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 * 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).
63 */
64
65struct 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 */
96
97    /*
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().
101     */
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 */
106
107    /*
108     * Page fetching state. These variables belong to dio_refill_pages().
109     */
110    int curr_page; /* changes */
111    int total_pages; /* doesn't change */
112    unsigned long curr_user_address;/* changes */
113
114    /*
115     * Page queue. These variables belong to dio_refill_pages() and
116     * dio_get_page().
117     */
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() */
122
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) */
128
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 */
134};
135
136/*
137 * How many pages are in the queue?
138 */
139static inline unsigned dio_pages_present(struct dio *dio)
140{
141    return dio->tail - dio->head;
142}
143
144/*
145 * Go grab and pin some userspace pages. Typically we'll get 64 at a time.
146 */
147static int dio_refill_pages(struct dio *dio)
148{
149    int ret;
150    int nr_pages;
151
152    nr_pages = min(dio->total_pages - dio->curr_page, DIO_PAGES);
153    ret = get_user_pages_fast(
154        dio->curr_user_address, /* Where from? */
155        nr_pages, /* How many pages? */
156        dio->rw == READ, /* Write to memory? */
157        &dio->pages[0]); /* Put results here */
158
159    if (ret < 0 && dio->blocks_available && (dio->rw & WRITE)) {
160        struct page *page = ZERO_PAGE(0);
161        /*
162         * A memory fault, but the filesystem has some outstanding
163         * mapped blocks. We need to use those blocks up to avoid
164         * leaking stale data in the file.
165         */
166        if (dio->page_errors == 0)
167            dio->page_errors = ret;
168        page_cache_get(page);
169        dio->pages[0] = page;
170        dio->head = 0;
171        dio->tail = 1;
172        ret = 0;
173        goto out;
174    }
175
176    if (ret >= 0) {
177        dio->curr_user_address += ret * PAGE_SIZE;
178        dio->curr_page += ret;
179        dio->head = 0;
180        dio->tail = ret;
181        ret = 0;
182    }
183out:
184    return ret;
185}
186
187/*
188 * Get another userspace page. Returns an ERR_PTR on error. Pages are
189 * buffered inside the dio so that we can call get_user_pages() against a
190 * decent number of pages, less frequently. To provide nicer use of the
191 * L1 cache.
192 */
193static struct page *dio_get_page(struct dio *dio)
194{
195    if (dio_pages_present(dio) == 0) {
196        int ret;
197
198        ret = dio_refill_pages(dio);
199        if (ret)
200            return ERR_PTR(ret);
201        BUG_ON(dio_pages_present(dio) == 0);
202    }
203    return dio->pages[dio->head++];
204}
205
206/**
207 * dio_complete() - called when all DIO BIO I/O has been completed
208 * @offset: the byte offset in the file of the completed operation
209 *
210 * This releases locks as dictated by the locking type, lets interested parties
211 * know that a DIO operation has completed, and calculates the resulting return
212 * code for the operation.
213 *
214 * It lets the filesystem know if it registered an interest earlier via
215 * get_block. Pass the private field of the map buffer_head so that
216 * filesystems can use it to hold additional state between get_block calls and
217 * dio_complete.
218 */
219static int dio_complete(struct dio *dio, loff_t offset, int ret)
220{
221    ssize_t transferred = 0;
222
223    /*
224     * AIO submission can race with bio completion to get here while
225     * expecting to have the last io completed by bio completion.
226     * In that case -EIOCBQUEUED is in fact not an error we want
227     * to preserve through this call.
