linux - fs/buffer.c

3379 lines · 87.4 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	return head;
870	/*
871	* In case anything failed, we just free everything we got.
872	*/
873	no_grow:
874	if (head) {
875	do {
876	bh = head;
877	head = head->b_this_page;
878	free_buffer_head(bh);
879	} while (head);
880	}
881
882	/*
883	* Return failure for non-async IO requests. Async IO requests
884	* are not allowed to fail, so we have to wait until buffer heads
885	* become available. But we don't want tasks sleeping with
886	* partially complete buffers, so all were released above.
887	*/
888	if (!retry)
889	return NULL;
890
891	/* We're _really_ low on memory. Now we just
892	* wait for old buffer heads to become free due to
893	* finishing IO. Since this is an async request and
894	* the reserve list is empty, we're sure there are
895	* async buffer heads in use.
896	*/
897	free_more_memory();
898	goto try_again;
899	}
900	EXPORT_SYMBOL_GPL(alloc_page_buffers);
901
902	static inline void
903	link_dev_buffers(struct page page, struct buffer_head head)
904	{
905	struct buffer_head bh, tail;
906
907	bh = head;
908	do {
909	tail = bh;
910	bh = bh->b_this_page;
911	} while (bh);
912	tail->b_this_page = head;
913	attach_page_buffers(page, head);
914	}
915
916	static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
917	{
918	sector_t retval = ~((sector_t)0);
919	loff_t sz = i_size_read(bdev->bd_inode);
920
921	if (sz) {
922	unsigned int sizebits = blksize_bits(size);
923	retval = (sz >> sizebits);
924	}
925	return retval;
926	}
927
928	/*
929	* Initialise the state of a blockdev page's buffers.
930	*/
931	static sector_t
932	init_page_buffers(struct page page, struct block_device bdev,
933	sector_t block, int size)
934	{
935	struct buffer_head *head = page_buffers(page);
936	struct buffer_head *bh = head;
937	int uptodate = PageUptodate(page);
938	sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
939
940	do {
941	if (!buffer_mapped(bh)) {
942	init_buffer(bh, NULL, NULL);
943	bh->b_bdev = bdev;
944	bh->b_blocknr = block;
945	if (uptodate)
946	set_buffer_uptodate(bh);
947	if (block < end_block)
948	set_buffer_mapped(bh);
949	}
950	block++;
951	bh = bh->b_this_page;
952	} while (bh != head);
953
954	/*
955	* Caller needs to validate requested block against end of device.
956	*/
957	return end_block;
958	}
959
960	/*
961	* Create the page-cache page that contains the requested block.
962	*
963	* This is used purely for blockdev mappings.
964	*/
965	static int
966	grow_dev_page(struct block_device *bdev, sector_t block,
967	pgoff_t index, int size, int sizebits)
968	{
969	struct inode *inode = bdev->bd_inode;
970	struct page *page;
971	struct buffer_head *bh;
972	sector_t end_block;
973	int ret = 0; /* Will call free_more_memory() */
974
975	page = find_or_create_page(inode->i_mapping, index,
976	(mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS)\|__GFP_MOVABLE);
977	if (!page)
978	return ret;
979
980	BUG_ON(!PageLocked(page));
981
982	if (page_has_buffers(page)) {
983	bh = page_buffers(page);
984	if (bh->b_size == size) {
985	end_block = init_page_buffers(page, bdev,
986	index << sizebits, size);
987	goto done;
988	}
989	if (!try_to_free_buffers(page))
990	goto failed;
991	}
992
993	/*
994	* Allocate some buffers for this page
995	*/
996	bh = alloc_page_buffers(page, size, 0);
997	if (!bh)
998	goto failed;
999
1000	/*
1001	* Link the page to the buffers and initialise them. Take the
1002	* lock to be atomic wrt __find_get_block(), which does not
1003	* run under the page lock.
1004	*/
1005	spin_lock(&inode->i_mapping->private_lock);
1006	link_dev_buffers(page, bh);
1007	end_block = init_page_buffers(page, bdev, index << sizebits, size);
1008	spin_unlock(&inode->i_mapping->private_lock);
1009	done:
1010	ret = (block < end_block) ? 1 : -ENXIO;
1011	failed:
1012	unlock_page(page);
1013	page_cache_release(page);
1014	return ret;
1015	}
1016
1017	/*
1018	* Create buffers for the specified block device block's page. If
1019	* that page was dirty, the buffers are set dirty also.
1020	*/
1021	static int
1022	grow_buffers(struct block_device *bdev, sector_t block, int size)
1023	{
1024	pgoff_t index;
1025	int sizebits;
1026
1027	sizebits = -1;
1028	do {
1029	sizebits++;
1030	} while ((size << sizebits) < PAGE_SIZE);
1031
1032	index = block >> sizebits;
1033
1034	/*
1035	* Check for a block which wants to lie outside our maximum possible
1036	* pagecache index. (this comparison is done using sector_t types).
1037	*/
1038	if (unlikely(index != block >> sizebits)) {
1039	char b[BDEVNAME_SIZE];
1040
1041	printk(KERN_ERR "%s: requested out-of-range block %llu for "
1042	"device %s\n",
1043	__func__, (unsigned long long)block,
1044	bdevname(bdev, b));
1045	return -EIO;
1046	}
1047
1048	/* Create a page with the proper size buffers.. */
1049	return grow_dev_page(bdev, block, index, size, sizebits);
1050	}
1051
1052	static struct buffer_head *
1053	__getblk_slow(struct block_device *bdev, sector_t block, int size)
1054	{
1055	/* Size must be multiple of hard sectorsize */
1056	if (unlikely(size & (bdev_logical_block_size(bdev)-1) \|\|
1057	(size < 512 \|\| size > PAGE_SIZE))) {
1058	printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1059	size);
1060	printk(KERN_ERR "logical block size: %d\n",
1061	bdev_logical_block_size(bdev));
1062
1063	dump_stack();
1064	return NULL;
1065	}
1066
1067	for (;;) {
1068	struct buffer_head *bh;
1069	int ret;
1070
1071	bh = __find_get_block(bdev, block, size);
1072	if (bh)
1073	return bh;
1074
1075	ret = grow_buffers(bdev, block, size);
1076	if (ret < 0)
1077	return NULL;
1078	if (ret == 0)
1079	free_more_memory();
1080	}
1081	}
1082
1083	/*
1084	* The relationship between dirty buffers and dirty pages:
1085	*
1086	* Whenever a page has any dirty buffers, the page's dirty bit is set, and
1087	* the page is tagged dirty in its radix tree.
1088	*
1089	* At all times, the dirtiness of the buffers represents the dirtiness of
1090	* subsections of the page. If the page has buffers, the page dirty bit is
1091	* merely a hint about the true dirty state.
1092	*
1093	* When a page is set dirty in its entirety, all its buffers are marked dirty
1094	* (if the page has buffers).
1095	*
1096	* When a buffer is marked dirty, its page is dirtied, but the page's other
1097	* buffers are not.
1098	*
1099	* Also. When blockdev buffers are explicitly read with bread(), they
1100	* individually become uptodate. But their backing page remains not
1101	* uptodate - even if all of its buffers are uptodate. A subsequent
1102	* block_read_full_page() against that page will discover all the uptodate
1103	* buffers, will set the page uptodate and will perform no I/O.
1104	*/
1105
1106	/**
1107	* mark_buffer_dirty - mark a buffer_head as needing writeout
1108	* @bh: the buffer_head to mark dirty
1109	*
1110	* mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1111	* backing page dirty, then tag the page as dirty in its address_space's radix
1112	* tree and then attach the address_space's inode to its superblock's dirty
1113	* inode list.
1114	*
1115	* mark_buffer_dirty() is atomic. It takes bh->b_page->mapping->private_lock,
1116	* mapping->tree_lock and mapping->host->i_lock.
1117	*/
1118	void mark_buffer_dirty(struct buffer_head *bh)
1119	{
1120	WARN_ON_ONCE(!buffer_uptodate(bh));
1121
1122	trace_block_dirty_buffer(bh);
1123
1124	/*
1125	* Very carefully optimize the it-is-already-dirty case.
1126	*
1127	* Don't let the final "is it dirty" escape to before we
1128	* perhaps modified the buffer.
1129	*/
1130	if (buffer_dirty(bh)) {
1131	smp_mb();
1132	if (buffer_dirty(bh))
1133	return;
1134	}
1135
1136	if (!test_set_buffer_dirty(bh)) {
1137	struct page *page = bh->b_page;
1138	if (!TestSetPageDirty(page)) {
1139	struct address_space *mapping = page_mapping(page);
1140	if (mapping)
1141	__set_page_dirty(page, mapping, 0);
1142	}
1143	}
1144	}
1145	EXPORT_SYMBOL(mark_buffer_dirty);
1146
1147	/*
1148	* Decrement a buffer_head's reference count. If all buffers against a page
1149	* have zero reference count, are clean and unlocked, and if the page is clean
1150	* and unlocked then try_to_free_buffers() may strip the buffers from the page
1151	* in preparation for freeing it (sometimes, rarely, buffers are removed from
1152	* a page but it ends up not being freed, and buffers may later be reattached).
1153	*/
1154	void __brelse(struct buffer_head * buf)
1155	{
1156	if (atomic_read(&buf->b_count)) {
1157	put_bh(buf);
1158	return;
1159	}
1160	WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1161	}
1162	EXPORT_SYMBOL(__brelse);
1163
1164	/*
1165	* bforget() is like brelse(), except it discards any
1166	* potentially dirty data.
1167	*/
1168	void __bforget(struct buffer_head *bh)
1169	{
1170	clear_buffer_dirty(bh);
1171	if (bh->b_assoc_map) {
1172	struct address_space *buffer_mapping = bh->b_page->mapping;
1173
1174	spin_lock(&buffer_mapping->private_lock);
1175	list_del_init(&bh->b_assoc_buffers);
1176	bh->b_assoc_map = NULL;
1177	spin_unlock(&buffer_mapping->private_lock);
1178	}
1179	__brelse(bh);
1180	}
1181	EXPORT_SYMBOL(__bforget);
1182
1183	static struct buffer_head __bread_slow(struct buffer_head bh)
1184	{
1185	lock_buffer(bh);
1186	if (buffer_uptodate(bh)) {
1187	unlock_buffer(bh);
1188	return bh;
1189	} else {
1190	get_bh(bh);
1191	bh->b_end_io = end_buffer_read_sync;
1192	submit_bh(READ, bh);
1193	wait_on_buffer(bh);
1194	if (buffer_uptodate(bh))
1195	return bh;
1196	}
1197	brelse(bh);
1198	return NULL;
1199	}
1200
1201	/*
1202	* Per-cpu buffer LRU implementation. To reduce the cost of __find_get_block().
