dcc5faa573bae6677964453cf5a2392310c73c32
[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/smp_lock.h>
28 #include <linux/capability.h>
29 #include <linux/blkdev.h>
30 #include <linux/file.h>
31 #include <linux/quotaops.h>
32 #include <linux/highmem.h>
33 #include <linux/module.h>
34 #include <linux/writeback.h>
35 #include <linux/hash.h>
36 #include <linux/suspend.h>
37 #include <linux/buffer_head.h>
38 #include <linux/task_io_accounting_ops.h>
39 #include <linux/bio.h>
40 #include <linux/notifier.h>
41 #include <linux/cpu.h>
42 #include <linux/bitops.h>
43 #include <linux/mpage.h>
44 #include <linux/bit_spinlock.h>
45
46 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
47 static void invalidate_bh_lrus(void);
48
49 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
50
51 inline void
52 init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
53 {
54         bh->b_end_io = handler;
55         bh->b_private = private;
56 }
57
58 static int sync_buffer(void *word)
59 {
60         struct block_device *bd;
61         struct buffer_head *bh
62                 = container_of(word, struct buffer_head, b_state);
63
64         smp_mb();
65         bd = bh->b_bdev;
66         if (bd)
67                 blk_run_address_space(bd->bd_inode->i_mapping);
68         io_schedule();
69         return 0;
70 }
71
72 void fastcall __lock_buffer(struct buffer_head *bh)
73 {
74         wait_on_bit_lock(&bh->b_state, BH_Lock, sync_buffer,
75                                                         TASK_UNINTERRUPTIBLE);
76 }
77 EXPORT_SYMBOL(__lock_buffer);
78
79 void fastcall unlock_buffer(struct buffer_head *bh)
80 {
81         smp_mb__before_clear_bit();
82         clear_buffer_locked(bh);
83         smp_mb__after_clear_bit();
84         wake_up_bit(&bh->b_state, BH_Lock);
85 }
86
87 /*
88  * Block until a buffer comes unlocked.  This doesn't stop it
89  * from becoming locked again - you have to lock it yourself
90  * if you want to preserve its state.
91  */
92 void __wait_on_buffer(struct buffer_head * bh)
93 {
94         wait_on_bit(&bh->b_state, BH_Lock, sync_buffer, TASK_UNINTERRUPTIBLE);
95 }
96
97 static void
98 __clear_page_buffers(struct page *page)
99 {
100         ClearPagePrivate(page);
101         set_page_private(page, 0);
102         page_cache_release(page);
103 }
104
105 static void buffer_io_error(struct buffer_head *bh)
106 {
107         char b[BDEVNAME_SIZE];
108
109         printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
110                         bdevname(bh->b_bdev, b),
111                         (unsigned long long)bh->b_blocknr);
112 }
113
114 /*
115  * Default synchronous end-of-IO handler..  Just mark it up-to-date and
116  * unlock the buffer. This is what ll_rw_block uses too.
117  */
118 void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
119 {
120         if (uptodate) {
121                 set_buffer_uptodate(bh);
122         } else {
123                 /* This happens, due to failed READA attempts. */
124                 clear_buffer_uptodate(bh);
125         }
126         unlock_buffer(bh);
127         put_bh(bh);
128 }
129
130 void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
131 {
132         char b[BDEVNAME_SIZE];
133
134         if (uptodate) {
135                 set_buffer_uptodate(bh);
136         } else {
137                 if (!buffer_eopnotsupp(bh) && printk_ratelimit()) {
138                         buffer_io_error(bh);
139                         printk(KERN_WARNING "lost page write due to "
140                                         "I/O error on %s\n",
141                                        bdevname(bh->b_bdev, b));
142                 }
143                 set_buffer_write_io_error(bh);
144                 clear_buffer_uptodate(bh);
145         }
146         unlock_buffer(bh);
147         put_bh(bh);
148 }
149
150 /*
151  * Write out and wait upon all the dirty data associated with a block
152  * device via its mapping.  Does not take the superblock lock.
153  */
154 int sync_blockdev(struct block_device *bdev)
155 {
156         int ret = 0;
157
158         if (bdev)
159                 ret = filemap_write_and_wait(bdev->bd_inode->i_mapping);
160         return ret;
161 }
162 EXPORT_SYMBOL(sync_blockdev);
163
164 /*
165  * Write out and wait upon all dirty data associated with this
166  * device.   Filesystem data as well as the underlying block
167  * device.  Takes the superblock lock.
168  */
169 int fsync_bdev(struct block_device *bdev)
170 {
171         struct super_block *sb = get_super(bdev);
172         if (sb) {
173                 int res = fsync_super(sb);
174                 drop_super(sb);
175                 return res;
176         }
177         return sync_blockdev(bdev);
178 }
179
180 /**
181  * freeze_bdev  --  lock a filesystem and force it into a consistent state
182  * @bdev:       blockdevice to lock
183  *
184  * This takes the block device bd_mount_sem to make sure no new mounts
185  * happen on bdev until thaw_bdev() is called.
186  * If a superblock is found on this device, we take the s_umount semaphore
187  * on it to make sure nobody unmounts until the snapshot creation is done.
188  */
189 struct super_block *freeze_bdev(struct block_device *bdev)
190 {
191         struct super_block *sb;
192
193         down(&bdev->bd_mount_sem);
194         sb = get_super(bdev);
195         if (sb && !(sb->s_flags & MS_RDONLY)) {
196                 sb->s_frozen = SB_FREEZE_WRITE;
197                 smp_wmb();
198
199                 __fsync_super(sb);
200
201                 sb->s_frozen = SB_FREEZE_TRANS;
202                 smp_wmb();
203
204                 sync_blockdev(sb->s_bdev);
205
206                 if (sb->s_op->write_super_lockfs)
207                         sb->s_op->write_super_lockfs(sb);
208         }
209
210         sync_blockdev(bdev);
211         return sb;      /* thaw_bdev releases s->s_umount and bd_mount_sem */
212 }
213 EXPORT_SYMBOL(freeze_bdev);
214
215 /**
216  * thaw_bdev  -- unlock filesystem
217  * @bdev:       blockdevice to unlock
218  * @sb:         associated superblock
219  *
220  * Unlocks the filesystem and marks it writeable again after freeze_bdev().
221  */
222 void thaw_bdev(struct block_device *bdev, struct super_block *sb)
223 {
224         if (sb) {
225                 BUG_ON(sb->s_bdev != bdev);
226
227                 if (sb->s_op->unlockfs)
228                         sb->s_op->unlockfs(sb);
229                 sb->s_frozen = SB_UNFROZEN;
230                 smp_wmb();
231                 wake_up(&sb->s_wait_unfrozen);
232                 drop_super(sb);
233         }
234
235         up(&bdev->bd_mount_sem);
236 }
237 EXPORT_SYMBOL(thaw_bdev);
238
239 /*
240  * Various filesystems appear to want __find_get_block to be non-blocking.
241  * But it's the page lock which protects the buffers.  To get around this,
242  * we get exclusion from try_to_free_buffers with the blockdev mapping's
243  * private_lock.
244  *
245  * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
246  * may be quite high.  This code could TryLock the page, and if that
247  * succeeds, there is no need to take private_lock. (But if
248  * private_lock is contended then so is mapping->tree_lock).
249  */
250 static struct buffer_head *
251 __find_get_block_slow(struct block_device *bdev, sector_t block)
252 {
253         struct inode *bd_inode = bdev->bd_inode;
254         struct address_space *bd_mapping = bd_inode->i_mapping;
255         struct buffer_head *ret = NULL;
256         pgoff_t index;
257         struct buffer_head *bh;
258         struct buffer_head *head;
259         struct page *page;
260         int all_mapped = 1;
261
262         index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
263         page = find_get_page(bd_mapping, index);
264         if (!page)
265                 goto out;
266
267         spin_lock(&bd_mapping->private_lock);
268         if (!page_has_buffers(page))
269                 goto out_unlock;
270         head = page_buffers(page);
271         bh = head;
272         do {
273                 if (bh->b_blocknr == block) {
274                         ret = bh;
275                         get_bh(bh);
276                         goto out_unlock;
277                 }
278                 if (!buffer_mapped(bh))
279                         all_mapped = 0;
280                 bh = bh->b_this_page;
281         } while (bh != head);
282
283         /* we might be here because some of the buffers on this page are
284          * not mapped.  This is due to various races between
285          * file io on the block device and getblk.  It gets dealt with
286          * elsewhere, don't buffer_error if we had some unmapped buffers
287          */
288         if (all_mapped) {
289                 printk("__find_get_block_slow() failed. "
290                         "block=%llu, b_blocknr=%llu\n",
291                         (unsigned long long)block,
292                         (unsigned long long)bh->b_blocknr);
293                 printk("b_state=0x%08lx, b_size=%zu\n",
294                         bh->b_state, bh->b_size);
295                 printk("device blocksize: %d\n", 1 << bd_inode->i_blkbits);
296         }
297 out_unlock:
298         spin_unlock(&bd_mapping->private_lock);
299         page_cache_release(page);
300 out:
301         return ret;
302 }
303
304 /* If invalidate_buffers() will trash dirty buffers, it means some kind
305    of fs corruption is going on. Trashing dirty data always imply losing
306    information that was supposed to be just stored on the physical layer
307    by the user.
308
309    Thus invalidate_buffers in general usage is not allwowed to trash
310    dirty buffers. For example ioctl(FLSBLKBUF) expects dirty data to
311    be preserved.  These buffers are simply skipped.
312   
313    We also skip buffers which are still in use.  For example this can
314    happen if a userspace program is reading the block device.
315
316    NOTE: In the case where the user removed a removable-media-disk even if
317    there's still dirty data not synced on disk (due a bug in the device driver
318    or due an error of the user), by not destroying the dirty buffers we could
319    generate corruption also on the next media inserted, thus a parameter is
320    necessary to handle this case in the most safe way possible (trying
321    to not corrupt also the new disk inserted with the data belonging to
322    the old now corrupted disk). Also for the ramdisk the natural thing
323    to do in order to release the ramdisk memory is to destroy dirty buffers.
324
325    These are two special cases. Normal usage imply the device driver
326    to issue a sync on the device (without waiting I/O completion) and
327    then an invalidate_buffers call that doesn't trash dirty buffers.
328
329    For handling cache coherency with the blkdev pagecache the 'update' case
330    is been introduced. It is needed to re-read from disk any pinned
331    buffer. NOTE: re-reading from disk is destructive so we can do it only
332    when we assume nobody is changing the buffercache under our I/O and when
333    we think the disk contains more recent information than the buffercache.
334    The update == 1 pass marks the buffers we need to update, the update == 2
335    pass does the actual I/O. */
336 void invalidate_bdev(struct block_device *bdev, int destroy_dirty_buffers)
337 {
338         struct address_space *mapping = bdev->bd_inode->i_mapping;
339
340         if (mapping->nrpages == 0)
341                 return;
342
343         invalidate_bh_lrus();
344         /*
345          * FIXME: what about destroy_dirty_buffers?
346          * We really want to use invalidate_inode_pages2() for
347          * that, but not until that's cleaned up.
348          */
349         invalidate_mapping_pages(mapping, 0, -1);
350 }
351
352 /*
353  * Kick pdflush then try to free up some ZONE_NORMAL memory.
354  */
355 static void free_more_memory(void)
356 {
357         struct zone **zones;
358         pg_data_t *pgdat;
359
360         wakeup_pdflush(1024);
361         yield();
362
363         for_each_online_pgdat(pgdat) {
364                 zones = pgdat->node_zonelists[gfp_zone(GFP_NOFS)].zones;
365                 if (*zones)
366                         try_to_free_pages(zones, GFP_NOFS);
367         }
368 }
369
370 /*
371  * I/O completion handler for block_read_full_page() - pages
372  * which come unlocked at the end of I/O.
373  */
374 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
375 {
376         unsigned long flags;
377         struct buffer_head *first;
378         struct buffer_head *tmp;
379         struct page *page;
380         int page_uptodate = 1;
381
382         BUG_ON(!buffer_async_read(bh));
383
384         page = bh->b_page;
385         if (uptodate) {
386                 set_buffer_uptodate(bh);
387         } else {
388                 clear_buffer_uptodate(bh);
389                 if (printk_ratelimit())
390                         buffer_io_error(bh);
391                 SetPageError(page);
392         }
393
394         /*
395          * Be _very_ careful from here on. Bad things can happen if
396          * two buffer heads end IO at almost the same time and both
397          * decide that the page is now completely done.
398          */
399         first = page_buffers(page);
400         local_irq_save(flags);
401         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
402         clear_buffer_async_read(bh);
403         unlock_buffer(bh);
404         tmp = bh;
405         do {
406                 if (!buffer_uptodate(tmp))
407                         page_uptodate = 0;
408                 if (buffer_async_read(tmp)) {
409                         BUG_ON(!buffer_locked(tmp));
410                         goto still_busy;
411                 }
412                 tmp = tmp->b_this_page;
413         } while (tmp != bh);
414         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
415         local_irq_restore(flags);
416
417         /*
418          * If none of the buffers had errors and they are all
419          * uptodate then we can set the page uptodate.
