fs: convert core functions to zero_user_page
[linux-2.6.git] / fs / buffer.c
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/mm.h>
25 #include <linux/percpu.h>
26 #include <linux/slab.h>
27 #include <linux/capability.h>
28 #include <linux/blkdev.h>
29 #include <linux/file.h>
30 #include <linux/quotaops.h>
31 #include <linux/highmem.h>
32 #include <linux/module.h>
33 #include <linux/writeback.h>
34 #include <linux/hash.h>
35 #include <linux/suspend.h>
36 #include <linux/buffer_head.h>
37 #include <linux/task_io_accounting_ops.h>
38 #include <linux/bio.h>
39 #include <linux/notifier.h>
40 #include <linux/cpu.h>
41 #include <linux/bitops.h>
42 #include <linux/mpage.h>
43 #include <linux/bit_spinlock.h>
44
45 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
46
47 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
48
49 inline void
50 init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
51 {
52         bh->b_end_io = handler;
53         bh->b_private = private;
54 }
55
56 static int sync_buffer(void *word)
57 {
58         struct block_device *bd;
59         struct buffer_head *bh
60                 = container_of(word, struct buffer_head, b_state);
61
62         smp_mb();
63         bd = bh->b_bdev;
64         if (bd)
65                 blk_run_address_space(bd->bd_inode->i_mapping);
66         io_schedule();
67         return 0;
68 }
69
70 void fastcall __lock_buffer(struct buffer_head *bh)
71 {
72         wait_on_bit_lock(&bh->b_state, BH_Lock, sync_buffer,
73                                                         TASK_UNINTERRUPTIBLE);
74 }
75 EXPORT_SYMBOL(__lock_buffer);
76
77 void fastcall unlock_buffer(struct buffer_head *bh)
78 {
79         smp_mb__before_clear_bit();
80         clear_buffer_locked(bh);
81         smp_mb__after_clear_bit();
82         wake_up_bit(&bh->b_state, BH_Lock);
83 }
84
85 /*
86  * Block until a buffer comes unlocked.  This doesn't stop it
87  * from becoming locked again - you have to lock it yourself
88  * if you want to preserve its state.
89  */
90 void __wait_on_buffer(struct buffer_head * bh)
91 {
92         wait_on_bit(&bh->b_state, BH_Lock, sync_buffer, TASK_UNINTERRUPTIBLE);
93 }
94
95 static void
96 __clear_page_buffers(struct page *page)
97 {
98         ClearPagePrivate(page);
99         set_page_private(page, 0);
100         page_cache_release(page);
101 }
102
103 static void buffer_io_error(struct buffer_head *bh)
104 {
105         char b[BDEVNAME_SIZE];
106
107         printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
108                         bdevname(bh->b_bdev, b),
109                         (unsigned long long)bh->b_blocknr);
110 }
111
112 /*
113  * Default synchronous end-of-IO handler..  Just mark it up-to-date and
114  * unlock the buffer. This is what ll_rw_block uses too.
115  */
116 void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
117 {
118         if (uptodate) {
119                 set_buffer_uptodate(bh);
120         } else {
121                 /* This happens, due to failed READA attempts. */
122                 clear_buffer_uptodate(bh);
123         }
124         unlock_buffer(bh);
125         put_bh(bh);
126 }
127
128 void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
129 {
130         char b[BDEVNAME_SIZE];
131
132         if (uptodate) {
133                 set_buffer_uptodate(bh);
134         } else {
135                 if (!buffer_eopnotsupp(bh) && printk_ratelimit()) {
136                         buffer_io_error(bh);
137                         printk(KERN_WARNING "lost page write due to "
138                                         "I/O error on %s\n",
139                                        bdevname(bh->b_bdev, b));
140                 }
141                 set_buffer_write_io_error(bh);
142                 clear_buffer_uptodate(bh);
143         }
144         unlock_buffer(bh);
145         put_bh(bh);
146 }
147
148 /*
149  * Write out and wait upon all the dirty data associated with a block
150  * device via its mapping.  Does not take the superblock lock.
151  */
152 int sync_blockdev(struct block_device *bdev)
153 {
154         int ret = 0;
155
156         if (bdev)
157                 ret = filemap_write_and_wait(bdev->bd_inode->i_mapping);
158         return ret;
159 }
160 EXPORT_SYMBOL(sync_blockdev);
161
162 /*
163  * Write out and wait upon all dirty data associated with this
164  * device.   Filesystem data as well as the underlying block
165  * device.  Takes the superblock lock.
166  */
167 int fsync_bdev(struct block_device *bdev)
168 {
169         struct super_block *sb = get_super(bdev);
170         if (sb) {
171                 int res = fsync_super(sb);
172                 drop_super(sb);
173                 return res;
174         }
175         return sync_blockdev(bdev);
176 }
177
178 /**
179  * freeze_bdev  --  lock a filesystem and force it into a consistent state
180  * @bdev:       blockdevice to lock
181  *
182  * This takes the block device bd_mount_sem to make sure no new mounts
183  * happen on bdev until thaw_bdev() is called.
184  * If a superblock is found on this device, we take the s_umount semaphore
185  * on it to make sure nobody unmounts until the snapshot creation is done.
186  */
187 struct super_block *freeze_bdev(struct block_device *bdev)
188 {
189         struct super_block *sb;
190
191         down(&bdev->bd_mount_sem);
192         sb = get_super(bdev);
193         if (sb && !(sb->s_flags & MS_RDONLY)) {
194                 sb->s_frozen = SB_FREEZE_WRITE;
195                 smp_wmb();
196
197                 __fsync_super(sb);
198
199                 sb->s_frozen = SB_FREEZE_TRANS;
200                 smp_wmb();
201
202                 sync_blockdev(sb->s_bdev);
203
204                 if (sb->s_op->write_super_lockfs)
205                         sb->s_op->write_super_lockfs(sb);
206         }
207
208         sync_blockdev(bdev);
209         return sb;      /* thaw_bdev releases s->s_umount and bd_mount_sem */
210 }
211 EXPORT_SYMBOL(freeze_bdev);
212
213 /**
214  * thaw_bdev  -- unlock filesystem
215  * @bdev:       blockdevice to unlock
216  * @sb:         associated superblock
217  *
218  * Unlocks the filesystem and marks it writeable again after freeze_bdev().
219  */
220 void thaw_bdev(struct block_device *bdev, struct super_block *sb)
221 {
222         if (sb) {
223                 BUG_ON(sb->s_bdev != bdev);
224
225                 if (sb->s_op->unlockfs)
226                         sb->s_op->unlockfs(sb);
227                 sb->s_frozen = SB_UNFROZEN;
228                 smp_wmb();
229                 wake_up(&sb->s_wait_unfrozen);
230                 drop_super(sb);
231         }
232
233         up(&bdev->bd_mount_sem);
234 }
235 EXPORT_SYMBOL(thaw_bdev);
236
237 /*
238  * Various filesystems appear to want __find_get_block to be non-blocking.
239  * But it's the page lock which protects the buffers.  To get around this,
240  * we get exclusion from try_to_free_buffers with the blockdev mapping's
241  * private_lock.
242  *
243  * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
244  * may be quite high.  This code could TryLock the page, and if that
245  * succeeds, there is no need to take private_lock. (But if
246  * private_lock is contended then so is mapping->tree_lock).
247  */
248 static struct buffer_head *
249 __find_get_block_slow(struct block_device *bdev, sector_t block)
250 {
251         struct inode *bd_inode = bdev->bd_inode;
252         struct address_space *bd_mapping = bd_inode->i_mapping;
253         struct buffer_head *ret = NULL;
254         pgoff_t index;
255         struct buffer_head *bh;
256         struct buffer_head *head;
257         struct page *page;
258         int all_mapped = 1;
259
260         index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
261         page = find_get_page(bd_mapping, index);
262         if (!page)
263                 goto out;
264
265         spin_lock(&bd_mapping->private_lock);
266         if (!page_has_buffers(page))
267                 goto out_unlock;
268         head = page_buffers(page);
269         bh = head;
270         do {
271                 if (bh->b_blocknr == block) {
272                         ret = bh;
273                         get_bh(bh);
274                         goto out_unlock;
275                 }
276                 if (!buffer_mapped(bh))
277                         all_mapped = 0;
278                 bh = bh->b_this_page;
279         } while (bh != head);
280
281         /* we might be here because some of the buffers on this page are
282          * not mapped.  This is due to various races between
283          * file io on the block device and getblk.  It gets dealt with
284          * elsewhere, don't buffer_error if we had some unmapped buffers
285          */
286         if (all_mapped) {
287                 printk("__find_get_block_slow() failed. "
288                         "block=%llu, b_blocknr=%llu\n",
289                         (unsigned long long)block,
290                         (unsigned long long)bh->b_blocknr);
291                 printk("b_state=0x%08lx, b_size=%zu\n",
292                         bh->b_state, bh->b_size);
293                 printk("device blocksize: %d\n", 1 << bd_inode->i_blkbits);
294         }
295 out_unlock:
296         spin_unlock(&bd_mapping->private_lock);
297         page_cache_release(page);
298 out:
299         return ret;
300 }
301
302 /* If invalidate_buffers() will trash dirty buffers, it means some kind
303    of fs corruption is going on. Trashing dirty data always imply losing
304    information that was supposed to be just stored on the physical layer
305    by the user.
306
307    Thus invalidate_buffers in general usage is not allwowed to trash
308    dirty buffers. For example ioctl(FLSBLKBUF) expects dirty data to
309    be preserved.  These buffers are simply skipped.
310   
311    We also skip buffers which are still in use.  For example this can
312    happen if a userspace program is reading the block device.
313
314    NOTE: In the case where the user removed a removable-media-disk even if
315    there's still dirty data not synced on disk (due a bug in the device driver
316    or due an error of the user), by not destroying the dirty buffers we could
317    generate corruption also on the next media inserted, thus a parameter is
318    necessary to handle this case in the most safe way possible (trying
319    to not corrupt also the new disk inserted with the data belonging to
320    the old now corrupted disk). Also for the ramdisk the natural thing
321    to do in order to release the ramdisk memory is to destroy dirty buffers.
322
323    These are two special cases. Normal usage imply the device driver
324    to issue a sync on the device (without waiting I/O completion) and
325    then an invalidate_buffers call that doesn't trash dirty buffers.
326
327    For handling cache coherency with the blkdev pagecache the 'update' case
328    is been introduced. It is needed to re-read from disk any pinned
329    buffer. NOTE: re-reading from disk is destructive so we can do it only
330    when we assume nobody is changing the buffercache under our I/O and when
331    we think the disk contains more recent information than the buffercache.
332    The update == 1 pass marks the buffers we need to update, the update == 2
333    pass does the actual I/O. */
334 void invalidate_bdev(struct block_device *bdev)
335 {
336         struct address_space *mapping = bdev->bd_inode->i_mapping;
337
338         if (mapping->nrpages == 0)
339                 return;
340
341         invalidate_bh_lrus();
342         invalidate_mapping_pages(mapping, 0, -1);
343 }
344
345 /*
346  * Kick pdflush then try to free up some ZONE_NORMAL memory.
347  */
348 static void free_more_memory(void)
349 {
350         struct zone **zones;
351         pg_data_t *pgdat;
352
353         wakeup_pdflush(1024);
354         yield();
355
356         for_each_online_pgdat(pgdat) {
357                 zones = pgdat->node_zonelists[gfp_zone(GFP_NOFS)].zones;
358                 if (*zones)
359                         try_to_free_pages(zones, GFP_NOFS);
360         }
361 }
362
363 /*
364  * I/O completion handler for block_read_full_page() - pages
365  * which come unlocked at the end of I/O.
366  */
367 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
368 {
369         unsigned long flags;
370         struct buffer_head *first;
371         struct buffer_head *tmp;
372         struct page *page;
373         int page_uptodate = 1;
374
375         BUG_ON(!buffer_async_read(bh));
376
377         page = bh->b_page;
378         if (uptodate) {
379                 set_buffer_uptodate(bh);
380         } else {
381                 clear_buffer_uptodate(bh);
382                 if (printk_ratelimit())
383                         buffer_io_error(bh);
384                 SetPageError(page);
385         }
386
387         /*
388          * Be _very_ careful from here on. Bad things can happen if
389          * two buffer heads end IO at almost the same time and both
390          * decide that the page is now completely done.
391          */
392         first = page_buffers(page);
393         local_irq_save(flags);
394         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
395         clear_buffer_async_read(bh);
396         unlock_buffer(bh);
397         tmp = bh;
398         do {
399                 if (!buffer_uptodate(tmp))
400                         page_uptodate = 0;
401                 if (buffer_async_read(tmp)) {
402                         BUG_ON(!buffer_locked(tmp));
403                         goto still_busy;
404                 }
405                 tmp = tmp->b_this_page;
406         } while (tmp != bh);
407         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
408         local_irq_restore(flags);
409
410         /*
411          * If none of the buffers had errors and they are all
412          * uptodate then we can set the page uptodate.
