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    akpm@zip.com.au
  10  *              Initial version
  11  * 27Jun2002    axboe@suse.de
  12  *              use bio_add_page() to build bio's just the right size
  13  */
  14
  15 #include <linux/kernel.h>
  16 #include <linux/module.h>
  17 #include <linux/mm.h>
  18 #include <linux/kdev_t.h>
  19 #include <linux/bio.h>
  20 #include <linux/fs.h>
  21 #include <linux/buffer_head.h>
  22 #include <linux/blkdev.h>
  23 #include <linux/highmem.h>
  24 #include <linux/prefetch.h>
  25 #include <linux/mpage.h>
  26 #include <linux/writeback.h>
  27 #include <linux/backing-dev.h>
  28 #include <linux/pagevec.h>
  29
  30 /*
  31  * I/O completion handler for multipage BIOs.
  32  *
  33  * The mpage code never puts partial pages into a BIO (except for end-of-file).
  34  * If a page does not map to a contiguous run of blocks then it simply falls
  35  * back to block_read_full_page().
  36  *
  37  * Why is this?  If a page's completion depends on a number of different BIOs
  38  * which can complete in any order (or at the same time) then determining the
  39  * status of that page is hard.  See end_buffer_async_read() for the details.
  40  * There is no point in duplicating all that complexity.
  41  */
  42 static int mpage_end_io_read(struct bio *bio, unsigned int bytes_done, int err)
  43 {
  44         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  45         struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
  46
  47         if (bio->bi_size)
  48                 return 1;
  49
  50         do {
  51                 struct page *page = bvec->bv_page;
  52
  53                 if (--bvec >= bio->bi_io_vec)
  54                         prefetchw(&bvec->bv_page->flags);
  55
  56                 if (uptodate) {
  57                         SetPageUptodate(page);
  58                 } else {
  59                         ClearPageUptodate(page);
  60                         SetPageError(page);
  61                 }
  62                 unlock_page(page);
  63         } while (bvec >= bio->bi_io_vec);
  64         bio_put(bio);
  65         return 0;
  66 }
  67
  68 static int mpage_end_io_write(struct bio *bio, unsigned int bytes_done, int err)
  69 {
  70         const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
  71         struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
  72
  73         if (bio->bi_size)
  74                 return 1;
  75
  76         do {
  77                 struct page *page = bvec->bv_page;
  78
  79                 if (--bvec >= bio->bi_io_vec)
  80                         prefetchw(&bvec->bv_page->flags);
  81
  82                 if (!uptodate){
  83                         SetPageError(page);
  84                         if (page->mapping)
  85                                 set_bit(AS_EIO, &page->mapping->flags);
  86                 }
  87                 end_page_writeback(page);
  88         } while (bvec >= bio->bi_io_vec);
  89         bio_put(bio);
  90         return 0;
  91 }
  92
  93 static struct bio *mpage_bio_submit(int rw, struct bio *bio)
  94 {
  95         bio->bi_end_io = mpage_end_io_read;
  96         if (rw == WRITE)
  97                 bio->bi_end_io = mpage_end_io_write;
  98         submit_bio(rw, bio);
  99         return NULL;
 100 }
 101
 102 static struct bio *
 103 mpage_alloc(struct block_device *bdev,
 104                 sector_t first_sector, int nr_vecs,
 105                 gfp_t gfp_flags)
 106 {
 107         struct bio *bio;
 108
 109         bio = bio_alloc(gfp_flags, nr_vecs);
 110
 111         if (bio == NULL && (current->flags & PF_MEMALLOC)) {
 112                 while (!bio && (nr_vecs /= 2))
 113                         bio = bio_alloc(gfp_flags, nr_vecs);
 114         }
 115
 116         if (bio) {
 117                 bio->bi_bdev = bdev;
 118                 bio->bi_sector = first_sector;
 119         }
 120         return bio;
 121 }
 122
 123 /*
 124  * support function for mpage_readpages.  The fs supplied get_block might
 125  * return an up to date buffer.  This is used to map that buffer into
 126  * the page, which allows readpage to avoid triggering a duplicate call
 127  * to get_block.
 128  *
 129  * The idea is to avoid adding buffers to pages that don't already have
 130  * them.  So when the buffer is up to date and the page size == block size,
 131  * this marks the page up to date instead of adding new buffers.
