arm: socfpga: Enable ARM_TWD for socfpga
[linux-2.6.git] / fs / direct-io.c
blob0e04142d5962312fcb055738479247b2364a252e
1 /*
2 * fs/direct-io.c
4 * Copyright (C) 2002, Linus Torvalds.
6 * O_DIRECT
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.
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>
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
46 #define DIO_PAGES 64
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.
56 * If blkfactor is zero then the user's request was aligned to the filesystem's
57 * blocksize.
60 /* dio_state only used in the submission path */
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 size_t size; /* total request size (doesn't change)*/
75 sector_t block_in_file; /* Current offset into the underlying
76 file in dio_block units. */
77 unsigned blocks_available; /* At block_in_file. changes */
78 int reap_counter; /* rate limit reaping */
79 sector_t final_block_in_request;/* doesn't change */
80 unsigned first_block_in_page; /* doesn't change, Used only once */
81 int boundary; /* prev block is at a boundary */
82 get_block_t *get_block; /* block mapping function */
83 dio_submit_t *submit_io; /* IO submition function */
85 loff_t logical_offset_in_bio; /* current first logical block in bio */
86 sector_t final_block_in_bio; /* current final block in bio + 1 */
87 sector_t next_block_for_io; /* next block to be put under IO,
88 in dio_blocks units */
91 * Deferred addition of a page to the dio. These variables are
92 * private to dio_send_cur_page(), submit_page_section() and
93 * dio_bio_add_page().
95 struct page *cur_page; /* The page */
96 unsigned cur_page_offset; /* Offset into it, in bytes */
97 unsigned cur_page_len; /* Nr of bytes at cur_page_offset */
98 sector_t cur_page_block; /* Where it starts */
99 loff_t cur_page_fs_offset; /* Offset in file */
102 * Page fetching state. These variables belong to dio_refill_pages().
104 int curr_page; /* changes */
105 int total_pages; /* doesn't change */
106 unsigned long curr_user_address;/* changes */
109 * Page queue. These variables belong to dio_refill_pages() and
110 * dio_get_page().
112 unsigned head; /* next page to process */
113 unsigned tail; /* last valid page + 1 */
116 /* dio_state communicated between submission path and end_io */
117 struct dio {
118 int flags; /* doesn't change */
119 int rw;
120 struct inode *inode;
121 loff_t i_size; /* i_size when submitted */
122 dio_iodone_t *end_io; /* IO completion function */
124 void *private; /* copy from map_bh.b_private */
126 /* BIO completion state */
127 spinlock_t bio_lock; /* protects BIO fields below */
128 int page_errors; /* errno from get_user_pages() */
129 int is_async; /* is IO async ? */
130 bool defer_completion; /* defer AIO completion to workqueue? */
131 int io_error; /* IO error in completion path */
132 unsigned long refcount; /* direct_io_worker() and bios */
133 struct bio *bio_list; /* singly linked via bi_private */
134 struct task_struct *waiter; /* waiting task (NULL if none) */
136 /* AIO related stuff */
137 struct kiocb *iocb; /* kiocb */
138 ssize_t result; /* IO result */
141 * pages[] (and any fields placed after it) are not zeroed out at
142 * allocation time. Don't add new fields after pages[] unless you
143 * wish that they not be zeroed.
145 union {
146 struct page *pages[DIO_PAGES]; /* page buffer */
147 struct work_struct complete_work;/* deferred AIO completion */
149 } ____cacheline_aligned_in_smp;
151 static struct kmem_cache *dio_cache __read_mostly;
154 * How many pages are in the queue?
156 static inline unsigned dio_pages_present(struct dio_submit *sdio)
158 return sdio->tail - sdio->head;
162 * Go grab and pin some userspace pages. Typically we'll get 64 at a time.
164 static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
166 int ret;
167 int nr_pages;
169 nr_pages = min(sdio->total_pages - sdio->curr_page, DIO_PAGES);
170 ret = get_user_pages_fast(
171 sdio->curr_user_address, /* Where from? */
172 nr_pages, /* How many pages? */
173 dio->rw == READ, /* Write to memory? */
174 &dio->pages[0]); /* Put results here */
176 if (ret < 0 && sdio->blocks_available && (dio->rw & WRITE)) {
177 struct page *page = ZERO_PAGE(0);
179 * A memory fault, but the filesystem has some outstanding
180 * mapped blocks. We need to use those blocks up to avoid
181 * leaking stale data in the file.
183 if (dio->page_errors == 0)
184 dio->page_errors = ret;
185 page_cache_get(page);
186 dio->pages[0] = page;
187 sdio->head = 0;
188 sdio->tail = 1;
189 ret = 0;
190 goto out;
193 if (ret >= 0) {
194 sdio->curr_user_address += ret * PAGE_SIZE;
195 sdio->curr_page += ret;
196 sdio->head = 0;
197 sdio->tail = ret;
198 ret = 0;
200 out:
201 return ret;
205 * Get another userspace page. Returns an ERR_PTR on error. Pages are
206 * buffered inside the dio so that we can call get_user_pages() against a
207 * decent number of pages, less frequently. To provide nicer use of the
208 * L1 cache.
