linux - fs/buffer.c

3370 lines · 87.2 KiB

1	/*
2	* linux/fs/buffer.c
3	*
4	* Copyright (C) 1991, 1992, 2002 Linus Torvalds
5	*/
6
7	/*
8	* Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
9	*
10	* Removed a lot of unnecessary code and simplified things now that
11	* the buffer cache isn't our primary cache - Andrew Tridgell 12/96
12	*
13	* Speed up hash, lru, and free list operations. Use gfp() for allocating
14	* hash table, use SLAB cache for buffer heads. SMP threading. -DaveM
15	*
16	* Added 32k buffer block sizes - these are required older ARM systems. - RMK
17	*
18	* async buffer flushing, 1999 Andrea Arcangeli <[email protected]>
19	*/
20
21	#include <linux/kernel.h>
22	#include <linux/syscalls.h>
23	#include <linux/fs.h>
24	#include <linux/mm.h>
25	#include <linux/percpu.h>
26	#include <linux/slab.h>
27	#include <linux/capability.h>
28	#include <linux/blkdev.h>
29	#include <linux/file.h>
30	#include <linux/quotaops.h>
31	#include <linux/highmem.h>
32	#include <linux/export.h>
33	#include <linux/writeback.h>
34	#include <linux/hash.h>
35	#include <linux/suspend.h>
36	#include <linux/buffer_head.h>
37	#include <linux/task_io_accounting_ops.h>
38	#include <linux/bio.h>
39	#include <linux/notifier.h>
40	#include <linux/cpu.h>
41	#include <linux/bitops.h>
42	#include <linux/mpage.h>
43	#include <linux/bit_spinlock.h>
44	#include <trace/events/block.h>
45
46	static int fsync_buffers_list(spinlock_t lock, struct list_head list);
47
48	#define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
49
50	void init_buffer(struct buffer_head bh, bh_end_io_t handler, void *private)
51	{
52	bh->b_end_io = handler;
53	bh->b_private = private;
54	}
55	EXPORT_SYMBOL(init_buffer);
56
57	inline void touch_buffer(struct buffer_head *bh)
58	{
59	trace_block_touch_buffer(bh);
60	mark_page_accessed(bh->b_page);
61	}
62	EXPORT_SYMBOL(touch_buffer);
63
64	static int sleep_on_buffer(void *word)
65	{
66	io_schedule();
67	return 0;
68	}
69
70	void __lock_buffer(struct buffer_head *bh)
71	{
72	wait_on_bit_lock(&bh->b_state, BH_Lock, sleep_on_buffer,
73	TASK_UNINTERRUPTIBLE);
74	}
75	EXPORT_SYMBOL(__lock_buffer);
76
77	void unlock_buffer(struct buffer_head *bh)
78	{
79	clear_bit_unlock(BH_Lock, &bh->b_state);
80	smp_mb__after_clear_bit();
81	wake_up_bit(&bh->b_state, BH_Lock);
82	}
83	EXPORT_SYMBOL(unlock_buffer);
84
85	/*
86	* Block until a buffer comes unlocked. This doesn't stop it
87	* from becoming locked again - you have to lock it yourself
88	* if you want to preserve its state.
89	*/
90	void __wait_on_buffer(struct buffer_head * bh)
91	{
92	wait_on_bit(&bh->b_state, BH_Lock, sleep_on_buffer, TASK_UNINTERRUPTIBLE);
93	}
94	EXPORT_SYMBOL(__wait_on_buffer);
95
96	static void
97	__clear_page_buffers(struct page *page)
98	{
99	ClearPagePrivate(page);
100	set_page_private(page, 0);
101	page_cache_release(page);
102	}
103
104
105	static int quiet_error(struct buffer_head *bh)
106	{
107	if (!test_bit(BH_Quiet, &bh->b_state) && printk_ratelimit())
108	return 0;
109	return 1;
110	}
111
112
113	static void buffer_io_error(struct buffer_head *bh)
114	{
115	char b[BDEVNAME_SIZE];
116	printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
117	bdevname(bh->b_bdev, b),
118	(unsigned long long)bh->b_blocknr);
119	}
120
121	/*
122	* End-of-IO handler helper function which does not touch the bh after
123	* unlocking it.
124	* Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
125	* a race there is benign: unlock_buffer() only use the bh's address for
126	* hashing after unlocking the buffer, so it doesn't actually touch the bh
127	* itself.
128	*/
129	static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
130	{
131	if (uptodate) {
132	set_buffer_uptodate(bh);
133	} else {
134	/* This happens, due to failed READA attempts. */
135	clear_buffer_uptodate(bh);
136	}
137	unlock_buffer(bh);
138	}
139
140	/*
141	* Default synchronous end-of-IO handler.. Just mark it up-to-date and
142	* unlock the buffer. This is what ll_rw_block uses too.
143	*/
144	void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
145	{
146	__end_buffer_read_notouch(bh, uptodate);
147	put_bh(bh);
148	}
149	EXPORT_SYMBOL(end_buffer_read_sync);
150
151	void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
152	{
153	char b[BDEVNAME_SIZE];
154
155	if (uptodate) {
156	set_buffer_uptodate(bh);
157	} else {
158	if (!quiet_error(bh)) {
159	buffer_io_error(bh);
160	printk(KERN_WARNING "lost page write due to "
161	"I/O error on %s\n",
162	bdevname(bh->b_bdev, b));
163	}
164	set_buffer_write_io_error(bh);
165	clear_buffer_uptodate(bh);
166	}
167	unlock_buffer(bh);
168	put_bh(bh);
169	}
170	EXPORT_SYMBOL(end_buffer_write_sync);
171
172	/*
173	* Various filesystems appear to want __find_get_block to be non-blocking.
174	* But it's the page lock which protects the buffers. To get around this,
175	* we get exclusion from try_to_free_buffers with the blockdev mapping's
176	* private_lock.
177	*
178	* Hack idea: for the blockdev mapping, i_bufferlist_lock contention
179	* may be quite high. This code could TryLock the page, and if that
180	* succeeds, there is no need to take private_lock. (But if
181	* private_lock is contended then so is mapping->tree_lock).
182	*/
183	static struct buffer_head *
184	__find_get_block_slow(struct block_device *bdev, sector_t block)
185	{
186	struct inode *bd_inode = bdev->bd_inode;
187	struct address_space *bd_mapping = bd_inode->i_mapping;
188	struct buffer_head *ret = NULL;
189	pgoff_t index;
190	struct buffer_head *bh;
191	struct buffer_head *head;
192	struct page *page;
193	int all_mapped = 1;
194
195	index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
196	page = find_get_page(bd_mapping, index);
197	if (!page)
198	goto out;
199
200	spin_lock(&bd_mapping->private_lock);
201	if (!page_has_buffers(page))
202	goto out_unlock;
203	head = page_buffers(page);
204	bh = head;
205	do {
206	if (!buffer_mapped(bh))
207	all_mapped = 0;
208	else if (bh->b_blocknr == block) {
209	ret = bh;
210	get_bh(bh);
211	goto out_unlock;
212	}
213	bh = bh->b_this_page;
214	} while (bh != head);
215
216	/* we might be here because some of the buffers on this page are
217	* not mapped. This is due to various races between
218	* file io on the block device and getblk. It gets dealt with
219	* elsewhere, don't buffer_error if we had some unmapped buffers
220	*/
221	if (all_mapped) {
222	char b[BDEVNAME_SIZE];
223
224	printk("__find_get_block_slow() failed. "
225	"block=%llu, b_blocknr=%llu\n",
226	(unsigned long long)block,
227	(unsigned long long)bh->b_blocknr);
228	printk("b_state=0x%08lx, b_size=%zu\n",
229	bh->b_state, bh->b_size);
230	printk("device %s blocksize: %d\n", bdevname(bdev, b),
231	1 << bd_inode->i_blkbits);
232	}
233	out_unlock:
234	spin_unlock(&bd_mapping->private_lock);
235	page_cache_release(page);
236	out:
237	return ret;
238	}
239
240	/*
241	* Kick the writeback threads then try to free up some ZONE_NORMAL memory.
242	*/
243	static void free_more_memory(void)
244	{
245	struct zone *zone;
246	int nid;
247
248	wakeup_flusher_threads(1024, WB_REASON_FREE_MORE_MEM);
249	yield();
250
251	for_each_online_node(nid) {
252	(void)first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
253	gfp_zone(GFP_NOFS), NULL,
254	&zone);
255	if (zone)
256	try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
257	GFP_NOFS, NULL);
258	}
259	}
260
261	/*
262	* I/O completion handler for block_read_full_page() - pages
263	* which come unlocked at the end of I/O.
264	*/
265	static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
266	{
267	unsigned long flags;
268	struct buffer_head *first;
269	struct buffer_head *tmp;
270	struct page *page;
271	int page_uptodate = 1;
272
273	BUG_ON(!buffer_async_read(bh));
274
275	page = bh->b_page;
276	if (uptodate) {
277	set_buffer_uptodate(bh);
278	} else {
279	clear_buffer_uptodate(bh);
280	if (!quiet_error(bh))
281	buffer_io_error(bh);
282	SetPageError(page);
283	}
284
285	/*
286	* Be _very_ careful from here on. Bad things can happen if
287	* two buffer heads end IO at almost the same time and both
288	* decide that the page is now completely done.
289	*/
290	first = page_buffers(page);
291	local_irq_save(flags);
292	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
293	clear_buffer_async_read(bh);
294	unlock_buffer(bh);
295	tmp = bh;
296	do {
297	if (!buffer_uptodate(tmp))
298	page_uptodate = 0;
299	if (buffer_async_read(tmp)) {
300	BUG_ON(!buffer_locked(tmp));
301	goto still_busy;
302	}
303	tmp = tmp->b_this_page;
304	} while (tmp != bh);
305	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
306	local_irq_restore(flags);
307
308	/*
309	* If none of the buffers had errors and they are all
310	* uptodate then we can set the page uptodate.
311	*/
312	if (page_uptodate && !PageError(page))
313	SetPageUptodate(page);
314	unlock_page(page);
315	return;
316
317	still_busy:
318	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
319	local_irq_restore(flags);
320	return;
321	}
322
323	/*
324	* Completion handler for block_write_full_page() - pages which are unlocked
325	* during I/O, and which have PageWriteback cleared upon I/O completion.
326	*/
327	void end_buffer_async_write(struct buffer_head *bh, int uptodate)
328	{
329	char b[BDEVNAME_SIZE];
330	unsigned long flags;
331	struct buffer_head *first;
332	struct buffer_head *tmp;
333	struct page *page;
334
335	BUG_ON(!buffer_async_write(bh));
336
337	page = bh->b_page;
338	if (uptodate) {
339	set_buffer_uptodate(bh);
340	} else {
341	if (!quiet_error(bh)) {
342	buffer_io_error(bh);
343	printk(KERN_WARNING "lost page write due to "
344	"I/O error on %s\n",
345	bdevname(bh->b_bdev, b));
346	}
347	set_bit(AS_EIO, &page->mapping->flags);
348	set_buffer_write_io_error(bh);
349	clear_buffer_uptodate(bh);
350	SetPageError(page);
351	}
352
353	first = page_buffers(page);
354	local_irq_save(flags);
355	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
356
357	clear_buffer_async_write(bh);
358	unlock_buffer(bh);
359	tmp = bh->b_this_page;
360	while (tmp != bh) {
361	if (buffer_async_write(tmp)) {
362	BUG_ON(!buffer_locked(tmp));
363	goto still_busy;
364	}
365	tmp = tmp->b_this_page;
366	}
367	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
368	local_irq_restore(flags);
369	end_page_writeback(page);
370	return;
371
372	still_busy:
373	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
374	local_irq_restore(flags);
375	return;
376	}
377	EXPORT_SYMBOL(end_buffer_async_write);
378
379	/*
380	* If a page's buffers are under async readin (end_buffer_async_read
381	* completion) then there is a possibility that another thread of
382	* control could lock one of the buffers after it has completed
383	* but while some of the other buffers have not completed. This
384	* locked buffer would confuse end_buffer_async_read() into not unlocking
385	* the page. So the absence of BH_Async_Read tells end_buffer_async_read()
386	* that this buffer is not under async I/O.
387	*
388	* The page comes unlocked when it has no locked buffer_async buffers
389	* left.
390	*
391	* PageLocked prevents anyone starting new async I/O reads any of
392	* the buffers.
393	*
394	* PageWriteback is used to prevent simultaneous writeout of the same
395	* page.
396	*
397	* PageLocked prevents anyone from starting writeback of a page which is
398	* under read I/O (PageWriteback is only ever set against a locked page).
399	*/
400	static void mark_buffer_async_read(struct buffer_head *bh)
401	{
402	bh->b_end_io = end_buffer_async_read;
403	set_buffer_async_read(bh);
404	}
405
406	static void mark_buffer_async_write_endio(struct buffer_head *bh,
407	bh_end_io_t *handler)
408	{
409	bh->b_end_io = handler;
410	set_buffer_async_write(bh);
411	}
412
413	void mark_buffer_async_write(struct buffer_head *bh)
414	{
415	mark_buffer_async_write_endio(bh, end_buffer_async_write);
416	}
417	EXPORT_SYMBOL(mark_buffer_async_write);
418
419
420	/*
421	* fs/buffer.c contains helper functions for buffer-backed address space's
422	* fsync functions. A common requirement for buffer-based filesystems is
423	* that certain data from the backing blockdev needs to be written out for
424	* a successful fsync(). For example, ext2 indirect blocks need to be
425	* written back and waited upon before fsync() returns.
426	*
427	* The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
428	* inode_has_buffers() and invalidate_inode_buffers() are provided for the
429	* management of a list of dependent buffers at ->i_mapping->private_list.
430	*
431	* Locking is a little subtle: try_to_free_buffers() will remove buffers
432	* from their controlling inode's queue when they are being freed. But
433	* try_to_free_buffers() will be operating against the blockdev mapping
434	* at the time, not against the S_ISREG file which depends on those buffers.
435	* So the locking for private_list is via the private_lock in the address_space
436	* which backs the buffers. Which is different from the address_space
437	* against which the buffers are listed. So for a particular address_space,
438	* mapping->private_lock does not protect mapping->private_list! In fact,
439	* mapping->private_list will always be protected by the backing blockdev's
440	* ->private_lock.
