linux/fs/direct-io.c
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   1/*
   2 * fs/direct-io.c
   3 *
   4 * Copyright (C) 2002, Linus Torvalds.
   5 *
   6 * O_DIRECT
   7 *
   8 * 04Jul2002    Andrew Morton
   9 *              Initial version
  10 * 11Sep2002    janetinc@us.ibm.com
  11 *              added readv/writev support.
  12 * 29Oct2002    Andrew Morton
  13 *              rewrote bio_add_page() support.
  14 * 30Oct2002    pbadari@us.ibm.com
  15 *              added support for non-aligned IO.
  16 * 06Nov2002    pbadari@us.ibm.com
  17 *              added asynchronous IO support.
  18 * 21Jul2003    nathans@sgi.com
  19 *              added IO completion notifier.
  20 */
  21
  22#include <linux/kernel.h>
  23#include <linux/module.h>
  24#include <linux/types.h>
  25#include <linux/fs.h>
  26#include <linux/mm.h>
  27#include <linux/slab.h>
  28#include <linux/highmem.h>
  29#include <linux/pagemap.h>
  30#include <linux/task_io_accounting_ops.h>
  31#include <linux/bio.h>
  32#include <linux/wait.h>
  33#include <linux/err.h>
  34#include <linux/blkdev.h>
  35#include <linux/buffer_head.h>
  36#include <linux/rwsem.h>
  37#include <linux/uio.h>
  38#include <linux/atomic.h>
  39#include <linux/prefetch.h>
  40
  41/*
  42 * How many user pages to map in one call to get_user_pages().  This determines
  43 * the size of a structure in the slab cache
  44 */
  45#define DIO_PAGES       64
  46
  47/*
  48 * This code generally works in units of "dio_blocks".  A dio_block is
  49 * somewhere between the hard sector size and the filesystem block size.  it
  50 * is determined on a per-invocation basis.   When talking to the filesystem
  51 * we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity
  52 * down by dio->blkfactor.  Similarly, fs-blocksize quantities are converted
  53 * to bio_block quantities by shifting left by blkfactor.
  54 *
  55 * If blkfactor is zero then the user's request was aligned to the filesystem's
  56 * blocksize.
  57 */
  58
  59/* dio_state only used in the submission path */
  60
  61struct dio_submit {
  62        struct bio *bio;                /* bio under assembly */
  63        unsigned blkbits;               /* doesn't change */
  64        unsigned blkfactor;             /* When we're using an alignment which
  65                                           is finer than the filesystem's soft
  66                                           blocksize, this specifies how much
  67                                           finer.  blkfactor=2 means 1/4-block
  68                                           alignment.  Does not change */
  69        unsigned start_zero_done;       /* flag: sub-blocksize zeroing has
  70                                           been performed at the start of a
  71                                           write */
  72        int pages_in_io;                /* approximate total IO pages */
  73        size_t  size;                   /* total request size (doesn't change)*/
  74        sector_t block_in_file;         /* Current offset into the underlying
  75                                           file in dio_block units. */
  76        unsigned blocks_available;      /* At block_in_file.  changes */
  77        int reap_counter;               /* rate limit reaping */
  78        sector_t final_block_in_request;/* doesn't change */
  79        unsigned first_block_in_page;   /* doesn't change, Used only once */
  80        int boundary;                   /* prev block is at a boundary */
  81        get_block_t *get_block;         /* block mapping function */
  82        dio_submit_t *submit_io;        /* IO submition function */
  83
  84        loff_t logical_offset_in_bio;   /* current first logical block in bio */
  85        sector_t final_block_in_bio;    /* current final block in bio + 1 */
  86        sector_t next_block_for_io;     /* next block to be put under IO,
  87                                           in dio_blocks units */
  88
  89        /*
  90         * Deferred addition of a page to the dio.  These variables are
  91         * private to dio_send_cur_page(), submit_page_section() and
  92         * dio_bio_add_page().
  93         */
  94        struct page *cur_page;          /* The page */
  95        unsigned cur_page_offset;       /* Offset into it, in bytes */
  96        unsigned cur_page_len;          /* Nr of bytes at cur_page_offset */
  97        sector_t cur_page_block;        /* Where it starts */
  98        loff_t cur_page_fs_offset;      /* Offset in file */
  99
 100        /*
 101         * Page fetching state. These variables belong to dio_refill_pages().
 102         */
 103        int curr_page;                  /* changes */
 104        int total_pages;                /* doesn't change */
 105        unsigned long curr_user_address;/* changes */
 106
 107        /*
 108         * Page queue.  These variables belong to dio_refill_pages() and
 109         * dio_get_page().
 110         */
 111        unsigned head;                  /* next page to process */
 112        unsigned tail;                  /* last valid page + 1 */
 113};
 114
 115/* dio_state communicated between submission path and end_io */
 116struct dio {
 117        int flags;                      /* doesn't change */
 118        int rw;
 119        struct inode *inode;
 120        loff_t i_size;                  /* i_size when submitted */
 121        dio_iodone_t *end_io;           /* IO completion function */
 122
 123        void *private;                  /* copy from map_bh.b_private */
 124
 125        /* BIO completion state */
 126        spinlock_t bio_lock;            /* protects BIO fields below */
 127        int page_errors;                /* errno from get_user_pages() */
 128        int is_async;                   /* is IO async ? */
 129        int io_error;                   /* IO error in completion path */
 130        unsigned long refcount;         /* direct_io_worker() and bios */
 131        struct bio *bio_list;           /* singly linked via bi_private */
 132        struct task_struct *waiter;     /* waiting task (NULL if none) */
 133
 134        /* AIO related stuff */
 135        struct kiocb *iocb;             /* kiocb */
 136        ssize_t result;                 /* IO result */
 137
 138        /*
 139         * pages[] (and any fields placed after it) are not zeroed out at
 140         * allocation time.  Don't add new fields after pages[] unless you
 141         * wish that they not be zeroed.
 142         */
 143        struct page *pages[DIO_PAGES];  /* page buffer */
 144} ____cacheline_aligned_in_smp;
 145
 146static struct kmem_cache *dio_cache __read_mostly;
 147
 148/*
 149 * How many pages are in the queue?
