xref: /openbmc/linux/fs/direct-io.c (revision 6774def6)
1 /*
2  * fs/direct-io.c
3  *
4  * Copyright (C) 2002, Linus Torvalds.
5  *
6  * O_DIRECT
7  *
8  * 04Jul2002	Andrew Morton
9  *		Initial version
10  * 11Sep2002	janetinc@us.ibm.com
11  * 		added readv/writev support.
12  * 29Oct2002	Andrew Morton
13  *		rewrote bio_add_page() support.
14  * 30Oct2002	pbadari@us.ibm.com
15  *		added support for non-aligned IO.
16  * 06Nov2002	pbadari@us.ibm.com
17  *		added asynchronous IO support.
18  * 21Jul2003	nathans@sgi.com
19  *		added IO completion notifier.
20  */
21 
22 #include <linux/kernel.h>
23 #include <linux/module.h>
24 #include <linux/types.h>
25 #include <linux/fs.h>
26 #include <linux/mm.h>
27 #include <linux/slab.h>
28 #include <linux/highmem.h>
29 #include <linux/pagemap.h>
30 #include <linux/task_io_accounting_ops.h>
31 #include <linux/bio.h>
32 #include <linux/wait.h>
33 #include <linux/err.h>
34 #include <linux/blkdev.h>
35 #include <linux/buffer_head.h>
36 #include <linux/rwsem.h>
37 #include <linux/uio.h>
38 #include <linux/atomic.h>
39 #include <linux/prefetch.h>
40 #include <linux/aio.h>
41 
42 /*
43  * How many user pages to map in one call to get_user_pages().  This determines
44  * the size of a structure in the slab cache
45  */
46 #define DIO_PAGES	64
47 
48 /*
49  * This code generally works in units of "dio_blocks".  A dio_block is
50  * somewhere between the hard sector size and the filesystem block size.  it
51  * is determined on a per-invocation basis.   When talking to the filesystem
52  * we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity
53  * down by dio->blkfactor.  Similarly, fs-blocksize quantities are converted
54  * to bio_block quantities by shifting left by blkfactor.
55  *
56  * If blkfactor is zero then the user's request was aligned to the filesystem's
57  * blocksize.
58  */
59 
60 /* dio_state only used in the submission path */
61 
62 struct dio_submit {
63 	struct bio *bio;		/* bio under assembly */
64 	unsigned blkbits;		/* doesn't change */
65 	unsigned blkfactor;		/* When we're using an alignment which
66 					   is finer than the filesystem's soft
67 					   blocksize, this specifies how much
68 					   finer.  blkfactor=2 means 1/4-block
69 					   alignment.  Does not change */
70 	unsigned start_zero_done;	/* flag: sub-blocksize zeroing has
71 					   been performed at the start of a
72 					   write */
73 	int pages_in_io;		/* approximate total IO pages */
74 	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 	int boundary;			/* prev block is at a boundary */
80 	get_block_t *get_block;		/* block mapping function */
81 	dio_submit_t *submit_io;	/* IO submition function */
82 
83 	loff_t logical_offset_in_bio;	/* current first logical block in bio */
84 	sector_t final_block_in_bio;	/* current final block in bio + 1 */
85 	sector_t next_block_for_io;	/* next block to be put under IO,
86 					   in dio_blocks units */
87 
88 	/*
89 	 * Deferred addition of a page to the dio.  These variables are
90 	 * private to dio_send_cur_page(), submit_page_section() and
91 	 * dio_bio_add_page().
92 	 */
93 	struct page *cur_page;		/* The page */
94 	unsigned cur_page_offset;	/* Offset into it, in bytes */
95 	unsigned cur_page_len;		/* Nr of bytes at cur_page_offset */
96 	sector_t cur_page_block;	/* Where it starts */
97 	loff_t cur_page_fs_offset;	/* Offset in file */
98 
99 	struct iov_iter *iter;
100 	/*
101 	 * Page queue.  These variables belong to dio_refill_pages() and
102 	 * dio_get_page().
103 	 */
104 	unsigned head;			/* next page to process */
105 	unsigned tail;			/* last valid page + 1 */
106 	size_t from, to;
107 };
108 
109 /* dio_state communicated between submission path and end_io */
110 struct dio {
111 	int flags;			/* doesn't change */
112 	int rw;
113 	struct inode *inode;
114 	loff_t i_size;			/* i_size when submitted */
115 	dio_iodone_t *end_io;		/* IO completion function */
116 
117 	void *private;			/* copy from map_bh.b_private */
118 
119 	/* BIO completion state */
120 	spinlock_t bio_lock;		/* protects BIO fields below */
121 	int page_errors;		/* errno from get_user_pages() */
122 	int is_async;			/* is IO async ? */
123 	bool defer_completion;		/* defer AIO completion to workqueue? */
124 	int io_error;			/* IO error in completion path */
125 	unsigned long refcount;		/* direct_io_worker() and bios */
126 	struct bio *bio_list;		/* singly linked via bi_private */
127 	struct task_struct *waiter;	/* waiting task (NULL if none) */
128 
129 	/* AIO related stuff */
130 	struct kiocb *iocb;		/* kiocb */
131 	ssize_t result;                 /* IO result */
132 
133 	/*
134 	 * pages[] (and any fields placed after it) are not zeroed out at
135 	 * allocation time.  Don't add new fields after pages[] unless you
136 	 * wish that they not be zeroed.
137 	 */
138 	union {
139 		struct page *pages[DIO_PAGES];	/* page buffer */
140 		struct work_struct complete_work;/* deferred AIO completion */
141 	};
142 } ____cacheline_aligned_in_smp;
143 
144 static struct kmem_cache *dio_cache __read_mostly;
145 
146 /*
147  * How many pages are in the queue?
148  */
149 static inline unsigned dio_pages_present(struct dio_submit *sdio)
150 {
151 	return sdio->tail - sdio->head;
152 }
153 
154 /*
155  * Go grab and pin some userspace pages.   Typically we'll get 64 at a time.
156  */
157 static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
158 {
159 	ssize_t ret;
160 
161 	ret = iov_iter_get_pages(sdio->iter, dio->pages, LONG_MAX, DIO_PAGES,
162 				&sdio->from);
163 
164 	if (ret < 0 && sdio->blocks_available && (dio->rw & WRITE)) {
165 		struct page *page = ZERO_PAGE(0);
166 		/*
167 		 * A memory fault, but the filesystem has some outstanding
168 		 * mapped blocks.  We need to use those blocks up to avoid
169 		 * leaking stale data in the file.