 132  */
 133 static void
 134 map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
 135 {
 136         struct inode *inode = page->mapping->host;
 137         struct buffer_head *page_bh, *head;
 138         int block = 0;
 139
 140         if (!page_has_buffers(page)) {
 141                 /*
 142                  * don't make any buffers if there is only one buffer on
 143                  * the page and the page just needs to be set up to date
 144                  */
 145                 if (inode->i_blkbits == PAGE_CACHE_SHIFT &&
 146                     buffer_uptodate(bh)) {
 147                         SetPageUptodate(page);
 148                         return;
 149                 }
 150                 create_empty_buffers(page, 1 << inode->i_blkbits, 0);
 151         }
 152         head = page_buffers(page);
 153         page_bh = head;
 154         do {
 155                 if (block == page_block) {
 156                         page_bh->b_state = bh->b_state;
 157                         page_bh->b_bdev = bh->b_bdev;
 158                         page_bh->b_blocknr = bh->b_blocknr;
 159                         break;
 160                 }
 161                 page_bh = page_bh->b_this_page;
 162                 block++;
 163         } while (page_bh != head);
 164 }
 165
 166 /*
 167  * This is the worker routine which does all the work of mapping the disk
 168  * blocks and constructs largest possible bios, submits them for IO if the
 169  * blocks are not contiguous on the disk.
 170  *
 171  * We pass a buffer_head back and forth and use its buffer_mapped() flag to
 172  * represent the validity of its disk mapping and to decide when to do the next
 173  * get_block() call.
 174  */
 175 static struct bio *
 176 do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 177                 sector_t *last_block_in_bio, struct buffer_head *map_bh,
 178                 unsigned long *first_logical_block, get_block_t get_block)
 179 {
 180         struct inode *inode = page->mapping->host;
 181         const unsigned blkbits = inode->i_blkbits;
 182         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
 183         const unsigned blocksize = 1 << blkbits;
 184         sector_t block_in_file;
 185         sector_t last_block;
 186         sector_t last_block_in_file;
 187         sector_t blocks[MAX_BUF_PER_PAGE];
 188         unsigned page_block;
 189         unsigned first_hole = blocks_per_page;
 190         struct block_device *bdev = NULL;
 191         int length;
 192         int fully_mapped = 1;
 193         unsigned nblocks;
 194         unsigned relative_block;
 195
 196         if (page_has_buffers(page))
 197                 goto confused;
 198
 199         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
 200         last_block = block_in_file + nr_pages * blocks_per_page;
 201         last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
 202         if (last_block > last_block_in_file)
 203                 last_block = last_block_in_file;
 204         page_block = 0;
 205
 206         /*
 207          * Map blocks using the result from the previous get_blocks call first.
 208          */
 209         nblocks = map_bh->b_size >> blkbits;
 210         if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
 211                         block_in_file < (*first_logical_block + nblocks)) {
 212                 unsigned map_offset = block_in_file - *first_logical_block;
 213                 unsigned last = nblocks - map_offset;
 214
 215                 for (relative_block = 0; ; relative_block++) {
 216                         if (relative_block == last) {
 217                                 clear_buffer_mapped(map_bh);
 218                                 break;
 219                         }
 220                         if (page_block == blocks_per_page)
 221                                 break;
 222                         blocks[page_block] = map_bh->b_blocknr + map_offset +
 223                                                 relative_block;
 224                         page_block++;
 225                         block_in_file++;
 226                 }
 227                 bdev = map_bh->b_bdev;
 228         }
 229
 230         /*
 231          * Then do more get_blocks calls until we are done with this page.