420          */
421         if (page_uptodate && !PageError(page))
422                 SetPageUptodate(page);
423         unlock_page(page);
424         return;
425
426 still_busy:
427         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
428         local_irq_restore(flags);
429         return;
430 }
431
432 /*
433  * Completion handler for block_write_full_page() - pages which are unlocked
434  * during I/O, and which have PageWriteback cleared upon I/O completion.
435  */
436 static void end_buffer_async_write(struct buffer_head *bh, int uptodate)
437 {
438         char b[BDEVNAME_SIZE];
439         unsigned long flags;
440         struct buffer_head *first;
441         struct buffer_head *tmp;
442         struct page *page;
443
444         BUG_ON(!buffer_async_write(bh));
445
446         page = bh->b_page;
447         if (uptodate) {
448                 set_buffer_uptodate(bh);
449         } else {
450                 if (printk_ratelimit()) {
451                         buffer_io_error(bh);
452                         printk(KERN_WARNING "lost page write due to "
453                                         "I/O error on %s\n",
454                                bdevname(bh->b_bdev, b));
455                 }
456                 set_bit(AS_EIO, &page->mapping->flags);
457                 set_buffer_write_io_error(bh);
458                 clear_buffer_uptodate(bh);
459                 SetPageError(page);
460         }
461
462         first = page_buffers(page);
463         local_irq_save(flags);
464         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
465
466         clear_buffer_async_write(bh);
467         unlock_buffer(bh);
468         tmp = bh->b_this_page;
469         while (tmp != bh) {
470                 if (buffer_async_write(tmp)) {
471                         BUG_ON(!buffer_locked(tmp));
472                         goto still_busy;
473                 }
474                 tmp = tmp->b_this_page;
475         }
476         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
477         local_irq_restore(flags);
478         end_page_writeback(page);
479         return;
480
481 still_busy:
482         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
483         local_irq_restore(flags);
484         return;
485 }
486
487 /*
488  * If a page's buffers are under async readin (end_buffer_async_read
489  * completion) then there is a possibility that another thread of
490  * control could lock one of the buffers after it has completed
491  * but while some of the other buffers have not completed.  This
492  * locked buffer would confuse end_buffer_async_read() into not unlocking
493  * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
494  * that this buffer is not under async I/O.
495  *
496  * The page comes unlocked when it has no locked buffer_async buffers
497  * left.
498  *
499  * PageLocked prevents anyone starting new async I/O reads any of
500  * the buffers.
501  *
502  * PageWriteback is used to prevent simultaneous writeout of the same
503  * page.
504  *
505  * PageLocked prevents anyone from starting writeback of a page which is
506  * under read I/O (PageWriteback is only ever set against a locked page).
507  */
508 static void mark_buffer_async_read(struct buffer_head *bh)
509 {
510         bh->b_end_io = end_buffer_async_read;
511         set_buffer_async_read(bh);
512 }
513
514 void mark_buffer_async_write(struct buffer_head *bh)
515 {
516         bh->b_end_io = end_buffer_async_write;
517         set_buffer_async_write(bh);
518 }
519 EXPORT_SYMBOL(mark_buffer_async_write);
520
521
522 /*
523  * fs/buffer.c contains helper functions for buffer-backed address space's
524  * fsync functions.  A common requirement for buffer-based filesystems is
525  * that certain data from the backing blockdev needs to be written out for
526  * a successful fsync().  For example, ext2 indirect blocks need to be
527  * written back and waited upon before fsync() returns.
528  *
529  * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
530  * inode_has_buffers() and invalidate_inode_buffers() are provided for the
531  * management of a list of dependent buffers at ->i_mapping->private_list.
532  *
533  * Locking is a little subtle: try_to_free_buffers() will remove buffers
534  * from their controlling inode's queue when they are being freed.  But
535  * try_to_free_buffers() will be operating against the *blockdev* mapping
536  * at the time, not against the S_ISREG file which depends on those buffers.
537  * So the locking for private_list is via the private_lock in the address_space
538  * which backs the buffers.  Which is different from the address_space 
539  * against which the buffers are listed.  So for a particular address_space,
540  * mapping->private_lock does *not* protect mapping->private_list!  In fact,
541  * mapping->private_list will always be protected by the backing blockdev's
542  * ->private_lock.
543  *
544  * Which introduces a requirement: all buffers on an address_space's
545  * ->private_list must be from the same address_space: the blockdev's.
546  *
547  * address_spaces which do not place buffers at ->private_list via these
548  * utility functions are free to use private_lock and private_list for
549  * whatever they want.  The only requirement is that list_empty(private_list)
550  * be true at clear_inode() time.
551  *
552  * FIXME: clear_inode should not call invalidate_inode_buffers().  The
553  * filesystems should do that.  invalidate_inode_buffers() should just go
554  * BUG_ON(!list_empty).
555  *
556  * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
557  * take an address_space, not an inode.  And it should be called
558  * mark_buffer_dirty_fsync() to clearly define why those buffers are being
559  * queued up.
560  *
561  * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
562  * list if it is already on a list.  Because if the buffer is on a list,
563  * it *must* already be on the right one.  If not, the filesystem is being
564  * silly.  This will save a ton of locking.  But first we have to ensure
565  * that buffers are taken *off* the old inode's list when they are freed
566  * (presumably in truncate).  That requires careful auditing of all
567  * filesystems (do it inside bforget()).  It could also be done by bringing
568  * b_inode back.
569  */
570
571 /*
572  * The buffer's backing address_space's private_lock must be held
573  */
574 static inline void __remove_assoc_queue(struct buffer_head *bh)
575 {
576         list_del_init(&bh->b_assoc_buffers);
577         WARN_ON(!bh->b_assoc_map);
578         if (buffer_write_io_error(bh))
579                 set_bit(AS_EIO, &bh->b_assoc_map->flags);
580         bh->b_assoc_map = NULL;
581 }
582
583 int inode_has_buffers(struct inode *inode)
584 {
585         return !list_empty(&inode->i_data.private_list);
586 }
587
588 /*
589  * osync is designed to support O_SYNC io.  It waits synchronously for
590  * all already-submitted IO to complete, but does not queue any new
591  * writes to the disk.
592  *
593  * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
594  * you dirty the buffers, and then use osync_inode_buffers to wait for
595  * completion.  Any other dirty buffers which are not yet queued for
596  * write will not be flushed to disk by the osync.
597  */
598 static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
599 {
600         struct buffer_head *bh;
601         struct list_head *p;
602         int err = 0;
603
604         spin_lock(lock);
605 repeat:
606         list_for_each_prev(p, list) {
607                 bh = BH_ENTRY(p);
608                 if (buffer_locked(bh)) {
609                         get_bh(bh);
610                         spin_unlock(lock);
611                         wait_on_buffer(bh);
612                         if (!buffer_uptodate(bh))
613                                 err = -EIO;
614                         brelse(bh);
615                         spin_lock(lock);
616                         goto repeat;
617                 }
618         }
619         spin_unlock(lock);
620         return err;
621 }
622
623 /**
624  * sync_mapping_buffers - write out and wait upon a mapping's "associated"
625  *                        buffers
626  * @mapping: the mapping which wants those buffers written
627  *
628  * Starts I/O against the buffers at mapping->private_list, and waits upon
629  * that I/O.
630  *
631  * Basically, this is a convenience function for fsync().
632  * @mapping is a file or directory which needs those buffers to be written for
633  * a successful fsync().
634  */
635 int sync_mapping_buffers(struct address_space *mapping)
636 {
637         struct address_space *buffer_mapping = mapping->assoc_mapping;
638
639         if (buffer_mapping == NULL || list_empty(&mapping->private_list))
640                 return 0;
641
642         return fsync_buffers_list(&buffer_mapping->private_lock,
643                                         &mapping->private_list);
644 }
645 EXPORT_SYMBOL(sync_mapping_buffers);
646
647 /*
648  * Called when we've recently written block `bblock', and it is known that
649  * `bblock' was for a buffer_boundary() buffer.  This means that the block at
650  * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
651  * dirty, schedule it for IO.  So that indirects merge nicely with their data.
652  */
653 void write_boundary_block(struct block_device *bdev,
654                         sector_t bblock, unsigned blocksize)
655 {
656         struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
657         if (bh) {
658                 if (buffer_dirty(bh))
659                         ll_rw_block(WRITE, 1, &bh);
660                 put_bh(bh);
661         }
662 }
663
664 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
665 {
666         struct address_space *mapping = inode->i_mapping;
667         struct address_space *buffer_mapping = bh->b_page->mapping;
668
669         mark_buffer_dirty(bh);
670         if (!mapping->assoc_mapping) {
671                 mapping->assoc_mapping = buffer_mapping;
672         } else {
673                 BUG_ON(mapping->assoc_mapping != buffer_mapping);
674         }
675         if (list_empty(&bh->b_assoc_buffers)) {
676                 spin_lock(&buffer_mapping->private_lock);
677                 list_move_tail(&bh->b_assoc_buffers,
678                                 &mapping->private_list);
679                 bh->b_assoc_map = mapping;
680                 spin_unlock(&buffer_mapping->private_lock);
681         }
682 }
683 EXPORT_SYMBOL(mark_buffer_dirty_inode);
684
685 /*
686  * Add a page to the dirty page list.
687  *
688  * It is a sad fact of life that this function is called from several places
689  * deeply under spinlocking.  It may not sleep.
690  *
691  * If the page has buffers, the uptodate buffers are set dirty, to preserve
692  * dirty-state coherency between the page and the buffers.  It the page does
693  * not have buffers then when they are later attached they will all be set
694  * dirty.
695  *
696  * The buffers are dirtied before the page is dirtied.  There's a small race
697  * window in which a writepage caller may see the page cleanness but not the
698  * buffer dirtiness.  That's fine.  If this code were to set the page dirty
699  * before the buffers, a concurrent writepage caller could clear the page dirty
700  * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
701  * page on the dirty page list.
702  *
703  * We use private_lock to lock against try_to_free_buffers while using the
704  * page's buffer list.  Also use this to protect against clean buffers being
705  * added to the page after it was set dirty.
706  *
707  * FIXME: may need to call ->reservepage here as well.  That's rather up to the
708  * address_space though.
709  */
710 int __set_page_dirty_buffers(struct page *page)
711 {
712         struct address_space * const mapping = page_mapping(page);
713
714         if (unlikely(!mapping))
715                 return !TestSetPageDirty(page);
716
717         spin_lock(&mapping->private_lock);
718         if (page_has_buffers(page)) {
719                 struct buffer_head *head = page_buffers(page);
720                 struct buffer_head *bh = head;
721
722                 do {
723                         set_buffer_dirty(bh);
724                         bh = bh->b_this_page;
725                 } while (bh != head);
726         }
727         spin_unlock(&mapping->private_lock);
728
729         if (TestSetPageDirty(page))
730                 return 0;
731
732         write_lock_irq(&mapping->tree_lock);
733         if (page->mapping) {    /* Race with truncate? */
734                 if (mapping_cap_account_dirty(mapping)) {
735                         __inc_zone_page_state(page, NR_FILE_DIRTY);
736                         task_io_account_write(PAGE_CACHE_SIZE);
737                 }
738                 radix_tree_tag_set(&mapping->page_tree,
739                                 page_index(page), PAGECACHE_TAG_DIRTY);
740         }
741         write_unlock_irq(&mapping->tree_lock);
742         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
743         return 1;
744 }
745 EXPORT_SYMBOL(__set_page_dirty_buffers);
746
747 /*
748  * Write out and wait upon a list of buffers.
749  *
750  * We have conflicting pressures: we want to make sure that all
751  * initially dirty buffers get waited on, but that any subsequently
752  * dirtied buffers don't.  After all, we don't want fsync to last
753  * forever if somebody is actively writing to the file.
754  *
755  * Do this in two main stages: first we copy dirty buffers to a
756  * temporary inode list, queueing the writes as we go.  Then we clean
757  * up, waiting for those writes to complete.
758  * 
759  * During this second stage, any subsequent updates to the file may end
760  * up refiling the buffer on the original inode's dirty list again, so
761  * there is a chance we will end up with a buffer queued for write but
762  * not yet completed on that list.  So, as a final cleanup we go through
763  * the osync code to catch these locked, dirty buffers without requeuing
764  * any newly dirty buffers for write.
765  */
766 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
767 {
768         struct buffer_head *bh;
769         struct list_head tmp;
770         int err = 0, err2;
771
772         INIT_LIST_HEAD(&tmp);
773
774         spin_lock(lock);
775         while (!list_empty(list)) {
776                 bh = BH_ENTRY(list->next);
777                 __remove_assoc_queue(bh);
778                 if (buffer_dirty(bh) || buffer_locked(bh)) {
779                         list_add(&bh->b_assoc_buffers, &tmp);
780                         if (buffer_dirty(bh)) {
781                                 get_bh(bh);
782                                 spin_unlock(lock);
783                                 /*
784                                  * Ensure any pending I/O completes so that
785                                  * ll_rw_block() actually writes the current
786                                  * contents - it is a noop if I/O is still in
787                                  * flight on potentially older contents.
