linux - fs/buffer.c

3471 lines · 90.2 KiB

1	/*
2	* linux/fs/buffer.c
3	*
4	* Copyright (C) 1991, 1992, 2002 Linus Torvalds
5	*/
6
7	/*
8	* Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
9	*
10	* Removed a lot of unnecessary code and simplified things now that
11	* the buffer cache isn't our primary cache - Andrew Tridgell 12/96
12	*
13	* Speed up hash, lru, and free list operations. Use gfp() for allocating
14	* hash table, use SLAB cache for buffer heads. SMP threading. -DaveM
15	*
16	* Added 32k buffer block sizes - these are required older ARM systems. - RMK
17	*
18	* async buffer flushing, 1999 Andrea Arcangeli <[email protected]>
19	*/
20
21	#include <linux/kernel.h>
22	#include <linux/sched/signal.h>
23	#include <linux/syscalls.h>
24	#include <linux/fs.h>
25	#include <linux/iomap.h>
26	#include <linux/mm.h>
27	#include <linux/percpu.h>
28	#include <linux/slab.h>
29	#include <linux/capability.h>
30	#include <linux/blkdev.h>
31	#include <linux/file.h>
32	#include <linux/quotaops.h>
33	#include <linux/highmem.h>
34	#include <linux/export.h>
35	#include <linux/backing-dev.h>
36	#include <linux/writeback.h>
37	#include <linux/hash.h>
38	#include <linux/suspend.h>
39	#include <linux/buffer_head.h>
40	#include <linux/task_io_accounting_ops.h>
41	#include <linux/bio.h>
42	#include <linux/cpu.h>
43	#include <linux/bitops.h>
44	#include <linux/mpage.h>
45	#include <linux/bit_spinlock.h>
46	#include <linux/pagevec.h>
47	#include <linux/sched/mm.h>
48	#include <trace/events/block.h>
49
50	static int fsync_buffers_list(spinlock_t lock, struct list_head list);
51	static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
52	enum rw_hint hint, struct writeback_control *wbc);
53
54	#define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
55
56	inline void touch_buffer(struct buffer_head *bh)
57	{
58	trace_block_touch_buffer(bh);
59	mark_page_accessed(bh->b_page);
60	}
61	EXPORT_SYMBOL(touch_buffer);
62
63	void __lock_buffer(struct buffer_head *bh)
64	{
65	wait_on_bit_lock_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
66	}
67	EXPORT_SYMBOL(__lock_buffer);
68
69	void unlock_buffer(struct buffer_head *bh)
70	{
71	clear_bit_unlock(BH_Lock, &bh->b_state);
72	smp_mb__after_atomic();
73	wake_up_bit(&bh->b_state, BH_Lock);
74	}
75	EXPORT_SYMBOL(unlock_buffer);
76
77	/*
78	* Returns if the page has dirty or writeback buffers. If all the buffers
79	* are unlocked and clean then the PageDirty information is stale. If
80	* any of the pages are locked, it is assumed they are locked for IO.
81	*/
82	void buffer_check_dirty_writeback(struct page *page,
83	bool dirty, bool writeback)
84	{
85	struct buffer_head head, bh;
86	*dirty = false;
87	*writeback = false;
88
89	BUG_ON(!PageLocked(page));
90
91	if (!page_has_buffers(page))
92	return;
93
94	if (PageWriteback(page))
95	*writeback = true;
96
97	head = page_buffers(page);
98	bh = head;
99	do {
100	if (buffer_locked(bh))
101	*writeback = true;
102
103	if (buffer_dirty(bh))
104	*dirty = true;
105
106	bh = bh->b_this_page;
107	} while (bh != head);
108	}
109	EXPORT_SYMBOL(buffer_check_dirty_writeback);
110
111	/*
112	* Block until a buffer comes unlocked. This doesn't stop it
113	* from becoming locked again - you have to lock it yourself
114	* if you want to preserve its state.
115	*/
116	void __wait_on_buffer(struct buffer_head * bh)
117	{
118	wait_on_bit_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
119	}
120	EXPORT_SYMBOL(__wait_on_buffer);
121
122	static void
123	__clear_page_buffers(struct page *page)
124	{
125	ClearPagePrivate(page);
126	set_page_private(page, 0);
127	put_page(page);
128	}
129
130	static void buffer_io_error(struct buffer_head bh, char msg)
131	{
132	if (!test_bit(BH_Quiet, &bh->b_state))
133	printk_ratelimited(KERN_ERR
134	"Buffer I/O error on dev %pg, logical block %llu%s\n",
135	bh->b_bdev, (unsigned long long)bh->b_blocknr, msg);
136	}
137
138	/*
139	* End-of-IO handler helper function which does not touch the bh after
140	* unlocking it.
141	* Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
142	* a race there is benign: unlock_buffer() only use the bh's address for
143	* hashing after unlocking the buffer, so it doesn't actually touch the bh
144	* itself.
145	*/
146	static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
147	{
148	if (uptodate) {
149	set_buffer_uptodate(bh);
150	} else {
151	/* This happens, due to failed read-ahead attempts. */
152	clear_buffer_uptodate(bh);
153	}
154	unlock_buffer(bh);
155	}
156
157	/*
158	* Default synchronous end-of-IO handler.. Just mark it up-to-date and
159	* unlock the buffer. This is what ll_rw_block uses too.
160	*/
161	void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
162	{
163	__end_buffer_read_notouch(bh, uptodate);
164	put_bh(bh);
165	}
166	EXPORT_SYMBOL(end_buffer_read_sync);
167
168	void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
169	{
170	if (uptodate) {
171	set_buffer_uptodate(bh);
172	} else {
173	buffer_io_error(bh, ", lost sync page write");
174	mark_buffer_write_io_error(bh);
175	clear_buffer_uptodate(bh);
176	}
177	unlock_buffer(bh);
178	put_bh(bh);
179	}
180	EXPORT_SYMBOL(end_buffer_write_sync);
181
182	/*
183	* Various filesystems appear to want __find_get_block to be non-blocking.
184	* But it's the page lock which protects the buffers. To get around this,
185	* we get exclusion from try_to_free_buffers with the blockdev mapping's
186	* private_lock.
187	*
188	* Hack idea: for the blockdev mapping, private_lock contention
189	* may be quite high. This code could TryLock the page, and if that
190	* succeeds, there is no need to take private_lock.
191	*/
192	static struct buffer_head *
193	__find_get_block_slow(struct block_device *bdev, sector_t block)
194	{
195	struct inode *bd_inode = bdev->bd_inode;
196	struct address_space *bd_mapping = bd_inode->i_mapping;
197	struct buffer_head *ret = NULL;
198	pgoff_t index;
199	struct buffer_head *bh;
200	struct buffer_head *head;
201	struct page *page;
202	int all_mapped = 1;
203	static DEFINE_RATELIMIT_STATE(last_warned, HZ, 1);
204
205	index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
206	page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
207	if (!page)
208	goto out;
209
210	spin_lock(&bd_mapping->private_lock);
211	if (!page_has_buffers(page))
212	goto out_unlock;
213	head = page_buffers(page);
214	bh = head;
215	do {
216	if (!buffer_mapped(bh))
217	all_mapped = 0;
218	else if (bh->b_blocknr == block) {
219	ret = bh;
220	get_bh(bh);
221	goto out_unlock;
222	}
223	bh = bh->b_this_page;
224	} while (bh != head);
225
226	/* we might be here because some of the buffers on this page are
227	* not mapped. This is due to various races between
228	* file io on the block device and getblk. It gets dealt with
229	* elsewhere, don't buffer_error if we had some unmapped buffers
230	*/
231	ratelimit_set_flags(&last_warned, RATELIMIT_MSG_ON_RELEASE);
232	if (all_mapped && __ratelimit(&last_warned)) {
233	printk("__find_get_block_slow() failed. block=%llu, "
234	"b_blocknr=%llu, b_state=0x%08lx, b_size=%zu, "
235	"device %pg blocksize: %d\n",
236	(unsigned long long)block,
237	(unsigned long long)bh->b_blocknr,
238	bh->b_state, bh->b_size, bdev,
239	1 << bd_inode->i_blkbits);
240	}
241	out_unlock:
242	spin_unlock(&bd_mapping->private_lock);
243	put_page(page);
244	out:
245	return ret;
246	}
247
248	/*
249	* I/O completion handler for block_read_full_page() - pages
250	* which come unlocked at the end of I/O.
251	*/
252	static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
253	{
254	unsigned long flags;
255	struct buffer_head *first;
256	struct buffer_head *tmp;
257	struct page *page;
258	int page_uptodate = 1;
259
260	BUG_ON(!buffer_async_read(bh));
261
262	page = bh->b_page;
263	if (uptodate) {
264	set_buffer_uptodate(bh);
265	} else {
266	clear_buffer_uptodate(bh);
267	buffer_io_error(bh, ", async page read");
268	SetPageError(page);
269	}
270
271	/*
272	* Be _very_ careful from here on. Bad things can happen if
273	* two buffer heads end IO at almost the same time and both
274	* decide that the page is now completely done.
275	*/
276	first = page_buffers(page);
277	local_irq_save(flags);
278	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
279	clear_buffer_async_read(bh);
280	unlock_buffer(bh);
281	tmp = bh;
282	do {
283	if (!buffer_uptodate(tmp))
284	page_uptodate = 0;
285	if (buffer_async_read(tmp)) {
286	BUG_ON(!buffer_locked(tmp));
287	goto still_busy;
288	}
289	tmp = tmp->b_this_page;
290	} while (tmp != bh);
291	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
292	local_irq_restore(flags);
293
294	/*
295	* If none of the buffers had errors and they are all
296	* uptodate then we can set the page uptodate.
297	*/
298	if (page_uptodate && !PageError(page))
299	SetPageUptodate(page);
300	unlock_page(page);
301	return;
302
303	still_busy:
304	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
305	local_irq_restore(flags);
306	return;
307	}
308
309	/*
310	* Completion handler for block_write_full_page() - pages which are unlocked
311	* during I/O, and which have PageWriteback cleared upon I/O completion.
312	*/
313	void end_buffer_async_write(struct buffer_head *bh, int uptodate)
314	{
315	unsigned long flags;
316	struct buffer_head *first;
317	struct buffer_head *tmp;
318	struct page *page;
319
320	BUG_ON(!buffer_async_write(bh));
321
322	page = bh->b_page;
323	if (uptodate) {
324	set_buffer_uptodate(bh);
325	} else {
326	buffer_io_error(bh, ", lost async page write");
327	mark_buffer_write_io_error(bh);
328	clear_buffer_uptodate(bh);
329	SetPageError(page);
330	}
331
332	first = page_buffers(page);
333	local_irq_save(flags);
334	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
335
336	clear_buffer_async_write(bh);
337	unlock_buffer(bh);
338	tmp = bh->b_this_page;
339	while (tmp != bh) {
340	if (buffer_async_write(tmp)) {
341	BUG_ON(!buffer_locked(tmp));
342	goto still_busy;
343	}
344	tmp = tmp->b_this_page;
345	}
346	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
347	local_irq_restore(flags);
348	end_page_writeback(page);
349	return;
350
351	still_busy:
352	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
353	local_irq_restore(flags);
354	return;
355	}
356	EXPORT_SYMBOL(end_buffer_async_write);
357
358	/*
359	* If a page's buffers are under async readin (end_buffer_async_read
360	* completion) then there is a possibility that another thread of
361	* control could lock one of the buffers after it has completed
362	* but while some of the other buffers have not completed. This
363	* locked buffer would confuse end_buffer_async_read() into not unlocking
364	* the page. So the absence of BH_Async_Read tells end_buffer_async_read()
365	* that this buffer is not under async I/O.
366	*
367	* The page comes unlocked when it has no locked buffer_async buffers
368	* left.
369	*
370	* PageLocked prevents anyone starting new async I/O reads any of
371	* the buffers.
372	*
373	* PageWriteback is used to prevent simultaneous writeout of the same
374	* page.
375	*
376	* PageLocked prevents anyone from starting writeback of a page which is
377	* under read I/O (PageWriteback is only ever set against a locked page).
378	*/
379	static void mark_buffer_async_read(struct buffer_head *bh)
380	{
381	bh->b_end_io = end_buffer_async_read;
382	set_buffer_async_read(bh);
383	}
384
385	static void mark_buffer_async_write_endio(struct buffer_head *bh,
386	bh_end_io_t *handler)
387	{
388	bh->b_end_io = handler;
389	set_buffer_async_write(bh);
390	}
391
392	void mark_buffer_async_write(struct buffer_head *bh)
393	{
394	mark_buffer_async_write_endio(bh, end_buffer_async_write);
395	}
396	EXPORT_SYMBOL(mark_buffer_async_write);
397
398
399	/*
400	* fs/buffer.c contains helper functions for buffer-backed address space's
401	* fsync functions. A common requirement for buffer-based filesystems is
402	* that certain data from the backing blockdev needs to be written out for
403	* a successful fsync(). For example, ext2 indirect blocks need to be
404	* written back and waited upon before fsync() returns.
405	*
406	* The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
407	* inode_has_buffers() and invalidate_inode_buffers() are provided for the
408	* management of a list of dependent buffers at ->i_mapping->private_list.
409	*
410	* Locking is a little subtle: try_to_free_buffers() will remove buffers
411	* from their controlling inode's queue when they are being freed. But
412	* try_to_free_buffers() will be operating against the blockdev mapping
413	* at the time, not against the S_ISREG file which depends on those buffers.
414	* So the locking for private_list is via the private_lock in the address_space
415	* which backs the buffers. Which is different from the address_space
416	* against which the buffers are listed. So for a particular address_space,
417	* mapping->private_lock does not protect mapping->private_list! In fact,
418	* mapping->private_list will always be protected by the backing blockdev's
419	* ->private_lock.
420	*
421	* Which introduces a requirement: all buffers on an address_space's
422	* ->private_list must be from the same address_space: the blockdev's.
423	*
424	* address_spaces which do not place buffers at ->private_list via these
425	* utility functions are free to use private_lock and private_list for
426	* whatever they want. The only requirement is that list_empty(private_list)
427	* be true at clear_inode() time.
428	*
429	* FIXME: clear_inode should not call invalidate_inode_buffers(). The
430	* filesystems should do that. invalidate_inode_buffers() should just go
431	* BUG_ON(!list_empty).
432	*
433	* FIXME: mark_buffer_dirty_inode() is a data-plane operation. It should
434	* take an address_space, not an inode. And it should be called
435	* mark_buffer_dirty_fsync() to clearly define why those buffers are being
436	* queued up.