1203	* The bhs[] array is sorted - newest buffer is at bhs[0]. Buffers have their
1204	* refcount elevated by one when they're in an LRU. A buffer can only appear
1205	* once in a particular CPU's LRU. A single buffer can be present in multiple
1206	* CPU's LRUs at the same time.
1207	*
1208	* This is a transparent caching front-end to sb_bread(), sb_getblk() and
1209	* sb_find_get_block().
1210	*
1211	* The LRUs themselves only need locking against invalidate_bh_lrus. We use
1212	* a local interrupt disable for that.
1213	*/
1214
1215	#define BH_LRU_SIZE 8
1216
1217	struct bh_lru {
1218	struct buffer_head *bhs[BH_LRU_SIZE];
1219	};
1220
1221	static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1222
1223	#ifdef CONFIG_SMP
1224	#define bh_lru_lock() local_irq_disable()
1225	#define bh_lru_unlock() local_irq_enable()
1226	#else
1227	#define bh_lru_lock() preempt_disable()
1228	#define bh_lru_unlock() preempt_enable()
1229	#endif
1230
1231	static inline void check_irqs_on(void)
1232	{
1233	#ifdef irqs_disabled
1234	BUG_ON(irqs_disabled());
1235	#endif
1236	}
1237
1238	/*
1239	* The LRU management algorithm is dopey-but-simple. Sorry.
1240	*/
1241	static void bh_lru_install(struct buffer_head *bh)
1242	{
1243	struct buffer_head *evictee = NULL;
1244
1245	check_irqs_on();
1246	bh_lru_lock();
1247	if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
1248	struct buffer_head *bhs[BH_LRU_SIZE];
1249	int in;
1250	int out = 0;
1251
1252	get_bh(bh);
1253	bhs[out++] = bh;
1254	for (in = 0; in < BH_LRU_SIZE; in++) {
1255	struct buffer_head *bh2 =
1256	__this_cpu_read(bh_lrus.bhs[in]);
1257
1258	if (bh2 == bh) {
1259	__brelse(bh2);
1260	} else {
1261	if (out >= BH_LRU_SIZE) {
1262	BUG_ON(evictee != NULL);
1263	evictee = bh2;
1264	} else {
1265	bhs[out++] = bh2;
1266	}
1267	}
1268	}
1269	while (out < BH_LRU_SIZE)
1270	bhs[out++] = NULL;
1271	memcpy(__this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
1272	}
1273	bh_lru_unlock();
1274
1275	if (evictee)
1276	__brelse(evictee);
1277	}
1278
1279	/*
1280	* Look up the bh in this cpu's LRU. If it's there, move it to the head.
1281	*/
1282	static struct buffer_head *
1283	lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1284	{
1285	struct buffer_head *ret = NULL;
1286	unsigned int i;
1287
1288	check_irqs_on();
1289	bh_lru_lock();
1290	for (i = 0; i < BH_LRU_SIZE; i++) {
1291	struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1292
1293	if (bh && bh->b_bdev == bdev &&
1294	bh->b_blocknr == block && bh->b_size == size) {
1295	if (i) {
1296	while (i) {
1297	__this_cpu_write(bh_lrus.bhs[i],
1298	__this_cpu_read(bh_lrus.bhs[i - 1]));
1299	i--;
1300	}
1301	__this_cpu_write(bh_lrus.bhs[0], bh);
1302	}
1303	get_bh(bh);
1304	ret = bh;
1305	break;
1306	}
1307	}
1308	bh_lru_unlock();
1309	return ret;
1310	}
1311
1312	/*
1313	* Perform a pagecache lookup for the matching buffer. If it's there, refresh
1314	* it in the LRU and mark it as accessed. If it is not present then return
1315	* NULL
1316	*/
1317	struct buffer_head *
1318	__find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1319	{
1320	struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1321
1322	if (bh == NULL) {
1323	bh = __find_get_block_slow(bdev, block);
1324	if (bh)
1325	bh_lru_install(bh);
1326	}
1327	if (bh)
1328	touch_buffer(bh);
1329	return bh;
1330	}
1331	EXPORT_SYMBOL(__find_get_block);
1332
1333	/*
1334	* __getblk will locate (and, if necessary, create) the buffer_head
1335	* which corresponds to the passed block_device, block and size. The
1336	* returned buffer has its reference count incremented.
1337	*
1338	* __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
1339	* attempt is failing. FIXME, perhaps?
1340	*/
1341	struct buffer_head *
1342	__getblk(struct block_device *bdev, sector_t block, unsigned size)
1343	{
1344	struct buffer_head *bh = __find_get_block(bdev, block, size);
1345
1346	might_sleep();
1347	if (bh == NULL)
1348	bh = __getblk_slow(bdev, block, size);
1349	return bh;
1350	}
1351	EXPORT_SYMBOL(__getblk);
1352
1353	/*
1354	* Do async read-ahead on a buffer..
1355	*/
1356	void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1357	{
1358	struct buffer_head *bh = __getblk(bdev, block, size);
1359	if (likely(bh)) {
1360	ll_rw_block(READA, 1, &bh);
1361	brelse(bh);
1362	}
1363	}
1364	EXPORT_SYMBOL(__breadahead);
1365
1366	/**
1367	* __bread() - reads a specified block and returns the bh
1368	* @bdev: the block_device to read from
1369	* @block: number of block
1370	* @size: size (in bytes) to read
1371	*
1372	* Reads a specified block, and returns buffer head that contains it.
1373	* It returns NULL if the block was unreadable.
1374	*/
1375	struct buffer_head *
1376	__bread(struct block_device *bdev, sector_t block, unsigned size)
1377	{
1378	struct buffer_head *bh = __getblk(bdev, block, size);
1379
1380	if (likely(bh) && !buffer_uptodate(bh))
1381	bh = __bread_slow(bh);
1382	return bh;
1383	}
1384	EXPORT_SYMBOL(__bread);
1385
1386	/*
1387	* invalidate_bh_lrus() is called rarely - but not only at unmount.
1388	* This doesn't race because it runs in each cpu either in irq
1389	* or with preempt disabled.
1390	*/
1391	static void invalidate_bh_lru(void *arg)
1392	{
1393	struct bh_lru *b = &get_cpu_var(bh_lrus);
1394	int i;
1395
1396	for (i = 0; i < BH_LRU_SIZE; i++) {
1397	brelse(b->bhs[i]);
1398	b->bhs[i] = NULL;
1399	}
1400	put_cpu_var(bh_lrus);
1401	}
1402
1403	static bool has_bh_in_lru(int cpu, void *dummy)
1404	{
1405	struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1406	int i;
1407
1408	for (i = 0; i < BH_LRU_SIZE; i++) {
1409	if (b->bhs[i])
1410	return 1;
1411	}
1412
1413	return 0;
1414	}
1415
1416	void invalidate_bh_lrus(void)
1417	{
1418	on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1419	}
1420	EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1421
1422	void set_bh_page(struct buffer_head *bh,
1423	struct page *page, unsigned long offset)
1424	{
1425	bh->b_page = page;
1426	BUG_ON(offset >= PAGE_SIZE);
1427	if (PageHighMem(page))
1428	/*
1429	* This catches illegal uses and preserves the offset:
1430	*/
1431	bh->b_data = (char *)(0 + offset);
1432	else
1433	bh->b_data = page_address(page) + offset;
1434	}
1435	EXPORT_SYMBOL(set_bh_page);
1436
1437	/*
1438	* Called when truncating a buffer on a page completely.
1439	*/
1440	static void discard_buffer(struct buffer_head * bh)
1441	{
1442	lock_buffer(bh);
1443	clear_buffer_dirty(bh);
1444	bh->b_bdev = NULL;
1445	clear_buffer_mapped(bh);
1446	clear_buffer_req(bh);
1447	clear_buffer_new(bh);
1448	clear_buffer_delay(bh);
1449	clear_buffer_unwritten(bh);
1450	unlock_buffer(bh);
1451	}
1452
1453	/**
1454	* block_invalidatepage - invalidate part or all of a buffer-backed page
1455	*
1456	* @page: the page which is affected
1457	* @offset: the index of the truncation point
1458	*
1459	* block_invalidatepage() is called when all or part of the page has become
1460	* invalidated by a truncate operation.
1461	*
1462	* block_invalidatepage() does not have to release all buffers, but it must
1463	* ensure that no dirty buffer is left outside @offset and that no I/O
1464	* is underway against any of the blocks which are outside the truncation
1465	* point. Because the caller is about to free (and possibly reuse) those
1466	* blocks on-disk.
1467	*/
1468	void block_invalidatepage(struct page *page, unsigned long offset)
1469	{
1470	struct buffer_head head, bh, *next;
1471	unsigned int curr_off = 0;
1472
1473	BUG_ON(!PageLocked(page));
1474	if (!page_has_buffers(page))
1475	goto out;
1476
1477	head = page_buffers(page);
1478	bh = head;
1479	do {
1480	unsigned int next_off = curr_off + bh->b_size;
1481	next = bh->b_this_page;
1482
1483	/*
1484	* is this block fully invalidated?
1485	*/
1486	if (offset <= curr_off)
1487	discard_buffer(bh);
1488	curr_off = next_off;
1489	bh = next;
1490	} while (bh != head);
1491
1492	/*
1493	* We release buffers only if the entire page is being invalidated.
1494	* The get_block cached value has been unconditionally invalidated,
1495	* so real IO is not possible anymore.
1496	*/
1497	if (offset == 0)
1498	try_to_release_page(page, 0);
1499	out:
1500	return;
1501	}
1502	EXPORT_SYMBOL(block_invalidatepage);
1503
1504	/*
1505	* We attach and possibly dirty the buffers atomically wrt
1506	* __set_page_dirty_buffers() via private_lock. try_to_free_buffers
1507	* is already excluded via the page lock.
