xref: /linux/fs/buffer.c (revision bcb63314e2c23f1ed622418b65f9409512659c73)
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 <andrea@suse.de>
19  */
20 
21 #include <linux/kernel.h>
22 #include <linux/syscalls.h>
23 #include <linux/fs.h>
24 #include <linux/iomap.h>
25 #include <linux/mm.h>
26 #include <linux/percpu.h>
27 #include <linux/slab.h>
28 #include <linux/capability.h>
29 #include <linux/blkdev.h>
30 #include <linux/file.h>
31 #include <linux/quotaops.h>
32 #include <linux/highmem.h>
33 #include <linux/export.h>
34 #include <linux/backing-dev.h>
35 #include <linux/writeback.h>
36 #include <linux/hash.h>
37 #include <linux/suspend.h>
38 #include <linux/buffer_head.h>
39 #include <linux/task_io_accounting_ops.h>
40 #include <linux/bio.h>
41 #include <linux/notifier.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 <trace/events/block.h>
48 
49 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
50 static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
51 			 unsigned long bio_flags,
52 			 struct writeback_control *wbc);
53 
54 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
55 
56 void init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
57 {
58 	bh->b_end_io = handler;
59 	bh->b_private = private;
60 }
61 EXPORT_SYMBOL(init_buffer);
62 
63 inline void touch_buffer(struct buffer_head *bh)
64 {
65 	trace_block_touch_buffer(bh);
66 	mark_page_accessed(bh->b_page);
67 }
68 EXPORT_SYMBOL(touch_buffer);
69 
70 void __lock_buffer(struct buffer_head *bh)
71 {
72 	wait_on_bit_lock_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
73 }
74 EXPORT_SYMBOL(__lock_buffer);
75 
76 void unlock_buffer(struct buffer_head *bh)
77 {
78 	clear_bit_unlock(BH_Lock, &bh->b_state);
79 	smp_mb__after_atomic();
80 	wake_up_bit(&bh->b_state, BH_Lock);
81 }
82 EXPORT_SYMBOL(unlock_buffer);
83 
84 /*
85  * Returns if the page has dirty or writeback buffers. If all the buffers
86  * are unlocked and clean then the PageDirty information is stale. If
87  * any of the pages are locked, it is assumed they are locked for IO.
88  */
89 void buffer_check_dirty_writeback(struct page *page,
90 				     bool *dirty, bool *writeback)
91 {
92 	struct buffer_head *head, *bh;
93 	*dirty = false;
94 	*writeback = false;
95 
96 	BUG_ON(!PageLocked(page));
97 
98 	if (!page_has_buffers(page))
99 		return;
100 
101 	if (PageWriteback(page))
102 		*writeback = true;
103 
104 	head = page_buffers(page);
105 	bh = head;
106 	do {
107 		if (buffer_locked(bh))
108 			*writeback = true;
109 
110 		if (buffer_dirty(bh))
111 			*dirty = true;
112 
113 		bh = bh->b_this_page;
114 	} while (bh != head);
115 }
116 EXPORT_SYMBOL(buffer_check_dirty_writeback);
117 
118 /*
119  * Block until a buffer comes unlocked.  This doesn't stop it
120  * from becoming locked again - you have to lock it yourself
121  * if you want to preserve its state.
122  */
123 void __wait_on_buffer(struct buffer_head * bh)
124 {
125 	wait_on_bit_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
126 }
127 EXPORT_SYMBOL(__wait_on_buffer);
128 
129 static void
130 __clear_page_buffers(struct page *page)
131 {
132 	ClearPagePrivate(page);
133 	set_page_private(page, 0);
134 	put_page(page);
135 }
136 
137 static void buffer_io_error(struct buffer_head *bh, char *msg)
138 {
139 	if (!test_bit(BH_Quiet, &bh->b_state))
140 		printk_ratelimited(KERN_ERR
141 			"Buffer I/O error on dev %pg, logical block %llu%s\n",
142 			bh->b_bdev, (unsigned long long)bh->b_blocknr, msg);
143 }
144 
145 /*
146  * End-of-IO handler helper function which does not touch the bh after
147  * unlocking it.
148  * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
149  * a race there is benign: unlock_buffer() only use the bh's address for
150  * hashing after unlocking the buffer, so it doesn't actually touch the bh
151  * itself.
152  */
153 static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
154 {
155 	if (uptodate) {
156 		set_buffer_uptodate(bh);
157 	} else {
158 		/* This happens, due to failed read-ahead attempts. */
159 		clear_buffer_uptodate(bh);
160 	}
161 	unlock_buffer(bh);
162 }
163 
164 /*
165  * Default synchronous end-of-IO handler..  Just mark it up-to-date and
166  * unlock the buffer. This is what ll_rw_block uses too.
167  */
168 void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
169 {
170 	__end_buffer_read_notouch(bh, uptodate);
171 	put_bh(bh);
172 }
173 EXPORT_SYMBOL(end_buffer_read_sync);
174 
175 void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
176 {
177 	if (uptodate) {
178 		set_buffer_uptodate(bh);
179 	} else {
180 		buffer_io_error(bh, ", lost sync page write");
181 		set_buffer_write_io_error(bh);
182 		clear_buffer_uptodate(bh);
183 	}
184 	unlock_buffer(bh);
185 	put_bh(bh);
186 }
187 EXPORT_SYMBOL(end_buffer_write_sync);
188 
189 /*
190  * Various filesystems appear to want __find_get_block to be non-blocking.
191  * But it's the page lock which protects the buffers.  To get around this,
192  * we get exclusion from try_to_free_buffers with the blockdev mapping's
193  * private_lock.
194  *
195  * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
196  * may be quite high.  This code could TryLock the page, and if that
197  * succeeds, there is no need to take private_lock. (But if
198  * private_lock is contended then so is mapping->tree_lock).
199  */
200 static struct buffer_head *
201 __find_get_block_slow(struct block_device *bdev, sector_t block)
202 {
203 	struct inode *bd_inode = bdev->bd_inode;
204 	struct address_space *bd_mapping = bd_inode->i_mapping;
205 	struct buffer_head *ret = NULL;
206 	pgoff_t index;
207 	struct buffer_head *bh;
208 	struct buffer_head *head;
209 	struct page *page;
210 	int all_mapped = 1;
211 
212 	index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
213 	page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
214 	if (!page)
215 		goto out;
216 
217 	spin_lock(&bd_mapping->private_lock);
218 	if (!page_has_buffers(page))
219 		goto out_unlock;
220 	head = page_buffers(page);
221 	bh = head;
222 	do {
223 		if (!buffer_mapped(bh))
224 			all_mapped = 0;
225 		else if (bh->b_blocknr == block) {
226 			ret = bh;
227 			get_bh(bh);
228 			goto out_unlock;
229 		}
230 		bh = bh->b_this_page;
231 	} while (bh != head);
232 
233 	/* we might be here because some of the buffers on this page are
234 	 * not mapped.  This is due to various races between
235 	 * file io on the block device and getblk.  It gets dealt with
236 	 * elsewhere, don't buffer_error if we had some unmapped buffers
237 	 */
238 	if (all_mapped) {
239 		printk("__find_get_block_slow() failed. "
240 			"block=%llu, b_blocknr=%llu\n",
241 			(unsigned long long)block,
242 			(unsigned long long)bh->b_blocknr);
243 		printk("b_state=0x%08lx, b_size=%zu\n",
244 			bh->b_state, bh->b_size);
245 		printk("device %pg blocksize: %d\n", bdev,
246 			1 << bd_inode->i_blkbits);
247 	}
248 out_unlock:
249 	spin_unlock(&bd_mapping->private_lock);
250 	put_page(page);
251 out:
252 	return ret;
253 }
254 
255 /*
256  * Kick the writeback threads then try to free up some ZONE_NORMAL memory.
257  */
258 static void free_more_memory(void)
259 {
260 	struct zoneref *z;
261 	int nid;
262 
263 	wakeup_flusher_threads(1024, WB_REASON_FREE_MORE_MEM);
264 	yield();
265 
266 	for_each_online_node(nid) {
267 
268 		z = first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
269 						gfp_zone(GFP_NOFS), NULL);
270 		if (z->zone)
271 			try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
272 						GFP_NOFS, NULL);
273 	}
274 }
275 
276 /*
277  * I/O completion handler for block_read_full_page() - pages
278  * which come unlocked at the end of I/O.
279  */
280 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
281 {
282 	unsigned long flags;
283 	struct buffer_head *first;
284 	struct buffer_head *tmp;
285 	struct page *page;
286 	int page_uptodate = 1;
287 
288 	BUG_ON(!buffer_async_read(bh));
289 
290 	page = bh->b_page;
291 	if (uptodate) {
292 		set_buffer_uptodate(bh);
293 	} else {
294 		clear_buffer_uptodate(bh);
295 		buffer_io_error(bh, ", async page read");
296 		SetPageError(page);
297 	}
298 
299 	/*
300 	 * Be _very_ careful from here on. Bad things can happen if
301 	 * two buffer heads end IO at almost the same time and both
302 	 * decide that the page is now completely done.
303 	 */
304 	first = page_buffers(page);
305 	local_irq_save(flags);
306 	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
307 	clear_buffer_async_read(bh);
308 	unlock_buffer(bh);
309 	tmp = bh;
310 	do {
311 		if (!buffer_uptodate(tmp))
312 			page_uptodate = 0;
313 		if (buffer_async_read(tmp)) {
314 			BUG_ON(!buffer_locked(tmp));
315 			goto still_busy;
316 		}
317 		tmp = tmp->b_this_page;
318 	} while (tmp != bh);
319 	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
320 	local_irq_restore(flags);
321 
322 	/*
323 	 * If none of the buffers had errors and they are all
324 	 * uptodate then we can set the page uptodate.
325 	 */
326 	if (page_uptodate && !PageError(page))
327 		SetPageUptodate(page);
328 	unlock_page(page);
329 	return;
330 
331 still_busy:
332 	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
333 	local_irq_restore(flags);
334 	return;
335 }
336 
337 /*
338  * Completion handler for block_write_full_page() - pages which are unlocked
339  * during I/O, and which have PageWriteback cleared upon I/O completion.
340  */
341 void end_buffer_async_write(struct buffer_head *bh, int uptodate)
342 {
343 	unsigned long flags;
344 	struct buffer_head *first;
345 	struct buffer_head *tmp;
346 	struct page *page;
347 
348 	BUG_ON(!buffer_async_write(bh));
349 
350 	page = bh->b_page;
351 	if (uptodate) {
352 		set_buffer_uptodate(bh);
353 	} else {
354 		buffer_io_error(bh, ", lost async page write");
355 		mapping_set_error(page->mapping, -EIO);
356 		set_buffer_write_io_error(bh);
357 		clear_buffer_uptodate(bh);
358 		SetPageError(page);
359 	}
360 
361 	first = page_buffers(page);
362 	local_irq_save(flags);
363 	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
364 
365 	clear_buffer_async_write(bh);
366 	unlock_buffer(bh);
367 	tmp = bh->b_this_page;
368 	while (tmp != bh) {
369 		if (buffer_async_write(tmp)) {
370 			BUG_ON(!buffer_locked(tmp));
371 			goto still_busy;
372 		}
373 		tmp = tmp->b_this_page;
374 	}
375 	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
376 	local_irq_restore(flags);
377 	end_page_writeback(page);
378 	return;
379 
380 still_busy:
381 	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
382 	local_irq_restore(flags);
383 	return;
384 }
385 EXPORT_SYMBOL(end_buffer_async_write);
386 
387 /*
388  * If a page's buffers are under async readin (end_buffer_async_read
389  * completion) then there is a possibility that another thread of
390  * control could lock one of the buffers after it has completed
391  * but while some of the other buffers have not completed.  This
392  * locked buffer would confuse end_buffer_async_read() into not unlocking
393  * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
394  * that this buffer is not under async I/O.
395  *
396  * The page comes unlocked when it has no locked buffer_async buffers
397  * left.
398  *
399  * PageLocked prevents anyone starting new async I/O reads any of
400  * the buffers.
401  *
402  * PageWriteback is used to prevent simultaneous writeout of the same
403  * page.
404  *
405  * PageLocked prevents anyone from starting writeback of a page which is
406  * under read I/O (PageWriteback is only ever set against a locked page).
407  */
408 static void mark_buffer_async_read(struct buffer_head *bh)
409 {
410 	bh->b_end_io = end_buffer_async_read;
411 	set_buffer_async_read(bh);
412 }
413 
414 static void mark_buffer_async_write_endio(struct buffer_head *bh,
415 					  bh_end_io_t *handler)
416 {
417 	bh->b_end_io = handler;
418 	set_buffer_async_write(bh);
419 }
420 
421 void mark_buffer_async_write(struct buffer_head *bh)
422 {
423 	mark_buffer_async_write_endio(bh, end_buffer_async_write);
424 }
425 EXPORT_SYMBOL(mark_buffer_async_write);
426 
427 
428 /*
429  * fs/buffer.c contains helper functions for buffer-backed address space's
430  * fsync functions.  A common requirement for buffer-based filesystems is
431  * that certain data from the backing blockdev needs to be written out for
432  * a successful fsync().  For example, ext2 indirect blocks need to be
433  * written back and waited upon before fsync() returns.
434  *
435  * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
436  * inode_has_buffers() and invalidate_inode_buffers() are provided for the
437  * management of a list of dependent buffers at ->i_mapping->private_list.
438  *
439  * Locking is a little subtle: try_to_free_buffers() will remove buffers
440  * from their controlling inode's queue when they are being freed.  But
441  * try_to_free_buffers() will be operating against the *blockdev* mapping
442  * at the time, not against the S_ISREG file which depends on those buffers.
443  * So the locking for private_list is via the private_lock in the address_space
444  * which backs the buffers.  Which is different from the address_space
445  * against which the buffers are listed.  So for a particular address_space,
446  * mapping->private_lock does *not* protect mapping->private_list!  In fact,
447  * mapping->private_list will always be protected by the backing blockdev's
448  * ->private_lock.
449  *
450  * Which introduces a requirement: all buffers on an address_space's
451  * ->private_list must be from the same address_space: the blockdev's.
452  *
453  * address_spaces which do not place buffers at ->private_list via these
454  * utility functions are free to use private_lock and private_list for
455  * whatever they want.  The only requirement is that list_empty(private_list)
456  * be true at clear_inode() time.
457  *
458  * FIXME: clear_inode should not call invalidate_inode_buffers().  The
459  * filesystems should do that.  invalidate_inode_buffers() should just go
460  * BUG_ON(!list_empty).
461  *
462  * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
463  * take an address_space, not an inode.  And it should be called
464  * mark_buffer_dirty_fsync() to clearly define why those buffers are being
465  * queued up.
466  *
467  * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
468  * list if it is already on a list.  Because if the buffer is on a list,
469  * it *must* already be on the right one.  If not, the filesystem is being
470  * silly.  This will save a ton of locking.  But first we have to ensure
471  * that buffers are taken *off* the old inode's list when they are freed
472  * (presumably in truncate).  That requires careful auditing of all
473  * filesystems (do it inside bforget()).  It could also be done by bringing
474  * b_inode back.
