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1/*
2 * fs/direct-io.c
3 *
4 * Copyright (C) 2002, Linus Torvalds.
5 *
6 * O_DIRECT
7 *
8 * 04Jul2002 akpm@zip.com.au
9 * Initial version
10 * 11Sep2002 janetinc@us.ibm.com
11 * added readv/writev support.
12 * 29Oct2002 akpm@zip.com.au
13 * rewrote bio_add_page() support.
14 * 30Oct2002 pbadari@us.ibm.com
15 * added support for non-aligned IO.
16 * 06Nov2002 pbadari@us.ibm.com
17 * added asynchronous IO support.
18 * 21Jul2003 nathans@sgi.com
19 * added IO completion notifier.
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/bio.h>
31#include <linux/wait.h>
32#include <linux/err.h>
33#include <linux/blkdev.h>
34#include <linux/buffer_head.h>
35#include <linux/rwsem.h>
36#include <linux/uio.h>
37#include <asm/atomic.h>
38
39/*
40 * How many user pages to map in one call to get_user_pages(). This determines
41 * the size of a structure on the stack.
42 */
43#define DIO_PAGES 64
44
45/*
46 * This code generally works in units of "dio_blocks". A dio_block is
47 * somewhere between the hard sector size and the filesystem block size. it
48 * is determined on a per-invocation basis. When talking to the filesystem
49 * we need to convert dio_blocks to fs_blocks by scaling the dio_block quantity
50 * down by dio->blkfactor. Similarly, fs-blocksize quantities are converted
51 * to bio_block quantities by shifting left by blkfactor.
52 *
53 * If blkfactor is zero then the user's request was aligned to the filesystem's
54 * blocksize.
55 *
56 * lock_type is DIO_LOCKING for regular files on direct-IO-naive filesystems.
57 * This determines whether we need to do the fancy locking which prevents
58 * direct-IO from being able to read uninitialised disk blocks. If its zero
59 * (blockdev) this locking is not done, and if it is DIO_OWN_LOCKING i_sem is
60 * not held for the entire direct write (taken briefly, initially, during a
61 * direct read though, but its never held for the duration of a direct-IO).
62 */
63
64struct dio {
65 /* BIO submission state */
66 struct bio *bio; /* bio under assembly */
67 struct inode *inode;
68 int rw;
69 int lock_type; /* doesn't change */
70 unsigned blkbits; /* doesn't change */
71 unsigned blkfactor; /* When we're using an alignment which
72 is finer than the filesystem's soft
73 blocksize, this specifies how much
74 finer. blkfactor=2 means 1/4-block
75 alignment. Does not change */
76 unsigned start_zero_done; /* flag: sub-blocksize zeroing has
77 been performed at the start of a
78 write */
79 int pages_in_io; /* approximate total IO pages */
80 size_t size; /* total request size (doesn't change)*/
81 sector_t block_in_file; /* Current offset into the underlying
82 file in dio_block units. */
83 unsigned blocks_available; /* At block_in_file. changes */
84 sector_t final_block_in_request;/* doesn't change */
85 unsigned first_block_in_page; /* doesn't change, Used only once */
86 int boundary; /* prev block is at a boundary */
87 int reap_counter; /* rate limit reaping */
88 get_blocks_t *get_blocks; /* block mapping function */
89 dio_iodone_t *end_io; /* IO completion function */
90 sector_t final_block_in_bio; /* current final block in bio + 1 */
91 sector_t next_block_for_io; /* next block to be put under IO,
92 in dio_blocks units */
93 struct buffer_head map_bh; /* last get_blocks() result */
94
95 /*
96 * Deferred addition of a page to the dio. These variables are
97 * private to dio_send_cur_page(), submit_page_section() and
98 * dio_bio_add_page().
99 */
100 struct page *cur_page; /* The page */
101 unsigned cur_page_offset; /* Offset into it, in bytes */
102 unsigned cur_page_len; /* Nr of bytes at cur_page_offset */
103 sector_t cur_page_block; /* Where it starts */
104
105 /*
106 * Page fetching state. These variables belong to dio_refill_pages().
107 */
108 int curr_page; /* changes */
109 int total_pages; /* doesn't change */
110 unsigned long curr_user_address;/* changes */
111
112 /*
113 * Page queue. These variables belong to dio_refill_pages() and
114 * dio_get_page().
115 */
116 struct page *pages[DIO_PAGES]; /* page buffer */
117 unsigned head; /* next page to process */
118 unsigned tail; /* last valid page + 1 */
119 int page_errors; /* errno from get_user_pages() */
120
121 /* BIO completion state */
122 spinlock_t bio_lock; /* protects BIO fields below */
123 int bio_count; /* nr bios to be completed */
124 int bios_in_flight; /* nr bios in flight */
125 struct bio *bio_list; /* singly linked via bi_private */
126 struct task_struct *waiter; /* waiting task (NULL if none) */
127
128 /* AIO related stuff */
129 struct kiocb *iocb; /* kiocb */
130 int is_async; /* is IO async ? */
131 ssize_t result; /* IO result */
132};
133
134/*
135 * How many pages are in the queue?