170 		 */
171 		if (dio->page_errors == 0)
172 			dio->page_errors = ret;
173 		page_cache_get(page);
174 		dio->pages[0] = page;
175 		sdio->head = 0;
176 		sdio->tail = 1;
177 		sdio->from = 0;
178 		sdio->to = PAGE_SIZE;
179 		return 0;
180 	}
181 
182 	if (ret >= 0) {
183 		iov_iter_advance(sdio->iter, ret);
184 		ret += sdio->from;
185 		sdio->head = 0;
186 		sdio->tail = (ret + PAGE_SIZE - 1) / PAGE_SIZE;
187 		sdio->to = ((ret - 1) & (PAGE_SIZE - 1)) + 1;
188 		return 0;
189 	}
190 	return ret;
191 }
192 
193 /*
194  * Get another userspace page.  Returns an ERR_PTR on error.  Pages are
195  * buffered inside the dio so that we can call get_user_pages() against a
196  * decent number of pages, less frequently.  To provide nicer use of the
197  * L1 cache.
198  */
199 static inline struct page *dio_get_page(struct dio *dio,
200 					struct dio_submit *sdio)
201 {
202 	if (dio_pages_present(sdio) == 0) {
203 		int ret;
204 
205 		ret = dio_refill_pages(dio, sdio);
206 		if (ret)
207 			return ERR_PTR(ret);
208 		BUG_ON(dio_pages_present(sdio) == 0);
209 	}
210 	return dio->pages[sdio->head];
211 }
212 
213 /**
214  * dio_complete() - called when all DIO BIO I/O has been completed
215  * @offset: the byte offset in the file of the completed operation
216  *
217  * This drops i_dio_count, lets interested parties know that a DIO operation
218  * has completed, and calculates the resulting return code for the operation.
219  *
220  * It lets the filesystem know if it registered an interest earlier via
221  * get_block.  Pass the private field of the map buffer_head so that
222  * filesystems can use it to hold additional state between get_block calls and
223  * dio_complete.
224  */
225 static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret,
226 		bool is_async)
227 {
228 	ssize_t transferred = 0;
229 
230 	/*
231 	 * AIO submission can race with bio completion to get here while
232 	 * expecting to have the last io completed by bio completion.
233 	 * In that case -EIOCBQUEUED is in fact not an error we want
234 	 * to preserve through this call.
235 	 */
236 	if (ret == -EIOCBQUEUED)
237 		ret = 0;
238 
239 	if (dio->result) {
240 		transferred = dio->result;
241 
242 		/* Check for short read case */
243 		if ((dio->rw == READ) && ((offset + transferred) > dio->i_size))
244 			transferred = dio->i_size - offset;
245 	}
246 
247 	if (ret == 0)
248 		ret = dio->page_errors;
249 	if (ret == 0)
250 		ret = dio->io_error;
251 	if (ret == 0)
252 		ret = transferred;
253 
254 	if (dio->end_io && dio->result)
255 		dio->end_io(dio->iocb, offset, transferred, dio->private);
256 
257 	inode_dio_done(dio->inode);
258 	if (is_async) {
259 		if (dio->rw & WRITE) {
260 			int err;
261 
262 			err = generic_write_sync(dio->iocb->ki_filp, offset,
263 						 transferred);
264 			if (err < 0 && ret > 0)
265 				ret = err;
266 		}
267 
268 		aio_complete(dio->iocb, ret, 0);
269 	}
270 
271 	kmem_cache_free(dio_cache, dio);
272 	return ret;
273 }
274 
275 static void dio_aio_complete_work(struct work_struct *work)
276 {
277 	struct dio *dio = container_of(work, struct dio, complete_work);
278 
279 	dio_complete(dio, dio->iocb->ki_pos, 0, true);
280 }
281 
282 static int dio_bio_complete(struct dio *dio, struct bio *bio);
283 
284 /*
285  * Asynchronous IO callback.
286  */
287 static void dio_bio_end_aio(struct bio *bio, int error)
288 {
289 	struct dio *dio = bio->bi_private;
290 	unsigned long remaining;
291 	unsigned long flags;
292 
293 	/* cleanup the bio */
294 	dio_bio_complete(dio, bio);
295 
296 	spin_lock_irqsave(&dio->bio_lock, flags);
297 	remaining = --dio->refcount;
298 	if (remaining == 1 && dio->waiter)
299 		wake_up_process(dio->waiter);
300 	spin_unlock_irqrestore(&dio->bio_lock, flags);
301 
302 	if (remaining == 0) {
303 		if (dio->result && dio->defer_completion) {
304 			INIT_WORK(&dio->complete_work, dio_aio_complete_work);
305 			queue_work(dio->inode->i_sb->s_dio_done_wq,
306 				   &dio->complete_work);
307 		} else {
308 			dio_complete(dio, dio->iocb->ki_pos, 0, true);
309 		}
310 	}
311 }
312 
313 /*
314  * The BIO completion handler simply queues the BIO up for the process-context
315  * handler.
316  *
317  * During I/O bi_private points at the dio.  After I/O, bi_private is used to
318  * implement a singly-linked list of completed BIOs, at dio->bio_list.
319  */
320 static void dio_bio_end_io(struct bio *bio, int error)
321 {
322 	struct dio *dio = bio->bi_private;
323 	unsigned long flags;
324 
325 	spin_lock_irqsave(&dio->bio_lock, flags);
326 	bio->bi_private = dio->bio_list;
327 	dio->bio_list = bio;
328 	if (--dio->refcount == 1 && dio->waiter)
329 		wake_up_process(dio->waiter);
330 	spin_unlock_irqrestore(&dio->bio_lock, flags);
331 }
332 
333 /**
334  * dio_end_io - handle the end io action for the given bio
335  * @bio: The direct io bio thats being completed
336  * @error: Error if there was one
337  *
338  * This is meant to be called by any filesystem that uses their own dio_submit_t
339  * so that the DIO specific endio actions are dealt with after the filesystem
340  * has done it's completion work.