437	*
438	* FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
439	* list if it is already on a list. Because if the buffer is on a list,
440	* it must already be on the right one. If not, the filesystem is being
441	* silly. This will save a ton of locking. But first we have to ensure
442	* that buffers are taken off the old inode's list when they are freed
443	* (presumably in truncate). That requires careful auditing of all
444	* filesystems (do it inside bforget()). It could also be done by bringing
445	* b_inode back.
446	*/
447
448	/*
449	* The buffer's backing address_space's private_lock must be held
450	*/
451	static void __remove_assoc_queue(struct buffer_head *bh)
452	{
453	list_del_init(&bh->b_assoc_buffers);
454	WARN_ON(!bh->b_assoc_map);
455	bh->b_assoc_map = NULL;
456	}
457
458	int inode_has_buffers(struct inode *inode)
459	{
460	return !list_empty(&inode->i_data.private_list);
461	}
462
463	/*
464	* osync is designed to support O_SYNC io. It waits synchronously for
465	* all already-submitted IO to complete, but does not queue any new
466	* writes to the disk.
467	*
468	* To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
469	* you dirty the buffers, and then use osync_inode_buffers to wait for
470	* completion. Any other dirty buffers which are not yet queued for
471	* write will not be flushed to disk by the osync.
472	*/
473	static int osync_buffers_list(spinlock_t lock, struct list_head list)
474	{
475	struct buffer_head *bh;
476	struct list_head *p;
477	int err = 0;
478
479	spin_lock(lock);
480	repeat:
481	list_for_each_prev(p, list) {
482	bh = BH_ENTRY(p);
483	if (buffer_locked(bh)) {
484	get_bh(bh);
485	spin_unlock(lock);
486	wait_on_buffer(bh);
487	if (!buffer_uptodate(bh))
488	err = -EIO;
489	brelse(bh);
490	spin_lock(lock);
491	goto repeat;
492	}
493	}
494	spin_unlock(lock);
495	return err;
496	}
497
498	void emergency_thaw_bdev(struct super_block *sb)
499	{
500	while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
501	printk(KERN_WARNING "Emergency Thaw on %pg\n", sb->s_bdev);
502	}
503
504	/**
505	* sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
506	* @mapping: the mapping which wants those buffers written
507	*
508	* Starts I/O against the buffers at mapping->private_list, and waits upon
509	* that I/O.
510	*
511	* Basically, this is a convenience function for fsync().
512	* @mapping is a file or directory which needs those buffers to be written for
513	* a successful fsync().
514	*/
515	int sync_mapping_buffers(struct address_space *mapping)
516	{
517	struct address_space *buffer_mapping = mapping->private_data;
518
519	if (buffer_mapping == NULL \|\| list_empty(&mapping->private_list))
520	return 0;
521
522	return fsync_buffers_list(&buffer_mapping->private_lock,
523	&mapping->private_list);
524	}
525	EXPORT_SYMBOL(sync_mapping_buffers);
526
527	/*
528	* Called when we've recently written block `bblock', and it is known that
529	* `bblock' was for a buffer_boundary() buffer. This means that the block at
530	* `bblock + 1' is probably a dirty indirect block. Hunt it down and, if it's
531	* dirty, schedule it for IO. So that indirects merge nicely with their data.
532	*/
533	void write_boundary_block(struct block_device *bdev,
534	sector_t bblock, unsigned blocksize)
535	{
536	struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
537	if (bh) {
538	if (buffer_dirty(bh))
539	ll_rw_block(REQ_OP_WRITE, 0, 1, &bh);
540	put_bh(bh);
541	}
542	}
543
544	void mark_buffer_dirty_inode(struct buffer_head bh, struct inode inode)
545	{
546	struct address_space *mapping = inode->i_mapping;
547	struct address_space *buffer_mapping = bh->b_page->mapping;
548
549	mark_buffer_dirty(bh);
550	if (!mapping->private_data) {
551	mapping->private_data = buffer_mapping;
552	} else {
553	BUG_ON(mapping->private_data != buffer_mapping);
554	}
555	if (!bh->b_assoc_map) {
556	spin_lock(&buffer_mapping->private_lock);
557	list_move_tail(&bh->b_assoc_buffers,
558	&mapping->private_list);
559	bh->b_assoc_map = mapping;
560	spin_unlock(&buffer_mapping->private_lock);
561	}
562	}
563	EXPORT_SYMBOL(mark_buffer_dirty_inode);
564
565	/*
566	* Mark the page dirty, and set it dirty in the page cache, and mark the inode
567	* dirty.
568	*
569	* If warn is true, then emit a warning if the page is not uptodate and has
570	* not been truncated.
571	*
572	* The caller must hold lock_page_memcg().
573	*/
574	void __set_page_dirty(struct page page, struct address_space mapping,
575	int warn)
576	{
577	unsigned long flags;
578
579	xa_lock_irqsave(&mapping->i_pages, flags);
580	if (page->mapping) { /* Race with truncate? */
581	WARN_ON_ONCE(warn && !PageUptodate(page));
582	account_page_dirtied(page, mapping);
583	__xa_set_mark(&mapping->i_pages, page_index(page),
584	PAGECACHE_TAG_DIRTY);
585	}
586	xa_unlock_irqrestore(&mapping->i_pages, flags);
587	}
588	EXPORT_SYMBOL_GPL(__set_page_dirty);
589
590	/*
591	* Add a page to the dirty page list.
592	*
593	* It is a sad fact of life that this function is called from several places
594	* deeply under spinlocking. It may not sleep.
595	*
596	* If the page has buffers, the uptodate buffers are set dirty, to preserve
597	* dirty-state coherency between the page and the buffers. It the page does
598	* not have buffers then when they are later attached they will all be set
599	* dirty.
600	*
601	* The buffers are dirtied before the page is dirtied. There's a small race
602	* window in which a writepage caller may see the page cleanness but not the
603	* buffer dirtiness. That's fine. If this code were to set the page dirty
604	* before the buffers, a concurrent writepage caller could clear the page dirty
605	* bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
606	* page on the dirty page list.
607	*
608	* We use private_lock to lock against try_to_free_buffers while using the
609	* page's buffer list. Also use this to protect against clean buffers being
610	* added to the page after it was set dirty.
611	*
612	* FIXME: may need to call ->reservepage here as well. That's rather up to the
613	* address_space though.
614	*/
615	int __set_page_dirty_buffers(struct page *page)
616	{
617	int newly_dirty;
618	struct address_space *mapping = page_mapping(page);
619
620	if (unlikely(!mapping))
621	return !TestSetPageDirty(page);
622
623	spin_lock(&mapping->private_lock);
624	if (page_has_buffers(page)) {
625	struct buffer_head *head = page_buffers(page);
626	struct buffer_head *bh = head;
627
628	do {
629	set_buffer_dirty(bh);
630	bh = bh->b_this_page;
631	} while (bh != head);
632	}
633	/*
634	* Lock out page->mem_cgroup migration to keep PageDirty
635	* synchronized with per-memcg dirty page counters.
636	*/
637	lock_page_memcg(page);
638	newly_dirty = !TestSetPageDirty(page);
639	spin_unlock(&mapping->private_lock);
640
641	if (newly_dirty)
642	__set_page_dirty(page, mapping, 1);
643
644	unlock_page_memcg(page);
645
646	if (newly_dirty)
647	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
648
649	return newly_dirty;
650	}
651	EXPORT_SYMBOL(__set_page_dirty_buffers);
652
653	/*
654	* Write out and wait upon a list of buffers.
655	*
656	* We have conflicting pressures: we want to make sure that all
657	* initially dirty buffers get waited on, but that any subsequently
658	* dirtied buffers don't. After all, we don't want fsync to last
659	* forever if somebody is actively writing to the file.
660	*
661	* Do this in two main stages: first we copy dirty buffers to a
662	* temporary inode list, queueing the writes as we go. Then we clean
663	* up, waiting for those writes to complete.
664	*
665	* During this second stage, any subsequent updates to the file may end
666	* up refiling the buffer on the original inode's dirty list again, so
667	* there is a chance we will end up with a buffer queued for write but
668	* not yet completed on that list. So, as a final cleanup we go through
669	* the osync code to catch these locked, dirty buffers without requeuing
670	* any newly dirty buffers for write.
671	*/
672	static int fsync_buffers_list(spinlock_t lock, struct list_head list)
673	{
674	struct buffer_head *bh;
675	struct list_head tmp;
676	struct address_space *mapping;
677	int err = 0, err2;
678	struct blk_plug plug;
679
680	INIT_LIST_HEAD(&tmp);
681	blk_start_plug(&plug);
682
683	spin_lock(lock);
684	while (!list_empty(list)) {
685	bh = BH_ENTRY(list->next);
686	mapping = bh->b_assoc_map;
687	__remove_assoc_queue(bh);
688	/* Avoid race with mark_buffer_dirty_inode() which does
689	* a lockless check and we rely on seeing the dirty bit */
690	smp_mb();
691	if (buffer_dirty(bh) \|\| buffer_locked(bh)) {
692	list_add(&bh->b_assoc_buffers, &tmp);
693	bh->b_assoc_map = mapping;
694	if (buffer_dirty(bh)) {
695	get_bh(bh);
696	spin_unlock(lock);
697	/*
698	* Ensure any pending I/O completes so that
699	* write_dirty_buffer() actually writes the
700	* current contents - it is a noop if I/O is
701	* still in flight on potentially older
702	* contents.
703	*/
704	write_dirty_buffer(bh, REQ_SYNC);
705
706	/*
707	* Kick off IO for the previous mapping. Note
708	* that we will not run the very last mapping,
709	* wait_on_buffer() will do that for us
710	* through sync_buffer().
711	*/
712	brelse(bh);
713	spin_lock(lock);
714	}
715	}
716	}
717
718	spin_unlock(lock);
719	blk_finish_plug(&plug);
720	spin_lock(lock);
721
722	while (!list_empty(&tmp)) {
723	bh = BH_ENTRY(tmp.prev);
724	get_bh(bh);
725	mapping = bh->b_assoc_map;
726	__remove_assoc_queue(bh);
727	/* Avoid race with mark_buffer_dirty_inode() which does
728	* a lockless check and we rely on seeing the dirty bit */
729	smp_mb();
730	if (buffer_dirty(bh)) {
731	list_add(&bh->b_assoc_buffers,
732	&mapping->private_list);
733	bh->b_assoc_map = mapping;
734	}
735	spin_unlock(lock);
736	wait_on_buffer(bh);
737	if (!buffer_uptodate(bh))
738	err = -EIO;
739	brelse(bh);
740	spin_lock(lock);
741	}
742
743	spin_unlock(lock);
744	err2 = osync_buffers_list(lock, list);
745	if (err)
746	return err;
747	else
748	return err2;
749	}
750
751	/*
752	* Invalidate any and all dirty buffers on a given inode. We are
753	* probably unmounting the fs, but that doesn't mean we have already
754	* done a sync(). Just drop the buffers from the inode list.
755	*
756	* NOTE: we take the inode's blockdev's mapping's private_lock. Which
757	* assumes that all the buffers are against the blockdev. Not true
758	* for reiserfs.
759	*/
760	void invalidate_inode_buffers(struct inode *inode)
761	{
762	if (inode_has_buffers(inode)) {
763	struct address_space *mapping = &inode->i_data;
764	struct list_head *list = &mapping->private_list;
765	struct address_space *buffer_mapping = mapping->private_data;
766
767	spin_lock(&buffer_mapping->private_lock);
768	while (!list_empty(list))
769	__remove_assoc_queue(BH_ENTRY(list->next));
770	spin_unlock(&buffer_mapping->private_lock);
771	}
772	}
773	EXPORT_SYMBOL(invalidate_inode_buffers);
774
775	/*
776	* Remove any clean buffers from the inode's buffer list. This is called
777	* when we're trying to free the inode itself. Those buffers can pin it.
778	*
779	* Returns true if all buffers were removed.
780	*/
781	int remove_inode_buffers(struct inode *inode)
782	{
783	int ret = 1;
784
785	if (inode_has_buffers(inode)) {
786	struct address_space *mapping = &inode->i_data;
787	struct list_head *list = &mapping->private_list;
788	struct address_space *buffer_mapping = mapping->private_data;
789
790	spin_lock(&buffer_mapping->private_lock);
791	while (!list_empty(list)) {
792	struct buffer_head *bh = BH_ENTRY(list->next);
793	if (buffer_dirty(bh)) {
794	ret = 0;
795	break;
796	}
797	__remove_assoc_queue(bh);
798	}
799	spin_unlock(&buffer_mapping->private_lock);
800	}
801	return ret;
802	}
803
804	/*
805	* Create the appropriate buffers when given a page for data area and
806	* the size of each buffer.. Use the bh->b_this_page linked list to
807	* follow the buffers created. Return NULL if unable to create more
808	* buffers.
809	*
810	* The retry flag is used to differentiate async IO (paging, swapping)
811	* which may not fail from ordinary buffer allocations.
812	*/
813	struct buffer_head alloc_page_buffers(struct page page, unsigned long size,
814	bool retry)
815	{
816	struct buffer_head bh, head;
817	gfp_t gfp = GFP_NOFS \| __GFP_ACCOUNT;
818	long offset;
819	struct mem_cgroup *memcg;
820
821	if (retry)
822	gfp \|= __GFP_NOFAIL;
823
824	memcg = get_mem_cgroup_from_page(page);
825	memalloc_use_memcg(memcg);
826
827	head = NULL;
828	offset = PAGE_SIZE;
829	while ((offset -= size) >= 0) {
830	bh = alloc_buffer_head(gfp);
831	if (!bh)
832	goto no_grow;
833
834	bh->b_this_page = head;
835	bh->b_blocknr = -1;
836	head = bh;
837
838	bh->b_size = size;
839
840	/* Link the buffer to its page */
841	set_bh_page(bh, page, offset);
842	}
843	out:
844	memalloc_unuse_memcg();
845	mem_cgroup_put(memcg);
846	return head;
847	/*
848	* In case anything failed, we just free everything we got.
849	*/
850	no_grow:
851	if (head) {
852	do {
853	bh = head;
854	head = head->b_this_page;
855	free_buffer_head(bh);
856	} while (head);
857	}
858
859	goto out;
860	}
861	EXPORT_SYMBOL_GPL(alloc_page_buffers);
862
863	static inline void
864	link_dev_buffers(struct page page, struct buffer_head head)
865	{
866	struct buffer_head bh, tail;
867
868	bh = head;
869	do {
870	tail = bh;
871	bh = bh->b_this_page;
872	} while (bh);
873	tail->b_this_page = head;
874	attach_page_buffers(page, head);
875	}
876
877	static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
878	{
879	sector_t retval = ~((sector_t)0);
880	loff_t sz = i_size_read(bdev->bd_inode);
881
882	if (sz) {
883	unsigned int sizebits = blksize_bits(size);
884	retval = (sz >> sizebits);
885	}
886	return retval;
887	}
888
889	/*
890	* Initialise the state of a blockdev page's buffers.
