4 * Copyright (C) 2002, Linus Torvalds.
8 * 04Jul2002 Andrew Morton
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>
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>
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
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.
55 * If blkfactor is zero then the user's request was aligned to the filesystem's
59 /* dio_state only used in the submission path */
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
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 */
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 */
88 * Deferred addition of a page to the dio. These variables are
89 * private to dio_send_cur_page(), submit_page_section() and
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 */
98 struct iov_iter *iter;
100 * Page queue. These variables belong to dio_refill_pages() and
103 unsigned head; /* next page to process */
104 unsigned tail; /* last valid page + 1 */
108 /* dio_state communicated between submission path and end_io */
110 int flags; /* doesn't change */
114 struct block_device *bio_bdev;
116 loff_t i_size; /* i_size when submitted */
117 dio_iodone_t *end_io; /* IO completion function */
119 void *private; /* copy from map_bh.b_private */
121 /* BIO completion state */
122 spinlock_t bio_lock; /* protects BIO fields below */
123 int page_errors; /* errno from get_user_pages() */
124 int is_async; /* is IO async ? */
125 bool defer_completion; /* defer AIO completion to workqueue? */
126 bool should_dirty; /* if pages should be dirtied */
127 int io_error; /* IO error in completion path */
128 unsigned long refcount; /* direct_io_worker() and bios */
129 struct bio *bio_list; /* singly linked via bi_private */
130 struct task_struct *waiter; /* waiting task (NULL if none) */
132 /* AIO related stuff */
133 struct kiocb *iocb; /* kiocb */
134 ssize_t result; /* IO result */
137 * pages[] (and any fields placed after it) are not zeroed out at
138 * allocation time. Don't add new fields after pages[] unless you
139 * wish that they not be zeroed.
142 struct page *pages[DIO_PAGES]; /* page buffer */
143 struct work_struct complete_work;/* deferred AIO completion */
145 } ____cacheline_aligned_in_smp;
147 static struct kmem_cache *dio_cache __read_mostly;
150 * How many pages are in the queue?
152 static inline unsigned dio_pages_present(struct dio_submit *sdio)
154 return sdio->tail - sdio->head;
158 * Go grab and pin some userspace pages. Typically we'll get 64 at a time.
160 static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
164 ret = iov_iter_get_pages(sdio->iter, dio->pages, LONG_MAX, DIO_PAGES,
167 if (ret < 0 && sdio->blocks_available && (dio->op == REQ_OP_WRITE)) {
168 struct page *page = ZERO_PAGE(0);
170 * A memory fault, but the filesystem has some outstanding
171 * mapped blocks. We need to use those blocks up to avoid
172 * leaking stale data in the file.
174 if (dio->page_errors == 0)
175 dio->page_errors = ret;
177 dio->pages[0] = page;
181 sdio->to = PAGE_SIZE;
186 iov_iter_advance(sdio->iter, ret);
189 sdio->tail = (ret + PAGE_SIZE - 1) / PAGE_SIZE;
190 sdio->to = ((ret - 1) & (PAGE_SIZE - 1)) + 1;
197 * Get another userspace page. Returns an ERR_PTR on error. Pages are
198 * buffered inside the dio so that we can call get_user_pages() against a
199 * decent number of pages, less frequently. To provide nicer use of the
202 static inline struct page *dio_get_page(struct dio *dio,
203 struct dio_submit *sdio)
205 if (dio_pages_present(sdio) == 0) {
208 ret = dio_refill_pages(dio, sdio);
211 BUG_ON(dio_pages_present(sdio) == 0);
213 return dio->pages[sdio->head];
217 * dio_complete() - called when all DIO BIO I/O has been completed
218 * @offset: the byte offset in the file of the completed operation
220 * This drops i_dio_count, lets interested parties know that a DIO operation
221 * has completed, and calculates the resulting return code for the operation.
223 * It lets the filesystem know if it registered an interest earlier via
224 * get_block. Pass the private field of the map buffer_head so that
225 * filesystems can use it to hold additional state between get_block calls and
228 static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
230 loff_t offset = dio->iocb->ki_pos;
231 ssize_t transferred = 0;
234 * AIO submission can race with bio completion to get here while
235 * expecting to have the last io completed by bio completion.
236 * In that case -EIOCBQUEUED is in fact not an error we want
237 * to preserve through this call.