341  */
342 void dio_end_io(struct bio *bio, int error)
343 {
344 	struct dio *dio = bio->bi_private;
345 
346 	if (dio->is_async)
347 		dio_bio_end_aio(bio, error);
348 	else
349 		dio_bio_end_io(bio, error);
350 }
351 EXPORT_SYMBOL_GPL(dio_end_io);
352 
353 static inline void
354 dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
355 	      struct block_device *bdev,
356 	      sector_t first_sector, int nr_vecs)
357 {
358 	struct bio *bio;
359 
360 	/*
361 	 * bio_alloc() is guaranteed to return a bio when called with
362 	 * __GFP_WAIT and we request a valid number of vectors.
363 	 */
364 	bio = bio_alloc(GFP_KERNEL, nr_vecs);
365 
366 	bio->bi_bdev = bdev;
367 	bio->bi_iter.bi_sector = first_sector;
368 	if (dio->is_async)
369 		bio->bi_end_io = dio_bio_end_aio;
370 	else
371 		bio->bi_end_io = dio_bio_end_io;
372 
373 	sdio->bio = bio;
374 	sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
375 }
376 
377 /*
378  * In the AIO read case we speculatively dirty the pages before starting IO.
379  * During IO completion, any of these pages which happen to have been written
380  * back will be redirtied by bio_check_pages_dirty().
381  *
382  * bios hold a dio reference between submit_bio and ->end_io.
383  */
384 static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
385 {
386 	struct bio *bio = sdio->bio;
387 	unsigned long flags;
388 
389 	bio->bi_private = dio;
390 
391 	spin_lock_irqsave(&dio->bio_lock, flags);
392 	dio->refcount++;
393 	spin_unlock_irqrestore(&dio->bio_lock, flags);
394 
395 	if (dio->is_async && dio->rw == READ)
396 		bio_set_pages_dirty(bio);
397 
398 	if (sdio->submit_io)
399 		sdio->submit_io(dio->rw, bio, dio->inode,
400 			       sdio->logical_offset_in_bio);
401 	else
402 		submit_bio(dio->rw, bio);
403 
404 	sdio->bio = NULL;
405 	sdio->boundary = 0;
406 	sdio->logical_offset_in_bio = 0;
407 }
408 
409 /*
410  * Release any resources in case of a failure
411  */
412 static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio)
413 {
414 	while (sdio->head < sdio->tail)
415 		page_cache_release(dio->pages[sdio->head++]);
416 }
417 
418 /*
419  * Wait for the next BIO to complete.  Remove it and return it.  NULL is
420  * returned once all BIOs have been completed.  This must only be called once
421  * all bios have been issued so that dio->refcount can only decrease.  This
422  * requires that that the caller hold a reference on the dio.
423  */
424 static struct bio *dio_await_one(struct dio *dio)
425 {
426 	unsigned long flags;
427 	struct bio *bio = NULL;
428 
429 	spin_lock_irqsave(&dio->bio_lock, flags);
430 
431 	/*
432 	 * Wait as long as the list is empty and there are bios in flight.  bio
433 	 * completion drops the count, maybe adds to the list, and wakes while
434 	 * holding the bio_lock so we don't need set_current_state()'s barrier
435 	 * and can call it after testing our condition.
436 	 */
437 	while (dio->refcount > 1 && dio->bio_list == NULL) {
438 		__set_current_state(TASK_UNINTERRUPTIBLE);
439 		dio->waiter = current;
440 		spin_unlock_irqrestore(&dio->bio_lock, flags);
441 		io_schedule();
442 		/* wake up sets us TASK_RUNNING */
443 		spin_lock_irqsave(&dio->bio_lock, flags);
444 		dio->waiter = NULL;
445 	}
446 	if (dio->bio_list) {
447 		bio = dio->bio_list;
448 		dio->bio_list = bio->bi_private;
449 	}
450 	spin_unlock_irqrestore(&dio->bio_lock, flags);
451 	return bio;
452 }
453 
454 /*
455  * Process one completed BIO.  No locks are held.
456  */
457 static int dio_bio_complete(struct dio *dio, struct bio *bio)
458 {
459 	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
460 	struct bio_vec *bvec;
461 	unsigned i;
462 
463 	if (!uptodate)
464 		dio->io_error = -EIO;
465 
466 	if (dio->is_async && dio->rw == READ) {
467 		bio_check_pages_dirty(bio);	/* transfers ownership */
468 	} else {
469 		bio_for_each_segment_all(bvec, bio, i) {
470 			struct page *page = bvec->bv_page;
471 
472 			if (dio->rw == READ && !PageCompound(page))
473 				set_page_dirty_lock(page);
474 			page_cache_release(page);
475 		}
476 		bio_put(bio);
477 	}
478 	return uptodate ? 0 : -EIO;
479 }
480 
481 /*
482  * Wait on and process all in-flight BIOs.  This must only be called once
483  * all bios have been issued so that the refcount can only decrease.
484  * This just waits for all bios to make it through dio_bio_complete.  IO
485  * errors are propagated through dio->io_error and should be propagated via
486  * dio_complete().
487  */
488 static void dio_await_completion(struct dio *dio)
489 {
490 	struct bio *bio;
491 	do {
492 		bio = dio_await_one(dio);
493 		if (bio)
494 			dio_bio_complete(dio, bio);
495 	} while (bio);
496 }
497 
498 /*
499  * A really large O_DIRECT read or write can generate a lot of BIOs.  So
500  * to keep the memory consumption sane we periodically reap any completed BIOs
501  * during the BIO generation phase.
502  *
503  * This also helps to limit the peak amount of pinned userspace memory.
504  */
505 static inline int dio_bio_reap(struct dio *dio, struct dio_submit *sdio)
506 {
507 	int ret = 0;
508 
509 	if (sdio->reap_counter++ >= 64) {
510 		while (dio->bio_list) {
511 			unsigned long flags;
512 			struct bio *bio;
513 			int ret2;
514 
515 			spin_lock_irqsave(&dio->bio_lock, flags);
516 			bio = dio->bio_list;
517 			dio->bio_list = bio->bi_private;
518 			spin_unlock_irqrestore(&dio->bio_lock, flags);
519 			ret2 = dio_bio_complete(dio, bio);
520 			if (ret == 0)
521 				ret = ret2;
522 		}
523 		sdio->reap_counter = 0;
524 	}
525 	return ret;
526 }
527 
528 /*
529  * Create workqueue for deferred direct IO completions. We allocate the
530  * workqueue when it's first needed. This avoids creating workqueue for
531  * filesystems that don't need it and also allows us to create the workqueue
532  * late enough so the we can include s_id in the name of the workqueue.