210 static inline struct page *dio_get_page(struct dio *dio,
211 struct dio_submit *sdio)
213 if (dio_pages_present(sdio) == 0) {
214 int ret;
216 ret = dio_refill_pages(dio, sdio);
217 if (ret)
218 return ERR_PTR(ret);
219 BUG_ON(dio_pages_present(sdio) == 0);
221 return dio->pages[sdio->head++];
225 * dio_complete() - called when all DIO BIO I/O has been completed
226 * @offset: the byte offset in the file of the completed operation
228 * This drops i_dio_count, lets interested parties know that a DIO operation
229 * has completed, and calculates the resulting return code for the operation.
231 * It lets the filesystem know if it registered an interest earlier via
232 * get_block. Pass the private field of the map buffer_head so that
233 * filesystems can use it to hold additional state between get_block calls and
234 * dio_complete.
236 static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret,
237 bool is_async)
239 ssize_t transferred = 0;
242 * AIO submission can race with bio completion to get here while
243 * expecting to have the last io completed by bio completion.
244 * In that case -EIOCBQUEUED is in fact not an error we want
245 * to preserve through this call.
247 if (ret == -EIOCBQUEUED)
248 ret = 0;
250 if (dio->result) {
251 transferred = dio->result;
253 /* Check for short read case */
254 if ((dio->rw == READ) && ((offset + transferred) > dio->i_size))
255 transferred = dio->i_size - offset;
258 if (ret == 0)
259 ret = dio->page_errors;
260 if (ret == 0)
261 ret = dio->io_error;
262 if (ret == 0)
263 ret = transferred;
265 if (dio->end_io && dio->result)
266 dio->end_io(dio->iocb, offset, transferred, dio->private);
268 inode_dio_done(dio->inode);
269 if (is_async) {
270 if (dio->rw & WRITE) {
271 int err;
273 err = generic_write_sync(dio->iocb->ki_filp, offset,
274 transferred);
275 if (err < 0 && ret > 0)
276 ret = err;
279 aio_complete(dio->iocb, ret, 0);
282 kmem_cache_free(dio_cache, dio);
283 return ret;
286 static void dio_aio_complete_work(struct work_struct *work)
288 struct dio *dio = container_of(work, struct dio, complete_work);
290 dio_complete(dio, dio->iocb->ki_pos, 0, true);
293 static int dio_bio_complete(struct dio *dio, struct bio *bio);
296 * Asynchronous IO callback.
298 static void dio_bio_end_aio(struct bio *bio, int error)
300 struct dio *dio = bio->bi_private;
301 unsigned long remaining;
302 unsigned long flags;
304 /* cleanup the bio */
305 dio_bio_complete(dio, bio);
307 spin_lock_irqsave(&dio->bio_lock, flags);
308 remaining = --dio->refcount;
309 if (remaining == 1 && dio->waiter)
310 wake_up_process(dio->waiter);
311 spin_unlock_irqrestore(&dio->bio_lock, flags);
313 if (remaining == 0) {
314 if (dio->result && dio->defer_completion) {
315 INIT_WORK(&dio->complete_work, dio_aio_complete_work);
316 queue_work(dio->inode->i_sb->s_dio_done_wq,
317 &dio->complete_work);
318 } else {
319 dio_complete(dio, dio->iocb->ki_pos, 0, true);
325 * The BIO completion handler simply queues the BIO up for the process-context
326 * handler.
328 * During I/O bi_private points at the dio. After I/O, bi_private is used to
329 * implement a singly-linked list of completed BIOs, at dio->bio_list.
331 static void dio_bio_end_io(struct bio *bio, int error)
333 struct dio *dio = bio->bi_private;
334 unsigned long flags;
336 spin_lock_irqsave(&dio->bio_lock, flags);
337 bio->bi_private = dio->bio_list;
338 dio->bio_list = bio;
339 if (--dio->refcount == 1 && dio->waiter)
340 wake_up_process(dio->waiter);
341 spin_unlock_irqrestore(&dio->bio_lock, flags);
345 * dio_end_io - handle the end io action for the given bio
346 * @bio: The direct io bio thats being completed
347 * @error: Error if there was one
349 * This is meant to be called by any filesystem that uses their own dio_submit_t
350 * so that the DIO specific endio actions are dealt with after the filesystem
351 * has done it's completion work.
353 void dio_end_io(struct bio *bio, int error)
355 struct dio *dio = bio->bi_private;
357 if (dio->is_async)
358 dio_bio_end_aio(bio, error);
359 else
360 dio_bio_end_io(bio, error);
362 EXPORT_SYMBOL_GPL(dio_end_io);
364 static inline void
365 dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
366 struct block_device *bdev,
367 sector_t first_sector, int nr_vecs)
369 struct bio *bio;
372 * bio_alloc() is guaranteed to return a bio when called with
373 * __GFP_WAIT and we request a valid number of vectors.