413          */
414         if (page_uptodate && !PageError(page))
415                 SetPageUptodate(page);
416         unlock_page(page);
417         return;
418
419 still_busy:
420         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
421         local_irq_restore(flags);
422         return;
423 }
424
425 /*
426  * Completion handler for block_write_full_page() - pages which are unlocked
427  * during I/O, and which have PageWriteback cleared upon I/O completion.
428  */
429 static void end_buffer_async_write(struct buffer_head *bh, int uptodate)
430 {
431         char b[BDEVNAME_SIZE];
432         unsigned long flags;
433         struct buffer_head *first;
434         struct buffer_head *tmp;
435         struct page *page;
436
437         BUG_ON(!buffer_async_write(bh));
438
439         page = bh->b_page;
440         if (uptodate) {
441                 set_buffer_uptodate(bh);
442         } else {
443                 if (printk_ratelimit()) {
444                         buffer_io_error(bh);
445                         printk(KERN_WARNING "lost page write due to "
446                                         "I/O error on %s\n",
447                                bdevname(bh->b_bdev, b));
448                 }
449                 set_bit(AS_EIO, &page->mapping->flags);
450                 set_buffer_write_io_error(bh);
451                 clear_buffer_uptodate(bh);
452                 SetPageError(page);
453         }
454
455         first = page_buffers(page);
456         local_irq_save(flags);
457         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
458
459         clear_buffer_async_write(bh);
460         unlock_buffer(bh);
461         tmp = bh->b_this_page;
462         while (tmp != bh) {
463                 if (buffer_async_write(tmp)) {
464                         BUG_ON(!buffer_locked(tmp));
465                         goto still_busy;
466                 }
467                 tmp = tmp->b_this_page;
468         }
469         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
470         local_irq_restore(flags);
471         end_page_writeback(page);
472         return;
473
474 still_busy:
475         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
476         local_irq_restore(flags);
477         return;
478 }
479
480 /*
481  * If a page's buffers are under async readin (end_buffer_async_read
482  * completion) then there is a possibility that another thread of
483  * control could lock one of the buffers after it has completed
484  * but while some of the other buffers have not completed.  This
485  * locked buffer would confuse end_buffer_async_read() into not unlocking
486  * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
487  * that this buffer is not under async I/O.
488  *
489  * The page comes unlocked when it has no locked buffer_async buffers
490  * left.
491  *
492  * PageLocked prevents anyone starting new async I/O reads any of
493  * the buffers.
494  *
495  * PageWriteback is used to prevent simultaneous writeout of the same
496  * page.
497  *
498  * PageLocked prevents anyone from starting writeback of a page which is
499  * under read I/O (PageWriteback is only ever set against a locked page).
500  */
501 static void mark_buffer_async_read(struct buffer_head *bh)
502 {
503         bh->b_end_io = end_buffer_async_read;
504         set_buffer_async_read(bh);
505 }
506
507 void mark_buffer_async_write(struct buffer_head *bh)
508 {
509         bh->b_end_io = end_buffer_async_write;
510         set_buffer_async_write(bh);
511 }
512 EXPORT_SYMBOL(mark_buffer_async_write);
513
514
515 /*
516  * fs/buffer.c contains helper functions for buffer-backed address space's
517  * fsync functions.  A common requirement for buffer-based filesystems is
518  * that certain data from the backing blockdev needs to be written out for
519  * a successful fsync().  For example, ext2 indirect blocks need to be
520  * written back and waited upon before fsync() returns.
521  *
522  * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
523  * inode_has_buffers() and invalidate_inode_buffers() are provided for the
524  * management of a list of dependent buffers at ->i_mapping->private_list.
525  *
526  * Locking is a little subtle: try_to_free_buffers() will remove buffers
527  * from their controlling inode's queue when they are being freed.  But
528  * try_to_free_buffers() will be operating against the *blockdev* mapping
529  * at the time, not against the S_ISREG file which depends on those buffers.
530  * So the locking for private_list is via the private_lock in the address_space
531  * which backs the buffers.  Which is different from the address_space 
532  * against which the buffers are listed.  So for a particular address_space,
533  * mapping->private_lock does *not* protect mapping->private_list!  In fact,
534  * mapping->private_list will always be protected by the backing blockdev's
535  * ->private_lock.
536  *
537  * Which introduces a requirement: all buffers on an address_space's
538  * ->private_list must be from the same address_space: the blockdev's.
539  *
540  * address_spaces which do not place buffers at ->private_list via these
541  * utility functions are free to use private_lock and private_list for
542  * whatever they want.  The only requirement is that list_empty(private_list)
543  * be true at clear_inode() time.
544  *
545  * FIXME: clear_inode should not call invalidate_inode_buffers().  The
546  * filesystems should do that.  invalidate_inode_buffers() should just go
547  * BUG_ON(!list_empty).
548  *
549  * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
550  * take an address_space, not an inode.  And it should be called
551  * mark_buffer_dirty_fsync() to clearly define why those buffers are being
552  * queued up.
553  *
554  * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
555  * list if it is already on a list.  Because if the buffer is on a list,
556  * it *must* already be on the right one.  If not, the filesystem is being
557  * silly.  This will save a ton of locking.  But first we have to ensure
558  * that buffers are taken *off* the old inode's list when they are freed
559  * (presumably in truncate).  That requires careful auditing of all
560  * filesystems (do it inside bforget()).  It could also be done by bringing
561  * b_inode back.
562  */
563
564 /*
565  * The buffer's backing address_space's private_lock must be held
566  */
567 static inline void __remove_assoc_queue(struct buffer_head *bh)
568 {
569         list_del_init(&bh->b_assoc_buffers);
570         WARN_ON(!bh->b_assoc_map);
571         if (buffer_write_io_error(bh))
572                 set_bit(AS_EIO, &bh->b_assoc_map->flags);
573         bh->b_assoc_map = NULL;
574 }
575
576 int inode_has_buffers(struct inode *inode)
577 {
578         return !list_empty(&inode->i_data.private_list);
579 }
580
581 /*
582  * osync is designed to support O_SYNC io.  It waits synchronously for
583  * all already-submitted IO to complete, but does not queue any new
584  * writes to the disk.
585  *
586  * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
587  * you dirty the buffers, and then use osync_inode_buffers to wait for
588  * completion.  Any other dirty buffers which are not yet queued for
589  * write will not be flushed to disk by the osync.
590  */
591 static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
592 {
593         struct buffer_head *bh;
594         struct list_head *p;
595         int err = 0;
596
597         spin_lock(lock);
598 repeat:
599         list_for_each_prev(p, list) {
600                 bh = BH_ENTRY(p);
601                 if (buffer_locked(bh)) {
602                         get_bh(bh);
603                         spin_unlock(lock);
604                         wait_on_buffer(bh);
605                         if (!buffer_uptodate(bh))
606                                 err = -EIO;
607                         brelse(bh);
608                         spin_lock(lock);
609                         goto repeat;
610                 }
611         }
612         spin_unlock(lock);
613         return err;
614 }
615
616 /**
617  * sync_mapping_buffers - write out and wait upon a mapping's "associated"
618  *                        buffers
619  * @mapping: the mapping which wants those buffers written
620  *
621  * Starts I/O against the buffers at mapping->private_list, and waits upon
622  * that I/O.
623  *
624  * Basically, this is a convenience function for fsync().
625  * @mapping is a file or directory which needs those buffers to be written for
626  * a successful fsync().
627  */
628 int sync_mapping_buffers(struct address_space *mapping)
629 {
630         struct address_space *buffer_mapping = mapping->assoc_mapping;
631
632         if (buffer_mapping == NULL || list_empty(&mapping->private_list))
633                 return 0;
634
635         return fsync_buffers_list(&buffer_mapping->private_lock,
636                                         &mapping->private_list);
637 }
638 EXPORT_SYMBOL(sync_mapping_buffers);
639
640 /*
641  * Called when we've recently written block `bblock', and it is known that
642  * `bblock' was for a buffer_boundary() buffer.  This means that the block at
643  * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
644  * dirty, schedule it for IO.  So that indirects merge nicely with their data.
645  */
646 void write_boundary_block(struct block_device *bdev,
647                         sector_t bblock, unsigned blocksize)
648 {
649         struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
650         if (bh) {
651                 if (buffer_dirty(bh))
652                         ll_rw_block(WRITE, 1, &bh);
653                 put_bh(bh);
654         }
655 }
656
657 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
658 {
659         struct address_space *mapping = inode->i_mapping;
660         struct address_space *buffer_mapping = bh->b_page->mapping;
661
662         mark_buffer_dirty(bh);
663         if (!mapping->assoc_mapping) {
664                 mapping->assoc_mapping = buffer_mapping;
665         } else {
666                 BUG_ON(mapping->assoc_mapping != buffer_mapping);
667         }
668         if (list_empty(&bh->b_assoc_buffers)) {
669                 spin_lock(&buffer_mapping->private_lock);
670                 list_move_tail(&bh->b_assoc_buffers,
671                                 &mapping->private_list);
672                 bh->b_assoc_map = mapping;
673                 spin_unlock(&buffer_mapping->private_lock);
674         }
675 }
676 EXPORT_SYMBOL(mark_buffer_dirty_inode);
677
678 /*
679  * Add a page to the dirty page list.
680  *
681  * It is a sad fact of life that this function is called from several places
682  * deeply under spinlocking.  It may not sleep.
683  *
684  * If the page has buffers, the uptodate buffers are set dirty, to preserve
685  * dirty-state coherency between the page and the buffers.  It the page does
686  * not have buffers then when they are later attached they will all be set
687  * dirty.
688  *
689  * The buffers are dirtied before the page is dirtied.  There's a small race
690  * window in which a writepage caller may see the page cleanness but not the
691  * buffer dirtiness.  That's fine.  If this code were to set the page dirty
692  * before the buffers, a concurrent writepage caller could clear the page dirty
693  * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
694  * page on the dirty page list.
695  *
696  * We use private_lock to lock against try_to_free_buffers while using the
697  * page's buffer list.  Also use this to protect against clean buffers being
698  * added to the page after it was set dirty.
699  *
700  * FIXME: may need to call ->reservepage here as well.  That's rather up to the
701  * address_space though.
702  */
703 int __set_page_dirty_buffers(struct page *page)
704 {
705         struct address_space * const mapping = page_mapping(page);
706
707         if (unlikely(!mapping))
708                 return !TestSetPageDirty(page);
709
710         spin_lock(&mapping->private_lock);
711         if (page_has_buffers(page)) {
712                 struct buffer_head *head = page_buffers(page);
713                 struct buffer_head *bh = head;
714
715                 do {
716                         set_buffer_dirty(bh);
717                         bh = bh->b_this_page;
718                 } while (bh != head);
719         }
720         spin_unlock(&mapping->private_lock);
721
722         if (TestSetPageDirty(page))
723                 return 0;
724
725         write_lock_irq(&mapping->tree_lock);
726         if (page->mapping) {    /* Race with truncate? */
727                 if (mapping_cap_account_dirty(mapping)) {
728                         __inc_zone_page_state(page, NR_FILE_DIRTY);
729                         task_io_account_write(PAGE_CACHE_SIZE);
730                 }
731                 radix_tree_tag_set(&mapping->page_tree,
732                                 page_index(page), PAGECACHE_TAG_DIRTY);
733         }
734         write_unlock_irq(&mapping->tree_lock);
735         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
736         return 1;
737 }
738 EXPORT_SYMBOL(__set_page_dirty_buffers);
739
740 /*
741  * Write out and wait upon a list of buffers.
742  *
743  * We have conflicting pressures: we want to make sure that all
744  * initially dirty buffers get waited on, but that any subsequently
745  * dirtied buffers don't.  After all, we don't want fsync to last
746  * forever if somebody is actively writing to the file.
747  *
748  * Do this in two main stages: first we copy dirty buffers to a
749  * temporary inode list, queueing the writes as we go.  Then we clean
750  * up, waiting for those writes to complete.
751  * 
752  * During this second stage, any subsequent updates to the file may end
753  * up refiling the buffer on the original inode's dirty list again, so
754  * there is a chance we will end up with a buffer queued for write but
755  * not yet completed on that list.  So, as a final cleanup we go through
756  * the osync code to catch these locked, dirty buffers without requeuing
757  * any newly dirty buffers for write.
758  */
759 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
760 {
761         struct buffer_head *bh;
762         struct list_head tmp;
763         int err = 0, err2;
764
765         INIT_LIST_HEAD(&tmp);
766
767         spin_lock(lock);
768         while (!list_empty(list)) {
769                 bh = BH_ENTRY(list->next);
770                 __remove_assoc_queue(bh);
771                 if (buffer_dirty(bh) || buffer_locked(bh)) {
772                         list_add(&bh->b_assoc_buffers, &tmp);
773                         if (buffer_dirty(bh)) {
774                                 get_bh(bh);
775                                 spin_unlock(lock);
776                                 /*
777                                  * Ensure any pending I/O completes so that
778                                  * ll_rw_block() actually writes the current
779                                  * contents - it is a noop if I/O is still in
780                                  * flight on potentially older contents.