1508	*/
1509	void create_empty_buffers(struct page *page,
1510	unsigned long blocksize, unsigned long b_state)
1511	{
1512	struct buffer_head bh, head, *tail;
1513
1514	head = alloc_page_buffers(page, blocksize, 1);
1515	bh = head;
1516	do {
1517	bh->b_state \|= b_state;
1518	tail = bh;
1519	bh = bh->b_this_page;
1520	} while (bh);
1521	tail->b_this_page = head;
1522
1523	spin_lock(&page->mapping->private_lock);
1524	if (PageUptodate(page) \|\| PageDirty(page)) {
1525	bh = head;
1526	do {
1527	if (PageDirty(page))
1528	set_buffer_dirty(bh);
1529	if (PageUptodate(page))
1530	set_buffer_uptodate(bh);
1531	bh = bh->b_this_page;
1532	} while (bh != head);
1533	}
1534	attach_page_buffers(page, head);
1535	spin_unlock(&page->mapping->private_lock);
1536	}
1537	EXPORT_SYMBOL(create_empty_buffers);
1538
1539	/*
1540	* We are taking a block for data and we don't want any output from any
1541	* buffer-cache aliases starting from return from that function and
1542	* until the moment when something will explicitly mark the buffer
1543	* dirty (hopefully that will not happen until we will free that block ;-)
1544	* We don't even need to mark it not-uptodate - nobody can expect
1545	* anything from a newly allocated buffer anyway. We used to used
1546	* unmap_buffer() for such invalidation, but that was wrong. We definitely
1547	* don't want to mark the alias unmapped, for example - it would confuse
1548	* anyone who might pick it with bread() afterwards...
1549	*
1550	* Also.. Note that bforget() doesn't lock the buffer. So there can
1551	* be writeout I/O going on against recently-freed buffers. We don't
1552	* wait on that I/O in bforget() - it's more efficient to wait on the I/O
1553	* only if we really need to. That happens here.
1554	*/
1555	void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1556	{
1557	struct buffer_head *old_bh;
1558
1559	might_sleep();
1560
1561	old_bh = __find_get_block_slow(bdev, block);
1562	if (old_bh) {
1563	clear_buffer_dirty(old_bh);
1564	wait_on_buffer(old_bh);
1565	clear_buffer_req(old_bh);
1566	__brelse(old_bh);
1567	}
1568	}
1569	EXPORT_SYMBOL(unmap_underlying_metadata);
1570
1571	/*
1572	* Size is a power-of-two in the range 512..PAGE_SIZE,
1573	* and the case we care about most is PAGE_SIZE.
1574	*
1575	* So this could possibly be written with those
1576	* constraints in mind (relevant mostly if some
1577	* architecture has a slow bit-scan instruction)
1578	*/
1579	static inline int block_size_bits(unsigned int blocksize)
1580	{
1581	return ilog2(blocksize);
1582	}
1583
1584	static struct buffer_head create_page_buffers(struct page page, struct inode *inode, unsigned int b_state)
1585	{
1586	BUG_ON(!PageLocked(page));
1587
1588	if (!page_has_buffers(page))
1589	create_empty_buffers(page, 1 << ACCESS_ONCE(inode->i_blkbits), b_state);
1590	return page_buffers(page);
1591	}
1592
1593	/*
1594	* NOTE! All mapped/uptodate combinations are valid:
1595	*
1596	* Mapped Uptodate Meaning
1597	*
1598	* No No "unknown" - must do get_block()
1599	* No Yes "hole" - zero-filled
1600	* Yes No "allocated" - allocated on disk, not read in
1601	* Yes Yes "valid" - allocated and up-to-date in memory.
1602	*
1603	* "Dirty" is valid only with the last case (mapped+uptodate).
1604	*/
1605
1606	/*
1607	* While block_write_full_page is writing back the dirty buffers under
1608	* the page lock, whoever dirtied the buffers may decide to clean them
1609	* again at any time. We handle that by only looking at the buffer
1610	* state inside lock_buffer().
1611	*
1612	* If block_write_full_page() is called for regular writeback
1613	* (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1614	* locked buffer. This only can happen if someone has written the buffer
1615	* directly, with submit_bh(). At the address_space level PageWriteback
1616	* prevents this contention from occurring.
1617	*
1618	* If block_write_full_page() is called with wbc->sync_mode ==
1619	* WB_SYNC_ALL, the writes are posted using WRITE_SYNC; this
1620	* causes the writes to be flagged as synchronous writes.
1621	*/
1622	static int __block_write_full_page(struct inode inode, struct page page,
1623	get_block_t get_block, struct writeback_control wbc,
1624	bh_end_io_t *handler)
1625	{
1626	int err;
1627	sector_t block;
1628	sector_t last_block;
1629	struct buffer_head bh, head;
1630	unsigned int blocksize, bbits;
1631	int nr_underway = 0;
1632	int write_op = (wbc->sync_mode == WB_SYNC_ALL ?
1633	WRITE_SYNC : WRITE);
1634
1635	head = create_page_buffers(page, inode,
1636	(1 << BH_Dirty)\|(1 << BH_Uptodate));
1637
1638	/*
1639	* Be very careful. We have no exclusion from __set_page_dirty_buffers
1640	* here, and the (potentially unmapped) buffers may become dirty at
1641	* any time. If a buffer becomes dirty here after we've inspected it
1642	* then we just miss that fact, and the page stays dirty.
1643	*
1644	* Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1645	* handle that here by just cleaning them.
1646	*/
1647
1648	bh = head;
1649	blocksize = bh->b_size;
1650	bbits = block_size_bits(blocksize);
1651
1652	block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1653	last_block = (i_size_read(inode) - 1) >> bbits;
1654
1655	/*
1656	* Get all the dirty buffers mapped to disk addresses and
1657	* handle any aliases from the underlying blockdev's mapping.
1658	*/
1659	do {
1660	if (block > last_block) {
1661	/*
1662	* mapped buffers outside i_size will occur, because
1663	* this page can be outside i_size when there is a
1664	* truncate in progress.
1665	*/
1666	/*
1667	* The buffer was zeroed by block_write_full_page()
1668	*/
1669	clear_buffer_dirty(bh);
1670	set_buffer_uptodate(bh);
1671	} else if ((!buffer_mapped(bh) \|\| buffer_delay(bh)) &&
1672	buffer_dirty(bh)) {
1673	WARN_ON(bh->b_size != blocksize);
1674	err = get_block(inode, block, bh, 1);
1675	if (err)
1676	goto recover;
1677	clear_buffer_delay(bh);
1678	if (buffer_new(bh)) {
1679	/* blockdev mappings never come here */
1680	clear_buffer_new(bh);
1681	unmap_underlying_metadata(bh->b_bdev,
1682	bh->b_blocknr);
1683	}
1684	}
1685	bh = bh->b_this_page;
1686	block++;
1687	} while (bh != head);
1688
1689	do {
1690	if (!buffer_mapped(bh))
1691	continue;
1692	/*
1693	* If it's a fully non-blocking write attempt and we cannot
1694	* lock the buffer then redirty the page. Note that this can
1695	* potentially cause a busy-wait loop from writeback threads
1696	* and kswapd activity, but those code paths have their own
1697	* higher-level throttling.
1698	*/
1699	if (wbc->sync_mode != WB_SYNC_NONE) {
1700	lock_buffer(bh);
1701	} else if (!trylock_buffer(bh)) {
1702	redirty_page_for_writepage(wbc, page);
1703	continue;
1704	}
1705	if (test_clear_buffer_dirty(bh)) {
1706	mark_buffer_async_write_endio(bh, handler);
1707	} else {
1708	unlock_buffer(bh);
1709	}
1710	} while ((bh = bh->b_this_page) != head);
1711
1712	/*
1713	* The page and its buffers are protected by PageWriteback(), so we can
1714	* drop the bh refcounts early.
1715	*/
1716	BUG_ON(PageWriteback(page));
1717	set_page_writeback(page);
1718
1719	do {
1720	struct buffer_head *next = bh->b_this_page;
1721	if (buffer_async_write(bh)) {
1722	submit_bh(write_op, bh);
1723	nr_underway++;
1724	}
1725	bh = next;
1726	} while (bh != head);
1727	unlock_page(page);
1728
1729	err = 0;
1730	done:
1731	if (nr_underway == 0) {
1732	/*
1733	* The page was marked dirty, but the buffers were
1734	* clean. Someone wrote them back by hand with
1735	* ll_rw_block/submit_bh. A rare case.
1736	*/
1737	end_page_writeback(page);
1738
1739	/*
1740	* The page and buffer_heads can be released at any time from
1741	* here on.
1742	*/
1743	}
1744	return err;
1745
1746	recover:
1747	/*
1748	* ENOSPC, or some other error. We may already have added some
1749	* blocks to the file, so we need to write these out to avoid
1750	* exposing stale data.
1751	* The page is currently locked and not marked for writeback
1752	*/
1753	bh = head;
1754	/* Recovery: lock and submit the mapped buffers */
1755	do {
1756	if (buffer_mapped(bh) && buffer_dirty(bh) &&
1757	!buffer_delay(bh)) {
1758	lock_buffer(bh);
1759	mark_buffer_async_write_endio(bh, handler);
1760	} else {
1761	/*
1762	* The buffer may have been set dirty during
1763	* attachment to a dirty page.
1764	*/
1765	clear_buffer_dirty(bh);
1766	}
1767	} while ((bh = bh->b_this_page) != head);
1768	SetPageError(page);
1769	BUG_ON(PageWriteback(page));
1770	mapping_set_error(page->mapping, err);
1771	set_page_writeback(page);
1772	do {
1773	struct buffer_head *next = bh->b_this_page;
1774	if (buffer_async_write(bh)) {
1775	clear_buffer_dirty(bh);
1776	submit_bh(write_op, bh);
1777	nr_underway++;
1778	}
1779	bh = next;
1780	} while (bh != head);
1781	unlock_page(page);
1782	goto done;
1783	}
1784
1785	/*
1786	* If a page has any new buffers, zero them out here, and mark them uptodate
1787	* and dirty so they'll be written out (in order to prevent uninitialised
1788	* block data from leaking). And clear the new bit.
