Kernel

Kernel Git Source Tree

Root/fs/direct-io.c

Source at commit 9845c1745d3d531a5b9544f5322c62bfb4d4e9bc created 1 year 2 months ago. By Xiangfu, rtc: jz4740 fix hwclock give time out
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 <linux/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 in the slab cache
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
58	/* dio_state only used in the submission path */
59
60	struct dio_submit {
61	struct bio bio; / bio under assembly */
62	unsigned blkbits; /* doesn't change */
63	unsigned blkfactor; /* When we're using an alignment which
64	is finer than the filesystem's soft
65	blocksize, this specifies how much
66	finer. blkfactor=2 means 1/4-block
67	alignment. Does not change */
68	unsigned start_zero_done; /* flag: sub-blocksize zeroing has
69	been performed at the start of a
70	write */
71	int pages_in_io; /* approximate total IO pages */
72	size_t size; /* total request size (doesn't change)*/
73	sector_t block_in_file; /* Current offset into the underlying
74	file in dio_block units. */
75	unsigned blocks_available; /* At block_in_file. changes */
76	int reap_counter; /* rate limit reaping */
77	sector_t final_block_in_request;/* doesn't change */
78	unsigned first_block_in_page; /* doesn't change, Used only once */
79	int boundary; /* prev block is at a boundary */
80	get_block_t get_block; / block mapping function */
81	dio_submit_t submit_io; / IO submition function */
82
83	loff_t logical_offset_in_bio; /* current first logical block in bio */
84	sector_t final_block_in_bio; /* current final block in bio + 1 */
85	sector_t next_block_for_io; /* next block to be put under IO,
86	in dio_blocks units */
87
88	/*
89	* Deferred addition of a page to the dio. These variables are
90	* private to dio_send_cur_page(), submit_page_section() and
91	* dio_bio_add_page().
92	*/
93	struct page cur_page; / The page */
94	unsigned cur_page_offset; /* Offset into it, in bytes */
95	unsigned cur_page_len; /* Nr of bytes at cur_page_offset */
96	sector_t cur_page_block; /* Where it starts */
97	loff_t cur_page_fs_offset; /* Offset in file */
98
99	/*
100	* Page fetching state. These variables belong to dio_refill_pages().
101	*/
102	int curr_page; /* changes */
103	int total_pages; /* doesn't change */
104	unsigned long curr_user_address;/* changes */
105
106	/*
107	* Page queue. These variables belong to dio_refill_pages() and
108	* dio_get_page().
109	*/
110	unsigned head; /* next page to process */
111	unsigned tail; /* last valid page + 1 */
112	};
113
114	/* dio_state communicated between submission path and end_io */
115	struct dio {
116	int flags; /* doesn't change */
117	int rw;
118	struct inode *inode;
119	loff_t i_size; /* i_size when submitted */
120	dio_iodone_t end_io; / IO completion function */
121
122	void private; / copy from map_bh.b_private */
123
124	/* BIO completion state */
125	spinlock_t bio_lock; /* protects BIO fields below */
126	int page_errors; /* errno from get_user_pages() */
127	int is_async; /* is IO async ? */
128	int io_error; /* IO error in completion path */
129	unsigned long refcount; /* direct_io_worker() and bios */
130	struct bio bio_list; / singly linked via bi_private */
131	struct task_struct waiter; / waiting task (NULL if none) */
132
133	/* AIO related stuff */
134	struct kiocb iocb; / kiocb */
135	ssize_t result; /* IO result */
136
137	/*
138	* pages[] (and any fields placed after it) are not zeroed out at
139	* allocation time. Don't add new fields after pages[] unless you
140	* wish that they not be zeroed.
141	*/
142	struct page pages[DIO_PAGES]; / page buffer */
143	} ____cacheline_aligned_in_smp;
144
145	static struct kmem_cache *dio_cache __read_mostly;
146
147	static void __inode_dio_wait(struct inode *inode)
148	{
149	wait_queue_head_t *wq = bit_waitqueue(&inode->i_state, __I_DIO_WAKEUP);
150	DEFINE_WAIT_BIT(q, &inode->i_state, __I_DIO_WAKEUP);
151
152	do {
153	prepare_to_wait(wq, &q.wait, TASK_UNINTERRUPTIBLE);
154	if (atomic_read(&inode->i_dio_count))
155	schedule();
156	} while (atomic_read(&inode->i_dio_count));
157	finish_wait(wq, &q.wait);
158	}
159
160	/**
161	* inode_dio_wait - wait for outstanding DIO requests to finish
162	* @inode: inode to wait for
163	*
164	* Waits for all pending direct I/O requests to finish so that we can
165	* proceed with a truncate or equivalent operation.
166	*
167	* Must be called under a lock that serializes taking new references
168	* to i_dio_count, usually by inode->i_mutex.
169	*/
170	void inode_dio_wait(struct inode *inode)
171	{
172	if (atomic_read(&inode->i_dio_count))
173	__inode_dio_wait(inode);
174	}
175	EXPORT_SYMBOL_GPL(inode_dio_wait);
176
177	/*
178	* inode_dio_done - signal finish of a direct I/O requests
179	* @inode: inode the direct I/O happens on
180	*
181	* This is called once we've finished processing a direct I/O request,
182	* and is used to wake up callers waiting for direct I/O to be quiesced.
183	*/
184	void inode_dio_done(struct inode *inode)
185	{
186	if (atomic_dec_and_test(&inode->i_dio_count))
187	wake_up_bit(&inode->i_state, __I_DIO_WAKEUP);
188	}
189	EXPORT_SYMBOL_GPL(inode_dio_done);
190
191	/*
192	* How many pages are in the queue?
193	*/
194	static inline unsigned dio_pages_present(struct dio_submit *sdio)
195	{
196	return sdio->tail - sdio->head;
197	}
198
199	/*
200	* Go grab and pin some userspace pages. Typically we'll get 64 at a time.
