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    dio_submit_t *submit_io; /* IO submition function */
86    loff_t logical_offset_in_bio; /* current first logical block in bio */
87    sector_t final_block_in_bio; /* current final block in bio + 1 */
88    sector_t next_block_for_io; /* next block to be put under IO,
89                       in dio_blocks units */
90    struct buffer_head map_bh; /* last get_block() result */
91
92    /*
93     * Deferred addition of a page to the dio. These variables are
94     * private to dio_send_cur_page(), submit_page_section() and
95     * dio_bio_add_page().
96     */
97    struct page *cur_page; /* The page */
98    unsigned cur_page_offset; /* Offset into it, in bytes */
99    unsigned cur_page_len; /* Nr of bytes at cur_page_offset */
100    sector_t cur_page_block; /* Where it starts */
101    loff_t cur_page_fs_offset; /* Offset in file */
102
103    /* BIO completion state */
104    spinlock_t bio_lock; /* protects BIO fields below */
105    unsigned long refcount; /* direct_io_worker() and bios */
106    struct bio *bio_list; /* singly linked via bi_private */
107    struct task_struct *waiter; /* waiting task (NULL if none) */
108
109    /* AIO related stuff */
110    struct kiocb *iocb; /* kiocb */
111    int is_async; /* is IO async ? */
112    int io_error; /* IO error in completion path */
113    ssize_t result; /* IO result */
114
115    /*
116     * Page fetching state. These variables belong to dio_refill_pages().
117     */
118    int curr_page; /* changes */
119    int total_pages; /* doesn't change */
120    unsigned long curr_user_address;/* changes */
121
122    /*
123     * Page queue. These variables belong to dio_refill_pages() and
124     * dio_get_page().
125     */
126    unsigned head; /* next page to process */
127    unsigned tail; /* last valid page + 1 */
128    int page_errors; /* errno from get_user_pages() */
129
130    /*
131     * pages[] (and any fields placed after it) are not zeroed out at
132     * allocation time. Don't add new fields after pages[] unless you
133     * wish that they not be zeroed.
134     */
135    struct page *pages[DIO_PAGES]; /* page buffer */
136};
137
138/*
139 * How many pages are in the queue?
140 */
141static inline unsigned dio_pages_present(struct dio *dio)
142{
143    return dio->tail - dio->head;
144}
145
146/*
147 * Go grab and pin some userspace pages. Typically we'll get 64 at a time.
148 */
149static int dio_refill_pages(struct dio *dio)
150{
151    int ret;
152    int nr_pages;
153
154    nr_pages = min(dio->total_pages - dio->curr_page, DIO_PAGES);
155    ret = get_user_pages_fast(
156        dio->curr_user_address, /* Where from? */
157        nr_pages, /* How many pages? */
158        dio->rw == READ, /* Write to memory? */
159        &dio->pages[0]); /* Put results here */
160
161    if (ret < 0 && dio->blocks_available && (dio->rw & WRITE)) {
162        struct page *page = ZERO_PAGE(0);
163        /*
164         * A memory fault, but the filesystem has some outstanding
165         * mapped blocks. We need to use those blocks up to avoid
166         * leaking stale data in the file.
167         */
168        if (dio->page_errors == 0)
169            dio->page_errors = ret;
170        page_cache_get(page);
171        dio->pages[0] = page;
172        dio->head = 0;
173        dio->tail = 1;
174        ret = 0;
175        goto out;
176    }
177
178    if (ret >= 0) {
179        dio->curr_user_address += ret * PAGE_SIZE;
180        dio->curr_page += ret;
181        dio->head = 0;
182        dio->tail = ret;
183        ret = 0;
184    }
185out:
186    return ret;
187}
188
189/*
190 * Get another userspace page. Returns an ERR_PTR on error. Pages are
191 * buffered inside the dio so that we can call get_user_pages() against a
192 * decent number of pages, less frequently. To provide nicer use of the
193 * L1 cache.
194 */
195static struct page *dio_get_page(struct dio *dio)
196{
197    if (dio_pages_present(dio) == 0) {
198        int ret;
199
200        ret = dio_refill_pages(dio);
201        if (ret)
202            return ERR_PTR(ret);
203        BUG_ON(dio_pages_present(dio) == 0);
204    }
205    return dio->pages[dio->head++];
206}
207
208/**
209 * dio_complete() - called when all DIO BIO I/O has been completed
210 * @offset: the byte offset in the file of the completed operation
211 *
212 * This releases locks as dictated by the locking type, lets interested parties
213 * know that a DIO operation has completed, and calculates the resulting return
214 * code for the operation.
215 *
216 * It lets the filesystem know if it registered an interest earlier via
217 * get_block. Pass the private field of the map buffer_head so that
218 * filesystems can use it to hold additional state between get_block calls and
219 * dio_complete.
220 */
221static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret, bool is_async)
222{
223    ssize_t transferred = 0;
224
225    /*
226     * AIO submission can race with bio completion to get here while
227     * expecting to have the last io completed by bio completion.
228     * In that case -EIOCBQUEUED is in fact not an error we want
229     * to preserve through this call.