228     */
229    if (ret == -EIOCBQUEUED)
230        ret = 0;
231
232    if (dio->result) {
233        transferred = dio->result;
234
235        /* Check for short read case */
236        if ((dio->rw == READ) && ((offset + transferred) > dio->i_size))
237            transferred = dio->i_size - offset;
238    }
239
240    if (dio->end_io && dio->result)
241        dio->end_io(dio->iocb, offset, transferred,
242                dio->map_bh.b_private);
243    if (dio->lock_type == 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        create = dio->rw & WRITE;
519        if (dio->lock_type == DIO_LOCKING) {
520            if (dio->block_in_file < (i_size_read(dio->inode) >>
521                            dio->blkbits))
522                create = 0;
523        } else if (dio->lock_type == DIO_NO_LOCKING) {
524            create = 0;
525        }
526
527        /*
528         * For writes inside i_size we forbid block creations: only
529         * overwrites are permitted. We fall back to buffered writes
530         * at a higher level for inside-i_size block-instantiating
531         * writes.
532         */
533        ret = (*dio->get_block)(dio->inode, fs_startblk,
534                        map_bh, create);
535    }
536    return ret;
537}
538
539/*
540 * There is no bio. Make one now.
541 */
542static int dio_new_bio(struct dio *dio, sector_t start_sector)
543{
544    sector_t sector;
545    int ret, nr_pages;
546
547    ret = dio_bio_reap(dio);
548    if (ret)
549        goto out;
550    sector = start_sector << (dio->blkbits - 9);
551    nr_pages = min(dio->pages_in_io, bio_get_nr_vecs(dio->map_bh.b_bdev));
552    BUG_ON(nr_pages <= 0);
553    ret = dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages);
554    dio->boundary = 0;
555out:
556    return ret;
557}
558
559/*
560 * Attempt to put the current chunk of 'cur_page' into the current BIO. If
561 * that was successful then update final_block_in_bio and take a ref against
562 * the just-added page.
563 *
564 * Return zero on success. Non-zero means the caller needs to start a new BIO.
565 */
566static int dio_bio_add_page(struct dio *dio)
567{
568    int ret;
569
570    ret = bio_add_page(dio->bio, dio->cur_page,
571            dio->cur_page_len, dio->cur_page_offset);
572    if (ret == dio->cur_page_len) {
573        /*
574         * Decrement count only, if we are done with this page
575         */
576        if ((dio->cur_page_len + dio->cur_page_offset) == PAGE_SIZE)
577            dio->pages_in_io--;
578        page_cache_get(dio->cur_page);
579        dio->final_block_in_bio = dio->cur_page_block +
580            (dio->cur_page_len >> dio->blkbits);
581        ret = 0;
582    } else {
583        ret = 1;
584    }
585    return ret;
586}
587        
588/*
589 * Put cur_page under IO. The section of cur_page which is described by
590 * cur_page_offset,cur_page_len is put into a BIO. The section of cur_page
591 * starts on-disk at cur_page_block.
592 *
593 * We take a ref against the page here (on behalf of its presence in the bio).
594 *
595 * The caller of this function is responsible for removing cur_page from the
596 * dio, and for dropping the refcount which came from that presence.
597 */
598static int dio_send_cur_page(struct dio *dio)
599{
600    int ret = 0;
601
602    if (dio->bio) {
603        /*
604         * See whether this new request is contiguous with the old
605         */
606        if (dio->final_block_in_bio != dio->cur_page_block)
607            dio_bio_submit(dio);
608        /*
609         * Submit now if the underlying fs is about to perform a
610         * metadata read
611         */
612        if (dio->boundary)
613            dio_bio_submit(dio);
614    }
615
616    if (dio->bio == NULL) {
617        ret = dio_new_bio(dio, dio->cur_page_block);
618        if (ret)
619            goto out;
620    }
621
622    if (dio_bio_add_page(dio) != 0) {
623        dio_bio_submit(dio);
624        ret = dio_new_bio(dio, dio->cur_page_block);
625        if (ret == 0) {
626            ret = dio_bio_add_page(dio);
627            BUG_ON(ret != 0);
628        }
629    }
630out:
631    return ret;
632}
633
634/*
635 * An autonomous function to put a chunk of a page under deferred IO.
636 *
637 * The caller doesn't actually know (or care) whether this piece of page is in
638 * a BIO, or is under IO or whatever. We just take care of all possible
639 * situations here. The separation between the logic of do_direct_IO() and
640 * that of submit_page_section() is important for clarity. Please don't break.
