block_write_full_page: switch synchronous writes to use WRITE_SYNC_PLUG
[linux-2.6.git] / fs / buffer.c
1 /*
2  *  linux/fs/buffer.c
3  *
4  *  Copyright (C) 1991, 1992, 2002  Linus Torvalds
5  */
6
7 /*
8  * Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
9  *
10  * Removed a lot of unnecessary code and simplified things now that
11  * the buffer cache isn't our primary cache - Andrew Tridgell 12/96
12  *
13  * Speed up hash, lru, and free list operations.  Use gfp() for allocating
14  * hash table, use SLAB cache for buffer heads. SMP threading.  -DaveM
15  *
16  * Added 32k buffer block sizes - these are required older ARM systems. - RMK
17  *
18  * async buffer flushing, 1999 Andrea Arcangeli <andrea@suse.de>
19  */
20
21 #include <linux/kernel.h>
22 #include <linux/syscalls.h>
23 #include <linux/fs.h>
24 #include <linux/mm.h>
25 #include <linux/percpu.h>
26 #include <linux/slab.h>
27 #include <linux/capability.h>
28 #include <linux/blkdev.h>
29 #include <linux/file.h>
30 #include <linux/quotaops.h>
31 #include <linux/highmem.h>
32 #include <linux/module.h>
33 #include <linux/writeback.h>
34 #include <linux/hash.h>
35 #include <linux/suspend.h>
36 #include <linux/buffer_head.h>
37 #include <linux/task_io_accounting_ops.h>
38 #include <linux/bio.h>
39 #include <linux/notifier.h>
40 #include <linux/cpu.h>
41 #include <linux/bitops.h>
42 #include <linux/mpage.h>
43 #include <linux/bit_spinlock.h>
44
45 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
46
47 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
48
49 inline void
50 init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
51 {
52         bh->b_end_io = handler;
53         bh->b_private = private;
54 }
55
56 static int sync_buffer(void *word)
57 {
58         struct block_device *bd;
59         struct buffer_head *bh
60                 = container_of(word, struct buffer_head, b_state);
61
62         smp_mb();
63         bd = bh->b_bdev;
64         if (bd)
65                 blk_run_address_space(bd->bd_inode->i_mapping);
66         io_schedule();
67         return 0;
68 }
69
70 void __lock_buffer(struct buffer_head *bh)
71 {
72         wait_on_bit_lock(&bh->b_state, BH_Lock, sync_buffer,
73                                                         TASK_UNINTERRUPTIBLE);
74 }
75 EXPORT_SYMBOL(__lock_buffer);
76
77 void unlock_buffer(struct buffer_head *bh)
78 {
79         clear_bit_unlock(BH_Lock, &bh->b_state);
80         smp_mb__after_clear_bit();
81         wake_up_bit(&bh->b_state, BH_Lock);
82 }
83
84 /*
85  * Block until a buffer comes unlocked.  This doesn't stop it
86  * from becoming locked again - you have to lock it yourself
87  * if you want to preserve its state.
88  */
89 void __wait_on_buffer(struct buffer_head * bh)
90 {
91         wait_on_bit(&bh->b_state, BH_Lock, sync_buffer, TASK_UNINTERRUPTIBLE);
92 }
93
94 static void
95 __clear_page_buffers(struct page *page)
96 {
97         ClearPagePrivate(page);
98         set_page_private(page, 0);
99         page_cache_release(page);
100 }
101
102
103 static int quiet_error(struct buffer_head *bh)
104 {
105         if (!test_bit(BH_Quiet, &bh->b_state) && printk_ratelimit())
106                 return 0;
107         return 1;
108 }
109
110
111 static void buffer_io_error(struct buffer_head *bh)
112 {
113         char b[BDEVNAME_SIZE];
114         printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
115                         bdevname(bh->b_bdev, b),
116                         (unsigned long long)bh->b_blocknr);
117 }
118
119 /*
120  * End-of-IO handler helper function which does not touch the bh after
121  * unlocking it.
122  * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
123  * a race there is benign: unlock_buffer() only use the bh's address for
124  * hashing after unlocking the buffer, so it doesn't actually touch the bh
125  * itself.
126  */
127 static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
128 {
129         if (uptodate) {
130                 set_buffer_uptodate(bh);
131         } else {
132                 /* This happens, due to failed READA attempts. */
133                 clear_buffer_uptodate(bh);
134         }
135         unlock_buffer(bh);
136 }
137
138 /*
139  * Default synchronous end-of-IO handler..  Just mark it up-to-date and
140  * unlock the buffer. This is what ll_rw_block uses too.
