summaryrefslogtreecommitdiffstats
path: root/fs/fs-writeback.c
blob: 271e5f44e8715c852b87620b73980c6cefe741fb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
/*
 * fs/fs-writeback.c
 *
 * Copyright (C) 2002, Linus Torvalds.
 *
 * Contains all the functions related to writing back and waiting
 * upon dirty inodes against superblocks, and writing back dirty
 * pages against inodes.  ie: data writeback.  Writeout of the
 * inode itself is not handled here.
 *
 * 10Apr2002	Andrew Morton
 *		Split out of fs/inode.c
 *		Additions for address_space-based writeback
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/buffer_head.h>
#include "internal.h"


/**
 * writeback_acquire - attempt to get exclusive writeback access to a device
 * @bdi: the device's backing_dev_info structure
 *
 * It is a waste of resources to have more than one pdflush thread blocked on
 * a single request queue.  Exclusion at the request_queue level is obtained
 * via a flag in the request_queue's backing_dev_info.state.
 *
 * Non-request_queue-backed address_spaces will share default_backing_dev_info,
 * unless they implement their own.  Which is somewhat inefficient, as this
 * may prevent concurrent writeback against multiple devices.
 */
static int writeback_acquire(struct backing_dev_info *bdi)
{
	return !test_and_set_bit(BDI_pdflush, &bdi->state);
}

/**
 * writeback_in_progress - determine whether there is writeback in progress
 * @bdi: the device's backing_dev_info structure.
 *
 * Determine whether there is writeback in progress against a backing device.
 */
int writeback_in_progress(struct backing_dev_info *bdi)
{
	return test_bit(BDI_pdflush, &bdi->state);
}

/**
 * writeback_release - relinquish exclusive writeback access against a device.
 * @bdi: the device's backing_dev_info structure
 */
static void writeback_release(struct backing_dev_info *bdi)
{
	BUG_ON(!writeback_in_progress(bdi));
	clear_bit(BDI_pdflush, &bdi->state);
}

static noinline void block_dump___mark_inode_dirty(struct inode *inode)
{
	if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
		struct dentry *dentry;
		const char *name = "?";

		dentry = d_find_alias(inode);
		if (dentry) {
			spin_lock(&dentry->d_lock);
			name = (const char *) dentry->d_name.name;
		}
		printk(KERN_DEBUG
		       "%s(%d): dirtied inode %lu (%s) on %s\n",
		       current->comm, task_pid_nr(current), inode->i_ino,
		       name, inode->i_sb->s_id);
		if (dentry) {
			spin_unlock(&dentry->d_lock);
			dput(dentry);
		}
	}
}

/**
 *	__mark_inode_dirty -	internal function
 *	@inode: inode to mark
 *	@flags: what kind of dirty (i.e. I_DIRTY_SYNC)
 *	Mark an inode as dirty. Callers should use mark_inode_dirty or
 *  	mark_inode_dirty_sync.
 *
 * Put the inode on the super block's dirty list.
 *
 * CAREFUL! We mark it dirty unconditionally, but move it onto the
 * dirty list only if it is hashed or if it refers to a blockdev.
 * If it was not hashed, it will never be added to the dirty list
 * even if it is later hashed, as it will have been marked dirty already.
 *
 * In short, make sure you hash any inodes _before_ you start marking
 * them dirty.
 *
 * This function *must* be atomic for the I_DIRTY_PAGES case -
 * set_page_dirty() is called under spinlock in several places.
 *
 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
 * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
 * the kernel-internal blockdev inode represents the dirtying time of the
 * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
 * page->mapping->host, so the page-dirtying time is recorded in the internal
 * blockdev inode.
 */
void __mark_inode_dirty(struct inode *inode, int flags)
{
	struct super_block *sb = inode->i_sb;

	/*
	 * Don't do this for I_DIRTY_PAGES - that doesn't actually
	 * dirty the inode itself
	 */
	if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
		if (sb->s_op->dirty_inode)
			sb->s_op->dirty_inode(inode);
	}

	/*
	 * make sure that changes are seen by all cpus before we test i_state
	 * -- mikulas
	 */
	smp_mb();