 150 */
 151static inline unsigned dio_pages_present(struct dio_submit *sdio)
 152{
 153        return sdio->tail - sdio->head;
 154}
 155
 156/*
 157 * Go grab and pin some userspace pages.   Typically we'll get 64 at a time.
 158 */
 159static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
 160{
 161        int ret;
 162        int nr_pages;
 163
 164        nr_pages = min(sdio->total_pages - sdio->curr_page, DIO_PAGES);
 165        ret = get_user_pages_fast(
 166                sdio->curr_user_address,                /* Where from? */
 167                nr_pages,                       /* How many pages? */
 168                dio->rw == READ,                /* Write to memory? */
 169                &dio->pages[0]);                /* Put results here */
 170
 171        if (ret < 0 && sdio->blocks_available && (dio->rw & WRITE)) {
 172                struct page *page = ZERO_PAGE(0);
 173                /*
 174                 * A memory fault, but the filesystem has some outstanding
 175                 * mapped blocks.  We need to use those blocks up to avoid
 176                 * leaking stale data in the file.
 177                 */
 178                if (dio->page_errors == 0)
 179                        dio->page_errors = ret;
 180                page_cache_get(page);
 181                dio->pages[0] = page;
 182                sdio->head = 0;
 183                sdio->tail = 1;
 184                ret = 0;
 185                goto out;
 186        }
 187
 188        if (ret >= 0) {
 189                sdio->curr_user_address += ret * PAGE_SIZE;
 190                sdio->curr_page += ret;
 191                sdio->head = 0;
 192                sdio->tail = ret;
 193                ret = 0;
 194        }
 195out:
 196        return ret;     
 197}
 198
 199/*
 200 * Get another userspace page.  Returns an ERR_PTR on error.  Pages are
 201 * buffered inside the dio so that we can call get_user_pages() against a
 202 * decent number of pages, less frequently.  To provide nicer use of the
 203 * L1 cache.
 204 */
 205static inline struct page *dio_get_page(struct dio *dio,
 206                struct dio_submit *sdio)
 207{
 208        if (dio_pages_present(sdio) == 0) {
 209                int ret;
 210
 211                ret = dio_refill_pages(dio, sdio);
 212                if (ret)
 213                        return ERR_PTR(ret);
 214                BUG_ON(dio_pages_present(sdio) == 0);
 215        }
 216        return dio->pages[sdio->head++];
 217}
 218
 219/**
 220 * dio_complete() - called when all DIO BIO I/O has been completed
 221 * @offset: the byte offset in the file of the completed operation
 222 *
 223 * This releases locks as dictated by the locking type, lets interested parties
 224 * know that a DIO operation has completed, and calculates the resulting return
 225 * code for the operation.
 226 *
 227 * It lets the filesystem know if it registered an interest earlier via
 228 * get_block.  Pass the private field of the map buffer_head so that
 229 * filesystems can use it to hold additional state between get_block calls and
 230 * dio_complete.
 231 */
 232static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret, bool is_async)
 233{
 234        ssize_t transferred = 0;
 235
 236        /*
 237         * AIO submission can race with bio completion to get here while
 238         * expecting to have the last io completed by bio completion.
 239         * In that case -EIOCBQUEUED is in fact not an error we want
 240         * to preserve through this call.
 241         */
 242        if (ret == -EIOCBQUEUED)
 243                ret = 0;
 244
 245        if (dio->result) {
 246                transferred = dio->result;
 247
 248                /* Check for short read case */
 249                if ((dio->rw == READ) && ((offset + transferred) > dio->i_size))
 250                        transferred = dio->i_size - offset;
 251        }
 252
 253        if (ret == 0)
 254                ret = dio->page_errors;
 255        if (ret == 0)
 256                ret = dio->io_error;
 257        if (ret == 0)
 258                ret = transferred;
 259
 260        if (dio->end_io && dio->result) {
 261                dio->end_io(dio->iocb, offset, transferred,
 262                            dio->private, ret, is_async);
 263        } else {
 264                if (is_async)
 265                        aio_complete(dio->iocb, ret, 0);
 266                inode_dio_done(dio->inode);
 267        }
 268
 269        return ret;
 270}
 271
 272static int dio_bio_complete(struct dio *dio, struct bio *bio);
 273/*
 274 * Asynchronous IO callback. 
 275 */
 276static void dio_bio_end_aio(struct bio *bio, int error)
 277{
 278        struct dio *dio = bio->bi_private;
 279        unsigned long remaining;
 280        unsigned long flags;
 281
 282        /* cleanup the bio */
 283        dio_bio_complete(dio, bio);
 284
 285        spin_lock_irqsave(&dio->bio_lock, flags);
 286        remaining = --dio->refcount;
 287        if (remaining == 1 && dio->waiter)
 288                wake_up_process(dio->waiter);
 289        spin_unlock_irqrestore(&dio->bio_lock, flags);
 290
 291        if (remaining == 0) {
 292                dio_complete(dio, dio->iocb->ki_pos, 0, true);
 293                kmem_cache_free(dio_cache, dio);
 294        }
 295}
 296
 297/*
 298 * The BIO completion handler simply queues the BIO up for the process-context
 299 * handler.
 300 *
 301 * During I/O bi_private points at the dio.  After I/O, bi_private is used to
 302 * implement a singly-linked list of completed BIOs, at dio->bio_list.
 303 */
 304static void dio_bio_end_io(struct bio *bio, int error)
 305{
 306        struct dio *dio = bio->bi_private;
 307        unsigned long flags;
 308
 309        spin_lock_irqsave(&dio->bio_lock, flags);
 310        bio->bi_private = dio->bio_list;
 311        dio->bio_list = bio;
 312        if (--dio->refcount == 1 && dio->waiter)
 313                wake_up_process(dio->waiter);
 314        spin_unlock_irqrestore(&dio->bio_lock, flags);
 315}
 316
 317/**
 318 * dio_end_io - handle the end io action for the given bio
 319 * @bio: The direct io bio thats being completed
 320 * @error: Error if there was one
 321 *
 322 * This is meant to be called by any filesystem that uses their own dio_submit_t
 323 * so that the DIO specific endio actions are dealt with after the filesystem
 324 * has done it's completion work.
