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#include <trace/events/block.h>
  45
  46static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
  47
  48#define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
  49
  50void init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
  51{
  52        bh->b_end_io = handler;
  53        bh->b_private = private;
  54}
  55EXPORT_SYMBOL(init_buffer);
  56
  57inline void touch_buffer(struct buffer_head *bh)
  58{
  59        trace_block_touch_buffer(bh);
  60        mark_page_accessed(bh->b_page);
  61}
  62EXPORT_SYMBOL(touch_buffer);
  63
  64static int sleep_on_buffer(void *word)
  65{
  66        io_schedule();
  67        return 0;
  68}
  69
  70void __lock_buffer(struct buffer_head *bh)
  71{
  72        wait_on_bit_lock(&bh->b_state, BH_Lock, sleep_on_buffer,
  73                                                        TASK_UNINTERRUPTIBLE);
  74}
  75EXPORT_SYMBOL(__lock_buffer);
  76
  77void unlock_buffer(struct buffer_head *bh)
  78{
  79        clear_bit_unlock(BH_Lock, &bh->b_state);
  80        smp_mb__after_clear_bit();
  81        wake_up_bit(&bh->b_state, BH_Lock);
  82}
  83EXPORT_SYMBOL(unlock_buffer);
  84
  85/*
  86 * Returns if the page has dirty or writeback buffers. If all the buffers
  87 * are unlocked and clean then the PageDirty information is stale. If
  88 * any of the pages are locked, it is assumed they are locked for IO.
  89 */
  90void buffer_check_dirty_writeback(struct page *page,
  91                                     bool *dirty, bool *writeback)
  92{
  93        struct buffer_head *head, *bh;
  94        *dirty = false;
  95        *writeback = false;
  96
  97        BUG_ON(!PageLocked(page));
  98
  99        if (!page_has_buffers(page))
 100                return;
 101
 102        if (PageWriteback(page))
 103                *writeback = true;
 104
 105        head = page_buffers(page);
 106        bh = head;
 107        do {
 108                if (buffer_locked(bh))
 109                        *writeback = true;
 110
 111                if (buffer_dirty(bh))
 112                        *dirty = true;
 113
 114                bh = bh->b_this_page;
 115        } while (bh != head);
 116}
 117EXPORT_SYMBOL(buffer_check_dirty_writeback);
 118
 119/*
 120 * Block until a buffer comes unlocked.  This doesn't stop it
 121 * from becoming locked again - you have to lock it yourself
 122 * if you want to preserve its state.
 123 */
 124void __wait_on_buffer(struct buffer_head * bh)
 125{
 126        wait_on_bit(&bh->b_state, BH_Lock, sleep_on_buffer, TASK_UNINTERRUPTIBLE);
 127}
 128EXPORT_SYMBOL(__wait_on_buffer);
 129
 130static void
 131__clear_page_buffers(struct page *page)
 132{
 133        ClearPagePrivate(page);
 134        set_page_private(page, 0);
 135        page_cache_release(page);
 136}
 137
 138
 139static int quiet_error(struct buffer_head *bh)
 140{
 141        if (!test_bit(BH_Quiet, &bh->b_state) && printk_ratelimit())
 142                return 0;
 143        return 1;
 144}
 145
 146
 147static void buffer_io_error(struct buffer_head *bh)
 148{
 149        char b[BDEVNAME_SIZE];
 150        printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
 151                        bdevname(bh->b_bdev, b),
 152                        (unsigned long long)bh->b_blocknr);
 153}
 154
 155/*
 156 * End-of-IO handler helper function which does not touch the bh after
 157 * unlocking it.
 158 * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
 159 * a race there is benign: unlock_buffer() only use the bh's address for
 160 * hashing after unlocking the buffer, so it doesn't actually touch the bh
 161 * itself.
 162 */
 163static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
 164{
 165        if (uptodate) {
 166                set_buffer_uptodate(bh);
 167        } else {
 168                /* This happens, due to failed READA attempts. */
 169                clear_buffer_uptodate(bh);
 170        }
 171        unlock_buffer(bh);
 172}
 173
 174/*
 175 * Default synchronous end-of-IO handler..  Just mark it up-to-date and
 176 * unlock the buffer. This is what ll_rw_block uses too.
 177 */
 178void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
 179{
 180        __end_buffer_read_notouch(bh, uptodate);
 181        put_bh(bh);
 182}
 183EXPORT_SYMBOL(end_buffer_read_sync);
 184
 185void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 186{
 187        char b[BDEVNAME_SIZE];
 188
 189        if (uptodate) {
 190                set_buffer_uptodate(bh);
 191        } else {
 192                if (!quiet_error(bh)) {
 193                        buffer_io_error(bh);
 194                        printk(KERN_WARNING "lost page write due to "
 195                                        "I/O error on %s\n",
 196                                       bdevname(bh->b_bdev, b));
 197                }
 198                set_buffer_write_io_error(bh);
 199                clear_buffer_uptodate(bh);
 200        }
 201        unlock_buffer(bh);
 202        put_bh(bh);
 203}
 204EXPORT_SYMBOL(end_buffer_write_sync);
 205
 206/*
 207 * Various filesystems appear to want __find_get_block to be non-blocking.
 208 * But it's the page lock which protects the buffers.  To get around this,
 209 * we get exclusion from try_to_free_buffers with the blockdev mapping's
 210 * private_lock.
 211 *
 212 * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
 213 * may be quite high.  This code could TryLock the page, and if that
 214 * succeeds, there is no need to take private_lock. (But if
 215 * private_lock is contended then so is mapping->tree_lock).
 216 */
 217static struct buffer_head *
 218__find_get_block_slow(struct block_device *bdev, sector_t block)
 219{
 220        struct inode *bd_inode = bdev->bd_inode;
 221        struct address_space *bd_mapping = bd_inode->i_mapping;
 222        struct buffer_head *ret = NULL;
 223        pgoff_t index;
 224        struct buffer_head *bh;
 225        struct buffer_head *head;
 226        struct page *page;
 227        int all_mapped = 1;
 228
 229        index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
 230        page = find_get_page(bd_mapping, index);
 231        if (!page)
 232                goto out;
 233
 234        spin_lock(&bd_mapping->private_lock);
 235        if (!page_has_buffers(page))
 236                goto out_unlock;
 237        head = page_buffers(page);
 238        bh = head;
 239        do {
 240                if (!buffer_mapped(bh))
 241                        all_mapped = 0;
 242                else if (bh->b_blocknr == block) {
 243                        ret = bh;
 244                        get_bh(bh);
 245                        goto out_unlock;
 246                }
 247                bh = bh->b_this_page;
 248        } while (bh != head);
 249
 250        /* we might be here because some of the buffers on this page are
 251         * not mapped.  This is due to various races between
 252         * file io on the block device and getblk.  It gets dealt with
 253         * elsewhere, don't buffer_error if we had some unmapped buffers
 254         */
 255        if (all_mapped) {
 256                char b[BDEVNAME_SIZE];
 257
 258                printk("__find_get_block_slow() failed. "
 259                        "block=%llu, b_blocknr=%llu\n",
 260                        (unsigned long long)block,
 261                        (unsigned long long)bh->b_blocknr);
 262                printk("b_state=0x%08lx, b_size=%zu\n",
 263                        bh->b_state, bh->b_size);
 264                printk("device %s blocksize: %d\n", bdevname(bdev, b),
 265                        1 << bd_inode->i_blkbits);
 266        }
 267out_unlock:
 268        spin_unlock(&bd_mapping->private_lock);
 269        page_cache_release(page);
 270out:
 271        return ret;
 272}
 273
 274/*
 275 * Kick the writeback threads then try to free up some ZONE_NORMAL memory.
 276 */
 277static void free_more_memory(void)
 278{
 279        struct zone *zone;
 280        int nid;
 281
 282        wakeup_flusher_threads(1024, WB_REASON_FREE_MORE_MEM);
 283        yield();
 284
 285        for_each_online_node(nid) {
 286                (void)first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
 287                                                gfp_zone(GFP_NOFS), NULL,
 288                                                &zone);
 289                if (zone)
 290                        try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
 291                                                GFP_NOFS, NULL);
 292        }
 293}
 294
 295/*
 296 * I/O completion handler for block_read_full_page() - pages
 297 * which come unlocked at the end of I/O.
 298 */
 299static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
 300{
 301        unsigned long flags;
 302        struct buffer_head *first;
 303        struct buffer_head *tmp;
 304        struct page *page;
 305        int page_uptodate = 1;
 306
 307        BUG_ON(!buffer_async_read(bh));
 308
 309        page = bh->b_page;
 310        if (uptodate) {
 311                set_buffer_uptodate(bh);
 312        } else {
 313                clear_buffer_uptodate(bh);
 314                if (!quiet_error(bh))
 315                        buffer_io_error(bh);
 316                SetPageError(page);
 317        }
 318
 319        /*
 320         * Be _very_ careful from here on. Bad things can happen if
 321         * two buffer heads end IO at almost the same time and both
 322         * decide that the page is now completely done.
 323         */
 324        first = page_buffers(page);
 325        local_irq_save(flags);
 326        bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
 327        clear_buffer_async_read(bh);
 328        unlock_buffer(bh);
 329        tmp = bh;
 330        do {
 331                if (!buffer_uptodate(tmp))
 332                        page_uptodate = 0;
 333                if (buffer_async_read(tmp)) {
 334                        BUG_ON(!buffer_locked(tmp));
 335                        goto still_busy;
 336                }
 337                tmp = tmp->b_this_page;
 338        } while (tmp != bh);
 339        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 340        local_irq_restore(flags);
 341
 342        /*
 343         * If none of the buffers had errors and they are all
 344         * uptodate then we can set the page uptodate.
 345         */
 346        if (page_uptodate && !PageError(page))
 347                SetPageUptodate(page);
 348        unlock_page(page);
 349        return;
 350
 351still_busy:
 352        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 353        local_irq_restore(flags);
 354        return;
 355}
 356
 357/*
 358 * Completion handler for block_write_full_page() - pages which are unlocked
 359 * during I/O, and which have PageWriteback cleared upon I/O completion.
 360 */
 361void end_buffer_async_write(struct buffer_head *bh, int uptodate)
 362{
 363        char b[BDEVNAME_SIZE];
 364        unsigned long flags;
 365        struct buffer_head *first;
 366        struct buffer_head *tmp;
 367        struct page *page;
 368
 369        BUG_ON(!buffer_async_write(bh));
 370
 371        page = bh->b_page;
 372        if (uptodate) {
 373                set_buffer_uptodate(bh);
 374        } else {
 375                if (!quiet_error(bh)) {
 376                        buffer_io_error(bh);
 377                        printk(KERN_WARNING "lost page write due to "
 378                                        "I/O error on %s\n",
 379                               bdevname(bh->b_bdev, b));
 380                }
 381                set_bit(AS_EIO, &page->mapping->flags);
 382                set_buffer_write_io_error(bh);
 383                clear_buffer_uptodate(bh);
 384                SetPageError(page);
 385        }
 386
 387        first = page_buffers(page);
 388        local_irq_save(flags);
 389        bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
 390
 391        clear_buffer_async_write(bh);
 392        unlock_buffer(bh);
 393        tmp = bh->b_this_page;
 394        while (tmp != bh) {
 395                if (buffer_async_write(tmp)) {
 396                        BUG_ON(!buffer_locked(tmp));
 397                        goto still_busy;
 398                }
 399                tmp = tmp->b_this_page;
 400        }
 401        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 402        local_irq_restore(flags);
 403        end_page_writeback(page);
 404        return;
 405
 406still_busy:
 407        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 408        local_irq_restore(flags);
 409        return;
 410}
 411EXPORT_SYMBOL(end_buffer_async_write);
 412
 413/*
 414 * If a page's buffers are under async readin (end_buffer_async_read
 415 * completion) then there is a possibility that another thread of
 416 * control could lock one of the buffers after it has completed
 417 * but while some of the other buffers have not completed.  This
 418 * locked buffer would confuse end_buffer_async_read() into not unlocking
 419 * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
 420 * that this buffer is not under async I/O.
 421 *
 422 * The page comes unlocked when it has no locked buffer_async buffers
 423 * left.
 424 *
 425 * PageLocked prevents anyone starting new async I/O reads any of
 426 * the buffers.
 427 *
 428 * PageWriteback is used to prevent simultaneous writeout of the same
 429 * page.
 430 *
 431 * PageLocked prevents anyone from starting writeback of a page which is
 432 * under read I/O (PageWriteback is only ever set against a locked page).
 433 */
 434static void mark_buffer_async_read(struct buffer_head *bh)
 435{
 436        bh->b_end_io = end_buffer_async_read;
 437        set_buffer_async_read(bh);
 438}
 439
 440static void mark_buffer_async_write_endio(struct buffer_head *bh,
 441                                          bh_end_io_t *handler)
 442{
 443        bh->b_end_io = handler;
 444        set_buffer_async_write(bh);
 445}
 446
 447void mark_buffer_async_write(struct buffer_head *bh)
 448{
 449        mark_buffer_async_write_endio(bh, end_buffer_async_write);
 450}
 451EXPORT_SYMBOL(mark_buffer_async_write);
 452
 453
 454/*
 455 * fs/buffer.c contains helper functions for buffer-backed address space's
 456 * fsync functions.  A common requirement for buffer-based filesystems is
 457 * that certain data from the backing blockdev needs to be written out for
 458 * a successful fsync().  For example, ext2 indirect blocks need to be
 459 * written back and waited upon before fsync() returns.
 460 *
 461 * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
 462 * inode_has_buffers() and invalidate_inode_buffers() are provided for the
 463 * management of a list of dependent buffers at ->i_mapping->private_list.
 464 *
 465 * Locking is a little subtle: try_to_free_buffers() will remove buffers
 466 * from their controlling inode's queue when they are being freed.  But
 467 * try_to_free_buffers() will be operating against the *blockdev* mapping
 468 * at the time, not against the S_ISREG file which depends on those buffers.
 469 * So the locking for private_list is via the private_lock in the address_space
 470 * which backs the buffers.  Which is different from the address_space 
 471 * against which the buffers are listed.  So for a particular address_space,
 472 * mapping->private_lock does *not* protect mapping->private_list!  In fact,
 473 * mapping->private_list will always be protected by the backing blockdev's
 474 * ->private_lock.