475  */
476 
477 /*
478  * The buffer's backing address_space's private_lock must be held
479  */
480 static void __remove_assoc_queue(struct buffer_head *bh)
481 {
482 	list_del_init(&bh->b_assoc_buffers);
483 	WARN_ON(!bh->b_assoc_map);
484 	if (buffer_write_io_error(bh))
485 		set_bit(AS_EIO, &bh->b_assoc_map->flags);
486 	bh->b_assoc_map = NULL;
487 }
488 
489 int inode_has_buffers(struct inode *inode)
490 {
491 	return !list_empty(&inode->i_data.private_list);
492 }
493 
494 /*
495  * osync is designed to support O_SYNC io.  It waits synchronously for
496  * all already-submitted IO to complete, but does not queue any new
497  * writes to the disk.
498  *
499  * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
500  * you dirty the buffers, and then use osync_inode_buffers to wait for
501  * completion.  Any other dirty buffers which are not yet queued for
502  * write will not be flushed to disk by the osync.
503  */
504 static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
505 {
506 	struct buffer_head *bh;
507 	struct list_head *p;
508 	int err = 0;
509 
510 	spin_lock(lock);
511 repeat:
512 	list_for_each_prev(p, list) {
513 		bh = BH_ENTRY(p);
514 		if (buffer_locked(bh)) {
515 			get_bh(bh);
516 			spin_unlock(lock);
517 			wait_on_buffer(bh);
518 			if (!buffer_uptodate(bh))
519 				err = -EIO;
520 			brelse(bh);
521 			spin_lock(lock);
522 			goto repeat;
523 		}
524 	}
525 	spin_unlock(lock);
526 	return err;
527 }
528 
529 static void do_thaw_one(struct super_block *sb, void *unused)
530 {
531 	while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
532 		printk(KERN_WARNING "Emergency Thaw on %pg\n", sb->s_bdev);
533 }
534 
535 static void do_thaw_all(struct work_struct *work)
536 {
537 	iterate_supers(do_thaw_one, NULL);
538 	kfree(work);
539 	printk(KERN_WARNING "Emergency Thaw complete\n");
540 }
541 
542 /**
543  * emergency_thaw_all -- forcibly thaw every frozen filesystem
544  *
545  * Used for emergency unfreeze of all filesystems via SysRq
546  */
547 void emergency_thaw_all(void)
548 {
549 	struct work_struct *work;
550 
551 	work = kmalloc(sizeof(*work), GFP_ATOMIC);
552 	if (work) {
553 		INIT_WORK(work, do_thaw_all);
554 		schedule_work(work);
555 	}
556 }
557 
558 /**
559  * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
560  * @mapping: the mapping which wants those buffers written
561  *
562  * Starts I/O against the buffers at mapping->private_list, and waits upon
563  * that I/O.
564  *
565  * Basically, this is a convenience function for fsync().
566  * @mapping is a file or directory which needs those buffers to be written for
567  * a successful fsync().
568  */
569 int sync_mapping_buffers(struct address_space *mapping)
570 {
571 	struct address_space *buffer_mapping = mapping->private_data;
572 
573 	if (buffer_mapping == NULL || list_empty(&mapping->private_list))
574 		return 0;
575 
576 	return fsync_buffers_list(&buffer_mapping->private_lock,
577 					&mapping->private_list);
578 }
579 EXPORT_SYMBOL(sync_mapping_buffers);
580 
581 /*
582  * Called when we've recently written block `bblock', and it is known that
583  * `bblock' was for a buffer_boundary() buffer.  This means that the block at
584  * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
585  * dirty, schedule it for IO.  So that indirects merge nicely with their data.
586  */
587 void write_boundary_block(struct block_device *bdev,
588 			sector_t bblock, unsigned blocksize)
589 {
590 	struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
591 	if (bh) {
592 		if (buffer_dirty(bh))
593 			ll_rw_block(REQ_OP_WRITE, 0, 1, &bh);
594 		put_bh(bh);
595 	}
596 }
597 
598 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
599 {
600 	struct address_space *mapping = inode->i_mapping;
601 	struct address_space *buffer_mapping = bh->b_page->mapping;
602 
603 	mark_buffer_dirty(bh);
604 	if (!mapping->private_data) {
605 		mapping->private_data = buffer_mapping;
606 	} else {
607 		BUG_ON(mapping->private_data != buffer_mapping);
608 	}
609 	if (!bh->b_assoc_map) {
610 		spin_lock(&buffer_mapping->private_lock);
611 		list_move_tail(&bh->b_assoc_buffers,
612 				&mapping->private_list);
613 		bh->b_assoc_map = mapping;
614 		spin_unlock(&buffer_mapping->private_lock);
615 	}
616 }
617 EXPORT_SYMBOL(mark_buffer_dirty_inode);
618 
619 /*
620  * Mark the page dirty, and set it dirty in the radix tree, and mark the inode
621  * dirty.
622  *
623  * If warn is true, then emit a warning if the page is not uptodate and has
624  * not been truncated.
625  *
626  * The caller must hold lock_page_memcg().
627  */
628 static void __set_page_dirty(struct page *page, struct address_space *mapping,
629 			     int warn)
630 {
631 	unsigned long flags;
632 
633 	spin_lock_irqsave(&mapping->tree_lock, flags);
634 	if (page->mapping) {	/* Race with truncate? */
635 		WARN_ON_ONCE(warn && !PageUptodate(page));
636 		account_page_dirtied(page, mapping);
637 		radix_tree_tag_set(&mapping->page_tree,
638 				page_index(page), PAGECACHE_TAG_DIRTY);
639 	}
640 	spin_unlock_irqrestore(&mapping->tree_lock, flags);
641 }
642 
643 /*
644  * Add a page to the dirty page list.
645  *
646  * It is a sad fact of life that this function is called from several places
647  * deeply under spinlocking.  It may not sleep.
648  *
649  * If the page has buffers, the uptodate buffers are set dirty, to preserve
650  * dirty-state coherency between the page and the buffers.  It the page does
651  * not have buffers then when they are later attached they will all be set
652  * dirty.
653  *
654  * The buffers are dirtied before the page is dirtied.  There's a small race
655  * window in which a writepage caller may see the page cleanness but not the
656  * buffer dirtiness.  That's fine.  If this code were to set the page dirty
657  * before the buffers, a concurrent writepage caller could clear the page dirty
658  * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
659  * page on the dirty page list.
660  *
661  * We use private_lock to lock against try_to_free_buffers while using the
662  * page's buffer list.  Also use this to protect against clean buffers being
663  * added to the page after it was set dirty.
664  *
665  * FIXME: may need to call ->reservepage here as well.  That's rather up to the
666  * address_space though.
667  */
668 int __set_page_dirty_buffers(struct page *page)
669 {
670 	int newly_dirty;
671 	struct address_space *mapping = page_mapping(page);
672 
673 	if (unlikely(!mapping))
674 		return !TestSetPageDirty(page);
675 
676 	spin_lock(&mapping->private_lock);
677 	if (page_has_buffers(page)) {
678 		struct buffer_head *head = page_buffers(page);
679 		struct buffer_head *bh = head;
680 
681 		do {
682 			set_buffer_dirty(bh);
683 			bh = bh->b_this_page;
684 		} while (bh != head);
685 	}
686 	/*
687 	 * Lock out page->mem_cgroup migration to keep PageDirty
688 	 * synchronized with per-memcg dirty page counters.
689 	 */
690 	lock_page_memcg(page);
691 	newly_dirty = !TestSetPageDirty(page);
692 	spin_unlock(&mapping->private_lock);
693 
694 	if (newly_dirty)
695 		__set_page_dirty(page, mapping, 1);
696 
697 	unlock_page_memcg(page);
698 
699 	if (newly_dirty)
700 		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
701 
702 	return newly_dirty;
703 }
704 EXPORT_SYMBOL(__set_page_dirty_buffers);
705 
706 /*
707  * Write out and wait upon a list of buffers.
708  *
709  * We have conflicting pressures: we want to make sure that all
710  * initially dirty buffers get waited on, but that any subsequently
711  * dirtied buffers don't.  After all, we don't want fsync to last
712  * forever if somebody is actively writing to the file.
713  *
714  * Do this in two main stages: first we copy dirty buffers to a
715  * temporary inode list, queueing the writes as we go.  Then we clean
716  * up, waiting for those writes to complete.
717  *
718  * During this second stage, any subsequent updates to the file may end
719  * up refiling the buffer on the original inode's dirty list again, so
720  * there is a chance we will end up with a buffer queued for write but
721  * not yet completed on that list.  So, as a final cleanup we go through
722  * the osync code to catch these locked, dirty buffers without requeuing
723  * any newly dirty buffers for write.
724  */
725 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
726 {
727 	struct buffer_head *bh;
728 	struct list_head tmp;
729 	struct address_space *mapping;
730 	int err = 0, err2;
731 	struct blk_plug plug;
732 
733 	INIT_LIST_HEAD(&tmp);
734 	blk_start_plug(&plug);
735 
736 	spin_lock(lock);
737 	while (!list_empty(list)) {
738 		bh = BH_ENTRY(list->next);
739 		mapping = bh->b_assoc_map;
740 		__remove_assoc_queue(bh);
741 		/* Avoid race with mark_buffer_dirty_inode() which does
742 		 * a lockless check and we rely on seeing the dirty bit */
743 		smp_mb();
744 		if (buffer_dirty(bh) || buffer_locked(bh)) {
745 			list_add(&bh->b_assoc_buffers, &tmp);
746 			bh->b_assoc_map = mapping;
747 			if (buffer_dirty(bh)) {
748 				get_bh(bh);
749 				spin_unlock(lock);
750 				/*
751 				 * Ensure any pending I/O completes so that
752 				 * write_dirty_buffer() actually writes the
753 				 * current contents - it is a noop if I/O is
754 				 * still in flight on potentially older
755 				 * contents.
756 				 */
757 				write_dirty_buffer(bh, REQ_SYNC);
758 
759 				/*
760 				 * Kick off IO for the previous mapping. Note
761 				 * that we will not run the very last mapping,
762 				 * wait_on_buffer() will do that for us
763 				 * through sync_buffer().
764 				 */
765 				brelse(bh);
766 				spin_lock(lock);
767 			}
768 		}
769 	}
770 
771 	spin_unlock(lock);
772 	blk_finish_plug(&plug);
773 	spin_lock(lock);
774 
775 	while (!list_empty(&tmp)) {
776 		bh = BH_ENTRY(tmp.prev);
777 		get_bh(bh);
778 		mapping = bh->b_assoc_map;
779 		__remove_assoc_queue(bh);
780 		/* Avoid race with mark_buffer_dirty_inode() which does
781 		 * a lockless check and we rely on seeing the dirty bit */
782 		smp_mb();
783 		if (buffer_dirty(bh)) {
784 			list_add(&bh->b_assoc_buffers,
785 				 &mapping->private_list);
786 			bh->b_assoc_map = mapping;
787 		}
788 		spin_unlock(lock);
789 		wait_on_buffer(bh);
790 		if (!buffer_uptodate(bh))
791 			err = -EIO;
792 		brelse(bh);
793 		spin_lock(lock);
794 	}
795 
796 	spin_unlock(lock);
797 	err2 = osync_buffers_list(lock, list);
798 	if (err)
799 		return err;
800 	else
801 		return err2;
802 }
803 
804 /*
805  * Invalidate any and all dirty buffers on a given inode.  We are
806  * probably unmounting the fs, but that doesn't mean we have already
807  * done a sync().  Just drop the buffers from the inode list.
808  *
809  * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
810  * assumes that all the buffers are against the blockdev.  Not true
811  * for reiserfs.
812  */
813 void invalidate_inode_buffers(struct inode *inode)
814 {
815 	if (inode_has_buffers(inode)) {
816 		struct address_space *mapping = &inode->i_data;
817 		struct list_head *list = &mapping->private_list;
818 		struct address_space *buffer_mapping = mapping->private_data;
819 
820 		spin_lock(&buffer_mapping->private_lock);
821 		while (!list_empty(list))
822 			__remove_assoc_queue(BH_ENTRY(list->next));
823 		spin_unlock(&buffer_mapping->private_lock);
824 	}
825 }
826 EXPORT_SYMBOL(invalidate_inode_buffers);
827 
828 /*
829  * Remove any clean buffers from the inode's buffer list.  This is called
830  * when we're trying to free the inode itself.  Those buffers can pin it.
831  *
832  * Returns true if all buffers were removed.
833  */
834 int remove_inode_buffers(struct inode *inode)
835 {
836 	int ret = 1;
837 
838 	if (inode_has_buffers(inode)) {
839 		struct address_space *mapping = &inode->i_data;
840 		struct list_head *list = &mapping->private_list;
841 		struct address_space *buffer_mapping = mapping->private_data;
842 
843 		spin_lock(&buffer_mapping->private_lock);
844 		while (!list_empty(list)) {
845 			struct buffer_head *bh = BH_ENTRY(list->next);
846 			if (buffer_dirty(bh)) {
847 				ret = 0;
848 				break;
849 			}
850 			__remove_assoc_queue(bh);
851 		}
852 		spin_unlock(&buffer_mapping->private_lock);
853 	}
854 	return ret;
855 }
856 
857 /*
858  * Create the appropriate buffers when given a page for data area and
859  * the size of each buffer.. Use the bh->b_this_page linked list to
860  * follow the buffers created.  Return NULL if unable to create more
861  * buffers.
862  *
863  * The retry flag is used to differentiate async IO (paging, swapping)
864  * which may not fail from ordinary buffer allocations.
865  */
866 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
867 		int retry)
868 {
869 	struct buffer_head *bh, *head;
870 	long offset;
871 
872 try_again:
873 	head = NULL;
874 	offset = PAGE_SIZE;
875 	while ((offset -= size) >= 0) {
876 		bh = alloc_buffer_head(GFP_NOFS);
877 		if (!bh)
878 			goto no_grow;
879 
880 		bh->b_this_page = head;
881 		bh->b_blocknr = -1;
882 		head = bh;
883 
884 		bh->b_size = size;
885 
886 		/* Link the buffer to its page */
887 		set_bh_page(bh, page, offset);
888 	}
889 	return head;
890 /*
891  * In case anything failed, we just free everything we got.
892  */
893 no_grow:
894 	if (head) {
895 		do {
896 			bh = head;
897 			head = head->b_this_page;
898 			free_buffer_head(bh);
899 		} while (head);
900 	}
901 
902 	/*
903 	 * Return failure for non-async IO requests.  Async IO requests
904 	 * are not allowed to fail, so we have to wait until buffer heads
905 	 * become available.  But we don't want tasks sleeping with
906 	 * partially complete buffers, so all were released above.
907 	 */
908 	if (!retry)
909 		return NULL;
910 
911 	/* We're _really_ low on memory. Now we just
912 	 * wait for old buffer heads to become free due to
913 	 * finishing IO.  Since this is an async request and
914 	 * the reserve list is empty, we're sure there are
915 	 * async buffer heads in use.