641 *
642 * The chunk of page starts on-disk at blocknr.
643 *
644 * We perform deferred IO, by recording the last-submitted page inside our
645 * private part of the dio structure. If possible, we just expand the IO
646 * across that page here.
647 *
648 * If that doesn't work out then we put the old page into the bio and add this
649 * page to the dio instead.
650 */
651static int
652submit_page_section(struct dio *dio, struct page *page,
653        unsigned offset, unsigned len, sector_t blocknr)
654{
655    int ret = 0;
656
657    if (dio->rw & WRITE) {
658        /*
659         * Read accounting is performed in submit_bio()
660         */
661        task_io_account_write(len);
662    }
663
664    /*
665     * Can we just grow the current page's presence in the dio?
666     */
667    if ( (dio->cur_page == page) &&
668        (dio->cur_page_offset + dio->cur_page_len == offset) &&
669        (dio->cur_page_block +
670            (dio->cur_page_len >> dio->blkbits) == blocknr)) {
671        dio->cur_page_len += len;
672
673        /*
674         * If dio->boundary then we want to schedule the IO now to
675         * avoid metadata seeks.
676         */
677        if (dio->boundary) {
678            ret = dio_send_cur_page(dio);
679            page_cache_release(dio->cur_page);
680            dio->cur_page = NULL;
681        }
682        goto out;
683    }
684
685    /*
686     * If there's a deferred page already there then send it.
687     */
688    if (dio->cur_page) {
689        ret = dio_send_cur_page(dio);
690        page_cache_release(dio->cur_page);
691        dio->cur_page = NULL;
692        if (ret)
693            goto out;
694    }
695
696    page_cache_get(page); /* It is in dio */
697    dio->cur_page = page;
698    dio->cur_page_offset = offset;
699    dio->cur_page_len = len;
700    dio->cur_page_block = blocknr;
701out:
702    return ret;
703}
704
705/*
706 * Clean any dirty buffers in the blockdev mapping which alias newly-created
707 * file blocks. Only called for S_ISREG files - blockdevs do not set
708 * buffer_new
709 */
710static void clean_blockdev_aliases(struct dio *dio)
711{
712    unsigned i;
713    unsigned nblocks;
714
715    nblocks = dio->map_bh.b_size >> dio->inode->i_blkbits;
716
717    for (i = 0; i < nblocks; i++) {
718        unmap_underlying_metadata(dio->map_bh.b_bdev,
719                    dio->map_bh.b_blocknr + i);
720    }
721}
722
723/*
724 * If we are not writing the entire block and get_block() allocated
725 * the block for us, we need to fill-in the unused portion of the
726 * block with zeros. This happens only if user-buffer, fileoffset or
727 * io length is not filesystem block-size multiple.
728 *
729 * `end' is zero if we're doing the start of the IO, 1 at the end of the
730 * IO.
731 */
732static void dio_zero_block(struct dio *dio, int end)
733{
734    unsigned dio_blocks_per_fs_block;
735    unsigned this_chunk_blocks; /* In dio_blocks */
736    unsigned this_chunk_bytes;
737    struct page *page;
738
739    dio->start_zero_done = 1;
740    if (!dio->blkfactor || !buffer_new(&dio->map_bh))
741        return;
742
743    dio_blocks_per_fs_block = 1 << dio->blkfactor;
744    this_chunk_blocks = dio->block_in_file & (dio_blocks_per_fs_block - 1);
745
746    if (!this_chunk_blocks)
747        return;
748
749    /*
750     * We need to zero out part of an fs block. It is either at the
751     * beginning or the end of the fs block.
752     */
753    if (end)
754        this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
755
756    this_chunk_bytes = this_chunk_blocks << dio->blkbits;
757
758    page = ZERO_PAGE(0);
759    if (submit_page_section(dio, page, 0, this_chunk_bytes,
760                dio->next_block_for_io))
761        return;
762
763    dio->next_block_for_io += this_chunk_blocks;
764}
765
766/*
767 * Walk the user pages, and the file, mapping blocks to disk and generating
768 * a sequence of (page,offset,len,block) mappings. These mappings are injected
769 * into submit_page_section(), which takes care of the next stage of submission
770 *
771 * Direct IO against a blockdev is different from a file. Because we can
772 * happily perform page-sized but 512-byte aligned IOs. It is important that
773 * blockdev IO be able to have fine alignment and large sizes.