 475 *
 476 * Which introduces a requirement: all buffers on an address_space's
 477 * ->private_list must be from the same address_space: the blockdev's.
 478 *
 479 * address_spaces which do not place buffers at ->private_list via these
 480 * utility functions are free to use private_lock and private_list for
 481 * whatever they want.  The only requirement is that list_empty(private_list)
 482 * be true at clear_inode() time.
 483 *
 484 * FIXME: clear_inode should not call invalidate_inode_buffers().  The
 485 * filesystems should do that.  invalidate_inode_buffers() should just go
 486 * BUG_ON(!list_empty).
 487 *
 488 * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
 489 * take an address_space, not an inode.  And it should be called
 490 * mark_buffer_dirty_fsync() to clearly define why those buffers are being
 491 * queued up.
 492 *
 493 * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
 494 * list if it is already on a list.  Because if the buffer is on a list,
 495 * it *must* already be on the right one.  If not, the filesystem is being
 496 * silly.  This will save a ton of locking.  But first we have to ensure
 497 * that buffers are taken *off* the old inode's list when they are freed
 498 * (presumably in truncate).  That requires careful auditing of all
 499 * filesystems (do it inside bforget()).  It could also be done by bringing
 500 * b_inode back.
 501 */
 502
 503/*
 504 * The buffer's backing address_space's private_lock must be held
 505 */
 506static void __remove_assoc_queue(struct buffer_head *bh)
 507{
 508        list_del_init(&bh->b_assoc_buffers);
 509        WARN_ON(!bh->b_assoc_map);
 510        if (buffer_write_io_error(bh))
 511                set_bit(AS_EIO, &bh->b_assoc_map->flags);
 512        bh->b_assoc_map = NULL;
 513}
 514
 515int inode_has_buffers(struct inode *inode)
 516{
 517        return !list_empty(&inode->i_data.private_list);
 518}
 519
 520/*
 521 * osync is designed to support O_SYNC io.  It waits synchronously for
 522 * all already-submitted IO to complete, but does not queue any new
 523 * writes to the disk.
 524 *
 525 * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
 526 * you dirty the buffers, and then use osync_inode_buffers to wait for
 527 * completion.  Any other dirty buffers which are not yet queued for
 528 * write will not be flushed to disk by the osync.
 529 */
 530static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
 531{
 532        struct buffer_head *bh;
 533        struct list_head *p;
 534        int err = 0;
 535
 536        spin_lock(lock);
 537repeat:
 538        list_for_each_prev(p, list) {
 539                bh = BH_ENTRY(p);
 540                if (buffer_locked(bh)) {
 541                        get_bh(bh);
 542                        spin_unlock(lock);
 543                        wait_on_buffer(bh);
 544                        if (!buffer_uptodate(bh))
 545                                err = -EIO;
 546                        brelse(bh);
 547                        spin_lock(lock);
 548                        goto repeat;
 549                }
 550        }
 551        spin_unlock(lock);
 552        return err;
 553}
 554
 555static void do_thaw_one(struct super_block *sb, void *unused)
 556{
 557        char b[BDEVNAME_SIZE];
 558        while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
 559                printk(KERN_WARNING "Emergency Thaw on %s\n",
 560                       bdevname(sb->s_bdev, b));
 561}
 562
 563static void do_thaw_all(struct work_struct *work)
 564{
 565        iterate_supers(do_thaw_one, NULL);
 566        kfree(work);
 567        printk(KERN_WARNING "Emergency Thaw complete\n");
 568}
 569
 570/**
 571 * emergency_thaw_all -- forcibly thaw every frozen filesystem
 572 *
 573 * Used for emergency unfreeze of all filesystems via SysRq
 574 */
 575void emergency_thaw_all(void)
 576{
 577        struct work_struct *work;
 578
 579        work = kmalloc(sizeof(*work), GFP_ATOMIC);
 580        if (work) {
 581                INIT_WORK(work, do_thaw_all);
 582                schedule_work(work);
 583        }
 584}
 585
 586/**
 587 * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
 588 * @mapping: the mapping which wants those buffers written
 589 *
 590 * Starts I/O against the buffers at mapping->private_list, and waits upon
 591 * that I/O.
 592 *
 593 * Basically, this is a convenience function for fsync().
 594 * @mapping is a file or directory which needs those buffers to be written for
 595 * a successful fsync().
 596 */
 597int sync_mapping_buffers(struct address_space *mapping)
 598{
 599        struct address_space *buffer_mapping = mapping->private_data;
 600
 601        if (buffer_mapping == NULL || list_empty(&mapping->private_list))
 602                return 0;
 603
 604        return fsync_buffers_list(&buffer_mapping->private_lock,
 605                                        &mapping->private_list);
 606}
 607EXPORT_SYMBOL(sync_mapping_buffers);
 608
 609/*
 610 * Called when we've recently written block `bblock', and it is known that
 611 * `bblock' was for a buffer_boundary() buffer.  This means that the block at
 612 * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
 613 * dirty, schedule it for IO.  So that indirects merge nicely with their data.
 614 */
 615void write_boundary_block(struct block_device *bdev,
 616                        sector_t bblock, unsigned blocksize)
 617{
 618        struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
 619        if (bh) {
 620                if (buffer_dirty(bh))
 621                        ll_rw_block(WRITE, 1, &bh);
 622                put_bh(bh);
 623        }
 624}
 625
 626void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
 627{
 628        struct address_space *mapping = inode->i_mapping;
 629        struct address_space *buffer_mapping = bh->b_page->mapping;
 630
 631        mark_buffer_dirty(bh);
 632        if (!mapping->private_data) {
 633                mapping->private_data = buffer_mapping;
 634        } else {
 635                BUG_ON(mapping->private_data != buffer_mapping);
 636        }
 637        if (!bh->b_assoc_map) {
 638                spin_lock(&buffer_mapping->private_lock);
 639                list_move_tail(&bh->b_assoc_buffers,
 640                                &mapping->private_list);
 641                bh->b_assoc_map = mapping;
 642                spin_unlock(&buffer_mapping->private_lock);
 643        }
 644}
 645EXPORT_SYMBOL(mark_buffer_dirty_inode);
 646
 647/*
 648 * Mark the page dirty, and set it dirty in the radix tree, and mark the inode
 649 * dirty.
 650 *
 651 * If warn is true, then emit a warning if the page is not uptodate and has
 652 * not been truncated.
 653 */
 654static void __set_page_dirty(struct page *page,
 655                struct address_space *mapping, int warn)
 656{
 657        spin_lock_irq(&mapping->tree_lock);
 658        if (page->mapping) {    /* Race with truncate? */
 659                WARN_ON_ONCE(warn && !PageUptodate(page));
 660                account_page_dirtied(page, mapping);
 661                radix_tree_tag_set(&mapping->page_tree,
 662                                page_index(page), PAGECACHE_TAG_DIRTY);
 663        }
 664        spin_unlock_irq(&mapping->tree_lock);
 665        __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 666}
 667
 668/*
 669 * Add a page to the dirty page list.
 670 *
 671 * It is a sad fact of life that this function is called from several places
 672 * deeply under spinlocking.  It may not sleep.
 673 *
 674 * If the page has buffers, the uptodate buffers are set dirty, to preserve
 675 * dirty-state coherency between the page and the buffers.  It the page does
 676 * not have buffers then when they are later attached they will all be set
 677 * dirty.
 678 *
 679 * The buffers are dirtied before the page is dirtied.  There's a small race
 680 * window in which a writepage caller may see the page cleanness but not the
 681 * buffer dirtiness.  That's fine.  If this code were to set the page dirty
 682 * before the buffers, a concurrent writepage caller could clear the page dirty
 683 * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
 684 * page on the dirty page list.
 685 *
 686 * We use private_lock to lock against try_to_free_buffers while using the
 687 * page's buffer list.  Also use this to protect against clean buffers being
 688 * added to the page after it was set dirty.
 689 *
 690 * FIXME: may need to call ->reservepage here as well.  That's rather up to the
 691 * address_space though.
 692 */
 693int __set_page_dirty_buffers(struct page *page)
 694{
 695        int newly_dirty;
 696        struct address_space *mapping = page_mapping(page);
 697
 698        if (unlikely(!mapping))
 699                return !TestSetPageDirty(page);
 700
 701        spin_lock(&mapping->private_lock);
 702        if (page_has_buffers(page)) {
 703                struct buffer_head *head = page_buffers(page);
 704                struct buffer_head *bh = head;
 705
 706                do {
 707                        set_buffer_dirty(bh);
 708                        bh = bh->b_this_page;
 709                } while (bh != head);
 710        }
 711        newly_dirty = !TestSetPageDirty(page);
 712        spin_unlock(&mapping->private_lock);
 713
 714        if (newly_dirty)
 715                __set_page_dirty(page, mapping, 1);
 716        return newly_dirty;
 717}
 718EXPORT_SYMBOL(__set_page_dirty_buffers);
 719
 720/*
 721 * Write out and wait upon a list of buffers.
 722 *
 723 * We have conflicting pressures: we want to make sure that all
 724 * initially dirty buffers get waited on, but that any subsequently
 725 * dirtied buffers don't.  After all, we don't want fsync to last
 726 * forever if somebody is actively writing to the file.
 727 *
 728 * Do this in two main stages: first we copy dirty buffers to a
 729 * temporary inode list, queueing the writes as we go.  Then we clean
 730 * up, waiting for those writes to complete.
 731 * 
 732 * During this second stage, any subsequent updates to the file may end
 733 * up refiling the buffer on the original inode's dirty list again, so
 734 * there is a chance we will end up with a buffer queued for write but
 735 * not yet completed on that list.  So, as a final cleanup we go through
 736 * the osync code to catch these locked, dirty buffers without requeuing
 737 * any newly dirty buffers for write.
 738 */
 739static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
 740{
 741        struct buffer_head *bh;
 742        struct list_head tmp;
 743        struct address_space *mapping;
 744        int err = 0, err2;
 745        struct blk_plug plug;
 746
 747        INIT_LIST_HEAD(&tmp);
 748        blk_start_plug(&plug);
 749
 750        spin_lock(lock);
 751        while (!list_empty(list)) {
 752                bh = BH_ENTRY(list->next);
 753                mapping = bh->b_assoc_map;
 754                __remove_assoc_queue(bh);
 755                /* Avoid race with mark_buffer_dirty_inode() which does
 756                 * a lockless check and we rely on seeing the dirty bit */
 757                smp_mb();
 758                if (buffer_dirty(bh) || buffer_locked(bh)) {
 759                        list_add(&bh->b_assoc_buffers, &tmp);
 760                        bh->b_assoc_map = mapping;
 761                        if (buffer_dirty(bh)) {
 762                                get_bh(bh);
 763                                spin_unlock(lock);
 764                                /*
 765                                 * Ensure any pending I/O completes so that
 766                                 * write_dirty_buffer() actually writes the
 767                                 * current contents - it is a noop if I/O is
 768                                 * still in flight on potentially older
 769                                 * contents.
 770                                 */
 771                                write_dirty_buffer(bh, WRITE_SYNC);
 772
 773                                /*
 774                                 * Kick off IO for the previous mapping. Note
 775                                 * that we will not run the very last mapping,
 776                                 * wait_on_buffer() will do that for us
 777                                 * through sync_buffer().
 778                                 */
 779                                brelse(bh);
 780                                spin_lock(lock);
 781                        }
 782                }
 783        }
 784
 785        spin_unlock(lock);
 786        blk_finish_plug(&plug);
 787        spin_lock(lock);
 788
 789        while (!list_empty(&tmp)) {
 790                bh = BH_ENTRY(tmp.prev);
 791                get_bh(bh);
 792                mapping = bh->b_assoc_map;
 793                __remove_assoc_queue(bh);
 794                /* Avoid race with mark_buffer_dirty_inode() which does
 795                 * a lockless check and we rely on seeing the dirty bit */
 796                smp_mb();
 797                if (buffer_dirty(bh)) {
 798                        list_add(&bh->b_assoc_buffers,
 799                                 &mapping->private_list);
 800                        bh->b_assoc_map = mapping;
 801                }
 802                spin_unlock(lock);
 803                wait_on_buffer(bh);
 804                if (!buffer_uptodate(bh))
 805                        err = -EIO;
 806                brelse(bh);
 807                spin_lock(lock);
 808        }
 809        
 810        spin_unlock(lock);
 811        err2 = osync_buffers_list(lock, list);
 812        if (err)
 813                return err;
 814        else
 815                return err2;
 816}
 817
 818/*
 819 * Invalidate any and all dirty buffers on a given inode.  We are
 820 * probably unmounting the fs, but that doesn't mean we have already
 821 * done a sync().  Just drop the buffers from the inode list.
 822 *
 823 * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
 824 * assumes that all the buffers are against the blockdev.  Not true
 825 * for reiserfs.
 826 */
 827void invalidate_inode_buffers(struct inode *inode)
 828{
 829        if (inode_has_buffers(inode)) {
 830                struct address_space *mapping = &inode->i_data;
 831                struct list_head *list = &mapping->private_list;
 832                struct address_space *buffer_mapping = mapping->private_data;
 833
 834                spin_lock(&buffer_mapping->private_lock);
 835                while (!list_empty(list))
 836                        __remove_assoc_queue(BH_ENTRY(list->next));
 837                spin_unlock(&buffer_mapping->private_lock);
 838        }
 839}
 840EXPORT_SYMBOL(invalidate_inode_buffers);
 841
 842/*
 843 * Remove any clean buffers from the inode's buffer list.  This is called
 844 * when we're trying to free the inode itself.  Those buffers can pin it.
 845 *
 846 * Returns true if all buffers were removed.