891	*/
892	static sector_t
893	init_page_buffers(struct page page, struct block_device bdev,
894	sector_t block, int size)
895	{
896	struct buffer_head *head = page_buffers(page);
897	struct buffer_head *bh = head;
898	int uptodate = PageUptodate(page);
899	sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
900
901	do {
902	if (!buffer_mapped(bh)) {
903	bh->b_end_io = NULL;
904	bh->b_private = NULL;
905	bh->b_bdev = bdev;
906	bh->b_blocknr = block;
907	if (uptodate)
908	set_buffer_uptodate(bh);
909	if (block < end_block)
910	set_buffer_mapped(bh);
911	}
912	block++;
913	bh = bh->b_this_page;
914	} while (bh != head);
915
916	/*
917	* Caller needs to validate requested block against end of device.
918	*/
919	return end_block;
920	}
921
922	/*
923	* Create the page-cache page that contains the requested block.
924	*
925	* This is used purely for blockdev mappings.
926	*/
927	static int
928	grow_dev_page(struct block_device *bdev, sector_t block,
929	pgoff_t index, int size, int sizebits, gfp_t gfp)
930	{
931	struct inode *inode = bdev->bd_inode;
932	struct page *page;
933	struct buffer_head *bh;
934	sector_t end_block;
935	int ret = 0; /* Will call free_more_memory() */
936	gfp_t gfp_mask;
937
938	gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) \| gfp;
939
940	/*
941	* XXX: __getblk_slow() can not really deal with failure and
942	* will endlessly loop on improvised global reclaim. Prefer
943	* looping in the allocator rather than here, at least that
944	* code knows what it's doing.
945	*/
946	gfp_mask \|= __GFP_NOFAIL;
947
948	page = find_or_create_page(inode->i_mapping, index, gfp_mask);
949
950	BUG_ON(!PageLocked(page));
951
952	if (page_has_buffers(page)) {
953	bh = page_buffers(page);
954	if (bh->b_size == size) {
955	end_block = init_page_buffers(page, bdev,
956	(sector_t)index << sizebits,
957	size);
958	goto done;
959	}
960	if (!try_to_free_buffers(page))
961	goto failed;
962	}
963
964	/*
965	* Allocate some buffers for this page
966	*/
967	bh = alloc_page_buffers(page, size, true);
968
969	/*
970	* Link the page to the buffers and initialise them. Take the
971	* lock to be atomic wrt __find_get_block(), which does not
972	* run under the page lock.
973	*/
974	spin_lock(&inode->i_mapping->private_lock);
975	link_dev_buffers(page, bh);
976	end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
977	size);
978	spin_unlock(&inode->i_mapping->private_lock);
979	done:
980	ret = (block < end_block) ? 1 : -ENXIO;
981	failed:
982	unlock_page(page);
983	put_page(page);
984	return ret;
985	}
986
987	/*
988	* Create buffers for the specified block device block's page. If
989	* that page was dirty, the buffers are set dirty also.
990	*/
991	static int
992	grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
993	{
994	pgoff_t index;
995	int sizebits;
996
997	sizebits = -1;
998	do {
999	sizebits++;
1000	} while ((size << sizebits) < PAGE_SIZE);
1001
1002	index = block >> sizebits;
1003
1004	/*
1005	* Check for a block which wants to lie outside our maximum possible
1006	* pagecache index. (this comparison is done using sector_t types).
1007	*/
1008	if (unlikely(index != block >> sizebits)) {
1009	printk(KERN_ERR "%s: requested out-of-range block %llu for "
1010	"device %pg\n",
1011	__func__, (unsigned long long)block,
1012	bdev);
1013	return -EIO;
1014	}
1015
1016	/* Create a page with the proper size buffers.. */
1017	return grow_dev_page(bdev, block, index, size, sizebits, gfp);
1018	}
1019
1020	static struct buffer_head *
1021	__getblk_slow(struct block_device *bdev, sector_t block,
1022	unsigned size, gfp_t gfp)
1023	{
1024	/* Size must be multiple of hard sectorsize */
1025	if (unlikely(size & (bdev_logical_block_size(bdev)-1) \|\|
1026	(size < 512 \|\| size > PAGE_SIZE))) {
1027	printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1028	size);
1029	printk(KERN_ERR "logical block size: %d\n",
1030	bdev_logical_block_size(bdev));
1031
1032	dump_stack();
1033	return NULL;
1034	}
1035
1036	for (;;) {
1037	struct buffer_head *bh;
1038	int ret;
1039
1040	bh = __find_get_block(bdev, block, size);
1041	if (bh)
1042	return bh;
1043
1044	ret = grow_buffers(bdev, block, size, gfp);
1045	if (ret < 0)
1046	return NULL;
1047	}
1048	}
1049
1050	/*
1051	* The relationship between dirty buffers and dirty pages:
1052	*
1053	* Whenever a page has any dirty buffers, the page's dirty bit is set, and
1054	* the page is tagged dirty in the page cache.
1055	*
1056	* At all times, the dirtiness of the buffers represents the dirtiness of
1057	* subsections of the page. If the page has buffers, the page dirty bit is
1058	* merely a hint about the true dirty state.
1059	*
1060	* When a page is set dirty in its entirety, all its buffers are marked dirty
1061	* (if the page has buffers).
1062	*
1063	* When a buffer is marked dirty, its page is dirtied, but the page's other
1064	* buffers are not.
1065	*
1066	* Also. When blockdev buffers are explicitly read with bread(), they
1067	* individually become uptodate. But their backing page remains not
1068	* uptodate - even if all of its buffers are uptodate. A subsequent
1069	* block_read_full_page() against that page will discover all the uptodate
1070	* buffers, will set the page uptodate and will perform no I/O.
1071	*/
1072
1073	/**
1074	* mark_buffer_dirty - mark a buffer_head as needing writeout
1075	* @bh: the buffer_head to mark dirty
1076	*
1077	* mark_buffer_dirty() will set the dirty bit against the buffer, then set
1078	* its backing page dirty, then tag the page as dirty in the page cache
1079	* and then attach the address_space's inode to its superblock's dirty
1080	* inode list.
1081	*
1082	* mark_buffer_dirty() is atomic. It takes bh->b_page->mapping->private_lock,
1083	* i_pages lock and mapping->host->i_lock.
1084	*/
1085	void mark_buffer_dirty(struct buffer_head *bh)
1086	{
1087	WARN_ON_ONCE(!buffer_uptodate(bh));
1088
1089	trace_block_dirty_buffer(bh);
1090
1091	/*
1092	* Very carefully optimize the it-is-already-dirty case.
1093	*
1094	* Don't let the final "is it dirty" escape to before we
1095	* perhaps modified the buffer.
1096	*/
1097	if (buffer_dirty(bh)) {
1098	smp_mb();
1099	if (buffer_dirty(bh))
1100	return;
1101	}
1102
1103	if (!test_set_buffer_dirty(bh)) {
1104	struct page *page = bh->b_page;
1105	struct address_space *mapping = NULL;
1106
1107	lock_page_memcg(page);
1108	if (!TestSetPageDirty(page)) {
1109	mapping = page_mapping(page);
1110	if (mapping)
1111	__set_page_dirty(page, mapping, 0);
1112	}
1113	unlock_page_memcg(page);
1114	if (mapping)
1115	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1116	}
1117	}
1118	EXPORT_SYMBOL(mark_buffer_dirty);
1119
1120	void mark_buffer_write_io_error(struct buffer_head *bh)
1121	{
1122	set_buffer_write_io_error(bh);
1123	/* FIXME: do we need to set this in both places? */
1124	if (bh->b_page && bh->b_page->mapping)
1125	mapping_set_error(bh->b_page->mapping, -EIO);
1126	if (bh->b_assoc_map)
1127	mapping_set_error(bh->b_assoc_map, -EIO);
1128	}
1129	EXPORT_SYMBOL(mark_buffer_write_io_error);
1130
1131	/*
1132	* Decrement a buffer_head's reference count. If all buffers against a page
1133	* have zero reference count, are clean and unlocked, and if the page is clean
1134	* and unlocked then try_to_free_buffers() may strip the buffers from the page
1135	* in preparation for freeing it (sometimes, rarely, buffers are removed from
1136	* a page but it ends up not being freed, and buffers may later be reattached).
1137	*/
1138	void __brelse(struct buffer_head * buf)
1139	{
1140	if (atomic_read(&buf->b_count)) {
1141	put_bh(buf);
1142	return;
1143	}
1144	WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1145	}
1146	EXPORT_SYMBOL(__brelse);
1147
1148	/*
1149	* bforget() is like brelse(), except it discards any
1150	* potentially dirty data.
1151	*/
1152	void __bforget(struct buffer_head *bh)
1153	{
1154	clear_buffer_dirty(bh);
1155	if (bh->b_assoc_map) {
1156	struct address_space *buffer_mapping = bh->b_page->mapping;
1157
1158	spin_lock(&buffer_mapping->private_lock);
1159	list_del_init(&bh->b_assoc_buffers);
1160	bh->b_assoc_map = NULL;
1161	spin_unlock(&buffer_mapping->private_lock);
1162	}
1163	__brelse(bh);
1164	}
1165	EXPORT_SYMBOL(__bforget);
1166
1167	static struct buffer_head __bread_slow(struct buffer_head bh)
1168	{
1169	lock_buffer(bh);
1170	if (buffer_uptodate(bh)) {
1171	unlock_buffer(bh);
1172	return bh;
1173	} else {
1174	get_bh(bh);
1175	bh->b_end_io = end_buffer_read_sync;
1176	submit_bh(REQ_OP_READ, 0, bh);
1177	wait_on_buffer(bh);
1178	if (buffer_uptodate(bh))
1179	return bh;
1180	}
1181	brelse(bh);
1182	return NULL;
1183	}
1184
1185	/*
1186	* Per-cpu buffer LRU implementation. To reduce the cost of __find_get_block().
1187	* The bhs[] array is sorted - newest buffer is at bhs[0]. Buffers have their
1188	* refcount elevated by one when they're in an LRU. A buffer can only appear
1189	* once in a particular CPU's LRU. A single buffer can be present in multiple
1190	* CPU's LRUs at the same time.
1191	*
1192	* This is a transparent caching front-end to sb_bread(), sb_getblk() and
1193	* sb_find_get_block().
1194	*
1195	* The LRUs themselves only need locking against invalidate_bh_lrus. We use
1196	* a local interrupt disable for that.
1197	*/
1198
1199	#define BH_LRU_SIZE 16
1200
1201	struct bh_lru {
1202	struct buffer_head *bhs[BH_LRU_SIZE];
1203	};
1204
1205	static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1206
1207	#ifdef CONFIG_SMP
1208	#define bh_lru_lock() local_irq_disable()
1209	#define bh_lru_unlock() local_irq_enable()
1210	#else
1211	#define bh_lru_lock() preempt_disable()
1212	#define bh_lru_unlock() preempt_enable()
1213	#endif
1214
1215	static inline void check_irqs_on(void)
1216	{
1217	#ifdef irqs_disabled
1218	BUG_ON(irqs_disabled());
1219	#endif
1220	}
1221
1222	/*
1223	* Install a buffer_head into this cpu's LRU. If not already in the LRU, it is
1224	* inserted at the front, and the buffer_head at the back if any is evicted.
1225	* Or, if already in the LRU it is moved to the front.
1226	*/
1227	static void bh_lru_install(struct buffer_head *bh)
1228	{
1229	struct buffer_head *evictee = bh;
1230	struct bh_lru *b;
1231	int i;
1232
1233	check_irqs_on();
1234	bh_lru_lock();
1235
1236	b = this_cpu_ptr(&bh_lrus);
1237	for (i = 0; i < BH_LRU_SIZE; i++) {
1238	swap(evictee, b->bhs[i]);
1239	if (evictee == bh) {
1240	bh_lru_unlock();
1241	return;
1242	}
1243	}
1244
1245	get_bh(bh);
1246	bh_lru_unlock();
1247	brelse(evictee);
1248	}
1249
1250	/*
1251	* Look up the bh in this cpu's LRU. If it's there, move it to the head.
1252	*/
1253	static struct buffer_head *
1254	lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1255	{
1256	struct buffer_head *ret = NULL;
1257	unsigned int i;
1258
1259	check_irqs_on();
1260	bh_lru_lock();
1261	for (i = 0; i < BH_LRU_SIZE; i++) {
1262	struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1263
1264	if (bh && bh->b_blocknr == block && bh->b_bdev == bdev &&
1265	bh->b_size == size) {
1266	if (i) {
1267	while (i) {
1268	__this_cpu_write(bh_lrus.bhs[i],
1269	__this_cpu_read(bh_lrus.bhs[i - 1]));
1270	i--;
1271	}
1272	__this_cpu_write(bh_lrus.bhs[0], bh);
1273	}
1274	get_bh(bh);
1275	ret = bh;
1276	break;
1277	}
1278	}
1279	bh_lru_unlock();
1280	return ret;
1281	}
1282
1283	/*
1284	* Perform a pagecache lookup for the matching buffer. If it's there, refresh
1285	* it in the LRU and mark it as accessed. If it is not present then return
1286	* NULL
1287	*/
1288	struct buffer_head *
1289	__find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1290	{
1291	struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1292
1293	if (bh == NULL) {
1294	/* __find_get_block_slow will mark the page accessed */
1295	bh = __find_get_block_slow(bdev, block);
1296	if (bh)
1297	bh_lru_install(bh);
1298	} else
1299	touch_buffer(bh);
1300
1301	return bh;
1302	}
1303	EXPORT_SYMBOL(__find_get_block);
1304
1305	/*
1306	* __getblk_gfp() will locate (and, if necessary, create) the buffer_head
1307	* which corresponds to the passed block_device, block and size. The
1308	* returned buffer has its reference count incremented.
1309	*
1310	* __getblk_gfp() will lock up the machine if grow_dev_page's
1311	* try_to_free_buffers() attempt is failing. FIXME, perhaps?
1312	*/
1313	struct buffer_head *
1314	__getblk_gfp(struct block_device *bdev, sector_t block,
1315	unsigned size, gfp_t gfp)
1316	{
1317	struct buffer_head *bh = __find_get_block(bdev, block, size);
1318
1319	might_sleep();
1320	if (bh == NULL)
1321	bh = __getblk_slow(bdev, block, size, gfp);
1322	return bh;
1323	}
1324	EXPORT_SYMBOL(__getblk_gfp);
1325
1326	/*
1327	* Do async read-ahead on a buffer..
