linux/fs/buffer.c
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   1/*
   2 *  linux/fs/buffer.c
   3 *
   4 *  Copyright (C) 1991, 1992, 2002  Linus Torvalds
   5 */
   6
   7/*
   8 * Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
   9 *
  10 * Removed a lot of unnecessary code and simplified things now that
  11 * the buffer cache isn't our primary cache - Andrew Tridgell 12/96
  12 *
  13 * Speed up hash, lru, and free list operations.  Use gfp() for allocating
  14 * hash table, use SLAB cache for buffer heads. SMP threading.  -DaveM
  15 *
  16 * Added 32k buffer block sizes - these are required older ARM systems. - RMK
  17 *
  18 * async buffer flushing, 1999 Andrea Arcangeli <andrea@suse.de>
  19 */
  20
  21#include <linux/kernel.h>
  22#include <linux/syscalls.h>
  23#include <linux/fs.h>
  24#include <linux/mm.h>
  25#include <linux/percpu.h>
  26#include <linux/slab.h>
  27#include <linux/capability.h>
  28#include <linux/blkdev.h>
  29#include <linux/file.h>
  30#include <linux/quotaops.h>
  31#include <linux/highmem.h>
  32#include <linux/export.h>
  33#include <linux/writeback.h>
  34#include <linux/hash.h>
  35#include <linux/suspend.h>
  36#include <linux/buffer_head.h>
  37#include <linux/task_io_accounting_ops.h>
  38#include <linux/bio.h>
  39#include <linux/notifier.h>
  40#include <linux/cpu.h>
  41#include <linux/bitops.h>
  42#include <linux/mpage.h>
  43#include <linux/bit_spinlock.h>
  44
  45static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
  46
  47#define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
  48
  49void init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
  50{
  51        bh->b_end_io = handler;
  52        bh->b_private = private;
  53}
  54EXPORT_SYMBOL(init_buffer);
  55
  56static int sleep_on_buffer(void *word)
  57{
  58        io_schedule();
  59        return 0;
  60}
  61
  62void __lock_buffer(struct buffer_head *bh)
  63{
  64        wait_on_bit_lock(&bh->b_state, BH_Lock, sleep_on_buffer,
  65                                                        TASK_UNINTERRUPTIBLE);
  66}
  67EXPORT_SYMBOL(__lock_buffer);
  68
  69void unlock_buffer(struct buffer_head *bh)
  70{
  71        clear_bit_unlock(BH_Lock, &bh->b_state);
  72        smp_mb__after_clear_bit();
  73        wake_up_bit(&bh->b_state, BH_Lock);
  74}
  75EXPORT_SYMBOL(unlock_buffer);
  76
  77/*
  78 * Block until a buffer comes unlocked.  This doesn't stop it
  79 * from becoming locked again - you have to lock it yourself
  80 * if you want to preserve its state.
  81 */
  82void __wait_on_buffer(struct buffer_head * bh)
  83{
  84        wait_on_bit(&bh->b_state, BH_Lock, sleep_on_buffer, TASK_UNINTERRUPTIBLE);
  85}
  86EXPORT_SYMBOL(__wait_on_buffer);
  87
  88static void
  89__clear_page_buffers(struct page *page)
  90{
  91        ClearPagePrivate(page);
  92        set_page_private(page, 0);
  93        page_cache_release(page);
  94}
  95
  96
  97static int quiet_error(struct buffer_head *bh)
  98{
  99        if (!test_bit(BH_Quiet, &bh->b_state) && printk_ratelimit())
 100                return 0;
 101        return 1;
 102}
 103
 104
 105static void buffer_io_error(struct buffer_head *bh)
 106{
 107        char b[BDEVNAME_SIZE];
 108        printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
 109                        bdevname(bh->b_bdev, b),
 110                        (unsigned long long)bh->b_blocknr);
 111}
 112
 113/*
 114 * End-of-IO handler helper function which does not touch the bh after
 115 * unlocking it.
 116 * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
 117 * a race there is benign: unlock_buffer() only use the bh's address for
 118 * hashing after unlocking the buffer, so it doesn't actually touch the bh
 119 * itself.
 120 */
 121static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
 122{
 123        if (uptodate) {
 124                set_buffer_uptodate(bh);
 125        } else {
 126                /* This happens, due to failed READA attempts. */
 127                clear_buffer_uptodate(bh);
 128        }
 129        unlock_buffer(bh);
 130}
 131
 132/*
 133 * Default synchronous end-of-IO handler..  Just mark it up-to-date and
 134 * unlock the buffer. This is what ll_rw_block uses too.
 135 */
 136void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
 137{
 138        __end_buffer_read_notouch(bh, uptodate);
 139        put_bh(bh);
 140}
 141EXPORT_SYMBOL(end_buffer_read_sync);
 142
 143void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 144{
 145        char b[BDEVNAME_SIZE];
 146
 147        if (uptodate) {
 148                set_buffer_uptodate(bh);
 149        } else {
 150                if (!quiet_error(bh)) {
 151                        buffer_io_error(bh);
 152                        printk(KERN_WARNING "lost page write due to "
 153                                        "I/O error on %s\n",
 154                                       bdevname(bh->b_bdev, b));
 155                }
 156                set_buffer_write_io_error(bh);
 157                clear_buffer_uptodate(bh);
 158        }
 159        unlock_buffer(bh);
 160        put_bh(bh);
 161}
 162EXPORT_SYMBOL(end_buffer_write_sync);
 163
 164/*
 165 * Various filesystems appear to want __find_get_block to be non-blocking.
 166 * But it's the page lock which protects the buffers.  To get around this,
 167 * we get exclusion from try_to_free_buffers with the blockdev mapping's
 168 * private_lock.
 169 *
 170 * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
 171 * may be quite high.  This code could TryLock the page, and if that
 172 * succeeds, there is no need to take private_lock. (But if
 173 * private_lock is contended then so is mapping->tree_lock).
 174 */
 175static struct buffer_head *
 176__find_get_block_slow(struct block_device *bdev, sector_t block)
 177{
 178        struct inode *bd_inode = bdev->bd_inode;
 179        struct address_space *bd_mapping = bd_inode->i_mapping;
 180        struct buffer_head *ret = NULL;
 181        pgoff_t index;
 182        struct buffer_head *bh;
 183        struct buffer_head *head;
 184        struct page *page;
 185        int all_mapped = 1;
 186
 187        index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
 188        page = find_get_page(bd_mapping, index);
 189        if (!page)
 190                goto out;
 191
 192        spin_lock(&bd_mapping->private_lock);
 193        if (!page_has_buffers(page))
 194                goto out_unlock;
 195        head = page_buffers(page);
 196        bh = head;
 197        do {
 198                if (!buffer_mapped(bh))
 199                        all_mapped = 0;
 200                else if (bh->b_blocknr == block) {
 201                        ret = bh;
 202                        get_bh(bh);
 203                        goto out_unlock;
 204                }
 205                bh = bh->b_this_page;
 206        } while (bh != head);
 207
 208        /* we might be here because some of the buffers on this page are
 209         * not mapped.  This is due to various races between
 210         * file io on the block device and getblk.  It gets dealt with
 211         * elsewhere, don't buffer_error if we had some unmapped buffers
 212         */
 213        if (all_mapped) {
 214                char b[BDEVNAME_SIZE];
 215
 216                printk("__find_get_block_slow() failed. "
 217                        "block=%llu, b_blocknr=%llu\n",
 218                        (unsigned long long)block,
 219                        (unsigned long long)bh->b_blocknr);
 220                printk("b_state=0x%08lx, b_size=%zu\n",
 221                        bh->b_state, bh->b_size);
 222                printk("device %s blocksize: %d\n", bdevname(bdev, b),
 223                        1 << bd_inode->i_blkbits);
 224        }
 225out_unlock:
 226        spin_unlock(&bd_mapping->private_lock);
 227        page_cache_release(page);
 228out:
 229        return ret;
 230}
 231
 232/*
 233 * Kick the writeback threads then try to free up some ZONE_NORMAL memory.
 234 */
 235static void free_more_memory(void)
 236{
 237        struct zone *zone;
 238        int nid;
 239
 240        wakeup_flusher_threads(1024, WB_REASON_FREE_MORE_MEM);
 241        yield();
 242
 243        for_each_online_node(nid) {
 244                (void)first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
 245                                                gfp_zone(GFP_NOFS), NULL,
 246                                                &zone);
 247                if (zone)
 248                        try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
 249                                                GFP_NOFS, NULL);
 250        }
 251}
 252
 253/*
 254 * I/O completion handler for block_read_full_page() - pages
 255 * which come unlocked at the end of I/O.
 256 */
 257static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
 258{
 259        unsigned long flags;
 260        struct buffer_head *first;
 261        struct buffer_head *tmp;
 262        struct page *page;
 263        int page_uptodate = 1;
 264
 265        BUG_ON(!buffer_async_read(bh));
 266
 267        page = bh->b_page;
 268        if (uptodate) {
 269                set_buffer_uptodate(bh);
 270        } else {
 271                clear_buffer_uptodate(bh);
 272                if (!quiet_error(bh))
 273                        buffer_io_error(bh);
 274                SetPageError(page);
 275        }
 276
 277        /*
 278         * Be _very_ careful from here on. Bad things can happen if
 279         * two buffer heads end IO at almost the same time and both
 280         * decide that the page is now completely done.
 281         */
 282        first = page_buffers(page);
 283        local_irq_save(flags);
 284        bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
 285        clear_buffer_async_read(bh);
 286        unlock_buffer(bh);
 287        tmp = bh;
 288        do {
 289                if (!buffer_uptodate(tmp))
 290                        page_uptodate = 0;
 291                if (buffer_async_read(tmp)) {
 292                        BUG_ON(!buffer_locked(tmp));
 293                        goto still_busy;
 294                }
 295                tmp = tmp->b_this_page;
 296        } while (tmp != bh);
 297        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 298        local_irq_restore(flags);
 299
 300        /*
 301         * If none of the buffers had errors and they are all
 302         * uptodate then we can set the page uptodate.
 303         */
 304        if (page_uptodate && !PageError(page))
 305                SetPageUptodate(page);
 306        unlock_page(page);
 307        return;
 308
 309still_busy:
 310        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 311        local_irq_restore(flags);
 312        return;
 313}
 314
 315/*
 316 * Completion handler for block_write_full_page() - pages which are unlocked
 317 * during I/O, and which have PageWriteback cleared upon I/O completion.
 318 */
 319void end_buffer_async_write(struct buffer_head *bh, int uptodate)
 320{
 321        char b[BDEVNAME_SIZE];
 322        unsigned long flags;
 323        struct buffer_head *first;
 324        struct buffer_head *tmp;
 325        struct page *page;
 326
 327        BUG_ON(!buffer_async_write(bh));
 328
 329        page = bh->b_page;
 330        if (uptodate) {
 331                set_buffer_uptodate(bh);
 332        } else {
 333                if (!quiet_error(bh)) {
 334                        buffer_io_error(bh);
 335                        printk(KERN_WARNING "lost page write due to "
 336                                        "I/O error on %s\n",
 337                               bdevname(bh->b_bdev, b));
 338                }
 339                set_bit(AS_EIO, &page->mapping->flags);
 340                set_buffer_write_io_error(bh);
 341                clear_buffer_uptodate(bh);
 342                SetPageError(page);
 343        }
 344
 345        first = page_buffers(page);
 346        local_irq_save(flags);
 347        bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
 348
 349        clear_buffer_async_write(bh);
 350        unlock_buffer(bh);
 351        tmp = bh->b_this_page;
 352        while (tmp != bh) {
 353                if (buffer_async_write(tmp)) {
 354                        BUG_ON(!buffer_locked(tmp));
 355                        goto still_busy;
 356                }
 357                tmp = tmp->b_this_page;
 358        }
 359        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 360        local_irq_restore(flags);
 361        end_page_writeback(page);
 362        return;
 363
 364still_busy:
 365        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 366        local_irq_restore(flags);
 367        return;
 368}
 369EXPORT_SYMBOL(end_buffer_async_write);
 370
 371/*
 372 * If a page's buffers are under async readin (end_buffer_async_read
 373 * completion) then there is a possibility that another thread of
 374 * control could lock one of the buffers after it has completed
 375 * but while some of the other buffers have not completed.  This
 376 * locked buffer would confuse end_buffer_async_read() into not unlocking
 377 * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
 378 * that this buffer is not under async I/O.
 379 *
 380 * The page comes unlocked when it has no locked buffer_async buffers
 381 * left.
 382 *
 383 * PageLocked prevents anyone starting new async I/O reads any of
 384 * the buffers.
 385 *
 386 * PageWriteback is used to prevent simultaneous writeout of the same
 387 * page.
 388 *
 389 * PageLocked prevents anyone from starting writeback of a page which is
 390 * under read I/O (PageWriteback is only ever set against a locked page).
 391 */
 392static void mark_buffer_async_read(struct buffer_head *bh)
 393{
 394        bh->b_end_io = end_buffer_async_read;
 395        set_buffer_async_read(bh);
 396}
 397
 398static void mark_buffer_async_write_endio(struct buffer_head *bh,
 399                                          bh_end_io_t *handler)
 400{
 401        bh->b_end_io = handler;
 402        set_buffer_async_write(bh);
 403}
 404
 405void mark_buffer_async_write(struct buffer_head *bh)
 406{
 407        mark_buffer_async_write_endio(bh, end_buffer_async_write);
 408}
 409EXPORT_SYMBOL(mark_buffer_async_write);
 410
 411
 412/*
 413 * fs/buffer.c contains helper functions for buffer-backed address space's
 414 * fsync functions.  A common requirement for buffer-based filesystems is
 415 * that certain data from the backing blockdev needs to be written out for
 416 * a successful fsync().  For example, ext2 indirect blocks need to be
 417 * written back and waited upon before fsync() returns.
 418 *
 419 * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
 420 * inode_has_buffers() and invalidate_inode_buffers() are provided for the
 421 * management of a list of dependent buffers at ->i_mapping->private_list.