1789	*/
1790	void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1791	{
1792	unsigned int block_start, block_end;
1793	struct buffer_head head, bh;
1794
1795	BUG_ON(!PageLocked(page));
1796	if (!page_has_buffers(page))
1797	return;
1798
1799	bh = head = page_buffers(page);
1800	block_start = 0;
1801	do {
1802	block_end = block_start + bh->b_size;
1803
1804	if (buffer_new(bh)) {
1805	if (block_end > from && block_start < to) {
1806	if (!PageUptodate(page)) {
1807	unsigned start, size;
1808
1809	start = max(from, block_start);
1810	size = min(to, block_end) - start;
1811
1812	zero_user(page, start, size);
1813	set_buffer_uptodate(bh);
1814	}
1815
1816	clear_buffer_new(bh);
1817	mark_buffer_dirty(bh);
1818	}
1819	}
1820
1821	block_start = block_end;
1822	bh = bh->b_this_page;
1823	} while (bh != head);
1824	}
1825	EXPORT_SYMBOL(page_zero_new_buffers);
1826
1827	int __block_write_begin(struct page *page, loff_t pos, unsigned len,
1828	get_block_t *get_block)
1829	{
1830	unsigned from = pos & (PAGE_CACHE_SIZE - 1);
1831	unsigned to = from + len;
1832	struct inode *inode = page->mapping->host;
1833	unsigned block_start, block_end;
1834	sector_t block;
1835	int err = 0;
1836	unsigned blocksize, bbits;
1837	struct buffer_head bh, head, wait[2], *wait_bh=wait;
1838
1839	BUG_ON(!PageLocked(page));
1840	BUG_ON(from > PAGE_CACHE_SIZE);
1841	BUG_ON(to > PAGE_CACHE_SIZE);
1842	BUG_ON(from > to);
1843
1844	head = create_page_buffers(page, inode, 0);
1845	blocksize = head->b_size;
1846	bbits = block_size_bits(blocksize);
1847
1848	block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1849
1850	for(bh = head, block_start = 0; bh != head \|\| !block_start;
1851	block++, block_start=block_end, bh = bh->b_this_page) {
1852	block_end = block_start + blocksize;
1853	if (block_end <= from \|\| block_start >= to) {
1854	if (PageUptodate(page)) {
1855	if (!buffer_uptodate(bh))
1856	set_buffer_uptodate(bh);
1857	}
1858	continue;
1859	}
1860	if (buffer_new(bh))
1861	clear_buffer_new(bh);
1862	if (!buffer_mapped(bh)) {
1863	WARN_ON(bh->b_size != blocksize);
1864	err = get_block(inode, block, bh, 1);
1865	if (err)
1866	break;
1867	if (buffer_new(bh)) {
1868	unmap_underlying_metadata(bh->b_bdev,
1869	bh->b_blocknr);
1870	if (PageUptodate(page)) {
1871	clear_buffer_new(bh);
1872	set_buffer_uptodate(bh);
1873	mark_buffer_dirty(bh);
1874	continue;
1875	}
1876	if (block_end > to \|\| block_start < from)
1877	zero_user_segments(page,
1878	to, block_end,
1879	block_start, from);
1880	continue;
1881	}
1882	}
1883	if (PageUptodate(page)) {
1884	if (!buffer_uptodate(bh))
1885	set_buffer_uptodate(bh);
1886	continue;
1887	}
1888	if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1889	!buffer_unwritten(bh) &&
1890	(block_start < from \|\| block_end > to)) {
1891	ll_rw_block(READ, 1, &bh);
1892	*wait_bh++=bh;
1893	}
1894	}
1895	/*
1896	* If we issued read requests - let them complete.
1897	*/
1898	while(wait_bh > wait) {
1899	wait_on_buffer(*--wait_bh);
1900	if (!buffer_uptodate(*wait_bh))
1901	err = -EIO;
1902	}
1903	if (unlikely(err))
1904	page_zero_new_buffers(page, from, to);
1905	return err;
1906	}
1907	EXPORT_SYMBOL(__block_write_begin);
1908
1909	static int __block_commit_write(struct inode inode, struct page page,
1910	unsigned from, unsigned to)
1911	{
1912	unsigned block_start, block_end;
1913	int partial = 0;
1914	unsigned blocksize;
1915	struct buffer_head bh, head;
1916
1917	bh = head = page_buffers(page);
1918	blocksize = bh->b_size;
1919
1920	block_start = 0;
1921	do {
1922	block_end = block_start + blocksize;
1923	if (block_end <= from \|\| block_start >= to) {
1924	if (!buffer_uptodate(bh))
1925	partial = 1;
1926	} else {
1927	set_buffer_uptodate(bh);
1928	mark_buffer_dirty(bh);
1929	}
1930	clear_buffer_new(bh);
1931
1932	block_start = block_end;
1933	bh = bh->b_this_page;
1934	} while (bh != head);
1935
1936	/*
1937	* If this is a partial write which happened to make all buffers
1938	* uptodate then we can optimize away a bogus readpage() for
1939	* the next read(). Here we 'discover' whether the page went
1940	* uptodate as a result of this (potentially partial) write.
1941	*/
1942	if (!partial)
1943	SetPageUptodate(page);
1944	return 0;
1945	}
1946
1947	/*
1948	* block_write_begin takes care of the basic task of block allocation and
1949	* bringing partial write blocks uptodate first.
1950	*
1951	* The filesystem needs to handle block truncation upon failure.
1952	*/
1953	int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
1954	unsigned flags, struct page *pagep, get_block_t get_block)
1955	{
1956	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
1957	struct page *page;
1958	int status;
1959
1960	page = grab_cache_page_write_begin(mapping, index, flags);
1961	if (!page)
1962	return -ENOMEM;
1963
1964	status = __block_write_begin(page, pos, len, get_block);
1965	if (unlikely(status)) {
1966	unlock_page(page);
1967	page_cache_release(page);
1968	page = NULL;
1969	}
1970
1971	*pagep = page;
1972	return status;
1973	}
1974	EXPORT_SYMBOL(block_write_begin);
1975
1976	int block_write_end(struct file file, struct address_space mapping,
1977	loff_t pos, unsigned len, unsigned copied,
1978	struct page page, void fsdata)
1979	{
1980	struct inode *inode = mapping->host;
1981	unsigned start;
1982
1983	start = pos & (PAGE_CACHE_SIZE - 1);
1984
1985	if (unlikely(copied < len)) {
1986	/*
1987	* The buffers that were written will now be uptodate, so we
1988	* don't have to worry about a readpage reading them and
1989	* overwriting a partial write. However if we have encountered
1990	* a short write and only partially written into a buffer, it
1991	* will not be marked uptodate, so a readpage might come in and
1992	* destroy our partial write.
1993	*
1994	* Do the simplest thing, and just treat any short write to a
1995	* non uptodate page as a zero-length write, and force the
1996	* caller to redo the whole thing.
1997	*/
1998	if (!PageUptodate(page))
1999	copied = 0;
2000
2001	page_zero_new_buffers(page, start+copied, start+len);
2002	}
2003	flush_dcache_page(page);
2004
2005	/* This could be a short (even 0-length) commit */
2006	__block_commit_write(inode, page, start, start+copied);
2007
2008	return copied;
2009	}
2010	EXPORT_SYMBOL(block_write_end);
2011
2012	int generic_write_end(struct file file, struct address_space mapping,
2013	loff_t pos, unsigned len, unsigned copied,
2014	struct page page, void fsdata)
2015	{
2016	struct inode *inode = mapping->host;
2017	int i_size_changed = 0;
2018
2019	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2020
2021	/*
2022	* No need to use i_size_read() here, the i_size
2023	* cannot change under us because we hold i_mutex.
2024	*
2025	* But it's important to update i_size while still holding page lock:
2026	* page writeout could otherwise come in and zero beyond i_size.
2027	*/
2028	if (pos+copied > inode->i_size) {
2029	i_size_write(inode, pos+copied);
2030	i_size_changed = 1;
2031	}
2032
2033	unlock_page(page);
2034	page_cache_release(page);
2035
2036	/*
2037	* Don't mark the inode dirty under page lock. First, it unnecessarily
2038	* makes the holding time of page lock longer. Second, it forces lock
2039	* ordering of page lock and transaction start for journaling
2040	* filesystems.
2041	*/
2042	if (i_size_changed)
2043	mark_inode_dirty(inode);
2044
2045	return copied;
2046	}
2047	EXPORT_SYMBOL(generic_write_end);
2048
2049	/*
2050	* block_is_partially_uptodate checks whether buffers within a page are
2051	* uptodate or not.
2052	*
2053	* Returns true if all buffers which correspond to a file portion
2054	* we want to read are uptodate.
2055	*/
2056	int block_is_partially_uptodate(struct page page, read_descriptor_t desc,
2057	unsigned long from)
2058	{
2059	unsigned block_start, block_end, blocksize;
2060	unsigned to;
2061	struct buffer_head bh, head;
2062	int ret = 1;
2063
2064	if (!page_has_buffers(page))
2065	return 0;
2066
2067	head = page_buffers(page);
2068	blocksize = head->b_size;
2069	to = min_t(unsigned, PAGE_CACHE_SIZE - from, desc->count);
2070	to = from + to;
2071	if (from < blocksize && to > PAGE_CACHE_SIZE - blocksize)
2072	return 0;
2073
2074	bh = head;
2075	block_start = 0;
2076	do {
2077	block_end = block_start + blocksize;
2078	if (block_end > from && block_start < to) {
2079	if (!buffer_uptodate(bh)) {
2080	ret = 0;
2081	break;
2082	}
2083	if (block_end >= to)
2084	break;
2085	}
2086	block_start = block_end;
2087	bh = bh->b_this_page;
2088	} while (bh != head);
2089
2090	return ret;
2091	}
2092	EXPORT_SYMBOL(block_is_partially_uptodate);
2093
2094	/*
2095	* Generic "read page" function for block devices that have the normal
2096	* get_block functionality. This is most of the block device filesystems.
2097	* Reads the page asynchronously --- the unlock_buffer() and
2098	* set/clear_buffer_uptodate() functions propagate buffer state into the
2099	* page struct once IO has completed.
2100	*/
2101	int block_read_full_page(struct page page, get_block_t get_block)
2102	{
2103	struct inode *inode = page->mapping->host;
2104	sector_t iblock, lblock;
2105	struct buffer_head bh, head, *arr[MAX_BUF_PER_PAGE];
2106	unsigned int blocksize, bbits;
2107	int nr, i;
2108	int fully_mapped = 1;
2109
2110	head = create_page_buffers(page, inode, 0);
2111	blocksize = head->b_size;
2112	bbits = block_size_bits(blocksize);
2113
2114	iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
2115	lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2116	bh = head;
2117	nr = 0;
2118	i = 0;
2119
2120	do {
2121	if (buffer_uptodate(bh))
2122	continue;
2123
2124	if (!buffer_mapped(bh)) {
2125	int err = 0;
2126
2127	fully_mapped = 0;
2128	if (iblock < lblock) {
2129	WARN_ON(bh->b_size != blocksize);
2130	err = get_block(inode, iblock, bh, 0);
2131	if (err)
2132	SetPageError(page);
2133	}
2134	if (!buffer_mapped(bh)) {
2135	zero_user(page, i * blocksize, blocksize);
2136	if (!err)
2137	set_buffer_uptodate(bh);
2138	continue;
2139	}
2140	/*
2141	* get_block() might have updated the buffer
2142	* synchronously
2143	*/
2144	if (buffer_uptodate(bh))
2145	continue;
2146	}
2147	arr[nr++] = bh;
2148	} while (i++, iblock++, (bh = bh->b_this_page) != head);
2149
2150	if (fully_mapped)
2151	SetPageMappedToDisk(page);
2152
2153	if (!nr) {
2154	/*
2155	* All buffers are uptodate - we can set the page uptodate
2156	* as well. But not if get_block() returned an error.
