[XFS] move v_iocount from bhv_vnode to xfs_inode
[wrt350n-kernel.git] / fs / direct-io.c
blob901dc55e9f54f444d3368c39af72fcab082726e5
1 /*
2 * fs/direct-io.c
4 * Copyright (C) 2002, Linus Torvalds.
6 * O_DIRECT
8 * 04Jul2002 akpm@zip.com.au
9 * Initial version
10 * 11Sep2002 janetinc@us.ibm.com
11 * added readv/writev support.
12 * 29Oct2002 akpm@zip.com.au
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 <asm/atomic.h>
41 * How many user pages to map in one call to get_user_pages(). This determines
42 * the size of a structure on the stack.
44 #define DIO_PAGES 64
47 * This code generally works in units of "dio_blocks". A dio_block is
48 * somewhere between the hard sector size and the filesystem block size. it
49 * is determined on a per-invocation basis. When talking to the filesystem
50 * we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity
51 * down by dio->blkfactor. Similarly, fs-blocksize quantities are converted
52 * to bio_block quantities by shifting left by blkfactor.
54 * If blkfactor is zero then the user's request was aligned to the filesystem's
55 * blocksize.
57 * lock_type is DIO_LOCKING for regular files on direct-IO-naive filesystems.
58 * This determines whether we need to do the fancy locking which prevents
59 * direct-IO from being able to read uninitialised disk blocks. If its zero
60 * (blockdev) this locking is not done, and if it is DIO_OWN_LOCKING i_mutex is
61 * not held for the entire direct write (taken briefly, initially, during a
62 * direct read though, but its never held for the duration of a direct-IO).
65 struct dio {
66 /* BIO submission state */
67 struct bio *bio; /* bio under assembly */
68 struct inode *inode;
69 int rw;
70 loff_t i_size; /* i_size when submitted */
71 int lock_type; /* doesn't change */
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
80 write */
81 int pages_in_io; /* approximate total IO pages */
82 size_t size; /* total request size (doesn't change)*/
83 sector_t block_in_file; /* Current offset into the underlying
84 file in dio_block units. */
85 unsigned blocks_available; /* At block_in_file. changes */
86 sector_t final_block_in_request;/* doesn't change */
87 unsigned first_block_in_page; /* doesn't change, Used only once */
88 int boundary; /* prev block is at a boundary */
89 int reap_counter; /* rate limit reaping */
90 get_block_t *get_block; /* block mapping function */
91 dio_iodone_t *end_io; /* IO completion function */
92 sector_t final_block_in_bio; /* current final block in bio + 1 */
93 sector_t next_block_for_io; /* next block to be put under IO,
94 in dio_blocks units */
95 struct buffer_head map_bh; /* last get_block() result */
98 * Deferred addition of a page to the dio. These variables are
99 * private to dio_send_cur_page(), submit_page_section() and
100 * dio_bio_add_page().
102 struct page *cur_page; /* The page */
103 unsigned cur_page_offset; /* Offset into it, in bytes */
104 unsigned cur_page_len; /* Nr of bytes at cur_page_offset */
105 sector_t cur_page_block; /* Where it starts */
108 * Page fetching state. These variables belong to dio_refill_pages().
110 int curr_page; /* changes */
111 int total_pages; /* doesn't change */
112 unsigned long curr_user_address;/* changes */
115 * Page queue. These variables belong to dio_refill_pages() and
116 * dio_get_page().
118 struct page *pages[DIO_PAGES]; /* page buffer */
119 unsigned head; /* next page to process */
120 unsigned tail; /* last valid page + 1 */
121 int page_errors; /* errno from get_user_pages() */
123 /* BIO completion state */
124 spinlock_t bio_lock; /* protects BIO fields below */
125 unsigned long refcount; /* direct_io_worker() and bios */
126 struct bio *bio_list; /* singly linked via bi_private */
127 struct task_struct *waiter; /* waiting task (NULL if none) */
129 /* AIO related stuff */
130 struct kiocb *iocb; /* kiocb */
131 int is_async; /* is IO async ? */
132 int io_error; /* IO error in completion path */
133 ssize_t result; /* IO result */
137 * How many pages are in the queue?
139 static inline unsigned dio_pages_present(struct dio *dio)
141 return dio->tail - dio->head;
145 * Go grab and pin some userspace pages. Typically we'll get 64 at a time.
147 static int dio_refill_pages(struct dio *dio)
149 int ret;
150 int nr_pages;
152 nr_pages = min(dio->total_pages - dio->curr_page, DIO_PAGES);
153 down_read(&current->mm->mmap_sem);
154 ret = get_user_pages(
155 current, /* Task for fault acounting */
156 current->mm, /* whose pages? */
157 dio->curr_user_address, /* Where from? */
158 nr_pages, /* How many pages? */
159 dio->rw == READ, /* Write to memory? */
160 0, /* force (?) */
161 &dio->pages[0],
162 NULL); /* vmas */
163 up_read(&current->mm->mmap_sem);
165 if (ret < 0 && dio->blocks_available && (dio->rw & WRITE)) {
166 struct page *page = ZERO_PAGE(dio->curr_user_address);
168 * A memory fault, but the filesystem has some outstanding
169 * mapped blocks. We need to use those blocks up to avoid
170 * leaking stale data in the file.
