1 // SPDX-License-Identifier: GPL-2.0-only
5 * Copyright (C) 2002, Linus Torvalds.
9 * 04Jul2002 Andrew Morton
11 * 11Sep2002 janetinc@us.ibm.com
12 * added readv/writev support.
13 * 29Oct2002 Andrew Morton
14 * rewrote bio_add_page() support.
15 * 30Oct2002 pbadari@us.ibm.com
16 * added support for non-aligned IO.
17 * 06Nov2002 pbadari@us.ibm.com
18 * added asynchronous IO support.
19 * 21Jul2003 nathans@sgi.com
20 * added IO completion notifier.
23 #include <linux/kernel.h>
24 #include <linux/module.h>
25 #include <linux/types.h>
28 #include <linux/slab.h>
29 #include <linux/highmem.h>
30 #include <linux/pagemap.h>
31 #include <linux/task_io_accounting_ops.h>
32 #include <linux/bio.h>
33 #include <linux/wait.h>
34 #include <linux/err.h>
35 #include <linux/blkdev.h>
36 #include <linux/buffer_head.h>
37 #include <linux/rwsem.h>
38 #include <linux/uio.h>
39 #include <linux/atomic.h>
40 #include <linux/prefetch.h>
45 * How many user pages to map in one call to get_user_pages(). This determines
46 * the size of a structure in the slab cache
51 * Flags for dio_complete()
53 #define DIO_COMPLETE_ASYNC 0x01 /* This is async IO */
54 #define DIO_COMPLETE_INVALIDATE 0x02 /* Can invalidate pages */
57 * This code generally works in units of "dio_blocks". A dio_block is
58 * somewhere between the hard sector size and the filesystem block size. it
59 * is determined on a per-invocation basis. When talking to the filesystem
60 * we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity
61 * down by dio->blkfactor. Similarly, fs-blocksize quantities are converted
62 * to bio_block quantities by shifting left by blkfactor.
64 * If blkfactor is zero then the user's request was aligned to the filesystem's
68 /* dio_state only used in the submission path */
71 struct bio *bio; /* bio under assembly */
72 unsigned blkbits; /* doesn't change */
73 unsigned blkfactor; /* When we're using an alignment which
74 is finer than the filesystem's soft
75 blocksize, this specifies how much
76 finer. blkfactor=2 means 1/4-block
77 alignment. Does not change */
78 unsigned start_zero_done; /* flag: sub-blocksize zeroing has
79 been performed at the start of a
81 int pages_in_io; /* approximate total IO pages */
82 sector_t block_in_file; /* Current offset into the underlying
83 file in dio_block units. */
84 unsigned blocks_available; /* At block_in_file. changes */
85 int reap_counter; /* rate limit reaping */
86 sector_t final_block_in_request;/* doesn't change */
87 int boundary; /* prev block is at a boundary */
88 get_block_t *get_block; /* block mapping function */
90 loff_t logical_offset_in_bio; /* current first logical block in bio */
91 sector_t final_block_in_bio; /* current final block in bio + 1 */
92 sector_t next_block_for_io; /* next block to be put under IO,
93 in dio_blocks units */
96 * Deferred addition of a page to the dio. These variables are
97 * private to dio_send_cur_page(), submit_page_section() and
100 struct page *cur_page; /* The page */
101 unsigned cur_page_offset; /* Offset into it, in bytes */
102 unsigned cur_page_len; /* Nr of bytes at cur_page_offset */
103 sector_t cur_page_block; /* Where it starts */
104 loff_t cur_page_fs_offset; /* Offset in file */
106 struct iov_iter *iter;
108 * Page queue. These variables belong to dio_refill_pages() and
111 unsigned head; /* next page to process */
112 unsigned tail; /* last valid page + 1 */
116 /* dio_state communicated between submission path and end_io */
118 int flags; /* doesn't change */
119 blk_opf_t opf; /* request operation type and flags */
120 struct gendisk *bio_disk;
122 loff_t i_size; /* i_size when submitted */
123 dio_iodone_t *end_io; /* IO completion function */
125 void *private; /* copy from map_bh.b_private */
127 /* BIO completion state */
128 spinlock_t bio_lock; /* protects BIO fields below */
129 int page_errors; /* errno from get_user_pages() */
130 int is_async; /* is IO async ? */
131 bool defer_completion; /* defer AIO completion to workqueue? */
132 bool should_dirty; /* if pages should be dirtied */
133 int io_error; /* IO error in completion path */
134 unsigned long refcount; /* direct_io_worker() and bios */
135 struct bio *bio_list; /* singly linked via bi_private */
136 struct task_struct *waiter; /* waiting task (NULL if none) */
138 /* AIO related stuff */
139 struct kiocb *iocb; /* kiocb */
140 ssize_t result; /* IO result */
143 * pages[] (and any fields placed after it) are not zeroed out at
144 * allocation time. Don't add new fields after pages[] unless you
145 * wish that they not be zeroed.