788                                  */
789                                 ll_rw_block(SWRITE, 1, &bh);
790                                 brelse(bh);
791                                 spin_lock(lock);
792                         }
793                 }
794         }
795
796         while (!list_empty(&tmp)) {
797                 bh = BH_ENTRY(tmp.prev);
798                 list_del_init(&bh->b_assoc_buffers);
799                 get_bh(bh);
800                 spin_unlock(lock);
801                 wait_on_buffer(bh);
802                 if (!buffer_uptodate(bh))
803                         err = -EIO;
804                 brelse(bh);
805                 spin_lock(lock);
806         }
807         
808         spin_unlock(lock);
809         err2 = osync_buffers_list(lock, list);
810         if (err)
811                 return err;
812         else
813                 return err2;
814 }
815
816 /*
817  * Invalidate any and all dirty buffers on a given inode.  We are
818  * probably unmounting the fs, but that doesn't mean we have already
819  * done a sync().  Just drop the buffers from the inode list.
820  *
821  * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
822  * assumes that all the buffers are against the blockdev.  Not true
823  * for reiserfs.
824  */
825 void invalidate_inode_buffers(struct inode *inode)
826 {
827         if (inode_has_buffers(inode)) {
828                 struct address_space *mapping = &inode->i_data;
829                 struct list_head *list = &mapping->private_list;
830                 struct address_space *buffer_mapping = mapping->assoc_mapping;
831
832                 spin_lock(&buffer_mapping->private_lock);
833                 while (!list_empty(list))
834                         __remove_assoc_queue(BH_ENTRY(list->next));
835                 spin_unlock(&buffer_mapping->private_lock);
836         }
837 }
838
839 /*
840  * Remove any clean buffers from the inode's buffer list.  This is called
841  * when we're trying to free the inode itself.  Those buffers can pin it.
842  *
843  * Returns true if all buffers were removed.
844  */
845 int remove_inode_buffers(struct inode *inode)
846 {
847         int ret = 1;
848
849         if (inode_has_buffers(inode)) {
850                 struct address_space *mapping = &inode->i_data;
851                 struct list_head *list = &mapping->private_list;
852                 struct address_space *buffer_mapping = mapping->assoc_mapping;
853
854                 spin_lock(&buffer_mapping->private_lock);
855                 while (!list_empty(list)) {
856                         struct buffer_head *bh = BH_ENTRY(list->next);
857                         if (buffer_dirty(bh)) {
858                                 ret = 0;
859                                 break;
860                         }
861                         __remove_assoc_queue(bh);
862                 }
863                 spin_unlock(&buffer_mapping->private_lock);
864         }
865         return ret;
866 }
867
868 /*
869  * Create the appropriate buffers when given a page for data area and
870  * the size of each buffer.. Use the bh->b_this_page linked list to
871  * follow the buffers created.  Return NULL if unable to create more
872  * buffers.
873  *
874  * The retry flag is used to differentiate async IO (paging, swapping)
875  * which may not fail from ordinary buffer allocations.
876  */
877 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
878                 int retry)
879 {
880         struct buffer_head *bh, *head;
881         long offset;
882
883 try_again:
884         head = NULL;
885         offset = PAGE_SIZE;
886         while ((offset -= size) >= 0) {
887                 bh = alloc_buffer_head(GFP_NOFS);
888                 if (!bh)
889                         goto no_grow;
890
891                 bh->b_bdev = NULL;
892                 bh->b_this_page = head;
893                 bh->b_blocknr = -1;
894                 head = bh;
895
896                 bh->b_state = 0;
897                 atomic_set(&bh->b_count, 0);
898                 bh->b_private = NULL;
899                 bh->b_size = size;
900
901                 /* Link the buffer to its page */
902                 set_bh_page(bh, page, offset);
903
904                 init_buffer(bh, NULL, NULL);
905         }
906         return head;
907 /*
908  * In case anything failed, we just free everything we got.
909  */
910 no_grow:
911         if (head) {
912                 do {
913                         bh = head;
914                         head = head->b_this_page;
915                         free_buffer_head(bh);
916                 } while (head);
917         }
918
919         /*
920          * Return failure for non-async IO requests.  Async IO requests
921          * are not allowed to fail, so we have to wait until buffer heads
922          * become available.  But we don't want tasks sleeping with 
923          * partially complete buffers, so all were released above.
924          */
925         if (!retry)
926                 return NULL;
927
928         /* We're _really_ low on memory. Now we just
929          * wait for old buffer heads to become free due to
930          * finishing IO.  Since this is an async request and
931          * the reserve list is empty, we're sure there are 
932          * async buffer heads in use.
933          */
934         free_more_memory();
935         goto try_again;
936 }
937 EXPORT_SYMBOL_GPL(alloc_page_buffers);
938
939 static inline void
940 link_dev_buffers(struct page *page, struct buffer_head *head)
941 {
942         struct buffer_head *bh, *tail;
943
944         bh = head;
945         do {
946                 tail = bh;
947                 bh = bh->b_this_page;
948         } while (bh);
949         tail->b_this_page = head;
950         attach_page_buffers(page, head);
951 }
952
953 /*
954  * Initialise the state of a blockdev page's buffers.
955  */ 
956 static void
957 init_page_buffers(struct page *page, struct block_device *bdev,
958                         sector_t block, int size)
959 {
960         struct buffer_head *head = page_buffers(page);
961         struct buffer_head *bh = head;
962         int uptodate = PageUptodate(page);
963
964         do {
965                 if (!buffer_mapped(bh)) {
966                         init_buffer(bh, NULL, NULL);
967                         bh->b_bdev = bdev;
968                         bh->b_blocknr = block;
969                         if (uptodate)
970                                 set_buffer_uptodate(bh);
971                         set_buffer_mapped(bh);
972                 }
973                 block++;
974                 bh = bh->b_this_page;
975         } while (bh != head);
976 }
977
978 /*
979  * Create the page-cache page that contains the requested block.
980  *
981  * This is user purely for blockdev mappings.
982  */
983 static struct page *
984 grow_dev_page(struct block_device *bdev, sector_t block,
985                 pgoff_t index, int size)
986 {
987         struct inode *inode = bdev->bd_inode;
988         struct page *page;
989         struct buffer_head *bh;
990
991         page = find_or_create_page(inode->i_mapping, index, GFP_NOFS);
992         if (!page)
993                 return NULL;
994
995         BUG_ON(!PageLocked(page));
996
997         if (page_has_buffers(page)) {
998                 bh = page_buffers(page);
999                 if (bh->b_size == size) {
1000                         init_page_buffers(page, bdev, block, size);
1001                         return page;
1002                 }
1003                 if (!try_to_free_buffers(page))
1004                         goto failed;
1005         }
1006
1007         /*
1008          * Allocate some buffers for this page
1009          */
1010         bh = alloc_page_buffers(page, size, 0);
1011         if (!bh)
1012                 goto failed;
1013
1014         /*
1015          * Link the page to the buffers and initialise them.  Take the
1016          * lock to be atomic wrt __find_get_block(), which does not
1017          * run under the page lock.
1018          */
1019         spin_lock(&inode->i_mapping->private_lock);
1020         link_dev_buffers(page, bh);
1021         init_page_buffers(page, bdev, block, size);
1022         spin_unlock(&inode->i_mapping->private_lock);
1023         return page;
1024
1025 failed:
1026         BUG();
1027         unlock_page(page);
1028         page_cache_release(page);
1029         return NULL;
1030 }
1031
1032 /*
1033  * Create buffers for the specified block device block's page.  If
1034  * that page was dirty, the buffers are set dirty also.
1035  *
1036  * Except that's a bug.  Attaching dirty buffers to a dirty
1037  * blockdev's page can result in filesystem corruption, because
1038  * some of those buffers may be aliases of filesystem data.
1039  * grow_dev_page() will go BUG() if this happens.
1040  */
1041 static int
1042 grow_buffers(struct block_device *bdev, sector_t block, int size)
1043 {
1044         struct page *page;
1045         pgoff_t index;
1046         int sizebits;
1047
1048         sizebits = -1;
1049         do {
1050                 sizebits++;
1051         } while ((size << sizebits) < PAGE_SIZE);
1052
1053         index = block >> sizebits;
1054
1055         /*
1056          * Check for a block which wants to lie outside our maximum possible
1057          * pagecache index.  (this comparison is done using sector_t types).
1058          */
1059         if (unlikely(index != block >> sizebits)) {
1060                 char b[BDEVNAME_SIZE];
1061
1062                 printk(KERN_ERR "%s: requested out-of-range block %llu for "
1063                         "device %s\n",
1064                         __FUNCTION__, (unsigned long long)block,
1065                         bdevname(bdev, b));
1066                 return -EIO;
1067         }
1068         block = index << sizebits;
1069         /* Create a page with the proper size buffers.. */
1070         page = grow_dev_page(bdev, block, index, size);
1071         if (!page)
1072                 return 0;
1073         unlock_page(page);
1074         page_cache_release(page);
1075         return 1;
1076 }
1077
1078 static struct buffer_head *
1079 __getblk_slow(struct block_device *bdev, sector_t block, int size)
1080 {
1081         /* Size must be multiple of hard sectorsize */
1082         if (unlikely(size & (bdev_hardsect_size(bdev)-1) ||
1083                         (size < 512 || size > PAGE_SIZE))) {
1084                 printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1085                                         size);
1086                 printk(KERN_ERR "hardsect size: %d\n",
1087                                         bdev_hardsect_size(bdev));
1088
1089                 dump_stack();
1090                 return NULL;
1091         }
1092
1093         for (;;) {
1094                 struct buffer_head * bh;
1095                 int ret;
1096
1097                 bh = __find_get_block(bdev, block, size);
1098                 if (bh)
1099                         return bh;
1100
1101                 ret = grow_buffers(bdev, block, size);
1102                 if (ret < 0)
1103                         return NULL;
1104                 if (ret == 0)
1105                         free_more_memory();
1106         }
1107 }
1108
1109 /*
1110  * The relationship between dirty buffers and dirty pages:
1111  *
1112  * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1113  * the page is tagged dirty in its radix tree.
1114  *
1115  * At all times, the dirtiness of the buffers represents the dirtiness of
1116  * subsections of the page.  If the page has buffers, the page dirty bit is
1117  * merely a hint about the true dirty state.
1118  *
1119  * When a page is set dirty in its entirety, all its buffers are marked dirty
1120  * (if the page has buffers).
1121  *
1122  * When a buffer is marked dirty, its page is dirtied, but the page's other
1123  * buffers are not.
1124  *
1125  * Also.  When blockdev buffers are explicitly read with bread(), they
1126  * individually become uptodate.  But their backing page remains not
1127  * uptodate - even if all of its buffers are uptodate.  A subsequent
1128  * block_read_full_page() against that page will discover all the uptodate
1129  * buffers, will set the page uptodate and will perform no I/O.
1130  */
1131
1132 /**
1133  * mark_buffer_dirty - mark a buffer_head as needing writeout
1134  * @bh: the buffer_head to mark dirty
1135  *
1136  * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1137  * backing page dirty, then tag the page as dirty in its address_space's radix
1138  * tree and then attach the address_space's inode to its superblock's dirty
1139  * inode list.
1140  *
1141  * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1142  * mapping->tree_lock and the global inode_lock.
1143  */
1144 void fastcall mark_buffer_dirty(struct buffer_head *bh)
1145 {
1146         if (!buffer_dirty(bh) && !test_set_buffer_dirty(bh))
1147                 __set_page_dirty_nobuffers(bh->b_page);
1148 }
1149
1150 /*
1151  * Decrement a buffer_head's reference count.  If all buffers against a page
1152  * have zero reference count, are clean and unlocked, and if the page is clean
1153  * and unlocked then try_to_free_buffers() may strip the buffers from the page
1154  * in preparation for freeing it (sometimes, rarely, buffers are removed from
1155  * a page but it ends up not being freed, and buffers may later be reattached).
1156  */
1157 void __brelse(struct buffer_head * buf)
1158 {
1159         if (atomic_read(&buf->b_count)) {
1160                 put_bh(buf);
1161                 return;
1162         }
1163         printk(KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1164         WARN_ON(1);
1165 }
1166
1167 /*
1168  * bforget() is like brelse(), except it discards any
1169  * potentially dirty data.
1170  */
1171 void __bforget(struct buffer_head *bh)
1172 {
1173         clear_buffer_dirty(bh);
1174         if (!list_empty(&bh->b_assoc_buffers)) {
1175                 struct address_space *buffer_mapping = bh->b_page->mapping;
1176
1177                 spin_lock(&buffer_mapping->private_lock);
1178                 list_del_init(&bh->b_assoc_buffers);
1179                 bh->b_assoc_map = NULL;
1180                 spin_unlock(&buffer_mapping->private_lock);
1181         }
1182         __brelse(bh);
1183 }
1184
1185 static struct buffer_head *__bread_slow(struct buffer_head *bh)
1186 {
1187         lock_buffer(bh);
1188         if (buffer_uptodate(bh)) {
1189                 unlock_buffer(bh);
1190                 return bh;
1191         } else {
1192                 get_bh(bh);
1193                 bh->b_end_io = end_buffer_read_sync;
1194                 submit_bh(READ, bh);
1195                 wait_on_buffer(bh);
1196                 if (buffer_uptodate(bh))
1197                         return bh;
1198         }
1199         brelse(bh);
1200         return NULL;
1201 }
1202
1203 /*
1204  * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1205  * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1206  * refcount elevated by one when they're in an LRU.  A buffer can only appear
1207  * once in a particular CPU's LRU.  A single buffer can be present in multiple
1208  * CPU's LRUs at the same time.