	/* avoid the locking if we can */
	if ((inode->i_state & flags) == flags)
		return;

	if (unlikely(block_dump))
		block_dump___mark_inode_dirty(inode);

	spin_lock(&inode_lock);
	if ((inode->i_state & flags) != flags) {
		const int was_dirty = inode->i_state & I_DIRTY;

		inode->i_state |= flags;

		/*
		 * If the inode is being synced, just update its dirty state.
		 * The unlocker will place the inode on the appropriate
		 * superblock list, based upon its state.
		 */
		if (inode->i_state & I_SYNC)
			goto out;

		/*
		 * Only add valid (hashed) inodes to the superblock's
		 * dirty list.  Add blockdev inodes as well.
		 */
		if (!S_ISBLK(inode->i_mode)) {
			if (hlist_unhashed(&inode->i_hash))
				goto out;
		}
		if (inode->i_state & (I_FREEING|I_CLEAR))
			goto out;

		/*
		 * If the inode was already on s_dirty/s_io/s_more_io, don't
		 * reposition it (that would break s_dirty time-ordering).
		 */
		if (!was_dirty) {
			inode->dirtied_when = jiffies;
			list_move(&inode->i_list, &sb->s_dirty);
		}
	}
out:
	spin_unlock(&inode_lock);
}

EXPORT_SYMBOL(__mark_inode_dirty);

static int write_inode(struct inode *inode, int sync)
{
	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
		return inode->i_sb->s_op->write_inode(inode, sync);
	return 0;
}

/*
 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
 * furthest end of its superblock's dirty-inode list.
 *
 * Before stamping the inode's ->dirtied_when, we check to see whether it is
 * already the most-recently-dirtied inode on the s_dirty list.  If that is
 * the case then the inode must have been redirtied while it was being written
 * out and we don't reset its dirtied_when.
 */
static void redirty_tail(struct inode *inode)
{
	struct super_block *sb = inode->i_sb;

	if (!list_empty(&sb->s_dirty)) {
		struct inode *tail_inode;

		tail_inode = list_entry(sb->s_dirty.next, struct inode, i_list);
		if (time_before(inode->dirtied_when,
				tail_inode->dirtied_when))
			inode->dirtied_when = jiffies;
	}
	list_move(&inode->i_list, &sb->s_dirty);
}

/*
 * requeue inode for re-scanning after sb->s_io list is exhausted.
 */
static void requeue_io(struct inode *inode)
{
	list_move(&inode->i_list, &inode->i_sb->s_more_io);
}

static void inode_sync_complete(struct inode *inode)
{
	/*
	 * Prevent speculative execution through spin_unlock(&inode_lock);
	 */
	smp_mb();
	wake_up_bit(&inode->i_state, __I_SYNC);
}

static bool inode_dirtied_after(struct inode *inode, unsigned long t)
{
	bool ret = time_after(inode->dirtied_when, t);
#ifndef CONFIG_64BIT
	/*
	 * For inodes being constantly redirtied, dirtied_when can get stuck.
	 * It _appears_ to be in the future, but is actually in distant past.
	 * This test is necessary to prevent such wrapped-around relative times
	 * from permanently stopping the whole pdflush writeback.
	 */
	ret = ret && time_before_eq(inode->dirtied_when, jiffies);
#endif
	return ret;
}

/*
 * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
 */
static void move_expired_inodes(struct list_head *delaying_queue,
			       struct list_head *dispatch_queue,
				unsigned long *older_than_this)
{
	while (!list_empty(delaying_queue)) {
		struct inode *inode = list_entry(delaying_queue->prev,
						struct inode, i_list);
		if (older_than_this &&
		    inode_dirtied_after(inode, *older_than_this))
			break;
		list_move(&inode->i_list, dispatch_queue);
	}
}

/*
 * Queue all expired dirty inodes for io, eldest first.
 */
static void queue_io(struct super_block *sb,
				unsigned long *older_than_this)
{
	list_splice_init(&sb->s_more_io, sb->s_io.prev);
	move_expired_inodes(&sb->s_dirty, &sb->s_io, older_than_this);
}

int sb_has_dirty_inodes(struct super_block *sb)
{
	return !list_empty(&sb->s_dirty) ||
	       !list_empty(&sb->s_io) ||
	       !list_empty(&sb->s_more_io);
}
EXPORT_SYMBOL(sb_has_dirty_inodes);

