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TOMOYO Linux Cross Reference
Linux/fs/direct-io.c

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  1 /*
  2  * fs/direct-io.c
  3  *
  4  * Copyright (C) 2002, Linus Torvalds.
  5  *
  6  * O_DIRECT
  7  *
  8  * 04Jul2002    Andrew Morton
  9  *              Initial version
 10  * 11Sep2002    janetinc@us.ibm.com
 11  *              added readv/writev support.
 12  * 29Oct2002    Andrew Morton
 13  *              rewrote bio_add_page() support.
 14  * 30Oct2002    pbadari@us.ibm.com
 15  *              added support for non-aligned IO.
 16  * 06Nov2002    pbadari@us.ibm.com
 17  *              added asynchronous IO support.
 18  * 21Jul2003    nathans@sgi.com
 19  *              added IO completion notifier.
 20  */
 21 
 22 #include <linux/kernel.h>
 23 #include <linux/module.h>
 24 #include <linux/types.h>
 25 #include <linux/fs.h>
 26 #include <linux/mm.h>
 27 #include <linux/slab.h>
 28 #include <linux/highmem.h>
 29 #include <linux/pagemap.h>
 30 #include <linux/task_io_accounting_ops.h>
 31 #include <linux/bio.h>
 32 #include <linux/wait.h>
 33 #include <linux/err.h>
 34 #include <linux/blkdev.h>
 35 #include <linux/buffer_head.h>
 36 #include <linux/rwsem.h>
 37 #include <linux/uio.h>
 38 #include <linux/atomic.h>
 39 #include <linux/prefetch.h>
 40 
 41 /*
 42  * How many user pages to map in one call to get_user_pages().  This determines
 43  * the size of a structure in the slab cache
 44  */
 45 #define DIO_PAGES       64
 46 
 47 /*
 48  * This code generally works in units of "dio_blocks".  A dio_block is
 49  * somewhere between the hard sector size and the filesystem block size.  it
 50  * is determined on a per-invocation basis.   When talking to the filesystem
 51  * we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity
 52  * down by dio->blkfactor.  Similarly, fs-blocksize quantities are converted
 53  * to bio_block quantities by shifting left by blkfactor.
 54  *
 55  * If blkfactor is zero then the user's request was aligned to the filesystem's
 56  * blocksize.
 57  */
 58 
 59 /* dio_state only used in the submission path */
 60 
 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         sector_t block_in_file;         /* Current offset into the underlying
 74                                            file in dio_block units. */
 75         unsigned blocks_available;      /* At block_in_file.  changes */
 76         int reap_counter;               /* rate limit reaping */
 77         sector_t final_block_in_request;/* doesn't change */
 78         int boundary;                   /* prev block is at a boundary */
 79         get_block_t *get_block;         /* block mapping function */
 80         dio_submit_t *submit_io;        /* IO submition function */
 81 
 82         loff_t logical_offset_in_bio;   /* current first logical block in bio */
 83         sector_t final_block_in_bio;    /* current final block in bio + 1 */
 84         sector_t next_block_for_io;     /* next block to be put under IO,
 85                                            in dio_blocks units */
 86 
 87         /*
 88          * Deferred addition of a page to the dio.  These variables are
 89          * private to dio_send_cur_page(), submit_page_section() and
 90          * dio_bio_add_page().
 91          */
 92         struct page *cur_page;          /* The page */
 93         unsigned cur_page_offset;       /* Offset into it, in bytes */
 94         unsigned cur_page_len;          /* Nr of bytes at cur_page_offset */
 95         sector_t cur_page_block;        /* Where it starts */
 96         loff_t cur_page_fs_offset;      /* Offset in file */
 97 
 98         struct iov_iter *iter;
 99         /*
100          * Page queue.  These variables belong to dio_refill_pages() and
101          * dio_get_page().
102          */
103         unsigned head;                  /* next page to process */
104         unsigned tail;                  /* last valid page + 1 */
105         size_t from, to;
106 };
107 
108 /* dio_state communicated between submission path and end_io */
109 struct dio {
110         int flags;                      /* doesn't change */
111         int rw;
112         blk_qc_t bio_cookie;
113         struct block_device *bio_bdev;
114         struct inode *inode;
115         loff_t i_size;                  /* i_size when submitted */
116         dio_iodone_t *end_io;           /* IO completion function */
117 
118         void *private;                  /* copy from map_bh.b_private */
119 
120         /* BIO completion state */
121         spinlock_t bio_lock;            /* protects BIO fields below */
122         int page_errors;                /* errno from get_user_pages() */
123         int is_async;                   /* is IO async ? */
124         bool defer_completion;          /* defer AIO completion to workqueue? */
125         bool should_dirty;              /* if pages should be dirtied */
126         int io_error;                   /* IO error in completion path */
127         unsigned long refcount;         /* direct_io_worker() and bios */
128         struct bio *bio_list;           /* singly linked via bi_private */
129         struct task_struct *waiter;     /* waiting task (NULL if none) */
130 
131         /* AIO related stuff */
132         struct kiocb *iocb;             /* kiocb */
133         ssize_t result;                 /* IO result */
134 
135         /*
136          * pages[] (and any fields placed after it) are not zeroed out at
137          * allocation time.  Don't add new fields after pages[] unless you
138          * wish that they not be zeroed.
139          */
140         union {
141                 struct page *pages[DIO_PAGES];  /* page buffer */
142                 struct work_struct complete_work;/* deferred AIO completion */
143         };
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         ssize_t ret;
162 
163         ret = iov_iter_get_pages(sdio->iter, dio->pages, LONG_MAX, DIO_PAGES,
164                                 &sdio->from);
165 
166         if (ret < 0 && sdio->blocks_available && (dio->rw & WRITE)) {
167                 struct page *page = ZERO_PAGE(0);
168                 /*
169                  * A memory fault, but the filesystem has some outstanding
170                  * mapped blocks.  We need to use those blocks up to avoid
171                  * leaking stale data in the file.