 847 */
 848int remove_inode_buffers(struct inode *inode)
 849{
 850        int ret = 1;
 851
 852        if (inode_has_buffers(inode)) {
 853                struct address_space *mapping = &inode->i_data;
 854                struct list_head *list = &mapping->private_list;
 855                struct address_space *buffer_mapping = mapping->private_data;
 856
 857                spin_lock(&buffer_mapping->private_lock);
 858                while (!list_empty(list)) {
 859                        struct buffer_head *bh = BH_ENTRY(list->next);
 860                        if (buffer_dirty(bh)) {
 861                                ret = 0;
 862                                break;
 863                        }
 864                        __remove_assoc_queue(bh);
 865                }
 866                spin_unlock(&buffer_mapping->private_lock);
 867        }
 868        return ret;
 869}
 870
 871/*
 872 * Create the appropriate buffers when given a page for data area and
 873 * the size of each buffer.. Use the bh->b_this_page linked list to
 874 * follow the buffers created.  Return NULL if unable to create more
 875 * buffers.
 876 *
 877 * The retry flag is used to differentiate async IO (paging, swapping)
 878 * which may not fail from ordinary buffer allocations.
 879 */
 880struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
 881                int retry)
 882{
 883        struct buffer_head *bh, *head;
 884        long offset;
 885
 886try_again:
 887        head = NULL;
 888        offset = PAGE_SIZE;
 889        while ((offset -= size) >= 0) {
 890                bh = alloc_buffer_head(GFP_NOFS);
 891                if (!bh)
 892                        goto no_grow;
 893
 894                bh->b_this_page = head;
 895                bh->b_blocknr = -1;
 896                head = bh;
 897
 898                bh->b_size = size;
 899
 900                /* Link the buffer to its page */
 901                set_bh_page(bh, page, offset);
 902        }
 903        return head;
 904/*
 905 * In case anything failed, we just free everything we got.
 906 */
 907no_grow:
 908        if (head) {
 909                do {
 910                        bh = head;
 911                        head = head->b_this_page;
 912                        free_buffer_head(bh);
 913                } while (head);
 914        }
 915
 916        /*
 917         * Return failure for non-async IO requests.  Async IO requests
 918         * are not allowed to fail, so we have to wait until buffer heads
 919         * become available.  But we don't want tasks sleeping with 
 920         * partially complete buffers, so all were released above.
 921         */
 922        if (!retry)
 923                return NULL;
 924
 925        /* We're _really_ low on memory. Now we just
 926         * wait for old buffer heads to become free due to
 927         * finishing IO.  Since this is an async request and
 928         * the reserve list is empty, we're sure there are 
 929         * async buffer heads in use.
 930         */
 931        free_more_memory();
 932        goto try_again;
 933}
 934EXPORT_SYMBOL_GPL(alloc_page_buffers);
 935
 936static inline void
 937link_dev_buffers(struct page *page, struct buffer_head *head)
 938{
 939        struct buffer_head *bh, *tail;
 940
 941        bh = head;
 942        do {
 943                tail = bh;
 944                bh = bh->b_this_page;
 945        } while (bh);
 946        tail->b_this_page = head;
 947        attach_page_buffers(page, head);
 948}
 949
 950static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
 951{
 952        sector_t retval = ~((sector_t)0);
 953        loff_t sz = i_size_read(bdev->bd_inode);
 954
 955        if (sz) {
 956                unsigned int sizebits = blksize_bits(size);
 957                retval = (sz >> sizebits);
 958        }
 959        return retval;
 960}
 961
 962/*
 963 * Initialise the state of a blockdev page's buffers.
 964 */ 
 965static sector_t
 966init_page_buffers(struct page *page, struct block_device *bdev,
 967                        sector_t block, int size)
 968{
 969        struct buffer_head *head = page_buffers(page);
 970        struct buffer_head *bh = head;
 971        int uptodate = PageUptodate(page);
 972        sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
 973
 974        do {
 975                if (!buffer_mapped(bh)) {
 976                        init_buffer(bh, NULL, NULL);
 977                        bh->b_bdev = bdev;
 978                        bh->b_blocknr = block;
 979                        if (uptodate)
 980                                set_buffer_uptodate(bh);
 981                        if (block < end_block)
 982                                set_buffer_mapped(bh);
 983                }
 984                block++;
 985                bh = bh->b_this_page;
 986        } while (bh != head);
 987
 988        /*
 989         * Caller needs to validate requested block against end of device.
 990         */
 991        return end_block;
 992}
 993
 994/*
 995 * Create the page-cache page that contains the requested block.
 996 *
 997 * This is used purely for blockdev mappings.
 998 */
 999static int
1000grow_dev_page(struct block_device *bdev, sector_t block,
1001                pgoff_t index, int size, int sizebits)
1002{
1003        struct inode *inode = bdev->bd_inode;
1004        struct page *page;
1005        struct buffer_head *bh;
1006        sector_t end_block;
1007        int ret = 0;            /* Will call free_more_memory() */
1008
1009        page = find_or_create_page(inode->i_mapping, index,
1010                (mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS)|__GFP_MOVABLE);
1011        if (!page)
1012                return ret;
1013
1014        BUG_ON(!PageLocked(page));
1015
1016        if (page_has_buffers(page)) {
1017                bh = page_buffers(page);
1018                if (bh->b_size == size) {
1019                        end_block = init_page_buffers(page, bdev,
1020                                                index << sizebits, size);
1021                        goto done;
1022                }
1023                if (!try_to_free_buffers(page))
1024                        goto failed;
1025        }
1026
1027        /*
1028         * Allocate some buffers for this page
1029         */
1030        bh = alloc_page_buffers(page, size, 0);
1031        if (!bh)
1032                goto failed;
1033
1034        /*
1035         * Link the page to the buffers and initialise them.  Take the
1036         * lock to be atomic wrt __find_get_block(), which does not
1037         * run under the page lock.
1038         */
1039        spin_lock(&inode->i_mapping->private_lock);
1040        link_dev_buffers(page, bh);
1041        end_block = init_page_buffers(page, bdev, index << sizebits, size);
1042        spin_unlock(&inode->i_mapping->private_lock);
1043done:
1044        ret = (block < end_block) ? 1 : -ENXIO;
1045failed:
1046        unlock_page(page);
1047        page_cache_release(page);
1048        return ret;
1049}
1050
1051/*
1052 * Create buffers for the specified block device block's page.  If
1053 * that page was dirty, the buffers are set dirty also.
1054 */
1055static int
1056grow_buffers(struct block_device *bdev, sector_t block, int size)
1057{
1058        pgoff_t index;
1059        int sizebits;
1060
1061        sizebits = -1;
1062        do {
1063                sizebits++;
1064        } while ((size << sizebits) < PAGE_SIZE);
1065
1066        index = block >> sizebits;
1067
1068        /*
1069         * Check for a block which wants to lie outside our maximum possible
1070         * pagecache index.  (this comparison is done using sector_t types).
1071         */
1072        if (unlikely(index != block >> sizebits)) {
1073                char b[BDEVNAME_SIZE];
1074
1075                printk(KERN_ERR "%s: requested out-of-range block %llu for "
1076                        "device %s\n",
1077                        __func__, (unsigned long long)block,
1078                        bdevname(bdev, b));
1079                return -EIO;
1080        }
1081
1082        /* Create a page with the proper size buffers.. */
1083        return grow_dev_page(bdev, block, index, size, sizebits);
1084}
1085
1086static struct buffer_head *
1087__getblk_slow(struct block_device *bdev, sector_t block, int size)
1088{
1089        /* Size must be multiple of hard sectorsize */
1090        if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
1091                        (size < 512 || size > PAGE_SIZE))) {
1092                printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1093                                        size);
1094                printk(KERN_ERR "logical block size: %d\n",
1095                                        bdev_logical_block_size(bdev));
1096
1097                dump_stack();
1098                return NULL;
1099        }
1100
1101        for (;;) {
1102                struct buffer_head *bh;
1103                int ret;
1104
1105                bh = __find_get_block(bdev, block, size);
1106                if (bh)
1107                        return bh;
1108
1109                ret = grow_buffers(bdev, block, size);
1110                if (ret < 0)
1111                        return NULL;
1112                if (ret == 0)
1113                        free_more_memory();
1114        }
1115}
1116
1117/*
1118 * The relationship between dirty buffers and dirty pages:
1119 *
1120 * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1121 * the page is tagged dirty in its radix tree.
1122 *
1123 * At all times, the dirtiness of the buffers represents the dirtiness of
1124 * subsections of the page.  If the page has buffers, the page dirty bit is
1125 * merely a hint about the true dirty state.
1126 *
1127 * When a page is set dirty in its entirety, all its buffers are marked dirty
1128 * (if the page has buffers).
1129 *
1130 * When a buffer is marked dirty, its page is dirtied, but the page's other
1131 * buffers are not.
1132 *
1133 * Also.  When blockdev buffers are explicitly read with bread(), they
1134 * individually become uptodate.  But their backing page remains not
1135 * uptodate - even if all of its buffers are uptodate.  A subsequent
1136 * block_read_full_page() against that page will discover all the uptodate
1137 * buffers, will set the page uptodate and will perform no I/O.
1138 */
1139
1140/**
1141 * mark_buffer_dirty - mark a buffer_head as needing writeout
1142 * @bh: the buffer_head to mark dirty
1143 *
1144 * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1145 * backing page dirty, then tag the page as dirty in its address_space's radix
1146 * tree and then attach the address_space's inode to its superblock's dirty
1147 * inode list.
1148 *
1149 * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1150 * mapping->tree_lock and mapping->host->i_lock.
1151 */
1152void mark_buffer_dirty(struct buffer_head *bh)
1153{
1154        WARN_ON_ONCE(!buffer_uptodate(bh));
1155
1156        trace_block_dirty_buffer(bh);
1157
1158        /*
1159         * Very *carefully* optimize the it-is-already-dirty case.
1160         *
1161         * Don't let the final "is it dirty" escape to before we
1162         * perhaps modified the buffer.
1163         */
1164        if (buffer_dirty(bh)) {
1165                smp_mb();
1166                if (buffer_dirty(bh))
1167                        return;
1168        }
1169
1170        if (!test_set_buffer_dirty(bh)) {
1171                struct page *page = bh->b_page;
1172                if (!TestSetPageDirty(page)) {
1173                        struct address_space *mapping = page_mapping(page);
1174                        if (mapping)
1175                                __set_page_dirty(page, mapping, 0);
1176                }
1177        }
1178}
1179EXPORT_SYMBOL(mark_buffer_dirty);
1180
1181/*
1182 * Decrement a buffer_head's reference count.  If all buffers against a page
1183 * have zero reference count, are clean and unlocked, and if the page is clean
1184 * and unlocked then try_to_free_buffers() may strip the buffers from the page
1185 * in preparation for freeing it (sometimes, rarely, buffers are removed from
1186 * a page but it ends up not being freed, and buffers may later be reattached).
1187 */
1188void __brelse(struct buffer_head * buf)
1189{
1190        if (atomic_read(&buf->b_count)) {
1191                put_bh(buf);
1192                return;
1193        }
1194        WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1195}
1196EXPORT_SYMBOL(__brelse);
1197
1198/*
1199 * bforget() is like brelse(), except it discards any
1200 * potentially dirty data.
1201 */
1202void __bforget(struct buffer_head *bh)
1203{
1204        clear_buffer_dirty(bh);
1205        if (bh->b_assoc_map) {
1206                struct address_space *buffer_mapping = bh->b_page->mapping;
1207
1208                spin_lock(&buffer_mapping->private_lock);
1209                list_del_init(&bh->b_assoc_buffers);
1210                bh->b_assoc_map = NULL;
1211                spin_unlock(&buffer_mapping->private_lock);
1212        }
1213        __brelse(bh);
1214}
1215EXPORT_SYMBOL(__bforget);
1216
1217static struct buffer_head *__bread_slow(struct buffer_head *bh)
1218{
1219        lock_buffer(bh);
1220        if (buffer_uptodate(bh)) {
1221                unlock_buffer(bh);
1222                return bh;
1223        } else {
1224                get_bh(bh);
1225                bh->b_end_io = end_buffer_read_sync;
1226                submit_bh(READ, bh);
1227                wait_on_buffer(bh);
1228                if (buffer_uptodate(bh))
1229                        return bh;
1230        }
1231        brelse(bh);
1232        return NULL;
1233}
1234
1235/*
1236 * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1237 * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1238 * refcount elevated by one when they're in an LRU.  A buffer can only appear
1239 * once in a particular CPU's LRU.  A single buffer can be present in multiple
1240 * CPU's LRUs at the same time.
1241 *
1242 * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1243 * sb_find_get_block().
1244 *
1245 * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1246 * a local interrupt disable for that.
1247 */
1248
1249#define BH_LRU_SIZE     8
1250
1251struct bh_lru {
1252        struct buffer_head *bhs[BH_LRU_SIZE];
1253};
1254
1255static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1256
1257#ifdef CONFIG_SMP
1258#define bh_lru_lock()   local_irq_disable()
1259#define bh_lru_unlock() local_irq_enable()
1260#else
1261#define bh_lru_lock()   preempt_disable()
1262#define bh_lru_unlock() preempt_enable()
1263#endif
1264
1265static inline void check_irqs_on(void)
1266{
1267#ifdef irqs_disabled
1268        BUG_ON(irqs_disabled());
1269#endif
1270}
1271
1272/*
1273 * The LRU management algorithm is dopey-but-simple.  Sorry.