141  */
142 void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
143 {
144         __end_buffer_read_notouch(bh, uptodate);
145         put_bh(bh);
146 }
147
148 void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
149 {
150         char b[BDEVNAME_SIZE];
151
152         if (uptodate) {
153                 set_buffer_uptodate(bh);
154         } else {
155                 if (!buffer_eopnotsupp(bh) && !quiet_error(bh)) {
156                         buffer_io_error(bh);
157                         printk(KERN_WARNING "lost page write due to "
158                                         "I/O error on %s\n",
159                                        bdevname(bh->b_bdev, b));
160                 }
161                 set_buffer_write_io_error(bh);
162                 clear_buffer_uptodate(bh);
163         }
164         unlock_buffer(bh);
165         put_bh(bh);
166 }
167
168 /*
169  * Various filesystems appear to want __find_get_block to be non-blocking.
170  * But it's the page lock which protects the buffers.  To get around this,
171  * we get exclusion from try_to_free_buffers with the blockdev mapping's
172  * private_lock.
173  *
174  * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
175  * may be quite high.  This code could TryLock the page, and if that
176  * succeeds, there is no need to take private_lock. (But if
177  * private_lock is contended then so is mapping->tree_lock).
178  */
179 static struct buffer_head *
180 __find_get_block_slow(struct block_device *bdev, sector_t block)
181 {
182         struct inode *bd_inode = bdev->bd_inode;
183         struct address_space *bd_mapping = bd_inode->i_mapping;
184         struct buffer_head *ret = NULL;
185         pgoff_t index;
186         struct buffer_head *bh;
187         struct buffer_head *head;
188         struct page *page;
189         int all_mapped = 1;
190
191         index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
192         page = find_get_page(bd_mapping, index);
193         if (!page)
194                 goto out;
195
196         spin_lock(&bd_mapping->private_lock);
197         if (!page_has_buffers(page))
198                 goto out_unlock;
199         head = page_buffers(page);
200         bh = head;
201         do {
202                 if (!buffer_mapped(bh))
203                         all_mapped = 0;
204                 else if (bh->b_blocknr == block) {
205                         ret = bh;
206                         get_bh(bh);
207                         goto out_unlock;
208                 }
209                 bh = bh->b_this_page;
210         } while (bh != head);
211
212         /* we might be here because some of the buffers on this page are
213          * not mapped.  This is due to various races between
214          * file io on the block device and getblk.  It gets dealt with
215          * elsewhere, don't buffer_error if we had some unmapped buffers
216          */
217         if (all_mapped) {
218                 printk("__find_get_block_slow() failed. "
219                         "block=%llu, b_blocknr=%llu\n",
220                         (unsigned long long)block,
221                         (unsigned long long)bh->b_blocknr);
222                 printk("b_state=0x%08lx, b_size=%zu\n",
223                         bh->b_state, bh->b_size);
224                 printk("device blocksize: %d\n", 1 << bd_inode->i_blkbits);
225         }
226 out_unlock:
227         spin_unlock(&bd_mapping->private_lock);
228         page_cache_release(page);
229 out:
230         return ret;
231 }
232
233 /* If invalidate_buffers() will trash dirty buffers, it means some kind
234    of fs corruption is going on. Trashing dirty data always imply losing
235    information that was supposed to be just stored on the physical layer
236    by the user.
237
238    Thus invalidate_buffers in general usage is not allwowed to trash
239    dirty buffers. For example ioctl(FLSBLKBUF) expects dirty data to
240    be preserved.  These buffers are simply skipped.
241   
242    We also skip buffers which are still in use.  For example this can
243    happen if a userspace program is reading the block device.
244
245    NOTE: In the case where the user removed a removable-media-disk even if
246    there's still dirty data not synced on disk (due a bug in the device driver
247    or due an error of the user), by not destroying the dirty buffers we could
248    generate corruption also on the next media inserted, thus a parameter is
249    necessary to handle this case in the most safe way possible (trying
250    to not corrupt also the new disk inserted with the data belonging to
251    the old now corrupted disk). Also for the ramdisk the natural thing
252    to do in order to release the ramdisk memory is to destroy dirty buffers.
253
254    These are two special cases. Normal usage imply the device driver
255    to issue a sync on the device (without waiting I/O completion) and
256    then an invalidate_buffers call that doesn't trash dirty buffers.