172 if (dio->page_errors == 0)
173 dio->page_errors = ret;
174 page_cache_get(page);
175 dio->pages[0] = page;
176 dio->head = 0;
177 dio->tail = 1;
178 ret = 0;
179 goto out;
182 if (ret >= 0) {
183 dio->curr_user_address += ret * PAGE_SIZE;
184 dio->curr_page += ret;
185 dio->head = 0;
186 dio->tail = ret;
187 ret = 0;
189 out:
190 return ret;
194 * Get another userspace page. Returns an ERR_PTR on error. Pages are
195 * buffered inside the dio so that we can call get_user_pages() against a
196 * decent number of pages, less frequently. To provide nicer use of the
197 * L1 cache.
199 static struct page *dio_get_page(struct dio *dio)
201 if (dio_pages_present(dio) == 0) {
202 int ret;
204 ret = dio_refill_pages(dio);
205 if (ret)
206 return ERR_PTR(ret);
207 BUG_ON(dio_pages_present(dio) == 0);
209 return dio->pages[dio->head++];
213 * dio_complete() - called when all DIO BIO I/O has been completed
214 * @offset: the byte offset in the file of the completed operation
216 * This releases locks as dictated by the locking type, lets interested parties
217 * know that a DIO operation has completed, and calculates the resulting return
218 * code for the operation.
220 * It lets the filesystem know if it registered an interest earlier via
221 * get_block. Pass the private field of the map buffer_head so that
222 * filesystems can use it to hold additional state between get_block calls and
223 * dio_complete.
225 static int dio_complete(struct dio *dio, loff_t offset, int ret)
227 ssize_t transferred = 0;
230 * AIO submission can race with bio completion to get here while
231 * expecting to have the last io completed by bio completion.
232 * In that case -EIOCBQUEUED is in fact not an error we want
233 * to preserve through this call.
235 if (ret == -EIOCBQUEUED)
236 ret = 0;
238 if (dio->result) {
239 transferred = dio->result;
241 /* Check for short read case */
242 if ((dio->rw == READ) && ((offset + transferred) > dio->i_size))
243 transferred = dio->i_size - offset;
246 if (dio->end_io && dio->result)
247 dio->end_io(dio->iocb, offset, transferred,
248 dio->map_bh.b_private);
249 if (dio->lock_type == DIO_LOCKING)
250 /* lockdep: non-owner release */
251 up_read_non_owner(&dio->inode->i_alloc_sem);
253 if (ret == 0)
254 ret = dio->page_errors;
255 if (ret == 0)
256 ret = dio->io_error;
257 if (ret == 0)
258 ret = transferred;
260 return ret;
263 static int dio_bio_complete(struct dio *dio, struct bio *bio);
265 * Asynchronous IO callback.
267 static int dio_bio_end_aio(struct bio *bio, unsigned int bytes_done, int error)
269 struct dio *dio = bio->bi_private;
270 unsigned long remaining;
271 unsigned long flags;
273 if (bio->bi_size)
274 return 1;
276 /* cleanup the bio */
277 dio_bio_complete(dio, bio);
279 spin_lock_irqsave(&dio->bio_lock, flags);
280 remaining = --dio->refcount;
281 if (remaining == 1 && dio->waiter)
282 wake_up_process(dio->waiter);
283 spin_unlock_irqrestore(&dio->bio_lock, flags);
285 if (remaining == 0) {
286 int ret = dio_complete(dio, dio->iocb->ki_pos, 0);
287 aio_complete(dio->iocb, ret, 0);
288 kfree(dio);
291 return 0;
295 * The BIO completion handler simply queues the BIO up for the process-context
296 * handler.
298 * During I/O bi_private points at the dio. After I/O, bi_private is used to
299 * implement a singly-linked list of completed BIOs, at dio->bio_list.
301 static int dio_bio_end_io(struct bio *bio, unsigned int bytes_done, int error)
303 struct dio *dio = bio->bi_private;
304 unsigned long flags;
306 if (bio->bi_size)
307 return 1;
309 spin_lock_irqsave(&dio->bio_lock, flags);
310 bio->bi_private = dio->bio_list;
311 dio->bio_list = bio;
312 if (--dio->refcount == 1 && dio->waiter)
313 wake_up_process(dio->waiter);
314 spin_unlock_irqrestore(&dio->bio_lock, flags);
315 return 0;
318 static int
319 dio_bio_alloc(struct dio *dio, struct block_device *bdev,
320 sector_t first_sector, int nr_vecs)
322 struct bio *bio;
324 bio = bio_alloc(GFP_KERNEL, nr_vecs);
325 if (bio == NULL)
326 return -ENOMEM;
328 bio->bi_bdev = bdev;
329 bio->bi_sector = first_sector;
330 if (dio->is_async)
331 bio->bi_end_io = dio_bio_end_aio;
332 else
333 bio->bi_end_io = dio_bio_end_io;
335 dio->bio = bio;
336 return 0;
340 * In the AIO read case we speculatively dirty the pages before starting IO.
