_block) {
 626                        write_boundary_block(boundary_bdev,
 627                                        boundary_block, 1 << blkbits);
 628                }
 629        } else {
 630                mpd->last_block_in_bio = blocks[blocks_per_page - 1];
 631        }
 632        goto out;
 633
 634confused:
 635        if (bio)
 636                bio = mpage_bio_submit(WRITE, bio);
 637
 638        if (mpd->use_writepage) {
 639                ret = mapping->a_ops->writepage(page, wbc);
 640        } else {
 641                ret = -EAGAIN;
 642                goto out;
 643        }
 644        /*
 645         * The caller has a ref on the inode, so *mapping is stable
 646         */
 647        mapping_set_error(mapping, ret);
 648out:
 649        mpd->bio = bio;
 650        return ret;
 651}
 652
 653/**
 654 * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
 655 * @mapping: address space structure to write
 656 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 657 * @get_block: the filesystem's block mapper function.
 658 *             If this is NULL then use a_ops->writepage.  Otherwise, go
 659 *             direct-to-BIO.
 660 *
 661 * This is a library function, which implements the writepages()
 662 * address_space_operation.
 663 *
 664 * If a page is already under I/O, generic_writepages() skips it, even
 665 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 666 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 667 * and msync() need to guarantee that all the data which was dirty at the time
 668 * the call was made get new I/O started against them.  If wbc->sync_mode is
 669 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 670 * existing IO to complete.
 671 */
 672int
 673mpage_writepages(struct address_space *mapping,
 674                struct writeback_control *wbc, get_block_t get_block)
 675{
 676        struct blk_plug plug;
 677        int ret;
 678
 679        blk_start_plug(&plug);
 680
 681        if (!get_block)
 682                ret = generic_writepages(mapping, wbc);
 683        else {
 684                struct mpage_data mpd = {
 685                        .bio = NULL,
 686                        .last_block_in_bio = 0,
 687                        .get_block = get_block,
 688                        .use_writepage = 1,
 689                };
 690
 691                ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
 692                if (mpd.bio)
 693                        mpage_bio_submit(WRITE, mpd.bio);
 694        }
 695        blk_finish_plug(&plug);
 696        return ret;
 697}
 698EXPORT_SYMBOL(mpage_writepages);
 699
 700int mpage_writepage(struct page *page, get_block_t get_block,
 701        struct writeback_control *wbc)
 702{
 703        struct mpage_data mpd = {
 704                .bio = NULL,
 705                .last_block_in_bio = 0,
 706                .get_block = get_block,
 707                .use_writepage = 0,
 708        };
 709        int ret = __mpage_writepage(page, wbc, &mpd);
 710        if (mpd.bio)
 711                mpage_bio_submit(WRITE, mpd.bio);
 712        return ret;
 713}
 714EXPORT_SYMBOL(mpage_writepage);
 715
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.