1328	*/
1329	void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1330	{
1331	struct buffer_head *bh = __getblk(bdev, block, size);
1332	if (likely(bh)) {
1333	ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
1334	brelse(bh);
1335	}
1336	}
1337	EXPORT_SYMBOL(__breadahead);
1338
1339	/**
1340	* __bread_gfp() - reads a specified block and returns the bh
1341	* @bdev: the block_device to read from
1342	* @block: number of block
1343	* @size: size (in bytes) to read
1344	* @gfp: page allocation flag
1345	*
1346	* Reads a specified block, and returns buffer head that contains it.
1347	* The page cache can be allocated from non-movable area
1348	* not to prevent page migration if you set gfp to zero.
1349	* It returns NULL if the block was unreadable.
1350	*/
1351	struct buffer_head *
1352	__bread_gfp(struct block_device *bdev, sector_t block,
1353	unsigned size, gfp_t gfp)
1354	{
1355	struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
1356
1357	if (likely(bh) && !buffer_uptodate(bh))
1358	bh = __bread_slow(bh);
1359	return bh;
1360	}
1361	EXPORT_SYMBOL(__bread_gfp);
1362
1363	/*
1364	* invalidate_bh_lrus() is called rarely - but not only at unmount.
1365	* This doesn't race because it runs in each cpu either in irq
1366	* or with preempt disabled.
1367	*/
1368	static void invalidate_bh_lru(void *arg)
1369	{
1370	struct bh_lru *b = &get_cpu_var(bh_lrus);
1371	int i;
1372
1373	for (i = 0; i < BH_LRU_SIZE; i++) {
1374	brelse(b->bhs[i]);
1375	b->bhs[i] = NULL;
1376	}
1377	put_cpu_var(bh_lrus);
1378	}
1379
1380	static bool has_bh_in_lru(int cpu, void *dummy)
1381	{
1382	struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1383	int i;
1384
1385	for (i = 0; i < BH_LRU_SIZE; i++) {
1386	if (b->bhs[i])
1387	return 1;
1388	}
1389
1390	return 0;
1391	}
1392
1393	void invalidate_bh_lrus(void)
1394	{
1395	on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1396	}
1397	EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1398
1399	void set_bh_page(struct buffer_head *bh,
1400	struct page *page, unsigned long offset)
1401	{
1402	bh->b_page = page;
1403	BUG_ON(offset >= PAGE_SIZE);
1404	if (PageHighMem(page))
1405	/*
1406	* This catches illegal uses and preserves the offset:
1407	*/
1408	bh->b_data = (char *)(0 + offset);
1409	else
1410	bh->b_data = page_address(page) + offset;
1411	}
1412	EXPORT_SYMBOL(set_bh_page);
1413
1414	/*
1415	* Called when truncating a buffer on a page completely.
1416	*/
1417
1418	/* Bits that are cleared during an invalidate */
1419	#define BUFFER_FLAGS_DISCARD \
1420	(1 << BH_Mapped \| 1 << BH_New \| 1 << BH_Req \| \
1421	1 << BH_Delay \| 1 << BH_Unwritten)
1422
1423	static void discard_buffer(struct buffer_head * bh)
1424	{
1425	unsigned long b_state, b_state_old;
1426
1427	lock_buffer(bh);
1428	clear_buffer_dirty(bh);
1429	bh->b_bdev = NULL;
1430	b_state = bh->b_state;
1431	for (;;) {
1432	b_state_old = cmpxchg(&bh->b_state, b_state,
1433	(b_state & ~BUFFER_FLAGS_DISCARD));
1434	if (b_state_old == b_state)
1435	break;
1436	b_state = b_state_old;
1437	}
1438	unlock_buffer(bh);
1439	}
1440
1441	/**
1442	* block_invalidatepage - invalidate part or all of a buffer-backed page
1443	*
1444	* @page: the page which is affected
1445	* @offset: start of the range to invalidate
1446	* @length: length of the range to invalidate
1447	*
1448	* block_invalidatepage() is called when all or part of the page has become
1449	* invalidated by a truncate operation.
1450	*
1451	* block_invalidatepage() does not have to release all buffers, but it must
1452	* ensure that no dirty buffer is left outside @offset and that no I/O
1453	* is underway against any of the blocks which are outside the truncation
1454	* point. Because the caller is about to free (and possibly reuse) those
1455	* blocks on-disk.
1456	*/
1457	void block_invalidatepage(struct page *page, unsigned int offset,
1458	unsigned int length)
1459	{
1460	struct buffer_head head, bh, *next;
1461	unsigned int curr_off = 0;
1462	unsigned int stop = length + offset;
1463
1464	BUG_ON(!PageLocked(page));
1465	if (!page_has_buffers(page))
1466	goto out;
1467
1468	/*
1469	* Check for overflow
1470	*/
1471	BUG_ON(stop > PAGE_SIZE \|\| stop < length);
1472
1473	head = page_buffers(page);
1474	bh = head;
1475	do {
1476	unsigned int next_off = curr_off + bh->b_size;
1477	next = bh->b_this_page;
1478
1479	/*
1480	* Are we still fully in range ?
1481	*/
1482	if (next_off > stop)
1483	goto out;
1484
1485	/*
1486	* is this block fully invalidated?
1487	*/
1488	if (offset <= curr_off)
1489	discard_buffer(bh);
1490	curr_off = next_off;
1491	bh = next;
1492	} while (bh != head);
1493
1494	/*
1495	* We release buffers only if the entire page is being invalidated.
1496	* The get_block cached value has been unconditionally invalidated,
1497	* so real IO is not possible anymore.
1498	*/
1499	if (length == PAGE_SIZE)
1500	try_to_release_page(page, 0);
1501	out:
1502	return;
1503	}
1504	EXPORT_SYMBOL(block_invalidatepage);
1505
1506
1507	/*
1508	* We attach and possibly dirty the buffers atomically wrt
1509	* __set_page_dirty_buffers() via private_lock. try_to_free_buffers
1510	* is already excluded via the page lock.
1511	*/
1512	void create_empty_buffers(struct page *page,
1513	unsigned long blocksize, unsigned long b_state)
1514	{
1515	struct buffer_head bh, head, *tail;
1516
1517	head = alloc_page_buffers(page, blocksize, true);
1518	bh = head;
1519	do {
1520	bh->b_state \|= b_state;
1521	tail = bh;
1522	bh = bh->b_this_page;
1523	} while (bh);
1524	tail->b_this_page = head;
1525
1526	spin_lock(&page->mapping->private_lock);
1527	if (PageUptodate(page) \|\| PageDirty(page)) {
1528	bh = head;
1529	do {
1530	if (PageDirty(page))
1531	set_buffer_dirty(bh);
1532	if (PageUptodate(page))
1533	set_buffer_uptodate(bh);
1534	bh = bh->b_this_page;
1535	} while (bh != head);
1536	}
1537	attach_page_buffers(page, head);
1538	spin_unlock(&page->mapping->private_lock);
1539	}
1540	EXPORT_SYMBOL(create_empty_buffers);
1541
1542	/**
1543	* clean_bdev_aliases: clean a range of buffers in block device
1544	* @bdev: Block device to clean buffers in
1545	* @block: Start of a range of blocks to clean
1546	* @len: Number of blocks to clean
1547	*
1548	* We are taking a range of blocks for data and we don't want writeback of any
1549	* buffer-cache aliases starting from return from this function and until the
1550	* moment when something will explicitly mark the buffer dirty (hopefully that
1551	* will not happen until we will free that block ;-) We don't even need to mark
1552	* it not-uptodate - nobody can expect anything from a newly allocated buffer
1553	* anyway. We used to use unmap_buffer() for such invalidation, but that was
1554	* wrong. We definitely don't want to mark the alias unmapped, for example - it
1555	* would confuse anyone who might pick it with bread() afterwards...
1556	*
1557	* Also.. Note that bforget() doesn't lock the buffer. So there can be
1558	* writeout I/O going on against recently-freed buffers. We don't wait on that
1559	* I/O in bforget() - it's more efficient to wait on the I/O only if we really
1560	* need to. That happens here.
1561	*/
1562	void clean_bdev_aliases(struct block_device *bdev, sector_t block, sector_t len)
1563	{
1564	struct inode *bd_inode = bdev->bd_inode;
1565	struct address_space *bd_mapping = bd_inode->i_mapping;
1566	struct pagevec pvec;
1567	pgoff_t index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
1568	pgoff_t end;
1569	int i, count;
1570	struct buffer_head *bh;
1571	struct buffer_head *head;
1572
1573	end = (block + len - 1) >> (PAGE_SHIFT - bd_inode->i_blkbits);
1574	pagevec_init(&pvec);
1575	while (pagevec_lookup_range(&pvec, bd_mapping, &index, end)) {
1576	count = pagevec_count(&pvec);
1577	for (i = 0; i < count; i++) {
1578	struct page *page = pvec.pages[i];
1579
1580	if (!page_has_buffers(page))
1581	continue;
1582	/*
1583	* We use page lock instead of bd_mapping->private_lock
1584	* to pin buffers here since we can afford to sleep and
1585	* it scales better than a global spinlock lock.
1586	*/
1587	lock_page(page);
1588	/* Recheck when the page is locked which pins bhs */
1589	if (!page_has_buffers(page))
1590	goto unlock_page;
1591	head = page_buffers(page);
1592	bh = head;
1593	do {
1594	if (!buffer_mapped(bh) \|\| (bh->b_blocknr < block))
1595	goto next;
1596	if (bh->b_blocknr >= block + len)
1597	break;
1598	clear_buffer_dirty(bh);
1599	wait_on_buffer(bh);
1600	clear_buffer_req(bh);
1601	next:
1602	bh = bh->b_this_page;
1603	} while (bh != head);
1604	unlock_page:
1605	unlock_page(page);
1606	}
1607	pagevec_release(&pvec);
1608	cond_resched();
1609	/* End of range already reached? */
1610	if (index > end \|\| !index)
1611	break;
1612	}
1613	}
1614	EXPORT_SYMBOL(clean_bdev_aliases);
1615
1616	/*
1617	* Size is a power-of-two in the range 512..PAGE_SIZE,
1618	* and the case we care about most is PAGE_SIZE.
1619	*
1620	* So this could possibly be written with those
1621	* constraints in mind (relevant mostly if some
1622	* architecture has a slow bit-scan instruction)
1623	*/
1624	static inline int block_size_bits(unsigned int blocksize)
1625	{
1626	return ilog2(blocksize);
1627	}
1628
1629	static struct buffer_head create_page_buffers(struct page page, struct inode *inode, unsigned int b_state)
1630	{
1631	BUG_ON(!PageLocked(page));
1632
1633	if (!page_has_buffers(page))
1634	create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
1635	b_state);
1636	return page_buffers(page);
1637	}
1638
1639	/*
1640	* NOTE! All mapped/uptodate combinations are valid:
1641	*
1642	* Mapped Uptodate Meaning
1643	*
1644	* No No "unknown" - must do get_block()
1645	* No Yes "hole" - zero-filled
1646	* Yes No "allocated" - allocated on disk, not read in
1647	* Yes Yes "valid" - allocated and up-to-date in memory.
1648	*
1649	* "Dirty" is valid only with the last case (mapped+uptodate).
1650	*/
1651
1652	/*
1653	* While block_write_full_page is writing back the dirty buffers under
1654	* the page lock, whoever dirtied the buffers may decide to clean them
1655	* again at any time. We handle that by only looking at the buffer
1656	* state inside lock_buffer().
1657	*
1658	* If block_write_full_page() is called for regular writeback
1659	* (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1660	* locked buffer. This only can happen if someone has written the buffer
1661	* directly, with submit_bh(). At the address_space level PageWriteback
1662	* prevents this contention from occurring.
1663	*
1664	* If block_write_full_page() is called with wbc->sync_mode ==
1665	* WB_SYNC_ALL, the writes are posted using REQ_SYNC; this
1666	* causes the writes to be flagged as synchronous writes.
1667	*/
1668	int __block_write_full_page(struct inode inode, struct page page,
1669	get_block_t get_block, struct writeback_control wbc,
1670	bh_end_io_t *handler)
1671	{
1672	int err;
1673	sector_t block;
1674	sector_t last_block;
1675	struct buffer_head bh, head;
1676	unsigned int blocksize, bbits;
1677	int nr_underway = 0;
1678	int write_flags = wbc_to_write_flags(wbc);
1679
1680	head = create_page_buffers(page, inode,
1681	(1 << BH_Dirty)\|(1 << BH_Uptodate));
1682
1683	/*
1684	* Be very careful. We have no exclusion from __set_page_dirty_buffers
1685	* here, and the (potentially unmapped) buffers may become dirty at
1686	* any time. If a buffer becomes dirty here after we've inspected it
1687	* then we just miss that fact, and the page stays dirty.
1688	*
1689	* Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1690	* handle that here by just cleaning them.
1691	*/
1692
1693	bh = head;
1694	blocksize = bh->b_size;
1695	bbits = block_size_bits(blocksize);
1696
1697	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
1698	last_block = (i_size_read(inode) - 1) >> bbits;
1699
1700	/*
1701	* Get all the dirty buffers mapped to disk addresses and
1702	* handle any aliases from the underlying blockdev's mapping.
1703	*/
1704	do {
1705	if (block > last_block) {
1706	/*
1707	* mapped buffers outside i_size will occur, because
1708	* this page can be outside i_size when there is a
1709	* truncate in progress.
1710	*/
1711	/*
1712	* The buffer was zeroed by block_write_full_page()
1713	*/
1714	clear_buffer_dirty(bh);
1715	set_buffer_uptodate(bh);
1716	} else if ((!buffer_mapped(bh) \|\| buffer_delay(bh)) &&
1717	buffer_dirty(bh)) {
1718	WARN_ON(bh->b_size != blocksize);
1719	err = get_block(inode, block, bh, 1);
1720	if (err)
1721	goto recover;
1722	clear_buffer_delay(bh);
1723	if (buffer_new(bh)) {
1724	/* blockdev mappings never come here */
1725	clear_buffer_new(bh);
1726	clean_bdev_bh_alias(bh);
1727	}
1728	}
1729	bh = bh->b_this_page;
1730	block++;
1731	} while (bh != head);
1732
1733	do {
1734	if (!buffer_mapped(bh))
1735	continue;
1736	/*
1737	* If it's a fully non-blocking write attempt and we cannot
1738	* lock the buffer then redirty the page. Note that this can
1739	* potentially cause a busy-wait loop from writeback threads
1740	* and kswapd activity, but those code paths have their own
1741	* higher-level throttling.