201	*/
202	static inline int dio_refill_pages(struct dio dio, struct dio_submit sdio)
203	{
204	int ret;
205	int nr_pages;
206
207	nr_pages = min(sdio->total_pages - sdio->curr_page, DIO_PAGES);
208	ret = get_user_pages_fast(
209	sdio->curr_user_address, /* Where from? */
210	nr_pages, /* How many pages? */
211	dio->rw == READ, /* Write to memory? */
212	&dio->pages[0]); /* Put results here */
213
214	if (ret < 0 && sdio->blocks_available && (dio->rw & WRITE)) {
215	struct page *page = ZERO_PAGE(0);
216	/*
217	* A memory fault, but the filesystem has some outstanding
218	* mapped blocks. We need to use those blocks up to avoid
219	* leaking stale data in the file.
220	*/
221	if (dio->page_errors == 0)
222	dio->page_errors = ret;
223	page_cache_get(page);
224	dio->pages[0] = page;
225	sdio->head = 0;
226	sdio->tail = 1;
227	ret = 0;
228	goto out;
229	}
230
231	if (ret >= 0) {
232	sdio->curr_user_address += ret * PAGE_SIZE;
233	sdio->curr_page += ret;
234	sdio->head = 0;
235	sdio->tail = ret;
236	ret = 0;
237	}
238	out:
239	return ret;
240	}
241
242	/*
243	* Get another userspace page. Returns an ERR_PTR on error. Pages are
244	* buffered inside the dio so that we can call get_user_pages() against a
245	* decent number of pages, less frequently. To provide nicer use of the
246	* L1 cache.
247	*/
248	static inline struct page dio_get_page(struct dio dio,
249	struct dio_submit *sdio)
250	{
251	if (dio_pages_present(sdio) == 0) {
252	int ret;
253
254	ret = dio_refill_pages(dio, sdio);
255	if (ret)
256	return ERR_PTR(ret);
257	BUG_ON(dio_pages_present(sdio) == 0);
258	}
259	return dio->pages[sdio->head++];
260	}
261
262	/**
263	* dio_complete() - called when all DIO BIO I/O has been completed
264	* @offset: the byte offset in the file of the completed operation
265	*
266	* This releases locks as dictated by the locking type, lets interested parties
267	* know that a DIO operation has completed, and calculates the resulting return
268	* code for the operation.
269	*
270	* It lets the filesystem know if it registered an interest earlier via
271	* get_block. Pass the private field of the map buffer_head so that
272	* filesystems can use it to hold additional state between get_block calls and
273	* dio_complete.
274	*/
275	static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret, bool is_async)
276	{
277	ssize_t transferred = 0;
278
279	/*
280	* AIO submission can race with bio completion to get here while
281	* expecting to have the last io completed by bio completion.
282	* In that case -EIOCBQUEUED is in fact not an error we want
283	* to preserve through this call.
284	*/
285	if (ret == -EIOCBQUEUED)
286	ret = 0;
287
288	if (dio->result) {
289	transferred = dio->result;
290
291	/* Check for short read case */
292	if ((dio->rw == READ) && ((offset + transferred) > dio->i_size))
293	transferred = dio->i_size - offset;
294	}
295
296	if (ret == 0)
297	ret = dio->page_errors;
298	if (ret == 0)
299	ret = dio->io_error;
300	if (ret == 0)
301	ret = transferred;
302
303	if (dio->end_io && dio->result) {
304	dio->end_io(dio->iocb, offset, transferred,
305	dio->private, ret, is_async);
306	} else {
307	if (is_async)
308	aio_complete(dio->iocb, ret, 0);
309	inode_dio_done(dio->inode);
310	}
311
312	return ret;
313	}
314
315	static int dio_bio_complete(struct dio dio, struct bio bio);
316	/*
317	* Asynchronous IO callback.
318	*/
319	static void dio_bio_end_aio(struct bio *bio, int error)
320	{
321	struct dio *dio = bio->bi_private;
322	unsigned long remaining;
323	unsigned long flags;
324
325	/* cleanup the bio */
326	dio_bio_complete(dio, bio);
327
328	spin_lock_irqsave(&dio->bio_lock, flags);
329	remaining = --dio->refcount;
330	if (remaining == 1 && dio->waiter)
331	wake_up_process(dio->waiter);
332	spin_unlock_irqrestore(&dio->bio_lock, flags);
333
334	if (remaining == 0) {
335	dio_complete(dio, dio->iocb->ki_pos, 0, true);
336	kmem_cache_free(dio_cache, dio);
337	}
338	}
339
340	/*
341	* The BIO completion handler simply queues the BIO up for the process-context
342	* handler.
343	*
344	* During I/O bi_private points at the dio. After I/O, bi_private is used to
345	* implement a singly-linked list of completed BIOs, at dio->bio_list.
346	*/
347	static void dio_bio_end_io(struct bio *bio, int error)
348	{
349	struct dio *dio = bio->bi_private;
350	unsigned long flags;
351
352	spin_lock_irqsave(&dio->bio_lock, flags);
353	bio->bi_private = dio->bio_list;
354	dio->bio_list = bio;
355	if (--dio->refcount == 1 && dio->waiter)
356	wake_up_process(dio->waiter);
357	spin_unlock_irqrestore(&dio->bio_lock, flags);
358	}
359
360	/**
361	* dio_end_io - handle the end io action for the given bio
362	* @bio: The direct io bio thats being completed
363	* @error: Error if there was one
364	*
365	* This is meant to be called by any filesystem that uses their own dio_submit_t
366	* so that the DIO specific endio actions are dealt with after the filesystem
367	* has done it's completion work.
