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/backing-dev.h>
  34#include <linux/writeback.h>
  35#include <linux/hash.h>
  36#include <linux/suspend.h>
  37#include <linux/buffer_head.h>
  38#include <linux/task_io_accounting_ops.h>
  39#include <linux/bio.h>
  40#include <linux/notifier.h>
  41#include <linux/cpu.h>
  42#include <linux/bitops.h>
  43#include <linux/mpage.h>
  44#include <linux/bit_spinlock.h>
  45#include <trace/events/block.h>
  46
  47static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
  48static int submit_bh_wbc(int rw, struct buffer_head *bh,
  49                         unsigned long bio_flags,
  50                         struct writeback_control *wbc);
  51
  52#define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
  53
  54void init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
  55{
  56        bh->b_end_io = handler;
  57        bh->b_private = private;
  58}
  59EXPORT_SYMBOL(init_buffer);
  60
  61inline void touch_buffer(struct buffer_head *bh)
  62{
  63        trace_block_touch_buffer(bh);
  64        mark_page_accessed(bh->b_page);
  65}
  66EXPORT_SYMBOL(touch_buffer);
  67
  68void __lock_buffer(struct buffer_head *bh)
  69{
  70        wait_on_bit_lock_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
  71}
  72EXPORT_SYMBOL(__lock_buffer);
  73
  74void unlock_buffer(struct buffer_head *bh)
  75{
  76        clear_bit_unlock(BH_Lock, &bh->b_state);
  77        smp_mb__after_atomic();
  78        wake_up_bit(&bh->b_state, BH_Lock);
  79}
  80EXPORT_SYMBOL(unlock_buffer);
  81
  82/*
  83 * Returns if the page has dirty or writeback buffers. If all the buffers
  84 * are unlocked and clean then the PageDirty information is stale. If
  85 * any of the pages are locked, it is assumed they are locked for IO.
  86 */
  87void buffer_check_dirty_writeback(struct page *page,
  88                                     bool *dirty, bool *writeback)
  89{
  90        struct buffer_head *head, *bh;
  91        *dirty = false;
  92        *writeback = false;
  93
  94        BUG_ON(!PageLocked(page));
  95
  96        if (!page_has_buffers(page))
  97                return;
  98
  99        if (PageWriteback(page))
 100                *writeback = true;
 101
 102        head = page_buffers(page);
 103        bh = head;
 104        do {
 105                if (buffer_locked(bh))
 106                        *writeback = true;
 107
 108                if (buffer_dirty(bh))
 109                        *dirty = true;
 110
 111                bh = bh->b_this_page;
 112        } while (bh != head);
 113}
 114EXPORT_SYMBOL(buffer_check_dirty_writeback);
 115
 116/*
 117 * Block until a buffer comes unlocked.  This doesn't stop it
 118 * from becoming locked again - you have to lock it yourself
 119 * if you want to preserve its state.
 120 */
 121void __wait_on_buffer(struct buffer_head * bh)
 122{
 123        wait_on_bit_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
 124}
 125EXPORT_SYMBOL(__wait_on_buffer);
 126
 127static void
 128__clear_page_buffers(struct page *page)
 129{
 130        ClearPagePrivate(page);
 131        set_page_private(page, 0);
 132        page_cache_release(page);
 133}
 134
 135static void buffer_io_error(struct buffer_head *bh, char *msg)
 136{
 137        char b[BDEVNAME_SIZE];
 138
 139        if (!test_bit(BH_Quiet, &bh->b_state))
 140                printk_ratelimited(KERN_ERR
 141                        "Buffer I/O error on dev %s, logical block %llu%s\n",
 142                        bdevname(bh->b_bdev, b),
 143                        (unsigned long long)bh->b_blocknr, msg);
 144}
 145
 146/*
 147 * End-of-IO handler helper function which does not touch the bh after
 148 * unlocking it.
 149 * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
 150 * a race there is benign: unlock_buffer() only use the bh's address for
 151 * hashing after unlocking the buffer, so it doesn't actually touch the bh
 152 * itself.
 153 */
 154static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
 155{
 156        if (uptodate) {
 157                set_buffer_uptodate(bh);
 158        } else {
 159                /* This happens, due to failed READA attempts. */
 160                clear_buffer_uptodate(bh);
 161        }
 162        unlock_buffer(bh);
 163}
 164
 165/*
 166 * Default synchronous end-of-IO handler..  Just mark it up-to-date and
 167 * unlock the buffer. This is what ll_rw_block uses too.
 168 */
 169void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
 170{
 171        __end_buffer_read_notouch(bh, uptodate);
 172        put_bh(bh);
 173}
 174EXPORT_SYMBOL(end_buffer_read_sync);
 175
 176void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 177{
 178        if (uptodate) {
 179                set_buffer_uptodate(bh);
 180        } else {
 181                buffer_io_error(bh, ", lost sync page write");
 182                set_buffer_write_io_error(bh);
 183                clear_buffer_uptodate(bh);
 184        }
 185        unlock_buffer(bh);
 186        put_bh(bh);
 187}
 188EXPORT_SYMBOL(end_buffer_write_sync);
 189
 190/*
 191 * Various filesystems appear to want __find_get_block to be non-blocking.
 192 * But it's the page lock which protects the buffers.  To get around this,
 193 * we get exclusion from try_to_free_buffers with the blockdev mapping's
 194 * private_lock.
 195 *
 196 * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
 197 * may be quite high.  This code could TryLock the page, and if that
 198 * succeeds, there is no need to take private_lock. (But if
 199 * private_lock is contended then so is mapping->tree_lock).
 200 */
 201static struct buffer_head *
 202__find_get_block_slow(struct block_device *bdev, sector_t block)
 203{
 204        struct inode *bd_inode = bdev->bd_inode;
 205        struct address_space *bd_mapping = bd_inode->i_mapping;
 206        struct buffer_head *ret = NULL;
 207        pgoff_t index;
 208        struct buffer_head *bh;
 209        struct buffer_head *head;
 210        struct page *page;
 211        int all_mapped = 1;
 212
 213        index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
 214        page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
 215        if (!page)
 216                goto out;
 217
 218        spin_lock(&bd_mapping->private_lock);
 219        if (!page_has_buffers(page))
 220                goto out_unlock;
 221        head = page_buffers(page);
 222        bh = head;
 223        do {
 224                if (!buffer_mapped(bh))
 225                        all_mapped = 0;
 226                else if (bh->b_blocknr == block) {
 227                        ret = bh;
 228                        get_bh(bh);
 229                        goto out_unlock;
 230                }
 231                bh = bh->b_this_page;
 232        } while (bh != head);
 233
 234        /* we might be here because some of the buffers on this page are
 235         * not mapped.  This is due to various races between
 236         * file io on the block device and getblk.  It gets dealt with
 237         * elsewhere, don't buffer_error if we had some unmapped buffers
 238         */
 239        if (all_mapped) {
 240                char b[BDEVNAME_SIZE];
 241
 242                printk("__find_get_block_slow() failed. "
 243                        "block=%llu, b_blocknr=%llu\n",
 244                        (unsigned long long)block,
 245                        (unsigned long long)bh->b_blocknr);
 246                printk("b_state=0x%08lx, b_size=%zu\n",
 247                        bh->b_state, bh->b_size);
 248                printk("device %s blocksize: %d\n", bdevname(bdev, b),
 249                        1 << bd_inode->i_blkbits);
 250        }
 251out_unlock:
 252        spin_unlock(&bd_mapping->private_lock);
 253        page_cache_release(page);
 254out:
 255        return ret;
 256}
 257
 258/*
 259 * Kick the writeback threads then try to free up some ZONE_NORMAL memory.
 260 */
 261static void free_more_memory(void)
 262{
 263        struct zone *zone;
 264        int nid;
 265
 266        wakeup_flusher_threads(1024, WB_REASON_FREE_MORE_MEM);
 267        yield();
 268
 269        for_each_online_node(nid) {
 270                (void)first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
 271                                                gfp_zone(GFP_NOFS), NULL,
 272                                                &zone);
 273                if (zone)
 274                        try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
 275                                                GFP_NOFS, NULL);
 276        }
 277}
 278
 279/*
 280 * I/O completion handler for block_read_full_page() - pages
 281 * which come unlocked at the end of I/O.
 282 */
 283static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
 284{
 285        unsigned long flags;
 286        struct buffer_head *first;
 287        struct buffer_head *tmp;
 288        struct page *page;
 289        int page_uptodate = 1;
 290
 291        BUG_ON(!buffer_async_read(bh));
 292
 293        page = bh->b_page;
 294        if (uptodate) {
 295                set_buffer_uptodate(bh);
 296        } else {
 297                clear_buffer_uptodate(bh);
 298                buffer_io_error(bh, ", async page read");
 299                SetPageError(page);
 300        }
 301
 302        /*
 303         * Be _very_ careful from here on. Bad things can happen if
 304         * two buffer heads end IO at almost the same time and both
 305         * decide that the page is now completely done.
 306         */
 307        first = page_buffers(page);
 308        local_irq_save(flags);
 309        bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
 310        clear_buffer_async_read(bh);
 311        unlock_buffer(bh);
 312        tmp = bh;
 313        do {
 314                if (!buffer_uptodate(tmp))
 315                        page_uptodate = 0;
 316                if (buffer_async_read(tmp)) {
 317                        BUG_ON(!buffer_locked(tmp));
 318                        goto still_busy;
 319                }
 320                tmp = tmp->b_this_page;
 321        } while (tmp != bh);
 322        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 323        local_irq_restore(flags);
 324
 325        /*
 326         * If none of the buffers had errors and they are all
 327         * uptodate then we can set the page uptodate.
 328         */
 329        if (page_uptodate && !PageError(page))
 330                SetPageUptodate(page);
 331        unlock_page(page);
 332        return;
 333
 334still_busy:
 335        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 336        local_irq_restore(flags);
 337        return;
 338}
 339
 340/*
 341 * Completion handler for block_write_full_page() - pages which are unlocked
 342 * during I/O, and which have PageWriteback cleared upon I/O completion.
 343 */
 344void end_buffer_async_write(struct buffer_head *bh, int uptodate)
 345{
 346        unsigned long flags;
 347        struct buffer_head *first;
 348        struct buffer_head *tmp;
 349        struct page *page;
 350
 351        BUG_ON(!buffer_async_write(bh));
 352
 353        page = bh->b_page;
 354        if (uptodate) {
 355                set_buffer_uptodate(bh);
 356        } else {
 357                buffer_io_error(bh, ", lost async page write");
 358                set_bit(AS_EIO, &page->mapping->flags);
 359                set_buffer_write_io_error(bh);
 360                clear_buffer_uptodate(bh);
 361                SetPageError(page);
 362        }
 363
 364        first = page_buffers(page);
 365        local_irq_save(flags);
 366        bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
 367
 368        clear_buffer_async_write(bh);
 369        unlock_buffer(bh);
 370        tmp = bh->b_this_page;
 371        while (tmp != bh) {
 372                if (buffer_async_write(tmp)) {
 373                        BUG_ON(!buffer_locked(tmp));
 374                        goto still_busy;
 375                }
 376                tmp = tmp->b_this_page;
 377        }
 378        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 379        local_irq_restore(flags);
 380        end_page_writeback(page);
 381        return;
 382
 383still_busy:
 384        bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 385        local_irq_restore(flags);
 386        return;
 387}
 388EXPORT_SYMBOL(end_buffer_async_write);
 389
 390/*
 391 * If a page's buffers are under async readin (end_buffer_async_read
 392 * completion) then there is a possibility that another thread of
 393 * control could lock one of the buffers after it has completed
 394 * but while some of the other buffers have not completed.  This
 395 * locked buffer would confuse end_buffer_async_read() into not unlocking
 396 * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
 397 * that this buffer is not under async I/O.
 398 *
 399 * The page comes unlocked when it has no locked buffer_async buffers
 400 * left.
 401 *
 402 * PageLocked prevents anyone starting new async I/O reads any of
 403 * the buffers.
 404 *
 405 * PageWriteback is used to prevent simultaneous writeout of the same
 406 * page.
 407 *
 408 * PageLocked prevents anyone from starting writeback of a page which is
 409 * under read I/O (PageWriteback is only ever set against a locked page).
 410 */
 411static void mark_buffer_async_read(struct buffer_head *bh)
 412{
 413        bh->b_end_io = end_buffer_async_read;
 414        set_buffer_async_read(bh);
 415}
 416
 417static void mark_buffer_async_write_endio(struct buffer_head *bh,
 418                                          bh_end_io_t *handler)
 419{
 420        bh->b_end_io = handler;
 421        set_buffer_async_write(bh);
 422}
 423
 424void mark_buffer_async_write(struct buffer_head *bh)
 425{
 426        mark_buffer_async_write_endio(bh, end_buffer_async_write);
 427}
 428EXPORT_SYMBOL(mark_buffer_async_write);
 429
 430
 431/*
 432 * fs/buffer.c contains helper functions for buffer-backed address space's
 433 * fsync functions.  A common requirement for buffer-based filesystems is
 434 * that certain data from the backing blockdev needs to be written out for
 435 * a successful fsync().  For example, ext2 indirect blocks need to be
 436 * written back and waited upon before fsync() returns.
 437 *
 438 * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
 439 * inode_has_buffers() and invalidate_inode_buffers() are provided for the
 440 * management of a list of dependent buffers at ->i_mapping->private_list.
 441 *
 442 * Locking is a little subtle: try_to_free_buffers() will remove buffers
 443 * from their controlling inode's queue when they are being freed.  But
 444 * try_to_free_buffers() will be operating against the *blockdev* mapping
 445 * at the time, not against the S_ISREG file which depends on those buffers.
 446 * So the locking for private_list is via the private_lock in the address_space
 447 * which backs the buffers.  Which is different from the address_space 
 448 * against which the buffers are listed.  So for a particular address_space,
 449 * mapping->private_lock does *not* protect mapping->private_list!  In fact,
 450 * mapping->private_list will always be protected by the backing blockdev's
 451 * ->private_lock.
 452 *
 453 * Which introduces a requirement: all buffers on an address_space's
 454 * ->private_list must be from the same address_space: the blockdev's.