781                                  */
782                                 ll_rw_block(SWRITE, 1, &bh);
783                                 brelse(bh);
784                                 spin_lock(lock);
785                         }
786                 }
787         }
788
789         while (!list_empty(&tmp)) {
790                 bh = BH_ENTRY(tmp.prev);
791                 list_del_init(&bh->b_assoc_buffers);
792                 get_bh(bh);
793                 spin_unlock(lock);
794                 wait_on_buffer(bh);
795                 if (!buffer_uptodate(bh))
796                         err = -EIO;
797                 brelse(bh);
798                 spin_lock(lock);
799         }
800         
801         spin_unlock(lock);
802         err2 = osync_buffers_list(lock, list);
803         if (err)
804                 return err;
805         else
806                 return err2;
807 }
808
809 /*
810  * Invalidate any and all dirty buffers on a given inode.  We are
811  * probably unmounting the fs, but that doesn't mean we have already
812  * done a sync().  Just drop the buffers from the inode list.
813  *
814  * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
815  * assumes that all the buffers are against the blockdev.  Not true
816  * for reiserfs.
817  */
818 void invalidate_inode_buffers(struct inode *inode)
819 {
820         if (inode_has_buffers(inode)) {
821                 struct address_space *mapping = &inode->i_data;
822                 struct list_head *list = &mapping->private_list;
823                 struct address_space *buffer_mapping = mapping->assoc_mapping;
824
825                 spin_lock(&buffer_mapping->private_lock);
826                 while (!list_empty(list))
827                         __remove_assoc_queue(BH_ENTRY(list->next));
828                 spin_unlock(&buffer_mapping->private_lock);
829         }
830 }
831
832 /*
833  * Remove any clean buffers from the inode's buffer list.  This is called
834  * when we're trying to free the inode itself.  Those buffers can pin it.
835  *
836  * Returns true if all buffers were removed.
837  */
838 int remove_inode_buffers(struct inode *inode)
839 {
840         int ret = 1;
841
842         if (inode_has_buffers(inode)) {
843                 struct address_space *mapping = &inode->i_data;
844                 struct list_head *list = &mapping->private_list;
845                 struct address_space *buffer_mapping = mapping->assoc_mapping;
846
847                 spin_lock(&buffer_mapping->private_lock);
848                 while (!list_empty(list)) {
849                         struct buffer_head *bh = BH_ENTRY(list->next);
850                         if (buffer_dirty(bh)) {
851                                 ret = 0;
852                                 break;
853                         }
854                         __remove_assoc_queue(bh);
855                 }
856                 spin_unlock(&buffer_mapping->private_lock);
857         }
858         return ret;
859 }
860
861 /*
862  * Create the appropriate buffers when given a page for data area and
863  * the size of each buffer.. Use the bh->b_this_page linked list to
864  * follow the buffers created.  Return NULL if unable to create more
865  * buffers.
866  *
867  * The retry flag is used to differentiate async IO (paging, swapping)
868  * which may not fail from ordinary buffer allocations.
869  */
870 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
871                 int retry)
872 {
873         struct buffer_head *bh, *head;
874         long offset;
875
876 try_again:
877         head = NULL;
878         offset = PAGE_SIZE;
879         while ((offset -= size) >= 0) {
880                 bh = alloc_buffer_head(GFP_NOFS);
881                 if (!bh)
882                         goto no_grow;
883
884                 bh->b_bdev = NULL;
885                 bh->b_this_page = head;
886                 bh->b_blocknr = -1;
887                 head = bh;
888
889                 bh->b_state = 0;
890                 atomic_set(&bh->b_count, 0);
891                 bh->b_private = NULL;
892                 bh->b_size = size;
893
894                 /* Link the buffer to its page */
895                 set_bh_page(bh, page, offset);
896
897                 init_buffer(bh, NULL, NULL);
898         }
899         return head;
900 /*
901  * In case anything failed, we just free everything we got.
902  */
903 no_grow:
904         if (head) {
905                 do {
906                         bh = head;
907                         head = head->b_this_page;
908                         free_buffer_head(bh);
909                 } while (head);
910         }
911
912         /*
913          * Return failure for non-async IO requests.  Async IO requests
914          * are not allowed to fail, so we have to wait until buffer heads
915          * become available.  But we don't want tasks sleeping with 
916          * partially complete buffers, so all were released above.
917          */
918         if (!retry)
919                 return NULL;
920
921         /* We're _really_ low on memory. Now we just
922          * wait for old buffer heads to become free due to
923          * finishing IO.  Since this is an async request and
924          * the reserve list is empty, we're sure there are 
925          * async buffer heads in use.
926          */
927         free_more_memory();
928         goto try_again;
929 }
930 EXPORT_SYMBOL_GPL(alloc_page_buffers);
931
932 static inline void
933 link_dev_buffers(struct page *page, struct buffer_head *head)
934 {
935         struct buffer_head *bh, *tail;
936
937         bh = head;
938         do {
939                 tail = bh;
940                 bh = bh->b_this_page;
941         } while (bh);
942         tail->b_this_page = head;
943         attach_page_buffers(page, head);
944 }
945
946 /*
947  * Initialise the state of a blockdev page's buffers.
948  */ 
949 static void
950 init_page_buffers(struct page *page, struct block_device *bdev,
951                         sector_t block, int size)
952 {
953         struct buffer_head *head = page_buffers(page);
954         struct buffer_head *bh = head;
955         int uptodate = PageUptodate(page);
956
957         do {
958                 if (!buffer_mapped(bh)) {
959                         init_buffer(bh, NULL, NULL);
960                         bh->b_bdev = bdev;
961                         bh->b_blocknr = block;
962                         if (uptodate)
963                                 set_buffer_uptodate(bh);
964                         set_buffer_mapped(bh);
965                 }
966                 block++;
967                 bh = bh->b_this_page;
968         } while (bh != head);
969 }
970
971 /*
972  * Create the page-cache page that contains the requested block.
973  *
974  * This is user purely for blockdev mappings.
975  */
976 static struct page *
977 grow_dev_page(struct block_device *bdev, sector_t block,
978                 pgoff_t index, int size)
979 {
980         struct inode *inode = bdev->bd_inode;
981         struct page *page;
982         struct buffer_head *bh;
983
984         page = find_or_create_page(inode->i_mapping, index, GFP_NOFS);
985         if (!page)
986                 return NULL;
987
988         BUG_ON(!PageLocked(page));
989
990         if (page_has_buffers(page)) {
991                 bh = page_buffers(page);
992                 if (bh->b_size == size) {
993                         init_page_buffers(page, bdev, block, size);
994                         return page;
995                 }
996                 if (!try_to_free_buffers(page))
997                         goto failed;
998         }
999
1000         /*
1001          * Allocate some buffers for this page
1002          */
1003         bh = alloc_page_buffers(page, size, 0);
1004         if (!bh)
1005                 goto failed;
1006
1007         /*
1008          * Link the page to the buffers and initialise them.  Take the
1009          * lock to be atomic wrt __find_get_block(), which does not
1010          * run under the page lock.
1011          */
1012         spin_lock(&inode->i_mapping->private_lock);
1013         link_dev_buffers(page, bh);
1014         init_page_buffers(page, bdev, block, size);
1015         spin_unlock(&inode->i_mapping->private_lock);
1016         return page;
1017
1018 failed:
1019         BUG();
1020         unlock_page(page);
1021         page_cache_release(page);
1022         return NULL;
1023 }
1024
1025 /*
1026  * Create buffers for the specified block device block's page.  If
1027  * that page was dirty, the buffers are set dirty also.
1028  *
1029  * Except that's a bug.  Attaching dirty buffers to a dirty
1030  * blockdev's page can result in filesystem corruption, because
1031  * some of those buffers may be aliases of filesystem data.
1032  * grow_dev_page() will go BUG() if this happens.
1033  */
1034 static int
1035 grow_buffers(struct block_device *bdev, sector_t block, int size)
1036 {
1037         struct page *page;
1038         pgoff_t index;
1039         int sizebits;
1040
1041         sizebits = -1;
1042         do {
1043                 sizebits++;
1044         } while ((size << sizebits) < PAGE_SIZE);
1045
1046         index = block >> sizebits;
1047
1048         /*
1049          * Check for a block which wants to lie outside our maximum possible
1050          * pagecache index.  (this comparison is done using sector_t types).
1051          */
1052         if (unlikely(index != block >> sizebits)) {
1053                 char b[BDEVNAME_SIZE];
1054
1055                 printk(KERN_ERR "%s: requested out-of-range block %llu for "
1056                         "device %s\n",
1057                         __FUNCTION__, (unsigned long long)block,
1058                         bdevname(bdev, b));
1059                 return -EIO;
1060         }
1061         block = index << sizebits;
1062         /* Create a page with the proper size buffers.. */
1063         page = grow_dev_page(bdev, block, index, size);
1064         if (!page)
1065                 return 0;
1066         unlock_page(page);
1067         page_cache_release(page);
1068         return 1;
1069 }
1070
1071 static struct buffer_head *
1072 __getblk_slow(struct block_device *bdev, sector_t block, int size)
1073 {
1074         /* Size must be multiple of hard sectorsize */
1075         if (unlikely(size & (bdev_hardsect_size(bdev)-1) ||
1076                         (size < 512 || size > PAGE_SIZE))) {
1077                 printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1078                                         size);
1079                 printk(KERN_ERR "hardsect size: %d\n",
1080                                         bdev_hardsect_size(bdev));
1081
1082                 dump_stack();
1083                 return NULL;
1084         }
1085
1086         for (;;) {
1087                 struct buffer_head * bh;
1088                 int ret;
1089
1090                 bh = __find_get_block(bdev, block, size);
1091                 if (bh)
1092                         return bh;
1093
1094                 ret = grow_buffers(bdev, block, size);
1095                 if (ret < 0)
1096                         return NULL;
1097                 if (ret == 0)
1098                         free_more_memory();
1099         }
1100 }
1101
1102 /*
1103  * The relationship between dirty buffers and dirty pages:
1104  *
1105  * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1106  * the page is tagged dirty in its radix tree.
1107  *
1108  * At all times, the dirtiness of the buffers represents the dirtiness of
1109  * subsections of the page.  If the page has buffers, the page dirty bit is
1110  * merely a hint about the true dirty state.
1111  *
1112  * When a page is set dirty in its entirety, all its buffers are marked dirty
1113  * (if the page has buffers).
1114  *
1115  * When a buffer is marked dirty, its page is dirtied, but the page's other
1116  * buffers are not.
1117  *
1118  * Also.  When blockdev buffers are explicitly read with bread(), they
1119  * individually become uptodate.  But their backing page remains not
1120  * uptodate - even if all of its buffers are uptodate.  A subsequent
1121  * block_read_full_page() against that page will discover all the uptodate
1122  * buffers, will set the page uptodate and will perform no I/O.
1123  */
1124
1125 /**
1126  * mark_buffer_dirty - mark a buffer_head as needing writeout
1127  * @bh: the buffer_head to mark dirty
1128  *
1129  * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1130  * backing page dirty, then tag the page as dirty in its address_space's radix
1131  * tree and then attach the address_space's inode to its superblock's dirty
1132  * inode list.
1133  *
1134  * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1135  * mapping->tree_lock and the global inode_lock.
1136  */
1137 void fastcall mark_buffer_dirty(struct buffer_head *bh)
1138 {
1139         if (!buffer_dirty(bh) && !test_set_buffer_dirty(bh))
1140                 __set_page_dirty_nobuffers(bh->b_page);
1141 }
1142
1143 /*
1144  * Decrement a buffer_head's reference count.  If all buffers against a page
1145  * have zero reference count, are clean and unlocked, and if the page is clean
1146  * and unlocked then try_to_free_buffers() may strip the buffers from the page
1147  * in preparation for freeing it (sometimes, rarely, buffers are removed from
1148  * a page but it ends up not being freed, and buffers may later be reattached).
1149  */
1150 void __brelse(struct buffer_head * buf)
1151 {
1152         if (atomic_read(&buf->b_count)) {
1153                 put_bh(buf);
1154                 return;
1155         }
1156         printk(KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1157         WARN_ON(1);
1158 }
1159
1160 /*
1161  * bforget() is like brelse(), except it discards any
1162  * potentially dirty data.