172                  */
173                 if (dio->page_errors == 0)
174                         dio->page_errors = ret;
175                 page_cache_get(page);
176                 dio->pages[0] = page;
177                 sdio->head = 0;
178                 sdio->tail = 1;
179                 sdio->from = 0;
180                 sdio->to = PAGE_SIZE;
181                 return 0;
182         }
183 
184         if (ret >= 0) {
185                 iov_iter_advance(sdio->iter, ret);
186                 ret += sdio->from;
187                 sdio->head = 0;
188                 sdio->tail = (ret + PAGE_SIZE - 1) / PAGE_SIZE;
189                 sdio->to = ((ret - 1) & (PAGE_SIZE - 1)) + 1;
190                 return 0;
191         }
192         return ret;     
193 }
194 
195 /*
196  * Get another userspace page.  Returns an ERR_PTR on error.  Pages are
197  * buffered inside the dio so that we can call get_user_pages() against a
198  * decent number of pages, less frequently.  To provide nicer use of the
199  * L1 cache.
200  */
201 static inline struct page *dio_get_page(struct dio *dio,
202                                         struct dio_submit *sdio)
203 {
204         if (dio_pages_present(sdio) == 0) {
205                 int ret;
206 
207                 ret = dio_refill_pages(dio, sdio);
208                 if (ret)
209                         return ERR_PTR(ret);
210                 BUG_ON(dio_pages_present(sdio) == 0);
211         }
212         return dio->pages[sdio->head];
213 }
214 
215 /**
216  * dio_complete() - called when all DIO BIO I/O has been completed
217  * @offset: the byte offset in the file of the completed operation
218  *
219  * This drops i_dio_count, lets interested parties know that a DIO operation
220  * has completed, and calculates the resulting return code for the operation.
221  *
222  * It lets the filesystem know if it registered an interest earlier via
223  * get_block.  Pass the private field of the map buffer_head so that
224  * filesystems can use it to hold additional state between get_block calls and
225  * dio_complete.
226  */
227 static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret,
228                 bool is_async)
229 {
230         ssize_t transferred = 0;
231 
232         /*
233          * AIO submission can race with bio completion to get here while
234          * expecting to have the last io completed by bio completion.
235          * In that case -EIOCBQUEUED is in fact not an error we want
236          * to preserve through this call.
237          */
238         if (ret == -EIOCBQUEUED)
239                 ret = 0;
240 
241         if (dio->result) {
242                 transferred = dio->result;
243 
244                 /* Check for short read case */
245                 if ((dio->rw == READ) && ((offset + transferred) > dio->i_size))
246                         transferred = dio->i_size - offset;
247         }
248 
249         if (ret == 0)
250                 ret = dio->page_errors;
251         if (ret == 0)
252                 ret = dio->io_error;
253         if (ret == 0)
254                 ret = transferred;
255 
256         if (dio->end_io && dio->result)
257                 dio->end_io(dio->iocb, offset, transferred, dio->private);
258 
259         if (!(dio->flags & DIO_SKIP_DIO_COUNT))
260                 inode_dio_end(dio->inode);
261 
262         if (is_async) {
263                 if (dio->rw & WRITE) {
264                         int err;
265 
266                         err = generic_write_sync(dio->iocb->ki_filp, offset,
267                                                  transferred);
268                         if (err < 0 && ret > 0)
269                                 ret = err;
270                 }
271 
272                 dio->iocb->ki_complete(dio->iocb, ret, 0);
273         }
274 
275         kmem_cache_free(dio_cache, dio);
276         return ret;
277 }
278 
279 static void dio_aio_complete_work(struct work_struct *work)
280 {
281         struct dio *dio = container_of(work, struct dio, complete_work);
282 
283         dio_complete(dio, dio->iocb->ki_pos, 0, true);
284 }
285 
286 static int dio_bio_complete(struct dio *dio, struct bio *bio);
287 
288 /*
289  * Asynchronous IO callback. 
290  */
291 static void dio_bio_end_aio(struct bio *bio)
292 {
293         struct dio *dio = bio->bi_private;
294         unsigned long remaining;
295         unsigned long flags;
296 
297         /* cleanup the bio */
298         dio_bio_complete(dio, bio);
299 
300         spin_lock_irqsave(&dio->bio_lock, flags);
301         remaining = --dio->refcount;
302         if (remaining == 1 && dio->waiter)
303                 wake_up_process(dio->waiter);
304         spin_unlock_irqrestore(&dio->bio_lock, flags);
305 
306         if (remaining == 0) {
307                 if (dio->result && dio->defer_completion) {
308                         INIT_WORK(&dio->complete_work, dio_aio_complete_work);
309                         queue_work(dio->inode->i_sb->s_dio_done_wq,
310                                    &dio->complete_work);
311                 } else {
312                         dio_complete(dio, dio->iocb->ki_pos, 0, true);
313                 }
314         }
315 }
316 
317 /*
318  * The BIO completion handler simply queues the BIO up for the process-context
319  * handler.
320  *
321  * During I/O bi_private points at the dio.  After I/O, bi_private is used to
322  * implement a singly-linked list of completed BIOs, at dio->bio_list.
323  */
324 static void dio_bio_end_io(struct bio *bio)
325 {
326         struct dio *dio = bio->bi_private;
327         unsigned long flags;
328 
329         spin_lock_irqsave(&dio->bio_lock, flags);
330         bio->bi_private = dio->bio_list;
331         dio->bio_list = bio;
332         if (--dio->refcount == 1 && dio->waiter)
333                 wake_up_process(dio->waiter);
334         spin_unlock_irqrestore(&dio->bio_lock, flags);
335 }
336 
337 /**
338  * dio_end_io - handle the end io action for the given bio
339  * @bio: The direct io bio thats being completed
340  * @error: Error if there was one
341  *
342  * This is meant to be called by any filesystem that uses their own dio_submit_t
343  * so that the DIO specific endio actions are dealt with after the filesystem
344  * has done it's completion work.
345  */
346 void dio_end_io(struct bio *bio, int error)
347 {
348         struct dio *dio = bio->bi_private;
349 
350         if (dio->is_async)
351                 dio_bio_end_aio(bio);
352         else
353                 dio_bio_end_io(bio);
354 }
355 EXPORT_SYMBOL_GPL(dio_end_io);
356 
357 static inline void
358 dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
359               struct block_device *bdev,
360               sector_t first_sector, int nr_vecs)
361 {
362         struct bio *bio;
363 
364         /*
365          * bio_alloc() is guaranteed to return a bio when called with
366          * __GFP_RECLAIM and we request a valid number of vectors.