375 bio = bio_alloc(GFP_KERNEL, nr_vecs);
377 bio->bi_bdev = bdev;
378 bio->bi_sector = first_sector;
379 if (dio->is_async)
380 bio->bi_end_io = dio_bio_end_aio;
381 else
382 bio->bi_end_io = dio_bio_end_io;
384 sdio->bio = bio;
385 sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
389 * In the AIO read case we speculatively dirty the pages before starting IO.
390 * During IO completion, any of these pages which happen to have been written
391 * back will be redirtied by bio_check_pages_dirty().
393 * bios hold a dio reference between submit_bio and ->end_io.
395 static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
397 struct bio *bio = sdio->bio;
398 unsigned long flags;
400 bio->bi_private = dio;
402 spin_lock_irqsave(&dio->bio_lock, flags);
403 dio->refcount++;
404 spin_unlock_irqrestore(&dio->bio_lock, flags);
406 if (dio->is_async && dio->rw == READ)
407 bio_set_pages_dirty(bio);
409 if (sdio->submit_io)
410 sdio->submit_io(dio->rw, bio, dio->inode,
411 sdio->logical_offset_in_bio);
412 else
413 submit_bio(dio->rw, bio);
415 sdio->bio = NULL;
416 sdio->boundary = 0;
417 sdio->logical_offset_in_bio = 0;
421 * Release any resources in case of a failure
423 static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio)
425 while (dio_pages_present(sdio))
426 page_cache_release(dio_get_page(dio, sdio));
430 * Wait for the next BIO to complete. Remove it and return it. NULL is
431 * returned once all BIOs have been completed. This must only be called once
432 * all bios have been issued so that dio->refcount can only decrease. This
433 * requires that that the caller hold a reference on the dio.
435 static struct bio *dio_await_one(struct dio *dio)
437 unsigned long flags;
438 struct bio *bio = NULL;
440 spin_lock_irqsave(&dio->bio_lock, flags);
443 * Wait as long as the list is empty and there are bios in flight. bio
444 * completion drops the count, maybe adds to the list, and wakes while
445 * holding the bio_lock so we don't need set_current_state()'s barrier
446 * and can call it after testing our condition.
448 while (dio->refcount > 1 && dio->bio_list == NULL) {
449 __set_current_state(TASK_UNINTERRUPTIBLE);
450 dio->waiter = current;
451 spin_unlock_irqrestore(&dio->bio_lock, flags);
452 io_schedule();
453 /* wake up sets us TASK_RUNNING */
454 spin_lock_irqsave(&dio->bio_lock, flags);
455 dio->waiter = NULL;
457 if (dio->bio_list) {
458 bio = dio->bio_list;
459 dio->bio_list = bio->bi_private;
461 spin_unlock_irqrestore(&dio->bio_lock, flags);
462 return bio;
466 * Process one completed BIO. No locks are held.
468 static int dio_bio_complete(struct dio *dio, struct bio *bio)
470 const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
471 struct bio_vec *bvec;
472 unsigned i;
474 if (!uptodate)
475 dio->io_error = -EIO;
477 if (dio->is_async && dio->rw == READ) {
478 bio_check_pages_dirty(bio); /* transfers ownership */
479 } else {
480 bio_for_each_segment_all(bvec, bio, i) {
481 struct page *page = bvec->bv_page;
483 if (dio->rw == READ && !PageCompound(page))
484 set_page_dirty_lock(page);
485 page_cache_release(page);
487 bio_put(bio);
489 return uptodate ? 0 : -EIO;
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().
499 static void dio_await_completion(struct dio *dio)
501 struct bio *bio;
502 do {
503 bio = dio_await_one(dio);
504 if (bio)
505 dio_bio_complete(dio, bio);
506 } while (bio);
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.
514 * This also helps to limit the peak amount of pinned userspace memory.
516 static inline int dio_bio_reap(struct dio *dio, struct dio_submit *sdio)
518 int ret = 0;
520 if (sdio->reap_counter++ >= 64) {
521 while (dio->bio_list) {
522 unsigned long flags;
523 struct bio *bio;
524 int ret2;
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;
534 sdio->reap_counter = 0;
536 return ret;
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.
545 static int sb_init_dio_done_wq(struct super_block *sb)
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;
554 * This has to be atomic as more DIOs can race to create the workqueue
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;
563 static int dio_set_defer_completion(struct dio *dio)
565 struct super_block *sb = dio->inode->i_sb;
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;
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).
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.
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.
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.
590 * If *any* of the mapped blocks are new, then the fs must set buffer_new().
591 * This isn't very efficient...
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.
598 static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
599 struct buffer_head *map_bh)
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;
609 * If there was a memory error and we've overwritten all the
610 * mapped blocks then we can now return that memory error
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;
620 map_bh->b_state = 0;
621 map_bh->b_size = fs_count << i_blkbits;
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.
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.