257
258    For handling cache coherency with the blkdev pagecache the 'update' case
259    is been introduced. It is needed to re-read from disk any pinned
260    buffer. NOTE: re-reading from disk is destructive so we can do it only
261    when we assume nobody is changing the buffercache under our I/O and when
262    we think the disk contains more recent information than the buffercache.
263    The update == 1 pass marks the buffers we need to update, the update == 2
264    pass does the actual I/O. */
265 void invalidate_bdev(struct block_device *bdev)
266 {
267         struct address_space *mapping = bdev->bd_inode->i_mapping;
268
269         if (mapping->nrpages == 0)
270                 return;
271
272         invalidate_bh_lrus();
273         invalidate_mapping_pages(mapping, 0, -1);
274 }
275
276 /*
277  * Kick pdflush then try to free up some ZONE_NORMAL memory.
278  */
279 static void free_more_memory(void)
280 {
281         struct zone *zone;
282         int nid;
283
284         wakeup_pdflush(1024);
285         yield();
286
287         for_each_online_node(nid) {
288                 (void)first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
289                                                 gfp_zone(GFP_NOFS), NULL,
290                                                 &zone);
291                 if (zone)
292                         try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
293                                                 GFP_NOFS, NULL);
294         }
295 }
296
297 /*
298  * I/O completion handler for block_read_full_page() - pages
299  * which come unlocked at the end of I/O.
300  */
301 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
302 {
303         unsigned long flags;
304         struct buffer_head *first;
305         struct buffer_head *tmp;
306         struct page *page;
307         int page_uptodate = 1;
308
309         BUG_ON(!buffer_async_read(bh));
310
311         page = bh->b_page;
312         if (uptodate) {
313                 set_buffer_uptodate(bh);
314         } else {
315                 clear_buffer_uptodate(bh);
316                 if (!quiet_error(bh))
317                         buffer_io_error(bh);
318                 SetPageError(page);
319         }
320
321         /*
322          * Be _very_ careful from here on. Bad things can happen if
323          * two buffer heads end IO at almost the same time and both
324          * decide that the page is now completely done.
325          */
326         first = page_buffers(page);
327         local_irq_save(flags);
328         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
329         clear_buffer_async_read(bh);
330         unlock_buffer(bh);
331         tmp = bh;
332         do {
333                 if (!buffer_uptodate(tmp))
334                         page_uptodate = 0;
335                 if (buffer_async_read(tmp)) {
336                         BUG_ON(!buffer_locked(tmp));
337                         goto still_busy;
338                 }
339                 tmp = tmp->b_this_page;
340         } while (tmp != bh);
341         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
342         local_irq_restore(flags);
343
344         /*
345          * If none of the buffers had errors and they are all
346          * uptodate then we can set the page uptodate.
347          */
348         if (page_uptodate && !PageError(page))
349                 SetPageUptodate(page);
350         unlock_page(page);
351         return;
352
353 still_busy:
354         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
355         local_irq_restore(flags);
356         return;
357 }
358
359 /*
360  * Completion handler for block_write_full_page() - pages which are unlocked
361  * during I/O, and which have PageWriteback cleared upon I/O completion.
362  */
363 static void end_buffer_async_write(struct buffer_head *bh, int uptodate)
364 {
365         char b[BDEVNAME_SIZE];
366         unsigned long flags;
367         struct buffer_head *first;
368         struct buffer_head *tmp;
369         struct page *page;
370
371         BUG_ON(!buffer_async_write(bh));
372
373         page = bh->b_page;
374         if (uptodate) {
375                 set_buffer_uptodate(bh);
376         } else {
377                 if (!quiet_error(bh)) {
378                         buffer_io_error(bh);
379                         printk(KERN_WARNING "lost page write due to "
380                                         "I/O error on %s\n",
381                                bdevname(bh->b_bdev, b));
382                 }
383                 set_bit(AS_EIO, &page->mapping->flags);
384                 set_buffer_write_io_error(bh);
385                 clear_buffer_uptodate(bh);
386                 SetPageError(page);
387         }
388
389         first = page_buffers(page);
390         local_irq_save(flags);
391         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
392
393         clear_buffer_async_write(bh);
394         unlock_buffer(bh);
395         tmp = bh->b_this_page;
396         while (tmp != bh) {
397                 if (buffer_async_write(tmp)) {
398                         BUG_ON(!buffer_locked(tmp));
399                         goto still_busy;
400                 }
401                 tmp = tmp->b_this_page;
402         }
403         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
404         local_irq_restore(flags);
405         end_page_writeback(page);
406         return;
407
408 still_busy:
409         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
410         local_irq_restore(flags);
411         return;
412 }
413
414 /*
415  * If a page's buffers are under async readin (end_buffer_async_read
416  * completion) then there is a possibility that another thread of
417  * control could lock one of the buffers after it has completed
418  * but while some of the other buffers have not completed.  This
419  * locked buffer would confuse end_buffer_async_read() into not unlocking
420  * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
421  * that this buffer is not under async I/O.