 232          */
 233         map_bh->b_page = page;
 234         while (page_block < blocks_per_page) {
 235                 map_bh->b_state = 0;
 236                 map_bh->b_size = 0;
 237
 238                 if (block_in_file < last_block) {
 239                         map_bh->b_size = (last_block-block_in_file) << blkbits;
 240                         if (get_block(inode, block_in_file, map_bh, 0))
 241                                 goto confused;
 242                         *first_logical_block = block_in_file;
 243                 }
 244
 245                 if (!buffer_mapped(map_bh)) {
 246                         fully_mapped = 0;
 247                         if (first_hole == blocks_per_page)
 248                                 first_hole = page_block;
 249                         page_block++;
 250                         block_in_file++;
 251                         clear_buffer_mapped(map_bh);
 252                         continue;
 253                 }
 254
 255                 /* some filesystems will copy data into the page during
 256                  * the get_block call, in which case we don't want to
 257                  * read it again.  map_buffer_to_page copies the data
 258                  * we just collected from get_block into the page's buffers
 259                  * so readpage doesn't have to repeat the get_block call
 260                  */
 261                 if (buffer_uptodate(map_bh)) {
 262                         map_buffer_to_page(page, map_bh, page_block);
 263                         goto confused;
 264                 }
 265
 266                 if (first_hole != blocks_per_page)
 267                         goto confused;          /* hole -> non-hole */
 268
 269                 /* Contiguous blocks? */
 270                 if (page_block && blocks[page_block-1] != map_bh->b_blocknr-1)
 271                         goto confused;
 272                 nblocks = map_bh->b_size >> blkbits;
 273                 for (relative_block = 0; ; relative_block++) {
 274                         if (relative_block == nblocks) {
 275                                 clear_buffer_mapped(map_bh);
 276                                 break;
 277                         } else if (page_block == blocks_per_page)
 278                                 break;
 279                         blocks[page_block] = map_bh->b_blocknr+relative_block;
 280                         page_block++;
 281                         block_in_file++;
 282                 }
 283                 bdev = map_bh->b_bdev;
 284         }
 285
 286         if (first_hole != blocks_per_page) {
 287                 char *kaddr = kmap_atomic(page, KM_USER0);
 288                 memset(kaddr + (first_hole << blkbits), 0,
 289                                 PAGE_CACHE_SIZE - (first_hole << blkbits));
 290                 flush_dcache_page(page);
 291                 kunmap_atomic(kaddr, KM_USER0);
 292                 if (first_hole == 0) {
 293                         SetPageUptodate(page);
 294                         unlock_page(page);
 295                         goto out;
 296                 }
 297         } else if (fully_mapped) {
 298                 SetPageMappedToDisk(page);
 299         }
 300
 301         /*
 302          * This page will go to BIO.  Do we need to send this BIO off first?
 303          */
 304         if (bio && (*last_block_in_bio != blocks[0] - 1))
 305                 bio = mpage_bio_submit(READ, bio);
 306
 307 alloc_new:
 308         if (bio == NULL) {
 309                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 310                                 min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
 311                                 GFP_KERNEL);
 312                 if (bio == NULL)
 313                         goto confused;
 314         }
 315
 316         length = first_hole << blkbits;
 317         if (bio_add_page(bio, page, length, 0) < length) {
 318                 bio = mpage_bio_submit(READ, bio);
 319                 goto alloc_new;
 320         }
 321
 322         if (buffer_boundary(map_bh) || (first_hole != blocks_per_page))
 323                 bio = mpage_bio_submit(READ, bio);
 324         else
 325                 *last_block_in_bio = blocks[blocks_per_page - 1];
 326 out:
 327         return bio;
 328
 329 confused:
 330         if (bio)
 331                 bio = mpage_bio_submit(READ, bio);
 332         if (!PageUptodate(page))
 333                 block_read_full_page(page, get_block);
 334         else
 335                 unlock_page(page);
 336         goto out;
 337 }
 338
 339 /**
 340  * mpage_readpages - populate an address space with some pages, and
 341  *                       start reads against them.
 342  *
 343  * @mapping: the address_space
 344  * @pages: The address of a list_head which contains the target pages.  These
 345  *   pages have their ->index populated and are otherwise uninitialised.
 346  *
 347  *   The page at @pages->prev has the lowest file offset, and reads should be
 348  *   issued in @pages->prev to @pages->next order.
 349  *
 350  * @nr_pages: The number of pages at *@pages
 351  * @get_block: The filesystem's block mapper function.
 352  *
 353  * This function walks the pages and the blocks within each page, building and
 354  * emitting large BIOs.
 355  *
 356  * If anything unusual happens, such as:
 357  *
 358  * - encountering a page which has buffers
 359  * - encountering a page which has a non-hole after a hole
 360  * - encountering a page with non-contiguous blocks
 361  *
 362  * then this code just gives up and calls the buffer_head-based read function.
 363  * It does handle a page which has holes at the end - that is a common case:
 364  * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
 365  *
 366  * BH_Boundary explanation:
 367  *
 368  * There is a problem.  The mpage read code assembles several pages, gets all
 369  * their disk mappings, and then submits them all.  That's fine, but obtaining
 370  * the disk mappings may require I/O.  Reads of indirect blocks, for example.