916 	 */
917 	free_more_memory();
918 	goto try_again;
919 }
920 EXPORT_SYMBOL_GPL(alloc_page_buffers);
921 
922 static inline void
923 link_dev_buffers(struct page *page, struct buffer_head *head)
924 {
925 	struct buffer_head *bh, *tail;
926 
927 	bh = head;
928 	do {
929 		tail = bh;
930 		bh = bh->b_this_page;
931 	} while (bh);
932 	tail->b_this_page = head;
933 	attach_page_buffers(page, head);
934 }
935 
936 static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
937 {
938 	sector_t retval = ~((sector_t)0);
939 	loff_t sz = i_size_read(bdev->bd_inode);
940 
941 	if (sz) {
942 		unsigned int sizebits = blksize_bits(size);
943 		retval = (sz >> sizebits);
944 	}
945 	return retval;
946 }
947 
948 /*
949  * Initialise the state of a blockdev page's buffers.
950  */
951 static sector_t
952 init_page_buffers(struct page *page, struct block_device *bdev,
953 			sector_t block, int size)
954 {
955 	struct buffer_head *head = page_buffers(page);
956 	struct buffer_head *bh = head;
957 	int uptodate = PageUptodate(page);
958 	sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
959 
960 	do {
961 		if (!buffer_mapped(bh)) {
962 			init_buffer(bh, NULL, NULL);
963 			bh->b_bdev = bdev;
964 			bh->b_blocknr = block;
965 			if (uptodate)
966 				set_buffer_uptodate(bh);
967 			if (block < end_block)
968 				set_buffer_mapped(bh);
969 		}
970 		block++;
971 		bh = bh->b_this_page;
972 	} while (bh != head);
973 
974 	/*
975 	 * Caller needs to validate requested block against end of device.
976 	 */
977 	return end_block;
978 }
979 
980 /*
981  * Create the page-cache page that contains the requested block.
982  *
983  * This is used purely for blockdev mappings.
984  */
985 static int
986 grow_dev_page(struct block_device *bdev, sector_t block,
987 	      pgoff_t index, int size, int sizebits, gfp_t gfp)
988 {
989 	struct inode *inode = bdev->bd_inode;
990 	struct page *page;
991 	struct buffer_head *bh;
992 	sector_t end_block;
993 	int ret = 0;		/* Will call free_more_memory() */
994 	gfp_t gfp_mask;
995 
996 	gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) | gfp;
997 
998 	/*
999 	 * XXX: __getblk_slow() can not really deal with failure and
1000 	 * will endlessly loop on improvised global reclaim.  Prefer
1001 	 * looping in the allocator rather than here, at least that
1002 	 * code knows what it's doing.
1003 	 */
1004 	gfp_mask |= __GFP_NOFAIL;
1005 
1006 	page = find_or_create_page(inode->i_mapping, index, gfp_mask);
1007 	if (!page)
1008 		return ret;
1009 
1010 	BUG_ON(!PageLocked(page));
1011 
1012 	if (page_has_buffers(page)) {
1013 		bh = page_buffers(page);
1014 		if (bh->b_size == size) {
1015 			end_block = init_page_buffers(page, bdev,
1016 						(sector_t)index << sizebits,
1017 						size);
1018 			goto done;
1019 		}
1020 		if (!try_to_free_buffers(page))
1021 			goto failed;
1022 	}
1023 
1024 	/*
1025 	 * Allocate some buffers for this page
1026 	 */
1027 	bh = alloc_page_buffers(page, size, 0);
1028 	if (!bh)
1029 		goto failed;
1030 
1031 	/*
1032 	 * Link the page to the buffers and initialise them.  Take the
1033 	 * lock to be atomic wrt __find_get_block(), which does not
1034 	 * run under the page lock.
1035 	 */
1036 	spin_lock(&inode->i_mapping->private_lock);
1037 	link_dev_buffers(page, bh);
1038 	end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
1039 			size);
1040 	spin_unlock(&inode->i_mapping->private_lock);
1041 done:
1042 	ret = (block < end_block) ? 1 : -ENXIO;
1043 failed:
1044 	unlock_page(page);
1045 	put_page(page);
1046 	return ret;
1047 }
1048 
1049 /*
1050  * Create buffers for the specified block device block's page.  If
1051  * that page was dirty, the buffers are set dirty also.
1052  */
1053 static int
1054 grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
1055 {
1056 	pgoff_t index;
1057 	int sizebits;
1058 
1059 	sizebits = -1;
1060 	do {
1061 		sizebits++;
1062 	} while ((size << sizebits) < PAGE_SIZE);
1063 
1064 	index = block >> sizebits;
1065 
1066 	/*
1067 	 * Check for a block which wants to lie outside our maximum possible
1068 	 * pagecache index.  (this comparison is done using sector_t types).
1069 	 */
1070 	if (unlikely(index != block >> sizebits)) {
1071 		printk(KERN_ERR "%s: requested out-of-range block %llu for "
1072 			"device %pg\n",
1073 			__func__, (unsigned long long)block,
1074 			bdev);
1075 		return -EIO;
1076 	}
1077 
1078 	/* Create a page with the proper size buffers.. */
1079 	return grow_dev_page(bdev, block, index, size, sizebits, gfp);
1080 }
1081 
1082 static struct buffer_head *
1083 __getblk_slow(struct block_device *bdev, sector_t block,
1084 	     unsigned size, gfp_t gfp)
1085 {
1086 	/* Size must be multiple of hard sectorsize */
1087 	if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
1088 			(size < 512 || size > PAGE_SIZE))) {
1089 		printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1090 					size);
1091 		printk(KERN_ERR "logical block size: %d\n",
1092 					bdev_logical_block_size(bdev));
1093 
1094 		dump_stack();
1095 		return NULL;
1096 	}
1097 
1098 	for (;;) {
1099 		struct buffer_head *bh;
1100 		int ret;
1101 
1102 		bh = __find_get_block(bdev, block, size);
1103 		if (bh)
1104 			return bh;
1105 
1106 		ret = grow_buffers(bdev, block, size, gfp);
1107 		if (ret < 0)
1108 			return NULL;
1109 		if (ret == 0)
1110 			free_more_memory();
1111 	}
1112 }
1113 
1114 /*
1115  * The relationship between dirty buffers and dirty pages:
1116  *
1117  * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1118  * the page is tagged dirty in its radix tree.
1119  *
1120  * At all times, the dirtiness of the buffers represents the dirtiness of
1121  * subsections of the page.  If the page has buffers, the page dirty bit is
1122  * merely a hint about the true dirty state.
1123  *
1124  * When a page is set dirty in its entirety, all its buffers are marked dirty
1125  * (if the page has buffers).
1126  *
1127  * When a buffer is marked dirty, its page is dirtied, but the page's other
1128  * buffers are not.
1129  *
1130  * Also.  When blockdev buffers are explicitly read with bread(), they
1131  * individually become uptodate.  But their backing page remains not
1132  * uptodate - even if all of its buffers are uptodate.  A subsequent
1133  * block_read_full_page() against that page will discover all the uptodate
1134  * buffers, will set the page uptodate and will perform no I/O.
1135  */
1136 
1137 /**
1138  * mark_buffer_dirty - mark a buffer_head as needing writeout
1139  * @bh: the buffer_head to mark dirty
1140  *
1141  * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1142  * backing page dirty, then tag the page as dirty in its address_space's radix
1143  * tree and then attach the address_space's inode to its superblock's dirty
1144  * inode list.
1145  *
1146  * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1147  * mapping->tree_lock and mapping->host->i_lock.
1148  */
1149 void mark_buffer_dirty(struct buffer_head *bh)
1150 {
1151 	WARN_ON_ONCE(!buffer_uptodate(bh));
1152 
1153 	trace_block_dirty_buffer(bh);
1154 
1155 	/*
1156 	 * Very *carefully* optimize the it-is-already-dirty case.
1157 	 *
1158 	 * Don't let the final "is it dirty" escape to before we
1159 	 * perhaps modified the buffer.
1160 	 */
1161 	if (buffer_dirty(bh)) {
1162 		smp_mb();
1163 		if (buffer_dirty(bh))
1164 			return;
1165 	}
1166 
1167 	if (!test_set_buffer_dirty(bh)) {
1168 		struct page *page = bh->b_page;
1169 		struct address_space *mapping = NULL;
1170 
1171 		lock_page_memcg(page);
1172 		if (!TestSetPageDirty(page)) {
1173 			mapping = page_mapping(page);
1174 			if (mapping)
1175 				__set_page_dirty(page, mapping, 0);
1176 		}
1177 		unlock_page_memcg(page);
1178 		if (mapping)
1179 			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1180 	}
1181 }
1182 EXPORT_SYMBOL(mark_buffer_dirty);
1183 
1184 /*
1185  * Decrement a buffer_head's reference count.  If all buffers against a page
1186  * have zero reference count, are clean and unlocked, and if the page is clean
1187  * and unlocked then try_to_free_buffers() may strip the buffers from the page
1188  * in preparation for freeing it (sometimes, rarely, buffers are removed from
1189  * a page but it ends up not being freed, and buffers may later be reattached).
1190  */
1191 void __brelse(struct buffer_head * buf)
1192 {
1193 	if (atomic_read(&buf->b_count)) {
1194 		put_bh(buf);
1195 		return;
1196 	}
1197 	WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1198 }
1199 EXPORT_SYMBOL(__brelse);
1200 
1201 /*
1202  * bforget() is like brelse(), except it discards any
1203  * potentially dirty data.
1204  */
1205 void __bforget(struct buffer_head *bh)
1206 {
1207 	clear_buffer_dirty(bh);
1208 	if (bh->b_assoc_map) {
1209 		struct address_space *buffer_mapping = bh->b_page->mapping;
1210 
1211 		spin_lock(&buffer_mapping->private_lock);
1212 		list_del_init(&bh->b_assoc_buffers);
1213 		bh->b_assoc_map = NULL;
1214 		spin_unlock(&buffer_mapping->private_lock);
1215 	}
1216 	__brelse(bh);
1217 }
1218 EXPORT_SYMBOL(__bforget);
1219 
1220 static struct buffer_head *__bread_slow(struct buffer_head *bh)
1221 {
1222 	lock_buffer(bh);
1223 	if (buffer_uptodate(bh)) {
1224 		unlock_buffer(bh);
1225 		return bh;
1226 	} else {
1227 		get_bh(bh);
1228 		bh->b_end_io = end_buffer_read_sync;
1229 		submit_bh(REQ_OP_READ, 0, bh);
1230 		wait_on_buffer(bh);
1231 		if (buffer_uptodate(bh))
1232 			return bh;
1233 	}
1234 	brelse(bh);
1235 	return NULL;
1236 }
1237 
1238 /*
1239  * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1240  * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1241  * refcount elevated by one when they're in an LRU.  A buffer can only appear
1242  * once in a particular CPU's LRU.  A single buffer can be present in multiple
1243  * CPU's LRUs at the same time.
1244  *
1245  * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1246  * sb_find_get_block().
1247  *
1248  * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1249  * a local interrupt disable for that.
1250  */
1251 
1252 #define BH_LRU_SIZE	16
1253 
1254 struct bh_lru {
1255 	struct buffer_head *bhs[BH_LRU_SIZE];
1256 };
1257 
1258 static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1259 
1260 #ifdef CONFIG_SMP
1261 #define bh_lru_lock()	local_irq_disable()
1262 #define bh_lru_unlock()	local_irq_enable()
1263 #else
1264 #define bh_lru_lock()	preempt_disable()
1265 #define bh_lru_unlock()	preempt_enable()
1266 #endif
1267 
1268 static inline void check_irqs_on(void)
1269 {
1270 #ifdef irqs_disabled
1271 	BUG_ON(irqs_disabled());
1272 #endif
1273 }
1274 
1275 /*
1276  * The LRU management algorithm is dopey-but-simple.  Sorry.
1277  */
1278 static void bh_lru_install(struct buffer_head *bh)
1279 {
1280 	struct buffer_head *evictee = NULL;
1281 
1282 	check_irqs_on();
1283 	bh_lru_lock();
1284 	if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
1285 		struct buffer_head *bhs[BH_LRU_SIZE];
1286 		int in;
1287 		int out = 0;
1288 
1289 		get_bh(bh);
1290 		bhs[out++] = bh;
1291 		for (in = 0; in < BH_LRU_SIZE; in++) {
1292 			struct buffer_head *bh2 =
1293 				__this_cpu_read(bh_lrus.bhs[in]);
1294 
1295 			if (bh2 == bh) {
1296 				__brelse(bh2);
1297 			} else {
1298 				if (out >= BH_LRU_SIZE) {
1299 					BUG_ON(evictee != NULL);
1300 					evictee = bh2;
1301 				} else {
1302 					bhs[out++] = bh2;
1303 				}
1304 			}
1305 		}
1306 		while (out < BH_LRU_SIZE)
1307 			bhs[out++] = NULL;
1308 		memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
1309 	}
1310 	bh_lru_unlock();
1311 
1312 	if (evictee)
1313 		__brelse(evictee);
1314 }
1315 
1316 /*
1317  * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1318  */
1319 static struct buffer_head *
1320 lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1321 {
1322 	struct buffer_head *ret = NULL;
1323 	unsigned int i;
1324 
1325 	check_irqs_on();
1326 	bh_lru_lock();
1327 	for (i = 0; i < BH_LRU_SIZE; i++) {
1328 		struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1329 
1330 		if (bh && bh->b_blocknr == block && bh->b_bdev == bdev &&
1331 		    bh->b_size == size) {
1332 			if (i) {
1333 				while (i) {
1334 					__this_cpu_write(bh_lrus.bhs[i],
1335 						__this_cpu_read(bh_lrus.bhs[i - 1]));
1336 					i--;
1337 				}
1338 				__this_cpu_write(bh_lrus.bhs[0], bh);
1339 			}
1340 			get_bh(bh);
1341 			ret = bh;
1342 			break;
1343 		}
1344 	}
1345 	bh_lru_unlock();
1346 	return ret;
1347 }
1348 
1349 /*
1350  * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1351  * it in the LRU and mark it as accessed.  If it is not present then return
1352  * NULL
1353  */
1354 struct buffer_head *
1355 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1356 {
1357 	struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1358 
1359 	if (bh == NULL) {
1360 		/* __find_get_block_slow will mark the page accessed */
1361 		bh = __find_get_block_slow(bdev, block);
1362 		if (bh)
1363 			bh_lru_install(bh);
1364 	} else
1365 		touch_buffer(bh);
1366 
1367 	return bh;
1368 }
1369 EXPORT_SYMBOL(__find_get_block);
1370 
1371 /*
1372  * __getblk_gfp() will locate (and, if necessary, create) the buffer_head
1373  * which corresponds to the passed block_device, block and size. The
1374  * returned buffer has its reference count incremented.
1375  *
1376  * __getblk_gfp() will lock up the machine if grow_dev_page's
1377  * try_to_free_buffers() attempt is failing.  FIXME, perhaps?
1378  */
1379 struct buffer_head *
1380 __getblk_gfp(struct block_device *bdev, sector_t block,
1381 	     unsigned size, gfp_t gfp)
1382 {
1383 	struct buffer_head *bh = __find_get_block(bdev, block, size);
1384 
1385 	might_sleep();
1386 	if (bh == NULL)
1387 		bh = __getblk_slow(bdev, block, size, gfp);
1388 	return bh;
1389 }
1390 EXPORT_SYMBOL(__getblk_gfp);
1391 
1392 /*
1393  * Do async read-ahead on a buffer..