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;
641 ret = (*sdio->get_block)(dio->inode, fs_startblk,
642 map_bh, create);
644 /* Store for completion */
645 dio->private = map_bh->b_private;
647 if (ret == 0 && buffer_defer_completion(map_bh))
648 ret = dio_set_defer_completion(dio);
650 return ret;
654 * There is no bio. Make one now.
656 static inline int dio_new_bio(struct dio *dio, struct dio_submit *sdio,
657 sector_t start_sector, struct buffer_head *map_bh)
659 sector_t sector;
660 int ret, nr_pages;
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_get_nr_vecs(map_bh->b_bdev));
667 nr_pages = min(nr_pages, BIO_MAX_PAGES);
668 BUG_ON(nr_pages <= 0);
669 dio_bio_alloc(dio, sdio, map_bh->b_bdev, sector, nr_pages);
670 sdio->boundary = 0;
671 out:
672 return ret;
676 * Attempt to put the current chunk of 'cur_page' into the current BIO. If
677 * that was successful then update final_block_in_bio and take a ref against
678 * the just-added page.
680 * Return zero on success. Non-zero means the caller needs to start a new BIO.
682 static inline int dio_bio_add_page(struct dio_submit *sdio)
684 int ret;
686 ret = bio_add_page(sdio->bio, sdio->cur_page,
687 sdio->cur_page_len, sdio->cur_page_offset);
688 if (ret == sdio->cur_page_len) {
690 * Decrement count only, if we are done with this page
692 if ((sdio->cur_page_len + sdio->cur_page_offset) == PAGE_SIZE)
693 sdio->pages_in_io--;
694 page_cache_get(sdio->cur_page);
695 sdio->final_block_in_bio = sdio->cur_page_block +
696 (sdio->cur_page_len >> sdio->blkbits);
697 ret = 0;
698 } else {
699 ret = 1;
701 return ret;
705 * Put cur_page under IO. The section of cur_page which is described by
706 * cur_page_offset,cur_page_len is put into a BIO. The section of cur_page
707 * starts on-disk at cur_page_block.
709 * We take a ref against the page here (on behalf of its presence in the bio).
711 * The caller of this function is responsible for removing cur_page from the
712 * dio, and for dropping the refcount which came from that presence.
714 static inline int dio_send_cur_page(struct dio *dio, struct dio_submit *sdio,
715 struct buffer_head *map_bh)
717 int ret = 0;
719 if (sdio->bio) {
720 loff_t cur_offset = sdio->cur_page_fs_offset;
721 loff_t bio_next_offset = sdio->logical_offset_in_bio +
722 sdio->bio->bi_size;
725 * See whether this new request is contiguous with the old.
727 * Btrfs cannot handle having logically non-contiguous requests
728 * submitted. For example if you have
730 * Logical: [0-4095][HOLE][8192-12287]
731 * Physical: [0-4095] [4096-8191]
733 * We cannot submit those pages together as one BIO. So if our
734 * current logical offset in the file does not equal what would
735 * be the next logical offset in the bio, submit the bio we
736 * have.
738 if (sdio->final_block_in_bio != sdio->cur_page_block ||
739 cur_offset != bio_next_offset)
740 dio_bio_submit(dio, sdio);
743 if (sdio->bio == NULL) {
744 ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
745 if (ret)
746 goto out;
749 if (dio_bio_add_page(sdio) != 0) {
750 dio_bio_submit(dio, sdio);
751 ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
752 if (ret == 0) {
753 ret = dio_bio_add_page(sdio);
754 BUG_ON(ret != 0);
757 out:
758 return ret;
762 * An autonomous function to put a chunk of a page under deferred IO.
764 * The caller doesn't actually know (or care) whether this piece of page is in
765 * a BIO, or is under IO or whatever. We just take care of all possible
766 * situations here. The separation between the logic of do_direct_IO() and
767 * that of submit_page_section() is important for clarity. Please don't break.
769 * The chunk of page starts on-disk at blocknr.
771 * We perform deferred IO, by recording the last-submitted page inside our
772 * private part of the dio structure. If possible, we just expand the IO
773 * across that page here.
775 * If that doesn't work out then we put the old page into the bio and add this
776 * page to the dio instead.
778 static inline int
779 submit_page_section(struct dio *dio, struct dio_submit *sdio, struct page *page,
780 unsigned offset, unsigned len, sector_t blocknr,
781 struct buffer_head *map_bh)
783 int ret = 0;
785 if (dio->rw & WRITE) {
787 * Read accounting is performed in submit_bio()
789 task_io_account_write(len);
793 * Can we just grow the current page's presence in the dio?
795 if (sdio->cur_page == page &&
796 sdio->cur_page_offset + sdio->cur_page_len == offset &&
797 sdio->cur_page_block +
798 (sdio->cur_page_len >> sdio->blkbits) == blocknr) {
799 sdio->cur_page_len += len;
800 goto out;
804 * If there's a deferred page already there then send it.