 455 *
 456 * address_spaces which do not place buffers at ->private_list via these
 457 * utility functions are free to use private_lock and private_list for
 458 * whatever they want.  The only requirement is that list_empty(private_list)
 459 * be true at clear_inode() time.
 460 *
 461 * FIXME: clear_inode should not call invalidate_inode_buffers().  The
 462 * filesystems should do that.  invalidate_inode_buffers() should just go
 463 * BUG_ON(!list_empty).
 464 *
 465 * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
 466 * take an address_space, not an inode.  And it should be called
 467 * mark_buffer_dirty_fsync() to clearly define why those buffers are being
 468 * queued up.
 469 *
 470 * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
 471 * list if it is already on a list.  Because if the buffer is on a list,
 472 * it *must* already be on the right one.  If not, the filesystem is being
 473 * silly.  This will save a ton of locking.  But first we have to ensure
 474 * that buffers are taken *off* the old inode's list when they are freed
 475 * (presumably in truncate).  That requires careful auditing of all
 476 * filesystems (do it inside bforget()).  It could also be done by bringing
 477 * b_inode back.
 478 */
 479
 480/*
 481 * The buffer's backing address_space's private_lock must be held
 482 */
 483static void __remove_assoc_queue(struct buffer_head *bh)
 484{
 485        list_del_init(&bh->b_assoc_buffers);
 486        WARN_ON(!bh->b_assoc_map);
 487        if (buffer_write_io_error(bh))
 488                set_bit(AS_EIO, &bh->b_assoc_map->flags);
 489        bh->b_assoc_map = NULL;
 490}
 491
 492int inode_has_buffers(struct inode *inode)
 493{
 494        return !list_empty(&inode->i_data.private_list);
 495}
 496
 497/*
 498 * osync is designed to support O_SYNC io.  It waits synchronously for
 499 * all already-submitted IO to complete, but does not queue any new
 500 * writes to the disk.
 501 *
 502 * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
 503 * you dirty the buffers, and then use osync_inode_buffers to wait for
 504 * completion.  Any other dirty buffers which are not yet queued for
 505 * write will not be flushed to disk by the osync.
 506 */
 507static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
 508{
 509        struct buffer_head *bh;
 510        struct list_head *p;
 511        int err = 0;
 512
 513        spin_lock(lock);
 514repeat:
 515        list_for_each_prev(p, list) {
 516                bh = BH_ENTRY(p);
 517                if (buffer_locked(bh)) {
 518                        get_bh(bh);
 519                        spin_unlock(lock);
 520                        wait_on_buffer(bh);
 521                        if (!buffer_uptodate(bh))
 522                                err = -EIO;
 523                        brelse(bh);
 524                        spin_lock(lock);
 525                        goto repeat;
 526                }
 527        }
 528        spin_unlock(lock);
 529        return err;
 530}
 531
 532static void do_thaw_one(struct super_block *sb, void *unused)
 533{
 534        char b[BDEVNAME_SIZE];
 535        while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
 536                printk(KERN_WARNING "Emergency Thaw on %s\n",
 537                       bdevname(sb->s_bdev, b));
 538}
 539
 540static void do_thaw_all(struct work_struct *work)
 541{
 542        iterate_supers(do_thaw_one, NULL);
 543        kfree(work);
 544        printk(KERN_WARNING "Emergency Thaw complete\n");
 545}
 546
 547/**
 548 * emergency_thaw_all -- forcibly thaw every frozen filesystem
 549 *
 550 * Used for emergency unfreeze of all filesystems via SysRq
 551 */
 552void emergency_thaw_all(void)
 553{
 554        struct work_struct *work;
 555
 556        work = kmalloc(sizeof(*work), GFP_ATOMIC);
 557        if (work) {
 558                INIT_WORK(work, do_thaw_all);
 559                schedule_work(work);
 560        }
 561}
 562
 563/**
 564 * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
 565 * @mapping: the mapping which wants those buffers written
 566 *
 567 * Starts I/O against the buffers at mapping->private_list, and waits upon
 568 * that I/O.
 569 *
 570 * Basically, this is a convenience function for fsync().
 571 * @mapping is a file or directory which needs those buffers to be written for
 572 * a successful fsync().
 573 */
 574int sync_mapping_buffers(struct address_space *mapping)
 575{
 576        struct address_space *buffer_mapping = mapping->private_data;
 577
 578        if (buffer_mapping == NULL || list_empty(&mapping->private_list))
 579                return 0;
 580
 581        return fsync_buffers_list(&buffer_mapping->private_lock,
 582                                        &mapping->private_list);
 583}
 584EXPORT_SYMBOL(sync_mapping_buffers);
 585
 586/*
 587 * Called when we've recently written block `bblock', and it is known that
 588 * `bblock' was for a buffer_boundary() buffer.  This means that the block at
 589 * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
 590 * dirty, schedule it for IO.  So that indirects merge nicely with their data.
 591 */
 592void write_boundary_block(struct block_device *bdev,
 593                        sector_t bblock, unsigned blocksize)
 594{
 595        struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
 596        if (bh) {
 597                if (buffer_dirty(bh))
 598                        ll_rw_block(WRITE, 1, &bh);
 599                put_bh(bh);
 600        }
 601}
 602
 603void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
 604{
 605        struct address_space *mapping = inode->i_mapping;
 606        struct address_space *buffer_mapping = bh->b_page->mapping;
 607
 608        mark_buffer_dirty(bh);
 609        if (!mapping->private_data) {
 610                mapping->private_data = buffer_mapping;
 611        } else {
 612                BUG_ON(mapping->private_data != buffer_mapping);
 613        }
 614        if (!bh->b_assoc_map) {
 615                spin_lock(&buffer_mapping->private_lock);
 616                list_move_tail(&bh->b_assoc_buffers,
 617                                &mapping->private_list);
 618                bh->b_assoc_map = mapping;
 619                spin_unlock(&buffer_mapping->private_lock);
 620        }
 621}
 622EXPORT_SYMBOL(mark_buffer_dirty_inode);
 623
 624/*
 625 * Mark the page dirty, and set it dirty in the radix tree, and mark the inode
 626 * dirty.
 627 *
 628 * If warn is true, then emit a warning if the page is not uptodate and has
 629 * not been truncated.
 630 *
 631 * The caller must hold mem_cgroup_begin_page_stat() lock.
 632 */
 633static void __set_page_dirty(struct page *page, struct address_space *mapping,
 634                             struct mem_cgroup *memcg, int warn)
 635{
 636        unsigned long flags;
 637
 638        spin_lock_irqsave(&mapping->tree_lock, flags);
 639        if (page->mapping) {    /* Race with truncate? */
 640                WARN_ON_ONCE(warn && !PageUptodate(page));
 641                account_page_dirtied(page, mapping, memcg);
 642                radix_tree_tag_set(&mapping->page_tree,
 643                                page_index(page), PAGECACHE_TAG_DIRTY);
 644        }
 645        spin_unlock_irqrestore(&mapping->tree_lock, flags);
 646}
 647
 648/*
 649 * Add a page to the dirty page list.
 650 *
 651 * It is a sad fact of life that this function is called from several places
 652 * deeply under spinlocking.  It may not sleep.
 653 *
 654 * If the page has buffers, the uptodate buffers are set dirty, to preserve
 655 * dirty-state coherency between the page and the buffers.  It the page does
 656 * not have buffers then when they are later attached they will all be set
 657 * dirty.
 658 *
 659 * The buffers are dirtied before the page is dirtied.  There's a small race
 660 * window in which a writepage caller may see the page cleanness but not the
 661 * buffer dirtiness.  That's fine.  If this code were to set the page dirty
 662 * before the buffers, a concurrent writepage caller could clear the page dirty
 663 * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
 664 * page on the dirty page list.
 665 *
 666 * We use private_lock to lock against try_to_free_buffers while using the
 667 * page's buffer list.  Also use this to protect against clean buffers being
 668 * added to the page after it was set dirty.
 669 *
 670 * FIXME: may need to call ->reservepage here as well.  That's rather up to the
 671 * address_space though.
 672 */
 673int __set_page_dirty_buffers(struct page *page)
 674{
 675        int newly_dirty;
 676        struct mem_cgroup *memcg;
 677        struct address_space *mapping = page_mapping(page);
 678
 679        if (unlikely(!mapping))
 680                return !TestSetPageDirty(page);
 681
 682        spin_lock(&mapping->private_lock);
 683        if (page_has_buffers(page)) {
 684                struct buffer_head *head = page_buffers(page);
 685                struct buffer_head *bh = head;
 686
 687                do {
 688                        set_buffer_dirty(bh);
 689                        bh = bh->b_this_page;
 690                } while (bh != head);
 691        }
 692        /*
 693         * Use mem_group_begin_page_stat() to keep PageDirty synchronized with
 694         * per-memcg dirty page counters.
 695         */
 696        memcg = mem_cgroup_begin_page_stat(page);
 697        newly_dirty = !TestSetPageDirty(page);
 698        spin_unlock(&mapping->private_lock);
 699
 700        if (newly_dirty)
 701                __set_page_dirty(page, mapping, memcg, 1);
 702
 703        mem_cgroup_end_page_stat(memcg);
 704
 705        if (newly_dirty)
 706                __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 707
 708        return newly_dirty;
 709}
 710EXPORT_SYMBOL(__set_page_dirty_buffers);
 711
 712/*
 713 * Write out and wait upon a list of buffers.
 714 *
 715 * We have conflicting pressures: we want to make sure that all
 716 * initially dirty buffers get waited on, but that any subsequently
 717 * dirtied buffers don't.  After all, we don't want fsync to last
 718 * forever if somebody is actively writing to the file.
 719 *
 720 * Do this in two main stages: first we copy dirty buffers to a
 721 * temporary inode list, queueing the writes as we go.  Then we clean
 722 * up, waiting for those writes to complete.
 723 * 
 724 * During this second stage, any subsequent updates to the file may end
 725 * up refiling the buffer on the original inode's dirty list again, so
 726 * there is a chance we will end up with a buffer queued for write but
 727 * not yet completed on that list.  So, as a final cleanup we go through
 728 * the osync code to catch these locked, dirty buffers without requeuing
 729 * any newly dirty buffers for write.
 730 */
 731static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
 732{
 733        struct buffer_head *bh;
 734        struct list_head tmp;
 735        struct address_space *mapping;
 736        int err = 0, err2;
 737        struct blk_plug plug;
 738
 739        INIT_LIST_HEAD(&tmp);
 740        blk_start_plug(&plug);
 741
 742        spin_lock(lock);
 743        while (!list_empty(list)) {
 744                bh = BH_ENTRY(list->next);
 745                mapping = bh->b_assoc_map;
 746                __remove_assoc_queue(bh);
 747                /* Avoid race with mark_buffer_dirty_inode() which does
 748                 * a lockless check and we rely on seeing the dirty bit */
 749                smp_mb();
 750                if (buffer_dirty(bh) || buffer_locked(bh)) {
 751                        list_add(&bh->b_assoc_buffers, &tmp);
 752                        bh->b_assoc_map = mapping;
 753                        if (buffer_dirty(bh)) {
 754                                get_bh(bh);
 755                                spin_unlock(lock);
 756                                /*
 757                                 * Ensure any pending I/O completes so that
 758                                 * write_dirty_buffer() actually writes the
 759                                 * current contents - it is a noop if I/O is
 760                                 * still in flight on potentially older
 761                                 * contents.
 762                                 */
 763                                write_dirty_buffer(bh, WRITE_SYNC);
 764
 765                                /*
 766                                 * Kick off IO for the previous mapping. Note
 767                                 * that we will not run the very last mapping,
 768                                 * wait_on_buffer() will do that for us
 769                                 * through sync_buffer().
 770                                 */
 771                                brelse(bh);
 772                                spin_lock(lock);
 773                        }
 774                }
 775        }
 776
 777        spin_unlock(lock);
 778        blk_finish_plug(&plug);
 779        spin_lock(lock);
 780
 781        while (!list_empty(&tmp)) {
 782                bh = BH_ENTRY(tmp.prev);
 783                get_bh(bh);
 784                mapping = bh->b_assoc_map;
 785                __remove_assoc_queue(bh);
 786                /* Avoid race with mark_buffer_dirty_inode() which does
 787                 * a lockless check and we rely on seeing the dirty bit */
 788                smp_mb();
 789                if (buffer_dirty(bh)) {
 790                        list_add(&bh->b_assoc_buffers,
 791                                 &mapping->private_list);
 792                        bh->b_assoc_map = mapping;
 793                }
 794                spin_unlock(lock);
 795                wait_on_buffer(bh);
 796                if (!buffer_uptodate(bh))
 797                        err = -EIO;
 798                brelse(bh);
 799                spin_lock(lock);
 800        }
 801        
 802        spin_unlock(lock);
 803        err2 = osync_buffers_list(lock, list);
 804        if (err)
 805                return err;
 806        else
 807                return err2;
 808}
 809
 810/*
 811 * Invalidate any and all dirty buffers on a given inode.  We are
 812 * probably unmounting the fs, but that doesn't mean we have already
 813 * done a sync().  Just drop the buffers from the inode list.
 814 *
 815 * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
 816 * assumes that all the buffers are against the blockdev.  Not true
 817 * for reiserfs.
 818 */
 819void invalidate_inode_buffers(struct inode *inode)
 820{
 821        if (inode_has_buffers(inode)) {
 822                struct address_space *mapping = &inode->i_data;
 823                struct list_head *list = &mapping->private_list;
 824                struct address_space *buffer_mapping = mapping->private_data;
 825
 826                spin_lock(&buffer_mapping->private_lock);
 827                while (!list_empty(list))
 828                        __remove_assoc_queue(BH_ENTRY(list->next));
 829                spin_unlock(&buffer_mapping->private_lock);
 830        }
 831}
 832EXPORT_SYMBOL(invalidate_inode_buffers);
 833
 834/*
 835 * Remove any clean buffers from the inode's buffer list.  This is called
 836 * when we're trying to free the inode itself.  Those buffers can pin it.
 837 *
 838 * Returns true if all buffers were removed.