 422 *
 423 * Locking is a little subtle: try_to_free_buffers() will remove buffers
 424 * from their controlling inode's queue when they are being freed.  But
 425 * try_to_free_buffers() will be operating against the *blockdev* mapping
 426 * at the time, not against the S_ISREG file which depends on those buffers.
 427 * So the locking for private_list is via the private_lock in the address_space
 428 * which backs the buffers.  Which is different from the address_space 
 429 * against which the buffers are listed.  So for a particular address_space,
 430 * mapping->private_lock does *not* protect mapping->private_list!  In fact,
 431 * mapping->private_list will always be protected by the backing blockdev's
 432 * ->private_lock.
 433 *
 434 * Which introduces a requirement: all buffers on an address_space's
 435 * ->private_list must be from the same address_space: the blockdev's.
 436 *
 437 * address_spaces which do not place buffers at ->private_list via these
 438 * utility functions are free to use private_lock and private_list for
 439 * whatever they want.  The only requirement is that list_empty(private_list)
 440 * be true at clear_inode() time.
 441 *
 442 * FIXME: clear_inode should not call invalidate_inode_buffers().  The
 443 * filesystems should do that.  invalidate_inode_buffers() should just go
 444 * BUG_ON(!list_empty).
 445 *
 446 * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
 447 * take an address_space, not an inode.  And it should be called
 448 * mark_buffer_dirty_fsync() to clearly define why those buffers are being
 449 * queued up.
 450 *
 451 * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
 452 * list if it is already on a list.  Because if the buffer is on a list,
 453 * it *must* already be on the right one.  If not, the filesystem is being
 454 * silly.  This will save a ton of locking.  But first we have to ensure
 455 * that buffers are taken *off* the old inode's list when they are freed
 456 * (presumably in truncate).  That requires careful auditing of all
 457 * filesystems (do it inside bforget()).  It could also be done by bringing
 458 * b_inode back.
 459 */
 460
 461/*
 462 * The buffer's backing address_space's private_lock must be held
 463 */
 464static void __remove_assoc_queue(struct buffer_head *bh)
 465{
 466        list_del_init(&bh->b_assoc_buffers);
 467        WARN_ON(!bh->b_assoc_map);
 468        if (buffer_write_io_error(bh))
 469                set_bit(AS_EIO, &bh->b_assoc_map->flags);
 470        bh->b_assoc_map = NULL;
 471}
 472
 473int inode_has_buffers(struct inode *inode)
 474{
 475        return !list_empty(&inode->i_data.private_list);
 476}
 477
 478/*
 479 * osync is designed to support O_SYNC io.  It waits synchronously for
 480 * all already-submitted IO to complete, but does not queue any new
 481 * writes to the disk.
 482 *
 483 * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
 484 * you dirty the buffers, and then use osync_inode_buffers to wait for
 485 * completion.  Any other dirty buffers which are not yet queued for
 486 * write will not be flushed to disk by the osync.
 487 */
 488static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
 489{
 490        struct buffer_head *bh;
 491        struct list_head *p;
 492        int err = 0;
 493
 494        spin_lock(lock);
 495repeat:
 496        list_for_each_prev(p, list) {
 497                bh = BH_ENTRY(p);
 498                if (buffer_locked(bh)) {
 499                        get_bh(bh);
 500                        spin_unlock(lock);
 501                        wait_on_buffer(bh);
 502                        if (!buffer_uptodate(bh))
 503                                err = -EIO;
 504                        brelse(bh);
 505                        spin_lock(lock);
 506                        goto repeat;
 507                }
 508        }
 509        spin_unlock(lock);
 510        return err;
 511}
 512
 513static void do_thaw_one(struct super_block *sb, void *unused)
 514{
 515        char b[BDEVNAME_SIZE];
 516        while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
 517                printk(KERN_WARNING "Emergency Thaw on %s\n",
 518                       bdevname(sb->s_bdev, b));
 519}
 520
 521static void do_thaw_all(struct work_struct *work)
 522{
 523        iterate_supers(do_thaw_one, NULL);
 524        kfree(work);
 525        printk(KERN_WARNING "Emergency Thaw complete\n");
 526}
 527
 528/**
 529 * emergency_thaw_all -- forcibly thaw every frozen filesystem
 530 *
 531 * Used for emergency unfreeze of all filesystems via SysRq
 532 */
 533void emergency_thaw_all(void)
 534{
 535        struct work_struct *work;
 536
 537        work = kmalloc(sizeof(*work), GFP_ATOMIC);
 538        if (work) {
 539                INIT_WORK(work, do_thaw_all);
 540                schedule_work(work);
 541        }
 542}
 543
 544/**
 545 * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
 546 * @mapping: the mapping which wants those buffers written
 547 *
 548 * Starts I/O against the buffers at mapping->private_list, and waits upon
 549 * that I/O.
 550 *
 551 * Basically, this is a convenience function for fsync().
 552 * @mapping is a file or directory which needs those buffers to be written for
 553 * a successful fsync().
 554 */
 555int sync_mapping_buffers(struct address_space *mapping)
 556{
 557        struct address_space *buffer_mapping = mapping->private_data;
 558
 559        if (buffer_mapping == NULL || list_empty(&mapping->private_list))
 560                return 0;
 561
 562        return fsync_buffers_list(&buffer_mapping->private_lock,
 563                                        &mapping->private_list);
 564}
 565EXPORT_SYMBOL(sync_mapping_buffers);
 566
 567/*
 568 * Called when we've recently written block `bblock', and it is known that
 569 * `bblock' was for a buffer_boundary() buffer.  This means that the block at
 570 * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
 571 * dirty, schedule it for IO.  So that indirects merge nicely with their data.
 572 */
 573void write_boundary_block(struct block_device *bdev,
 574                        sector_t bblock, unsigned blocksize)
 575{
 576        struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
 577        if (bh) {
 578                if (buffer_dirty(bh))
 579                        ll_rw_block(WRITE, 1, &bh);
 580                put_bh(bh);
 581        }
 582}
 583
 584void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
 585{
 586        struct address_space *mapping = inode->i_mapping;
 587        struct address_space *buffer_mapping = bh->b_page->mapping;
 588
 589        mark_buffer_dirty(bh);
 590        if (!mapping->private_data) {
 591                mapping->private_data = buffer_mapping;
 592        } else {
 593                BUG_ON(mapping->private_data != buffer_mapping);
 594        }
 595        if (!bh->b_assoc_map) {
 596                spin_lock(&buffer_mapping->private_lock);
 597                list_move_tail(&bh->b_assoc_buffers,
 598                                &mapping->private_list);
 599                bh->b_assoc_map = mapping;
 600                spin_unlock(&buffer_mapping->private_lock);
 601        }
 602}
 603EXPORT_SYMBOL(mark_buffer_dirty_inode);
 604
 605/*
 606 * Mark the page dirty, and set it dirty in the radix tree, and mark the inode
 607 * dirty.
 608 *
 609 * If warn is true, then emit a warning if the page is not uptodate and has
 610 * not been truncated.
 611 */
 612static void __set_page_dirty(struct page *page,
 613                struct address_space *mapping, int warn)
 614{
 615        spin_lock_irq(&mapping->tree_lock);
 616        if (page->mapping) {    /* Race with truncate? */
 617                WARN_ON_ONCE(warn && !PageUptodate(page));
 618                account_page_dirtied(page, mapping);
 619                radix_tree_tag_set(&mapping->page_tree,
 620                                page_index(page), PAGECACHE_TAG_DIRTY);
 621        }
 622        spin_unlock_irq(&mapping->tree_lock);
 623        __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 624}
 625
 626/*
 627 * Add a page to the dirty page list.
 628 *
 629 * It is a sad fact of life that this function is called from several places
 630 * deeply under spinlocking.  It may not sleep.
 631 *
 632 * If the page has buffers, the uptodate buffers are set dirty, to preserve
 633 * dirty-state coherency between the page and the buffers.  It the page does
 634 * not have buffers then when they are later attached they will all be set
 635 * dirty.
 636 *
 637 * The buffers are dirtied before the page is dirtied.  There's a small race
 638 * window in which a writepage caller may see the page cleanness but not the
 639 * buffer dirtiness.  That's fine.  If this code were to set the page dirty
 640 * before the buffers, a concurrent writepage caller could clear the page dirty
 641 * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
 642 * page on the dirty page list.
 643 *
 644 * We use private_lock to lock against try_to_free_buffers while using the
 645 * page's buffer list.  Also use this to protect against clean buffers being
 646 * added to the page after it was set dirty.
 647 *
 648 * FIXME: may need to call ->reservepage here as well.  That's rather up to the
 649 * address_space though.
 650 */
 651int __set_page_dirty_buffers(struct page *page)
 652{
 653        int newly_dirty;
 654        struct address_space *mapping = page_mapping(page);
 655
 656        if (unlikely(!mapping))
 657                return !TestSetPageDirty(page);
 658
 659        spin_lock(&mapping->private_lock);
 660        if (page_has_buffers(page)) {
 661                struct buffer_head *head = page_buffers(page);
 662                struct buffer_head *bh = head;
 663
 664                do {
 665                        set_buffer_dirty(bh);
 666                        bh = bh->b_this_page;
 667                } while (bh != head);
 668        }
 669        newly_dirty = !TestSetPageDirty(page);
 670        spin_unlock(&mapping->private_lock);
 671
 672        if (newly_dirty)
 673                __set_page_dirty(page, mapping, 1);
 674        return newly_dirty;
 675}
 676EXPORT_SYMBOL(__set_page_dirty_buffers);
 677
 678/*
 679 * Write out and wait upon a list of buffers.
 680 *
 681 * We have conflicting pressures: we want to make sure that all
 682 * initially dirty buffers get waited on, but that any subsequently
 683 * dirtied buffers don't.  After all, we don't want fsync to last
 684 * forever if somebody is actively writing to the file.
 685 *
 686 * Do this in two main stages: first we copy dirty buffers to a
 687 * temporary inode list, queueing the writes as we go.  Then we clean
 688 * up, waiting for those writes to complete.
 689 * 
 690 * During this second stage, any subsequent updates to the file may end
 691 * up refiling the buffer on the original inode's dirty list again, so
 692 * there is a chance we will end up with a buffer queued for write but
 693 * not yet completed on that list.  So, as a final cleanup we go through
 694 * the osync code to catch these locked, dirty buffers without requeuing
 695 * any newly dirty buffers for write.
 696 */
 697static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
 698{
 699        struct buffer_head *bh;
 700        struct list_head tmp;
 701        struct address_space *mapping;
 702        int err = 0, err2;
 703        struct blk_plug plug;
 704
 705        INIT_LIST_HEAD(&tmp);
 706        blk_start_plug(&plug);
 707
 708        spin_lock(lock);
 709        while (!list_empty(list)) {
 710                bh = BH_ENTRY(list->next);
 711                mapping = bh->b_assoc_map;
 712                __remove_assoc_queue(bh);
 713                /* Avoid race with mark_buffer_dirty_inode() which does
 714                 * a lockless check and we rely on seeing the dirty bit */
 715                smp_mb();
 716                if (buffer_dirty(bh) || buffer_locked(bh)) {
 717                        list_add(&bh->b_assoc_buffers, &tmp);
 718                        bh->b_assoc_map = mapping;
 719                        if (buffer_dirty(bh)) {
 720                                get_bh(bh);
 721                                spin_unlock(lock);
 722                                /*
 723                                 * Ensure any pending I/O completes so that
 724                                 * write_dirty_buffer() actually writes the
 725                                 * current contents - it is a noop if I/O is
 726                                 * still in flight on potentially older
 727                                 * contents.
 728                                 */
 729                                write_dirty_buffer(bh, WRITE_SYNC);
 730
 731                                /*
 732                                 * Kick off IO for the previous mapping. Note
 733                                 * that we will not run the very last mapping,
 734                                 * wait_on_buffer() will do that for us
 735                                 * through sync_buffer().
 736                                 */
 737                                brelse(bh);
 738                                spin_lock(lock);
 739                        }
 740                }
 741        }
 742
 743        spin_unlock(lock);
 744        blk_finish_plug(&plug);
 745        spin_lock(lock);
 746
 747        while (!list_empty(&tmp)) {
 748                bh = BH_ENTRY(tmp.prev);
 749                get_bh(bh);
 750                mapping = bh->b_assoc_map;
 751                __remove_assoc_queue(bh);
 752                /* Avoid race with mark_buffer_dirty_inode() which does
 753                 * a lockless check and we rely on seeing the dirty bit */
 754                smp_mb();
 755                if (buffer_dirty(bh)) {
 756                        list_add(&bh->b_assoc_buffers,
 757                                 &mapping->private_list);
 758                        bh->b_assoc_map = mapping;
 759                }
 760                spin_unlock(lock);
 761                wait_on_buffer(bh);
 762                if (!buffer_uptodate(bh))
 763                        err = -EIO;
 764                brelse(bh);
 765                spin_lock(lock);
 766        }
 767        
 768        spin_unlock(lock);
 769        err2 = osync_buffers_list(lock, list);
 770        if (err)
 771                return err;
 772        else
 773                return err2;
 774}
 775
 776/*
 777 * Invalidate any and all dirty buffers on a given inode.  We are
 778 * probably unmounting the fs, but that doesn't mean we have already
 779 * done a sync().  Just drop the buffers from the inode list.
 780 *
 781 * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
 782 * assumes that all the buffers are against the blockdev.  Not true
 783 * for reiserfs.
 784 */
 785void invalidate_inode_buffers(struct inode *inode)
 786{
 787        if (inode_has_buffers(inode)) {
 788                struct address_space *mapping = &inode->i_data;
 789                struct list_head *list = &mapping->private_list;
 790                struct address_space *buffer_mapping = mapping->private_data;
 791
 792                spin_lock(&buffer_mapping->private_lock);
 793                while (!list_empty(list))
 794                        __remove_assoc_queue(BH_ENTRY(list->next));
 795                spin_unlock(&buffer_mapping->private_lock);
 796        }
 797}
 798EXPORT_SYMBOL(invalidate_inode_buffers);
 799
 800/*
 801 * Remove any clean buffers from the inode's buffer list.  This is called
 802 * when we're trying to free the inode itself.  Those buffers can pin it.