422  *
423  * The page comes unlocked when it has no locked buffer_async buffers
424  * left.
425  *
426  * PageLocked prevents anyone starting new async I/O reads any of
427  * the buffers.
428  *
429  * PageWriteback is used to prevent simultaneous writeout of the same
430  * page.
431  *
432  * PageLocked prevents anyone from starting writeback of a page which is
433  * under read I/O (PageWriteback is only ever set against a locked page).
434  */
435 static void mark_buffer_async_read(struct buffer_head *bh)
436 {
437         bh->b_end_io = end_buffer_async_read;
438         set_buffer_async_read(bh);
439 }
440
441 void mark_buffer_async_write(struct buffer_head *bh)
442 {
443         bh->b_end_io = end_buffer_async_write;
444         set_buffer_async_write(bh);
445 }
446 EXPORT_SYMBOL(mark_buffer_async_write);
447
448
449 /*
450  * fs/buffer.c contains helper functions for buffer-backed address space's
451  * fsync functions.  A common requirement for buffer-based filesystems is
452  * that certain data from the backing blockdev needs to be written out for
453  * a successful fsync().  For example, ext2 indirect blocks need to be
454  * written back and waited upon before fsync() returns.
455  *
456  * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
457  * inode_has_buffers() and invalidate_inode_buffers() are provided for the
458  * management of a list of dependent buffers at ->i_mapping->private_list.
459  *
460  * Locking is a little subtle: try_to_free_buffers() will remove buffers
461  * from their controlling inode's queue when they are being freed.  But
462  * try_to_free_buffers() will be operating against the *blockdev* mapping
463  * at the time, not against the S_ISREG file which depends on those buffers.
464  * So the locking for private_list is via the private_lock in the address_space
465  * which backs the buffers.  Which is different from the address_space 
466  * against which the buffers are listed.  So for a particular address_space,
467  * mapping->private_lock does *not* protect mapping->private_list!  In fact,
468  * mapping->private_list will always be protected by the backing blockdev's
469  * ->private_lock.
470  *
471  * Which introduces a requirement: all buffers on an address_space's
472  * ->private_list must be from the same address_space: the blockdev's.
473  *
474  * address_spaces which do not place buffers at ->private_list via these
475  * utility functions are free to use private_lock and private_list for
476  * whatever they want.  The only requirement is that list_empty(private_list)
477  * be true at clear_inode() time.
478  *
479  * FIXME: clear_inode should not call invalidate_inode_buffers().  The
480  * filesystems should do that.  invalidate_inode_buffers() should just go
481  * BUG_ON(!list_empty).
482  *
483  * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
484  * take an address_space, not an inode.  And it should be called
485  * mark_buffer_dirty_fsync() to clearly define why those buffers are being
486  * queued up.
487  *
488  * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
489  * list if it is already on a list.  Because if the buffer is on a list,
490  * it *must* already be on the right one.  If not, the filesystem is being
491  * silly.  This will save a ton of locking.  But first we have to ensure
492  * that buffers are taken *off* the old inode's list when they are freed
493  * (presumably in truncate).  That requires careful auditing of all
494  * filesystems (do it inside bforget()).  It could also be done by bringing
495  * b_inode back.
496  */
497
498 /*
499  * The buffer's backing address_space's private_lock must be held
500  */
501 static void __remove_assoc_queue(struct buffer_head *bh)
502 {
503         list_del_init(&bh->b_assoc_buffers);
504         WARN_ON(!bh->b_assoc_map);
505         if (buffer_write_io_error(bh))
506                 set_bit(AS_EIO, &bh->b_assoc_map->flags);
507         bh->b_assoc_map = NULL;
508 }
509
510 int inode_has_buffers(struct inode *inode)
511 {
512         return !list_empty(&inode->i_data.private_list);
513 }
514
515 /*
516  * osync is designed to support O_SYNC io.  It waits synchronously for
517  * all already-submitted IO to complete, but does not queue any new
518  * writes to the disk.