239 if (ret == -EIOCBQUEUED)
243 transferred = dio->result;
245 /* Check for short read case */
246 if ((dio->op == REQ_OP_READ) &&
247 ((offset + transferred) > dio->i_size))
248 transferred = dio->i_size - offset;
249 /* ignore EFAULT if some IO has been done */
250 if (unlikely(ret == -EFAULT) && transferred)
255 ret = dio->page_errors;
265 err = dio->end_io(dio->iocb, offset, ret, dio->private);
270 if (!(dio->flags & DIO_SKIP_DIO_COUNT))
271 inode_dio_end(dio->inode);
275 * generic_write_sync expects ki_pos to have been updated
276 * already, but the submission path only does this for
279 dio->iocb->ki_pos += transferred;
281 if (dio->op == REQ_OP_WRITE)
282 ret = generic_write_sync(dio->iocb, transferred);
283 dio->iocb->ki_complete(dio->iocb, ret, 0);
286 kmem_cache_free(dio_cache, dio);
290 static void dio_aio_complete_work(struct work_struct *work)
292 struct dio *dio = container_of(work, struct dio, complete_work);
294 dio_complete(dio, 0, true);
297 static blk_status_t dio_bio_complete(struct dio *dio, struct bio *bio);
300 * Asynchronous IO callback.
302 static void dio_bio_end_aio(struct bio *bio)
304 struct dio *dio = bio->bi_private;
305 unsigned long remaining;
308 /* cleanup the bio */
309 dio_bio_complete(dio, bio);
311 spin_lock_irqsave(&dio->bio_lock, flags);
312 remaining = --dio->refcount;
313 if (remaining == 1 && dio->waiter)
314 wake_up_process(dio->waiter);
315 spin_unlock_irqrestore(&dio->bio_lock, flags);
317 if (remaining == 0) {
318 if (dio->result && dio->defer_completion) {
319 INIT_WORK(&dio->complete_work, dio_aio_complete_work);
320 queue_work(dio->inode->i_sb->s_dio_done_wq,
321 &dio->complete_work);
323 dio_complete(dio, 0, true);
329 * The BIO completion handler simply queues the BIO up for the process-context
332 * During I/O bi_private points at the dio. After I/O, bi_private is used to
333 * implement a singly-linked list of completed BIOs, at dio->bio_list.
335 static void dio_bio_end_io(struct bio *bio)
337 struct dio *dio = bio->bi_private;
340 spin_lock_irqsave(&dio->bio_lock, flags);
341 bio->bi_private = dio->bio_list;
343 if (--dio->refcount == 1 && dio->waiter)
344 wake_up_process(dio->waiter);
345 spin_unlock_irqrestore(&dio->bio_lock, flags);
349 * dio_end_io - handle the end io action for the given bio
350 * @bio: The direct io bio thats being completed
352 * This is meant to be called by any filesystem that uses their own dio_submit_t
353 * so that the DIO specific endio actions are dealt with after the filesystem
354 * has done it's completion work.
356 void dio_end_io(struct bio *bio)
358 struct dio *dio = bio->bi_private;
361 dio_bio_end_aio(bio);
365 EXPORT_SYMBOL_GPL(dio_end_io);
368 dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
369 struct block_device *bdev,
370 sector_t first_sector, int nr_vecs)
375 * bio_alloc() is guaranteed to return a bio when called with
376 * __GFP_RECLAIM and we request a valid number of vectors.
378 bio = bio_alloc(GFP_KERNEL, nr_vecs);
381 bio->bi_iter.bi_sector = first_sector;
382 bio_set_op_attrs(bio, dio->op, dio->op_flags);
384 bio->bi_end_io = dio_bio_end_aio;
386 bio->bi_end_io = dio_bio_end_io;
389 sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
393 * In the AIO read case we speculatively dirty the pages before starting IO.
394 * During IO completion, any of these pages which happen to have been written
395 * back will be redirtied by bio_check_pages_dirty().
397 * bios hold a dio reference between submit_bio and ->end_io.
399 static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
401 struct bio *bio = sdio->bio;
404 bio->bi_private = dio;
406 spin_lock_irqsave(&dio->bio_lock, flags);
408 spin_unlock_irqrestore(&dio->bio_lock, flags);
410 if (dio->is_async && dio->op == REQ_OP_READ && dio->should_dirty)
411 bio_set_pages_dirty(bio);
413 dio->bio_bdev = bio->bi_bdev;
415 if (sdio->submit_io) {
416 sdio->submit_io(bio, dio->inode, sdio->logical_offset_in_bio);
417 dio->bio_cookie = BLK_QC_T_NONE;
419 dio->bio_cookie = submit_bio(bio);
423 sdio->logical_offset_in_bio = 0;
427 * Release any resources in case of a failure
429 static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio)
431 while (sdio->head < sdio->tail)
432 put_page(dio->pages[sdio->head++]);
436 * Wait for the next BIO to complete. Remove it and return it. NULL is
437 * returned once all BIOs have been completed. This must only be called once
438 * all bios have been issued so that dio->refcount can only decrease. This
439 * requires that that the caller hold a reference on the dio.