 803 *
 804 * Returns true if all buffers were removed.
 805 */
 806int remove_inode_buffers(struct inode *inode)
 807{
 808        int ret = 1;
 809
 810        if (inode_has_buffers(inode)) {
 811                struct address_space *mapping = &inode->i_data;
 812                struct list_head *list = &mapping->private_list;
 813                struct address_space *buffer_mapping = mapping->private_data;
 814
 815                spin_lock(&buffer_mapping->private_lock);
 816                while (!list_empty(list)) {
 817                        struct buffer_head *bh = BH_ENTRY(list->next);
 818                        if (buffer_dirty(bh)) {
 819                                ret = 0;
 820                                break;
 821                        }
 822                        __remove_assoc_queue(bh);
 823                }
 824                spin_unlock(&buffer_mapping->private_lock);
 825        }
 826        return ret;
 827}
 828
 829/*
 830 * Create the appropriate buffers when given a page for data area and
 831 * the size of each buffer.. Use the bh->b_this_page linked list to
 832 * follow the buffers created.  Return NULL if unable to create more
 833 * buffers.
 834 *
 835 * The retry flag is used to differentiate async IO (paging, swapping)
 836 * which may not fail from ordinary buffer allocations.
 837 */
 838struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
 839                int retry)
 840{
 841        struct buffer_head *bh, *head;
 842        long offset;
 843
 844try_again:
 845        head = NULL;
 846        offset = PAGE_SIZE;
 847        while ((offset -= size) >= 0) {
 848                bh = alloc_buffer_head(GFP_NOFS);
 849                if (!bh)
 850                        goto no_grow;
 851
 852                bh->b_this_page = head;
 853                bh->b_blocknr = -1;
 854                head = bh;
 855
 856                bh->b_size = size;
 857
 858                /* Link the buffer to its page */
 859                set_bh_page(bh, page, offset);
 860
 861                init_buffer(bh, NULL, NULL);
 862        }
 863        return head;
 864/*
 865 * In case anything failed, we just free everything we got.
 866 */
 867no_grow:
 868        if (head) {
 869                do {
 870                        bh = head;
 871                        head = head->b_this_page;
 872                        free_buffer_head(bh);
 873                } while (head);
 874        }
 875
 876        /*
 877         * Return failure for non-async IO requests.  Async IO requests
 878         * are not allowed to fail, so we have to wait until buffer heads
 879         * become available.  But we don't want tasks sleeping with 
 880         * partially complete buffers, so all were released above.
 881         */
 882        if (!retry)
 883                return NULL;
 884
 885        /* We're _really_ low on memory. Now we just
 886         * wait for old buffer heads to become free due to
 887         * finishing IO.  Since this is an async request and
 888         * the reserve list is empty, we're sure there are 
 889         * async buffer heads in use.
 890         */
 891        free_more_memory();
 892        goto try_again;
 893}
 894EXPORT_SYMBOL_GPL(alloc_page_buffers);
 895
 896static inline void
 897link_dev_buffers(struct page *page, struct buffer_head *head)
 898{
 899        struct buffer_head *bh, *tail;
 900
 901        bh = head;
 902        do {
 903                tail = bh;
 904                bh = bh->b_this_page;
 905        } while (bh);
 906        tail->b_this_page = head;
 907        attach_page_buffers(page, head);
 908}
 909
 910static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
 911{
 912        sector_t retval = ~((sector_t)0);
 913        loff_t sz = i_size_read(bdev->bd_inode);
 914
 915        if (sz) {
 916                unsigned int sizebits = blksize_bits(size);
 917                retval = (sz >> sizebits);
 918        }
 919        return retval;
 920}
 921
 922/*
 923 * Initialise the state of a blockdev page's buffers.
 924 */ 
 925static sector_t
 926init_page_buffers(struct page *page, struct block_device *bdev,
 927                        sector_t block, int size)
 928{
 929        struct buffer_head *head = page_buffers(page);
 930        struct buffer_head *bh = head;
 931        int uptodate = PageUptodate(page);
 932        sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
 933
 934        do {
 935                if (!buffer_mapped(bh)) {
 936                        init_buffer(bh, NULL, NULL);
 937                        bh->b_bdev = bdev;
 938                        bh->b_blocknr = block;
 939                        if (uptodate)
 940                                set_buffer_uptodate(bh);
 941                        if (block < end_block)
 942                                set_buffer_mapped(bh);
 943                }
 944                block++;
 945                bh = bh->b_this_page;
 946        } while (bh != head);
 947
 948        /*
 949         * Caller needs to validate requested block against end of device.
 950         */
 951        return end_block;
 952}
 953
 954/*
 955 * Create the page-cache page that contains the requested block.
 956 *
 957 * This is used purely for blockdev mappings.
 958 */
 959static int
 960grow_dev_page(struct block_device *bdev, sector_t block,
 961                pgoff_t index, int size, int sizebits)
 962{
 963        struct inode *inode = bdev->bd_inode;
 964        struct page *page;
 965        struct buffer_head *bh;
 966        sector_t end_block;
 967        int ret = 0;            /* Will call free_more_memory() */
 968
 969        page = find_or_create_page(inode->i_mapping, index,
 970                (mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS)|__GFP_MOVABLE);
 971        if (!page)
 972                return ret;
 973
 974        BUG_ON(!PageLocked(page));
 975
 976        if (page_has_buffers(page)) {
 977                bh = page_buffers(page);
 978                if (bh->b_size == size) {
 979                        end_block = init_page_buffers(page, bdev,
 980                                                index << sizebits, size);
 981                        goto done;
 982                }
 983                if (!try_to_free_buffers(page))
 984                        goto failed;
 985        }
 986
 987        /*
 988         * Allocate some buffers for this page
 989         */
 990        bh = alloc_page_buffers(page, size, 0);
 991        if (!bh)
 992                goto failed;
 993
 994        /*
 995         * Link the page to the buffers and initialise them.  Take the
 996         * lock to be atomic wrt __find_get_block(), which does not
 997         * run under the page lock.
 998         */
 999        spin_lock(&inode->i_mapping->private_lock);
1000        link_dev_buffers(page, bh);
1001        end_block = init_page_buffers(page, bdev, index << sizebits, size);
1002        spin_unlock(&inode->i_mapping->private_lock);
1003done:
1004        ret = (block < end_block) ? 1 : -ENXIO;
1005failed:
1006        unlock_page(page);
1007        page_cache_release(page);
1008        return ret;
1009}
1010
1011/*
1012 * Create buffers for the specified block device block's page.  If
1013 * that page was dirty, the buffers are set dirty also.
1014 */
1015static int
1016grow_buffers(struct block_device *bdev, sector_t block, int size)
1017{
1018        pgoff_t index;
1019        int sizebits;
1020
1021        sizebits = -1;
1022        do {
1023                sizebits++;
1024        } while ((size << sizebits) < PAGE_SIZE);
1025
1026        index = block >> sizebits;
1027
1028        /*
1029         * Check for a block which wants to lie outside our maximum possible
1030         * pagecache index.  (this comparison is done using sector_t types).
1031         */
1032        if (unlikely(index != block >> sizebits)) {
1033                char b[BDEVNAME_SIZE];
1034
1035                printk(KERN_ERR "%s: requested out-of-range block %llu for "
1036                        "device %s\n",
1037                        __func__, (unsigned long long)block,
1038                        bdevname(bdev, b));
1039                return -EIO;
1040        }
1041
1042        /* Create a page with the proper size buffers.. */
1043        return grow_dev_page(bdev, block, index, size, sizebits);
1044}
1045
1046static struct buffer_head *
1047__getblk_slow(struct block_device *bdev, sector_t block, int size)
1048{
1049        /* Size must be multiple of hard sectorsize */
1050        if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
1051                        (size < 512 || size > PAGE_SIZE))) {
1052                printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1053                                        size);
1054                printk(KERN_ERR "logical block size: %d\n",
1055                                        bdev_logical_block_size(bdev));
1056
1057                dump_stack();
1058                return NULL;
1059        }
1060
1061        for (;;) {
1062                struct buffer_head *bh;
1063                int ret;
1064
1065                bh = __find_get_block(bdev, block, size);
1066                if (bh)
1067                        return bh;
1068
1069                ret = grow_buffers(bdev, block, size);
1070                if (ret < 0)
1071                        return NULL;
1072                if (ret == 0)
1073                        free_more_memory();
1074        }
1075}
1076
1077/*
1078 * The relationship between dirty buffers and dirty pages:
1079 *
1080 * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1081 * the page is tagged dirty in its radix tree.
1082 *
1083 * At all times, the dirtiness of the buffers represents the dirtiness of
1084 * subsections of the page.  If the page has buffers, the page dirty bit is
1085 * merely a hint about the true dirty state.
1086 *
1087 * When a page is set dirty in its entirety, all its buffers are marked dirty
1088 * (if the page has buffers).
1089 *
1090 * When a buffer is marked dirty, its page is dirtied, but the page's other
1091 * buffers are not.
1092 *
1093 * Also.  When blockdev buffers are explicitly read with bread(), they
1094 * individually become uptodate.  But their backing page remains not
1095 * uptodate - even if all of its buffers are uptodate.  A subsequent
1096 * block_read_full_page() against that page will discover all the uptodate
1097 * buffers, will set the page uptodate and will perform no I/O.
1098 */
1099
1100/**
1101 * mark_buffer_dirty - mark a buffer_head as needing writeout
1102 * @bh: the buffer_head to mark dirty
1103 *
1104 * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1105 * backing page dirty, then tag the page as dirty in its address_space's radix
1106 * tree and then attach the address_space's inode to its superblock's dirty
1107 * inode list.
1108 *
1109 * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1110 * mapping->tree_lock and mapping->host->i_lock.
1111 */
1112void mark_buffer_dirty(struct buffer_head *bh)
1113{
1114        WARN_ON_ONCE(!buffer_uptodate(bh));
1115
1116        /*
1117         * Very *carefully* optimize the it-is-already-dirty case.
1118         *
1119         * Don't let the final "is it dirty" escape to before we
1120         * perhaps modified the buffer.
1121         */
1122        if (buffer_dirty(bh)) {
1123                smp_mb();
1124                if (buffer_dirty(bh))
1125                        return;
1126        }
1127
1128        if (!test_set_buffer_dirty(bh)) {
1129                struct page *page = bh->b_page;
1130                if (!TestSetPageDirty(page)) {
1131                        struct address_space *mapping = page_mapping(page);
1132                        if (mapping)
1133                                __set_page_dirty(page, mapping, 0);
1134                }
1135        }
1136}
1137EXPORT_SYMBOL(mark_buffer_dirty);
1138
1139/*
1140 * Decrement a buffer_head's reference count.  If all buffers against a page
1141 * have zero reference count, are clean and unlocked, and if the page is clean
1142 * and unlocked then try_to_free_buffers() may strip the buffers from the page
1143 * in preparation for freeing it (sometimes, rarely, buffers are removed from
1144 * a page but it ends up not being freed, and buffers may later be reattached).
1145 */
1146void __brelse(struct buffer_head * buf)
1147{
1148        if (atomic_read(&buf->b_count)) {
1149                put_bh(buf);
1150                return;
1151        }
1152        WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1153}
1154EXPORT_SYMBOL(__brelse);
1155
1156/*
1157 * bforget() is like brelse(), except it discards any
1158 * potentially dirty data.
1159 */
1160void __bforget(struct buffer_head *bh)
1161{
1162        clear_buffer_dirty(bh);
1163        if (bh->b_assoc_map) {
1164                struct address_space *buffer_mapping = bh->b_page->mapping;
1165
1166                spin_lock(&buffer_mapping->private_lock);
1167                list_del_init(&bh->b_assoc_buffers);
1168                bh->b_assoc_map = NULL;
1169                spin_unlock(&buffer_mapping->private_lock);
1170        }
1171        __brelse(bh);
1172}
1173EXPORT_SYMBOL(__bforget);
1174
1175static struct buffer_head *__bread_slow(struct buffer_head *bh)
1176{
1177        lock_buffer(bh);
1178        if (buffer_uptodate(bh)) {
1179                unlock_buffer(bh);
1180                return bh;
1181        } else {
1182                get_bh(bh);
1183                bh->b_end_io = end_buffer_read_sync;
1184                submit_bh(READ, bh);
1185                wait_on_buffer(bh);
1186                if (buffer_uptodate(bh))
1187                        return bh;
1188        }
1189        brelse(bh);
1190        return NULL;
1191}
1192
1193/*
1194 * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1195 * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1196 * refcount elevated by one when they're in an LRU.  A buffer can only appear
1197 * once in a particular CPU's LRU.  A single buffer can be present in multiple
1198 * CPU's LRUs at the same time.
1199 *
1200 * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1201 * sb_find_get_block().
1202 *
1203 * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1204 * a local interrupt disable for that.
1205 */
1206
1207#define BH_LRU_SIZE     8
1208
1209struct bh_lru {
1210        struct buffer_head *bhs[BH_LRU_SIZE];
1211};
1212
1213static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1214
1215#ifdef CONFIG_SMP
1216#define bh_lru_lock()   local_irq_disable()
1217#define bh_lru_unlock() local_irq_enable()
1218#else
1219#define bh_lru_lock()   preempt_disable()
1220#define bh_lru_unlock() preempt_enable()
1221#endif
1222
1223static inline void check_irqs_on(void)
1224{
1225#ifdef irqs_disabled
1226        BUG_ON(irqs_disabled());
1227#endif
1228}
1229
1230/*
1231 * The LRU management algorithm is dopey-but-simple.  Sorry.