 325 */
 326void dio_end_io(struct bio *bio, int error)
 327{
 328        struct dio *dio = bio->bi_private;
 329
 330        if (dio->is_async)
 331                dio_bio_end_aio(bio, error);
 332        else
 333                dio_bio_end_io(bio, error);
 334}
 335EXPORT_SYMBOL_GPL(dio_end_io);
 336
 337static inline void
 338dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
 339              struct block_device *bdev,
 340              sector_t first_sector, int nr_vecs)
 341{
 342        struct bio *bio;
 343
 344        /*
 345         * bio_alloc() is guaranteed to return a bio when called with
 346         * __GFP_WAIT and we request a valid number of vectors.
 347         */
 348        bio = bio_alloc(GFP_KERNEL, nr_vecs);
 349
 350        bio->bi_bdev = bdev;
 351        bio->bi_sector = first_sector;
 352        if (dio->is_async)
 353                bio->bi_end_io = dio_bio_end_aio;
 354        else
 355                bio->bi_end_io = dio_bio_end_io;
 356
 357        sdio->bio = bio;
 358        sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
 359}
 360
 361/*
 362 * In the AIO read case we speculatively dirty the pages before starting IO.
 363 * During IO completion, any of these pages which happen to have been written
 364 * back will be redirtied by bio_check_pages_dirty().
 365 *
 366 * bios hold a dio reference between submit_bio and ->end_io.
 367 */
 368static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
 369{
 370        struct bio *bio = sdio->bio;
 371        unsigned long flags;
 372
 373        bio->bi_private = dio;
 374
 375        spin_lock_irqsave(&dio->bio_lock, flags);
 376        dio->refcount++;
 377        spin_unlock_irqrestore(&dio->bio_lock, flags);
 378
 379        if (dio->is_async && dio->rw == READ)
 380                bio_set_pages_dirty(bio);
 381
 382        if (sdio->submit_io)
 383                sdio->submit_io(dio->rw, bio, dio->inode,
 384                               sdio->logical_offset_in_bio);
 385        else
 386                submit_bio(dio->rw, bio);
 387
 388        sdio->bio = NULL;
 389        sdio->boundary = 0;
 390        sdio->logical_offset_in_bio = 0;
 391}
 392
 393/*
 394 * Release any resources in case of a failure
 395 */
 396static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio)
 397{
 398        while (dio_pages_present(sdio))
 399                page_cache_release(dio_get_page(dio, sdio));
 400}
 401
 402/*
 403 * Wait for the next BIO to complete.  Remove it and return it.  NULL is
 404 * returned once all BIOs have been completed.  This must only be called once
 405 * all bios have been issued so that dio->refcount can only decrease.  This
 406 * requires that that the caller hold a reference on the dio.
 407 */
 408static struct bio *dio_await_one(struct dio *dio)
 409{
 410        unsigned long flags;
 411        struct bio *bio = NULL;
 412
 413        spin_lock_irqsave(&dio->bio_lock, flags);
 414
 415        /*
 416         * Wait as long as the list is empty and there are bios in flight.  bio
 417         * completion drops the count, maybe adds to the list, and wakes while
 418         * holding the bio_lock so we don't need set_current_state()'s barrier
 419         * and can call it after testing our condition.
 420         */
 421        while (dio->refcount > 1 && dio->bio_list == NULL) {
 422                __set_current_state(TASK_UNINTERRUPTIBLE);
 423                dio->waiter = current;
 424                spin_unlock_irqrestore(&dio->bio_lock, flags);
 425                io_schedule();
 426                /* wake up sets us TASK_RUNNING */
 427                spin_lock_irqsave(&dio->bio_lock, flags);
 428                dio->waiter = NULL;
 429        }
 430        if (dio->bio_list) {
 431                bio = dio->bio_list;
 432                dio->bio_list = bio->bi_private;
 433        }
 434        spin_unlock_irqrestore(&dio->bio_lock, flags);
 435        return bio;
 436}
 437
 438/*
 439 * Process one completed BIO.  No locks are held.
 440 */
 441static int dio_bio_complete(struct dio *dio, struct bio *bio)
 442{
 443        const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
 444        struct bio_vec *bvec = bio->bi_io_vec;
 445        int page_no;
 446
 447        if (!uptodate)
 448                dio->io_error = -EIO;
 449
 450        if (dio->is_async && dio->rw == READ) {
 451                bio_check_pages_dirty(bio);     /* transfers ownership */
 452        } else {
 453                for (page_no = 0; page_no < bio->bi_vcnt; page_no++) {
 454                        struct page *page = bvec[page_no].bv_page;
 455
 456                        if (dio->rw == READ && !PageCompound(page))
 457                                set_page_dirty_lock(page);
 458                        page_cache_release(page);
 459                }
 460                bio_put(bio);
 461        }
 462        return uptodate ? 0 : -EIO;
 463}
 464
 465/*
 466 * Wait on and process all in-flight BIOs.  This must only be called once
 467 * all bios have been issued so that the refcount can only decrease.
 468 * This just waits for all bios to make it through dio_bio_complete.  IO
 469 * errors are propagated through dio->io_error and should be propagated via
 470 * dio_complete().
 471 */
 472static void dio_await_completion(struct dio *dio)
 473{
 474        struct bio *bio;
 475        do {
 476                bio = dio_await_one(dio);
 477                if (bio)
 478                        dio_bio_complete(dio, bio);
 479        } while (bio);
 480}
 481
 482/*
 483 * A really large O_DIRECT read or write can generate a lot of BIOs.  So
 484 * to keep the memory consumption sane we periodically reap any completed BIOs
 485 * during the BIO generation phase.
 486 *
 487 * This also helps to limit the peak amount of pinned userspace memory.
 488 */
 489static inline int dio_bio_reap(struct dio *dio, struct dio_submit *sdio)
 490{
 491        int ret = 0;
 492
 493        if (sdio->reap_counter++ >= 64) {
 494                while (dio->bio_list) {
 495                        unsigned long flags;
 496                        struct bio *bio;
 497                        int ret2;
 498
 499                        spin_lock_irqsave(&dio->bio_lock, flags);
 500                        bio = dio->bio_list;
 501                        dio->bio_list = bio->bi_private;
 502                        spin_unlock_irqrestore(&dio->bio_lock, flags);
 503                        ret2 = dio_bio_complete(dio, bio);
 504                        if (ret == 0)
 505                                ret = ret2;
 506                }
 507                sdio->reap_counter = 0;
 508        }
 509        return ret;
 510}
 511
 512/*
 513 * Call into the fs to map some more disk blocks.  We record the current number
 514 * of available blocks at sdio->blocks_available.  These are in units of the
 515 * fs blocksize, (1 << inode->i_blkbits).