1394  */
1395 void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1396 {
1397 	struct buffer_head *bh = __getblk(bdev, block, size);
1398 	if (likely(bh)) {
1399 		ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
1400 		brelse(bh);
1401 	}
1402 }
1403 EXPORT_SYMBOL(__breadahead);
1404 
1405 /**
1406  *  __bread_gfp() - reads a specified block and returns the bh
1407  *  @bdev: the block_device to read from
1408  *  @block: number of block
1409  *  @size: size (in bytes) to read
1410  *  @gfp: page allocation flag
1411  *
1412  *  Reads a specified block, and returns buffer head that contains it.
1413  *  The page cache can be allocated from non-movable area
1414  *  not to prevent page migration if you set gfp to zero.
1415  *  It returns NULL if the block was unreadable.
1416  */
1417 struct buffer_head *
1418 __bread_gfp(struct block_device *bdev, sector_t block,
1419 		   unsigned size, gfp_t gfp)
1420 {
1421 	struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
1422 
1423 	if (likely(bh) && !buffer_uptodate(bh))
1424 		bh = __bread_slow(bh);
1425 	return bh;
1426 }
1427 EXPORT_SYMBOL(__bread_gfp);
1428 
1429 /*
1430  * invalidate_bh_lrus() is called rarely - but not only at unmount.
1431  * This doesn't race because it runs in each cpu either in irq
1432  * or with preempt disabled.
1433  */
1434 static void invalidate_bh_lru(void *arg)
1435 {
1436 	struct bh_lru *b = &get_cpu_var(bh_lrus);
1437 	int i;
1438 
1439 	for (i = 0; i < BH_LRU_SIZE; i++) {
1440 		brelse(b->bhs[i]);
1441 		b->bhs[i] = NULL;
1442 	}
1443 	put_cpu_var(bh_lrus);
1444 }
1445 
1446 static bool has_bh_in_lru(int cpu, void *dummy)
1447 {
1448 	struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1449 	int i;
1450 
1451 	for (i = 0; i < BH_LRU_SIZE; i++) {
1452 		if (b->bhs[i])
1453 			return 1;
1454 	}
1455 
1456 	return 0;
1457 }
1458 
1459 void invalidate_bh_lrus(void)
1460 {
1461 	on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1462 }
1463 EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1464 
1465 void set_bh_page(struct buffer_head *bh,
1466 		struct page *page, unsigned long offset)
1467 {
1468 	bh->b_page = page;
1469 	BUG_ON(offset >= PAGE_SIZE);
1470 	if (PageHighMem(page))
1471 		/*
1472 		 * This catches illegal uses and preserves the offset:
1473 		 */
1474 		bh->b_data = (char *)(0 + offset);
1475 	else
1476 		bh->b_data = page_address(page) + offset;
1477 }
1478 EXPORT_SYMBOL(set_bh_page);
1479 
1480 /*
1481  * Called when truncating a buffer on a page completely.
1482  */
1483 
1484 /* Bits that are cleared during an invalidate */
1485 #define BUFFER_FLAGS_DISCARD \
1486 	(1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
1487 	 1 << BH_Delay | 1 << BH_Unwritten)
1488 
1489 static void discard_buffer(struct buffer_head * bh)
1490 {
1491 	unsigned long b_state, b_state_old;
1492 
1493 	lock_buffer(bh);
1494 	clear_buffer_dirty(bh);
1495 	bh->b_bdev = NULL;
1496 	b_state = bh->b_state;
1497 	for (;;) {
1498 		b_state_old = cmpxchg(&bh->b_state, b_state,
1499 				      (b_state & ~BUFFER_FLAGS_DISCARD));
1500 		if (b_state_old == b_state)
1501 			break;
1502 		b_state = b_state_old;
1503 	}
1504 	unlock_buffer(bh);
1505 }
1506 
1507 /**
1508  * block_invalidatepage - invalidate part or all of a buffer-backed page
1509  *
1510  * @page: the page which is affected
1511  * @offset: start of the range to invalidate
1512  * @length: length of the range to invalidate
1513  *
1514  * block_invalidatepage() is called when all or part of the page has become
1515  * invalidated by a truncate operation.
1516  *
1517  * block_invalidatepage() does not have to release all buffers, but it must
1518  * ensure that no dirty buffer is left outside @offset and that no I/O
1519  * is underway against any of the blocks which are outside the truncation
1520  * point.  Because the caller is about to free (and possibly reuse) those
1521  * blocks on-disk.
1522  */
1523 void block_invalidatepage(struct page *page, unsigned int offset,
1524 			  unsigned int length)
1525 {
1526 	struct buffer_head *head, *bh, *next;
1527 	unsigned int curr_off = 0;
1528 	unsigned int stop = length + offset;
1529 
1530 	BUG_ON(!PageLocked(page));
1531 	if (!page_has_buffers(page))
1532 		goto out;
1533 
1534 	/*
1535 	 * Check for overflow
1536 	 */
1537 	BUG_ON(stop > PAGE_SIZE || stop < length);
1538 
1539 	head = page_buffers(page);
1540 	bh = head;
1541 	do {
1542 		unsigned int next_off = curr_off + bh->b_size;
1543 		next = bh->b_this_page;
1544 
1545 		/*
1546 		 * Are we still fully in range ?
1547 		 */
1548 		if (next_off > stop)
1549 			goto out;
1550 
1551 		/*
1552 		 * is this block fully invalidated?
1553 		 */
1554 		if (offset <= curr_off)
1555 			discard_buffer(bh);
1556 		curr_off = next_off;
1557 		bh = next;
1558 	} while (bh != head);
1559 
1560 	/*
1561 	 * We release buffers only if the entire page is being invalidated.
1562 	 * The get_block cached value has been unconditionally invalidated,
1563 	 * so real IO is not possible anymore.
1564 	 */
1565 	if (offset == 0)
1566 		try_to_release_page(page, 0);
1567 out:
1568 	return;
1569 }
1570 EXPORT_SYMBOL(block_invalidatepage);
1571 
1572 
1573 /*
1574  * We attach and possibly dirty the buffers atomically wrt
1575  * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1576  * is already excluded via the page lock.
1577  */
1578 void create_empty_buffers(struct page *page,
1579 			unsigned long blocksize, unsigned long b_state)
1580 {
1581 	struct buffer_head *bh, *head, *tail;
1582 
1583 	head = alloc_page_buffers(page, blocksize, 1);
1584 	bh = head;
1585 	do {
1586 		bh->b_state |= b_state;
1587 		tail = bh;
1588 		bh = bh->b_this_page;
1589 	} while (bh);
1590 	tail->b_this_page = head;
1591 
1592 	spin_lock(&page->mapping->private_lock);
1593 	if (PageUptodate(page) || PageDirty(page)) {
1594 		bh = head;
1595 		do {
1596 			if (PageDirty(page))
1597 				set_buffer_dirty(bh);
1598 			if (PageUptodate(page))
1599 				set_buffer_uptodate(bh);
1600 			bh = bh->b_this_page;
1601 		} while (bh != head);
1602 	}
1603 	attach_page_buffers(page, head);
1604 	spin_unlock(&page->mapping->private_lock);
1605 }
1606 EXPORT_SYMBOL(create_empty_buffers);
1607 
1608 /**
1609  * clean_bdev_aliases: clean a range of buffers in block device
1610  * @bdev: Block device to clean buffers in
1611  * @block: Start of a range of blocks to clean
1612  * @len: Number of blocks to clean
1613  *
1614  * We are taking a range of blocks for data and we don't want writeback of any
1615  * buffer-cache aliases starting from return from this function and until the
1616  * moment when something will explicitly mark the buffer dirty (hopefully that
1617  * will not happen until we will free that block ;-) We don't even need to mark
1618  * it not-uptodate - nobody can expect anything from a newly allocated buffer
1619  * anyway. We used to use unmap_buffer() for such invalidation, but that was
1620  * wrong. We definitely don't want to mark the alias unmapped, for example - it
1621  * would confuse anyone who might pick it with bread() afterwards...
1622  *
1623  * Also..  Note that bforget() doesn't lock the buffer.  So there can be
1624  * writeout I/O going on against recently-freed buffers.  We don't wait on that
1625  * I/O in bforget() - it's more efficient to wait on the I/O only if we really
1626  * need to.  That happens here.
1627  */
1628 void clean_bdev_aliases(struct block_device *bdev, sector_t block, sector_t len)
1629 {
1630 	struct inode *bd_inode = bdev->bd_inode;
1631 	struct address_space *bd_mapping = bd_inode->i_mapping;
1632 	struct pagevec pvec;
1633 	pgoff_t index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
1634 	pgoff_t end;
1635 	int i;
1636 	struct buffer_head *bh;
1637 	struct buffer_head *head;
1638 
1639 	end = (block + len - 1) >> (PAGE_SHIFT - bd_inode->i_blkbits);
1640 	pagevec_init(&pvec, 0);
1641 	while (index <= end && pagevec_lookup(&pvec, bd_mapping, index,
1642 			min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
1643 		for (i = 0; i < pagevec_count(&pvec); i++) {
1644 			struct page *page = pvec.pages[i];
1645 
1646 			index = page->index;
1647 			if (index > end)
1648 				break;
1649 			if (!page_has_buffers(page))
1650 				continue;
1651 			/*
1652 			 * We use page lock instead of bd_mapping->private_lock
1653 			 * to pin buffers here since we can afford to sleep and
1654 			 * it scales better than a global spinlock lock.
1655 			 */
1656 			lock_page(page);
1657 			/* Recheck when the page is locked which pins bhs */
1658 			if (!page_has_buffers(page))
1659 				goto unlock_page;
1660 			head = page_buffers(page);
1661 			bh = head;
1662 			do {
1663 				if (!buffer_mapped(bh))
1664 					goto next;
1665 				if (bh->b_blocknr >= block + len)
1666 					break;
1667 				clear_buffer_dirty(bh);
1668 				wait_on_buffer(bh);
1669 				clear_buffer_req(bh);
1670 next:
1671 				bh = bh->b_this_page;
1672 			} while (bh != head);
1673 unlock_page:
1674 			unlock_page(page);
1675 		}
1676 		pagevec_release(&pvec);
1677 		cond_resched();
1678 		index++;
1679 	}
1680 }
1681 EXPORT_SYMBOL(clean_bdev_aliases);
1682 
1683 /*
1684  * Size is a power-of-two in the range 512..PAGE_SIZE,
1685  * and the case we care about most is PAGE_SIZE.
1686  *
1687  * So this *could* possibly be written with those
1688  * constraints in mind (relevant mostly if some
1689  * architecture has a slow bit-scan instruction)
1690  */
1691 static inline int block_size_bits(unsigned int blocksize)
1692 {
1693 	return ilog2(blocksize);
1694 }
1695 
1696 static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
1697 {
1698 	BUG_ON(!PageLocked(page));
1699 
1700 	if (!page_has_buffers(page))
1701 		create_empty_buffers(page, 1 << ACCESS_ONCE(inode->i_blkbits), b_state);
1702 	return page_buffers(page);
1703 }
1704 
1705 /*
1706  * NOTE! All mapped/uptodate combinations are valid:
1707  *
1708  *	Mapped	Uptodate	Meaning
1709  *
1710  *	No	No		"unknown" - must do get_block()
1711  *	No	Yes		"hole" - zero-filled
1712  *	Yes	No		"allocated" - allocated on disk, not read in
1713  *	Yes	Yes		"valid" - allocated and up-to-date in memory.
1714  *
1715  * "Dirty" is valid only with the last case (mapped+uptodate).
1716  */
1717 
1718 /*
1719  * While block_write_full_page is writing back the dirty buffers under
1720  * the page lock, whoever dirtied the buffers may decide to clean them
1721  * again at any time.  We handle that by only looking at the buffer
1722  * state inside lock_buffer().
1723  *
1724  * If block_write_full_page() is called for regular writeback
1725  * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1726  * locked buffer.   This only can happen if someone has written the buffer
1727  * directly, with submit_bh().  At the address_space level PageWriteback
1728  * prevents this contention from occurring.
1729  *
1730  * If block_write_full_page() is called with wbc->sync_mode ==
1731  * WB_SYNC_ALL, the writes are posted using REQ_SYNC; this
1732  * causes the writes to be flagged as synchronous writes.
1733  */
1734 int __block_write_full_page(struct inode *inode, struct page *page,
1735 			get_block_t *get_block, struct writeback_control *wbc,
1736 			bh_end_io_t *handler)
1737 {
1738 	int err;
1739 	sector_t block;
1740 	sector_t last_block;
1741 	struct buffer_head *bh, *head;
1742 	unsigned int blocksize, bbits;
1743 	int nr_underway = 0;
1744 	int write_flags = wbc_to_write_flags(wbc);
1745 
1746 	head = create_page_buffers(page, inode,
1747 					(1 << BH_Dirty)|(1 << BH_Uptodate));
1748 
1749 	/*
1750 	 * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1751 	 * here, and the (potentially unmapped) buffers may become dirty at
1752 	 * any time.  If a buffer becomes dirty here after we've inspected it
1753 	 * then we just miss that fact, and the page stays dirty.
1754 	 *
1755 	 * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1756 	 * handle that here by just cleaning them.
1757 	 */
1758 
1759 	bh = head;
1760 	blocksize = bh->b_size;
1761 	bbits = block_size_bits(blocksize);
1762 
1763 	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
1764 	last_block = (i_size_read(inode) - 1) >> bbits;
1765 
1766 	/*
1767 	 * Get all the dirty buffers mapped to disk addresses and
1768 	 * handle any aliases from the underlying blockdev's mapping.
1769 	 */
1770 	do {
1771 		if (block > last_block) {
1772 			/*
1773 			 * mapped buffers outside i_size will occur, because
1774 			 * this page can be outside i_size when there is a
1775 			 * truncate in progress.
1776 			 */
1777 			/*
1778 			 * The buffer was zeroed by block_write_full_page()
1779 			 */
1780 			clear_buffer_dirty(bh);
1781 			set_buffer_uptodate(bh);
1782 		} else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1783 			   buffer_dirty(bh)) {
1784 			WARN_ON(bh->b_size != blocksize);
1785 			err = get_block(inode, block, bh, 1);
1786 			if (err)
1787 				goto recover;
1788 			clear_buffer_delay(bh);
1789 			if (buffer_new(bh)) {
1790 				/* blockdev mappings never come here */
1791 				clear_buffer_new(bh);
1792 				clean_bdev_bh_alias(bh);
1793 			}
1794 		}
1795 		bh = bh->b_this_page;
1796 		block++;
1797 	} while (bh != head);
1798 
1799 	do {
1800 		if (!buffer_mapped(bh))
1801 			continue;
1802 		/*
1803 		 * If it's a fully non-blocking write attempt and we cannot
1804 		 * lock the buffer then redirty the page.  Note that this can
1805 		 * potentially cause a busy-wait loop from writeback threads
1806 		 * and kswapd activity, but those code paths have their own
1807 		 * higher-level throttling.
1808 		 */
1809 		if (wbc->sync_mode != WB_SYNC_NONE) {
1810 			lock_buffer(bh);
1811 		} else if (!trylock_buffer(bh)) {
1812 			redirty_page_for_writepage(wbc, page);
1813 			continue;
1814 		}
1815 		if (test_clear_buffer_dirty(bh)) {
1816 			mark_buffer_async_write_endio(bh, handler);
1817 		} else {
1818 			unlock_buffer(bh);
1819 		}
1820 	} while ((bh = bh->b_this_page) != head);
1821 
1822 	/*
1823 	 * The page and its buffers are protected by PageWriteback(), so we can
1824 	 * drop the bh refcounts early.