1232 */
1233static void bh_lru_install(struct buffer_head *bh)
1234{
1235        struct buffer_head *evictee = NULL;
1236
1237        check_irqs_on();
1238        bh_lru_lock();
1239        if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
1240                struct buffer_head *bhs[BH_LRU_SIZE];
1241                int in;
1242                int out = 0;
1243
1244                get_bh(bh);
1245                bhs[out++] = bh;
1246                for (in = 0; in < BH_LRU_SIZE; in++) {
1247                        struct buffer_head *bh2 =
1248                                __this_cpu_read(bh_lrus.bhs[in]);
1249
1250                        if (bh2 == bh) {
1251                                __brelse(bh2);
1252                        } else {
1253                                if (out >= BH_LRU_SIZE) {
1254                                        BUG_ON(evictee != NULL);
1255                                        evictee = bh2;
1256                                } else {
1257                                        bhs[out++] = bh2;
1258                                }
1259                        }
1260                }
1261                while (out < BH_LRU_SIZE)
1262                        bhs[out++] = NULL;
1263                memcpy(__this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
1264        }
1265        bh_lru_unlock();
1266
1267        if (evictee)
1268                __brelse(evictee);
1269}
1270
1271/*
1272 * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1273 */
1274static struct buffer_head *
1275lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1276{
1277        struct buffer_head *ret = NULL;
1278        unsigned int i;
1279
1280        check_irqs_on();
1281        bh_lru_lock();
1282        for (i = 0; i < BH_LRU_SIZE; i++) {
1283                struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1284
1285                if (bh && bh->b_bdev == bdev &&
1286                                bh->b_blocknr == block && bh->b_size == size) {
1287                        if (i) {
1288                                while (i) {
1289                                        __this_cpu_write(bh_lrus.bhs[i],
1290                                                __this_cpu_read(bh_lrus.bhs[i - 1]));
1291                                        i--;
1292                                }
1293                                __this_cpu_write(bh_lrus.bhs[0], bh);
1294                        }
1295                        get_bh(bh);
1296                        ret = bh;
1297                        break;
1298                }
1299        }
1300        bh_lru_unlock();
1301        return ret;
1302}
1303
1304/*
1305 * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1306 * it in the LRU and mark it as accessed.  If it is not present then return
1307 * NULL
1308 */
1309struct buffer_head *
1310__find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1311{
1312        struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1313
1314        if (bh == NULL) {
1315                bh = __find_get_block_slow(bdev, block);
1316                if (bh)
1317                        bh_lru_install(bh);
1318        }
1319        if (bh)
1320                touch_buffer(bh);
1321        return bh;
1322}
1323EXPORT_SYMBOL(__find_get_block);
1324
1325/*
1326 * __getblk will locate (and, if necessary, create) the buffer_head
1327 * which corresponds to the passed block_device, block and size. The
1328 * returned buffer has its reference count incremented.
1329 *
1330 * __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
1331 * attempt is failing.  FIXME, perhaps?
1332 */
1333struct buffer_head *
1334__getblk(struct block_device *bdev, sector_t block, unsigned size)
1335{
1336        struct buffer_head *bh = __find_get_block(bdev, block, size);
1337
1338        might_sleep();
1339        if (bh == NULL)
1340                bh = __getblk_slow(bdev, block, size);
1341        return bh;
1342}
1343EXPORT_SYMBOL(__getblk);
1344
1345/*
1346 * Do async read-ahead on a buffer..
1347 */
1348void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1349{
1350        struct buffer_head *bh = __getblk(bdev, block, size);
1351        if (likely(bh)) {
1352                ll_rw_block(READA, 1, &bh);
1353                brelse(bh);
1354        }
1355}
1356EXPORT_SYMBOL(__breadahead);
1357
1358/**
1359 *  __bread() - reads a specified block and returns the bh
1360 *  @bdev: the block_device to read from
1361 *  @block: number of block
1362 *  @size: size (in bytes) to read
1363 * 
1364 *  Reads a specified block, and returns buffer head that contains it.
1365 *  It returns NULL if the block was unreadable.
1366 */
1367struct buffer_head *
1368__bread(struct block_device *bdev, sector_t block, unsigned size)
1369{
1370        struct buffer_head *bh = __getblk(bdev, block, size);
1371
1372        if (likely(bh) && !buffer_uptodate(bh))
1373                bh = __bread_slow(bh);
1374        return bh;
1375}
1376EXPORT_SYMBOL(__bread);
1377
1378/*
1379 * invalidate_bh_lrus() is called rarely - but not only at unmount.
1380 * This doesn't race because it runs in each cpu either in irq
1381 * or with preempt disabled.
1382 */
1383static void invalidate_bh_lru(void *arg)
1384{
1385        struct bh_lru *b = &get_cpu_var(bh_lrus);
1386        int i;
1387
1388        for (i = 0; i < BH_LRU_SIZE; i++) {
1389                brelse(b->bhs[i]);
1390                b->bhs[i] = NULL;
1391        }
1392        put_cpu_var(bh_lrus);
1393}
1394
1395static bool has_bh_in_lru(int cpu, void *dummy)
1396{
1397        struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1398        int i;
1399        
1400        for (i = 0; i < BH_LRU_SIZE; i++) {
1401                if (b->bhs[i])
1402                        return 1;
1403        }
1404
1405        return 0;
1406}
1407
1408void invalidate_bh_lrus(void)
1409{
1410        on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1411}
1412EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1413
1414void set_bh_page(struct buffer_head *bh,
1415                struct page *page, unsigned long offset)
1416{
1417        bh->b_page = page;
1418        BUG_ON(offset >= PAGE_SIZE);
1419        if (PageHighMem(page))
1420                /*
1421                 * This catches illegal uses and preserves the offset:
1422                 */
1423                bh->b_data = (char *)(0 + offset);
1424        else
1425                bh->b_data = page_address(page) + offset;
1426}
1427EXPORT_SYMBOL(set_bh_page);
1428
1429/*
1430 * Called when truncating a buffer on a page completely.
1431 */
1432static void discard_buffer(struct buffer_head * bh)
1433{
1434        lock_buffer(bh);
1435        clear_buffer_dirty(bh);
1436        bh->b_bdev = NULL;
1437        clear_buffer_mapped(bh);
1438        clear_buffer_req(bh);
1439        clear_buffer_new(bh);
1440        clear_buffer_delay(bh);
1441        clear_buffer_unwritten(bh);
1442        unlock_buffer(bh);
1443}
1444
1445/**
1446 * block_invalidatepage - invalidate part or all of a buffer-backed page
1447 *
1448 * @page: the page which is affected
1449 * @offset: the index of the truncation point
1450 *
1451 * block_invalidatepage() is called when all or part of the page has become
1452 * invalidated by a truncate operation.
1453 *
1454 * block_invalidatepage() does not have to release all buffers, but it must
1455 * ensure that no dirty buffer is left outside @offset and that no I/O
1456 * is underway against any of the blocks which are outside the truncation
1457 * point.  Because the caller is about to free (and possibly reuse) those
1458 * blocks on-disk.
1459 */
1460void block_invalidatepage(struct page *page, unsigned long offset)
1461{
1462        struct buffer_head *head, *bh, *next;
1463        unsigned int curr_off = 0;
1464
1465        BUG_ON(!PageLocked(page));
1466        if (!page_has_buffers(page))
1467                goto out;
1468
1469        head = page_buffers(page);
1470        bh = head;
1471        do {
1472                unsigned int next_off = curr_off + bh->b_size;
1473                next = bh->b_this_page;
1474
1475                /*
1476                 * is this block fully invalidated?
1477                 */
1478                if (offset <= curr_off)
1479                        discard_buffer(bh);
1480                curr_off = next_off;
1481                bh = next;
1482        } while (bh != head);
1483
1484        /*
1485         * We release buffers only if the entire page is being invalidated.
1486         * The get_block cached value has been unconditionally invalidated,
1487         * so real IO is not possible anymore.
1488         */
1489        if (offset == 0)
1490                try_to_release_page(page, 0);
1491out:
1492        return;
1493}
1494EXPORT_SYMBOL(block_invalidatepage);
1495
1496/*
1497 * We attach and possibly dirty the buffers atomically wrt
1498 * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1499 * is already excluded via the page lock.
1500 */
1501void create_empty_buffers(struct page *page,
1502                        unsigned long blocksize, unsigned long b_state)
1503{
1504        struct buffer_head *bh, *head, *tail;
1505
1506        head = alloc_page_buffers(page, blocksize, 1);
1507        bh = head;
1508        do {
1509                bh->b_state |= b_state;
1510                tail = bh;
1511                bh = bh->b_this_page;
1512        } while (bh);
1513        tail->b_this_page = head;
1514
1515        spin_lock(&page->mapping->private_lock);
1516        if (PageUptodate(page) || PageDirty(page)) {
1517                bh = head;
1518                do {
1519                        if (PageDirty(page))
1520                                set_buffer_dirty(bh);
1521                        if (PageUptodate(page))
1522                                set_buffer_uptodate(bh);
1523                        bh = bh->b_this_page;
1524                } while (bh != head);
1525        }
1526        attach_page_buffers(page, head);
1527        spin_unlock(&page->mapping->private_lock);
1528}
1529EXPORT_SYMBOL(create_empty_buffers);
1530
1531/*
1532 * We are taking a block for data and we don't want any output from any
1533 * buffer-cache aliases starting from return from that function and
1534 * until the moment when something will explicitly mark the buffer
1535 * dirty (hopefully that will not happen until we will free that block ;-)
1536 * We don't even need to mark it not-uptodate - nobody can expect
1537 * anything from a newly allocated buffer anyway. We used to used
1538 * unmap_buffer() for such invalidation, but that was wrong. We definitely
1539 * don't want to mark the alias unmapped, for example - it would confuse
1540 * anyone who might pick it with bread() afterwards...
1541 *
1542 * Also..  Note that bforget() doesn't lock the buffer.  So there can
1543 * be writeout I/O going on against recently-freed buffers.  We don't
1544 * wait on that I/O in bforget() - it's more efficient to wait on the I/O
1545 * only if we really need to.  That happens here.
1546 */
1547void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1548{
1549        struct buffer_head *old_bh;
1550
1551        might_sleep();
1552
1553        old_bh = __find_get_block_slow(bdev, block);
1554        if (old_bh) {
1555                clear_buffer_dirty(old_bh);
1556                wait_on_buffer(old_bh);
1557                clear_buffer_req(old_bh);
1558                __brelse(old_bh);
1559        }
1560}
1561EXPORT_SYMBOL(unmap_underlying_metadata);
1562
1563/*
1564 * Size is a power-of-two in the range 512..PAGE_SIZE,
1565 * and the case we care about most is PAGE_SIZE.
1566 *
1567 * So this *could* possibly be written with those
1568 * constraints in mind (relevant mostly if some
1569 * architecture has a slow bit-scan instruction)
1570 */
1571static inline int block_size_bits(unsigned int blocksize)
1572{
1573        return ilog2(blocksize);
1574}
1575
1576static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
1577{
1578        BUG_ON(!PageLocked(page));
1579
1580        if (!page_has_buffers(page))
1581                create_empty_buffers(page, 1 << ACCESS_ONCE(inode->i_blkbits), b_state);
1582        return page_buffers(page);
1583}
1584
1585/*
1586 * NOTE! All mapped/uptodate combinations are valid:
1587 *
1588 *      Mapped  Uptodate        Meaning
1589 *
1590 *      No      No              "unknown" - must do get_block()
1591 *      No      Yes             "hole" - zero-filled
1592 *      Yes     No              "allocated" - allocated on disk, not read in
1593 *      Yes     Yes             "valid" - allocated and up-to-date in memory.
1594 *
1595 * "Dirty" is valid only with the last case (mapped+uptodate).
1596 */
1597
1598/*
1599 * While block_write_full_page is writing back the dirty buffers under
1600 * the page lock, whoever dirtied the buffers may decide to clean them
1601 * again at any time.  We handle that by only looking at the buffer
1602 * state inside lock_buffer().
1603 *
1604 * If block_write_full_page() is called for regular writeback
1605 * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1606 * locked buffer.   This only can happen if someone has written the buffer
1607 * directly, with submit_bh().  At the address_space level PageWriteback
1608 * prevents this contention from occurring.
1609 *
1610 * If block_write_full_page() is called with wbc->sync_mode ==
1611 * WB_SYNC_ALL, the writes are posted using WRITE_SYNC; this
1612 * causes the writes to be flagged as synchronous writes.
1613 */
1614static int __block_write_full_page(struct inode *inode, struct page *page,
1615                        get_block_t *get_block, struct writeback_control *wbc,
1616                        bh_end_io_t *handler)
1617{
1618        int err;
1619        sector_t block;
1620        sector_t last_block;
1621        struct buffer_head *bh, *head;
1622        unsigned int blocksize, bbits;
1623        int nr_underway = 0;
1624        int write_op = (wbc->sync_mode == WB_SYNC_ALL ?
1625                        WRITE_SYNC : WRITE);
1626
1627        head = create_page_buffers(page, inode,
1628                                        (1 << BH_Dirty)|(1 << BH_Uptodate));
1629
1630        /*
1631         * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1632         * here, and the (potentially unmapped) buffers may become dirty at
1633         * any time.  If a buffer becomes dirty here after we've inspected it
1634         * then we just miss that fact, and the page stays dirty.
1635         *
1636         * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1637         * handle that here by just cleaning them.
1638         */
1639
1640        bh = head;
1641        blocksize = bh->b_size;
1642        bbits = block_size_bits(blocksize);
1643
1644        block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1645        last_block = (i_size_read(inode) - 1) >> bbits;
1646
1647        /*
1648         * Get all the dirty buffers mapped to disk addresses and
1649         * handle any aliases from the underlying blockdev's mapping.
1650         */
1651        do {
1652                if (block > last_block) {
1653                        /*
1654                         * mapped buffers outside i_size will occur, because
1655                         * this page can be outside i_size when there is a
1656                         * truncate in progress.
1657                         */
1658                        /*
1659                         * The buffer was zeroed by block_write_full_page()
1660                         */
1661                        clear_buffer_dirty(bh);
1662                        set_buffer_uptodate(bh);
1663                } else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1664                           buffer_dirty(bh)) {
1665                        WARN_ON(bh->b_size != blocksize);
1666                        err = get_block(inode, block, bh, 1);
1667                        if (err)
1668                                goto recover;
1669                        clear_buffer_delay(bh);
1670                        if (buffer_new(bh)) {
1671                                /* blockdev mappings never come here */
1672                                clear_buffer_new(bh);
1673                                unmap_underlying_metadata(bh->b_bdev,
1674                                                        bh->b_blocknr);
1675                        }
1676                }
1677                bh = bh->b_this_page;
1678                block++;
1679        } while (bh != head);
1680
1681        do {
1682                if (!buffer_mapped(bh))
1683                        continue;
1684                /*
1685                 * If it's a fully non-blocking write attempt and we cannot
1686                 * lock the buffer then redirty the page.  Note that this can
1687                 * potentially cause a busy-wait loop from writeback threads
1688                 * and kswapd activity, but those code paths have their own
1689                 * higher-level throttling.