 839 */
 840int remove_inode_buffers(struct inode *inode)
 841{
 842        int ret = 1;
 843
 844        if (inode_has_buffers(inode)) {
 845                struct address_space *mapping = &inode->i_data;
 846                struct list_head *list = &mapping->private_list;
 847                struct address_space *buffer_mapping = mapping->private_data;
 848
 849                spin_lock(&buffer_mapping->private_lock);
 850                while (!list_empty(list)) {
 851                        struct buffer_head *bh = BH_ENTRY(list->next);
 852                        if (buffer_dirty(bh)) {
 853                                ret = 0;
 854                                break;
 855                        }
 856                        __remove_assoc_queue(bh);
 857                }
 858                spin_unlock(&buffer_mapping->private_lock);
 859        }
 860        return ret;
 861}
 862
 863/*
 864 * Create the appropriate buffers when given a page for data area and
 865 * the size of each buffer.. Use the bh->b_this_page linked list to
 866 * follow the buffers created.  Return NULL if unable to create more
 867 * buffers.
 868 *
 869 * The retry flag is used to differentiate async IO (paging, swapping)
 870 * which may not fail from ordinary buffer allocations.
 871 */
 872struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
 873                int retry)
 874{
 875        struct buffer_head *bh, *head;
 876        long offset;
 877
 878try_again:
 879        head = NULL;
 880        offset = PAGE_SIZE;
 881        while ((offset -= size) >= 0) {
 882                bh = alloc_buffer_head(GFP_NOFS);
 883                if (!bh)
 884                        goto no_grow;
 885
 886                bh->b_this_page = head;
 887                bh->b_blocknr = -1;
 888                head = bh;
 889
 890                bh->b_size = size;
 891
 892                /* Link the buffer to its page */
 893                set_bh_page(bh, page, offset);
 894        }
 895        return head;
 896/*
 897 * In case anything failed, we just free everything we got.
 898 */
 899no_grow:
 900        if (head) {
 901                do {
 902                        bh = head;
 903                        head = head->b_this_page;
 904                        free_buffer_head(bh);
 905                } while (head);
 906        }
 907
 908        /*
 909         * Return failure for non-async IO requests.  Async IO requests
 910         * are not allowed to fail, so we have to wait until buffer heads
 911         * become available.  But we don't want tasks sleeping with 
 912         * partially complete buffers, so all were released above.
 913         */
 914        if (!retry)
 915                return NULL;
 916
 917        /* We're _really_ low on memory. Now we just
 918         * wait for old buffer heads to become free due to
 919         * finishing IO.  Since this is an async request and
 920         * the reserve list is empty, we're sure there are 
 921         * async buffer heads in use.
 922         */
 923        free_more_memory();
 924        goto try_again;
 925}
 926EXPORT_SYMBOL_GPL(alloc_page_buffers);
 927
 928static inline void
 929link_dev_buffers(struct page *page, struct buffer_head *head)
 930{
 931        struct buffer_head *bh, *tail;
 932
 933        bh = head;
 934        do {
 935                tail = bh;
 936                bh = bh->b_this_page;
 937        } while (bh);
 938        tail->b_this_page = head;
 939        attach_page_buffers(page, head);
 940}
 941
 942static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
 943{
 944        sector_t retval = ~((sector_t)0);
 945        loff_t sz = i_size_read(bdev->bd_inode);
 946
 947        if (sz) {
 948                unsigned int sizebits = blksize_bits(size);
 949                retval = (sz >> sizebits);
 950        }
 951        return retval;
 952}
 953
 954/*
 955 * Initialise the state of a blockdev page's buffers.
 956 */ 
 957static sector_t
 958init_page_buffers(struct page *page, struct block_device *bdev,
 959                        sector_t block, int size)
 960{
 961        struct buffer_head *head = page_buffers(page);
 962        struct buffer_head *bh = head;
 963        int uptodate = PageUptodate(page);
 964        sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
 965
 966        do {
 967                if (!buffer_mapped(bh)) {
 968                        init_buffer(bh, NULL, NULL);
 969                        bh->b_bdev = bdev;
 970                        bh->b_blocknr = block;
 971                        if (uptodate)
 972                                set_buffer_uptodate(bh);
 973                        if (block < end_block)
 974                                set_buffer_mapped(bh);
 975                }
 976                block++;
 977                bh = bh->b_this_page;
 978        } while (bh != head);
 979
 980        /*
 981         * Caller needs to validate requested block against end of device.
 982         */
 983        return end_block;
 984}
 985
 986/*
 987 * Create the page-cache page that contains the requested block.
 988 *
 989 * This is used purely for blockdev mappings.
 990 */
 991static int
 992grow_dev_page(struct block_device *bdev, sector_t block,
 993              pgoff_t index, int size, int sizebits, gfp_t gfp)
 994{
 995        struct inode *inode = bdev->bd_inode;
 996        struct page *page;
 997        struct buffer_head *bh;
 998        sector_t end_block;
 999        int ret = 0;            /* Will call free_more_memory() */
1000        gfp_t gfp_mask;
1001
1002        gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) | gfp;
1003
1004        /*
1005         * XXX: __getblk_slow() can not really deal with failure and
1006         * will endlessly loop on improvised global reclaim.  Prefer
1007         * looping in the allocator rather than here, at least that
1008         * code knows what it's doing.
1009         */
1010        gfp_mask |= __GFP_NOFAIL;
1011
1012        page = find_or_create_page(inode->i_mapping, index, gfp_mask);
1013        if (!page)
1014                return ret;
1015
1016        BUG_ON(!PageLocked(page));
1017
1018        if (page_has_buffers(page)) {
1019                bh = page_buffers(page);
1020                if (bh->b_size == size) {
1021                        end_block = init_page_buffers(page, bdev,
1022                                                (sector_t)index << sizebits,
1023                                                size);
1024                        goto done;
1025                }
1026                if (!try_to_free_buffers(page))
1027                        goto failed;
1028        }
1029
1030        /*
1031         * Allocate some buffers for this page
1032         */
1033        bh = alloc_page_buffers(page, size, 0);
1034        if (!bh)
1035                goto failed;
1036
1037        /*
1038         * Link the page to the buffers and initialise them.  Take the
1039         * lock to be atomic wrt __find_get_block(), which does not
1040         * run under the page lock.
1041         */
1042        spin_lock(&inode->i_mapping->private_lock);
1043        link_dev_buffers(page, bh);
1044        end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
1045                        size);
1046        spin_unlock(&inode->i_mapping->private_lock);
1047done:
1048        ret = (block < end_block) ? 1 : -ENXIO;
1049failed:
1050        unlock_page(page);
1051        page_cache_release(page);
1052        return ret;
1053}
1054
1055/*
1056 * Create buffers for the specified block device block's page.  If
1057 * that page was dirty, the buffers are set dirty also.
1058 */
1059static int
1060grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
1061{
1062        pgoff_t index;
1063        int sizebits;
1064
1065        sizebits = -1;
1066        do {
1067                sizebits++;
1068        } while ((size << sizebits) < PAGE_SIZE);
1069
1070        index = block >> sizebits;
1071
1072        /*
1073         * Check for a block which wants to lie outside our maximum possible
1074         * pagecache index.  (this comparison is done using sector_t types).
1075         */
1076        if (unlikely(index != block >> sizebits)) {
1077                char b[BDEVNAME_SIZE];
1078
1079                printk(KERN_ERR "%s: requested out-of-range block %llu for "
1080                        "device %s\n",
1081                        __func__, (unsigned long long)block,
1082                        bdevname(bdev, b));
1083                return -EIO;
1084        }
1085
1086        /* Create a page with the proper size buffers.. */
1087        return grow_dev_page(bdev, block, index, size, sizebits, gfp);
1088}
1089
1090struct buffer_head *
1091__getblk_slow(struct block_device *bdev, sector_t block,
1092             unsigned size, gfp_t gfp)
1093{
1094        /* Size must be multiple of hard sectorsize */
1095        if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
1096                        (size < 512 || size > PAGE_SIZE))) {
1097                printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1098                                        size);
1099                printk(KERN_ERR "logical block size: %d\n",
1100                                        bdev_logical_block_size(bdev));
1101
1102                dump_stack();
1103                return NULL;
1104        }
1105
1106        for (;;) {
1107                struct buffer_head *bh;
1108                int ret;
1109
1110                bh = __find_get_block(bdev, block, size);
1111                if (bh)
1112                        return bh;
1113
1114                ret = grow_buffers(bdev, block, size, gfp);
1115                if (ret < 0)
1116                        return NULL;
1117                if (ret == 0)
1118                        free_more_memory();
1119        }
1120}
1121EXPORT_SYMBOL(__getblk_slow);
1122
1123/*
1124 * The relationship between dirty buffers and dirty pages:
1125 *
1126 * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1127 * the page is tagged dirty in its radix tree.
1128 *
1129 * At all times, the dirtiness of the buffers represents the dirtiness of
1130 * subsections of the page.  If the page has buffers, the page dirty bit is
1131 * merely a hint about the true dirty state.
1132 *
1133 * When a page is set dirty in its entirety, all its buffers are marked dirty
1134 * (if the page has buffers).
1135 *
1136 * When a buffer is marked dirty, its page is dirtied, but the page's other
1137 * buffers are not.
1138 *
1139 * Also.  When blockdev buffers are explicitly read with bread(), they
1140 * individually become uptodate.  But their backing page remains not
1141 * uptodate - even if all of its buffers are uptodate.  A subsequent
1142 * block_read_full_page() against that page will discover all the uptodate
1143 * buffers, will set the page uptodate and will perform no I/O.
1144 */
1145
1146/**
1147 * mark_buffer_dirty - mark a buffer_head as needing writeout
1148 * @bh: the buffer_head to mark dirty
1149 *
1150 * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1151 * backing page dirty, then tag the page as dirty in its address_space's radix
1152 * tree and then attach the address_space's inode to its superblock's dirty
1153 * inode list.
1154 *
1155 * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1156 * mapping->tree_lock and mapping->host->i_lock.
1157 */
1158void mark_buffer_dirty(struct buffer_head *bh)
1159{
1160        WARN_ON_ONCE(!buffer_uptodate(bh));
1161
1162        trace_block_dirty_buffer(bh);
1163
1164        /*
1165         * Very *carefully* optimize the it-is-already-dirty case.
1166         *
1167         * Don't let the final "is it dirty" escape to before we
1168         * perhaps modified the buffer.
1169         */
1170        if (buffer_dirty(bh)) {
1171                smp_mb();
1172                if (buffer_dirty(bh))
1173                        return;
1174        }
1175
1176        if (!test_set_buffer_dirty(bh)) {
1177                struct page *page = bh->b_page;
1178                struct address_space *mapping = NULL;
1179                struct mem_cgroup *memcg;
1180
1181                memcg = mem_cgroup_begin_page_stat(page);
1182                if (!TestSetPageDirty(page)) {
1183                        mapping = page_mapping(page);
1184                        if (mapping)
1185                                __set_page_dirty(page, mapping, memcg, 0);
1186                }
1187                mem_cgroup_end_page_stat(memcg);
1188                if (mapping)
1189                        __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1190        }
1191}
1192EXPORT_SYMBOL(mark_buffer_dirty);
1193
1194/*
1195 * Decrement a buffer_head's reference count.  If all buffers against a page
1196 * have zero reference count, are clean and unlocked, and if the page is clean
1197 * and unlocked then try_to_free_buffers() may strip the buffers from the page
1198 * in preparation for freeing it (sometimes, rarely, buffers are removed from
1199 * a page but it ends up not being freed, and buffers may later be reattached).
1200 */
1201void __brelse(struct buffer_head * buf)
1202{
1203        if (atomic_read(&buf->b_count)) {
1204                put_bh(buf);
1205                return;
1206        }
1207        WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1208}
1209EXPORT_SYMBOL(__brelse);
1210
1211/*
1212 * bforget() is like brelse(), except it discards any
1213 * potentially dirty data.
1214 */
1215void __bforget(struct buffer_head *bh)
1216{
1217        clear_buffer_dirty(bh);
1218        if (bh->b_assoc_map) {
1219                struct address_space *buffer_mapping = bh->b_page->mapping;
1220
1221                spin_lock(&buffer_mapping->private_lock);
1222                list_del_init(&bh->b_assoc_buffers);
1223                bh->b_assoc_map = NULL;
1224                spin_unlock(&buffer_mapping->private_lock);
1225        }
1226        __brelse(bh);
1227}
1228EXPORT_SYMBOL(__bforget);
1229
1230static struct buffer_head *__bread_slow(struct buffer_head *bh)
1231{
1232        lock_buffer(bh);
1233        if (buffer_uptodate(bh)) {
1234                unlock_buffer(bh);
1235                return bh;
1236        } else {
1237                get_bh(bh);
1238                bh->b_end_io = end_buffer_read_sync;
1239                submit_bh(READ, bh);
1240                wait_on_buffer(bh);
1241                if (buffer_uptodate(bh))
1242                        return bh;
1243        }
1244        brelse(bh);
1245        return NULL;
1246}
1247
1248/*
1249 * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1250 * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1251 * refcount elevated by one when they're in an LRU.  A buffer can only appear
1252 * once in a particular CPU's LRU.  A single buffer can be present in multiple
1253 * CPU's LRUs at the same time.
1254 *
1255 * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1256 * sb_find_get_block().
1257 *
1258 * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1259 * a local interrupt disable for that.
1260 */
1261
1262#define BH_LRU_SIZE     16
1263
1264struct bh_lru {
1265        struct buffer_head *bhs[BH_LRU_SIZE];
1266};
1267
1268static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1269
1270#ifdef CONFIG_SMP
1271#define bh_lru_lock()   local_irq_disable()
1272#define bh_lru_unlock() local_irq_enable()
1273#else
1274#define bh_lru_lock()   preempt_disable()
1275#define bh_lru_unlock() preempt_enable()
1276#endif
1277
1278static inline void check_irqs_on(void)
1279{
1280#ifdef irqs_disabled
1281        BUG_ON(irqs_disabled());
1282#endif
1283}
1284
1285/*
1286 * The LRU management algorithm is dopey-but-simple.  Sorry.