1163  */
1164 void __bforget(struct buffer_head *bh)
1165 {
1166         clear_buffer_dirty(bh);
1167         if (!list_empty(&bh->b_assoc_buffers)) {
1168                 struct address_space *buffer_mapping = bh->b_page->mapping;
1169
1170                 spin_lock(&buffer_mapping->private_lock);
1171                 list_del_init(&bh->b_assoc_buffers);
1172                 bh->b_assoc_map = NULL;
1173                 spin_unlock(&buffer_mapping->private_lock);
1174         }
1175         __brelse(bh);
1176 }
1177
1178 static struct buffer_head *__bread_slow(struct buffer_head *bh)
1179 {
1180         lock_buffer(bh);
1181         if (buffer_uptodate(bh)) {
1182                 unlock_buffer(bh);
1183                 return bh;
1184         } else {
1185                 get_bh(bh);
1186                 bh->b_end_io = end_buffer_read_sync;
1187                 submit_bh(READ, bh);
1188                 wait_on_buffer(bh);
1189                 if (buffer_uptodate(bh))
1190                         return bh;
1191         }
1192         brelse(bh);
1193         return NULL;
1194 }
1195
1196 /*
1197  * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1198  * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1199  * refcount elevated by one when they're in an LRU.  A buffer can only appear
1200  * once in a particular CPU's LRU.  A single buffer can be present in multiple
1201  * CPU's LRUs at the same time.
1202  *
1203  * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1204  * sb_find_get_block().
1205  *
1206  * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1207  * a local interrupt disable for that.
1208  */
1209
1210 #define BH_LRU_SIZE     8
1211
1212 struct bh_lru {
1213         struct buffer_head *bhs[BH_LRU_SIZE];
1214 };
1215
1216 static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1217
1218 #ifdef CONFIG_SMP
1219 #define bh_lru_lock()   local_irq_disable()
1220 #define bh_lru_unlock() local_irq_enable()
1221 #else
1222 #define bh_lru_lock()   preempt_disable()
1223 #define bh_lru_unlock() preempt_enable()
1224 #endif
1225
1226 static inline void check_irqs_on(void)
1227 {
1228 #ifdef irqs_disabled
1229         BUG_ON(irqs_disabled());
1230 #endif
1231 }
1232
1233 /*
1234  * The LRU management algorithm is dopey-but-simple.  Sorry.
1235  */
1236 static void bh_lru_install(struct buffer_head *bh)
1237 {
1238         struct buffer_head *evictee = NULL;
1239         struct bh_lru *lru;
1240
1241         check_irqs_on();
1242         bh_lru_lock();
1243         lru = &__get_cpu_var(bh_lrus);
1244         if (lru->bhs[0] != bh) {
1245                 struct buffer_head *bhs[BH_LRU_SIZE];
1246                 int in;
1247                 int out = 0;
1248
1249                 get_bh(bh);
1250                 bhs[out++] = bh;
1251                 for (in = 0; in < BH_LRU_SIZE; in++) {
1252                         struct buffer_head *bh2 = lru->bhs[in];
1253
1254                         if (bh2 == bh) {
1255                                 __brelse(bh2);
1256                         } else {
1257                                 if (out >= BH_LRU_SIZE) {
1258                                         BUG_ON(evictee != NULL);
1259                                         evictee = bh2;
1260                                 } else {
1261                                         bhs[out++] = bh2;
1262                                 }
1263                         }
1264                 }
1265                 while (out < BH_LRU_SIZE)
1266                         bhs[out++] = NULL;
1267                 memcpy(lru->bhs, bhs, sizeof(bhs));
1268         }
1269         bh_lru_unlock();
1270
1271         if (evictee)
1272                 __brelse(evictee);
1273 }
1274
1275 /*
1276  * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1277  */
1278 static struct buffer_head *
1279 lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1280 {
1281         struct buffer_head *ret = NULL;
1282         struct bh_lru *lru;
1283         unsigned int i;
1284
1285         check_irqs_on();
1286         bh_lru_lock();
1287         lru = &__get_cpu_var(bh_lrus);
1288         for (i = 0; i < BH_LRU_SIZE; i++) {
1289                 struct buffer_head *bh = lru->bhs[i];
1290
1291                 if (bh && bh->b_bdev == bdev &&
1292                                 bh->b_blocknr == block && bh->b_size == size) {
1293                         if (i) {
1294                                 while (i) {
1295                                         lru->bhs[i] = lru->bhs[i - 1];
1296                                         i--;
1297                                 }
1298                                 lru->bhs[0] = bh;
1299                         }
1300                         get_bh(bh);
1301                         ret = bh;
1302                         break;
1303                 }
1304         }
1305         bh_lru_unlock();
1306         return ret;
1307 }
1308
1309 /*
1310  * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1311  * it in the LRU and mark it as accessed.  If it is not present then return
1312  * NULL
1313  */
1314 struct buffer_head *
1315 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1316 {
1317         struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1318
1319         if (bh == NULL) {
1320                 bh = __find_get_block_slow(bdev, block);
1321                 if (bh)
1322                         bh_lru_install(bh);
1323         }
1324         if (bh)
1325                 touch_buffer(bh);
1326         return bh;
1327 }
1328 EXPORT_SYMBOL(__find_get_block);
1329
1330 /*
1331  * __getblk will locate (and, if necessary, create) the buffer_head
1332  * which corresponds to the passed block_device, block and size. The
1333  * returned buffer has its reference count incremented.
1334  *
1335  * __getblk() cannot fail - it just keeps trying.  If you pass it an
1336  * illegal block number, __getblk() will happily return a buffer_head
1337  * which represents the non-existent block.  Very weird.
1338  *
1339  * __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
1340  * attempt is failing.  FIXME, perhaps?
1341  */
1342 struct buffer_head *
1343 __getblk(struct block_device *bdev, sector_t block, unsigned size)
1344 {
1345         struct buffer_head *bh = __find_get_block(bdev, block, size);
1346
1347         might_sleep();
1348         if (bh == NULL)
1349                 bh = __getblk_slow(bdev, block, size);
1350         return bh;
1351 }
1352 EXPORT_SYMBOL(__getblk);
1353
1354 /*
1355  * Do async read-ahead on a buffer..
1356  */
1357 void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1358 {
1359         struct buffer_head *bh = __getblk(bdev, block, size);
1360         if (likely(bh)) {
1361                 ll_rw_block(READA, 1, &bh);
1362                 brelse(bh);
1363         }
1364 }
1365 EXPORT_SYMBOL(__breadahead);
1366
1367 /**
1368  *  __bread() - reads a specified block and returns the bh
1369  *  @bdev: the block_device to read from
1370  *  @block: number of block
1371  *  @size: size (in bytes) to read
1372  * 
1373  *  Reads a specified block, and returns buffer head that contains it.
1374  *  It returns NULL if the block was unreadable.
1375  */
1376 struct buffer_head *
1377 __bread(struct block_device *bdev, sector_t block, unsigned size)
1378 {
1379         struct buffer_head *bh = __getblk(bdev, block, size);
1380
1381         if (likely(bh) && !buffer_uptodate(bh))
1382                 bh = __bread_slow(bh);
1383         return bh;
1384 }
1385 EXPORT_SYMBOL(__bread);
1386
1387 /*
1388  * invalidate_bh_lrus() is called rarely - but not only at unmount.
1389  * This doesn't race because it runs in each cpu either in irq
1390  * or with preempt disabled.
1391  */
1392 static void invalidate_bh_lru(void *arg)
1393 {
1394         struct bh_lru *b = &get_cpu_var(bh_lrus);
1395         int i;
1396
1397         for (i = 0; i < BH_LRU_SIZE; i++) {
1398                 brelse(b->bhs[i]);
1399                 b->bhs[i] = NULL;
1400         }
1401         put_cpu_var(bh_lrus);
1402 }
1403         
1404 void invalidate_bh_lrus(void)
1405 {
1406         on_each_cpu(invalidate_bh_lru, NULL, 1, 1);
1407 }
1408
1409 void set_bh_page(struct buffer_head *bh,
1410                 struct page *page, unsigned long offset)
1411 {
1412         bh->b_page = page;
1413         BUG_ON(offset >= PAGE_SIZE);
1414         if (PageHighMem(page))
1415                 /*
1416                  * This catches illegal uses and preserves the offset:
1417                  */
1418                 bh->b_data = (char *)(0 + offset);
1419         else
1420                 bh->b_data = page_address(page) + offset;
1421 }
1422 EXPORT_SYMBOL(set_bh_page);
1423
1424 /*
1425  * Called when truncating a buffer on a page completely.
1426  */
1427 static void discard_buffer(struct buffer_head * bh)
1428 {
1429         lock_buffer(bh);
1430         clear_buffer_dirty(bh);
1431         bh->b_bdev = NULL;
1432         clear_buffer_mapped(bh);
1433         clear_buffer_req(bh);
1434         clear_buffer_new(bh);
1435         clear_buffer_delay(bh);
1436         clear_buffer_unwritten(bh);
1437         unlock_buffer(bh);
1438 }
1439
1440 /**
1441  * block_invalidatepage - invalidate part of all of a buffer-backed page
1442  *
1443  * @page: the page which is affected
1444  * @offset: the index of the truncation point
1445  *
1446  * block_invalidatepage() is called when all or part of the page has become
1447  * invalidatedby a truncate operation.
1448  *
1449  * block_invalidatepage() does not have to release all buffers, but it must
1450  * ensure that no dirty buffer is left outside @offset and that no I/O
1451  * is underway against any of the blocks which are outside the truncation
1452  * point.  Because the caller is about to free (and possibly reuse) those
1453  * blocks on-disk.
1454  */
1455 void block_invalidatepage(struct page *page, unsigned long offset)
1456 {
1457         struct buffer_head *head, *bh, *next;
1458         unsigned int curr_off = 0;
1459
1460         BUG_ON(!PageLocked(page));
1461         if (!page_has_buffers(page))
1462                 goto out;
1463
1464         head = page_buffers(page);
1465         bh = head;
1466         do {
1467                 unsigned int next_off = curr_off + bh->b_size;
1468                 next = bh->b_this_page;
1469
1470                 /*
1471                  * is this block fully invalidated?
1472                  */
1473                 if (offset <= curr_off)
1474                         discard_buffer(bh);
1475                 curr_off = next_off;
1476                 bh = next;
1477         } while (bh != head);
1478
1479         /*
1480          * We release buffers only if the entire page is being invalidated.
1481          * The get_block cached value has been unconditionally invalidated,
1482          * so real IO is not possible anymore.
1483          */
1484         if (offset == 0)
1485                 try_to_release_page(page, 0);
1486 out:
1487         return;
1488 }
1489 EXPORT_SYMBOL(block_invalidatepage);
1490
1491 /*
1492  * We attach and possibly dirty the buffers atomically wrt
1493  * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1494  * is already excluded via the page lock.
1495  */
1496 void create_empty_buffers(struct page *page,
1497                         unsigned long blocksize, unsigned long b_state)
1498 {
1499         struct buffer_head *bh, *head, *tail;
1500
1501         head = alloc_page_buffers(page, blocksize, 1);
1502         bh = head;
1503         do {
1504                 bh->b_state |= b_state;
1505                 tail = bh;
1506                 bh = bh->b_this_page;
1507         } while (bh);
1508         tail->b_this_page = head;
1509
1510         spin_lock(&page->mapping->private_lock);
1511         if (PageUptodate(page) || PageDirty(page)) {
1512                 bh = head;
1513                 do {
1514                         if (PageDirty(page))
1515                                 set_buffer_dirty(bh);
1516                         if (PageUptodate(page))
1517                                 set_buffer_uptodate(bh);
1518                         bh = bh->b_this_page;
1519                 } while (bh != head);
1520         }
1521         attach_page_buffers(page, head);
1522         spin_unlock(&page->mapping->private_lock);
1523 }
1524 EXPORT_SYMBOL(create_empty_buffers);
1525
1526 /*
1527  * We are taking a block for data and we don't want any output from any
1528  * buffer-cache aliases starting from return from that function and
1529  * until the moment when something will explicitly mark the buffer
1530  * dirty (hopefully that will not happen until we will free that block ;-)
1531  * We don't even need to mark it not-uptodate - nobody can expect
1532  * anything from a newly allocated buffer anyway. We used to used
1533  * unmap_buffer() for such invalidation, but that was wrong. We definitely
1534  * don't want to mark the alias unmapped, for example - it would confuse
1535  * anyone who might pick it with bread() afterwards...
1536  *
1537  * Also..  Note that bforget() doesn't lock the buffer.  So there can
1538  * be writeout I/O going on against recently-freed buffers.  We don't
1539  * wait on that I/O in bforget() - it's more efficient to wait on the I/O
1540  * only if we really need to.  That happens here.
1541  */
1542 void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1543 {
1544         struct buffer_head *old_bh;
1545
1546         might_sleep();
1547
1548         old_bh = __find_get_block_slow(bdev, block);
1549         if (old_bh) {
1550                 clear_buffer_dirty(old_bh);
1551                 wait_on_buffer(old_bh);
1552                 clear_buffer_req(old_bh);
1553                 __brelse(old_bh);
1554         }
1555 }
1556 EXPORT_SYMBOL(unmap_underlying_metadata);
1557
1558 /*
1559  * NOTE! All mapped/uptodate combinations are valid:
1560  *
1561  *      Mapped  Uptodate        Meaning
1562  *
1563  *      No      No              "unknown" - must do get_block()
1564  *      No      Yes             "hole" - zero-filled
1565  *      Yes     No              "allocated" - allocated on disk, not read in
1566  *      Yes     Yes             "valid" - allocated and up-to-date in memory.