1690                 */
1691                if (wbc->sync_mode != WB_SYNC_NONE) {
1692                        lock_buffer(bh);
1693                } else if (!trylock_buffer(bh)) {
1694                        redirty_page_for_writepage(wbc, page);
1695                        continue;
1696                }
1697                if (test_clear_buffer_dirty(bh)) {
1698                        mark_buffer_async_write_endio(bh, handler);
1699                } else {
1700                        unlock_buffer(bh);
1701                }
1702        } while ((bh = bh->b_this_page) != head);
1703
1704        /*
1705         * The page and its buffers are protected by PageWriteback(), so we can
1706         * drop the bh refcounts early.
1707         */
1708        BUG_ON(PageWriteback(page));
1709        set_page_writeback(page);
1710
1711        do {
1712                struct buffer_head *next = bh->b_this_page;
1713                if (buffer_async_write(bh)) {
1714                        submit_bh(write_op, bh);
1715                        nr_underway++;
1716                }
1717                bh = next;
1718        } while (bh != head);
1719        unlock_page(page);
1720
1721        err = 0;
1722done:
1723        if (nr_underway == 0) {
1724                /*
1725                 * The page was marked dirty, but the buffers were
1726                 * clean.  Someone wrote them back by hand with
1727                 * ll_rw_block/submit_bh.  A rare case.
1728                 */
1729                end_page_writeback(page);
1730
1731                /*
1732                 * The page and buffer_heads can be released at any time from
1733                 * here on.
1734                 */
1735        }
1736        return err;
1737
1738recover:
1739        /*
1740         * ENOSPC, or some other error.  We may already have added some
1741         * blocks to the file, so we need to write these out to avoid
1742         * exposing stale data.
1743         * The page is currently locked and not marked for writeback
1744         */
1745        bh = head;
1746        /* Recovery: lock and submit the mapped buffers */
1747        do {
1748                if (buffer_mapped(bh) && buffer_dirty(bh) &&
1749                    !buffer_delay(bh)) {
1750                        lock_buffer(bh);
1751                        mark_buffer_async_write_endio(bh, handler);
1752                } else {
1753                        /*
1754                         * The buffer may have been set dirty during
1755                         * attachment to a dirty page.
1756                         */
1757                        clear_buffer_dirty(bh);
1758                }
1759        } while ((bh = bh->b_this_page) != head);
1760        SetPageError(page);
1761        BUG_ON(PageWriteback(page));
1762        mapping_set_error(page->mapping, err);
1763        set_page_writeback(page);
1764        do {
1765                struct buffer_head *next = bh->b_this_page;
1766                if (buffer_async_write(bh)) {
1767                        clear_buffer_dirty(bh);
1768                        submit_bh(write_op, bh);
1769                        nr_underway++;
1770                }
1771                bh = next;
1772        } while (bh != head);
1773        unlock_page(page);
1774        goto done;
1775}
1776
1777/*
1778 * If a page has any new buffers, zero them out here, and mark them uptodate
1779 * and dirty so they'll be written out (in order to prevent uninitialised
1780 * block data from leaking). And clear the new bit.
1781 */
1782void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1783{
1784        unsigned int block_start, block_end;
1785        struct buffer_head *head, *bh;
1786
1787        BUG_ON(!PageLocked(page));
1788        if (!page_has_buffers(page))
1789                return;
1790
1791        bh = head = page_buffers(page);
1792        block_start = 0;
1793        do {
1794                block_end = block_start + bh->b_size;
1795
1796                if (buffer_new(bh)) {
1797                        if (block_end > from && block_start < to) {
1798                                if (!PageUptodate(page)) {
1799                                        unsigned start, size;
1800
1801                                        start = max(from, block_start);
1802                                        size = min(to, block_end) - start;
1803
1804                                        zero_user(page, start, size);
1805                                        set_buffer_uptodate(bh);
1806                                }
1807
1808                                clear_buffer_new(bh);
1809                                mark_buffer_dirty(bh);
1810                        }
1811                }
1812
1813                block_start = block_end;
1814                bh = bh->b_this_page;
1815        } while (bh != head);
1816}
1817EXPORT_SYMBOL(page_zero_new_buffers);
1818
1819int __block_write_begin(struct page *page, loff_t pos, unsigned len,
1820                get_block_t *get_block)
1821{
1822        unsigned from = pos & (PAGE_CACHE_SIZE - 1);
1823        unsigned to = from + len;
1824        struct inode *inode = page->mapping->host;
1825        unsigned block_start, block_end;
1826        sector_t block;
1827        int err = 0;
1828        unsigned blocksize, bbits;
1829        struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1830
1831        BUG_ON(!PageLocked(page));
1832        BUG_ON(from > PAGE_CACHE_SIZE);
1833        BUG_ON(to > PAGE_CACHE_SIZE);
1834        BUG_ON(from > to);
1835
1836        head = create_page_buffers(page, inode, 0);
1837        blocksize = head->b_size;
1838        bbits = block_size_bits(blocksize);
1839
1840        block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1841
1842        for(bh = head, block_start = 0; bh != head || !block_start;
1843            block++, block_start=block_end, bh = bh->b_this_page) {
1844                block_end = block_start + blocksize;
1845                if (block_end <= from || block_start >= to) {
1846                        if (PageUptodate(page)) {
1847                                if (!buffer_uptodate(bh))
1848                                        set_buffer_uptodate(bh);
1849                        }
1850                        continue;
1851                }
1852                if (buffer_new(bh))
1853                        clear_buffer_new(bh);
1854                if (!buffer_mapped(bh)) {
1855                        WARN_ON(bh->b_size != blocksize);
1856                        err = get_block(inode, block, bh, 1);
1857                        if (err)
1858                                break;
1859                        if (buffer_new(bh)) {
1860                                unmap_underlying_metadata(bh->b_bdev,
1861                                                        bh->b_blocknr);
1862                                if (PageUptodate(page)) {
1863                                        clear_buffer_new(bh);
1864                                        set_buffer_uptodate(bh);
1865                                        mark_buffer_dirty(bh);
1866                                        continue;
1867                                }
1868                                if (block_end > to || block_start < from)
1869                                        zero_user_segments(page,
1870                                                to, block_end,
1871                                                block_start, from);
1872                                continue;
1873                        }
1874                }
1875                if (PageUptodate(page)) {
1876                        if (!buffer_uptodate(bh))
1877                                set_buffer_uptodate(bh);
1878                        continue; 
1879                }
1880                if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1881                    !buffer_unwritten(bh) &&
1882                     (block_start < from || block_end > to)) {
1883                        ll_rw_block(READ, 1, &bh);
1884                        *wait_bh++=bh;
1885                }
1886        }
1887        /*
1888         * If we issued read requests - let them complete.
1889         */
1890        while(wait_bh > wait) {
1891                wait_on_buffer(*--wait_bh);
1892                if (!buffer_uptodate(*wait_bh))
1893                        err = -EIO;
1894        }
1895        if (unlikely(err))
1896                page_zero_new_buffers(page, from, to);
1897        return err;
1898}
1899EXPORT_SYMBOL(__block_write_begin);
1900
1901static int __block_commit_write(struct inode *inode, struct page *page,
1902                unsigned from, unsigned to)
1903{
1904        unsigned block_start, block_end;
1905        int partial = 0;
1906        unsigned blocksize;
1907        struct buffer_head *bh, *head;
1908
1909        bh = head = page_buffers(page);
1910        blocksize = bh->b_size;
1911
1912        block_start = 0;
1913        do {
1914                block_end = block_start + blocksize;
1915                if (block_end <= from || block_start >= to) {
1916                        if (!buffer_uptodate(bh))
1917                                partial = 1;
1918                } else {
1919                        set_buffer_uptodate(bh);
1920                        mark_buffer_dirty(bh);
1921                }
1922                clear_buffer_new(bh);
1923
1924                block_start = block_end;
1925                bh = bh->b_this_page;
1926        } while (bh != head);
1927
1928        /*
1929         * If this is a partial write which happened to make all buffers
1930         * uptodate then we can optimize away a bogus readpage() for
1931         * the next read(). Here we 'discover' whether the page went
1932         * uptodate as a result of this (potentially partial) write.
1933         */
1934        if (!partial)
1935                SetPageUptodate(page);
1936        return 0;
1937}
1938
1939/*
1940 * block_write_begin takes care of the basic task of block allocation and
1941 * bringing partial write blocks uptodate first.
1942 *
1943 * The filesystem needs to handle block truncation upon failure.
1944 */
1945int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
1946                unsigned flags, struct page **pagep, get_block_t *get_block)
1947{
1948        pgoff_t index = pos >> PAGE_CACHE_SHIFT;
1949        struct page *page;
1950        int status;
1951
1952        page = grab_cache_page_write_begin(mapping, index, flags);
1953        if (!page)
1954                return -ENOMEM;
1955
1956        status = __block_write_begin(page, pos, len, get_block);
1957        if (unlikely(status)) {
1958                unlock_page(page);
1959                page_cache_release(page);
1960                page = NULL;
1961        }
1962
1963        *pagep = page;
1964        return status;
1965}
1966EXPORT_SYMBOL(block_write_begin);
1967
1968int block_write_end(struct file *file, struct address_space *mapping,
1969                        loff_t pos, unsigned len, unsigned copied,
1970                        struct page *page, void *fsdata)
1971{
1972        struct inode *inode = mapping->host;
1973        unsigned start;
1974
1975        start = pos & (PAGE_CACHE_SIZE - 1);
1976
1977        if (unlikely(copied < len)) {
1978                /*
1979                 * The buffers that were written will now be uptodate, so we
1980                 * don't have to worry about a readpage reading them and
1981                 * overwriting a partial write. However if we have encountered
1982                 * a short write and only partially written into a buffer, it
1983                 * will not be marked uptodate, so a readpage might come in and
1984                 * destroy our partial write.
1985                 *
1986                 * Do the simplest thing, and just treat any short write to a
1987                 * non uptodate page as a zero-length write, and force the
1988                 * caller to redo the whole thing.
1989                 */
1990                if (!PageUptodate(page))
1991                        copied = 0;
1992
1993                page_zero_new_buffers(page, start+copied, start+len);
1994        }
1995        flush_dcache_page(page);
1996
1997        /* This could be a short (even 0-length) commit */
1998        __block_commit_write(inode, page, start, start+copied);
1999
2000        return copied;
2001}
2002EXPORT_SYMBOL(block_write_end);
2003
2004int generic_write_end(struct file *file, struct address_space *mapping,
2005                        loff_t pos, unsigned len, unsigned copied,
2006                        struct page *page, void *fsdata)
2007{
2008        struct inode *inode = mapping->host;
2009        int i_size_changed = 0;
2010
2011        copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2012
2013        /*
2014         * No need to use i_size_read() here, the i_size
2015         * cannot change under us because we hold i_mutex.
2016         *
2017         * But it's important to update i_size while still holding page lock:
2018         * page writeout could otherwise come in and zero beyond i_size.
2019         */
2020        if (pos+copied > inode->i_size) {
2021                i_size_write(inode, pos+copied);
2022                i_size_changed = 1;
2023        }
2024
2025        unlock_page(page);
2026        page_cache_release(page);
2027
2028        /*
2029         * Don't mark the inode dirty under page lock. First, it unnecessarily
2030         * makes the holding time of page lock longer. Second, it forces lock
2031         * ordering of page lock and transaction start for journaling
2032         * filesystems.
2033         */
2034        if (i_size_changed)
2035                mark_inode_dirty(inode);
2036
2037        return copied;
2038}
2039EXPORT_SYMBOL(generic_write_end);
2040
2041/*
2042 * block_is_partially_uptodate checks whether buffers within a page are
2043 * uptodate or not.
2044 *
2045 * Returns true if all buffers which correspond to a file portion
2046 * we want to read are uptodate.
2047 */
2048int block_is_partially_uptodate(struct page *page, read_descriptor_t *desc,
2049                                        unsigned long from)
2050{
2051        unsigned block_start, block_end, blocksize;
2052        unsigned to;
2053        struct buffer_head *bh, *head;
2054        int ret = 1;
2055
2056        if (!page_has_buffers(page))
2057                return 0;
2058
2059        head = page_buffers(page);
2060        blocksize = head->b_size;
2061        to = min_t(unsigned, PAGE_CACHE_SIZE - from, desc->count);
2062        to = from + to;
2063        if (from < blocksize && to > PAGE_CACHE_SIZE - blocksize)
2064                return 0;
2065
2066        bh = head;
2067        block_start = 0;
2068        do {
2069                block_end = block_start + blocksize;
2070                if (block_end > from && block_start < to) {
2071                        if (!buffer_uptodate(bh)) {
2072                                ret = 0;
2073                                break;
2074                        }
2075                        if (block_end >= to)
2076                                break;
2077                }
2078                block_start = block_end;
2079                bh = bh->b_this_page;
2080        } while (bh != head);
2081
2082        return ret;
2083}
2084EXPORT_SYMBOL(block_is_partially_uptodate);
2085
2086/*
2087 * Generic "read page" function for block devices that have the normal
2088 * get_block functionality. This is most of the block device filesystems.
2089 * Reads the page asynchronously --- the unlock_buffer() and
2090 * set/clear_buffer_uptodate() functions propagate buffer state into the
2091 * page struct once IO has completed.