1742	*/
1743	if (wbc->sync_mode != WB_SYNC_NONE) {
1744	lock_buffer(bh);
1745	} else if (!trylock_buffer(bh)) {
1746	redirty_page_for_writepage(wbc, page);
1747	continue;
1748	}
1749	if (test_clear_buffer_dirty(bh)) {
1750	mark_buffer_async_write_endio(bh, handler);
1751	} else {
1752	unlock_buffer(bh);
1753	}
1754	} while ((bh = bh->b_this_page) != head);
1755
1756	/*
1757	* The page and its buffers are protected by PageWriteback(), so we can
1758	* drop the bh refcounts early.
1759	*/
1760	BUG_ON(PageWriteback(page));
1761	set_page_writeback(page);
1762
1763	do {
1764	struct buffer_head *next = bh->b_this_page;
1765	if (buffer_async_write(bh)) {
1766	submit_bh_wbc(REQ_OP_WRITE, write_flags, bh,
1767	inode->i_write_hint, wbc);
1768	nr_underway++;
1769	}
1770	bh = next;
1771	} while (bh != head);
1772	unlock_page(page);
1773
1774	err = 0;
1775	done:
1776	if (nr_underway == 0) {
1777	/*
1778	* The page was marked dirty, but the buffers were
1779	* clean. Someone wrote them back by hand with
1780	* ll_rw_block/submit_bh. A rare case.
1781	*/
1782	end_page_writeback(page);
1783
1784	/*
1785	* The page and buffer_heads can be released at any time from
1786	* here on.
1787	*/
1788	}
1789	return err;
1790
1791	recover:
1792	/*
1793	* ENOSPC, or some other error. We may already have added some
1794	* blocks to the file, so we need to write these out to avoid
1795	* exposing stale data.
1796	* The page is currently locked and not marked for writeback
1797	*/
1798	bh = head;
1799	/* Recovery: lock and submit the mapped buffers */
1800	do {
1801	if (buffer_mapped(bh) && buffer_dirty(bh) &&
1802	!buffer_delay(bh)) {
1803	lock_buffer(bh);
1804	mark_buffer_async_write_endio(bh, handler);
1805	} else {
1806	/*
1807	* The buffer may have been set dirty during
1808	* attachment to a dirty page.
1809	*/
1810	clear_buffer_dirty(bh);
1811	}
1812	} while ((bh = bh->b_this_page) != head);
1813	SetPageError(page);
1814	BUG_ON(PageWriteback(page));
1815	mapping_set_error(page->mapping, err);
1816	set_page_writeback(page);
1817	do {
1818	struct buffer_head *next = bh->b_this_page;
1819	if (buffer_async_write(bh)) {
1820	clear_buffer_dirty(bh);
1821	submit_bh_wbc(REQ_OP_WRITE, write_flags, bh,
1822	inode->i_write_hint, wbc);
1823	nr_underway++;
1824	}
1825	bh = next;
1826	} while (bh != head);
1827	unlock_page(page);
1828	goto done;
1829	}
1830	EXPORT_SYMBOL(__block_write_full_page);
1831
1832	/*
1833	* If a page has any new buffers, zero them out here, and mark them uptodate
1834	* and dirty so they'll be written out (in order to prevent uninitialised
1835	* block data from leaking). And clear the new bit.
1836	*/
1837	void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1838	{
1839	unsigned int block_start, block_end;
1840	struct buffer_head head, bh;
1841
1842	BUG_ON(!PageLocked(page));
1843	if (!page_has_buffers(page))
1844	return;
1845
1846	bh = head = page_buffers(page);
1847	block_start = 0;
1848	do {
1849	block_end = block_start + bh->b_size;
1850
1851	if (buffer_new(bh)) {
1852	if (block_end > from && block_start < to) {
1853	if (!PageUptodate(page)) {
1854	unsigned start, size;
1855
1856	start = max(from, block_start);
1857	size = min(to, block_end) - start;
1858
1859	zero_user(page, start, size);
1860	set_buffer_uptodate(bh);
1861	}
1862
1863	clear_buffer_new(bh);
1864	mark_buffer_dirty(bh);
1865	}
1866	}
1867
1868	block_start = block_end;
1869	bh = bh->b_this_page;
1870	} while (bh != head);
1871	}
1872	EXPORT_SYMBOL(page_zero_new_buffers);
1873
1874	static void
1875	iomap_to_bh(struct inode inode, sector_t block, struct buffer_head bh,
1876	struct iomap *iomap)
1877	{
1878	loff_t offset = block << inode->i_blkbits;
1879
1880	bh->b_bdev = iomap->bdev;
1881
1882	/*
1883	* Block points to offset in file we need to map, iomap contains
1884	* the offset at which the map starts. If the map ends before the
1885	* current block, then do not map the buffer and let the caller
1886	* handle it.
1887	*/
1888	BUG_ON(offset >= iomap->offset + iomap->length);
1889
1890	switch (iomap->type) {
1891	case IOMAP_HOLE:
1892	/*
1893	* If the buffer is not up to date or beyond the current EOF,
1894	* we need to mark it as new to ensure sub-block zeroing is
1895	* executed if necessary.
1896	*/
1897	if (!buffer_uptodate(bh) \|\|
1898	(offset >= i_size_read(inode)))
1899	set_buffer_new(bh);
1900	break;
1901	case IOMAP_DELALLOC:
1902	if (!buffer_uptodate(bh) \|\|
1903	(offset >= i_size_read(inode)))
1904	set_buffer_new(bh);
1905	set_buffer_uptodate(bh);
1906	set_buffer_mapped(bh);
1907	set_buffer_delay(bh);
1908	break;
1909	case IOMAP_UNWRITTEN:
1910	/*
1911	* For unwritten regions, we always need to ensure that regions
1912	* in the block we are not writing to are zeroed. Mark the
1913	* buffer as new to ensure this.
1914	*/
1915	set_buffer_new(bh);
1916	set_buffer_unwritten(bh);
1917	/* FALLTHRU */
1918	case IOMAP_MAPPED:
1919	if ((iomap->flags & IOMAP_F_NEW) \|\|
1920	offset >= i_size_read(inode))
1921	set_buffer_new(bh);
1922	bh->b_blocknr = (iomap->addr + offset - iomap->offset) >>
1923	inode->i_blkbits;
1924	set_buffer_mapped(bh);
1925	break;
1926	}
1927	}
1928
1929	int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
1930	get_block_t get_block, struct iomap iomap)
1931	{
1932	unsigned from = pos & (PAGE_SIZE - 1);
1933	unsigned to = from + len;
1934	struct inode *inode = page->mapping->host;
1935	unsigned block_start, block_end;
1936	sector_t block;
1937	int err = 0;
1938	unsigned blocksize, bbits;
1939	struct buffer_head bh, head, wait[2], *wait_bh=wait;
1940
1941	BUG_ON(!PageLocked(page));
1942	BUG_ON(from > PAGE_SIZE);
1943	BUG_ON(to > PAGE_SIZE);
1944	BUG_ON(from > to);
1945
1946	head = create_page_buffers(page, inode, 0);
1947	blocksize = head->b_size;
1948	bbits = block_size_bits(blocksize);
1949
1950	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
1951
1952	for(bh = head, block_start = 0; bh != head \|\| !block_start;
1953	block++, block_start=block_end, bh = bh->b_this_page) {
1954	block_end = block_start + blocksize;
1955	if (block_end <= from \|\| block_start >= to) {
1956	if (PageUptodate(page)) {
1957	if (!buffer_uptodate(bh))
1958	set_buffer_uptodate(bh);
1959	}
1960	continue;
1961	}
1962	if (buffer_new(bh))
1963	clear_buffer_new(bh);
1964	if (!buffer_mapped(bh)) {
1965	WARN_ON(bh->b_size != blocksize);
1966	if (get_block) {
1967	err = get_block(inode, block, bh, 1);
1968	if (err)
1969	break;
1970	} else {
1971	iomap_to_bh(inode, block, bh, iomap);
1972	}
1973
1974	if (buffer_new(bh)) {
1975	clean_bdev_bh_alias(bh);
1976	if (PageUptodate(page)) {
1977	clear_buffer_new(bh);
1978	set_buffer_uptodate(bh);
1979	mark_buffer_dirty(bh);
1980	continue;
1981	}
1982	if (block_end > to \|\| block_start < from)
1983	zero_user_segments(page,
1984	to, block_end,
1985	block_start, from);
1986	continue;
1987	}
1988	}
1989	if (PageUptodate(page)) {
1990	if (!buffer_uptodate(bh))
1991	set_buffer_uptodate(bh);
1992	continue;
1993	}
1994	if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1995	!buffer_unwritten(bh) &&
1996	(block_start < from \|\| block_end > to)) {
1997	ll_rw_block(REQ_OP_READ, 0, 1, &bh);
1998	*wait_bh++=bh;
1999	}
2000	}
2001	/*
2002	* If we issued read requests - let them complete.
2003	*/
2004	while(wait_bh > wait) {
2005	wait_on_buffer(*--wait_bh);
2006	if (!buffer_uptodate(*wait_bh))
2007	err = -EIO;
2008	}
2009	if (unlikely(err))
2010	page_zero_new_buffers(page, from, to);
2011	return err;
2012	}
2013
2014	int __block_write_begin(struct page *page, loff_t pos, unsigned len,
2015	get_block_t *get_block)
2016	{
2017	return __block_write_begin_int(page, pos, len, get_block, NULL);
2018	}
2019	EXPORT_SYMBOL(__block_write_begin);
2020
2021	static int __block_commit_write(struct inode inode, struct page page,
2022	unsigned from, unsigned to)
2023	{
2024	unsigned block_start, block_end;
2025	int partial = 0;
2026	unsigned blocksize;
2027	struct buffer_head bh, head;
2028
2029	bh = head = page_buffers(page);
2030	blocksize = bh->b_size;
2031
2032	block_start = 0;
2033	do {
2034	block_end = block_start + blocksize;
2035	if (block_end <= from \|\| block_start >= to) {
2036	if (!buffer_uptodate(bh))
2037	partial = 1;
2038	} else {
2039	set_buffer_uptodate(bh);
2040	mark_buffer_dirty(bh);
2041	}
2042	clear_buffer_new(bh);
2043
2044	block_start = block_end;
2045	bh = bh->b_this_page;
2046	} while (bh != head);
2047
2048	/*
2049	* If this is a partial write which happened to make all buffers
2050	* uptodate then we can optimize away a bogus readpage() for
2051	* the next read(). Here we 'discover' whether the page went
2052	* uptodate as a result of this (potentially partial) write.
2053	*/
2054	if (!partial)
2055	SetPageUptodate(page);
2056	return 0;
2057	}
2058
2059	/*
2060	* block_write_begin takes care of the basic task of block allocation and
2061	* bringing partial write blocks uptodate first.
2062	*
2063	* The filesystem needs to handle block truncation upon failure.
2064	*/
2065	int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
2066	unsigned flags, struct page *pagep, get_block_t get_block)
2067	{
2068	pgoff_t index = pos >> PAGE_SHIFT;
2069	struct page *page;
2070	int status;
2071
2072	page = grab_cache_page_write_begin(mapping, index, flags);
2073	if (!page)
2074	return -ENOMEM;
2075
2076	status = __block_write_begin(page, pos, len, get_block);
2077	if (unlikely(status)) {
2078	unlock_page(page);
2079	put_page(page);
2080	page = NULL;
2081	}
2082
2083	*pagep = page;
2084	return status;
2085	}
2086	EXPORT_SYMBOL(block_write_begin);
2087
2088	int __generic_write_end(struct inode *inode, loff_t pos, unsigned copied,
2089	struct page *page)
2090	{
2091	loff_t old_size = inode->i_size;
2092	bool i_size_changed = false;
2093
2094	/*
2095	* No need to use i_size_read() here, the i_size cannot change under us
2096	* because we hold i_rwsem.
2097	*
2098	* But it's important to update i_size while still holding page lock:
2099	* page writeout could otherwise come in and zero beyond i_size.
2100	*/
2101	if (pos + copied > inode->i_size) {
2102	i_size_write(inode, pos + copied);
2103	i_size_changed = true;
2104	}
2105
2106	unlock_page(page);
2107	put_page(page);
2108
2109	if (old_size < pos)
2110	pagecache_isize_extended(inode, old_size, pos);
2111	/*
2112	* Don't mark the inode dirty under page lock. First, it unnecessarily
2113	* makes the holding time of page lock longer. Second, it forces lock
2114	* ordering of page lock and transaction start for journaling
2115	* filesystems.
2116	*/
2117	if (i_size_changed)
2118	mark_inode_dirty(inode);
2119	return copied;
2120	}
2121
2122	int block_write_end(struct file file, struct address_space mapping,
2123	loff_t pos, unsigned len, unsigned copied,
2124	struct page page, void fsdata)
2125	{
2126	struct inode *inode = mapping->host;
2127	unsigned start;
2128
2129	start = pos & (PAGE_SIZE - 1);
2130
2131	if (unlikely(copied < len)) {
2132	/*
2133	* The buffers that were written will now be uptodate, so we
2134	* don't have to worry about a readpage reading them and
2135	* overwriting a partial write. However if we have encountered
2136	* a short write and only partially written into a buffer, it
2137	* will not be marked uptodate, so a readpage might come in and
2138	* destroy our partial write.
2139	*
2140	* Do the simplest thing, and just treat any short write to a
2141	* non uptodate page as a zero-length write, and force the
2142	* caller to redo the whole thing.
2143	*/
2144	if (!PageUptodate(page))
2145	copied = 0;
2146
2147	page_zero_new_buffers(page, start+copied, start+len);
2148	}
2149	flush_dcache_page(page);
2150
2151	/* This could be a short (even 0-length) commit */
2152	__block_commit_write(inode, page, start, start+copied);
2153
2154	return copied;
2155	}
2156	EXPORT_SYMBOL(block_write_end);
2157
2158	int generic_write_end(struct file file, struct address_space mapping,
2159	loff_t pos, unsigned len, unsigned copied,
2160	struct page page, void fsdata)
2161	{
2162	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2163	return __generic_write_end(mapping->host, pos, copied, page);
2164	}
2165	EXPORT_SYMBOL(generic_write_end);
2166
2167	/*
2168	* block_is_partially_uptodate checks whether buffers within a page are
2169	* uptodate or not.
2170	*
2171	* Returns true if all buffers which correspond to a file portion
2172	* we want to read are uptodate.