136 */
137static inline unsigned dio_pages_present(struct dio *dio)
138{
139 return dio->tail - dio->head;
140}
141
142/*
143 * Go grab and pin some userspace pages. Typically we'll get 64 at a time.
144 */
145static int dio_refill_pages(struct dio *dio)
146{
147 int ret;
148 int nr_pages;
149
150 nr_pages = min(dio->total_pages - dio->curr_page, DIO_PAGES);
151 down_read(&current->mm->mmap_sem);
152 ret = get_user_pages(
153 current, /* Task for fault acounting */
154 current->mm, /* whose pages? */
155 dio->curr_user_address, /* Where from? */
156 nr_pages, /* How many pages? */
157 dio->rw == READ, /* Write to memory? */
158 0, /* force (?) */
159 &dio->pages[0],
160 NULL); /* vmas */
161 up_read(&current->mm->mmap_sem);
162
163 if (ret < 0 && dio->blocks_available && (dio->rw == WRITE)) {
164 /*
165 * A memory fault, but the filesystem has some outstanding
166 * mapped blocks. We need to use those blocks up to avoid
167 * leaking stale data in the file.
168 */
169 if (dio->page_errors == 0)
170 dio->page_errors = ret;
171 dio->pages[0] = ZERO_PAGE(dio->curr_user_address);
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 * Called when all DIO BIO I/O has been completed - let the filesystem
210 * know, if it registered an interest earlier via get_blocks. Pass the
211 * private field of the map buffer_head so that filesystems can use it
212 * to hold additional state between get_blocks calls and dio_complete.
213 */
214static void dio_complete(struct dio *dio, loff_t offset, ssize_t bytes)
215{
216 if (dio->end_io && dio->result)
217 dio->end_io(dio->inode, offset, bytes, dio->map_bh.b_private);
218 if (dio->lock_type == DIO_LOCKING)
219 up_read(&dio->inode->i_alloc_sem);
220}
221
222/*
223 * Called when a BIO has been processed. If the count goes to zero then IO is
224 * complete and we can signal this to the AIO layer.
225 */
226static void finished_one_bio(struct dio *dio)
227{
228 unsigned long flags;
229
230 spin_lock_irqsave(&dio->bio_lock, flags);
231 if (dio->bio_count == 1) {
232 if (dio->is_async) {
233 /*
234 * Last reference to the dio is going away.
235 * Drop spinlock and complete the DIO.
236 */
237 spin_unlock_irqrestore(&dio->bio_lock, flags);
238 dio_complete(dio, dio->block_in_file << dio->blkbits,
239 dio->result);
240 /* Complete AIO later if falling back to buffered i/o */
241 if (dio->result == dio->size ||
242 ((dio->rw == READ) && dio->result)) {
243 aio_complete(dio->iocb, dio->result, 0);
244 kfree(dio);
245 return;
246 } else {
247 /*
248 * Falling back to buffered
249 */
250 spin_lock_irqsave(&dio->bio_lock, flags);
251 dio->bio_count--;
252 if (dio->waiter)
253 wake_up_process(dio->waiter);
254 spin_unlock_irqrestore(&dio->bio_lock, flags);
255 return;
256 }
257 }
258 }
259 dio->bio_count--;
260 spin_unlock_irqrestore(&dio->bio_lock, flags);
261}
262
263static int dio_bio_complete(struct dio *dio, struct bio *bio);
264/*
265 * Asynchronous IO callback.
266 */
267static int dio_bio_end_aio(struct bio *bio, unsigned int bytes_done, int error)
268{
269 struct dio *dio = bio->bi_private;
270
271 if (bio->bi_size)
272 return 1;
273
274 /* cleanup the bio */
275 dio_bio_complete(dio, bio);
276 return 0;
277}
278
279/*
280 * The BIO completion handler simply queues the BIO up for the process-context
281 * handler.
282 *
283 * During I/O bi_private points at the dio. After I/O, bi_private is used to
284 * implement a singly-linked list of completed BIOs, at dio->bio_list.
285 */
286static int dio_bio_end_io(struct bio *bio, unsigned int bytes_done, int error)
287{
288 struct dio *dio = bio->bi_private;
289 unsigned long flags;
290
291 if (bio->bi_size)
292 return 1;
293
294 spin_lock_irqsave(&dio->bio_lock, flags);
295 bio->bi_private = dio->bio_list;
296 dio->bio_list = bio;
297 dio->bios_in_flight--;
298 if (dio->waiter && dio->bios_in_flight == 0)
299 wake_up_process(dio->waiter);
300 spin_unlock_irqrestore(&dio->bio_lock, flags);
301 return 0;
302}
303
304static int
305dio_bio_alloc(struct dio *dio, struct block_device *bdev,
306 sector_t first_sector, int nr_vecs)
307{
308 struct bio *bio;
309
310 bio = bio_alloc(GFP_KERNEL, nr_vecs);
311 if (bio == NULL)
312 return -ENOMEM;
313
314 bio->bi_bdev = bdev;
315 bio->bi_sector = first_sector;
316 if (dio->is_async)
317 bio->bi_end_io = dio_bio_end_aio;
318 else
319 bio->bi_end_io = dio_bio_end_io;
320
321 dio->bio = bio;
322 return 0;
323}
324
325/*
326 * In the AIO read case we speculatively dirty the pages before starting IO.