148 struct page *pages[DIO_PAGES]; /* page buffer */
149 struct work_struct complete_work;/* deferred AIO completion */
151 } ____cacheline_aligned_in_smp;
153 static struct kmem_cache *dio_cache __read_mostly;
156 * How many pages are in the queue?
158 static inline unsigned dio_pages_present(struct dio_submit *sdio)
160 return sdio->tail - sdio->head;
164 * Go grab and pin some userspace pages. Typically we'll get 64 at a time.
166 static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
168 const enum req_op dio_op = dio->opf & REQ_OP_MASK;
171 ret = iov_iter_get_pages2(sdio->iter, dio->pages, LONG_MAX, DIO_PAGES,
174 if (ret < 0 && sdio->blocks_available && dio_op == REQ_OP_WRITE) {
175 struct page *page = ZERO_PAGE(0);
177 * A memory fault, but the filesystem has some outstanding
178 * mapped blocks. We need to use those blocks up to avoid
179 * leaking stale data in the file.
181 if (dio->page_errors == 0)
182 dio->page_errors = ret;
184 dio->pages[0] = page;
188 sdio->to = PAGE_SIZE;
195 sdio->tail = (ret + PAGE_SIZE - 1) / PAGE_SIZE;
196 sdio->to = ((ret - 1) & (PAGE_SIZE - 1)) + 1;
203 * Get another userspace page. Returns an ERR_PTR on error. Pages are
204 * buffered inside the dio so that we can call get_user_pages() against a
205 * decent number of pages, less frequently. To provide nicer use of the
208 static inline struct page *dio_get_page(struct dio *dio,
209 struct dio_submit *sdio)
211 if (dio_pages_present(sdio) == 0) {
214 ret = dio_refill_pages(dio, sdio);
217 BUG_ON(dio_pages_present(sdio) == 0);
219 return dio->pages[sdio->head];
223 * dio_complete() - called when all DIO BIO I/O has been completed
225 * This drops i_dio_count, lets interested parties know that a DIO operation
226 * has completed, and calculates the resulting return code for the operation.
228 * It lets the filesystem know if it registered an interest earlier via
229 * get_block. Pass the private field of the map buffer_head so that
230 * filesystems can use it to hold additional state between get_block calls and
233 static ssize_t dio_complete(struct dio *dio, ssize_t ret, unsigned int flags)
235 const enum req_op dio_op = dio->opf & REQ_OP_MASK;
236 loff_t offset = dio->iocb->ki_pos;
237 ssize_t transferred = 0;
241 * AIO submission can race with bio completion to get here while
242 * expecting to have the last io completed by bio completion.
243 * In that case -EIOCBQUEUED is in fact not an error we want
244 * to preserve through this call.
246 if (ret == -EIOCBQUEUED)
250 transferred = dio->result;
252 /* Check for short read case */
253 if (dio_op == REQ_OP_READ &&
254 ((offset + transferred) > dio->i_size))
255 transferred = dio->i_size - offset;
256 /* ignore EFAULT if some IO has been done */
257 if (unlikely(ret == -EFAULT) && transferred)
262 ret = dio->page_errors;
270 err = dio->end_io(dio->iocb, offset, ret, dio->private);
276 * Try again to invalidate clean pages which might have been cached by
277 * non-direct readahead, or faulted in by get_user_pages() if the source
278 * of the write was an mmap'ed region of the file we're writing. Either
279 * one is a pretty crazy thing to do, so we don't support it 100%. If
280 * this invalidation fails, tough, the write still worked...
282 * And this page cache invalidation has to be after dio->end_io(), as
283 * some filesystems convert unwritten extents to real allocations in
284 * end_io() when necessary, otherwise a racing buffer read would cache
285 * zeros from unwritten extents.