1567  *
1568  * "Dirty" is valid only with the last case (mapped+uptodate).
1569  */
1570
1571 /*
1572  * While block_write_full_page is writing back the dirty buffers under
1573  * the page lock, whoever dirtied the buffers may decide to clean them
1574  * again at any time.  We handle that by only looking at the buffer
1575  * state inside lock_buffer().
1576  *
1577  * If block_write_full_page() is called for regular writeback
1578  * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1579  * locked buffer.   This only can happen if someone has written the buffer
1580  * directly, with submit_bh().  At the address_space level PageWriteback
1581  * prevents this contention from occurring.
1582  */
1583 static int __block_write_full_page(struct inode *inode, struct page *page,
1584                         get_block_t *get_block, struct writeback_control *wbc)
1585 {
1586         int err;
1587         sector_t block;
1588         sector_t last_block;
1589         struct buffer_head *bh, *head;
1590         const unsigned blocksize = 1 << inode->i_blkbits;
1591         int nr_underway = 0;
1592
1593         BUG_ON(!PageLocked(page));
1594
1595         last_block = (i_size_read(inode) - 1) >> inode->i_blkbits;
1596
1597         if (!page_has_buffers(page)) {
1598                 create_empty_buffers(page, blocksize,
1599                                         (1 << BH_Dirty)|(1 << BH_Uptodate));
1600         }
1601
1602         /*
1603          * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1604          * here, and the (potentially unmapped) buffers may become dirty at
1605          * any time.  If a buffer becomes dirty here after we've inspected it
1606          * then we just miss that fact, and the page stays dirty.
1607          *
1608          * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1609          * handle that here by just cleaning them.
1610          */
1611
1612         block = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
1613         head = page_buffers(page);
1614         bh = head;
1615
1616         /*
1617          * Get all the dirty buffers mapped to disk addresses and
1618          * handle any aliases from the underlying blockdev's mapping.
1619          */
1620         do {
1621                 if (block > last_block) {
1622                         /*
1623                          * mapped buffers outside i_size will occur, because
1624                          * this page can be outside i_size when there is a
1625                          * truncate in progress.
1626                          */
1627                         /*
1628                          * The buffer was zeroed by block_write_full_page()
1629                          */
1630                         clear_buffer_dirty(bh);
1631                         set_buffer_uptodate(bh);
1632                 } else if (!buffer_mapped(bh) && buffer_dirty(bh)) {
1633                         WARN_ON(bh->b_size != blocksize);
1634                         err = get_block(inode, block, bh, 1);
1635                         if (err)
1636                                 goto recover;
1637                         if (buffer_new(bh)) {
1638                                 /* blockdev mappings never come here */
1639                                 clear_buffer_new(bh);
1640                                 unmap_underlying_metadata(bh->b_bdev,
1641                                                         bh->b_blocknr);
1642                         }
1643                 }
1644                 bh = bh->b_this_page;
1645                 block++;
1646         } while (bh != head);
1647
1648         do {
1649                 if (!buffer_mapped(bh))
1650                         continue;
1651                 /*
1652                  * If it's a fully non-blocking write attempt and we cannot
1653                  * lock the buffer then redirty the page.  Note that this can
1654                  * potentially cause a busy-wait loop from pdflush and kswapd
1655                  * activity, but those code paths have their own higher-level
1656                  * throttling.
1657                  */
1658                 if (wbc->sync_mode != WB_SYNC_NONE || !wbc->nonblocking) {
1659                         lock_buffer(bh);
1660                 } else if (test_set_buffer_locked(bh)) {
1661                         redirty_page_for_writepage(wbc, page);
1662                         continue;
1663                 }
1664                 if (test_clear_buffer_dirty(bh)) {
1665                         mark_buffer_async_write(bh);
1666                 } else {
1667                         unlock_buffer(bh);
1668                 }
1669         } while ((bh = bh->b_this_page) != head);
1670
1671         /*
1672          * The page and its buffers are protected by PageWriteback(), so we can
1673          * drop the bh refcounts early.
1674          */
1675         BUG_ON(PageWriteback(page));
1676         set_page_writeback(page);
1677
1678         do {
1679                 struct buffer_head *next = bh->b_this_page;
1680                 if (buffer_async_write(bh)) {
1681                         submit_bh(WRITE, bh);
1682                         nr_underway++;
1683                 }
1684                 bh = next;
1685         } while (bh != head);
1686         unlock_page(page);
1687
1688         err = 0;
1689 done:
1690         if (nr_underway == 0) {
1691                 /*
1692                  * The page was marked dirty, but the buffers were
1693                  * clean.  Someone wrote them back by hand with
1694                  * ll_rw_block/submit_bh.  A rare case.
1695                  */
1696                 end_page_writeback(page);
1697
1698                 /*
1699                  * The page and buffer_heads can be released at any time from
1700                  * here on.
1701                  */
1702                 wbc->pages_skipped++;   /* We didn't write this page */
1703         }
1704         return err;
1705
1706 recover:
1707         /*
1708          * ENOSPC, or some other error.  We may already have added some
1709          * blocks to the file, so we need to write these out to avoid
1710          * exposing stale data.
1711          * The page is currently locked and not marked for writeback
1712          */
1713         bh = head;
1714         /* Recovery: lock and submit the mapped buffers */
1715         do {
1716                 if (buffer_mapped(bh) && buffer_dirty(bh)) {
1717                         lock_buffer(bh);
1718                         mark_buffer_async_write(bh);
1719                 } else {
1720                         /*
1721                          * The buffer may have been set dirty during
1722                          * attachment to a dirty page.
1723                          */
1724                         clear_buffer_dirty(bh);
1725                 }
1726         } while ((bh = bh->b_this_page) != head);
1727         SetPageError(page);
1728         BUG_ON(PageWriteback(page));
1729         mapping_set_error(page->mapping, err);
1730         set_page_writeback(page);
1731         do {
1732                 struct buffer_head *next = bh->b_this_page;
1733                 if (buffer_async_write(bh)) {
1734                         clear_buffer_dirty(bh);
1735                         submit_bh(WRITE, bh);
1736                         nr_underway++;
1737                 }
1738                 bh = next;
1739         } while (bh != head);
1740         unlock_page(page);
1741         goto done;
1742 }
1743
1744 static int __block_prepare_write(struct inode *inode, struct page *page,
1745                 unsigned from, unsigned to, get_block_t *get_block)
1746 {
1747         unsigned block_start, block_end;
1748         sector_t block;
1749         int err = 0;
1750         unsigned blocksize, bbits;
1751         struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1752
1753         BUG_ON(!PageLocked(page));
1754         BUG_ON(from > PAGE_CACHE_SIZE);
1755         BUG_ON(to > PAGE_CACHE_SIZE);
1756         BUG_ON(from > to);
1757
1758         blocksize = 1 << inode->i_blkbits;
1759         if (!page_has_buffers(page))
1760                 create_empty_buffers(page, blocksize, 0);
1761         head = page_buffers(page);
1762
1763         bbits = inode->i_blkbits;
1764         block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1765
1766         for(bh = head, block_start = 0; bh != head || !block_start;
1767             block++, block_start=block_end, bh = bh->b_this_page) {
1768                 block_end = block_start + blocksize;
1769                 if (block_end <= from || block_start >= to) {
1770                         if (PageUptodate(page)) {
1771                                 if (!buffer_uptodate(bh))
1772                                         set_buffer_uptodate(bh);
1773                         }
1774                         continue;
1775                 }
1776                 if (buffer_new(bh))
1777                         clear_buffer_new(bh);
1778                 if (!buffer_mapped(bh)) {
1779                         WARN_ON(bh->b_size != blocksize);
1780                         err = get_block(inode, block, bh, 1);
1781                         if (err)
1782                                 break;
1783                         if (buffer_new(bh)) {
1784                                 unmap_underlying_metadata(bh->b_bdev,
1785                                                         bh->b_blocknr);
1786                                 if (PageUptodate(page)) {
1787                                         set_buffer_uptodate(bh);
1788                                         continue;
1789                                 }
1790                                 if (block_end > to || block_start < from) {
1791                                         void *kaddr;
1792
1793                                         kaddr = kmap_atomic(page, KM_USER0);
1794                                         if (block_end > to)
1795                                                 memset(kaddr+to, 0,
1796                                                         block_end-to);
1797                                         if (block_start < from)
1798                                                 memset(kaddr+block_start,
1799                                                         0, from-block_start);
1800                                         flush_dcache_page(page);
1801                                         kunmap_atomic(kaddr, KM_USER0);
1802                                 }
1803                                 continue;
1804                         }
1805                 }
1806                 if (PageUptodate(page)) {
1807                         if (!buffer_uptodate(bh))
1808                                 set_buffer_uptodate(bh);
1809                         continue; 
1810                 }
1811                 if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1812                     !buffer_unwritten(bh) &&
1813                      (block_start < from || block_end > to)) {
1814                         ll_rw_block(READ, 1, &bh);
1815                         *wait_bh++=bh;
1816                 }
1817         }
1818         /*
1819          * If we issued read requests - let them complete.
1820          */
1821         while(wait_bh > wait) {
1822                 wait_on_buffer(*--wait_bh);
1823                 if (!buffer_uptodate(*wait_bh))
1824                         err = -EIO;
1825         }
1826         if (!err) {
1827                 bh = head;
1828                 do {
1829                         if (buffer_new(bh))
1830                                 clear_buffer_new(bh);
1831                 } while ((bh = bh->b_this_page) != head);
1832                 return 0;
1833         }
1834         /* Error case: */
1835         /*
1836          * Zero out any newly allocated blocks to avoid exposing stale
1837          * data.  If BH_New is set, we know that the block was newly
1838          * allocated in the above loop.
1839          */
1840         bh = head;
1841         block_start = 0;
1842         do {
1843                 block_end = block_start+blocksize;
1844                 if (block_end <= from)
1845                         goto next_bh;
1846                 if (block_start >= to)
1847                         break;
1848                 if (buffer_new(bh)) {
1849                         clear_buffer_new(bh);
1850                         zero_user_page(page, block_start, bh->b_size, KM_USER0);
1851                         set_buffer_uptodate(bh);
1852                         mark_buffer_dirty(bh);
1853                 }
1854 next_bh:
1855                 block_start = block_end;
1856                 bh = bh->b_this_page;
1857         } while (bh != head);
1858         return err;
1859 }
1860
1861 static int __block_commit_write(struct inode *inode, struct page *page,
1862                 unsigned from, unsigned to)
1863 {
1864         unsigned block_start, block_end;
1865         int partial = 0;
1866         unsigned blocksize;
1867         struct buffer_head *bh, *head;
1868
1869         blocksize = 1 << inode->i_blkbits;
1870
1871         for(bh = head = page_buffers(page), block_start = 0;
1872             bh != head || !block_start;
1873             block_start=block_end, bh = bh->b_this_page) {
1874                 block_end = block_start + blocksize;
1875                 if (block_end <= from || block_start >= to) {
1876                         if (!buffer_uptodate(bh))
1877                                 partial = 1;
1878                 } else {
1879                         set_buffer_uptodate(bh);
1880                         mark_buffer_dirty(bh);
1881                 }
1882         }
1883
1884         /*
1885          * If this is a partial write which happened to make all buffers
1886          * uptodate then we can optimize away a bogus readpage() for
1887          * the next read(). Here we 'discover' whether the page went
1888          * uptodate as a result of this (potentially partial) write.
1889          */
1890         if (!partial)
1891                 SetPageUptodate(page);
1892         return 0;
1893 }
1894
1895 /*
1896  * Generic "read page" function for block devices that have the normal
1897  * get_block functionality. This is most of the block device filesystems.
1898  * Reads the page asynchronously --- the unlock_buffer() and
1899  * set/clear_buffer_uptodate() functions propagate buffer state into the
1900  * page struct once IO has completed.