441	*
442	* Which introduces a requirement: all buffers on an address_space's
443	* ->private_list must be from the same address_space: the blockdev's.
444	*
445	* address_spaces which do not place buffers at ->private_list via these
446	* utility functions are free to use private_lock and private_list for
447	* whatever they want. The only requirement is that list_empty(private_list)
448	* be true at clear_inode() time.
449	*
450	* FIXME: clear_inode should not call invalidate_inode_buffers(). The
451	* filesystems should do that. invalidate_inode_buffers() should just go
452	* BUG_ON(!list_empty).
453	*
454	* FIXME: mark_buffer_dirty_inode() is a data-plane operation. It should
455	* take an address_space, not an inode. And it should be called
456	* mark_buffer_dirty_fsync() to clearly define why those buffers are being
457	* queued up.
458	*
459	* FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
460	* list if it is already on a list. Because if the buffer is on a list,
461	* it must already be on the right one. If not, the filesystem is being
462	* silly. This will save a ton of locking. But first we have to ensure
463	* that buffers are taken off the old inode's list when they are freed
464	* (presumably in truncate). That requires careful auditing of all
465	* filesystems (do it inside bforget()). It could also be done by bringing
466	* b_inode back.
467	*/
468
469	/*
470	* The buffer's backing address_space's private_lock must be held
471	*/
472	static void __remove_assoc_queue(struct buffer_head *bh)
473	{
474	list_del_init(&bh->b_assoc_buffers);
475	WARN_ON(!bh->b_assoc_map);
476	if (buffer_write_io_error(bh))
477	set_bit(AS_EIO, &bh->b_assoc_map->flags);
478	bh->b_assoc_map = NULL;
479	}
480
481	int inode_has_buffers(struct inode *inode)
482	{
483	return !list_empty(&inode->i_data.private_list);
484	}
485
486	/*
487	* osync is designed to support O_SYNC io. It waits synchronously for
488	* all already-submitted IO to complete, but does not queue any new
489	* writes to the disk.
490	*
491	* To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
492	* you dirty the buffers, and then use osync_inode_buffers to wait for
493	* completion. Any other dirty buffers which are not yet queued for
494	* write will not be flushed to disk by the osync.
495	*/
496	static int osync_buffers_list(spinlock_t lock, struct list_head list)
497	{
498	struct buffer_head *bh;
499	struct list_head *p;
500	int err = 0;
501
502	spin_lock(lock);
503	repeat:
504	list_for_each_prev(p, list) {
505	bh = BH_ENTRY(p);
506	if (buffer_locked(bh)) {
507	get_bh(bh);
508	spin_unlock(lock);
509	wait_on_buffer(bh);
510	if (!buffer_uptodate(bh))
511	err = -EIO;
512	brelse(bh);
513	spin_lock(lock);
514	goto repeat;
515	}
516	}
517	spin_unlock(lock);
518	return err;
519	}
520
521	static void do_thaw_one(struct super_block sb, void unused)
522	{
523	char b[BDEVNAME_SIZE];
524	while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
525	printk(KERN_WARNING "Emergency Thaw on %s\n",
526	bdevname(sb->s_bdev, b));
527	}
528
529	static void do_thaw_all(struct work_struct *work)
530	{
531	iterate_supers(do_thaw_one, NULL);
532	kfree(work);
533	printk(KERN_WARNING "Emergency Thaw complete\n");
534	}
535
536	/**
537	* emergency_thaw_all -- forcibly thaw every frozen filesystem
538	*
539	* Used for emergency unfreeze of all filesystems via SysRq
540	*/
541	void emergency_thaw_all(void)
542	{
543	struct work_struct *work;
544
545	work = kmalloc(sizeof(*work), GFP_ATOMIC);
546	if (work) {
547	INIT_WORK(work, do_thaw_all);
548	schedule_work(work);
549	}
550	}
551
552	/**
553	* sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
554	* @mapping: the mapping which wants those buffers written
555	*
556	* Starts I/O against the buffers at mapping->private_list, and waits upon
557	* that I/O.
558	*
559	* Basically, this is a convenience function for fsync().
560	* @mapping is a file or directory which needs those buffers to be written for
561	* a successful fsync().
562	*/
563	int sync_mapping_buffers(struct address_space *mapping)
564	{
565	struct address_space *buffer_mapping = mapping->private_data;
566
567	if (buffer_mapping == NULL \|\| list_empty(&mapping->private_list))
568	return 0;
569
570	return fsync_buffers_list(&buffer_mapping->private_lock,
571	&mapping->private_list);
572	}
573	EXPORT_SYMBOL(sync_mapping_buffers);
574
575	/*
576	* Called when we've recently written block `bblock', and it is known that
577	* `bblock' was for a buffer_boundary() buffer. This means that the block at
578	* `bblock + 1' is probably a dirty indirect block. Hunt it down and, if it's
579	* dirty, schedule it for IO. So that indirects merge nicely with their data.
580	*/
581	void write_boundary_block(struct block_device *bdev,
582	sector_t bblock, unsigned blocksize)
583	{
584	struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
585	if (bh) {
586	if (buffer_dirty(bh))
587	ll_rw_block(WRITE, 1, &bh);
588	put_bh(bh);
589	}
590	}
591
592	void mark_buffer_dirty_inode(struct buffer_head bh, struct inode inode)
593	{
594	struct address_space *mapping = inode->i_mapping;
595	struct address_space *buffer_mapping = bh->b_page->mapping;
596
597	mark_buffer_dirty(bh);
598	if (!mapping->private_data) {
599	mapping->private_data = buffer_mapping;
600	} else {
601	BUG_ON(mapping->private_data != buffer_mapping);
602	}
603	if (!bh->b_assoc_map) {
604	spin_lock(&buffer_mapping->private_lock);
605	list_move_tail(&bh->b_assoc_buffers,
606	&mapping->private_list);
607	bh->b_assoc_map = mapping;
608	spin_unlock(&buffer_mapping->private_lock);
609	}
610	}
611	EXPORT_SYMBOL(mark_buffer_dirty_inode);
612
613	/*
614	* Mark the page dirty, and set it dirty in the radix tree, and mark the inode
615	* dirty.
616	*
617	* If warn is true, then emit a warning if the page is not uptodate and has
618	* not been truncated.
619	*/
620	static void __set_page_dirty(struct page *page,
621	struct address_space *mapping, int warn)
622	{
623	spin_lock_irq(&mapping->tree_lock);
624	if (page->mapping) { /* Race with truncate? */
625	WARN_ON_ONCE(warn && !PageUptodate(page));
626	account_page_dirtied(page, mapping);
627	radix_tree_tag_set(&mapping->page_tree,
628	page_index(page), PAGECACHE_TAG_DIRTY);
629	}
630	spin_unlock_irq(&mapping->tree_lock);
631	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
632	}
633
634	/*
635	* Add a page to the dirty page list.
636	*
637	* It is a sad fact of life that this function is called from several places
638	* deeply under spinlocking. It may not sleep.
639	*
640	* If the page has buffers, the uptodate buffers are set dirty, to preserve
641	* dirty-state coherency between the page and the buffers. It the page does
642	* not have buffers then when they are later attached they will all be set
643	* dirty.
644	*
645	* The buffers are dirtied before the page is dirtied. There's a small race
646	* window in which a writepage caller may see the page cleanness but not the
647	* buffer dirtiness. That's fine. If this code were to set the page dirty
648	* before the buffers, a concurrent writepage caller could clear the page dirty
649	* bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
650	* page on the dirty page list.
651	*
652	* We use private_lock to lock against try_to_free_buffers while using the
653	* page's buffer list. Also use this to protect against clean buffers being
654	* added to the page after it was set dirty.
655	*
656	* FIXME: may need to call ->reservepage here as well. That's rather up to the
657	* address_space though.
658	*/
659	int __set_page_dirty_buffers(struct page *page)
660	{
661	int newly_dirty;
662	struct address_space *mapping = page_mapping(page);
663
664	if (unlikely(!mapping))
665	return !TestSetPageDirty(page);
666
667	spin_lock(&mapping->private_lock);
668	if (page_has_buffers(page)) {
669	struct buffer_head *head = page_buffers(page);
670	struct buffer_head *bh = head;
671
672	do {
673	set_buffer_dirty(bh);
674	bh = bh->b_this_page;
675	} while (bh != head);
676	}
677	newly_dirty = !TestSetPageDirty(page);
678	spin_unlock(&mapping->private_lock);
679
680	if (newly_dirty)
681	__set_page_dirty(page, mapping, 1);
682	return newly_dirty;
683	}
684	EXPORT_SYMBOL(__set_page_dirty_buffers);
685
686	/*
687	* Write out and wait upon a list of buffers.
688	*
689	* We have conflicting pressures: we want to make sure that all
690	* initially dirty buffers get waited on, but that any subsequently
691	* dirtied buffers don't. After all, we don't want fsync to last
692	* forever if somebody is actively writing to the file.
693	*
694	* Do this in two main stages: first we copy dirty buffers to a
695	* temporary inode list, queueing the writes as we go. Then we clean
696	* up, waiting for those writes to complete.
697	*
698	* During this second stage, any subsequent updates to the file may end
699	* up refiling the buffer on the original inode's dirty list again, so
700	* there is a chance we will end up with a buffer queued for write but
701	* not yet completed on that list. So, as a final cleanup we go through
702	* the osync code to catch these locked, dirty buffers without requeuing
703	* any newly dirty buffers for write.
704	*/
705	static int fsync_buffers_list(spinlock_t lock, struct list_head list)
706	{
707	struct buffer_head *bh;
708	struct list_head tmp;
709	struct address_space *mapping;
710	int err = 0, err2;
711	struct blk_plug plug;
712
713	INIT_LIST_HEAD(&tmp);
714	blk_start_plug(&plug);
715
716	spin_lock(lock);
717	while (!list_empty(list)) {
718	bh = BH_ENTRY(list->next);
719	mapping = bh->b_assoc_map;
720	__remove_assoc_queue(bh);
721	/* Avoid race with mark_buffer_dirty_inode() which does
722	* a lockless check and we rely on seeing the dirty bit */
723	smp_mb();
724	if (buffer_dirty(bh) \|\| buffer_locked(bh)) {
725	list_add(&bh->b_assoc_buffers, &tmp);
726	bh->b_assoc_map = mapping;
727	if (buffer_dirty(bh)) {
728	get_bh(bh);
729	spin_unlock(lock);
730	/*
731	* Ensure any pending I/O completes so that
732	* write_dirty_buffer() actually writes the
733	* current contents - it is a noop if I/O is
734	* still in flight on potentially older
735	* contents.
736	*/
737	write_dirty_buffer(bh, WRITE_SYNC);
738
739	/*
740	* Kick off IO for the previous mapping. Note
741	* that we will not run the very last mapping,
742	* wait_on_buffer() will do that for us
743	* through sync_buffer().
744	*/
745	brelse(bh);
746	spin_lock(lock);
747	}
748	}
749	}
750
751	spin_unlock(lock);
752	blk_finish_plug(&plug);
753	spin_lock(lock);
754
755	while (!list_empty(&tmp)) {
756	bh = BH_ENTRY(tmp.prev);
757	get_bh(bh);
758	mapping = bh->b_assoc_map;
759	__remove_assoc_queue(bh);
760	/* Avoid race with mark_buffer_dirty_inode() which does
761	* a lockless check and we rely on seeing the dirty bit */
762	smp_mb();
763	if (buffer_dirty(bh)) {
764	list_add(&bh->b_assoc_buffers,
765	&mapping->private_list);
766	bh->b_assoc_map = mapping;
767	}
768	spin_unlock(lock);
769	wait_on_buffer(bh);
770	if (!buffer_uptodate(bh))
771	err = -EIO;
772	brelse(bh);
773	spin_lock(lock);
774	}
775
776	spin_unlock(lock);
777	err2 = osync_buffers_list(lock, list);
778	if (err)
779	return err;
780	else
781	return err2;
782	}
783
784	/*
785	* Invalidate any and all dirty buffers on a given inode. We are
786	* probably unmounting the fs, but that doesn't mean we have already
787	* done a sync(). Just drop the buffers from the inode list.
788	*
789	* NOTE: we take the inode's blockdev's mapping's private_lock. Which
790	* assumes that all the buffers are against the blockdev. Not true
791	* for reiserfs.
792	*/
793	void invalidate_inode_buffers(struct inode *inode)
794	{
795	if (inode_has_buffers(inode)) {
796	struct address_space *mapping = &inode->i_data;
797	struct list_head *list = &mapping->private_list;
798	struct address_space *buffer_mapping = mapping->private_data;
799
800	spin_lock(&buffer_mapping->private_lock);
801	while (!list_empty(list))
802	__remove_assoc_queue(BH_ENTRY(list->next));
803	spin_unlock(&buffer_mapping->private_lock);
804	}
805	}
806	EXPORT_SYMBOL(invalidate_inode_buffers);
807
808	/*
809	* Remove any clean buffers from the inode's buffer list. This is called
810	* when we're trying to free the inode itself. Those buffers can pin it.
811	*
812	* Returns true if all buffers were removed.
813	*/
814	int remove_inode_buffers(struct inode *inode)
815	{
816	int ret = 1;
817
818	if (inode_has_buffers(inode)) {
819	struct address_space *mapping = &inode->i_data;
820	struct list_head *list = &mapping->private_list;
821	struct address_space *buffer_mapping = mapping->private_data;
822
823	spin_lock(&buffer_mapping->private_lock);
824	while (!list_empty(list)) {
825	struct buffer_head *bh = BH_ENTRY(list->next);
826	if (buffer_dirty(bh)) {
827	ret = 0;
828	break;
829	}
830	__remove_assoc_queue(bh);
831	}
832	spin_unlock(&buffer_mapping->private_lock);
833	}
834	return ret;
835	}
836
837	/*
838	* Create the appropriate buffers when given a page for data area and
839	* the size of each buffer.. Use the bh->b_this_page linked list to
840	* follow the buffers created. Return NULL if unable to create more
841	* buffers.