/*
 * Wait for writeback on an inode to complete.
 */
static void inode_wait_for_writeback(struct inode *inode)
{
	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
	wait_queue_head_t *wqh;

	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
	do {
		spin_unlock(&inode_lock);
		__wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
		spin_lock(&inode_lock);
	} while (inode->i_state & I_SYNC);
}

/*
 * Write out an inode's dirty pages.  Called under inode_lock.  Either the
 * caller has ref on the inode (either via __iget or via syscall against an fd)
 * or the inode has I_WILL_FREE set (via generic_forget_inode)
 *
 * If `wait' is set, wait on the writeout.
 *
 * The whole writeout design is quite complex and fragile.  We want to avoid
 * starvation of particular inodes when others are being redirtied, prevent
 * livelocks, etc.
 *
 * Called under inode_lock.
 */
static int
writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
{
	struct address_space *mapping = inode->i_mapping;
	int wait = wbc->sync_mode == WB_SYNC_ALL;
	unsigned dirty;
	int ret;

	if (!atomic_read(&inode->i_count))
		WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
	else
		WARN_ON(inode->i_state & I_WILL_FREE);

	if (inode->i_state & I_SYNC) {
		/*
		 * If this inode is locked for writeback and we are not doing
		 * writeback-for-data-integrity, move it to s_more_io so that
		 * writeback can proceed with the other inodes on s_io.
		 *
		 * We'll have another go at writing back this inode when we
		 * completed a full scan of s_io.
		 */
		if (!wait) {
			requeue_io(inode);
			return 0;
		}

		/*
		 * It's a data-integrity sync.  We must wait.
		 */
		inode_wait_for_writeback(inode);
	}

	BUG_ON(inode->i_state & I_SYNC);

	/* Set I_SYNC, reset I_DIRTY */
	dirty = inode->i_state & I_DIRTY;
	inode->i_state |= I_SYNC;
	inode->i_state &= ~I_DIRTY;

	spin_unlock(&inode_lock);

	ret = do_writepages(mapping, wbc);

	/* Don't write the inode if only I_DIRTY_PAGES was set */
	if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
		int err = write_inode(inode, wait);
		if (ret == 0)
			ret = err;
	}

	if (wait) {
		int err = filemap_fdatawait(mapping);
		if (ret == 0)
			ret = err;
	}

	spin_lock(&inode_lock);
	inode->i_state &= ~I_SYNC;
	if (!(inode->i_state & (I_FREEING | I_CLEAR))) {
		if (!(inode->i_state & I_DIRTY) &&
		    mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
			/*
			 * We didn't write back all the pages.  nfs_writepages()
			 * sometimes bales out without doing anything. Redirty
			 * the inode; Move it from s_io onto s_more_io/s_dirty.
			 */
			/*
			 * akpm: if the caller was the kupdate function we put
			 * this inode at the head of s_dirty so it gets first
			 * consideration.  Otherwise, move it to the tail, for
			 * the reasons described there.  I'm not really sure
			 * how much sense this makes.  Presumably I had a good
			 * reasons for doing it this way, and I'd rather not
			 * muck with it at present.
			 */
			if (wbc->for_kupdate) {
				/*
				 * For the kupdate function we move the inode
				 * to s_more_io so it will get more writeout as
				 * soon as the queue becomes uncongested.
				 */
				inode->i_state |= I_DIRTY_PAGES;
				if (wbc->nr_to_write <= 0) {
					/*
					 * slice used up: queue for next turn
					 */
					requeue_io(inode);
				} else {
					/*
					 * somehow blocked: retry later
					 */
					redirty_tail(inode);
				}
			} else {
				/*
				 * Otherwise fully redirty the inode so that
				 * other inodes on this superblock will get some
				 * writeout.  Otherwise heavy writing to one
				 * file would indefinitely suspend writeout of
				 * all the other files.
				 */
				inode->i_state |= I_DIRTY_PAGES;
				redirty_tail(inode);
			}
		} else if (inode->i_state & I_DIRTY) {
			/*
			 * Someone redirtied the inode while were writing back
			 * the pages.
			 */
			redirty_tail(inode);
		} else if (atomic_read(&inode->i_count)) {
			/*
			 * The inode is clean, inuse
			 */
			list_move(&inode->i_list, &inode_in_use);
		} else {
			/*
			 * The inode is clean, unused
			 */
			list_move(&inode->i_list, &inode_unused);
		}
	}
	inode_sync_complete(inode);
	return ret;
}

