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