2157	*/
2158	if (!PageError(page))
2159	SetPageUptodate(page);
2160	unlock_page(page);
2161	return 0;
2162	}
2163
2164	/* Stage two: lock the buffers */
2165	for (i = 0; i < nr; i++) {
2166	bh = arr[i];
2167	lock_buffer(bh);
2168	mark_buffer_async_read(bh);
2169	}
2170
2171	/*
2172	* Stage 3: start the IO. Check for uptodateness
2173	* inside the buffer lock in case another process reading
2174	* the underlying blockdev brought it uptodate (the sct fix).
2175	*/
2176	for (i = 0; i < nr; i++) {
2177	bh = arr[i];
2178	if (buffer_uptodate(bh))
2179	end_buffer_async_read(bh, 1);
2180	else
2181	submit_bh(READ, bh);
2182	}
2183	return 0;
2184	}
2185	EXPORT_SYMBOL(block_read_full_page);
2186
2187	/* utility function for filesystems that need to do work on expanding
2188	* truncates. Uses filesystem pagecache writes to allow the filesystem to
2189	* deal with the hole.
2190	*/
2191	int generic_cont_expand_simple(struct inode *inode, loff_t size)
2192	{
2193	struct address_space *mapping = inode->i_mapping;
2194	struct page *page;
2195	void *fsdata;
2196	int err;
2197
2198	err = inode_newsize_ok(inode, size);
2199	if (err)
2200	goto out;
2201
2202	err = pagecache_write_begin(NULL, mapping, size, 0,
2203	AOP_FLAG_UNINTERRUPTIBLE\|AOP_FLAG_CONT_EXPAND,
2204	&page, &fsdata);
2205	if (err)
2206	goto out;
2207
2208	err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2209	BUG_ON(err > 0);
2210
2211	out:
2212	return err;
2213	}
2214	EXPORT_SYMBOL(generic_cont_expand_simple);
2215
2216	static int cont_expand_zero(struct file file, struct address_space mapping,
2217	loff_t pos, loff_t *bytes)
2218	{
2219	struct inode *inode = mapping->host;
2220	unsigned blocksize = 1 << inode->i_blkbits;
2221	struct page *page;
2222	void *fsdata;
2223	pgoff_t index, curidx;
2224	loff_t curpos;
2225	unsigned zerofrom, offset, len;
2226	int err = 0;
2227
2228	index = pos >> PAGE_CACHE_SHIFT;
2229	offset = pos & ~PAGE_CACHE_MASK;
2230
2231	while (index > (curidx = (curpos = *bytes)>>PAGE_CACHE_SHIFT)) {
2232	zerofrom = curpos & ~PAGE_CACHE_MASK;
2233	if (zerofrom & (blocksize-1)) {
2234	*bytes \|= (blocksize-1);
2235	(*bytes)++;
2236	}
2237	len = PAGE_CACHE_SIZE - zerofrom;
2238
2239	err = pagecache_write_begin(file, mapping, curpos, len,
2240	AOP_FLAG_UNINTERRUPTIBLE,
2241	&page, &fsdata);
2242	if (err)
2243	goto out;
2244	zero_user(page, zerofrom, len);
2245	err = pagecache_write_end(file, mapping, curpos, len, len,
2246	page, fsdata);
2247	if (err < 0)
2248	goto out;
2249	BUG_ON(err != len);
2250	err = 0;
2251
2252	balance_dirty_pages_ratelimited(mapping);
2253	}
2254
2255	/* page covers the boundary, find the boundary offset */
2256	if (index == curidx) {
2257	zerofrom = curpos & ~PAGE_CACHE_MASK;
2258	/* if we will expand the thing last block will be filled */
2259	if (offset <= zerofrom) {
2260	goto out;
2261	}
2262	if (zerofrom & (blocksize-1)) {
2263	*bytes \|= (blocksize-1);
2264	(*bytes)++;
2265	}
2266	len = offset - zerofrom;
2267
2268	err = pagecache_write_begin(file, mapping, curpos, len,
2269	AOP_FLAG_UNINTERRUPTIBLE,
2270	&page, &fsdata);
2271	if (err)
2272	goto out;
2273	zero_user(page, zerofrom, len);
2274	err = pagecache_write_end(file, mapping, curpos, len, len,
2275	page, fsdata);
2276	if (err < 0)
2277	goto out;
2278	BUG_ON(err != len);
2279	err = 0;
2280	}
2281	out:
2282	return err;
2283	}
2284
2285	/*
2286	* For moronic filesystems that do not allow holes in file.
2287	* We may have to extend the file.
2288	*/
2289	int cont_write_begin(struct file file, struct address_space mapping,
2290	loff_t pos, unsigned len, unsigned flags,
2291	struct page pagep, void fsdata,
2292	get_block_t get_block, loff_t bytes)
2293	{
2294	struct inode *inode = mapping->host;
2295	unsigned blocksize = 1 << inode->i_blkbits;
2296	unsigned zerofrom;
2297	int err;
2298
2299	err = cont_expand_zero(file, mapping, pos, bytes);
2300	if (err)
2301	return err;
2302
2303	zerofrom = *bytes & ~PAGE_CACHE_MASK;
2304	if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2305	*bytes \|= (blocksize-1);
2306	(*bytes)++;
2307	}
2308
2309	return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2310	}
2311	EXPORT_SYMBOL(cont_write_begin);
2312
2313	int block_commit_write(struct page *page, unsigned from, unsigned to)
2314	{
2315	struct inode *inode = page->mapping->host;
2316	__block_commit_write(inode,page,from,to);
2317	return 0;
2318	}
2319	EXPORT_SYMBOL(block_commit_write);
2320
2321	/*
2322	* block_page_mkwrite() is not allowed to change the file size as it gets
2323	* called from a page fault handler when a page is first dirtied. Hence we must
2324	* be careful to check for EOF conditions here. We set the page up correctly
2325	* for a written page which means we get ENOSPC checking when writing into
2326	* holes and correct delalloc and unwritten extent mapping on filesystems that
2327	* support these features.
2328	*
2329	* We are not allowed to take the i_mutex here so we have to play games to
2330	* protect against truncate races as the page could now be beyond EOF. Because
2331	* truncate writes the inode size before removing pages, once we have the
2332	* page lock we can determine safely if the page is beyond EOF. If it is not
2333	* beyond EOF, then the page is guaranteed safe against truncation until we
2334	* unlock the page.
2335	*
2336	* Direct callers of this function should protect against filesystem freezing
2337	* using sb_start_write() - sb_end_write() functions.
2338	*/
2339	int __block_page_mkwrite(struct vm_area_struct vma, struct vm_fault vmf,
2340	get_block_t get_block)
2341	{
2342	struct page *page = vmf->page;
2343	struct inode *inode = file_inode(vma->vm_file);
2344	unsigned long end;
2345	loff_t size;
2346	int ret;
2347
2348	lock_page(page);
2349	size = i_size_read(inode);
2350	if ((page->mapping != inode->i_mapping) \|\|
2351	(page_offset(page) > size)) {
2352	/* We overload EFAULT to mean page got truncated */
2353	ret = -EFAULT;
2354	goto out_unlock;
2355	}
2356
2357	/* page is wholly or partially inside EOF */
2358	if (((page->index + 1) << PAGE_CACHE_SHIFT) > size)
2359	end = size & ~PAGE_CACHE_MASK;
2360	else
2361	end = PAGE_CACHE_SIZE;
2362
2363	ret = __block_write_begin(page, 0, end, get_block);
2364	if (!ret)
2365	ret = block_commit_write(page, 0, end);
2366
2367	if (unlikely(ret < 0))
2368	goto out_unlock;
2369	set_page_dirty(page);
2370	wait_for_stable_page(page);
2371	return 0;
2372	out_unlock:
2373	unlock_page(page);
2374	return ret;
2375	}
2376	EXPORT_SYMBOL(__block_page_mkwrite);
2377
2378	int block_page_mkwrite(struct vm_area_struct vma, struct vm_fault vmf,
2379	get_block_t get_block)
2380	{
2381	int ret;
2382	struct super_block *sb = file_inode(vma->vm_file)->i_sb;
2383
2384	sb_start_pagefault(sb);
2385
2386	/*
2387	* Update file times before taking page lock. We may end up failing the
2388	* fault so this update may be superfluous but who really cares...
2389	*/
2390	file_update_time(vma->vm_file);
2391
2392	ret = __block_page_mkwrite(vma, vmf, get_block);
2393	sb_end_pagefault(sb);
2394	return block_page_mkwrite_return(ret);
2395	}
2396	EXPORT_SYMBOL(block_page_mkwrite);
2397
2398	/*
2399	* nobh_write_begin()'s prereads are special: the buffer_heads are freed
2400	* immediately, while under the page lock. So it needs a special end_io
2401	* handler which does not touch the bh after unlocking it.
2402	*/
2403	static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2404	{
2405	__end_buffer_read_notouch(bh, uptodate);
2406	}
2407
2408	/*
2409	* Attach the singly-linked list of buffers created by nobh_write_begin, to
2410	* the page (converting it to circular linked list and taking care of page
2411	* dirty races).
2412	*/
2413	static void attach_nobh_buffers(struct page page, struct buffer_head head)
2414	{
2415	struct buffer_head *bh;
2416
2417	BUG_ON(!PageLocked(page));
2418
2419	spin_lock(&page->mapping->private_lock);
2420	bh = head;
2421	do {
2422	if (PageDirty(page))
2423	set_buffer_dirty(bh);
2424	if (!bh->b_this_page)
2425	bh->b_this_page = head;
2426	bh = bh->b_this_page;
2427	} while (bh != head);
2428	attach_page_buffers(page, head);
2429	spin_unlock(&page->mapping->private_lock);
2430	}
2431
2432	/*
2433	* On entry, the page is fully not uptodate.
2434	* On exit the page is fully uptodate in the areas outside (from,to)
2435	* The filesystem needs to handle block truncation upon failure.