806 if (sdio->cur_page) {
807 ret = dio_send_cur_page(dio, sdio, map_bh);
808 page_cache_release(sdio->cur_page);
809 sdio->cur_page = NULL;
810 if (ret)
811 return ret;
814 page_cache_get(page); /* It is in dio */
815 sdio->cur_page = page;
816 sdio->cur_page_offset = offset;
817 sdio->cur_page_len = len;
818 sdio->cur_page_block = blocknr;
819 sdio->cur_page_fs_offset = sdio->block_in_file << sdio->blkbits;
820 out:
822 * If sdio->boundary then we want to schedule the IO now to
823 * avoid metadata seeks.
825 if (sdio->boundary) {
826 ret = dio_send_cur_page(dio, sdio, map_bh);
827 dio_bio_submit(dio, sdio);
828 page_cache_release(sdio->cur_page);
829 sdio->cur_page = NULL;
831 return ret;
835 * Clean any dirty buffers in the blockdev mapping which alias newly-created
836 * file blocks. Only called for S_ISREG files - blockdevs do not set
837 * buffer_new
839 static void clean_blockdev_aliases(struct dio *dio, struct buffer_head *map_bh)
841 unsigned i;
842 unsigned nblocks;
844 nblocks = map_bh->b_size >> dio->inode->i_blkbits;
846 for (i = 0; i < nblocks; i++) {
847 unmap_underlying_metadata(map_bh->b_bdev,
848 map_bh->b_blocknr + i);
853 * If we are not writing the entire block and get_block() allocated
854 * the block for us, we need to fill-in the unused portion of the
855 * block with zeros. This happens only if user-buffer, fileoffset or
856 * io length is not filesystem block-size multiple.
858 * `end' is zero if we're doing the start of the IO, 1 at the end of the
859 * IO.
861 static inline void dio_zero_block(struct dio *dio, struct dio_submit *sdio,
862 int end, struct buffer_head *map_bh)
864 unsigned dio_blocks_per_fs_block;
865 unsigned this_chunk_blocks; /* In dio_blocks */
866 unsigned this_chunk_bytes;
867 struct page *page;
869 sdio->start_zero_done = 1;
870 if (!sdio->blkfactor || !buffer_new(map_bh))
871 return;
873 dio_blocks_per_fs_block = 1 << sdio->blkfactor;
874 this_chunk_blocks = sdio->block_in_file & (dio_blocks_per_fs_block - 1);
876 if (!this_chunk_blocks)
877 return;
880 * We need to zero out part of an fs block. It is either at the
881 * beginning or the end of the fs block.
883 if (end)
884 this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
886 this_chunk_bytes = this_chunk_blocks << sdio->blkbits;
888 page = ZERO_PAGE(0);
889 if (submit_page_section(dio, sdio, page, 0, this_chunk_bytes,
890 sdio->next_block_for_io, map_bh))
891 return;
893 sdio->next_block_for_io += this_chunk_blocks;
897 * Walk the user pages, and the file, mapping blocks to disk and generating
898 * a sequence of (page,offset,len,block) mappings. These mappings are injected
899 * into submit_page_section(), which takes care of the next stage of submission
901 * Direct IO against a blockdev is different from a file. Because we can
902 * happily perform page-sized but 512-byte aligned IOs. It is important that
903 * blockdev IO be able to have fine alignment and large sizes.
905 * So what we do is to permit the ->get_block function to populate bh.b_size
906 * with the size of IO which is permitted at this offset and this i_blkbits.
908 * For best results, the blockdev should be set up with 512-byte i_blkbits and
909 * it should set b_size to PAGE_SIZE or more inside get_block(). This gives
910 * fine alignment but still allows this function to work in PAGE_SIZE units.