368	*/
369	void dio_end_io(struct bio *bio, int error)
370	{
371	struct dio *dio = bio->bi_private;
372
373	if (dio->is_async)
374	dio_bio_end_aio(bio, error);
375	else
376	dio_bio_end_io(bio, error);
377	}
378	EXPORT_SYMBOL_GPL(dio_end_io);
379
380	static inline void
381	dio_bio_alloc(struct dio dio, struct dio_submit sdio,
382	struct block_device *bdev,
383	sector_t first_sector, int nr_vecs)
384	{
385	struct bio *bio;
386
387	/*
388	* bio_alloc() is guaranteed to return a bio when called with
389	* __GFP_WAIT and we request a valid number of vectors.
390	*/
391	bio = bio_alloc(GFP_KERNEL, nr_vecs);
392
393	bio->bi_bdev = bdev;
394	bio->bi_sector = first_sector;
395	if (dio->is_async)
396	bio->bi_end_io = dio_bio_end_aio;
397	else
398	bio->bi_end_io = dio_bio_end_io;
399
400	sdio->bio = bio;
401	sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
402	}
403
404	/*
405	* In the AIO read case we speculatively dirty the pages before starting IO.
406	* During IO completion, any of these pages which happen to have been written
407	* back will be redirtied by bio_check_pages_dirty().
408	*
409	* bios hold a dio reference between submit_bio and ->end_io.
410	*/
411	static inline void dio_bio_submit(struct dio dio, struct dio_submit sdio)
412	{
413	struct bio *bio = sdio->bio;
414	unsigned long flags;
415
416	bio->bi_private = dio;
417
418	spin_lock_irqsave(&dio->bio_lock, flags);
419	dio->refcount++;
420	spin_unlock_irqrestore(&dio->bio_lock, flags);
421
422	if (dio->is_async && dio->rw == READ)
423	bio_set_pages_dirty(bio);
424
425	if (sdio->submit_io)
426	sdio->submit_io(dio->rw, bio, dio->inode,
427	sdio->logical_offset_in_bio);
428	else
429	submit_bio(dio->rw, bio);
430
431	sdio->bio = NULL;
432	sdio->boundary = 0;
433	sdio->logical_offset_in_bio = 0;
434	}
435
436	/*
437	* Release any resources in case of a failure
438	*/
439	static inline void dio_cleanup(struct dio dio, struct dio_submit sdio)
440	{
441	while (dio_pages_present(sdio))
442	page_cache_release(dio_get_page(dio, sdio));
443	}
444
445	/*
446	* Wait for the next BIO to complete. Remove it and return it. NULL is
447	* returned once all BIOs have been completed. This must only be called once
448	* all bios have been issued so that dio->refcount can only decrease. This
449	* requires that that the caller hold a reference on the dio.
450	*/
451	static struct bio dio_await_one(struct dio dio)
452	{
453	unsigned long flags;
454	struct bio *bio = NULL;
455
456	spin_lock_irqsave(&dio->bio_lock, flags);
457
458	/*
459	* Wait as long as the list is empty and there are bios in flight. bio
460	* completion drops the count, maybe adds to the list, and wakes while
461	* holding the bio_lock so we don't need set_current_state()'s barrier
462	* and can call it after testing our condition.
463	*/
464	while (dio->refcount > 1 && dio->bio_list == NULL) {
465	__set_current_state(TASK_UNINTERRUPTIBLE);
466	dio->waiter = current;
467	spin_unlock_irqrestore(&dio->bio_lock, flags);
468	io_schedule();
469	/* wake up sets us TASK_RUNNING */
470	spin_lock_irqsave(&dio->bio_lock, flags);
471	dio->waiter = NULL;
472	}
473	if (dio->bio_list) {
474	bio = dio->bio_list;
475	dio->bio_list = bio->bi_private;
476	}
477	spin_unlock_irqrestore(&dio->bio_lock, flags);
478	return bio;
479	}
480
481	/*
482	* Process one completed BIO. No locks are held.
483	*/
484	static int dio_bio_complete(struct dio dio, struct bio bio)
485	{
486	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
487	struct bio_vec *bvec = bio->bi_io_vec;
488	int page_no;
489
490	if (!uptodate)
491	dio->io_error = -EIO;
492
493	if (dio->is_async && dio->rw == READ) {
494	bio_check_pages_dirty(bio); /* transfers ownership */
495	} else {
496	for (page_no = 0; page_no < bio->bi_vcnt; page_no++) {
497	struct page *page = bvec[page_no].bv_page;
498
499	if (dio->rw == READ && !PageCompound(page))
500	set_page_dirty_lock(page);
501	page_cache_release(page);
502	}
503	bio_put(bio);
504	}
505	return uptodate ? 0 : -EIO;
506	}
507
508	/*
509	* Wait on and process all in-flight BIOs. This must only be called once
510	* all bios have been issued so that the refcount can only decrease.
511	* This just waits for all bios to make it through dio_bio_complete. IO
512	* errors are propagated through dio->io_error and should be propagated via
513	* dio_complete().
514	*/
515	static void dio_await_completion(struct dio *dio)
516	{
517	struct bio *bio;
518	do {
519	bio = dio_await_one(dio);
520	if (bio)
521	dio_bio_complete(dio, bio);
522	} while (bio);
523	}
524
525	/*
526	* A really large O_DIRECT read or write can generate a lot of BIOs. So
527	* to keep the memory consumption sane we periodically reap any completed BIOs
528	* during the BIO generation phase.
529	*
530	* This also helps to limit the peak amount of pinned userspace memory.