2092 */
2093int block_read_full_page(struct page *page, get_block_t *get_block)
2094{
2095        struct inode *inode = page->mapping->host;
2096        sector_t iblock, lblock;
2097        struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2098        unsigned int blocksize, bbits;
2099        int nr, i;
2100        int fully_mapped = 1;
2101
2102        head = create_page_buffers(page, inode, 0);
2103        blocksize = head->b_size;
2104        bbits = block_size_bits(blocksize);
2105
2106        iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
2107        lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2108        bh = head;
2109        nr = 0;
2110        i = 0;
2111
2112        do {
2113                if (buffer_uptodate(bh))
2114                        continue;
2115
2116                if (!buffer_mapped(bh)) {
2117                        int err = 0;
2118
2119                        fully_mapped = 0;
2120                        if (iblock < lblock) {
2121                                WARN_ON(bh->b_size != blocksize);
2122                                err = get_block(inode, iblock, bh, 0);
2123                                if (err)
2124                                        SetPageError(page);
2125                        }
2126                        if (!buffer_mapped(bh)) {
2127                                zero_user(page, i * blocksize, blocksize);
2128                                if (!err)
2129                                        set_buffer_uptodate(bh);
2130                                continue;
2131                        }
2132                        /*
2133                         * get_block() might have updated the buffer
2134                         * synchronously
2135                         */
2136                        if (buffer_uptodate(bh))
2137                                continue;
2138                }
2139                arr[nr++] = bh;
2140        } while (i++, iblock++, (bh = bh->b_this_page) != head);
2141
2142        if (fully_mapped)
2143                SetPageMappedToDisk(page);
2144
2145        if (!nr) {
2146                /*
2147                 * All buffers are uptodate - we can set the page uptodate
2148                 * as well. But not if get_block() returned an error.
2149                 */
2150                if (!PageError(page))
2151                        SetPageUptodate(page);
2152                unlock_page(page);
2153                return 0;
2154        }
2155
2156        /* Stage two: lock the buffers */
2157        for (i = 0; i < nr; i++) {
2158                bh = arr[i];
2159                lock_buffer(bh);
2160                mark_buffer_async_read(bh);
2161        }
2162
2163        /*
2164         * Stage 3: start the IO.  Check for uptodateness
2165         * inside the buffer lock in case another process reading
2166         * the underlying blockdev brought it uptodate (the sct fix).
2167         */
2168        for (i = 0; i < nr; i++) {
2169                bh = arr[i];
2170                if (buffer_uptodate(bh))
2171                        end_buffer_async_read(bh, 1);
2172                else
2173                        submit_bh(READ, bh);
2174        }
2175        return 0;
2176}
2177EXPORT_SYMBOL(block_read_full_page);
2178
2179/* utility function for filesystems that need to do work on expanding
2180 * truncates.  Uses filesystem pagecache writes to allow the filesystem to
2181 * deal with the hole.  
2182 */
2183int generic_cont_expand_simple(struct inode *inode, loff_t size)
2184{
2185        struct address_space *mapping = inode->i_mapping;
2186        struct page *page;
2187        void *fsdata;
2188        int err;
2189
2190        err = inode_newsize_ok(inode, size);
2191        if (err)
2192                goto out;
2193
2194        err = pagecache_write_begin(NULL, mapping, size, 0,
2195                                AOP_FLAG_UNINTERRUPTIBLE|AOP_FLAG_CONT_EXPAND,
2196                                &page, &fsdata);
2197        if (err)
2198                goto out;
2199
2200        err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2201        BUG_ON(err > 0);
2202
2203out:
2204        return err;
2205}
2206EXPORT_SYMBOL(generic_cont_expand_simple);
2207
2208static int cont_expand_zero(struct file *file, struct address_space *mapping,
2209                            loff_t pos, loff_t *bytes)
2210{
2211        struct inode *inode = mapping->host;
2212        unsigned blocksize = 1 << inode->i_blkbits;
2213        struct page *page;
2214        void *fsdata;
2215        pgoff_t index, curidx;
2216        loff_t curpos;
2217        unsigned zerofrom, offset, len;
2218        int err = 0;
2219
2220        index = pos >> PAGE_CACHE_SHIFT;
2221        offset = pos & ~PAGE_CACHE_MASK;
2222
2223        while (index > (curidx = (curpos = *bytes)>>PAGE_CACHE_SHIFT)) {
2224                zerofrom = curpos & ~PAGE_CACHE_MASK;
2225                if (zerofrom & (blocksize-1)) {
2226                        *bytes |= (blocksize-1);
2227                        (*bytes)++;
2228                }
2229                len = PAGE_CACHE_SIZE - zerofrom;
2230
2231                err = pagecache_write_begin(file, mapping, curpos, len,
2232                                                AOP_FLAG_UNINTERRUPTIBLE,
2233                                                &page, &fsdata);
2234                if (err)
2235                        goto out;
2236                zero_user(page, zerofrom, len);
2237                err = pagecache_write_end(file, mapping, curpos, len, len,
2238                                                page, fsdata);
2239                if (err < 0)
2240                        goto out;
2241                BUG_ON(err != len);
2242                err = 0;
2243
2244                balance_dirty_pages_ratelimited(mapping);
2245        }
2246
2247        /* page covers the boundary, find the boundary offset */
2248        if (index == curidx) {
2249                zerofrom = curpos & ~PAGE_CACHE_MASK;
2250                /* if we will expand the thing last block will be filled */
2251                if (offset <= zerofrom) {
2252                        goto out;
2253                }
2254                if (zerofrom & (blocksize-1)) {
2255                        *bytes |= (blocksize-1);
2256                        (*bytes)++;
2257                }
2258                len = offset - zerofrom;
2259
2260                err = pagecache_write_begin(file, mapping, curpos, len,
2261                                                AOP_FLAG_UNINTERRUPTIBLE,
2262                                                &page, &fsdata);
2263                if (err)
2264                        goto out;
2265                zero_user(page, zerofrom, len);
2266                err = pagecache_write_end(file, mapping, curpos, len, len,
2267                                                page, fsdata);
2268                if (err < 0)
2269                        goto out;
2270                BUG_ON(err != len);
2271                err = 0;
2272        }
2273out:
2274        return err;
2275}
2276
2277/*
2278 * For moronic filesystems that do not allow holes in file.
2279 * We may have to extend the file.
2280 */
2281int cont_write_begin(struct file *file, struct address_space *mapping,
2282                        loff_t pos, unsigned len, unsigned flags,
2283                        struct page **pagep, void **fsdata,
2284                        get_block_t *get_block, loff_t *bytes)
2285{
2286        struct inode *inode = mapping->host;
2287        unsigned blocksize = 1 << inode->i_blkbits;
2288        unsigned zerofrom;
2289        int err;
2290
2291        err = cont_expand_zero(file, mapping, pos, bytes);
2292        if (err)
2293                return err;
2294
2295        zerofrom = *bytes & ~PAGE_CACHE_MASK;
2296        if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2297                *bytes |= (blocksize-1);
2298                (*bytes)++;
2299        }
2300
2301        return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2302}
2303EXPORT_SYMBOL(cont_write_begin);
2304
2305int block_commit_write(struct page *page, unsigned from, unsigned to)
2306{
2307        struct inode *inode = page->mapping->host;
2308        __block_commit_write(inode,page,from,to);
2309        return 0;
2310}
2311EXPORT_SYMBOL(block_commit_write);
2312
2313/*
2314 * block_page_mkwrite() is not allowed to change the file size as it gets
2315 * called from a page fault handler when a page is first dirtied. Hence we must
2316 * be careful to check for EOF conditions here. We set the page up correctly
2317 * for a written page which means we get ENOSPC checking when writing into
2318 * holes and correct delalloc and unwritten extent mapping on filesystems that
2319 * support these features.
2320 *
2321 * We are not allowed to take the i_mutex here so we have to play games to
2322 * protect against truncate races as the page could now be beyond EOF.  Because
2323 * truncate writes the inode size before removing pages, once we have the
2324 * page lock we can determine safely if the page is beyond EOF. If it is not
2325 * beyond EOF, then the page is guaranteed safe against truncation until we
2326 * unlock the page.
2327 *
2328 * Direct callers of this function should protect against filesystem freezing
2329 * using sb_start_write() - sb_end_write() functions.
2330 */
2331int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2332                         get_block_t get_block)
2333{
2334        struct page *page = vmf->page;
2335        struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
2336        unsigned long end;
2337        loff_t size;
2338        int ret;
2339
2340        lock_page(page);
2341        size = i_size_read(inode);
2342        if ((page->mapping != inode->i_mapping) ||
2343            (page_offset(page) > size)) {
2344                /* We overload EFAULT to mean page got truncated */
2345                ret = -EFAULT;
2346                goto out_unlock;
2347        }
2348
2349        /* page is wholly or partially inside EOF */
2350        if (((page->index + 1) << PAGE_CACHE_SHIFT) > size)
2351                end = size & ~PAGE_CACHE_MASK;
2352        else
2353                end = PAGE_CACHE_SIZE;
2354
2355        ret = __block_write_begin(page, 0, end, get_block);
2356        if (!ret)
2357                ret = block_commit_write(page, 0, end);
2358
2359        if (unlikely(ret < 0))
2360                goto out_unlock;
2361        set_page_dirty(page);
2362        wait_on_page_writeback(page);
2363        return 0;
2364out_unlock:
2365        unlock_page(page);
2366        return ret;
2367}
2368EXPORT_SYMBOL(__block_page_mkwrite);
2369
2370int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2371                   get_block_t get_block)
2372{
2373        int ret;
2374        struct super_block *sb = vma->vm_file->f_path.dentry->d_inode->i_sb;
2375
2376        sb_start_pagefault(sb);
2377
2378        /*
2379         * Update file times before taking page lock. We may end up failing the
2380         * fault so this update may be superfluous but who really cares...
2381         */
2382        file_update_time(vma->vm_file);
2383
2384        ret = __block_page_mkwrite(vma, vmf, get_block);
2385        sb_end_pagefault(sb);
2386        return block_page_mkwrite_return(ret);
2387}
2388EXPORT_SYMBOL(block_page_mkwrite);
2389
2390/*
2391 * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2392 * immediately, while under the page lock.  So it needs a special end_io
2393 * handler which does not touch the bh after unlocking it.
2394 */
2395static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2396{
2397        __end_buffer_read_notouch(bh, uptodate);
2398}
2399
2400/*
2401 * Attach the singly-linked list of buffers created by nobh_write_begin, to
2402 * the page (converting it to circular linked list and taking care of page
2403 * dirty races).
2404 */
2405static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2406{
2407        struct buffer_head *bh;
2408
2409        BUG_ON(!PageLocked(page));
2410
2411        spin_lock(&page->mapping->private_lock);
2412        bh = head;
2413        do {
2414                if (PageDirty(page))
2415                        set_buffer_dirty(bh);
2416                if (!bh->b_this_page)
2417                        bh->b_this_page = head;
2418                bh = bh->b_this_page;
2419        } while (bh != head);
2420        attach_page_buffers(page, head);
2421        spin_unlock(&page->mapping->private_lock);
2422}
2423
2424/*
2425 * On entry, the page is fully not uptodate.
2426 * On exit the page is fully uptodate in the areas outside (from,to)
2427 * The filesystem needs to handle block truncation upon failure.
2428 */
2429int nobh_write_begin(struct address_space *mapping,
2430                        loff_t pos, unsigned len, unsigned flags,
2431                        struct page **pagep, void **fsdata,
2432                        get_block_t *get_block)
2433{
2434        struct inode *inode = mapping->host;
2435        const unsigned blkbits = inode->i_blkbits;
2436        const unsigned blocksize = 1 << blkbits;
2437        struct buffer_head *head, *bh;
2438        struct page *page;
2439        pgoff_t index;
2440        unsigned from, to;
2441        unsigned block_in_page;
2442        unsigned block_start, block_end;
2443        sector_t block_in_file;
2444        int nr_reads = 0;
2445        int ret = 0;
2446        int is_mapped_to_disk = 1;
2447
2448        index = pos >> PAGE_CACHE_SHIFT;
2449        from = pos & (PAGE_CACHE_SIZE - 1);
2450        to = from + len;
2451
2452        page = grab_cache_page_write_begin(mapping, index, flags);
2453        if (!page)
2454                return -ENOMEM;
2455        *pagep = page;
2456        *fsdata = NULL;
2457
2458        if (page_has_buffers(page)) {
2459                ret = __block_write_begin(page, pos, len, get_block);
2460                if (unlikely(ret))
2461                        goto out_release;
2462                return ret;
2463        }
2464
2465        if (PageMappedToDisk(page))
2466                return 0;
2467
2468        /*
2469         * Allocate buffers so that we can keep track of state, and potentially
2470         * attach them to the page if an error occurs. In the common case of
2471         * no error, they will just be freed again without ever being attached
2472         * to the page (which is all OK, because we're under the page lock).
2473         *
2474         * Be careful: the buffer linked list is a NULL terminated one, rather
2475         * than the circular one we're used to.
2476         */
2477        head = alloc_page_buffers(page, blocksize, 0);
2478        if (!head) {
2479                ret = -ENOMEM;
2480                goto out_release;
2481        }
2482
2483        block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
2484
2485        /*
2486         * We loop across all blocks in the page, whether or not they are
2487         * part of the affected region.  This is so we can discover if the
2488         * page is fully mapped-to-disk.
2489         */
2490        for (block_start = 0, block_in_page = 0, bh = head;
2491                  block_start < PAGE_CACHE_SIZE;
2492                  block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2493                int create;
2494
2495                block_end = block_start + blocksize;
2496                bh->b_state = 0;
2497                create = 1;
2498                if (block_start >= to)
2499                        create = 0;
2500                ret = get_block(inode, block_in_file + block_in_page,
2501                                        bh, create);
2502                if (ret)
2503                        goto failed;
2504                if (!buffer_mapped(bh))
2505                        is_mapped_to_disk = 0;
2506                if (buffer_new(bh))
2507                        unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
2508                if (PageUptodate(page)) {
2509                        set_buffer_uptodate(bh);
2510                        continue;
2511                }
2512                if (buffer_new(bh) || !buffer_mapped(bh)) {
2513                        zero_user_segments(page, block_start, from,
2514                                                        to, block_end);
2515                        continue;
2516                }
2517                if (buffer_uptodate(bh))
2518                        continue;       /* reiserfs does this */
2519                if (block_start < from || block_end > to) {
2520                        lock_buffer(bh);
2521                        bh->b_end_io = end_buffer_read_nobh;
2522                        submit_bh(READ, bh);
2523                        nr_reads++;
2524                }
2525        }
2526
2527        if (nr_reads) {
2528                /*
2529                 * The page is locked, so these buffers are protected from
2530                 * any VM or truncate activity.  Hence we don't need to care
2531                 * for the buffer_head refcounts.