 516 *
 517 * The fs is allowed to map lots of blocks at once.  If it wants to do that,
 518 * it uses the passed inode-relative block number as the file offset, as usual.
 519 *
 520 * get_block() is passed the number of i_blkbits-sized blocks which direct_io
 521 * has remaining to do.  The fs should not map more than this number of blocks.
 522 *
 523 * If the fs has mapped a lot of blocks, it should populate bh->b_size to
 524 * indicate how much contiguous disk space has been made available at
 525 * bh->b_blocknr.
 526 *
 527 * If *any* of the mapped blocks are new, then the fs must set buffer_new().
 528 * This isn't very efficient...
 529 *
 530 * In the case of filesystem holes: the fs may return an arbitrarily-large
 531 * hole by returning an appropriate value in b_size and by clearing
 532 * buffer_mapped().  However the direct-io code will only process holes one
 533 * block at a time - it will repeatedly call get_block() as it walks the hole.
 534 */
 535static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
 536                           struct buffer_head *map_bh)
 537{
 538        int ret;
 539        sector_t fs_startblk;   /* Into file, in filesystem-sized blocks */
 540        sector_t fs_endblk;     /* Into file, in filesystem-sized blocks */
 541        unsigned long fs_count; /* Number of filesystem-sized blocks */
 542        int create;
 543        unsigned int i_blkbits = sdio->blkbits + sdio->blkfactor;
 544
 545        /*
 546         * If there was a memory error and we've overwritten all the
 547         * mapped blocks then we can now return that memory error
 548         */
 549        ret = dio->page_errors;
 550        if (ret == 0) {
 551                BUG_ON(sdio->block_in_file >= sdio->final_block_in_request);
 552                fs_startblk = sdio->block_in_file >> sdio->blkfactor;
 553                fs_endblk = (sdio->final_block_in_request - 1) >>
 554                                        sdio->blkfactor;
 555                fs_count = fs_endblk - fs_startblk + 1;
 556
 557                map_bh->b_state = 0;
 558                map_bh->b_size = fs_count << i_blkbits;
 559
 560                /*
 561                 * For writes inside i_size on a DIO_SKIP_HOLES filesystem we
 562                 * forbid block creations: only overwrites are permitted.
 563                 * We will return early to the caller once we see an
 564                 * unmapped buffer head returned, and the caller will fall
 565                 * back to buffered I/O.
 566                 *
 567                 * Otherwise the decision is left to the get_blocks method,
 568                 * which may decide to handle it or also return an unmapped
 569                 * buffer head.
 570                 */
 571                create = dio->rw & WRITE;
 572                if (dio->flags & DIO_SKIP_HOLES) {
 573                        if (sdio->block_in_file < (i_size_read(dio->inode) >>
 574                                                        sdio->blkbits))
 575                                create = 0;
 576                }
 577
 578                ret = (*sdio->get_block)(dio->inode, fs_startblk,
 579                                                map_bh, create);
 580
 581                /* Store for completion */
 582                dio->private = map_bh->b_private;
 583        }
 584        return ret;
 585}
 586
 587/*
 588 * There is no bio.  Make one now.
 589 */
 590static inline int dio_new_bio(struct dio *dio, struct dio_submit *sdio,
 591                sector_t start_sector, struct buffer_head *map_bh)
 592{
 593        sector_t sector;
 594        int ret, nr_pages;
 595
 596        ret = dio_bio_reap(dio, sdio);
 597        if (ret)
 598                goto out;
 599        sector = start_sector << (sdio->blkbits - 9);
 600        nr_pages = min(sdio->pages_in_io, bio_get_nr_vecs(map_bh->b_bdev));
 601        nr_pages = min(nr_pages, BIO_MAX_PAGES);
 602        BUG_ON(nr_pages <= 0);
 603        dio_bio_alloc(dio, sdio, map_bh->b_bdev, sector, nr_pages);
 604        sdio->boundary = 0;
 605out:
 606        return ret;
 607}
 608
 609/*
 610 * Attempt to put the current chunk of 'cur_page' into the current BIO.  If
 611 * that was successful then update final_block_in_bio and take a ref against
 612 * the just-added page.
 613 *
 614 * Return zero on success.  Non-zero means the caller needs to start a new BIO.
 615 */
 616static inline int dio_bio_add_page(struct dio_submit *sdio)
 617{
 618        int ret;
 619
 620        ret = bio_add_page(sdio->bio, sdio->cur_page,
 621                        sdio->cur_page_len, sdio->cur_page_offset);
 622        if (ret == sdio->cur_page_len) {
 623                /*
 624                 * Decrement count only, if we are done with this page
 625                 */
 626                if ((sdio->cur_page_len + sdio->cur_page_offset) == PAGE_SIZE)
 627                        sdio->pages_in_io--;
 628                page_cache_get(sdio->cur_page);
 629                sdio->final_block_in_bio = sdio->cur_page_block +
 630                        (sdio->cur_page_len >> sdio->blkbits);
 631                ret = 0;
 632        } else {
 633                ret = 1;
 634        }
 635        return ret;
 636}
 637                
 638/*
 639 * Put cur_page under IO.  The section of cur_page which is described by
 640 * cur_page_offset,cur_page_len is put into a BIO.  The section of cur_page
 641 * starts on-disk at cur_page_block.
 642 *
 643 * We take a ref against the page here (on behalf of its presence in the bio).
 644 *
 645 * The caller of this function is responsible for removing cur_page from the
 646 * dio, and for dropping the refcount which came from that presence.
 647 */
 648static inline int dio_send_cur_page(struct dio *dio, struct dio_submit *sdio,
 649                struct buffer_head *map_bh)
 650{
 651        int ret = 0;
 652
 653        if (sdio->bio) {
 654                loff_t cur_offset = sdio->cur_page_fs_offset;
 655                loff_t bio_next_offset = sdio->logical_offset_in_bio +
 656                        sdio->bio->bi_size;
 657
 658                /*
 659                 * See whether this new request is contiguous with the old.