531	*/
532	static inline int dio_bio_reap(struct dio dio, struct dio_submit sdio)
533	{
534	int ret = 0;
535
536	if (sdio->reap_counter++ >= 64) {
537	while (dio->bio_list) {
538	unsigned long flags;
539	struct bio *bio;
540	int ret2;
541
542	spin_lock_irqsave(&dio->bio_lock, flags);
543	bio = dio->bio_list;
544	dio->bio_list = bio->bi_private;
545	spin_unlock_irqrestore(&dio->bio_lock, flags);
546	ret2 = dio_bio_complete(dio, bio);
547	if (ret == 0)
548	ret = ret2;
549	}
550	sdio->reap_counter = 0;
551	}
552	return ret;
553	}
554
555	/*
556	* Call into the fs to map some more disk blocks. We record the current number
557	* of available blocks at sdio->blocks_available. These are in units of the
558	* fs blocksize, (1 << inode->i_blkbits).
559	*
560	* The fs is allowed to map lots of blocks at once. If it wants to do that,
561	* it uses the passed inode-relative block number as the file offset, as usual.
562	*
563	* get_block() is passed the number of i_blkbits-sized blocks which direct_io
564	* has remaining to do. The fs should not map more than this number of blocks.
565	*
566	* If the fs has mapped a lot of blocks, it should populate bh->b_size to
567	* indicate how much contiguous disk space has been made available at
568	* bh->b_blocknr.
569	*
570	* If any of the mapped blocks are new, then the fs must set buffer_new().
571	* This isn't very efficient...
572	*
573	* In the case of filesystem holes: the fs may return an arbitrarily-large
574	* hole by returning an appropriate value in b_size and by clearing
575	* buffer_mapped(). However the direct-io code will only process holes one
576	* block at a time - it will repeatedly call get_block() as it walks the hole.
577	*/
578	static int get_more_blocks(struct dio dio, struct dio_submit sdio,
579	struct buffer_head *map_bh)
580	{
581	int ret;
582	sector_t fs_startblk; /* Into file, in filesystem-sized blocks */
583	unsigned long fs_count; /* Number of filesystem-sized blocks */
584	unsigned long dio_count;/* Number of dio_block-sized blocks */
585	unsigned long blkmask;
586	int create;
587
588	/*
589	* If there was a memory error and we've overwritten all the
590	* mapped blocks then we can now return that memory error
591	*/
592	ret = dio->page_errors;
593	if (ret == 0) {
594	BUG_ON(sdio->block_in_file >= sdio->final_block_in_request);
595	fs_startblk = sdio->block_in_file >> sdio->blkfactor;
596	dio_count = sdio->final_block_in_request - sdio->block_in_file;
597	fs_count = dio_count >> sdio->blkfactor;
598	blkmask = (1 << sdio->blkfactor) - 1;
599	if (dio_count & blkmask)
600	fs_count++;
601
602	map_bh->b_state = 0;
603	map_bh->b_size = fs_count << dio->inode->i_blkbits;
604
605	/*
606	* For writes inside i_size on a DIO_SKIP_HOLES filesystem we
607	* forbid block creations: only overwrites are permitted.
608	* We will return early to the caller once we see an
609	* unmapped buffer head returned, and the caller will fall
610	* back to buffered I/O.
611	*
612	* Otherwise the decision is left to the get_blocks method,
613	* which may decide to handle it or also return an unmapped
614	* buffer head.
615	*/
616	create = dio->rw & WRITE;
617	if (dio->flags & DIO_SKIP_HOLES) {
618	if (sdio->block_in_file < (i_size_read(dio->inode) >>
619	sdio->blkbits))
620	create = 0;
621	}
622
623	ret = (*sdio->get_block)(dio->inode, fs_startblk,
624	map_bh, create);
625
626	/* Store for completion */
627	dio->private = map_bh->b_private;
628	}
629	return ret;
630	}
631
632	/*
633	* There is no bio. Make one now.
634	*/
635	static inline int dio_new_bio(struct dio dio, struct dio_submit sdio,
636	sector_t start_sector, struct buffer_head *map_bh)
637	{
638	sector_t sector;
639	int ret, nr_pages;
640
641	ret = dio_bio_reap(dio, sdio);
642	if (ret)
643	goto out;
644	sector = start_sector << (sdio->blkbits - 9);
645	nr_pages = min(sdio->pages_in_io, bio_get_nr_vecs(map_bh->b_bdev));
646	nr_pages = min(nr_pages, BIO_MAX_PAGES);
647	BUG_ON(nr_pages <= 0);
648	dio_bio_alloc(dio, sdio, map_bh->b_bdev, sector, nr_pages);
649	sdio->boundary = 0;
650	out:
651	return ret;
652	}
653
654	/*
655	* Attempt to put the current chunk of 'cur_page' into the current BIO. If
656	* that was successful then update final_block_in_bio and take a ref against
657	* the just-added page.
658	*
659	* Return zero on success. Non-zero means the caller needs to start a new BIO.
660	*/
661	static inline int dio_bio_add_page(struct dio_submit *sdio)
662	{
663	int ret;
664
665	ret = bio_add_page(sdio->bio, sdio->cur_page,
666	sdio->cur_page_len, sdio->cur_page_offset);
667	if (ret == sdio->cur_page_len) {
668	/*
669	* Decrement count only, if we are done with this page
670	*/
671	if ((sdio->cur_page_len + sdio->cur_page_offset) == PAGE_SIZE)
672	sdio->pages_in_io--;
673	page_cache_get(sdio->cur_page);
674	sdio->final_block_in_bio = sdio->cur_page_block +
675	(sdio->cur_page_len >> sdio->blkbits);
676	ret = 0;
677	} else {
678	ret = 1;
679	}
680	return ret;
681	}
682
683	/*
684	* Put cur_page under IO. The section of cur_page which is described by
685	* cur_page_offset,cur_page_len is put into a BIO. The section of cur_page
686	* starts on-disk at cur_page_block.
687	*
688	* We take a ref against the page here (on behalf of its presence in the bio).
689	*
690	* The caller of this function is responsible for removing cur_page from the
691	* dio, and for dropping the refcount which came from that presence.