327 * During IO completion, any of these pages which happen to have been written
328 * back will be redirtied by bio_check_pages_dirty().
329 */
330static void dio_bio_submit(struct dio *dio)
331{
332 struct bio *bio = dio->bio;
333 unsigned long flags;
334
335 bio->bi_private = dio;
336 spin_lock_irqsave(&dio->bio_lock, flags);
337 dio->bio_count++;
338 dio->bios_in_flight++;
339 spin_unlock_irqrestore(&dio->bio_lock, flags);
340 if (dio->is_async && dio->rw == READ)
341 bio_set_pages_dirty(bio);
342 submit_bio(dio->rw, bio);
343
344 dio->bio = NULL;
345 dio->boundary = 0;
346}
347
348/*
349 * Release any resources in case of a failure
350 */
351static void dio_cleanup(struct dio *dio)
352{
353 while (dio_pages_present(dio))
354 page_cache_release(dio_get_page(dio));
355}
356
357/*
358 * Wait for the next BIO to complete. Remove it and return it.
359 */
360static struct bio *dio_await_one(struct dio *dio)
361{
362 unsigned long flags;
363 struct bio *bio;
364
365 spin_lock_irqsave(&dio->bio_lock, flags);
366 while (dio->bio_list == NULL) {
367 set_current_state(TASK_UNINTERRUPTIBLE);
368 if (dio->bio_list == NULL) {
369 dio->waiter = current;
370 spin_unlock_irqrestore(&dio->bio_lock, flags);
371 blk_run_address_space(dio->inode->i_mapping);
372 io_schedule();
373 spin_lock_irqsave(&dio->bio_lock, flags);
374 dio->waiter = NULL;
375 }
376 set_current_state(TASK_RUNNING);
377 }
378 bio = dio->bio_list;
379 dio->bio_list = bio->bi_private;
380 spin_unlock_irqrestore(&dio->bio_lock, flags);
381 return bio;
382}
383
384/*
385 * Process one completed BIO. No locks are held.
386 */
387static int dio_bio_complete(struct dio *dio, struct bio *bio)
388{
389 const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
390 struct bio_vec *bvec = bio->bi_io_vec;
391 int page_no;
392
393 if (!uptodate)
394 dio->result = -EIO;
395
396 if (dio->is_async && dio->rw == READ) {
397 bio_check_pages_dirty(bio); /* transfers ownership */
398 } else {
399 for (page_no = 0; page_no < bio->bi_vcnt; page_no++) {
400 struct page *page = bvec[page_no].bv_page;
401
402 if (dio->rw == READ && !PageCompound(page))
403 set_page_dirty_lock(page);
404 page_cache_release(page);
405 }
406 bio_put(bio);
407 }
408 finished_one_bio(dio);
409 return uptodate ? 0 : -EIO;
410}
411
412/*
413 * Wait on and process all in-flight BIOs.
414 */
415static int dio_await_completion(struct dio *dio)
416{
417 int ret = 0;
418
419 if (dio->bio)
420 dio_bio_submit(dio);
421
422 /*
423 * The bio_lock is not held for the read of bio_count.
424 * This is ok since it is the dio_bio_complete() that changes
425 * bio_count.
426 */
427 while (dio->bio_count) {
428 struct bio *bio = dio_await_one(dio);
429 int ret2;
430
431 ret2 = dio_bio_complete(dio, bio);
432 if (ret == 0)
433 ret = ret2;
434 }
435 return ret;
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_blocks() 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_blocks() 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 map_bh->b_state = 0;
508 map_bh->b_size = 0;
509 BUG_ON(dio->block_in_file >= dio->final_block_in_request);
510 fs_startblk = dio->block_in_file >> dio->blkfactor;
511 dio_count = dio->final_block_in_request - dio->block_in_file;
512 fs_count = dio_count >> dio->blkfactor;
513 blkmask = (1 << dio->blkfactor) - 1;
514 if (dio_count & blkmask)
515 fs_count++;
516
517 create = dio->rw == WRITE;
518 if (dio->lock_type == DIO_LOCKING) {
519 if (dio->block_in_file < (i_size_read(dio->inode) >>
520 dio->blkbits))
521 create = 0;
522 } else if (dio->lock_type == DIO_NO_LOCKING) {
523 create = 0;
524 }
525 /*
526 * For writes inside i_size we forbid block creations: only
527 * overwrites are permitted. We fall back to buffered writes
528 * at a higher level for inside-i_size block-instantiating
529 * writes.
530 */
531 ret = (*dio->get_blocks)(dio->inode, fs_startblk, fs_count,
532 map_bh, create);
533 }
534 return ret;
535}
536
537/*
538 * There is no bio. Make one now.