774 *
775 * So what we do is to permit the ->get_block function to populate bh.b_size
776 * with the size of IO which is permitted at this offset and this i_blkbits.
777 *
778 * For best results, the blockdev should be set up with 512-byte i_blkbits and
779 * it should set b_size to PAGE_SIZE or more inside get_block(). This gives
780 * fine alignment but still allows this function to work in PAGE_SIZE units.
781 */
782static int do_direct_IO(struct dio *dio)
783{
784    const unsigned blkbits = dio->blkbits;
785    const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
786    struct page *page;
787    unsigned block_in_page;
788    struct buffer_head *map_bh = &dio->map_bh;
789    int ret = 0;
790
791    /* The I/O can start at any block offset within the first page */
792    block_in_page = dio->first_block_in_page;
793
794    while (dio->block_in_file < dio->final_block_in_request) {
795        page = dio_get_page(dio);
796        if (IS_ERR(page)) {
797            ret = PTR_ERR(page);
798            goto out;
799        }
800
801        while (block_in_page < blocks_per_page) {
802            unsigned offset_in_page = block_in_page << blkbits;
803            unsigned this_chunk_bytes; /* # of bytes mapped */
804            unsigned this_chunk_blocks; /* # of blocks */
805            unsigned u;
806
807            if (dio->blocks_available == 0) {
808                /*
809                 * Need to go and map some more disk
810                 */
811                unsigned long blkmask;
812                unsigned long dio_remainder;
813
814                ret = get_more_blocks(dio);
815                if (ret) {
816                    page_cache_release(page);
817                    goto out;
818                }
819                if (!buffer_mapped(map_bh))
820                    goto do_holes;
821
822                dio->blocks_available =
823                        map_bh->b_size >> dio->blkbits;
824                dio->next_block_for_io =
825                    map_bh->b_blocknr << dio->blkfactor;
826                if (buffer_new(map_bh))
827                    clean_blockdev_aliases(dio);
828
829                if (!dio->blkfactor)
830                    goto do_holes;
831
832                blkmask = (1 << dio->blkfactor) - 1;
833                dio_remainder = (dio->block_in_file & blkmask);
834
835                /*
836                 * If we are at the start of IO and that IO
837                 * starts partway into a fs-block,
838                 * dio_remainder will be non-zero. If the IO
839                 * is a read then we can simply advance the IO
840                 * cursor to the first block which is to be
841                 * read. But if the IO is a write and the
842                 * block was newly allocated we cannot do that;
843                 * the start of the fs block must be zeroed out
844                 * on-disk
845                 */
846                if (!buffer_new(map_bh))
847                    dio->next_block_for_io += dio_remainder;
848                dio->blocks_available -= dio_remainder;
849            }
850do_holes:
851            /* Handle holes */
852            if (!buffer_mapped(map_bh)) {
853                loff_t i_size_aligned;
854
855                /* AKPM: eargh, -ENOTBLK is a hack */
856                if (dio->rw & WRITE) {
857                    page_cache_release(page);
858                    return -ENOTBLK;
859                }
860
861                /*
862                 * Be sure to account for a partial block as the
863                 * last block in the file
864                 */
865                i_size_aligned = ALIGN(i_size_read(dio->inode),
866                            1 << blkbits);
867                if (dio->block_in_file >=
868                        i_size_aligned >> blkbits) {
869                    /* We hit eof */
870                    page_cache_release(page);
871                    goto out;
872                }
873                zero_user(page, block_in_page << blkbits,
874                        1 << blkbits);
875                dio->block_in_file++;
876                block_in_page++;
877                goto next_block;
878            }
879
880            /*
881             * If we're performing IO which has an alignment which
882             * is finer than the underlying fs, go check to see if
883             * we must zero out the start of this block.