1274 */
1275static void bh_lru_install(struct buffer_head *bh)
1276{
1277        struct buffer_head *evictee = NULL;
1278
1279        check_irqs_on();
1280        bh_lru_lock();
1281        if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
1282                struct buffer_head *bhs[BH_LRU_SIZE];
1283                int in;
1284                int out = 0;
1285
1286                get_bh(bh);
1287                bhs[out++] = bh;
1288                for (in = 0; in < BH_LRU_SIZE; in++) {
1289                        struct buffer_head *bh2 =
1290                                __this_cpu_read(bh_lrus.bhs[in]);
1291
1292                        if (bh2 == bh) {
1293                                __brelse(bh2);
1294                        } else {
1295                                if (out >= BH_LRU_SIZE) {
1296                                        BUG_ON(evictee != NULL);
1297                                        evictee = bh2;
1298                                } else {
1299                                        bhs[out++] = bh2;
1300                                }
1301                        }
1302                }
1303                while (out < BH_LRU_SIZE)
1304                        bhs[out++] = NULL;
1305                memcpy(__this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
1306        }
1307        bh_lru_unlock();
1308
1309        if (evictee)
1310                __brelse(evictee);
1311}
1312
1313/*
1314 * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1315 */
1316static struct buffer_head *
1317lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1318{
1319        struct buffer_head *ret = NULL;
1320        unsigned int i;
1321
1322        check_irqs_on();
1323        bh_lru_lock();
1324        for (i = 0; i < BH_LRU_SIZE; i++) {
1325                struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1326
1327                if (bh && bh->b_bdev == bdev &&
1328                                bh->b_blocknr == block && bh->b_size == size) {
1329                        if (i) {
1330                                while (i) {
1331                                        __this_cpu_write(bh_lrus.bhs[i],
1332                                                __this_cpu_read(bh_lrus.bhs[i - 1]));
1333                                        i--;
1334                                }
1335                                __this_cpu_write(bh_lrus.bhs[0], bh);
1336                        }
1337                        get_bh(bh);
1338                        ret = bh;
1339                        break;
1340                }
1341        }
1342        bh_lru_unlock();
1343        return ret;
1344}
1345
1346/*
1347 * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1348 * it in the LRU and mark it as accessed.  If it is not present then return
1349 * NULL
1350 */
1351struct buffer_head *
1352__find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1353{
1354        struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1355
1356        if (bh == NULL) {
1357                bh = __find_get_block_slow(bdev, block);
1358                if (bh)
1359                        bh_lru_install(bh);
1360        }
1361        if (bh)
1362                touch_buffer(bh);
1363        return bh;
1364}
1365EXPORT_SYMBOL(__find_get_block);
1366
1367/*
1368 * __getblk will locate (and, if necessary, create) the buffer_head
1369 * which corresponds to the passed block_device, block and size. The
1370 * returned buffer has its reference count incremented.
1371 *
1372 * __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
1373 * attempt is failing.  FIXME, perhaps?
1374 */
1375struct buffer_head *
1376__getblk(struct block_device *bdev, sector_t block, unsigned size)
1377{
1378        struct buffer_head *bh = __find_get_block(bdev, block, size);
1379
1380        might_sleep();
1381        if (bh == NULL)
1382                bh = __getblk_slow(bdev, block, size);
1383        return bh;
1384}
1385EXPORT_SYMBOL(__getblk);
1386
1387/*
1388 * Do async read-ahead on a buffer..
1389 */
1390void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1391{
1392        struct buffer_head *bh = __getblk(bdev, block, size);
1393        if (likely(bh)) {
1394                ll_rw_block(READA, 1, &bh);
1395                brelse(bh);
1396        }
1397}
1398EXPORT_SYMBOL(__breadahead);
1399
1400/**
1401 *  __bread() - reads a specified block and returns the bh
1402 *  @bdev: the block_device to read from
1403 *  @block: number of block
1404 *  @size: size (in bytes) to read
1405 * 
1406 *  Reads a specified block, and returns buffer head that contains it.
1407 *  It returns NULL if the block was unreadable.
1408 */
1409struct buffer_head *
1410__bread(struct block_device *bdev, sector_t block, unsigned size)
1411{
1412        struct buffer_head *bh = __getblk(bdev, block, size);
1413
1414        if (likely(bh) && !buffer_uptodate(bh))
1415                bh = __bread_slow(bh);
1416        return bh;
1417}
1418EXPORT_SYMBOL(__bread);
1419
1420/*
1421 * invalidate_bh_lrus() is called rarely - but not only at unmount.
1422 * This doesn't race because it runs in each cpu either in irq
1423 * or with preempt disabled.
1424 */
1425static void invalidate_bh_lru(void *arg)
1426{
1427        struct bh_lru *b = &get_cpu_var(bh_lrus);
1428        int i;
1429
1430        for (i = 0; i < BH_LRU_SIZE; i++) {
1431                brelse(b->bhs[i]);
1432                b->bhs[i] = NULL;
1433        }
1434        put_cpu_var(bh_lrus);
1435}
1436
1437static bool has_bh_in_lru(int cpu, void *dummy)
1438{
1439        struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1440        int i;
1441        
1442        for (i = 0; i < BH_LRU_SIZE; i++) {
1443                if (b->bhs[i])
1444                        return 1;
1445        }
1446
1447        return 0;
1448}
1449
1450void invalidate_bh_lrus(void)
1451{
1452        on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1453}
1454EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1455
1456void set_bh_page(struct buffer_head *bh,
1457                struct page *page, unsigned long offset)
1458{
1459        bh->b_page = page;
1460        BUG_ON(offset >= PAGE_SIZE);
1461        if (PageHighMem(page))
1462                /*
1463                 * This catches illegal uses and preserves the offset:
1464                 */
1465                bh->b_data = (char *)(0 + offset);
1466        else
1467                bh->b_data = page_address(page) + offset;
1468}
1469EXPORT_SYMBOL(set_bh_page);
1470
1471/*
1472 * Called when truncating a buffer on a page completely.
1473 */
1474static void discard_buffer(struct buffer_head * bh)
1475{
1476        lock_buffer(bh);
1477        clear_buffer_dirty(bh);
1478        bh->b_bdev = NULL;
1479        clear_buffer_mapped(bh);
1480        clear_buffer_req(bh);
1481        clear_buffer_new(bh);
1482        clear_buffer_delay(bh);
1483        clear_buffer_unwritten(bh);
1484        unlock_buffer(bh);
1485}
1486
1487/**
1488 * block_invalidatepage - invalidate part or all of a buffer-backed page
1489 *
1490 * @page: the page which is affected
1491 * @offset: start of the range to invalidate
1492 * @length: length of the range to invalidate
1493 *
1494 * block_invalidatepage() is called when all or part of the page has become
1495 * invalidated by a truncate operation.
1496 *
1497 * block_invalidatepage() does not have to release all buffers, but it must
1498 * ensure that no dirty buffer is left outside @offset and that no I/O
1499 * is underway against any of the blocks which are outside the truncation
1500 * point.  Because the caller is about to free (and possibly reuse) those
1501 * blocks on-disk.
1502 */
1503void block_invalidatepage(struct page *page, unsigned int offset,
1504                          unsigned int length)
1505{
1506        struct buffer_head *head, *bh, *next;
1507        unsigned int curr_off = 0;
1508        unsigned int stop = length + offset;
1509
1510        BUG_ON(!PageLocked(page));
1511        if (!page_has_buffers(page))
1512                goto out;
1513
1514        /*
1515         * Check for overflow
1516         */
1517        BUG_ON(stop > PAGE_CACHE_SIZE || stop < length);
1518
1519        head = page_buffers(page);
1520        bh = head;
1521        do {
1522                unsigned int next_off = curr_off + bh->b_size;
1523                next = bh->b_this_page;
1524
1525                /*
1526                 * Are we still fully in range ?
1527                 */
1528                if (next_off > stop)
1529                        goto out;
1530
1531                /*
1532                 * is this block fully invalidated?
1533                 */
1534                if (offset <= curr_off)
1535                        discard_buffer(bh);
1536                curr_off = next_off;
1537                bh = next;
1538        } while (bh != head);
1539
1540        /*
1541         * We release buffers only if the entire page is being invalidated.
1542         * The get_block cached value has been unconditionally invalidated,
1543         * so real IO is not possible anymore.
1544         */
1545        if (offset == 0)
1546                try_to_release_page(page, 0);
1547out:
1548        return;
1549}
1550EXPORT_SYMBOL(block_invalidatepage);
1551
1552
1553/*
1554 * We attach and possibly dirty the buffers atomically wrt
1555 * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1556 * is already excluded via the page lock.
1557 */
1558void create_empty_buffers(struct page *page,
1559                        unsigned long blocksize, unsigned long b_state)
1560{
1561        struct buffer_head *bh, *head, *tail;
1562
1563        head = alloc_page_buffers(page, blocksize, 1);
1564        bh = head;
1565        do {
1566                bh->b_state |= b_state;
1567                tail = bh;
1568                bh = bh->b_this_page;
1569        } while (bh);
1570        tail->b_this_page = head;
1571
1572        spin_lock(&page->mapping->private_lock);
1573        if (PageUptodate(page) || PageDirty(page)) {
1574                bh = head;
1575                do {
1576                        if (PageDirty(page))
1577                                set_buffer_dirty(bh);
1578                        if (PageUptodate(page))
1579                                set_buffer_uptodate(bh);
1580                        bh = bh->b_this_page;
1581                } while (bh != head);
1582        }
1583        attach_page_buffers(page, head);
1584        spin_unlock(&page->mapping->private_lock);
1585}
1586EXPORT_SYMBOL(create_empty_buffers);
1587
1588/*
1589 * We are taking a block for data and we don't want any output from any
1590 * buffer-cache aliases starting from return from that function and
1591 * until the moment when something will explicitly mark the buffer
1592 * dirty (hopefully that will not happen until we will free that block ;-)
1593 * We don't even need to mark it not-uptodate - nobody can expect
1594 * anything from a newly allocated buffer anyway. We used to used
1595 * unmap_buffer() for such invalidation, but that was wrong. We definitely
1596 * don't want to mark the alias unmapped, for example - it would confuse
1597 * anyone who might pick it with bread() afterwards...
1598 *
1599 * Also..  Note that bforget() doesn't lock the buffer.  So there can
1600 * be writeout I/O going on against recently-freed buffers.  We don't
1601 * wait on that I/O in bforget() - it's more efficient to wait on the I/O
1602 * only if we really need to.  That happens here.
1603 */
1604void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1605{
1606        struct buffer_head *old_bh;
1607
1608        might_sleep();
1609
1610        old_bh = __find_get_block_slow(bdev, block);
1611        if (old_bh) {
1612                clear_buffer_dirty(old_bh);
1613                wait_on_buffer(old_bh);
1614                clear_buffer_req(old_bh);
1615                __brelse(old_bh);
1616        }
1617}
1618EXPORT_SYMBOL(unmap_underlying_metadata);
1619
1620/*
1621 * Size is a power-of-two in the range 512..PAGE_SIZE,
1622 * and the case we care about most is PAGE_SIZE.
1623 *
1624 * So this *could* possibly be written with those
1625 * constraints in mind (relevant mostly if some
1626 * architecture has a slow bit-scan instruction)
1627 */
1628static inline int block_size_bits(unsigned int blocksize)
1629{
1630        return ilog2(blocksize);
1631}
1632
1633static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
1634{
1635        BUG_ON(!PageLocked(page));
1636
1637        if (!page_has_buffers(page))
1638                create_empty_buffers(page, 1 << ACCESS_ONCE(inode->i_blkbits), b_state);
1639        return page_buffers(page);
1640}
1641
1642/*
1643 * NOTE! All mapped/uptodate combinations are valid:
1644 *
1645 *      Mapped  Uptodate        Meaning
1646 *
1647 *      No      No              "unknown" - must do get_block()
1648 *      No      Yes             "hole" - zero-filled
1649 *      Yes     No              "allocated" - allocated on disk, not read in
1650 *      Yes     Yes             "valid" - allocated and up-to-date in memory.
1651 *
1652 * "Dirty" is valid only with the last case (mapped+uptodate).
1653 */
1654
1655/*
1656 * While block_write_full_page is writing back the dirty buffers under
1657 * the page lock, whoever dirtied the buffers may decide to clean them
1658 * again at any time.  We handle that by only looking at the buffer
1659 * state inside lock_buffer().
1660 *
1661 * If block_write_full_page() is called for regular writeback
1662 * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1663 * locked buffer.   This only can happen if someone has written the buffer
1664 * directly, with submit_bh().  At the address_space level PageWriteback
1665 * prevents this contention from occurring.
1666 *
1667 * If block_write_full_page() is called with wbc->sync_mode ==
1668 * WB_SYNC_ALL, the writes are posted using WRITE_SYNC; this
1669 * causes the writes to be flagged as synchronous writes.
1670 */
1671static int __block_write_full_page(struct inode *inode, struct page *page,
1672                        get_block_t *get_block, struct writeback_control *wbc,
1673                        bh_end_io_t *handler)
1674{
1675        int err;
1676        sector_t block;
1677        sector_t last_block;
1678        struct buffer_head *bh, *head;
1679        unsigned int blocksize, bbits;
1680        int nr_underway = 0;
1681        int write_op = (wbc->sync_mode == WB_SYNC_ALL ?
1682                        WRITE_SYNC : WRITE);
1683
1684        head = create_page_buffers(page, inode,
1685                                        (1 << BH_Dirty)|(1 << BH_Uptodate));
1686
1687        /*
1688         * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1689         * here, and the (potentially unmapped) buffers may become dirty at
1690         * any time.  If a buffer becomes dirty here after we've inspected it
1691         * then we just miss that fact, and the page stays dirty.
1692         *
1693         * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1694         * handle that here by just cleaning them.
1695         */
1696
1697        bh = head;
1698        blocksize = bh->b_size;
1699        bbits = block_size_bits(blocksize);
1700
1701        block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1702        last_block = (i_size_read(inode) - 1) >> bbits;
1703
1704        /*
1705         * Get all the dirty buffers mapped to disk addresses and
1706         * handle any aliases from the underlying blockdev's mapping.
1707         */
1708        do {
1709                if (block > last_block) {
1710                        /*
1711                         * mapped buffers outside i_size will occur, because
1712                         * this page can be outside i_size when there is a
1713                         * truncate in progress.
1714                         */
1715                        /*
1716                         * The buffer was zeroed by block_write_full_page()
1717                         */
1718                        clear_buffer_dirty(bh);
1719                        set_buffer_uptodate(bh);
1720                } else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1721                           buffer_dirty(bh)) {
1722                        WARN_ON(bh->b_size != blocksize);
1723                        err = get_block(inode, block, bh, 1);
1724                        if (err)
1725                                goto recover;
1726                        clear_buffer_delay(bh);
1727                        if (buffer_new(bh)) {
1728                                /* blockdev mappings never come here */
1729                                clear_buffer_new(bh);
1730                                unmap_underlying_metadata(bh->b_bdev,
1731                                                        bh->b_blocknr);
1732                        }
1733                }
1734                bh = bh->b_this_page;
1735                block++;
1736        } while (bh != head);
1737
1738        do {
1739                if (!buffer_mapped(bh))
1740                        continue;
1741                /*
1742                 * If it's a fully non-blocking write attempt and we cannot
1743                 * lock the buffer then redirty the page.  Note that this can
1744                 * potentially cause a busy-wait loop from writeback threads
1745                 * and kswapd activity, but those code paths have their own
1746                 * higher-level throttling.