533  */
534 static int sb_init_dio_done_wq(struct super_block *sb)
535 {
536 	struct workqueue_struct *old;
537 	struct workqueue_struct *wq = alloc_workqueue("dio/%s",
538 						      WQ_MEM_RECLAIM, 0,
539 						      sb->s_id);
540 	if (!wq)
541 		return -ENOMEM;
542 	/*
543 	 * This has to be atomic as more DIOs can race to create the workqueue
544 	 */
545 	old = cmpxchg(&sb->s_dio_done_wq, NULL, wq);
546 	/* Someone created workqueue before us? Free ours... */
547 	if (old)
548 		destroy_workqueue(wq);
549 	return 0;
550 }
551 
552 static int dio_set_defer_completion(struct dio *dio)
553 {
554 	struct super_block *sb = dio->inode->i_sb;
555 
556 	if (dio->defer_completion)
557 		return 0;
558 	dio->defer_completion = true;
559 	if (!sb->s_dio_done_wq)
560 		return sb_init_dio_done_wq(sb);
561 	return 0;
562 }
563 
564 /*
565  * Call into the fs to map some more disk blocks.  We record the current number
566  * of available blocks at sdio->blocks_available.  These are in units of the
567  * fs blocksize, (1 << inode->i_blkbits).
568  *
569  * The fs is allowed to map lots of blocks at once.  If it wants to do that,
570  * it uses the passed inode-relative block number as the file offset, as usual.
571  *
572  * get_block() is passed the number of i_blkbits-sized blocks which direct_io
573  * has remaining to do.  The fs should not map more than this number of blocks.
574  *
575  * If the fs has mapped a lot of blocks, it should populate bh->b_size to
576  * indicate how much contiguous disk space has been made available at
577  * bh->b_blocknr.
578  *
579  * If *any* of the mapped blocks are new, then the fs must set buffer_new().
580  * This isn't very efficient...
581  *
582  * In the case of filesystem holes: the fs may return an arbitrarily-large
583  * hole by returning an appropriate value in b_size and by clearing
584  * buffer_mapped().  However the direct-io code will only process holes one
585  * block at a time - it will repeatedly call get_block() as it walks the hole.
586  */
587 static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
588 			   struct buffer_head *map_bh)
589 {
590 	int ret;
591 	sector_t fs_startblk;	/* Into file, in filesystem-sized blocks */
592 	sector_t fs_endblk;	/* Into file, in filesystem-sized blocks */
593 	unsigned long fs_count;	/* Number of filesystem-sized blocks */
594 	int create;
595 	unsigned int i_blkbits = sdio->blkbits + sdio->blkfactor;
596 
597 	/*
598 	 * If there was a memory error and we've overwritten all the
599 	 * mapped blocks then we can now return that memory error
600 	 */
601 	ret = dio->page_errors;
602 	if (ret == 0) {
603 		BUG_ON(sdio->block_in_file >= sdio->final_block_in_request);
604 		fs_startblk = sdio->block_in_file >> sdio->blkfactor;
605 		fs_endblk = (sdio->final_block_in_request - 1) >>
606 					sdio->blkfactor;
607 		fs_count = fs_endblk - fs_startblk + 1;
608 
609 		map_bh->b_state = 0;
610 		map_bh->b_size = fs_count << i_blkbits;
611 
612 		/*
613 		 * For writes inside i_size on a DIO_SKIP_HOLES filesystem we
614 		 * forbid block creations: only overwrites are permitted.
615 		 * We will return early to the caller once we see an
616 		 * unmapped buffer head returned, and the caller will fall
617 		 * back to buffered I/O.
618 		 *
619 		 * Otherwise the decision is left to the get_blocks method,
620 		 * which may decide to handle it or also return an unmapped
621 		 * buffer head.
622 		 */
623 		create = dio->rw & WRITE;
624 		if (dio->flags & DIO_SKIP_HOLES) {
625 			if (sdio->block_in_file < (i_size_read(dio->inode) >>
626 							sdio->blkbits))
627 				create = 0;
628 		}
629 
630 		ret = (*sdio->get_block)(dio->inode, fs_startblk,
631 						map_bh, create);
632 
633 		/* Store for completion */
634 		dio->private = map_bh->b_private;
635 
636 		if (ret == 0 && buffer_defer_completion(map_bh))
637 			ret = dio_set_defer_completion(dio);
638 	}
639 	return ret;
640 }
641 
642 /*
643  * There is no bio.  Make one now.
644  */
645 static inline int dio_new_bio(struct dio *dio, struct dio_submit *sdio,
646 		sector_t start_sector, struct buffer_head *map_bh)
647 {
648 	sector_t sector;
649 	int ret, nr_pages;
650 
651 	ret = dio_bio_reap(dio, sdio);
652 	if (ret)
653 		goto out;
654 	sector = start_sector << (sdio->blkbits - 9);
655 	nr_pages = min(sdio->pages_in_io, bio_get_nr_vecs(map_bh->b_bdev));
656 	BUG_ON(nr_pages <= 0);
657 	dio_bio_alloc(dio, sdio, map_bh->b_bdev, sector, nr_pages);
658 	sdio->boundary = 0;
659 out:
660 	return ret;
661 }
662 
663 /*
664  * Attempt to put the current chunk of 'cur_page' into the current BIO.  If
665  * that was successful then update final_block_in_bio and take a ref against
666  * the just-added page.
667  *
668  * Return zero on success.  Non-zero means the caller needs to start a new BIO.
669  */
670 static inline int dio_bio_add_page(struct dio_submit *sdio)
671 {
672 	int ret;
673 
674 	ret = bio_add_page(sdio->bio, sdio->cur_page,
675 			sdio->cur_page_len, sdio->cur_page_offset);
676 	if (ret == sdio->cur_page_len) {
677 		/*
678 		 * Decrement count only, if we are done with this page
679 		 */
680 		if ((sdio->cur_page_len + sdio->cur_page_offset) == PAGE_SIZE)
681 			sdio->pages_in_io--;
682 		page_cache_get(sdio->cur_page);
683 		sdio->final_block_in_bio = sdio->cur_page_block +
684 			(sdio->cur_page_len >> sdio->blkbits);
685 		ret = 0;
686 	} else {
687 		ret = 1;
688 	}
689 	return ret;
690 }
691 
692 /*
693  * Put cur_page under IO.  The section of cur_page which is described by
694  * cur_page_offset,cur_page_len is put into a BIO.  The section of cur_page
695  * starts on-disk at cur_page_block.