 660                 *
 661                 * Btrfs cannot handle having logically non-contiguous requests
 662                 * submitted.  For example if you have
 663                 *
 664                 * Logical:  [0-4095][HOLE][8192-12287]
 665                 * Physical: [0-4095]      [4096-8191]
 666                 *
 667                 * We cannot submit those pages together as one BIO.  So if our
 668                 * current logical offset in the file does not equal what would
 669                 * be the next logical offset in the bio, submit the bio we
 670                 * have.
 671                 */
 672                if (sdio->final_block_in_bio != sdio->cur_page_block ||
 673                    cur_offset != bio_next_offset)
 674                        dio_bio_submit(dio, sdio);
 675                /*
 676                 * Submit now if the underlying fs is about to perform a
 677                 * metadata read
 678                 */
 679                else if (sdio->boundary)
 680                        dio_bio_submit(dio, sdio);
 681        }
 682
 683        if (sdio->bio == NULL) {
 684                ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
 685                if (ret)
 686                        goto out;
 687        }
 688
 689        if (dio_bio_add_page(sdio) != 0) {
 690                dio_bio_submit(dio, sdio);
 691                ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
 692                if (ret == 0) {
 693                        ret = dio_bio_add_page(sdio);
 694                        BUG_ON(ret != 0);
 695                }
 696        }
 697out:
 698        return ret;
 699}
 700
 701/*
 702 * An autonomous function to put a chunk of a page under deferred IO.
 703 *
 704 * The caller doesn't actually know (or care) whether this piece of page is in
 705 * a BIO, or is under IO or whatever.  We just take care of all possible 
 706 * situations here.  The separation between the logic of do_direct_IO() and
 707 * that of submit_page_section() is important for clarity.  Please don't break.
 708 *
 709 * The chunk of page starts on-disk at blocknr.
 710 *
 711 * We perform deferred IO, by recording the last-submitted page inside our
 712 * private part of the dio structure.  If possible, we just expand the IO
 713 * across that page here.
 714 *
 715 * If that doesn't work out then we put the old page into the bio and add this
 716 * page to the dio instead.
 717 */
 718static inline int
 719submit_page_section(struct dio *dio, struct dio_submit *sdio, struct page *page,
 720                    unsigned offset, unsigned len, sector_t blocknr,
 721                    struct buffer_head *map_bh)
 722{
 723        int ret = 0;
 724
 725        if (dio->rw & WRITE) {
 726                /*
 727                 * Read accounting is performed in submit_bio()
 728                 */
 729                task_io_account_write(len);
 730        }
 731
 732        /*
 733         * Can we just grow the current page's presence in the dio?
 734         */
 735        if (sdio->cur_page == page &&
 736            sdio->cur_page_offset + sdio->cur_page_len == offset &&
 737            sdio->cur_page_block +
 738            (sdio->cur_page_len >> sdio->blkbits) == blocknr) {
 739                sdio->cur_page_len += len;
 740
 741                /*
 742                 * If sdio->boundary then we want to schedule the IO now to
 743                 * avoid metadata seeks.
 744                 */
 745                if (sdio->boundary) {
 746                        ret = dio_send_cur_page(dio, sdio, map_bh);
 747                        page_cache_release(sdio->cur_page);
 748                        sdio->cur_page = NULL;
 749                }
 750                goto out;
 751        }
 752
 753        /*
 754         * If there's a deferred page already there then send it.
 755         */
 756        if (sdio->cur_page) {
 757                ret = dio_send_cur_page(dio, sdio, map_bh);
 758                page_cache_release(sdio->cur_page);
 759                sdio->cur_page = NULL;
 760                if (ret)
 761                        goto out;
 762        }
 763
 764        page_cache_get(page);           /* It is in dio */
 765        sdio->cur_page = page;
 766        sdio->cur_page_offset = offset;
 767        sdio->cur_page_len = len;
 768        sdio->cur_page_block = blocknr;
 769        sdio->cur_page_fs_offset = sdio->block_in_file << sdio->blkbits;
 770out:
 771        return ret;
 772}
 773
 774/*
 775 * Clean any dirty buffers in the blockdev mapping which alias newly-created
 776 * file blocks.  Only called for S_ISREG files - blockdevs do not set
 777 * buffer_new
 778 */
 779static void clean_blockdev_aliases(struct dio *dio, struct buffer_head *map_bh)
 780{
 781        unsigned i;
 782        unsigned nblocks;
 783
 784        nblocks = map_bh->b_size >> dio->inode->i_blkbits;
 785
 786        for (i = 0; i < nblocks; i++) {
 787                unmap_underlying_metadata(map_bh->b_bdev,
 788                                          map_bh->b_blocknr + i);
 789        }
 790}
 791
 792/*
 793 * If we are not writing the entire block and get_block() allocated
 794 * the block for us, we need to fill-in the unused portion of the
 795 * block with zeros. This happens only if user-buffer, fileoffset or
 796 * io length is not filesystem block-size multiple.
 797 *
 798 * `end' is zero if we're doing the start of the IO, 1 at the end of the
 799 * IO.
 800 */
 801static inline void dio_zero_block(struct dio *dio, struct dio_submit *sdio,
 802                int end, struct buffer_head *map_bh)
 803{
 804        unsigned dio_blocks_per_fs_block;
 805        unsigned this_chunk_blocks;     /* In dio_blocks */
 806        unsigned this_chunk_bytes;
 807        struct page *page;
 808
 809        sdio->start_zero_done = 1;
 810        if (!sdio->blkfactor || !buffer_new(map_bh))
 811                return;
 812
 813        dio_blocks_per_fs_block = 1 << sdio->blkfactor;
 814        this_chunk_blocks = sdio->block_in_file & (dio_blocks_per_fs_block - 1);
 815
 816        if (!this_chunk_blocks)
 817                return;
 818
 819        /*
 820         * We need to zero out part of an fs block.  It is either at the
 821         * beginning or the end of the fs block.