692	*/
693	static inline int dio_send_cur_page(struct dio dio, struct dio_submit sdio,
694	struct buffer_head *map_bh)
695	{
696	int ret = 0;
697
698	if (sdio->bio) {
699	loff_t cur_offset = sdio->cur_page_fs_offset;
700	loff_t bio_next_offset = sdio->logical_offset_in_bio +
701	sdio->bio->bi_size;
702
703	/*
704	* See whether this new request is contiguous with the old.
705	*
706	* Btrfs cannot handle having logically non-contiguous requests
707	* submitted. For example if you have
708	*
709	* Logical: [0-4095][HOLE][8192-12287]
710	* Physical: [0-4095] [4096-8191]
711	*
712	* We cannot submit those pages together as one BIO. So if our
713	* current logical offset in the file does not equal what would
714	* be the next logical offset in the bio, submit the bio we
715	* have.
716	*/
717	if (sdio->final_block_in_bio != sdio->cur_page_block \|\|
718	cur_offset != bio_next_offset)
719	dio_bio_submit(dio, sdio);
720	/*
721	* Submit now if the underlying fs is about to perform a
722	* metadata read
723	*/
724	else if (sdio->boundary)
725	dio_bio_submit(dio, sdio);
726	}
727
728	if (sdio->bio == NULL) {
729	ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
730	if (ret)
731	goto out;
732	}
733
734	if (dio_bio_add_page(sdio) != 0) {
735	dio_bio_submit(dio, sdio);
736	ret = dio_new_bio(dio, sdio, sdio->cur_page_block, map_bh);
737	if (ret == 0) {
738	ret = dio_bio_add_page(sdio);
739	BUG_ON(ret != 0);
740	}
741	}
742	out:
743	return ret;
744	}
745
746	/*
747	* An autonomous function to put a chunk of a page under deferred IO.
748	*
749	* The caller doesn't actually know (or care) whether this piece of page is in
750	* a BIO, or is under IO or whatever. We just take care of all possible
751	* situations here. The separation between the logic of do_direct_IO() and
752	* that of submit_page_section() is important for clarity. Please don't break.
753	*
754	* The chunk of page starts on-disk at blocknr.
755	*
756	* We perform deferred IO, by recording the last-submitted page inside our
757	* private part of the dio structure. If possible, we just expand the IO
758	* across that page here.
759	*
760	* If that doesn't work out then we put the old page into the bio and add this
761	* page to the dio instead.
762	*/
763	static inline int
764	submit_page_section(struct dio dio, struct dio_submit sdio, struct page *page,
765	unsigned offset, unsigned len, sector_t blocknr,
766	struct buffer_head *map_bh)
767	{
768	int ret = 0;
769
770	if (dio->rw & WRITE) {
771	/*
772	* Read accounting is performed in submit_bio()
773	*/
774	task_io_account_write(len);
775	}
776
777	/*
778	* Can we just grow the current page's presence in the dio?
779	*/
780	if (sdio->cur_page == page &&
781	sdio->cur_page_offset + sdio->cur_page_len == offset &&
782	sdio->cur_page_block +
783	(sdio->cur_page_len >> sdio->blkbits) == blocknr) {
784	sdio->cur_page_len += len;
785
786	/*
787	* If sdio->boundary then we want to schedule the IO now to
788	* avoid metadata seeks.
789	*/
790	if (sdio->boundary) {
791	ret = dio_send_cur_page(dio, sdio, map_bh);
792	page_cache_release(sdio->cur_page);
793	sdio->cur_page = NULL;
794	}
795	goto out;
796	}
797
798	/*
799	* If there's a deferred page already there then send it.
800	*/
801	if (sdio->cur_page) {
802	ret = dio_send_cur_page(dio, sdio, map_bh);
803	page_cache_release(sdio->cur_page);
804	sdio->cur_page = NULL;
805	if (ret)
806	goto out;
807	}
808
809	page_cache_get(page); /* It is in dio */
810	sdio->cur_page = page;
811	sdio->cur_page_offset = offset;
812	sdio->cur_page_len = len;
813	sdio->cur_page_block = blocknr;
814	sdio->cur_page_fs_offset = sdio->block_in_file << sdio->blkbits;
815	out:
816	return ret;
817	}
818
819	/*
820	* Clean any dirty buffers in the blockdev mapping which alias newly-created
821	* file blocks. Only called for S_ISREG files - blockdevs do not set
822	* buffer_new
823	*/
824	static void clean_blockdev_aliases(struct dio dio, struct buffer_head map_bh)
825	{
826	unsigned i;
827	unsigned nblocks;
828
829	nblocks = map_bh->b_size >> dio->inode->i_blkbits;
830
831	for (i = 0; i < nblocks; i++) {
832	unmap_underlying_metadata(map_bh->b_bdev,
833	map_bh->b_blocknr + i);
834	}
835	}
836
837	/*
838	* If we are not writing the entire block and get_block() allocated
839	* the block for us, we need to fill-in the unused portion of the
840	* block with zeros. This happens only if user-buffer, fileoffset or
841	* io length is not filesystem block-size multiple.
842	*
843	* `end' is zero if we're doing the start of the IO, 1 at the end of the
844	* IO.
845	*/
846	static inline void dio_zero_block(struct dio dio, struct dio_submit sdio,
847	int end, struct buffer_head *map_bh)
848	{
849	unsigned dio_blocks_per_fs_block;
850	unsigned this_chunk_blocks; /* In dio_blocks */
851	unsigned this_chunk_bytes;
852	struct page *page;
853
854	sdio->start_zero_done = 1;
855	if (!sdio->blkfactor \|\| !buffer_new(map_bh))
856	return;
857
858	dio_blocks_per_fs_block = 1 << sdio->blkfactor;
859	this_chunk_blocks = sdio->block_in_file & (dio_blocks_per_fs_block - 1);
860
861	if (!this_chunk_blocks)
862	return;
863
864	/*
865	* We need to zero out part of an fs block. It is either at the
866	* beginning or the end of the fs block.