367          */
368         bio = bio_alloc(GFP_KERNEL, nr_vecs);
369 
370         bio->bi_bdev = bdev;
371         bio->bi_iter.bi_sector = first_sector;
372         if (dio->is_async)
373                 bio->bi_end_io = dio_bio_end_aio;
374         else
375                 bio->bi_end_io = dio_bio_end_io;
376 
377         sdio->bio = bio;
378         sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
379 }
380 
381 /*
382  * In the AIO read case we speculatively dirty the pages before starting IO.
383  * During IO completion, any of these pages which happen to have been written
384  * back will be redirtied by bio_check_pages_dirty().
385  *
386  * bios hold a dio reference between submit_bio and ->end_io.
387  */
388 static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
389 {
390         struct bio *bio = sdio->bio;
391         unsigned long flags;
392 
393         bio->bi_private = dio;
394 
395         spin_lock_irqsave(&dio->bio_lock, flags);
396         dio->refcount++;
397         spin_unlock_irqrestore(&dio->bio_lock, flags);
398 
399         if (dio->is_async && dio->rw == READ && dio->should_dirty)
400                 bio_set_pages_dirty(bio);
401 
402         dio->bio_bdev = bio->bi_bdev;
403 
404         if (sdio->submit_io) {
405                 sdio->submit_io(dio->rw, bio, dio->inode,
406                                sdio->logical_offset_in_bio);
407                 dio->bio_cookie = BLK_QC_T_NONE;
408         } else
409                 dio->bio_cookie = submit_bio(dio->rw, bio);
410 
411         sdio->bio = NULL;
412         sdio->boundary = 0;
413         sdio->logical_offset_in_bio = 0;
414 }
415 
416 /*
417  * Release any resources in case of a failure
418  */
419 static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio)
420 {
421         while (sdio->head < sdio->tail)
422                 page_cache_release(dio->pages[sdio->head++]);
423 }
424 
425 /*
426  * Wait for the next BIO to complete.  Remove it and return it.  NULL is
427  * returned once all BIOs have been completed.  This must only be called once
428  * all bios have been issued so that dio->refcount can only decrease.  This
429  * requires that that the caller hold a reference on the dio.
430  */
431 static struct bio *dio_await_one(struct dio *dio)
432 {
433         unsigned long flags;
434         struct bio *bio = NULL;
435 
436         spin_lock_irqsave(&dio->bio_lock, flags);
437 
438         /*
439          * Wait as long as the list is empty and there are bios in flight.  bio
440          * completion drops the count, maybe adds to the list, and wakes while
441          * holding the bio_lock so we don't need set_current_state()'s barrier
442          * and can call it after testing our condition.
443          */
444         while (dio->refcount > 1 && dio->bio_list == NULL) {
445                 __set_current_state(TASK_UNINTERRUPTIBLE);
446                 dio->waiter = current;
447                 spin_unlock_irqrestore(&dio->bio_lock, flags);
448                 if (!blk_poll(bdev_get_queue(dio->bio_bdev), dio->bio_cookie))
449                         io_schedule();
450                 /* wake up sets us TASK_RUNNING */
451                 spin_lock_irqsave(&dio->bio_lock, flags);
452                 dio->waiter = NULL;
453         }
454         if (dio->bio_list) {
455                 bio = dio->bio_list;
456                 dio->bio_list = bio->bi_private;
457         }
458         spin_unlock_irqrestore(&dio->bio_lock, flags);
459         return bio;
460 }
461 
462 /*
463  * Process one completed BIO.  No locks are held.
464  */
465 static int dio_bio_complete(struct dio *dio, struct bio *bio)
466 {
467         struct bio_vec *bvec;
468         unsigned i;
469         int err;
470 
471         if (bio->bi_error)
472                 dio->io_error = -EIO;
473 
474         if (dio->is_async && dio->rw == READ && dio->should_dirty) {
475                 err = bio->bi_error;
476                 bio_check_pages_dirty(bio);     /* transfers ownership */
477         } else {
478                 bio_for_each_segment_all(bvec, bio, i) {
479                         struct page *page = bvec->bv_page;
480 
481                         if (dio->rw == READ && !PageCompound(page) &&
482                                         dio->should_dirty)
483                                 set_page_dirty_lock(page);
484                         page_cache_release(page);
485                 }
486                 err = bio->bi_error;
487                 bio_put(bio);
488         }
489         return err;
490 }
491 
492 /*
493  * Wait on and process all in-flight BIOs.  This must only be called once
494  * all bios have been issued so that the refcount can only decrease.
495  * This just waits for all bios to make it through dio_bio_complete.  IO
496  * errors are propagated through dio->io_error and should be propagated via
497  * dio_complete().
498  */
499 static void dio_await_completion(struct dio *dio)
500 {
501         struct bio *bio;
502         do {
503                 bio = dio_await_one(dio);
504                 if (bio)
505                         dio_bio_complete(dio, bio);
506         } while (bio);
507 }
508 
509 /*
510  * A really large O_DIRECT read or write can generate a lot of BIOs.  So
511  * to keep the memory consumption sane we periodically reap any completed BIOs
512  * during the BIO generation phase.
513  *
514  * This also helps to limit the peak amount of pinned userspace memory.
515  */
516 static inline int dio_bio_reap(struct dio *dio, struct dio_submit *sdio)
517 {
518         int ret = 0;
519 
520         if (sdio->reap_counter++ >= 64) {
521                 while (dio->bio_list) {
522                         unsigned long flags;
523                         struct bio *bio;
524                         int ret2;
525 
526                         spin_lock_irqsave(&dio->bio_lock, flags);
527                         bio = dio->bio_list;
528                         dio->bio_list = bio->bi_private;
529                         spin_unlock_irqrestore(&dio->bio_lock, flags);
530                         ret2 = dio_bio_complete(dio, bio);
531                         if (ret == 0)
532                                 ret = ret2;
533                 }
534                 sdio->reap_counter = 0;
535         }
536         return ret;
537 }
538 
539 /*
540  * Create workqueue for deferred direct IO completions. We allocate the
541  * workqueue when it's first needed. This avoids creating workqueue for
542  * filesystems that don't need it and also allows us to create the workqueue
543  * late enough so the we can include s_id in the name of the workqueue.
