Root/fs/direct-io.c

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

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