2173	*/
2174	int block_is_partially_uptodate(struct page *page, unsigned long from,
2175	unsigned long count)
2176	{
2177	unsigned block_start, block_end, blocksize;
2178	unsigned to;
2179	struct buffer_head bh, head;
2180	int ret = 1;
2181
2182	if (!page_has_buffers(page))
2183	return 0;
2184
2185	head = page_buffers(page);
2186	blocksize = head->b_size;
2187	to = min_t(unsigned, PAGE_SIZE - from, count);
2188	to = from + to;
2189	if (from < blocksize && to > PAGE_SIZE - blocksize)
2190	return 0;
2191
2192	bh = head;
2193	block_start = 0;
2194	do {
2195	block_end = block_start + blocksize;
2196	if (block_end > from && block_start < to) {
2197	if (!buffer_uptodate(bh)) {
2198	ret = 0;
2199	break;
2200	}
2201	if (block_end >= to)
2202	break;
2203	}
2204	block_start = block_end;
2205	bh = bh->b_this_page;
2206	} while (bh != head);
2207
2208	return ret;
2209	}
2210	EXPORT_SYMBOL(block_is_partially_uptodate);
2211
2212	/*
2213	* Generic "read page" function for block devices that have the normal
2214	* get_block functionality. This is most of the block device filesystems.
2215	* Reads the page asynchronously --- the unlock_buffer() and
2216	* set/clear_buffer_uptodate() functions propagate buffer state into the
2217	* page struct once IO has completed.
2218	*/
2219	int block_read_full_page(struct page page, get_block_t get_block)
2220	{
2221	struct inode *inode = page->mapping->host;
2222	sector_t iblock, lblock;
2223	struct buffer_head bh, head, *arr[MAX_BUF_PER_PAGE];
2224	unsigned int blocksize, bbits;
2225	int nr, i;
2226	int fully_mapped = 1;
2227
2228	head = create_page_buffers(page, inode, 0);
2229	blocksize = head->b_size;
2230	bbits = block_size_bits(blocksize);
2231
2232	iblock = (sector_t)page->index << (PAGE_SHIFT - bbits);
2233	lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2234	bh = head;
2235	nr = 0;
2236	i = 0;
2237
2238	do {
2239	if (buffer_uptodate(bh))
2240	continue;
2241
2242	if (!buffer_mapped(bh)) {
2243	int err = 0;
2244
2245	fully_mapped = 0;
2246	if (iblock < lblock) {
2247	WARN_ON(bh->b_size != blocksize);
2248	err = get_block(inode, iblock, bh, 0);
2249	if (err)
2250	SetPageError(page);
2251	}
2252	if (!buffer_mapped(bh)) {
2253	zero_user(page, i * blocksize, blocksize);
2254	if (!err)
2255	set_buffer_uptodate(bh);
2256	continue;
2257	}
2258	/*
2259	* get_block() might have updated the buffer
2260	* synchronously
2261	*/
2262	if (buffer_uptodate(bh))
2263	continue;
2264	}
2265	arr[nr++] = bh;
2266	} while (i++, iblock++, (bh = bh->b_this_page) != head);
2267
2268	if (fully_mapped)
2269	SetPageMappedToDisk(page);
2270
2271	if (!nr) {
2272	/*
2273	* All buffers are uptodate - we can set the page uptodate
2274	* as well. But not if get_block() returned an error.
2275	*/
2276	if (!PageError(page))
2277	SetPageUptodate(page);
2278	unlock_page(page);
2279	return 0;
2280	}
2281
2282	/* Stage two: lock the buffers */
2283	for (i = 0; i < nr; i++) {
2284	bh = arr[i];
2285	lock_buffer(bh);
2286	mark_buffer_async_read(bh);
2287	}
2288
2289	/*
2290	* Stage 3: start the IO. Check for uptodateness
2291	* inside the buffer lock in case another process reading
2292	* the underlying blockdev brought it uptodate (the sct fix).
2293	*/
2294	for (i = 0; i < nr; i++) {
2295	bh = arr[i];
2296	if (buffer_uptodate(bh))
2297	end_buffer_async_read(bh, 1);
2298	else
2299	submit_bh(REQ_OP_READ, 0, bh);
2300	}
2301	return 0;
2302	}
2303	EXPORT_SYMBOL(block_read_full_page);
2304
2305	/* utility function for filesystems that need to do work on expanding
2306	* truncates. Uses filesystem pagecache writes to allow the filesystem to
2307	* deal with the hole.
2308	*/
2309	int generic_cont_expand_simple(struct inode *inode, loff_t size)
2310	{
2311	struct address_space *mapping = inode->i_mapping;
2312	struct page *page;
2313	void *fsdata;
2314	int err;
2315
2316	err = inode_newsize_ok(inode, size);
2317	if (err)
2318	goto out;
2319
2320	err = pagecache_write_begin(NULL, mapping, size, 0,
2321	AOP_FLAG_CONT_EXPAND, &page, &fsdata);
2322	if (err)
2323	goto out;
2324
2325	err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2326	BUG_ON(err > 0);
2327
2328	out:
2329	return err;
2330	}
2331	EXPORT_SYMBOL(generic_cont_expand_simple);
2332
2333	static int cont_expand_zero(struct file file, struct address_space mapping,
2334	loff_t pos, loff_t *bytes)
2335	{
2336	struct inode *inode = mapping->host;
2337	unsigned int blocksize = i_blocksize(inode);
2338	struct page *page;
2339	void *fsdata;
2340	pgoff_t index, curidx;
2341	loff_t curpos;
2342	unsigned zerofrom, offset, len;
2343	int err = 0;
2344
2345	index = pos >> PAGE_SHIFT;
2346	offset = pos & ~PAGE_MASK;
2347
2348	while (index > (curidx = (curpos = *bytes)>>PAGE_SHIFT)) {
2349	zerofrom = curpos & ~PAGE_MASK;
2350	if (zerofrom & (blocksize-1)) {
2351	*bytes \|= (blocksize-1);
2352	(*bytes)++;
2353	}
2354	len = PAGE_SIZE - zerofrom;
2355
2356	err = pagecache_write_begin(file, mapping, curpos, len, 0,
2357	&page, &fsdata);
2358	if (err)
2359	goto out;
2360	zero_user(page, zerofrom, len);
2361	err = pagecache_write_end(file, mapping, curpos, len, len,
2362	page, fsdata);
2363	if (err < 0)
2364	goto out;
2365	BUG_ON(err != len);
2366	err = 0;
2367
2368	balance_dirty_pages_ratelimited(mapping);
2369
2370	if (fatal_signal_pending(current)) {
2371	err = -EINTR;
2372	goto out;
2373	}
2374	}
2375
2376	/* page covers the boundary, find the boundary offset */
2377	if (index == curidx) {
2378	zerofrom = curpos & ~PAGE_MASK;
2379	/* if we will expand the thing last block will be filled */
2380	if (offset <= zerofrom) {
2381	goto out;
2382	}
2383	if (zerofrom & (blocksize-1)) {
2384	*bytes \|= (blocksize-1);
2385	(*bytes)++;
2386	}
2387	len = offset - zerofrom;
2388
2389	err = pagecache_write_begin(file, mapping, curpos, len, 0,
2390	&page, &fsdata);
2391	if (err)
2392	goto out;
2393	zero_user(page, zerofrom, len);
2394	err = pagecache_write_end(file, mapping, curpos, len, len,
2395	page, fsdata);
2396	if (err < 0)
2397	goto out;
2398	BUG_ON(err != len);
2399	err = 0;
2400	}
2401	out:
2402	return err;
2403	}
2404
2405	/*
2406	* For moronic filesystems that do not allow holes in file.
2407	* We may have to extend the file.
2408	*/
2409	int cont_write_begin(struct file file, struct address_space mapping,
2410	loff_t pos, unsigned len, unsigned flags,
2411	struct page pagep, void fsdata,
2412	get_block_t get_block, loff_t bytes)
2413	{
2414	struct inode *inode = mapping->host;
2415	unsigned int blocksize = i_blocksize(inode);
2416	unsigned int zerofrom;
2417	int err;
2418
2419	err = cont_expand_zero(file, mapping, pos, bytes);
2420	if (err)
2421	return err;
2422
2423	zerofrom = *bytes & ~PAGE_MASK;
2424	if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2425	*bytes \|= (blocksize-1);
2426	(*bytes)++;
2427	}
2428
2429	return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2430	}
2431	EXPORT_SYMBOL(cont_write_begin);
2432
2433	int block_commit_write(struct page *page, unsigned from, unsigned to)
2434	{
2435	struct inode *inode = page->mapping->host;
2436	__block_commit_write(inode,page,from,to);
2437	return 0;
2438	}
2439	EXPORT_SYMBOL(block_commit_write);
2440
2441	/*
2442	* block_page_mkwrite() is not allowed to change the file size as it gets
2443	* called from a page fault handler when a page is first dirtied. Hence we must
2444	* be careful to check for EOF conditions here. We set the page up correctly
2445	* for a written page which means we get ENOSPC checking when writing into
2446	* holes and correct delalloc and unwritten extent mapping on filesystems that
2447	* support these features.
2448	*
2449	* We are not allowed to take the i_mutex here so we have to play games to
2450	* protect against truncate races as the page could now be beyond EOF. Because
2451	* truncate writes the inode size before removing pages, once we have the
2452	* page lock we can determine safely if the page is beyond EOF. If it is not
2453	* beyond EOF, then the page is guaranteed safe against truncation until we
2454	* unlock the page.
2455	*
2456	* Direct callers of this function should protect against filesystem freezing
2457	* using sb_start_pagefault() - sb_end_pagefault() functions.
2458	*/
2459	int block_page_mkwrite(struct vm_area_struct vma, struct vm_fault vmf,
2460	get_block_t get_block)
2461	{
2462	struct page *page = vmf->page;
2463	struct inode *inode = file_inode(vma->vm_file);
2464	unsigned long end;
2465	loff_t size;
2466	int ret;
2467
2468	lock_page(page);
2469	size = i_size_read(inode);
2470	if ((page->mapping != inode->i_mapping) \|\|
2471	(page_offset(page) > size)) {
2472	/* We overload EFAULT to mean page got truncated */
2473	ret = -EFAULT;
2474	goto out_unlock;
2475	}
2476
2477	/* page is wholly or partially inside EOF */
2478	if (((page->index + 1) << PAGE_SHIFT) > size)
2479	end = size & ~PAGE_MASK;
2480	else
2481	end = PAGE_SIZE;
2482
2483	ret = __block_write_begin(page, 0, end, get_block);
2484	if (!ret)
2485	ret = block_commit_write(page, 0, end);
2486
2487	if (unlikely(ret < 0))
2488	goto out_unlock;
2489	set_page_dirty(page);
2490	wait_for_stable_page(page);
2491	return 0;
2492	out_unlock:
2493	unlock_page(page);
2494	return ret;
2495	}
2496	EXPORT_SYMBOL(block_page_mkwrite);
2497
2498	/*
2499	* nobh_write_begin()'s prereads are special: the buffer_heads are freed
2500	* immediately, while under the page lock. So it needs a special end_io
2501	* handler which does not touch the bh after unlocking it.
2502	*/
2503	static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2504	{
2505	__end_buffer_read_notouch(bh, uptodate);
2506	}
2507
2508	/*
2509	* Attach the singly-linked list of buffers created by nobh_write_begin, to
2510	* the page (converting it to circular linked list and taking care of page
2511	* dirty races).
2512	*/
2513	static void attach_nobh_buffers(struct page page, struct buffer_head head)
2514	{
2515	struct buffer_head *bh;
2516
2517	BUG_ON(!PageLocked(page));
2518
2519	spin_lock(&page->mapping->private_lock);
2520	bh = head;
2521	do {
2522	if (PageDirty(page))
2523	set_buffer_dirty(bh);
2524	if (!bh->b_this_page)
2525	bh->b_this_page = head;
2526	bh = bh->b_this_page;
2527	} while (bh != head);
2528	attach_page_buffers(page, head);
2529	spin_unlock(&page->mapping->private_lock);
2530	}
2531
2532	/*
2533	* On entry, the page is fully not uptodate.
2534	* On exit the page is fully uptodate in the areas outside (from,to)
2535	* The filesystem needs to handle block truncation upon failure.
2536	*/
2537	int nobh_write_begin(struct address_space *mapping,
2538	loff_t pos, unsigned len, unsigned flags,
2539	struct page pagep, void fsdata,
2540	get_block_t *get_block)
2541	{
2542	struct inode *inode = mapping->host;
2543	const unsigned blkbits = inode->i_blkbits;
2544	const unsigned blocksize = 1 << blkbits;
2545	struct buffer_head head, bh;
2546	struct page *page;
2547	pgoff_t index;
2548	unsigned from, to;
2549	unsigned block_in_page;
2550	unsigned block_start, block_end;
2551	sector_t block_in_file;
2552	int nr_reads = 0;
2553	int ret = 0;
2554	int is_mapped_to_disk = 1;
2555
2556	index = pos >> PAGE_SHIFT;
2557	from = pos & (PAGE_SIZE - 1);
2558	to = from + len;
2559
2560	page = grab_cache_page_write_begin(mapping, index, flags);
2561	if (!page)
2562	return -ENOMEM;
2563	*pagep = page;
2564	*fsdata = NULL;
2565
2566	if (page_has_buffers(page)) {
2567	ret = __block_write_begin(page, pos, len, get_block);
2568	if (unlikely(ret))
2569	goto out_release;
2570	return ret;
2571	}
2572
2573	if (PageMappedToDisk(page))
2574	return 0;
2575
2576	/*
2577	* Allocate buffers so that we can keep track of state, and potentially
2578	* attach them to the page if an error occurs. In the common case of
2579	* no error, they will just be freed again without ever being attached
2580	* to the page (which is all OK, because we're under the page lock).
2581	*
2582	* Be careful: the buffer linked list is a NULL terminated one, rather
2583	* than the circular one we're used to.
2584	*/
2585	head = alloc_page_buffers(page, blocksize, false);
2586	if (!head) {
2587	ret = -ENOMEM;
2588	goto out_release;
2589	}
2590
2591	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
2592
2593	/*
2594	* We loop across all blocks in the page, whether or not they are
2595	* part of the affected region. This is so we can discover if the
2596	* page is fully mapped-to-disk.