544  */
545 static int sb_init_dio_done_wq(struct super_block *sb)
546 {
547         struct workqueue_struct *old;
548         struct workqueue_struct *wq = alloc_workqueue("dio/%s",
549                                                       WQ_MEM_RECLAIM, 0,
550                                                       sb->s_id);
551         if (!wq)
552                 return -ENOMEM;
553         /*
554          * This has to be atomic as more DIOs can race to create the workqueue
555          */
556         old = cmpxchg(&sb->s_dio_done_wq, NULL, wq);
557         /* Someone created workqueue before us? Free ours... */
558         if (old)
559                 destroy_workqueue(wq);
560         return 0;
561 }
562 
563 static int dio_set_defer_completion(struct dio *dio)
564 {
565         struct super_block *sb = dio->inode->i_sb;
566 
567         if (dio->defer_completion)
568                 return 0;
569         dio->defer_completion = true;
570         if (!sb->s_dio_done_wq)
571                 return sb_init_dio_done_wq(sb);
572         return 0;
573 }
574 
575 /*
576  * Call into the fs to map some more disk blocks.  We record the current number
577  * of available blocks at sdio->blocks_available.  These are in units of the
578  * fs blocksize, (1 << inode->i_blkbits).
579  *
580  * The fs is allowed to map lots of blocks at once.  If it wants to do that,
581  * it uses the passed inode-relative block number as the file offset, as usual.
582  *
583  * get_block() is passed the number of i_blkbits-sized blocks which direct_io
584  * has remaining to do.  The fs should not map more than this number of blocks.
585  *
586  * If the fs has mapped a lot of blocks, it should populate bh->b_size to
587  * indicate how much contiguous disk space has been made available at
588  * bh->b_blocknr.
589  *
590  * If *any* of the mapped blocks are new, then the fs must set buffer_new().
591  * This isn't very efficient...
592  *
593  * In the case of filesystem holes: the fs may return an arbitrarily-large
594  * hole by returning an appropriate value in b_size and by clearing
595  * buffer_mapped().  However the direct-io code will only process holes one
596  * block at a time - it will repeatedly call get_block() as it walks the hole.
597  */
598 static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
599                            struct buffer_head *map_bh)
600 {
601         int ret;
602         sector_t fs_startblk;   /* Into file, in filesystem-sized blocks */
603         sector_t fs_endblk;     /* Into file, in filesystem-sized blocks */
604         unsigned long fs_count; /* Number of filesystem-sized blocks */
605         int create;
606         unsigned int i_blkbits = sdio->blkbits + sdio->blkfactor;
607 
608         /*
609          * If there was a memory error and we've overwritten all the
610          * mapped blocks then we can now return that memory error
611          */
612         ret = dio->page_errors;
613         if (ret == 0) {
614                 BUG_ON(sdio->block_in_file >= sdio->final_block_in_request);
615                 fs_startblk = sdio->block_in_file >> sdio->blkfactor;
616                 fs_endblk = (sdio->final_block_in_request - 1) >>
617                                         sdio->blkfactor;
618                 fs_count = fs_endblk - fs_startblk + 1;
619 
620                 map_bh->b_state = 0;
621                 map_bh->b_size = fs_count << i_blkbits;
622 
623                 /*
624                  * For writes inside i_size on a DIO_SKIP_HOLES filesystem we
625                  * forbid block creations: only overwrites are permitted.
626                  * We will return early to the caller once we see an
627                  * unmapped buffer head returned, and the caller will fall
628                  * back to buffered I/O.
629                  *
630                  * Otherwise the decision is left to the get_blocks method,
631                  * which may decide to handle it or also return an unmapped
632                  * buffer head.
633                  */
634                 create = dio->rw & WRITE;
635                 if (dio->flags & DIO_SKIP_HOLES) {
636                         if (sdio->block_in_file < (i_size_read(dio->inode) >>
637                                                         sdio->blkbits))
638                                 create = 0;
639                 }
640 
641                 ret = (*sdio->get_block)(dio->inode, fs_startblk,
642                                                 map_bh, create);
643 
644                 /* Store for completion */
645                 dio->private = map_bh->b_private;
646 
647                 if (ret == 0 && buffer_defer_completion(map_bh))
648                         ret = dio_set_defer_completion(dio);
649         }
650         return ret;
651 }
652 
653 /*
654  * There is no bio.  Make one now.
655  */
656 static inline int dio_new_bio(struct dio *dio, struct dio_submit *sdio,
657                 sector_t start_sector, struct buffer_head *map_bh)
658 {
659         sector_t sector;
660         int ret, nr_pages;
661 
662         ret = dio_bio_reap(dio, sdio);
663         if (ret)
664                 goto out;
665         sector = start_sector << (sdio->blkbits - 9);
666         nr_pages = min(sdio->pages_in_io, BIO_MAX_PAGES);
667         BUG_ON(nr_pages <= 0);
668         dio_bio_alloc(dio, sdio, map_bh->b_bdev, sector, nr_pages);
669         sdio->boundary = 0;
670 out:
671         return ret;
672 }
673 
674 /*
675  * Attempt to put the current chunk of 'cur_page' into the current BIO.  If
676  * that was successful then update final_block_in_bio and take a ref against
677  * the just-added page.
678  *
679  * Return zero on success.  Non-zero means the caller needs to start a new BIO.
680  */
681 static inline int dio_bio_add_page(struct dio_submit *sdio)
682 {
683         int ret;
684 
685         ret = bio_add_page(sdio->bio, sdio->cur_page,
686                         sdio->cur_page_len, sdio->cur_page_offset);
687         if (ret == sdio->cur_page_len) {
688                 /*
689                  * Decrement count only, if we are done with this page
690                  */
691                 if ((sdio->cur_page_len + sdio->cur_page_offset) == PAGE_SIZE)
692                         sdio->pages_in_io--;
693                 page_cache_get(sdio->cur_page);
694                 sdio->final_block_in_bio = sdio->cur_page_block +
695                         (sdio->cur_page_len >> sdio->blkbits);
696                 ret = 0;
697         } else {
698                 ret = 1;
699         }
700         return ret;
701 }
702                 
703 /*
704  * Put cur_page under IO.  The section of cur_page which is described by
705  * cur_page_offset,cur_page_len is put into a BIO.  The section of cur_page
706  * starts on-disk at cur_page_block.