/*
 * Write out a superblock's list of dirty inodes.  A wait will be performed
 * upon no inodes, all inodes or the final one, depending upon sync_mode.
 *
 * If older_than_this is non-NULL, then only write out inodes which
 * had their first dirtying at a time earlier than *older_than_this.
 *
 * If we're a pdflush thread, then implement pdflush collision avoidance
 * against the entire list.
 *
 * If `bdi' is non-zero then we're being asked to writeback a specific queue.
 * This function assumes that the blockdev superblock's inodes are backed by
 * a variety of queues, so all inodes are searched.  For other superblocks,
 * assume that all inodes are backed by the same queue.
 *
 * FIXME: this linear search could get expensive with many fileystems.  But
 * how to fix?  We need to go from an address_space to all inodes which share
 * a queue with that address_space.  (Easy: have a global "dirty superblocks"
 * list).
 *
 * The inodes to be written are parked on sb->s_io.  They are moved back onto
 * sb->s_dirty as they are selected for writing.  This way, none can be missed
 * on the writer throttling path, and we get decent balancing between many
 * throttled threads: we don't want them all piling up on inode_sync_wait.
 */
static void generic_sync_sb_inodes(struct super_block *sb,
				   struct writeback_control *wbc)
{
	const unsigned long start = jiffies;	/* livelock avoidance */
	int sync = wbc->sync_mode == WB_SYNC_ALL;

	spin_lock(&inode_lock);
	if (!wbc->for_kupdate || list_empty(&sb->s_io))
		queue_io(sb, wbc->older_than_this);

	while (!list_empty(&sb->s_io)) {
		struct inode *inode = list_entry(sb->s_io.prev,
						struct inode, i_list);
		struct address_space *mapping = inode->i_mapping;
		struct backing_dev_info *bdi = mapping->backing_dev_info;
		long pages_skipped;

		if (!bdi_cap_writeback_dirty(bdi)) {
			redirty_tail(inode);
			if (sb_is_blkdev_sb(sb)) {
				/*
				 * Dirty memory-backed blockdev: the ramdisk
				 * driver does this.  Skip just this inode
				 */
				continue;
			}
			/*
			 * Dirty memory-backed inode against a filesystem other
			 * than the kernel-internal bdev filesystem.  Skip the
			 * entire superblock.
			 */
			break;
		}

		if (inode->i_state & (I_NEW | I_WILL_FREE)) {
			requeue_io(inode);
			continue;
		}

		if (wbc->nonblocking && bdi_write_congested(bdi)) {
			wbc->encountered_congestion = 1;
			if (!sb_is_blkdev_sb(sb))
				break;		/* Skip a congested fs */
			requeue_io(inode);
			continue;		/* Skip a congested blockdev */
		}

		if (wbc->bdi && bdi != wbc->bdi) {
			if (!sb_is_blkdev_sb(sb))
				break;		/* fs has the wrong queue */
			requeue_io(inode);
			continue;		/* blockdev has wrong queue */
		}

		/*
		 * Was this inode dirtied after sync_sb_inodes was called?
		 * This keeps sync from extra jobs and livelock.
		 */
		if (inode_dirtied_after(inode, start))
			break;

		/* Is another pdflush already flushing this queue? */
		if (current_is_pdflush() && !writeback_acquire(bdi))
			break;

		BUG_ON(inode->i_state & (I_FREEING | I_CLEAR));
		__iget(inode);
		pages_skipped = wbc->pages_skipped;
		writeback_single_inode(inode, wbc);
		if (current_is_pdflush())
			writeback_release(bdi);
		if (wbc->pages_skipped != pages_skipped) {
			/*
			 * writeback is not making progress due to locked
			 * buffers.  Skip this inode for now.
			 */
			redirty_tail(inode);
		}
		spin_unlock(&inode_lock);
		iput(inode);
		cond_resched();
		spin_lock(&inode_lock);
		if (wbc->nr_to_write <= 0) {
			wbc->more_io = 1;
			break;
		}
		if (!list_empty(&sb->s_more_io))
			wbc->more_io = 1;
	}

	if (sync) {
		struct inode *inode, *old_inode = NULL;