1825 	 */
1826 	BUG_ON(PageWriteback(page));
1827 	set_page_writeback(page);
1828 
1829 	do {
1830 		struct buffer_head *next = bh->b_this_page;
1831 		if (buffer_async_write(bh)) {
1832 			submit_bh_wbc(REQ_OP_WRITE, write_flags, bh, 0, wbc);
1833 			nr_underway++;
1834 		}
1835 		bh = next;
1836 	} while (bh != head);
1837 	unlock_page(page);
1838 
1839 	err = 0;
1840 done:
1841 	if (nr_underway == 0) {
1842 		/*
1843 		 * The page was marked dirty, but the buffers were
1844 		 * clean.  Someone wrote them back by hand with
1845 		 * ll_rw_block/submit_bh.  A rare case.
1846 		 */
1847 		end_page_writeback(page);
1848 
1849 		/*
1850 		 * The page and buffer_heads can be released at any time from
1851 		 * here on.
1852 		 */
1853 	}
1854 	return err;
1855 
1856 recover:
1857 	/*
1858 	 * ENOSPC, or some other error.  We may already have added some
1859 	 * blocks to the file, so we need to write these out to avoid
1860 	 * exposing stale data.
1861 	 * The page is currently locked and not marked for writeback
1862 	 */
1863 	bh = head;
1864 	/* Recovery: lock and submit the mapped buffers */
1865 	do {
1866 		if (buffer_mapped(bh) && buffer_dirty(bh) &&
1867 		    !buffer_delay(bh)) {
1868 			lock_buffer(bh);
1869 			mark_buffer_async_write_endio(bh, handler);
1870 		} else {
1871 			/*
1872 			 * The buffer may have been set dirty during
1873 			 * attachment to a dirty page.
1874 			 */
1875 			clear_buffer_dirty(bh);
1876 		}
1877 	} while ((bh = bh->b_this_page) != head);
1878 	SetPageError(page);
1879 	BUG_ON(PageWriteback(page));
1880 	mapping_set_error(page->mapping, err);
1881 	set_page_writeback(page);
1882 	do {
1883 		struct buffer_head *next = bh->b_this_page;
1884 		if (buffer_async_write(bh)) {
1885 			clear_buffer_dirty(bh);
1886 			submit_bh_wbc(REQ_OP_WRITE, write_flags, bh, 0, wbc);
1887 			nr_underway++;
1888 		}
1889 		bh = next;
1890 	} while (bh != head);
1891 	unlock_page(page);
1892 	goto done;
1893 }
1894 EXPORT_SYMBOL(__block_write_full_page);
1895 
1896 /*
1897  * If a page has any new buffers, zero them out here, and mark them uptodate
1898  * and dirty so they'll be written out (in order to prevent uninitialised
1899  * block data from leaking). And clear the new bit.
1900  */
1901 void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1902 {
1903 	unsigned int block_start, block_end;
1904 	struct buffer_head *head, *bh;
1905 
1906 	BUG_ON(!PageLocked(page));
1907 	if (!page_has_buffers(page))
1908 		return;
1909 
1910 	bh = head = page_buffers(page);
1911 	block_start = 0;
1912 	do {
1913 		block_end = block_start + bh->b_size;
1914 
1915 		if (buffer_new(bh)) {
1916 			if (block_end > from && block_start < to) {
1917 				if (!PageUptodate(page)) {
1918 					unsigned start, size;
1919 
1920 					start = max(from, block_start);
1921 					size = min(to, block_end) - start;
1922 
1923 					zero_user(page, start, size);
1924 					set_buffer_uptodate(bh);
1925 				}
1926 
1927 				clear_buffer_new(bh);
1928 				mark_buffer_dirty(bh);
1929 			}
1930 		}
1931 
1932 		block_start = block_end;
1933 		bh = bh->b_this_page;
1934 	} while (bh != head);
1935 }
1936 EXPORT_SYMBOL(page_zero_new_buffers);
1937 
1938 static void
1939 iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
1940 		struct iomap *iomap)
1941 {
1942 	loff_t offset = block << inode->i_blkbits;
1943 
1944 	bh->b_bdev = iomap->bdev;
1945 
1946 	/*
1947 	 * Block points to offset in file we need to map, iomap contains
1948 	 * the offset at which the map starts. If the map ends before the
1949 	 * current block, then do not map the buffer and let the caller
1950 	 * handle it.
1951 	 */
1952 	BUG_ON(offset >= iomap->offset + iomap->length);
1953 
1954 	switch (iomap->type) {
1955 	case IOMAP_HOLE:
1956 		/*
1957 		 * If the buffer is not up to date or beyond the current EOF,
1958 		 * we need to mark it as new to ensure sub-block zeroing is
1959 		 * executed if necessary.
1960 		 */
1961 		if (!buffer_uptodate(bh) ||
1962 		    (offset >= i_size_read(inode)))
1963 			set_buffer_new(bh);
1964 		break;
1965 	case IOMAP_DELALLOC:
1966 		if (!buffer_uptodate(bh) ||
1967 		    (offset >= i_size_read(inode)))
1968 			set_buffer_new(bh);
1969 		set_buffer_uptodate(bh);
1970 		set_buffer_mapped(bh);
1971 		set_buffer_delay(bh);
1972 		break;
1973 	case IOMAP_UNWRITTEN:
1974 		/*
1975 		 * For unwritten regions, we always need to ensure that
1976 		 * sub-block writes cause the regions in the block we are not
1977 		 * writing to are zeroed. Set the buffer as new to ensure this.
1978 		 */
1979 		set_buffer_new(bh);
1980 		set_buffer_unwritten(bh);
1981 		/* FALLTHRU */
1982 	case IOMAP_MAPPED:
1983 		if (offset >= i_size_read(inode))
1984 			set_buffer_new(bh);
1985 		bh->b_blocknr = (iomap->blkno >> (inode->i_blkbits - 9)) +
1986 				((offset - iomap->offset) >> inode->i_blkbits);
1987 		set_buffer_mapped(bh);
1988 		break;
1989 	}
1990 }
1991 
1992 int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
1993 		get_block_t *get_block, struct iomap *iomap)
1994 {
1995 	unsigned from = pos & (PAGE_SIZE - 1);
1996 	unsigned to = from + len;
1997 	struct inode *inode = page->mapping->host;
1998 	unsigned block_start, block_end;
1999 	sector_t block;
2000 	int err = 0;
2001 	unsigned blocksize, bbits;
2002 	struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
2003 
2004 	BUG_ON(!PageLocked(page));
2005 	BUG_ON(from > PAGE_SIZE);
2006 	BUG_ON(to > PAGE_SIZE);
2007 	BUG_ON(from > to);
2008 
2009 	head = create_page_buffers(page, inode, 0);
2010 	blocksize = head->b_size;
2011 	bbits = block_size_bits(blocksize);
2012 
2013 	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
2014 
2015 	for(bh = head, block_start = 0; bh != head || !block_start;
2016 	    block++, block_start=block_end, bh = bh->b_this_page) {
2017 		block_end = block_start + blocksize;
2018 		if (block_end <= from || block_start >= to) {
2019 			if (PageUptodate(page)) {
2020 				if (!buffer_uptodate(bh))
2021 					set_buffer_uptodate(bh);
2022 			}
2023 			continue;
2024 		}
2025 		if (buffer_new(bh))
2026 			clear_buffer_new(bh);
2027 		if (!buffer_mapped(bh)) {
2028 			WARN_ON(bh->b_size != blocksize);
2029 			if (get_block) {
2030 				err = get_block(inode, block, bh, 1);
2031 				if (err)
2032 					break;
2033 			} else {
2034 				iomap_to_bh(inode, block, bh, iomap);
2035 			}
2036 
2037 			if (buffer_new(bh)) {
2038 				clean_bdev_bh_alias(bh);
2039 				if (PageUptodate(page)) {
2040 					clear_buffer_new(bh);
2041 					set_buffer_uptodate(bh);
2042 					mark_buffer_dirty(bh);
2043 					continue;
2044 				}
2045 				if (block_end > to || block_start < from)
2046 					zero_user_segments(page,
2047 						to, block_end,
2048 						block_start, from);
2049 				continue;
2050 			}
2051 		}
2052 		if (PageUptodate(page)) {
2053 			if (!buffer_uptodate(bh))
2054 				set_buffer_uptodate(bh);
2055 			continue;
2056 		}
2057 		if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
2058 		    !buffer_unwritten(bh) &&
2059 		     (block_start < from || block_end > to)) {
2060 			ll_rw_block(REQ_OP_READ, 0, 1, &bh);
2061 			*wait_bh++=bh;
2062 		}
2063 	}
2064 	/*
2065 	 * If we issued read requests - let them complete.
2066 	 */
2067 	while(wait_bh > wait) {
2068 		wait_on_buffer(*--wait_bh);
2069 		if (!buffer_uptodate(*wait_bh))
2070 			err = -EIO;
2071 	}
2072 	if (unlikely(err))
2073 		page_zero_new_buffers(page, from, to);
2074 	return err;
2075 }
2076 
2077 int __block_write_begin(struct page *page, loff_t pos, unsigned len,
2078 		get_block_t *get_block)
2079 {
2080 	return __block_write_begin_int(page, pos, len, get_block, NULL);
2081 }
2082 EXPORT_SYMBOL(__block_write_begin);
2083 
2084 static int __block_commit_write(struct inode *inode, struct page *page,
2085 		unsigned from, unsigned to)
2086 {
2087 	unsigned block_start, block_end;
2088 	int partial = 0;
2089 	unsigned blocksize;
2090 	struct buffer_head *bh, *head;
2091 
2092 	bh = head = page_buffers(page);
2093 	blocksize = bh->b_size;
2094 
2095 	block_start = 0;
2096 	do {
2097 		block_end = block_start + blocksize;
2098 		if (block_end <= from || block_start >= to) {
2099 			if (!buffer_uptodate(bh))
2100 				partial = 1;
2101 		} else {
2102 			set_buffer_uptodate(bh);
2103 			mark_buffer_dirty(bh);
2104 		}
2105 		clear_buffer_new(bh);
2106 
2107 		block_start = block_end;
2108 		bh = bh->b_this_page;
2109 	} while (bh != head);
2110 
2111 	/*
2112 	 * If this is a partial write which happened to make all buffers
2113 	 * uptodate then we can optimize away a bogus readpage() for
2114 	 * the next read(). Here we 'discover' whether the page went
2115 	 * uptodate as a result of this (potentially partial) write.
2116 	 */
2117 	if (!partial)
2118 		SetPageUptodate(page);
2119 	return 0;
2120 }
2121 
2122 /*
2123  * block_write_begin takes care of the basic task of block allocation and
2124  * bringing partial write blocks uptodate first.
2125  *
2126  * The filesystem needs to handle block truncation upon failure.
2127  */
2128 int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
2129 		unsigned flags, struct page **pagep, get_block_t *get_block)
2130 {
2131 	pgoff_t index = pos >> PAGE_SHIFT;
2132 	struct page *page;
2133 	int status;
2134 
2135 	page = grab_cache_page_write_begin(mapping, index, flags);
2136 	if (!page)
2137 		return -ENOMEM;
2138 
2139 	status = __block_write_begin(page, pos, len, get_block);
2140 	if (unlikely(status)) {
2141 		unlock_page(page);
2142 		put_page(page);
2143 		page = NULL;
2144 	}
2145 
2146 	*pagep = page;
2147 	return status;
2148 }
2149 EXPORT_SYMBOL(block_write_begin);
2150 
2151 int block_write_end(struct file *file, struct address_space *mapping,
2152 			loff_t pos, unsigned len, unsigned copied,
2153 			struct page *page, void *fsdata)
2154 {
2155 	struct inode *inode = mapping->host;
2156 	unsigned start;
2157 
2158 	start = pos & (PAGE_SIZE - 1);
2159 
2160 	if (unlikely(copied < len)) {
2161 		/*
2162 		 * The buffers that were written will now be uptodate, so we
2163 		 * don't have to worry about a readpage reading them and
2164 		 * overwriting a partial write. However if we have encountered
2165 		 * a short write and only partially written into a buffer, it
2166 		 * will not be marked uptodate, so a readpage might come in and
2167 		 * destroy our partial write.
2168 		 *
2169 		 * Do the simplest thing, and just treat any short write to a
2170 		 * non uptodate page as a zero-length write, and force the
2171 		 * caller to redo the whole thing.
2172 		 */
2173 		if (!PageUptodate(page))
2174 			copied = 0;
2175 
2176 		page_zero_new_buffers(page, start+copied, start+len);
2177 	}
2178 	flush_dcache_page(page);
2179 
2180 	/* This could be a short (even 0-length) commit */
2181 	__block_commit_write(inode, page, start, start+copied);
2182 
2183 	return copied;
2184 }
2185 EXPORT_SYMBOL(block_write_end);
2186 
2187 int generic_write_end(struct file *file, struct address_space *mapping,
2188 			loff_t pos, unsigned len, unsigned copied,
2189 			struct page *page, void *fsdata)
2190 {
2191 	struct inode *inode = mapping->host;
2192 	loff_t old_size = inode->i_size;
2193 	int i_size_changed = 0;
2194 
2195 	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2196 
2197 	/*
2198 	 * No need to use i_size_read() here, the i_size
2199 	 * cannot change under us because we hold i_mutex.
2200 	 *
2201 	 * But it's important to update i_size while still holding page lock:
2202 	 * page writeout could otherwise come in and zero beyond i_size.
2203 	 */
2204 	if (pos+copied > inode->i_size) {
2205 		i_size_write(inode, pos+copied);
2206 		i_size_changed = 1;
2207 	}
2208 
2209 	unlock_page(page);
2210 	put_page(page);
2211 
2212 	if (old_size < pos)
2213 		pagecache_isize_extended(inode, old_size, pos);
2214 	/*
2215 	 * Don't mark the inode dirty under page lock. First, it unnecessarily
2216 	 * makes the holding time of page lock longer. Second, it forces lock
2217 	 * ordering of page lock and transaction start for journaling
2218 	 * filesystems.
2219 	 */
2220 	if (i_size_changed)
2221 		mark_inode_dirty(inode);
2222 
2223 	return copied;
2224 }
2225 EXPORT_SYMBOL(generic_write_end);
2226 
2227 /*
2228  * block_is_partially_uptodate checks whether buffers within a page are
2229  * uptodate or not.
2230  *
2231  * Returns true if all buffers which correspond to a file portion
2232  * we want to read are uptodate.