842	*
843	* The retry flag is used to differentiate async IO (paging, swapping)
844	* which may not fail from ordinary buffer allocations.
845	*/
846	struct buffer_head alloc_page_buffers(struct page page, unsigned long size,
847	int retry)
848	{
849	struct buffer_head bh, head;
850	long offset;
851
852	try_again:
853	head = NULL;
854	offset = PAGE_SIZE;
855	while ((offset -= size) >= 0) {
856	bh = alloc_buffer_head(GFP_NOFS);
857	if (!bh)
858	goto no_grow;
859
860	bh->b_this_page = head;
861	bh->b_blocknr = -1;
862	head = bh;
863
864	bh->b_size = size;
865
866	/* Link the buffer to its page */
867	set_bh_page(bh, page, offset);
868
869	init_buffer(bh, NULL, NULL);
870	}
871	return head;
872	/*
873	* In case anything failed, we just free everything we got.
874	*/
875	no_grow:
876	if (head) {
877	do {
878	bh = head;
879	head = head->b_this_page;
880	free_buffer_head(bh);
881	} while (head);
882	}
883
884	/*
885	* Return failure for non-async IO requests. Async IO requests
886	* are not allowed to fail, so we have to wait until buffer heads
887	* become available. But we don't want tasks sleeping with
888	* partially complete buffers, so all were released above.
889	*/
890	if (!retry)
891	return NULL;
892
893	/* We're _really_ low on memory. Now we just
894	* wait for old buffer heads to become free due to
895	* finishing IO. Since this is an async request and
896	* the reserve list is empty, we're sure there are
897	* async buffer heads in use.
898	*/
899	free_more_memory();
900	goto try_again;
901	}
902	EXPORT_SYMBOL_GPL(alloc_page_buffers);
903
904	static inline void
905	link_dev_buffers(struct page page, struct buffer_head head)
906	{
907	struct buffer_head bh, tail;
908
909	bh = head;
910	do {
911	tail = bh;
912	bh = bh->b_this_page;
913	} while (bh);
914	tail->b_this_page = head;
915	attach_page_buffers(page, head);
916	}
917
918	static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
919	{
920	sector_t retval = ~((sector_t)0);
921	loff_t sz = i_size_read(bdev->bd_inode);
922
923	if (sz) {
924	unsigned int sizebits = blksize_bits(size);
925	retval = (sz >> sizebits);
926	}
927	return retval;
928	}
929
930	/*
931	* Initialise the state of a blockdev page's buffers.
932	*/
933	static sector_t
934	init_page_buffers(struct page page, struct block_device bdev,
935	sector_t block, int size)
936	{
937	struct buffer_head *head = page_buffers(page);
938	struct buffer_head *bh = head;
939	int uptodate = PageUptodate(page);
940	sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
941
942	do {
943	if (!buffer_mapped(bh)) {
944	init_buffer(bh, NULL, NULL);
945	bh->b_bdev = bdev;
946	bh->b_blocknr = block;
947	if (uptodate)
948	set_buffer_uptodate(bh);
949	if (block < end_block)
950	set_buffer_mapped(bh);
951	}
952	block++;
953	bh = bh->b_this_page;
954	} while (bh != head);
955
956	/*
957	* Caller needs to validate requested block against end of device.
958	*/
959	return end_block;
960	}
961
962	/*
963	* Create the page-cache page that contains the requested block.
964	*
965	* This is used purely for blockdev mappings.
966	*/
967	static int
968	grow_dev_page(struct block_device *bdev, sector_t block,
969	pgoff_t index, int size, int sizebits)
970	{
971	struct inode *inode = bdev->bd_inode;
972	struct page *page;
973	struct buffer_head *bh;
974	sector_t end_block;
975	int ret = 0; /* Will call free_more_memory() */
976
977	page = find_or_create_page(inode->i_mapping, index,
978	(mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS)\|__GFP_MOVABLE);
979	if (!page)
980	return ret;
981
982	BUG_ON(!PageLocked(page));
983
984	if (page_has_buffers(page)) {
985	bh = page_buffers(page);
986	if (bh->b_size == size) {
987	end_block = init_page_buffers(page, bdev,
988	index << sizebits, size);
989	goto done;
990	}
991	if (!try_to_free_buffers(page))
992	goto failed;
993	}
994
995	/*
996	* Allocate some buffers for this page
997	*/
998	bh = alloc_page_buffers(page, size, 0);
999	if (!bh)
1000	goto failed;
1001
1002	/*
1003	* Link the page to the buffers and initialise them. Take the
1004	* lock to be atomic wrt __find_get_block(), which does not
1005	* run under the page lock.
1006	*/
1007	spin_lock(&inode->i_mapping->private_lock);
1008	link_dev_buffers(page, bh);
1009	end_block = init_page_buffers(page, bdev, index << sizebits, size);
1010	spin_unlock(&inode->i_mapping->private_lock);
1011	done:
1012	ret = (block < end_block) ? 1 : -ENXIO;
1013	failed:
1014	unlock_page(page);
1015	page_cache_release(page);
1016	return ret;
1017	}
1018
1019	/*
1020	* Create buffers for the specified block device block's page. If
1021	* that page was dirty, the buffers are set dirty also.
1022	*/
1023	static int
1024	grow_buffers(struct block_device *bdev, sector_t block, int size)
1025	{
1026	pgoff_t index;
1027	int sizebits;
1028
1029	sizebits = -1;
1030	do {
1031	sizebits++;
1032	} while ((size << sizebits) < PAGE_SIZE);
1033
1034	index = block >> sizebits;
1035
1036	/*
1037	* Check for a block which wants to lie outside our maximum possible
1038	* pagecache index. (this comparison is done using sector_t types).
1039	*/
1040	if (unlikely(index != block >> sizebits)) {
1041	char b[BDEVNAME_SIZE];
1042
1043	printk(KERN_ERR "%s: requested out-of-range block %llu for "
1044	"device %s\n",
1045	__func__, (unsigned long long)block,
1046	bdevname(bdev, b));
1047	return -EIO;
1048	}
1049
1050	/* Create a page with the proper size buffers.. */
1051	return grow_dev_page(bdev, block, index, size, sizebits);
1052	}
1053
1054	static struct buffer_head *
1055	__getblk_slow(struct block_device *bdev, sector_t block, int size)
1056	{
1057	/* Size must be multiple of hard sectorsize */
1058	if (unlikely(size & (bdev_logical_block_size(bdev)-1) \|\|
1059	(size < 512 \|\| size > PAGE_SIZE))) {
1060	printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1061	size);
1062	printk(KERN_ERR "logical block size: %d\n",
1063	bdev_logical_block_size(bdev));
1064
1065	dump_stack();
1066	return NULL;
1067	}
1068
1069	for (;;) {
1070	struct buffer_head *bh;
1071	int ret;
1072
1073	bh = __find_get_block(bdev, block, size);
1074	if (bh)
1075	return bh;
1076
1077	ret = grow_buffers(bdev, block, size);
1078	if (ret < 0)
1079	return NULL;
1080	if (ret == 0)
1081	free_more_memory();
1082	}
1083	}
1084
1085	/*
1086	* The relationship between dirty buffers and dirty pages:
1087	*
1088	* Whenever a page has any dirty buffers, the page's dirty bit is set, and
1089	* the page is tagged dirty in its radix tree.
1090	*
1091	* At all times, the dirtiness of the buffers represents the dirtiness of
1092	* subsections of the page. If the page has buffers, the page dirty bit is
1093	* merely a hint about the true dirty state.
1094	*
1095	* When a page is set dirty in its entirety, all its buffers are marked dirty
1096	* (if the page has buffers).
1097	*
1098	* When a buffer is marked dirty, its page is dirtied, but the page's other
1099	* buffers are not.
1100	*
1101	* Also. When blockdev buffers are explicitly read with bread(), they
1102	* individually become uptodate. But their backing page remains not
1103	* uptodate - even if all of its buffers are uptodate. A subsequent
1104	* block_read_full_page() against that page will discover all the uptodate
1105	* buffers, will set the page uptodate and will perform no I/O.
1106	*/
1107
1108	/**
1109	* mark_buffer_dirty - mark a buffer_head as needing writeout
1110	* @bh: the buffer_head to mark dirty
1111	*
1112	* mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1113	* backing page dirty, then tag the page as dirty in its address_space's radix
1114	* tree and then attach the address_space's inode to its superblock's dirty
1115	* inode list.
1116	*
1117	* mark_buffer_dirty() is atomic. It takes bh->b_page->mapping->private_lock,
1118	* mapping->tree_lock and mapping->host->i_lock.
1119	*/
1120	void mark_buffer_dirty(struct buffer_head *bh)
1121	{
1122	WARN_ON_ONCE(!buffer_uptodate(bh));
1123
1124	trace_block_dirty_buffer(bh);
1125
1126	/*
1127	* Very carefully optimize the it-is-already-dirty case.
1128	*
1129	* Don't let the final "is it dirty" escape to before we
1130	* perhaps modified the buffer.
1131	*/
1132	if (buffer_dirty(bh)) {
1133	smp_mb();
1134	if (buffer_dirty(bh))
1135	return;
1136	}
1137
1138	if (!test_set_buffer_dirty(bh)) {
1139	struct page *page = bh->b_page;
1140	if (!TestSetPageDirty(page)) {
1141	struct address_space *mapping = page_mapping(page);
1142	if (mapping)
1143	__set_page_dirty(page, mapping, 0);
1144	}
1145	}
1146	}
1147	EXPORT_SYMBOL(mark_buffer_dirty);
1148
1149	/*
1150	* Decrement a buffer_head's reference count. If all buffers against a page
1151	* have zero reference count, are clean and unlocked, and if the page is clean
1152	* and unlocked then try_to_free_buffers() may strip the buffers from the page
1153	* in preparation for freeing it (sometimes, rarely, buffers are removed from
1154	* a page but it ends up not being freed, and buffers may later be reattached).
1155	*/
1156	void __brelse(struct buffer_head * buf)
1157	{
1158	if (atomic_read(&buf->b_count)) {
1159	put_bh(buf);
1160	return;
1161	}
1162	WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1163	}
1164	EXPORT_SYMBOL(__brelse);
1165
1166	/*
1167	* bforget() is like brelse(), except it discards any
1168	* potentially dirty data.
1169	*/
1170	void __bforget(struct buffer_head *bh)
1171	{
1172	clear_buffer_dirty(bh);
1173	if (bh->b_assoc_map) {
1174	struct address_space *buffer_mapping = bh->b_page->mapping;
1175
1176	spin_lock(&buffer_mapping->private_lock);
1177	list_del_init(&bh->b_assoc_buffers);
1178	bh->b_assoc_map = NULL;
1179	spin_unlock(&buffer_mapping->private_lock);
1180	}
1181	__brelse(bh);
1182	}
1183	EXPORT_SYMBOL(__bforget);
1184
1185	static struct buffer_head __bread_slow(struct buffer_head bh)
1186	{
1187	lock_buffer(bh);
1188	if (buffer_uptodate(bh)) {
1189	unlock_buffer(bh);
1190	return bh;
1191	} else {
1192	get_bh(bh);
1193	bh->b_end_io = end_buffer_read_sync;
1194	submit_bh(READ, bh);
1195	wait_on_buffer(bh);
1196	if (buffer_uptodate(bh))
1197	return bh;
1198	}
1199	brelse(bh);
1200	return NULL;
1201	}
1202
1203	/*
1204	* Per-cpu buffer LRU implementation. To reduce the cost of __find_get_block().
1205	* The bhs[] array is sorted - newest buffer is at bhs[0]. Buffers have their
1206	* refcount elevated by one when they're in an LRU. A buffer can only appear
1207	* once in a particular CPU's LRU. A single buffer can be present in multiple
1208	* CPU's LRUs at the same time.
1209	*
1210	* This is a transparent caching front-end to sb_bread(), sb_getblk() and
1211	* sb_find_get_block().
1212	*
1213	* The LRUs themselves only need locking against invalidate_bh_lrus. We use
1214	* a local interrupt disable for that.
1215	*/
1216
1217	#define BH_LRU_SIZE 8
1218
1219	struct bh_lru {
1220	struct buffer_head *bhs[BH_LRU_SIZE];
1221	};
1222
1223	static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1224
1225	#ifdef CONFIG_SMP
1226	#define bh_lru_lock() local_irq_disable()
1227	#define bh_lru_unlock() local_irq_enable()
1228	#else
1229	#define bh_lru_lock() preempt_disable()
1230	#define bh_lru_unlock() preempt_enable()
1231	#endif
1232
1233	static inline void check_irqs_on(void)
1234	{
1235	#ifdef irqs_disabled
1236	BUG_ON(irqs_disabled());
1237	#endif
1238	}
1239
1240	/*
1241	* The LRU management algorithm is dopey-but-simple. Sorry.
1242	*/
1243	static void bh_lru_install(struct buffer_head *bh)
1244	{
1245	struct buffer_head *evictee = NULL;
1246
1247	check_irqs_on();
1248	bh_lru_lock();
1249	if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
1250	struct buffer_head *bhs[BH_LRU_SIZE];
1251	int in;
1252	int out = 0;
1253
1254	get_bh(bh);
1255	bhs[out++] = bh;
1256	for (in = 0; in < BH_LRU_SIZE; in++) {
1257	struct buffer_head *bh2 =
1258	__this_cpu_read(bh_lrus.bhs[in]);
1259
1260	if (bh2 == bh) {
1261	__brelse(bh2);
1262	} else {
1263	if (out >= BH_LRU_SIZE) {
1264	BUG_ON(evictee != NULL);
1265	evictee = bh2;
1266	} else {
1267	bhs[out++] = bh2;
1268	}
1269	}
1270	}
1271	while (out < BH_LRU_SIZE)
1272	bhs[out++] = NULL;
1273	memcpy(__this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
1274	}
1275	bh_lru_unlock();
1276
1277	if (evictee)
1278	__brelse(evictee);
1279	}
1280
1281	/*
1282	* Look up the bh in this cpu's LRU. If it's there, move it to the head.