 822         */
 823        if (end) 
 824                this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
 825
 826        this_chunk_bytes = this_chunk_blocks << sdio->blkbits;
 827
 828        page = ZERO_PAGE(0);
 829        if (submit_page_section(dio, sdio, page, 0, this_chunk_bytes,
 830                                sdio->next_block_for_io, map_bh))
 831                return;
 832
 833        sdio->next_block_for_io += this_chunk_blocks;
 834}
 835
 836/*
 837 * Walk the user pages, and the file, mapping blocks to disk and generating
 838 * a sequence of (page,offset,len,block) mappings.  These mappings are injected
 839 * into submit_page_section(), which takes care of the next stage of submission
 840 *
 841 * Direct IO against a blockdev is different from a file.  Because we can
 842 * happily perform page-sized but 512-byte aligned IOs.  It is important that
 843 * blockdev IO be able to have fine alignment and large sizes.
 844 *
 845 * So what we do is to permit the ->get_block function to populate bh.b_size
 846 * with the size of IO which is permitted at this offset and this i_blkbits.
 847 *
 848 * For best results, the blockdev should be set up with 512-byte i_blkbits and
 849 * it should set b_size to PAGE_SIZE or more inside get_block().  This gives
 850 * fine alignment but still allows this function to work in PAGE_SIZE units.
 851 */
 852static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
 853                        struct buffer_head *map_bh)
 854{
 855        const unsigned blkbits = sdio->blkbits;
 856        const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
 857        struct page *page;
 858        unsigned block_in_page;
 859        int ret = 0;
 860
 861        /* The I/O can start at any block offset within the first page */
 862        block_in_page = sdio->first_block_in_page;
 863
 864        while (sdio->block_in_file < sdio->final_block_in_request) {
 865                page = dio_get_page(dio, sdio);
 866                if (IS_ERR(page)) {
 867                        ret = PTR_ERR(page);
 868                        goto out;
 869                }
 870
 871                while (block_in_page < blocks_per_page) {
 872                        unsigned offset_in_page = block_in_page << blkbits;
 873                        unsigned this_chunk_bytes;      /* # of bytes mapped */
 874                        unsigned this_chunk_blocks;     /* # of blocks */
 875                        unsigned u;
 876
 877                        if (sdio->blocks_available == 0) {
 878                                /*
 879                                 * Need to go and map some more disk
 880                                 */
 881                                unsigned long blkmask;
 882                                unsigned long dio_remainder;
 883
 884                                ret = get_more_blocks(dio, sdio, map_bh);
 885                                if (ret) {
 886                                        page_cache_release(page);
 887                                        goto out;
 888                                }
 889                                if (!buffer_mapped(map_bh))
 890                                        goto do_holes;
 891
 892                                sdio->blocks_available =
 893                                                map_bh->b_size >> sdio->blkbits;
 894                                sdio->next_block_for_io =
 895                                        map_bh->b_blocknr << sdio->blkfactor;
 896                                if (buffer_new(map_bh))
 897                                        clean_blockdev_aliases(dio, map_bh);
 898
 899                                if (!sdio->blkfactor)
 900                                        goto do_holes;
 901
 902                                blkmask = (1 << sdio->blkfactor) - 1;
 903                                dio_remainder = (sdio->block_in_file & blkmask);
 904
 905                                /*
 906                                 * If we are at the start of IO and that IO
 907                                 * starts partway into a fs-block,
 908                                 * dio_remainder will be non-zero.  If the IO
 909                                 * is a read then we can simply advance the IO
 910                                 * cursor to the first block which is to be
 911                                 * read.  But if the IO is a write and the
 912                                 * block was newly allocated we cannot do that;
 913                                 * the start of the fs block must be zeroed out
 914                                 * on-disk
 915                                 */
 916                                if (!buffer_new(map_bh))
 917                                        sdio->next_block_for_io += dio_remainder;
 918                                sdio->blocks_available -= dio_remainder;
 919                        }
 920do_holes:
 921                        /* Handle holes */
 922                        if (!buffer_mapped(map_bh)) {
 923                                loff_t i_size_aligned;
 924
 925                                /* AKPM: eargh, -ENOTBLK is a hack */
 926                                if (dio->rw & WRITE) {
 927                                        page_cache_release(page);
 928                                        return -ENOTBLK;
 929                                }
 930
 931                                /*
 932                                 * Be sure to account for a partial block as the
 933                                 * last block in the file
 934                                 */
 935                                i_size_aligned = ALIGN(i_size_read(dio->inode),
 936                                                        1 << blkbits);
 937                                if (sdio->block_in_file >=
 938                                                i_size_aligned >> blkbits) {
 939                                        /* We hit eof */
 940                                        page_cache_release(page);
 941                                        goto out;
 942                                }
 943                                zero_user(page, block_in_page << blkbits,
 944                                                1 << blkbits);
 945                                sdio->block_in_file++;
 946                                block_in_page++;
 947                                goto next_block;
 948                        }
 949
 950                        /*
 951                         * If we're performing IO which has an alignment which
 952                         * is finer than the underlying fs, go check to see if
 953                         * we must zero out the start of this block.
 954                         */
 955                        if (unlikely(sdio->blkfactor && !sdio->start_zero_done))
 956                                dio_zero_block(dio, sdio, 0, map_bh);
 957
 958                        /*
 959                         * Work out, in this_chunk_blocks, how much disk we
 960                         * can add to this page
 961                         */
 962                        this_chunk_blocks = sdio->blocks_available;
 963                        u = (PAGE_SIZE - offset_in_page) >> blkbits;
 964                        if (this_chunk_blocks > u)
 965                                this_chunk_blocks = u;
 966                        u = sdio->final_block_in_request - sdio->block_in_file;
 967                        if (this_chunk_blocks > u)
 968                                this_chunk_blocks = u;
 969                        this_chunk_bytes = this_chunk_blocks << blkbits;
 970                        BUG_ON(this_chunk_bytes == 0);
 971
 972                        sdio->boundary = buffer_boundary(map_bh);
 973                        ret = submit_page_section(dio, sdio, page,
 974                                                  offset_in_page,
 975                                                  this_chunk_bytes,
 976                                                  sdio->next_block_for_io,
 977                                                  map_bh);
 978                        if (ret) {
 979                                page_cache_release(page);
 980                                goto out;
 981                        }
 982                        sdio->next_block_for_io += this_chunk_blocks;
 983
 984                        sdio->block_in_file += this_chunk_blocks;
 985                        block_in_page += this_chunk_blocks;
 986                        sdio->blocks_available -= this_chunk_blocks;
 987next_block:
 988                        BUG_ON(sdio->block_in_file > sdio->final_block_in_request);
 989                        if (sdio->block_in_file == sdio->final_block_in_request)
 990                                break;
 991                }
 992
 993                /* Drop the ref which was taken in get_user_pages() */
 994                page_cache_release(page);
 995                block_in_page = 0;
 996        }
 997out:
 998        return ret;
 999}
1000
1001static inline int drop_refcount(struct dio *dio)
1002{
1003        int ret2;
1004        unsigned long flags;
1005
1006        /*
1007         * Sync will always be dropping the final ref and completing the
1008         * operation.  AIO can if it was a broken operation described above or
1009         * in fact if all the bios race to complete before we get here.  In
1010         * that case dio_complete() translates the EIOCBQUEUED into the proper
1011         * return code that the caller will hand to aio_complete().