1287 */
1288static void bh_lru_install(struct buffer_head *bh)
1289{
1290        struct buffer_head *evictee = NULL;
1291
1292        check_irqs_on();
1293        bh_lru_lock();
1294        if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
1295                struct buffer_head *bhs[BH_LRU_SIZE];
1296                int in;
1297                int out = 0;
1298
1299                get_bh(bh);
1300                bhs[out++] = bh;
1301                for (in = 0; in < BH_LRU_SIZE; in++) {
1302                        struct buffer_head *bh2 =
1303                                __this_cpu_read(bh_lrus.bhs[in]);
1304
1305                        if (bh2 == bh) {
1306                                __brelse(bh2);
1307                        } else {
1308                                if (out >= BH_LRU_SIZE) {
1309                                        BUG_ON(evictee != NULL);
1310                                        evictee = bh2;
1311                                } else {
1312                                        bhs[out++] = bh2;
1313                                }
1314                        }
1315                }
1316                while (out < BH_LRU_SIZE)
1317                        bhs[out++] = NULL;
1318                memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
1319        }
1320        bh_lru_unlock();
1321
1322        if (evictee)
1323                __brelse(evictee);
1324}
1325
1326/*
1327 * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1328 */
1329static struct buffer_head *
1330lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1331{
1332        struct buffer_head *ret = NULL;
1333        unsigned int i;
1334
1335        check_irqs_on();
1336        bh_lru_lock();
1337        for (i = 0; i < BH_LRU_SIZE; i++) {
1338                struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1339
1340                if (bh && bh->b_blocknr == block && bh->b_bdev == bdev &&
1341                    bh->b_size == size) {
1342                        if (i) {
1343                                while (i) {
1344                                        __this_cpu_write(bh_lrus.bhs[i],
1345                                                __this_cpu_read(bh_lrus.bhs[i - 1]));
1346                                        i--;
1347                                }
1348                                __this_cpu_write(bh_lrus.bhs[0], bh);
1349                        }
1350                        get_bh(bh);
1351                        ret = bh;
1352                        break;
1353                }
1354        }
1355        bh_lru_unlock();
1356        return ret;
1357}
1358
1359/*
1360 * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1361 * it in the LRU and mark it as accessed.  If it is not present then return
1362 * NULL
1363 */
1364struct buffer_head *
1365__find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1366{
1367        struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1368
1369        if (bh == NULL) {
1370                /* __find_get_block_slow will mark the page accessed */
1371                bh = __find_get_block_slow(bdev, block);
1372                if (bh)
1373                        bh_lru_install(bh);
1374        } else
1375                touch_buffer(bh);
1376
1377        return bh;
1378}
1379EXPORT_SYMBOL(__find_get_block);
1380
1381/*
1382 * __getblk_gfp() will locate (and, if necessary, create) the buffer_head
1383 * which corresponds to the passed block_device, block and size. The
1384 * returned buffer has its reference count incremented.
1385 *
1386 * __getblk_gfp() will lock up the machine if grow_dev_page's
1387 * try_to_free_buffers() attempt is failing.  FIXME, perhaps?
1388 */
1389struct buffer_head *
1390__getblk_gfp(struct block_device *bdev, sector_t block,
1391             unsigned size, gfp_t gfp)
1392{
1393        struct buffer_head *bh = __find_get_block(bdev, block, size);
1394
1395        might_sleep();
1396        if (bh == NULL)
1397                bh = __getblk_slow(bdev, block, size, gfp);
1398        return bh;
1399}
1400EXPORT_SYMBOL(__getblk_gfp);
1401
1402/*
1403 * Do async read-ahead on a buffer..
1404 */
1405void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1406{
1407        struct buffer_head *bh = __getblk(bdev, block, size);
1408        if (likely(bh)) {
1409                ll_rw_block(READA, 1, &bh);
1410                brelse(bh);
1411        }
1412}
1413EXPORT_SYMBOL(__breadahead);
1414
1415/**
1416 *  __bread_gfp() - reads a specified block and returns the bh
1417 *  @bdev: the block_device to read from
1418 *  @block: number of block
1419 *  @size: size (in bytes) to read
1420 *  @gfp: page allocation flag
1421 *
1422 *  Reads a specified block, and returns buffer head that contains it.
1423 *  The page cache can be allocated from non-movable area
1424 *  not to prevent page migration if you set gfp to zero.
1425 *  It returns NULL if the block was unreadable.
1426 */
1427struct buffer_head *
1428__bread_gfp(struct block_device *bdev, sector_t block,
1429                   unsigned size, gfp_t gfp)
1430{
1431        struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
1432
1433        if (likely(bh) && !buffer_uptodate(bh))
1434                bh = __bread_slow(bh);
1435        return bh;
1436}
1437EXPORT_SYMBOL(__bread_gfp);
1438
1439/*
1440 * invalidate_bh_lrus() is called rarely - but not only at unmount.
1441 * This doesn't race because it runs in each cpu either in irq
1442 * or with preempt disabled.
1443 */
1444static void invalidate_bh_lru(void *arg)
1445{
1446        struct bh_lru *b = &get_cpu_var(bh_lrus);
1447        int i;
1448
1449        for (i = 0; i < BH_LRU_SIZE; i++) {
1450                brelse(b->bhs[i]);
1451                b->bhs[i] = NULL;
1452        }
1453        put_cpu_var(bh_lrus);
1454}
1455
1456static bool has_bh_in_lru(int cpu, void *dummy)
1457{
1458        struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1459        int i;
1460        
1461        for (i = 0; i < BH_LRU_SIZE; i++) {
1462                if (b->bhs[i])
1463                        return 1;
1464        }
1465
1466        return 0;
1467}
1468
1469void invalidate_bh_lrus(void)
1470{
1471        on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1472}
1473EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1474
1475void set_bh_page(struct buffer_head *bh,
1476                struct page *page, unsigned long offset)
1477{
1478        bh->b_page = page;
1479        BUG_ON(offset >= PAGE_SIZE);
1480        if (PageHighMem(page))
1481                /*
1482                 * This catches illegal uses and preserves the offset:
1483                 */
1484                bh->b_data = (char *)(0 + offset);
1485        else
1486                bh->b_data = page_address(page) + offset;
1487}
1488EXPORT_SYMBOL(set_bh_page);
1489
1490/*
1491 * Called when truncating a buffer on a page completely.
1492 */
1493
1494/* Bits that are cleared during an invalidate */
1495#define BUFFER_FLAGS_DISCARD \
1496        (1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
1497         1 << BH_Delay | 1 << BH_Unwritten)
1498
1499static void discard_buffer(struct buffer_head * bh)
1500{
1501        unsigned long b_state, b_state_old;
1502
1503        lock_buffer(bh);
1504        clear_buffer_dirty(bh);
1505        bh->b_bdev = NULL;
1506        b_state = bh->b_state;
1507        for (;;) {
1508                b_state_old = cmpxchg(&bh->b_state, b_state,
1509                                      (b_state & ~BUFFER_FLAGS_DISCARD));
1510                if (b_state_old == b_state)
1511                        break;
1512                b_state = b_state_old;
1513        }
1514        unlock_buffer(bh);
1515}
1516
1517/**
1518 * block_invalidatepage - invalidate part or all of a buffer-backed page
1519 *
1520 * @page: the page which is affected
1521 * @offset: start of the range to invalidate
1522 * @length: length of the range to invalidate
1523 *
1524 * block_invalidatepage() is called when all or part of the page has become
1525 * invalidated by a truncate operation.
1526 *
1527 * block_invalidatepage() does not have to release all buffers, but it must
1528 * ensure that no dirty buffer is left outside @offset and that no I/O
1529 * is underway against any of the blocks which are outside the truncation
1530 * point.  Because the caller is about to free (and possibly reuse) those
1531 * blocks on-disk.
1532 */
1533void block_invalidatepage(struct page *page, unsigned int offset,
1534                          unsigned int length)
1535{
1536        struct buffer_head *head, *bh, *next;
1537        unsigned int curr_off = 0;
1538        unsigned int stop = length + offset;
1539
1540        BUG_ON(!PageLocked(page));
1541        if (!page_has_buffers(page))
1542                goto out;
1543
1544        /*
1545         * Check for overflow
1546         */
1547        BUG_ON(stop > PAGE_CACHE_SIZE || stop < length);
1548
1549        head = page_buffers(page);
1550        bh = head;
1551        do {
1552                unsigned int next_off = curr_off + bh->b_size;
1553                next = bh->b_this_page;
1554
1555                /*
1556                 * Are we still fully in range ?
1557                 */
1558                if (next_off > stop)
1559                        goto out;
1560
1561                /*
1562                 * is this block fully invalidated?
1563                 */
1564                if (offset <= curr_off)
1565                        discard_buffer(bh);
1566                curr_off = next_off;
1567                bh = next;
1568        } while (bh != head);
1569
1570        /*
1571         * We release buffers only if the entire page is being invalidated.
1572         * The get_block cached value has been unconditionally invalidated,
1573         * so real IO is not possible anymore.
1574         */
1575        if (offset == 0)
1576                try_to_release_page(page, 0);
1577out:
1578        return;
1579}
1580EXPORT_SYMBOL(block_invalidatepage);
1581
1582
1583/*
1584 * We attach and possibly dirty the buffers atomically wrt
1585 * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1586 * is already excluded via the page lock.
1587 */
1588void create_empty_buffers(struct page *page,
1589                        unsigned long blocksize, unsigned long b_state)
1590{
1591        struct buffer_head *bh, *head, *tail;
1592
1593        head = alloc_page_buffers(page, blocksize, 1);
1594        bh = head;
1595        do {
1596                bh->b_state |= b_state;
1597                tail = bh;
1598                bh = bh->b_this_page;
1599        } while (bh);
1600        tail->b_this_page = head;
1601
1602        spin_lock(&page->mapping->private_lock);
1603        if (PageUptodate(page) || PageDirty(page)) {
1604                bh = head;
1605                do {
1606                        if (PageDirty(page))
1607                                set_buffer_dirty(bh);
1608                        if (PageUptodate(page))
1609                                set_buffer_uptodate(bh);
1610                        bh = bh->b_this_page;
1611                } while (bh != head);
1612        }
1613        attach_page_buffers(page, head);
1614        spin_unlock(&page->mapping->private_lock);
1615}
1616EXPORT_SYMBOL(create_empty_buffers);
1617
1618/*
1619 * We are taking a block for data and we don't want any output from any
1620 * buffer-cache aliases starting from return from that function and
1621 * until the moment when something will explicitly mark the buffer
1622 * dirty (hopefully that will not happen until we will free that block ;-)
1623 * We don't even need to mark it not-uptodate - nobody can expect
1624 * anything from a newly allocated buffer anyway. We used to used
1625 * unmap_buffer() for such invalidation, but that was wrong. We definitely
1626 * don't want to mark the alias unmapped, for example - it would confuse
1627 * anyone who might pick it with bread() afterwards...
1628 *
1629 * Also..  Note that bforget() doesn't lock the buffer.  So there can
1630 * be writeout I/O going on against recently-freed buffers.  We don't
1631 * wait on that I/O in bforget() - it's more efficient to wait on the I/O
1632 * only if we really need to.  That happens here.
1633 */
1634void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1635{
1636        struct buffer_head *old_bh;
1637
1638        might_sleep();
1639
1640        old_bh = __find_get_block_slow(bdev, block);
1641        if (old_bh) {
1642                clear_buffer_dirty(old_bh);
1643                wait_on_buffer(old_bh);
1644                clear_buffer_req(old_bh);
1645                __brelse(old_bh);
1646        }
1647}
1648EXPORT_SYMBOL(unmap_underlying_metadata);
1649
1650/*
1651 * Size is a power-of-two in the range 512..PAGE_SIZE,
1652 * and the case we care about most is PAGE_SIZE.
1653 *
1654 * So this *could* possibly be written with those
1655 * constraints in mind (relevant mostly if some
1656 * architecture has a slow bit-scan instruction)
1657 */
1658static inline int block_size_bits(unsigned int blocksize)
1659{
1660        return ilog2(blocksize);
1661}
1662
1663static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
1664{
1665        BUG_ON(!PageLocked(page));
1666
1667        if (!page_has_buffers(page))
1668                create_empty_buffers(page, 1 << ACCESS_ONCE(inode->i_blkbits), b_state);
1669        return page_buffers(page);
1670}
1671
1672/*
1673 * NOTE! All mapped/uptodate combinations are valid:
1674 *
1675 *      Mapped  Uptodate        Meaning
1676 *
1677 *      No      No              "unknown" - must do get_block()
1678 *      No      Yes             "hole" - zero-filled
1679 *      Yes     No              "allocated" - allocated on disk, not read in
1680 *      Yes     Yes             "valid" - allocated and up-to-date in memory.
1681 *
1682 * "Dirty" is valid only with the last case (mapped+uptodate).
1683 */
1684
1685/*
1686 * While block_write_full_page is writing back the dirty buffers under
1687 * the page lock, whoever dirtied the buffers may decide to clean them
1688 * again at any time.  We handle that by only looking at the buffer
1689 * state inside lock_buffer().
1690 *
1691 * If block_write_full_page() is called for regular writeback
1692 * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1693 * locked buffer.   This only can happen if someone has written the buffer
1694 * directly, with submit_bh().  At the address_space level PageWriteback
1695 * prevents this contention from occurring.
1696 *
1697 * If block_write_full_page() is called with wbc->sync_mode ==
1698 * WB_SYNC_ALL, the writes are posted using WRITE_SYNC; this
1699 * causes the writes to be flagged as synchronous writes.
1700 */
1701static int __block_write_full_page(struct inode *inode, struct page *page,
1702                        get_block_t *get_block, struct writeback_control *wbc,
1703                        bh_end_io_t *handler)
1704{
1705        int err;
1706        sector_t block;
1707        sector_t last_block;
1708        struct buffer_head *bh, *head;
1709        unsigned int blocksize, bbits;
1710        int nr_underway = 0;
1711        int write_op = (wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE);
1712
1713        head = create_page_buffers(page, inode,
1714                                        (1 << BH_Dirty)|(1 << BH_Uptodate));
1715
1716        /*
1717         * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1718         * here, and the (potentially unmapped) buffers may become dirty at
1719         * any time.  If a buffer becomes dirty here after we've inspected it
1720         * then we just miss that fact, and the page stays dirty.