 371  *
 372  * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
 373  * submitted in the following order:
 374  *      12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
 375  * because the indirect block has to be read to get the mappings of blocks
 376  * 13,14,15,16.  Obviously, this impacts performance.
 377  *
 378  * So what we do it to allow the filesystem's get_block() function to set
 379  * BH_Boundary when it maps block 11.  BH_Boundary says: mapping of the block
 380  * after this one will require I/O against a block which is probably close to
 381  * this one.  So you should push what I/O you have currently accumulated.
 382  *
 383  * This all causes the disk requests to be issued in the correct order.
 384  */
 385 int
 386 mpage_readpages(struct address_space *mapping, struct list_head *pages,
 387                                 unsigned nr_pages, get_block_t get_block)
 388 {
 389         struct bio *bio = NULL;
 390         unsigned page_idx;
 391         sector_t last_block_in_bio = 0;
 392         struct pagevec lru_pvec;
 393         struct buffer_head map_bh;
 394         unsigned long first_logical_block = 0;
 395
 396         clear_buffer_mapped(&map_bh);
 397         pagevec_init(&lru_pvec, 0);
 398         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
 399                 struct page *page = list_entry(pages->prev, struct page, lru);
 400
 401                 prefetchw(&page->flags);
 402                 list_del(&page->lru);
 403                 if (!add_to_page_cache(page, mapping,
 404                                         page->index, GFP_KERNEL)) {
 405                         bio = do_mpage_readpage(bio, page,
 406                                         nr_pages - page_idx,
 407                                         &last_block_in_bio, &map_bh,
 408                                         &first_logical_block,
 409                                         get_block);
 410                         if (!pagevec_add(&lru_pvec, page))
 411                                 __pagevec_lru_add(&lru_pvec);
 412                 } else {
 413                         page_cache_release(page);
 414                 }
 415         }
 416         pagevec_lru_add(&lru_pvec);
 417         BUG_ON(!list_empty(pages));
 418         if (bio)
 419                 mpage_bio_submit(READ, bio);
 420         return 0;
 421 }
 422 EXPORT_SYMBOL(mpage_readpages);
 423
 424 /*
 425  * This isn't called much at all
 426  */
 427 int mpage_readpage(struct page *page, get_block_t get_block)
 428 {
 429         struct bio *bio = NULL;
 430         sector_t last_block_in_bio = 0;
 431         struct buffer_head map_bh;
 432         unsigned long first_logical_block = 0;
 433
 434         clear_buffer_mapped(&map_bh);
 435         bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
 436                         &map_bh, &first_logical_block, get_block);
 437         if (bio)
 438                 mpage_bio_submit(READ, bio);
 439         return 0;
 440 }
 441 EXPORT_SYMBOL(mpage_readpage);
 442
 443 /*
 444  * Writing is not so simple.
 445  *
 446  * If the page has buffers then they will be used for obtaining the disk
 447  * mapping.  We only support pages which are fully mapped-and-dirty, with a
 448  * special case for pages which are unmapped at the end: end-of-file.
 449  *
 450  * If the page has no buffers (preferred) then the page is mapped here.
 451  *
 452  * If all blocks are found to be contiguous then the page can go into the
 453  * BIO.  Otherwise fall back to the mapping's writepage().
 454  *
 455  * FIXME: This code wants an estimate of how many pages are still to be
 456  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
 457  * just allocate full-size (16-page) BIOs.