696  *
697  * We take a ref against the page here (on behalf of its presence in the bio).
698  *
699  * The caller of this function is responsible for removing cur_page from the
700  * dio, and for dropping the refcount which came from that presence.
701  */
702 static inline int dio_send_cur_page(struct dio *dio, struct dio_submit *sdio,
703 		struct buffer_head *map_bh)
704 {
705 	int ret = 0;
706 
707 	if (sdio->bio) {
708 		loff_t cur_offset = sdio->cur_page_fs_offset;
709 		loff_t bio_next_offset = sdio->logical_offset_in_bio +
710 			sdio->bio->bi_iter.bi_size;
711 
712 		/*
713 		 * See whether this new request is contiguous with the old.
714 		 *
715 		 * Btrfs cannot handle having logically non-contiguous requests
716 		 * submitted.  For example if you have
717 		 *
718 		 * Logical:  [0-4095][HOLE][8192-12287]
719 		 * Physical: [0-4095]      [4096-8191]
720 		 *
721 		 * We cannot submit those pages together as one BIO.  So if our
722 		 * current logical offset in the file does not equal what would
723 		 * be the next logical offset in the bio, submit the bio we
724 		 * have.
725 		 */
726 		if (sdio->final_block_in_bio != sdio->cur_page_block ||
727 		    cur_offset != bio_next_offset)
728 			dio_bio_submit(dio, sdio);
729 	}
730 
731 	if (sdio->bio == NULL) {
732 		ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
733 		if (ret)
734 			goto out;
735 	}
736 
737 	if (dio_bio_add_page(sdio) != 0) {
738 		dio_bio_submit(dio, sdio);
739 		ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
740 		if (ret == 0) {
741 			ret = dio_bio_add_page(sdio);
742 			BUG_ON(ret != 0);
743 		}
744 	}
745 out:
746 	return ret;
747 }
748 
749 /*
750  * An autonomous function to put a chunk of a page under deferred IO.
751  *
752  * The caller doesn't actually know (or care) whether this piece of page is in
753  * a BIO, or is under IO or whatever.  We just take care of all possible
754  * situations here.  The separation between the logic of do_direct_IO() and
755  * that of submit_page_section() is important for clarity.  Please don't break.
756  *
757  * The chunk of page starts on-disk at blocknr.
758  *
759  * We perform deferred IO, by recording the last-submitted page inside our
760  * private part of the dio structure.  If possible, we just expand the IO
761  * across that page here.
762  *
763  * If that doesn't work out then we put the old page into the bio and add this
764  * page to the dio instead.
765  */
766 static inline int
767 submit_page_section(struct dio *dio, struct dio_submit *sdio, struct page *page,
768 		    unsigned offset, unsigned len, sector_t blocknr,
769 		    struct buffer_head *map_bh)
770 {
771 	int ret = 0;
772 
773 	if (dio->rw & WRITE) {
774 		/*
775 		 * Read accounting is performed in submit_bio()
776 		 */
777 		task_io_account_write(len);
778 	}
779 
780 	/*
781 	 * Can we just grow the current page's presence in the dio?
782 	 */
783 	if (sdio->cur_page == page &&
784 	    sdio->cur_page_offset + sdio->cur_page_len == offset &&
785 	    sdio->cur_page_block +
786 	    (sdio->cur_page_len >> sdio->blkbits) == blocknr) {
787 		sdio->cur_page_len += len;
788 		goto out;
789 	}
790 
791 	/*
792 	 * If there's a deferred page already there then send it.
793 	 */
794 	if (sdio->cur_page) {
795 		ret = dio_send_cur_page(dio, sdio, map_bh);
796 		page_cache_release(sdio->cur_page);
797 		sdio->cur_page = NULL;
798 		if (ret)
799 			return ret;
800 	}
801 
802 	page_cache_get(page);		/* It is in dio */
803 	sdio->cur_page = page;
804 	sdio->cur_page_offset = offset;
805 	sdio->cur_page_len = len;
806 	sdio->cur_page_block = blocknr;
807 	sdio->cur_page_fs_offset = sdio->block_in_file << sdio->blkbits;
808 out:
809 	/*
810 	 * If sdio->boundary then we want to schedule the IO now to
811 	 * avoid metadata seeks.
812 	 */
813 	if (sdio->boundary) {
814 		ret = dio_send_cur_page(dio, sdio, map_bh);
815 		dio_bio_submit(dio, sdio);
816 		page_cache_release(sdio->cur_page);
817 		sdio->cur_page = NULL;
818 	}
819 	return ret;
820 }
821 
822 /*
823  * Clean any dirty buffers in the blockdev mapping which alias newly-created
824  * file blocks.  Only called for S_ISREG files - blockdevs do not set
825  * buffer_new
826  */
827 static void clean_blockdev_aliases(struct dio *dio, struct buffer_head *map_bh)
828 {
829 	unsigned i;
830 	unsigned nblocks;
831 
832 	nblocks = map_bh->b_size >> dio->inode->i_blkbits;
833 
834 	for (i = 0; i < nblocks; i++) {
835 		unmap_underlying_metadata(map_bh->b_bdev,
836 					  map_bh->b_blocknr + i);
837 	}
838 }
839 
840 /*
841  * If we are not writing the entire block and get_block() allocated
842  * the block for us, we need to fill-in the unused portion of the
843  * block with zeros. This happens only if user-buffer, fileoffset or
844  * io length is not filesystem block-size multiple.
845  *
846  * `end' is zero if we're doing the start of the IO, 1 at the end of the
847  * IO.
