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