1901  */
1902 int block_read_full_page(struct page *page, get_block_t *get_block)
1903 {
1904         struct inode *inode = page->mapping->host;
1905         sector_t iblock, lblock;
1906         struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
1907         unsigned int blocksize;
1908         int nr, i;
1909         int fully_mapped = 1;
1910
1911         BUG_ON(!PageLocked(page));
1912         blocksize = 1 << inode->i_blkbits;
1913         if (!page_has_buffers(page))
1914                 create_empty_buffers(page, blocksize, 0);
1915         head = page_buffers(page);
1916
1917         iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
1918         lblock = (i_size_read(inode)+blocksize-1) >> inode->i_blkbits;
1919         bh = head;
1920         nr = 0;
1921         i = 0;
1922
1923         do {
1924                 if (buffer_uptodate(bh))
1925                         continue;
1926
1927                 if (!buffer_mapped(bh)) {
1928                         int err = 0;
1929
1930                         fully_mapped = 0;
1931                         if (iblock < lblock) {
1932                                 WARN_ON(bh->b_size != blocksize);
1933                                 err = get_block(inode, iblock, bh, 0);
1934                                 if (err)
1935                                         SetPageError(page);
1936                         }
1937                         if (!buffer_mapped(bh)) {
1938                                 zero_user_page(page, i * blocksize, blocksize,
1939                                                 KM_USER0);
1940                                 if (!err)
1941                                         set_buffer_uptodate(bh);
1942                                 continue;
1943                         }
1944                         /*
1945                          * get_block() might have updated the buffer
1946                          * synchronously
1947                          */
1948                         if (buffer_uptodate(bh))
1949                                 continue;
1950                 }
1951                 arr[nr++] = bh;
1952         } while (i++, iblock++, (bh = bh->b_this_page) != head);
1953
1954         if (fully_mapped)
1955                 SetPageMappedToDisk(page);
1956
1957         if (!nr) {
1958                 /*
1959                  * All buffers are uptodate - we can set the page uptodate
1960                  * as well. But not if get_block() returned an error.
1961                  */
1962                 if (!PageError(page))
1963                         SetPageUptodate(page);
1964                 unlock_page(page);
1965                 return 0;
1966         }
1967
1968         /* Stage two: lock the buffers */
1969         for (i = 0; i < nr; i++) {
1970                 bh = arr[i];
1971                 lock_buffer(bh);
1972                 mark_buffer_async_read(bh);
1973         }
1974
1975         /*
1976          * Stage 3: start the IO.  Check for uptodateness
1977          * inside the buffer lock in case another process reading
1978          * the underlying blockdev brought it uptodate (the sct fix).
1979          */
1980         for (i = 0; i < nr; i++) {
1981                 bh = arr[i];
1982                 if (buffer_uptodate(bh))
1983                         end_buffer_async_read(bh, 1);
1984                 else
1985                         submit_bh(READ, bh);
1986         }
1987         return 0;
1988 }
1989
1990 /* utility function for filesystems that need to do work on expanding
1991  * truncates.  Uses prepare/commit_write to allow the filesystem to
1992  * deal with the hole.  
1993  */
1994 static int __generic_cont_expand(struct inode *inode, loff_t size,
1995                                  pgoff_t index, unsigned int offset)
1996 {
1997         struct address_space *mapping = inode->i_mapping;
1998         struct page *page;
1999         unsigned long limit;
2000         int err;
2001
2002         err = -EFBIG;
2003         limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
2004         if (limit != RLIM_INFINITY && size > (loff_t)limit) {
2005                 send_sig(SIGXFSZ, current, 0);
2006                 goto out;
2007         }
2008         if (size > inode->i_sb->s_maxbytes)
2009                 goto out;
2010
2011         err = -ENOMEM;
2012         page = grab_cache_page(mapping, index);
2013         if (!page)
2014                 goto out;
2015         err = mapping->a_ops->prepare_write(NULL, page, offset, offset);
2016         if (err) {
2017                 /*
2018                  * ->prepare_write() may have instantiated a few blocks
2019                  * outside i_size.  Trim these off again.
2020                  */
2021                 unlock_page(page);
2022                 page_cache_release(page);
2023                 vmtruncate(inode, inode->i_size);
2024                 goto out;
2025         }
2026
2027         err = mapping->a_ops->commit_write(NULL, page, offset, offset);
2028
2029         unlock_page(page);
2030         page_cache_release(page);
2031         if (err > 0)
2032                 err = 0;
2033 out:
2034         return err;
2035 }
2036
2037 int generic_cont_expand(struct inode *inode, loff_t size)
2038 {
2039         pgoff_t index;
2040         unsigned int offset;
2041
2042         offset = (size & (PAGE_CACHE_SIZE - 1)); /* Within page */
2043
2044         /* ugh.  in prepare/commit_write, if from==to==start of block, we
2045         ** skip the prepare.  make sure we never send an offset for the start
2046         ** of a block
2047         */
2048         if ((offset & (inode->i_sb->s_blocksize - 1)) == 0) {
2049                 /* caller must handle this extra byte. */
2050                 offset++;
2051         }
2052         index = size >> PAGE_CACHE_SHIFT;
2053
2054         return __generic_cont_expand(inode, size, index, offset);
2055 }
2056
2057 int generic_cont_expand_simple(struct inode *inode, loff_t size)
2058 {
2059         loff_t pos = size - 1;
2060         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
2061         unsigned int offset = (pos & (PAGE_CACHE_SIZE - 1)) + 1;
2062
2063         /* prepare/commit_write can handle even if from==to==start of block. */
2064         return __generic_cont_expand(inode, size, index, offset);
2065 }
2066
2067 /*
2068  * For moronic filesystems that do not allow holes in file.
2069  * We may have to extend the file.
2070  */
2071
2072 int cont_prepare_write(struct page *page, unsigned offset,
2073                 unsigned to, get_block_t *get_block, loff_t *bytes)
2074 {
2075         struct address_space *mapping = page->mapping;
2076         struct inode *inode = mapping->host;
2077         struct page *new_page;
2078         pgoff_t pgpos;
2079         long status;
2080         unsigned zerofrom;
2081         unsigned blocksize = 1 << inode->i_blkbits;
2082
2083         while(page->index > (pgpos = *bytes>>PAGE_CACHE_SHIFT)) {
2084                 status = -ENOMEM;
2085                 new_page = grab_cache_page(mapping, pgpos);
2086                 if (!new_page)
2087                         goto out;
2088                 /* we might sleep */
2089                 if (*bytes>>PAGE_CACHE_SHIFT != pgpos) {
2090                         unlock_page(new_page);
2091                         page_cache_release(new_page);
2092                         continue;
2093                 }
2094                 zerofrom = *bytes & ~PAGE_CACHE_MASK;
2095                 if (zerofrom & (blocksize-1)) {
2096                         *bytes |= (blocksize-1);
2097                         (*bytes)++;
2098                 }
2099                 status = __block_prepare_write(inode, new_page, zerofrom,
2100                                                 PAGE_CACHE_SIZE, get_block);
2101                 if (status)
2102                         goto out_unmap;
2103                 zero_user_page(page, zerofrom, PAGE_CACHE_SIZE - zerofrom,
2104                                 KM_USER0);
2105                 generic_commit_write(NULL, new_page, zerofrom, PAGE_CACHE_SIZE);
2106                 unlock_page(new_page);
2107                 page_cache_release(new_page);
2108         }
2109
2110         if (page->index < pgpos) {
2111                 /* completely inside the area */
2112                 zerofrom = offset;
2113         } else {
2114                 /* page covers the boundary, find the boundary offset */
2115                 zerofrom = *bytes & ~PAGE_CACHE_MASK;
2116
2117                 /* if we will expand the thing last block will be filled */
2118                 if (to > zerofrom && (zerofrom & (blocksize-1))) {
2119                         *bytes |= (blocksize-1);
2120                         (*bytes)++;
2121                 }
2122
2123                 /* starting below the boundary? Nothing to zero out */
2124                 if (offset <= zerofrom)
2125                         zerofrom = offset;
2126         }
2127         status = __block_prepare_write(inode, page, zerofrom, to, get_block);
2128         if (status)
2129                 goto out1;
2130         if (zerofrom < offset) {
2131                 zero_user_page(page, zerofrom, offset - zerofrom, KM_USER0);
2132                 __block_commit_write(inode, page, zerofrom, offset);
2133         }
2134         return 0;
2135 out1:
2136         ClearPageUptodate(page);
2137         return status;
2138
2139 out_unmap:
2140         ClearPageUptodate(new_page);
2141         unlock_page(new_page);
2142         page_cache_release(new_page);
2143 out:
2144         return status;
2145 }
2146
2147 int block_prepare_write(struct page *page, unsigned from, unsigned to,
2148                         get_block_t *get_block)
2149 {
2150         struct inode *inode = page->mapping->host;
2151         int err = __block_prepare_write(inode, page, from, to, get_block);
2152         if (err)
2153                 ClearPageUptodate(page);
2154         return err;
2155 }
2156
2157 int block_commit_write(struct page *page, unsigned from, unsigned to)
2158 {
2159         struct inode *inode = page->mapping->host;
2160         __block_commit_write(inode,page,from,to);
2161         return 0;
2162 }
2163
2164 int generic_commit_write(struct file *file, struct page *page,
2165                 unsigned from, unsigned to)
2166 {
2167         struct inode *inode = page->mapping->host;
2168         loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
2169         __block_commit_write(inode,page,from,to);
2170         /*
2171          * No need to use i_size_read() here, the i_size
2172          * cannot change under us because we hold i_mutex.
2173          */
2174         if (pos > inode->i_size) {
2175                 i_size_write(inode, pos);
2176                 mark_inode_dirty(inode);
2177         }
2178         return 0;
2179 }
2180
2181
2182 /*
2183  * nobh_prepare_write()'s prereads are special: the buffer_heads are freed
2184  * immediately, while under the page lock.  So it needs a special end_io
2185  * handler which does not touch the bh after unlocking it.
2186  *
2187  * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
2188  * a race there is benign: unlock_buffer() only use the bh's address for
2189  * hashing after unlocking the buffer, so it doesn't actually touch the bh
2190  * itself.
2191  */
2192 static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2193 {
2194         if (uptodate) {
2195                 set_buffer_uptodate(bh);
2196         } else {
2197                 /* This happens, due to failed READA attempts. */
2198                 clear_buffer_uptodate(bh);
2199         }
2200         unlock_buffer(bh);
2201 }
2202
2203 /*
2204  * On entry, the page is fully not uptodate.
2205  * On exit the page is fully uptodate in the areas outside (from,to)
2206  */
2207 int nobh_prepare_write(struct page *page, unsigned from, unsigned to,
2208                         get_block_t *get_block)
2209 {
2210         struct inode *inode = page->mapping->host;
2211         const unsigned blkbits = inode->i_blkbits;
2212         const unsigned blocksize = 1 << blkbits;
2213         struct buffer_head map_bh;
2214         struct buffer_head *read_bh[MAX_BUF_PER_PAGE];
2215         unsigned block_in_page;
2216         unsigned block_start;
2217         sector_t block_in_file;
2218         char *kaddr;
2219         int nr_reads = 0;
2220         int i;
2221         int ret = 0;
2222         int is_mapped_to_disk = 1;
2223
2224         if (PageMappedToDisk(page))
2225                 return 0;
2226
2227         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
2228         map_bh.b_page = page;
2229
2230         /*
2231          * We loop across all blocks in the page, whether or not they are
2232          * part of the affected region.  This is so we can discover if the
2233          * page is fully mapped-to-disk.
2234          */
2235         for (block_start = 0, block_in_page = 0;
2236                   block_start < PAGE_CACHE_SIZE;
2237                   block_in_page++, block_start += blocksize) {
2238                 unsigned block_end = block_start + blocksize;
2239                 int create;
2240
2241                 map_bh.b_state = 0;
2242                 create = 1;
2243                 if (block_start >= to)
2244                         create = 0;
2245                 map_bh.b_size = blocksize;
2246                 ret = get_block(inode, block_in_file + block_in_page,
2247                                         &map_bh, create);
2248                 if (ret)
2249                         goto failed;
2250                 if (!buffer_mapped(&map_bh))
2251                         is_mapped_to_disk = 0;
2252                 if (buffer_new(&map_bh))
2253                         unmap_underlying_metadata(map_bh.b_bdev,
2254                                                         map_bh.b_blocknr);
2255                 if (PageUptodate(page))
2256                         continue;
2257                 if (buffer_new(&map_bh) || !buffer_mapped(&map_bh)) {
2258                         kaddr = kmap_atomic(page, KM_USER0);
2259                         if (block_start < from)
2260                                 memset(kaddr+block_start, 0, from-block_start);
2261                         if (block_end > to)
2262                                 memset(kaddr + to, 0, block_end - to);
2263                         flush_dcache_page(page);
2264                         kunmap_atomic(kaddr, KM_USER0);
2265                         continue;
2266                 }
2267                 if (buffer_uptodate(&map_bh))
2268                         continue;       /* reiserfs does this */
2269                 if (block_start < from || block_end > to) {
2270                         struct buffer_head *bh = alloc_buffer_head(GFP_NOFS);
2271
2272                         if (!bh) {
2273                                 ret = -ENOMEM;
2274                                 goto failed;
2275                         }
2276                         bh->b_state = map_bh.b_state;
2277                         atomic_set(&bh->b_count, 0);
2278                         bh->b_this_page = NULL;
2279                         bh->b_page = page;
2280                         bh->b_blocknr = map_bh.b_blocknr;
2281                         bh->b_size = blocksize;
2282                         bh->b_data = (char *)(long)block_start;
2283                         bh->b_bdev = map_bh.b_bdev;
2284                         bh->b_private = NULL;
2285                         read_bh[nr_reads++] = bh;
2286                 }
2287         }
2288
2289         if (nr_reads) {
2290                 struct buffer_head *bh;
2291
2292                 /*
2293                  * The page is locked, so these buffers are protected from
2294                  * any VM or truncate activity.  Hence we don't need to care
2295                  * for the buffer_head refcounts.