441 static struct bio *dio_await_one(struct dio *dio)
444 struct bio *bio = NULL;
446 spin_lock_irqsave(&dio->bio_lock, flags);
449 * Wait as long as the list is empty and there are bios in flight. bio
450 * completion drops the count, maybe adds to the list, and wakes while
451 * holding the bio_lock so we don't need set_current_state()'s barrier
452 * and can call it after testing our condition.
454 while (dio->refcount > 1 && dio->bio_list == NULL) {
455 __set_current_state(TASK_UNINTERRUPTIBLE);
456 dio->waiter = current;
457 spin_unlock_irqrestore(&dio->bio_lock, flags);
458 if (!(dio->iocb->ki_flags & IOCB_HIPRI) ||
459 !blk_mq_poll(bdev_get_queue(dio->bio_bdev), dio->bio_cookie))
461 /* wake up sets us TASK_RUNNING */
462 spin_lock_irqsave(&dio->bio_lock, flags);
467 dio->bio_list = bio->bi_private;
469 spin_unlock_irqrestore(&dio->bio_lock, flags);
474 * Process one completed BIO. No locks are held.
476 static blk_status_t dio_bio_complete(struct dio *dio, struct bio *bio)
478 struct bio_vec *bvec;
480 blk_status_t err = bio->bi_status;
483 dio->io_error = -EIO;
485 if (dio->is_async && dio->op == REQ_OP_READ && dio->should_dirty) {
486 bio_check_pages_dirty(bio); /* transfers ownership */
488 bio_for_each_segment_all(bvec, bio, i) {
489 struct page *page = bvec->bv_page;
491 if (dio->op == REQ_OP_READ && !PageCompound(page) &&
493 set_page_dirty_lock(page);
502 * Wait on and process all in-flight BIOs. This must only be called once
503 * all bios have been issued so that the refcount can only decrease.
504 * This just waits for all bios to make it through dio_bio_complete. IO
505 * errors are propagated through dio->io_error and should be propagated via
508 static void dio_await_completion(struct dio *dio)
512 bio = dio_await_one(dio);
514 dio_bio_complete(dio, bio);
519 * A really large O_DIRECT read or write can generate a lot of BIOs. So
520 * to keep the memory consumption sane we periodically reap any completed BIOs
521 * during the BIO generation phase.
523 * This also helps to limit the peak amount of pinned userspace memory.
525 static inline int dio_bio_reap(struct dio *dio, struct dio_submit *sdio)
529 if (sdio->reap_counter++ >= 64) {
530 while (dio->bio_list) {
535 spin_lock_irqsave(&dio->bio_lock, flags);
537 dio->bio_list = bio->bi_private;
538 spin_unlock_irqrestore(&dio->bio_lock, flags);
539 ret2 = blk_status_to_errno(dio_bio_complete(dio, bio));
543 sdio->reap_counter = 0;
549 * Create workqueue for deferred direct IO completions. We allocate the
550 * workqueue when it's first needed. This avoids creating workqueue for
551 * filesystems that don't need it and also allows us to create the workqueue
552 * late enough so the we can include s_id in the name of the workqueue.
554 int sb_init_dio_done_wq(struct super_block *sb)
556 struct workqueue_struct *old;
557 struct workqueue_struct *wq = alloc_workqueue("dio/%s",
563 * This has to be atomic as more DIOs can race to create the workqueue
565 old = cmpxchg(&sb->s_dio_done_wq, NULL, wq);
566 /* Someone created workqueue before us? Free ours... */
568 destroy_workqueue(wq);
572 static int dio_set_defer_completion(struct dio *dio)
574 struct super_block *sb = dio->inode->i_sb;
576 if (dio->defer_completion)
578 dio->defer_completion = true;
579 if (!sb->s_dio_done_wq)
580 return sb_init_dio_done_wq(sb);
585 * Call into the fs to map some more disk blocks. We record the current number
586 * of available blocks at sdio->blocks_available. These are in units of the
587 * fs blocksize, i_blocksize(inode).
589 * The fs is allowed to map lots of blocks at once. If it wants to do that,
590 * it uses the passed inode-relative block number as the file offset, as usual.
592 * get_block() is passed the number of i_blkbits-sized blocks which direct_io
593 * has remaining to do. The fs should not map more than this number of blocks.