884             */
885            if (unlikely(dio->blkfactor && !dio->start_zero_done))
886                dio_zero_block(dio, 0);
887
888            /*
889             * Work out, in this_chunk_blocks, how much disk we
890             * can add to this page
891             */
892            this_chunk_blocks = dio->blocks_available;
893            u = (PAGE_SIZE - offset_in_page) >> blkbits;
894            if (this_chunk_blocks > u)
895                this_chunk_blocks = u;
896            u = dio->final_block_in_request - dio->block_in_file;
897            if (this_chunk_blocks > u)
898                this_chunk_blocks = u;
899            this_chunk_bytes = this_chunk_blocks << blkbits;
900            BUG_ON(this_chunk_bytes == 0);
901
902            dio->boundary = buffer_boundary(map_bh);
903            ret = submit_page_section(dio, page, offset_in_page,
904                this_chunk_bytes, dio->next_block_for_io);
905            if (ret) {
906                page_cache_release(page);
907                goto out;
908            }
909            dio->next_block_for_io += this_chunk_blocks;
910
911            dio->block_in_file += this_chunk_blocks;
912            block_in_page += this_chunk_blocks;
913            dio->blocks_available -= this_chunk_blocks;
914next_block:
915            BUG_ON(dio->block_in_file > dio->final_block_in_request);
916            if (dio->block_in_file == dio->final_block_in_request)
917                break;
918        }
919
920        /* Drop the ref which was taken in get_user_pages() */
921        page_cache_release(page);
922        block_in_page = 0;
923    }
924out:
925    return ret;
926}
927
928/*
929 * Releases both i_mutex and i_alloc_sem
930 */
931static ssize_t
932direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
933    const struct iovec *iov, loff_t offset, unsigned long nr_segs,
934    unsigned blkbits, get_block_t get_block, dio_iodone_t end_io,
935    struct dio *dio)
936{
937    unsigned long user_addr;
938    unsigned long flags;
939    int seg;
940    ssize_t ret = 0;
941    ssize_t ret2;
942    size_t bytes;
943
944    dio->inode = inode;
945    dio->rw = rw;
946    dio->blkbits = blkbits;
947    dio->blkfactor = inode->i_blkbits - blkbits;
948    dio->block_in_file = offset >> blkbits;
949
950    dio->get_block = get_block;
951    dio->end_io = end_io;
952    dio->final_block_in_bio = -1;
953    dio->next_block_for_io = -1;
954
955    dio->iocb = iocb;
956    dio->i_size = i_size_read(inode);
957
958    spin_lock_init(&dio->bio_lock);
959    dio->refcount = 1;
960
961    /*
962     * In case of non-aligned buffers, we may need 2 more
963     * pages since we need to zero out first and last block.
964     */
965    if (unlikely(dio->blkfactor))
966        dio->pages_in_io = 2;
967
968    for (seg = 0; seg < nr_segs; seg++) {
969        user_addr = (unsigned long)iov[seg].iov_base;
970        dio->pages_in_io +=
971            ((user_addr+iov[seg].iov_len +PAGE_SIZE-1)/PAGE_SIZE
972                - user_addr/PAGE_SIZE);
973    }
974
975    for (seg = 0; seg < nr_segs; seg++) {
976        user_addr = (unsigned long)iov[seg].iov_base;
977        dio->size += bytes = iov[seg].iov_len;
978
979        /* Index into the first page of the first block */
980        dio->first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits;
981        dio->final_block_in_request = dio->block_in_file +
982                        (bytes >> blkbits);
983        /* Page fetching state */
984        dio->head = 0;
985        dio->tail = 0;
986        dio->curr_page = 0;
987
988        dio->total_pages = 0;
989        if (user_addr & (PAGE_SIZE-1)) {
990            dio->total_pages++;
991            bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1));
992        }
993        dio->total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
994        dio->curr_user_address = user_addr;
995    
996        ret = do_direct_IO(dio);
997
998        dio->result += iov[seg].iov_len -
999            ((dio->final_block_in_request - dio->block_in_file) <<
1000                    blkbits);
1001
1002        if (ret) {
1003            dio_cleanup(dio);
1004            break;
1005        }
1006    } /* end iovec loop */
1007
1008    if (ret == -ENOTBLK && (rw & WRITE)) {
1009        /*
1010         * The remaining part of the request will be
1011         * be handled by buffered I/O when we return
1012         */
1013        ret = 0;
1014    }
1015    /*
1016     * There may be some unwritten disk at the end of a part-written
1017     * fs-block-sized block. Go zero that now.