287 if (flags & DIO_COMPLETE_INVALIDATE &&
288 ret > 0 && dio_op == REQ_OP_WRITE &&
289 dio->inode->i_mapping->nrpages) {
290 err = invalidate_inode_pages2_range(dio->inode->i_mapping,
291 offset >> PAGE_SHIFT,
292 (offset + ret - 1) >> PAGE_SHIFT);
294 dio_warn_stale_pagecache(dio->iocb->ki_filp);
297 inode_dio_end(dio->inode);
299 if (flags & DIO_COMPLETE_ASYNC) {
301 * generic_write_sync expects ki_pos to have been updated
302 * already, but the submission path only does this for
305 dio->iocb->ki_pos += transferred;
307 if (ret > 0 && dio_op == REQ_OP_WRITE)
308 ret = generic_write_sync(dio->iocb, ret);
309 dio->iocb->ki_complete(dio->iocb, ret);
312 kmem_cache_free(dio_cache, dio);
316 static void dio_aio_complete_work(struct work_struct *work)
318 struct dio *dio = container_of(work, struct dio, complete_work);
320 dio_complete(dio, 0, DIO_COMPLETE_ASYNC | DIO_COMPLETE_INVALIDATE);
323 static blk_status_t dio_bio_complete(struct dio *dio, struct bio *bio);
326 * Asynchronous IO callback.
328 static void dio_bio_end_aio(struct bio *bio)
330 struct dio *dio = bio->bi_private;
331 const enum req_op dio_op = dio->opf & REQ_OP_MASK;
332 unsigned long remaining;
334 bool defer_completion = false;
336 /* cleanup the bio */
337 dio_bio_complete(dio, bio);
339 spin_lock_irqsave(&dio->bio_lock, flags);
340 remaining = --dio->refcount;
341 if (remaining == 1 && dio->waiter)
342 wake_up_process(dio->waiter);
343 spin_unlock_irqrestore(&dio->bio_lock, flags);
345 if (remaining == 0) {
347 * Defer completion when defer_completion is set or
348 * when the inode has pages mapped and this is AIO write.
349 * We need to invalidate those pages because there is a
350 * chance they contain stale data in the case buffered IO
351 * went in between AIO submission and completion into the
355 defer_completion = dio->defer_completion ||
356 (dio_op == REQ_OP_WRITE &&
357 dio->inode->i_mapping->nrpages);
358 if (defer_completion) {
359 INIT_WORK(&dio->complete_work, dio_aio_complete_work);
360 queue_work(dio->inode->i_sb->s_dio_done_wq,
361 &dio->complete_work);
363 dio_complete(dio, 0, DIO_COMPLETE_ASYNC);
369 * The BIO completion handler simply queues the BIO up for the process-context
372 * During I/O bi_private points at the dio. After I/O, bi_private is used to
373 * implement a singly-linked list of completed BIOs, at dio->bio_list.
375 static void dio_bio_end_io(struct bio *bio)
377 struct dio *dio = bio->bi_private;
380 spin_lock_irqsave(&dio->bio_lock, flags);
381 bio->bi_private = dio->bio_list;
383 if (--dio->refcount == 1 && dio->waiter)
384 wake_up_process(dio->waiter);
385 spin_unlock_irqrestore(&dio->bio_lock, flags);
389 dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
390 struct block_device *bdev,
391 sector_t first_sector, int nr_vecs)
396 * bio_alloc() is guaranteed to return a bio when allowed to sleep and
397 * we request a valid number of vectors.
399 bio = bio_alloc(bdev, nr_vecs, dio->opf, GFP_KERNEL);
400 bio->bi_iter.bi_sector = first_sector;
402 bio->bi_end_io = dio_bio_end_aio;
404 bio->bi_end_io = dio_bio_end_io;
405 /* for now require references for all pages */
406 bio_set_flag(bio, BIO_PAGE_REFFED);
408 sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
412 * In the AIO read case we speculatively dirty the pages before starting IO.
413 * During IO completion, any of these pages which happen to have been written
414 * back will be redirtied by bio_check_pages_dirty().
416 * bios hold a dio reference between submit_bio and ->end_io.
418 static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
420 const enum req_op dio_op = dio->opf & REQ_OP_MASK;
421 struct bio *bio = sdio->bio;
424 bio->bi_private = dio;
426 spin_lock_irqsave(&dio->bio_lock, flags);
428 spin_unlock_irqrestore(&dio->bio_lock, flags);
430 if (dio->is_async && dio_op == REQ_OP_READ && dio->should_dirty)
431 bio_set_pages_dirty(bio);
433 dio->bio_disk = bio->bi_bdev->bd_disk;
439 sdio->logical_offset_in_bio = 0;
443 * Release any resources in case of a failure
445 static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio)
447 while (sdio->head < sdio->tail)
448 put_page(dio->pages[sdio->head++]);
452 * Wait for the next BIO to complete. Remove it and return it. NULL is
453 * returned once all BIOs have been completed. This must only be called once
454 * all bios have been issued so that dio->refcount can only decrease. This
455 * requires that the caller hold a reference on the dio.