595 * If the fs has mapped a lot of blocks, it should populate bh->b_size to
596 * indicate how much contiguous disk space has been made available at
599 * If *any* of the mapped blocks are new, then the fs must set buffer_new().
600 * This isn't very efficient...
602 * In the case of filesystem holes: the fs may return an arbitrarily-large
603 * hole by returning an appropriate value in b_size and by clearing
604 * buffer_mapped(). However the direct-io code will only process holes one
605 * block at a time - it will repeatedly call get_block() as it walks the hole.
607 static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
608 struct buffer_head *map_bh)
611 sector_t fs_startblk; /* Into file, in filesystem-sized blocks */
612 sector_t fs_endblk; /* Into file, in filesystem-sized blocks */
613 unsigned long fs_count; /* Number of filesystem-sized blocks */
615 unsigned int i_blkbits = sdio->blkbits + sdio->blkfactor;
618 * If there was a memory error and we've overwritten all the
619 * mapped blocks then we can now return that memory error
621 ret = dio->page_errors;
623 BUG_ON(sdio->block_in_file >= sdio->final_block_in_request);
624 fs_startblk = sdio->block_in_file >> sdio->blkfactor;
625 fs_endblk = (sdio->final_block_in_request - 1) >>
627 fs_count = fs_endblk - fs_startblk + 1;
630 map_bh->b_size = fs_count << i_blkbits;
633 * For writes that could fill holes inside i_size on a
634 * DIO_SKIP_HOLES filesystem we forbid block creations: only
635 * overwrites are permitted. We will return early to the caller
636 * once we see an unmapped buffer head returned, and the caller
637 * will fall back to buffered I/O.
639 * Otherwise the decision is left to the get_blocks method,
640 * which may decide to handle it or also return an unmapped
643 create = dio->op == REQ_OP_WRITE;
644 if (dio->flags & DIO_SKIP_HOLES) {
645 if (fs_startblk <= ((i_size_read(dio->inode) - 1) >>
650 ret = (*sdio->get_block)(dio->inode, fs_startblk,
653 /* Store for completion */
654 dio->private = map_bh->b_private;
656 if (ret == 0 && buffer_defer_completion(map_bh))
657 ret = dio_set_defer_completion(dio);
663 * There is no bio. Make one now.
665 static inline int dio_new_bio(struct dio *dio, struct dio_submit *sdio,
666 sector_t start_sector, struct buffer_head *map_bh)
671 ret = dio_bio_reap(dio, sdio);
674 sector = start_sector << (sdio->blkbits - 9);
675 nr_pages = min(sdio->pages_in_io, BIO_MAX_PAGES);
676 BUG_ON(nr_pages <= 0);
677 dio_bio_alloc(dio, sdio, map_bh->b_bdev, sector, nr_pages);
684 * Attempt to put the current chunk of 'cur_page' into the current BIO. If
685 * that was successful then update final_block_in_bio and take a ref against
686 * the just-added page.
688 * Return zero on success. Non-zero means the caller needs to start a new BIO.
690 static inline int dio_bio_add_page(struct dio_submit *sdio)
694 ret = bio_add_page(sdio->bio, sdio->cur_page,
695 sdio->cur_page_len, sdio->cur_page_offset);
696 if (ret == sdio->cur_page_len) {
698 * Decrement count only, if we are done with this page
700 if ((sdio->cur_page_len + sdio->cur_page_offset) == PAGE_SIZE)
702 get_page(sdio->cur_page);
703 sdio->final_block_in_bio = sdio->cur_page_block +
704 (sdio->cur_page_len >> sdio->blkbits);
713 * Put cur_page under IO. The section of cur_page which is described by
714 * cur_page_offset,cur_page_len is put into a BIO. The section of cur_page
715 * starts on-disk at cur_page_block.
717 * We take a ref against the page here (on behalf of its presence in the bio).
719 * The caller of this function is responsible for removing cur_page from the
720 * dio, and for dropping the refcount which came from that presence.
722 static inline int dio_send_cur_page(struct dio *dio, struct dio_submit *sdio,
723 struct buffer_head *map_bh)
728 loff_t cur_offset = sdio->cur_page_fs_offset;
729 loff_t bio_next_offset = sdio->logical_offset_in_bio +
730 sdio->bio->bi_iter.bi_size;
733 * See whether this new request is contiguous with the old.