230     */
231    if (ret == -EIOCBQUEUED)
232        ret = 0;
233
234    if (dio->result) {
235        transferred = dio->result;
236
237        /* Check for short read case */
238        if ((dio->rw == READ) && ((offset + transferred) > dio->i_size))
239            transferred = dio->i_size - offset;
240    }
241
242    if (ret == 0)
243        ret = dio->page_errors;
244    if (ret == 0)
245        ret = dio->io_error;
246    if (ret == 0)
247        ret = transferred;
248
249    if (dio->end_io && dio->result) {
250        dio->end_io(dio->iocb, offset, transferred,
251                dio->map_bh.b_private, ret, is_async);
252    } else if (is_async) {
253        aio_complete(dio->iocb, ret, 0);
254    }
255
256    if (dio->flags & DIO_LOCKING)
257        /* lockdep: non-owner release */
258        up_read_non_owner(&dio->inode->i_alloc_sem);
259
260    return ret;
261}
262
263static int dio_bio_complete(struct dio *dio, struct bio *bio);
264/*
265 * Asynchronous IO callback.
266 */
267static void dio_bio_end_aio(struct bio *bio, int error)
268{
269    struct dio *dio = bio->bi_private;
270    unsigned long remaining;
271    unsigned long flags;
272
273    /* cleanup the bio */
274    dio_bio_complete(dio, bio);
275
276    spin_lock_irqsave(&dio->bio_lock, flags);
277    remaining = --dio->refcount;
278    if (remaining == 1 && dio->waiter)
279        wake_up_process(dio->waiter);
280    spin_unlock_irqrestore(&dio->bio_lock, flags);
281
282    if (remaining == 0) {
283        dio_complete(dio, dio->iocb->ki_pos, 0, true);
284        kfree(dio);
285    }
286}
287
288/*
289 * The BIO completion handler simply queues the BIO up for the process-context
290 * handler.
291 *
292 * During I/O bi_private points at the dio. After I/O, bi_private is used to
293 * implement a singly-linked list of completed BIOs, at dio->bio_list.
294 */
295static void dio_bio_end_io(struct bio *bio, int error)
296{
297    struct dio *dio = bio->bi_private;
298    unsigned long flags;
299
300    spin_lock_irqsave(&dio->bio_lock, flags);
301    bio->bi_private = dio->bio_list;
302    dio->bio_list = bio;
303    if (--dio->refcount == 1 && dio->waiter)
304        wake_up_process(dio->waiter);
305    spin_unlock_irqrestore(&dio->bio_lock, flags);
306}
307
308/**
309 * dio_end_io - handle the end io action for the given bio
310 * @bio: The direct io bio thats being completed
311 * @error: Error if there was one
312 *
313 * This is meant to be called by any filesystem that uses their own dio_submit_t
314 * so that the DIO specific endio actions are dealt with after the filesystem
315 * has done it's completion work.
316 */
317void dio_end_io(struct bio *bio, int error)
318{
319    struct dio *dio = bio->bi_private;
320
321    if (dio->is_async)
322        dio_bio_end_aio(bio, error);
323    else
324        dio_bio_end_io(bio, error);
325}
326EXPORT_SYMBOL_GPL(dio_end_io);
327
328static void
329dio_bio_alloc(struct dio *dio, struct block_device *bdev,
330        sector_t first_sector, int nr_vecs)
331{
332    struct bio *bio;
333
334    /*
335     * bio_alloc() is guaranteed to return a bio when called with
336     * __GFP_WAIT and we request a valid number of vectors.
337     */
338    bio = bio_alloc(GFP_KERNEL, nr_vecs);
339
340    bio->bi_bdev = bdev;
341    bio->bi_sector = first_sector;
342    if (dio->is_async)
343        bio->bi_end_io = dio_bio_end_aio;
344    else
345        bio->bi_end_io = dio_bio_end_io;
346
347    dio->bio = bio;
348    dio->logical_offset_in_bio = dio->cur_page_fs_offset;
349}
350
351/*
352 * In the AIO read case we speculatively dirty the pages before starting IO.
353 * During IO completion, any of these pages which happen to have been written
354 * back will be redirtied by bio_check_pages_dirty().
355 *
356 * bios hold a dio reference between submit_bio and ->end_io.
357 */
358static void dio_bio_submit(struct dio *dio)
359{
360    struct bio *bio = dio->bio;
361    unsigned long flags;
362
363    bio->bi_private = dio;
364
365    spin_lock_irqsave(&dio->bio_lock, flags);
366    dio->refcount++;
367    spin_unlock_irqrestore(&dio->bio_lock, flags);
368
369    if (dio->is_async && dio->rw == READ)
370        bio_set_pages_dirty(bio);
371
372    if (dio->submit_io)
373        dio->submit_io(dio->rw, bio, dio->inode,
374                   dio->logical_offset_in_bio);
375    else
376        submit_bio(dio->rw, bio);
377
378    dio->bio = NULL;
379    dio->boundary = 0;
380    dio->logical_offset_in_bio = 0;
381}
382
383/*
384 * Release any resources in case of a failure
385 */
386static void dio_cleanup(struct dio *dio)
387{
388    while (dio_pages_present(dio))
389        page_cache_release(dio_get_page(dio));
390}
391
392/*
393 * Wait for the next BIO to complete. Remove it and return it. NULL is
394 * returned once all BIOs have been completed. This must only be called once
395 * all bios have been issued so that dio->refcount can only decrease. This
396 * requires that that the caller hold a reference on the dio.