1747                 */
1748                if (wbc->sync_mode != WB_SYNC_NONE) {
1749                        lock_buffer(bh);
1750                } else if (!trylock_buffer(bh)) {
1751                        redirty_page_for_writepage(wbc, page);
1752                        continue;
1753                }
1754                if (test_clear_buffer_dirty(bh)) {
1755                        mark_buffer_async_write_endio(bh, handler);
1756                } else {
1757                        unlock_buffer(bh);
1758                }
1759        } while ((bh = bh->b_this_page) != head);
1760
1761        /*
1762         * The page and its buffers are protected by PageWriteback(), so we can
1763         * drop the bh refcounts early.
1764         */
1765        BUG_ON(PageWriteback(page));
1766        set_page_writeback(page);
1767
1768        do {
1769                struct buffer_head *next = bh->b_this_page;
1770                if (buffer_async_write(bh)) {
1771                        submit_bh(write_op, bh);
1772                        nr_underway++;
1773                }
1774                bh = next;
1775        } while (bh != head);
1776        unlock_page(page);
1777
1778        err = 0;
1779done:
1780        if (nr_underway == 0) {
1781                /*
1782                 * The page was marked dirty, but the buffers were
1783                 * clean.  Someone wrote them back by hand with
1784                 * ll_rw_block/submit_bh.  A rare case.
1785                 */
1786                end_page_writeback(page);
1787
1788                /*
1789                 * The page and buffer_heads can be released at any time from
1790                 * here on.
1791                 */
1792        }
1793        return err;
1794
1795recover:
1796        /*
1797         * ENOSPC, or some other error.  We may already have added some
1798         * blocks to the file, so we need to write these out to avoid
1799         * exposing stale data.
1800         * The page is currently locked and not marked for writeback
1801         */
1802        bh = head;
1803        /* Recovery: lock and submit the mapped buffers */
1804        do {
1805                if (buffer_mapped(bh) && buffer_dirty(bh) &&
1806                    !buffer_delay(bh)) {
1807                        lock_buffer(bh);
1808                        mark_buffer_async_write_endio(bh, handler);
1809                } else {
1810                        /*
1811                         * The buffer may have been set dirty during
1812                         * attachment to a dirty page.
1813                         */
1814                        clear_buffer_dirty(bh);
1815                }
1816        } while ((bh = bh->b_this_page) != head);
1817        SetPageError(page);
1818        BUG_ON(PageWriteback(page));
1819        mapping_set_error(page->mapping, err);
1820        set_page_writeback(page);
1821        do {
1822                struct buffer_head *next = bh->b_this_page;
1823                if (buffer_async_write(bh)) {
1824                        clear_buffer_dirty(bh);
1825                        submit_bh(write_op, bh);
1826                        nr_underway++;
1827                }
1828                bh = next;
1829        } while (bh != head);
1830        unlock_page(page);
1831        goto done;
1832}
1833
1834/*
1835 * If a page has any new buffers, zero them out here, and mark them uptodate
1836 * and dirty so they'll be written out (in order to prevent uninitialised
1837 * block data from leaking). And clear the new bit.
1838 */
1839void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1840{
1841        unsigned int block_start, block_end;
1842        struct buffer_head *head, *bh;
1843
1844        BUG_ON(!PageLocked(page));
1845        if (!page_has_buffers(page))
1846                return;
1847
1848        bh = head = page_buffers(page);
1849        block_start = 0;
1850        do {
1851                block_end = block_start + bh->b_size;
1852
1853                if (buffer_new(bh)) {
1854                        if (block_end > from && block_start < to) {
1855                                if (!PageUptodate(page)) {
1856                                        unsigned start, size;
1857
1858                                        start = max(from, block_start);
1859                                        size = min(to, block_end) - start;
1860
1861                                        zero_user(page, start, size);
1862                                        set_buffer_uptodate(bh);
1863                                }
1864
1865                                clear_buffer_new(bh);
1866                                mark_buffer_dirty(bh);
1867                        }
1868                }
1869
1870                block_start = block_end;
1871                bh = bh->b_this_page;
1872        } while (bh != head);
1873}
1874EXPORT_SYMBOL(page_zero_new_buffers);
1875
1876int __block_write_begin(struct page *page, loff_t pos, unsigned len,
1877                get_block_t *get_block)
1878{
1879        unsigned from = pos & (PAGE_CACHE_SIZE - 1);
1880        unsigned to = from + len;
1881        struct inode *inode = page->mapping->host;
1882        unsigned block_start, block_end;
1883        sector_t block;
1884        int err = 0;
1885        unsigned blocksize, bbits;
1886        struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1887
1888        BUG_ON(!PageLocked(page));
1889        BUG_ON(from > PAGE_CACHE_SIZE);
1890        BUG_ON(to > PAGE_CACHE_SIZE);
1891        BUG_ON(from > to);
1892
1893        head = create_page_buffers(page, inode, 0);
1894        blocksize = head->b_size;
1895        bbits = block_size_bits(blocksize);
1896
1897        block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1898
1899        for(bh = head, block_start = 0; bh != head || !block_start;
1900            block++, block_start=block_end, bh = bh->b_this_page) {
1901                block_end = block_start + blocksize;
1902                if (block_end <= from || block_start >= to) {
1903                        if (PageUptodate(page)) {
1904                                if (!buffer_uptodate(bh))
1905                                        set_buffer_uptodate(bh);
1906                        }
1907                        continue;
1908                }
1909                if (buffer_new(bh))
1910                        clear_buffer_new(bh);
1911                if (!buffer_mapped(bh)) {
1912                        WARN_ON(bh->b_size != blocksize);
1913                        err = get_block(inode, block, bh, 1);
1914                        if (err)
1915                                break;
1916                        if (buffer_new(bh)) {
1917                                unmap_underlying_metadata(bh->b_bdev,
1918                                                        bh->b_blocknr);
1919                                if (PageUptodate(page)) {
1920                                        clear_buffer_new(bh);
1921                                        set_buffer_uptodate(bh);
1922                                        mark_buffer_dirty(bh);
1923                                        continue;
1924                                }
1925                                if (block_end > to || block_start < from)
1926                                        zero_user_segments(page,
1927                                                to, block_end,
1928                                                block_start, from);
1929                                continue;
1930                        }
1931                }
1932                if (PageUptodate(page)) {
1933                        if (!buffer_uptodate(bh))
1934                                set_buffer_uptodate(bh);
1935                        continue; 
1936                }
1937                if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1938                    !buffer_unwritten(bh) &&
1939                     (block_start < from || block_end > to)) {
1940                        ll_rw_block(READ, 1, &bh);
1941                        *wait_bh++=bh;
1942                }
1943        }
1944        /*
1945         * If we issued read requests - let them complete.
1946         */
1947        while(wait_bh > wait) {
1948                wait_on_buffer(*--wait_bh);
1949                if (!buffer_uptodate(*wait_bh))
1950                        err = -EIO;
1951        }
1952        if (unlikely(err))
1953                page_zero_new_buffers(page, from, to);
1954        return err;
1955}
1956EXPORT_SYMBOL(__block_write_begin);
1957
1958static int __block_commit_write(struct inode *inode, struct page *page,
1959                unsigned from, unsigned to)
1960{
1961        unsigned block_start, block_end;
1962        int partial = 0;
1963        unsigned blocksize;
1964        struct buffer_head *bh, *head;
1965
1966        bh = head = page_buffers(page);
1967        blocksize = bh->b_size;
1968
1969        block_start = 0;
1970        do {
1971                block_end = block_start + blocksize;
1972                if (block_end <= from || block_start >= to) {
1973                        if (!buffer_uptodate(bh))
1974                                partial = 1;
1975                } else {
1976                        set_buffer_uptodate(bh);
1977                        mark_buffer_dirty(bh);
1978                }
1979                clear_buffer_new(bh);
1980
1981                block_start = block_end;
1982                bh = bh->b_this_page;
1983        } while (bh != head);
1984
1985        /*
1986         * If this is a partial write which happened to make all buffers
1987         * uptodate then we can optimize away a bogus readpage() for
1988         * the next read(). Here we 'discover' whether the page went
1989         * uptodate as a result of this (potentially partial) write.
1990         */
1991        if (!partial)
1992                SetPageUptodate(page);
1993        return 0;
1994}
1995
1996/*
1997 * block_write_begin takes care of the basic task of block allocation and
1998 * bringing partial write blocks uptodate first.
1999 *
2000 * The filesystem needs to handle block truncation upon failure.
2001 */
2002int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
2003                unsigned flags, struct page **pagep, get_block_t *get_block)
2004{
2005        pgoff_t index = pos >> PAGE_CACHE_SHIFT;
2006        struct page *page;
2007        int status;
2008
2009        page = grab_cache_page_write_begin(mapping, index, flags);
2010        if (!page)
2011                return -ENOMEM;
2012
2013        status = __block_write_begin(page, pos, len, get_block);
2014        if (unlikely(status)) {
2015                unlock_page(page);
2016                page_cache_release(page);
2017                page = NULL;
2018        }
2019
2020        *pagep = page;
2021        return status;
2022}
2023EXPORT_SYMBOL(block_write_begin);
2024
2025int block_write_end(struct file *file, struct address_space *mapping,
2026                        loff_t pos, unsigned len, unsigned copied,
2027                        struct page *page, void *fsdata)
2028{
2029        struct inode *inode = mapping->host;
2030        unsigned start;
2031
2032        start = pos & (PAGE_CACHE_SIZE - 1);
2033
2034        if (unlikely(copied < len)) {
2035                /*
2036                 * The buffers that were written will now be uptodate, so we
2037                 * don't have to worry about a readpage reading them and
2038                 * overwriting a partial write. However if we have encountered
2039                 * a short write and only partially written into a buffer, it
2040                 * will not be marked uptodate, so a readpage might come in and
2041                 * destroy our partial write.
2042                 *
2043                 * Do the simplest thing, and just treat any short write to a
2044                 * non uptodate page as a zero-length write, and force the
2045                 * caller to redo the whole thing.
2046                 */
2047                if (!PageUptodate(page))
2048                        copied = 0;
2049
2050                page_zero_new_buffers(page, start+copied, start+len);
2051        }
2052        flush_dcache_page(page);
2053
2054        /* This could be a short (even 0-length) commit */
2055        __block_commit_write(inode, page, start, start+copied);
2056
2057        return copied;
2058}
2059EXPORT_SYMBOL(block_write_end);
2060
2061int generic_write_end(struct file *file, struct address_space *mapping,
2062                        loff_t pos, unsigned len, unsigned copied,
2063                        struct page *page, void *fsdata)
2064{
2065        struct inode *inode = mapping->host;
2066        int i_size_changed = 0;
2067
2068        copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2069
2070        /*
2071         * No need to use i_size_read() here, the i_size
2072         * cannot change under us because we hold i_mutex.
2073         *
2074         * But it's important to update i_size while still holding page lock:
2075         * page writeout could otherwise come in and zero beyond i_size.
2076         */
2077        if (pos+copied > inode->i_size) {
2078                i_size_write(inode, pos+copied);
2079                i_size_changed = 1;
2080        }
2081
2082        unlock_page(page);
2083        page_cache_release(page);
2084
2085        /*
2086         * Don't mark the inode dirty under page lock. First, it unnecessarily
2087         * makes the holding time of page lock longer. Second, it forces lock
2088         * ordering of page lock and transaction start for journaling
2089         * filesystems.
2090         */
2091        if (i_size_changed)
2092                mark_inode_dirty(inode);
2093
2094        return copied;
2095}
2096EXPORT_SYMBOL(generic_write_end);
2097
2098/*
2099 * block_is_partially_uptodate checks whether buffers within a page are
2100 * uptodate or not.
2101 *
2102 * Returns true if all buffers which correspond to a file portion
2103 * we want to read are uptodate.
2104 */
2105int block_is_partially_uptodate(struct page *page, read_descriptor_t *desc,
2106                                        unsigned long from)
2107{
2108        unsigned block_start, block_end, blocksize;
2109        unsigned to;
2110        struct buffer_head *bh, *head;
2111        int ret = 1;
2112
2113        if (!page_has_buffers(page))
2114                return 0;
2115
2116        head = page_buffers(page);
2117        blocksize = head->b_size;
2118        to = min_t(unsigned, PAGE_CACHE_SIZE - from, desc->count);
2119        to = from + to;
2120        if (from < blocksize && to > PAGE_CACHE_SIZE - blocksize)
2121                return 0;
2122
2123        bh = head;
2124        block_start = 0;
2125        do {
2126                block_end = block_start + blocksize;
2127                if (block_end > from && block_start < to) {
2128                        if (!buffer_uptodate(bh)) {
2129                                ret = 0;
2130                                break;
2131                        }
2132                        if (block_end >= to)
2133                                break;
2134                }
2135                block_start = block_end;
2136                bh = bh->b_this_page;
2137        } while (bh != head);
2138
2139        return ret;
2140}
2141EXPORT_SYMBOL(block_is_partially_uptodate);
2142
2143/*
2144 * Generic "read page" function for block devices that have the normal
2145 * get_block functionality. This is most of the block device filesystems.
2146 * Reads the page asynchronously --- the unlock_buffer() and
2147 * set/clear_buffer_uptodate() functions propagate buffer state into the
2148 * page struct once IO has completed.