867	*/
868	if (end)
869	this_chunk_blocks = dio_blocks_per_fs_block - this_chunk_blocks;
870
871	this_chunk_bytes = this_chunk_blocks << sdio->blkbits;
872
873	page = ZERO_PAGE(0);
874	if (submit_page_section(dio, sdio, page, 0, this_chunk_bytes,
875	sdio->next_block_for_io, map_bh))
876	return;
877
878	sdio->next_block_for_io += this_chunk_blocks;
879	}
880
881	/*
882	* Walk the user pages, and the file, mapping blocks to disk and generating
883	* a sequence of (page,offset,len,block) mappings. These mappings are injected
884	* into submit_page_section(), which takes care of the next stage of submission
885	*
886	* Direct IO against a blockdev is different from a file. Because we can
887	* happily perform page-sized but 512-byte aligned IOs. It is important that
888	* blockdev IO be able to have fine alignment and large sizes.
889	*
890	* So what we do is to permit the ->get_block function to populate bh.b_size
891	* with the size of IO which is permitted at this offset and this i_blkbits.
892	*
893	* For best results, the blockdev should be set up with 512-byte i_blkbits and
894	* it should set b_size to PAGE_SIZE or more inside get_block(). This gives
895	* fine alignment but still allows this function to work in PAGE_SIZE units.
896	*/
897	static int do_direct_IO(struct dio dio, struct dio_submit sdio,
898	struct buffer_head *map_bh)
899	{
900	const unsigned blkbits = sdio->blkbits;
901	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
902	struct page *page;
903	unsigned block_in_page;
904	int ret = 0;
905
906	/* The I/O can start at any block offset within the first page */
907	block_in_page = sdio->first_block_in_page;
908
909	while (sdio->block_in_file < sdio->final_block_in_request) {
910	page = dio_get_page(dio, sdio);
911	if (IS_ERR(page)) {
912	ret = PTR_ERR(page);
913	goto out;
914	}
915
916	while (block_in_page < blocks_per_page) {
917	unsigned offset_in_page = block_in_page << blkbits;
918	unsigned this_chunk_bytes; /* # of bytes mapped */
919	unsigned this_chunk_blocks; /* # of blocks */
920	unsigned u;
921
922	if (sdio->blocks_available == 0) {
923	/*
924	* Need to go and map some more disk
925	*/
926	unsigned long blkmask;
927	unsigned long dio_remainder;
928
929	ret = get_more_blocks(dio, sdio, map_bh);
930	if (ret) {
931	page_cache_release(page);
932	goto out;
933	}
934	if (!buffer_mapped(map_bh))
935	goto do_holes;
936
937	sdio->blocks_available =
938	map_bh->b_size >> sdio->blkbits;
939	sdio->next_block_for_io =
940	map_bh->b_blocknr << sdio->blkfactor;
941	if (buffer_new(map_bh))
942	clean_blockdev_aliases(dio, map_bh);
943
944	if (!sdio->blkfactor)
945	goto do_holes;
946
947	blkmask = (1 << sdio->blkfactor) - 1;
948	dio_remainder = (sdio->block_in_file & blkmask);
949
950	/*
951	* If we are at the start of IO and that IO
952	* starts partway into a fs-block,
953	* dio_remainder will be non-zero. If the IO
954	* is a read then we can simply advance the IO
955	* cursor to the first block which is to be
956	* read. But if the IO is a write and the
957	* block was newly allocated we cannot do that;
958	* the start of the fs block must be zeroed out
959	* on-disk
960	*/
961	if (!buffer_new(map_bh))
962	sdio->next_block_for_io += dio_remainder;
963	sdio->blocks_available -= dio_remainder;
964	}
965	do_holes:
966	/* Handle holes */
967	if (!buffer_mapped(map_bh)) {
968	loff_t i_size_aligned;
969
970	/* AKPM: eargh, -ENOTBLK is a hack */
971	if (dio->rw & WRITE) {
972	page_cache_release(page);
973	return -ENOTBLK;
974	}
975
976	/*
977	* Be sure to account for a partial block as the
978	* last block in the file
979	*/
980	i_size_aligned = ALIGN(i_size_read(dio->inode),
981	1 << blkbits);
982	if (sdio->block_in_file >=
983	i_size_aligned >> blkbits) {
984	/* We hit eof */
985	page_cache_release(page);
986	goto out;
987	}
988	zero_user(page, block_in_page << blkbits,
989	1 << blkbits);
990	sdio->block_in_file++;
991	block_in_page++;
992	goto next_block;
993	}
994
995	/*
996	* If we're performing IO which has an alignment which
997	* is finer than the underlying fs, go check to see if
998	* we must zero out the start of this block.
999	*/
1000	if (unlikely(sdio->blkfactor && !sdio->start_zero_done))
1001	dio_zero_block(dio, sdio, 0, map_bh);
1002
1003	/*
1004	* Work out, in this_chunk_blocks, how much disk we
1005	* can add to this page
1006	*/
1007	this_chunk_blocks = sdio->blocks_available;
1008	u = (PAGE_SIZE - offset_in_page) >> blkbits;
1009	if (this_chunk_blocks > u)
1010	this_chunk_blocks = u;
1011	u = sdio->final_block_in_request - sdio->block_in_file;
1012	if (this_chunk_blocks > u)
1013	this_chunk_blocks = u;
1014	this_chunk_bytes = this_chunk_blocks << blkbits;
1015	BUG_ON(this_chunk_bytes == 0);
1016
1017	sdio->boundary = buffer_boundary(map_bh);
1018	ret = submit_page_section(dio, sdio, page,
1019	offset_in_page,
1020	this_chunk_bytes,
1021	sdio->next_block_for_io,
1022	map_bh);
1023	if (ret) {
1024	page_cache_release(page);
1025	goto out;
1026	}
1027	sdio->next_block_for_io += this_chunk_blocks;
1028
1029	sdio->block_in_file += this_chunk_blocks;
1030	block_in_page += this_chunk_blocks;
1031	sdio->blocks_available -= this_chunk_blocks;
1032	next_block:
1033	BUG_ON(sdio->block_in_file > sdio->final_block_in_request);
1034	if (sdio->block_in_file == sdio->final_block_in_request)
1035	break;
1036	}
1037
1038	/* Drop the ref which was taken in get_user_pages() */
1039	page_cache_release(page);
1040	block_in_page = 0;
1041	}
1042	out:
1043	return ret;
1044	}
1045
1046	static inline int drop_refcount(struct dio *dio)
1047	{
1048	int ret2;
1049	unsigned long flags;
1050
1051	/*
1052	* Sync will always be dropping the final ref and completing the
1053	* operation. AIO can if it was a broken operation described above or
1054	* in fact if all the bios race to complete before we get here. In
1055	* that case dio_complete() translates the EIOCBQUEUED into the proper
1056	* return code that the caller will hand to aio_complete().