397 */
398static struct bio *dio_await_one(struct dio *dio)
399{
400    unsigned long flags;
401    struct bio *bio = NULL;
402
403    spin_lock_irqsave(&dio->bio_lock, flags);
404
405    /*
406     * Wait as long as the list is empty and there are bios in flight. bio
407     * completion drops the count, maybe adds to the list, and wakes while
408     * holding the bio_lock so we don't need set_current_state()'s barrier
409     * and can call it after testing our condition.
410     */
411    while (dio->refcount > 1 && dio->bio_list == NULL) {
412        __set_current_state(TASK_UNINTERRUPTIBLE);
413        dio->waiter = current;
414        spin_unlock_irqrestore(&dio->bio_lock, flags);
415        io_schedule();
416        /* wake up sets us TASK_RUNNING */
417        spin_lock_irqsave(&dio->bio_lock, flags);
418        dio->waiter = NULL;
419    }
420    if (dio->bio_list) {
421        bio = dio->bio_list;
422        dio->bio_list = bio->bi_private;
423    }
424    spin_unlock_irqrestore(&dio->bio_lock, flags);
425    return bio;
426}
427
428/*
429 * Process one completed BIO. No locks are held.
430 */
431static int dio_bio_complete(struct dio *dio, struct bio *bio)
432{
433    const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
434    struct bio_vec *bvec = bio->bi_io_vec;
435    int page_no;
436
437    if (!uptodate)
438        dio->io_error = -EIO;
439
440    if (dio->is_async && dio->rw == READ) {
441        bio_check_pages_dirty(bio); /* transfers ownership */
442    } else {
443        for (page_no = 0; page_no < bio->bi_vcnt; page_no++) {
444            struct page *page = bvec[page_no].bv_page;
445
446            if (dio->rw == READ && !PageCompound(page))
447                set_page_dirty_lock(page);
448            page_cache_release(page);
449        }
450        bio_put(bio);
451    }
452    return uptodate ? 0 : -EIO;
453}
454
455/*
456 * Wait on and process all in-flight BIOs. This must only be called once
457 * all bios have been issued so that the refcount can only decrease.
458 * This just waits for all bios to make it through dio_bio_complete. IO
459 * errors are propagated through dio->io_error and should be propagated via
460 * dio_complete().
461 */
462static void dio_await_completion(struct dio *dio)
463{
464    struct bio *bio;
465    do {
466        bio = dio_await_one(dio);
467        if (bio)
468            dio_bio_complete(dio, bio);
469    } while (bio);
470}
471
472/*
473 * A really large O_DIRECT read or write can generate a lot of BIOs. So
474 * to keep the memory consumption sane we periodically reap any completed BIOs
475 * during the BIO generation phase.
476 *
477 * This also helps to limit the peak amount of pinned userspace memory.
478 */
479static int dio_bio_reap(struct dio *dio)
480{
481    int ret = 0;
482
483    if (dio->reap_counter++ >= 64) {
484        while (dio->bio_list) {
485            unsigned long flags;
486            struct bio *bio;
487            int ret2;
488
489            spin_lock_irqsave(&dio->bio_lock, flags);
490            bio = dio->bio_list;
491            dio->bio_list = bio->bi_private;
492            spin_unlock_irqrestore(&dio->bio_lock, flags);
493            ret2 = dio_bio_complete(dio, bio);
494            if (ret == 0)
495                ret = ret2;
496        }
497        dio->reap_counter = 0;
498    }
499    return ret;
500}
501
502/*
503 * Call into the fs to map some more disk blocks. We record the current number
504 * of available blocks at dio->blocks_available. These are in units of the
505 * fs blocksize, (1 << inode->i_blkbits).
506 *
507 * The fs is allowed to map lots of blocks at once. If it wants to do that,
508 * it uses the passed inode-relative block number as the file offset, as usual.
509 *
510 * get_block() is passed the number of i_blkbits-sized blocks which direct_io
511 * has remaining to do. The fs should not map more than this number of blocks.
512 *
513 * If the fs has mapped a lot of blocks, it should populate bh->b_size to
514 * indicate how much contiguous disk space has been made available at
515 * bh->b_blocknr.
516 *
517 * If *any* of the mapped blocks are new, then the fs must set buffer_new().
518 * This isn't very efficient...
519 *
520 * In the case of filesystem holes: the fs may return an arbitrarily-large
521 * hole by returning an appropriate value in b_size and by clearing
522 * buffer_mapped(). However the direct-io code will only process holes one
523 * block at a time - it will repeatedly call get_block() as it walks the hole.