1721         *
1722         * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1723         * handle that here by just cleaning them.
1724         */
1725
1726        bh = head;
1727        blocksize = bh->b_size;
1728        bbits = block_size_bits(blocksize);
1729
1730        block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1731        last_block = (i_size_read(inode) - 1) >> bbits;
1732
1733        /*
1734         * Get all the dirty buffers mapped to disk addresses and
1735         * handle any aliases from the underlying blockdev's mapping.
1736         */
1737        do {
1738                if (block > last_block) {
1739                        /*
1740                         * mapped buffers outside i_size will occur, because
1741                         * this page can be outside i_size when there is a
1742                         * truncate in progress.
1743                         */
1744                        /*
1745                         * The buffer was zeroed by block_write_full_page()
1746                         */
1747                        clear_buffer_dirty(bh);
1748                        set_buffer_uptodate(bh);
1749                } else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1750                           buffer_dirty(bh)) {
1751                        WARN_ON(bh->b_size != blocksize);
1752                        err = get_block(inode, block, bh, 1);
1753                        if (err)
1754                                goto recover;
1755                        clear_buffer_delay(bh);
1756                        if (buffer_new(bh)) {
1757                                /* blockdev mappings never come here */
1758                                clear_buffer_new(bh);
1759                                unmap_underlying_metadata(bh->b_bdev,
1760                                                        bh->b_blocknr);
1761                        }
1762                }
1763                bh = bh->b_this_page;
1764                block++;
1765        } while (bh != head);
1766
1767        do {
1768                if (!buffer_mapped(bh))
1769                        continue;
1770                /*
1771                 * If it's a fully non-blocking write attempt and we cannot
1772                 * lock the buffer then redirty the page.  Note that this can
1773                 * potentially cause a busy-wait loop from writeback threads
1774                 * and kswapd activity, but those code paths have their own
1775                 * higher-level throttling.
1776                 */
1777                if (wbc->sync_mode != WB_SYNC_NONE) {
1778                        lock_buffer(bh);
1779                } else if (!trylock_buffer(bh)) {
1780                        redirty_page_for_writepage(wbc, page);
1781                        continue;
1782                }
1783                if (test_clear_buffer_dirty(bh)) {
1784                        mark_buffer_async_write_endio(bh, handler);
1785                } else {
1786                        unlock_buffer(bh);
1787                }
1788        } while ((bh = bh->b_this_page) != head);
1789
1790        /*
1791         * The page and its buffers are protected by PageWriteback(), so we can
1792         * drop the bh refcounts early.
1793         */
1794        BUG_ON(PageWriteback(page));
1795        set_page_writeback(page);
1796
1797        do {
1798                struct buffer_head *next = bh->b_this_page;
1799                if (buffer_async_write(bh)) {
1800                        submit_bh_wbc(write_op, bh, 0, wbc);
1801                        nr_underway++;
1802                }
1803                bh = next;
1804        } while (bh != head);
1805        unlock_page(page);
1806
1807        err = 0;
1808done:
1809        if (nr_underway == 0) {
1810                /*
1811                 * The page was marked dirty, but the buffers were
1812                 * clean.  Someone wrote them back by hand with
1813                 * ll_rw_block/submit_bh.  A rare case.
1814                 */
1815                end_page_writeback(page);
1816
1817                /*
1818                 * The page and buffer_heads can be released at any time from
1819                 * here on.
1820                 */
1821        }
1822        return err;
1823
1824recover:
1825        /*
1826         * ENOSPC, or some other error.  We may already have added some
1827         * blocks to the file, so we need to write these out to avoid
1828         * exposing stale data.
1829         * The page is currently locked and not marked for writeback
1830         */
1831        bh = head;
1832        /* Recovery: lock and submit the mapped buffers */
1833        do {
1834                if (buffer_mapped(bh) && buffer_dirty(bh) &&
1835                    !buffer_delay(bh)) {
1836                        lock_buffer(bh);
1837                        mark_buffer_async_write_endio(bh, handler);
1838                } else {
1839                        /*
1840                         * The buffer may have been set dirty during
1841                         * attachment to a dirty page.
1842                         */
1843                        clear_buffer_dirty(bh);
1844                }
1845        } while ((bh = bh->b_this_page) != head);
1846        SetPageError(page);
1847        BUG_ON(PageWriteback(page));
1848        mapping_set_error(page->mapping, err);
1849        set_page_writeback(page);
1850        do {
1851                struct buffer_head *next = bh->b_this_page;
1852                if (buffer_async_write(bh)) {
1853                        clear_buffer_dirty(bh);
1854                        submit_bh_wbc(write_op, bh, 0, wbc);
1855                        nr_underway++;
1856                }
1857                bh = next;
1858        } while (bh != head);
1859        unlock_page(page);
1860        goto done;
1861}
1862
1863/*
1864 * If a page has any new buffers, zero them out here, and mark them uptodate
1865 * and dirty so they'll be written out (in order to prevent uninitialised
1866 * block data from leaking). And clear the new bit.
1867 */
1868void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1869{
1870        unsigned int block_start, block_end;
1871        struct buffer_head *head, *bh;
1872
1873        BUG_ON(!PageLocked(page));
1874        if (!page_has_buffers(page))
1875                return;
1876
1877        bh = head = page_buffers(page);
1878        block_start = 0;
1879        do {
1880                block_end = block_start + bh->b_size;
1881
1882                if (buffer_new(bh)) {
1883                        if (block_end > from && block_start < to) {
1884                                if (!PageUptodate(page)) {
1885                                        unsigned start, size;
1886
1887                                        start = max(from, block_start);
1888                                        size = min(to, block_end) - start;
1889
1890                                        zero_user(page, start, size);
1891                                        set_buffer_uptodate(bh);
1892                                }
1893
1894                                clear_buffer_new(bh);
1895                                mark_buffer_dirty(bh);
1896                        }
1897                }
1898
1899                block_start = block_end;
1900                bh = bh->b_this_page;
1901        } while (bh != head);
1902}
1903EXPORT_SYMBOL(page_zero_new_buffers);
1904
1905int __block_write_begin(struct page *page, loff_t pos, unsigned len,
1906                get_block_t *get_block)
1907{
1908        unsigned from = pos & (PAGE_CACHE_SIZE - 1);
1909        unsigned to = from + len;
1910        struct inode *inode = page->mapping->host;
1911        unsigned block_start, block_end;
1912        sector_t block;
1913        int err = 0;
1914        unsigned blocksize, bbits;
1915        struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1916
1917        BUG_ON(!PageLocked(page));
1918        BUG_ON(from > PAGE_CACHE_SIZE);
1919        BUG_ON(to > PAGE_CACHE_SIZE);
1920        BUG_ON(from > to);
1921
1922        head = create_page_buffers(page, inode, 0);
1923        blocksize = head->b_size;
1924        bbits = block_size_bits(blocksize);
1925
1926        block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1927
1928        for(bh = head, block_start = 0; bh != head || !block_start;
1929            block++, block_start=block_end, bh = bh->b_this_page) {
1930                block_end = block_start + blocksize;
1931                if (block_end <= from || block_start >= to) {
1932                        if (PageUptodate(page)) {
1933                                if (!buffer_uptodate(bh))
1934                                        set_buffer_uptodate(bh);
1935                        }
1936                        continue;
1937                }
1938                if (buffer_new(bh))
1939                        clear_buffer_new(bh);
1940                if (!buffer_mapped(bh)) {
1941                        WARN_ON(bh->b_size != blocksize);
1942                        err = get_block(inode, block, bh, 1);
1943                        if (err)
1944                                break;
1945                        if (buffer_new(bh)) {
1946                                unmap_underlying_metadata(bh->b_bdev,
1947                                                        bh->b_blocknr);
1948                                if (PageUptodate(page)) {
1949                                        clear_buffer_new(bh);
1950                                        set_buffer_uptodate(bh);
1951                                        mark_buffer_dirty(bh);
1952                                        continue;
1953                                }
1954                                if (block_end > to || block_start < from)
1955                                        zero_user_segments(page,
1956                                                to, block_end,
1957                                                block_start, from);
1958                                continue;
1959                        }
1960                }
1961                if (PageUptodate(page)) {
1962                        if (!buffer_uptodate(bh))
1963                                set_buffer_uptodate(bh);
1964                        continue; 
1965                }
1966                if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1967                    !buffer_unwritten(bh) &&
1968                     (block_start < from || block_end > to)) {
1969                        ll_rw_block(READ, 1, &bh);
1970                        *wait_bh++=bh;
1971                }
1972        }
1973        /*
1974         * If we issued read requests - let them complete.
1975         */
1976        while(wait_bh > wait) {
1977                wait_on_buffer(*--wait_bh);
1978                if (!buffer_uptodate(*wait_bh))
1979                        err = -EIO;
1980        }
1981        if (unlikely(err))
1982                page_zero_new_buffers(page, from, to);
1983        return err;
1984}
1985EXPORT_SYMBOL(__block_write_begin);
1986
1987static int __block_commit_write(struct inode *inode, struct page *page,
1988                unsigned from, unsigned to)
1989{
1990        unsigned block_start, block_end;
1991        int partial = 0;
1992        unsigned blocksize;
1993        struct buffer_head *bh, *head;
1994
1995        bh = head = page_buffers(page);
1996        blocksize = bh->b_size;
1997
1998        block_start = 0;
1999        do {
2000                block_end = block_start + blocksize;
2001                if (block_end <= from || block_start >= to) {
2002                        if (!buffer_uptodate(bh))
2003                                partial = 1;
2004                } else {
2005                        set_buffer_uptodate(bh);
2006                        mark_buffer_dirty(bh);
2007                }
2008                clear_buffer_new(bh);
2009
2010                block_start = block_end;
2011                bh = bh->b_this_page;
2012        } while (bh != head);
2013
2014        /*
2015         * If this is a partial write which happened to make all buffers
2016         * uptodate then we can optimize away a bogus readpage() for
2017         * the next read(). Here we 'discover' whether the page went
2018         * uptodate as a result of this (potentially partial) write.
2019         */
2020        if (!partial)
2021                SetPageUptodate(page);
2022        return 0;
2023}
2024
2025/*
2026 * block_write_begin takes care of the basic task of block allocation and
2027 * bringing partial write blocks uptodate first.
2028 *
2029 * The filesystem needs to handle block truncation upon failure.
2030 */
2031int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
2032                unsigned flags, struct page **pagep, get_block_t *get_block)
2033{
2034        pgoff_t index = pos >> PAGE_CACHE_SHIFT;
2035        struct page *page;
2036        int status;
2037
2038        page = grab_cache_page_write_begin(mapping, index, flags);
2039        if (!page)
2040                return -ENOMEM;
2041
2042        status = __block_write_begin(page, pos, len, get_block);
2043        if (unlikely(status)) {
2044                unlock_page(page);
2045                page_cache_release(page);
2046                page = NULL;
2047        }
2048
2049        *pagep = page;
2050        return status;
2051}
2052EXPORT_SYMBOL(block_write_begin);
2053
2054int block_write_end(struct file *file, struct address_space *mapping,
2055                        loff_t pos, unsigned len, unsigned copied,
2056                        struct page *page, void *fsdata)
2057{
2058        struct inode *inode = mapping->host;
2059        unsigned start;
2060
2061        start = pos & (PAGE_CACHE_SIZE - 1);
2062
2063        if (unlikely(copied < len)) {
2064                /*
2065                 * The buffers that were written will now be uptodate, so we
2066                 * don't have to worry about a readpage reading them and
2067                 * overwriting a partial write. However if we have encountered
2068                 * a short write and only partially written into a buffer, it
2069                 * will not be marked uptodate, so a readpage might come in and
2070                 * destroy our partial write.
2071                 *
2072                 * Do the simplest thing, and just treat any short write to a
2073                 * non uptodate page as a zero-length write, and force the
2074                 * caller to redo the whole thing.
2075                 */
2076                if (!PageUptodate(page))
2077                        copied = 0;
2078
2079                page_zero_new_buffers(page, start+copied, start+len);
2080        }
2081        flush_dcache_page(page);
2082
2083        /* This could be a short (even 0-length) commit */
2084        __block_commit_write(inode, page, start, start+copied);
2085
2086        return copied;
2087}
2088EXPORT_SYMBOL(block_write_end);
2089
2090int generic_write_end(struct file *file, struct address_space *mapping,
2091                        loff_t pos, unsigned len, unsigned copied,
2092                        struct page *page, void *fsdata)
2093{
2094        struct inode *inode = mapping->host;
2095        loff_t old_size = inode->i_size;
2096        int i_size_changed = 0;
2097
2098        copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2099
2100        /*
2101         * No need to use i_size_read() here, the i_size
2102         * cannot change under us because we hold i_mutex.
2103         *
2104         * But it's important to update i_size while still holding page lock:
2105         * page writeout could otherwise come in and zero beyond i_size.
2106         */
2107        if (pos+copied > inode->i_size) {
2108                i_size_write(inode, pos+copied);
2109                i_size_changed = 1;
2110        }
2111
2112        unlock_page(page);
2113        page_cache_release(page);
2114
2115        if (old_size < pos)
2116                pagecache_isize_extended(inode, old_size, pos);
2117        /*
2118         * Don't mark the inode dirty under page lock. First, it unnecessarily
2119         * makes the holding time of page lock longer. Second, it forces lock
2120         * ordering of page lock and transaction start for journaling
2121         * filesystems.
2122         */
2123        if (i_size_changed)
2124                mark_inode_dirty(inode);
2125
2126        return copied;
2127}
2128EXPORT_SYMBOL(generic_write_end);
2129
2130/*
2131 * block_is_partially_uptodate checks whether buffers within a page are
2132 * uptodate or not.
2133 *
2134 * Returns true if all buffers which correspond to a file portion
2135 * we want to read are uptodate.