2436	*/
2437	int nobh_write_begin(struct address_space *mapping,
2438	loff_t pos, unsigned len, unsigned flags,
2439	struct page pagep, void fsdata,
2440	get_block_t *get_block)
2441	{
2442	struct inode *inode = mapping->host;
2443	const unsigned blkbits = inode->i_blkbits;
2444	const unsigned blocksize = 1 << blkbits;
2445	struct buffer_head head, bh;
2446	struct page *page;
2447	pgoff_t index;
2448	unsigned from, to;
2449	unsigned block_in_page;
2450	unsigned block_start, block_end;
2451	sector_t block_in_file;
2452	int nr_reads = 0;
2453	int ret = 0;
2454	int is_mapped_to_disk = 1;
2455
2456	index = pos >> PAGE_CACHE_SHIFT;
2457	from = pos & (PAGE_CACHE_SIZE - 1);
2458	to = from + len;
2459
2460	page = grab_cache_page_write_begin(mapping, index, flags);
2461	if (!page)
2462	return -ENOMEM;
2463	*pagep = page;
2464	*fsdata = NULL;
2465
2466	if (page_has_buffers(page)) {
2467	ret = __block_write_begin(page, pos, len, get_block);
2468	if (unlikely(ret))
2469	goto out_release;
2470	return ret;
2471	}
2472
2473	if (PageMappedToDisk(page))
2474	return 0;
2475
2476	/*
2477	* Allocate buffers so that we can keep track of state, and potentially
2478	* attach them to the page if an error occurs. In the common case of
2479	* no error, they will just be freed again without ever being attached
2480	* to the page (which is all OK, because we're under the page lock).
2481	*
2482	* Be careful: the buffer linked list is a NULL terminated one, rather
2483	* than the circular one we're used to.
2484	*/
2485	head = alloc_page_buffers(page, blocksize, 0);
2486	if (!head) {
2487	ret = -ENOMEM;
2488	goto out_release;
2489	}
2490
2491	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
2492
2493	/*
2494	* We loop across all blocks in the page, whether or not they are
2495	* part of the affected region. This is so we can discover if the
2496	* page is fully mapped-to-disk.
2497	*/
2498	for (block_start = 0, block_in_page = 0, bh = head;
2499	block_start < PAGE_CACHE_SIZE;
2500	block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2501	int create;
2502
2503	block_end = block_start + blocksize;
2504	bh->b_state = 0;
2505	create = 1;
2506	if (block_start >= to)
2507	create = 0;
2508	ret = get_block(inode, block_in_file + block_in_page,
2509	bh, create);
2510	if (ret)
2511	goto failed;
2512	if (!buffer_mapped(bh))
2513	is_mapped_to_disk = 0;
2514	if (buffer_new(bh))
2515	unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
2516	if (PageUptodate(page)) {
2517	set_buffer_uptodate(bh);
2518	continue;
2519	}
2520	if (buffer_new(bh) \|\| !buffer_mapped(bh)) {
2521	zero_user_segments(page, block_start, from,
2522	to, block_end);
2523	continue;
2524	}
2525	if (buffer_uptodate(bh))
2526	continue; /* reiserfs does this */
2527	if (block_start < from \|\| block_end > to) {
2528	lock_buffer(bh);
2529	bh->b_end_io = end_buffer_read_nobh;
2530	submit_bh(READ, bh);
2531	nr_reads++;
2532	}
2533	}
2534
2535	if (nr_reads) {
2536	/*
2537	* The page is locked, so these buffers are protected from
2538	* any VM or truncate activity. Hence we don't need to care
2539	* for the buffer_head refcounts.
2540	*/
2541	for (bh = head; bh; bh = bh->b_this_page) {
2542	wait_on_buffer(bh);
2543	if (!buffer_uptodate(bh))
2544	ret = -EIO;
2545	}
2546	if (ret)
2547	goto failed;
2548	}
2549
2550	if (is_mapped_to_disk)
2551	SetPageMappedToDisk(page);
2552
2553	fsdata = head; / to be released by nobh_write_end */
2554
2555	return 0;
2556
2557	failed:
2558	BUG_ON(!ret);
2559	/*
2560	* Error recovery is a bit difficult. We need to zero out blocks that
2561	* were newly allocated, and dirty them to ensure they get written out.
2562	* Buffers need to be attached to the page at this point, otherwise
2563	* the handling of potential IO errors during writeout would be hard
2564	* (could try doing synchronous writeout, but what if that fails too?)
2565	*/
2566	attach_nobh_buffers(page, head);
2567	page_zero_new_buffers(page, from, to);
2568
2569	out_release:
2570	unlock_page(page);
2571	page_cache_release(page);
2572	*pagep = NULL;
2573
2574	return ret;
2575	}
2576	EXPORT_SYMBOL(nobh_write_begin);
2577
2578	int nobh_write_end(struct file file, struct address_space mapping,
2579	loff_t pos, unsigned len, unsigned copied,
2580	struct page page, void fsdata)
2581	{
2582	struct inode *inode = page->mapping->host;
2583	struct buffer_head *head = fsdata;
2584	struct buffer_head *bh;
2585	BUG_ON(fsdata != NULL && page_has_buffers(page));
2586
2587	if (unlikely(copied < len) && head)
2588	attach_nobh_buffers(page, head);
2589	if (page_has_buffers(page))
2590	return generic_write_end(file, mapping, pos, len,
2591	copied, page, fsdata);
2592
2593	SetPageUptodate(page);
2594	set_page_dirty(page);
2595	if (pos+copied > inode->i_size) {
2596	i_size_write(inode, pos+copied);
2597	mark_inode_dirty(inode);
2598	}
2599
2600	unlock_page(page);
2601	page_cache_release(page);
2602
2603	while (head) {
2604	bh = head;
2605	head = head->b_this_page;
2606	free_buffer_head(bh);
2607	}
2608
2609	return copied;
2610	}
2611	EXPORT_SYMBOL(nobh_write_end);
2612
2613	/*
2614	* nobh_writepage() - based on block_full_write_page() except
2615	* that it tries to operate without attaching bufferheads to
2616	* the page.
2617	*/
2618	int nobh_writepage(struct page page, get_block_t get_block,
2619	struct writeback_control *wbc)
2620	{
2621	struct inode * const inode = page->mapping->host;
2622	loff_t i_size = i_size_read(inode);
2623	const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2624	unsigned offset;
2625	int ret;
2626
2627	/* Is the page fully inside i_size? */
2628	if (page->index < end_index)
2629	goto out;
2630
2631	/* Is the page fully outside i_size? (truncate in progress) */
2632	offset = i_size & (PAGE_CACHE_SIZE-1);
2633	if (page->index >= end_index+1 \|\| !offset) {
2634	/*
2635	* The page may have dirty, unmapped buffers. For example,
2636	* they may have been added in ext3_writepage(). Make them
2637	* freeable here, so the page does not leak.
2638	*/
2639	#if 0
2640	/* Not really sure about this - do we need this ? */
2641	if (page->mapping->a_ops->invalidatepage)
2642	page->mapping->a_ops->invalidatepage(page, offset);
2643	#endif
2644	unlock_page(page);
2645	return 0; /* don't care */
2646	}
2647
2648	/*
2649	* The page straddles i_size. It must be zeroed out on each and every
2650	* writepage invocation because it may be mmapped. "A file is mapped
2651	* in multiples of the page size. For a file that is not a multiple of
2652	* the page size, the remaining memory is zeroed when mapped, and
2653	* writes to that region are not written out to the file."
2654	*/
2655	zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2656	out:
2657	ret = mpage_writepage(page, get_block, wbc);
2658	if (ret == -EAGAIN)
2659	ret = __block_write_full_page(inode, page, get_block, wbc,
2660	end_buffer_async_write);
2661	return ret;
2662	}
2663	EXPORT_SYMBOL(nobh_writepage);
2664
2665	int nobh_truncate_page(struct address_space *mapping,
2666	loff_t from, get_block_t *get_block)
2667	{
2668	pgoff_t index = from >> PAGE_CACHE_SHIFT;
2669	unsigned offset = from & (PAGE_CACHE_SIZE-1);
2670	unsigned blocksize;
2671	sector_t iblock;
2672	unsigned length, pos;
2673	struct inode *inode = mapping->host;
2674	struct page *page;
2675	struct buffer_head map_bh;
2676	int err;
2677
2678	blocksize = 1 << inode->i_blkbits;
2679	length = offset & (blocksize - 1);
2680
2681	/* Block boundary? Nothing to do */
2682	if (!length)
2683	return 0;
2684
2685	length = blocksize - length;
2686	iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2687
2688	page = grab_cache_page(mapping, index);
2689	err = -ENOMEM;
2690	if (!page)
2691	goto out;
2692
2693	if (page_has_buffers(page)) {
2694	has_buffers:
2695	unlock_page(page);
2696	page_cache_release(page);
2697	return block_truncate_page(mapping, from, get_block);
2698	}
2699
2700	/* Find the buffer that contains "offset" */
2701	pos = blocksize;
2702	while (offset >= pos) {
2703	iblock++;
2704	pos += blocksize;
2705	}
2706
2707	map_bh.b_size = blocksize;
2708	map_bh.b_state = 0;
2709	err = get_block(inode, iblock, &map_bh, 0);
2710	if (err)
2711	goto unlock;
2712	/* unmapped? It's a hole - nothing to do */
2713	if (!buffer_mapped(&map_bh))
2714	goto unlock;
2715
2716	/* Ok, it's mapped. Make sure it's up-to-date */
2717	if (!PageUptodate(page)) {
2718	err = mapping->a_ops->readpage(NULL, page);
2719	if (err) {
2720	page_cache_release(page);
2721	goto out;
2722	}
2723	lock_page(page);
2724	if (!PageUptodate(page)) {
2725	err = -EIO;
2726	goto unlock;
2727	}
2728	if (page_has_buffers(page))
2729	goto has_buffers;
2730	}
2731	zero_user(page, offset, length);
2732	set_page_dirty(page);
2733	err = 0;
2734
2735	unlock:
2736	unlock_page(page);
2737	page_cache_release(page);
2738	out:
2739	return err;
2740	}
2741	EXPORT_SYMBOL(nobh_truncate_page);
2742
2743	int block_truncate_page(struct address_space *mapping,
2744	loff_t from, get_block_t *get_block)
2745	{
2746	pgoff_t index = from >> PAGE_CACHE_SHIFT;
2747	unsigned offset = from & (PAGE_CACHE_SIZE-1);
2748	unsigned blocksize;
2749	sector_t iblock;
2750	unsigned length, pos;
2751	struct inode *inode = mapping->host;
2752	struct page *page;
2753	struct buffer_head *bh;
2754	int err;
2755
2756	blocksize = 1 << inode->i_blkbits;
2757	length = offset & (blocksize - 1);
2758
2759	/* Block boundary? Nothing to do */
2760	if (!length)
2761	return 0;
2762
2763	length = blocksize - length;
2764	iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2765
2766	page = grab_cache_page(mapping, index);
2767	err = -ENOMEM;
2768	if (!page)
2769	goto out;
2770
2771	if (!page_has_buffers(page))
2772	create_empty_buffers(page, blocksize, 0);
2773
2774	/* Find the buffer that contains "offset" */
2775	bh = page_buffers(page);
2776	pos = blocksize;
2777	while (offset >= pos) {
2778	bh = bh->b_this_page;
2779	iblock++;
2780	pos += blocksize;
2781	}
2782
2783	err = 0;
2784	if (!buffer_mapped(bh)) {
2785	WARN_ON(bh->b_size != blocksize);
2786	err = get_block(inode, iblock, bh, 0);
2787	if (err)
2788	goto unlock;
2789	/* unmapped? It's a hole - nothing to do */
2790	if (!buffer_mapped(bh))
2791	goto unlock;
2792	}
2793
2794	/* Ok, it's mapped. Make sure it's up-to-date */
2795	if (PageUptodate(page))
2796	set_buffer_uptodate(bh);
2797
2798	if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2799	err = -EIO;
2800	ll_rw_block(READ, 1, &bh);
2801	wait_on_buffer(bh);
2802	/* Uhhuh. Read error. Complain and punt. */
2803	if (!buffer_uptodate(bh))
2804	goto unlock;
2805	}
2806
2807	zero_user(page, offset, length);
2808	mark_buffer_dirty(bh);
2809	err = 0;
2810
2811	unlock:
2812	unlock_page(page);
2813	page_cache_release(page);
2814	out:
2815	return err;
2816	}
2817	EXPORT_SYMBOL(block_truncate_page);
2818
2819	/*
2820	* The generic ->writepage function for buffer-backed address_spaces
2821	* this form passes in the end_io handler used to finish the IO.