		/*
		 * Data integrity sync. Must wait for all pages under writeback,
		 * because there may have been pages dirtied before our sync
		 * call, but which had writeout started before we write it out.
		 * In which case, the inode may not be on the dirty list, but
		 * we still have to wait for that writeout.
		 */
		list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
			struct address_space *mapping;

			if (inode->i_state &
					(I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
				continue;
			mapping = inode->i_mapping;
			if (mapping->nrpages == 0)
				continue;
			__iget(inode);
			spin_unlock(&inode_lock);
			/*
			 * We hold a reference to 'inode' so it couldn't have
			 * been removed from s_inodes list while we dropped the
			 * inode_lock.  We cannot iput the inode now as we can
			 * be holding the last reference and we cannot iput it
			 * under inode_lock. So we keep the reference and iput
			 * it later.
			 */
			iput(old_inode);
			old_inode = inode;

			filemap_fdatawait(mapping);

			cond_resched();

			spin_lock(&inode_lock);
		}
		spin_unlock(&inode_lock);
		iput(old_inode);
	} else
		spin_unlock(&inode_lock);

	return;		/* Leave any unwritten inodes on s_io */
}

/*
 * Start writeback of dirty pagecache data against all unlocked inodes.
 *
 * Note:
 * We don't need to grab a reference to superblock here. If it has non-empty
 * ->s_dirty it's hadn't been killed yet and kill_super() won't proceed
 * past sync_inodes_sb() until the ->s_dirty/s_io/s_more_io lists are all
 * empty. Since __sync_single_inode() regains inode_lock before it finally moves
 * inode from superblock lists we are OK.
 *
 * If `older_than_this' is non-zero then only flush inodes which have a
 * flushtime older than *older_than_this.
 *
 * If `bdi' is non-zero then we will scan the first inode against each
 * superblock until we find the matching ones.  One group will be the dirty
 * inodes against a filesystem.  Then when we hit the dummy blockdev superblock,
 * sync_sb_inodes will seekout the blockdev which matches `bdi'.  Maybe not
 * super-efficient but we're about to do a ton of I/O...
 */
void
writeback_inodes(struct writeback_control *wbc)
{
	struct super_block *sb;

	might_sleep();
	spin_lock(&sb_lock);
restart:
	list_for_each_entry_reverse(sb, &super_blocks, s_list) {
		if (sb_has_dirty_inodes(sb)) {
			/* we're making our own get_super here */
			sb->s_count++;
			spin_unlock(&sb_lock);
			/*
			 * If we can't get the readlock, there's no sense in
			 * waiting around, most of the time the FS is going to
			 * be unmounted by the time it is released.
			 */
			if (down_read_trylock(&sb->s_umount)) {
				if (sb->s_root)
					generic_sync_sb_inodes(sb, wbc);
				up_read(&sb->s_umount);
			}
			spin_lock(&sb_lock);
			if (__put_super_and_need_restart(sb))
				goto restart;
		}
		if (wbc->nr_to_write <= 0)
			break;
	}
	spin_unlock(&sb_lock);
}

/**
 * writeback_inodes_sb	-	writeback dirty inodes from given super_block
 * @sb: the superblock
 *
 * Start writeback on some inodes on this super_block. No guarantees are made
 * on how many (if any) will be written, and this function does not wait
 * for IO completion of submitted IO. The number of pages submitted is
 * returned.
 */
long writeback_inodes_sb(struct super_block *sb)
{
	struct writeback_control wbc = {
		.sync_mode	= WB_SYNC_NONE,
		.range_start	= 0,
		.range_end	= LLONG_MAX,
	};
	unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
	long nr_to_write;

	nr_to_write = nr_dirty + nr_unstable +
			(inodes_stat.nr_inodes - inodes_stat.nr_unused);

	wbc.nr_to_write = nr_to_write;
	generic_sync_sb_inodes(sb, &wbc);
	return nr_to_write - wbc.nr_to_write;
}
EXPORT_SYMBOL(writeback_inodes_sb);