2149 */
2150int block_read_full_page(struct page *page, get_block_t *get_block)
2151{
2152        struct inode *inode = page->mapping->host;
2153        sector_t iblock, lblock;
2154        struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2155        unsigned int blocksize, bbits;
2156        int nr, i;
2157        int fully_mapped = 1;
2158
2159        head = create_page_buffers(page, inode, 0);
2160        blocksize = head->b_size;
2161        bbits = block_size_bits(blocksize);
2162
2163        iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
2164        lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2165        bh = head;
2166        nr = 0;
2167        i = 0;
2168
2169        do {
2170                if (buffer_uptodate(bh))
2171                        continue;
2172
2173                if (!buffer_mapped(bh)) {
2174                        int err = 0;
2175
2176                        fully_mapped = 0;
2177                        if (iblock < lblock) {
2178                                WARN_ON(bh->b_size != blocksize);
2179                                err = get_block(inode, iblock, bh, 0);
2180                                if (err)
2181                                        SetPageError(page);
2182                        }
2183                        if (!buffer_mapped(bh)) {
2184                                zero_user(page, i * blocksize, blocksize);
2185                                if (!err)
2186                                        set_buffer_uptodate(bh);
2187                                continue;
2188                        }
2189                        /*
2190                         * get_block() might have updated the buffer
2191                         * synchronously
2192                         */
2193                        if (buffer_uptodate(bh))
2194                                continue;
2195                }
2196                arr[nr++] = bh;
2197        } while (i++, iblock++, (bh = bh->b_this_page) != head);
2198
2199        if (fully_mapped)
2200                SetPageMappedToDisk(page);
2201
2202        if (!nr) {
2203                /*
2204                 * All buffers are uptodate - we can set the page uptodate
2205                 * as well. But not if get_block() returned an error.
2206                 */
2207                if (!PageError(page))
2208                        SetPageUptodate(page);
2209                unlock_page(page);
2210                return 0;
2211        }
2212
2213        /* Stage two: lock the buffers */
2214        for (i = 0; i < nr; i++) {
2215                bh = arr[i];
2216                lock_buffer(bh);
2217                mark_buffer_async_read(bh);
2218        }
2219
2220        /*
2221         * Stage 3: start the IO.  Check for uptodateness
2222         * inside the buffer lock in case another process reading
2223         * the underlying blockdev brought it uptodate (the sct fix).
2224         */
2225        for (i = 0; i < nr; i++) {
2226                bh = arr[i];
2227                if (buffer_uptodate(bh))
2228                        end_buffer_async_read(bh, 1);
2229                else
2230                        submit_bh(READ, bh);
2231        }
2232        return 0;
2233}
2234EXPORT_SYMBOL(block_read_full_page);
2235
2236/* utility function for filesystems that need to do work on expanding
2237 * truncates.  Uses filesystem pagecache writes to allow the filesystem to
2238 * deal with the hole.  
2239 */
2240int generic_cont_expand_simple(struct inode *inode, loff_t size)
2241{
2242        struct address_space *mapping = inode->i_mapping;
2243        struct page *page;
2244        void *fsdata;
2245        int err;
2246
2247        err = inode_newsize_ok(inode, size);
2248        if (err)
2249                goto out;
2250
2251        err = pagecache_write_begin(NULL, mapping, size, 0,
2252                                AOP_FLAG_UNINTERRUPTIBLE|AOP_FLAG_CONT_EXPAND,
2253                                &page, &fsdata);
2254        if (err)
2255                goto out;
2256
2257        err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2258        BUG_ON(err > 0);
2259
2260out:
2261        return err;
2262}
2263EXPORT_SYMBOL(generic_cont_expand_simple);
2264
2265static int cont_expand_zero(struct file *file, struct address_space *mapping,
2266                            loff_t pos, loff_t *bytes)
2267{
2268        struct inode *inode = mapping->host;
2269        unsigned blocksize = 1 << inode->i_blkbits;
2270        struct page *page;
2271        void *fsdata;
2272        pgoff_t index, curidx;
2273        loff_t curpos;
2274        unsigned zerofrom, offset, len;
2275        int err = 0;
2276
2277        index = pos >> PAGE_CACHE_SHIFT;
2278        offset = pos & ~PAGE_CACHE_MASK;
2279
2280        while (index > (curidx = (curpos = *bytes)>>PAGE_CACHE_SHIFT)) {
2281                zerofrom = curpos & ~PAGE_CACHE_MASK;
2282                if (zerofrom & (blocksize-1)) {
2283                        *bytes |= (blocksize-1);
2284                        (*bytes)++;
2285                }
2286                len = PAGE_CACHE_SIZE - zerofrom;
2287
2288                err = pagecache_write_begin(file, mapping, curpos, len,
2289                                                AOP_FLAG_UNINTERRUPTIBLE,
2290                                                &page, &fsdata);
2291                if (err)
2292                        goto out;
2293                zero_user(page, zerofrom, len);
2294                err = pagecache_write_end(file, mapping, curpos, len, len,
2295                                                page, fsdata);
2296                if (err < 0)
2297                        goto out;
2298                BUG_ON(err != len);
2299                err = 0;
2300
2301                balance_dirty_pages_ratelimited(mapping);
2302        }
2303
2304        /* page covers the boundary, find the boundary offset */
2305        if (index == curidx) {
2306                zerofrom = curpos & ~PAGE_CACHE_MASK;
2307                /* if we will expand the thing last block will be filled */
2308                if (offset <= zerofrom) {
2309                        goto out;
2310                }
2311                if (zerofrom & (blocksize-1)) {
2312                        *bytes |= (blocksize-1);
2313                        (*bytes)++;
2314                }
2315                len = offset - zerofrom;
2316
2317                err = pagecache_write_begin(file, mapping, curpos, len,
2318                                                AOP_FLAG_UNINTERRUPTIBLE,
2319                                                &page, &fsdata);
2320                if (err)
2321                        goto out;
2322                zero_user(page, zerofrom, len);
2323                err = pagecache_write_end(file, mapping, curpos, len, len,
2324                                                page, fsdata);
2325                if (err < 0)
2326                        goto out;
2327                BUG_ON(err != len);
2328                err = 0;
2329        }
2330out:
2331        return err;
2332}
2333
2334/*
2335 * For moronic filesystems that do not allow holes in file.
2336 * We may have to extend the file.
2337 */
2338int cont_write_begin(struct file *file, struct address_space *mapping,
2339                        loff_t pos, unsigned len, unsigned flags,
2340                        struct page **pagep, void **fsdata,
2341                        get_block_t *get_block, loff_t *bytes)
2342{
2343        struct inode *inode = mapping->host;
2344        unsigned blocksize = 1 << inode->i_blkbits;
2345        unsigned zerofrom;
2346        int err;
2347
2348        err = cont_expand_zero(file, mapping, pos, bytes);
2349        if (err)
2350                return err;
2351
2352        zerofrom = *bytes & ~PAGE_CACHE_MASK;
2353        if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2354                *bytes |= (blocksize-1);
2355                (*bytes)++;
2356        }
2357
2358        return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2359}
2360EXPORT_SYMBOL(cont_write_begin);
2361
2362int block_commit_write(struct page *page, unsigned from, unsigned to)
2363{
2364        struct inode *inode = page->mapping->host;
2365        __block_commit_write(inode,page,from,to);
2366        return 0;
2367}
2368EXPORT_SYMBOL(block_commit_write);
2369
2370/*
2371 * block_page_mkwrite() is not allowed to change the file size as it gets
2372 * called from a page fault handler when a page is first dirtied. Hence we must
2373 * be careful to check for EOF conditions here. We set the page up correctly
2374 * for a written page which means we get ENOSPC checking when writing into
2375 * holes and correct delalloc and unwritten extent mapping on filesystems that
2376 * support these features.
2377 *
2378 * We are not allowed to take the i_mutex here so we have to play games to
2379 * protect against truncate races as the page could now be beyond EOF.  Because
2380 * truncate writes the inode size before removing pages, once we have the
2381 * page lock we can determine safely if the page is beyond EOF. If it is not
2382 * beyond EOF, then the page is guaranteed safe against truncation until we
2383 * unlock the page.
2384 *
2385 * Direct callers of this function should protect against filesystem freezing
2386 * using sb_start_write() - sb_end_write() functions.
2387 */
2388int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2389                         get_block_t get_block)
2390{
2391        struct page *page = vmf->page;
2392        struct inode *inode = file_inode(vma->vm_file);
2393        unsigned long end;
2394        loff_t size;
2395        int ret;
2396
2397        lock_page(page);
2398        size = i_size_read(inode);
2399        if ((page->mapping != inode->i_mapping) ||
2400            (page_offset(page) > size)) {
2401                /* We overload EFAULT to mean page got truncated */
2402                ret = -EFAULT;
2403                goto out_unlock;
2404        }
2405
2406        /* page is wholly or partially inside EOF */
2407        if (((page->index + 1) << PAGE_CACHE_SHIFT) > size)
2408                end = size & ~PAGE_CACHE_MASK;
2409        else
2410                end = PAGE_CACHE_SIZE;
2411
2412        ret = __block_write_begin(page, 0, end, get_block);
2413        if (!ret)
2414                ret = block_commit_write(page, 0, end);
2415
2416        if (unlikely(ret < 0))
2417                goto out_unlock;
2418        set_page_dirty(page);
2419        wait_for_stable_page(page);
2420        return 0;
2421out_unlock:
2422        unlock_page(page);
2423        return ret;
2424}
2425EXPORT_SYMBOL(__block_page_mkwrite);
2426
2427int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2428                   get_block_t get_block)
2429{
2430        int ret;
2431        struct super_block *sb = file_inode(vma->vm_file)->i_sb;
2432
2433        sb_start_pagefault(sb);
2434
2435        /*
2436         * Update file times before taking page lock. We may end up failing the
2437         * fault so this update may be superfluous but who really cares...
2438         */
2439        file_update_time(vma->vm_file);
2440
2441        ret = __block_page_mkwrite(vma, vmf, get_block);
2442        sb_end_pagefault(sb);
2443        return block_page_mkwrite_return(ret);
2444}
2445EXPORT_SYMBOL(block_page_mkwrite);
2446
2447/*
2448 * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2449 * immediately, while under the page lock.  So it needs a special end_io
2450 * handler which does not touch the bh after unlocking it.
2451 */
2452static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2453{
2454        __end_buffer_read_notouch(bh, uptodate);
2455}
2456
2457/*
2458 * Attach the singly-linked list of buffers created by nobh_write_begin, to
2459 * the page (converting it to circular linked list and taking care of page
2460 * dirty races).
2461 */
2462static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2463{
2464        struct buffer_head *bh;
2465
2466        BUG_ON(!PageLocked(page));
2467
2468        spin_lock(&page->mapping->private_lock);
2469        bh = head;
2470        do {
2471                if (PageDirty(page))
2472                        set_buffer_dirty(bh);
2473                if (!bh->b_this_page)
2474                        bh->b_this_page = head;
2475                bh = bh->b_this_page;
2476        } while (bh != head);
2477        attach_page_buffers(page, head);
2478        spin_unlock(&page->mapping->private_lock);
2479}
2480
2481/*
2482 * On entry, the page is fully not uptodate.
2483 * On exit the page is fully uptodate in the areas outside (from,to)
2484 * The filesystem needs to handle block truncation upon failure.
2485 */
2486int nobh_write_begin(struct address_space *mapping,
2487                        loff_t pos, unsigned len, unsigned flags,
2488                        struct page **pagep, void **fsdata,
2489                        get_block_t *get_block)
2490{
2491        struct inode *inode = mapping->host;
2492        const unsigned blkbits = inode->i_blkbits;
2493        const unsigned blocksize = 1 << blkbits;
2494        struct buffer_head *head, *bh;
2495        struct page *page;
2496        pgoff_t index;
2497        unsigned from, to;
2498        unsigned block_in_page;
2499        unsigned block_start, block_end;
2500        sector_t block_in_file;
2501        int nr_reads = 0;
2502        int ret = 0;
2503        int is_mapped_to_disk = 1;
2504
2505        index = pos >> PAGE_CACHE_SHIFT;
2506        from = pos & (PAGE_CACHE_SIZE - 1);
2507        to = from + len;
2508
2509        page = grab_cache_page_write_begin(mapping, index, flags);
2510        if (!page)
2511                return -ENOMEM;
2512        *pagep = page;
2513        *fsdata = NULL;
2514
2515        if (page_has_buffers(page)) {
2516                ret = __block_write_begin(page, pos, len, get_block);
2517                if (unlikely(ret))
2518                        goto out_release;
2519                return ret;
2520        }
2521
2522        if (PageMappedToDisk(page))
2523                return 0;
2524
2525        /*
2526         * Allocate buffers so that we can keep track of state, and potentially
2527         * attach them to the page if an error occurs. In the common case of
2528         * no error, they will just be freed again without ever being attached
2529         * to the page (which is all OK, because we're under the page lock).
2530         *
2531         * Be careful: the buffer linked list is a NULL terminated one, rather
2532         * than the circular one we're used to.
2533         */
2534        head = alloc_page_buffers(page, blocksize, 0);
2535        if (!head) {
2536                ret = -ENOMEM;
2537                goto out_release;
2538        }
2539
2540        block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
2541
2542        /*
2543         * We loop across all blocks in the page, whether or not they are
2544         * part of the affected region.  This is so we can discover if the
2545         * page is fully mapped-to-disk.
2546         */
2547        for (block_start = 0, block_in_page = 0, bh = head;
2548                  block_start < PAGE_CACHE_SIZE;
2549                  block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2550                int create;
2551
2552                block_end = block_start + blocksize;
2553                bh->b_state = 0;
2554                create = 1;
2555                if (block_start >= to)
2556                        create = 0;
2557                ret = get_block(inode, block_in_file + block_in_page,
2558                                        bh, create);
2559                if (ret)
2560                        goto failed;
2561                if (!buffer_mapped(bh))
2562                        is_mapped_to_disk = 0;
2563                if (buffer_new(bh))
2564                        unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
2565                if (PageUptodate(page)) {
2566                        set_buffer_uptodate(bh);
2567                        continue;
2568                }
2569                if (buffer_new(bh) || !buffer_mapped(bh)) {
2570                        zero_user_segments(page, block_start, from,
2571                                                        to, block_end);
2572                        continue;
2573                }
2574                if (buffer_uptodate(bh))
2575                        continue;       /* reiserfs does this */
2576                if (block_start < from || block_end > to) {
2577                        lock_buffer(bh);
2578                        bh->b_end_io = end_buffer_read_nobh;
2579                        submit_bh(READ, bh);
2580                        nr_reads++;
2581                }
2582        }
2583
2584        if (nr_reads) {
2585                /*
2586                 * The page is locked, so these buffers are protected from
2587                 * any VM or truncate activity.  Hence we don't need to care
2588                 * for the buffer_head refcounts.