457 static struct bio *dio_await_one(struct dio *dio)
460 struct bio *bio = NULL;
462 spin_lock_irqsave(&dio->bio_lock, flags);
465 * Wait as long as the list is empty and there are bios in flight. bio
466 * completion drops the count, maybe adds to the list, and wakes while
467 * holding the bio_lock so we don't need set_current_state()'s barrier
468 * and can call it after testing our condition.
470 while (dio->refcount > 1 && dio->bio_list == NULL) {
471 __set_current_state(TASK_UNINTERRUPTIBLE);
472 dio->waiter = current;
473 spin_unlock_irqrestore(&dio->bio_lock, flags);
475 /* wake up sets us TASK_RUNNING */
476 spin_lock_irqsave(&dio->bio_lock, flags);
481 dio->bio_list = bio->bi_private;
483 spin_unlock_irqrestore(&dio->bio_lock, flags);
488 * Process one completed BIO. No locks are held.
490 static blk_status_t dio_bio_complete(struct dio *dio, struct bio *bio)
492 blk_status_t err = bio->bi_status;
493 const enum req_op dio_op = dio->opf & REQ_OP_MASK;
494 bool should_dirty = dio_op == REQ_OP_READ && dio->should_dirty;
497 if (err == BLK_STS_AGAIN && (bio->bi_opf & REQ_NOWAIT))
498 dio->io_error = -EAGAIN;
500 dio->io_error = -EIO;
503 if (dio->is_async && should_dirty) {
504 bio_check_pages_dirty(bio); /* transfers ownership */
506 bio_release_pages(bio, should_dirty);
513 * Wait on and process all in-flight BIOs. This must only be called once
514 * all bios have been issued so that the refcount can only decrease.
515 * This just waits for all bios to make it through dio_bio_complete. IO
516 * errors are propagated through dio->io_error and should be propagated via
519 static void dio_await_completion(struct dio *dio)
523 bio = dio_await_one(dio);
525 dio_bio_complete(dio, bio);
530 * A really large O_DIRECT read or write can generate a lot of BIOs. So
531 * to keep the memory consumption sane we periodically reap any completed BIOs
532 * during the BIO generation phase.
534 * This also helps to limit the peak amount of pinned userspace memory.
536 static inline int dio_bio_reap(struct dio *dio, struct dio_submit *sdio)
540 if (sdio->reap_counter++ >= 64) {
541 while (dio->bio_list) {
546 spin_lock_irqsave(&dio->bio_lock, flags);
548 dio->bio_list = bio->bi_private;
549 spin_unlock_irqrestore(&dio->bio_lock, flags);
550 ret2 = blk_status_to_errno(dio_bio_complete(dio, bio));
554 sdio->reap_counter = 0;
559 static int dio_set_defer_completion(struct dio *dio)
561 struct super_block *sb = dio->inode->i_sb;
563 if (dio->defer_completion)
565 dio->defer_completion = true;
566 if (!sb->s_dio_done_wq)
567 return sb_init_dio_done_wq(sb);
572 * Call into the fs to map some more disk blocks. We record the current number
573 * of available blocks at sdio->blocks_available. These are in units of the
574 * fs blocksize, i_blocksize(inode).
576 * The fs is allowed to map lots of blocks at once. If it wants to do that,
577 * it uses the passed inode-relative block number as the file offset, as usual.
579 * get_block() is passed the number of i_blkbits-sized blocks which direct_io
580 * has remaining to do. The fs should not map more than this number of blocks.
582 * If the fs has mapped a lot of blocks, it should populate bh->b_size to
583 * indicate how much contiguous disk space has been made available at
586 * If *any* of the mapped blocks are new, then the fs must set buffer_new().
587 * This isn't very efficient...
589 * In the case of filesystem holes: the fs may return an arbitrarily-large
590 * hole by returning an appropriate value in b_size and by clearing
591 * buffer_mapped(). However the direct-io code will only process holes one
592 * block at a time - it will repeatedly call get_block() as it walks the hole.