/**
 * sync_inodes_sb	-	sync sb inode pages
 * @sb: the superblock
 *
 * This function writes and waits on any dirty inode belonging to this
 * super_block. The number of pages synced is returned.
 */
long sync_inodes_sb(struct super_block *sb)
{
	struct writeback_control wbc = {
		.sync_mode	= WB_SYNC_ALL,
		.range_start	= 0,
		.range_end	= LLONG_MAX,
	};
	long nr_to_write = LONG_MAX; /* doesn't actually matter */

	wbc.nr_to_write = nr_to_write;
	generic_sync_sb_inodes(sb, &wbc);
	return nr_to_write - wbc.nr_to_write;
}
EXPORT_SYMBOL(sync_inodes_sb);

/**
 * write_inode_now	-	write an inode to disk
 * @inode: inode to write to disk
 * @sync: whether the write should be synchronous or not
 *
 * This function commits an inode to disk immediately if it is dirty. This is
 * primarily needed by knfsd.
 *
 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
 */
int write_inode_now(struct inode *inode, int sync)
{
	int ret;
	struct writeback_control wbc = {
		.nr_to_write = LONG_MAX,
		.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
		.range_start = 0,
		.range_end = LLONG_MAX,
	};

	if (!mapping_cap_writeback_dirty(inode->i_mapping))
		wbc.nr_to_write = 0;

	might_sleep();
	spin_lock(&inode_lock);
	ret = writeback_single_inode(inode, &wbc);
	spin_unlock(&inode_lock);
	if (sync)
		inode_sync_wait(inode);
	return ret;
}
EXPORT_SYMBOL(write_inode_now);

/**
 * sync_inode - write an inode and its pages to disk.
 * @inode: the inode to sync
 * @wbc: controls the writeback mode
 *
 * sync_inode() will write an inode and its pages to disk.  It will also
 * correctly update the inode on its superblock's dirty inode lists and will
 * update inode->i_state.
 *
 * The caller must have a ref on the inode.
 */
int sync_inode(struct inode *inode, struct writeback_control *wbc)
{
	int ret;

	spin_lock(&inode_lock);
	ret = writeback_single_inode(inode, wbc);
	spin_unlock(&inode_lock);
	return ret;
}
EXPORT_SYMBOL(sync_inode);

/**
 * generic_osync_inode - flush all dirty data for a given inode to disk
 * @inode: inode to write
 * @mapping: the address_space that should be flushed
 * @what:  what to write and wait upon
 *
 * This can be called by file_write functions for files which have the
 * O_SYNC flag set, to flush dirty writes to disk.
 *
 * @what is a bitmask, specifying which part of the inode's data should be
 * written and waited upon.
 *
 *    OSYNC_DATA:     i_mapping's dirty data
 *    OSYNC_METADATA: the buffers at i_mapping->private_list
 *    OSYNC_INODE:    the inode itself
 */

int generic_osync_inode(struct inode *inode, struct address_space *mapping, int what)
{
	int err = 0;
	int need_write_inode_now = 0;
	int err2;

	if (what & OSYNC_DATA)
		err = filemap_fdatawrite(mapping);
	if (what & (OSYNC_METADATA|OSYNC_DATA)) {
		err2 = sync_mapping_buffers(mapping);
		if (!err)
			err = err2;
	}
	if (what & OSYNC_DATA) {
		err2 = filemap_fdatawait(mapping);
		if (!err)
			err = err2;
	}

	spin_lock(&inode_lock);
	if ((inode->i_state & I_DIRTY) &&
	    ((what & OSYNC_INODE) || (inode->i_state & I_DIRTY_DATASYNC)))
		need_write_inode_now = 1;
	spin_unlock(&inode_lock);

	if (need_write_inode_now) {
		err2 = write_inode_now(inode, 1);
		if (!err)
			err = err2;
	}
	else
		inode_sync_wait(inode);

	return err;
}
EXPORT_SYMBOL(generic_osync_inode);