912 static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
913 struct buffer_head *map_bh)
915 const unsigned blkbits = sdio->blkbits;
916 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
917 struct page *page;
918 unsigned block_in_page;
919 int ret = 0;
921 /* The I/O can start at any block offset within the first page */
922 block_in_page = sdio->first_block_in_page;
924 while (sdio->block_in_file < sdio->final_block_in_request) {
925 page = dio_get_page(dio, sdio);
926 if (IS_ERR(page)) {
927 ret = PTR_ERR(page);
928 goto out;
931 while (block_in_page < blocks_per_page) {
932 unsigned offset_in_page = block_in_page << blkbits;
933 unsigned this_chunk_bytes; /* # of bytes mapped */
934 unsigned this_chunk_blocks; /* # of blocks */
935 unsigned u;
937 if (sdio->blocks_available == 0) {
939 * Need to go and map some more disk
941 unsigned long blkmask;
942 unsigned long dio_remainder;
944 ret = get_more_blocks(dio, sdio, map_bh);
945 if (ret) {
946 page_cache_release(page);
947 goto out;
949 if (!buffer_mapped(map_bh))
950 goto do_holes;
952 sdio->blocks_available =
953 map_bh->b_size >> sdio->blkbits;
954 sdio->next_block_for_io =
955 map_bh->b_blocknr << sdio->blkfactor;
956 if (buffer_new(map_bh))
957 clean_blockdev_aliases(dio, map_bh);
959 if (!sdio->blkfactor)
960 goto do_holes;
962 blkmask = (1 << sdio->blkfactor) - 1;
963 dio_remainder = (sdio->block_in_file & blkmask);
966 * If we are at the start of IO and that IO
967 * starts partway into a fs-block,
968 * dio_remainder will be non-zero. If the IO
969 * is a read then we can simply advance the IO
970 * cursor to the first block which is to be
971 * read. But if the IO is a write and the
972 * block was newly allocated we cannot do that;
973 * the start of the fs block must be zeroed out
974 * on-disk
976 if (!buffer_new(map_bh))
977 sdio->next_block_for_io += dio_remainder;
978 sdio->blocks_available -= dio_remainder;
980 do_holes:
981 /* Handle holes */
982 if (!buffer_mapped(map_bh)) {
983 loff_t i_size_aligned;
985 /* AKPM: eargh, -ENOTBLK is a hack */
986 if (dio->rw & WRITE) {
987 page_cache_release(page);
988 return -ENOTBLK;
992 * Be sure to account for a partial block as the
993 * last block in the file
995 i_size_aligned = ALIGN(i_size_read(dio->inode),
996 1 << blkbits);
997 if (sdio->block_in_file >=
998 i_size_aligned >> blkbits) {
999 /* We hit eof */
1000 page_cache_release(page);
1001 goto out;
1003 zero_user(page, block_in_page << blkbits,
1004 1 << blkbits);
1005 sdio->block_in_file++;
1006 block_in_page++;
1007 goto next_block;
1011 * If we're performing IO which has an alignment which
1012 * is finer than the underlying fs, go check to see if
1013 * we must zero out the start of this block.
1015 if (unlikely(sdio->blkfactor && !sdio->start_zero_done))
1016 dio_zero_block(dio, sdio, 0, map_bh);
1019 * Work out, in this_chunk_blocks, how much disk we
1020 * can add to this page
1022 this_chunk_blocks = sdio->blocks_available;
1023 u = (PAGE_SIZE - offset_in_page) >> blkbits;
1024 if (this_chunk_blocks > u)
1025 this_chunk_blocks = u;
1026 u = sdio->final_block_in_request - sdio->block_in_file;
1027 if (this_chunk_blocks > u)
1028 this_chunk_blocks = u;
1029 this_chunk_bytes = this_chunk_blocks << blkbits;
1030 BUG_ON(this_chunk_bytes == 0);
1032 if (this_chunk_blocks == sdio->blocks_available)
1033 sdio->boundary = buffer_boundary(map_bh);
1034 ret = submit_page_section(dio, sdio, page,
1035 offset_in_page,
1036 this_chunk_bytes,
1037 sdio->next_block_for_io,
1038 map_bh);
1039 if (ret) {
1040 page_cache_release(page);
1041 goto out;
1043 sdio->next_block_for_io += this_chunk_blocks;
1045 sdio->block_in_file += this_chunk_blocks;
1046 block_in_page += this_chunk_blocks;
1047 sdio->blocks_available -= this_chunk_blocks;
1048 next_block:
1049 BUG_ON(sdio->block_in_file > sdio->final_block_in_request);
1050 if (sdio->block_in_file == sdio->final_block_in_request)
1051 break;
1054 /* Drop the ref which was taken in get_user_pages() */
1055 page_cache_release(page);
1056 block_in_page = 0;
1058 out:
1059 return ret;
1062 static inline int drop_refcount(struct dio *dio)
1064 int ret2;
1065 unsigned long flags;
1068 * Sync will always be dropping the final ref and completing the
1069 * operation. AIO can if it was a broken operation described above or
1070 * in fact if all the bios race to complete before we get here. In
1071 * that case dio_complete() translates the EIOCBQUEUED into the proper
1072 * return code that the caller will hand to aio_complete().
1074 * This is managed by the bio_lock instead of being an atomic_t so that
1075 * completion paths can drop their ref and use the remaining count to
1076 * decide to wake the submission path atomically.
1078 spin_lock_irqsave(&dio->bio_lock, flags);
1079 ret2 = --dio->refcount;
1080 spin_unlock_irqrestore(&dio->bio_lock, flags);
1081 return ret2;
1085 * This is a library function for use by filesystem drivers.
1087 * The locking rules are governed by the flags parameter:
1088 * - if the flags value contains DIO_LOCKING we use a fancy locking
1089 * scheme for dumb filesystems.
1090 * For writes this function is called under i_mutex and returns with
1091 * i_mutex held, for reads, i_mutex is not held on entry, but it is
1092 * taken and dropped again before returning.
1093 * - if the flags value does NOT contain DIO_LOCKING we don't use any
1094 * internal locking but rather rely on the filesystem to synchronize
1095 * direct I/O reads/writes versus each other and truncate.