2136 */
2137int block_is_partially_uptodate(struct page *page, unsigned long from,
2138                                        unsigned long count)
2139{
2140        unsigned block_start, block_end, blocksize;
2141        unsigned to;
2142        struct buffer_head *bh, *head;
2143        int ret = 1;
2144
2145        if (!page_has_buffers(page))
2146                return 0;
2147
2148        head = page_buffers(page);
2149        blocksize = head->b_size;
2150        to = min_t(unsigned, PAGE_CACHE_SIZE - from, count);
2151        to = from + to;
2152        if (from < blocksize && to > PAGE_CACHE_SIZE - blocksize)
2153                return 0;
2154
2155        bh = head;
2156        block_start = 0;
2157        do {
2158                block_end = block_start + blocksize;
2159                if (block_end > from && block_start < to) {
2160                        if (!buffer_uptodate(bh)) {
2161                                ret = 0;
2162                                break;
2163                        }
2164                        if (block_end >= to)
2165                                break;
2166                }
2167                block_start = block_end;
2168                bh = bh->b_this_page;
2169        } while (bh != head);
2170
2171        return ret;
2172}
2173EXPORT_SYMBOL(block_is_partially_uptodate);
2174
2175/*
2176 * Generic "read page" function for block devices that have the normal
2177 * get_block functionality. This is most of the block device filesystems.
2178 * Reads the page asynchronously --- the unlock_buffer() and
2179 * set/clear_buffer_uptodate() functions propagate buffer state into the
2180 * page struct once IO has completed.
2181 */
2182int block_read_full_page(struct page *page, get_block_t *get_block)
2183{
2184        struct inode *inode = page->mapping->host;
2185        sector_t iblock, lblock;
2186        struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2187        unsigned int blocksize, bbits;
2188        int nr, i;
2189        int fully_mapped = 1;
2190
2191        head = create_page_buffers(page, inode, 0);
2192        blocksize = head->b_size;
2193        bbits = block_size_bits(blocksize);
2194
2195        iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
2196        lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2197        bh = head;
2198        nr = 0;
2199        i = 0;
2200
2201        do {
2202                if (buffer_uptodate(bh))
2203                        continue;
2204
2205                if (!buffer_mapped(bh)) {
2206                        int err = 0;
2207
2208                        fully_mapped = 0;
2209                        if (iblock < lblock) {
2210                                WARN_ON(bh->b_size != blocksize);
2211                                err = get_block(inode, iblock, bh, 0);
2212                                if (err)
2213                                        SetPageError(page);
2214                        }
2215                        if (!buffer_mapped(bh)) {
2216                                zero_user(page, i * blocksize, blocksize);
2217                                if (!err)
2218                                        set_buffer_uptodate(bh);
2219                                continue;
2220                        }
2221                        /*
2222                         * get_block() might have updated the buffer
2223                         * synchronously
2224                         */
2225                        if (buffer_uptodate(bh))
2226                                continue;
2227                }
2228                arr[nr++] = bh;
2229        } while (i++, iblock++, (bh = bh->b_this_page) != head);
2230
2231        if (fully_mapped)
2232                SetPageMappedToDisk(page);
2233
2234        if (!nr) {
2235                /*
2236                 * All buffers are uptodate - we can set the page uptodate
2237                 * as well. But not if get_block() returned an error.
2238                 */
2239                if (!PageError(page))
2240                        SetPageUptodate(page);
2241                unlock_page(page);
2242                return 0;
2243        }
2244
2245        /* Stage two: lock the buffers */
2246        for (i = 0; i < nr; i++) {
2247                bh = arr[i];
2248                lock_buffer(bh);
2249                mark_buffer_async_read(bh);
2250        }
2251
2252        /*
2253         * Stage 3: start the IO.  Check for uptodateness
2254         * inside the buffer lock in case another process reading
2255         * the underlying blockdev brought it uptodate (the sct fix).
2256         */
2257        for (i = 0; i < nr; i++) {
2258                bh = arr[i];
2259                if (buffer_uptodate(bh))
2260                        end_buffer_async_read(bh, 1);
2261                else
2262                        submit_bh(READ, bh);
2263        }
2264        return 0;
2265}
2266EXPORT_SYMBOL(block_read_full_page);
2267
2268/* utility function for filesystems that need to do work on expanding
2269 * truncates.  Uses filesystem pagecache writes to allow the filesystem to
2270 * deal with the hole.  
2271 */
2272int generic_cont_expand_simple(struct inode *inode, loff_t size)
2273{
2274        struct address_space *mapping = inode->i_mapping;
2275        struct page *page;
2276        void *fsdata;
2277        int err;
2278
2279        err = inode_newsize_ok(inode, size);
2280        if (err)
2281                goto out;
2282
2283        err = pagecache_write_begin(NULL, mapping, size, 0,
2284                                AOP_FLAG_UNINTERRUPTIBLE|AOP_FLAG_CONT_EXPAND,
2285                                &page, &fsdata);
2286        if (err)
2287                goto out;
2288
2289        err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2290        BUG_ON(err > 0);
2291
2292out:
2293        return err;
2294}
2295EXPORT_SYMBOL(generic_cont_expand_simple);
2296
2297static int cont_expand_zero(struct file *file, struct address_space *mapping,
2298                            loff_t pos, loff_t *bytes)
2299{
2300        struct inode *inode = mapping->host;
2301        unsigned blocksize = 1 << inode->i_blkbits;
2302        struct page *page;
2303        void *fsdata;
2304        pgoff_t index, curidx;
2305        loff_t curpos;
2306        unsigned zerofrom, offset, len;
2307        int err = 0;
2308
2309        index = pos >> PAGE_CACHE_SHIFT;
2310        offset = pos & ~PAGE_CACHE_MASK;
2311
2312        while (index > (curidx = (curpos = *bytes)>>PAGE_CACHE_SHIFT)) {
2313                zerofrom = curpos & ~PAGE_CACHE_MASK;
2314                if (zerofrom & (blocksize-1)) {
2315                        *bytes |= (blocksize-1);
2316                        (*bytes)++;
2317                }
2318                len = PAGE_CACHE_SIZE - zerofrom;
2319
2320                err = pagecache_write_begin(file, mapping, curpos, len,
2321                                                AOP_FLAG_UNINTERRUPTIBLE,
2322                                                &page, &fsdata);
2323                if (err)
2324                        goto out;
2325                zero_user(page, zerofrom, len);
2326                err = pagecache_write_end(file, mapping, curpos, len, len,
2327                                                page, fsdata);
2328                if (err < 0)
2329                        goto out;
2330                BUG_ON(err != len);
2331                err = 0;
2332
2333                balance_dirty_pages_ratelimited(mapping);
2334
2335                if (unlikely(fatal_signal_pending(current))) {
2336                        err = -EINTR;
2337                        goto out;
2338                }
2339        }
2340
2341        /* page covers the boundary, find the boundary offset */
2342        if (index == curidx) {
2343                zerofrom = curpos & ~PAGE_CACHE_MASK;
2344                /* if we will expand the thing last block will be filled */
2345                if (offset <= zerofrom) {
2346                        goto out;
2347                }
2348                if (zerofrom & (blocksize-1)) {
2349                        *bytes |= (blocksize-1);
2350                        (*bytes)++;
2351                }
2352                len = offset - zerofrom;
2353
2354                err = pagecache_write_begin(file, mapping, curpos, len,
2355                                                AOP_FLAG_UNINTERRUPTIBLE,
2356                                                &page, &fsdata);
2357                if (err)
2358                        goto out;
2359                zero_user(page, zerofrom, len);
2360                err = pagecache_write_end(file, mapping, curpos, len, len,
2361                                                page, fsdata);
2362                if (err < 0)
2363                        goto out;
2364                BUG_ON(err != len);
2365                err = 0;
2366        }
2367out:
2368        return err;
2369}
2370
2371/*
2372 * For moronic filesystems that do not allow holes in file.
2373 * We may have to extend the file.
2374 */
2375int cont_write_begin(struct file *file, struct address_space *mapping,
2376                        loff_t pos, unsigned len, unsigned flags,
2377                        struct page **pagep, void **fsdata,
2378                        get_block_t *get_block, loff_t *bytes)
2379{
2380        struct inode *inode = mapping->host;
2381        unsigned blocksize = 1 << inode->i_blkbits;
2382        unsigned zerofrom;
2383        int err;
2384
2385        err = cont_expand_zero(file, mapping, pos, bytes);
2386        if (err)
2387                return err;
2388
2389        zerofrom = *bytes & ~PAGE_CACHE_MASK;
2390        if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2391                *bytes |= (blocksize-1);
2392                (*bytes)++;
2393        }
2394
2395        return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2396}
2397EXPORT_SYMBOL(cont_write_begin);
2398
2399int block_commit_write(struct page *page, unsigned from, unsigned to)
2400{
2401        struct inode *inode = page->mapping->host;
2402        __block_commit_write(inode,page,from,to);
2403        return 0;
2404}
2405EXPORT_SYMBOL(block_commit_write);
2406
2407/*
2408 * block_page_mkwrite() is not allowed to change the file size as it gets
2409 * called from a page fault handler when a page is first dirtied. Hence we must
2410 * be careful to check for EOF conditions here. We set the page up correctly
2411 * for a written page which means we get ENOSPC checking when writing into
2412 * holes and correct delalloc and unwritten extent mapping on filesystems that
2413 * support these features.
2414 *
2415 * We are not allowed to take the i_mutex here so we have to play games to
2416 * protect against truncate races as the page could now be beyond EOF.  Because
2417 * truncate writes the inode size before removing pages, once we have the
2418 * page lock we can determine safely if the page is beyond EOF. If it is not
2419 * beyond EOF, then the page is guaranteed safe against truncation until we
2420 * unlock the page.
2421 *
2422 * Direct callers of this function should protect against filesystem freezing
2423 * using sb_start_pagefault() - sb_end_pagefault() functions.
2424 */
2425int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2426                         get_block_t get_block)
2427{
2428        struct page *page = vmf->page;
2429        struct inode *inode = file_inode(vma->vm_file);
2430        unsigned long end;
2431        loff_t size;
2432        int ret;
2433
2434        lock_page(page);
2435        size = i_size_read(inode);
2436        if ((page->mapping != inode->i_mapping) ||
2437            (page_offset(page) > size)) {
2438                /* We overload EFAULT to mean page got truncated */
2439                ret = -EFAULT;
2440                goto out_unlock;
2441        }
2442
2443        /* page is wholly or partially inside EOF */
2444        if (((page->index + 1) << PAGE_CACHE_SHIFT) > size)
2445                end = size & ~PAGE_CACHE_MASK;
2446        else
2447                end = PAGE_CACHE_SIZE;
2448
2449        ret = __block_write_begin(page, 0, end, get_block);
2450        if (!ret)
2451                ret = block_commit_write(page, 0, end);
2452
2453        if (unlikely(ret < 0))
2454                goto out_unlock;
2455        set_page_dirty(page);
2456        wait_for_stable_page(page);
2457        return 0;
2458out_unlock:
2459        unlock_page(page);
2460        return ret;
2461}
2462EXPORT_SYMBOL(block_page_mkwrite);
2463
2464/*
2465 * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2466 * immediately, while under the page lock.  So it needs a special end_io
2467 * handler which does not touch the bh after unlocking it.
2468 */
2469static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2470{
2471        __end_buffer_read_notouch(bh, uptodate);
2472}
2473
2474/*
2475 * Attach the singly-linked list of buffers created by nobh_write_begin, to
2476 * the page (converting it to circular linked list and taking care of page
2477 * dirty races).
2478 */
2479static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2480{
2481        struct buffer_head *bh;
2482
2483        BUG_ON(!PageLocked(page));
2484
2485        spin_lock(&page->mapping->private_lock);
2486        bh = head;
2487        do {
2488                if (PageDirty(page))
2489                        set_buffer_dirty(bh);
2490                if (!bh->b_this_page)
2491                        bh->b_this_page = head;
2492                bh = bh->b_this_page;
2493        } while (bh != head);
2494        attach_page_buffers(page, head);
2495        spin_unlock(&page->mapping->private_lock);
2496}
2497
2498/*
2499 * On entry, the page is fully not uptodate.
2500 * On exit the page is fully uptodate in the areas outside (from,to)
2501 * The filesystem needs to handle block truncation upon failure.
2502 */
2503int nobh_write_begin(struct address_space *mapping,
2504                        loff_t pos, unsigned len, unsigned flags,
2505                        struct page **pagep, void **fsdata,
2506                        get_block_t *get_block)
2507{
2508        struct inode *inode = mapping->host;
2509        const unsigned blkbits = inode->i_blkbits;
2510        const unsigned blocksize = 1 << blkbits;
2511        struct buffer_head *head, *bh;
2512        struct page *page;
2513        pgoff_t index;
2514        unsigned from, to;
2515        unsigned block_in_page;
2516        unsigned block_start, block_end;
2517        sector_t block_in_file;
2518        int nr_reads = 0;
2519        int ret = 0;
2520        int is_mapped_to_disk = 1;
2521
2522        index = pos >> PAGE_CACHE_SHIFT;
2523        from = pos & (PAGE_CACHE_SIZE - 1);
2524        to = from + len;
2525
2526        page = grab_cache_page_write_begin(mapping, index, flags);
2527        if (!page)
2528                return -ENOMEM;
2529        *pagep = page;
2530        *fsdata = NULL;
2531
2532        if (page_has_buffers(page)) {
2533                ret = __block_write_begin(page, pos, len, get_block);
2534                if (unlikely(ret))
2535                        goto out_release;
2536                return ret;
2537        }
2538
2539        if (PageMappedToDisk(page))
2540                return 0;
2541
2542        /*
2543         * Allocate buffers so that we can keep track of state, and potentially
2544         * attach them to the page if an error occurs. In the common case of
2545         * no error, they will just be freed again without ever being attached
2546         * to the page (which is all OK, because we're under the page lock).
2547         *
2548         * Be careful: the buffer linked list is a NULL terminated one, rather
2549         * than the circular one we're used to.
2550         */
2551        head = alloc_page_buffers(page, blocksize, 0);
2552        if (!head) {
2553                ret = -ENOMEM;
2554                goto out_release;
2555        }
2556
2557        block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
2558
2559        /*
2560         * We loop across all blocks in the page, whether or not they are
2561         * part of the affected region.  This is so we can discover if the
2562         * page is fully mapped-to-disk.