2822	*/
2823	int block_write_full_page_endio(struct page page, get_block_t get_block,
2824	struct writeback_control wbc, bh_end_io_t handler)
2825	{
2826	struct inode * const inode = page->mapping->host;
2827	loff_t i_size = i_size_read(inode);
2828	const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2829	unsigned offset;
2830
2831	/* Is the page fully inside i_size? */
2832	if (page->index < end_index)
2833	return __block_write_full_page(inode, page, get_block, wbc,
2834	handler);
2835
2836	/* Is the page fully outside i_size? (truncate in progress) */
2837	offset = i_size & (PAGE_CACHE_SIZE-1);
2838	if (page->index >= end_index+1 \|\| !offset) {
2839	/*
2840	* The page may have dirty, unmapped buffers. For example,
2841	* they may have been added in ext3_writepage(). Make them
2842	* freeable here, so the page does not leak.
2843	*/
2844	do_invalidatepage(page, 0);
2845	unlock_page(page);
2846	return 0; /* don't care */
2847	}
2848
2849	/*
2850	* The page straddles i_size. It must be zeroed out on each and every
2851	* writepage invocation because it may be mmapped. "A file is mapped
2852	* in multiples of the page size. For a file that is not a multiple of
2853	* the page size, the remaining memory is zeroed when mapped, and
2854	* writes to that region are not written out to the file."
2855	*/
2856	zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2857	return __block_write_full_page(inode, page, get_block, wbc, handler);
2858	}
2859	EXPORT_SYMBOL(block_write_full_page_endio);
2860
2861	/*
2862	* The generic ->writepage function for buffer-backed address_spaces
2863	*/
2864	int block_write_full_page(struct page page, get_block_t get_block,
2865	struct writeback_control *wbc)
2866	{
2867	return block_write_full_page_endio(page, get_block, wbc,
2868	end_buffer_async_write);
2869	}
2870	EXPORT_SYMBOL(block_write_full_page);
2871
2872	sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2873	get_block_t *get_block)
2874	{
2875	struct buffer_head tmp;
2876	struct inode *inode = mapping->host;
2877	tmp.b_state = 0;
2878	tmp.b_blocknr = 0;
2879	tmp.b_size = 1 << inode->i_blkbits;
2880	get_block(inode, block, &tmp, 0);
2881	return tmp.b_blocknr;
2882	}
2883	EXPORT_SYMBOL(generic_block_bmap);
2884
2885	static void end_bio_bh_io_sync(struct bio *bio, int err)
2886	{
2887	struct buffer_head *bh = bio->bi_private;
2888
2889	if (err == -EOPNOTSUPP) {
2890	set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
2891	}
2892
2893	if (unlikely (test_bit(BIO_QUIET,&bio->bi_flags)))
2894	set_bit(BH_Quiet, &bh->b_state);
2895
2896	bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
2897	bio_put(bio);
2898	}
2899
2900	/*
2901	* This allows us to do IO even on the odd last sectors
2902	* of a device, even if the bh block size is some multiple
2903	* of the physical sector size.
2904	*
2905	* We'll just truncate the bio to the size of the device,
2906	* and clear the end of the buffer head manually.
2907	*
2908	* Truly out-of-range accesses will turn into actual IO
2909	* errors, this only handles the "we need to be able to
2910	* do IO at the final sector" case.
2911	*/
2912	static void guard_bh_eod(int rw, struct bio bio, struct buffer_head bh)
2913	{
2914	sector_t maxsector;
2915	unsigned bytes;
2916
2917	maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
2918	if (!maxsector)
2919	return;
2920
2921	/*
2922	* If the whole IO is past the end of the device,
2923	* let it through, and the IO layer will turn it into
2924	* an EIO.
2925	*/
2926	if (unlikely(bio->bi_sector >= maxsector))
2927	return;
2928
2929	maxsector -= bio->bi_sector;
2930	bytes = bio->bi_size;
2931	if (likely((bytes >> 9) <= maxsector))
2932	return;
2933
2934	/* Uhhuh. We've got a bh that straddles the device size! */
2935	bytes = maxsector << 9;
2936
2937	/* Truncate the bio.. */
2938	bio->bi_size = bytes;
2939	bio->bi_io_vec[0].bv_len = bytes;
2940
2941	/* ..and clear the end of the buffer for reads */
2942	if ((rw & RW_MASK) == READ) {
2943	void *kaddr = kmap_atomic(bh->b_page);
2944	memset(kaddr + bh_offset(bh) + bytes, 0, bh->b_size - bytes);
2945	kunmap_atomic(kaddr);
2946	flush_dcache_page(bh->b_page);
2947	}
2948	}
2949
2950	int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags)
2951	{
2952	struct bio *bio;
2953	int ret = 0;
2954
2955	BUG_ON(!buffer_locked(bh));
2956	BUG_ON(!buffer_mapped(bh));
2957	BUG_ON(!bh->b_end_io);
2958	BUG_ON(buffer_delay(bh));
2959	BUG_ON(buffer_unwritten(bh));
2960
2961	/*
2962	* Only clear out a write error when rewriting
2963	*/
2964	if (test_set_buffer_req(bh) && (rw & WRITE))
2965	clear_buffer_write_io_error(bh);
2966
2967	/*
2968	* from here on down, it's all bio -- do the initial mapping,
2969	* submit_bio -> generic_make_request may further map this bio around
2970	*/
2971	bio = bio_alloc(GFP_NOIO, 1);
2972
2973	bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
2974	bio->bi_bdev = bh->b_bdev;
2975	bio->bi_io_vec[0].bv_page = bh->b_page;
2976	bio->bi_io_vec[0].bv_len = bh->b_size;
2977	bio->bi_io_vec[0].bv_offset = bh_offset(bh);
2978
2979	bio->bi_vcnt = 1;
2980	bio->bi_size = bh->b_size;
2981
2982	bio->bi_end_io = end_bio_bh_io_sync;
2983	bio->bi_private = bh;
2984	bio->bi_flags \|= bio_flags;
2985
2986	/* Take care of bh's that straddle the end of the device */
2987	guard_bh_eod(rw, bio, bh);
2988
2989	if (buffer_meta(bh))
2990	rw \|= REQ_META;
2991	if (buffer_prio(bh))
2992	rw \|= REQ_PRIO;
2993
2994	bio_get(bio);
2995	submit_bio(rw, bio);
2996
2997	if (bio_flagged(bio, BIO_EOPNOTSUPP))
2998	ret = -EOPNOTSUPP;
2999
3000	bio_put(bio);
3001	return ret;
3002	}
3003	EXPORT_SYMBOL_GPL(_submit_bh);
3004
3005	int submit_bh(int rw, struct buffer_head *bh)
3006	{
3007	return _submit_bh(rw, bh, 0);
3008	}
3009	EXPORT_SYMBOL(submit_bh);
3010
3011	/**
3012	* ll_rw_block: low-level access to block devices (DEPRECATED)
3013	* @rw: whether to %READ or %WRITE or maybe %READA (readahead)
3014	* @nr: number of &struct buffer_heads in the array
3015	* @bhs: array of pointers to &struct buffer_head
3016	*
3017	* ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3018	* requests an I/O operation on them, either a %READ or a %WRITE. The third
3019	* %READA option is described in the documentation for generic_make_request()
3020	* which ll_rw_block() calls.
3021	*
3022	* This function drops any buffer that it cannot get a lock on (with the
3023	* BH_Lock state bit), any buffer that appears to be clean when doing a write
3024	* request, and any buffer that appears to be up-to-date when doing read
3025	* request. Further it marks as clean buffers that are processed for
3026	* writing (the buffer cache won't assume that they are actually clean
3027	* until the buffer gets unlocked).
3028	*
3029	* ll_rw_block sets b_end_io to simple completion handler that marks
3030	* the buffer up-to-date (if approriate), unlocks the buffer and wakes
3031	* any waiters.
3032	*
3033	* All of the buffers must be for the same device, and must also be a
3034	* multiple of the current approved size for the device.
3035	*/
3036	void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
3037	{
3038	int i;
3039
3040	for (i = 0; i < nr; i++) {
3041	struct buffer_head *bh = bhs[i];
3042
3043	if (!trylock_buffer(bh))
3044	continue;
3045	if (rw == WRITE) {
3046	if (test_clear_buffer_dirty(bh)) {
3047	bh->b_end_io = end_buffer_write_sync;
3048	get_bh(bh);
3049	submit_bh(WRITE, bh);
3050	continue;
3051	}
3052	} else {
3053	if (!buffer_uptodate(bh)) {
3054	bh->b_end_io = end_buffer_read_sync;
3055	get_bh(bh);
3056	submit_bh(rw, bh);
3057	continue;
3058	}
3059	}
3060	unlock_buffer(bh);
3061	}
3062	}
3063	EXPORT_SYMBOL(ll_rw_block);
3064
3065	void write_dirty_buffer(struct buffer_head *bh, int rw)
3066	{
3067	lock_buffer(bh);
3068	if (!test_clear_buffer_dirty(bh)) {
3069	unlock_buffer(bh);
3070	return;
3071	}
3072	bh->b_end_io = end_buffer_write_sync;
3073	get_bh(bh);
3074	submit_bh(rw, bh);
3075	}
3076	EXPORT_SYMBOL(write_dirty_buffer);
3077
3078	/*
3079	* For a data-integrity writeout, we need to wait upon any in-progress I/O
3080	* and then start new I/O and then wait upon it. The caller must have a ref on
3081	* the buffer_head.