1097 * To help with locking against truncate we incremented the i_dio_count
1098 * counter before starting direct I/O, and decrement it once we are done.
1099 * Truncate can wait for it to reach zero to provide exclusion. It is
1100 * expected that filesystem provide exclusion between new direct I/O
1101 * and truncates. For DIO_LOCKING filesystems this is done by i_mutex,
1102 * but other filesystems need to take care of this on their own.
1104 * NOTE: if you pass "sdio" to anything by pointer make sure that function
1105 * is always inlined. Otherwise gcc is unable to split the structure into
1106 * individual fields and will generate much worse code. This is important
1107 * for the whole file.
1109 static inline ssize_t
1110 do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
1111 struct block_device *bdev, const struct iovec *iov, loff_t offset,
1112 unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io,
1113 dio_submit_t submit_io, int flags)
1115 int seg;
1116 size_t size;
1117 unsigned long addr;
1118 unsigned i_blkbits = ACCESS_ONCE(inode->i_blkbits);
1119 unsigned blkbits = i_blkbits;
1120 unsigned blocksize_mask = (1 << blkbits) - 1;
1121 ssize_t retval = -EINVAL;
1122 loff_t end = offset;
1123 struct dio *dio;
1124 struct dio_submit sdio = { 0, };
1125 unsigned long user_addr;
1126 size_t bytes;
1127 struct buffer_head map_bh = { 0, };
1128 struct blk_plug plug;
1130 if (rw & WRITE)
1131 rw = WRITE_ODIRECT;
1134 * Avoid references to bdev if not absolutely needed to give
1135 * the early prefetch in the caller enough time.
1138 if (offset & blocksize_mask) {
1139 if (bdev)
1140 blkbits = blksize_bits(bdev_logical_block_size(bdev));
1141 blocksize_mask = (1 << blkbits) - 1;
1142 if (offset & blocksize_mask)
1143 goto out;
1146 /* Check the memory alignment. Blocks cannot straddle pages */
1147 for (seg = 0; seg < nr_segs; seg++) {
1148 addr = (unsigned long)iov[seg].iov_base;
1149 size = iov[seg].iov_len;
1150 end += size;
1151 if (unlikely((addr & blocksize_mask) ||
1152 (size & blocksize_mask))) {
1153 if (bdev)
1154 blkbits = blksize_bits(
1155 bdev_logical_block_size(bdev));
1156 blocksize_mask = (1 << blkbits) - 1;
1157 if ((addr & blocksize_mask) || (size & blocksize_mask))
1158 goto out;
1162 /* watch out for a 0 len io from a tricksy fs */
1163 if (rw == READ && end == offset)
1164 return 0;
1166 dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
1167 retval = -ENOMEM;
1168 if (!dio)
1169 goto out;
1171 * Believe it or not, zeroing out the page array caused a .5%
1172 * performance regression in a database benchmark. So, we take
1173 * care to only zero out what's needed.
1175 memset(dio, 0, offsetof(struct dio, pages));
1177 dio->flags = flags;
1178 if (dio->flags & DIO_LOCKING) {
1179 if (rw == READ) {
1180 struct address_space *mapping =
1181 iocb->ki_filp->f_mapping;
1183 /* will be released by direct_io_worker */
1184 mutex_lock(&inode->i_mutex);
1186 retval = filemap_write_and_wait_range(mapping, offset,
1187 end - 1);
1188 if (retval) {
1189 mutex_unlock(&inode->i_mutex);
1190 kmem_cache_free(dio_cache, dio);
1191 goto out;
1197 * For file extending writes updating i_size before data
1198 * writeouts complete can expose uninitialized blocks. So
1199 * even for AIO, we need to wait for i/o to complete before
1200 * returning in this case.
1202 dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) &&
1203 (end > i_size_read(inode)));
1204 dio->inode = inode;
1205 dio->rw = rw;
1208 * For AIO O_(D)SYNC writes we need to defer completions to a workqueue
1209 * so that we can call ->fsync.
1211 if (dio->is_async && (rw & WRITE) &&
1212 ((iocb->ki_filp->f_flags & O_DSYNC) ||
1213 IS_SYNC(iocb->ki_filp->f_mapping->host))) {
1214 retval = dio_set_defer_completion(dio);
1215 if (retval) {
1217 * We grab i_mutex only for reads so we don't have
1218 * to release it here
1220 kmem_cache_free(dio_cache, dio);
1221 goto out;
1226 * Will be decremented at I/O completion time.
1228 atomic_inc(&inode->i_dio_count);
1230 retval = 0;
1231 sdio.blkbits = blkbits;
1232 sdio.blkfactor = i_blkbits - blkbits;
1233 sdio.block_in_file = offset >> blkbits;
1235 sdio.get_block = get_block;
1236 dio->end_io = end_io;
1237 sdio.submit_io = submit_io;
1238 sdio.final_block_in_bio = -1;
1239 sdio.next_block_for_io = -1;
1241 dio->iocb = iocb;
1242 dio->i_size = i_size_read(inode);
1244 spin_lock_init(&dio->bio_lock);
1245 dio->refcount = 1;
1248 * In case of non-aligned buffers, we may need 2 more
1249 * pages since we need to zero out first and last block.