1057	*
1058	* This is managed by the bio_lock instead of being an atomic_t so that
1059	* completion paths can drop their ref and use the remaining count to
1060	* decide to wake the submission path atomically.
1061	*/
1062	spin_lock_irqsave(&dio->bio_lock, flags);
1063	ret2 = --dio->refcount;
1064	spin_unlock_irqrestore(&dio->bio_lock, flags);
1065	return ret2;
1066	}
1067
1068	/*
1069	* This is a library function for use by filesystem drivers.
1070	*
1071	* The locking rules are governed by the flags parameter:
1072	* - if the flags value contains DIO_LOCKING we use a fancy locking
1073	* scheme for dumb filesystems.
1074	* For writes this function is called under i_mutex and returns with
1075	* i_mutex held, for reads, i_mutex is not held on entry, but it is
1076	* taken and dropped again before returning.
1077	* - if the flags value does NOT contain DIO_LOCKING we don't use any
1078	* internal locking but rather rely on the filesystem to synchronize
1079	* direct I/O reads/writes versus each other and truncate.
1080	*
1081	* To help with locking against truncate we incremented the i_dio_count
1082	* counter before starting direct I/O, and decrement it once we are done.
1083	* Truncate can wait for it to reach zero to provide exclusion. It is
1084	* expected that filesystem provide exclusion between new direct I/O
1085	* and truncates. For DIO_LOCKING filesystems this is done by i_mutex,
1086	* but other filesystems need to take care of this on their own.
1087	*
1088	* NOTE: if you pass "sdio" to anything by pointer make sure that function
1089	* is always inlined. Otherwise gcc is unable to split the structure into
1090	* individual fields and will generate much worse code. This is important
1091	* for the whole file.
1092	*/
1093	ssize_t
1094	__blockdev_direct_IO(int rw, struct kiocb iocb, struct inode inode,
1095	struct block_device bdev, const struct iovec iov, loff_t offset,
1096	unsigned long nr_segs, get_block_t get_block, dio_iodone_t end_io,
1097	dio_submit_t submit_io, int flags)
1098	{
1099	int seg;
1100	size_t size;
1101	unsigned long addr;
1102	unsigned blkbits = inode->i_blkbits;
1103	unsigned bdev_blkbits = 0;
1104	unsigned blocksize_mask = (1 << blkbits) - 1;
1105	ssize_t retval = -EINVAL;
1106	loff_t end = offset;
1107	struct dio *dio;
1108	struct dio_submit sdio = { 0, };
1109	unsigned long user_addr;
1110	size_t bytes;
1111	struct buffer_head map_bh = { 0, };
1112
1113	if (rw & WRITE)
1114	rw = WRITE_ODIRECT;
1115
1116	if (bdev)
1117	bdev_blkbits = blksize_bits(bdev_logical_block_size(bdev));
1118
1119	if (offset & blocksize_mask) {
1120	if (bdev)
1121	blkbits = bdev_blkbits;
1122	blocksize_mask = (1 << blkbits) - 1;
1123	if (offset & blocksize_mask)
1124	goto out;
1125	}
1126
1127	/* Check the memory alignment. Blocks cannot straddle pages */
1128	for (seg = 0; seg < nr_segs; seg++) {
1129	addr = (unsigned long)iov[seg].iov_base;
1130	size = iov[seg].iov_len;
1131	end += size;
1132	if ((addr & blocksize_mask) \|\| (size & blocksize_mask)) {
1133	if (bdev)
1134	blkbits = bdev_blkbits;
1135	blocksize_mask = (1 << blkbits) - 1;
1136	if ((addr & blocksize_mask) \|\| (size & blocksize_mask))
1137	goto out;
1138	}
1139	}
1140
1141	/* watch out for a 0 len io from a tricksy fs */
1142	if (rw == READ && end == offset)
1143	return 0;
1144
1145	dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
1146	retval = -ENOMEM;
1147	if (!dio)
1148	goto out;
1149	/*
1150	* Believe it or not, zeroing out the page array caused a .5%
1151	* performance regression in a database benchmark. So, we take
1152	* care to only zero out what's needed.
1153	*/
1154	memset(dio, 0, offsetof(struct dio, pages));
1155
1156	dio->flags = flags;
1157	if (dio->flags & DIO_LOCKING) {
1158	if (rw == READ) {
1159	struct address_space *mapping =
1160	iocb->ki_filp->f_mapping;
1161
1162	/* will be released by direct_io_worker */
1163	mutex_lock(&inode->i_mutex);
1164
1165	retval = filemap_write_and_wait_range(mapping, offset,
1166	end - 1);
1167	if (retval) {
1168	mutex_unlock(&inode->i_mutex);
1169	kmem_cache_free(dio_cache, dio);
1170	goto out;
1171	}
1172	}
1173	}
1174
1175	/*
1176	* Will be decremented at I/O completion time.