1209  *
1210  * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1211  * sb_find_get_block().
1212  *
1213  * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1214  * a local interrupt disable for that.
1215  */
1216
1217 #define BH_LRU_SIZE     8
1218
1219 struct bh_lru {
1220         struct buffer_head *bhs[BH_LRU_SIZE];
1221 };
1222
1223 static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1224
1225 #ifdef CONFIG_SMP
1226 #define bh_lru_lock()   local_irq_disable()
1227 #define bh_lru_unlock() local_irq_enable()
1228 #else
1229 #define bh_lru_lock()   preempt_disable()
1230 #define bh_lru_unlock() preempt_enable()
1231 #endif
1232
1233 static inline void check_irqs_on(void)
1234 {
1235 #ifdef irqs_disabled
1236         BUG_ON(irqs_disabled());
1237 #endif
1238 }
1239
1240 /*
1241  * The LRU management algorithm is dopey-but-simple.  Sorry.
1242  */
1243 static void bh_lru_install(struct buffer_head *bh)
1244 {
1245         struct buffer_head *evictee = NULL;
1246         struct bh_lru *lru;
1247
1248         check_irqs_on();
1249         bh_lru_lock();
1250         lru = &__get_cpu_var(bh_lrus);
1251         if (lru->bhs[0] != bh) {
1252                 struct buffer_head *bhs[BH_LRU_SIZE];
1253                 int in;
1254                 int out = 0;
1255
1256                 get_bh(bh);
1257                 bhs[out++] = bh;
1258                 for (in = 0; in < BH_LRU_SIZE; in++) {
1259                         struct buffer_head *bh2 = lru->bhs[in];
1260
1261                         if (bh2 == bh) {
1262                                 __brelse(bh2);
1263                         } else {
1264                                 if (out >= BH_LRU_SIZE) {
1265                                         BUG_ON(evictee != NULL);
1266                                         evictee = bh2;
1267                                 } else {
1268                                         bhs[out++] = bh2;
1269                                 }
1270                         }
1271                 }
1272                 while (out < BH_LRU_SIZE)
1273                         bhs[out++] = NULL;
1274                 memcpy(lru->bhs, bhs, sizeof(bhs));
1275         }
1276         bh_lru_unlock();
1277
1278         if (evictee)
1279                 __brelse(evictee);
1280 }
1281
1282 /*
1283  * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1284  */
1285 static struct buffer_head *
1286 lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1287 {
1288         struct buffer_head *ret = NULL;
1289         struct bh_lru *lru;
1290         unsigned int i;
1291
1292         check_irqs_on();
1293         bh_lru_lock();
1294         lru = &__get_cpu_var(bh_lrus);
1295         for (i = 0; i < BH_LRU_SIZE; i++) {
1296                 struct buffer_head *bh = lru->bhs[i];
1297
1298                 if (bh && bh->b_bdev == bdev &&
1299                                 bh->b_blocknr == block && bh->b_size == size) {
1300                         if (i) {
1301                                 while (i) {
1302                                         lru->bhs[i] = lru->bhs[i - 1];
1303                                         i--;
1304                                 }
1305                                 lru->bhs[0] = bh;
1306                         }
1307                         get_bh(bh);
1308                         ret = bh;
1309                         break;
1310                 }
1311         }
1312         bh_lru_unlock();
1313         return ret;
1314 }
1315
1316 /*
1317  * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1318  * it in the LRU and mark it as accessed.  If it is not present then return
1319  * NULL
1320  */
1321 struct buffer_head *
1322 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1323 {
1324         struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1325
1326         if (bh == NULL) {
1327                 bh = __find_get_block_slow(bdev, block);
1328                 if (bh)
1329                         bh_lru_install(bh);
1330         }
1331         if (bh)
1332                 touch_buffer(bh);
1333         return bh;
1334 }
1335 EXPORT_SYMBOL(__find_get_block);
1336
1337 /*
1338  * __getblk will locate (and, if necessary, create) the buffer_head
1339  * which corresponds to the passed block_device, block and size. The
1340  * returned buffer has its reference count incremented.
1341  *
1342  * __getblk() cannot fail - it just keeps trying.  If you pass it an
1343  * illegal block number, __getblk() will happily return a buffer_head
1344  * which represents the non-existent block.  Very weird.
1345  *
1346  * __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
1347  * attempt is failing.  FIXME, perhaps?
1348  */
1349 struct buffer_head *
1350 __getblk(struct block_device *bdev, sector_t block, unsigned size)
1351 {
1352         struct buffer_head *bh = __find_get_block(bdev, block, size);
1353
1354         might_sleep();
1355         if (bh == NULL)
1356                 bh = __getblk_slow(bdev, block, size);
1357         return bh;
1358 }
1359 EXPORT_SYMBOL(__getblk);
1360
1361 /*
1362  * Do async read-ahead on a buffer..
1363  */
1364 void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1365 {
1366         struct buffer_head *bh = __getblk(bdev, block, size);
1367         if (likely(bh)) {
1368                 ll_rw_block(READA, 1, &bh);
1369                 brelse(bh);
1370         }
1371 }
1372 EXPORT_SYMBOL(__breadahead);
1373
1374 /**
1375  *  __bread() - reads a specified block and returns the bh
1376  *  @bdev: the block_device to read from
1377  *  @block: number of block
1378  *  @size: size (in bytes) to read
1379  * 
1380  *  Reads a specified block, and returns buffer head that contains it.
1381  *  It returns NULL if the block was unreadable.
1382  */
1383 struct buffer_head *
1384 __bread(struct block_device *bdev, sector_t block, unsigned size)
1385 {
1386         struct buffer_head *bh = __getblk(bdev, block, size);
1387
1388         if (likely(bh) && !buffer_uptodate(bh))
1389                 bh = __bread_slow(bh);
1390         return bh;
1391 }
1392 EXPORT_SYMBOL(__bread);
1393
1394 /*
1395  * invalidate_bh_lrus() is called rarely - but not only at unmount.
1396  * This doesn't race because it runs in each cpu either in irq
1397  * or with preempt disabled.
1398  */
1399 static void invalidate_bh_lru(void *arg)
1400 {
1401         struct bh_lru *b = &get_cpu_var(bh_lrus);
1402         int i;
1403
1404         for (i = 0; i < BH_LRU_SIZE; i++) {
1405                 brelse(b->bhs[i]);
1406                 b->bhs[i] = NULL;
1407         }
1408         put_cpu_var(bh_lrus);
1409 }
1410         
1411 static void invalidate_bh_lrus(void)
1412 {
1413         on_each_cpu(invalidate_bh_lru, NULL, 1, 1);
1414 }
1415
1416 void set_bh_page(struct buffer_head *bh,
1417                 struct page *page, unsigned long offset)
1418 {
1419         bh->b_page = page;
1420         BUG_ON(offset >= PAGE_SIZE);
1421         if (PageHighMem(page))
1422                 /*
1423                  * This catches illegal uses and preserves the offset:
1424                  */
1425                 bh->b_data = (char *)(0 + offset);
1426         else
1427                 bh->b_data = page_address(page) + offset;
1428 }
1429 EXPORT_SYMBOL(set_bh_page);
1430
1431 /*
1432  * Called when truncating a buffer on a page completely.
1433  */
1434 static void discard_buffer(struct buffer_head * bh)
1435 {
1436         lock_buffer(bh);
1437         clear_buffer_dirty(bh);
1438         bh->b_bdev = NULL;
1439         clear_buffer_mapped(bh);
1440         clear_buffer_req(bh);
1441         clear_buffer_new(bh);
1442         clear_buffer_delay(bh);
1443         clear_buffer_unwritten(bh);
1444         unlock_buffer(bh);
1445 }
1446
1447 /**
1448  * block_invalidatepage - invalidate part of all of a buffer-backed page
1449  *
1450  * @page: the page which is affected
1451  * @offset: the index of the truncation point
1452  *
1453  * block_invalidatepage() is called when all or part of the page has become
1454  * invalidatedby a truncate operation.
1455  *
1456  * block_invalidatepage() does not have to release all buffers, but it must
1457  * ensure that no dirty buffer is left outside @offset and that no I/O
1458  * is underway against any of the blocks which are outside the truncation
1459  * point.  Because the caller is about to free (and possibly reuse) those
1460  * blocks on-disk.
1461  */
1462 void block_invalidatepage(struct page *page, unsigned long offset)
1463 {
1464         struct buffer_head *head, *bh, *next;
1465         unsigned int curr_off = 0;
1466
1467         BUG_ON(!PageLocked(page));
1468         if (!page_has_buffers(page))
1469                 goto out;
1470
1471         head = page_buffers(page);
1472         bh = head;
1473         do {
1474                 unsigned int next_off = curr_off + bh->b_size;
1475                 next = bh->b_this_page;
1476
1477                 /*
1478                  * is this block fully invalidated?
1479                  */
1480                 if (offset <= curr_off)
1481                         discard_buffer(bh);
1482                 curr_off = next_off;
1483                 bh = next;
1484         } while (bh != head);
1485
1486         /*
1487          * We release buffers only if the entire page is being invalidated.
1488          * The get_block cached value has been unconditionally invalidated,
1489          * so real IO is not possible anymore.
1490          */
1491         if (offset == 0)
1492                 try_to_release_page(page, 0);
1493 out:
1494         return;
1495 }
1496 EXPORT_SYMBOL(block_invalidatepage);
1497
1498 /*
1499  * We attach and possibly dirty the buffers atomically wrt
1500  * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1501  * is already excluded via the page lock.
1502  */
1503 void create_empty_buffers(struct page *page,
1504                         unsigned long blocksize, unsigned long b_state)
1505 {
1506         struct buffer_head *bh, *head, *tail;
1507
1508         head = alloc_page_buffers(page, blocksize, 1);
1509         bh = head;
1510         do {
1511                 bh->b_state |= b_state;
1512                 tail = bh;
1513                 bh = bh->b_this_page;
1514         } while (bh);
1515         tail->b_this_page = head;
1516
1517         spin_lock(&page->mapping->private_lock);
1518         if (PageUptodate(page) || PageDirty(page)) {
1519                 bh = head;
1520                 do {
1521                         if (PageDirty(page))
1522                                 set_buffer_dirty(bh);
1523                         if (PageUptodate(page))
1524                                 set_buffer_uptodate(bh);
1525                         bh = bh->b_this_page;
1526                 } while (bh != head);
1527         }
1528         attach_page_buffers(page, head);
1529         spin_unlock(&page->mapping->private_lock);
1530 }
1531 EXPORT_SYMBOL(create_empty_buffers);
1532
1533 /*
1534  * We are taking a block for data and we don't want any output from any
1535  * buffer-cache aliases starting from return from that function and
1536  * until the moment when something will explicitly mark the buffer
1537  * dirty (hopefully that will not happen until we will free that block ;-)
1538  * We don't even need to mark it not-uptodate - nobody can expect
1539  * anything from a newly allocated buffer anyway. We used to used
1540  * unmap_buffer() for such invalidation, but that was wrong. We definitely
1541  * don't want to mark the alias unmapped, for example - it would confuse
1542  * anyone who might pick it with bread() afterwards...
1543  *
1544  * Also..  Note that bforget() doesn't lock the buffer.  So there can
1545  * be writeout I/O going on against recently-freed buffers.  We don't
1546  * wait on that I/O in bforget() - it's more efficient to wait on the I/O
1547  * only if we really need to.  That happens here.
1548  */
1549 void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1550 {
1551         struct buffer_head *old_bh;
1552
1553         might_sleep();
1554
1555         old_bh = __find_get_block_slow(bdev, block);
1556         if (old_bh) {
1557                 clear_buffer_dirty(old_bh);
1558                 wait_on_buffer(old_bh);
1559                 clear_buffer_req(old_bh);
1560                 __brelse(old_bh);
1561         }
1562 }
1563 EXPORT_SYMBOL(unmap_underlying_metadata);
1564
1565 /*
1566  * NOTE! All mapped/uptodate combinations are valid:
1567  *
1568  *      Mapped  Uptodate        Meaning
1569  *
1570  *      No      No              "unknown" - must do get_block()
1571  *      No      Yes             "hole" - zero-filled
1572  *      Yes     No              "allocated" - allocated on disk, not read in
1573  *      Yes     Yes             "valid" - allocated and up-to-date in memory.
1574  *
1575  * "Dirty" is valid only with the last case (mapped+uptodate).
1576  */
1577
1578 /*
1579  * While block_write_full_page is writing back the dirty buffers under
1580  * the page lock, whoever dirtied the buffers may decide to clean them
1581  * again at any time.  We handle that by only looking at the buffer
1582  * state inside lock_buffer().