341 * During IO completion, any of these pages which happen to have been written
342 * back will be redirtied by bio_check_pages_dirty().
344 * bios hold a dio reference between submit_bio and ->end_io.
346 static void dio_bio_submit(struct dio *dio)
348 struct bio *bio = dio->bio;
349 unsigned long flags;
351 bio->bi_private = dio;
353 spin_lock_irqsave(&dio->bio_lock, flags);
354 dio->refcount++;
355 spin_unlock_irqrestore(&dio->bio_lock, flags);
357 if (dio->is_async && dio->rw == READ)
358 bio_set_pages_dirty(bio);
360 submit_bio(dio->rw, bio);
362 dio->bio = NULL;
363 dio->boundary = 0;
367 * Release any resources in case of a failure
369 static void dio_cleanup(struct dio *dio)
371 while (dio_pages_present(dio))
372 page_cache_release(dio_get_page(dio));
376 * Wait for the next BIO to complete. Remove it and return it. NULL is
377 * returned once all BIOs have been completed. This must only be called once
378 * all bios have been issued so that dio->refcount can only decrease. This
379 * requires that that the caller hold a reference on the dio.
381 static struct bio *dio_await_one(struct dio *dio)
383 unsigned long flags;
384 struct bio *bio = NULL;
386 spin_lock_irqsave(&dio->bio_lock, flags);
389 * Wait as long as the list is empty and there are bios in flight. bio
390 * completion drops the count, maybe adds to the list, and wakes while
391 * holding the bio_lock so we don't need set_current_state()'s barrier
392 * and can call it after testing our condition.
394 while (dio->refcount > 1 && dio->bio_list == NULL) {
395 __set_current_state(TASK_UNINTERRUPTIBLE);
396 dio->waiter = current;
397 spin_unlock_irqrestore(&dio->bio_lock, flags);
398 io_schedule();
399 /* wake up sets us TASK_RUNNING */
400 spin_lock_irqsave(&dio->bio_lock, flags);
401 dio->waiter = NULL;
403 if (dio->bio_list) {
404 bio = dio->bio_list;
405 dio->bio_list = bio->bi_private;
407 spin_unlock_irqrestore(&dio->bio_lock, flags);
408 return bio;
412 * Process one completed BIO. No locks are held.
414 static int dio_bio_complete(struct dio *dio, struct bio *bio)
416 const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
417 struct bio_vec *bvec = bio->bi_io_vec;
418 int page_no;
420 if (!uptodate)
421 dio->io_error = -EIO;
423 if (dio->is_async && dio->rw == READ) {
424 bio_check_pages_dirty(bio); /* transfers ownership */
425 } else {
426 for (page_no = 0; page_no < bio->bi_vcnt; page_no++) {
427 struct page *page = bvec[page_no].bv_page;
429 if (dio->rw == READ && !PageCompound(page))
430 set_page_dirty_lock(page);
431 page_cache_release(page);
433 bio_put(bio);
435 return uptodate ? 0 : -EIO;
439 * Wait on and process all in-flight BIOs. This must only be called once
440 * all bios have been issued so that the refcount can only decrease.
441 * This just waits for all bios to make it through dio_bio_complete. IO
442 * errors are propagated through dio->io_error and should be propagated via
443 * dio_complete().
445 static void dio_await_completion(struct dio *dio)
447 struct bio *bio;
448 do {
449 bio = dio_await_one(dio);
450 if (bio)
451 dio_bio_complete(dio, bio);
452 } while (bio);
456 * A really large O_DIRECT read or write can generate a lot of BIOs. So
457 * to keep the memory consumption sane we periodically reap any completed BIOs
458 * during the BIO generation phase.
460 * This also helps to limit the peak amount of pinned userspace memory.
462 static int dio_bio_reap(struct dio *dio)
464 int ret = 0;
466 if (dio->reap_counter++ >= 64) {
467 while (dio->bio_list) {
468 unsigned long flags;
469 struct bio *bio;
470 int ret2;
472 spin_lock_irqsave(&dio->bio_lock, flags);
473 bio = dio->bio_list;
474 dio->bio_list = bio->bi_private;
475 spin_unlock_irqrestore(&dio->bio_lock, flags);
476 ret2 = dio_bio_complete(dio, bio);
477 if (ret == 0)
478 ret = ret2;
480 dio->reap_counter = 0;
482 return ret;
486 * Call into the fs to map some more disk blocks. We record the current number
487 * of available blocks at dio->blocks_available. These are in units of the
488 * fs blocksize, (1 << inode->i_blkbits).