2296                  */
2297                 for (i = 0; i < nr_reads; i++) {
2298                         bh = read_bh[i];
2299                         lock_buffer(bh);
2300                         bh->b_end_io = end_buffer_read_nobh;
2301                         submit_bh(READ, bh);
2302                 }
2303                 for (i = 0; i < nr_reads; i++) {
2304                         bh = read_bh[i];
2305                         wait_on_buffer(bh);
2306                         if (!buffer_uptodate(bh))
2307                                 ret = -EIO;
2308                         free_buffer_head(bh);
2309                         read_bh[i] = NULL;
2310                 }
2311                 if (ret)
2312                         goto failed;
2313         }
2314
2315         if (is_mapped_to_disk)
2316                 SetPageMappedToDisk(page);
2317
2318         return 0;
2319
2320 failed:
2321         for (i = 0; i < nr_reads; i++) {
2322                 if (read_bh[i])
2323                         free_buffer_head(read_bh[i]);
2324         }
2325
2326         /*
2327          * Error recovery is pretty slack.  Clear the page and mark it dirty
2328          * so we'll later zero out any blocks which _were_ allocated.
2329          */
2330         zero_user_page(page, 0, PAGE_CACHE_SIZE, KM_USER0);
2331         SetPageUptodate(page);
2332         set_page_dirty(page);
2333         return ret;
2334 }
2335 EXPORT_SYMBOL(nobh_prepare_write);
2336
2337 /*
2338  * Make sure any changes to nobh_commit_write() are reflected in
2339  * nobh_truncate_page(), since it doesn't call commit_write().
2340  */
2341 int nobh_commit_write(struct file *file, struct page *page,
2342                 unsigned from, unsigned to)
2343 {
2344         struct inode *inode = page->mapping->host;
2345         loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
2346
2347         SetPageUptodate(page);
2348         set_page_dirty(page);
2349         if (pos > inode->i_size) {
2350                 i_size_write(inode, pos);
2351                 mark_inode_dirty(inode);
2352         }
2353         return 0;
2354 }
2355 EXPORT_SYMBOL(nobh_commit_write);
2356
2357 /*
2358  * nobh_writepage() - based on block_full_write_page() except
2359  * that it tries to operate without attaching bufferheads to
2360  * the page.
2361  */
2362 int nobh_writepage(struct page *page, get_block_t *get_block,
2363                         struct writeback_control *wbc)
2364 {
2365         struct inode * const inode = page->mapping->host;
2366         loff_t i_size = i_size_read(inode);
2367         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2368         unsigned offset;
2369         int ret;
2370
2371         /* Is the page fully inside i_size? */
2372         if (page->index < end_index)
2373                 goto out;
2374
2375         /* Is the page fully outside i_size? (truncate in progress) */
2376         offset = i_size & (PAGE_CACHE_SIZE-1);
2377         if (page->index >= end_index+1 || !offset) {
2378                 /*
2379                  * The page may have dirty, unmapped buffers.  For example,
2380                  * they may have been added in ext3_writepage().  Make them
2381                  * freeable here, so the page does not leak.
2382                  */
2383 #if 0
2384                 /* Not really sure about this  - do we need this ? */
2385                 if (page->mapping->a_ops->invalidatepage)
2386                         page->mapping->a_ops->invalidatepage(page, offset);
2387 #endif
2388                 unlock_page(page);
2389                 return 0; /* don't care */
2390         }
2391
2392         /*
2393          * The page straddles i_size.  It must be zeroed out on each and every
2394          * writepage invocation because it may be mmapped.  "A file is mapped
2395          * in multiples of the page size.  For a file that is not a multiple of
2396          * the  page size, the remaining memory is zeroed when mapped, and
2397          * writes to that region are not written out to the file."
2398          */
2399         zero_user_page(page, offset, PAGE_CACHE_SIZE - offset, KM_USER0);
2400 out:
2401         ret = mpage_writepage(page, get_block, wbc);
2402         if (ret == -EAGAIN)
2403                 ret = __block_write_full_page(inode, page, get_block, wbc);
2404         return ret;
2405 }
2406 EXPORT_SYMBOL(nobh_writepage);
2407
2408 /*
2409  * This function assumes that ->prepare_write() uses nobh_prepare_write().
2410  */
2411 int nobh_truncate_page(struct address_space *mapping, loff_t from)
2412 {
2413         struct inode *inode = mapping->host;
2414         unsigned blocksize = 1 << inode->i_blkbits;
2415         pgoff_t index = from >> PAGE_CACHE_SHIFT;
2416         unsigned offset = from & (PAGE_CACHE_SIZE-1);
2417         unsigned to;
2418         struct page *page;
2419         const struct address_space_operations *a_ops = mapping->a_ops;
2420         int ret = 0;
2421
2422         if ((offset & (blocksize - 1)) == 0)
2423                 goto out;
2424
2425         ret = -ENOMEM;
2426         page = grab_cache_page(mapping, index);
2427         if (!page)
2428                 goto out;
2429
2430         to = (offset + blocksize) & ~(blocksize - 1);
2431         ret = a_ops->prepare_write(NULL, page, offset, to);
2432         if (ret == 0) {
2433                 zero_user_page(page, offset, PAGE_CACHE_SIZE - offset,
2434                                 KM_USER0);
2435                 /*
2436                  * It would be more correct to call aops->commit_write()
2437                  * here, but this is more efficient.
2438                  */
2439                 SetPageUptodate(page);
2440                 set_page_dirty(page);
2441         }
2442         unlock_page(page);
2443         page_cache_release(page);
2444 out:
2445         return ret;
2446 }
2447 EXPORT_SYMBOL(nobh_truncate_page);
2448
2449 int block_truncate_page(struct address_space *mapping,
2450                         loff_t from, get_block_t *get_block)
2451 {
2452         pgoff_t index = from >> PAGE_CACHE_SHIFT;
2453         unsigned offset = from & (PAGE_CACHE_SIZE-1);
2454         unsigned blocksize;
2455         sector_t iblock;
2456         unsigned length, pos;
2457         struct inode *inode = mapping->host;
2458         struct page *page;
2459         struct buffer_head *bh;
2460         int err;
2461
2462         blocksize = 1 << inode->i_blkbits;
2463         length = offset & (blocksize - 1);
2464
2465         /* Block boundary? Nothing to do */
2466         if (!length)
2467                 return 0;
2468
2469         length = blocksize - length;
2470         iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2471         
2472         page = grab_cache_page(mapping, index);
2473         err = -ENOMEM;
2474         if (!page)
2475                 goto out;
2476
2477         if (!page_has_buffers(page))
2478                 create_empty_buffers(page, blocksize, 0);
2479
2480         /* Find the buffer that contains "offset" */
2481         bh = page_buffers(page);
2482         pos = blocksize;
2483         while (offset >= pos) {
2484                 bh = bh->b_this_page;
2485                 iblock++;
2486                 pos += blocksize;
2487         }
2488
2489         err = 0;
2490         if (!buffer_mapped(bh)) {
2491                 WARN_ON(bh->b_size != blocksize);
2492                 err = get_block(inode, iblock, bh, 0);
2493                 if (err)
2494                         goto unlock;
2495                 /* unmapped? It's a hole - nothing to do */
2496                 if (!buffer_mapped(bh))
2497                         goto unlock;
2498         }
2499
2500         /* Ok, it's mapped. Make sure it's up-to-date */
2501         if (PageUptodate(page))
2502                 set_buffer_uptodate(bh);
2503
2504         if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2505                 err = -EIO;
2506                 ll_rw_block(READ, 1, &bh);
2507                 wait_on_buffer(bh);
2508                 /* Uhhuh. Read error. Complain and punt. */
2509                 if (!buffer_uptodate(bh))
2510                         goto unlock;
2511         }
2512
2513         zero_user_page(page, offset, length, KM_USER0);
2514         mark_buffer_dirty(bh);
2515         err = 0;
2516
2517 unlock:
2518         unlock_page(page);
2519         page_cache_release(page);
2520 out:
2521         return err;
2522 }
2523
2524 /*
2525  * The generic ->writepage function for buffer-backed address_spaces
2526  */
2527 int block_write_full_page(struct page *page, get_block_t *get_block,
2528                         struct writeback_control *wbc)
2529 {
2530         struct inode * const inode = page->mapping->host;
2531         loff_t i_size = i_size_read(inode);
2532         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2533         unsigned offset;
2534
2535         /* Is the page fully inside i_size? */
2536         if (page->index < end_index)
2537                 return __block_write_full_page(inode, page, get_block, wbc);
2538
2539         /* Is the page fully outside i_size? (truncate in progress) */
2540         offset = i_size & (PAGE_CACHE_SIZE-1);
2541         if (page->index >= end_index+1 || !offset) {
2542                 /*
2543                  * The page may have dirty, unmapped buffers.  For example,
2544                  * they may have been added in ext3_writepage().  Make them
2545                  * freeable here, so the page does not leak.
2546                  */
2547                 do_invalidatepage(page, 0);
2548                 unlock_page(page);
2549                 return 0; /* don't care */
2550         }
2551
2552         /*
2553          * The page straddles i_size.  It must be zeroed out on each and every
2554          * writepage invokation because it may be mmapped.  "A file is mapped
2555          * in multiples of the page size.  For a file that is not a multiple of
2556          * the  page size, the remaining memory is zeroed when mapped, and
2557          * writes to that region are not written out to the file."
2558          */
2559         zero_user_page(page, offset, PAGE_CACHE_SIZE - offset, KM_USER0);
2560         return __block_write_full_page(inode, page, get_block, wbc);
2561 }
2562
2563 sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2564                             get_block_t *get_block)
2565 {
2566         struct buffer_head tmp;
2567         struct inode *inode = mapping->host;
2568         tmp.b_state = 0;
2569         tmp.b_blocknr = 0;
2570         tmp.b_size = 1 << inode->i_blkbits;
2571         get_block(inode, block, &tmp, 0);
2572         return tmp.b_blocknr;
2573 }
2574
2575 static int end_bio_bh_io_sync(struct bio *bio, unsigned int bytes_done, int err)
2576 {
2577         struct buffer_head *bh = bio->bi_private;
2578
2579         if (bio->bi_size)
2580                 return 1;
2581
2582         if (err == -EOPNOTSUPP) {
2583                 set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
2584                 set_bit(BH_Eopnotsupp, &bh->b_state);
2585         }
2586
2587         bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
2588         bio_put(bio);
2589         return 0;
2590 }
2591
2592 int submit_bh(int rw, struct buffer_head * bh)
2593 {
2594         struct bio *bio;
2595         int ret = 0;
2596
2597         BUG_ON(!buffer_locked(bh));
2598         BUG_ON(!buffer_mapped(bh));
2599         BUG_ON(!bh->b_end_io);
2600
2601         if (buffer_ordered(bh) && (rw == WRITE))
2602                 rw = WRITE_BARRIER;
2603
2604         /*
2605          * Only clear out a write error when rewriting, should this
2606          * include WRITE_SYNC as well?
2607          */
2608         if (test_set_buffer_req(bh) && (rw == WRITE || rw == WRITE_BARRIER))
2609                 clear_buffer_write_io_error(bh);
2610
2611         /*
2612          * from here on down, it's all bio -- do the initial mapping,
2613          * submit_bio -> generic_make_request may further map this bio around
2614          */
2615         bio = bio_alloc(GFP_NOIO, 1);
2616
2617         bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
2618         bio->bi_bdev = bh->b_bdev;
2619         bio->bi_io_vec[0].bv_page = bh->b_page;
2620         bio->bi_io_vec[0].bv_len = bh->b_size;
2621         bio->bi_io_vec[0].bv_offset = bh_offset(bh);
2622
2623         bio->bi_vcnt = 1;
2624         bio->bi_idx = 0;
2625         bio->bi_size = bh->b_size;
2626
2627         bio->bi_end_io = end_bio_bh_io_sync;
2628         bio->bi_private = bh;
2629
2630         bio_get(bio);
2631         submit_bio(rw, bio);
2632
2633         if (bio_flagged(bio, BIO_EOPNOTSUPP))
2634                 ret = -EOPNOTSUPP;
2635
2636         bio_put(bio);
2637         return ret;
2638 }
2639
2640 /**
2641  * ll_rw_block: low-level access to block devices (DEPRECATED)
2642  * @rw: whether to %READ or %WRITE or %SWRITE or maybe %READA (readahead)
2643  * @nr: number of &struct buffer_heads in the array
2644  * @bhs: array of pointers to &struct buffer_head
2645  *
2646  * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
2647  * requests an I/O operation on them, either a %READ or a %WRITE.  The third
2648  * %SWRITE is like %WRITE only we make sure that the *current* data in buffers
2649  * are sent to disk. The fourth %READA option is described in the documentation
2650  * for generic_make_request() which ll_rw_block() calls.