1583  *
1584  * If block_write_full_page() is called for regular writeback
1585  * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1586  * locked buffer.   This only can happen if someone has written the buffer
1587  * directly, with submit_bh().  At the address_space level PageWriteback
1588  * prevents this contention from occurring.
1589  */
1590 static int __block_write_full_page(struct inode *inode, struct page *page,
1591                         get_block_t *get_block, struct writeback_control *wbc)
1592 {
1593         int err;
1594         sector_t block;
1595         sector_t last_block;
1596         struct buffer_head *bh, *head;
1597         const unsigned blocksize = 1 << inode->i_blkbits;
1598         int nr_underway = 0;
1599
1600         BUG_ON(!PageLocked(page));
1601
1602         last_block = (i_size_read(inode) - 1) >> inode->i_blkbits;
1603
1604         if (!page_has_buffers(page)) {
1605                 create_empty_buffers(page, blocksize,
1606                                         (1 << BH_Dirty)|(1 << BH_Uptodate));
1607         }
1608
1609         /*
1610          * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1611          * here, and the (potentially unmapped) buffers may become dirty at
1612          * any time.  If a buffer becomes dirty here after we've inspected it
1613          * then we just miss that fact, and the page stays dirty.
1614          *
1615          * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1616          * handle that here by just cleaning them.
1617          */
1618
1619         block = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
1620         head = page_buffers(page);
1621         bh = head;
1622
1623         /*
1624          * Get all the dirty buffers mapped to disk addresses and
1625          * handle any aliases from the underlying blockdev's mapping.
1626          */
1627         do {
1628                 if (block > last_block) {
1629                         /*
1630                          * mapped buffers outside i_size will occur, because
1631                          * this page can be outside i_size when there is a
1632                          * truncate in progress.
1633                          */
1634                         /*
1635                          * The buffer was zeroed by block_write_full_page()
1636                          */
1637                         clear_buffer_dirty(bh);
1638                         set_buffer_uptodate(bh);
1639                 } else if (!buffer_mapped(bh) && buffer_dirty(bh)) {
1640                         WARN_ON(bh->b_size != blocksize);
1641                         err = get_block(inode, block, bh, 1);
1642                         if (err)
1643                                 goto recover;
1644                         if (buffer_new(bh)) {
1645                                 /* blockdev mappings never come here */
1646                                 clear_buffer_new(bh);
1647                                 unmap_underlying_metadata(bh->b_bdev,
1648                                                         bh->b_blocknr);
1649                         }
1650                 }
1651                 bh = bh->b_this_page;
1652                 block++;
1653         } while (bh != head);
1654
1655         do {
1656                 if (!buffer_mapped(bh))
1657                         continue;
1658                 /*
1659                  * If it's a fully non-blocking write attempt and we cannot
1660                  * lock the buffer then redirty the page.  Note that this can
1661                  * potentially cause a busy-wait loop from pdflush and kswapd
1662                  * activity, but those code paths have their own higher-level
1663                  * throttling.
1664                  */
1665                 if (wbc->sync_mode != WB_SYNC_NONE || !wbc->nonblocking) {
1666                         lock_buffer(bh);
1667                 } else if (test_set_buffer_locked(bh)) {
1668                         redirty_page_for_writepage(wbc, page);
1669                         continue;
1670                 }
1671                 if (test_clear_buffer_dirty(bh)) {
1672                         mark_buffer_async_write(bh);
1673                 } else {
1674                         unlock_buffer(bh);
1675                 }
1676         } while ((bh = bh->b_this_page) != head);
1677
1678         /*
1679          * The page and its buffers are protected by PageWriteback(), so we can
1680          * drop the bh refcounts early.
1681          */
1682         BUG_ON(PageWriteback(page));
1683         set_page_writeback(page);
1684
1685         do {
1686                 struct buffer_head *next = bh->b_this_page;
1687                 if (buffer_async_write(bh)) {
1688                         submit_bh(WRITE, bh);
1689                         nr_underway++;
1690                 }
1691                 bh = next;
1692         } while (bh != head);
1693         unlock_page(page);
1694
1695         err = 0;
1696 done:
1697         if (nr_underway == 0) {
1698                 /*
1699                  * The page was marked dirty, but the buffers were
1700                  * clean.  Someone wrote them back by hand with
1701                  * ll_rw_block/submit_bh.  A rare case.
1702                  */
1703                 end_page_writeback(page);
1704
1705                 /*
1706                  * The page and buffer_heads can be released at any time from
1707                  * here on.
1708                  */
1709                 wbc->pages_skipped++;   /* We didn't write this page */
1710         }
1711         return err;
1712
1713 recover:
1714         /*
1715          * ENOSPC, or some other error.  We may already have added some
1716          * blocks to the file, so we need to write these out to avoid
1717          * exposing stale data.
1718          * The page is currently locked and not marked for writeback
1719          */
1720         bh = head;
1721         /* Recovery: lock and submit the mapped buffers */
1722         do {
1723                 if (buffer_mapped(bh) && buffer_dirty(bh)) {
1724                         lock_buffer(bh);
1725                         mark_buffer_async_write(bh);
1726                 } else {
1727                         /*
1728                          * The buffer may have been set dirty during
1729                          * attachment to a dirty page.
1730                          */
1731                         clear_buffer_dirty(bh);
1732                 }
1733         } while ((bh = bh->b_this_page) != head);
1734         SetPageError(page);
1735         BUG_ON(PageWriteback(page));
1736         set_page_writeback(page);
1737         do {
1738                 struct buffer_head *next = bh->b_this_page;
1739                 if (buffer_async_write(bh)) {
1740                         clear_buffer_dirty(bh);
1741                         submit_bh(WRITE, bh);
1742                         nr_underway++;
1743                 }
1744                 bh = next;
1745         } while (bh != head);
1746         unlock_page(page);
1747         goto done;
1748 }
1749
1750 static int __block_prepare_write(struct inode *inode, struct page *page,
1751                 unsigned from, unsigned to, get_block_t *get_block)
1752 {
1753         unsigned block_start, block_end;
1754         sector_t block;
1755         int err = 0;
1756         unsigned blocksize, bbits;
1757         struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1758
1759         BUG_ON(!PageLocked(page));
1760         BUG_ON(from > PAGE_CACHE_SIZE);
1761         BUG_ON(to > PAGE_CACHE_SIZE);
1762         BUG_ON(from > to);
1763
1764         blocksize = 1 << inode->i_blkbits;
1765         if (!page_has_buffers(page))
1766                 create_empty_buffers(page, blocksize, 0);
1767         head = page_buffers(page);
1768
1769         bbits = inode->i_blkbits;
1770         block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1771
1772         for(bh = head, block_start = 0; bh != head || !block_start;
1773             block++, block_start=block_end, bh = bh->b_this_page) {
1774                 block_end = block_start + blocksize;
1775                 if (block_end <= from || block_start >= to) {
1776                         if (PageUptodate(page)) {
1777                                 if (!buffer_uptodate(bh))
1778                                         set_buffer_uptodate(bh);
1779                         }
1780                         continue;
1781                 }
1782                 if (buffer_new(bh))
1783                         clear_buffer_new(bh);
1784                 if (!buffer_mapped(bh)) {
1785                         WARN_ON(bh->b_size != blocksize);
1786                         err = get_block(inode, block, bh, 1);
1787                         if (err)
1788                                 break;
1789                         if (buffer_new(bh)) {
1790                                 unmap_underlying_metadata(bh->b_bdev,
1791                                                         bh->b_blocknr);
1792                                 if (PageUptodate(page)) {
1793                                         set_buffer_uptodate(bh);
1794                                         continue;
1795                                 }
1796                                 if (block_end > to || block_start < from) {
1797                                         void *kaddr;
1798
1799                                         kaddr = kmap_atomic(page, KM_USER0);
1800                                         if (block_end > to)
1801                                                 memset(kaddr+to, 0,
1802                                                         block_end-to);
1803                                         if (block_start < from)
1804                                                 memset(kaddr+block_start,
1805                                                         0, from-block_start);
1806                                         flush_dcache_page(page);
1807                                         kunmap_atomic(kaddr, KM_USER0);
1808                                 }
1809                                 continue;
1810                         }
1811                 }
1812                 if (PageUptodate(page)) {
1813                         if (!buffer_uptodate(bh))
1814                                 set_buffer_uptodate(bh);
1815                         continue; 
1816                 }
1817                 if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1818                     !buffer_unwritten(bh) &&
1819                      (block_start < from || block_end > to)) {
1820                         ll_rw_block(READ, 1, &bh);
1821                         *wait_bh++=bh;
1822                 }
1823         }
1824         /*
1825          * If we issued read requests - let them complete.
1826          */
1827         while(wait_bh > wait) {
1828                 wait_on_buffer(*--wait_bh);
1829                 if (!buffer_uptodate(*wait_bh))
1830                         err = -EIO;
1831         }
1832         if (!err) {
1833                 bh = head;
1834                 do {
1835                         if (buffer_new(bh))
1836                                 clear_buffer_new(bh);
1837                 } while ((bh = bh->b_this_page) != head);
1838                 return 0;
1839         }
1840         /* Error case: */
1841         /*
1842          * Zero out any newly allocated blocks to avoid exposing stale
1843          * data.  If BH_New is set, we know that the block was newly
1844          * allocated in the above loop.
1845          */
1846         bh = head;
1847         block_start = 0;
1848         do {
1849                 block_end = block_start+blocksize;
1850                 if (block_end <= from)
1851                         goto next_bh;
1852                 if (block_start >= to)
1853                         break;
1854                 if (buffer_new(bh)) {
1855                         void *kaddr;
1856
1857                         clear_buffer_new(bh);
1858                         kaddr = kmap_atomic(page, KM_USER0);
1859                         memset(kaddr+block_start, 0, bh->b_size);
1860                         flush_dcache_page(page);
1861                         kunmap_atomic(kaddr, KM_USER0);
1862                         set_buffer_uptodate(bh);
1863                         mark_buffer_dirty(bh);
1864                 }
1865 next_bh:
1866                 block_start = block_end;
1867                 bh = bh->b_this_page;
1868         } while (bh != head);
1869         return err;
1870 }
1871
1872 static int __block_commit_write(struct inode *inode, struct page *page,
1873                 unsigned from, unsigned to)
1874 {
1875         unsigned block_start, block_end;
1876         int partial = 0;
1877         unsigned blocksize;
1878         struct buffer_head *bh, *head;
1879
1880         blocksize = 1 << inode->i_blkbits;
1881
1882         for(bh = head = page_buffers(page), block_start = 0;
1883             bh != head || !block_start;
1884             block_start=block_end, bh = bh->b_this_page) {
1885                 block_end = block_start + blocksize;
1886                 if (block_end <= from || block_start >= to) {
1887                         if (!buffer_uptodate(bh))
1888                                 partial = 1;
1889                 } else {
1890                         set_buffer_uptodate(bh);
1891                         mark_buffer_dirty(bh);
1892                 }
1893         }
1894
1895         /*
1896          * If this is a partial write which happened to make all buffers
1897          * uptodate then we can optimize away a bogus readpage() for
1898          * the next read(). Here we 'discover' whether the page went
1899          * uptodate as a result of this (potentially partial) write.
1900          */
1901         if (!partial)
1902                 SetPageUptodate(page);
1903         return 0;
1904 }
1905
1906 /*
1907  * Generic "read page" function for block devices that have the normal
1908  * get_block functionality. This is most of the block device filesystems.
1909  * Reads the page asynchronously --- the unlock_buffer() and
1910  * set/clear_buffer_uptodate() functions propagate buffer state into the
1911  * page struct once IO has completed.
1912  */
1913 int block_read_full_page(struct page *page, get_block_t *get_block)
1914 {
1915         struct inode *inode = page->mapping->host;
1916         sector_t iblock, lblock;
1917         struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
1918         unsigned int blocksize;
1919         int nr, i;
1920         int fully_mapped = 1;
1921
1922         BUG_ON(!PageLocked(page));
1923         blocksize = 1 << inode->i_blkbits;
1924         if (!page_has_buffers(page))
1925                 create_empty_buffers(page, blocksize, 0);
1926         head = page_buffers(page);
1927
1928         iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
1929         lblock = (i_size_read(inode)+blocksize-1) >> inode->i_blkbits;
1930         bh = head;
1931         nr = 0;
1932         i = 0;
1933
1934         do {
1935                 if (buffer_uptodate(bh))
1936                         continue;
1937
1938                 if (!buffer_mapped(bh)) {
1939                         int err = 0;
1940
1941                         fully_mapped = 0;
1942                         if (iblock < lblock) {
1943                                 WARN_ON(bh->b_size != blocksize);
1944                                 err = get_block(inode, iblock, bh, 0);
1945                                 if (err)
1946                                         SetPageError(page);
1947                         }
1948                         if (!buffer_mapped(bh)) {
1949                                 void *kaddr = kmap_atomic(page, KM_USER0);
1950                                 memset(kaddr + i * blocksize, 0, blocksize);
1951                                 flush_dcache_page(page);
1952                                 kunmap_atomic(kaddr, KM_USER0);
1953                                 if (!err)
1954                                         set_buffer_uptodate(bh);
1955                                 continue;
1956                         }
1957                         /*
1958                          * get_block() might have updated the buffer
1959                          * synchronously
1960                          */
1961                         if (buffer_uptodate(bh))
1962                                 continue;
1963                 }
1964                 arr[nr++] = bh;
1965         } while (i++, iblock++, (bh = bh->b_this_page) != head);
1966
1967         if (fully_mapped)
1968                 SetPageMappedToDisk(page);
1969
1970         if (!nr) {
1971                 /*
1972                  * All buffers are uptodate - we can set the page uptodate
1973                  * as well. But not if get_block() returned an error.