2563         */
2564        for (block_start = 0, block_in_page = 0, bh = head;
2565                  block_start < PAGE_CACHE_SIZE;
2566                  block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2567                int create;
2568
2569                block_end = block_start + blocksize;
2570                bh->b_state = 0;
2571                create = 1;
2572                if (block_start >= to)
2573                        create = 0;
2574                ret = get_block(inode, block_in_file + block_in_page,
2575                                        bh, create);
2576                if (ret)
2577                        goto failed;
2578                if (!buffer_mapped(bh))
2579                        is_mapped_to_disk = 0;
2580                if (buffer_new(bh))
2581                        unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
2582                if (PageUptodate(page)) {
2583                        set_buffer_uptodate(bh);
2584                        continue;
2585                }
2586                if (buffer_new(bh) || !buffer_mapped(bh)) {
2587                        zero_user_segments(page, block_start, from,
2588                                                        to, block_end);
2589                        continue;
2590                }
2591                if (buffer_uptodate(bh))
2592                        continue;       /* reiserfs does this */
2593                if (block_start < from || block_end > to) {
2594                        lock_buffer(bh);
2595                        bh->b_end_io = end_buffer_read_nobh;
2596                        submit_bh(READ, bh);
2597                        nr_reads++;
2598                }
2599        }
2600
2601        if (nr_reads) {
2602                /*
2603                 * The page is locked, so these buffers are protected from
2604                 * any VM or truncate activity.  Hence we don't need to care
2605                 * for the buffer_head refcounts.
2606                 */
2607                for (bh = head; bh; bh = bh->b_this_page) {
2608                        wait_on_buffer(bh);
2609                        if (!buffer_uptodate(bh))
2610                                ret = -EIO;
2611                }
2612                if (ret)
2613                        goto failed;
2614        }
2615
2616        if (is_mapped_to_disk)
2617                SetPageMappedToDisk(page);
2618
2619        *fsdata = head; /* to be released by nobh_write_end */
2620
2621        return 0;
2622
2623failed:
2624        BUG_ON(!ret);
2625        /*
2626         * Error recovery is a bit difficult. We need to zero out blocks that
2627         * were newly allocated, and dirty them to ensure they get written out.
2628         * Buffers need to be attached to the page at this point, otherwise
2629         * the handling of potential IO errors during writeout would be hard
2630         * (could try doing synchronous writeout, but what if that fails too?)
2631         */
2632        attach_nobh_buffers(page, head);
2633        page_zero_new_buffers(page, from, to);
2634
2635out_release:
2636        unlock_page(page);
2637        page_cache_release(page);
2638        *pagep = NULL;
2639
2640        return ret;
2641}
2642EXPORT_SYMBOL(nobh_write_begin);
2643
2644int nobh_write_end(struct file *file, struct address_space *mapping,
2645                        loff_t pos, unsigned len, unsigned copied,
2646                        struct page *page, void *fsdata)
2647{
2648        struct inode *inode = page->mapping->host;
2649        struct buffer_head *head = fsdata;
2650        struct buffer_head *bh;
2651        BUG_ON(fsdata != NULL && page_has_buffers(page));
2652
2653        if (unlikely(copied < len) && head)
2654                attach_nobh_buffers(page, head);
2655        if (page_has_buffers(page))
2656                return generic_write_end(file, mapping, pos, len,
2657                                        copied, page, fsdata);
2658
2659        SetPageUptodate(page);
2660        set_page_dirty(page);
2661        if (pos+copied > inode->i_size) {
2662                i_size_write(inode, pos+copied);
2663                mark_inode_dirty(inode);
2664        }
2665
2666        unlock_page(page);
2667        page_cache_release(page);
2668
2669        while (head) {
2670                bh = head;
2671                head = head->b_this_page;
2672                free_buffer_head(bh);
2673        }
2674
2675        return copied;
2676}
2677EXPORT_SYMBOL(nobh_write_end);
2678
2679/*
2680 * nobh_writepage() - based on block_full_write_page() except
2681 * that it tries to operate without attaching bufferheads to
2682 * the page.
2683 */
2684int nobh_writepage(struct page *page, get_block_t *get_block,
2685                        struct writeback_control *wbc)
2686{
2687        struct inode * const inode = page->mapping->host;
2688        loff_t i_size = i_size_read(inode);
2689        const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2690        unsigned offset;
2691        int ret;
2692
2693        /* Is the page fully inside i_size? */
2694        if (page->index < end_index)
2695                goto out;
2696
2697        /* Is the page fully outside i_size? (truncate in progress) */
2698        offset = i_size & (PAGE_CACHE_SIZE-1);
2699        if (page->index >= end_index+1 || !offset) {
2700                /*
2701                 * The page may have dirty, unmapped buffers.  For example,
2702                 * they may have been added in ext3_writepage().  Make them
2703                 * freeable here, so the page does not leak.
2704                 */
2705#if 0
2706                /* Not really sure about this  - do we need this ? */
2707                if (page->mapping->a_ops->invalidatepage)
2708                        page->mapping->a_ops->invalidatepage(page, offset);
2709#endif
2710                unlock_page(page);
2711                return 0; /* don't care */
2712        }
2713
2714        /*
2715         * The page straddles i_size.  It must be zeroed out on each and every
2716         * writepage invocation because it may be mmapped.  "A file is mapped
2717         * in multiples of the page size.  For a file that is not a multiple of
2718         * the  page size, the remaining memory is zeroed when mapped, and
2719         * writes to that region are not written out to the file."
2720         */
2721        zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2722out:
2723        ret = mpage_writepage(page, get_block, wbc);
2724        if (ret == -EAGAIN)
2725                ret = __block_write_full_page(inode, page, get_block, wbc,
2726                                              end_buffer_async_write);
2727        return ret;
2728}
2729EXPORT_SYMBOL(nobh_writepage);
2730
2731int nobh_truncate_page(struct address_space *mapping,
2732                        loff_t from, get_block_t *get_block)
2733{
2734        pgoff_t index = from >> PAGE_CACHE_SHIFT;
2735        unsigned offset = from & (PAGE_CACHE_SIZE-1);
2736        unsigned blocksize;
2737        sector_t iblock;
2738        unsigned length, pos;
2739        struct inode *inode = mapping->host;
2740        struct page *page;
2741        struct buffer_head map_bh;
2742        int err;
2743
2744        blocksize = 1 << inode->i_blkbits;
2745        length = offset & (blocksize - 1);
2746
2747        /* Block boundary? Nothing to do */
2748        if (!length)
2749                return 0;
2750
2751        length = blocksize - length;
2752        iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2753
2754        page = grab_cache_page(mapping, index);
2755        err = -ENOMEM;
2756        if (!page)
2757                goto out;
2758
2759        if (page_has_buffers(page)) {
2760has_buffers:
2761                unlock_page(page);
2762                page_cache_release(page);
2763                return block_truncate_page(mapping, from, get_block);
2764        }
2765
2766        /* Find the buffer that contains "offset" */
2767        pos = blocksize;
2768        while (offset >= pos) {
2769                iblock++;
2770                pos += blocksize;
2771        }
2772
2773        map_bh.b_size = blocksize;
2774        map_bh.b_state = 0;
2775        err = get_block(inode, iblock, &map_bh, 0);
2776        if (err)
2777                goto unlock;
2778        /* unmapped? It's a hole - nothing to do */
2779        if (!buffer_mapped(&map_bh))
2780                goto unlock;
2781
2782        /* Ok, it's mapped. Make sure it's up-to-date */
2783        if (!PageUptodate(page)) {
2784                err = mapping->a_ops->readpage(NULL, page);
2785                if (err) {
2786                        page_cache_release(page);
2787                        goto out;
2788                }
2789                lock_page(page);
2790                if (!PageUptodate(page)) {
2791                        err = -EIO;
2792                        goto unlock;
2793                }
2794                if (page_has_buffers(page))
2795                        goto has_buffers;
2796        }
2797        zero_user(page, offset, length);
2798        set_page_dirty(page);
2799        err = 0;
2800
2801unlock:
2802        unlock_page(page);
2803        page_cache_release(page);
2804out:
2805        return err;
2806}
2807EXPORT_SYMBOL(nobh_truncate_page);
2808
2809int block_truncate_page(struct address_space *mapping,
2810                        loff_t from, get_block_t *get_block)
2811{
2812        pgoff_t index = from >> PAGE_CACHE_SHIFT;
2813        unsigned offset = from & (PAGE_CACHE_SIZE-1);
2814        unsigned blocksize;
2815        sector_t iblock;
2816        unsigned length, pos;
2817        struct inode *inode = mapping->host;
2818        struct page *page;
2819        struct buffer_head *bh;
2820        int err;
2821
2822        blocksize = 1 << inode->i_blkbits;
2823        length = offset & (blocksize - 1);
2824
2825        /* Block boundary? Nothing to do */
2826        if (!length)
2827                return 0;
2828
2829        length = blocksize - length;
2830        iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2831        
2832        page = grab_cache_page(mapping, index);
2833        err = -ENOMEM;
2834        if (!page)
2835                goto out;
2836
2837        if (!page_has_buffers(page))
2838                create_empty_buffers(page, blocksize, 0);
2839
2840        /* Find the buffer that contains "offset" */
2841        bh = page_buffers(page);
2842        pos = blocksize;
2843        while (offset >= pos) {
2844                bh = bh->b_this_page;
2845                iblock++;
2846                pos += blocksize;
2847        }
2848
2849        err = 0;
2850        if (!buffer_mapped(bh)) {
2851                WARN_ON(bh->b_size != blocksize);
2852                err = get_block(inode, iblock, bh, 0);
2853                if (err)
2854                        goto unlock;
2855                /* unmapped? It's a hole - nothing to do */
2856                if (!buffer_mapped(bh))
2857                        goto unlock;
2858        }
2859
2860        /* Ok, it's mapped. Make sure it's up-to-date */
2861        if (PageUptodate(page))
2862                set_buffer_uptodate(bh);
2863
2864        if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2865                err = -EIO;
2866                ll_rw_block(READ, 1, &bh);
2867                wait_on_buffer(bh);
2868                /* Uhhuh. Read error. Complain and punt. */
2869                if (!buffer_uptodate(bh))
2870                        goto unlock;
2871        }
2872
2873        zero_user(page, offset, length);
2874        mark_buffer_dirty(bh);
2875        err = 0;
2876
2877unlock:
2878        unlock_page(page);
2879        page_cache_release(page);
2880out:
2881        return err;
2882}
2883EXPORT_SYMBOL(block_truncate_page);
2884
2885/*
2886 * The generic ->writepage function for buffer-backed address_spaces
2887 */
2888int block_write_full_page(struct page *page, get_block_t *get_block,
2889                        struct writeback_control *wbc)
2890{
2891        struct inode * const inode = page->mapping->host;
2892        loff_t i_size = i_size_read(inode);
2893        const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2894        unsigned offset;
2895
2896        /* Is the page fully inside i_size? */
2897        if (page->index < end_index)
2898                return __block_write_full_page(inode, page, get_block, wbc,
2899                                               end_buffer_async_write);
2900
2901        /* Is the page fully outside i_size? (truncate in progress) */
2902        offset = i_size & (PAGE_CACHE_SIZE-1);
2903        if (page->index >= end_index+1 || !offset) {
2904                /*
2905                 * The page may have dirty, unmapped buffers.  For example,
2906                 * they may have been added in ext3_writepage().  Make them
2907                 * freeable here, so the page does not leak.
2908                 */
2909                do_invalidatepage(page, 0, PAGE_CACHE_SIZE);
2910                unlock_page(page);
2911                return 0; /* don't care */
2912        }
2913
2914        /*
2915         * The page straddles i_size.  It must be zeroed out on each and every
2916         * writepage invocation because it may be mmapped.  "A file is mapped
2917         * in multiples of the page size.  For a file that is not a multiple of
2918         * the  page size, the remaining memory is zeroed when mapped, and
2919         * writes to that region are not written out to the file."
2920         */
2921        zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2922        return __block_write_full_page(inode, page, get_block, wbc,
2923                                                        end_buffer_async_write);
2924}
2925EXPORT_SYMBOL(block_write_full_page);
2926
2927sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2928                            get_block_t *get_block)
2929{
2930        struct buffer_head tmp;
2931        struct inode *inode = mapping->host;
2932        tmp.b_state = 0;
2933        tmp.b_blocknr = 0;
2934        tmp.b_size = 1 << inode->i_blkbits;
2935        get_block(inode, block, &tmp, 0);
2936        return tmp.b_blocknr;
2937}
2938EXPORT_SYMBOL(generic_block_bmap);
2939
2940static void end_bio_bh_io_sync(struct bio *bio)
2941{
2942        struct buffer_head *bh = bio->bi_private;
2943
2944        if (unlikely(bio_flagged(bio, BIO_QUIET)))
2945                set_bit(BH_Quiet, &bh->b_state);
2946
2947        bh->b_end_io(bh, !bio->bi_error);
2948        bio_put(bio);
2949}
2950
2951/*
2952 * This allows us to do IO even on the odd last sectors
2953 * of a device, even if the block size is some multiple
2954 * of the physical sector size.
2955 *
2956 * We'll just truncate the bio to the size of the device,
2957 * and clear the end of the buffer head manually.
2958 *
2959 * Truly out-of-range accesses will turn into actual IO
2960 * errors, this only handles the "we need to be able to
2961 * do IO at the final sector" case.
2962 */
2963void guard_bio_eod(int rw, struct bio *bio)
2964{
2965        sector_t maxsector;
2966        struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
2967        unsigned truncated_bytes;
2968
2969        maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
2970        if (!maxsector)
2971                return;
2972
2973        /*
2974         * If the *whole* IO is past the end of the device,
2975         * let it through, and the IO layer will turn it into
2976         * an EIO.