539 */
540static int dio_new_bio(struct dio *dio, sector_t start_sector)
541{
542 sector_t sector;
543 int ret, nr_pages;
544
545 ret = dio_bio_reap(dio);
546 if (ret)
547 goto out;
548 sector = start_sector << (dio->blkbits - 9);
549 nr_pages = min(dio->pages_in_io, bio_get_nr_vecs(dio->map_bh.b_bdev));
550 BUG_ON(nr_pages <= 0);
551 ret = dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages);
552 dio->boundary = 0;
553out:
554 return ret;
555}
556
557/*
558 * Attempt to put the current chunk of 'cur_page' into the current BIO. If
559 * that was successful then update final_block_in_bio and take a ref against
560 * the just-added page.
561 *
562 * Return zero on success. Non-zero means the caller needs to start a new BIO.
563 */
564static int dio_bio_add_page(struct dio *dio)
565{
566 int ret;
567
568 ret = bio_add_page(dio->bio, dio->cur_page,
569 dio->cur_page_len, dio->cur_page_offset);
570 if (ret == dio->cur_page_len) {
571 /*
572 * Decrement count only, if we are done with this page
573 */
574 if ((dio->cur_page_len + dio->cur_page_offset) == PAGE_SIZE)
575 dio->pages_in_io--;
576 page_cache_get(dio->cur_page);
577 dio->final_block_in_bio = dio->cur_page_block +
578 (dio->cur_page_len >> dio->blkbits);
579 ret = 0;
580 } else {
581 ret = 1;
582 }
583 return ret;
584}
585
586/*
587 * Put cur_page under IO. The section of cur_page which is described by
588 * cur_page_offset,cur_page_len is put into a BIO. The section of cur_page
589 * starts on-disk at cur_page_block.
590 *
591 * We take a ref against the page here (on behalf of its presence in the bio).
592 *
593 * The caller of this function is responsible for removing cur_page from the
594 * dio, and for dropping the refcount which came from that presence.
595 */
596static int dio_send_cur_page(struct dio *dio)
597{
598 int ret = 0;
599
600 if (dio->bio) {
601 /*
602 * See whether this new request is contiguous with the old
603 */
604 if (dio->final_block_in_bio != dio->cur_page_block)
605 dio_bio_submit(dio);
606 /*
607 * Submit now if the underlying fs is about to perform a
608 * metadata read
609 */
610 if (dio->boundary)
611 dio_bio_submit(dio);
612 }
613
614 if (dio->bio == NULL) {
615 ret = dio_new_bio(dio, dio->cur_page_block);
616 if (ret)
617 goto out;
618 }
619
620 if (dio_bio_add_page(dio) != 0) {
621 dio_bio_submit(dio);
622 ret = dio_new_bio(dio, dio->cur_page_block);
623 if (ret == 0) {
624 ret = dio_bio_add_page(dio);
625 BUG_ON(ret != 0);
626 }
627 }
628out:
629 return ret;
630}
631
632/*
633 * An autonomous function to put a chunk of a page under deferred IO.
634 *
635 * The caller doesn't actually know (or care) whether this piece of page is in
636 * a BIO, or is under IO or whatever. We just take care of all possible
637 * situations here. The separation between the logic of do_direct_IO() and
638 * that of submit_page_section() is important for clarity. Please don't break.
639 *
640 * The chunk of page starts on-disk at blocknr.
641 *
642 * We perform deferred IO, by recording the last-submitted page inside our
643 * private part of the dio structure. If possible, we just expand the IO
644 * across that page here.
645 *
646 * If that doesn't work out then we put the old page into the bio and add this
647 * page to the dio instead.
648 */
649static int
650submit_page_section(struct dio *dio, struct page *page,
651 unsigned offset, unsigned len, sector_t blocknr)
652{
653 int ret = 0;
654
655 /*
656 * Can we just grow the current page's presence in the dio?
657 */
658 if ( (dio->cur_page == page) &&
659 (dio->cur_page_offset + dio->cur_page_len == offset) &&
660 (dio->cur_page_block +
661 (dio->cur_page_len >> dio->blkbits) == blocknr)) {
662 dio->cur_page_len += len;
663
664 /*
665 * If dio->boundary then we want to schedule the IO now to
666 * avoid metadata seeks.
667 */
668 if (dio->boundary) {
669 ret = dio_send_cur_page(dio);
670 page_cache_release(dio->cur_page);
671 dio->cur_page = NULL;
672 }
673 goto out;
674 }
675
676 /*
677 * If there's a deferred page already there then send it.