707  *
708  * We take a ref against the page here (on behalf of its presence in the bio).
709  *
710  * The caller of this function is responsible for removing cur_page from the
711  * dio, and for dropping the refcount which came from that presence.
712  */
713 static inline int dio_send_cur_page(struct dio *dio, struct dio_submit *sdio,
714                 struct buffer_head *map_bh)
715 {
716         int ret = 0;
717 
718         if (sdio->bio) {
719                 loff_t cur_offset = sdio->cur_page_fs_offset;
720                 loff_t bio_next_offset = sdio->logical_offset_in_bio +
721                         sdio->bio->bi_iter.bi_size;
722 
723                 /*
724                  * See whether this new request is contiguous with the old.
725                  *
726                  * Btrfs cannot handle having logically non-contiguous requests
727                  * submitted.  For example if you have
728                  *
729                  * Logical:  [0-4095][HOLE][8192-12287]
730                  * Physical: [0-4095]      [4096-8191]
731                  *
732                  * We cannot submit those pages together as one BIO.  So if our
733                  * current logical offset in the file does not equal what would
734                  * be the next logical offset in the bio, submit the bio we
735                  * have.
736                  */
737                 if (sdio->final_block_in_bio != sdio->cur_page_block ||
738                     cur_offset != bio_next_offset)
739                         dio_bio_submit(dio, sdio);
740         }
741 
742         if (sdio->bio == NULL) {
743                 ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
744                 if (ret)
745                         goto out;
746         }
747 
748         if (dio_bio_add_page(sdio) != 0) {
749                 dio_bio_submit(dio, sdio);
750                 ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
751                 if (ret == 0) {
752                         ret = dio_bio_add_page(sdio);
753                         BUG_ON(ret != 0);
754                 }
755         }
756 out:
757         return ret;
758 }
759 
760 /*
761  * An autonomous function to put a chunk of a page under deferred IO.
762  *
763  * The caller doesn't actually know (or care) whether this piece of page is in
764  * a BIO, or is under IO or whatever.  We just take care of all possible 
765  * situations here.  The separation between the logic of do_direct_IO() and
766  * that of submit_page_section() is important for clarity.  Please don't break.
767  *
768  * The chunk of page starts on-disk at blocknr.
769  *
770  * We perform deferred IO, by recording the last-submitted page inside our
771  * private part of the dio structure.  If possible, we just expand the IO
772  * across that page here.
773  *
774  * If that doesn't work out then we put the old page into the bio and add this
775  * page to the dio instead.
776  */
777 static inline int
778 submit_page_section(struct dio *dio, struct dio_submit *sdio, struct page *page,
779                     unsigned offset, unsigned len, sector_t blocknr,
780                     struct buffer_head *map_bh)
781 {
782         int ret = 0;
783 
784         if (dio->rw & WRITE) {
785                 /*
786                  * Read accounting is performed in submit_bio()
787                  */
788                 task_io_account_write(len);
789         }
790 
791         /*
792          * Can we just grow the current page's presence in the dio?
793          */
794         if (sdio->cur_page == page &&
795             sdio->cur_page_offset + sdio->cur_page_len == offset &&
796             sdio->cur_page_block +
797             (sdio->cur_page_len >> sdio->blkbits) == blocknr) {
798                 sdio->cur_page_len += len;
799                 goto out;
800         }
801 
802         /*
803          * If there's a deferred page already there then send it.
804          */
805         if (sdio->cur_page) {
806                 ret = dio_send_cur_page(dio, sdio, map_bh);
807                 page_cache_release(sdio->cur_page);
808                 sdio->cur_page = NULL;
809                 if (ret)
810                         return ret;
811         }
812 
813         page_cache_get(page);           /* It is in dio */
814         sdio->cur_page = page;
815         sdio->cur_page_offset = offset;
816         sdio->cur_page_len = len;
817         sdio->cur_page_block = blocknr;
818         sdio->cur_page_fs_offset = sdio->block_in_file << sdio->blkbits;
819 out:
820         /*
821          * If sdio->boundary then we want to schedule the IO now to
822          * avoid metadata seeks.
823          */
824         if (sdio->boundary) {
825                 ret = dio_send_cur_page(dio, sdio, map_bh);
826                 dio_bio_submit(dio, sdio);
827                 page_cache_release(sdio->cur_page);
828                 sdio->cur_page = NULL;
829         }
830         return ret;
831 }
832 
833 /*
834  * Clean any dirty buffers in the blockdev mapping which alias newly-created
835  * file blocks.  Only called for S_ISREG files - blockdevs do not set
836  * buffer_new
837  */
838 static void clean_blockdev_aliases(struct dio *dio, struct buffer_head *map_bh)
839 {
840         unsigned i;
841         unsigned nblocks;
842 
843         nblocks = map_bh->b_size >> dio->inode->i_blkbits;
844 
845         for (i = 0; i < nblocks; i++) {
846                 unmap_underlying_metadata(map_bh->b_bdev,
847                                           map_bh->b_blocknr + i);
848         }
849 }
850 
851 /*
852  * If we are not writing the entire block and get_block() allocated
853  * the block for us, we need to fill-in the unused portion of the
854  * block with zeros. This happens only if user-buffer, fileoffset or
855  * io length is not filesystem block-size multiple.
856  *
857  * `end' is zero if we're doing the start of the IO, 1 at the end of the
858  * IO.
859  */
860 static inline void dio_zero_block(struct dio *dio, struct dio_submit *sdio,
861                 int end, struct buffer_head *map_bh)
862 {
863         unsigned dio_blocks_per_fs_block;
864         unsigned this_chunk_blocks;     /* In dio_blocks */
865         unsigned this_chunk_bytes;
866         struct page *page;
867 
868         sdio->start_zero_done = 1;
869         if (!sdio->blkfactor || !buffer_new(map_bh))
870                 return;
871 
872         dio_blocks_per_fs_block = 1 << sdio->blkfactor;
873         this_chunk_blocks = sdio->block_in_file & (dio_blocks_per_fs_block - 1);
874 
875         if (!this_chunk_blocks)
876                 return;
877 
878         /*
879          * We need to zero out part of an fs block.  It is either at the
880          * beginning or the end of the fs block.