490 * The fs is allowed to map lots of blocks at once. If it wants to do that,
491 * it uses the passed inode-relative block number as the file offset, as usual.
493 * get_block() is passed the number of i_blkbits-sized blocks which direct_io
494 * has remaining to do. The fs should not map more than this number of blocks.
496 * If the fs has mapped a lot of blocks, it should populate bh->b_size to
497 * indicate how much contiguous disk space has been made available at
498 * bh->b_blocknr.
500 * If *any* of the mapped blocks are new, then the fs must set buffer_new().
501 * This isn't very efficient...
503 * In the case of filesystem holes: the fs may return an arbitrarily-large
504 * hole by returning an appropriate value in b_size and by clearing
505 * buffer_mapped(). However the direct-io code will only process holes one
506 * block at a time - it will repeatedly call get_block() as it walks the hole.
508 static int get_more_blocks(struct dio *dio)
510 int ret;
511 struct buffer_head *map_bh = &dio->map_bh;
512 sector_t fs_startblk; /* Into file, in filesystem-sized blocks */
513 unsigned long fs_count; /* Number of filesystem-sized blocks */
514 unsigned long dio_count;/* Number of dio_block-sized blocks */
515 unsigned long blkmask;
516 int create;
519 * If there was a memory error and we've overwritten all the
520 * mapped blocks then we can now return that memory error
522 ret = dio->page_errors;
523 if (ret == 0) {
524 BUG_ON(dio->block_in_file >= dio->final_block_in_request);
525 fs_startblk = dio->block_in_file >> dio->blkfactor;
526 dio_count = dio->final_block_in_request - dio->block_in_file;
527 fs_count = dio_count >> dio->blkfactor;
528 blkmask = (1 << dio->blkfactor) - 1;
529 if (dio_count & blkmask)
530 fs_count++;
532 map_bh->b_state = 0;
533 map_bh->b_size = fs_count << dio->inode->i_blkbits;
535 create = dio->rw & WRITE;
536 if (dio->lock_type == DIO_LOCKING) {
537 if (dio->block_in_file < (i_size_read(dio->inode) >>
538 dio->blkbits))
539 create = 0;
540 } else if (dio->lock_type == DIO_NO_LOCKING) {
541 create = 0;
545 * For writes inside i_size we forbid block creations: only
546 * overwrites are permitted. We fall back to buffered writes
547 * at a higher level for inside-i_size block-instantiating
548 * writes.
550 ret = (*dio->get_block)(dio->inode, fs_startblk,
551 map_bh, create);
553 return ret;
557 * There is no bio. Make one now.
559 static int dio_new_bio(struct dio *dio, sector_t start_sector)
561 sector_t sector;
562 int ret, nr_pages;
564 ret = dio_bio_reap(dio);
565 if (ret)
566 goto out;
567 sector = start_sector << (dio->blkbits - 9);
568 nr_pages = min(dio->pages_in_io, bio_get_nr_vecs(dio->map_bh.b_bdev));
569 BUG_ON(nr_pages <= 0);
570 ret = dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages);
571 dio->boundary = 0;
572 out:
573 return ret;
577 * Attempt to put the current chunk of 'cur_page' into the current BIO. If
578 * that was successful then update final_block_in_bio and take a ref against
579 * the just-added page.
581 * Return zero on success. Non-zero means the caller needs to start a new BIO.
583 static int dio_bio_add_page(struct dio *dio)
585 int ret;
587 ret = bio_add_page(dio->bio, dio->cur_page,
588 dio->cur_page_len, dio->cur_page_offset);
589 if (ret == dio->cur_page_len) {
591 * Decrement count only, if we are done with this page
593 if ((dio->cur_page_len + dio->cur_page_offset) == PAGE_SIZE)
594 dio->pages_in_io--;
595 page_cache_get(dio->cur_page);
596 dio->final_block_in_bio = dio->cur_page_block +
597 (dio->cur_page_len >> dio->blkbits);
598 ret = 0;
599 } else {
600 ret = 1;
602 return ret;
606 * Put cur_page under IO. The section of cur_page which is described by
607 * cur_page_offset,cur_page_len is put into a BIO. The section of cur_page
608 * starts on-disk at cur_page_block.
610 * We take a ref against the page here (on behalf of its presence in the bio).
612 * The caller of this function is responsible for removing cur_page from the
613 * dio, and for dropping the refcount which came from that presence.
615 static int dio_send_cur_page(struct dio *dio)
617 int ret = 0;
619 if (dio->bio) {
621 * See whether this new request is contiguous with the old
623 if (dio->final_block_in_bio != dio->cur_page_block)
624 dio_bio_submit(dio);
626 * Submit now if the underlying fs is about to perform a
627 * metadata read
629 if (dio->boundary)
630 dio_bio_submit(dio);
633 if (dio->bio == NULL) {
634 ret = dio_new_bio(dio, dio->cur_page_block);
635 if (ret)
636 goto out;
639 if (dio_bio_add_page(dio) != 0) {
640 dio_bio_submit(dio);
641 ret = dio_new_bio(dio, dio->cur_page_block);
642 if (ret == 0) {
643 ret = dio_bio_add_page(dio);
644 BUG_ON(ret != 0);
647 out:
648 return ret;
652 * An autonomous function to put a chunk of a page under deferred IO.