594 static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
595 struct buffer_head *map_bh)
597 const enum req_op dio_op = dio->opf & REQ_OP_MASK;
599 sector_t fs_startblk; /* Into file, in filesystem-sized blocks */
600 sector_t fs_endblk; /* Into file, in filesystem-sized blocks */
601 unsigned long fs_count; /* Number of filesystem-sized blocks */
603 unsigned int i_blkbits = sdio->blkbits + sdio->blkfactor;
607 * If there was a memory error and we've overwritten all the
608 * mapped blocks then we can now return that memory error
610 ret = dio->page_errors;
612 BUG_ON(sdio->block_in_file >= sdio->final_block_in_request);
613 fs_startblk = sdio->block_in_file >> sdio->blkfactor;
614 fs_endblk = (sdio->final_block_in_request - 1) >>
616 fs_count = fs_endblk - fs_startblk + 1;
619 map_bh->b_size = fs_count << i_blkbits;
622 * For writes that could fill holes inside i_size on a
623 * DIO_SKIP_HOLES filesystem we forbid block creations: only
624 * overwrites are permitted. We will return early to the caller
625 * once we see an unmapped buffer head returned, and the caller
626 * will fall back to buffered I/O.
628 * Otherwise the decision is left to the get_blocks method,
629 * which may decide to handle it or also return an unmapped
632 create = dio_op == REQ_OP_WRITE;
633 if (dio->flags & DIO_SKIP_HOLES) {
634 i_size = i_size_read(dio->inode);
635 if (i_size && fs_startblk <= (i_size - 1) >> i_blkbits)
639 ret = (*sdio->get_block)(dio->inode, fs_startblk,
642 /* Store for completion */
643 dio->private = map_bh->b_private;
645 if (ret == 0 && buffer_defer_completion(map_bh))
646 ret = dio_set_defer_completion(dio);
652 * There is no bio. Make one now.
654 static inline int dio_new_bio(struct dio *dio, struct dio_submit *sdio,
655 sector_t start_sector, struct buffer_head *map_bh)
660 ret = dio_bio_reap(dio, sdio);
663 sector = start_sector << (sdio->blkbits - 9);
664 nr_pages = bio_max_segs(sdio->pages_in_io);
665 BUG_ON(nr_pages <= 0);
666 dio_bio_alloc(dio, sdio, map_bh->b_bdev, sector, nr_pages);
673 * Attempt to put the current chunk of 'cur_page' into the current BIO. If
674 * that was successful then update final_block_in_bio and take a ref against
675 * the just-added page.
677 * Return zero on success. Non-zero means the caller needs to start a new BIO.
679 static inline int dio_bio_add_page(struct dio_submit *sdio)
683 ret = bio_add_page(sdio->bio, sdio->cur_page,
684 sdio->cur_page_len, sdio->cur_page_offset);
685 if (ret == sdio->cur_page_len) {
687 * Decrement count only, if we are done with this page
689 if ((sdio->cur_page_len + sdio->cur_page_offset) == PAGE_SIZE)
691 get_page(sdio->cur_page);
692 sdio->final_block_in_bio = sdio->cur_page_block +
693 (sdio->cur_page_len >> sdio->blkbits);
702 * Put cur_page under IO. The section of cur_page which is described by
703 * cur_page_offset,cur_page_len is put into a BIO. The section of cur_page
704 * starts on-disk at cur_page_block.
706 * We take a ref against the page here (on behalf of its presence in the bio).
708 * The caller of this function is responsible for removing cur_page from the
709 * dio, and for dropping the refcount which came from that presence.
711 static inline int dio_send_cur_page(struct dio *dio, struct dio_submit *sdio,
712 struct buffer_head *map_bh)
717 loff_t cur_offset = sdio->cur_page_fs_offset;
718 loff_t bio_next_offset = sdio->logical_offset_in_bio +
719 sdio->bio->bi_iter.bi_size;
722 * See whether this new request is contiguous with the old.
724 * Btrfs cannot handle having logically non-contiguous requests
725 * submitted. For example if you have
727 * Logical: [0-4095][HOLE][8192-12287]
728 * Physical: [0-4095] [4096-8191]
730 * We cannot submit those pages together as one BIO. So if our
731 * current logical offset in the file does not equal what would
732 * be the next logical offset in the bio, submit the bio we
735 if (sdio->final_block_in_bio != sdio->cur_page_block ||
736 cur_offset != bio_next_offset)
737 dio_bio_submit(dio, sdio);
740 if (sdio->bio == NULL) {
741 ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
746 if (dio_bio_add_page(sdio) != 0) {
747 dio_bio_submit(dio, sdio);
748 ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
750 ret = dio_bio_add_page(sdio);
759 * An autonomous function to put a chunk of a page under deferred IO.
761 * The caller doesn't actually know (or care) whether this piece of page is in
762 * a BIO, or is under IO or whatever. We just take care of all possible
763 * situations here. The separation between the logic of do_direct_IO() and
764 * that of submit_page_section() is important for clarity. Please don't break.
766 * The chunk of page starts on-disk at blocknr.