524 */
525static int get_more_blocks(struct dio *dio)
526{
527    int ret;
528    struct buffer_head *map_bh = &dio->map_bh;
529    sector_t fs_startblk; /* Into file, in filesystem-sized blocks */
530    unsigned long fs_count; /* Number of filesystem-sized blocks */
531    unsigned long dio_count;/* Number of dio_block-sized blocks */
532    unsigned long blkmask;
533    int create;
534
535    /*
536     * If there was a memory error and we've overwritten all the
537     * mapped blocks then we can now return that memory error
538     */
539    ret = dio->page_errors;
540    if (ret == 0) {
541        BUG_ON(dio->block_in_file >= dio->final_block_in_request);
542        fs_startblk = dio->block_in_file >> dio->blkfactor;
543        dio_count = dio->final_block_in_request - dio->block_in_file;
544        fs_count = dio_count >> dio->blkfactor;
545        blkmask = (1 << dio->blkfactor) - 1;
546        if (dio_count & blkmask)
547            fs_count++;
548
549        map_bh->b_state = 0;
550        map_bh->b_size = fs_count << dio->inode->i_blkbits;
551
552        /*
553         * For writes inside i_size on a DIO_SKIP_HOLES filesystem we
554         * forbid block creations: only overwrites are permitted.
555         * We will return early to the caller once we see an
556         * unmapped buffer head returned, and the caller will fall
557         * back to buffered I/O.
558         *
559         * Otherwise the decision is left to the get_blocks method,
560         * which may decide to handle it or also return an unmapped
561         * buffer head.
562         */
563        create = dio->rw & WRITE;
564        if (dio->flags & DIO_SKIP_HOLES) {
565            if (dio->block_in_file < (i_size_read(dio->inode) >>
566                            dio->blkbits))
567                create = 0;
568        }
569
570        ret = (*dio->get_block)(dio->inode, fs_startblk,
571                        map_bh, create);
572    }
573    return ret;
574}
575
576/*
577 * There is no bio. Make one now.
578 */
579static int dio_new_bio(struct dio *dio, sector_t start_sector)
580{
581    sector_t sector;
582    int ret, nr_pages;
583
584    ret = dio_bio_reap(dio);
585    if (ret)
586        goto out;
587    sector = start_sector << (dio->blkbits - 9);
588    nr_pages = min(dio->pages_in_io, bio_get_nr_vecs(dio->map_bh.b_bdev));
589    nr_pages = min(nr_pages, BIO_MAX_PAGES);
590    BUG_ON(nr_pages <= 0);
591    dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages);
592    dio->boundary = 0;
593out:
594    return ret;
595}
596
597/*
598 * Attempt to put the current chunk of 'cur_page' into the current BIO. If
599 * that was successful then update final_block_in_bio and take a ref against
600 * the just-added page.
601 *
602 * Return zero on success. Non-zero means the caller needs to start a new BIO.
603 */
604static int dio_bio_add_page(struct dio *dio)
605{
606    int ret;
607
608    ret = bio_add_page(dio->bio, dio->cur_page,
609            dio->cur_page_len, dio->cur_page_offset);
610    if (ret == dio->cur_page_len) {
611        /*
612         * Decrement count only, if we are done with this page
613         */
614        if ((dio->cur_page_len + dio->cur_page_offset) == PAGE_SIZE)
615            dio->pages_in_io--;
616        page_cache_get(dio->cur_page);
617        dio->final_block_in_bio = dio->cur_page_block +
618            (dio->cur_page_len >> dio->blkbits);
619        ret = 0;
620    } else {
621        ret = 1;
622    }
623    return ret;
624}
625        
626/*
627 * Put cur_page under IO. The section of cur_page which is described by
628 * cur_page_offset,cur_page_len is put into a BIO. The section of cur_page
629 * starts on-disk at cur_page_block.
630 *
631 * We take a ref against the page here (on behalf of its presence in the bio).
632 *
633 * The caller of this function is responsible for removing cur_page from the
634 * dio, and for dropping the refcount which came from that presence.
635 */
636static int dio_send_cur_page(struct dio *dio)
637{
638    int ret = 0;
639
640    if (dio->bio) {
641        loff_t cur_offset = dio->cur_page_fs_offset;
642        loff_t bio_next_offset = dio->logical_offset_in_bio +
643            dio->bio->bi_size;
644
645        /*
646         * See whether this new request is contiguous with the old.
647         *
648         * Btrfs cannot handle having logically non-contiguous requests
649         * submitted. For example if you have
650         *
651         * Logical: [0-4095][HOLE][8192-12287]
652         * Physical: [0-4095] [4096-8191]
653         *
654         * We cannot submit those pages together as one BIO. So if our
655         * current logical offset in the file does not equal what would
656         * be the next logical offset in the bio, submit the bio we
657         * have.
658         */
659        if (dio->final_block_in_bio != dio->cur_page_block ||
660            cur_offset != bio_next_offset)
661            dio_bio_submit(dio);
662        /*
663         * Submit now if the underlying fs is about to perform a
664         * metadata read
665         */
666        else if (dio->boundary)
667            dio_bio_submit(dio);
668    }
669
670    if (dio->bio == NULL) {
671        ret = dio_new_bio(dio, dio->cur_page_block);
672        if (ret)
673            goto out;
674    }
675
676    if (dio_bio_add_page(dio) != 0) {
677        dio_bio_submit(dio);
678        ret = dio_new_bio(dio, dio->cur_page_block);
679        if (ret == 0) {
680            ret = dio_bio_add_page(dio);
681            BUG_ON(ret != 0);
682        }
683    }
684out:
685    return ret;
686}
687
688/*
689 * An autonomous function to put a chunk of a page under deferred IO.