654 * The caller doesn't actually know (or care) whether this piece of page is in
655 * a BIO, or is under IO or whatever. We just take care of all possible
656 * situations here. The separation between the logic of do_direct_IO() and
657 * that of submit_page_section() is important for clarity. Please don't break.
659 * The chunk of page starts on-disk at blocknr.
661 * We perform deferred IO, by recording the last-submitted page inside our
662 * private part of the dio structure. If possible, we just expand the IO
663 * across that page here.
665 * If that doesn't work out then we put the old page into the bio and add this
666 * page to the dio instead.
668 static int
669 submit_page_section(struct dio *dio, struct page *page,
670 unsigned offset, unsigned len, sector_t blocknr)
672 int ret = 0;
674 if (dio->rw & WRITE) {
676 * Read accounting is performed in submit_bio()
678 task_io_account_write(len);
682 * Can we just grow the current page's presence in the dio?
684 if ( (dio->cur_page == page) &&
685 (dio->cur_page_offset + dio->cur_page_len == offset) &&
686 (dio->cur_page_block +
687 (dio->cur_page_len >> dio->blkbits) == blocknr)) {
688 dio->cur_page_len += len;
691 * If dio->boundary then we want to schedule the IO now to
692 * avoid metadata seeks.
694 if (dio->boundary) {
695 ret = dio_send_cur_page(dio);
696 page_cache_release(dio->cur_page);
697 dio->cur_page = NULL;
699 goto out;
703 * If there's a deferred page already there then send it.
705 if (dio->cur_page) {
706 ret = dio_send_cur_page(dio);
707 page_cache_release(dio->cur_page);
708 dio->cur_page = NULL;
709 if (ret)
710 goto out;
713 page_cache_get(page); /* It is in dio */
714 dio->cur_page = page;
715 dio->cur_page_offset = offset;
716 dio->cur_page_len = len;
717 dio->cur_page_block = blocknr;
718 out:
719 return ret;
723 * Clean any dirty buffers in the blockdev mapping which alias newly-created
724 * file blocks. Only called for S_ISREG files - blockdevs do not set
725 * buffer_new
727 static void clean_blockdev_aliases(struct dio *dio)
729 unsigned i;
730 unsigned nblocks;
732 nblocks = dio->map_bh.b_size >> dio->inode->i_blkbits;
734 for (i = 0; i < nblocks; i++) {
735 unmap_underlying_metadata(dio->map_bh.b_bdev,
736 dio->map_bh.b_blocknr + i);
741 * If we are not writing the entire block and get_block() allocated
742 * the block for us, we need to fill-in the unused portion of the
743 * block with zeros. This happens only if user-buffer, fileoffset or
744 * io length is not filesystem block-size multiple.
746 * `end' is zero if we're doing the start of the IO, 1 at the end of the
747 * IO.
749 static void dio_zero_block(struct dio *dio, int end)
751 unsigned dio_blocks_per_fs_block;
752 unsigned this_chunk_blocks; /* In dio_blocks */
753 unsigned this_chunk_bytes;
754 struct page *page;
756 dio->start_zero_done = 1;
757 if (!dio->blkfactor || !buffer_new(&dio->map_bh))
758 return;
760 dio_blocks_per_fs_block = 1 << dio->blkfactor;
761 this_chunk_blocks = dio->block_in_file & (dio_blocks_per_fs_block - 1);
763 if (!this_chunk_blocks)
764 return;
767 * We need to zero out part of an fs block. It is either at the
768 * beginning or the end of the fs block.
770 if (end)
771 this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
773 this_chunk_bytes = this_chunk_blocks << dio->blkbits;
775 page = ZERO_PAGE(dio->curr_user_address);
776 if (submit_page_section(dio, page, 0, this_chunk_bytes,
777 dio->next_block_for_io))
778 return;
780 dio->next_block_for_io += this_chunk_blocks;
784 * Walk the user pages, and the file, mapping blocks to disk and generating
785 * a sequence of (page,offset,len,block) mappings. These mappings are injected
786 * into submit_page_section(), which takes care of the next stage of submission
788 * Direct IO against a blockdev is different from a file. Because we can
789 * happily perform page-sized but 512-byte aligned IOs. It is important that
790 * blockdev IO be able to have fine alignment and large sizes.
792 * So what we do is to permit the ->get_block function to populate bh.b_size
793 * with the size of IO which is permitted at this offset and this i_blkbits.
795 * For best results, the blockdev should be set up with 512-byte i_blkbits and
796 * it should set b_size to PAGE_SIZE or more inside get_block(). This gives
797 * fine alignment but still allows this function to work in PAGE_SIZE units.