519  *
520  * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
521  * you dirty the buffers, and then use osync_inode_buffers to wait for
522  * completion.  Any other dirty buffers which are not yet queued for
523  * write will not be flushed to disk by the osync.
524  */
525 static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
526 {
527         struct buffer_head *bh;
528         struct list_head *p;
529         int err = 0;
530
531         spin_lock(lock);
532 repeat:
533         list_for_each_prev(p, list) {
534                 bh = BH_ENTRY(p);
535                 if (buffer_locked(bh)) {
536                         get_bh(bh);
537                         spin_unlock(lock);
538                         wait_on_buffer(bh);
539                         if (!buffer_uptodate(bh))
540                                 err = -EIO;
541                         brelse(bh);
542                         spin_lock(lock);
543                         goto repeat;
544                 }
545         }
546         spin_unlock(lock);
547         return err;
548 }
549
550 void do_thaw_all(unsigned long unused)
551 {
552         struct super_block *sb;
553         char b[BDEVNAME_SIZE];
554
555         spin_lock(&sb_lock);
556 restart:
557         list_for_each_entry(sb, &super_blocks, s_list) {
558                 sb->s_count++;
559                 spin_unlock(&sb_lock);
560                 down_read(&sb->s_umount);
561                 while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
562                         printk(KERN_WARNING "Emergency Thaw on %s\n",
563                                bdevname(sb->s_bdev, b));
564                 up_read(&sb->s_umount);
565                 spin_lock(&sb_lock);
566                 if (__put_super_and_need_restart(sb))
567                         goto restart;
568         }
569         spin_unlock(&sb_lock);
570         printk(KERN_WARNING "Emergency Thaw complete\n");
571 }
572
573 /**
574  * emergency_thaw_all -- forcibly thaw every frozen filesystem
575  *
576  * Used for emergency unfreeze of all filesystems via SysRq
577  */
578 void emergency_thaw_all(void)
579 {
580         pdflush_operation(do_thaw_all, 0);
581 }
582
583 /**
584  * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
585  * @mapping: the mapping which wants those buffers written
586  *
587  * Starts I/O against the buffers at mapping->private_list, and waits upon
588  * that I/O.
589  *
590  * Basically, this is a convenience function for fsync().
591  * @mapping is a file or directory which needs those buffers to be written for
592  * a successful fsync().
593  */
594 int sync_mapping_buffers(struct address_space *mapping)
595 {
596         struct address_space *buffer_mapping = mapping->assoc_mapping;
597
598         if (buffer_mapping == NULL || list_empty(&mapping->private_list))
599                 return 0;
600
601         return fsync_buffers_list(&buffer_mapping->private_lock,
602                                         &mapping->private_list);
603 }
604 EXPORT_SYMBOL(sync_mapping_buffers);
605
606 /*
607  * Called when we've recently written block `bblock', and it is known that
608  * `bblock' was for a buffer_boundary() buffer.  This means that the block at
609  * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
610  * dirty, schedule it for IO.  So that indirects merge nicely with their data.
611  */
612 void write_boundary_block(struct block_device *bdev,
613                         sector_t bblock, unsigned blocksize)
614 {
615         struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
616         if (bh) {
617                 if (buffer_dirty(bh))
618                         ll_rw_block(WRITE, 1, &bh);
619                 put_bh(bh);
620         }
621 }
622
623 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
624 {
625         struct address_space *mapping = inode->i_mapping;
626         struct address_space *buffer_mapping = bh->b_page->mapping;
627
628         mark_buffer_dirty(bh);
629         if (!mapping->assoc_mapping) {
630                 mapping->assoc_mapping = buffer_mapping;
631         } else {
632                 BUG_ON(mapping->assoc_mapping != buffer_mapping);
633         }
634         if (!bh->b_assoc_map) {
635                 spin_lock(&buffer_mapping->private_lock);
636                 list_move_tail(&bh->b_assoc_buffers,
637                                 &mapping->private_list);
638                 bh->b_assoc_map = mapping;
639                 spin_unlock(&buffer_mapping->private_lock);
640         }
641 }
642 EXPORT_SYMBOL(mark_buffer_dirty_inode);
643
644 /*
645  * Mark the page dirty, and set it dirty in the radix tree, and mark the inode
646  * dirty.