848  */
849 static inline void dio_zero_block(struct dio *dio, struct dio_submit *sdio,
850 		int end, struct buffer_head *map_bh)
851 {
852 	unsigned dio_blocks_per_fs_block;
853 	unsigned this_chunk_blocks;	/* In dio_blocks */
854 	unsigned this_chunk_bytes;
855 	struct page *page;
856 
857 	sdio->start_zero_done = 1;
858 	if (!sdio->blkfactor || !buffer_new(map_bh))
859 		return;
860 
861 	dio_blocks_per_fs_block = 1 << sdio->blkfactor;
862 	this_chunk_blocks = sdio->block_in_file & (dio_blocks_per_fs_block - 1);
863 
864 	if (!this_chunk_blocks)
865 		return;
866 
867 	/*
868 	 * We need to zero out part of an fs block.  It is either at the
869 	 * beginning or the end of the fs block.
870 	 */
871 	if (end)
872 		this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
873 
874 	this_chunk_bytes = this_chunk_blocks << sdio->blkbits;
875 
876 	page = ZERO_PAGE(0);
877 	if (submit_page_section(dio, sdio, page, 0, this_chunk_bytes,
878 				sdio->next_block_for_io, map_bh))
879 		return;
880 
881 	sdio->next_block_for_io += this_chunk_blocks;
882 }
883 
884 /*
885  * Walk the user pages, and the file, mapping blocks to disk and generating
886  * a sequence of (page,offset,len,block) mappings.  These mappings are injected
887  * into submit_page_section(), which takes care of the next stage of submission
888  *
889  * Direct IO against a blockdev is different from a file.  Because we can
890  * happily perform page-sized but 512-byte aligned IOs.  It is important that
891  * blockdev IO be able to have fine alignment and large sizes.
892  *
893  * So what we do is to permit the ->get_block function to populate bh.b_size
894  * with the size of IO which is permitted at this offset and this i_blkbits.
895  *
896  * For best results, the blockdev should be set up with 512-byte i_blkbits and
897  * it should set b_size to PAGE_SIZE or more inside get_block().  This gives
898  * fine alignment but still allows this function to work in PAGE_SIZE units.
899  */
900 static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
901 			struct buffer_head *map_bh)
902 {
903 	const unsigned blkbits = sdio->blkbits;
904 	int ret = 0;
905 
906 	while (sdio->block_in_file < sdio->final_block_in_request) {
907 		struct page *page;
908 		size_t from, to;
909 
910 		page = dio_get_page(dio, sdio);
911 		if (IS_ERR(page)) {
912 			ret = PTR_ERR(page);
913 			goto out;
914 		}
915 		from = sdio->head ? 0 : sdio->from;
916 		to = (sdio->head == sdio->tail - 1) ? sdio->to : PAGE_SIZE;
917 		sdio->head++;
918 
919 		while (from < to) {
920 			unsigned this_chunk_bytes;	/* # of bytes mapped */
921 			unsigned this_chunk_blocks;	/* # of blocks */
922 			unsigned u;
923 
924 			if (sdio->blocks_available == 0) {
925 				/*
926 				 * Need to go and map some more disk
927 				 */
928 				unsigned long blkmask;
929 				unsigned long dio_remainder;
930 
931 				ret = get_more_blocks(dio, sdio, map_bh);
932 				if (ret) {
933 					page_cache_release(page);
934 					goto out;
935 				}
936 				if (!buffer_mapped(map_bh))
937 					goto do_holes;
938 
939 				sdio->blocks_available =
940 						map_bh->b_size >> sdio->blkbits;
941 				sdio->next_block_for_io =
942 					map_bh->b_blocknr << sdio->blkfactor;
943 				if (buffer_new(map_bh))
944 					clean_blockdev_aliases(dio, map_bh);
945 
946 				if (!sdio->blkfactor)
947 					goto do_holes;
948 
949 				blkmask = (1 << sdio->blkfactor) - 1;
950 				dio_remainder = (sdio->block_in_file & blkmask);
951 
952 				/*
953 				 * If we are at the start of IO and that IO
954 				 * starts partway into a fs-block,
955 				 * dio_remainder will be non-zero.  If the IO
956 				 * is a read then we can simply advance the IO
957 				 * cursor to the first block which is to be
958 				 * read.  But if the IO is a write and the
959 				 * block was newly allocated we cannot do that;
960 				 * the start of the fs block must be zeroed out
961 				 * on-disk
962 				 */
963 				if (!buffer_new(map_bh))
964 					sdio->next_block_for_io += dio_remainder;
965 				sdio->blocks_available -= dio_remainder;
966 			}
967 do_holes:
968 			/* Handle holes */
969 			if (!buffer_mapped(map_bh)) {
970 				loff_t i_size_aligned;
971 
972 				/* AKPM: eargh, -ENOTBLK is a hack */
973 				if (dio->rw & WRITE) {
974 					page_cache_release(page);
975 					return -ENOTBLK;
976 				}
977 
978 				/*
979 				 * Be sure to account for a partial block as the
980 				 * last block in the file
981 				 */
982 				i_size_aligned = ALIGN(i_size_read(dio->inode),
983 							1 << blkbits);
984 				if (sdio->block_in_file >=
985 						i_size_aligned >> blkbits) {
986 					/* We hit eof */
987 					page_cache_release(page);
988 					goto out;
989 				}
990 				zero_user(page, from, 1 << blkbits);
991 				sdio->block_in_file++;
992 				from += 1 << blkbits;
993 				dio->result += 1 << blkbits;
994 				goto next_block;
995 			}
996 
997 			/*
998 			 * If we're performing IO which has an alignment which
999 			 * is finer than the underlying fs, go check to see if
1000 			 * we must zero out the start of this block.