 458  */
 459 static struct bio *
 460 __mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
 461         sector_t *last_block_in_bio, int *ret, struct writeback_control *wbc,
 462         writepage_t writepage_fn)
 463 {
 464         struct address_space *mapping = page->mapping;
 465         struct inode *inode = page->mapping->host;
 466         const unsigned blkbits = inode->i_blkbits;
 467         unsigned long end_index;
 468         const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
 469         sector_t last_block;
 470         sector_t block_in_file;
 471         sector_t blocks[MAX_BUF_PER_PAGE];
 472         unsigned page_block;
 473         unsigned first_unmapped = blocks_per_page;
 474         struct block_device *bdev = NULL;
 475         int boundary = 0;
 476         sector_t boundary_block = 0;
 477         struct block_device *boundary_bdev = NULL;
 478         int length;
 479         struct buffer_head map_bh;
 480         loff_t i_size = i_size_read(inode);
 481
 482         if (page_has_buffers(page)) {
 483                 struct buffer_head *head = page_buffers(page);
 484                 struct buffer_head *bh = head;
 485
 486                 /* If they're all mapped and dirty, do it */
 487                 page_block = 0;
 488                 do {
 489                         BUG_ON(buffer_locked(bh));
 490                         if (!buffer_mapped(bh)) {
 491                                 /*
 492                                  * unmapped dirty buffers are created by
 493                                  * __set_page_dirty_buffers -> mmapped data
 494                                  */
 495                                 if (buffer_dirty(bh))
 496                                         goto confused;
 497                                 if (first_unmapped == blocks_per_page)
 498                                         first_unmapped = page_block;
 499                                 continue;
 500                         }
 501
 502                         if (first_unmapped != blocks_per_page)
 503                                 goto confused;  /* hole -> non-hole */
 504
 505                         if (!buffer_dirty(bh) || !buffer_uptodate(bh))
 506                                 goto confused;
 507                         if (page_block) {
 508                                 if (bh->b_blocknr != blocks[page_block-1] + 1)
 509                                         goto confused;
 510                         }
 511                         blocks[page_block++] = bh->b_blocknr;
 512                         boundary = buffer_boundary(bh);
 513                         if (boundary) {
 514                                 boundary_block = bh->b_blocknr;
 515                                 boundary_bdev = bh->b_bdev;
 516                         }
 517                         bdev = bh->b_bdev;
 518                 } while ((bh = bh->b_this_page) != head);
 519
 520                 if (first_unmapped)
 521                         goto page_is_mapped;
 522
 523                 /*
 524                  * Page has buffers, but they are all unmapped. The page was
 525                  * created by pagein or read over a hole which was handled by
 526                  * block_read_full_page().  If this address_space is also
 527                  * using mpage_readpages then this can rarely happen.
 528                  */
 529                 goto confused;
 530         }
 531
 532         /*
 533          * The page has no buffers: map it to disk
 534          */
 535         BUG_ON(!PageUptodate(page));
 536         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
 537         last_block = (i_size - 1) >> blkbits;
 538         map_bh.b_page = page;
 539         for (page_block = 0; page_block < blocks_per_page; ) {
 540
 541                 map_bh.b_state = 0;
 542                 map_bh.b_size = 1 << blkbits;
 543                 if (get_block(inode, block_in_file, &map_bh, 1))
 544                         goto confused;
 545                 if (buffer_new(&map_bh))
 546                         unmap_underlying_metadata(map_bh.b_bdev,
 547                                                 map_bh.b_blocknr);
 548                 if (buffer_boundary(&map_bh)) {
 549                         boundary_block = map_bh.b_blocknr;
 550                         boundary_bdev = map_bh.b_bdev;
 551                 }
 552                 if (page_block) {
 553                         if (map_bh.b_blocknr != blocks[page_block-1] + 1)
 554                                 goto confused;
 555                 }
 556                 blocks[page_block++] = map_bh.b_blocknr;
 557                 boundary = buffer_boundary(&map_bh);
 558                 bdev = map_bh.b_bdev;
 559                 if (block_in_file == last_block)
 560                         break;
 561                 block_in_file++;
 562         }
 563         BUG_ON(page_block == 0);
 564
 565         first_unmapped = page_block;
 566
 567 page_is_mapped:
 568         end_index = i_size >> PAGE_CACHE_SHIFT;
 569         if (page->index >= end_index) {
 570                 /*
 571                  * The page straddles i_size.  It must be zeroed out on each
 572                  * and every writepage invokation because it may be mmapped.
 573                  * "A file is mapped in multiples of the page size.  For a file
 574                  * that is not a multiple of the page size, the remaining memory
 575                  * is zeroed when mapped, and writes to that region are not
 576                  * written out to the file."
 577                  */
 578                 unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);
 579                 char *kaddr;
 580
 581                 if (page->index > end_index || !offset)
 582                         goto confused;
 583                 kaddr = kmap_atomic(page, KM_USER0);
 584                 memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
 585                 flush_dcache_page(page);
 586                 kunmap_atomic(kaddr, KM_USER0);
 587         }
 588
 589         /*
 590          * This page will go to BIO.  Do we need to send this BIO off first?