690 *
691 * The caller doesn't actually know (or care) whether this piece of page is in
692 * a BIO, or is under IO or whatever. We just take care of all possible
693 * situations here. The separation between the logic of do_direct_IO() and
694 * that of submit_page_section() is important for clarity. Please don't break.
695 *
696 * The chunk of page starts on-disk at blocknr.
697 *
698 * We perform deferred IO, by recording the last-submitted page inside our
699 * private part of the dio structure. If possible, we just expand the IO
700 * across that page here.
701 *
702 * If that doesn't work out then we put the old page into the bio and add this
703 * page to the dio instead.
704 */
705static int
706submit_page_section(struct dio *dio, struct page *page,
707        unsigned offset, unsigned len, sector_t blocknr)
708{
709    int ret = 0;
710
711    if (dio->rw & WRITE) {
712        /*
713         * Read accounting is performed in submit_bio()
714         */
715        task_io_account_write(len);
716    }
717
718    /*
719     * Can we just grow the current page's presence in the dio?
720     */
721    if ( (dio->cur_page == page) &&
722        (dio->cur_page_offset + dio->cur_page_len == offset) &&
723        (dio->cur_page_block +
724            (dio->cur_page_len >> dio->blkbits) == blocknr)) {
725        dio->cur_page_len += len;
726
727        /*
728         * If dio->boundary then we want to schedule the IO now to
729         * avoid metadata seeks.
730         */
731        if (dio->boundary) {
732            ret = dio_send_cur_page(dio);
733            page_cache_release(dio->cur_page);
734            dio->cur_page = NULL;
735        }
736        goto out;
737    }
738
739    /*
740     * If there's a deferred page already there then send it.
741     */
742    if (dio->cur_page) {
743        ret = dio_send_cur_page(dio);
744        page_cache_release(dio->cur_page);
745        dio->cur_page = NULL;
746        if (ret)
747            goto out;
748    }
749
750    page_cache_get(page); /* It is in dio */
751    dio->cur_page = page;
752    dio->cur_page_offset = offset;
753    dio->cur_page_len = len;
754    dio->cur_page_block = blocknr;
755    dio->cur_page_fs_offset = dio->block_in_file << dio->blkbits;
756out:
757    return ret;
758}
759
760/*
761 * Clean any dirty buffers in the blockdev mapping which alias newly-created
762 * file blocks. Only called for S_ISREG files - blockdevs do not set
763 * buffer_new
764 */
765static void clean_blockdev_aliases(struct dio *dio)
766{
767    unsigned i;
768    unsigned nblocks;
769
770    nblocks = dio->map_bh.b_size >> dio->inode->i_blkbits;
771
772    for (i = 0; i < nblocks; i++) {
773        unmap_underlying_metadata(dio->map_bh.b_bdev,
774                    dio->map_bh.b_blocknr + i);
775    }
776}
777
778/*
779 * If we are not writing the entire block and get_block() allocated
780 * the block for us, we need to fill-in the unused portion of the
781 * block with zeros. This happens only if user-buffer, fileoffset or
782 * io length is not filesystem block-size multiple.
783 *
784 * `end' is zero if we're doing the start of the IO, 1 at the end of the
785 * IO.
786 */
787static void dio_zero_block(struct dio *dio, int end)
788{
789    unsigned dio_blocks_per_fs_block;
790    unsigned this_chunk_blocks; /* In dio_blocks */
791    unsigned this_chunk_bytes;
792    struct page *page;
793
794    dio->start_zero_done = 1;
795    if (!dio->blkfactor || !buffer_new(&dio->map_bh))
796        return;
797
798    dio_blocks_per_fs_block = 1 << dio->blkfactor;
799    this_chunk_blocks = dio->block_in_file & (dio_blocks_per_fs_block - 1);
800
801    if (!this_chunk_blocks)
802        return;
803
804    /*
805     * We need to zero out part of an fs block. It is either at the
806     * beginning or the end of the fs block.
807     */
808    if (end)
809        this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
810
811    this_chunk_bytes = this_chunk_blocks << dio->blkbits;
812
813    page = ZERO_PAGE(0);
814    if (submit_page_section(dio, page, 0, this_chunk_bytes,
815                dio->next_block_for_io))
816        return;
817
818    dio->next_block_for_io += this_chunk_blocks;
819}
820
821/*
822 * Walk the user pages, and the file, mapping blocks to disk and generating
823 * a sequence of (page,offset,len,block) mappings. These mappings are injected
824 * into submit_page_section(), which takes care of the next stage of submission
825 *
826 * Direct IO against a blockdev is different from a file. Because we can
827 * happily perform page-sized but 512-byte aligned IOs. It is important that
828 * blockdev IO be able to have fine alignment and large sizes.