1001 			 */
1002 			if (unlikely(sdio->blkfactor && !sdio->start_zero_done))
1003 				dio_zero_block(dio, sdio, 0, map_bh);
1004 
1005 			/*
1006 			 * Work out, in this_chunk_blocks, how much disk we
1007 			 * can add to this page
1008 			 */
1009 			this_chunk_blocks = sdio->blocks_available;
1010 			u = (to - from) >> blkbits;
1011 			if (this_chunk_blocks > u)
1012 				this_chunk_blocks = u;
1013 			u = sdio->final_block_in_request - sdio->block_in_file;
1014 			if (this_chunk_blocks > u)
1015 				this_chunk_blocks = u;
1016 			this_chunk_bytes = this_chunk_blocks << blkbits;
1017 			BUG_ON(this_chunk_bytes == 0);
1018 
1019 			if (this_chunk_blocks == sdio->blocks_available)
1020 				sdio->boundary = buffer_boundary(map_bh);
1021 			ret = submit_page_section(dio, sdio, page,
1022 						  from,
1023 						  this_chunk_bytes,
1024 						  sdio->next_block_for_io,
1025 						  map_bh);
1026 			if (ret) {
1027 				page_cache_release(page);
1028 				goto out;
1029 			}
1030 			sdio->next_block_for_io += this_chunk_blocks;
1031 
1032 			sdio->block_in_file += this_chunk_blocks;
1033 			from += this_chunk_bytes;
1034 			dio->result += this_chunk_bytes;
1035 			sdio->blocks_available -= this_chunk_blocks;
1036 next_block:
1037 			BUG_ON(sdio->block_in_file > sdio->final_block_in_request);
1038 			if (sdio->block_in_file == sdio->final_block_in_request)
1039 				break;
1040 		}
1041 
1042 		/* Drop the ref which was taken in get_user_pages() */
1043 		page_cache_release(page);
1044 	}
1045 out:
1046 	return ret;
1047 }
1048 
1049 static inline int drop_refcount(struct dio *dio)
1050 {
1051 	int ret2;
1052 	unsigned long flags;
1053 
1054 	/*
1055 	 * Sync will always be dropping the final ref and completing the
1056 	 * operation.  AIO can if it was a broken operation described above or
1057 	 * in fact if all the bios race to complete before we get here.  In
1058 	 * that case dio_complete() translates the EIOCBQUEUED into the proper
1059 	 * return code that the caller will hand to aio_complete().
1060 	 *
1061 	 * This is managed by the bio_lock instead of being an atomic_t so that
1062 	 * completion paths can drop their ref and use the remaining count to
1063 	 * decide to wake the submission path atomically.
1064 	 */
1065 	spin_lock_irqsave(&dio->bio_lock, flags);
1066 	ret2 = --dio->refcount;
1067 	spin_unlock_irqrestore(&dio->bio_lock, flags);
1068 	return ret2;
1069 }
1070 
1071 /*
1072  * This is a library function for use by filesystem drivers.
1073  *
1074  * The locking rules are governed by the flags parameter:
1075  *  - if the flags value contains DIO_LOCKING we use a fancy locking
1076  *    scheme for dumb filesystems.
1077  *    For writes this function is called under i_mutex and returns with
1078  *    i_mutex held, for reads, i_mutex is not held on entry, but it is
1079  *    taken and dropped again before returning.
1080  *  - if the flags value does NOT contain DIO_LOCKING we don't use any
1081  *    internal locking but rather rely on the filesystem to synchronize
1082  *    direct I/O reads/writes versus each other and truncate.
1083  *
1084  * To help with locking against truncate we incremented the i_dio_count
1085  * counter before starting direct I/O, and decrement it once we are done.
1086  * Truncate can wait for it to reach zero to provide exclusion.  It is
1087  * expected that filesystem provide exclusion between new direct I/O
1088  * and truncates.  For DIO_LOCKING filesystems this is done by i_mutex,
1089  * but other filesystems need to take care of this on their own.
1090  *
1091  * NOTE: if you pass "sdio" to anything by pointer make sure that function
1092  * is always inlined. Otherwise gcc is unable to split the structure into
1093  * individual fields and will generate much worse code. This is important
1094  * for the whole file.
1095  */
1096 static inline ssize_t
1097 do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
1098 	struct block_device *bdev, struct iov_iter *iter, loff_t offset,
1099 	get_block_t get_block, dio_iodone_t end_io,
1100 	dio_submit_t submit_io,	int flags)
1101 {
1102 	unsigned i_blkbits = ACCESS_ONCE(inode->i_blkbits);
1103 	unsigned blkbits = i_blkbits;
1104 	unsigned blocksize_mask = (1 << blkbits) - 1;
1105 	ssize_t retval = -EINVAL;
1106 	size_t count = iov_iter_count(iter);
1107 	loff_t end = offset + count;
1108 	struct dio *dio;
1109 	struct dio_submit sdio = { 0, };
1110 	struct buffer_head map_bh = { 0, };
1111 	struct blk_plug plug;
1112 	unsigned long align = offset | iov_iter_alignment(iter);
1113 
1114 	if (rw & WRITE)
1115 		rw = WRITE_ODIRECT;
1116 
1117 	/*
1118 	 * Avoid references to bdev if not absolutely needed to give
1119 	 * the early prefetch in the caller enough time.
1120 	 */
1121 
1122 	if (align & blocksize_mask) {
1123 		if (bdev)
1124 			blkbits = blksize_bits(bdev_logical_block_size(bdev));
1125 		blocksize_mask = (1 << blkbits) - 1;
1126 		if (align & blocksize_mask)
1127 			goto out;
1128 	}
1129 
1130 	/* watch out for a 0 len io from a tricksy fs */
1131 	if (rw == READ && !iov_iter_count(iter))
1132 		return 0;
1133 
1134 	dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
1135 	retval = -ENOMEM;
1136 	if (!dio)
1137 		goto out;
1138 	/*
1139 	 * Believe it or not, zeroing out the page array caused a .5%
1140 	 * performance regression in a database benchmark.  So, we take
1141 	 * care to only zero out what's needed.
1142 	 */
1143 	memset(dio, 0, offsetof(struct dio, pages));
1144 
1145 	dio->flags = flags;
1146 	if (dio->flags & DIO_LOCKING) {
1147 		if (rw == READ) {
1148 			struct address_space *mapping =
1149 					iocb->ki_filp->f_mapping;
1150 
1151 			/* will be released by direct_io_worker */
1152 			mutex_lock(&inode->i_mutex);
1153 
1154 			retval = filemap_write_and_wait_range(mapping, offset,
1155 							      end - 1);
1156 			if (retval) {
1157 				mutex_unlock(&inode->i_mutex);
1158 				kmem_cache_free(dio_cache, dio);
1159 				goto out;
1160 			}
1161 		}
1162 	}
1163 
1164 	/*
1165 	 * For file extending writes updating i_size before data writeouts
1166 	 * complete can expose uninitialized blocks in dumb filesystems.
1167 	 * In that case we need to wait for I/O completion even if asked
1168 	 * for an asynchronous write.