 591          */
 592         if (bio && *last_block_in_bio != blocks[0] - 1)
 593                 bio = mpage_bio_submit(WRITE, bio);
 594
 595 alloc_new:
 596         if (bio == NULL) {
 597                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
 598                                 bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
 599                 if (bio == NULL)
 600                         goto confused;
 601         }
 602
 603         /*
 604          * Must try to add the page before marking the buffer clean or
 605          * the confused fail path above (OOM) will be very confused when
 606          * it finds all bh marked clean (i.e. it will not write anything)
 607          */
 608         length = first_unmapped << blkbits;
 609         if (bio_add_page(bio, page, length, 0) < length) {
 610                 bio = mpage_bio_submit(WRITE, bio);
 611                 goto alloc_new;
 612         }
 613
 614         /*
 615          * OK, we have our BIO, so we can now mark the buffers clean.  Make
 616          * sure to only clean buffers which we know we'll be writing.
 617          */
 618         if (page_has_buffers(page)) {
 619                 struct buffer_head *head = page_buffers(page);
 620                 struct buffer_head *bh = head;
 621                 unsigned buffer_counter = 0;
 622
 623                 do {
 624                         if (buffer_counter++ == first_unmapped)
 625                                 break;
 626                         clear_buffer_dirty(bh);
 627                         bh = bh->b_this_page;
 628                 } while (bh != head);
 629
 630                 /*
 631                  * we cannot drop the bh if the page is not uptodate
 632                  * or a concurrent readpage would fail to serialize with the bh
 633                  * and it would read from disk before we reach the platter.
 634                  */
 635                 if (buffer_heads_over_limit && PageUptodate(page))
 636                         try_to_free_buffers(page);
 637         }
 638
 639         BUG_ON(PageWriteback(page));
 640         set_page_writeback(page);
 641         unlock_page(page);
 642         if (boundary || (first_unmapped != blocks_per_page)) {
 643                 bio = mpage_bio_submit(WRITE, bio);
 644                 if (boundary_block) {
 645                         write_boundary_block(boundary_bdev,
 646                                         boundary_block, 1 << blkbits);
 647                 }
 648         } else {
 649                 *last_block_in_bio = blocks[blocks_per_page - 1];
 650         }
 651         goto out;
 652
 653 confused:
 654         if (bio)
 655                 bio = mpage_bio_submit(WRITE, bio);
 656
 657         if (writepage_fn) {
 658                 *ret = (*writepage_fn)(page, wbc);
 659         } else {
 660                 *ret = -EAGAIN;
 661                 goto out;
 662         }
 663         /*
 664          * The caller has a ref on the inode, so *mapping is stable
 665          */
 666         if (*ret) {
 667                 if (*ret == -ENOSPC)
 668                         set_bit(AS_ENOSPC, &mapping->flags);
 669                 else
 670                         set_bit(AS_EIO, &mapping->flags);
 671         }
 672 out:
 673         return bio;
 674 }
 675
 676 /**
 677  * mpage_writepages - walk the list of dirty pages of the given
 678  * address space and writepage() all of them.
 679  *
 680  * @mapping: address space structure to write
 681  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 682  * @get_block: the filesystem's block mapper function.
 683  *             If this is NULL then use a_ops->writepage.  Otherwise, go
 684  *             direct-to-BIO.
 685  *
 686  * This is a library function, which implements the writepages()
 687  * address_space_operation.
 688  *
 689  * If a page is already under I/O, generic_writepages() skips it, even
 690  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 691  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 692  * and msync() need to guarantee that all the data which was dirty at the time
 693  * the call was made get new I/O started against them.  If wbc->sync_mode is
 694  * WB_SYNC_ALL then we were called for data integrity and we must wait for
 695  * existing IO to complete.