647  *
648  * If warn is true, then emit a warning if the page is not uptodate and has
649  * not been truncated.
650  */
651 static void __set_page_dirty(struct page *page,
652                 struct address_space *mapping, int warn)
653 {
654         spin_lock_irq(&mapping->tree_lock);
655         if (page->mapping) {    /* Race with truncate? */
656                 WARN_ON_ONCE(warn && !PageUptodate(page));
657                 account_page_dirtied(page, mapping);
658                 radix_tree_tag_set(&mapping->page_tree,
659                                 page_index(page), PAGECACHE_TAG_DIRTY);
660         }
661         spin_unlock_irq(&mapping->tree_lock);
662         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
663 }
664
665 /*
666  * Add a page to the dirty page list.
667  *
668  * It is a sad fact of life that this function is called from several places
669  * deeply under spinlocking.  It may not sleep.
670  *
671  * If the page has buffers, the uptodate buffers are set dirty, to preserve
672  * dirty-state coherency between the page and the buffers.  It the page does
673  * not have buffers then when they are later attached they will all be set
674  * dirty.
675  *
676  * The buffers are dirtied before the page is dirtied.  There's a small race
677  * window in which a writepage caller may see the page cleanness but not the
678  * buffer dirtiness.  That's fine.  If this code were to set the page dirty
679  * before the buffers, a concurrent writepage caller could clear the page dirty
680  * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
681  * page on the dirty page list.
682  *
683  * We use private_lock to lock against try_to_free_buffers while using the
684  * page's buffer list.  Also use this to protect against clean buffers being
685  * added to the page after it was set dirty.
686  *
687  * FIXME: may need to call ->reservepage here as well.  That's rather up to the
688  * address_space though.
689  */
690 int __set_page_dirty_buffers(struct page *page)
691 {
692         int newly_dirty;
693         struct address_space *mapping = page_mapping(page);
694
695         if (unlikely(!mapping))
696                 return !TestSetPageDirty(page);
697
698         spin_lock(&mapping->private_lock);
699         if (page_has_buffers(page)) {
700                 struct buffer_head *head = page_buffers(page);
701                 struct buffer_head *bh = head;
702
703                 do {
704                         set_buffer_dirty(bh);
705                         bh = bh->b_this_page;
706                 } while (bh != head);
707         }
708         newly_dirty = !TestSetPageDirty(page);
709         spin_unlock(&mapping->private_lock);
710
711         if (newly_dirty)
712                 __set_page_dirty(page, mapping, 1);
713         return newly_dirty;
714 }
715 EXPORT_SYMBOL(__set_page_dirty_buffers);
716
717 /*
718  * Write out and wait upon a list of buffers.
719  *
720  * We have conflicting pressures: we want to make sure that all
721  * initially dirty buffers get waited on, but that any subsequently
722  * dirtied buffers don't.  After all, we don't want fsync to last
723  * forever if somebody is actively writing to the file.
724  *
725  * Do this in two main stages: first we copy dirty buffers to a
726  * temporary inode list, queueing the writes as we go.  Then we clean
727  * up, waiting for those writes to complete.
728  * 
729  * During this second stage, any subsequent updates to the file may end
730  * up refiling the buffer on the original inode's dirty list again, so
731  * there is a chance we will end up with a buffer queued for write but
732  * not yet completed on that list.  So, as a final cleanup we go through
733  * the osync code to catch these locked, dirty buffers without requeuing
734  * any newly dirty buffers for write.
735  */
736 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
737 {
738         struct buffer_head *bh;
739         struct list_head tmp;
740         struct address_space *mapping, *prev_mapping = NULL;
741         int err = 0, err2;
742
743         INIT_LIST_HEAD(&tmp);
744
745         spin_lock(lock);
746         while (!list_empty(list)) {
747                 bh = BH_ENTRY(list->next);
748                 mapping = bh->b_assoc_map;
749                 __remove_assoc_queue(bh);
750                 /* Avoid race with mark_buffer_dirty_inode() which does
751                  * a lockless check and we rely on seeing the dirty bit */
752                 smp_mb();
753                 if (buffer_dirty(bh) || buffer_locked(bh)) {
754                         list_add(&bh->b_assoc_buffers, &tmp);
755                         bh->b_assoc_map = mapping;
756                         if (buffer_dirty(bh)) {
757                                 get_bh(bh);
758                                 spin_unlock(lock);
759                                 /*
760                                  * Ensure any pending I/O completes so that
761                                  * ll_rw_block() actually writes the current
762                                  * contents - it is a noop if I/O is still in
763                                  * flight on potentially older contents.