768 * We perform deferred IO, by recording the last-submitted page inside our
769 * private part of the dio structure. If possible, we just expand the IO
770 * across that page here.
772 * If that doesn't work out then we put the old page into the bio and add this
773 * page to the dio instead.
776 submit_page_section(struct dio *dio, struct dio_submit *sdio, struct page *page,
777 unsigned offset, unsigned len, sector_t blocknr,
778 struct buffer_head *map_bh)
780 const enum req_op dio_op = dio->opf & REQ_OP_MASK;
782 int boundary = sdio->boundary; /* dio_send_cur_page may clear it */
784 if (dio_op == REQ_OP_WRITE) {
786 * Read accounting is performed in submit_bio()
788 task_io_account_write(len);
792 * Can we just grow the current page's presence in the dio?
794 if (sdio->cur_page == page &&
795 sdio->cur_page_offset + sdio->cur_page_len == offset &&
796 sdio->cur_page_block +
797 (sdio->cur_page_len >> sdio->blkbits) == blocknr) {
798 sdio->cur_page_len += len;
803 * If there's a deferred page already there then send it.
805 if (sdio->cur_page) {
806 ret = dio_send_cur_page(dio, sdio, map_bh);
807 put_page(sdio->cur_page);
808 sdio->cur_page = NULL;
813 get_page(page); /* It is in dio */
814 sdio->cur_page = page;
815 sdio->cur_page_offset = offset;
816 sdio->cur_page_len = len;
817 sdio->cur_page_block = blocknr;
818 sdio->cur_page_fs_offset = sdio->block_in_file << sdio->blkbits;
821 * If boundary then we want to schedule the IO now to
822 * avoid metadata seeks.
825 ret = dio_send_cur_page(dio, sdio, map_bh);
827 dio_bio_submit(dio, sdio);
828 put_page(sdio->cur_page);
829 sdio->cur_page = NULL;
835 * If we are not writing the entire block and get_block() allocated
836 * the block for us, we need to fill-in the unused portion of the
837 * block with zeros. This happens only if user-buffer, fileoffset or
838 * io length is not filesystem block-size multiple.
840 * `end' is zero if we're doing the start of the IO, 1 at the end of the
843 static inline void dio_zero_block(struct dio *dio, struct dio_submit *sdio,
844 int end, struct buffer_head *map_bh)
846 unsigned dio_blocks_per_fs_block;
847 unsigned this_chunk_blocks; /* In dio_blocks */
848 unsigned this_chunk_bytes;
851 sdio->start_zero_done = 1;
852 if (!sdio->blkfactor || !buffer_new(map_bh))
855 dio_blocks_per_fs_block = 1 << sdio->blkfactor;
856 this_chunk_blocks = sdio->block_in_file & (dio_blocks_per_fs_block - 1);
858 if (!this_chunk_blocks)
862 * We need to zero out part of an fs block. It is either at the
863 * beginning or the end of the fs block.
866 this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
868 this_chunk_bytes = this_chunk_blocks << sdio->blkbits;
871 if (submit_page_section(dio, sdio, page, 0, this_chunk_bytes,
872 sdio->next_block_for_io, map_bh))
875 sdio->next_block_for_io += this_chunk_blocks;
879 * Walk the user pages, and the file, mapping blocks to disk and generating
880 * a sequence of (page,offset,len,block) mappings. These mappings are injected
881 * into submit_page_section(), which takes care of the next stage of submission
883 * Direct IO against a blockdev is different from a file. Because we can
884 * happily perform page-sized but 512-byte aligned IOs. It is important that
885 * blockdev IO be able to have fine alignment and large sizes.
887 * So what we do is to permit the ->get_block function to populate bh.b_size
888 * with the size of IO which is permitted at this offset and this i_blkbits.
890 * For best results, the blockdev should be set up with 512-byte i_blkbits and
891 * it should set b_size to PAGE_SIZE or more inside get_block(). This gives
892 * fine alignment but still allows this function to work in PAGE_SIZE units.