1251 if (unlikely(sdio.blkfactor))
1252 sdio.pages_in_io = 2;
1254 for (seg = 0; seg < nr_segs; seg++) {
1255 user_addr = (unsigned long)iov[seg].iov_base;
1256 sdio.pages_in_io +=
1257 ((user_addr + iov[seg].iov_len + PAGE_SIZE-1) /
1258 PAGE_SIZE - user_addr / PAGE_SIZE);
1261 blk_start_plug(&plug);
1263 for (seg = 0; seg < nr_segs; seg++) {
1264 user_addr = (unsigned long)iov[seg].iov_base;
1265 sdio.size += bytes = iov[seg].iov_len;
1267 /* Index into the first page of the first block */
1268 sdio.first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits;
1269 sdio.final_block_in_request = sdio.block_in_file +
1270 (bytes >> blkbits);
1271 /* Page fetching state */
1272 sdio.head = 0;
1273 sdio.tail = 0;
1274 sdio.curr_page = 0;
1276 sdio.total_pages = 0;
1277 if (user_addr & (PAGE_SIZE-1)) {
1278 sdio.total_pages++;
1279 bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1));
1281 sdio.total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
1282 sdio.curr_user_address = user_addr;
1284 retval = do_direct_IO(dio, &sdio, &map_bh);
1286 dio->result += iov[seg].iov_len -
1287 ((sdio.final_block_in_request - sdio.block_in_file) <<
1288 blkbits);
1290 if (retval) {
1291 dio_cleanup(dio, &sdio);
1292 break;
1294 } /* end iovec loop */
1296 if (retval == -ENOTBLK) {
1298 * The remaining part of the request will be
1299 * be handled by buffered I/O when we return
1301 retval = 0;
1304 * There may be some unwritten disk at the end of a part-written
1305 * fs-block-sized block. Go zero that now.
1307 dio_zero_block(dio, &sdio, 1, &map_bh);
1309 if (sdio.cur_page) {
1310 ssize_t ret2;
1312 ret2 = dio_send_cur_page(dio, &sdio, &map_bh);
1313 if (retval == 0)
1314 retval = ret2;
1315 page_cache_release(sdio.cur_page);
1316 sdio.cur_page = NULL;
1318 if (sdio.bio)
1319 dio_bio_submit(dio, &sdio);
1321 blk_finish_plug(&plug);
1324 * It is possible that, we return short IO due to end of file.
1325 * In that case, we need to release all the pages we got hold on.
1327 dio_cleanup(dio, &sdio);
1330 * All block lookups have been performed. For READ requests
1331 * we can let i_mutex go now that its achieved its purpose
1332 * of protecting us from looking up uninitialized blocks.
1334 if (rw == READ && (dio->flags & DIO_LOCKING))
1335 mutex_unlock(&dio->inode->i_mutex);
1338 * The only time we want to leave bios in flight is when a successful
1339 * partial aio read or full aio write have been setup. In that case
1340 * bio completion will call aio_complete. The only time it's safe to
1341 * call aio_complete is when we return -EIOCBQUEUED, so we key on that.
1342 * This had *better* be the only place that raises -EIOCBQUEUED.
1344 BUG_ON(retval == -EIOCBQUEUED);
1345 if (dio->is_async && retval == 0 && dio->result &&
1346 ((rw == READ) || (dio->result == sdio.size)))
1347 retval = -EIOCBQUEUED;
1349 if (retval != -EIOCBQUEUED)
1350 dio_await_completion(dio);
1352 if (drop_refcount(dio) == 0) {
1353 retval = dio_complete(dio, offset, retval, false);
1354 } else
1355 BUG_ON(retval != -EIOCBQUEUED);
1357 out:
1358 return retval;
1361 ssize_t
1362 __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
1363 struct block_device *bdev, const struct iovec *iov, loff_t offset,
1364 unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io,
1365 dio_submit_t submit_io, int flags)
1368 * The block device state is needed in the end to finally
1369 * submit everything. Since it's likely to be cache cold
1370 * prefetch it here as first thing to hide some of the
1371 * latency.
1373 * Attempt to prefetch the pieces we likely need later.
1375 prefetch(&bdev->bd_disk->part_tbl);
1376 prefetch(bdev->bd_queue);
1377 prefetch((char *)bdev->bd_queue + SMP_CACHE_BYTES);
1379 return do_blockdev_direct_IO(rw, iocb, inode, bdev, iov, offset,
1380 nr_segs, get_block, end_io,
1381 submit_io, flags);
1384 EXPORT_SYMBOL(__blockdev_direct_IO);
1386 static __init int dio_init(void)
1388 dio_cache = KMEM_CACHE(dio, SLAB_PANIC);
1389 return 0;
1391 module_init(dio_init)