1283	*/
1284	static struct buffer_head *
1285	lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1286	{
1287	struct buffer_head *ret = NULL;
1288	unsigned int i;
1289
1290	check_irqs_on();
1291	bh_lru_lock();
1292	for (i = 0; i < BH_LRU_SIZE; i++) {
1293	struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1294
1295	if (bh && bh->b_bdev == bdev &&
1296	bh->b_blocknr == block && bh->b_size == size) {
1297	if (i) {
1298	while (i) {
1299	__this_cpu_write(bh_lrus.bhs[i],
1300	__this_cpu_read(bh_lrus.bhs[i - 1]));
1301	i--;
1302	}
1303	__this_cpu_write(bh_lrus.bhs[0], bh);
1304	}
1305	get_bh(bh);
1306	ret = bh;
1307	break;
1308	}
1309	}
1310	bh_lru_unlock();
1311	return ret;
1312	}
1313
1314	/*
1315	* Perform a pagecache lookup for the matching buffer. If it's there, refresh
1316	* it in the LRU and mark it as accessed. If it is not present then return
1317	* NULL
1318	*/
1319	struct buffer_head *
1320	__find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1321	{
1322	struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1323
1324	if (bh == NULL) {
1325	bh = __find_get_block_slow(bdev, block);
1326	if (bh)
1327	bh_lru_install(bh);
1328	}
1329	if (bh)
1330	touch_buffer(bh);
1331	return bh;
1332	}
1333	EXPORT_SYMBOL(__find_get_block);
1334
1335	/*
1336	* __getblk will locate (and, if necessary, create) the buffer_head
1337	* which corresponds to the passed block_device, block and size. The
1338	* returned buffer has its reference count incremented.
1339	*
1340	* __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
1341	* attempt is failing. FIXME, perhaps?
1342	*/
1343	struct buffer_head *
1344	__getblk(struct block_device *bdev, sector_t block, unsigned size)
1345	{
1346	struct buffer_head *bh = __find_get_block(bdev, block, size);
1347
1348	might_sleep();
1349	if (bh == NULL)
1350	bh = __getblk_slow(bdev, block, size);
1351	return bh;
1352	}
1353	EXPORT_SYMBOL(__getblk);
1354
1355	/*
1356	* Do async read-ahead on a buffer..
1357	*/
1358	void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1359	{
1360	struct buffer_head *bh = __getblk(bdev, block, size);
1361	if (likely(bh)) {
1362	ll_rw_block(READA, 1, &bh);
1363	brelse(bh);
1364	}
1365	}
1366	EXPORT_SYMBOL(__breadahead);
1367
1368	/**
1369	* __bread() - reads a specified block and returns the bh
1370	* @bdev: the block_device to read from
1371	* @block: number of block
1372	* @size: size (in bytes) to read
1373	*
1374	* Reads a specified block, and returns buffer head that contains it.
1375	* It returns NULL if the block was unreadable.
1376	*/
1377	struct buffer_head *
1378	__bread(struct block_device *bdev, sector_t block, unsigned size)
1379	{
1380	struct buffer_head *bh = __getblk(bdev, block, size);
1381
1382	if (likely(bh) && !buffer_uptodate(bh))
1383	bh = __bread_slow(bh);
1384	return bh;
1385	}
1386	EXPORT_SYMBOL(__bread);
1387
1388	/*
1389	* invalidate_bh_lrus() is called rarely - but not only at unmount.
1390	* This doesn't race because it runs in each cpu either in irq
1391	* or with preempt disabled.
1392	*/
1393	static void invalidate_bh_lru(void *arg)
1394	{
1395	struct bh_lru *b = &get_cpu_var(bh_lrus);
1396	int i;
1397
1398	for (i = 0; i < BH_LRU_SIZE; i++) {
1399	brelse(b->bhs[i]);
1400	b->bhs[i] = NULL;
1401	}
1402	put_cpu_var(bh_lrus);
1403	}
1404
1405	static bool has_bh_in_lru(int cpu, void *dummy)
1406	{
1407	struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1408	int i;
1409
1410	for (i = 0; i < BH_LRU_SIZE; i++) {
1411	if (b->bhs[i])
1412	return 1;
1413	}
1414
1415	return 0;
1416	}
1417
1418	void invalidate_bh_lrus(void)
1419	{
1420	on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1421	}
1422	EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1423
1424	void set_bh_page(struct buffer_head *bh,
1425	struct page *page, unsigned long offset)
1426	{
1427	bh->b_page = page;
1428	BUG_ON(offset >= PAGE_SIZE);
1429	if (PageHighMem(page))
1430	/*
1431	* This catches illegal uses and preserves the offset:
1432	*/
1433	bh->b_data = (char *)(0 + offset);
1434	else
1435	bh->b_data = page_address(page) + offset;
1436	}
1437	EXPORT_SYMBOL(set_bh_page);
1438
1439	/*
1440	* Called when truncating a buffer on a page completely.
1441	*/
1442	static void discard_buffer(struct buffer_head * bh)
1443	{
1444	lock_buffer(bh);
1445	clear_buffer_dirty(bh);
1446	bh->b_bdev = NULL;
1447	clear_buffer_mapped(bh);
1448	clear_buffer_req(bh);
1449	clear_buffer_new(bh);
1450	clear_buffer_delay(bh);
1451	clear_buffer_unwritten(bh);
1452	unlock_buffer(bh);
1453	}
1454
1455	/**
1456	* block_invalidatepage - invalidate part or all of a buffer-backed page
1457	*
1458	* @page: the page which is affected
1459	* @offset: the index of the truncation point
1460	*
1461	* block_invalidatepage() is called when all or part of the page has become
1462	* invalidated by a truncate operation.
1463	*
1464	* block_invalidatepage() does not have to release all buffers, but it must
1465	* ensure that no dirty buffer is left outside @offset and that no I/O
1466	* is underway against any of the blocks which are outside the truncation
1467	* point. Because the caller is about to free (and possibly reuse) those
1468	* blocks on-disk.
1469	*/
1470	void block_invalidatepage(struct page *page, unsigned long offset)
1471	{
1472	struct buffer_head head, bh, *next;
1473	unsigned int curr_off = 0;
1474
1475	BUG_ON(!PageLocked(page));
1476	if (!page_has_buffers(page))
1477	goto out;
1478
1479	head = page_buffers(page);
1480	bh = head;
1481	do {
1482	unsigned int next_off = curr_off + bh->b_size;
1483	next = bh->b_this_page;
1484
1485	/*
1486	* is this block fully invalidated?
1487	*/
1488	if (offset <= curr_off)
1489	discard_buffer(bh);
1490	curr_off = next_off;
1491	bh = next;
1492	} while (bh != head);
1493
1494	/*
1495	* We release buffers only if the entire page is being invalidated.
1496	* The get_block cached value has been unconditionally invalidated,
1497	* so real IO is not possible anymore.
1498	*/
1499	if (offset == 0)
1500	try_to_release_page(page, 0);
1501	out:
1502	return;
1503	}
1504	EXPORT_SYMBOL(block_invalidatepage);
1505
1506	/*
1507	* We attach and possibly dirty the buffers atomically wrt
1508	* __set_page_dirty_buffers() via private_lock. try_to_free_buffers
1509	* is already excluded via the page lock.
1510	*/
1511	void create_empty_buffers(struct page *page,
1512	unsigned long blocksize, unsigned long b_state)
1513	{
1514	struct buffer_head bh, head, *tail;
1515
1516	head = alloc_page_buffers(page, blocksize, 1);
1517	bh = head;
1518	do {
1519	bh->b_state \|= b_state;
1520	tail = bh;
1521	bh = bh->b_this_page;
1522	} while (bh);
1523	tail->b_this_page = head;
1524
1525	spin_lock(&page->mapping->private_lock);
1526	if (PageUptodate(page) \|\| PageDirty(page)) {
1527	bh = head;
1528	do {
1529	if (PageDirty(page))
1530	set_buffer_dirty(bh);
1531	if (PageUptodate(page))
1532	set_buffer_uptodate(bh);
1533	bh = bh->b_this_page;
1534	} while (bh != head);
1535	}
1536	attach_page_buffers(page, head);
1537	spin_unlock(&page->mapping->private_lock);
1538	}
1539	EXPORT_SYMBOL(create_empty_buffers);
1540
1541	/*
1542	* We are taking a block for data and we don't want any output from any
1543	* buffer-cache aliases starting from return from that function and
1544	* until the moment when something will explicitly mark the buffer
1545	* dirty (hopefully that will not happen until we will free that block ;-)
1546	* We don't even need to mark it not-uptodate - nobody can expect
1547	* anything from a newly allocated buffer anyway. We used to used
1548	* unmap_buffer() for such invalidation, but that was wrong. We definitely
1549	* don't want to mark the alias unmapped, for example - it would confuse
1550	* anyone who might pick it with bread() afterwards...
1551	*
1552	* Also.. Note that bforget() doesn't lock the buffer. So there can
1553	* be writeout I/O going on against recently-freed buffers. We don't
1554	* wait on that I/O in bforget() - it's more efficient to wait on the I/O
1555	* only if we really need to. That happens here.
1556	*/
1557	void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1558	{
1559	struct buffer_head *old_bh;
1560
1561	might_sleep();
1562
1563	old_bh = __find_get_block_slow(bdev, block);
1564	if (old_bh) {
1565	clear_buffer_dirty(old_bh);
1566	wait_on_buffer(old_bh);
1567	clear_buffer_req(old_bh);
1568	__brelse(old_bh);
1569	}
1570	}
1571	EXPORT_SYMBOL(unmap_underlying_metadata);
1572
1573	/*
1574	* Size is a power-of-two in the range 512..PAGE_SIZE,
1575	* and the case we care about most is PAGE_SIZE.
1576	*
1577	* So this could possibly be written with those
1578	* constraints in mind (relevant mostly if some
1579	* architecture has a slow bit-scan instruction)
1580	*/
1581	static inline int block_size_bits(unsigned int blocksize)
1582	{
1583	return ilog2(blocksize);
1584	}
1585
1586	static struct buffer_head create_page_buffers(struct page page, struct inode *inode, unsigned int b_state)
1587	{
1588	BUG_ON(!PageLocked(page));
1589
1590	if (!page_has_buffers(page))
1591	create_empty_buffers(page, 1 << ACCESS_ONCE(inode->i_blkbits), b_state);
1592	return page_buffers(page);
1593	}
1594
1595	/*
1596	* NOTE! All mapped/uptodate combinations are valid:
1597	*
1598	* Mapped Uptodate Meaning
1599	*
1600	* No No "unknown" - must do get_block()
1601	* No Yes "hole" - zero-filled
1602	* Yes No "allocated" - allocated on disk, not read in
1603	* Yes Yes "valid" - allocated and up-to-date in memory.
1604	*
1605	* "Dirty" is valid only with the last case (mapped+uptodate).
1606	*/
1607
1608	/*
1609	* While block_write_full_page is writing back the dirty buffers under
1610	* the page lock, whoever dirtied the buffers may decide to clean them
1611	* again at any time. We handle that by only looking at the buffer
1612	* state inside lock_buffer().
1613	*
1614	* If block_write_full_page() is called for regular writeback
1615	* (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1616	* locked buffer. This only can happen if someone has written the buffer
1617	* directly, with submit_bh(). At the address_space level PageWriteback
1618	* prevents this contention from occurring.
1619	*
1620	* If block_write_full_page() is called with wbc->sync_mode ==
1621	* WB_SYNC_ALL, the writes are posted using WRITE_SYNC; this
1622	* causes the writes to be flagged as synchronous writes.
1623	*/
1624	static int __block_write_full_page(struct inode inode, struct page page,
1625	get_block_t get_block, struct writeback_control wbc,
1626	bh_end_io_t *handler)
1627	{
1628	int err;
1629	sector_t block;
1630	sector_t last_block;
1631	struct buffer_head bh, head;
1632	unsigned int blocksize, bbits;
1633	int nr_underway = 0;
1634	int write_op = (wbc->sync_mode == WB_SYNC_ALL ?
1635	WRITE_SYNC : WRITE);
1636
1637	head = create_page_buffers(page, inode,
1638	(1 << BH_Dirty)\|(1 << BH_Uptodate));
1639
1640	/*
1641	* Be very careful. We have no exclusion from __set_page_dirty_buffers
1642	* here, and the (potentially unmapped) buffers may become dirty at
1643	* any time. If a buffer becomes dirty here after we've inspected it
1644	* then we just miss that fact, and the page stays dirty.
1645	*
1646	* Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1647	* handle that here by just cleaning them.
1648	*/
1649
1650	bh = head;
1651	blocksize = bh->b_size;
1652	bbits = block_size_bits(blocksize);
1653
1654	block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1655	last_block = (i_size_read(inode) - 1) >> bbits;
1656
1657	/*
1658	* Get all the dirty buffers mapped to disk addresses and
1659	* handle any aliases from the underlying blockdev's mapping.
1660	*/
1661	do {
1662	if (block > last_block) {
1663	/*
1664	* mapped buffers outside i_size will occur, because
1665	* this page can be outside i_size when there is a
1666	* truncate in progress.
1667	*/
1668	/*
1669	* The buffer was zeroed by block_write_full_page()
1670	*/
1671	clear_buffer_dirty(bh);
1672	set_buffer_uptodate(bh);
1673	} else if ((!buffer_mapped(bh) \|\| buffer_delay(bh)) &&
1674	buffer_dirty(bh)) {
1675	WARN_ON(bh->b_size != blocksize);
1676	err = get_block(inode, block, bh, 1);
1677	if (err)
1678	goto recover;
1679	clear_buffer_delay(bh);
1680	if (buffer_new(bh)) {
1681	/* blockdev mappings never come here */
1682	clear_buffer_new(bh);
1683	unmap_underlying_metadata(bh->b_bdev,
1684	bh->b_blocknr);
1685	}
1686	}
1687	bh = bh->b_this_page;
1688	block++;
1689	} while (bh != head);
1690
1691	do {
1692	if (!buffer_mapped(bh))
1693	continue;
1694	/*
1695	* If it's a fully non-blocking write attempt and we cannot
1696	* lock the buffer then redirty the page. Note that this can
1697	* potentially cause a busy-wait loop from writeback threads
1698	* and kswapd activity, but those code paths have their own
1699	* higher-level throttling.