2651  *
2652  * This function drops any buffer that it cannot get a lock on (with the
2653  * BH_Lock state bit) unless SWRITE is required, any buffer that appears to be
2654  * clean when doing a write request, and any buffer that appears to be
2655  * up-to-date when doing read request.  Further it marks as clean buffers that
2656  * are processed for writing (the buffer cache won't assume that they are
2657  * actually clean until the buffer gets unlocked).
2658  *
2659  * ll_rw_block sets b_end_io to simple completion handler that marks
2660  * the buffer up-to-date (if approriate), unlocks the buffer and wakes
2661  * any waiters. 
2662  *
2663  * All of the buffers must be for the same device, and must also be a
2664  * multiple of the current approved size for the device.
2665  */
2666 void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
2667 {
2668         int i;
2669
2670         for (i = 0; i < nr; i++) {
2671                 struct buffer_head *bh = bhs[i];
2672
2673                 if (rw == SWRITE)
2674                         lock_buffer(bh);
2675                 else if (test_set_buffer_locked(bh))
2676                         continue;
2677
2678                 if (rw == WRITE || rw == SWRITE) {
2679                         if (test_clear_buffer_dirty(bh)) {
2680                                 bh->b_end_io = end_buffer_write_sync;
2681                                 get_bh(bh);
2682                                 submit_bh(WRITE, bh);
2683                                 continue;
2684                         }
2685                 } else {
2686                         if (!buffer_uptodate(bh)) {
2687                                 bh->b_end_io = end_buffer_read_sync;
2688                                 get_bh(bh);
2689                                 submit_bh(rw, bh);
2690                                 continue;
2691                         }
2692                 }
2693                 unlock_buffer(bh);
2694         }
2695 }
2696
2697 /*
2698  * For a data-integrity writeout, we need to wait upon any in-progress I/O
2699  * and then start new I/O and then wait upon it.  The caller must have a ref on
2700  * the buffer_head.
2701  */
2702 int sync_dirty_buffer(struct buffer_head *bh)
2703 {
2704         int ret = 0;
2705
2706         WARN_ON(atomic_read(&bh->b_count) < 1);
2707         lock_buffer(bh);
2708         if (test_clear_buffer_dirty(bh)) {
2709                 get_bh(bh);
2710                 bh->b_end_io = end_buffer_write_sync;
2711                 ret = submit_bh(WRITE, bh);
2712                 wait_on_buffer(bh);
2713                 if (buffer_eopnotsupp(bh)) {
2714                         clear_buffer_eopnotsupp(bh);
2715                         ret = -EOPNOTSUPP;
2716                 }
2717                 if (!ret && !buffer_uptodate(bh))
2718                         ret = -EIO;
2719         } else {
2720                 unlock_buffer(bh);
2721         }
2722         return ret;
2723 }
2724
2725 /*
2726  * try_to_free_buffers() checks if all the buffers on this particular page
2727  * are unused, and releases them if so.
2728  *
2729  * Exclusion against try_to_free_buffers may be obtained by either
2730  * locking the page or by holding its mapping's private_lock.
2731  *
2732  * If the page is dirty but all the buffers are clean then we need to
2733  * be sure to mark the page clean as well.  This is because the page
2734  * may be against a block device, and a later reattachment of buffers
2735  * to a dirty page will set *all* buffers dirty.  Which would corrupt
2736  * filesystem data on the same device.
2737  *
2738  * The same applies to regular filesystem pages: if all the buffers are
2739  * clean then we set the page clean and proceed.  To do that, we require
2740  * total exclusion from __set_page_dirty_buffers().  That is obtained with
2741  * private_lock.
2742  *
2743  * try_to_free_buffers() is non-blocking.
2744  */
2745 static inline int buffer_busy(struct buffer_head *bh)
2746 {
2747         return atomic_read(&bh->b_count) |
2748                 (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
2749 }
2750
2751 static int
2752 drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
2753 {
2754         struct buffer_head *head = page_buffers(page);
2755         struct buffer_head *bh;
2756
2757         bh = head;
2758         do {
2759                 if (buffer_write_io_error(bh) && page->mapping)
2760                         set_bit(AS_EIO, &page->mapping->flags);
2761                 if (buffer_busy(bh))
2762                         goto failed;
2763                 bh = bh->b_this_page;
2764         } while (bh != head);
2765
2766         do {
2767                 struct buffer_head *next = bh->b_this_page;
2768
2769                 if (!list_empty(&bh->b_assoc_buffers))
2770                         __remove_assoc_queue(bh);
2771                 bh = next;
2772         } while (bh != head);
2773         *buffers_to_free = head;
2774         __clear_page_buffers(page);
2775         return 1;
2776 failed:
2777         return 0;
2778 }
2779
2780 int try_to_free_buffers(struct page *page)
2781 {
2782         struct address_space * const mapping = page->mapping;
2783         struct buffer_head *buffers_to_free = NULL;
2784         int ret = 0;
2785
2786         BUG_ON(!PageLocked(page));
2787         if (PageWriteback(page))
2788                 return 0;
2789
2790         if (mapping == NULL) {          /* can this still happen? */
2791                 ret = drop_buffers(page, &buffers_to_free);
2792                 goto out;
2793         }
2794
2795         spin_lock(&mapping->private_lock);
2796         ret = drop_buffers(page, &buffers_to_free);
2797
2798         /*
2799          * If the filesystem writes its buffers by hand (eg ext3)
2800          * then we can have clean buffers against a dirty page.  We
2801          * clean the page here; otherwise the VM will never notice
2802          * that the filesystem did any IO at all.
2803          *
2804          * Also, during truncate, discard_buffer will have marked all
2805          * the page's buffers clean.  We discover that here and clean
2806          * the page also.
2807          *
2808          * private_lock must be held over this entire operation in order
2809          * to synchronise against __set_page_dirty_buffers and prevent the
2810          * dirty bit from being lost.
2811          */
2812         if (ret)
2813                 cancel_dirty_page(page, PAGE_CACHE_SIZE);
2814         spin_unlock(&mapping->private_lock);
2815 out:
2816         if (buffers_to_free) {
2817                 struct buffer_head *bh = buffers_to_free;
2818
2819                 do {
2820                         struct buffer_head *next = bh->b_this_page;
2821                         free_buffer_head(bh);
2822                         bh = next;
2823                 } while (bh != buffers_to_free);
2824         }
2825         return ret;
2826 }
2827 EXPORT_SYMBOL(try_to_free_buffers);
2828
2829 void block_sync_page(struct page *page)
2830 {
2831         struct address_space *mapping;
2832
2833         smp_mb();
2834         mapping = page_mapping(page);
2835         if (mapping)
2836                 blk_run_backing_dev(mapping->backing_dev_info, page);
2837 }
2838
2839 /*
2840  * There are no bdflush tunables left.  But distributions are
2841  * still running obsolete flush daemons, so we terminate them here.
2842  *
2843  * Use of bdflush() is deprecated and will be removed in a future kernel.
2844  * The `pdflush' kernel threads fully replace bdflush daemons and this call.
2845  */
2846 asmlinkage long sys_bdflush(int func, long data)
2847 {
2848         static int msg_count;
2849
2850         if (!capable(CAP_SYS_ADMIN))
2851                 return -EPERM;
2852
2853         if (msg_count < 5) {
2854                 msg_count++;
2855                 printk(KERN_INFO
2856                         "warning: process `%s' used the obsolete bdflush"
2857                         " system call\n", current->comm);
2858                 printk(KERN_INFO "Fix your initscripts?\n");
2859         }
2860
2861         if (func == 1)
2862                 do_exit(0);
2863         return 0;
2864 }
2865
2866 /*
2867  * Buffer-head allocation
2868  */
2869 static struct kmem_cache *bh_cachep;
2870
2871 /*
2872  * Once the number of bh's in the machine exceeds this level, we start
2873  * stripping them in writeback.
2874  */
2875 static int max_buffer_heads;
2876
2877 int buffer_heads_over_limit;
2878
2879 struct bh_accounting {
2880         int nr;                 /* Number of live bh's */
2881         int ratelimit;          /* Limit cacheline bouncing */
2882 };
2883
2884 static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
2885
2886 static void recalc_bh_state(void)
2887 {
2888         int i;
2889         int tot = 0;
2890
2891         if (__get_cpu_var(bh_accounting).ratelimit++ < 4096)
2892                 return;
2893         __get_cpu_var(bh_accounting).ratelimit = 0;
2894         for_each_online_cpu(i)
2895                 tot += per_cpu(bh_accounting, i).nr;
2896         buffer_heads_over_limit = (tot > max_buffer_heads);
2897 }
2898         
2899 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
2900 {
2901         struct buffer_head *ret = kmem_cache_alloc(bh_cachep, gfp_flags);
2902         if (ret) {
2903                 get_cpu_var(bh_accounting).nr++;
2904                 recalc_bh_state();
2905                 put_cpu_var(bh_accounting);
2906         }
2907         return ret;
2908 }
2909 EXPORT_SYMBOL(alloc_buffer_head);
2910
2911 void free_buffer_head(struct buffer_head *bh)
2912 {
2913         BUG_ON(!list_empty(&bh->b_assoc_buffers));
2914         kmem_cache_free(bh_cachep, bh);
2915         get_cpu_var(bh_accounting).nr--;
2916         recalc_bh_state();
2917         put_cpu_var(bh_accounting);
2918 }
2919 EXPORT_SYMBOL(free_buffer_head);
2920
2921 static void
2922 init_buffer_head(void *data, struct kmem_cache *cachep, unsigned long flags)
2923 {
2924         if (flags & SLAB_CTOR_CONSTRUCTOR) {
2925                 struct buffer_head * bh = (struct buffer_head *)data;
2926
2927                 memset(bh, 0, sizeof(*bh));
2928                 INIT_LIST_HEAD(&bh->b_assoc_buffers);
2929         }
2930 }
2931
2932 static void buffer_exit_cpu(int cpu)
2933 {
2934         int i;
2935         struct bh_lru *b = &per_cpu(bh_lrus, cpu);
2936
2937         for (i = 0; i < BH_LRU_SIZE; i++) {
2938                 brelse(b->bhs[i]);
2939                 b->bhs[i] = NULL;
2940         }
2941         get_cpu_var(bh_accounting).nr += per_cpu(bh_accounting, cpu).nr;
2942         per_cpu(bh_accounting, cpu).nr = 0;
2943         put_cpu_var(bh_accounting);
2944 }
2945
2946 static int buffer_cpu_notify(struct notifier_block *self,
2947                               unsigned long action, void *hcpu)
2948 {
2949         if (action == CPU_DEAD)
2950                 buffer_exit_cpu((unsigned long)hcpu);
2951         return NOTIFY_OK;
2952 }
2953
2954 void __init buffer_init(void)
2955 {
2956         int nrpages;
2957
2958         bh_cachep = kmem_cache_create("buffer_head",
2959                                         sizeof(struct buffer_head), 0,
2960                                         (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
2961                                         SLAB_MEM_SPREAD),
2962                                         init_buffer_head,
2963                                         NULL);
2964
2965         /*
2966          * Limit the bh occupancy to 10% of ZONE_NORMAL
2967          */
2968         nrpages = (nr_free_buffer_pages() * 10) / 100;
2969         max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
2970         hotcpu_notifier(buffer_cpu_notify, 0);
2971 }
2972
2973 EXPORT_SYMBOL(__bforget);
2974 EXPORT_SYMBOL(__brelse);
2975 EXPORT_SYMBOL(__wait_on_buffer);
2976 EXPORT_SYMBOL(block_commit_write);
2977 EXPORT_SYMBOL(block_prepare_write);
2978 EXPORT_SYMBOL(block_read_full_page);
2979 EXPORT_SYMBOL(block_sync_page);
2980 EXPORT_SYMBOL(block_truncate_page);
2981 EXPORT_SYMBOL(block_write_full_page);
2982 EXPORT_SYMBOL(cont_prepare_write);
2983 EXPORT_SYMBOL(end_buffer_read_sync);
2984 EXPORT_SYMBOL(end_buffer_write_sync);
2985 EXPORT_SYMBOL(file_fsync);
2986 EXPORT_SYMBOL(fsync_bdev);
2987 EXPORT_SYMBOL(generic_block_bmap);
2988 EXPORT_SYMBOL(generic_commit_write);
2989 EXPORT_SYMBOL(generic_cont_expand);
2990 EXPORT_SYMBOL(generic_cont_expand_simple);
2991 EXPORT_SYMBOL(init_buffer);
2992 EXPORT_SYMBOL(invalidate_bdev);
2993 EXPORT_SYMBOL(ll_rw_block);
2994 EXPORT_SYMBOL(mark_buffer_dirty);
2995 EXPORT_SYMBOL(submit_bh);
2996 EXPORT_SYMBOL(sync_dirty_buffer);
2997 EXPORT_SYMBOL(unlock_buffer);