764                                  */
765                                 ll_rw_block(SWRITE_SYNC_PLUG, 1, &bh);
766
767                                 /*
768                                  * Kick off IO for the previous mapping. Note
769                                  * that we will not run the very last mapping,
770                                  * wait_on_buffer() will do that for us
771                                  * through sync_buffer().
772                                  */
773                                 if (prev_mapping && prev_mapping != mapping)
774                                         blk_run_address_space(prev_mapping);
775                                 prev_mapping = mapping;
776
777                                 brelse(bh);
778                                 spin_lock(lock);
779                         }
780                 }
781         }
782
783         while (!list_empty(&tmp)) {
784                 bh = BH_ENTRY(tmp.prev);
785                 get_bh(bh);
786                 mapping = bh->b_assoc_map;
787                 __remove_assoc_queue(bh);
788                 /* Avoid race with mark_buffer_dirty_inode() which does
789                  * a lockless check and we rely on seeing the dirty bit */
790                 smp_mb();
791                 if (buffer_dirty(bh)) {
792                         list_add(&bh->b_assoc_buffers,
793                                  &mapping->private_list);
794                         bh->b_assoc_map = mapping;
795                 }
796                 spin_unlock(lock);
797                 wait_on_buffer(bh);
798                 if (!buffer_uptodate(bh))
799                         err = -EIO;
800                 brelse(bh);
801                 spin_lock(lock);
802         }
803         
804         spin_unlock(lock);
805         err2 = osync_buffers_list(lock, list);
806         if (err)
807                 return err;
808         else
809                 return err2;
810 }
811
812 /*
813  * Invalidate any and all dirty buffers on a given inode.  We are
814  * probably unmounting the fs, but that doesn't mean we have already
815  * done a sync().  Just drop the buffers from the inode list.
816  *
817  * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
818  * assumes that all the buffers are against the blockdev.  Not true
819  * for reiserfs.
820  */
821 void invalidate_inode_buffers(struct inode *inode)
822 {
823         if (inode_has_buffers(inode)) {
824                 struct address_space *mapping = &inode->i_data;
825                 struct list_head *list = &mapping->private_list;
826                 struct address_space *buffer_mapping = mapping->assoc_mapping;
827
828                 spin_lock(&buffer_mapping->private_lock);
829                 while (!list_empty(list))
830                         __remove_assoc_queue(BH_ENTRY(list->next));
831                 spin_unlock(&buffer_mapping->private_lock);
832         }
833 }
834 EXPORT_SYMBOL(invalidate_inode_buffers);
835
836 /*
837  * Remove any clean buffers from the inode's buffer list.  This is called
838  * when we're trying to free the inode itself.  Those buffers can pin it.
839  *
840  * Returns true if all buffers were removed.
841  */
842 int remove_inode_buffers(struct inode *inode)
843 {
844         int ret = 1;
845
846         if (inode_has_buffers(inode)) {
847                 struct address_space *mapping = &inode->i_data;
848                 struct list_head *list = &mapping->private_list;
849                 struct address_space *buffer_mapping = mapping->assoc_mapping;
850
851                 spin_lock(&buffer_mapping->private_lock);
852                 while (!list_empty(list)) {
853                         struct buffer_head *bh = BH_ENTRY(list->next);
854                         if (buffer_dirty(bh)) {
855                                 ret = 0;
856                                 break;
857                         }
858                         __remove_assoc_queue(bh);
859                 }
860                 spin_unlock(&buffer_mapping->private_lock);
861         }
862         return ret;
863 }
864
865 /*
866  * Create the appropriate buffers when given a page for data area and
867  * the size of each buffer.. Use the bh->b_this_page linked list to
868  * follow the buffers created.  Return NULL if unable to create more
869  * buffers.
870  *
871  * The retry flag is used to differentiate async IO (paging, swapping)
872  * which may not fail from ordinary buffer allocations.
