The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/fs/direct-io.c

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

Cache object: 4ed1d311593250628fe915920ad8b5f7


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