678 */
679 if (dio->cur_page) {
680 ret = dio_send_cur_page(dio);
681 page_cache_release(dio->cur_page);
682 dio->cur_page = NULL;
683 if (ret)
684 goto out;
685 }
686
687 page_cache_get(page); /* It is in dio */
688 dio->cur_page = page;
689 dio->cur_page_offset = offset;
690 dio->cur_page_len = len;
691 dio->cur_page_block = blocknr;
692out:
693 return ret;
694}
695
696/*
697 * Clean any dirty buffers in the blockdev mapping which alias newly-created
698 * file blocks. Only called for S_ISREG files - blockdevs do not set
699 * buffer_new
700 */
701static void clean_blockdev_aliases(struct dio *dio)
702{
703 unsigned i;
704 unsigned nblocks;
705
706 nblocks = dio->map_bh.b_size >> dio->inode->i_blkbits;
707
708 for (i = 0; i < nblocks; i++) {
709 unmap_underlying_metadata(dio->map_bh.b_bdev,
710 dio->map_bh.b_blocknr + i);
711 }
712}
713
714/*
715 * If we are not writing the entire block and get_block() allocated
716 * the block for us, we need to fill-in the unused portion of the
717 * block with zeros. This happens only if user-buffer, fileoffset or
718 * io length is not filesystem block-size multiple.
719 *
720 * `end' is zero if we're doing the start of the IO, 1 at the end of the
721 * IO.
722 */
723static void dio_zero_block(struct dio *dio, int end)
724{
725 unsigned dio_blocks_per_fs_block;
726 unsigned this_chunk_blocks; /* In dio_blocks */
727 unsigned this_chunk_bytes;
728 struct page *page;
729
730 dio->start_zero_done = 1;
731 if (!dio->blkfactor || !buffer_new(&dio->map_bh))
732 return;
733
734 dio_blocks_per_fs_block = 1 << dio->blkfactor;
735 this_chunk_blocks = dio->block_in_file & (dio_blocks_per_fs_block - 1);
736
737 if (!this_chunk_blocks)
738 return;
739
740 /*
741 * We need to zero out part of an fs block. It is either at the
742 * beginning or the end of the fs block.
743 */
744 if (end)
745 this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
746
747 this_chunk_bytes = this_chunk_blocks << dio->blkbits;
748
749 page = ZERO_PAGE(dio->curr_user_address);
750 if (submit_page_section(dio, page, 0, this_chunk_bytes,
751 dio->next_block_for_io))
752 return;
753
754 dio->next_block_for_io += this_chunk_blocks;
755}
756
757/*
758 * Walk the user pages, and the file, mapping blocks to disk and generating
759 * a sequence of (page,offset,len,block) mappings. These mappings are injected
760 * into submit_page_section(), which takes care of the next stage of submission
761 *
762 * Direct IO against a blockdev is different from a file. Because we can
763 * happily perform page-sized but 512-byte aligned IOs. It is important that
764 * blockdev IO be able to have fine alignment and large sizes.
765 *
766 * So what we do is to permit the ->get_blocks function to populate bh.b_size
767 * with the size of IO which is permitted at this offset and this i_blkbits.
768 *
769 * For best results, the blockdev should be set up with 512-byte i_blkbits and
770 * it should set b_size to PAGE_SIZE or more inside get_blocks(). This gives
771 * fine alignment but still allows this function to work in PAGE_SIZE units.
772 */
773static int do_direct_IO(struct dio *dio)
774{
775 const unsigned blkbits = dio->blkbits;
776 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
777 struct page *page;
778 unsigned block_in_page;
779 struct buffer_head *map_bh = &dio->map_bh;
780 int ret = 0;
781
782 /* The I/O can start at any block offset within the first page */
783 block_in_page = dio->first_block_in_page;
784
785 while (dio->block_in_file < dio->final_block_in_request) {
786 page = dio_get_page(dio);
787 if (IS_ERR(page)) {
788 ret = PTR_ERR(page);
789 goto out;
790 }
791
792 while (block_in_page < blocks_per_page) {
793 unsigned offset_in_page = block_in_page << blkbits;
794 unsigned this_chunk_bytes; /* # of bytes mapped */
795 unsigned this_chunk_blocks; /* # of blocks */
796 unsigned u;
797
798 if (dio->blocks_available == 0) {
799 /*
800 * Need to go and map some more disk
801 */
802 unsigned long blkmask;
803 unsigned long dio_remainder;
804
805 ret = get_more_blocks(dio);
806 if (ret) {
807 page_cache_release(page);
808 goto out;
809 }
810 if (!buffer_mapped(map_bh))
811 goto do_holes;
812
813 dio->blocks_available =
814 map_bh->b_size >> dio->blkbits;
815 dio->next_block_for_io =
816 map_bh->b_blocknr << dio->blkfactor;
817 if (buffer_new(map_bh))
818 clean_blockdev_aliases(dio);
819
820 if (!dio->blkfactor)
821 goto do_holes;
822
823 blkmask = (1 << dio->blkfactor) - 1;
824 dio_remainder = (dio->block_in_file & blkmask);
825
826 /*
827 * If we are at the start of IO and that IO
828 * starts partway into a fs-block,
829 * dio_remainder will be non-zero. If the IO
830 * is a read then we can simply advance the IO
831 * cursor to the first block which is to be
832 * read. But if the IO is a write and the
833 * block was newly allocated we cannot do that;
834 * the start of the fs block must be zeroed out
835 * on-disk
836 */
837 if (!buffer_new(map_bh))
838 dio->next_block_for_io += dio_remainder;
839 dio->blocks_available -= dio_remainder;
840 }
841do_holes:
842 /* Handle holes */
843 if (!buffer_mapped(map_bh)) {
844 char *kaddr;
845
846 /* AKPM: eargh, -ENOTBLK is a hack */
847 if (dio->rw == WRITE) {
848 page_cache_release(page);
849 return -ENOTBLK;
850 }
851
852 if (dio->block_in_file >=
853 i_size_read(dio->inode)>>blkbits) {
854 /* We hit eof */
855 page_cache_release(page);
856 goto out;
857 }
858 kaddr = kmap_atomic(page, KM_USER0);
859 memset(kaddr + (block_in_page << blkbits),
860 0, 1 << blkbits);
861 flush_dcache_page(page);
862 kunmap_atomic(kaddr, KM_USER0);
863 dio->block_in_file++;
864 block_in_page++;
865 goto next_block;
866 }
867
868 /*
869 * If we're performing IO which has an alignment which
870 * is finer than the underlying fs, go check to see if
871 * we must zero out the start of this block.