2597	*/
2598	for (block_start = 0, block_in_page = 0, bh = head;
2599	block_start < PAGE_SIZE;
2600	block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2601	int create;
2602
2603	block_end = block_start + blocksize;
2604	bh->b_state = 0;
2605	create = 1;
2606	if (block_start >= to)
2607	create = 0;
2608	ret = get_block(inode, block_in_file + block_in_page,
2609	bh, create);
2610	if (ret)
2611	goto failed;
2612	if (!buffer_mapped(bh))
2613	is_mapped_to_disk = 0;
2614	if (buffer_new(bh))
2615	clean_bdev_bh_alias(bh);
2616	if (PageUptodate(page)) {
2617	set_buffer_uptodate(bh);
2618	continue;
2619	}
2620	if (buffer_new(bh) \|\| !buffer_mapped(bh)) {
2621	zero_user_segments(page, block_start, from,
2622	to, block_end);
2623	continue;
2624	}
2625	if (buffer_uptodate(bh))
2626	continue; /* reiserfs does this */
2627	if (block_start < from \|\| block_end > to) {
2628	lock_buffer(bh);
2629	bh->b_end_io = end_buffer_read_nobh;
2630	submit_bh(REQ_OP_READ, 0, bh);
2631	nr_reads++;
2632	}
2633	}
2634
2635	if (nr_reads) {
2636	/*
2637	* The page is locked, so these buffers are protected from
2638	* any VM or truncate activity. Hence we don't need to care
2639	* for the buffer_head refcounts.
2640	*/
2641	for (bh = head; bh; bh = bh->b_this_page) {
2642	wait_on_buffer(bh);
2643	if (!buffer_uptodate(bh))
2644	ret = -EIO;
2645	}
2646	if (ret)
2647	goto failed;
2648	}
2649
2650	if (is_mapped_to_disk)
2651	SetPageMappedToDisk(page);
2652
2653	fsdata = head; / to be released by nobh_write_end */
2654
2655	return 0;
2656
2657	failed:
2658	BUG_ON(!ret);
2659	/*
2660	* Error recovery is a bit difficult. We need to zero out blocks that
2661	* were newly allocated, and dirty them to ensure they get written out.
2662	* Buffers need to be attached to the page at this point, otherwise
2663	* the handling of potential IO errors during writeout would be hard
2664	* (could try doing synchronous writeout, but what if that fails too?)
2665	*/
2666	attach_nobh_buffers(page, head);
2667	page_zero_new_buffers(page, from, to);
2668
2669	out_release:
2670	unlock_page(page);
2671	put_page(page);
2672	*pagep = NULL;
2673
2674	return ret;
2675	}
2676	EXPORT_SYMBOL(nobh_write_begin);
2677
2678	int nobh_write_end(struct file file, struct address_space mapping,
2679	loff_t pos, unsigned len, unsigned copied,
2680	struct page page, void fsdata)
2681	{
2682	struct inode *inode = page->mapping->host;
2683	struct buffer_head *head = fsdata;
2684	struct buffer_head *bh;
2685	BUG_ON(fsdata != NULL && page_has_buffers(page));
2686
2687	if (unlikely(copied < len) && head)
2688	attach_nobh_buffers(page, head);
2689	if (page_has_buffers(page))
2690	return generic_write_end(file, mapping, pos, len,
2691	copied, page, fsdata);
2692
2693	SetPageUptodate(page);
2694	set_page_dirty(page);
2695	if (pos+copied > inode->i_size) {
2696	i_size_write(inode, pos+copied);
2697	mark_inode_dirty(inode);
2698	}
2699
2700	unlock_page(page);
2701	put_page(page);
2702
2703	while (head) {
2704	bh = head;
2705	head = head->b_this_page;
2706	free_buffer_head(bh);
2707	}
2708
2709	return copied;
2710	}
2711	EXPORT_SYMBOL(nobh_write_end);
2712
2713	/*
2714	* nobh_writepage() - based on block_full_write_page() except
2715	* that it tries to operate without attaching bufferheads to
2716	* the page.
2717	*/
2718	int nobh_writepage(struct page page, get_block_t get_block,
2719	struct writeback_control *wbc)
2720	{
2721	struct inode * const inode = page->mapping->host;
2722	loff_t i_size = i_size_read(inode);
2723	const pgoff_t end_index = i_size >> PAGE_SHIFT;
2724	unsigned offset;
2725	int ret;
2726
2727	/* Is the page fully inside i_size? */
2728	if (page->index < end_index)
2729	goto out;
2730
2731	/* Is the page fully outside i_size? (truncate in progress) */
2732	offset = i_size & (PAGE_SIZE-1);
2733	if (page->index >= end_index+1 \|\| !offset) {
2734	/*
2735	* The page may have dirty, unmapped buffers. For example,
2736	* they may have been added in ext3_writepage(). Make them
2737	* freeable here, so the page does not leak.
2738	*/
2739	#if 0
2740	/* Not really sure about this - do we need this ? */
2741	if (page->mapping->a_ops->invalidatepage)
2742	page->mapping->a_ops->invalidatepage(page, offset);
2743	#endif
2744	unlock_page(page);
2745	return 0; /* don't care */
2746	}
2747
2748	/*
2749	* The page straddles i_size. It must be zeroed out on each and every
2750	* writepage invocation because it may be mmapped. "A file is mapped
2751	* in multiples of the page size. For a file that is not a multiple of
2752	* the page size, the remaining memory is zeroed when mapped, and
2753	* writes to that region are not written out to the file."
2754	*/
2755	zero_user_segment(page, offset, PAGE_SIZE);
2756	out:
2757	ret = mpage_writepage(page, get_block, wbc);
2758	if (ret == -EAGAIN)
2759	ret = __block_write_full_page(inode, page, get_block, wbc,
2760	end_buffer_async_write);
2761	return ret;
2762	}
2763	EXPORT_SYMBOL(nobh_writepage);
2764
2765	int nobh_truncate_page(struct address_space *mapping,
2766	loff_t from, get_block_t *get_block)
2767	{
2768	pgoff_t index = from >> PAGE_SHIFT;
2769	unsigned offset = from & (PAGE_SIZE-1);
2770	unsigned blocksize;
2771	sector_t iblock;
2772	unsigned length, pos;
2773	struct inode *inode = mapping->host;
2774	struct page *page;
2775	struct buffer_head map_bh;
2776	int err;
2777
2778	blocksize = i_blocksize(inode);
2779	length = offset & (blocksize - 1);
2780
2781	/* Block boundary? Nothing to do */
2782	if (!length)
2783	return 0;
2784
2785	length = blocksize - length;
2786	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2787
2788	page = grab_cache_page(mapping, index);
2789	err = -ENOMEM;
2790	if (!page)
2791	goto out;
2792
2793	if (page_has_buffers(page)) {
2794	has_buffers:
2795	unlock_page(page);
2796	put_page(page);
2797	return block_truncate_page(mapping, from, get_block);
2798	}
2799
2800	/* Find the buffer that contains "offset" */
2801	pos = blocksize;
2802	while (offset >= pos) {
2803	iblock++;
2804	pos += blocksize;
2805	}
2806
2807	map_bh.b_size = blocksize;
2808	map_bh.b_state = 0;
2809	err = get_block(inode, iblock, &map_bh, 0);
2810	if (err)
2811	goto unlock;
2812	/* unmapped? It's a hole - nothing to do */
2813	if (!buffer_mapped(&map_bh))
2814	goto unlock;
2815
2816	/* Ok, it's mapped. Make sure it's up-to-date */
2817	if (!PageUptodate(page)) {
2818	err = mapping->a_ops->readpage(NULL, page);
2819	if (err) {
2820	put_page(page);
2821	goto out;
2822	}
2823	lock_page(page);
2824	if (!PageUptodate(page)) {
2825	err = -EIO;
2826	goto unlock;
2827	}
2828	if (page_has_buffers(page))
2829	goto has_buffers;
2830	}
2831	zero_user(page, offset, length);
2832	set_page_dirty(page);
2833	err = 0;
2834
2835	unlock:
2836	unlock_page(page);
2837	put_page(page);
2838	out:
2839	return err;
2840	}
2841	EXPORT_SYMBOL(nobh_truncate_page);
2842
2843	int block_truncate_page(struct address_space *mapping,
2844	loff_t from, get_block_t *get_block)
2845	{
2846	pgoff_t index = from >> PAGE_SHIFT;
2847	unsigned offset = from & (PAGE_SIZE-1);
2848	unsigned blocksize;
2849	sector_t iblock;
2850	unsigned length, pos;
2851	struct inode *inode = mapping->host;
2852	struct page *page;
2853	struct buffer_head *bh;
2854	int err;
2855
2856	blocksize = i_blocksize(inode);
2857	length = offset & (blocksize - 1);
2858
2859	/* Block boundary? Nothing to do */
2860	if (!length)
2861	return 0;
2862
2863	length = blocksize - length;
2864	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2865
2866	page = grab_cache_page(mapping, index);
2867	err = -ENOMEM;
2868	if (!page)
2869	goto out;
2870
2871	if (!page_has_buffers(page))
2872	create_empty_buffers(page, blocksize, 0);
2873
2874	/* Find the buffer that contains "offset" */
2875	bh = page_buffers(page);
2876	pos = blocksize;
2877	while (offset >= pos) {
2878	bh = bh->b_this_page;
2879	iblock++;
2880	pos += blocksize;
2881	}
2882
2883	err = 0;
2884	if (!buffer_mapped(bh)) {
2885	WARN_ON(bh->b_size != blocksize);
2886	err = get_block(inode, iblock, bh, 0);
2887	if (err)
2888	goto unlock;
2889	/* unmapped? It's a hole - nothing to do */
2890	if (!buffer_mapped(bh))
2891	goto unlock;
2892	}
2893
2894	/* Ok, it's mapped. Make sure it's up-to-date */
2895	if (PageUptodate(page))
2896	set_buffer_uptodate(bh);
2897
2898	if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2899	err = -EIO;
2900	ll_rw_block(REQ_OP_READ, 0, 1, &bh);
2901	wait_on_buffer(bh);
2902	/* Uhhuh. Read error. Complain and punt. */
2903	if (!buffer_uptodate(bh))
2904	goto unlock;
2905	}
2906
2907	zero_user(page, offset, length);
2908	mark_buffer_dirty(bh);
2909	err = 0;
2910
2911	unlock:
2912	unlock_page(page);
2913	put_page(page);
2914	out:
2915	return err;
2916	}
2917	EXPORT_SYMBOL(block_truncate_page);
2918
2919	/*
2920	* The generic ->writepage function for buffer-backed address_spaces
2921	*/
2922	int block_write_full_page(struct page page, get_block_t get_block,
2923	struct writeback_control *wbc)
2924	{
2925	struct inode * const inode = page->mapping->host;
2926	loff_t i_size = i_size_read(inode);
2927	const pgoff_t end_index = i_size >> PAGE_SHIFT;
2928	unsigned offset;
2929
2930	/* Is the page fully inside i_size? */
2931	if (page->index < end_index)
2932	return __block_write_full_page(inode, page, get_block, wbc,
2933	end_buffer_async_write);
2934
2935	/* Is the page fully outside i_size? (truncate in progress) */
2936	offset = i_size & (PAGE_SIZE-1);
2937	if (page->index >= end_index+1 \|\| !offset) {
2938	/*
2939	* The page may have dirty, unmapped buffers. For example,
2940	* they may have been added in ext3_writepage(). Make them
2941	* freeable here, so the page does not leak.
2942	*/
2943	do_invalidatepage(page, 0, PAGE_SIZE);
2944	unlock_page(page);
2945	return 0; /* don't care */
2946	}
2947
2948	/*
2949	* The page straddles i_size. It must be zeroed out on each and every
2950	* writepage invocation because it may be mmapped. "A file is mapped
2951	* in multiples of the page size. For a file that is not a multiple of
2952	* the page size, the remaining memory is zeroed when mapped, and
2953	* writes to that region are not written out to the file."
2954	*/
2955	zero_user_segment(page, offset, PAGE_SIZE);
2956	return __block_write_full_page(inode, page, get_block, wbc,
2957	end_buffer_async_write);
2958	}
2959	EXPORT_SYMBOL(block_write_full_page);
2960
2961	sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2962	get_block_t *get_block)
2963	{
2964	struct inode *inode = mapping->host;
2965	struct buffer_head tmp = {
2966	.b_size = i_blocksize(inode),
2967	};
2968
2969	get_block(inode, block, &tmp, 0);
2970	return tmp.b_blocknr;
2971	}
2972	EXPORT_SYMBOL(generic_block_bmap);
2973
2974	static void end_bio_bh_io_sync(struct bio *bio)
2975	{
2976	struct buffer_head *bh = bio->bi_private;
2977
2978	if (unlikely(bio_flagged(bio, BIO_QUIET)))
2979	set_bit(BH_Quiet, &bh->b_state);
2980
2981	bh->b_end_io(bh, !bio->bi_status);
2982	bio_put(bio);
2983	}
2984
2985	/*
2986	* This allows us to do IO even on the odd last sectors
2987	* of a device, even if the block size is some multiple
2988	* of the physical sector size.
2989	*
2990	* We'll just truncate the bio to the size of the device,
2991	* and clear the end of the buffer head manually.
2992	*
2993	* Truly out-of-range accesses will turn into actual IO
2994	* errors, this only handles the "we need to be able to
2995	* do IO at the final sector" case.
2996	*/
2997	void guard_bio_eod(int op, struct bio *bio)
2998	{
2999	sector_t maxsector;
3000	struct bio_vec *bvec = bio_last_bvec_all(bio);
3001	unsigned truncated_bytes;
3002	struct hd_struct *part;
3003
3004	rcu_read_lock();
3005	part = __disk_get_part(bio->bi_disk, bio->bi_partno);
3006	if (part)
3007	maxsector = part_nr_sects_read(part);
3008	else
3009	maxsector = get_capacity(bio->bi_disk);
3010	rcu_read_unlock();
3011
3012	if (!maxsector)
3013	return;
3014
3015	/*
3016	* If the whole IO is past the end of the device,
3017	* let it through, and the IO layer will turn it into
3018	* an EIO.