799 static int do_direct_IO(struct dio *dio)
801 const unsigned blkbits = dio->blkbits;
802 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
803 struct page *page;
804 unsigned block_in_page;
805 struct buffer_head *map_bh = &dio->map_bh;
806 int ret = 0;
808 /* The I/O can start at any block offset within the first page */
809 block_in_page = dio->first_block_in_page;
811 while (dio->block_in_file < dio->final_block_in_request) {
812 page = dio_get_page(dio);
813 if (IS_ERR(page)) {
814 ret = PTR_ERR(page);
815 goto out;
818 while (block_in_page < blocks_per_page) {
819 unsigned offset_in_page = block_in_page << blkbits;
820 unsigned this_chunk_bytes; /* # of bytes mapped */
821 unsigned this_chunk_blocks; /* # of blocks */
822 unsigned u;
824 if (dio->blocks_available == 0) {
826 * Need to go and map some more disk
828 unsigned long blkmask;
829 unsigned long dio_remainder;
831 ret = get_more_blocks(dio);
832 if (ret) {
833 page_cache_release(page);
834 goto out;
836 if (!buffer_mapped(map_bh))
837 goto do_holes;
839 dio->blocks_available =
840 map_bh->b_size >> dio->blkbits;
841 dio->next_block_for_io =
842 map_bh->b_blocknr << dio->blkfactor;
843 if (buffer_new(map_bh))
844 clean_blockdev_aliases(dio);
846 if (!dio->blkfactor)
847 goto do_holes;
849 blkmask = (1 << dio->blkfactor) - 1;
850 dio_remainder = (dio->block_in_file & blkmask);
853 * If we are at the start of IO and that IO
854 * starts partway into a fs-block,
855 * dio_remainder will be non-zero. If the IO
856 * is a read then we can simply advance the IO
857 * cursor to the first block which is to be
858 * read. But if the IO is a write and the
859 * block was newly allocated we cannot do that;
860 * the start of the fs block must be zeroed out
861 * on-disk
863 if (!buffer_new(map_bh))
864 dio->next_block_for_io += dio_remainder;
865 dio->blocks_available -= dio_remainder;
867 do_holes:
868 /* Handle holes */
869 if (!buffer_mapped(map_bh)) {
870 loff_t i_size_aligned;
872 /* AKPM: eargh, -ENOTBLK is a hack */
873 if (dio->rw & WRITE) {
874 page_cache_release(page);
875 return -ENOTBLK;
879 * Be sure to account for a partial block as the
880 * last block in the file
882 i_size_aligned = ALIGN(i_size_read(dio->inode),
883 1 << blkbits);
884 if (dio->block_in_file >=
885 i_size_aligned >> blkbits) {
886 /* We hit eof */
887 page_cache_release(page);
888 goto out;
890 zero_user_page(page, block_in_page << blkbits,
891 1 << blkbits, KM_USER0);
892 dio->block_in_file++;
893 block_in_page++;
894 goto next_block;
898 * If we're performing IO which has an alignment which
899 * is finer than the underlying fs, go check to see if
900 * we must zero out the start of this block.
902 if (unlikely(dio->blkfactor && !dio->start_zero_done))
903 dio_zero_block(dio, 0);
906 * Work out, in this_chunk_blocks, how much disk we
907 * can add to this page
909 this_chunk_blocks = dio->blocks_available;
910 u = (PAGE_SIZE - offset_in_page) >> blkbits;
911 if (this_chunk_blocks > u)
912 this_chunk_blocks = u;
913 u = dio->final_block_in_request - dio->block_in_file;
914 if (this_chunk_blocks > u)
915 this_chunk_blocks = u;
916 this_chunk_bytes = this_chunk_blocks << blkbits;
917 BUG_ON(this_chunk_bytes == 0);
919 dio->boundary = buffer_boundary(map_bh);
920 ret = submit_page_section(dio, page, offset_in_page,
921 this_chunk_bytes, dio->next_block_for_io);
922 if (ret) {
923 page_cache_release(page);
924 goto out;
926 dio->next_block_for_io += this_chunk_blocks;
928 dio->block_in_file += this_chunk_blocks;
929 block_in_page += this_chunk_blocks;
930 dio->blocks_available -= this_chunk_blocks;
931 next_block:
932 BUG_ON(dio->block_in_file > dio->final_block_in_request);
933 if (dio->block_in_file == dio->final_block_in_request)
934 break;
937 /* Drop the ref which was taken in get_user_pages() */
938 page_cache_release(page);
939 block_in_page = 0;
941 out:
942 return ret;
946 * Releases both i_mutex and i_alloc_sem
948 static ssize_t
949 direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
950 const struct iovec *iov, loff_t offset, unsigned long nr_segs,
951 unsigned blkbits, get_block_t get_block, dio_iodone_t end_io,
952 struct dio *dio)
954 unsigned long user_addr;
955 unsigned long flags;
956 int seg;
957 ssize_t ret = 0;
958 ssize_t ret2;
959 size_t bytes;
961 dio->inode = inode;
962 dio->rw = rw;
963 dio->blkbits = blkbits;
964 dio->blkfactor = inode->i_blkbits - blkbits;
965 dio->block_in_file = offset >> blkbits;
967 dio->get_block = get_block;
968 dio->end_io = end_io;
969 dio->final_block_in_bio = -1;
970 dio->next_block_for_io = -1;
972 dio->iocb = iocb;
973 dio->i_size = i_size_read(inode);
975 spin_lock_init(&dio->bio_lock);
976 dio->refcount = 1;
979 * In case of non-aligned buffers, we may need 2 more
980 * pages since we need to zero out first and last block.