829 *
830 * So what we do is to permit the ->get_block function to populate bh.b_size
831 * with the size of IO which is permitted at this offset and this i_blkbits.
832 *
833 * For best results, the blockdev should be set up with 512-byte i_blkbits and
834 * it should set b_size to PAGE_SIZE or more inside get_block(). This gives
835 * fine alignment but still allows this function to work in PAGE_SIZE units.
836 */
837static int do_direct_IO(struct dio *dio)
838{
839    const unsigned blkbits = dio->blkbits;
840    const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
841    struct page *page;
842    unsigned block_in_page;
843    struct buffer_head *map_bh = &dio->map_bh;
844    int ret = 0;
845
846    /* The I/O can start at any block offset within the first page */
847    block_in_page = dio->first_block_in_page;
848
849    while (dio->block_in_file < dio->final_block_in_request) {
850        page = dio_get_page(dio);
851        if (IS_ERR(page)) {
852            ret = PTR_ERR(page);
853            goto out;
854        }
855
856        while (block_in_page < blocks_per_page) {
857            unsigned offset_in_page = block_in_page << blkbits;
858            unsigned this_chunk_bytes; /* # of bytes mapped */
859            unsigned this_chunk_blocks; /* # of blocks */
860            unsigned u;
861
862            if (dio->blocks_available == 0) {
863                /*
864                 * Need to go and map some more disk
865                 */
866                unsigned long blkmask;
867                unsigned long dio_remainder;
868
869                ret = get_more_blocks(dio);
870                if (ret) {
871                    page_cache_release(page);
872                    goto out;
873                }
874                if (!buffer_mapped(map_bh))
875                    goto do_holes;
876
877                dio->blocks_available =
878                        map_bh->b_size >> dio->blkbits;
879                dio->next_block_for_io =
880                    map_bh->b_blocknr << dio->blkfactor;
881                if (buffer_new(map_bh))
882                    clean_blockdev_aliases(dio);
883
884                if (!dio->blkfactor)
885                    goto do_holes;
886
887                blkmask = (1 << dio->blkfactor) - 1;
888                dio_remainder = (dio->block_in_file & blkmask);
889
890                /*
891                 * If we are at the start of IO and that IO
892                 * starts partway into a fs-block,
893                 * dio_remainder will be non-zero. If the IO
894                 * is a read then we can simply advance the IO
895                 * cursor to the first block which is to be
896                 * read. But if the IO is a write and the
897                 * block was newly allocated we cannot do that;
898                 * the start of the fs block must be zeroed out
899                 * on-disk
900                 */
901                if (!buffer_new(map_bh))
902                    dio->next_block_for_io += dio_remainder;
903                dio->blocks_available -= dio_remainder;
904            }
905do_holes:
906            /* Handle holes */
907            if (!buffer_mapped(map_bh)) {
908                loff_t i_size_aligned;
909
910                /* AKPM: eargh, -ENOTBLK is a hack */
911                if (dio->rw & WRITE) {
912                    page_cache_release(page);
913                    return -ENOTBLK;
914                }
915
916                /*
917                 * Be sure to account for a partial block as the
918                 * last block in the file
919                 */
920                i_size_aligned = ALIGN(i_size_read(dio->inode),
921                            1 << blkbits);
922                if (dio->block_in_file >=
923                        i_size_aligned >> blkbits) {
924                    /* We hit eof */
925                    page_cache_release(page);
926                    goto out;
927                }
928                zero_user(page, block_in_page << blkbits,
929                        1 << blkbits);
930                dio->block_in_file++;
931                block_in_page++;
932                goto next_block;
933            }
934
935            /*
936             * If we're performing IO which has an alignment which
937             * is finer than the underlying fs, go check to see if
938             * we must zero out the start of this block.
939             */
940            if (unlikely(dio->blkfactor && !dio->start_zero_done))
941                dio_zero_block(dio, 0);
942
943            /*
944             * Work out, in this_chunk_blocks, how much disk we
945             * can add to this page
946             */
947            this_chunk_blocks = dio->blocks_available;
948            u = (PAGE_SIZE - offset_in_page) >> blkbits;
949            if (this_chunk_blocks > u)
950                this_chunk_blocks = u;
951            u = dio->final_block_in_request - dio->block_in_file;
952            if (this_chunk_blocks > u)
953                this_chunk_blocks = u;
954            this_chunk_bytes = this_chunk_blocks << blkbits;
955            BUG_ON(this_chunk_bytes == 0);
956
957            dio->boundary = buffer_boundary(map_bh);
958            ret = submit_page_section(dio, page, offset_in_page,
959                this_chunk_bytes, dio->next_block_for_io);
960            if (ret) {
961                page_cache_release(page);
962                goto out;
963            }
964            dio->next_block_for_io += this_chunk_blocks;
965
966            dio->block_in_file += this_chunk_blocks;
967            block_in_page += this_chunk_blocks;
968            dio->blocks_available -= this_chunk_blocks;
969next_block:
970            BUG_ON(dio->block_in_file > dio->final_block_in_request);
971            if (dio->block_in_file == dio->final_block_in_request)
972                break;
973        }
974
975        /* Drop the ref which was taken in get_user_pages() */
976        page_cache_release(page);
977        block_in_page = 0;
978    }
979out:
980    return ret;
981}
982
983/*
984 * Releases both i_mutex and i_alloc_sem
985 */
986static ssize_t
987direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
988    const struct iovec *iov, loff_t offset, unsigned long nr_segs,
989    unsigned blkbits, get_block_t get_block, dio_iodone_t end_io,
990    dio_submit_t submit_io, struct dio *dio)
991{
992    unsigned long user_addr;
993    unsigned long flags;
994    int seg;
995    ssize_t ret = 0;
996    ssize_t ret2;
997    size_t bytes;
998
999    dio->inode = inode;
1000    dio->rw = rw;
1001    dio->blkbits = blkbits;
1002    dio->blkfactor = inode->i_blkbits - blkbits;
1003    dio->block_in_file = offset >> blkbits;
1004
1005    dio->get_block = get_block;
1006    dio->end_io = end_io;
1007    dio->submit_io = submit_io;
1008    dio->final_block_in_bio = -1;
1009    dio->next_block_for_io = -1;
1010
1011    dio->iocb = iocb;
1012    dio->i_size = i_size_read(inode);
1013
1014    spin_lock_init(&dio->bio_lock);
1015    dio->refcount = 1;
1016
1017    /*
1018     * In case of non-aligned buffers, we may need 2 more
1019     * pages since we need to zero out first and last block.