2977         */
2978        if (unlikely(bio->bi_iter.bi_sector >= maxsector))
2979                return;
2980
2981        maxsector -= bio->bi_iter.bi_sector;
2982        if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))
2983                return;
2984
2985        /* Uhhuh. We've got a bio that straddles the device size! */
2986        truncated_bytes = bio->bi_iter.bi_size - (maxsector << 9);
2987
2988        /* Truncate the bio.. */
2989        bio->bi_iter.bi_size -= truncated_bytes;
2990        bvec->bv_len -= truncated_bytes;
2991
2992        /* ..and clear the end of the buffer for reads */
2993        if ((rw & RW_MASK) == READ) {
2994                zero_user(bvec->bv_page, bvec->bv_offset + bvec->bv_len,
2995                                truncated_bytes);
2996        }
2997}
2998
2999static int submit_bh_wbc(int rw, struct buffer_head *bh,
3000                         unsigned long bio_flags, struct writeback_control *wbc)
3001{
3002        struct bio *bio;
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        if (wbc) {
3023                wbc_init_bio(wbc, bio);
3024                wbc_account_io(wbc, bh->b_page, bh->b_size);
3025        }
3026
3027        bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
3028        bio->bi_bdev = bh->b_bdev;
3029
3030        bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
3031        BUG_ON(bio->bi_iter.bi_size != bh->b_size);
3032
3033        bio->bi_end_io = end_bio_bh_io_sync;
3034        bio->bi_private = bh;
3035        bio->bi_flags |= bio_flags;
3036
3037        /* Take care of bh's that straddle the end of the device */
3038        guard_bio_eod(rw, bio);
3039
3040        if (buffer_meta(bh))
3041                rw |= REQ_META;
3042        if (buffer_prio(bh))
3043                rw |= REQ_PRIO;
3044
3045        submit_bio(rw, bio);
3046        return 0;
3047}
3048
3049int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags)
3050{
3051        return submit_bh_wbc(rw, bh, bio_flags, NULL);
3052}
3053EXPORT_SYMBOL_GPL(_submit_bh);
3054
3055int submit_bh(int rw, struct buffer_head *bh)
3056{
3057        return submit_bh_wbc(rw, bh, 0, NULL);
3058}
3059EXPORT_SYMBOL(submit_bh);
3060
3061/**
3062 * ll_rw_block: low-level access to block devices (DEPRECATED)
3063 * @rw: whether to %READ or %WRITE or maybe %READA (readahead)
3064 * @nr: number of &struct buffer_heads in the array
3065 * @bhs: array of pointers to &struct buffer_head
3066 *
3067 * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3068 * requests an I/O operation on them, either a %READ or a %WRITE.  The third
3069 * %READA option is described in the documentation for generic_make_request()
3070 * which ll_rw_block() calls.
3071 *
3072 * This function drops any buffer that it cannot get a lock on (with the
3073 * BH_Lock state bit), any buffer that appears to be clean when doing a write
3074 * request, and any buffer that appears to be up-to-date when doing read
3075 * request.  Further it marks as clean buffers that are processed for
3076 * writing (the buffer cache won't assume that they are actually clean
3077 * until the buffer gets unlocked).
3078 *
3079 * ll_rw_block sets b_end_io to simple completion handler that marks
3080 * the buffer up-to-date (if appropriate), unlocks the buffer and wakes
3081 * any waiters. 
3082 *
3083 * All of the buffers must be for the same device, and must also be a
3084 * multiple of the current approved size for the device.
3085 */
3086void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
3087{
3088        int i;
3089
3090        for (i = 0; i < nr; i++) {
3091                struct buffer_head *bh = bhs[i];
3092
3093                if (!trylock_buffer(bh))
3094                        continue;
3095                if (rw == WRITE) {
3096                        if (test_clear_buffer_dirty(bh)) {
3097                                bh->b_end_io = end_buffer_write_sync;
3098                                get_bh(bh);
3099                                submit_bh(WRITE, bh);
3100                                continue;
3101                        }
3102                } else {
3103                        if (!buffer_uptodate(bh)) {
3104                                bh->b_end_io = end_buffer_read_sync;
3105                                get_bh(bh);
3106                                submit_bh(rw, bh);
3107                                continue;
3108                        }
3109                }
3110                unlock_buffer(bh);
3111        }
3112}
3113EXPORT_SYMBOL(ll_rw_block);
3114
3115void write_dirty_buffer(struct buffer_head *bh, int rw)
3116{
3117        lock_buffer(bh);
3118        if (!test_clear_buffer_dirty(bh)) {
3119                unlock_buffer(bh);
3120                return;
3121        }
3122        bh->b_end_io = end_buffer_write_sync;
3123        get_bh(bh);
3124        submit_bh(rw, bh);
3125}
3126EXPORT_SYMBOL(write_dirty_buffer);
3127
3128/*
3129 * For a data-integrity writeout, we need to wait upon any in-progress I/O
3130 * and then start new I/O and then wait upon it.  The caller must have a ref on
3131 * the buffer_head.
3132 */
3133int __sync_dirty_buffer(struct buffer_head *bh, int rw)
3134{
3135        int ret = 0;
3136
3137        WARN_ON(atomic_read(&bh->b_count) < 1);
3138        lock_buffer(bh);
3139        if (test_clear_buffer_dirty(bh)) {
3140                get_bh(bh);
3141                bh->b_end_io = end_buffer_write_sync;
3142                ret = submit_bh(rw, bh);
3143                wait_on_buffer(bh);
3144                if (!ret && !buffer_uptodate(bh))
3145                        ret = -EIO;
3146        } else {
3147                unlock_buffer(bh);
3148        }
3149        return ret;
3150}
3151EXPORT_SYMBOL(__sync_dirty_buffer);
3152
3153int sync_dirty_buffer(struct buffer_head *bh)
3154{
3155        return __sync_dirty_buffer(bh, WRITE_SYNC);
3156}
3157EXPORT_SYMBOL(sync_dirty_buffer);
3158
3159/*
3160 * try_to_free_buffers() checks if all the buffers on this particular page
3161 * are unused, and releases them if so.
3162 *
3163 * Exclusion against try_to_free_buffers may be obtained by either
3164 * locking the page or by holding its mapping's private_lock.
3165 *
3166 * If the page is dirty but all the buffers are clean then we need to
3167 * be sure to mark the page clean as well.  This is because the page
3168 * may be against a block device, and a later reattachment of buffers
3169 * to a dirty page will set *all* buffers dirty.  Which would corrupt
3170 * filesystem data on the same device.
3171 *
3172 * The same applies to regular filesystem pages: if all the buffers are
3173 * clean then we set the page clean and proceed.  To do that, we require
3174 * total exclusion from __set_page_dirty_buffers().  That is obtained with
3175 * private_lock.
3176 *
3177 * try_to_free_buffers() is non-blocking.
3178 */
3179static inline int buffer_busy(struct buffer_head *bh)
3180{
3181        return atomic_read(&bh->b_count) |
3182                (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3183}
3184
3185static int
3186drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
3187{
3188        struct buffer_head *head = page_buffers(page);
3189        struct buffer_head *bh;
3190
3191        bh = head;
3192        do {
3193                if (buffer_write_io_error(bh) && page->mapping)
3194                        set_bit(AS_EIO, &page->mapping->flags);
3195                if (buffer_busy(bh))
3196                        goto failed;
3197                bh = bh->b_this_page;
3198        } while (bh != head);
3199
3200        do {
3201                struct buffer_head *next = bh->b_this_page;
3202
3203                if (bh->b_assoc_map)
3204                        __remove_assoc_queue(bh);
3205                bh = next;
3206        } while (bh != head);
3207        *buffers_to_free = head;
3208        __clear_page_buffers(page);
3209        return 1;
3210failed:
3211        return 0;
3212}
3213
3214int try_to_free_buffers(struct page *page)
3215{
3216        struct address_space * const mapping = page->mapping;
3217        struct buffer_head *buffers_to_free = NULL;
3218        int ret = 0;
3219
3220        BUG_ON(!PageLocked(page));
3221        if (PageWriteback(page))
3222                return 0;
3223
3224        if (mapping == NULL) {          /* can this still happen? */
3225                ret = drop_buffers(page, &buffers_to_free);
3226                goto out;
3227        }
3228
3229        spin_lock(&mapping->private_lock);
3230        ret = drop_buffers(page, &buffers_to_free);
3231
3232        /*
3233         * If the filesystem writes its buffers by hand (eg ext3)
3234         * then we can have clean buffers against a dirty page.  We
3235         * clean the page here; otherwise the VM will never notice
3236         * that the filesystem did any IO at all.
3237         *
3238         * Also, during truncate, discard_buffer will have marked all
3239         * the page's buffers clean.  We discover that here and clean
3240         * the page also.
3241         *
3242         * private_lock must be held over this entire operation in order
3243         * to synchronise against __set_page_dirty_buffers and prevent the
3244         * dirty bit from being lost.
3245         */
3246        if (ret)
3247                cancel_dirty_page(page);
3248        spin_unlock(&mapping->private_lock);
3249out:
3250        if (buffers_to_free) {
3251                struct buffer_head *bh = buffers_to_free;
3252
3253                do {
3254                        struct buffer_head *next = bh->b_this_page;
3255                        free_buffer_head(bh);
3256                        bh = next;
3257                } while (bh != buffers_to_free);
3258        }
3259        return ret;
3260}
3261EXPORT_SYMBOL(try_to_free_buffers);
3262
3263/*
3264 * There are no bdflush tunables left.  But distributions are
3265 * still running obsolete flush daemons, so we terminate them here.
3266 *
3267 * Use of bdflush() is deprecated and will be removed in a future kernel.
3268 * The `flush-X' kernel threads fully replace bdflush daemons and this call.
3269 */
3270SYSCALL_DEFINE2(bdflush, int, func, long, data)
3271{
3272        static int msg_count;
3273
3274        if (!capable(CAP_SYS_ADMIN))
3275                return -EPERM;
3276
3277        if (msg_count < 5) {
3278                msg_count++;
3279                printk(KERN_INFO
3280                        "warning: process `%s' used the obsolete bdflush"
3281                        " system call\n", current->comm);
3282                printk(KERN_INFO "Fix your initscripts?\n");
3283        }
3284
3285        if (func == 1)
3286                do_exit(0);
3287        return 0;
3288}
3289
3290/*
3291 * Buffer-head allocation
3292 */
3293static struct kmem_cache *bh_cachep __read_mostly;
3294
3295/*
3296 * Once the number of bh's in the machine exceeds this level, we start
3297 * stripping them in writeback.
3298 */
3299static unsigned long max_buffer_heads;
3300
3301int buffer_heads_over_limit;
3302
3303struct bh_accounting {
3304        int nr;                 /* Number of live bh's */
3305        int ratelimit;          /* Limit cacheline bouncing */
3306};
3307
3308static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3309
3310static void recalc_bh_state(void)
3311{
3312        int i;
3313        int tot = 0;
3314
3315        if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3316                return;
3317        __this_cpu_write(bh_accounting.ratelimit, 0);
3318        for_each_online_cpu(i)
3319                tot += per_cpu(bh_accounting, i).nr;
3320        buffer_heads_over_limit = (tot > max_buffer_heads);
3321}
3322
3323struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3324{
3325        struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3326        if (ret) {
3327                INIT_LIST_HEAD(&ret->b_assoc_buffers);
3328                preempt_disable();
3329                __this_cpu_inc(bh_accounting.nr);
3330                recalc_bh_state();
3331                preempt_enable();
3332        }
3333        return ret;
3334}
3335EXPORT_SYMBOL(alloc_buffer_head);
3336
3337void free_buffer_head(struct buffer_head *bh)
3338{
3339        BUG_ON(!list_empty(&bh->b_assoc_buffers));
3340        kmem_cache_free(bh_cachep, bh);
3341        preempt_disable();
3342        __this_cpu_dec(bh_accounting.nr);
3343        recalc_bh_state();
3344        preempt_enable();
3345}
3346EXPORT_SYMBOL(free_buffer_head);
3347
3348static void buffer_exit_cpu(int cpu)
3349{
3350        int i;
3351        struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3352
3353        for (i = 0; i < BH_LRU_SIZE; i++) {
3354                brelse(b->bhs[i]);
3355                b->bhs[i] = NULL;
3356        }
3357        this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3358        per_cpu(bh_accounting, cpu).nr = 0;
3359}
3360
3361static int buffer_cpu_notify(struct notifier_block *self,
3362                              unsigned long action, void *hcpu)
3363{
3364        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN)
3365                buffer_exit_cpu((unsigned long)hcpu);
3366        return NOTIFY_OK;
3367}
3368
3369/**
3370 * bh_uptodate_or_lock - Test whether the buffer is uptodate
3371 * @bh: struct buffer_head
3372 *
3373 * Return true if the buffer is up-to-date and false,
3374 * with the buffer locked, if not.
3375 */
3376int bh_uptodate_or_lock(struct buffer_head *bh)
3377{
3378        if (!buffer_uptodate(bh)) {
3379                lock_buffer(bh);
3380                if (!buffer_uptodate(bh))
3381                        return 0;
3382                unlock_buffer(bh);
3383        }
3384        return 1;
3385}
3386EXPORT_SYMBOL(bh_uptodate_or_lock);
3387
3388/**
3389 * bh_submit_read - Submit a locked buffer for reading
3390 * @bh: struct buffer_head
3391 *
3392 * Returns zero on success and -EIO on error.
3393 */
3394int bh_submit_read(struct buffer_head *bh)
3395{
3396        BUG_ON(!buffer_locked(bh));
3397
3398        if (buffer_uptodate(bh)) {
3399                unlock_buffer(bh);
3400                return 0;
3401        }
3402
3403        get_bh(bh);
3404        bh->b_end_io = end_buffer_read_sync;
3405        submit_bh(READ, bh);
3406        wait_on_buffer(bh);
3407        if (buffer_uptodate(bh))
3408                return 0;
3409        return -EIO;
3410}
3411EXPORT_SYMBOL(bh_submit_read);
3412
3413void __init buffer_init(void)
3414{
3415        unsigned long nrpages;
3416
3417        bh_cachep = kmem_cache_create("buffer_head",
3418                        sizeof(struct buffer_head), 0,
3419                                (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3420                                SLAB_MEM_SPREAD),
3421                                NULL);
3422
3423        /*
3424         * Limit the bh occupancy to 10% of ZONE_NORMAL
3425         */
3426        nrpages = (nr_free_buffer_pages() * 10) / 100;
3427        max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3428        hotcpu_notifier(buffer_cpu_notify, 0);
3429}
3430