1974                  */
1975                 if (!PageError(page))
1976                         SetPageUptodate(page);
1977                 unlock_page(page);
1978                 return 0;
1979         }
1980
1981         /* Stage two: lock the buffers */
1982         for (i = 0; i < nr; i++) {
1983                 bh = arr[i];
1984                 lock_buffer(bh);
1985                 mark_buffer_async_read(bh);
1986         }
1987
1988         /*
1989          * Stage 3: start the IO.  Check for uptodateness
1990          * inside the buffer lock in case another process reading
1991          * the underlying blockdev brought it uptodate (the sct fix).
1992          */
1993         for (i = 0; i < nr; i++) {
1994                 bh = arr[i];
1995                 if (buffer_uptodate(bh))
1996                         end_buffer_async_read(bh, 1);
1997                 else
1998                         submit_bh(READ, bh);
1999         }
2000         return 0;
2001 }
2002
2003 /* utility function for filesystems that need to do work on expanding
2004  * truncates.  Uses prepare/commit_write to allow the filesystem to
2005  * deal with the hole.  
2006  */
2007 static int __generic_cont_expand(struct inode *inode, loff_t size,
2008                                  pgoff_t index, unsigned int offset)
2009 {
2010         struct address_space *mapping = inode->i_mapping;
2011         struct page *page;
2012         unsigned long limit;
2013         int err;
2014
2015         err = -EFBIG;
2016         limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
2017         if (limit != RLIM_INFINITY && size > (loff_t)limit) {
2018                 send_sig(SIGXFSZ, current, 0);
2019                 goto out;
2020         }
2021         if (size > inode->i_sb->s_maxbytes)
2022                 goto out;
2023
2024         err = -ENOMEM;
2025         page = grab_cache_page(mapping, index);
2026         if (!page)
2027                 goto out;
2028         err = mapping->a_ops->prepare_write(NULL, page, offset, offset);
2029         if (err) {
2030                 /*
2031                  * ->prepare_write() may have instantiated a few blocks
2032                  * outside i_size.  Trim these off again.
2033                  */
2034                 unlock_page(page);
2035                 page_cache_release(page);
2036                 vmtruncate(inode, inode->i_size);
2037                 goto out;
2038         }
2039
2040         err = mapping->a_ops->commit_write(NULL, page, offset, offset);
2041
2042         unlock_page(page);
2043         page_cache_release(page);
2044         if (err > 0)
2045                 err = 0;
2046 out:
2047         return err;
2048 }
2049
2050 int generic_cont_expand(struct inode *inode, loff_t size)
2051 {
2052         pgoff_t index;
2053         unsigned int offset;
2054
2055         offset = (size & (PAGE_CACHE_SIZE - 1)); /* Within page */
2056
2057         /* ugh.  in prepare/commit_write, if from==to==start of block, we
2058         ** skip the prepare.  make sure we never send an offset for the start
2059         ** of a block
2060         */
2061         if ((offset & (inode->i_sb->s_blocksize - 1)) == 0) {
2062                 /* caller must handle this extra byte. */
2063                 offset++;
2064         }
2065         index = size >> PAGE_CACHE_SHIFT;
2066
2067         return __generic_cont_expand(inode, size, index, offset);
2068 }
2069
2070 int generic_cont_expand_simple(struct inode *inode, loff_t size)
2071 {
2072         loff_t pos = size - 1;
2073         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
2074         unsigned int offset = (pos & (PAGE_CACHE_SIZE - 1)) + 1;
2075
2076         /* prepare/commit_write can handle even if from==to==start of block. */
2077         return __generic_cont_expand(inode, size, index, offset);
2078 }
2079
2080 /*
2081  * For moronic filesystems that do not allow holes in file.
2082  * We may have to extend the file.
2083  */
2084
2085 int cont_prepare_write(struct page *page, unsigned offset,
2086                 unsigned to, get_block_t *get_block, loff_t *bytes)
2087 {
2088         struct address_space *mapping = page->mapping;
2089         struct inode *inode = mapping->host;
2090         struct page *new_page;
2091         pgoff_t pgpos;
2092         long status;
2093         unsigned zerofrom;
2094         unsigned blocksize = 1 << inode->i_blkbits;
2095         void *kaddr;
2096
2097         while(page->index > (pgpos = *bytes>>PAGE_CACHE_SHIFT)) {
2098                 status = -ENOMEM;
2099                 new_page = grab_cache_page(mapping, pgpos);
2100                 if (!new_page)
2101                         goto out;
2102                 /* we might sleep */
2103                 if (*bytes>>PAGE_CACHE_SHIFT != pgpos) {
2104                         unlock_page(new_page);
2105                         page_cache_release(new_page);
2106                         continue;
2107                 }
2108                 zerofrom = *bytes & ~PAGE_CACHE_MASK;
2109                 if (zerofrom & (blocksize-1)) {
2110                         *bytes |= (blocksize-1);
2111                         (*bytes)++;
2112                 }
2113                 status = __block_prepare_write(inode, new_page, zerofrom,
2114                                                 PAGE_CACHE_SIZE, get_block);
2115                 if (status)
2116                         goto out_unmap;
2117                 kaddr = kmap_atomic(new_page, KM_USER0);
2118                 memset(kaddr+zerofrom, 0, PAGE_CACHE_SIZE-zerofrom);
2119                 flush_dcache_page(new_page);
2120                 kunmap_atomic(kaddr, KM_USER0);
2121                 generic_commit_write(NULL, new_page, zerofrom, PAGE_CACHE_SIZE);
2122                 unlock_page(new_page);
2123                 page_cache_release(new_page);
2124         }
2125
2126         if (page->index < pgpos) {
2127                 /* completely inside the area */
2128                 zerofrom = offset;
2129         } else {
2130                 /* page covers the boundary, find the boundary offset */
2131                 zerofrom = *bytes & ~PAGE_CACHE_MASK;
2132
2133                 /* if we will expand the thing last block will be filled */
2134                 if (to > zerofrom && (zerofrom & (blocksize-1))) {
2135                         *bytes |= (blocksize-1);
2136                         (*bytes)++;
2137                 }
2138
2139                 /* starting below the boundary? Nothing to zero out */
2140                 if (offset <= zerofrom)
2141                         zerofrom = offset;
2142         }
2143         status = __block_prepare_write(inode, page, zerofrom, to, get_block);
2144         if (status)
2145                 goto out1;
2146         if (zerofrom < offset) {
2147                 kaddr = kmap_atomic(page, KM_USER0);
2148                 memset(kaddr+zerofrom, 0, offset-zerofrom);
2149                 flush_dcache_page(page);
2150                 kunmap_atomic(kaddr, KM_USER0);
2151                 __block_commit_write(inode, page, zerofrom, offset);
2152         }
2153         return 0;
2154 out1:
2155         ClearPageUptodate(page);
2156         return status;
2157
2158 out_unmap:
2159         ClearPageUptodate(new_page);
2160         unlock_page(new_page);
2161         page_cache_release(new_page);
2162 out:
2163         return status;
2164 }
2165
2166 int block_prepare_write(struct page *page, unsigned from, unsigned to,
2167                         get_block_t *get_block)
2168 {
2169         struct inode *inode = page->mapping->host;
2170         int err = __block_prepare_write(inode, page, from, to, get_block);
2171         if (err)
2172                 ClearPageUptodate(page);
2173         return err;
2174 }
2175
2176 int block_commit_write(struct page *page, unsigned from, unsigned to)
2177 {
2178         struct inode *inode = page->mapping->host;
2179         __block_commit_write(inode,page,from,to);
2180         return 0;
2181 }
2182
2183 int generic_commit_write(struct file *file, struct page *page,
2184                 unsigned from, unsigned to)
2185 {
2186         struct inode *inode = page->mapping->host;
2187         loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
2188         __block_commit_write(inode,page,from,to);
2189         /*
2190          * No need to use i_size_read() here, the i_size
2191          * cannot change under us because we hold i_mutex.
2192          */
2193         if (pos > inode->i_size) {
2194                 i_size_write(inode, pos);
2195                 mark_inode_dirty(inode);
2196         }
2197         return 0;
2198 }
2199
2200
2201 /*
2202  * nobh_prepare_write()'s prereads are special: the buffer_heads are freed
2203  * immediately, while under the page lock.  So it needs a special end_io
2204  * handler which does not touch the bh after unlocking it.
2205  *
2206  * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
2207  * a race there is benign: unlock_buffer() only use the bh's address for
2208  * hashing after unlocking the buffer, so it doesn't actually touch the bh
2209  * itself.
2210  */
2211 static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2212 {
2213         if (uptodate) {
2214                 set_buffer_uptodate(bh);
2215         } else {
2216                 /* This happens, due to failed READA attempts. */
2217                 clear_buffer_uptodate(bh);
2218         }
2219         unlock_buffer(bh);
2220 }
2221
2222 /*
2223  * On entry, the page is fully not uptodate.
2224  * On exit the page is fully uptodate in the areas outside (from,to)
2225  */
2226 int nobh_prepare_write(struct page *page, unsigned from, unsigned to,
2227                         get_block_t *get_block)
2228 {
2229         struct inode *inode = page->mapping->host;
2230         const unsigned blkbits = inode->i_blkbits;
2231         const unsigned blocksize = 1 << blkbits;
2232         struct buffer_head map_bh;
2233         struct buffer_head *read_bh[MAX_BUF_PER_PAGE];
2234         unsigned block_in_page;
2235         unsigned block_start;
2236         sector_t block_in_file;
2237         char *kaddr;
2238         int nr_reads = 0;
2239         int i;
2240         int ret = 0;
2241         int is_mapped_to_disk = 1;
2242
2243         if (PageMappedToDisk(page))
2244                 return 0;
2245
2246         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
2247         map_bh.b_page = page;
2248
2249         /*
2250          * We loop across all blocks in the page, whether or not they are
2251          * part of the affected region.  This is so we can discover if the
2252          * page is fully mapped-to-disk.
2253          */
2254         for (block_start = 0, block_in_page = 0;
2255                   block_start < PAGE_CACHE_SIZE;
2256                   block_in_page++, block_start += blocksize) {
2257                 unsigned block_end = block_start + blocksize;
2258                 int create;
2259
2260                 map_bh.b_state = 0;
2261                 create = 1;
2262                 if (block_start >= to)
2263                         create = 0;
2264                 map_bh.b_size = blocksize;
2265                 ret = get_block(inode, block_in_file + block_in_page,
2266                                         &map_bh, create);
2267                 if (ret)
2268                         goto failed;
2269                 if (!buffer_mapped(&map_bh))
2270                         is_mapped_to_disk = 0;
2271                 if (buffer_new(&map_bh))
2272                         unmap_underlying_metadata(map_bh.b_bdev,
2273                                                         map_bh.b_blocknr);
2274                 if (PageUptodate(page))
2275                         continue;
2276                 if (buffer_new(&map_bh) || !buffer_mapped(&map_bh)) {
2277                         kaddr = kmap_atomic(page, KM_USER0);
2278                         if (block_start < from)
2279                                 memset(kaddr+block_start, 0, from-block_start);
2280                         if (block_end > to)
2281                                 memset(kaddr + to, 0, block_end - to);
2282                         flush_dcache_page(page);
2283                         kunmap_atomic(kaddr, KM_USER0);
2284                         continue;
2285                 }
2286                 if (buffer_uptodate(&map_bh))
2287                         continue;       /* reiserfs does this */
2288                 if (block_start < from || block_end > to) {
2289                         struct buffer_head *bh = alloc_buffer_head(GFP_NOFS);
2290
2291                         if (!bh) {
2292                                 ret = -ENOMEM;
2293                                 goto failed;
2294                         }
2295                         bh->b_state = map_bh.b_state;
2296                         atomic_set(&bh->b_count, 0);
2297                         bh->b_this_page = NULL;
2298                         bh->b_page = page;
2299                         bh->b_blocknr = map_bh.b_blocknr;
2300                         bh->b_size = blocksize;
2301                         bh->b_data = (char *)(long)block_start;
2302                         bh->b_bdev = map_bh.b_bdev;
2303                         bh->b_private = NULL;
2304                         read_bh[nr_reads++] = bh;
2305                 }
2306         }
2307
2308         if (nr_reads) {
2309                 struct buffer_head *bh;
2310
2311                 /*
2312                  * The page is locked, so these buffers are protected from
2313                  * any VM or truncate activity.  Hence we don't need to care
2314                  * for the buffer_head refcounts.