1020     */
1021    if (unlikely(dio->blkfactor))
1022        dio->pages_in_io = 2;
1023
1024    for (seg = 0; seg < nr_segs; seg++) {
1025        user_addr = (unsigned long)iov[seg].iov_base;
1026        dio->pages_in_io +=
1027            ((user_addr+iov[seg].iov_len +PAGE_SIZE-1)/PAGE_SIZE
1028                - user_addr/PAGE_SIZE);
1029    }
1030
1031    for (seg = 0; seg < nr_segs; seg++) {
1032        user_addr = (unsigned long)iov[seg].iov_base;
1033        dio->size += bytes = iov[seg].iov_len;
1034
1035        /* Index into the first page of the first block */
1036        dio->first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits;
1037        dio->final_block_in_request = dio->block_in_file +
1038                        (bytes >> blkbits);
1039        /* Page fetching state */
1040        dio->head = 0;
1041        dio->tail = 0;
1042        dio->curr_page = 0;
1043
1044        dio->total_pages = 0;
1045        if (user_addr & (PAGE_SIZE-1)) {
1046            dio->total_pages++;
1047            bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1));
1048        }
1049        dio->total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
1050        dio->curr_user_address = user_addr;
1051    
1052        ret = do_direct_IO(dio);
1053
1054        dio->result += iov[seg].iov_len -
1055            ((dio->final_block_in_request - dio->block_in_file) <<
1056                    blkbits);
1057
1058        if (ret) {
1059            dio_cleanup(dio);
1060            break;
1061        }
1062    } /* end iovec loop */
1063
1064    if (ret == -ENOTBLK) {
1065        /*
1066         * The remaining part of the request will be
1067         * be handled by buffered I/O when we return
1068         */
1069        ret = 0;
1070    }
1071    /*
1072     * There may be some unwritten disk at the end of a part-written
1073     * fs-block-sized block. Go zero that now.
1074     */
1075    dio_zero_block(dio, 1);
1076
1077    if (dio->cur_page) {
1078        ret2 = dio_send_cur_page(dio);
1079        if (ret == 0)
1080            ret = ret2;
1081        page_cache_release(dio->cur_page);
1082        dio->cur_page = NULL;
1083    }
1084    if (dio->bio)
1085        dio_bio_submit(dio);
1086
1087    /*
1088     * It is possible that, we return short IO due to end of file.
1089     * In that case, we need to release all the pages we got hold on.
1090     */
1091    dio_cleanup(dio);
1092
1093    /*
1094     * All block lookups have been performed. For READ requests
1095     * we can let i_mutex go now that its achieved its purpose
1096     * of protecting us from looking up uninitialized blocks.
1097     */
1098    if (rw == READ && (dio->flags & DIO_LOCKING))
1099        mutex_unlock(&dio->inode->i_mutex);
1100
1101    /*
1102     * The only time we want to leave bios in flight is when a successful
1103     * partial aio read or full aio write have been setup. In that case
1104     * bio completion will call aio_complete. The only time it's safe to
1105     * call aio_complete is when we return -EIOCBQUEUED, so we key on that.
1106     * This had *better* be the only place that raises -EIOCBQUEUED.
1107     */
1108    BUG_ON(ret == -EIOCBQUEUED);
1109    if (dio->is_async && ret == 0 && dio->result &&
1110        ((rw & READ) || (dio->result == dio->size)))
1111        ret = -EIOCBQUEUED;
1112
1113    if (ret != -EIOCBQUEUED)
1114        dio_await_completion(dio);
1115
1116    /*
1117     * Sync will always be dropping the final ref and completing the
1118     * operation. AIO can if it was a broken operation described above or
1119     * in fact if all the bios race to complete before we get here. In
1120     * that case dio_complete() translates the EIOCBQUEUED into the proper
1121     * return code that the caller will hand to aio_complete().