2532                 */
2533                for (bh = head; bh; bh = bh->b_this_page) {
2534                        wait_on_buffer(bh);
2535                        if (!buffer_uptodate(bh))
2536                                ret = -EIO;
2537                }
2538                if (ret)
2539                        goto failed;
2540        }
2541
2542        if (is_mapped_to_disk)
2543                SetPageMappedToDisk(page);
2544
2545        *fsdata = head; /* to be released by nobh_write_end */
2546
2547        return 0;
2548
2549failed:
2550        BUG_ON(!ret);
2551        /*
2552         * Error recovery is a bit difficult. We need to zero out blocks that
2553         * were newly allocated, and dirty them to ensure they get written out.
2554         * Buffers need to be attached to the page at this point, otherwise
2555         * the handling of potential IO errors during writeout would be hard
2556         * (could try doing synchronous writeout, but what if that fails too?)
2557         */
2558        attach_nobh_buffers(page, head);
2559        page_zero_new_buffers(page, from, to);
2560
2561out_release:
2562        unlock_page(page);
2563        page_cache_release(page);
2564        *pagep = NULL;
2565
2566        return ret;
2567}
2568EXPORT_SYMBOL(nobh_write_begin);
2569
2570int nobh_write_end(struct file *file, struct address_space *mapping,
2571                        loff_t pos, unsigned len, unsigned copied,
2572                        struct page *page, void *fsdata)
2573{
2574        struct inode *inode = page->mapping->host;
2575        struct buffer_head *head = fsdata;
2576        struct buffer_head *bh;
2577        BUG_ON(fsdata != NULL && page_has_buffers(page));
2578
2579        if (unlikely(copied < len) && head)
2580                attach_nobh_buffers(page, head);
2581        if (page_has_buffers(page))
2582                return generic_write_end(file, mapping, pos, len,
2583                                        copied, page, fsdata);
2584
2585        SetPageUptodate(page);
2586        set_page_dirty(page);
2587        if (pos+copied > inode->i_size) {
2588                i_size_write(inode, pos+copied);
2589                mark_inode_dirty(inode);
2590        }
2591
2592        unlock_page(page);
2593        page_cache_release(page);
2594
2595        while (head) {
2596                bh = head;
2597                head = head->b_this_page;
2598                free_buffer_head(bh);
2599        }
2600
2601        return copied;
2602}
2603EXPORT_SYMBOL(nobh_write_end);
2604
2605/*
2606 * nobh_writepage() - based on block_full_write_page() except
2607 * that it tries to operate without attaching bufferheads to
2608 * the page.
2609 */
2610int nobh_writepage(struct page *page, get_block_t *get_block,
2611                        struct writeback_control *wbc)
2612{
2613        struct inode * const inode = page->mapping->host;
2614        loff_t i_size = i_size_read(inode);
2615        const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2616        unsigned offset;
2617        int ret;
2618
2619        /* Is the page fully inside i_size? */
2620        if (page->index < end_index)
2621                goto out;
2622
2623        /* Is the page fully outside i_size? (truncate in progress) */
2624        offset = i_size & (PAGE_CACHE_SIZE-1);
2625        if (page->index >= end_index+1 || !offset) {
2626                /*
2627                 * The page may have dirty, unmapped buffers.  For example,
2628                 * they may have been added in ext3_writepage().  Make them
2629                 * freeable here, so the page does not leak.
2630                 */
2631#if 0
2632                /* Not really sure about this  - do we need this ? */
2633                if (page->mapping->a_ops->invalidatepage)
2634                        page->mapping->a_ops->invalidatepage(page, offset);
2635#endif
2636                unlock_page(page);
2637                return 0; /* don't care */
2638        }
2639
2640        /*
2641         * The page straddles i_size.  It must be zeroed out on each and every
2642         * writepage invocation because it may be mmapped.  "A file is mapped
2643         * in multiples of the page size.  For a file that is not a multiple of
2644         * the  page size, the remaining memory is zeroed when mapped, and
2645         * writes to that region are not written out to the file."
2646         */
2647        zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2648out:
2649        ret = mpage_writepage(page, get_block, wbc);
2650        if (ret == -EAGAIN)
2651                ret = __block_write_full_page(inode, page, get_block, wbc,
2652                                              end_buffer_async_write);
2653        return ret;
2654}
2655EXPORT_SYMBOL(nobh_writepage);
2656
2657int nobh_truncate_page(struct address_space *mapping,
2658                        loff_t from, get_block_t *get_block)
2659{
2660        pgoff_t index = from >> PAGE_CACHE_SHIFT;
2661        unsigned offset = from & (PAGE_CACHE_SIZE-1);
2662        unsigned blocksize;
2663        sector_t iblock;
2664        unsigned length, pos;
2665        struct inode *inode = mapping->host;
2666        struct page *page;
2667        struct buffer_head map_bh;
2668        int err;
2669
2670        blocksize = 1 << inode->i_blkbits;
2671        length = offset & (blocksize - 1);
2672
2673        /* Block boundary? Nothing to do */
2674        if (!length)
2675                return 0;
2676
2677        length = blocksize - length;
2678        iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2679
2680        page = grab_cache_page(mapping, index);
2681        err = -ENOMEM;
2682        if (!page)
2683                goto out;
2684
2685        if (page_has_buffers(page)) {
2686has_buffers:
2687                unlock_page(page);
2688                page_cache_release(page);
2689                return block_truncate_page(mapping, from, get_block);
2690        }
2691
2692        /* Find the buffer that contains "offset" */
2693        pos = blocksize;
2694        while (offset >= pos) {
2695                iblock++;
2696                pos += blocksize;
2697        }
2698
2699        map_bh.b_size = blocksize;
2700        map_bh.b_state = 0;
2701        err = get_block(inode, iblock, &map_bh, 0);
2702        if (err)
2703                goto unlock;
2704        /* unmapped? It's a hole - nothing to do */
2705        if (!buffer_mapped(&map_bh))
2706                goto unlock;
2707
2708        /* Ok, it's mapped. Make sure it's up-to-date */
2709        if (!PageUptodate(page)) {
2710                err = mapping->a_ops->readpage(NULL, page);
2711                if (err) {
2712                        page_cache_release(page);
2713                        goto out;
2714                }
2715                lock_page(page);
2716                if (!PageUptodate(page)) {
2717                        err = -EIO;
2718                        goto unlock;
2719                }
2720                if (page_has_buffers(page))
2721                        goto has_buffers;
2722        }
2723        zero_user(page, offset, length);
2724        set_page_dirty(page);
2725        err = 0;
2726
2727unlock:
2728        unlock_page(page);
2729        page_cache_release(page);
2730out:
2731        return err;
2732}
2733EXPORT_SYMBOL(nobh_truncate_page);
2734
2735int block_truncate_page(struct address_space *mapping,
2736                        loff_t from, get_block_t *get_block)
2737{
2738        pgoff_t index = from >> PAGE_CACHE_SHIFT;
2739        unsigned offset = from & (PAGE_CACHE_SIZE-1);
2740        unsigned blocksize;
2741        sector_t iblock;
2742        unsigned length, pos;
2743        struct inode *inode = mapping->host;
2744        struct page *page;
2745        struct buffer_head *bh;
2746        int err;
2747
2748        blocksize = 1 << inode->i_blkbits;
2749        length = offset & (blocksize - 1);
2750
2751        /* Block boundary? Nothing to do */
2752        if (!length)
2753                return 0;
2754
2755        length = blocksize - length;
2756        iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2757        
2758        page = grab_cache_page(mapping, index);
2759        err = -ENOMEM;
2760        if (!page)
2761                goto out;
2762
2763        if (!page_has_buffers(page))
2764                create_empty_buffers(page, blocksize, 0);
2765
2766        /* Find the buffer that contains "offset" */
2767        bh = page_buffers(page);
2768        pos = blocksize;
2769        while (offset >= pos) {
2770                bh = bh->b_this_page;
2771                iblock++;
2772                pos += blocksize;
2773        }
2774
2775        err = 0;
2776        if (!buffer_mapped(bh)) {
2777                WARN_ON(bh->b_size != blocksize);
2778                err = get_block(inode, iblock, bh, 0);
2779                if (err)
2780                        goto unlock;
2781                /* unmapped? It's a hole - nothing to do */
2782                if (!buffer_mapped(bh))
2783                        goto unlock;
2784        }
2785
2786        /* Ok, it's mapped. Make sure it's up-to-date */
2787        if (PageUptodate(page))
2788                set_buffer_uptodate(bh);
2789
2790        if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2791                err = -EIO;
2792                ll_rw_block(READ, 1, &bh);
2793                wait_on_buffer(bh);
2794                /* Uhhuh. Read error. Complain and punt. */
2795                if (!buffer_uptodate(bh))
2796                        goto unlock;
2797        }
2798
2799        zero_user(page, offset, length);
2800        mark_buffer_dirty(bh);
2801        err = 0;
2802
2803unlock:
2804        unlock_page(page);
2805        page_cache_release(page);
2806out:
2807        return err;
2808}
2809EXPORT_SYMBOL(block_truncate_page);
2810
2811/*
2812 * The generic ->writepage function for buffer-backed address_spaces
2813 * this form passes in the end_io handler used to finish the IO.
2814 */
2815int block_write_full_page_endio(struct page *page, get_block_t *get_block,
2816                        struct writeback_control *wbc, bh_end_io_t *handler)
2817{
2818        struct inode * const inode = page->mapping->host;
2819        loff_t i_size = i_size_read(inode);
2820        const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2821        unsigned offset;
2822
2823        /* Is the page fully inside i_size? */
2824        if (page->index < end_index)
2825                return __block_write_full_page(inode, page, get_block, wbc,
2826                                               handler);
2827
2828        /* Is the page fully outside i_size? (truncate in progress) */
2829        offset = i_size & (PAGE_CACHE_SIZE-1);
2830        if (page->index >= end_index+1 || !offset) {
2831                /*
2832                 * The page may have dirty, unmapped buffers.  For example,
2833                 * they may have been added in ext3_writepage().  Make them
2834                 * freeable here, so the page does not leak.
2835                 */
2836                do_invalidatepage(page, 0);
2837                unlock_page(page);
2838                return 0; /* don't care */
2839        }
2840
2841        /*
2842         * The page straddles i_size.  It must be zeroed out on each and every
2843         * writepage invocation because it may be mmapped.  "A file is mapped
2844         * in multiples of the page size.  For a file that is not a multiple of
2845         * the  page size, the remaining memory is zeroed when mapped, and
2846         * writes to that region are not written out to the file."
2847         */
2848        zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2849        return __block_write_full_page(inode, page, get_block, wbc, handler);
2850}
2851EXPORT_SYMBOL(block_write_full_page_endio);
2852
2853/*
2854 * The generic ->writepage function for buffer-backed address_spaces
2855 */
2856int block_write_full_page(struct page *page, get_block_t *get_block,
2857                        struct writeback_control *wbc)
2858{
2859        return block_write_full_page_endio(page, get_block, wbc,
2860                                           end_buffer_async_write);
2861}
2862EXPORT_SYMBOL(block_write_full_page);
2863
2864sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2865                            get_block_t *get_block)
2866{
2867        struct buffer_head tmp;
2868        struct inode *inode = mapping->host;
2869        tmp.b_state = 0;
2870        tmp.b_blocknr = 0;
2871        tmp.b_size = 1 << inode->i_blkbits;
2872        get_block(inode, block, &tmp, 0);
2873        return tmp.b_blocknr;
2874}
2875EXPORT_SYMBOL(generic_block_bmap);
2876
2877static void end_bio_bh_io_sync(struct bio *bio, int err)
2878{
2879        struct buffer_head *bh = bio->bi_private;
2880
2881        if (err == -EOPNOTSUPP) {
2882                set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
2883        }
2884
2885        if (unlikely (test_bit(BIO_QUIET,&bio->bi_flags)))
2886                set_bit(BH_Quiet, &bh->b_state);
2887
2888        bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
2889        bio_put(bio);
2890}
2891
2892/*
2893 * This allows us to do IO even on the odd last sectors
2894 * of a device, even if the bh block size is some multiple
2895 * of the physical sector size.
2896 *
2897 * We'll just truncate the bio to the size of the device,
2898 * and clear the end of the buffer head manually.
2899 *
2900 * Truly out-of-range accesses will turn into actual IO
2901 * errors, this only handles the "we need to be able to
2902 * do IO at the final sector" case.
2903 */
2904static void guard_bh_eod(int rw, struct bio *bio, struct buffer_head *bh)
2905{
2906        sector_t maxsector;
2907        unsigned bytes;
2908
2909        maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
2910        if (!maxsector)
2911                return;
2912
2913        /*
2914         * If the *whole* IO is past the end of the device,
2915         * let it through, and the IO layer will turn it into
2916         * an EIO.