2589                 */
2590                for (bh = head; bh; bh = bh->b_this_page) {
2591                        wait_on_buffer(bh);
2592                        if (!buffer_uptodate(bh))
2593                                ret = -EIO;
2594                }
2595                if (ret)
2596                        goto failed;
2597        }
2598
2599        if (is_mapped_to_disk)
2600                SetPageMappedToDisk(page);
2601
2602        *fsdata = head; /* to be released by nobh_write_end */
2603
2604        return 0;
2605
2606failed:
2607        BUG_ON(!ret);
2608        /*
2609         * Error recovery is a bit difficult. We need to zero out blocks that
2610         * were newly allocated, and dirty them to ensure they get written out.
2611         * Buffers need to be attached to the page at this point, otherwise
2612         * the handling of potential IO errors during writeout would be hard
2613         * (could try doing synchronous writeout, but what if that fails too?)
2614         */
2615        attach_nobh_buffers(page, head);
2616        page_zero_new_buffers(page, from, to);
2617
2618out_release:
2619        unlock_page(page);
2620        page_cache_release(page);
2621        *pagep = NULL;
2622
2623        return ret;
2624}
2625EXPORT_SYMBOL(nobh_write_begin);
2626
2627int nobh_write_end(struct file *file, struct address_space *mapping,
2628                        loff_t pos, unsigned len, unsigned copied,
2629                        struct page *page, void *fsdata)
2630{
2631        struct inode *inode = page->mapping->host;
2632        struct buffer_head *head = fsdata;
2633        struct buffer_head *bh;
2634        BUG_ON(fsdata != NULL && page_has_buffers(page));
2635
2636        if (unlikely(copied < len) && head)
2637                attach_nobh_buffers(page, head);
2638        if (page_has_buffers(page))
2639                return generic_write_end(file, mapping, pos, len,
2640                                        copied, page, fsdata);
2641
2642        SetPageUptodate(page);
2643        set_page_dirty(page);
2644        if (pos+copied > inode->i_size) {
2645                i_size_write(inode, pos+copied);
2646                mark_inode_dirty(inode);
2647        }
2648
2649        unlock_page(page);
2650        page_cache_release(page);
2651
2652        while (head) {
2653                bh = head;
2654                head = head->b_this_page;
2655                free_buffer_head(bh);
2656        }
2657
2658        return copied;
2659}
2660EXPORT_SYMBOL(nobh_write_end);
2661
2662/*
2663 * nobh_writepage() - based on block_full_write_page() except
2664 * that it tries to operate without attaching bufferheads to
2665 * the page.
2666 */
2667int nobh_writepage(struct page *page, get_block_t *get_block,
2668                        struct writeback_control *wbc)
2669{
2670        struct inode * const inode = page->mapping->host;
2671        loff_t i_size = i_size_read(inode);
2672        const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2673        unsigned offset;
2674        int ret;
2675
2676        /* Is the page fully inside i_size? */
2677        if (page->index < end_index)
2678                goto out;
2679
2680        /* Is the page fully outside i_size? (truncate in progress) */
2681        offset = i_size & (PAGE_CACHE_SIZE-1);
2682        if (page->index >= end_index+1 || !offset) {
2683                /*
2684                 * The page may have dirty, unmapped buffers.  For example,
2685                 * they may have been added in ext3_writepage().  Make them
2686                 * freeable here, so the page does not leak.
2687                 */
2688#if 0
2689                /* Not really sure about this  - do we need this ? */
2690                if (page->mapping->a_ops->invalidatepage)
2691                        page->mapping->a_ops->invalidatepage(page, offset);
2692#endif
2693                unlock_page(page);
2694                return 0; /* don't care */
2695        }
2696
2697        /*
2698         * The page straddles i_size.  It must be zeroed out on each and every
2699         * writepage invocation because it may be mmapped.  "A file is mapped
2700         * in multiples of the page size.  For a file that is not a multiple of
2701         * the  page size, the remaining memory is zeroed when mapped, and
2702         * writes to that region are not written out to the file."
2703         */
2704        zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2705out:
2706        ret = mpage_writepage(page, get_block, wbc);
2707        if (ret == -EAGAIN)
2708                ret = __block_write_full_page(inode, page, get_block, wbc,
2709                                              end_buffer_async_write);
2710        return ret;
2711}
2712EXPORT_SYMBOL(nobh_writepage);
2713
2714int nobh_truncate_page(struct address_space *mapping,
2715                        loff_t from, get_block_t *get_block)
2716{
2717        pgoff_t index = from >> PAGE_CACHE_SHIFT;
2718        unsigned offset = from & (PAGE_CACHE_SIZE-1);
2719        unsigned blocksize;
2720        sector_t iblock;
2721        unsigned length, pos;
2722        struct inode *inode = mapping->host;
2723        struct page *page;
2724        struct buffer_head map_bh;
2725        int err;
2726
2727        blocksize = 1 << inode->i_blkbits;
2728        length = offset & (blocksize - 1);
2729
2730        /* Block boundary? Nothing to do */
2731        if (!length)
2732                return 0;
2733
2734        length = blocksize - length;
2735        iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2736
2737        page = grab_cache_page(mapping, index);
2738        err = -ENOMEM;
2739        if (!page)
2740                goto out;
2741
2742        if (page_has_buffers(page)) {
2743has_buffers:
2744                unlock_page(page);
2745                page_cache_release(page);
2746                return block_truncate_page(mapping, from, get_block);
2747        }
2748
2749        /* Find the buffer that contains "offset" */
2750        pos = blocksize;
2751        while (offset >= pos) {
2752                iblock++;
2753                pos += blocksize;
2754        }
2755
2756        map_bh.b_size = blocksize;
2757        map_bh.b_state = 0;
2758        err = get_block(inode, iblock, &map_bh, 0);
2759        if (err)
2760                goto unlock;
2761        /* unmapped? It's a hole - nothing to do */
2762        if (!buffer_mapped(&map_bh))
2763                goto unlock;
2764
2765        /* Ok, it's mapped. Make sure it's up-to-date */
2766        if (!PageUptodate(page)) {
2767                err = mapping->a_ops->readpage(NULL, page);
2768                if (err) {
2769                        page_cache_release(page);
2770                        goto out;
2771                }
2772                lock_page(page);
2773                if (!PageUptodate(page)) {
2774                        err = -EIO;
2775                        goto unlock;
2776                }
2777                if (page_has_buffers(page))
2778                        goto has_buffers;
2779        }
2780        zero_user(page, offset, length);
2781        set_page_dirty(page);
2782        err = 0;
2783
2784unlock:
2785        unlock_page(page);
2786        page_cache_release(page);
2787out:
2788        return err;
2789}
2790EXPORT_SYMBOL(nobh_truncate_page);
2791
2792int block_truncate_page(struct address_space *mapping,
2793                        loff_t from, get_block_t *get_block)
2794{
2795        pgoff_t index = from >> PAGE_CACHE_SHIFT;
2796        unsigned offset = from & (PAGE_CACHE_SIZE-1);
2797        unsigned blocksize;
2798        sector_t iblock;
2799        unsigned length, pos;
2800        struct inode *inode = mapping->host;
2801        struct page *page;
2802        struct buffer_head *bh;
2803        int err;
2804
2805        blocksize = 1 << inode->i_blkbits;
2806        length = offset & (blocksize - 1);
2807
2808        /* Block boundary? Nothing to do */
2809        if (!length)
2810                return 0;
2811
2812        length = blocksize - length;
2813        iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2814        
2815        page = grab_cache_page(mapping, index);
2816        err = -ENOMEM;
2817        if (!page)
2818                goto out;
2819
2820        if (!page_has_buffers(page))
2821                create_empty_buffers(page, blocksize, 0);
2822
2823        /* Find the buffer that contains "offset" */
2824        bh = page_buffers(page);
2825        pos = blocksize;
2826        while (offset >= pos) {
2827                bh = bh->b_this_page;
2828                iblock++;
2829                pos += blocksize;
2830        }
2831
2832        err = 0;
2833        if (!buffer_mapped(bh)) {
2834                WARN_ON(bh->b_size != blocksize);
2835                err = get_block(inode, iblock, bh, 0);
2836                if (err)
2837                        goto unlock;
2838                /* unmapped? It's a hole - nothing to do */
2839                if (!buffer_mapped(bh))
2840                        goto unlock;
2841        }
2842
2843        /* Ok, it's mapped. Make sure it's up-to-date */
2844        if (PageUptodate(page))
2845                set_buffer_uptodate(bh);
2846
2847        if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2848                err = -EIO;
2849                ll_rw_block(READ, 1, &bh);
2850                wait_on_buffer(bh);
2851                /* Uhhuh. Read error. Complain and punt. */
2852                if (!buffer_uptodate(bh))
2853                        goto unlock;
2854        }
2855
2856        zero_user(page, offset, length);
2857        mark_buffer_dirty(bh);
2858        err = 0;
2859
2860unlock:
2861        unlock_page(page);
2862        page_cache_release(page);
2863out:
2864        return err;
2865}
2866EXPORT_SYMBOL(block_truncate_page);
2867
2868/*
2869 * The generic ->writepage function for buffer-backed address_spaces
2870 * this form passes in the end_io handler used to finish the IO.
2871 */
2872int block_write_full_page_endio(struct page *page, get_block_t *get_block,
2873                        struct writeback_control *wbc, bh_end_io_t *handler)
2874{
2875        struct inode * const inode = page->mapping->host;
2876        loff_t i_size = i_size_read(inode);
2877        const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2878        unsigned offset;
2879
2880        /* Is the page fully inside i_size? */
2881        if (page->index < end_index)
2882                return __block_write_full_page(inode, page, get_block, wbc,
2883                                               handler);
2884
2885        /* Is the page fully outside i_size? (truncate in progress) */
2886        offset = i_size & (PAGE_CACHE_SIZE-1);
2887        if (page->index >= end_index+1 || !offset) {
2888                /*
2889                 * The page may have dirty, unmapped buffers.  For example,
2890                 * they may have been added in ext3_writepage().  Make them
2891                 * freeable here, so the page does not leak.
2892                 */
2893                do_invalidatepage(page, 0, PAGE_CACHE_SIZE);
2894                unlock_page(page);
2895                return 0; /* don't care */
2896        }
2897
2898        /*
2899         * The page straddles i_size.  It must be zeroed out on each and every
2900         * writepage invocation because it may be mmapped.  "A file is mapped
2901         * in multiples of the page size.  For a file that is not a multiple of
2902         * the  page size, the remaining memory is zeroed when mapped, and
2903         * writes to that region are not written out to the file."
2904         */
2905        zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2906        return __block_write_full_page(inode, page, get_block, wbc, handler);
2907}
2908EXPORT_SYMBOL(block_write_full_page_endio);
2909
2910/*
2911 * The generic ->writepage function for buffer-backed address_spaces
2912 */
2913int block_write_full_page(struct page *page, get_block_t *get_block,
2914                        struct writeback_control *wbc)
2915{
2916        return block_write_full_page_endio(page, get_block, wbc,
2917                                           end_buffer_async_write);
2918}
2919EXPORT_SYMBOL(block_write_full_page);
2920
2921sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2922                            get_block_t *get_block)
2923{
2924        struct buffer_head tmp;
2925        struct inode *inode = mapping->host;
2926        tmp.b_state = 0;
2927        tmp.b_blocknr = 0;
2928        tmp.b_size = 1 << inode->i_blkbits;
2929        get_block(inode, block, &tmp, 0);
2930        return tmp.b_blocknr;
2931}
2932EXPORT_SYMBOL(generic_block_bmap);
2933
2934static void end_bio_bh_io_sync(struct bio *bio, int err)
2935{
2936        struct buffer_head *bh = bio->bi_private;
2937
2938        if (err == -EOPNOTSUPP) {
2939                set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
2940        }
2941
2942        if (unlikely (test_bit(BIO_QUIET,&bio->bi_flags)))
2943                set_bit(BH_Quiet, &bh->b_state);
2944
2945        bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
2946        bio_put(bio);
2947}
2948
2949/*
2950 * This allows us to do IO even on the odd last sectors
2951 * of a device, even if the bh block size is some multiple
2952 * of the physical sector size.
2953 *
2954 * We'll just truncate the bio to the size of the device,
2955 * and clear the end of the buffer head manually.
2956 *
2957 * Truly out-of-range accesses will turn into actual IO
2958 * errors, this only handles the "we need to be able to
2959 * do IO at the final sector" case.
2960 */
2961static void guard_bh_eod(int rw, struct bio *bio, struct buffer_head *bh)
2962{
2963        sector_t maxsector;
2964        unsigned bytes;
2965
2966        maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
2967        if (!maxsector)
2968                return;
2969
2970        /*
2971         * If the *whole* IO is past the end of the device,
2972         * let it through, and the IO layer will turn it into
2973         * an EIO.