735 * Btrfs cannot handle having logically non-contiguous requests
736 * submitted. For example if you have
738 * Logical: [0-4095][HOLE][8192-12287]
739 * Physical: [0-4095] [4096-8191]
741 * We cannot submit those pages together as one BIO. So if our
742 * current logical offset in the file does not equal what would
743 * be the next logical offset in the bio, submit the bio we
746 if (sdio->final_block_in_bio != sdio->cur_page_block ||
747 cur_offset != bio_next_offset)
748 dio_bio_submit(dio, sdio);
751 if (sdio->bio == NULL) {
752 ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
757 if (dio_bio_add_page(sdio) != 0) {
758 dio_bio_submit(dio, sdio);
759 ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
761 ret = dio_bio_add_page(sdio);
770 * An autonomous function to put a chunk of a page under deferred IO.
772 * The caller doesn't actually know (or care) whether this piece of page is in
773 * a BIO, or is under IO or whatever. We just take care of all possible
774 * situations here. The separation between the logic of do_direct_IO() and
775 * that of submit_page_section() is important for clarity. Please don't break.
777 * The chunk of page starts on-disk at blocknr.
779 * We perform deferred IO, by recording the last-submitted page inside our
780 * private part of the dio structure. If possible, we just expand the IO
781 * across that page here.
783 * If that doesn't work out then we put the old page into the bio and add this
784 * page to the dio instead.
787 submit_page_section(struct dio *dio, struct dio_submit *sdio, struct page *page,
788 unsigned offset, unsigned len, sector_t blocknr,
789 struct buffer_head *map_bh)
793 if (dio->op == REQ_OP_WRITE) {
795 * Read accounting is performed in submit_bio()
797 task_io_account_write(len);
801 * Can we just grow the current page's presence in the dio?
803 if (sdio->cur_page == page &&
804 sdio->cur_page_offset + sdio->cur_page_len == offset &&
805 sdio->cur_page_block +
806 (sdio->cur_page_len >> sdio->blkbits) == blocknr) {
807 sdio->cur_page_len += len;
812 * If there's a deferred page already there then send it.
814 if (sdio->cur_page) {
815 ret = dio_send_cur_page(dio, sdio, map_bh);
816 put_page(sdio->cur_page);
817 sdio->cur_page = NULL;
822 get_page(page); /* It is in dio */
823 sdio->cur_page = page;
824 sdio->cur_page_offset = offset;
825 sdio->cur_page_len = len;
826 sdio->cur_page_block = blocknr;
827 sdio->cur_page_fs_offset = sdio->block_in_file << sdio->blkbits;
830 * If sdio->boundary then we want to schedule the IO now to
831 * avoid metadata seeks.
833 if (sdio->boundary) {
834 ret = dio_send_cur_page(dio, sdio, map_bh);
835 dio_bio_submit(dio, sdio);
836 put_page(sdio->cur_page);
837 sdio->cur_page = NULL;
843 * If we are not writing the entire block and get_block() allocated
844 * the block for us, we need to fill-in the unused portion of the
845 * block with zeros. This happens only if user-buffer, fileoffset or
846 * io length is not filesystem block-size multiple.
848 * `end' is zero if we're doing the start of the IO, 1 at the end of the
851 static inline void dio_zero_block(struct dio *dio, struct dio_submit *sdio,
852 int end, struct buffer_head *map_bh)
854 unsigned dio_blocks_per_fs_block;
855 unsigned this_chunk_blocks; /* In dio_blocks */
856 unsigned this_chunk_bytes;
859 sdio->start_zero_done = 1;
860 if (!sdio->blkfactor || !buffer_new(map_bh))
863 dio_blocks_per_fs_block = 1 << sdio->blkfactor;
864 this_chunk_blocks = sdio->block_in_file & (dio_blocks_per_fs_block - 1);
866 if (!this_chunk_blocks)
870 * We need to zero out part of an fs block. It is either at the
871 * beginning or the end of the fs block.
874 this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
876 this_chunk_bytes = this_chunk_blocks << sdio->blkbits;
879 if (submit_page_section(dio, sdio, page, 0, this_chunk_bytes,
880 sdio->next_block_for_io, map_bh))
883 sdio->next_block_for_io += this_chunk_blocks;
887 * Walk the user pages, and the file, mapping blocks to disk and generating
888 * a sequence of (page,offset,len,block) mappings. These mappings are injected
889 * into submit_page_section(), which takes care of the next stage of submission
891 * Direct IO against a blockdev is different from a file. Because we can
892 * happily perform page-sized but 512-byte aligned IOs. It is important that
893 * blockdev IO be able to have fine alignment and large sizes.
895 * So what we do is to permit the ->get_block function to populate bh.b_size
896 * with the size of IO which is permitted at this offset and this i_blkbits.
898 * For best results, the blockdev should be set up with 512-byte i_blkbits and
899 * it should set b_size to PAGE_SIZE or more inside get_block(). This gives
900 * fine alignment but still allows this function to work in PAGE_SIZE units.