2917         */
2918        if (unlikely(bio->bi_sector >= maxsector))
2919                return;
2920
2921        maxsector -= bio->bi_sector;
2922        bytes = bio->bi_size;
2923        if (likely((bytes >> 9) <= maxsector))
2924                return;
2925
2926        /* Uhhuh. We've got a bh that straddles the device size! */
2927        bytes = maxsector << 9;
2928
2929        /* Truncate the bio.. */
2930        bio->bi_size = bytes;
2931        bio->bi_io_vec[0].bv_len = bytes;
2932
2933        /* ..and clear the end of the buffer for reads */
2934        if ((rw & RW_MASK) == READ) {
2935                void *kaddr = kmap_atomic(bh->b_page);
2936                memset(kaddr + bh_offset(bh) + bytes, 0, bh->b_size - bytes);
2937                kunmap_atomic(kaddr);
2938                flush_dcache_page(bh->b_page);
2939        }
2940}
2941
2942int submit_bh(int rw, struct buffer_head * bh)
2943{
2944        struct bio *bio;
2945        int ret = 0;
2946
2947        BUG_ON(!buffer_locked(bh));
2948        BUG_ON(!buffer_mapped(bh));
2949        BUG_ON(!bh->b_end_io);
2950        BUG_ON(buffer_delay(bh));
2951        BUG_ON(buffer_unwritten(bh));
2952
2953        /*
2954         * Only clear out a write error when rewriting
2955         */
2956        if (test_set_buffer_req(bh) && (rw & WRITE))
2957                clear_buffer_write_io_error(bh);
2958
2959        /*
2960         * from here on down, it's all bio -- do the initial mapping,
2961         * submit_bio -> generic_make_request may further map this bio around
2962         */
2963        bio = bio_alloc(GFP_NOIO, 1);
2964
2965        bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
2966        bio->bi_bdev = bh->b_bdev;
2967        bio->bi_io_vec[0].bv_page = bh->b_page;
2968        bio->bi_io_vec[0].bv_len = bh->b_size;
2969        bio->bi_io_vec[0].bv_offset = bh_offset(bh);
2970
2971        bio->bi_vcnt = 1;
2972        bio->bi_idx = 0;
2973        bio->bi_size = bh->b_size;
2974
2975        bio->bi_end_io = end_bio_bh_io_sync;
2976        bio->bi_private = bh;
2977
2978        /* Take care of bh's that straddle the end of the device */
2979        guard_bh_eod(rw, bio, bh);
2980
2981        bio_get(bio);
2982        submit_bio(rw, bio);
2983
2984        if (bio_flagged(bio, BIO_EOPNOTSUPP))
2985                ret = -EOPNOTSUPP;
2986
2987        bio_put(bio);
2988        return ret;
2989}
2990EXPORT_SYMBOL(submit_bh);
2991
2992/**
2993 * ll_rw_block: low-level access to block devices (DEPRECATED)
2994 * @rw: whether to %READ or %WRITE or maybe %READA (readahead)
2995 * @nr: number of &struct buffer_heads in the array
2996 * @bhs: array of pointers to &struct buffer_head
2997 *
2998 * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
2999 * requests an I/O operation on them, either a %READ or a %WRITE.  The third
3000 * %READA option is described in the documentation for generic_make_request()
3001 * which ll_rw_block() calls.
3002 *
3003 * This function drops any buffer that it cannot get a lock on (with the
3004 * BH_Lock state bit), any buffer that appears to be clean when doing a write
3005 * request, and any buffer that appears to be up-to-date when doing read
3006 * request.  Further it marks as clean buffers that are processed for
3007 * writing (the buffer cache won't assume that they are actually clean
3008 * until the buffer gets unlocked).
3009 *
3010 * ll_rw_block sets b_end_io to simple completion handler that marks
3011 * the buffer up-to-date (if approriate), unlocks the buffer and wakes
3012 * any waiters. 
3013 *
3014 * All of the buffers must be for the same device, and must also be a
3015 * multiple of the current approved size for the device.
3016 */
3017void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
3018{
3019        int i;
3020
3021        for (i = 0; i < nr; i++) {
3022                struct buffer_head *bh = bhs[i];
3023
3024                if (!trylock_buffer(bh))
3025                        continue;
3026                if (rw == WRITE) {
3027                        if (test_clear_buffer_dirty(bh)) {
3028                                bh->b_end_io = end_buffer_write_sync;
3029                                get_bh(bh);
3030                                submit_bh(WRITE, bh);
3031                                continue;
3032                        }
3033                } else {
3034                        if (!buffer_uptodate(bh)) {
3035                                bh->b_end_io = end_buffer_read_sync;
3036                                get_bh(bh);
3037                                submit_bh(rw, bh);
3038                                continue;
3039                        }
3040                }
3041                unlock_buffer(bh);
3042        }
3043}
3044EXPORT_SYMBOL(ll_rw_block);
3045
3046void write_dirty_buffer(struct buffer_head *bh, int rw)
3047{
3048        lock_buffer(bh);
3049        if (!test_clear_buffer_dirty(bh)) {
3050                unlock_buffer(bh);
3051                return;
3052        }
3053        bh->b_end_io = end_buffer_write_sync;
3054        get_bh(bh);
3055        submit_bh(rw, bh);
3056}
3057EXPORT_SYMBOL(write_dirty_buffer);
3058
3059/*
3060 * For a data-integrity writeout, we need to wait upon any in-progress I/O
3061 * and then start new I/O and then wait upon it.  The caller must have a ref on
3062 * the buffer_head.
3063 */
3064int __sync_dirty_buffer(struct buffer_head *bh, int rw)
3065{
3066        int ret = 0;
3067
3068        WARN_ON(atomic_read(&bh->b_count) < 1);
3069        lock_buffer(bh);
3070        if (test_clear_buffer_dirty(bh)) {
3071                get_bh(bh);
3072                bh->b_end_io = end_buffer_write_sync;
3073                ret = submit_bh(rw, bh);
3074                wait_on_buffer(bh);
3075                if (!ret && !buffer_uptodate(bh))
3076                        ret = -EIO;
3077        } else {
3078                unlock_buffer(bh);
3079        }
3080        return ret;
3081}
3082EXPORT_SYMBOL(__sync_dirty_buffer);
3083
3084int sync_dirty_buffer(struct buffer_head *bh)
3085{
3086        return __sync_dirty_buffer(bh, WRITE_SYNC);
3087}
3088EXPORT_SYMBOL(sync_dirty_buffer);
3089
3090/*
3091 * try_to_free_buffers() checks if all the buffers on this particular page
3092 * are unused, and releases them if so.
3093 *
3094 * Exclusion against try_to_free_buffers may be obtained by either
3095 * locking the page or by holding its mapping's private_lock.
3096 *
3097 * If the page is dirty but all the buffers are clean then we need to
3098 * be sure to mark the page clean as well.  This is because the page
3099 * may be against a block device, and a later reattachment of buffers
3100 * to a dirty page will set *all* buffers dirty.  Which would corrupt
3101 * filesystem data on the same device.
3102 *
3103 * The same applies to regular filesystem pages: if all the buffers are
3104 * clean then we set the page clean and proceed.  To do that, we require
3105 * total exclusion from __set_page_dirty_buffers().  That is obtained with
3106 * private_lock.
3107 *
3108 * try_to_free_buffers() is non-blocking.
3109 */
3110static inline int buffer_busy(struct buffer_head *bh)
3111{
3112        return atomic_read(&bh->b_count) |
3113                (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3114}
3115
3116static int
3117drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
3118{
3119        struct buffer_head *head = page_buffers(page);
3120        struct buffer_head *bh;
3121
3122        bh = head;
3123        do {
3124                if (buffer_write_io_error(bh) && page->mapping)
3125                        set_bit(AS_EIO, &page->mapping->flags);
3126                if (buffer_busy(bh))
3127                        goto failed;
3128                bh = bh->b_this_page;
3129        } while (bh != head);
3130
3131        do {
3132                struct buffer_head *next = bh->b_this_page;
3133
3134                if (bh->b_assoc_map)
3135                        __remove_assoc_queue(bh);
3136                bh = next;
3137        } while (bh != head);
3138        *buffers_to_free = head;
3139        __clear_page_buffers(page);
3140        return 1;
3141failed:
3142        return 0;
3143}
3144
3145int try_to_free_buffers(struct page *page)
3146{
3147        struct address_space * const mapping = page->mapping;
3148        struct buffer_head *buffers_to_free = NULL;
3149        int ret = 0;
3150
3151        BUG_ON(!PageLocked(page));
3152        if (PageWriteback(page))
3153                return 0;
3154
3155        if (mapping == NULL) {          /* can this still happen? */
3156                ret = drop_buffers(page, &buffers_to_free);
3157                goto out;
3158        }
3159
3160        spin_lock(&mapping->private_lock);
3161        ret = drop_buffers(page, &buffers_to_free);
3162
3163        /*
3164         * If the filesystem writes its buffers by hand (eg ext3)
3165         * then we can have clean buffers against a dirty page.  We
3166         * clean the page here; otherwise the VM will never notice
3167         * that the filesystem did any IO at all.
3168         *
3169         * Also, during truncate, discard_buffer will have marked all
3170         * the page's buffers clean.  We discover that here and clean
3171         * the page also.
3172         *
3173         * private_lock must be held over this entire operation in order
3174         * to synchronise against __set_page_dirty_buffers and prevent the
3175         * dirty bit from being lost.
3176         */
3177        if (ret)
3178                cancel_dirty_page(page, PAGE_CACHE_SIZE);
3179        spin_unlock(&mapping->private_lock);
3180out:
3181        if (buffers_to_free) {
3182                struct buffer_head *bh = buffers_to_free;
3183
3184                do {
3185                        struct buffer_head *next = bh->b_this_page;
3186                        free_buffer_head(bh);
3187                        bh = next;
3188                } while (bh != buffers_to_free);
3189        }
3190        return ret;
3191}
3192EXPORT_SYMBOL(try_to_free_buffers);
3193
3194/*
3195 * There are no bdflush tunables left.  But distributions are
3196 * still running obsolete flush daemons, so we terminate them here.
3197 *
3198 * Use of bdflush() is deprecated and will be removed in a future kernel.
3199 * The `flush-X' kernel threads fully replace bdflush daemons and this call.
3200 */
3201SYSCALL_DEFINE2(bdflush, int, func, long, data)
3202{
3203        static int msg_count;
3204
3205        if (!capable(CAP_SYS_ADMIN))
3206                return -EPERM;
3207
3208        if (msg_count < 5) {
3209                msg_count++;
3210                printk(KERN_INFO
3211                        "warning: process `%s' used the obsolete bdflush"
3212                        " system call\n", current->comm);
3213                printk(KERN_INFO "Fix your initscripts?\n");
3214        }
3215
3216        if (func == 1)
3217                do_exit(0);
3218        return 0;
3219}
3220
3221/*
3222 * Buffer-head allocation
3223 */
3224static struct kmem_cache *bh_cachep __read_mostly;
3225
3226/*
3227 * Once the number of bh's in the machine exceeds this level, we start
3228 * stripping them in writeback.
3229 */
3230static int max_buffer_heads;
3231
3232int buffer_heads_over_limit;
3233
3234struct bh_accounting {
3235        int nr;                 /* Number of live bh's */
3236        int ratelimit;          /* Limit cacheline bouncing */
3237};
3238
3239static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3240
3241static void recalc_bh_state(void)
3242{
3243        int i;
3244        int tot = 0;
3245
3246        if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3247                return;
3248        __this_cpu_write(bh_accounting.ratelimit, 0);
3249        for_each_online_cpu(i)
3250                tot += per_cpu(bh_accounting, i).nr;
3251        buffer_heads_over_limit = (tot > max_buffer_heads);
3252}
3253
3254struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3255{
3256        struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3257        if (ret) {
3258                INIT_LIST_HEAD(&ret->b_assoc_buffers);
3259                preempt_disable();
3260                __this_cpu_inc(bh_accounting.nr);
3261                recalc_bh_state();
3262                preempt_enable();
3263        }
3264        return ret;
3265}
3266EXPORT_SYMBOL(alloc_buffer_head);
3267
3268void free_buffer_head(struct buffer_head *bh)
3269{
3270        BUG_ON(!list_empty(&bh->b_assoc_buffers));
3271        kmem_cache_free(bh_cachep, bh);
3272        preempt_disable();
3273        __this_cpu_dec(bh_accounting.nr);
3274        recalc_bh_state();
3275        preempt_enable();
3276}
3277EXPORT_SYMBOL(free_buffer_head);
3278
3279static void buffer_exit_cpu(int cpu)
3280{
3281        int i;
3282        struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3283
3284        for (i = 0; i < BH_LRU_SIZE; i++) {
3285                brelse(b->bhs[i]);
3286                b->bhs[i] = NULL;
3287        }
3288        this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3289        per_cpu(bh_accounting, cpu).nr = 0;
3290}
3291
3292static int buffer_cpu_notify(struct notifier_block *self,
3293                              unsigned long action, void *hcpu)
3294{
3295        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN)
3296                buffer_exit_cpu((unsigned long)hcpu);
3297        return NOTIFY_OK;
3298}
3299
3300/**
3301 * bh_uptodate_or_lock - Test whether the buffer is uptodate
3302 * @bh: struct buffer_head
3303 *
3304 * Return true if the buffer is up-to-date and false,
3305 * with the buffer locked, if not.
3306 */
3307int bh_uptodate_or_lock(struct buffer_head *bh)
3308{
3309        if (!buffer_uptodate(bh)) {
3310                lock_buffer(bh);
3311                if (!buffer_uptodate(bh))
3312                        return 0;
3313                unlock_buffer(bh);
3314        }
3315        return 1;
3316}
3317EXPORT_SYMBOL(bh_uptodate_or_lock);
3318
3319/**
3320 * bh_submit_read - Submit a locked buffer for reading
3321 * @bh: struct buffer_head
3322 *
3323 * Returns zero on success and -EIO on error.
3324 */
3325int bh_submit_read(struct buffer_head *bh)
3326{
3327        BUG_ON(!buffer_locked(bh));
3328
3329        if (buffer_uptodate(bh)) {
3330                unlock_buffer(bh);
3331                return 0;
3332        }
3333
3334        get_bh(bh);
3335        bh->b_end_io = end_buffer_read_sync;
3336        submit_bh(READ, bh);
3337        wait_on_buffer(bh);
3338        if (buffer_uptodate(bh))
3339                return 0;
3340        return -EIO;
3341}
3342EXPORT_SYMBOL(bh_submit_read);
3343
3344void __init buffer_init(void)
3345{
3346        int nrpages;
3347
3348        bh_cachep = kmem_cache_create("buffer_head",
3349                        sizeof(struct buffer_head), 0,
3350                                (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3351                                SLAB_MEM_SPREAD),
3352                                NULL);
3353
3354        /*
3355         * Limit the bh occupancy to 10% of ZONE_NORMAL
3356         */
3357        nrpages = (nr_free_buffer_pages() * 10) / 100;
3358        max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3359        hotcpu_notifier(buffer_cpu_notify, 0);
3360}
3361
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