1177	*/
1178	atomic_inc(&inode->i_dio_count);
1179
1180	/*
1181	* For file extending writes updating i_size before data
1182	* writeouts complete can expose uninitialized blocks. So
1183	* even for AIO, we need to wait for i/o to complete before
1184	* returning in this case.
1185	*/
1186	dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) &&
1187	(end > i_size_read(inode)));
1188
1189	retval = 0;
1190
1191	dio->inode = inode;
1192	dio->rw = rw;
1193	sdio.blkbits = blkbits;
1194	sdio.blkfactor = inode->i_blkbits - blkbits;
1195	sdio.block_in_file = offset >> blkbits;
1196
1197	sdio.get_block = get_block;
1198	dio->end_io = end_io;
1199	sdio.submit_io = submit_io;
1200	sdio.final_block_in_bio = -1;
1201	sdio.next_block_for_io = -1;
1202
1203	dio->iocb = iocb;
1204	dio->i_size = i_size_read(inode);
1205
1206	spin_lock_init(&dio->bio_lock);
1207	dio->refcount = 1;
1208
1209	/*
1210	* In case of non-aligned buffers, we may need 2 more
1211	* pages since we need to zero out first and last block.
1212	*/
1213	if (unlikely(sdio.blkfactor))
1214	sdio.pages_in_io = 2;
1215
1216	for (seg = 0; seg < nr_segs; seg++) {
1217	user_addr = (unsigned long)iov[seg].iov_base;
1218	sdio.pages_in_io +=
1219	((user_addr + iov[seg].iov_len + PAGE_SIZE-1) /
1220	PAGE_SIZE - user_addr / PAGE_SIZE);
1221	}
1222
1223	for (seg = 0; seg < nr_segs; seg++) {
1224	user_addr = (unsigned long)iov[seg].iov_base;
1225	sdio.size += bytes = iov[seg].iov_len;
1226
1227	/* Index into the first page of the first block */
1228	sdio.first_block_in_page = (user_addr & ~PAGE_MASK) >> blkbits;
1229	sdio.final_block_in_request = sdio.block_in_file +
1230	(bytes >> blkbits);
1231	/* Page fetching state */
1232	sdio.head = 0;
1233	sdio.tail = 0;
1234	sdio.curr_page = 0;
1235
1236	sdio.total_pages = 0;
1237	if (user_addr & (PAGE_SIZE-1)) {
1238	sdio.total_pages++;
1239	bytes -= PAGE_SIZE - (user_addr & (PAGE_SIZE - 1));
1240	}
1241	sdio.total_pages += (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
1242	sdio.curr_user_address = user_addr;
1243
1244	retval = do_direct_IO(dio, &sdio, &map_bh);
1245
1246	dio->result += iov[seg].iov_len -
1247	((sdio.final_block_in_request - sdio.block_in_file) <<
1248	blkbits);
1249
1250	if (retval) {
1251	dio_cleanup(dio, &sdio);
1252	break;
1253	}
1254	} /* end iovec loop */
1255
1256	if (retval == -ENOTBLK) {
1257	/*
1258	* The remaining part of the request will be
1259	* be handled by buffered I/O when we return
1260	*/
1261	retval = 0;
1262	}
1263	/*
1264	* There may be some unwritten disk at the end of a part-written
1265	* fs-block-sized block. Go zero that now.
1266	*/
1267	dio_zero_block(dio, &sdio, 1, &map_bh);
1268
1269	if (sdio.cur_page) {
1270	ssize_t ret2;
1271
1272	ret2 = dio_send_cur_page(dio, &sdio, &map_bh);
1273	if (retval == 0)
1274	retval = ret2;
1275	page_cache_release(sdio.cur_page);
1276	sdio.cur_page = NULL;
1277	}
1278	if (sdio.bio)
1279	dio_bio_submit(dio, &sdio);
1280
1281	/*
1282	* It is possible that, we return short IO due to end of file.
1283	* In that case, we need to release all the pages we got hold on.
1284	*/
1285	dio_cleanup(dio, &sdio);
1286
1287	/*
1288	* All block lookups have been performed. For READ requests
1289	* we can let i_mutex go now that its achieved its purpose
1290	* of protecting us from looking up uninitialized blocks.
1291	*/
1292	if (rw == READ && (dio->flags & DIO_LOCKING))
1293	mutex_unlock(&dio->inode->i_mutex);
1294
1295	/*
1296	* The only time we want to leave bios in flight is when a successful
1297	* partial aio read or full aio write have been setup. In that case
1298	* bio completion will call aio_complete. The only time it's safe to
1299	* call aio_complete is when we return -EIOCBQUEUED, so we key on that.
1300	* This had better be the only place that raises -EIOCBQUEUED.
1301	*/
1302	BUG_ON(retval == -EIOCBQUEUED);
1303	if (dio->is_async && retval == 0 && dio->result &&
1304	((rw & READ) \|\| (dio->result == sdio.size)))
1305	retval = -EIOCBQUEUED;
1306
1307	if (retval != -EIOCBQUEUED)
1308	dio_await_completion(dio);
1309
1310	if (drop_refcount(dio) == 0) {
1311	retval = dio_complete(dio, offset, retval, false);
1312	kmem_cache_free(dio_cache, dio);
1313	} else
1314	BUG_ON(retval != -EIOCBQUEUED);
1315
1316	out:
1317	return retval;
1318	}
1319	EXPORT_SYMBOL(__blockdev_direct_IO);
1320
1321	static __init int dio_init(void)
1322	{
1323	dio_cache = KMEM_CACHE(dio, SLAB_PANIC);
1324	return 0;
1325	}
1326	module_init(dio_init)
1327

Download this file

Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master

Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9

Kernel

Kernel Git Source Tree

Root/fs/direct-io.c

interactive