982 if (unlikely(dio->blkfactor))
983 dio->pages_in_io = 2;
985 for (seg = 0; seg < nr_segs; seg++) {
986 user_addr = (unsigned long)iov[seg].iov_base;
987 dio->pages_in_io +=
988 ((user_addr+iov[seg].iov_len +PAGE_SIZE-1)/PAGE_SIZE
989 - user_addr/PAGE_SIZE);
992 for (seg = 0; seg < nr_segs; seg++) {
993 user_addr = (unsigned long)iov[seg].iov_base;
994 dio->size += bytes = iov[seg].iov_len;
996 /* Index into the first page of the first block */
997 dio->first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits;
998 dio->final_block_in_request = dio->block_in_file +
999 (bytes >> blkbits);
1000 /* Page fetching state */
1001 dio->head = 0;
1002 dio->tail = 0;
1003 dio->curr_page = 0;
1005 dio->total_pages = 0;
1006 if (user_addr & (PAGE_SIZE-1)) {
1007 dio->total_pages++;
1008 bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1));
1010 dio->total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
1011 dio->curr_user_address = user_addr;
1013 ret = do_direct_IO(dio);
1015 dio->result += iov[seg].iov_len -
1016 ((dio->final_block_in_request - dio->block_in_file) <<
1017 blkbits);
1019 if (ret) {
1020 dio_cleanup(dio);
1021 break;
1023 } /* end iovec loop */
1025 if (ret == -ENOTBLK && (rw & WRITE)) {
1027 * The remaining part of the request will be
1028 * be handled by buffered I/O when we return
1030 ret = 0;
1033 * There may be some unwritten disk at the end of a part-written
1034 * fs-block-sized block. Go zero that now.
1036 dio_zero_block(dio, 1);
1038 if (dio->cur_page) {
1039 ret2 = dio_send_cur_page(dio);
1040 if (ret == 0)
1041 ret = ret2;
1042 page_cache_release(dio->cur_page);
1043 dio->cur_page = NULL;
1045 if (dio->bio)
1046 dio_bio_submit(dio);
1048 /* All IO is now issued, send it on its way */
1049 blk_run_address_space(inode->i_mapping);
1052 * It is possible that, we return short IO due to end of file.
1053 * In that case, we need to release all the pages we got hold on.
1055 dio_cleanup(dio);
1058 * All block lookups have been performed. For READ requests
1059 * we can let i_mutex go now that its achieved its purpose
1060 * of protecting us from looking up uninitialized blocks.
1062 if ((rw == READ) && (dio->lock_type == DIO_LOCKING))
1063 mutex_unlock(&dio->inode->i_mutex);
1066 * The only time we want to leave bios in flight is when a successful
1067 * partial aio read or full aio write have been setup. In that case
1068 * bio completion will call aio_complete. The only time it's safe to
1069 * call aio_complete is when we return -EIOCBQUEUED, so we key on that.
1070 * This had *better* be the only place that raises -EIOCBQUEUED.
1072 BUG_ON(ret == -EIOCBQUEUED);
1073 if (dio->is_async && ret == 0 && dio->result &&
1074 ((rw & READ) || (dio->result == dio->size)))
1075 ret = -EIOCBQUEUED;
1077 if (ret != -EIOCBQUEUED)
1078 dio_await_completion(dio);
1081 * Sync will always be dropping the final ref and completing the
1082 * operation. AIO can if it was a broken operation described above or
1083 * in fact if all the bios race to complete before we get here. In
1084 * that case dio_complete() translates the EIOCBQUEUED into the proper
1085 * return code that the caller will hand to aio_complete().
1087 * This is managed by the bio_lock instead of being an atomic_t so that
1088 * completion paths can drop their ref and use the remaining count to
1089 * decide to wake the submission path atomically.
1091 spin_lock_irqsave(&dio->bio_lock, flags);
1092 ret2 = --dio->refcount;
1093 spin_unlock_irqrestore(&dio->bio_lock, flags);
1095 if (ret2 == 0) {
1096 ret = dio_complete(dio, offset, ret);
1097 kfree(dio);
1098 } else
1099 BUG_ON(ret != -EIOCBQUEUED);
1101 return ret;
1105 * This is a library function for use by filesystem drivers.