1012         *
1013         * This is managed by the bio_lock instead of being an atomic_t so that
1014         * completion paths can drop their ref and use the remaining count to
1015         * decide to wake the submission path atomically.
1016         */
1017        spin_lock_irqsave(&dio->bio_lock, flags);
1018        ret2 = --dio->refcount;
1019        spin_unlock_irqrestore(&dio->bio_lock, flags);
1020        return ret2;
1021}
1022
1023/*
1024 * This is a library function for use by filesystem drivers.
1025 *
1026 * The locking rules are governed by the flags parameter:
1027 *  - if the flags value contains DIO_LOCKING we use a fancy locking
1028 *    scheme for dumb filesystems.
1029 *    For writes this function is called under i_mutex and returns with
1030 *    i_mutex held, for reads, i_mutex is not held on entry, but it is
1031 *    taken and dropped again before returning.
1032 *  - if the flags value does NOT contain DIO_LOCKING we don't use any
1033 *    internal locking but rather rely on the filesystem to synchronize
1034 *    direct I/O reads/writes versus each other and truncate.
1035 *
1036 * To help with locking against truncate we incremented the i_dio_count
1037 * counter before starting direct I/O, and decrement it once we are done.
1038 * Truncate can wait for it to reach zero to provide exclusion.  It is
1039 * expected that filesystem provide exclusion between new direct I/O
1040 * and truncates.  For DIO_LOCKING filesystems this is done by i_mutex,
1041 * but other filesystems need to take care of this on their own.
1042 *
1043 * NOTE: if you pass "sdio" to anything by pointer make sure that function
1044 * is always inlined. Otherwise gcc is unable to split the structure into
1045 * individual fields and will generate much worse code. This is important
1046 * for the whole file.
1047 */
1048static inline ssize_t
1049do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
1050        struct block_device *bdev, const struct iovec *iov, loff_t offset, 
1051        unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io,
1052        dio_submit_t submit_io, int flags)
1053{
1054        int seg;
1055        size_t size;
1056        unsigned long addr;
1057        unsigned i_blkbits = ACCESS_ONCE(inode->i_blkbits);
1058        unsigned blkbits = i_blkbits;
1059        unsigned blocksize_mask = (1 << blkbits) - 1;
1060        ssize_t retval = -EINVAL;
1061        loff_t end = offset;
1062        struct dio *dio;
1063        struct dio_submit sdio = { 0, };
1064        unsigned long user_addr;
1065        size_t bytes;
1066        struct buffer_head map_bh = { 0, };
1067        struct blk_plug plug;
1068
1069        if (rw & WRITE)
1070                rw = WRITE_ODIRECT;
1071
1072        /*
1073         * Avoid references to bdev if not absolutely needed to give
1074         * the early prefetch in the caller enough time.
1075         */
1076
1077        if (offset & blocksize_mask) {
1078                if (bdev)
1079                        blkbits = blksize_bits(bdev_logical_block_size(bdev));
1080                blocksize_mask = (1 << blkbits) - 1;
1081                if (offset & blocksize_mask)
1082                        goto out;
1083        }
1084
1085        /* Check the memory alignment.  Blocks cannot straddle pages */
1086        for (seg = 0; seg < nr_segs; seg++) {
1087                addr = (unsigned long)iov[seg].iov_base;
1088                size = iov[seg].iov_len;
1089                end += size;
1090                if (unlikely((addr & blocksize_mask) ||
1091                             (size & blocksize_mask))) {
1092                        if (bdev)
1093                                blkbits = blksize_bits(
1094                                         bdev_logical_block_size(bdev));
1095                        blocksize_mask = (1 << blkbits) - 1;
1096                        if ((addr & blocksize_mask) || (size & blocksize_mask))
1097                                goto out;
1098                }
1099        }
1100
1101        /* watch out for a 0 len io from a tricksy fs */
1102        if (rw == READ && end == offset)
1103                return 0;
1104
1105        dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
1106        retval = -ENOMEM;
1107        if (!dio)
1108                goto out;
1109        /*
1110         * Believe it or not, zeroing out the page array caused a .5%
1111         * performance regression in a database benchmark.  So, we take
1112         * care to only zero out what's needed.
1113         */
1114        memset(dio, 0, offsetof(struct dio, pages));
1115
1116        dio->flags = flags;
1117        if (dio->flags & DIO_LOCKING) {
1118                if (rw == READ) {
1119                        struct address_space *mapping =
1120                                        iocb->ki_filp->f_mapping;
1121
1122                        /* will be released by direct_io_worker */
1123                        mutex_lock(&inode->i_mutex);
1124
1125                        retval = filemap_write_and_wait_range(mapping, offset,
1126                                                              end - 1);
1127                        if (retval) {
1128                                mutex_unlock(&inode->i_mutex);
1129                                kmem_cache_free(dio_cache, dio);
1130                                goto out;
1131                        }
1132                }
1133        }
1134
1135        /*
1136         * Will be decremented at I/O completion time.
1137         */
1138        atomic_inc(&inode->i_dio_count);
1139
1140        /*
1141         * For file extending writes updating i_size before data
1142         * writeouts complete can expose uninitialized blocks. So
1143         * even for AIO, we need to wait for i/o to complete before
1144         * returning in this case.