1700	*/
1701	if (wbc->sync_mode != WB_SYNC_NONE) {
1702	lock_buffer(bh);
1703	} else if (!trylock_buffer(bh)) {
1704	redirty_page_for_writepage(wbc, page);
1705	continue;
1706	}
1707	if (test_clear_buffer_dirty(bh)) {
1708	mark_buffer_async_write_endio(bh, handler);
1709	} else {
1710	unlock_buffer(bh);
1711	}
1712	} while ((bh = bh->b_this_page) != head);
1713
1714	/*
1715	* The page and its buffers are protected by PageWriteback(), so we can
1716	* drop the bh refcounts early.
1717	*/
1718	BUG_ON(PageWriteback(page));
1719	set_page_writeback(page);
1720
1721	do {
1722	struct buffer_head *next = bh->b_this_page;
1723	if (buffer_async_write(bh)) {
1724	submit_bh(write_op, bh);
1725	nr_underway++;
1726	}
1727	bh = next;
1728	} while (bh != head);
1729	unlock_page(page);
1730
1731	err = 0;
1732	done:
1733	if (nr_underway == 0) {
1734	/*
1735	* The page was marked dirty, but the buffers were
1736	* clean. Someone wrote them back by hand with
1737	* ll_rw_block/submit_bh. A rare case.
1738	*/
1739	end_page_writeback(page);
1740
1741	/*
1742	* The page and buffer_heads can be released at any time from
1743	* here on.
1744	*/
1745	}
1746	return err;
1747
1748	recover:
1749	/*
1750	* ENOSPC, or some other error. We may already have added some
1751	* blocks to the file, so we need to write these out to avoid
1752	* exposing stale data.
1753	* The page is currently locked and not marked for writeback
1754	*/
1755	bh = head;
1756	/* Recovery: lock and submit the mapped buffers */
1757	do {
1758	if (buffer_mapped(bh) && buffer_dirty(bh) &&
1759	!buffer_delay(bh)) {
1760	lock_buffer(bh);
1761	mark_buffer_async_write_endio(bh, handler);
1762	} else {
1763	/*
1764	* The buffer may have been set dirty during
1765	* attachment to a dirty page.
1766	*/
1767	clear_buffer_dirty(bh);
1768	}
1769	} while ((bh = bh->b_this_page) != head);
1770	SetPageError(page);
1771	BUG_ON(PageWriteback(page));
1772	mapping_set_error(page->mapping, err);
1773	set_page_writeback(page);
1774	do {
1775	struct buffer_head *next = bh->b_this_page;
1776	if (buffer_async_write(bh)) {
1777	clear_buffer_dirty(bh);
1778	submit_bh(write_op, bh);
1779	nr_underway++;
1780	}
1781	bh = next;
1782	} while (bh != head);
1783	unlock_page(page);
1784	goto done;
1785	}
1786
1787	/*
1788	* If a page has any new buffers, zero them out here, and mark them uptodate
1789	* and dirty so they'll be written out (in order to prevent uninitialised
1790	* block data from leaking). And clear the new bit.
1791	*/
1792	void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1793	{
1794	unsigned int block_start, block_end;
1795	struct buffer_head head, bh;
1796
1797	BUG_ON(!PageLocked(page));
1798	if (!page_has_buffers(page))
1799	return;
1800
1801	bh = head = page_buffers(page);
1802	block_start = 0;
1803	do {
1804	block_end = block_start + bh->b_size;
1805
1806	if (buffer_new(bh)) {
1807	if (block_end > from && block_start < to) {
1808	if (!PageUptodate(page)) {
1809	unsigned start, size;
1810
1811	start = max(from, block_start);
1812	size = min(to, block_end) - start;
1813
1814	zero_user(page, start, size);
1815	set_buffer_uptodate(bh);
1816	}
1817
1818	clear_buffer_new(bh);
1819	mark_buffer_dirty(bh);
1820	}
1821	}
1822
1823	block_start = block_end;
1824	bh = bh->b_this_page;
1825	} while (bh != head);
1826	}
1827	EXPORT_SYMBOL(page_zero_new_buffers);
1828
1829	int __block_write_begin(struct page *page, loff_t pos, unsigned len,
1830	get_block_t *get_block)
1831	{
1832	unsigned from = pos & (PAGE_CACHE_SIZE - 1);
1833	unsigned to = from + len;
1834	struct inode *inode = page->mapping->host;
1835	unsigned block_start, block_end;
1836	sector_t block;
1837	int err = 0;
1838	unsigned blocksize, bbits;
1839	struct buffer_head bh, head, wait[2], *wait_bh=wait;
1840
1841	BUG_ON(!PageLocked(page));
1842	BUG_ON(from > PAGE_CACHE_SIZE);
1843	BUG_ON(to > PAGE_CACHE_SIZE);
1844	BUG_ON(from > to);
1845
1846	head = create_page_buffers(page, inode, 0);
1847	blocksize = head->b_size;
1848	bbits = block_size_bits(blocksize);
1849
1850	block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1851
1852	for(bh = head, block_start = 0; bh != head \|\| !block_start;
1853	block++, block_start=block_end, bh = bh->b_this_page) {
1854	block_end = block_start + blocksize;
1855	if (block_end <= from \|\| block_start >= to) {
1856	if (PageUptodate(page)) {
1857	if (!buffer_uptodate(bh))
1858	set_buffer_uptodate(bh);
1859	}
1860	continue;
1861	}
1862	if (buffer_new(bh))
1863	clear_buffer_new(bh);
1864	if (!buffer_mapped(bh)) {
1865	WARN_ON(bh->b_size != blocksize);
1866	err = get_block(inode, block, bh, 1);
1867	if (err)
1868	break;
1869	if (buffer_new(bh)) {
1870	unmap_underlying_metadata(bh->b_bdev,
1871	bh->b_blocknr);
1872	if (PageUptodate(page)) {
1873	clear_buffer_new(bh);
1874	set_buffer_uptodate(bh);
1875	mark_buffer_dirty(bh);
1876	continue;
1877	}
1878	if (block_end > to \|\| block_start < from)
1879	zero_user_segments(page,
1880	to, block_end,
1881	block_start, from);
1882	continue;
1883	}
1884	}
1885	if (PageUptodate(page)) {
1886	if (!buffer_uptodate(bh))
1887	set_buffer_uptodate(bh);
1888	continue;
1889	}
1890	if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1891	!buffer_unwritten(bh) &&
1892	(block_start < from \|\| block_end > to)) {
1893	ll_rw_block(READ, 1, &bh);
1894	*wait_bh++=bh;
1895	}
1896	}
1897	/*
1898	* If we issued read requests - let them complete.
1899	*/
1900	while(wait_bh > wait) {
1901	wait_on_buffer(*--wait_bh);
1902	if (!buffer_uptodate(*wait_bh))
1903	err = -EIO;
1904	}
1905	if (unlikely(err))
1906	page_zero_new_buffers(page, from, to);
1907	return err;
1908	}
1909	EXPORT_SYMBOL(__block_write_begin);
1910
1911	static int __block_commit_write(struct inode inode, struct page page,
1912	unsigned from, unsigned to)
1913	{
1914	unsigned block_start, block_end;
1915	int partial = 0;
1916	unsigned blocksize;
1917	struct buffer_head bh, head;
1918
1919	bh = head = page_buffers(page);
1920	blocksize = bh->b_size;
1921
1922	block_start = 0;
1923	do {
1924	block_end = block_start + blocksize;
1925	if (block_end <= from \|\| block_start >= to) {
1926	if (!buffer_uptodate(bh))
1927	partial = 1;
1928	} else {
1929	set_buffer_uptodate(bh);
1930	mark_buffer_dirty(bh);
1931	}
1932	clear_buffer_new(bh);
1933
1934	block_start = block_end;
1935	bh = bh->b_this_page;
1936	} while (bh != head);
1937
1938	/*
1939	* If this is a partial write which happened to make all buffers
1940	* uptodate then we can optimize away a bogus readpage() for
1941	* the next read(). Here we 'discover' whether the page went
1942	* uptodate as a result of this (potentially partial) write.
1943	*/
1944	if (!partial)
1945	SetPageUptodate(page);
1946	return 0;
1947	}
1948
1949	/*
1950	* block_write_begin takes care of the basic task of block allocation and
1951	* bringing partial write blocks uptodate first.
1952	*
1953	* The filesystem needs to handle block truncation upon failure.
1954	*/
1955	int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
1956	unsigned flags, struct page *pagep, get_block_t get_block)
1957	{
1958	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
1959	struct page *page;
1960	int status;
1961
1962	page = grab_cache_page_write_begin(mapping, index, flags);
1963	if (!page)
1964	return -ENOMEM;
1965
1966	status = __block_write_begin(page, pos, len, get_block);
1967	if (unlikely(status)) {
1968	unlock_page(page);
1969	page_cache_release(page);
1970	page = NULL;
1971	}
1972
1973	*pagep = page;
1974	return status;
1975	}
1976	EXPORT_SYMBOL(block_write_begin);
1977
1978	int block_write_end(struct file file, struct address_space mapping,
1979	loff_t pos, unsigned len, unsigned copied,
1980	struct page page, void fsdata)
1981	{
1982	struct inode *inode = mapping->host;
1983	unsigned start;
1984
1985	start = pos & (PAGE_CACHE_SIZE - 1);
1986
1987	if (unlikely(copied < len)) {
1988	/*
1989	* The buffers that were written will now be uptodate, so we
1990	* don't have to worry about a readpage reading them and
1991	* overwriting a partial write. However if we have encountered
1992	* a short write and only partially written into a buffer, it
1993	* will not be marked uptodate, so a readpage might come in and
1994	* destroy our partial write.
1995	*
1996	* Do the simplest thing, and just treat any short write to a
1997	* non uptodate page as a zero-length write, and force the
1998	* caller to redo the whole thing.
1999	*/
2000	if (!PageUptodate(page))
2001	copied = 0;
2002
2003	page_zero_new_buffers(page, start+copied, start+len);
2004	}
2005	flush_dcache_page(page);
2006
2007	/* This could be a short (even 0-length) commit */
2008	__block_commit_write(inode, page, start, start+copied);
2009
2010	return copied;
2011	}
2012	EXPORT_SYMBOL(block_write_end);
2013
2014	int generic_write_end(struct file file, struct address_space mapping,
2015	loff_t pos, unsigned len, unsigned copied,
2016	struct page page, void fsdata)
2017	{
2018	struct inode *inode = mapping->host;
2019	int i_size_changed = 0;
2020
2021	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2022
2023	/*
2024	* No need to use i_size_read() here, the i_size
2025	* cannot change under us because we hold i_mutex.
2026	*
2027	* But it's important to update i_size while still holding page lock:
2028	* page writeout could otherwise come in and zero beyond i_size.
2029	*/
2030	if (pos+copied > inode->i_size) {
2031	i_size_write(inode, pos+copied);
2032	i_size_changed = 1;
2033	}
2034
2035	unlock_page(page);
2036	page_cache_release(page);
2037
2038	/*
2039	* Don't mark the inode dirty under page lock. First, it unnecessarily
2040	* makes the holding time of page lock longer. Second, it forces lock
2041	* ordering of page lock and transaction start for journaling
2042	* filesystems.
2043	*/
2044	if (i_size_changed)
2045	mark_inode_dirty(inode);
2046
2047	return copied;
2048	}
2049	EXPORT_SYMBOL(generic_write_end);
2050
2051	/*
2052	* block_is_partially_uptodate checks whether buffers within a page are
2053	* uptodate or not.
2054	*
2055	* Returns true if all buffers which correspond to a file portion
2056	* we want to read are uptodate.
2057	*/
2058	int block_is_partially_uptodate(struct page page, read_descriptor_t desc,
2059	unsigned long from)
2060	{
2061	unsigned block_start, block_end, blocksize;
2062	unsigned to;
2063	struct buffer_head bh, head;
2064	int ret = 1;
2065
2066	if (!page_has_buffers(page))
2067	return 0;
2068
2069	head = page_buffers(page);
2070	blocksize = head->b_size;
2071	to = min_t(unsigned, PAGE_CACHE_SIZE - from, desc->count);
2072	to = from + to;
2073	if (from < blocksize && to > PAGE_CACHE_SIZE - blocksize)
2074	return 0;
2075
2076	bh = head;
2077	block_start = 0;
2078	do {
2079	block_end = block_start + blocksize;
2080	if (block_end > from && block_start < to) {
2081	if (!buffer_uptodate(bh)) {
2082	ret = 0;
2083	break;
2084	}
2085	if (block_end >= to)
2086	break;
2087	}
2088	block_start = block_end;
2089	bh = bh->b_this_page;
2090	} while (bh != head);
2091
2092	return ret;
2093	}
2094	EXPORT_SYMBOL(block_is_partially_uptodate);
2095
2096	/*
2097	* Generic "read page" function for block devices that have the normal
2098	* get_block functionality. This is most of the block device filesystems.
2099	* Reads the page asynchronously --- the unlock_buffer() and
2100	* set/clear_buffer_uptodate() functions propagate buffer state into the
2101	* page struct once IO has completed.
2102	*/
2103	int block_read_full_page(struct page page, get_block_t get_block)
2104	{
2105	struct inode *inode = page->mapping->host;
2106	sector_t iblock, lblock;
2107	struct buffer_head bh, head, *arr[MAX_BUF_PER_PAGE];
2108	unsigned int blocksize, bbits;
2109	int nr, i;
2110	int fully_mapped = 1;
2111
2112	head = create_page_buffers(page, inode, 0);
2113	blocksize = head->b_size;
2114	bbits = block_size_bits(blocksize);
2115
2116	iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
2117	lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2118	bh = head;
2119	nr = 0;
2120	i = 0;
2121
2122	do {
2123	if (buffer_uptodate(bh))
2124	continue;
2125
2126	if (!buffer_mapped(bh)) {
2127	int err = 0;
2128
2129	fully_mapped = 0;
2130	if (iblock < lblock) {
2131	WARN_ON(bh->b_size != blocksize);
2132	err = get_block(inode, iblock, bh, 0);
2133	if (err)
2134	SetPageError(page);
2135	}
2136	if (!buffer_mapped(bh)) {
2137	zero_user(page, i * blocksize, blocksize);
2138	if (!err)
2139	set_buffer_uptodate(bh);
2140	continue;
2141	}
2142	/*
2143	* get_block() might have updated the buffer
2144	* synchronously
2145	*/
2146	if (buffer_uptodate(bh))
2147	continue;
2148	}
2149	arr[nr++] = bh;
2150	} while (i++, iblock++, (bh = bh->b_this_page) != head);
2151
2152	if (fully_mapped)
2153	SetPageMappedToDisk(page);
2154
2155	if (!nr) {
2156	/*
2157	* All buffers are uptodate - we can set the page uptodate
2158	* as well. But not if get_block() returned an error.