1106 * The locking rules are governed by the dio_lock_type parameter.
1108 * DIO_NO_LOCKING (no locking, for raw block device access)
1109 * For writes, i_mutex is not held on entry; it is never taken.
1111 * DIO_LOCKING (simple locking for regular files)
1112 * For writes we are called under i_mutex and return with i_mutex held, even
1113 * though it is internally dropped.
1114 * For reads, i_mutex is not held on entry, but it is taken and dropped before
1115 * returning.
1117 * DIO_OWN_LOCKING (filesystem provides synchronisation and handling of
1118 * uninitialised data, allowing parallel direct readers and writers)
1119 * For writes we are called without i_mutex, return without it, never touch it.
1120 * For reads we are called under i_mutex and return with i_mutex held, even
1121 * though it may be internally dropped.
1123 * Additional i_alloc_sem locking requirements described inline below.
1125 ssize_t
1126 __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
1127 struct block_device *bdev, const struct iovec *iov, loff_t offset,
1128 unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io,
1129 int dio_lock_type)
1131 int seg;
1132 size_t size;
1133 unsigned long addr;
1134 unsigned blkbits = inode->i_blkbits;
1135 unsigned bdev_blkbits = 0;
1136 unsigned blocksize_mask = (1 << blkbits) - 1;
1137 ssize_t retval = -EINVAL;
1138 loff_t end = offset;
1139 struct dio *dio;
1140 int release_i_mutex = 0;
1141 int acquire_i_mutex = 0;
1143 if (rw & WRITE)
1144 rw = WRITE_SYNC;
1146 if (bdev)
1147 bdev_blkbits = blksize_bits(bdev_hardsect_size(bdev));
1149 if (offset & blocksize_mask) {
1150 if (bdev)
1151 blkbits = bdev_blkbits;
1152 blocksize_mask = (1 << blkbits) - 1;
1153 if (offset & blocksize_mask)
1154 goto out;
1157 /* Check the memory alignment. Blocks cannot straddle pages */
1158 for (seg = 0; seg < nr_segs; seg++) {
1159 addr = (unsigned long)iov[seg].iov_base;
1160 size = iov[seg].iov_len;
1161 end += size;
1162 if ((addr & blocksize_mask) || (size & blocksize_mask)) {
1163 if (bdev)
1164 blkbits = bdev_blkbits;
1165 blocksize_mask = (1 << blkbits) - 1;
1166 if ((addr & blocksize_mask) || (size & blocksize_mask))
1167 goto out;
1171 dio = kzalloc(sizeof(*dio), GFP_KERNEL);
1172 retval = -ENOMEM;
1173 if (!dio)
1174 goto out;
1177 * For block device access DIO_NO_LOCKING is used,
1178 * neither readers nor writers do any locking at all
1179 * For regular files using DIO_LOCKING,
1180 * readers need to grab i_mutex and i_alloc_sem
1181 * writers need to grab i_alloc_sem only (i_mutex is already held)
1182 * For regular files using DIO_OWN_LOCKING,
1183 * neither readers nor writers take any locks here
1185 dio->lock_type = dio_lock_type;
1186 if (dio_lock_type != DIO_NO_LOCKING) {
1187 /* watch out for a 0 len io from a tricksy fs */
1188 if (rw == READ && end > offset) {
1189 struct address_space *mapping;
1191 mapping = iocb->ki_filp->f_mapping;
1192 if (dio_lock_type != DIO_OWN_LOCKING) {
1193 mutex_lock(&inode->i_mutex);
1194 release_i_mutex = 1;
1197 retval = filemap_write_and_wait_range(mapping, offset,
1198 end - 1);
1199 if (retval) {
1200 kfree(dio);
1201 goto out;
1204 if (dio_lock_type == DIO_OWN_LOCKING) {
1205 mutex_unlock(&inode->i_mutex);
1206 acquire_i_mutex = 1;
1210 if (dio_lock_type == DIO_LOCKING)
1211 /* lockdep: not the owner will release it */
1212 down_read_non_owner(&inode->i_alloc_sem);
1216 * For file extending writes updating i_size before data
1217 * writeouts complete can expose uninitialized blocks. So
1218 * even for AIO, we need to wait for i/o to complete before
1219 * returning in this case.
1221 dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) &&
1222 (end > i_size_read(inode)));
1224 retval = direct_io_worker(rw, iocb, inode, iov, offset,
1225 nr_segs, blkbits, get_block, end_io, dio);
1227 if (rw == READ && dio_lock_type == DIO_LOCKING)
1228 release_i_mutex = 0;
1230 out:
1231 if (release_i_mutex)
1232 mutex_unlock(&inode->i_mutex);
1233 else if (acquire_i_mutex)
1234 mutex_lock(&inode->i_mutex);
1235 return retval;
1237 EXPORT_SYMBOL(__blockdev_direct_IO);