 696  */
 697 int
 698 mpage_writepages(struct address_space *mapping,
 699                 struct writeback_control *wbc, get_block_t get_block)
 700 {
 701         struct backing_dev_info *bdi = mapping->backing_dev_info;
 702         struct bio *bio = NULL;
 703         sector_t last_block_in_bio = 0;
 704         int ret = 0;
 705         int done = 0;
 706         int (*writepage)(struct page *page, struct writeback_control *wbc);
 707         struct pagevec pvec;
 708         int nr_pages;
 709         pgoff_t index;
 710         pgoff_t end = -1;               /* Inclusive */
 711         int scanned = 0;
 712         int is_range = 0;
 713
 714         if (wbc->nonblocking && bdi_write_congested(bdi)) {
 715                 wbc->encountered_congestion = 1;
 716                 return 0;
 717         }
 718
 719         writepage = NULL;
 720         if (get_block == NULL)
 721                 writepage = mapping->a_ops->writepage;
 722
 723         pagevec_init(&pvec, 0);
 724         if (wbc->sync_mode == WB_SYNC_NONE) {
 725                 index = mapping->writeback_index; /* Start from prev offset */
 726         } else {
 727                 index = 0;                        /* whole-file sweep */
 728                 scanned = 1;
 729         }
 730         if (wbc->start || wbc->end) {
 731                 index = wbc->start >> PAGE_CACHE_SHIFT;
 732                 end = wbc->end >> PAGE_CACHE_SHIFT;
 733                 is_range = 1;
 734                 scanned = 1;
 735         }
 736 retry:
 737         while (!done && (index <= end) &&
 738                         (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
 739                         PAGECACHE_TAG_DIRTY,
 740                         min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
 741                 unsigned i;
 742
 743                 scanned = 1;
 744                 for (i = 0; i < nr_pages; i++) {
 745                         struct page *page = pvec.pages[i];
 746
 747                         /*
 748                          * At this point we hold neither mapping->tree_lock nor
 749                          * lock on the page itself: the page may be truncated or
 750                          * invalidated (changing page->mapping to NULL), or even
 751                          * swizzled back from swapper_space to tmpfs file
 752                          * mapping
 753                          */
 754
 755                         lock_page(page);
 756
 757                         if (unlikely(page->mapping != mapping)) {
 758                                 unlock_page(page);
 759                                 continue;
 760                         }
 761
 762                         if (unlikely(is_range) && page->index > end) {
 763                                 done = 1;
 764                                 unlock_page(page);
 765                                 continue;
 766                         }
 767
 768                         if (wbc->sync_mode != WB_SYNC_NONE)
 769                                 wait_on_page_writeback(page);
 770
 771                         if (PageWriteback(page) ||
 772                                         !clear_page_dirty_for_io(page)) {
 773                                 unlock_page(page);
 774                                 continue;
 775                         }
 776
 777                         if (writepage) {
 778                                 ret = (*writepage)(page, wbc);
 779                                 if (ret) {
 780                                         if (ret == -ENOSPC)
 781                                                 set_bit(AS_ENOSPC,
 782                                                         &mapping->flags);
 783                                         else
 784                                                 set_bit(AS_EIO,
 785                                                         &mapping->flags);
 786                                 }
 787                         } else {
 788                                 bio = __mpage_writepage(bio, page, get_block,
 789                                                 &last_block_in_bio, &ret, wbc,
 790                                                 page->mapping->a_ops->writepage);
 791                         }
 792                         if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE))
 793                                 unlock_page(page);
 794                         if (ret || (--(wbc->nr_to_write) <= 0))
 795                                 done = 1;
 796                         if (wbc->nonblocking && bdi_write_congested(bdi)) {
 797                                 wbc->encountered_congestion = 1;
 798                                 done = 1;
 799                         }
 800                 }
 801                 pagevec_release(&pvec);
 802                 cond_resched();
 803         }
 804         if (!scanned && !done) {
 805                 /*
 806                  * We hit the last page and there is more work to be done: wrap
 807                  * back to the start of the file
 808                  */
 809                 scanned = 1;
 810                 index = 0;
 811                 goto retry;
 812         }
 813         if (!is_range)
 814                 mapping->writeback_index = index;
 815         if (bio)
 816                 mpage_bio_submit(WRITE, bio);
 817         return ret;
 818 }
 819 EXPORT_SYMBOL(mpage_writepages);
 820
 821 int mpage_writepage(struct page *page, get_block_t get_block,
 822         struct writeback_control *wbc)
 823 {
 824         int ret = 0;
 825         struct bio *bio;
 826         sector_t last_block_in_bio = 0;
 827
 828         bio = __mpage_writepage(NULL, page, get_block,
 829                         &last_block_in_bio, &ret, wbc, NULL);
 830         if (bio)
 831                 mpage_bio_submit(WRITE, bio);
 832
 833         return ret;
 834 }
 835 EXPORT_SYMBOL(mpage_writepage);