2233  */
2234 int block_is_partially_uptodate(struct page *page, unsigned long from,
2235 					unsigned long count)
2236 {
2237 	unsigned block_start, block_end, blocksize;
2238 	unsigned to;
2239 	struct buffer_head *bh, *head;
2240 	int ret = 1;
2241 
2242 	if (!page_has_buffers(page))
2243 		return 0;
2244 
2245 	head = page_buffers(page);
2246 	blocksize = head->b_size;
2247 	to = min_t(unsigned, PAGE_SIZE - from, count);
2248 	to = from + to;
2249 	if (from < blocksize && to > PAGE_SIZE - blocksize)
2250 		return 0;
2251 
2252 	bh = head;
2253 	block_start = 0;
2254 	do {
2255 		block_end = block_start + blocksize;
2256 		if (block_end > from && block_start < to) {
2257 			if (!buffer_uptodate(bh)) {
2258 				ret = 0;
2259 				break;
2260 			}
2261 			if (block_end >= to)
2262 				break;
2263 		}
2264 		block_start = block_end;
2265 		bh = bh->b_this_page;
2266 	} while (bh != head);
2267 
2268 	return ret;
2269 }
2270 EXPORT_SYMBOL(block_is_partially_uptodate);
2271 
2272 /*
2273  * Generic "read page" function for block devices that have the normal
2274  * get_block functionality. This is most of the block device filesystems.
2275  * Reads the page asynchronously --- the unlock_buffer() and
2276  * set/clear_buffer_uptodate() functions propagate buffer state into the
2277  * page struct once IO has completed.
2278  */
2279 int block_read_full_page(struct page *page, get_block_t *get_block)
2280 {
2281 	struct inode *inode = page->mapping->host;
2282 	sector_t iblock, lblock;
2283 	struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2284 	unsigned int blocksize, bbits;
2285 	int nr, i;
2286 	int fully_mapped = 1;
2287 
2288 	head = create_page_buffers(page, inode, 0);
2289 	blocksize = head->b_size;
2290 	bbits = block_size_bits(blocksize);
2291 
2292 	iblock = (sector_t)page->index << (PAGE_SHIFT - bbits);
2293 	lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2294 	bh = head;
2295 	nr = 0;
2296 	i = 0;
2297 
2298 	do {
2299 		if (buffer_uptodate(bh))
2300 			continue;
2301 
2302 		if (!buffer_mapped(bh)) {
2303 			int err = 0;
2304 
2305 			fully_mapped = 0;
2306 			if (iblock < lblock) {
2307 				WARN_ON(bh->b_size != blocksize);
2308 				err = get_block(inode, iblock, bh, 0);
2309 				if (err)
2310 					SetPageError(page);
2311 			}
2312 			if (!buffer_mapped(bh)) {
2313 				zero_user(page, i * blocksize, blocksize);
2314 				if (!err)
2315 					set_buffer_uptodate(bh);
2316 				continue;
2317 			}
2318 			/*
2319 			 * get_block() might have updated the buffer
2320 			 * synchronously
2321 			 */
2322 			if (buffer_uptodate(bh))
2323 				continue;
2324 		}
2325 		arr[nr++] = bh;
2326 	} while (i++, iblock++, (bh = bh->b_this_page) != head);
2327 
2328 	if (fully_mapped)
2329 		SetPageMappedToDisk(page);
2330 
2331 	if (!nr) {
2332 		/*
2333 		 * All buffers are uptodate - we can set the page uptodate
2334 		 * as well. But not if get_block() returned an error.
2335 		 */
2336 		if (!PageError(page))
2337 			SetPageUptodate(page);
2338 		unlock_page(page);
2339 		return 0;
2340 	}
2341 
2342 	/* Stage two: lock the buffers */
2343 	for (i = 0; i < nr; i++) {
2344 		bh = arr[i];
2345 		lock_buffer(bh);
2346 		mark_buffer_async_read(bh);
2347 	}
2348 
2349 	/*
2350 	 * Stage 3: start the IO.  Check for uptodateness
2351 	 * inside the buffer lock in case another process reading
2352 	 * the underlying blockdev brought it uptodate (the sct fix).
2353 	 */
2354 	for (i = 0; i < nr; i++) {
2355 		bh = arr[i];
2356 		if (buffer_uptodate(bh))
2357 			end_buffer_async_read(bh, 1);
2358 		else
2359 			submit_bh(REQ_OP_READ, 0, bh);
2360 	}
2361 	return 0;
2362 }
2363 EXPORT_SYMBOL(block_read_full_page);
2364 
2365 /* utility function for filesystems that need to do work on expanding
2366  * truncates.  Uses filesystem pagecache writes to allow the filesystem to
2367  * deal with the hole.
2368  */
2369 int generic_cont_expand_simple(struct inode *inode, loff_t size)
2370 {
2371 	struct address_space *mapping = inode->i_mapping;
2372 	struct page *page;
2373 	void *fsdata;
2374 	int err;
2375 
2376 	err = inode_newsize_ok(inode, size);
2377 	if (err)
2378 		goto out;
2379 
2380 	err = pagecache_write_begin(NULL, mapping, size, 0,
2381 				AOP_FLAG_UNINTERRUPTIBLE|AOP_FLAG_CONT_EXPAND,
2382 				&page, &fsdata);
2383 	if (err)
2384 		goto out;
2385 
2386 	err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2387 	BUG_ON(err > 0);
2388 
2389 out:
2390 	return err;
2391 }
2392 EXPORT_SYMBOL(generic_cont_expand_simple);
2393 
2394 static int cont_expand_zero(struct file *file, struct address_space *mapping,
2395 			    loff_t pos, loff_t *bytes)
2396 {
2397 	struct inode *inode = mapping->host;
2398 	unsigned blocksize = 1 << inode->i_blkbits;
2399 	struct page *page;
2400 	void *fsdata;
2401 	pgoff_t index, curidx;
2402 	loff_t curpos;
2403 	unsigned zerofrom, offset, len;
2404 	int err = 0;
2405 
2406 	index = pos >> PAGE_SHIFT;
2407 	offset = pos & ~PAGE_MASK;
2408 
2409 	while (index > (curidx = (curpos = *bytes)>>PAGE_SHIFT)) {
2410 		zerofrom = curpos & ~PAGE_MASK;
2411 		if (zerofrom & (blocksize-1)) {
2412 			*bytes |= (blocksize-1);
2413 			(*bytes)++;
2414 		}
2415 		len = PAGE_SIZE - zerofrom;
2416 
2417 		err = pagecache_write_begin(file, mapping, curpos, len,
2418 						AOP_FLAG_UNINTERRUPTIBLE,
2419 						&page, &fsdata);
2420 		if (err)
2421 			goto out;
2422 		zero_user(page, zerofrom, len);
2423 		err = pagecache_write_end(file, mapping, curpos, len, len,
2424 						page, fsdata);
2425 		if (err < 0)
2426 			goto out;
2427 		BUG_ON(err != len);
2428 		err = 0;
2429 
2430 		balance_dirty_pages_ratelimited(mapping);
2431 
2432 		if (unlikely(fatal_signal_pending(current))) {
2433 			err = -EINTR;
2434 			goto out;
2435 		}
2436 	}
2437 
2438 	/* page covers the boundary, find the boundary offset */
2439 	if (index == curidx) {
2440 		zerofrom = curpos & ~PAGE_MASK;
2441 		/* if we will expand the thing last block will be filled */
2442 		if (offset <= zerofrom) {
2443 			goto out;
2444 		}
2445 		if (zerofrom & (blocksize-1)) {
2446 			*bytes |= (blocksize-1);
2447 			(*bytes)++;
2448 		}
2449 		len = offset - zerofrom;
2450 
2451 		err = pagecache_write_begin(file, mapping, curpos, len,
2452 						AOP_FLAG_UNINTERRUPTIBLE,
2453 						&page, &fsdata);
2454 		if (err)
2455 			goto out;
2456 		zero_user(page, zerofrom, len);
2457 		err = pagecache_write_end(file, mapping, curpos, len, len,
2458 						page, fsdata);
2459 		if (err < 0)
2460 			goto out;
2461 		BUG_ON(err != len);
2462 		err = 0;
2463 	}
2464 out:
2465 	return err;
2466 }
2467 
2468 /*
2469  * For moronic filesystems that do not allow holes in file.
2470  * We may have to extend the file.
2471  */
2472 int cont_write_begin(struct file *file, struct address_space *mapping,
2473 			loff_t pos, unsigned len, unsigned flags,
2474 			struct page **pagep, void **fsdata,
2475 			get_block_t *get_block, loff_t *bytes)
2476 {
2477 	struct inode *inode = mapping->host;
2478 	unsigned blocksize = 1 << inode->i_blkbits;
2479 	unsigned zerofrom;
2480 	int err;
2481 
2482 	err = cont_expand_zero(file, mapping, pos, bytes);
2483 	if (err)
2484 		return err;
2485 
2486 	zerofrom = *bytes & ~PAGE_MASK;
2487 	if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2488 		*bytes |= (blocksize-1);
2489 		(*bytes)++;
2490 	}
2491 
2492 	return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2493 }
2494 EXPORT_SYMBOL(cont_write_begin);
2495 
2496 int block_commit_write(struct page *page, unsigned from, unsigned to)
2497 {
2498 	struct inode *inode = page->mapping->host;
2499 	__block_commit_write(inode,page,from,to);
2500 	return 0;
2501 }
2502 EXPORT_SYMBOL(block_commit_write);
2503 
2504 /*
2505  * block_page_mkwrite() is not allowed to change the file size as it gets
2506  * called from a page fault handler when a page is first dirtied. Hence we must
2507  * be careful to check for EOF conditions here. We set the page up correctly
2508  * for a written page which means we get ENOSPC checking when writing into
2509  * holes and correct delalloc and unwritten extent mapping on filesystems that
2510  * support these features.
2511  *
2512  * We are not allowed to take the i_mutex here so we have to play games to
2513  * protect against truncate races as the page could now be beyond EOF.  Because
2514  * truncate writes the inode size before removing pages, once we have the
2515  * page lock we can determine safely if the page is beyond EOF. If it is not
2516  * beyond EOF, then the page is guaranteed safe against truncation until we
2517  * unlock the page.
2518  *
2519  * Direct callers of this function should protect against filesystem freezing
2520  * using sb_start_pagefault() - sb_end_pagefault() functions.
2521  */
2522 int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2523 			 get_block_t get_block)
2524 {
2525 	struct page *page = vmf->page;
2526 	struct inode *inode = file_inode(vma->vm_file);
2527 	unsigned long end;
2528 	loff_t size;
2529 	int ret;
2530 
2531 	lock_page(page);
2532 	size = i_size_read(inode);
2533 	if ((page->mapping != inode->i_mapping) ||
2534 	    (page_offset(page) > size)) {
2535 		/* We overload EFAULT to mean page got truncated */
2536 		ret = -EFAULT;
2537 		goto out_unlock;
2538 	}
2539 
2540 	/* page is wholly or partially inside EOF */
2541 	if (((page->index + 1) << PAGE_SHIFT) > size)
2542 		end = size & ~PAGE_MASK;
2543 	else
2544 		end = PAGE_SIZE;
2545 
2546 	ret = __block_write_begin(page, 0, end, get_block);
2547 	if (!ret)
2548 		ret = block_commit_write(page, 0, end);
2549 
2550 	if (unlikely(ret < 0))
2551 		goto out_unlock;
2552 	set_page_dirty(page);
2553 	wait_for_stable_page(page);
2554 	return 0;
2555 out_unlock:
2556 	unlock_page(page);
2557 	return ret;
2558 }
2559 EXPORT_SYMBOL(block_page_mkwrite);
2560 
2561 /*
2562  * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2563  * immediately, while under the page lock.  So it needs a special end_io
2564  * handler which does not touch the bh after unlocking it.
2565  */
2566 static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2567 {
2568 	__end_buffer_read_notouch(bh, uptodate);
2569 }
2570 
2571 /*
2572  * Attach the singly-linked list of buffers created by nobh_write_begin, to
2573  * the page (converting it to circular linked list and taking care of page
2574  * dirty races).
2575  */
2576 static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2577 {
2578 	struct buffer_head *bh;
2579 
2580 	BUG_ON(!PageLocked(page));
2581 
2582 	spin_lock(&page->mapping->private_lock);
2583 	bh = head;
2584 	do {
2585 		if (PageDirty(page))
2586 			set_buffer_dirty(bh);
2587 		if (!bh->b_this_page)
2588 			bh->b_this_page = head;
2589 		bh = bh->b_this_page;
2590 	} while (bh != head);
2591 	attach_page_buffers(page, head);
2592 	spin_unlock(&page->mapping->private_lock);
2593 }
2594 
2595 /*
2596  * On entry, the page is fully not uptodate.
2597  * On exit the page is fully uptodate in the areas outside (from,to)
2598  * The filesystem needs to handle block truncation upon failure.
2599  */
2600 int nobh_write_begin(struct address_space *mapping,
2601 			loff_t pos, unsigned len, unsigned flags,
2602 			struct page **pagep, void **fsdata,
2603 			get_block_t *get_block)
2604 {
2605 	struct inode *inode = mapping->host;
2606 	const unsigned blkbits = inode->i_blkbits;
2607 	const unsigned blocksize = 1 << blkbits;
2608 	struct buffer_head *head, *bh;
2609 	struct page *page;
2610 	pgoff_t index;
2611 	unsigned from, to;
2612 	unsigned block_in_page;
2613 	unsigned block_start, block_end;
2614 	sector_t block_in_file;
2615 	int nr_reads = 0;
2616 	int ret = 0;
2617 	int is_mapped_to_disk = 1;
2618 
2619 	index = pos >> PAGE_SHIFT;
2620 	from = pos & (PAGE_SIZE - 1);
2621 	to = from + len;
2622 
2623 	page = grab_cache_page_write_begin(mapping, index, flags);
2624 	if (!page)
2625 		return -ENOMEM;
2626 	*pagep = page;
2627 	*fsdata = NULL;
2628 
2629 	if (page_has_buffers(page)) {
2630 		ret = __block_write_begin(page, pos, len, get_block);
2631 		if (unlikely(ret))
2632 			goto out_release;
2633 		return ret;
2634 	}
2635 
2636 	if (PageMappedToDisk(page))
2637 		return 0;
2638 
2639 	/*
2640 	 * Allocate buffers so that we can keep track of state, and potentially
2641 	 * attach them to the page if an error occurs. In the common case of
2642 	 * no error, they will just be freed again without ever being attached
2643 	 * to the page (which is all OK, because we're under the page lock).
2644 	 *
2645 	 * Be careful: the buffer linked list is a NULL terminated one, rather
2646 	 * than the circular one we're used to.
2647 	 */
2648 	head = alloc_page_buffers(page, blocksize, 0);
2649 	if (!head) {
2650 		ret = -ENOMEM;
2651 		goto out_release;
2652 	}
2653 
2654 	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
2655 
2656 	/*
2657 	 * We loop across all blocks in the page, whether or not they are
2658 	 * part of the affected region.  This is so we can discover if the
2659 	 * page is fully mapped-to-disk.
2660 	 */
2661 	for (block_start = 0, block_in_page = 0, bh = head;
2662 		  block_start < PAGE_SIZE;
2663 		  block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2664 		int create;
2665 
2666 		block_end = block_start + blocksize;
2667 		bh->b_state = 0;
2668 		create = 1;
2669 		if (block_start >= to)
2670 			create = 0;
2671 		ret = get_block(inode, block_in_file + block_in_page,
2672 					bh, create);
2673 		if (ret)
2674 			goto failed;
2675 		if (!buffer_mapped(bh))
2676 			is_mapped_to_disk = 0;
2677 		if (buffer_new(bh))
2678 			clean_bdev_bh_alias(bh);
2679 		if (PageUptodate(page)) {
2680 			set_buffer_uptodate(bh);
2681 			continue;
2682 		}
2683 		if (buffer_new(bh) || !buffer_mapped(bh)) {
2684 			zero_user_segments(page, block_start, from,
2685 							to, block_end);
2686 			continue;
2687 		}
2688 		if (buffer_uptodate(bh))
2689 			continue;	/* reiserfs does this */
2690 		if (block_start < from || block_end > to) {
2691 			lock_buffer(bh);
2692 			bh->b_end_io = end_buffer_read_nobh;
2693 			submit_bh(REQ_OP_READ, 0, bh);
2694 			nr_reads++;
2695 		}
2696 	}
2697 
2698 	if (nr_reads) {
2699 		/*
2700 		 * The page is locked, so these buffers are protected from
2701 		 * any VM or truncate activity.  Hence we don't need to care
2702 		 * for the buffer_head refcounts.