2159	*/
2160	if (!PageError(page))
2161	SetPageUptodate(page);
2162	unlock_page(page);
2163	return 0;
2164	}
2165
2166	/* Stage two: lock the buffers */
2167	for (i = 0; i < nr; i++) {
2168	bh = arr[i];
2169	lock_buffer(bh);
2170	mark_buffer_async_read(bh);
2171	}
2172
2173	/*
2174	* Stage 3: start the IO. Check for uptodateness
2175	* inside the buffer lock in case another process reading
2176	* the underlying blockdev brought it uptodate (the sct fix).
2177	*/
2178	for (i = 0; i < nr; i++) {
2179	bh = arr[i];
2180	if (buffer_uptodate(bh))
2181	end_buffer_async_read(bh, 1);
2182	else
2183	submit_bh(READ, bh);
2184	}
2185	return 0;
2186	}
2187	EXPORT_SYMBOL(block_read_full_page);
2188
2189	/* utility function for filesystems that need to do work on expanding
2190	* truncates. Uses filesystem pagecache writes to allow the filesystem to
2191	* deal with the hole.
2192	*/
2193	int generic_cont_expand_simple(struct inode *inode, loff_t size)
2194	{
2195	struct address_space *mapping = inode->i_mapping;
2196	struct page *page;
2197	void *fsdata;
2198	int err;
2199
2200	err = inode_newsize_ok(inode, size);
2201	if (err)
2202	goto out;
2203
2204	err = pagecache_write_begin(NULL, mapping, size, 0,
2205	AOP_FLAG_UNINTERRUPTIBLE\|AOP_FLAG_CONT_EXPAND,
2206	&page, &fsdata);
2207	if (err)
2208	goto out;
2209
2210	err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2211	BUG_ON(err > 0);
2212
2213	out:
2214	return err;
2215	}
2216	EXPORT_SYMBOL(generic_cont_expand_simple);
2217
2218	static int cont_expand_zero(struct file file, struct address_space mapping,
2219	loff_t pos, loff_t *bytes)
2220	{
2221	struct inode *inode = mapping->host;
2222	unsigned blocksize = 1 << inode->i_blkbits;
2223	struct page *page;
2224	void *fsdata;
2225	pgoff_t index, curidx;
2226	loff_t curpos;
2227	unsigned zerofrom, offset, len;
2228	int err = 0;
2229
2230	index = pos >> PAGE_CACHE_SHIFT;
2231	offset = pos & ~PAGE_CACHE_MASK;
2232
2233	while (index > (curidx = (curpos = *bytes)>>PAGE_CACHE_SHIFT)) {
2234	zerofrom = curpos & ~PAGE_CACHE_MASK;
2235	if (zerofrom & (blocksize-1)) {
2236	*bytes \|= (blocksize-1);
2237	(*bytes)++;
2238	}
2239	len = PAGE_CACHE_SIZE - zerofrom;
2240
2241	err = pagecache_write_begin(file, mapping, curpos, len,
2242	AOP_FLAG_UNINTERRUPTIBLE,
2243	&page, &fsdata);
2244	if (err)
2245	goto out;
2246	zero_user(page, zerofrom, len);
2247	err = pagecache_write_end(file, mapping, curpos, len, len,
2248	page, fsdata);
2249	if (err < 0)
2250	goto out;
2251	BUG_ON(err != len);
2252	err = 0;
2253
2254	balance_dirty_pages_ratelimited(mapping);
2255	}
2256
2257	/* page covers the boundary, find the boundary offset */
2258	if (index == curidx) {
2259	zerofrom = curpos & ~PAGE_CACHE_MASK;
2260	/* if we will expand the thing last block will be filled */
2261	if (offset <= zerofrom) {
2262	goto out;
2263	}
2264	if (zerofrom & (blocksize-1)) {
2265	*bytes \|= (blocksize-1);
2266	(*bytes)++;
2267	}
2268	len = offset - zerofrom;
2269
2270	err = pagecache_write_begin(file, mapping, curpos, len,
2271	AOP_FLAG_UNINTERRUPTIBLE,
2272	&page, &fsdata);
2273	if (err)
2274	goto out;
2275	zero_user(page, zerofrom, len);
2276	err = pagecache_write_end(file, mapping, curpos, len, len,
2277	page, fsdata);
2278	if (err < 0)
2279	goto out;
2280	BUG_ON(err != len);
2281	err = 0;
2282	}
2283	out:
2284	return err;
2285	}
2286
2287	/*
2288	* For moronic filesystems that do not allow holes in file.
2289	* We may have to extend the file.
2290	*/
2291	int cont_write_begin(struct file file, struct address_space mapping,
2292	loff_t pos, unsigned len, unsigned flags,
2293	struct page pagep, void fsdata,
2294	get_block_t get_block, loff_t bytes)
2295	{
2296	struct inode *inode = mapping->host;
2297	unsigned blocksize = 1 << inode->i_blkbits;
2298	unsigned zerofrom;
2299	int err;
2300
2301	err = cont_expand_zero(file, mapping, pos, bytes);
2302	if (err)
2303	return err;
2304
2305	zerofrom = *bytes & ~PAGE_CACHE_MASK;
2306	if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2307	*bytes \|= (blocksize-1);
2308	(*bytes)++;
2309	}
2310
2311	return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2312	}
2313	EXPORT_SYMBOL(cont_write_begin);
2314
2315	int block_commit_write(struct page *page, unsigned from, unsigned to)
2316	{
2317	struct inode *inode = page->mapping->host;
2318	__block_commit_write(inode,page,from,to);
2319	return 0;
2320	}
2321	EXPORT_SYMBOL(block_commit_write);
2322
2323	/*
2324	* block_page_mkwrite() is not allowed to change the file size as it gets
2325	* called from a page fault handler when a page is first dirtied. Hence we must
2326	* be careful to check for EOF conditions here. We set the page up correctly
2327	* for a written page which means we get ENOSPC checking when writing into
2328	* holes and correct delalloc and unwritten extent mapping on filesystems that
2329	* support these features.
2330	*
2331	* We are not allowed to take the i_mutex here so we have to play games to
2332	* protect against truncate races as the page could now be beyond EOF. Because
2333	* truncate writes the inode size before removing pages, once we have the
2334	* page lock we can determine safely if the page is beyond EOF. If it is not
2335	* beyond EOF, then the page is guaranteed safe against truncation until we
2336	* unlock the page.
2337	*
2338	* Direct callers of this function should protect against filesystem freezing
2339	* using sb_start_write() - sb_end_write() functions.
2340	*/
2341	int __block_page_mkwrite(struct vm_area_struct vma, struct vm_fault vmf,
2342	get_block_t get_block)
2343	{
2344	struct page *page = vmf->page;
2345	struct inode *inode = file_inode(vma->vm_file);
2346	unsigned long end;
2347	loff_t size;
2348	int ret;
2349
2350	lock_page(page);
2351	size = i_size_read(inode);
2352	if ((page->mapping != inode->i_mapping) \|\|
2353	(page_offset(page) > size)) {
2354	/* We overload EFAULT to mean page got truncated */
2355	ret = -EFAULT;
2356	goto out_unlock;
2357	}
2358
2359	/* page is wholly or partially inside EOF */
2360	if (((page->index + 1) << PAGE_CACHE_SHIFT) > size)
2361	end = size & ~PAGE_CACHE_MASK;
2362	else
2363	end = PAGE_CACHE_SIZE;
2364
2365	ret = __block_write_begin(page, 0, end, get_block);
2366	if (!ret)
2367	ret = block_commit_write(page, 0, end);
2368
2369	if (unlikely(ret < 0))
2370	goto out_unlock;
2371	set_page_dirty(page);
2372	wait_for_stable_page(page);
2373	return 0;
2374	out_unlock:
2375	unlock_page(page);
2376	return ret;
2377	}
2378	EXPORT_SYMBOL(__block_page_mkwrite);
2379
2380	int block_page_mkwrite(struct vm_area_struct vma, struct vm_fault vmf,
2381	get_block_t get_block)
2382	{
2383	int ret;
2384	struct super_block *sb = file_inode(vma->vm_file)->i_sb;
2385
2386	sb_start_pagefault(sb);
2387
2388	/*
2389	* Update file times before taking page lock. We may end up failing the
2390	* fault so this update may be superfluous but who really cares...
2391	*/
2392	file_update_time(vma->vm_file);
2393
2394	ret = __block_page_mkwrite(vma, vmf, get_block);
2395	sb_end_pagefault(sb);
2396	return block_page_mkwrite_return(ret);
2397	}
2398	EXPORT_SYMBOL(block_page_mkwrite);
2399
2400	/*
2401	* nobh_write_begin()'s prereads are special: the buffer_heads are freed
2402	* immediately, while under the page lock. So it needs a special end_io
2403	* handler which does not touch the bh after unlocking it.
2404	*/
2405	static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2406	{
2407	__end_buffer_read_notouch(bh, uptodate);
2408	}
2409
2410	/*
2411	* Attach the singly-linked list of buffers created by nobh_write_begin, to
2412	* the page (converting it to circular linked list and taking care of page
2413	* dirty races).
2414	*/
2415	static void attach_nobh_buffers(struct page page, struct buffer_head head)
2416	{
2417	struct buffer_head *bh;
2418
2419	BUG_ON(!PageLocked(page));
2420
2421	spin_lock(&page->mapping->private_lock);
2422	bh = head;
2423	do {
2424	if (PageDirty(page))
2425	set_buffer_dirty(bh);
2426	if (!bh->b_this_page)
2427	bh->b_this_page = head;
2428	bh = bh->b_this_page;
2429	} while (bh != head);
2430	attach_page_buffers(page, head);
2431	spin_unlock(&page->mapping->private_lock);
2432	}
2433
2434	/*
2435	* On entry, the page is fully not uptodate.
2436	* On exit the page is fully uptodate in the areas outside (from,to)
2437	* The filesystem needs to handle block truncation upon failure.
2438	*/
2439	int nobh_write_begin(struct address_space *mapping,
2440	loff_t pos, unsigned len, unsigned flags,
2441	struct page pagep, void fsdata,
2442	get_block_t *get_block)
2443	{
2444	struct inode *inode = mapping->host;
2445	const unsigned blkbits = inode->i_blkbits;
2446	const unsigned blocksize = 1 << blkbits;
2447	struct buffer_head head, bh;
2448	struct page *page;
2449	pgoff_t index;
2450	unsigned from, to;
2451	unsigned block_in_page;
2452	unsigned block_start, block_end;
2453	sector_t block_in_file;
2454	int nr_reads = 0;
2455	int ret = 0;
2456	int is_mapped_to_disk = 1;
2457
2458	index = pos >> PAGE_CACHE_SHIFT;
2459	from = pos & (PAGE_CACHE_SIZE - 1);
2460	to = from + len;
2461
2462	page = grab_cache_page_write_begin(mapping, index, flags);
2463	if (!page)
2464	return -ENOMEM;
2465	*pagep = page;
2466	*fsdata = NULL;
2467
2468	if (page_has_buffers(page)) {
2469	ret = __block_write_begin(page, pos, len, get_block);
2470	if (unlikely(ret))
2471	goto out_release;
2472	return ret;
2473	}
2474
2475	if (PageMappedToDisk(page))
2476	return 0;
2477
2478	/*
2479	* Allocate buffers so that we can keep track of state, and potentially
2480	* attach them to the page if an error occurs. In the common case of
2481	* no error, they will just be freed again without ever being attached
2482	* to the page (which is all OK, because we're under the page lock).
2483	*
2484	* Be careful: the buffer linked list is a NULL terminated one, rather
2485	* than the circular one we're used to.
2486	*/
2487	head = alloc_page_buffers(page, blocksize, 0);
2488	if (!head) {
2489	ret = -ENOMEM;
2490	goto out_release;
2491	}
2492
2493	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
2494
2495	/*
2496	* We loop across all blocks in the page, whether or not they are
2497	* part of the affected region. This is so we can discover if the
2498	* page is fully mapped-to-disk.
2499	*/
2500	for (block_start = 0, block_in_page = 0, bh = head;
2501	block_start < PAGE_CACHE_SIZE;
2502	block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2503	int create;
2504
2505	block_end = block_start + blocksize;
2506	bh->b_state = 0;
2507	create = 1;
2508	if (block_start >= to)
2509	create = 0;
2510	ret = get_block(inode, block_in_file + block_in_page,
2511	bh, create);
2512	if (ret)
2513	goto failed;
2514	if (!buffer_mapped(bh))
2515	is_mapped_to_disk = 0;
2516	if (buffer_new(bh))
2517	unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
2518	if (PageUptodate(page)) {
2519	set_buffer_uptodate(bh);
2520	continue;
2521	}
2522	if (buffer_new(bh) \|\| !buffer_mapped(bh)) {
2523	zero_user_segments(page, block_start, from,
2524	to, block_end);
2525	continue;
2526	}
2527	if (buffer_uptodate(bh))
2528	continue; /* reiserfs does this */
2529	if (block_start < from \|\| block_end > to) {
2530	lock_buffer(bh);
2531	bh->b_end_io = end_buffer_read_nobh;
2532	submit_bh(READ, bh);
2533	nr_reads++;
2534	}
2535	}
2536
2537	if (nr_reads) {
2538	/*
2539	* The page is locked, so these buffers are protected from
2540	* any VM or truncate activity. Hence we don't need to care
2541	* for the buffer_head refcounts.