1169 	 */
1170 	if (is_sync_kiocb(iocb))
1171 		dio->is_async = false;
1172 	else if (!(dio->flags & DIO_ASYNC_EXTEND) &&
1173             (rw & WRITE) && end > i_size_read(inode))
1174 		dio->is_async = false;
1175 	else
1176 		dio->is_async = true;
1177 
1178 	dio->inode = inode;
1179 	dio->rw = rw;
1180 
1181 	/*
1182 	 * For AIO O_(D)SYNC writes we need to defer completions to a workqueue
1183 	 * so that we can call ->fsync.
1184 	 */
1185 	if (dio->is_async && (rw & WRITE) &&
1186 	    ((iocb->ki_filp->f_flags & O_DSYNC) ||
1187 	     IS_SYNC(iocb->ki_filp->f_mapping->host))) {
1188 		retval = dio_set_defer_completion(dio);
1189 		if (retval) {
1190 			/*
1191 			 * We grab i_mutex only for reads so we don't have
1192 			 * to release it here
1193 			 */
1194 			kmem_cache_free(dio_cache, dio);
1195 			goto out;
1196 		}
1197 	}
1198 
1199 	/*
1200 	 * Will be decremented at I/O completion time.
1201 	 */
1202 	atomic_inc(&inode->i_dio_count);
1203 
1204 	retval = 0;
1205 	sdio.blkbits = blkbits;
1206 	sdio.blkfactor = i_blkbits - blkbits;
1207 	sdio.block_in_file = offset >> blkbits;
1208 
1209 	sdio.get_block = get_block;
1210 	dio->end_io = end_io;
1211 	sdio.submit_io = submit_io;
1212 	sdio.final_block_in_bio = -1;
1213 	sdio.next_block_for_io = -1;
1214 
1215 	dio->iocb = iocb;
1216 	dio->i_size = i_size_read(inode);
1217 
1218 	spin_lock_init(&dio->bio_lock);
1219 	dio->refcount = 1;
1220 
1221 	sdio.iter = iter;
1222 	sdio.final_block_in_request =
1223 		(offset + iov_iter_count(iter)) >> blkbits;
1224 
1225 	/*
1226 	 * In case of non-aligned buffers, we may need 2 more
1227 	 * pages since we need to zero out first and last block.
1228 	 */
1229 	if (unlikely(sdio.blkfactor))
1230 		sdio.pages_in_io = 2;
1231 
1232 	sdio.pages_in_io += iov_iter_npages(iter, INT_MAX);
1233 
1234 	blk_start_plug(&plug);
1235 
1236 	retval = do_direct_IO(dio, &sdio, &map_bh);
1237 	if (retval)
1238 		dio_cleanup(dio, &sdio);
1239 
1240 	if (retval == -ENOTBLK) {
1241 		/*
1242 		 * The remaining part of the request will be
1243 		 * be handled by buffered I/O when we return
1244 		 */
1245 		retval = 0;
1246 	}
1247 	/*
1248 	 * There may be some unwritten disk at the end of a part-written
1249 	 * fs-block-sized block.  Go zero that now.
1250 	 */
1251 	dio_zero_block(dio, &sdio, 1, &map_bh);
1252 
1253 	if (sdio.cur_page) {
1254 		ssize_t ret2;
1255 
1256 		ret2 = dio_send_cur_page(dio, &sdio, &map_bh);
1257 		if (retval == 0)
1258 			retval = ret2;
1259 		page_cache_release(sdio.cur_page);
1260 		sdio.cur_page = NULL;
1261 	}
1262 	if (sdio.bio)
1263 		dio_bio_submit(dio, &sdio);
1264 
1265 	blk_finish_plug(&plug);
1266 
1267 	/*
1268 	 * It is possible that, we return short IO due to end of file.
1269 	 * In that case, we need to release all the pages we got hold on.
1270 	 */
1271 	dio_cleanup(dio, &sdio);
1272 
1273 	/*
1274 	 * All block lookups have been performed. For READ requests
1275 	 * we can let i_mutex go now that its achieved its purpose
1276 	 * of protecting us from looking up uninitialized blocks.
1277 	 */
1278 	if (rw == READ && (dio->flags & DIO_LOCKING))
1279 		mutex_unlock(&dio->inode->i_mutex);
1280 
1281 	/*
1282 	 * The only time we want to leave bios in flight is when a successful
1283 	 * partial aio read or full aio write have been setup.  In that case
1284 	 * bio completion will call aio_complete.  The only time it's safe to
1285 	 * call aio_complete is when we return -EIOCBQUEUED, so we key on that.
1286 	 * This had *better* be the only place that raises -EIOCBQUEUED.
1287 	 */
1288 	BUG_ON(retval == -EIOCBQUEUED);
1289 	if (dio->is_async && retval == 0 && dio->result &&
1290 	    (rw == READ || dio->result == count))
1291 		retval = -EIOCBQUEUED;
1292 	else
1293 		dio_await_completion(dio);
1294 
1295 	if (drop_refcount(dio) == 0) {
1296 		retval = dio_complete(dio, offset, retval, false);
1297 	} else
1298 		BUG_ON(retval != -EIOCBQUEUED);
1299 
1300 out:
1301 	return retval;
1302 }
1303 
1304 ssize_t
1305 __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
1306 	struct block_device *bdev, struct iov_iter *iter, loff_t offset,
1307 	get_block_t get_block, dio_iodone_t end_io,
1308 	dio_submit_t submit_io,	int flags)
1309 {
1310 	/*
1311 	 * The block device state is needed in the end to finally
1312 	 * submit everything.  Since it's likely to be cache cold
1313 	 * prefetch it here as first thing to hide some of the
1314 	 * latency.
1315 	 *
1316 	 * Attempt to prefetch the pieces we likely need later.
1317 	 */
1318 	prefetch(&bdev->bd_disk->part_tbl);
1319 	prefetch(bdev->bd_queue);
1320 	prefetch((char *)bdev->bd_queue + SMP_CACHE_BYTES);
1321 
1322 	return do_blockdev_direct_IO(rw, iocb, inode, bdev, iter, offset,
1323 				     get_block, end_io, submit_io, flags);
1324 }
1325 
1326 EXPORT_SYMBOL(__blockdev_direct_IO);
1327 
1328 static __init int dio_init(void)
1329 {
1330 	dio_cache = KMEM_CACHE(dio, SLAB_PANIC);
1331 	return 0;
1332 }
1333 module_init(dio_init)
1334