2703 		 */
2704 		for (bh = head; bh; bh = bh->b_this_page) {
2705 			wait_on_buffer(bh);
2706 			if (!buffer_uptodate(bh))
2707 				ret = -EIO;
2708 		}
2709 		if (ret)
2710 			goto failed;
2711 	}
2712 
2713 	if (is_mapped_to_disk)
2714 		SetPageMappedToDisk(page);
2715 
2716 	*fsdata = head; /* to be released by nobh_write_end */
2717 
2718 	return 0;
2719 
2720 failed:
2721 	BUG_ON(!ret);
2722 	/*
2723 	 * Error recovery is a bit difficult. We need to zero out blocks that
2724 	 * were newly allocated, and dirty them to ensure they get written out.
2725 	 * Buffers need to be attached to the page at this point, otherwise
2726 	 * the handling of potential IO errors during writeout would be hard
2727 	 * (could try doing synchronous writeout, but what if that fails too?)
2728 	 */
2729 	attach_nobh_buffers(page, head);
2730 	page_zero_new_buffers(page, from, to);
2731 
2732 out_release:
2733 	unlock_page(page);
2734 	put_page(page);
2735 	*pagep = NULL;
2736 
2737 	return ret;
2738 }
2739 EXPORT_SYMBOL(nobh_write_begin);
2740 
2741 int nobh_write_end(struct file *file, struct address_space *mapping,
2742 			loff_t pos, unsigned len, unsigned copied,
2743 			struct page *page, void *fsdata)
2744 {
2745 	struct inode *inode = page->mapping->host;
2746 	struct buffer_head *head = fsdata;
2747 	struct buffer_head *bh;
2748 	BUG_ON(fsdata != NULL && page_has_buffers(page));
2749 
2750 	if (unlikely(copied < len) && head)
2751 		attach_nobh_buffers(page, head);
2752 	if (page_has_buffers(page))
2753 		return generic_write_end(file, mapping, pos, len,
2754 					copied, page, fsdata);
2755 
2756 	SetPageUptodate(page);
2757 	set_page_dirty(page);
2758 	if (pos+copied > inode->i_size) {
2759 		i_size_write(inode, pos+copied);
2760 		mark_inode_dirty(inode);
2761 	}
2762 
2763 	unlock_page(page);
2764 	put_page(page);
2765 
2766 	while (head) {
2767 		bh = head;
2768 		head = head->b_this_page;
2769 		free_buffer_head(bh);
2770 	}
2771 
2772 	return copied;
2773 }
2774 EXPORT_SYMBOL(nobh_write_end);
2775 
2776 /*
2777  * nobh_writepage() - based on block_full_write_page() except
2778  * that it tries to operate without attaching bufferheads to
2779  * the page.
2780  */
2781 int nobh_writepage(struct page *page, get_block_t *get_block,
2782 			struct writeback_control *wbc)
2783 {
2784 	struct inode * const inode = page->mapping->host;
2785 	loff_t i_size = i_size_read(inode);
2786 	const pgoff_t end_index = i_size >> PAGE_SHIFT;
2787 	unsigned offset;
2788 	int ret;
2789 
2790 	/* Is the page fully inside i_size? */
2791 	if (page->index < end_index)
2792 		goto out;
2793 
2794 	/* Is the page fully outside i_size? (truncate in progress) */
2795 	offset = i_size & (PAGE_SIZE-1);
2796 	if (page->index >= end_index+1 || !offset) {
2797 		/*
2798 		 * The page may have dirty, unmapped buffers.  For example,
2799 		 * they may have been added in ext3_writepage().  Make them
2800 		 * freeable here, so the page does not leak.
2801 		 */
2802 #if 0
2803 		/* Not really sure about this  - do we need this ? */
2804 		if (page->mapping->a_ops->invalidatepage)
2805 			page->mapping->a_ops->invalidatepage(page, offset);
2806 #endif
2807 		unlock_page(page);
2808 		return 0; /* don't care */
2809 	}
2810 
2811 	/*
2812 	 * The page straddles i_size.  It must be zeroed out on each and every
2813 	 * writepage invocation because it may be mmapped.  "A file is mapped
2814 	 * in multiples of the page size.  For a file that is not a multiple of
2815 	 * the  page size, the remaining memory is zeroed when mapped, and
2816 	 * writes to that region are not written out to the file."
2817 	 */
2818 	zero_user_segment(page, offset, PAGE_SIZE);
2819 out:
2820 	ret = mpage_writepage(page, get_block, wbc);
2821 	if (ret == -EAGAIN)
2822 		ret = __block_write_full_page(inode, page, get_block, wbc,
2823 					      end_buffer_async_write);
2824 	return ret;
2825 }
2826 EXPORT_SYMBOL(nobh_writepage);
2827 
2828 int nobh_truncate_page(struct address_space *mapping,
2829 			loff_t from, get_block_t *get_block)
2830 {
2831 	pgoff_t index = from >> PAGE_SHIFT;
2832 	unsigned offset = from & (PAGE_SIZE-1);
2833 	unsigned blocksize;
2834 	sector_t iblock;
2835 	unsigned length, pos;
2836 	struct inode *inode = mapping->host;
2837 	struct page *page;
2838 	struct buffer_head map_bh;
2839 	int err;
2840 
2841 	blocksize = 1 << inode->i_blkbits;
2842 	length = offset & (blocksize - 1);
2843 
2844 	/* Block boundary? Nothing to do */
2845 	if (!length)
2846 		return 0;
2847 
2848 	length = blocksize - length;
2849 	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2850 
2851 	page = grab_cache_page(mapping, index);
2852 	err = -ENOMEM;
2853 	if (!page)
2854 		goto out;
2855 
2856 	if (page_has_buffers(page)) {
2857 has_buffers:
2858 		unlock_page(page);
2859 		put_page(page);
2860 		return block_truncate_page(mapping, from, get_block);
2861 	}
2862 
2863 	/* Find the buffer that contains "offset" */
2864 	pos = blocksize;
2865 	while (offset >= pos) {
2866 		iblock++;
2867 		pos += blocksize;
2868 	}
2869 
2870 	map_bh.b_size = blocksize;
2871 	map_bh.b_state = 0;
2872 	err = get_block(inode, iblock, &map_bh, 0);
2873 	if (err)
2874 		goto unlock;
2875 	/* unmapped? It's a hole - nothing to do */
2876 	if (!buffer_mapped(&map_bh))
2877 		goto unlock;
2878 
2879 	/* Ok, it's mapped. Make sure it's up-to-date */
2880 	if (!PageUptodate(page)) {
2881 		err = mapping->a_ops->readpage(NULL, page);
2882 		if (err) {
2883 			put_page(page);
2884 			goto out;
2885 		}
2886 		lock_page(page);
2887 		if (!PageUptodate(page)) {
2888 			err = -EIO;
2889 			goto unlock;
2890 		}
2891 		if (page_has_buffers(page))
2892 			goto has_buffers;
2893 	}
2894 	zero_user(page, offset, length);
2895 	set_page_dirty(page);
2896 	err = 0;
2897 
2898 unlock:
2899 	unlock_page(page);
2900 	put_page(page);
2901 out:
2902 	return err;
2903 }
2904 EXPORT_SYMBOL(nobh_truncate_page);
2905 
2906 int block_truncate_page(struct address_space *mapping,
2907 			loff_t from, get_block_t *get_block)
2908 {
2909 	pgoff_t index = from >> PAGE_SHIFT;
2910 	unsigned offset = from & (PAGE_SIZE-1);
2911 	unsigned blocksize;
2912 	sector_t iblock;
2913 	unsigned length, pos;
2914 	struct inode *inode = mapping->host;
2915 	struct page *page;
2916 	struct buffer_head *bh;
2917 	int err;
2918 
2919 	blocksize = 1 << inode->i_blkbits;
2920 	length = offset & (blocksize - 1);
2921 
2922 	/* Block boundary? Nothing to do */
2923 	if (!length)
2924 		return 0;
2925 
2926 	length = blocksize - length;
2927 	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2928 
2929 	page = grab_cache_page(mapping, index);
2930 	err = -ENOMEM;
2931 	if (!page)
2932 		goto out;
2933 
2934 	if (!page_has_buffers(page))
2935 		create_empty_buffers(page, blocksize, 0);
2936 
2937 	/* Find the buffer that contains "offset" */
2938 	bh = page_buffers(page);
2939 	pos = blocksize;
2940 	while (offset >= pos) {
2941 		bh = bh->b_this_page;
2942 		iblock++;
2943 		pos += blocksize;
2944 	}
2945 
2946 	err = 0;
2947 	if (!buffer_mapped(bh)) {
2948 		WARN_ON(bh->b_size != blocksize);
2949 		err = get_block(inode, iblock, bh, 0);
2950 		if (err)
2951 			goto unlock;
2952 		/* unmapped? It's a hole - nothing to do */
2953 		if (!buffer_mapped(bh))
2954 			goto unlock;
2955 	}
2956 
2957 	/* Ok, it's mapped. Make sure it's up-to-date */
2958 	if (PageUptodate(page))
2959 		set_buffer_uptodate(bh);
2960 
2961 	if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2962 		err = -EIO;
2963 		ll_rw_block(REQ_OP_READ, 0, 1, &bh);
2964 		wait_on_buffer(bh);
2965 		/* Uhhuh. Read error. Complain and punt. */
2966 		if (!buffer_uptodate(bh))
2967 			goto unlock;
2968 	}
2969 
2970 	zero_user(page, offset, length);
2971 	mark_buffer_dirty(bh);
2972 	err = 0;
2973 
2974 unlock:
2975 	unlock_page(page);
2976 	put_page(page);
2977 out:
2978 	return err;
2979 }
2980 EXPORT_SYMBOL(block_truncate_page);
2981 
2982 /*
2983  * The generic ->writepage function for buffer-backed address_spaces
2984  */
2985 int block_write_full_page(struct page *page, get_block_t *get_block,
2986 			struct writeback_control *wbc)
2987 {
2988 	struct inode * const inode = page->mapping->host;
2989 	loff_t i_size = i_size_read(inode);
2990 	const pgoff_t end_index = i_size >> PAGE_SHIFT;
2991 	unsigned offset;
2992 
2993 	/* Is the page fully inside i_size? */
2994 	if (page->index < end_index)
2995 		return __block_write_full_page(inode, page, get_block, wbc,
2996 					       end_buffer_async_write);
2997 
2998 	/* Is the page fully outside i_size? (truncate in progress) */
2999 	offset = i_size & (PAGE_SIZE-1);
3000 	if (page->index >= end_index+1 || !offset) {
3001 		/*
3002 		 * The page may have dirty, unmapped buffers.  For example,
3003 		 * they may have been added in ext3_writepage().  Make them
3004 		 * freeable here, so the page does not leak.
3005 		 */
3006 		do_invalidatepage(page, 0, PAGE_SIZE);
3007 		unlock_page(page);
3008 		return 0; /* don't care */
3009 	}
3010 
3011 	/*
3012 	 * The page straddles i_size.  It must be zeroed out on each and every
3013 	 * writepage invocation because it may be mmapped.  "A file is mapped
3014 	 * in multiples of the page size.  For a file that is not a multiple of
3015 	 * the  page size, the remaining memory is zeroed when mapped, and
3016 	 * writes to that region are not written out to the file."
3017 	 */
3018 	zero_user_segment(page, offset, PAGE_SIZE);
3019 	return __block_write_full_page(inode, page, get_block, wbc,
3020 							end_buffer_async_write);
3021 }
3022 EXPORT_SYMBOL(block_write_full_page);
3023 
3024 sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
3025 			    get_block_t *get_block)
3026 {
3027 	struct buffer_head tmp;
3028 	struct inode *inode = mapping->host;
3029 	tmp.b_state = 0;
3030 	tmp.b_blocknr = 0;
3031 	tmp.b_size = 1 << inode->i_blkbits;
3032 	get_block(inode, block, &tmp, 0);
3033 	return tmp.b_blocknr;
3034 }
3035 EXPORT_SYMBOL(generic_block_bmap);
3036 
3037 static void end_bio_bh_io_sync(struct bio *bio)
3038 {
3039 	struct buffer_head *bh = bio->bi_private;
3040 
3041 	if (unlikely(bio_flagged(bio, BIO_QUIET)))
3042 		set_bit(BH_Quiet, &bh->b_state);
3043 
3044 	bh->b_end_io(bh, !bio->bi_error);
3045 	bio_put(bio);
3046 }
3047 
3048 /*
3049  * This allows us to do IO even on the odd last sectors
3050  * of a device, even if the block size is some multiple
3051  * of the physical sector size.
3052  *
3053  * We'll just truncate the bio to the size of the device,
3054  * and clear the end of the buffer head manually.
3055  *
3056  * Truly out-of-range accesses will turn into actual IO
3057  * errors, this only handles the "we need to be able to
3058  * do IO at the final sector" case.
3059  */
3060 void guard_bio_eod(int op, struct bio *bio)
3061 {
3062 	sector_t maxsector;
3063 	struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
3064 	unsigned truncated_bytes;
3065 
3066 	maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
3067 	if (!maxsector)
3068 		return;
3069 
3070 	/*
3071 	 * If the *whole* IO is past the end of the device,
3072 	 * let it through, and the IO layer will turn it into
3073 	 * an EIO.