872 */
873 if (unlikely(dio->blkfactor && !dio->start_zero_done))
874 dio_zero_block(dio, 0);
875
876 /*
877 * Work out, in this_chunk_blocks, how much disk we
878 * can add to this page
879 */
880 this_chunk_blocks = dio->blocks_available;
881 u = (PAGE_SIZE - offset_in_page) >> blkbits;
882 if (this_chunk_blocks > u)
883 this_chunk_blocks = u;
884 u = dio->final_block_in_request - dio->block_in_file;
885 if (this_chunk_blocks > u)
886 this_chunk_blocks = u;
887 this_chunk_bytes = this_chunk_blocks << blkbits;
888 BUG_ON(this_chunk_bytes == 0);
889
890 dio->boundary = buffer_boundary(map_bh);
891 ret = submit_page_section(dio, page, offset_in_page,
892 this_chunk_bytes, dio->next_block_for_io);
893 if (ret) {
894 page_cache_release(page);
895 goto out;
896 }
897 dio->next_block_for_io += this_chunk_blocks;
898
899 dio->block_in_file += this_chunk_blocks;
900 block_in_page += this_chunk_blocks;
901 dio->blocks_available -= this_chunk_blocks;
902next_block:
903 if (dio->block_in_file > dio->final_block_in_request)
904 BUG();
905 if (dio->block_in_file == dio->final_block_in_request)
906 break;
907 }
908
909 /* Drop the ref which was taken in get_user_pages() */
910 page_cache_release(page);
911 block_in_page = 0;
912 }
913out:
914 return ret;
915}
916
917/*
918 * Releases both i_sem and i_alloc_sem
919 */
920static ssize_t
921direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
922 const struct iovec *iov, loff_t offset, unsigned long nr_segs,
923 unsigned blkbits, get_blocks_t get_blocks, dio_iodone_t end_io,
924 struct dio *dio)
925{
926 unsigned long user_addr;
927 int seg;
928 ssize_t ret = 0;
929 ssize_t ret2;
930 size_t bytes;
931
932 dio->bio = NULL;
933 dio->inode = inode;
934 dio->rw = rw;
935 dio->blkbits = blkbits;
936 dio->blkfactor = inode->i_blkbits - blkbits;
937 dio->start_zero_done = 0;
938 dio->size = 0;
939 dio->block_in_file = offset >> blkbits;
940 dio->blocks_available = 0;
941 dio->cur_page = NULL;
942
943 dio->boundary = 0;
944 dio->reap_counter = 0;
945 dio->get_blocks = get_blocks;
946 dio->end_io = end_io;
947 dio->map_bh.b_private = NULL;
948 dio->final_block_in_bio = -1;
949 dio->next_block_for_io = -1;
950
951 dio->page_errors = 0;
952 dio->result = 0;
953 dio->iocb = iocb;
954
955 /*
956 * BIO completion state.
957 *
958 * ->bio_count starts out at one, and we decrement it to zero after all
959 * BIOs are submitted. This to avoid the situation where a really fast
960 * (or synchronous) device could take the count to zero while we're
961 * still submitting BIOs.
962 */
963 dio->bio_count = 1;
964 dio->bios_in_flight = 0;
965 spin_lock_init(&dio->bio_lock);
966 dio->bio_list = NULL;
967 dio->waiter = NULL;
968
969 /*
970 * In case of non-aligned buffers, we may need 2 more
971 * pages since we need to zero out first and last block.