1145         */
1146        dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) &&
1147                (end > i_size_read(inode)));
1148
1149        retval = 0;
1150
1151        dio->inode = inode;
1152        dio->rw = rw;
1153        sdio.blkbits = blkbits;
1154        sdio.blkfactor = i_blkbits - blkbits;
1155        sdio.block_in_file = offset >> blkbits;
1156
1157        sdio.get_block = get_block;
1158        dio->end_io = end_io;
1159        sdio.submit_io = submit_io;
1160        sdio.final_block_in_bio = -1;
1161        sdio.next_block_for_io = -1;
1162
1163        dio->iocb = iocb;
1164        dio->i_size = i_size_read(inode);
1165
1166        spin_lock_init(&dio->bio_lock);
1167        dio->refcount = 1;
1168
1169        /*
1170         * In case of non-aligned buffers, we may need 2 more
1171         * pages since we need to zero out first and last block.
1172         */
1173        if (unlikely(sdio.blkfactor))
1174                sdio.pages_in_io = 2;
1175
1176        for (seg = 0; seg < nr_segs; seg++) {
1177                user_addr = (unsigned long)iov[seg].iov_base;
1178                sdio.pages_in_io +=
1179                        ((user_addr + iov[seg].iov_len + PAGE_SIZE-1) /
1180                                PAGE_SIZE - user_addr / PAGE_SIZE);
1181        }
1182
1183        blk_start_plug(&plug);
1184
1185        for (seg = 0; seg < nr_segs; seg++) {
1186                user_addr = (unsigned long)iov[seg].iov_base;
1187                sdio.size += bytes = iov[seg].iov_len;
1188
1189                /* Index into the first page of the first block */
1190                sdio.first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits;
1191                sdio.final_block_in_request = sdio.block_in_file +
1192                                                (bytes >> blkbits);
1193                /* Page fetching state */
1194                sdio.head = 0;
1195                sdio.tail = 0;
1196                sdio.curr_page = 0;
1197
1198                sdio.total_pages = 0;
1199                if (user_addr & (PAGE_SIZE-1)) {
1200                        sdio.total_pages++;
1201                        bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1));
1202                }
1203                sdio.total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
1204                sdio.curr_user_address = user_addr;
1205
1206                retval = do_direct_IO(dio, &sdio, &map_bh);
1207
1208                dio->result += iov[seg].iov_len -
1209                        ((sdio.final_block_in_request - sdio.block_in_file) <<
1210                                        blkbits);
1211
1212                if (retval) {
1213                        dio_cleanup(dio, &sdio);
1214                        break;
1215                }
1216        } /* end iovec loop */
1217
1218        if (retval == -ENOTBLK) {
1219                /*
1220                 * The remaining part of the request will be
1221                 * be handled by buffered I/O when we return
1222                 */
1223                retval = 0;
1224        }
1225        /*
1226         * There may be some unwritten disk at the end of a part-written
1227         * fs-block-sized block.  Go zero that now.
1228         */
1229        dio_zero_block(dio, &sdio, 1, &map_bh);
1230
1231        if (sdio.cur_page) {
1232                ssize_t ret2;
1233
1234                ret2 = dio_send_cur_page(dio, &sdio, &map_bh);
1235                if (retval == 0)
1236                        retval = ret2;
1237                page_cache_release(sdio.cur_page);
1238                sdio.cur_page = NULL;
1239        }
1240        if (sdio.bio)
1241                dio_bio_submit(dio, &sdio);
1242
1243        blk_finish_plug(&plug);
1244
1245        /*
1246         * It is possible that, we return short IO due to end of file.
1247         * In that case, we need to release all the pages we got hold on.
1248         */
1249        dio_cleanup(dio, &sdio);
1250
1251        /*
1252         * All block lookups have been performed. For READ requests
1253         * we can let i_mutex go now that its achieved its purpose
1254         * of protecting us from looking up uninitialized blocks.
1255         */
1256        if (rw == READ && (dio->flags & DIO_LOCKING))
1257                mutex_unlock(&dio->inode->i_mutex);
1258
1259        /*
1260         * The only time we want to leave bios in flight is when a successful
1261         * partial aio read or full aio write have been setup.  In that case
1262         * bio completion will call aio_complete.  The only time it's safe to
1263         * call aio_complete is when we return -EIOCBQUEUED, so we key on that.
1264         * This had *better* be the only place that raises -EIOCBQUEUED.
1265         */
1266        BUG_ON(retval == -EIOCBQUEUED);
1267        if (dio->is_async && retval == 0 && dio->result &&
1268            ((rw == READ) || (dio->result == sdio.size)))
1269                retval = -EIOCBQUEUED;
1270
1271        if (retval != -EIOCBQUEUED)
1272                dio_await_completion(dio);
1273
1274        if (drop_refcount(dio) == 0) {
1275                retval = dio_complete(dio, offset, retval, false);
1276                kmem_cache_free(dio_cache, dio);
1277        } else
1278                BUG_ON(retval != -EIOCBQUEUED);
1279
1280out:
1281        return retval;
1282}
1283
1284ssize_t
1285__blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
1286        struct block_device *bdev, const struct iovec *iov, loff_t offset,
1287        unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io,
1288        dio_submit_t submit_io, int flags)
1289{
1290        /*
1291         * The block device state is needed in the end to finally
1292         * submit everything.  Since it's likely to be cache cold
1293         * prefetch it here as first thing to hide some of the
1294         * latency.
1295         *
1296         * Attempt to prefetch the pieces we likely need later.
1297         */
1298        prefetch(&bdev->bd_disk->part_tbl);
1299        prefetch(bdev->bd_queue);
1300        prefetch((char *)bdev->bd_queue + SMP_CACHE_BYTES);
1301
1302        return do_blockdev_direct_IO(rw, iocb, inode, bdev, iov, offset,
1303                                     nr_segs, get_block, end_io,
1304                                     submit_io, flags);
1305}
1306
1307EXPORT_SYMBOL(__blockdev_direct_IO);
1308
1309static __init int dio_init(void)
1310{
1311        dio_cache = KMEM_CACHE(dio, SLAB_PANIC);
1312        return 0;
1313}
1314module_init(dio_init)
1315
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