2542	*/
2543	for (bh = head; bh; bh = bh->b_this_page) {
2544	wait_on_buffer(bh);
2545	if (!buffer_uptodate(bh))
2546	ret = -EIO;
2547	}
2548	if (ret)
2549	goto failed;
2550	}
2551
2552	if (is_mapped_to_disk)
2553	SetPageMappedToDisk(page);
2554
2555	fsdata = head; / to be released by nobh_write_end */
2556
2557	return 0;
2558
2559	failed:
2560	BUG_ON(!ret);
2561	/*
2562	* Error recovery is a bit difficult. We need to zero out blocks that
2563	* were newly allocated, and dirty them to ensure they get written out.
2564	* Buffers need to be attached to the page at this point, otherwise
2565	* the handling of potential IO errors during writeout would be hard
2566	* (could try doing synchronous writeout, but what if that fails too?)
2567	*/
2568	attach_nobh_buffers(page, head);
2569	page_zero_new_buffers(page, from, to);
2570
2571	out_release:
2572	unlock_page(page);
2573	page_cache_release(page);
2574	*pagep = NULL;
2575
2576	return ret;
2577	}
2578	EXPORT_SYMBOL(nobh_write_begin);
2579
2580	int nobh_write_end(struct file file, struct address_space mapping,
2581	loff_t pos, unsigned len, unsigned copied,
2582	struct page page, void fsdata)
2583	{
2584	struct inode *inode = page->mapping->host;
2585	struct buffer_head *head = fsdata;
2586	struct buffer_head *bh;
2587	BUG_ON(fsdata != NULL && page_has_buffers(page));
2588
2589	if (unlikely(copied < len) && head)
2590	attach_nobh_buffers(page, head);
2591	if (page_has_buffers(page))
2592	return generic_write_end(file, mapping, pos, len,
2593	copied, page, fsdata);
2594
2595	SetPageUptodate(page);
2596	set_page_dirty(page);
2597	if (pos+copied > inode->i_size) {
2598	i_size_write(inode, pos+copied);
2599	mark_inode_dirty(inode);
2600	}
2601
2602	unlock_page(page);
2603	page_cache_release(page);
2604
2605	while (head) {
2606	bh = head;
2607	head = head->b_this_page;
2608	free_buffer_head(bh);
2609	}
2610
2611	return copied;
2612	}
2613	EXPORT_SYMBOL(nobh_write_end);
2614
2615	/*
2616	* nobh_writepage() - based on block_full_write_page() except
2617	* that it tries to operate without attaching bufferheads to
2618	* the page.
2619	*/
2620	int nobh_writepage(struct page page, get_block_t get_block,
2621	struct writeback_control *wbc)
2622	{
2623	struct inode * const inode = page->mapping->host;
2624	loff_t i_size = i_size_read(inode);
2625	const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2626	unsigned offset;
2627	int ret;
2628
2629	/* Is the page fully inside i_size? */
2630	if (page->index < end_index)
2631	goto out;
2632
2633	/* Is the page fully outside i_size? (truncate in progress) */
2634	offset = i_size & (PAGE_CACHE_SIZE-1);
2635	if (page->index >= end_index+1 \|\| !offset) {
2636	/*
2637	* The page may have dirty, unmapped buffers. For example,
2638	* they may have been added in ext3_writepage(). Make them
2639	* freeable here, so the page does not leak.
2640	*/
2641	#if 0
2642	/* Not really sure about this - do we need this ? */
2643	if (page->mapping->a_ops->invalidatepage)
2644	page->mapping->a_ops->invalidatepage(page, offset);
2645	#endif
2646	unlock_page(page);
2647	return 0; /* don't care */
2648	}
2649
2650	/*
2651	* The page straddles i_size. It must be zeroed out on each and every
2652	* writepage invocation because it may be mmapped. "A file is mapped
2653	* in multiples of the page size. For a file that is not a multiple of
2654	* the page size, the remaining memory is zeroed when mapped, and
2655	* writes to that region are not written out to the file."
2656	*/
2657	zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2658	out:
2659	ret = mpage_writepage(page, get_block, wbc);
2660	if (ret == -EAGAIN)
2661	ret = __block_write_full_page(inode, page, get_block, wbc,
2662	end_buffer_async_write);
2663	return ret;
2664	}
2665	EXPORT_SYMBOL(nobh_writepage);
2666
2667	int nobh_truncate_page(struct address_space *mapping,
2668	loff_t from, get_block_t *get_block)
2669	{
2670	pgoff_t index = from >> PAGE_CACHE_SHIFT;
2671	unsigned offset = from & (PAGE_CACHE_SIZE-1);
2672	unsigned blocksize;
2673	sector_t iblock;
2674	unsigned length, pos;
2675	struct inode *inode = mapping->host;
2676	struct page *page;
2677	struct buffer_head map_bh;
2678	int err;
2679
2680	blocksize = 1 << inode->i_blkbits;
2681	length = offset & (blocksize - 1);
2682
2683	/* Block boundary? Nothing to do */
2684	if (!length)
2685	return 0;
2686
2687	length = blocksize - length;
2688	iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2689
2690	page = grab_cache_page(mapping, index);
2691	err = -ENOMEM;
2692	if (!page)
2693	goto out;
2694
2695	if (page_has_buffers(page)) {
2696	has_buffers:
2697	unlock_page(page);
2698	page_cache_release(page);
2699	return block_truncate_page(mapping, from, get_block);
2700	}
2701
2702	/* Find the buffer that contains "offset" */
2703	pos = blocksize;
2704	while (offset >= pos) {
2705	iblock++;
2706	pos += blocksize;
2707	}
2708
2709	map_bh.b_size = blocksize;
2710	map_bh.b_state = 0;
2711	err = get_block(inode, iblock, &map_bh, 0);
2712	if (err)
2713	goto unlock;
2714	/* unmapped? It's a hole - nothing to do */
2715	if (!buffer_mapped(&map_bh))
2716	goto unlock;
2717
2718	/* Ok, it's mapped. Make sure it's up-to-date */
2719	if (!PageUptodate(page)) {
2720	err = mapping->a_ops->readpage(NULL, page);
2721	if (err) {
2722	page_cache_release(page);
2723	goto out;
2724	}
2725	lock_page(page);
2726	if (!PageUptodate(page)) {
2727	err = -EIO;
2728	goto unlock;
2729	}
2730	if (page_has_buffers(page))
2731	goto has_buffers;
2732	}
2733	zero_user(page, offset, length);
2734	set_page_dirty(page);
2735	err = 0;
2736
2737	unlock:
2738	unlock_page(page);
2739	page_cache_release(page);
2740	out:
2741	return err;
2742	}
2743	EXPORT_SYMBOL(nobh_truncate_page);
2744
2745	int block_truncate_page(struct address_space *mapping,
2746	loff_t from, get_block_t *get_block)
2747	{
2748	pgoff_t index = from >> PAGE_CACHE_SHIFT;
2749	unsigned offset = from & (PAGE_CACHE_SIZE-1);
2750	unsigned blocksize;
2751	sector_t iblock;
2752	unsigned length, pos;
2753	struct inode *inode = mapping->host;
2754	struct page *page;
2755	struct buffer_head *bh;
2756	int err;
2757
2758	blocksize = 1 << inode->i_blkbits;
2759	length = offset & (blocksize - 1);
2760
2761	/* Block boundary? Nothing to do */
2762	if (!length)
2763	return 0;
2764
2765	length = blocksize - length;
2766	iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2767
2768	page = grab_cache_page(mapping, index);
2769	err = -ENOMEM;
2770	if (!page)
2771	goto out;
2772
2773	if (!page_has_buffers(page))
2774	create_empty_buffers(page, blocksize, 0);
2775
2776	/* Find the buffer that contains "offset" */
2777	bh = page_buffers(page);
2778	pos = blocksize;
2779	while (offset >= pos) {
2780	bh = bh->b_this_page;
2781	iblock++;
2782	pos += blocksize;
2783	}
2784
2785	err = 0;
2786	if (!buffer_mapped(bh)) {
2787	WARN_ON(bh->b_size != blocksize);
2788	err = get_block(inode, iblock, bh, 0);
2789	if (err)
2790	goto unlock;
2791	/* unmapped? It's a hole - nothing to do */
2792	if (!buffer_mapped(bh))
2793	goto unlock;
2794	}
2795
2796	/* Ok, it's mapped. Make sure it's up-to-date */
2797	if (PageUptodate(page))
2798	set_buffer_uptodate(bh);
2799
2800	if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2801	err = -EIO;
2802	ll_rw_block(READ, 1, &bh);
2803	wait_on_buffer(bh);
2804	/* Uhhuh. Read error. Complain and punt. */
2805	if (!buffer_uptodate(bh))
2806	goto unlock;
2807	}
2808
2809	zero_user(page, offset, length);
2810	mark_buffer_dirty(bh);
2811	err = 0;
2812
2813	unlock:
2814	unlock_page(page);
2815	page_cache_release(page);
2816	out:
2817	return err;
2818	}
2819	EXPORT_SYMBOL(block_truncate_page);
2820
2821	/*
2822	* The generic ->writepage function for buffer-backed address_spaces
2823	* this form passes in the end_io handler used to finish the IO.
2824	*/
2825	int block_write_full_page_endio(struct page page, get_block_t get_block,
2826	struct writeback_control wbc, bh_end_io_t handler)
2827	{
2828	struct inode * const inode = page->mapping->host;
2829	loff_t i_size = i_size_read(inode);
2830	const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2831	unsigned offset;
2832
2833	/* Is the page fully inside i_size? */
2834	if (page->index < end_index)
2835	return __block_write_full_page(inode, page, get_block, wbc,
2836	handler);
2837
2838	/* Is the page fully outside i_size? (truncate in progress) */
2839	offset = i_size & (PAGE_CACHE_SIZE-1);
2840	if (page->index >= end_index+1 \|\| !offset) {
2841	/*
2842	* The page may have dirty, unmapped buffers. For example,
2843	* they may have been added in ext3_writepage(). Make them
2844	* freeable here, so the page does not leak.
2845	*/
2846	do_invalidatepage(page, 0);
2847	unlock_page(page);
2848	return 0; /* don't care */
2849	}
2850
2851	/*
2852	* The page straddles i_size. It must be zeroed out on each and every
2853	* writepage invocation because it may be mmapped. "A file is mapped
2854	* in multiples of the page size. For a file that is not a multiple of
2855	* the page size, the remaining memory is zeroed when mapped, and
2856	* writes to that region are not written out to the file."
2857	*/
2858	zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2859	return __block_write_full_page(inode, page, get_block, wbc, handler);
2860	}
2861	EXPORT_SYMBOL(block_write_full_page_endio);
2862
2863	/*
2864	* The generic ->writepage function for buffer-backed address_spaces
2865	*/
2866	int block_write_full_page(struct page page, get_block_t get_block,
2867	struct writeback_control *wbc)
2868	{
2869	return block_write_full_page_endio(page, get_block, wbc,
2870	end_buffer_async_write);
2871	}
2872	EXPORT_SYMBOL(block_write_full_page);
2873
2874	sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2875	get_block_t *get_block)
2876	{
2877	struct buffer_head tmp;
2878	struct inode *inode = mapping->host;
2879	tmp.b_state = 0;
2880	tmp.b_blocknr = 0;
2881	tmp.b_size = 1 << inode->i_blkbits;
2882	get_block(inode, block, &tmp, 0);
2883	return tmp.b_blocknr;
2884	}
2885	EXPORT_SYMBOL(generic_block_bmap);
2886
2887	static void end_bio_bh_io_sync(struct bio *bio, int err)
2888	{
2889	struct buffer_head *bh = bio->bi_private;
2890
2891	if (err == -EOPNOTSUPP) {
2892	set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
2893	}
2894
2895	if (unlikely (test_bit(BIO_QUIET,&bio->bi_flags)))
2896	set_bit(BH_Quiet, &bh->b_state);
2897
2898	bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
2899	bio_put(bio);
2900	}
2901
2902	/*
2903	* This allows us to do IO even on the odd last sectors
2904	* of a device, even if the bh block size is some multiple
2905	* of the physical sector size.
2906	*
2907	* We'll just truncate the bio to the size of the device,
2908	* and clear the end of the buffer head manually.
2909	*
2910	* Truly out-of-range accesses will turn into actual IO
2911	* errors, this only handles the "we need to be able to
2912	* do IO at the final sector" case.
2913	*/
2914	static void guard_bh_eod(int rw, struct bio bio, struct buffer_head bh)
2915	{
2916	sector_t maxsector;
2917	unsigned bytes;
2918
2919	maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
2920	if (!maxsector)
2921	return;
2922
2923	/*
2924	* If the whole IO is past the end of the device,
2925	* let it through, and the IO layer will turn it into
2926	* an EIO.