894 static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
895 struct buffer_head *map_bh)
897 const enum req_op dio_op = dio->opf & REQ_OP_MASK;
898 const unsigned blkbits = sdio->blkbits;
899 const unsigned i_blkbits = blkbits + sdio->blkfactor;
902 while (sdio->block_in_file < sdio->final_block_in_request) {
906 page = dio_get_page(dio, sdio);
911 from = sdio->head ? 0 : sdio->from;
912 to = (sdio->head == sdio->tail - 1) ? sdio->to : PAGE_SIZE;
916 unsigned this_chunk_bytes; /* # of bytes mapped */
917 unsigned this_chunk_blocks; /* # of blocks */
920 if (sdio->blocks_available == 0) {
922 * Need to go and map some more disk
924 unsigned long blkmask;
925 unsigned long dio_remainder;
927 ret = get_more_blocks(dio, sdio, map_bh);
932 if (!buffer_mapped(map_bh))
935 sdio->blocks_available =
936 map_bh->b_size >> blkbits;
937 sdio->next_block_for_io =
938 map_bh->b_blocknr << sdio->blkfactor;
939 if (buffer_new(map_bh)) {
943 map_bh->b_size >> i_blkbits);
946 if (!sdio->blkfactor)
949 blkmask = (1 << sdio->blkfactor) - 1;
950 dio_remainder = (sdio->block_in_file & blkmask);
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
963 if (!buffer_new(map_bh))
964 sdio->next_block_for_io += dio_remainder;
965 sdio->blocks_available -= dio_remainder;
969 if (!buffer_mapped(map_bh)) {
970 loff_t i_size_aligned;
972 /* AKPM: eargh, -ENOTBLK is a hack */
973 if (dio_op == REQ_OP_WRITE) {
979 * Be sure to account for a partial block as the
980 * last block in the file
982 i_size_aligned = ALIGN(i_size_read(dio->inode),
984 if (sdio->block_in_file >=
985 i_size_aligned >> blkbits) {
990 zero_user(page, from, 1 << blkbits);
991 sdio->block_in_file++;
992 from += 1 << blkbits;
993 dio->result += 1 << blkbits;
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.
1002 if (unlikely(sdio->blkfactor && !sdio->start_zero_done))
1003 dio_zero_block(dio, sdio, 0, map_bh);
1006 * Work out, in this_chunk_blocks, how much disk we
1007 * can add to this page
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);
1019 if (this_chunk_blocks == sdio->blocks_available)
1020 sdio->boundary = buffer_boundary(map_bh);
1021 ret = submit_page_section(dio, sdio, page,
1024 sdio->next_block_for_io,
1030 sdio->next_block_for_io += this_chunk_blocks;
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;
1037 BUG_ON(sdio->block_in_file > sdio->final_block_in_request);
1038 if (sdio->block_in_file == sdio->final_block_in_request)
1042 /* Drop the ref which was taken in get_user_pages() */
1049 static inline int drop_refcount(struct dio *dio)
1052 unsigned long flags;
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 ->complete().
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.
1065 spin_lock_irqsave(&dio->bio_lock, flags);
1066 ret2 = --dio->refcount;
1067 spin_unlock_irqrestore(&dio->bio_lock, flags);
1072 * This is a library function for use by filesystem drivers.
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.
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.
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.
1096 ssize_t __blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
1097 struct block_device *bdev, struct iov_iter *iter,
1098 get_block_t get_block, dio_iodone_t end_io,
1101 unsigned i_blkbits = READ_ONCE(inode->i_blkbits);
1102 unsigned blkbits = i_blkbits;
1103 unsigned blocksize_mask = (1 << blkbits) - 1;
1104 ssize_t retval = -EINVAL;
1105 const size_t count = iov_iter_count(iter);
1106 loff_t offset = iocb->ki_pos;
1107 const loff_t end = offset + count;
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);
1115 * Avoid references to bdev if not absolutely needed to give
1116 * the early prefetch in the caller enough time.
1119 /* watch out for a 0 len io from a tricksy fs */
1120 if (iov_iter_rw(iter) == READ && !count)
1123 dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
1127 * Believe it or not, zeroing out the page array caused a .5%
1128 * performance regression in a database benchmark. So, we take
1129 * care to only zero out what's needed.
1131 memset(dio, 0, offsetof(struct dio, pages));
1134 if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ) {
1135 /* will be released by direct_io_worker */
1139 /* Once we sampled i_size check for reads beyond EOF */
1140 dio->i_size = i_size_read(inode);
1141 if (iov_iter_rw(iter) == READ && offset >= dio->i_size) {
1146 if (align & blocksize_mask) {
1148 blkbits = blksize_bits(bdev_logical_block_size(bdev));
1149 blocksize_mask = (1 << blkbits) - 1;
1150 if (align & blocksize_mask)
1154 if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ) {
1155 struct address_space *mapping = iocb->ki_filp->f_mapping;
1157 retval = filemap_write_and_wait_range(mapping, offset, end - 1);
1163 * For file extending writes updating i_size before data writeouts
1164 * complete can expose uninitialized blocks in dumb filesystems.
1165 * In that case we need to wait for I/O completion even if asked
1166 * for an asynchronous write.