1018     */
1019    dio_zero_block(dio, 1);
1020
1021    if (dio->cur_page) {
1022        ret2 = dio_send_cur_page(dio);
1023        if (ret == 0)
1024            ret = ret2;
1025        page_cache_release(dio->cur_page);
1026        dio->cur_page = NULL;
1027    }
1028    if (dio->bio)
1029        dio_bio_submit(dio);
1030
1031    /* All IO is now issued, send it on its way */
1032    blk_run_address_space(inode->i_mapping);
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->lock_type == 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        dio_await_completion(dio);
1062
1063    /*
1064     * Sync will always be dropping the final ref and completing the
1065     * operation. AIO can if it was a broken operation described above or
1066     * in fact if all the bios race to complete before we get here. In
1067     * that case dio_complete() translates the EIOCBQUEUED into the proper
1068     * return code that the caller will hand to aio_complete().
1069     *
1070     * This is managed by the bio_lock instead of being an atomic_t so that
1071     * completion paths can drop their ref and use the remaining count to
1072     * decide to wake the submission path atomically.
1073     */
1074    spin_lock_irqsave(&dio->bio_lock, flags);
1075    ret2 = --dio->refcount;
1076    spin_unlock_irqrestore(&dio->bio_lock, flags);
1077
1078    if (ret2 == 0) {
1079        ret = dio_complete(dio, offset, ret);
1080        kfree(dio);
1081    } else
1082        BUG_ON(ret != -EIOCBQUEUED);
1083
1084    return ret;
1085}
1086
1087/*
1088 * This is a library function for use by filesystem drivers.
1089 * The locking rules are governed by the dio_lock_type parameter.
1090 *
1091 * DIO_NO_LOCKING (no locking, for raw block device access)
1092 * For writes, i_mutex is not held on entry; it is never taken.
1093 *
1094 * DIO_LOCKING (simple locking for regular files)
1095 * For writes we are called under i_mutex and return with i_mutex held, even
1096 * though it is internally dropped.
1097 * For reads, i_mutex is not held on entry, but it is taken and dropped before
1098 * returning.
1099 *
1100 * DIO_OWN_LOCKING (filesystem provides synchronisation and handling of
1101 * uninitialised data, allowing parallel direct readers and writers)
1102 * For writes we are called without i_mutex, return without it, never touch it.
1103 * For reads we are called under i_mutex and return with i_mutex held, even
1104 * though it may be internally dropped.
1105 *
1106 * Additional i_alloc_sem locking requirements described inline below.