1122     *
1123     * This is managed by the bio_lock instead of being an atomic_t so that
1124     * completion paths can drop their ref and use the remaining count to
1125     * decide to wake the submission path atomically.
1126     */
1127    spin_lock_irqsave(&dio->bio_lock, flags);
1128    ret2 = --dio->refcount;
1129    spin_unlock_irqrestore(&dio->bio_lock, flags);
1130
1131    if (ret2 == 0) {
1132        ret = dio_complete(dio, offset, ret, false);
1133        kfree(dio);
1134    } else
1135        BUG_ON(ret != -EIOCBQUEUED);
1136
1137    return ret;
1138}
1139
1140/*
1141 * This is a library function for use by filesystem drivers.
1142 *
1143 * The locking rules are governed by the flags parameter:
1144 * - if the flags value contains DIO_LOCKING we use a fancy locking
1145 * scheme for dumb filesystems.
1146 * For writes this function is called under i_mutex and returns with
1147 * i_mutex held, for reads, i_mutex is not held on entry, but it is
1148 * taken and dropped again before returning.
1149 * For reads and writes i_alloc_sem is taken in shared mode and released
1150 * on I/O completion (which may happen asynchronously after returning to
1151 * the caller).
1152 *
1153 * - if the flags value does NOT contain DIO_LOCKING we don't use any
1154 * internal locking but rather rely on the filesystem to synchronize
1155 * direct I/O reads/writes versus each other and truncate.
1156 * For reads and writes both i_mutex and i_alloc_sem are not held on
1157 * entry and are never taken.
1158 */
1159ssize_t
1160__blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
1161    struct block_device *bdev, const struct iovec *iov, loff_t offset,
1162    unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io,
1163    dio_submit_t submit_io, int flags)
1164{
1165    int seg;
1166    size_t size;
1167    unsigned long addr;
1168    unsigned blkbits = inode->i_blkbits;
1169    unsigned bdev_blkbits = 0;
1170    unsigned blocksize_mask = (1 << blkbits) - 1;
1171    ssize_t retval = -EINVAL;
1172    loff_t end = offset;
1173    struct dio *dio;
1174
1175    if (rw & WRITE)
1176        rw = WRITE_ODIRECT;
1177
1178    if (bdev)
1179        bdev_blkbits = blksize_bits(bdev_logical_block_size(bdev));
1180
1181    if (offset & blocksize_mask) {
1182        if (bdev)
1183             blkbits = bdev_blkbits;
1184        blocksize_mask = (1 << blkbits) - 1;
1185        if (offset & blocksize_mask)
1186            goto out;
1187    }
1188
1189    /* Check the memory alignment. Blocks cannot straddle pages */
1190    for (seg = 0; seg < nr_segs; seg++) {
1191        addr = (unsigned long)iov[seg].iov_base;
1192        size = iov[seg].iov_len;
1193        end += size;
1194        if ((addr & blocksize_mask) || (size & blocksize_mask)) {
1195            if (bdev)
1196                 blkbits = bdev_blkbits;
1197            blocksize_mask = (1 << blkbits) - 1;
1198            if ((addr & blocksize_mask) || (size & blocksize_mask))
1199                goto out;
1200        }
1201    }
1202
1203    dio = kmalloc(sizeof(*dio), GFP_KERNEL);
1204    retval = -ENOMEM;
1205    if (!dio)
1206        goto out;
1207    /*
1208     * Believe it or not, zeroing out the page array caused a .5%
1209     * performance regression in a database benchmark. So, we take
1210     * care to only zero out what's needed.
1211     */
1212    memset(dio, 0, offsetof(struct dio, pages));
1213
1214    dio->flags = flags;
1215    if (dio->flags & DIO_LOCKING) {
1216        /* watch out for a 0 len io from a tricksy fs */
1217        if (rw == READ && end > offset) {
1218            struct address_space *mapping =
1219                    iocb->ki_filp->f_mapping;
1220
1221            /* will be released by direct_io_worker */
1222            mutex_lock(&inode->i_mutex);
1223
1224            retval = filemap_write_and_wait_range(mapping, offset,
1225                                  end - 1);
1226            if (retval) {
1227                mutex_unlock(&inode->i_mutex);
1228                kfree(dio);
1229                goto out;
1230            }
1231        }
1232
1233        /*
1234         * Will be released at I/O completion, possibly in a
1235         * different thread.
1236         */
1237        down_read_non_owner(&inode->i_alloc_sem);
1238    }
1239
1240    /*
1241     * For file extending writes updating i_size before data
1242     * writeouts complete can expose uninitialized blocks. So
1243     * even for AIO, we need to wait for i/o to complete before
1244     * returning in this case.
1245     */
1246    dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) &&
1247        (end > i_size_read(inode)));
1248
1249    retval = direct_io_worker(rw, iocb, inode, iov, offset,
1250                nr_segs, blkbits, get_block, end_io,
1251                submit_io, dio);
1252
1253out:
1254    return retval;
1255}
1256EXPORT_SYMBOL(__blockdev_direct_IO);
1257

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