3074 	 */
3075 	if (unlikely(bio->bi_iter.bi_sector >= maxsector))
3076 		return;
3077 
3078 	maxsector -= bio->bi_iter.bi_sector;
3079 	if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))
3080 		return;
3081 
3082 	/* Uhhuh. We've got a bio that straddles the device size! */
3083 	truncated_bytes = bio->bi_iter.bi_size - (maxsector << 9);
3084 
3085 	/* Truncate the bio.. */
3086 	bio->bi_iter.bi_size -= truncated_bytes;
3087 	bvec->bv_len -= truncated_bytes;
3088 
3089 	/* ..and clear the end of the buffer for reads */
3090 	if (op == REQ_OP_READ) {
3091 		zero_user(bvec->bv_page, bvec->bv_offset + bvec->bv_len,
3092 				truncated_bytes);
3093 	}
3094 }
3095 
3096 static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
3097 			 unsigned long bio_flags, struct writeback_control *wbc)
3098 {
3099 	struct bio *bio;
3100 
3101 	BUG_ON(!buffer_locked(bh));
3102 	BUG_ON(!buffer_mapped(bh));
3103 	BUG_ON(!bh->b_end_io);
3104 	BUG_ON(buffer_delay(bh));
3105 	BUG_ON(buffer_unwritten(bh));
3106 
3107 	/*
3108 	 * Only clear out a write error when rewriting
3109 	 */
3110 	if (test_set_buffer_req(bh) && (op == REQ_OP_WRITE))
3111 		clear_buffer_write_io_error(bh);
3112 
3113 	/*
3114 	 * from here on down, it's all bio -- do the initial mapping,
3115 	 * submit_bio -> generic_make_request may further map this bio around
3116 	 */
3117 	bio = bio_alloc(GFP_NOIO, 1);
3118 
3119 	if (wbc) {
3120 		wbc_init_bio(wbc, bio);
3121 		wbc_account_io(wbc, bh->b_page, bh->b_size);
3122 	}
3123 
3124 	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
3125 	bio->bi_bdev = bh->b_bdev;
3126 
3127 	bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
3128 	BUG_ON(bio->bi_iter.bi_size != bh->b_size);
3129 
3130 	bio->bi_end_io = end_bio_bh_io_sync;
3131 	bio->bi_private = bh;
3132 	bio->bi_flags |= bio_flags;
3133 
3134 	/* Take care of bh's that straddle the end of the device */
3135 	guard_bio_eod(op, bio);
3136 
3137 	if (buffer_meta(bh))
3138 		op_flags |= REQ_META;
3139 	if (buffer_prio(bh))
3140 		op_flags |= REQ_PRIO;
3141 	bio_set_op_attrs(bio, op, op_flags);
3142 
3143 	submit_bio(bio);
3144 	return 0;
3145 }
3146 
3147 int _submit_bh(int op, int op_flags, struct buffer_head *bh,
3148 	       unsigned long bio_flags)
3149 {
3150 	return submit_bh_wbc(op, op_flags, bh, bio_flags, NULL);
3151 }
3152 EXPORT_SYMBOL_GPL(_submit_bh);
3153 
3154 int submit_bh(int op, int op_flags,  struct buffer_head *bh)
3155 {
3156 	return submit_bh_wbc(op, op_flags, bh, 0, NULL);
3157 }
3158 EXPORT_SYMBOL(submit_bh);
3159 
3160 /**
3161  * ll_rw_block: low-level access to block devices (DEPRECATED)
3162  * @op: whether to %READ or %WRITE
3163  * @op_flags: req_flag_bits
3164  * @nr: number of &struct buffer_heads in the array
3165  * @bhs: array of pointers to &struct buffer_head
3166  *
3167  * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3168  * requests an I/O operation on them, either a %REQ_OP_READ or a %REQ_OP_WRITE.
3169  * @op_flags contains flags modifying the detailed I/O behavior, most notably
3170  * %REQ_RAHEAD.
3171  *
3172  * This function drops any buffer that it cannot get a lock on (with the
3173  * BH_Lock state bit), any buffer that appears to be clean when doing a write
3174  * request, and any buffer that appears to be up-to-date when doing read
3175  * request.  Further it marks as clean buffers that are processed for
3176  * writing (the buffer cache won't assume that they are actually clean
3177  * until the buffer gets unlocked).
3178  *
3179  * ll_rw_block sets b_end_io to simple completion handler that marks
3180  * the buffer up-to-date (if appropriate), unlocks the buffer and wakes
3181  * any waiters.
3182  *
3183  * All of the buffers must be for the same device, and must also be a
3184  * multiple of the current approved size for the device.
3185  */
3186 void ll_rw_block(int op, int op_flags,  int nr, struct buffer_head *bhs[])
3187 {
3188 	int i;
3189 
3190 	for (i = 0; i < nr; i++) {
3191 		struct buffer_head *bh = bhs[i];
3192 
3193 		if (!trylock_buffer(bh))
3194 			continue;
3195 		if (op == WRITE) {
3196 			if (test_clear_buffer_dirty(bh)) {
3197 				bh->b_end_io = end_buffer_write_sync;
3198 				get_bh(bh);
3199 				submit_bh(op, op_flags, bh);
3200 				continue;
3201 			}
3202 		} else {
3203 			if (!buffer_uptodate(bh)) {
3204 				bh->b_end_io = end_buffer_read_sync;
3205 				get_bh(bh);
3206 				submit_bh(op, op_flags, bh);
3207 				continue;
3208 			}
3209 		}
3210 		unlock_buffer(bh);
3211 	}
3212 }
3213 EXPORT_SYMBOL(ll_rw_block);
3214 
3215 void write_dirty_buffer(struct buffer_head *bh, int op_flags)
3216 {
3217 	lock_buffer(bh);
3218 	if (!test_clear_buffer_dirty(bh)) {
3219 		unlock_buffer(bh);
3220 		return;
3221 	}
3222 	bh->b_end_io = end_buffer_write_sync;
3223 	get_bh(bh);
3224 	submit_bh(REQ_OP_WRITE, op_flags, bh);
3225 }
3226 EXPORT_SYMBOL(write_dirty_buffer);
3227 
3228 /*
3229  * For a data-integrity writeout, we need to wait upon any in-progress I/O
3230  * and then start new I/O and then wait upon it.  The caller must have a ref on
3231  * the buffer_head.
3232  */
3233 int __sync_dirty_buffer(struct buffer_head *bh, int op_flags)
3234 {
3235 	int ret = 0;
3236 
3237 	WARN_ON(atomic_read(&bh->b_count) < 1);
3238 	lock_buffer(bh);
3239 	if (test_clear_buffer_dirty(bh)) {
3240 		get_bh(bh);
3241 		bh->b_end_io = end_buffer_write_sync;
3242 		ret = submit_bh(REQ_OP_WRITE, op_flags, bh);
3243 		wait_on_buffer(bh);
3244 		if (!ret && !buffer_uptodate(bh))
3245 			ret = -EIO;
3246 	} else {
3247 		unlock_buffer(bh);
3248 	}
3249 	return ret;
3250 }
3251 EXPORT_SYMBOL(__sync_dirty_buffer);
3252 
3253 int sync_dirty_buffer(struct buffer_head *bh)
3254 {
3255 	return __sync_dirty_buffer(bh, REQ_SYNC);
3256 }
3257 EXPORT_SYMBOL(sync_dirty_buffer);
3258 
3259 /*
3260  * try_to_free_buffers() checks if all the buffers on this particular page
3261  * are unused, and releases them if so.
3262  *
3263  * Exclusion against try_to_free_buffers may be obtained by either
3264  * locking the page or by holding its mapping's private_lock.
3265  *
3266  * If the page is dirty but all the buffers are clean then we need to
3267  * be sure to mark the page clean as well.  This is because the page
3268  * may be against a block device, and a later reattachment of buffers
3269  * to a dirty page will set *all* buffers dirty.  Which would corrupt
3270  * filesystem data on the same device.
3271  *
3272  * The same applies to regular filesystem pages: if all the buffers are
3273  * clean then we set the page clean and proceed.  To do that, we require
3274  * total exclusion from __set_page_dirty_buffers().  That is obtained with
3275  * private_lock.
3276  *
3277  * try_to_free_buffers() is non-blocking.
3278  */
3279 static inline int buffer_busy(struct buffer_head *bh)
3280 {
3281 	return atomic_read(&bh->b_count) |
3282 		(bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3283 }
3284 
3285 static int
3286 drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
3287 {
3288 	struct buffer_head *head = page_buffers(page);
3289 	struct buffer_head *bh;
3290 
3291 	bh = head;
3292 	do {
3293 		if (buffer_write_io_error(bh) && page->mapping)
3294 			mapping_set_error(page->mapping, -EIO);
3295 		if (buffer_busy(bh))
3296 			goto failed;
3297 		bh = bh->b_this_page;
3298 	} while (bh != head);
3299 
3300 	do {
3301 		struct buffer_head *next = bh->b_this_page;
3302 
3303 		if (bh->b_assoc_map)
3304 			__remove_assoc_queue(bh);
3305 		bh = next;
3306 	} while (bh != head);
3307 	*buffers_to_free = head;
3308 	__clear_page_buffers(page);
3309 	return 1;
3310 failed:
3311 	return 0;
3312 }
3313 
3314 int try_to_free_buffers(struct page *page)
3315 {
3316 	struct address_space * const mapping = page->mapping;
3317 	struct buffer_head *buffers_to_free = NULL;
3318 	int ret = 0;
3319 
3320 	BUG_ON(!PageLocked(page));
3321 	if (PageWriteback(page))
3322 		return 0;
3323 
3324 	if (mapping == NULL) {		/* can this still happen? */
3325 		ret = drop_buffers(page, &buffers_to_free);
3326 		goto out;
3327 	}
3328 
3329 	spin_lock(&mapping->private_lock);
3330 	ret = drop_buffers(page, &buffers_to_free);
3331 
3332 	/*
3333 	 * If the filesystem writes its buffers by hand (eg ext3)
3334 	 * then we can have clean buffers against a dirty page.  We
3335 	 * clean the page here; otherwise the VM will never notice
3336 	 * that the filesystem did any IO at all.
3337 	 *
3338 	 * Also, during truncate, discard_buffer will have marked all
3339 	 * the page's buffers clean.  We discover that here and clean
3340 	 * the page also.
3341 	 *
3342 	 * private_lock must be held over this entire operation in order
3343 	 * to synchronise against __set_page_dirty_buffers and prevent the
3344 	 * dirty bit from being lost.
3345 	 */
3346 	if (ret)
3347 		cancel_dirty_page(page);
3348 	spin_unlock(&mapping->private_lock);
3349 out:
3350 	if (buffers_to_free) {
3351 		struct buffer_head *bh = buffers_to_free;
3352 
3353 		do {
3354 			struct buffer_head *next = bh->b_this_page;
3355 			free_buffer_head(bh);
3356 			bh = next;
3357 		} while (bh != buffers_to_free);
3358 	}
3359 	return ret;
3360 }
3361 EXPORT_SYMBOL(try_to_free_buffers);
3362 
3363 /*
3364  * There are no bdflush tunables left.  But distributions are
3365  * still running obsolete flush daemons, so we terminate them here.
3366  *
3367  * Use of bdflush() is deprecated and will be removed in a future kernel.
3368  * The `flush-X' kernel threads fully replace bdflush daemons and this call.
3369  */
3370 SYSCALL_DEFINE2(bdflush, int, func, long, data)
3371 {
3372 	static int msg_count;
3373 
3374 	if (!capable(CAP_SYS_ADMIN))
3375 		return -EPERM;
3376 
3377 	if (msg_count < 5) {
3378 		msg_count++;
3379 		printk(KERN_INFO
3380 			"warning: process `%s' used the obsolete bdflush"
3381 			" system call\n", current->comm);
3382 		printk(KERN_INFO "Fix your initscripts?\n");
3383 	}
3384 
3385 	if (func == 1)
3386 		do_exit(0);
3387 	return 0;
3388 }
3389 
3390 /*
3391  * Buffer-head allocation
3392  */
3393 static struct kmem_cache *bh_cachep __read_mostly;
3394 
3395 /*
3396  * Once the number of bh's in the machine exceeds this level, we start
3397  * stripping them in writeback.
3398  */
3399 static unsigned long max_buffer_heads;
3400 
3401 int buffer_heads_over_limit;
3402 
3403 struct bh_accounting {
3404 	int nr;			/* Number of live bh's */
3405 	int ratelimit;		/* Limit cacheline bouncing */
3406 };
3407 
3408 static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3409 
3410 static void recalc_bh_state(void)
3411 {
3412 	int i;
3413 	int tot = 0;
3414 
3415 	if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3416 		return;
3417 	__this_cpu_write(bh_accounting.ratelimit, 0);
3418 	for_each_online_cpu(i)
3419 		tot += per_cpu(bh_accounting, i).nr;
3420 	buffer_heads_over_limit = (tot > max_buffer_heads);
3421 }
3422 
3423 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3424 {
3425 	struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3426 	if (ret) {
3427 		INIT_LIST_HEAD(&ret->b_assoc_buffers);
3428 		preempt_disable();
3429 		__this_cpu_inc(bh_accounting.nr);
3430 		recalc_bh_state();
3431 		preempt_enable();
3432 	}
3433 	return ret;
3434 }
3435 EXPORT_SYMBOL(alloc_buffer_head);
3436 
3437 void free_buffer_head(struct buffer_head *bh)
3438 {
3439 	BUG_ON(!list_empty(&bh->b_assoc_buffers));
3440 	kmem_cache_free(bh_cachep, bh);
3441 	preempt_disable();
3442 	__this_cpu_dec(bh_accounting.nr);
3443 	recalc_bh_state();
3444 	preempt_enable();
3445 }
3446 EXPORT_SYMBOL(free_buffer_head);
3447 
3448 static int buffer_exit_cpu_dead(unsigned int cpu)
3449 {
3450 	int i;
3451 	struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3452 
3453 	for (i = 0; i < BH_LRU_SIZE; i++) {
3454 		brelse(b->bhs[i]);
3455 		b->bhs[i] = NULL;
3456 	}
3457 	this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3458 	per_cpu(bh_accounting, cpu).nr = 0;
3459 	return 0;
3460 }
3461 
3462 /**
3463  * bh_uptodate_or_lock - Test whether the buffer is uptodate
3464  * @bh: struct buffer_head
3465  *
3466  * Return true if the buffer is up-to-date and false,
3467  * with the buffer locked, if not.
3468  */
3469 int bh_uptodate_or_lock(struct buffer_head *bh)
3470 {
3471 	if (!buffer_uptodate(bh)) {
3472 		lock_buffer(bh);
3473 		if (!buffer_uptodate(bh))
3474 			return 0;
3475 		unlock_buffer(bh);
3476 	}
3477 	return 1;
3478 }
3479 EXPORT_SYMBOL(bh_uptodate_or_lock);
3480 
3481 /**
3482  * bh_submit_read - Submit a locked buffer for reading
3483  * @bh: struct buffer_head
3484  *
3485  * Returns zero on success and -EIO on error.
3486  */
3487 int bh_submit_read(struct buffer_head *bh)
3488 {
3489 	BUG_ON(!buffer_locked(bh));
3490 
3491 	if (buffer_uptodate(bh)) {
3492 		unlock_buffer(bh);
3493 		return 0;
3494 	}
3495 
3496 	get_bh(bh);
3497 	bh->b_end_io = end_buffer_read_sync;
3498 	submit_bh(REQ_OP_READ, 0, bh);
3499 	wait_on_buffer(bh);
3500 	if (buffer_uptodate(bh))
3501 		return 0;
3502 	return -EIO;
3503 }
3504 EXPORT_SYMBOL(bh_submit_read);
3505 
3506 void __init buffer_init(void)
3507 {
3508 	unsigned long nrpages;
3509 	int ret;
3510 
3511 	bh_cachep = kmem_cache_create("buffer_head",
3512 			sizeof(struct buffer_head), 0,
3513 				(SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3514 				SLAB_MEM_SPREAD),
3515 				NULL);
3516 
3517 	/*
3518 	 * Limit the bh occupancy to 10% of ZONE_NORMAL
3519 	 */
3520 	nrpages = (nr_free_buffer_pages() * 10) / 100;
3521 	max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3522 	ret = cpuhp_setup_state_nocalls(CPUHP_FS_BUFF_DEAD, "fs/buffer:dead",
3523 					NULL, buffer_exit_cpu_dead);
3524 	WARN_ON(ret < 0);
3525 }
3526