881          */
882         if (end) 
883                 this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
884 
885         this_chunk_bytes = this_chunk_blocks << sdio->blkbits;
886 
887         page = ZERO_PAGE(0);
888         if (submit_page_section(dio, sdio, page, 0, this_chunk_bytes,
889                                 sdio->next_block_for_io, map_bh))
890                 return;
891 
892         sdio->next_block_for_io += this_chunk_blocks;
893 }
894 
895 /*
896  * Walk the user pages, and the file, mapping blocks to disk and generating
897  * a sequence of (page,offset,len,block) mappings.  These mappings are injected
898  * into submit_page_section(), which takes care of the next stage of submission
899  *
900  * Direct IO against a blockdev is different from a file.  Because we can
901  * happily perform page-sized but 512-byte aligned IOs.  It is important that
902  * blockdev IO be able to have fine alignment and large sizes.
903  *
904  * So what we do is to permit the ->get_block function to populate bh.b_size
905  * with the size of IO which is permitted at this offset and this i_blkbits.
906  *
907  * For best results, the blockdev should be set up with 512-byte i_blkbits and
908  * it should set b_size to PAGE_SIZE or more inside get_block().  This gives
909  * fine alignment but still allows this function to work in PAGE_SIZE units.
910  */
911 static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
912                         struct buffer_head *map_bh)
913 {
914         const unsigned blkbits = sdio->blkbits;
915         int ret = 0;
916 
917         while (sdio->block_in_file < sdio->final_block_in_request) {
918                 struct page *page;
919                 size_t from, to;
920 
921                 page = dio_get_page(dio, sdio);
922                 if (IS_ERR(page)) {
923                         ret = PTR_ERR(page);
924                         goto out;
925                 }
926                 from = sdio->head ? 0 : sdio->from;
927                 to = (sdio->head == sdio->tail - 1) ? sdio->to : PAGE_SIZE;
928                 sdio->head++;
929 
930                 while (from < to) {
931                         unsigned this_chunk_bytes;      /* # of bytes mapped */
932                         unsigned this_chunk_blocks;     /* # of blocks */
933                         unsigned u;
934 
935                         if (sdio->blocks_available == 0) {
936                                 /*
937                                  * Need to go and map some more disk
938                                  */
939                                 unsigned long blkmask;
940                                 unsigned long dio_remainder;
941 
942                                 ret = get_more_blocks(dio, sdio, map_bh);
943                                 if (ret) {
944                                         page_cache_release(page);
945                                         goto out;
946                                 }
947                                 if (!buffer_mapped(map_bh))
948                                         goto do_holes;
949 
950                                 sdio->blocks_available =
951                                                 map_bh->b_size >> sdio->blkbits;
952                                 sdio->next_block_for_io =
953                                         map_bh->b_blocknr << sdio->blkfactor;
954                                 if (buffer_new(map_bh))
955                                         clean_blockdev_aliases(dio, map_bh);
956 
957                                 if (!sdio->blkfactor)
958                                         goto do_holes;
959 
960                                 blkmask = (1 << sdio->blkfactor) - 1;
961                                 dio_remainder = (sdio->block_in_file & blkmask);
962 
963                                 /*
964                                  * If we are at the start of IO and that IO
965                                  * starts partway into a fs-block,
966                                  * dio_remainder will be non-zero.  If the IO
967                                  * is a read then we can simply advance the IO
968                                  * cursor to the first block which is to be
969                                  * read.  But if the IO is a write and the
970                                  * block was newly allocated we cannot do that;
971                                  * the start of the fs block must be zeroed out
972                                  * on-disk
973                                  */
974                                 if (!buffer_new(map_bh))
975                                         sdio->next_block_for_io += dio_remainder;
976                                 sdio->blocks_available -= dio_remainder;
977                         }
978 do_holes:
979                         /* Handle holes */
980                         if (!buffer_mapped(map_bh)) {
981                                 loff_t i_size_aligned;
982 
983                                 /* AKPM: eargh, -ENOTBLK is a hack */
984                                 if (dio->rw & WRITE) {
985                                         page_cache_release(page);
986                                         return -ENOTBLK;
987                                 }
988 
989                                 /*
990                                  * Be sure to account for a partial block as the
991                                  * last block in the file
992                                  */
993                                 i_size_aligned = ALIGN(i_size_read(dio->inode),
994                                                         1 << blkbits);
995                                 if (sdio->block_in_file >=
996                                                 i_size_aligned >> blkbits) {
997                                         /* We hit eof */
998                                         page_cache_release(page);
999                                         goto out;
1000                                 }
1001                                 zero_user(page, from, 1 << blkbits);
1002                                 sdio->block_in_file++;
1003                                 from += 1 << blkbits;
1004                                 dio->result += 1 << blkbits;
1005                                 goto next_block;
1006                         }
1007 
1008                         /*
1009                          * If we're performing IO which has an alignment which
1010                          * is finer than the underlying fs, go check to see if
1011                          * we must zero out the start of this block.