2927	*/
2928	if (unlikely(bio->bi_sector >= maxsector))
2929	return;
2930
2931	maxsector -= bio->bi_sector;
2932	bytes = bio->bi_size;
2933	if (likely((bytes >> 9) <= maxsector))
2934	return;
2935
2936	/* Uhhuh. We've got a bh that straddles the device size! */
2937	bytes = maxsector << 9;
2938
2939	/* Truncate the bio.. */
2940	bio->bi_size = bytes;
2941	bio->bi_io_vec[0].bv_len = bytes;
2942
2943	/* ..and clear the end of the buffer for reads */
2944	if ((rw & RW_MASK) == READ) {
2945	void *kaddr = kmap_atomic(bh->b_page);
2946	memset(kaddr + bh_offset(bh) + bytes, 0, bh->b_size - bytes);
2947	kunmap_atomic(kaddr);
2948	flush_dcache_page(bh->b_page);
2949	}
2950	}
2951
2952	int submit_bh(int rw, struct buffer_head * bh)
2953	{
2954	struct bio *bio;
2955	int ret = 0;
2956
2957	BUG_ON(!buffer_locked(bh));
2958	BUG_ON(!buffer_mapped(bh));
2959	BUG_ON(!bh->b_end_io);
2960	BUG_ON(buffer_delay(bh));
2961	BUG_ON(buffer_unwritten(bh));
2962
2963	/*
2964	* Only clear out a write error when rewriting
2965	*/
2966	if (test_set_buffer_req(bh) && (rw & WRITE))
2967	clear_buffer_write_io_error(bh);
2968
2969	/*
2970	* from here on down, it's all bio -- do the initial mapping,
2971	* submit_bio -> generic_make_request may further map this bio around
2972	*/
2973	bio = bio_alloc(GFP_NOIO, 1);
2974
2975	bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
2976	bio->bi_bdev = bh->b_bdev;
2977	bio->bi_io_vec[0].bv_page = bh->b_page;
2978	bio->bi_io_vec[0].bv_len = bh->b_size;
2979	bio->bi_io_vec[0].bv_offset = bh_offset(bh);
2980
2981	bio->bi_vcnt = 1;
2982	bio->bi_idx = 0;
2983	bio->bi_size = bh->b_size;
2984
2985	bio->bi_end_io = end_bio_bh_io_sync;
2986	bio->bi_private = bh;
2987
2988	/* Take care of bh's that straddle the end of the device */
2989	guard_bh_eod(rw, bio, bh);
2990
2991	bio_get(bio);
2992	submit_bio(rw, bio);
2993
2994	if (bio_flagged(bio, BIO_EOPNOTSUPP))
2995	ret = -EOPNOTSUPP;
2996
2997	bio_put(bio);
2998	return ret;
2999	}
3000	EXPORT_SYMBOL(submit_bh);
3001
3002	/**
3003	* ll_rw_block: low-level access to block devices (DEPRECATED)
3004	* @rw: whether to %READ or %WRITE or maybe %READA (readahead)
3005	* @nr: number of &struct buffer_heads in the array
3006	* @bhs: array of pointers to &struct buffer_head
3007	*
3008	* ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3009	* requests an I/O operation on them, either a %READ or a %WRITE. The third
3010	* %READA option is described in the documentation for generic_make_request()
3011	* which ll_rw_block() calls.
3012	*
3013	* This function drops any buffer that it cannot get a lock on (with the
3014	* BH_Lock state bit), any buffer that appears to be clean when doing a write
3015	* request, and any buffer that appears to be up-to-date when doing read
3016	* request. Further it marks as clean buffers that are processed for
3017	* writing (the buffer cache won't assume that they are actually clean
3018	* until the buffer gets unlocked).
3019	*
3020	* ll_rw_block sets b_end_io to simple completion handler that marks
3021	* the buffer up-to-date (if approriate), unlocks the buffer and wakes
3022	* any waiters.
3023	*
3024	* All of the buffers must be for the same device, and must also be a
3025	* multiple of the current approved size for the device.
3026	*/
3027	void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
3028	{
3029	int i;
3030
3031	for (i = 0; i < nr; i++) {
3032	struct buffer_head *bh = bhs[i];
3033
3034	if (!trylock_buffer(bh))
3035	continue;
3036	if (rw == WRITE) {
3037	if (test_clear_buffer_dirty(bh)) {
3038	bh->b_end_io = end_buffer_write_sync;
3039	get_bh(bh);
3040	submit_bh(WRITE, bh);
3041	continue;
3042	}
3043	} else {
3044	if (!buffer_uptodate(bh)) {
3045	bh->b_end_io = end_buffer_read_sync;
3046	get_bh(bh);
3047	submit_bh(rw, bh);
3048	continue;
3049	}
3050	}
3051	unlock_buffer(bh);
3052	}
3053	}
3054	EXPORT_SYMBOL(ll_rw_block);
3055
3056	void write_dirty_buffer(struct buffer_head *bh, int rw)
3057	{
3058	lock_buffer(bh);
3059	if (!test_clear_buffer_dirty(bh)) {
3060	unlock_buffer(bh);
3061	return;
3062	}
3063	bh->b_end_io = end_buffer_write_sync;
3064	get_bh(bh);
3065	submit_bh(rw, bh);
3066	}
3067	EXPORT_SYMBOL(write_dirty_buffer);
3068
3069	/*
3070	* For a data-integrity writeout, we need to wait upon any in-progress I/O
3071	* and then start new I/O and then wait upon it. The caller must have a ref on
3072	* the buffer_head.
3073	*/
3074	int __sync_dirty_buffer(struct buffer_head *bh, int rw)
3075	{
3076	int ret = 0;
3077
3078	WARN_ON(atomic_read(&bh->b_count) < 1);
3079	lock_buffer(bh);
3080	if (test_clear_buffer_dirty(bh)) {
3081	get_bh(bh);
3082	bh->b_end_io = end_buffer_write_sync;
3083	ret = submit_bh(rw, bh);
3084	wait_on_buffer(bh);
3085	if (!ret && !buffer_uptodate(bh))
3086	ret = -EIO;
3087	} else {
3088	unlock_buffer(bh);
3089	}
3090	return ret;
3091	}
3092	EXPORT_SYMBOL(__sync_dirty_buffer);
3093
3094	int sync_dirty_buffer(struct buffer_head *bh)
3095	{
3096	return __sync_dirty_buffer(bh, WRITE_SYNC);
3097	}
3098	EXPORT_SYMBOL(sync_dirty_buffer);
3099
3100	/*
3101	* try_to_free_buffers() checks if all the buffers on this particular page
3102	* are unused, and releases them if so.
3103	*
3104	* Exclusion against try_to_free_buffers may be obtained by either
3105	* locking the page or by holding its mapping's private_lock.
3106	*
3107	* If the page is dirty but all the buffers are clean then we need to
3108	* be sure to mark the page clean as well. This is because the page
3109	* may be against a block device, and a later reattachment of buffers
3110	* to a dirty page will set all buffers dirty. Which would corrupt
3111	* filesystem data on the same device.
3112	*
3113	* The same applies to regular filesystem pages: if all the buffers are
3114	* clean then we set the page clean and proceed. To do that, we require
3115	* total exclusion from __set_page_dirty_buffers(). That is obtained with
3116	* private_lock.
3117	*
3118	* try_to_free_buffers() is non-blocking.
3119	*/
3120	static inline int buffer_busy(struct buffer_head *bh)
3121	{
3122	return atomic_read(&bh->b_count) \|
3123	(bh->b_state & ((1 << BH_Dirty) \| (1 << BH_Lock)));
3124	}
3125
3126	static int
3127	drop_buffers(struct page page, struct buffer_head *buffers_to_free)
3128	{
3129	struct buffer_head *head = page_buffers(page);
3130	struct buffer_head *bh;
3131
3132	bh = head;
3133	do {
3134	if (buffer_write_io_error(bh) && page->mapping)
3135	set_bit(AS_EIO, &page->mapping->flags);
3136	if (buffer_busy(bh))
3137	goto failed;
3138	bh = bh->b_this_page;
3139	} while (bh != head);
3140
3141	do {
3142	struct buffer_head *next = bh->b_this_page;
3143
3144	if (bh->b_assoc_map)
3145	__remove_assoc_queue(bh);
3146	bh = next;
3147	} while (bh != head);
3148	*buffers_to_free = head;
3149	__clear_page_buffers(page);
3150	return 1;
3151	failed:
3152	return 0;
3153	}
3154
3155	int try_to_free_buffers(struct page *page)
3156	{
3157	struct address_space * const mapping = page->mapping;
3158	struct buffer_head *buffers_to_free = NULL;
3159	int ret = 0;
3160
3161	BUG_ON(!PageLocked(page));
3162	if (PageWriteback(page))
3163	return 0;
3164
3165	if (mapping == NULL) { /* can this still happen? */
3166	ret = drop_buffers(page, &buffers_to_free);
3167	goto out;
3168	}
3169
3170	spin_lock(&mapping->private_lock);
3171	ret = drop_buffers(page, &buffers_to_free);
3172
3173	/*
3174	* If the filesystem writes its buffers by hand (eg ext3)
3175	* then we can have clean buffers against a dirty page. We
3176	* clean the page here; otherwise the VM will never notice
3177	* that the filesystem did any IO at all.
3178	*
3179	* Also, during truncate, discard_buffer will have marked all
3180	* the page's buffers clean. We discover that here and clean
3181	* the page also.
3182	*
3183	* private_lock must be held over this entire operation in order
3184	* to synchronise against __set_page_dirty_buffers and prevent the
3185	* dirty bit from being lost.
3186	*/
3187	if (ret)
3188	cancel_dirty_page(page, PAGE_CACHE_SIZE);
3189	spin_unlock(&mapping->private_lock);
3190	out:
3191	if (buffers_to_free) {
3192	struct buffer_head *bh = buffers_to_free;
3193
3194	do {
3195	struct buffer_head *next = bh->b_this_page;
3196	free_buffer_head(bh);
3197	bh = next;
3198	} while (bh != buffers_to_free);
3199	}
3200	return ret;
3201	}
3202	EXPORT_SYMBOL(try_to_free_buffers);
3203
3204	/*
3205	* There are no bdflush tunables left. But distributions are
3206	* still running obsolete flush daemons, so we terminate them here.
3207	*
3208	* Use of bdflush() is deprecated and will be removed in a future kernel.
3209	* The `flush-X' kernel threads fully replace bdflush daemons and this call.
3210	*/
3211	SYSCALL_DEFINE2(bdflush, int, func, long, data)
3212	{
3213	static int msg_count;
3214
3215	if (!capable(CAP_SYS_ADMIN))
3216	return -EPERM;
3217
3218	if (msg_count < 5) {
3219	msg_count++;
3220	printk(KERN_INFO
3221	"warning: process `%s' used the obsolete bdflush"
3222	" system call\n", current->comm);
3223	printk(KERN_INFO "Fix your initscripts?\n");
3224	}
3225
3226	if (func == 1)
3227	do_exit(0);
3228	return 0;
3229	}
3230
3231	/*
3232	* Buffer-head allocation
3233	*/
3234	static struct kmem_cache *bh_cachep __read_mostly;
3235
3236	/*
3237	* Once the number of bh's in the machine exceeds this level, we start
3238	* stripping them in writeback.
3239	*/
3240	static unsigned long max_buffer_heads;
3241
3242	int buffer_heads_over_limit;
3243
3244	struct bh_accounting {
3245	int nr; /* Number of live bh's */
3246	int ratelimit; /* Limit cacheline bouncing */
3247	};
3248
3249	static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3250
3251	static void recalc_bh_state(void)
3252	{
3253	int i;
3254	int tot = 0;
3255
3256	if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3257	return;
3258	__this_cpu_write(bh_accounting.ratelimit, 0);
3259	for_each_online_cpu(i)
3260	tot += per_cpu(bh_accounting, i).nr;
3261	buffer_heads_over_limit = (tot > max_buffer_heads);
3262	}
3263
3264	struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3265	{
3266	struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3267	if (ret) {
3268	INIT_LIST_HEAD(&ret->b_assoc_buffers);
3269	preempt_disable();
3270	__this_cpu_inc(bh_accounting.nr);
3271	recalc_bh_state();
3272	preempt_enable();
3273	}
3274	return ret;
3275	}
3276	EXPORT_SYMBOL(alloc_buffer_head);
3277
3278	void free_buffer_head(struct buffer_head *bh)
3279	{
3280	BUG_ON(!list_empty(&bh->b_assoc_buffers));
3281	kmem_cache_free(bh_cachep, bh);
3282	preempt_disable();
3283	__this_cpu_dec(bh_accounting.nr);
3284	recalc_bh_state();
3285	preempt_enable();
3286	}
3287	EXPORT_SYMBOL(free_buffer_head);
3288
3289	static void buffer_exit_cpu(int cpu)
3290	{
3291	int i;
3292	struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3293
3294	for (i = 0; i < BH_LRU_SIZE; i++) {
3295	brelse(b->bhs[i]);
3296	b->bhs[i] = NULL;
3297	}
3298	this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3299	per_cpu(bh_accounting, cpu).nr = 0;
3300	}
3301
3302	static int buffer_cpu_notify(struct notifier_block *self,
3303	unsigned long action, void *hcpu)
3304	{
3305	if (action == CPU_DEAD \|\| action == CPU_DEAD_FROZEN)
3306	buffer_exit_cpu((unsigned long)hcpu);
3307	return NOTIFY_OK;
3308	}
3309
3310	/**
3311	* bh_uptodate_or_lock - Test whether the buffer is uptodate
3312	* @bh: struct buffer_head
3313	*
3314	* Return true if the buffer is up-to-date and false,
3315	* with the buffer locked, if not.
3316	*/
3317	int bh_uptodate_or_lock(struct buffer_head *bh)
3318	{
3319	if (!buffer_uptodate(bh)) {
3320	lock_buffer(bh);
3321	if (!buffer_uptodate(bh))
3322	return 0;
3323	unlock_buffer(bh);
3324	}
3325	return 1;
3326	}
3327	EXPORT_SYMBOL(bh_uptodate_or_lock);
3328
3329	/**
3330	* bh_submit_read - Submit a locked buffer for reading
3331	* @bh: struct buffer_head
3332	*
3333	* Returns zero on success and -EIO on error.
3334	*/
3335	int bh_submit_read(struct buffer_head *bh)
3336	{
3337	BUG_ON(!buffer_locked(bh));
3338
3339	if (buffer_uptodate(bh)) {
3340	unlock_buffer(bh);
3341	return 0;
3342	}
3343
3344	get_bh(bh);
3345	bh->b_end_io = end_buffer_read_sync;
3346	submit_bh(READ, bh);
3347	wait_on_buffer(bh);
3348	if (buffer_uptodate(bh))
3349	return 0;
3350	return -EIO;
3351	}
3352	EXPORT_SYMBOL(bh_submit_read);
3353
3354	void __init buffer_init(void)
3355	{
3356	unsigned long nrpages;
3357
3358	bh_cachep = kmem_cache_create("buffer_head",
3359	sizeof(struct buffer_head), 0,
3360	(SLAB_RECLAIM_ACCOUNT\|SLAB_PANIC\|
3361	SLAB_MEM_SPREAD),
3362	NULL);
3363
3364	/*
3365	* Limit the bh occupancy to 10% of ZONE_NORMAL
3366	*/
3367	nrpages = (nr_free_buffer_pages() * 10) / 100;
3368	max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3369	hotcpu_notifier(buffer_cpu_notify, 0);
3370	}