3019	*/
3020	if (unlikely(bio->bi_iter.bi_sector >= maxsector))
3021	return;
3022
3023	maxsector -= bio->bi_iter.bi_sector;
3024	if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))
3025	return;
3026
3027	/* Uhhuh. We've got a bio that straddles the device size! */
3028	truncated_bytes = bio->bi_iter.bi_size - (maxsector << 9);
3029
3030	/*
3031	* The bio contains more than one segment which spans EOD, just return
3032	* and let IO layer turn it into an EIO
3033	*/
3034	if (truncated_bytes > bvec->bv_len)
3035	return;
3036
3037	/* Truncate the bio.. */
3038	bio->bi_iter.bi_size -= truncated_bytes;
3039	bvec->bv_len -= truncated_bytes;
3040
3041	/* ..and clear the end of the buffer for reads */
3042	if (op == REQ_OP_READ) {
3043	struct bio_vec bv;
3044
3045	mp_bvec_last_segment(bvec, &bv);
3046	zero_user(bv.bv_page, bv.bv_offset + bv.bv_len,
3047	truncated_bytes);
3048	}
3049	}
3050
3051	static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
3052	enum rw_hint write_hint, struct writeback_control *wbc)
3053	{
3054	struct bio *bio;
3055
3056	BUG_ON(!buffer_locked(bh));
3057	BUG_ON(!buffer_mapped(bh));
3058	BUG_ON(!bh->b_end_io);
3059	BUG_ON(buffer_delay(bh));
3060	BUG_ON(buffer_unwritten(bh));
3061
3062	/*
3063	* Only clear out a write error when rewriting
3064	*/
3065	if (test_set_buffer_req(bh) && (op == REQ_OP_WRITE))
3066	clear_buffer_write_io_error(bh);
3067
3068	/*
3069	* from here on down, it's all bio -- do the initial mapping,
3070	* submit_bio -> generic_make_request may further map this bio around
3071	*/
3072	bio = bio_alloc(GFP_NOIO, 1);
3073
3074	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
3075	bio_set_dev(bio, bh->b_bdev);
3076	bio->bi_write_hint = write_hint;
3077
3078	bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
3079	BUG_ON(bio->bi_iter.bi_size != bh->b_size);
3080
3081	bio->bi_end_io = end_bio_bh_io_sync;
3082	bio->bi_private = bh;
3083
3084	/* Take care of bh's that straddle the end of the device */
3085	guard_bio_eod(op, bio);
3086
3087	if (buffer_meta(bh))
3088	op_flags \|= REQ_META;
3089	if (buffer_prio(bh))
3090	op_flags \|= REQ_PRIO;
3091	bio_set_op_attrs(bio, op, op_flags);
3092
3093	if (wbc) {
3094	wbc_init_bio(wbc, bio);
3095	wbc_account_io(wbc, bh->b_page, bh->b_size);
3096	}
3097
3098	submit_bio(bio);
3099	return 0;
3100	}
3101
3102	int submit_bh(int op, int op_flags, struct buffer_head *bh)
3103	{
3104	return submit_bh_wbc(op, op_flags, bh, 0, NULL);
3105	}
3106	EXPORT_SYMBOL(submit_bh);
3107
3108	/**
3109	* ll_rw_block: low-level access to block devices (DEPRECATED)
3110	* @op: whether to %READ or %WRITE
3111	* @op_flags: req_flag_bits
3112	* @nr: number of &struct buffer_heads in the array
3113	* @bhs: array of pointers to &struct buffer_head
3114	*
3115	* ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3116	* requests an I/O operation on them, either a %REQ_OP_READ or a %REQ_OP_WRITE.
3117	* @op_flags contains flags modifying the detailed I/O behavior, most notably
3118	* %REQ_RAHEAD.
3119	*
3120	* This function drops any buffer that it cannot get a lock on (with the
3121	* BH_Lock state bit), any buffer that appears to be clean when doing a write
3122	* request, and any buffer that appears to be up-to-date when doing read
3123	* request. Further it marks as clean buffers that are processed for
3124	* writing (the buffer cache won't assume that they are actually clean
3125	* until the buffer gets unlocked).
3126	*
3127	* ll_rw_block sets b_end_io to simple completion handler that marks
3128	* the buffer up-to-date (if appropriate), unlocks the buffer and wakes
3129	* any waiters.
3130	*
3131	* All of the buffers must be for the same device, and must also be a
3132	* multiple of the current approved size for the device.
3133	*/
3134	void ll_rw_block(int op, int op_flags, int nr, struct buffer_head *bhs[])
3135	{
3136	int i;
3137
3138	for (i = 0; i < nr; i++) {
3139	struct buffer_head *bh = bhs[i];
3140
3141	if (!trylock_buffer(bh))
3142	continue;
3143	if (op == WRITE) {
3144	if (test_clear_buffer_dirty(bh)) {
3145	bh->b_end_io = end_buffer_write_sync;
3146	get_bh(bh);
3147	submit_bh(op, op_flags, bh);
3148	continue;
3149	}
3150	} else {
3151	if (!buffer_uptodate(bh)) {
3152	bh->b_end_io = end_buffer_read_sync;
3153	get_bh(bh);
3154	submit_bh(op, op_flags, bh);
3155	continue;
3156	}
3157	}
3158	unlock_buffer(bh);
3159	}
3160	}
3161	EXPORT_SYMBOL(ll_rw_block);
3162
3163	void write_dirty_buffer(struct buffer_head *bh, int op_flags)
3164	{
3165	lock_buffer(bh);
3166	if (!test_clear_buffer_dirty(bh)) {
3167	unlock_buffer(bh);
3168	return;
3169	}
3170	bh->b_end_io = end_buffer_write_sync;
3171	get_bh(bh);
3172	submit_bh(REQ_OP_WRITE, op_flags, bh);
3173	}
3174	EXPORT_SYMBOL(write_dirty_buffer);
3175
3176	/*
3177	* For a data-integrity writeout, we need to wait upon any in-progress I/O
3178	* and then start new I/O and then wait upon it. The caller must have a ref on
3179	* the buffer_head.
3180	*/
3181	int __sync_dirty_buffer(struct buffer_head *bh, int op_flags)
3182	{
3183	int ret = 0;
3184
3185	WARN_ON(atomic_read(&bh->b_count) < 1);
3186	lock_buffer(bh);
3187	if (test_clear_buffer_dirty(bh)) {
3188	get_bh(bh);
3189	bh->b_end_io = end_buffer_write_sync;
3190	ret = submit_bh(REQ_OP_WRITE, op_flags, bh);
3191	wait_on_buffer(bh);
3192	if (!ret && !buffer_uptodate(bh))
3193	ret = -EIO;
3194	} else {
3195	unlock_buffer(bh);
3196	}
3197	return ret;
3198	}
3199	EXPORT_SYMBOL(__sync_dirty_buffer);
3200
3201	int sync_dirty_buffer(struct buffer_head *bh)
3202	{
3203	return __sync_dirty_buffer(bh, REQ_SYNC);
3204	}
3205	EXPORT_SYMBOL(sync_dirty_buffer);
3206
3207	/*
3208	* try_to_free_buffers() checks if all the buffers on this particular page
3209	* are unused, and releases them if so.
3210	*
3211	* Exclusion against try_to_free_buffers may be obtained by either
3212	* locking the page or by holding its mapping's private_lock.
3213	*
3214	* If the page is dirty but all the buffers are clean then we need to
3215	* be sure to mark the page clean as well. This is because the page
3216	* may be against a block device, and a later reattachment of buffers
3217	* to a dirty page will set all buffers dirty. Which would corrupt
3218	* filesystem data on the same device.
3219	*
3220	* The same applies to regular filesystem pages: if all the buffers are
3221	* clean then we set the page clean and proceed. To do that, we require
3222	* total exclusion from __set_page_dirty_buffers(). That is obtained with
3223	* private_lock.
3224	*
3225	* try_to_free_buffers() is non-blocking.
3226	*/
3227	static inline int buffer_busy(struct buffer_head *bh)
3228	{
3229	return atomic_read(&bh->b_count) \|
3230	(bh->b_state & ((1 << BH_Dirty) \| (1 << BH_Lock)));
3231	}
3232
3233	static int
3234	drop_buffers(struct page page, struct buffer_head *buffers_to_free)
3235	{
3236	struct buffer_head *head = page_buffers(page);
3237	struct buffer_head *bh;
3238
3239	bh = head;
3240	do {
3241	if (buffer_busy(bh))
3242	goto failed;
3243	bh = bh->b_this_page;
3244	} while (bh != head);
3245
3246	do {
3247	struct buffer_head *next = bh->b_this_page;
3248
3249	if (bh->b_assoc_map)
3250	__remove_assoc_queue(bh);
3251	bh = next;
3252	} while (bh != head);
3253	*buffers_to_free = head;
3254	__clear_page_buffers(page);
3255	return 1;
3256	failed:
3257	return 0;
3258	}
3259
3260	int try_to_free_buffers(struct page *page)
3261	{
3262	struct address_space * const mapping = page->mapping;
3263	struct buffer_head *buffers_to_free = NULL;
3264	int ret = 0;
3265
3266	BUG_ON(!PageLocked(page));
3267	if (PageWriteback(page))
3268	return 0;
3269
3270	if (mapping == NULL) { /* can this still happen? */
3271	ret = drop_buffers(page, &buffers_to_free);
3272	goto out;
3273	}
3274
3275	spin_lock(&mapping->private_lock);
3276	ret = drop_buffers(page, &buffers_to_free);
3277
3278	/*
3279	* If the filesystem writes its buffers by hand (eg ext3)
3280	* then we can have clean buffers against a dirty page. We
3281	* clean the page here; otherwise the VM will never notice
3282	* that the filesystem did any IO at all.
3283	*
3284	* Also, during truncate, discard_buffer will have marked all
3285	* the page's buffers clean. We discover that here and clean
3286	* the page also.
3287	*
3288	* private_lock must be held over this entire operation in order
3289	* to synchronise against __set_page_dirty_buffers and prevent the
3290	* dirty bit from being lost.
3291	*/
3292	if (ret)
3293	cancel_dirty_page(page);
3294	spin_unlock(&mapping->private_lock);
3295	out:
3296	if (buffers_to_free) {
3297	struct buffer_head *bh = buffers_to_free;
3298
3299	do {
3300	struct buffer_head *next = bh->b_this_page;
3301	free_buffer_head(bh);
3302	bh = next;
3303	} while (bh != buffers_to_free);
3304	}
3305	return ret;
3306	}
3307	EXPORT_SYMBOL(try_to_free_buffers);
3308
3309	/*
3310	* There are no bdflush tunables left. But distributions are
3311	* still running obsolete flush daemons, so we terminate them here.
3312	*
3313	* Use of bdflush() is deprecated and will be removed in a future kernel.
3314	* The `flush-X' kernel threads fully replace bdflush daemons and this call.
3315	*/
3316	SYSCALL_DEFINE2(bdflush, int, func, long, data)
3317	{
3318	static int msg_count;
3319
3320	if (!capable(CAP_SYS_ADMIN))
3321	return -EPERM;
3322
3323	if (msg_count < 5) {
3324	msg_count++;
3325	printk(KERN_INFO
3326	"warning: process `%s' used the obsolete bdflush"
3327	" system call\n", current->comm);
3328	printk(KERN_INFO "Fix your initscripts?\n");
3329	}
3330
3331	if (func == 1)
3332	do_exit(0);
3333	return 0;
3334	}
3335
3336	/*
3337	* Buffer-head allocation
3338	*/
3339	static struct kmem_cache *bh_cachep __read_mostly;
3340
3341	/*
3342	* Once the number of bh's in the machine exceeds this level, we start
3343	* stripping them in writeback.
3344	*/
3345	static unsigned long max_buffer_heads;
3346
3347	int buffer_heads_over_limit;
3348
3349	struct bh_accounting {
3350	int nr; /* Number of live bh's */
3351	int ratelimit; /* Limit cacheline bouncing */
3352	};
3353
3354	static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3355
3356	static void recalc_bh_state(void)
3357	{
3358	int i;
3359	int tot = 0;
3360
3361	if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3362	return;
3363	__this_cpu_write(bh_accounting.ratelimit, 0);
3364	for_each_online_cpu(i)
3365	tot += per_cpu(bh_accounting, i).nr;
3366	buffer_heads_over_limit = (tot > max_buffer_heads);
3367	}
3368
3369	struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3370	{
3371	struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3372	if (ret) {
3373	INIT_LIST_HEAD(&ret->b_assoc_buffers);
3374	preempt_disable();
3375	__this_cpu_inc(bh_accounting.nr);
3376	recalc_bh_state();
3377	preempt_enable();
3378	}
3379	return ret;
3380	}
3381	EXPORT_SYMBOL(alloc_buffer_head);
3382
3383	void free_buffer_head(struct buffer_head *bh)
3384	{
3385	BUG_ON(!list_empty(&bh->b_assoc_buffers));
3386	kmem_cache_free(bh_cachep, bh);
3387	preempt_disable();
3388	__this_cpu_dec(bh_accounting.nr);
3389	recalc_bh_state();
3390	preempt_enable();
3391	}
3392	EXPORT_SYMBOL(free_buffer_head);
3393
3394	static int buffer_exit_cpu_dead(unsigned int cpu)
3395	{
3396	int i;
3397	struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3398
3399	for (i = 0; i < BH_LRU_SIZE; i++) {
3400	brelse(b->bhs[i]);
3401	b->bhs[i] = NULL;
3402	}
3403	this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3404	per_cpu(bh_accounting, cpu).nr = 0;
3405	return 0;
3406	}
3407
3408	/**
3409	* bh_uptodate_or_lock - Test whether the buffer is uptodate
3410	* @bh: struct buffer_head
3411	*
3412	* Return true if the buffer is up-to-date and false,
3413	* with the buffer locked, if not.
3414	*/
3415	int bh_uptodate_or_lock(struct buffer_head *bh)
3416	{
3417	if (!buffer_uptodate(bh)) {
3418	lock_buffer(bh);
3419	if (!buffer_uptodate(bh))
3420	return 0;
3421	unlock_buffer(bh);
3422	}
3423	return 1;
3424	}
3425	EXPORT_SYMBOL(bh_uptodate_or_lock);
3426
3427	/**
3428	* bh_submit_read - Submit a locked buffer for reading
3429	* @bh: struct buffer_head
3430	*
3431	* Returns zero on success and -EIO on error.
3432	*/
3433	int bh_submit_read(struct buffer_head *bh)
3434	{
3435	BUG_ON(!buffer_locked(bh));
3436
3437	if (buffer_uptodate(bh)) {
3438	unlock_buffer(bh);
3439	return 0;
3440	}
3441
3442	get_bh(bh);
3443	bh->b_end_io = end_buffer_read_sync;
3444	submit_bh(REQ_OP_READ, 0, bh);
3445	wait_on_buffer(bh);
3446	if (buffer_uptodate(bh))
3447	return 0;
3448	return -EIO;
3449	}
3450	EXPORT_SYMBOL(bh_submit_read);
3451
3452	void __init buffer_init(void)
3453	{
3454	unsigned long nrpages;
3455	int ret;
3456
3457	bh_cachep = kmem_cache_create("buffer_head",
3458	sizeof(struct buffer_head), 0,
3459	(SLAB_RECLAIM_ACCOUNT\|SLAB_PANIC\|
3460	SLAB_MEM_SPREAD),
3461	NULL);
3462
3463	/*
3464	* Limit the bh occupancy to 10% of ZONE_NORMAL
3465	*/
3466	nrpages = (nr_free_buffer_pages() * 10) / 100;
3467	max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3468	ret = cpuhp_setup_state_nocalls(CPUHP_FS_BUFF_DEAD, "fs/buffer:dead",
3469	NULL, buffer_exit_cpu_dead);
3470	WARN_ON(ret < 0);
3471	}