902 static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
903 struct buffer_head *map_bh)
905 const unsigned blkbits = sdio->blkbits;
906 const unsigned i_blkbits = blkbits + sdio->blkfactor;
909 while (sdio->block_in_file < sdio->final_block_in_request) {
913 page = dio_get_page(dio, sdio);
918 from = sdio->head ? 0 : sdio->from;
919 to = (sdio->head == sdio->tail - 1) ? sdio->to : PAGE_SIZE;
923 unsigned this_chunk_bytes; /* # of bytes mapped */
924 unsigned this_chunk_blocks; /* # of blocks */
927 if (sdio->blocks_available == 0) {
929 * Need to go and map some more disk
931 unsigned long blkmask;
932 unsigned long dio_remainder;
934 ret = get_more_blocks(dio, sdio, map_bh);
939 if (!buffer_mapped(map_bh))
942 sdio->blocks_available =
943 map_bh->b_size >> blkbits;
944 sdio->next_block_for_io =
945 map_bh->b_blocknr << sdio->blkfactor;
946 if (buffer_new(map_bh)) {
950 map_bh->b_size >> i_blkbits);
953 if (!sdio->blkfactor)
956 blkmask = (1 << sdio->blkfactor) - 1;
957 dio_remainder = (sdio->block_in_file & blkmask);
960 * If we are at the start of IO and that IO
961 * starts partway into a fs-block,
962 * dio_remainder will be non-zero. If the IO
963 * is a read then we can simply advance the IO
964 * cursor to the first block which is to be
965 * read. But if the IO is a write and the
966 * block was newly allocated we cannot do that;
967 * the start of the fs block must be zeroed out
970 if (!buffer_new(map_bh))
971 sdio->next_block_for_io += dio_remainder;
972 sdio->blocks_available -= dio_remainder;
976 if (!buffer_mapped(map_bh)) {
977 loff_t i_size_aligned;
979 /* AKPM: eargh, -ENOTBLK is a hack */
980 if (dio->op == REQ_OP_WRITE) {
986 * Be sure to account for a partial block as the
987 * last block in the file
989 i_size_aligned = ALIGN(i_size_read(dio->inode),
991 if (sdio->block_in_file >=
992 i_size_aligned >> blkbits) {
997 zero_user(page, from, 1 << blkbits);
998 sdio->block_in_file++;
999 from += 1 << blkbits;
1000 dio->result += 1 << blkbits;
1005 * If we're performing IO which has an alignment which
1006 * is finer than the underlying fs, go check to see if
1007 * we must zero out the start of this block.
1009 if (unlikely(sdio->blkfactor && !sdio->start_zero_done))
1010 dio_zero_block(dio, sdio, 0, map_bh);
1013 * Work out, in this_chunk_blocks, how much disk we
1014 * can add to this page
1016 this_chunk_blocks = sdio->blocks_available;
1017 u = (to - from) >> blkbits;
1018 if (this_chunk_blocks > u)
1019 this_chunk_blocks = u;
1020 u = sdio->final_block_in_request - sdio->block_in_file;
1021 if (this_chunk_blocks > u)
1022 this_chunk_blocks = u;
1023 this_chunk_bytes = this_chunk_blocks << blkbits;
1024 BUG_ON(this_chunk_bytes == 0);
1026 if (this_chunk_blocks == sdio->blocks_available)
1027 sdio->boundary = buffer_boundary(map_bh);
1028 ret = submit_page_section(dio, sdio, page,
1031 sdio->next_block_for_io,
1037 sdio->next_block_for_io += this_chunk_blocks;
1039 sdio->block_in_file += this_chunk_blocks;
1040 from += this_chunk_bytes;
1041 dio->result += this_chunk_bytes;
1042 sdio->blocks_available -= this_chunk_blocks;
1044 BUG_ON(sdio->block_in_file > sdio->final_block_in_request);
1045 if (sdio->block_in_file == sdio->final_block_in_request)
1049 /* Drop the ref which was taken in get_user_pages() */
1056 static inline int drop_refcount(struct dio *dio)
1059 unsigned long flags;
1062 * Sync will always be dropping the final ref and completing the
1063 * operation. AIO can if it was a broken operation described above or
1064 * in fact if all the bios race to complete before we get here. In
1065 * that case dio_complete() translates the EIOCBQUEUED into the proper
1066 * return code that the caller will hand to ->complete().
1068 * This is managed by the bio_lock instead of being an atomic_t so that
1069 * completion paths can drop their ref and use the remaining count to
1070 * decide to wake the submission path atomically.