1012                          */
1013                         if (unlikely(sdio->blkfactor && !sdio->start_zero_done))
1014                                 dio_zero_block(dio, sdio, 0, map_bh);
1015 
1016                         /*
1017                          * Work out, in this_chunk_blocks, how much disk we
1018                          * can add to this page
1019                          */
1020                         this_chunk_blocks = sdio->blocks_available;
1021                         u = (to - from) >> blkbits;
1022                         if (this_chunk_blocks > u)
1023                                 this_chunk_blocks = u;
1024                         u = sdio->final_block_in_request - sdio->block_in_file;
1025                         if (this_chunk_blocks > u)
1026                                 this_chunk_blocks = u;
1027                         this_chunk_bytes = this_chunk_blocks << blkbits;
1028                         BUG_ON(this_chunk_bytes == 0);
1029 
1030                         if (this_chunk_blocks == sdio->blocks_available)
1031                                 sdio->boundary = buffer_boundary(map_bh);
1032                         ret = submit_page_section(dio, sdio, page,
1033                                                   from,
1034                                                   this_chunk_bytes,
1035                                                   sdio->next_block_for_io,
1036                                                   map_bh);
1037                         if (ret) {
1038                                 page_cache_release(page);
1039                                 goto out;
1040                         }
1041                         sdio->next_block_for_io += this_chunk_blocks;
1042 
1043                         sdio->block_in_file += this_chunk_blocks;
1044                         from += this_chunk_bytes;
1045                         dio->result += this_chunk_bytes;
1046                         sdio->blocks_available -= this_chunk_blocks;
1047 next_block:
1048                         BUG_ON(sdio->block_in_file > sdio->final_block_in_request);
1049                         if (sdio->block_in_file == sdio->final_block_in_request)
1050                                 break;
1051                 }
1052 
1053                 /* Drop the ref which was taken in get_user_pages() */
1054                 page_cache_release(page);
1055         }
1056 out:
1057         return ret;
1058 }
1059 
1060 static inline int drop_refcount(struct dio *dio)
1061 {
1062         int ret2;
1063         unsigned long flags;
1064 
1065         /*
1066          * Sync will always be dropping the final ref and completing the
1067          * operation.  AIO can if it was a broken operation described above or
1068          * in fact if all the bios race to complete before we get here.  In
1069          * that case dio_complete() translates the EIOCBQUEUED into the proper
1070          * return code that the caller will hand to ->complete().
1071          *
1072          * This is managed by the bio_lock instead of being an atomic_t so that
1073          * completion paths can drop their ref and use the remaining count to
1074          * decide to wake the submission path atomically.
1075          */
1076         spin_lock_irqsave(&dio->bio_lock, flags);
1077         ret2 = --dio->refcount;
1078         spin_unlock_irqrestore(&dio->bio_lock, flags);
1079         return ret2;
1080 }
1081 
1082 /*
1083  * This is a library function for use by filesystem drivers.
1084  *
1085  * The locking rules are governed by the flags parameter:
1086  *  - if the flags value contains DIO_LOCKING we use a fancy locking
1087  *    scheme for dumb filesystems.
1088  *    For writes this function is called under i_mutex and returns with
1089  *    i_mutex held, for reads, i_mutex is not held on entry, but it is
1090  *    taken and dropped again before returning.
1091  *  - if the flags value does NOT contain DIO_LOCKING we don't use any
1092  *    internal locking but rather rely on the filesystem to synchronize
1093  *    direct I/O reads/writes versus each other and truncate.
1094  *
1095  * To help with locking against truncate we incremented the i_dio_count
1096  * counter before starting direct I/O, and decrement it once we are done.
1097  * Truncate can wait for it to reach zero to provide exclusion.  It is
1098  * expected that filesystem provide exclusion between new direct I/O
1099  * and truncates.  For DIO_LOCKING filesystems this is done by i_mutex,
1100  * but other filesystems need to take care of this on their own.
1101  *
1102  * NOTE: if you pass "sdio" to anything by pointer make sure that function
1103  * is always inlined. Otherwise gcc is unable to split the structure into
1104  * individual fields and will generate much worse code. This is important
1105  * for the whole file.
1106  */
1107 static inline ssize_t
1108 do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
1109                       struct block_device *bdev, struct iov_iter *iter,
1110                       loff_t offset, get_block_t get_block, dio_iodone_t end_io,
1111                       dio_submit_t submit_io, int flags)
1112 {
1113         unsigned i_blkbits = ACCESS_ONCE(inode->i_blkbits);
1114         unsigned blkbits = i_blkbits;
1115         unsigned blocksize_mask = (1 << blkbits) - 1;
1116         ssize_t retval = -EINVAL;
1117         size_t count = iov_iter_count(iter);
1118         loff_t end = offset + count;
1119         struct dio *dio;
1120         struct dio_submit sdio = { 0, };
1121         struct buffer_head map_bh = { 0, };
1122         struct blk_plug plug;
1123         unsigned long align = offset | iov_iter_alignment(iter);
1124 
1125         /*
1126          * Avoid references to bdev if not absolutely needed to give
1127          * the early prefetch in the caller enough time.
1128          */
1129 
1130         if (align & blocksize_mask) {
1131                 if (bdev)
1132                         blkbits = blksize_bits(bdev_logical_block_size(bdev));
1133                 blocksize_mask = (1 << blkbits) - 1;
1134                 if (align & blocksize_mask)
1135                         goto out;
1136         }
1137 
1138         /* watch out for a 0 len io from a tricksy fs */
1139         if (iov_iter_rw(iter) == READ && !iov_iter_count(iter))
1140                 return 0;
1141 
1142         dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
1143         retval = -ENOMEM;
1144         if (!dio)
1145                 goto out;
1146         /*
1147          * Believe it or not, zeroing out the page array caused a .5%
1148          * performance regression in a database benchmark.  So, we take
1149          * care to only zero out what's needed.
1150          */
1151         memset(dio, 0, offsetof(struct dio, pages));
1152 
1153         dio->flags = flags;
1154         if (dio->flags & DIO_LOCKING) {
1155                 if (iov_iter_rw(iter) == READ) {
1156                         struct address_space *mapping =
1157                                         iocb->ki_filp->f_mapping;
1158 
1159                         /* will be released by direct_io_worker */
1160                         inode_lock(inode);
1161 
1162                         retval = filemap_write_and_wait_range(mapping, offset,
1163                                                               end - 1);
1164                         if (retval) {
1165                                 inode_unlock(inode);
1166                                 kmem_cache_free(dio_cache, dio);
1167                                 goto out;
1168                         }
1169                 }
1170         }
1171 
1172         /* Once we sampled i_size check for reads beyond EOF */
1173         dio->i_size = i_size_read(inode);
1174         if (iov_iter_rw(iter) == READ && offset >= dio->i_size) {
1175                 if (dio->flags & DIO_LOCKING)
1176                         inode_unlock(inode);
1177                 kmem_cache_free(dio_cache, dio);
1178                 retval = 0;
1179                 goto out;
1180         }
1181 
1182         /*
1183          * For file extending writes updating i_size before data writeouts
1184          * complete can expose uninitialized blocks in dumb filesystems.
1185          * In that case we need to wait for I/O completion even if asked
1186          * for an asynchronous write.