2315                  */
2316                 for (i = 0; i < nr_reads; i++) {
2317                         bh = read_bh[i];
2318                         lock_buffer(bh);
2319                         bh->b_end_io = end_buffer_read_nobh;
2320                         submit_bh(READ, bh);
2321                 }
2322                 for (i = 0; i < nr_reads; i++) {
2323                         bh = read_bh[i];
2324                         wait_on_buffer(bh);
2325                         if (!buffer_uptodate(bh))
2326                                 ret = -EIO;
2327                         free_buffer_head(bh);
2328                         read_bh[i] = NULL;
2329                 }
2330                 if (ret)
2331                         goto failed;
2332         }
2333
2334         if (is_mapped_to_disk)
2335                 SetPageMappedToDisk(page);
2336
2337         return 0;
2338
2339 failed:
2340         for (i = 0; i < nr_reads; i++) {
2341                 if (read_bh[i])
2342                         free_buffer_head(read_bh[i]);
2343         }
2344
2345         /*
2346          * Error recovery is pretty slack.  Clear the page and mark it dirty
2347          * so we'll later zero out any blocks which _were_ allocated.
2348          */
2349         kaddr = kmap_atomic(page, KM_USER0);
2350         memset(kaddr, 0, PAGE_CACHE_SIZE);
2351         flush_dcache_page(page);
2352         kunmap_atomic(kaddr, KM_USER0);
2353         SetPageUptodate(page);
2354         set_page_dirty(page);
2355         return ret;
2356 }
2357 EXPORT_SYMBOL(nobh_prepare_write);
2358
2359 /*
2360  * Make sure any changes to nobh_commit_write() are reflected in
2361  * nobh_truncate_page(), since it doesn't call commit_write().
2362  */
2363 int nobh_commit_write(struct file *file, struct page *page,
2364                 unsigned from, unsigned to)
2365 {
2366         struct inode *inode = page->mapping->host;
2367         loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
2368
2369         SetPageUptodate(page);
2370         set_page_dirty(page);
2371         if (pos > inode->i_size) {
2372                 i_size_write(inode, pos);
2373                 mark_inode_dirty(inode);
2374         }
2375         return 0;
2376 }
2377 EXPORT_SYMBOL(nobh_commit_write);
2378
2379 /*
2380  * nobh_writepage() - based on block_full_write_page() except
2381  * that it tries to operate without attaching bufferheads to
2382  * the page.
2383  */
2384 int nobh_writepage(struct page *page, get_block_t *get_block,
2385                         struct writeback_control *wbc)
2386 {
2387         struct inode * const inode = page->mapping->host;
2388         loff_t i_size = i_size_read(inode);
2389         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2390         unsigned offset;
2391         void *kaddr;
2392         int ret;
2393
2394         /* Is the page fully inside i_size? */
2395         if (page->index < end_index)
2396                 goto out;
2397
2398         /* Is the page fully outside i_size? (truncate in progress) */
2399         offset = i_size & (PAGE_CACHE_SIZE-1);
2400         if (page->index >= end_index+1 || !offset) {
2401                 /*
2402                  * The page may have dirty, unmapped buffers.  For example,
2403                  * they may have been added in ext3_writepage().  Make them
2404                  * freeable here, so the page does not leak.
2405                  */
2406 #if 0
2407                 /* Not really sure about this  - do we need this ? */
2408                 if (page->mapping->a_ops->invalidatepage)
2409                         page->mapping->a_ops->invalidatepage(page, offset);
2410 #endif
2411                 unlock_page(page);
2412                 return 0; /* don't care */
2413         }
2414
2415         /*
2416          * The page straddles i_size.  It must be zeroed out on each and every
2417          * writepage invocation because it may be mmapped.  "A file is mapped
2418          * in multiples of the page size.  For a file that is not a multiple of
2419          * the  page size, the remaining memory is zeroed when mapped, and
2420          * writes to that region are not written out to the file."
2421          */
2422         kaddr = kmap_atomic(page, KM_USER0);
2423         memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
2424         flush_dcache_page(page);
2425         kunmap_atomic(kaddr, KM_USER0);
2426 out:
2427         ret = mpage_writepage(page, get_block, wbc);
2428         if (ret == -EAGAIN)
2429                 ret = __block_write_full_page(inode, page, get_block, wbc);
2430         return ret;
2431 }
2432 EXPORT_SYMBOL(nobh_writepage);
2433
2434 /*
2435  * This function assumes that ->prepare_write() uses nobh_prepare_write().
2436  */
2437 int nobh_truncate_page(struct address_space *mapping, loff_t from)
2438 {
2439         struct inode *inode = mapping->host;
2440         unsigned blocksize = 1 << inode->i_blkbits;
2441         pgoff_t index = from >> PAGE_CACHE_SHIFT;
2442         unsigned offset = from & (PAGE_CACHE_SIZE-1);
2443         unsigned to;
2444         struct page *page;
2445         const struct address_space_operations *a_ops = mapping->a_ops;
2446         char *kaddr;
2447         int ret = 0;
2448
2449         if ((offset & (blocksize - 1)) == 0)
2450                 goto out;
2451
2452         ret = -ENOMEM;
2453         page = grab_cache_page(mapping, index);
2454         if (!page)
2455                 goto out;
2456
2457         to = (offset + blocksize) & ~(blocksize - 1);
2458         ret = a_ops->prepare_write(NULL, page, offset, to);
2459         if (ret == 0) {
2460                 kaddr = kmap_atomic(page, KM_USER0);
2461                 memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
2462                 flush_dcache_page(page);
2463                 kunmap_atomic(kaddr, KM_USER0);
2464                 /*
2465                  * It would be more correct to call aops->commit_write()
2466                  * here, but this is more efficient.
2467                  */
2468                 SetPageUptodate(page);
2469                 set_page_dirty(page);
2470         }
2471         unlock_page(page);
2472         page_cache_release(page);
2473 out:
2474         return ret;
2475 }
2476 EXPORT_SYMBOL(nobh_truncate_page);
2477
2478 int block_truncate_page(struct address_space *mapping,
2479                         loff_t from, get_block_t *get_block)
2480 {
2481         pgoff_t index = from >> PAGE_CACHE_SHIFT;
2482         unsigned offset = from & (PAGE_CACHE_SIZE-1);
2483         unsigned blocksize;
2484         sector_t iblock;
2485         unsigned length, pos;
2486         struct inode *inode = mapping->host;
2487         struct page *page;
2488         struct buffer_head *bh;
2489         void *kaddr;
2490         int err;
2491
2492         blocksize = 1 << inode->i_blkbits;
2493         length = offset & (blocksize - 1);
2494
2495         /* Block boundary? Nothing to do */
2496         if (!length)
2497                 return 0;
2498
2499         length = blocksize - length;
2500         iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2501         
2502         page = grab_cache_page(mapping, index);
2503         err = -ENOMEM;
2504         if (!page)
2505                 goto out;
2506
2507         if (!page_has_buffers(page))
2508                 create_empty_buffers(page, blocksize, 0);
2509
2510         /* Find the buffer that contains "offset" */
2511         bh = page_buffers(page);
2512         pos = blocksize;
2513         while (offset >= pos) {
2514                 bh = bh->b_this_page;
2515                 iblock++;
2516                 pos += blocksize;
2517         }
2518
2519         err = 0;
2520         if (!buffer_mapped(bh)) {
2521                 WARN_ON(bh->b_size != blocksize);
2522                 err = get_block(inode, iblock, bh, 0);
2523                 if (err)
2524                         goto unlock;
2525                 /* unmapped? It's a hole - nothing to do */
2526                 if (!buffer_mapped(bh))
2527                         goto unlock;
2528         }
2529
2530         /* Ok, it's mapped. Make sure it's up-to-date */
2531         if (PageUptodate(page))
2532                 set_buffer_uptodate(bh);
2533
2534         if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2535                 err = -EIO;
2536                 ll_rw_block(READ, 1, &bh);
2537                 wait_on_buffer(bh);
2538                 /* Uhhuh. Read error. Complain and punt. */
2539                 if (!buffer_uptodate(bh))
2540                         goto unlock;
2541         }
2542
2543         kaddr = kmap_atomic(page, KM_USER0);
2544         memset(kaddr + offset, 0, length);
2545         flush_dcache_page(page);
2546         kunmap_atomic(kaddr, KM_USER0);
2547
2548         mark_buffer_dirty(bh);
2549         err = 0;
2550
2551 unlock:
2552         unlock_page(page);
2553         page_cache_release(page);
2554 out:
2555         return err;
2556 }
2557
2558 /*
2559  * The generic ->writepage function for buffer-backed address_spaces
2560  */
2561 int block_write_full_page(struct page *page, get_block_t *get_block,
2562                         struct writeback_control *wbc)
2563 {
2564         struct inode * const inode = page->mapping->host;
2565         loff_t i_size = i_size_read(inode);
2566         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2567         unsigned offset;
2568         void *kaddr;
2569
2570         /* Is the page fully inside i_size? */
2571         if (page->index < end_index)
2572                 return __block_write_full_page(inode, page, get_block, wbc);
2573
2574         /* Is the page fully outside i_size? (truncate in progress) */
2575         offset = i_size & (PAGE_CACHE_SIZE-1);
2576         if (page->index >= end_index+1 || !offset) {
2577                 /*
2578                  * The page may have dirty, unmapped buffers.  For example,
2579                  * they may have been added in ext3_writepage().  Make them
2580                  * freeable here, so the page does not leak.
2581                  */
2582                 do_invalidatepage(page, 0);
2583                 unlock_page(page);
2584                 return 0; /* don't care */
2585         }
2586
2587         /*
2588          * The page straddles i_size.  It must be zeroed out on each and every
2589          * writepage invokation because it may be mmapped.  "A file is mapped
2590          * in multiples of the page size.  For a file that is not a multiple of
2591          * the  page size, the remaining memory is zeroed when mapped, and
2592          * writes to that region are not written out to the file."
2593          */
2594         kaddr = kmap_atomic(page, KM_USER0);
2595         memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
2596         flush_dcache_page(page);
2597         kunmap_atomic(kaddr, KM_USER0);
2598         return __block_write_full_page(inode, page, get_block, wbc);
2599 }
2600
2601 sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2602                             get_block_t *get_block)
2603 {
2604         struct buffer_head tmp;
2605         struct inode *inode = mapping->host;
2606         tmp.b_state = 0;
2607         tmp.b_blocknr = 0;
2608         tmp.b_size = 1 << inode->i_blkbits;
2609         get_block(inode, block, &tmp, 0);
2610         return tmp.b_blocknr;
2611 }
2612
2613 static int end_bio_bh_io_sync(struct bio *bio, unsigned int bytes_done, int err)
2614 {
2615         struct buffer_head *bh = bio->bi_private;
2616
2617         if (bio->bi_size)
2618                 return 1;
2619
2620         if (err == -EOPNOTSUPP) {
2621                 set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
2622                 set_bit(BH_Eopnotsupp, &bh->b_state);
2623         }
2624
2625         bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
2626         bio_put(bio);
2627         return 0;
2628 }
2629
2630 int submit_bh(int rw, struct buffer_head * bh)
2631 {
2632         struct bio *bio;
2633         int ret = 0;
2634
2635         BUG_ON(!buffer_locked(bh));
2636         BUG_ON(!buffer_mapped(bh));
2637         BUG_ON(!bh->b_end_io);
2638
2639         if (buffer_ordered(bh) && (rw == WRITE))
2640                 rw = WRITE_BARRIER;
2641
2642         /*
2643          * Only clear out a write error when rewriting, should this
2644          * include WRITE_SYNC as well?
2645          */
2646         if (test_set_buffer_req(bh) && (rw == WRITE || rw == WRITE_BARRIER))
2647                 clear_buffer_write_io_error(bh);
2648
2649         /*
2650          * from here on down, it's all bio -- do the initial mapping,
2651          * submit_bio -> generic_make_request may further map this bio around
2652          */
2653         bio = bio_alloc(GFP_NOIO, 1);
2654
2655         bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
2656         bio->bi_bdev = bh->b_bdev;
2657         bio->bi_io_vec[0].bv_page = bh->b_page;
2658         bio->bi_io_vec[0].bv_len = bh->b_size;
2659         bio->bi_io_vec[0].bv_offset = bh_offset(bh);
2660
2661         bio->bi_vcnt = 1;
2662         bio->bi_idx = 0;
2663         bio->bi_size = bh->b_size;
2664
2665         bio->bi_end_io = end_bio_bh_io_sync;
2666         bio->bi_private = bh;
2667
2668         bio_get(bio);
2669         submit_bio(rw, bio);
2670
2671         if (bio_flagged(bio, BIO_EOPNOTSUPP))
2672                 ret = -EOPNOTSUPP;
2673
2674         bio_put(bio);
2675         return ret;
2676 }
2677
2678 /**
2679  * ll_rw_block: low-level access to block devices (DEPRECATED)
2680  * @rw: whether to %READ or %WRITE or %SWRITE or maybe %READA (readahead)
2681  * @nr: number of &struct buffer_heads in the array
2682  * @bhs: array of pointers to &struct buffer_head
2683  *
2684  * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
2685  * requests an I/O operation on them, either a %READ or a %WRITE.  The third
2686  * %SWRITE is like %WRITE only we make sure that the *current* data in buffers
2687  * are sent to disk. The fourth %READA option is described in the documentation
2688  * for generic_make_request() which ll_rw_block() calls.