1072 spin_lock_irqsave(&dio->bio_lock, flags);
1073 ret2 = --dio->refcount;
1074 spin_unlock_irqrestore(&dio->bio_lock, flags);
1079 * This is a library function for use by filesystem drivers.
1081 * The locking rules are governed by the flags parameter:
1082 * - if the flags value contains DIO_LOCKING we use a fancy locking
1083 * scheme for dumb filesystems.
1084 * For writes this function is called under i_mutex and returns with
1085 * i_mutex held, for reads, i_mutex is not held on entry, but it is
1086 * taken and dropped again before returning.
1087 * - if the flags value does NOT contain DIO_LOCKING we don't use any
1088 * internal locking but rather rely on the filesystem to synchronize
1089 * direct I/O reads/writes versus each other and truncate.
1091 * To help with locking against truncate we incremented the i_dio_count
1092 * counter before starting direct I/O, and decrement it once we are done.
1093 * Truncate can wait for it to reach zero to provide exclusion. It is
1094 * expected that filesystem provide exclusion between new direct I/O
1095 * and truncates. For DIO_LOCKING filesystems this is done by i_mutex,
1096 * but other filesystems need to take care of this on their own.
1098 * NOTE: if you pass "sdio" to anything by pointer make sure that function
1099 * is always inlined. Otherwise gcc is unable to split the structure into
1100 * individual fields and will generate much worse code. This is important
1101 * for the whole file.
1103 static inline ssize_t
1104 do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
1105 struct block_device *bdev, struct iov_iter *iter,
1106 get_block_t get_block, dio_iodone_t end_io,
1107 dio_submit_t submit_io, int flags)
1109 unsigned i_blkbits = ACCESS_ONCE(inode->i_blkbits);
1110 unsigned blkbits = i_blkbits;
1111 unsigned blocksize_mask = (1 << blkbits) - 1;
1112 ssize_t retval = -EINVAL;
1113 size_t count = iov_iter_count(iter);
1114 loff_t offset = iocb->ki_pos;
1115 loff_t end = offset + count;
1117 struct dio_submit sdio = { 0, };
1118 struct buffer_head map_bh = { 0, };
1119 struct blk_plug plug;
1120 unsigned long align = offset | iov_iter_alignment(iter);
1123 * Avoid references to bdev if not absolutely needed to give
1124 * the early prefetch in the caller enough time.
1127 if (align & blocksize_mask) {
1129 blkbits = blksize_bits(bdev_logical_block_size(bdev));
1130 blocksize_mask = (1 << blkbits) - 1;
1131 if (align & blocksize_mask)
1135 /* watch out for a 0 len io from a tricksy fs */
1136 if (iov_iter_rw(iter) == READ && !iov_iter_count(iter))
1139 dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
1144 * Believe it or not, zeroing out the page array caused a .5%
1145 * performance regression in a database benchmark. So, we take
1146 * care to only zero out what's needed.
1148 memset(dio, 0, offsetof(struct dio, pages));
1151 if (dio->flags & DIO_LOCKING) {
1152 if (iov_iter_rw(iter) == READ) {
1153 struct address_space *mapping =
1154 iocb->ki_filp->f_mapping;
1156 /* will be released by direct_io_worker */
1159 retval = filemap_write_and_wait_range(mapping, offset,
1162 inode_unlock(inode);
1163 kmem_cache_free(dio_cache, dio);
1169 /* Once we sampled i_size check for reads beyond EOF */
1170 dio->i_size = i_size_read(inode);
1171 if (iov_iter_rw(iter) == READ && offset >= dio->i_size) {
1172 if (dio->flags & DIO_LOCKING)
1173 inode_unlock(inode);
1174 kmem_cache_free(dio_cache, dio);
1180 * For file extending writes updating i_size before data writeouts
1181 * complete can expose uninitialized blocks in dumb filesystems.
1182 * In that case we need to wait for I/O completion even if asked
1183 * for an asynchronous write.
1185 if (is_sync_kiocb(iocb))
1186 dio->is_async = false;
1187 else if (!(dio->flags & DIO_ASYNC_EXTEND) &&
1188 iov_iter_rw(iter) == WRITE && end > i_size_read(inode))
1189 dio->is_async = false;
1191 dio->is_async = true;
1194 if (iov_iter_rw(iter) == WRITE) {
1195 dio->op = REQ_OP_WRITE;
1196 dio->op_flags = REQ_SYNC | REQ_IDLE;
1198 dio->op = REQ_OP_READ;
1202 * For AIO O_(D)SYNC writes we need to defer completions to a workqueue
1203 * so that we can call ->fsync.