1107 */
1108ssize_t
1109__blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
1110    struct block_device *bdev, const struct iovec *iov, loff_t offset,
1111    unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io,
1112    int dio_lock_type)
1113{
1114    int seg;
1115    size_t size;
1116    unsigned long addr;
1117    unsigned blkbits = inode->i_blkbits;
1118    unsigned bdev_blkbits = 0;
1119    unsigned blocksize_mask = (1 << blkbits) - 1;
1120    ssize_t retval = -EINVAL;
1121    loff_t end = offset;
1122    struct dio *dio;
1123    int release_i_mutex = 0;
1124    int acquire_i_mutex = 0;
1125
1126    if (rw & WRITE)
1127        rw = WRITE_ODIRECT;
1128
1129    if (bdev)
1130        bdev_blkbits = blksize_bits(bdev_logical_block_size(bdev));
1131
1132    if (offset & blocksize_mask) {
1133        if (bdev)
1134             blkbits = bdev_blkbits;
1135        blocksize_mask = (1 << blkbits) - 1;
1136        if (offset & blocksize_mask)
1137            goto out;
1138    }
1139
1140    /* Check the memory alignment. Blocks cannot straddle pages */
1141    for (seg = 0; seg < nr_segs; seg++) {
1142        addr = (unsigned long)iov[seg].iov_base;
1143        size = iov[seg].iov_len;
1144        end += size;
1145        if ((addr & blocksize_mask) || (size & blocksize_mask)) {
1146            if (bdev)
1147                 blkbits = bdev_blkbits;
1148            blocksize_mask = (1 << blkbits) - 1;
1149            if ((addr & blocksize_mask) || (size & blocksize_mask))
1150                goto out;
1151        }
1152    }
1153
1154    dio = kzalloc(sizeof(*dio), GFP_KERNEL);
1155    retval = -ENOMEM;
1156    if (!dio)
1157        goto out;
1158
1159    /*
1160     * For block device access DIO_NO_LOCKING is used,
1161     * neither readers nor writers do any locking at all
1162     * For regular files using DIO_LOCKING,
1163     * readers need to grab i_mutex and i_alloc_sem
1164     * writers need to grab i_alloc_sem only (i_mutex is already held)
1165     * For regular files using DIO_OWN_LOCKING,
1166     * neither readers nor writers take any locks here
1167     */
1168    dio->lock_type = dio_lock_type;
1169    if (dio_lock_type != DIO_NO_LOCKING) {
1170        /* watch out for a 0 len io from a tricksy fs */
1171        if (rw == READ && end > offset) {
1172            struct address_space *mapping;
1173
1174            mapping = iocb->ki_filp->f_mapping;
1175            if (dio_lock_type != DIO_OWN_LOCKING) {
1176                mutex_lock(&inode->i_mutex);
1177                release_i_mutex = 1;
1178            }
1179
1180            retval = filemap_write_and_wait_range(mapping, offset,
1181                                  end - 1);
1182            if (retval) {
1183                kfree(dio);
1184                goto out;
1185            }
1186
1187            if (dio_lock_type == DIO_OWN_LOCKING) {
1188                mutex_unlock(&inode->i_mutex);
1189                acquire_i_mutex = 1;
1190            }
1191        }
1192
1193        if (dio_lock_type == DIO_LOCKING)
1194            /* lockdep: not the owner will release it */
1195            down_read_non_owner(&inode->i_alloc_sem);
1196    }
1197
1198    /*
1199     * For file extending writes updating i_size before data
1200     * writeouts complete can expose uninitialized blocks. So
1201     * even for AIO, we need to wait for i/o to complete before
1202     * returning in this case.
1203     */
1204    dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) &&
1205        (end > i_size_read(inode)));
1206
1207    retval = direct_io_worker(rw, iocb, inode, iov, offset,
1208                nr_segs, blkbits, get_block, end_io, dio);
1209
1210    /*
1211     * In case of error extending write may have instantiated a few
1212     * blocks outside i_size. Trim these off again for DIO_LOCKING.
1213     * NOTE: DIO_NO_LOCK/DIO_OWN_LOCK callers have to handle this by
1214     * it's own meaner.
1215     */
1216    if (unlikely(retval < 0 && (rw & WRITE))) {
1217        loff_t isize = i_size_read(inode);
1218
1219        if (end > isize && dio_lock_type == DIO_LOCKING)
1220            vmtruncate(inode, isize);
1221    }
1222
1223    if (rw == READ && dio_lock_type == DIO_LOCKING)
1224        release_i_mutex = 0;
1225
1226out:
1227    if (release_i_mutex)
1228        mutex_unlock(&inode->i_mutex);
1229    else if (acquire_i_mutex)
1230        mutex_lock(&inode->i_mutex);
1231    return retval;
1232}
1233EXPORT_SYMBOL(__blockdev_direct_IO);
1234

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