972 */
973 if (unlikely(dio->blkfactor))
974 dio->pages_in_io = 2;
975 else
976 dio->pages_in_io = 0;
977
978 for (seg = 0; seg < nr_segs; seg++) {
979 user_addr = (unsigned long)iov[seg].iov_base;
980 dio->pages_in_io +=
981 ((user_addr+iov[seg].iov_len +PAGE_SIZE-1)/PAGE_SIZE
982 - user_addr/PAGE_SIZE);
983 }
984
985 for (seg = 0; seg < nr_segs; seg++) {
986 user_addr = (unsigned long)iov[seg].iov_base;
987 dio->size += bytes = iov[seg].iov_len;
988
989 /* Index into the first page of the first block */
990 dio->first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits;
991 dio->final_block_in_request = dio->block_in_file +
992 (bytes >> blkbits);
993 /* Page fetching state */
994 dio->head = 0;
995 dio->tail = 0;
996 dio->curr_page = 0;
997
998 dio->total_pages = 0;
999 if (user_addr & (PAGE_SIZE-1)) {
1000 dio->total_pages++;
1001 bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1));
1002 }
1003 dio->total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
1004 dio->curr_user_address = user_addr;
1005
1006 ret = do_direct_IO(dio);
1007
1008 dio->result += iov[seg].iov_len -
1009 ((dio->final_block_in_request - dio->block_in_file) <<
1010 blkbits);
1011
1012 if (ret) {
1013 dio_cleanup(dio);
1014 break;
1015 }
1016 } /* end iovec loop */
1017
1018 if (ret == -ENOTBLK && rw == WRITE) {
1019 /*
1020 * The remaining part of the request will be
1021 * be handled by buffered I/O when we return
1022 */
1023 ret = 0;
1024 }
1025 /*
1026 * There may be some unwritten disk at the end of a part-written
1027 * fs-block-sized block. Go zero that now.
1028 */
1029 dio_zero_block(dio, 1);
1030
1031 if (dio->cur_page) {
1032 ret2 = dio_send_cur_page(dio);
1033 if (ret == 0)
1034 ret = ret2;
1035 page_cache_release(dio->cur_page);
1036 dio->cur_page = NULL;
1037 }
1038 if (dio->bio)
1039 dio_bio_submit(dio);
1040
1041 /*
1042 * It is possible that, we return short IO due to end of file.
1043 * In that case, we need to release all the pages we got hold on.
1044 */
1045 dio_cleanup(dio);
1046
1047 /*
1048 * All block lookups have been performed. For READ requests
1049 * we can let i_sem go now that its achieved its purpose
1050 * of protecting us from looking up uninitialized blocks.
1051 */
1052 if ((rw == READ) && (dio->lock_type == DIO_LOCKING))
1053 up(&dio->inode->i_sem);
1054
1055 /*
1056 * OK, all BIOs are submitted, so we can decrement bio_count to truly
1057 * reflect the number of to-be-processed BIOs.
1058 */
1059 if (dio->is_async) {
1060 int should_wait = 0;
1061
1062 if (dio->result < dio->size && rw == WRITE) {
1063 dio->waiter = current;
1064 should_wait = 1;
1065 }
1066 if (ret == 0)
1067 ret = dio->result;
1068 finished_one_bio(dio); /* This can free the dio */
1069 blk_run_address_space(inode->i_mapping);
1070 if (should_wait) {
1071 unsigned long flags;
1072 /*
1073 * Wait for already issued I/O to drain out and
1074 * release its references to user-space pages
1075 * before returning to fallback on buffered I/O
1076 */
1077
1078 spin_lock_irqsave(&dio->bio_lock, flags);
1079 set_current_state(TASK_UNINTERRUPTIBLE);
1080 while (dio->bio_count) {
1081 spin_unlock_irqrestore(&dio->bio_lock, flags);
1082 io_schedule();
1083 spin_lock_irqsave(&dio->bio_lock, flags);
1084 set_current_state(TASK_UNINTERRUPTIBLE);
1085 }
1086 spin_unlock_irqrestore(&dio->bio_lock, flags);
1087 set_current_state(TASK_RUNNING);
1088 kfree(dio);
1089 }
1090 } else {
1091 ssize_t transferred = 0;
1092
1093 finished_one_bio(dio);
1094 ret2 = dio_await_completion(dio);
1095 if (ret == 0)
1096 ret = ret2;
1097 if (ret == 0)
1098 ret = dio->page_errors;
1099 if (dio->result) {
1100 loff_t i_size = i_size_read(inode);
1101
1102 transferred = dio->result;
1103 /*
1104 * Adjust the return value if the read crossed a
1105 * non-block-aligned EOF.
1106 */
1107 if (rw == READ && (offset + transferred > i_size))
1108 transferred = i_size - offset;
1109 }
1110 dio_complete(dio, offset, transferred);
1111 if (ret == 0)
1112 ret = transferred;
1113
1114 /* We could have also come here on an AIO file extend */
1115 if (!is_sync_kiocb(iocb) && rw == WRITE &&
1116 ret >= 0 && dio->result == dio->size)
1117 /*
1118 * For AIO writes where we have completed the
1119 * i/o, we have to mark the the aio complete.
1120 */
1121 aio_complete(iocb, ret, 0);
1122 kfree(dio);
1123 }
1124 return ret;
1125}
1126
1127/*
1128 * This is a library function for use by filesystem drivers.
1129 * The locking rules are governed by the dio_lock_type parameter.
1130 *
1131 * DIO_NO_LOCKING (no locking, for raw block device access)
1132 * For writes, i_sem is not held on entry; it is never taken.