1187          */
1188         if (is_sync_kiocb(iocb))
1189                 dio->is_async = false;
1190         else if (!(dio->flags & DIO_ASYNC_EXTEND) &&
1191                  iov_iter_rw(iter) == WRITE && end > i_size_read(inode))
1192                 dio->is_async = false;
1193         else
1194                 dio->is_async = true;
1195 
1196         dio->inode = inode;
1197         dio->rw = iov_iter_rw(iter) == WRITE ? WRITE_ODIRECT : READ;
1198 
1199         /*
1200          * For AIO O_(D)SYNC writes we need to defer completions to a workqueue
1201          * so that we can call ->fsync.
1202          */
1203         if (dio->is_async && iov_iter_rw(iter) == WRITE &&
1204             ((iocb->ki_filp->f_flags & O_DSYNC) ||
1205              IS_SYNC(iocb->ki_filp->f_mapping->host))) {
1206                 retval = dio_set_defer_completion(dio);
1207                 if (retval) {
1208                         /*
1209                          * We grab i_mutex only for reads so we don't have
1210                          * to release it here
1211                          */
1212                         kmem_cache_free(dio_cache, dio);
1213                         goto out;
1214                 }
1215         }
1216 
1217         /*
1218          * Will be decremented at I/O completion time.
1219          */
1220         if (!(dio->flags & DIO_SKIP_DIO_COUNT))
1221                 inode_dio_begin(inode);
1222 
1223         retval = 0;
1224         sdio.blkbits = blkbits;
1225         sdio.blkfactor = i_blkbits - blkbits;
1226         sdio.block_in_file = offset >> blkbits;
1227 
1228         sdio.get_block = get_block;
1229         dio->end_io = end_io;
1230         sdio.submit_io = submit_io;
1231         sdio.final_block_in_bio = -1;
1232         sdio.next_block_for_io = -1;
1233 
1234         dio->iocb = iocb;
1235 
1236         spin_lock_init(&dio->bio_lock);
1237         dio->refcount = 1;
1238 
1239         dio->should_dirty = (iter->type == ITER_IOVEC);
1240         sdio.iter = iter;
1241         sdio.final_block_in_request =
1242                 (offset + iov_iter_count(iter)) >> blkbits;
1243 
1244         /*
1245          * In case of non-aligned buffers, we may need 2 more
1246          * pages since we need to zero out first and last block.
1247          */
1248         if (unlikely(sdio.blkfactor))
1249                 sdio.pages_in_io = 2;
1250 
1251         sdio.pages_in_io += iov_iter_npages(iter, INT_MAX);
1252 
1253         blk_start_plug(&plug);
1254 
1255         retval = do_direct_IO(dio, &sdio, &map_bh);
1256         if (retval)
1257                 dio_cleanup(dio, &sdio);
1258 
1259         if (retval == -ENOTBLK) {
1260                 /*
1261                  * The remaining part of the request will be
1262                  * be handled by buffered I/O when we return
1263                  */
1264                 retval = 0;
1265         }
1266         /*
1267          * There may be some unwritten disk at the end of a part-written
1268          * fs-block-sized block.  Go zero that now.
1269          */
1270         dio_zero_block(dio, &sdio, 1, &map_bh);
1271 
1272         if (sdio.cur_page) {
1273                 ssize_t ret2;
1274 
1275                 ret2 = dio_send_cur_page(dio, &sdio, &map_bh);
1276                 if (retval == 0)
1277                         retval = ret2;
1278                 page_cache_release(sdio.cur_page);
1279                 sdio.cur_page = NULL;
1280         }
1281         if (sdio.bio)
1282                 dio_bio_submit(dio, &sdio);
1283 
1284         blk_finish_plug(&plug);
1285 
1286         /*
1287          * It is possible that, we return short IO due to end of file.
1288          * In that case, we need to release all the pages we got hold on.
1289          */
1290         dio_cleanup(dio, &sdio);
1291 
1292         /*
1293          * All block lookups have been performed. For READ requests
1294          * we can let i_mutex go now that its achieved its purpose
1295          * of protecting us from looking up uninitialized blocks.
1296          */
1297         if (iov_iter_rw(iter) == READ && (dio->flags & DIO_LOCKING))
1298                 inode_unlock(dio->inode);
1299 
1300         /*
1301          * The only time we want to leave bios in flight is when a successful
1302          * partial aio read or full aio write have been setup.  In that case
1303          * bio completion will call aio_complete.  The only time it's safe to
1304          * call aio_complete is when we return -EIOCBQUEUED, so we key on that.
1305          * This had *better* be the only place that raises -EIOCBQUEUED.
1306          */
1307         BUG_ON(retval == -EIOCBQUEUED);
1308         if (dio->is_async && retval == 0 && dio->result &&
1309             (iov_iter_rw(iter) == READ || dio->result == count))
1310                 retval = -EIOCBQUEUED;
1311         else
1312                 dio_await_completion(dio);
1313 
1314         if (drop_refcount(dio) == 0) {
1315                 retval = dio_complete(dio, offset, retval, false);
1316         } else
1317                 BUG_ON(retval != -EIOCBQUEUED);
1318 
1319 out:
1320         return retval;
1321 }
1322 
1323 ssize_t __blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
1324                              struct block_device *bdev, struct iov_iter *iter,
1325                              loff_t offset, get_block_t get_block,
1326                              dio_iodone_t end_io, dio_submit_t submit_io,
1327                              int flags)
1328 {
1329         /*
1330          * The block device state is needed in the end to finally
1331          * submit everything.  Since it's likely to be cache cold
1332          * prefetch it here as first thing to hide some of the
1333          * latency.
1334          *
1335          * Attempt to prefetch the pieces we likely need later.
1336          */
1337         prefetch(&bdev->bd_disk->part_tbl);
1338         prefetch(bdev->bd_queue);
1339         prefetch((char *)bdev->bd_queue + SMP_CACHE_BYTES);
1340 
1341         return do_blockdev_direct_IO(iocb, inode, bdev, iter, offset, get_block,
1342                                      end_io, submit_io, flags);
1343 }
1344 
1345 EXPORT_SYMBOL(__blockdev_direct_IO);
1346 
1347 static __init int dio_init(void)
1348 {
1349         dio_cache = KMEM_CACHE(dio, SLAB_PANIC);
1350         return 0;
1351 }
1352 module_init(dio_init)
1353 

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