3082	*/
3083	int __sync_dirty_buffer(struct buffer_head *bh, int rw)
3084	{
3085	int ret = 0;
3086
3087	WARN_ON(atomic_read(&bh->b_count) < 1);
3088	lock_buffer(bh);
3089	if (test_clear_buffer_dirty(bh)) {
3090	get_bh(bh);
3091	bh->b_end_io = end_buffer_write_sync;
3092	ret = submit_bh(rw, bh);
3093	wait_on_buffer(bh);
3094	if (!ret && !buffer_uptodate(bh))
3095	ret = -EIO;
3096	} else {
3097	unlock_buffer(bh);
3098	}
3099	return ret;
3100	}
3101	EXPORT_SYMBOL(__sync_dirty_buffer);
3102
3103	int sync_dirty_buffer(struct buffer_head *bh)
3104	{
3105	return __sync_dirty_buffer(bh, WRITE_SYNC);
3106	}
3107	EXPORT_SYMBOL(sync_dirty_buffer);
3108
3109	/*
3110	* try_to_free_buffers() checks if all the buffers on this particular page
3111	* are unused, and releases them if so.
3112	*
3113	* Exclusion against try_to_free_buffers may be obtained by either
3114	* locking the page or by holding its mapping's private_lock.
3115	*
3116	* If the page is dirty but all the buffers are clean then we need to
3117	* be sure to mark the page clean as well. This is because the page
3118	* may be against a block device, and a later reattachment of buffers
3119	* to a dirty page will set all buffers dirty. Which would corrupt
3120	* filesystem data on the same device.
3121	*
3122	* The same applies to regular filesystem pages: if all the buffers are
3123	* clean then we set the page clean and proceed. To do that, we require
3124	* total exclusion from __set_page_dirty_buffers(). That is obtained with
3125	* private_lock.
3126	*
3127	* try_to_free_buffers() is non-blocking.
3128	*/
3129	static inline int buffer_busy(struct buffer_head *bh)
3130	{
3131	return atomic_read(&bh->b_count) \|
3132	(bh->b_state & ((1 << BH_Dirty) \| (1 << BH_Lock)));
3133	}
3134
3135	static int
3136	drop_buffers(struct page page, struct buffer_head *buffers_to_free)
3137	{
3138	struct buffer_head *head = page_buffers(page);
3139	struct buffer_head *bh;
3140
3141	bh = head;
3142	do {
3143	if (buffer_write_io_error(bh) && page->mapping)
3144	set_bit(AS_EIO, &page->mapping->flags);
3145	if (buffer_busy(bh))
3146	goto failed;
3147	bh = bh->b_this_page;
3148	} while (bh != head);
3149
3150	do {
3151	struct buffer_head *next = bh->b_this_page;
3152
3153	if (bh->b_assoc_map)
3154	__remove_assoc_queue(bh);
3155	bh = next;
3156	} while (bh != head);
3157	*buffers_to_free = head;
3158	__clear_page_buffers(page);
3159	return 1;
3160	failed:
3161	return 0;
3162	}
3163
3164	int try_to_free_buffers(struct page *page)
3165	{
3166	struct address_space * const mapping = page->mapping;
3167	struct buffer_head *buffers_to_free = NULL;
3168	int ret = 0;
3169
3170	BUG_ON(!PageLocked(page));
3171	if (PageWriteback(page))
3172	return 0;
3173
3174	if (mapping == NULL) { /* can this still happen? */
3175	ret = drop_buffers(page, &buffers_to_free);
3176	goto out;
3177	}
3178
3179	spin_lock(&mapping->private_lock);
3180	ret = drop_buffers(page, &buffers_to_free);
3181
3182	/*
3183	* If the filesystem writes its buffers by hand (eg ext3)
3184	* then we can have clean buffers against a dirty page. We
3185	* clean the page here; otherwise the VM will never notice
3186	* that the filesystem did any IO at all.
3187	*
3188	* Also, during truncate, discard_buffer will have marked all
3189	* the page's buffers clean. We discover that here and clean
3190	* the page also.
3191	*
3192	* private_lock must be held over this entire operation in order
3193	* to synchronise against __set_page_dirty_buffers and prevent the
3194	* dirty bit from being lost.
3195	*/
3196	if (ret)
3197	cancel_dirty_page(page, PAGE_CACHE_SIZE);
3198	spin_unlock(&mapping->private_lock);
3199	out:
3200	if (buffers_to_free) {
3201	struct buffer_head *bh = buffers_to_free;
3202
3203	do {
3204	struct buffer_head *next = bh->b_this_page;
3205	free_buffer_head(bh);
3206	bh = next;
3207	} while (bh != buffers_to_free);
3208	}
3209	return ret;
3210	}
3211	EXPORT_SYMBOL(try_to_free_buffers);
3212
3213	/*
3214	* There are no bdflush tunables left. But distributions are
3215	* still running obsolete flush daemons, so we terminate them here.
3216	*
3217	* Use of bdflush() is deprecated and will be removed in a future kernel.
3218	* The `flush-X' kernel threads fully replace bdflush daemons and this call.
3219	*/
3220	SYSCALL_DEFINE2(bdflush, int, func, long, data)
3221	{
3222	static int msg_count;
3223
3224	if (!capable(CAP_SYS_ADMIN))
3225	return -EPERM;
3226
3227	if (msg_count < 5) {
3228	msg_count++;
3229	printk(KERN_INFO
3230	"warning: process `%s' used the obsolete bdflush"
3231	" system call\n", current->comm);
3232	printk(KERN_INFO "Fix your initscripts?\n");
3233	}
3234
3235	if (func == 1)
3236	do_exit(0);
3237	return 0;
3238	}
3239
3240	/*
3241	* Buffer-head allocation
3242	*/
3243	static struct kmem_cache *bh_cachep __read_mostly;
3244
3245	/*
3246	* Once the number of bh's in the machine exceeds this level, we start
3247	* stripping them in writeback.
3248	*/
3249	static unsigned long max_buffer_heads;
3250
3251	int buffer_heads_over_limit;
3252
3253	struct bh_accounting {
3254	int nr; /* Number of live bh's */
3255	int ratelimit; /* Limit cacheline bouncing */
3256	};
3257
3258	static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3259
3260	static void recalc_bh_state(void)
3261	{
3262	int i;
3263	int tot = 0;
3264
3265	if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3266	return;
3267	__this_cpu_write(bh_accounting.ratelimit, 0);
3268	for_each_online_cpu(i)
3269	tot += per_cpu(bh_accounting, i).nr;
3270	buffer_heads_over_limit = (tot > max_buffer_heads);
3271	}
3272
3273	struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3274	{
3275	struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3276	if (ret) {
3277	INIT_LIST_HEAD(&ret->b_assoc_buffers);
3278	preempt_disable();
3279	__this_cpu_inc(bh_accounting.nr);
3280	recalc_bh_state();
3281	preempt_enable();
3282	}
3283	return ret;
3284	}
3285	EXPORT_SYMBOL(alloc_buffer_head);
3286
3287	void free_buffer_head(struct buffer_head *bh)
3288	{
3289	BUG_ON(!list_empty(&bh->b_assoc_buffers));
3290	kmem_cache_free(bh_cachep, bh);
3291	preempt_disable();
3292	__this_cpu_dec(bh_accounting.nr);
3293	recalc_bh_state();
3294	preempt_enable();
3295	}
3296	EXPORT_SYMBOL(free_buffer_head);
3297
3298	static void buffer_exit_cpu(int cpu)
3299	{
3300	int i;
3301	struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3302
3303	for (i = 0; i < BH_LRU_SIZE; i++) {
3304	brelse(b->bhs[i]);
3305	b->bhs[i] = NULL;
3306	}
3307	this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3308	per_cpu(bh_accounting, cpu).nr = 0;
3309	}
3310
3311	static int buffer_cpu_notify(struct notifier_block *self,
3312	unsigned long action, void *hcpu)
3313	{
3314	if (action == CPU_DEAD \|\| action == CPU_DEAD_FROZEN)
3315	buffer_exit_cpu((unsigned long)hcpu);
3316	return NOTIFY_OK;
3317	}
3318
3319	/**
3320	* bh_uptodate_or_lock - Test whether the buffer is uptodate
3321	* @bh: struct buffer_head
3322	*
3323	* Return true if the buffer is up-to-date and false,
3324	* with the buffer locked, if not.
3325	*/
3326	int bh_uptodate_or_lock(struct buffer_head *bh)
3327	{
3328	if (!buffer_uptodate(bh)) {
3329	lock_buffer(bh);
3330	if (!buffer_uptodate(bh))
3331	return 0;
3332	unlock_buffer(bh);
3333	}
3334	return 1;
3335	}
3336	EXPORT_SYMBOL(bh_uptodate_or_lock);
3337
3338	/**
3339	* bh_submit_read - Submit a locked buffer for reading
3340	* @bh: struct buffer_head
3341	*
3342	* Returns zero on success and -EIO on error.
3343	*/
3344	int bh_submit_read(struct buffer_head *bh)
3345	{
3346	BUG_ON(!buffer_locked(bh));
3347
3348	if (buffer_uptodate(bh)) {
3349	unlock_buffer(bh);
3350	return 0;
3351	}
3352
3353	get_bh(bh);
3354	bh->b_end_io = end_buffer_read_sync;
3355	submit_bh(READ, bh);
3356	wait_on_buffer(bh);
3357	if (buffer_uptodate(bh))
3358	return 0;
3359	return -EIO;
3360	}
3361	EXPORT_SYMBOL(bh_submit_read);
3362
3363	void __init buffer_init(void)
3364	{
3365	unsigned long nrpages;
3366
3367	bh_cachep = kmem_cache_create("buffer_head",
3368	sizeof(struct buffer_head), 0,
3369	(SLAB_RECLAIM_ACCOUNT\|SLAB_PANIC\|
3370	SLAB_MEM_SPREAD),
3371	NULL);
3372
3373	/*
3374	* Limit the bh occupancy to 10% of ZONE_NORMAL
3375	*/
3376	nrpages = (nr_free_buffer_pages() * 10) / 100;
3377	max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3378	hotcpu_notifier(buffer_cpu_notify, 0);
3379	}