2974         */
2975        if (unlikely(bio->bi_sector >= maxsector))
2976                return;
2977
2978        maxsector -= bio->bi_sector;
2979        bytes = bio->bi_size;
2980        if (likely((bytes >> 9) <= maxsector))
2981                return;
2982
2983        /* Uhhuh. We've got a bh that straddles the device size! */
2984        bytes = maxsector << 9;
2985
2986        /* Truncate the bio.. */
2987        bio->bi_size = bytes;
2988        bio->bi_io_vec[0].bv_len = bytes;
2989
2990        /* ..and clear the end of the buffer for reads */
2991        if ((rw & RW_MASK) == READ) {
2992                void *kaddr = kmap_atomic(bh->b_page);
2993                memset(kaddr + bh_offset(bh) + bytes, 0, bh->b_size - bytes);
2994                kunmap_atomic(kaddr);
2995                flush_dcache_page(bh->b_page);
2996        }
2997}
2998
2999int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags)
3000{
3001        struct bio *bio;
3002        int ret = 0;
3003
3004        BUG_ON(!buffer_locked(bh));
3005        BUG_ON(!buffer_mapped(bh));
3006        BUG_ON(!bh->b_end_io);
3007        BUG_ON(buffer_delay(bh));
3008        BUG_ON(buffer_unwritten(bh));
3009
3010        /*
3011         * Only clear out a write error when rewriting
3012         */
3013        if (test_set_buffer_req(bh) && (rw & WRITE))
3014                clear_buffer_write_io_error(bh);
3015
3016        /*
3017         * from here on down, it's all bio -- do the initial mapping,
3018         * submit_bio -> generic_make_request may further map this bio around
3019         */
3020        bio = bio_alloc(GFP_NOIO, 1);
3021
3022        bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
3023        bio->bi_bdev = bh->b_bdev;
3024        bio->bi_io_vec[0].bv_page = bh->b_page;
3025        bio->bi_io_vec[0].bv_len = bh->b_size;
3026        bio->bi_io_vec[0].bv_offset = bh_offset(bh);
3027
3028        bio->bi_vcnt = 1;
3029        bio->bi_size = bh->b_size;
3030
3031        bio->bi_end_io = end_bio_bh_io_sync;
3032        bio->bi_private = bh;
3033        bio->bi_flags |= bio_flags;
3034
3035        /* Take care of bh's that straddle the end of the device */
3036        guard_bh_eod(rw, bio, bh);
3037
3038        if (buffer_meta(bh))
3039                rw |= REQ_META;
3040        if (buffer_prio(bh))
3041                rw |= REQ_PRIO;
3042
3043        bio_get(bio);
3044        submit_bio(rw, bio);
3045
3046        if (bio_flagged(bio, BIO_EOPNOTSUPP))
3047                ret = -EOPNOTSUPP;
3048
3049        bio_put(bio);
3050        return ret;
3051}
3052EXPORT_SYMBOL_GPL(_submit_bh);
3053
3054int submit_bh(int rw, struct buffer_head *bh)
3055{
3056        return _submit_bh(rw, bh, 0);
3057}
3058EXPORT_SYMBOL(submit_bh);
3059
3060/**
3061 * ll_rw_block: low-level access to block devices (DEPRECATED)
3062 * @rw: whether to %READ or %WRITE or maybe %READA (readahead)
3063 * @nr: number of &struct buffer_heads in the array
3064 * @bhs: array of pointers to &struct buffer_head
3065 *
3066 * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3067 * requests an I/O operation on them, either a %READ or a %WRITE.  The third
3068 * %READA option is described in the documentation for generic_make_request()
3069 * which ll_rw_block() calls.
3070 *
3071 * This function drops any buffer that it cannot get a lock on (with the
3072 * BH_Lock state bit), any buffer that appears to be clean when doing a write
3073 * request, and any buffer that appears to be up-to-date when doing read
3074 * request.  Further it marks as clean buffers that are processed for
3075 * writing (the buffer cache won't assume that they are actually clean
3076 * until the buffer gets unlocked).
3077 *
3078 * ll_rw_block sets b_end_io to simple completion handler that marks
3079 * the buffer up-to-date (if approriate), unlocks the buffer and wakes
3080 * any waiters. 
3081 *
3082 * All of the buffers must be for the same device, and must also be a
3083 * multiple of the current approved size for the device.
3084 */
3085void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
3086{
3087        int i;
3088
3089        for (i = 0; i < nr; i++) {
3090                struct buffer_head *bh = bhs[i];
3091
3092                if (!trylock_buffer(bh))
3093                        continue;
3094                if (rw == WRITE) {
3095                        if (test_clear_buffer_dirty(bh)) {
3096                                bh->b_end_io = end_buffer_write_sync;
3097                                get_bh(bh);
3098                                submit_bh(WRITE, bh);
3099                                continue;
3100                        }
3101                } else {
3102                        if (!buffer_uptodate(bh)) {
3103                                bh->b_end_io = end_buffer_read_sync;
3104                                get_bh(bh);
3105                                submit_bh(rw, bh);
3106                                continue;
3107                        }
3108                }
3109                unlock_buffer(bh);
3110        }
3111}
3112EXPORT_SYMBOL(ll_rw_block);
3113
3114void write_dirty_buffer(struct buffer_head *bh, int rw)
3115{
3116        lock_buffer(bh);
3117        if (!test_clear_buffer_dirty(bh)) {
3118                unlock_buffer(bh);
3119                return;
3120        }
3121        bh->b_end_io = end_buffer_write_sync;
3122        get_bh(bh);
3123        submit_bh(rw, bh);
3124}
3125EXPORT_SYMBOL(write_dirty_buffer);
3126
3127/*
3128 * For a data-integrity writeout, we need to wait upon any in-progress I/O
3129 * and then start new I/O and then wait upon it.  The caller must have a ref on
3130 * the buffer_head.
3131 */
3132int __sync_dirty_buffer(struct buffer_head *bh, int rw)
3133{
3134        int ret = 0;
3135
3136        WARN_ON(atomic_read(&bh->b_count) < 1);
3137        lock_buffer(bh);
3138        if (test_clear_buffer_dirty(bh)) {
3139                get_bh(bh);
3140                bh->b_end_io = end_buffer_write_sync;
3141                ret = submit_bh(rw, bh);
3142                wait_on_buffer(bh);
3143                if (!ret && !buffer_uptodate(bh))
3144                        ret = -EIO;
3145        } else {
3146                unlock_buffer(bh);
3147        }
3148        return ret;
3149}
3150EXPORT_SYMBOL(__sync_dirty_buffer);
3151
3152int sync_dirty_buffer(struct buffer_head *bh)
3153{
3154        return __sync_dirty_buffer(bh, WRITE_SYNC);
3155}
3156EXPORT_SYMBOL(sync_dirty_buffer);
3157
3158/*
3159 * try_to_free_buffers() checks if all the buffers on this particular page
3160 * are unused, and releases them if so.
3161 *
3162 * Exclusion against try_to_free_buffers may be obtained by either
3163 * locking the page or by holding its mapping's private_lock.
3164 *
3165 * If the page is dirty but all the buffers are clean then we need to
3166 * be sure to mark the page clean as well.  This is because the page
3167 * may be against a block device, and a later reattachment of buffers
3168 * to a dirty page will set *all* buffers dirty.  Which would corrupt
3169 * filesystem data on the same device.
3170 *
3171 * The same applies to regular filesystem pages: if all the buffers are
3172 * clean then we set the page clean and proceed.  To do that, we require
3173 * total exclusion from __set_page_dirty_buffers().  That is obtained with
3174 * private_lock.
3175 *
3176 * try_to_free_buffers() is non-blocking.
3177 */
3178static inline int buffer_busy(struct buffer_head *bh)
3179{
3180        return atomic_read(&bh->b_count) |
3181                (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3182}
3183
3184static int
3185drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
3186{
3187        struct buffer_head *head = page_buffers(page);
3188        struct buffer_head *bh;
3189
3190        bh = head;
3191        do {
3192                if (buffer_write_io_error(bh) && page->mapping)
3193                        set_bit(AS_EIO, &page->mapping->flags);
3194                if (buffer_busy(bh))
3195                        goto failed;
3196                bh = bh->b_this_page;
3197        } while (bh != head);
3198
3199        do {
3200                struct buffer_head *next = bh->b_this_page;
3201
3202                if (bh->b_assoc_map)
3203                        __remove_assoc_queue(bh);
3204                bh = next;
3205        } while (bh != head);
3206        *buffers_to_free = head;
3207        __clear_page_buffers(page);
3208        return 1;
3209failed:
3210        return 0;
3211}
3212
3213int try_to_free_buffers(struct page *page)
3214{
3215        struct address_space * const mapping = page->mapping;
3216        struct buffer_head *buffers_to_free = NULL;
3217        int ret = 0;
3218
3219        BUG_ON(!PageLocked(page));
3220        if (PageWriteback(page))
3221                return 0;
3222
3223        if (mapping == NULL) {          /* can this still happen? */
3224                ret = drop_buffers(page, &buffers_to_free);
3225                goto out;
3226        }
3227
3228        spin_lock(&mapping->private_lock);
3229        ret = drop_buffers(page, &buffers_to_free);
3230
3231        /*
3232         * If the filesystem writes its buffers by hand (eg ext3)
3233         * then we can have clean buffers against a dirty page.  We
3234         * clean the page here; otherwise the VM will never notice
3235         * that the filesystem did any IO at all.
3236         *
3237         * Also, during truncate, discard_buffer will have marked all
3238         * the page's buffers clean.  We discover that here and clean
3239         * the page also.
3240         *
3241         * private_lock must be held over this entire operation in order
3242         * to synchronise against __set_page_dirty_buffers and prevent the
3243         * dirty bit from being lost.
3244         */
3245        if (ret)
3246                cancel_dirty_page(page, PAGE_CACHE_SIZE);
3247        spin_unlock(&mapping->private_lock);
3248out:
3249        if (buffers_to_free) {
3250                struct buffer_head *bh = buffers_to_free;
3251
3252                do {
3253                        struct buffer_head *next = bh->b_this_page;
3254                        free_buffer_head(bh);
3255                        bh = next;
3256                } while (bh != buffers_to_free);
3257        }
3258        return ret;
3259}
3260EXPORT_SYMBOL(try_to_free_buffers);
3261
3262/*
3263 * There are no bdflush tunables left.  But distributions are
3264 * still running obsolete flush daemons, so we terminate them here.
3265 *
3266 * Use of bdflush() is deprecated and will be removed in a future kernel.
3267 * The `flush-X' kernel threads fully replace bdflush daemons and this call.
3268 */
3269SYSCALL_DEFINE2(bdflush, int, func, long, data)
3270{
3271        static int msg_count;
3272
3273        if (!capable(CAP_SYS_ADMIN))
3274                return -EPERM;
3275
3276        if (msg_count < 5) {
3277                msg_count++;
3278                printk(KERN_INFO
3279                        "warning: process `%s' used the obsolete bdflush"
3280                        " system call\n", current->comm);
3281                printk(KERN_INFO "Fix your initscripts?\n");
3282        }
3283
3284        if (func == 1)
3285                do_exit(0);
3286        return 0;
3287}
3288
3289/*
3290 * Buffer-head allocation
3291 */
3292static struct kmem_cache *bh_cachep __read_mostly;
3293
3294/*
3295 * Once the number of bh's in the machine exceeds this level, we start
3296 * stripping them in writeback.
3297 */
3298static unsigned long max_buffer_heads;
3299
3300int buffer_heads_over_limit;
3301
3302struct bh_accounting {
3303        int nr;                 /* Number of live bh's */
3304        int ratelimit;          /* Limit cacheline bouncing */
3305};
3306
3307static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3308
3309static void recalc_bh_state(void)
3310{
3311        int i;
3312        int tot = 0;
3313
3314        if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3315                return;
3316        __this_cpu_write(bh_accounting.ratelimit, 0);
3317        for_each_online_cpu(i)
3318                tot += per_cpu(bh_accounting, i).nr;
3319        buffer_heads_over_limit = (tot > max_buffer_heads);
3320}
3321
3322struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3323{
3324        struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3325        if (ret) {
3326                INIT_LIST_HEAD(&ret->b_assoc_buffers);
3327                preempt_disable();
3328                __this_cpu_inc(bh_accounting.nr);
3329                recalc_bh_state();
3330                preempt_enable();
3331        }
3332        return ret;
3333}
3334EXPORT_SYMBOL(alloc_buffer_head);
3335
3336void free_buffer_head(struct buffer_head *bh)
3337{
3338        BUG_ON(!list_empty(&bh->b_assoc_buffers));
3339        kmem_cache_free(bh_cachep, bh);
3340        preempt_disable();
3341        __this_cpu_dec(bh_accounting.nr);
3342        recalc_bh_state();
3343        preempt_enable();
3344}
3345EXPORT_SYMBOL(free_buffer_head);
3346
3347static void buffer_exit_cpu(int cpu)
3348{
3349        int i;
3350        struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3351
3352        for (i = 0; i < BH_LRU_SIZE; i++) {
3353                brelse(b->bhs[i]);
3354                b->bhs[i] = NULL;
3355        }
3356        this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3357        per_cpu(bh_accounting, cpu).nr = 0;
3358}
3359
3360static int buffer_cpu_notify(struct notifier_block *self,
3361                              unsigned long action, void *hcpu)
3362{
3363        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN)
3364                buffer_exit_cpu((unsigned long)hcpu);
3365        return NOTIFY_OK;
3366}
3367
3368/**
3369 * bh_uptodate_or_lock - Test whether the buffer is uptodate
3370 * @bh: struct buffer_head
3371 *
3372 * Return true if the buffer is up-to-date and false,
3373 * with the buffer locked, if not.
3374 */
3375int bh_uptodate_or_lock(struct buffer_head *bh)
3376{
3377        if (!buffer_uptodate(bh)) {
3378                lock_buffer(bh);
3379                if (!buffer_uptodate(bh))
3380                        return 0;
3381                unlock_buffer(bh);
3382        }
3383        return 1;
3384}
3385EXPORT_SYMBOL(bh_uptodate_or_lock);
3386
3387/**
3388 * bh_submit_read - Submit a locked buffer for reading
3389 * @bh: struct buffer_head
3390 *
3391 * Returns zero on success and -EIO on error.
3392 */
3393int bh_submit_read(struct buffer_head *bh)
3394{
3395        BUG_ON(!buffer_locked(bh));
3396
3397        if (buffer_uptodate(bh)) {
3398                unlock_buffer(bh);
3399                return 0;
3400        }
3401
3402        get_bh(bh);
3403        bh->b_end_io = end_buffer_read_sync;
3404        submit_bh(READ, bh);
3405        wait_on_buffer(bh);
3406        if (buffer_uptodate(bh))
3407                return 0;
3408        return -EIO;
3409}
3410EXPORT_SYMBOL(bh_submit_read);
3411
3412void __init buffer_init(void)
3413{
3414        unsigned long nrpages;
3415
3416        bh_cachep = kmem_cache_create("buffer_head",
3417                        sizeof(struct buffer_head), 0,
3418                                (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3419                                SLAB_MEM_SPREAD),
3420                                NULL);
3421
3422        /*
3423         * Limit the bh occupancy to 10% of ZONE_NORMAL
3424         */
3425        nrpages = (nr_free_buffer_pages() * 10) / 100;
3426        max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3427        hotcpu_notifier(buffer_cpu_notify, 0);
3428}
3429
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