1168 if (is_sync_kiocb(iocb))
1169 dio->is_async = false;
1170 else if (iov_iter_rw(iter) == WRITE && end > i_size_read(inode))
1171 dio->is_async = false;
1173 dio->is_async = true;
1176 if (iov_iter_rw(iter) == WRITE) {
1177 dio->opf = REQ_OP_WRITE | REQ_SYNC | REQ_IDLE;
1178 if (iocb->ki_flags & IOCB_NOWAIT)
1179 dio->opf |= REQ_NOWAIT;
1181 dio->opf = REQ_OP_READ;
1185 * For AIO O_(D)SYNC writes we need to defer completions to a workqueue
1186 * so that we can call ->fsync.
1188 if (dio->is_async && iov_iter_rw(iter) == WRITE) {
1190 if (iocb_is_dsync(iocb))
1191 retval = dio_set_defer_completion(dio);
1192 else if (!dio->inode->i_sb->s_dio_done_wq) {
1194 * In case of AIO write racing with buffered read we
1195 * need to defer completion. We can't decide this now,
1196 * however the workqueue needs to be initialized here.
1198 retval = sb_init_dio_done_wq(dio->inode->i_sb);
1205 * Will be decremented at I/O completion time.
1207 inode_dio_begin(inode);
1210 sdio.blkbits = blkbits;
1211 sdio.blkfactor = i_blkbits - blkbits;
1212 sdio.block_in_file = offset >> blkbits;
1214 sdio.get_block = get_block;
1215 dio->end_io = end_io;
1216 sdio.final_block_in_bio = -1;
1217 sdio.next_block_for_io = -1;
1221 spin_lock_init(&dio->bio_lock);
1224 dio->should_dirty = user_backed_iter(iter) && iov_iter_rw(iter) == READ;
1226 sdio.final_block_in_request = end >> blkbits;
1229 * In case of non-aligned buffers, we may need 2 more
1230 * pages since we need to zero out first and last block.
1232 if (unlikely(sdio.blkfactor))
1233 sdio.pages_in_io = 2;
1235 sdio.pages_in_io += iov_iter_npages(iter, INT_MAX);
1237 blk_start_plug(&plug);
1239 retval = do_direct_IO(dio, &sdio, &map_bh);
1241 dio_cleanup(dio, &sdio);
1243 if (retval == -ENOTBLK) {
1245 * The remaining part of the request will be
1246 * handled by buffered I/O when we return
1251 * There may be some unwritten disk at the end of a part-written
1252 * fs-block-sized block. Go zero that now.
1254 dio_zero_block(dio, &sdio, 1, &map_bh);
1256 if (sdio.cur_page) {
1259 ret2 = dio_send_cur_page(dio, &sdio, &map_bh);
1262 put_page(sdio.cur_page);
1263 sdio.cur_page = NULL;
1266 dio_bio_submit(dio, &sdio);
1268 blk_finish_plug(&plug);
1271 * It is possible that, we return short IO due to end of file.
1272 * In that case, we need to release all the pages we got hold on.
1274 dio_cleanup(dio, &sdio);
1277 * All block lookups have been performed. For READ requests
1278 * we can let i_mutex go now that its achieved its purpose
1279 * of protecting us from looking up uninitialized blocks.
1281 if (iov_iter_rw(iter) == READ && (dio->flags & DIO_LOCKING))
1282 inode_unlock(dio->inode);
1285 * The only time we want to leave bios in flight is when a successful
1286 * partial aio read or full aio write have been setup. In that case
1287 * bio completion will call aio_complete. The only time it's safe to
1288 * call aio_complete is when we return -EIOCBQUEUED, so we key on that.
1289 * This had *better* be the only place that raises -EIOCBQUEUED.
1291 BUG_ON(retval == -EIOCBQUEUED);
1292 if (dio->is_async && retval == 0 && dio->result &&
1293 (iov_iter_rw(iter) == READ || dio->result == count))
1294 retval = -EIOCBQUEUED;
1296 dio_await_completion(dio);
1298 if (drop_refcount(dio) == 0) {
1299 retval = dio_complete(dio, retval, DIO_COMPLETE_INVALIDATE);
1301 BUG_ON(retval != -EIOCBQUEUED);
1306 if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ)
1307 inode_unlock(inode);
1309 kmem_cache_free(dio_cache, dio);
1312 EXPORT_SYMBOL(__blockdev_direct_IO);
1314 static __init int dio_init(void)
1316 dio_cache = KMEM_CACHE(dio, SLAB_PANIC);
1319 module_init(dio_init)