1133 *
1134 * DIO_LOCKING (simple locking for regular files)
1135 * For writes we are called under i_sem and return with i_sem held, even though
1136 * it is internally dropped.
1137 * For reads, i_sem is not held on entry, but it is taken and dropped before
1138 * returning.
1139 *
1140 * DIO_OWN_LOCKING (filesystem provides synchronisation and handling of
1141 * uninitialised data, allowing parallel direct readers and writers)
1142 * For writes we are called without i_sem, return without it, never touch it.
1143 * For reads, i_sem is held on entry and will be released before returning.
1144 *
1145 * Additional i_alloc_sem locking requirements described inline below.
1146 */
1147ssize_t
1148__blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
1149 struct block_device *bdev, const struct iovec *iov, loff_t offset,
1150 unsigned long nr_segs, get_blocks_t get_blocks, dio_iodone_t end_io,
1151 int dio_lock_type)
1152{
1153 int seg;
1154 size_t size;
1155 unsigned long addr;
1156 unsigned blkbits = inode->i_blkbits;
1157 unsigned bdev_blkbits = 0;
1158 unsigned blocksize_mask = (1 << blkbits) - 1;
1159 ssize_t retval = -EINVAL;
1160 loff_t end = offset;
1161 struct dio *dio;
1162 int reader_with_isem = (rw == READ && dio_lock_type == DIO_OWN_LOCKING);
1163
1164 if (rw & WRITE)
1165 current->flags |= PF_SYNCWRITE;
1166
1167 if (bdev)
1168 bdev_blkbits = blksize_bits(bdev_hardsect_size(bdev));
1169
1170 if (offset & blocksize_mask) {
1171 if (bdev)
1172 blkbits = bdev_blkbits;
1173 blocksize_mask = (1 << blkbits) - 1;
1174 if (offset & blocksize_mask)
1175 goto out;
1176 }
1177
1178 /* Check the memory alignment. Blocks cannot straddle pages */
1179 for (seg = 0; seg < nr_segs; seg++) {
1180 addr = (unsigned long)iov[seg].iov_base;
1181 size = iov[seg].iov_len;
1182 end += size;
1183 if ((addr & blocksize_mask) || (size & blocksize_mask)) {
1184 if (bdev)
1185 blkbits = bdev_blkbits;
1186 blocksize_mask = (1 << blkbits) - 1;
1187 if ((addr & blocksize_mask) || (size & blocksize_mask))
1188 goto out;
1189 }
1190 }
1191
1192 dio = kmalloc(sizeof(*dio), GFP_KERNEL);
1193 retval = -ENOMEM;
1194 if (!dio)
1195 goto out;
1196
1197 /*
1198 * For block device access DIO_NO_LOCKING is used,
1199 * neither readers nor writers do any locking at all
1200 * For regular files using DIO_LOCKING,
1201 * readers need to grab i_sem and i_alloc_sem
1202 * writers need to grab i_alloc_sem only (i_sem is already held)
1203 * For regular files using DIO_OWN_LOCKING,
1204 * neither readers nor writers take any locks here
1205 * (i_sem is already held and release for writers here)
1206 */
1207 dio->lock_type = dio_lock_type;
1208 if (dio_lock_type != DIO_NO_LOCKING) {
1209 /* watch out for a 0 len io from a tricksy fs */
1210 if (rw == READ && end > offset) {
1211 struct address_space *mapping;
1212
1213 mapping = iocb->ki_filp->f_mapping;
1214 if (dio_lock_type != DIO_OWN_LOCKING) {
1215 down(&inode->i_sem);
1216 reader_with_isem = 1;
1217 }
1218
1219 retval = filemap_write_and_wait_range(mapping, offset,
1220 end - 1);
1221 if (retval) {
1222 kfree(dio);
1223 goto out;
1224 }
1225
1226 if (dio_lock_type == DIO_OWN_LOCKING) {
1227 up(&inode->i_sem);
1228 reader_with_isem = 0;
1229 }
1230 }
1231
1232 if (dio_lock_type == DIO_LOCKING)
1233 down_read(&inode->i_alloc_sem);
1234 }
1235
1236 /*
1237 * For file extending writes updating i_size before data
1238 * writeouts complete can expose uninitialized blocks. So
1239 * even for AIO, we need to wait for i/o to complete before
1240 * returning in this case.
1241 */
1242 dio->is_async = !is_sync_kiocb(iocb) && !((rw == WRITE) &&
1243 (end > i_size_read(inode)));
1244
1245 retval = direct_io_worker(rw, iocb, inode, iov, offset,
1246 nr_segs, blkbits, get_blocks, end_io, dio);
1247
1248 if (rw == READ && dio_lock_type == DIO_LOCKING)
1249 reader_with_isem = 0;
1250
1251out:
1252 if (reader_with_isem)
1253 up(&inode->i_sem);
1254 if (rw & WRITE)
1255 current->flags &= ~PF_SYNCWRITE;
1256 return retval;
1257}
1258EXPORT_SYMBOL(__blockdev_direct_IO);
generated by cgit v1.2.2 (git 2.25.0) at 2024-12-28 11:22:56 -0500