2689  *
2690  * This function drops any buffer that it cannot get a lock on (with the
2691  * BH_Lock state bit) unless SWRITE is required, any buffer that appears to be
2692  * clean when doing a write request, and any buffer that appears to be
2693  * up-to-date when doing read request.  Further it marks as clean buffers that
2694  * are processed for writing (the buffer cache won't assume that they are
2695  * actually clean until the buffer gets unlocked).
2696  *
2697  * ll_rw_block sets b_end_io to simple completion handler that marks
2698  * the buffer up-to-date (if approriate), unlocks the buffer and wakes
2699  * any waiters. 
2700  *
2701  * All of the buffers must be for the same device, and must also be a
2702  * multiple of the current approved size for the device.
2703  */
2704 void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
2705 {
2706         int i;
2707
2708         for (i = 0; i < nr; i++) {
2709                 struct buffer_head *bh = bhs[i];
2710
2711                 if (rw == SWRITE)
2712                         lock_buffer(bh);
2713                 else if (test_set_buffer_locked(bh))
2714                         continue;
2715
2716                 if (rw == WRITE || rw == SWRITE) {
2717                         if (test_clear_buffer_dirty(bh)) {
2718                                 bh->b_end_io = end_buffer_write_sync;
2719                                 get_bh(bh);
2720                                 submit_bh(WRITE, bh);
2721                                 continue;
2722                         }
2723                 } else {
2724                         if (!buffer_uptodate(bh)) {
2725                                 bh->b_end_io = end_buffer_read_sync;
2726                                 get_bh(bh);
2727                                 submit_bh(rw, bh);
2728                                 continue;
2729                         }
2730                 }
2731                 unlock_buffer(bh);
2732         }
2733 }
2734
2735 /*
2736  * For a data-integrity writeout, we need to wait upon any in-progress I/O
2737  * and then start new I/O and then wait upon it.  The caller must have a ref on
2738  * the buffer_head.
2739  */
2740 int sync_dirty_buffer(struct buffer_head *bh)
2741 {
2742         int ret = 0;
2743
2744         WARN_ON(atomic_read(&bh->b_count) < 1);
2745         lock_buffer(bh);
2746         if (test_clear_buffer_dirty(bh)) {
2747                 get_bh(bh);
2748                 bh->b_end_io = end_buffer_write_sync;
2749                 ret = submit_bh(WRITE, bh);
2750                 wait_on_buffer(bh);
2751                 if (buffer_eopnotsupp(bh)) {
2752                         clear_buffer_eopnotsupp(bh);
2753                         ret = -EOPNOTSUPP;
2754                 }
2755                 if (!ret && !buffer_uptodate(bh))
2756                         ret = -EIO;
2757         } else {
2758                 unlock_buffer(bh);
2759         }
2760         return ret;
2761 }
2762
2763 /*
2764  * try_to_free_buffers() checks if all the buffers on this particular page
2765  * are unused, and releases them if so.
2766  *
2767  * Exclusion against try_to_free_buffers may be obtained by either
2768  * locking the page or by holding its mapping's private_lock.
2769  *
2770  * If the page is dirty but all the buffers are clean then we need to
2771  * be sure to mark the page clean as well.  This is because the page
2772  * may be against a block device, and a later reattachment of buffers
2773  * to a dirty page will set *all* buffers dirty.  Which would corrupt
2774  * filesystem data on the same device.
2775  *
2776  * The same applies to regular filesystem pages: if all the buffers are
2777  * clean then we set the page clean and proceed.  To do that, we require
2778  * total exclusion from __set_page_dirty_buffers().  That is obtained with
2779  * private_lock.
2780  *
2781  * try_to_free_buffers() is non-blocking.
2782  */
2783 static inline int buffer_busy(struct buffer_head *bh)
2784 {
2785         return atomic_read(&bh->b_count) |
2786                 (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
2787 }
2788
2789 static int
2790 drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
2791 {
2792         struct buffer_head *head = page_buffers(page);
2793         struct buffer_head *bh;
2794
2795         bh = head;
2796         do {
2797                 if (buffer_write_io_error(bh) && page->mapping)
2798                         set_bit(AS_EIO, &page->mapping->flags);
2799                 if (buffer_busy(bh))
2800                         goto failed;
2801                 bh = bh->b_this_page;
2802         } while (bh != head);
2803
2804         do {
2805                 struct buffer_head *next = bh->b_this_page;
2806
2807                 if (!list_empty(&bh->b_assoc_buffers))
2808                         __remove_assoc_queue(bh);
2809                 bh = next;
2810         } while (bh != head);
2811         *buffers_to_free = head;
2812         __clear_page_buffers(page);
2813         return 1;
2814 failed:
2815         return 0;
2816 }
2817
2818 int try_to_free_buffers(struct page *page)
2819 {
2820         struct address_space * const mapping = page->mapping;
2821         struct buffer_head *buffers_to_free = NULL;
2822         int ret = 0;
2823
2824         BUG_ON(!PageLocked(page));
2825         if (PageWriteback(page))
2826                 return 0;
2827
2828         if (mapping == NULL) {          /* can this still happen? */
2829                 ret = drop_buffers(page, &buffers_to_free);
2830                 goto out;
2831         }
2832
2833         spin_lock(&mapping->private_lock);
2834         ret = drop_buffers(page, &buffers_to_free);
2835
2836         /*
2837          * If the filesystem writes its buffers by hand (eg ext3)
2838          * then we can have clean buffers against a dirty page.  We
2839          * clean the page here; otherwise the VM will never notice
2840          * that the filesystem did any IO at all.
2841          *
2842          * Also, during truncate, discard_buffer will have marked all
2843          * the page's buffers clean.  We discover that here and clean
2844          * the page also.
2845          *
2846          * private_lock must be held over this entire operation in order
2847          * to synchronise against __set_page_dirty_buffers and prevent the
2848          * dirty bit from being lost.
2849          */
2850         if (ret)
2851                 cancel_dirty_page(page, PAGE_CACHE_SIZE);
2852         spin_unlock(&mapping->private_lock);
2853 out:
2854         if (buffers_to_free) {
2855                 struct buffer_head *bh = buffers_to_free;
2856
2857                 do {
2858                         struct buffer_head *next = bh->b_this_page;
2859                         free_buffer_head(bh);
2860                         bh = next;
2861                 } while (bh != buffers_to_free);
2862         }
2863         return ret;
2864 }
2865 EXPORT_SYMBOL(try_to_free_buffers);
2866
2867 void block_sync_page(struct page *page)
2868 {
2869         struct address_space *mapping;
2870
2871         smp_mb();
2872         mapping = page_mapping(page);
2873         if (mapping)
2874                 blk_run_backing_dev(mapping->backing_dev_info, page);
2875 }
2876
2877 /*
2878  * There are no bdflush tunables left.  But distributions are
2879  * still running obsolete flush daemons, so we terminate them here.
2880  *
2881  * Use of bdflush() is deprecated and will be removed in a future kernel.
2882  * The `pdflush' kernel threads fully replace bdflush daemons and this call.
2883  */
2884 asmlinkage long sys_bdflush(int func, long data)
2885 {
2886         static int msg_count;
2887
2888         if (!capable(CAP_SYS_ADMIN))
2889                 return -EPERM;
2890
2891         if (msg_count < 5) {
2892                 msg_count++;
2893                 printk(KERN_INFO
2894                         "warning: process `%s' used the obsolete bdflush"
2895                         " system call\n", current->comm);
2896                 printk(KERN_INFO "Fix your initscripts?\n");
2897         }
2898
2899         if (func == 1)
2900                 do_exit(0);
2901         return 0;
2902 }
2903
2904 /*
2905  * Buffer-head allocation
2906  */
2907 static struct kmem_cache *bh_cachep;
2908
2909 /*
2910  * Once the number of bh's in the machine exceeds this level, we start
2911  * stripping them in writeback.
2912  */
2913 static int max_buffer_heads;
2914
2915 int buffer_heads_over_limit;
2916
2917 struct bh_accounting {
2918         int nr;                 /* Number of live bh's */
2919         int ratelimit;          /* Limit cacheline bouncing */
2920 };
2921
2922 static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
2923
2924 static void recalc_bh_state(void)
2925 {
2926         int i;
2927         int tot = 0;
2928
2929         if (__get_cpu_var(bh_accounting).ratelimit++ < 4096)
2930                 return;
2931         __get_cpu_var(bh_accounting).ratelimit = 0;
2932         for_each_online_cpu(i)
2933                 tot += per_cpu(bh_accounting, i).nr;
2934         buffer_heads_over_limit = (tot > max_buffer_heads);
2935 }
2936         
2937 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
2938 {
2939         struct buffer_head *ret = kmem_cache_alloc(bh_cachep, gfp_flags);
2940         if (ret) {
2941                 get_cpu_var(bh_accounting).nr++;
2942                 recalc_bh_state();
2943                 put_cpu_var(bh_accounting);
2944         }
2945         return ret;
2946 }
2947 EXPORT_SYMBOL(alloc_buffer_head);
2948
2949 void free_buffer_head(struct buffer_head *bh)
2950 {
2951         BUG_ON(!list_empty(&bh->b_assoc_buffers));
2952         kmem_cache_free(bh_cachep, bh);
2953         get_cpu_var(bh_accounting).nr--;
2954         recalc_bh_state();
2955         put_cpu_var(bh_accounting);
2956 }
2957 EXPORT_SYMBOL(free_buffer_head);
2958
2959 static void
2960 init_buffer_head(void *data, struct kmem_cache *cachep, unsigned long flags)
2961 {
2962         if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
2963                             SLAB_CTOR_CONSTRUCTOR) {
2964                 struct buffer_head * bh = (struct buffer_head *)data;
2965
2966                 memset(bh, 0, sizeof(*bh));
2967                 INIT_LIST_HEAD(&bh->b_assoc_buffers);
2968         }
2969 }
2970
2971 static void buffer_exit_cpu(int cpu)
2972 {
2973         int i;
2974         struct bh_lru *b = &per_cpu(bh_lrus, cpu);
2975
2976         for (i = 0; i < BH_LRU_SIZE; i++) {
2977                 brelse(b->bhs[i]);
2978                 b->bhs[i] = NULL;
2979         }
2980         get_cpu_var(bh_accounting).nr += per_cpu(bh_accounting, cpu).nr;
2981         per_cpu(bh_accounting, cpu).nr = 0;
2982         put_cpu_var(bh_accounting);
2983 }
2984
2985 static int buffer_cpu_notify(struct notifier_block *self,
2986                               unsigned long action, void *hcpu)
2987 {
2988         if (action == CPU_DEAD)
2989                 buffer_exit_cpu((unsigned long)hcpu);
2990         return NOTIFY_OK;
2991 }
2992
2993 void __init buffer_init(void)
2994 {
2995         int nrpages;
2996
2997         bh_cachep = kmem_cache_create("buffer_head",
2998                                         sizeof(struct buffer_head), 0,
2999                                         (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3000                                         SLAB_MEM_SPREAD),
3001                                         init_buffer_head,
3002                                         NULL);
3003
3004         /*
3005          * Limit the bh occupancy to 10% of ZONE_NORMAL
3006          */
3007         nrpages = (nr_free_buffer_pages() * 10) / 100;
3008         max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3009         hotcpu_notifier(buffer_cpu_notify, 0);
3010 }
3011
3012 EXPORT_SYMBOL(__bforget);
3013 EXPORT_SYMBOL(__brelse);
3014 EXPORT_SYMBOL(__wait_on_buffer);
3015 EXPORT_SYMBOL(block_commit_write);
3016 EXPORT_SYMBOL(block_prepare_write);
3017 EXPORT_SYMBOL(block_read_full_page);
3018 EXPORT_SYMBOL(block_sync_page);
3019 EXPORT_SYMBOL(block_truncate_page);
3020 EXPORT_SYMBOL(block_write_full_page);
3021 EXPORT_SYMBOL(cont_prepare_write);
3022 EXPORT_SYMBOL(end_buffer_read_sync);
3023 EXPORT_SYMBOL(end_buffer_write_sync);
3024 EXPORT_SYMBOL(file_fsync);
3025 EXPORT_SYMBOL(fsync_bdev);
3026 EXPORT_SYMBOL(generic_block_bmap);
3027 EXPORT_SYMBOL(generic_commit_write);
3028 EXPORT_SYMBOL(generic_cont_expand);
3029 EXPORT_SYMBOL(generic_cont_expand_simple);
3030 EXPORT_SYMBOL(init_buffer);
3031 EXPORT_SYMBOL(invalidate_bdev);
3032 EXPORT_SYMBOL(ll_rw_block);
3033 EXPORT_SYMBOL(mark_buffer_dirty);
3034 EXPORT_SYMBOL(submit_bh);
3035 EXPORT_SYMBOL(sync_dirty_buffer);
3036 EXPORT_SYMBOL(unlock_buffer);