1205 if (dio->is_async && iov_iter_rw(iter) == WRITE &&
1206 ((iocb->ki_filp->f_flags & O_DSYNC) ||
1207 IS_SYNC(iocb->ki_filp->f_mapping->host))) {
1208 retval = dio_set_defer_completion(dio);
1211 * We grab i_mutex only for reads so we don't have
1212 * to release it here
1214 kmem_cache_free(dio_cache, dio);
1220 * Will be decremented at I/O completion time.
1222 if (!(dio->flags & DIO_SKIP_DIO_COUNT))
1223 inode_dio_begin(inode);
1226 sdio.blkbits = blkbits;
1227 sdio.blkfactor = i_blkbits - blkbits;
1228 sdio.block_in_file = offset >> blkbits;
1230 sdio.get_block = get_block;
1231 dio->end_io = end_io;
1232 sdio.submit_io = submit_io;
1233 sdio.final_block_in_bio = -1;
1234 sdio.next_block_for_io = -1;
1238 spin_lock_init(&dio->bio_lock);
1241 dio->should_dirty = (iter->type == ITER_IOVEC);
1243 sdio.final_block_in_request =
1244 (offset + iov_iter_count(iter)) >> blkbits;
1247 * In case of non-aligned buffers, we may need 2 more
1248 * pages since we need to zero out first and last block.
1250 if (unlikely(sdio.blkfactor))
1251 sdio.pages_in_io = 2;
1253 sdio.pages_in_io += iov_iter_npages(iter, INT_MAX);
1255 blk_start_plug(&plug);
1257 retval = do_direct_IO(dio, &sdio, &map_bh);
1259 dio_cleanup(dio, &sdio);
1261 if (retval == -ENOTBLK) {
1263 * The remaining part of the request will be
1264 * be handled by buffered I/O when we return
1269 * There may be some unwritten disk at the end of a part-written
1270 * fs-block-sized block. Go zero that now.
1272 dio_zero_block(dio, &sdio, 1, &map_bh);
1274 if (sdio.cur_page) {
1277 ret2 = dio_send_cur_page(dio, &sdio, &map_bh);
1280 put_page(sdio.cur_page);
1281 sdio.cur_page = NULL;
1284 dio_bio_submit(dio, &sdio);
1286 blk_finish_plug(&plug);
1289 * It is possible that, we return short IO due to end of file.
1290 * In that case, we need to release all the pages we got hold on.
1292 dio_cleanup(dio, &sdio);
1295 * All block lookups have been performed. For READ requests
1296 * we can let i_mutex go now that its achieved its purpose
1297 * of protecting us from looking up uninitialized blocks.
1299 if (iov_iter_rw(iter) == READ && (dio->flags & DIO_LOCKING))
1300 inode_unlock(dio->inode);
1303 * The only time we want to leave bios in flight is when a successful
1304 * partial aio read or full aio write have been setup. In that case
1305 * bio completion will call aio_complete. The only time it's safe to
1306 * call aio_complete is when we return -EIOCBQUEUED, so we key on that.
1307 * This had *better* be the only place that raises -EIOCBQUEUED.
1309 BUG_ON(retval == -EIOCBQUEUED);
1310 if (dio->is_async && retval == 0 && dio->result &&
1311 (iov_iter_rw(iter) == READ || dio->result == count))
1312 retval = -EIOCBQUEUED;
1314 dio_await_completion(dio);
1316 if (drop_refcount(dio) == 0) {
1317 retval = dio_complete(dio, retval, false);
1319 BUG_ON(retval != -EIOCBQUEUED);
1325 ssize_t __blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
1326 struct block_device *bdev, struct iov_iter *iter,
1327 get_block_t get_block,
1328 dio_iodone_t end_io, dio_submit_t submit_io,
1332 * The block device state is needed in the end to finally
1333 * submit everything. Since it's likely to be cache cold
1334 * prefetch it here as first thing to hide some of the
1337 * Attempt to prefetch the pieces we likely need later.
1339 prefetch(&bdev->bd_disk->part_tbl);
1340 prefetch(bdev->bd_queue);
1341 prefetch((char *)bdev->bd_queue + SMP_CACHE_BYTES);
1343 return do_blockdev_direct_IO(iocb, inode, bdev, iter, get_block,
1344 end_io, submit_io, flags);
1347 EXPORT_SYMBOL(__blockdev_direct_IO);
1349 static __init int dio_init(void)
1351 dio_cache = KMEM_CACHE(dio, SLAB_PANIC);
1354 module_init(dio_init)