873  */
874 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
875                 int retry)
876 {
877         struct buffer_head *bh, *head;
878         long offset;
879
880 try_again:
881         head = NULL;
882         offset = PAGE_SIZE;
883         while ((offset -= size) >= 0) {
884                 bh = alloc_buffer_head(GFP_NOFS);
885                 if (!bh)
886                         goto no_grow;
887
888                 bh->b_bdev = NULL;
889                 bh->b_this_page = head;
890                 bh->b_blocknr = -1;
891                 head = bh;
892
893                 bh->b_state = 0;
894                 atomic_set(&bh->b_count, 0);
895                 bh->b_private = NULL;
896                 bh->b_size = size;
897
898                 /* Link the buffer to its page */
899                 set_bh_page(bh, page, offset);
900
901                 init_buffer(bh, NULL, NULL);
902         }
903         return head;
904 /*
905  * In case anything failed, we just free everything we got.
906  */
907 no_grow:
908         if (head) {
909                 do {
910                         bh = head;
911                         head = head->b_this_page;
912                         free_buffer_head(bh);
913                 } while (head);
914         }
915
916         /*
917          * Return failure for non-async IO requests.  Async IO requests
918          * are not allowed to fail, so we have to wait until buffer heads
919          * become available.  But we don't want tasks sleeping with 
920          * partially complete buffers, so all were released above.
921          */
922         if (!retry)
923                 return NULL;
924
925         /* We're _really_ low on memory. Now we just
926          * wait for old buffer heads to become free due to
927          * finishing IO.  Since this is an async request and
928          * the reserve list is empty, we're sure there are 
929          * async buffer heads in use.
930          */
931         free_more_memory();
932         goto try_again;
933 }
934 EXPORT_SYMBOL_GPL(alloc_page_buffers);
935
936 static inline void
937 link_dev_buffers(struct page *page, struct buffer_head *head)
938 {
939         struct buffer_head *bh, *tail;
940
941         bh = head;
942         do {
943                 tail = bh;
944                 bh = bh->b_this_page;
945         } while (bh);
946         tail->b_this_page = head;
947         attach_page_buffers(page, head);
948 }
949
950 /*
951  * Initialise the state of a blockdev page's buffers.
952  */ 
953 static void
954 init_page_buffers(struct page *page, struct block_device *bdev,
955                         sector_t block, int size)
956 {
957         struct buffer_head *head = page_buffers(page);
958         struct buffer_head *bh = head;
959         int uptodate = PageUptodate(page);
960
961         do {
962                 if (!buffer_mapped(bh)) {
963                         init_buffer(bh, NULL, NULL);
964                         bh->b_bdev = bdev;
965                         bh->b_blocknr = block;
966                         if (uptodate)
967                                 set_buffer_uptodate(bh);
968                         set_buffer_mapped(bh);
969                 }
970                 block++;
971                 bh = bh->b_this_page;
972         } while (bh != head);
973 }
974
975 /*
976  * Create the page-cache page that contains the requested block.
977  *
978  * This is user purely for blockdev mappings.
979  */
980 static struct page *
981 grow_dev_page(struct block_device *bdev, sector_t block,
982                 pgoff_t index, int size)
983 {
984         struct inode *inode = bdev->bd_inode;
985         struct page *page;
986         struct buffer_head *bh;
987
988         page = find_or_create_page(inode->i_mapping, index,
989                 (mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS)|__GFP_MOVABLE);
990         if (!page)
991                 return NULL;
992
993         BUG_ON(!PageLocked(page));
994
995         if (page_has_buffers(page)) {
996                 bh = page_buffers(page);
997                 if (bh->b_size == size) {
998                         init_page_buffers(page, bdev, block, size);
999                         return page;
1000                 }
1001                 if (!try_to_free_buffers(page))
1002                         goto failed;
1003         }
1004
1005         /*
1006          * Allocate some buffers for this page
1007          */
1008         bh = alloc_page_buffers(page, size, 0);
1009         if (!bh)
1010                 goto failed;
1011
1012         /*
1013          * Link the page to the buffers and initialise them.  Take the
1014          * lock to be atomic wrt __find_get_block(), which does not
1015          * run under the page lock.
1016          */
1017         spin_lock(&inode->i_mapping->private_lock);
1018         link_dev_buffers(page, bh);
1019         init_page_buffers(page, bdev, block, size);
1020         spin_unlock(&inode->i_mapping->private_lock);
1021         return page;
1022
1023 failed:
1024         BUG();
1025         unlock_page(page);
1026         page_cache_release(page);
1027         return NULL;
1028 }
1029
1030 /*
1031  * Create buffers for the specified block device block's page.  If
1032  * that page was dirty, the buffers are set dirty also.
1033  */
1034 static int
1035 grow_buffers(struct block_device *bdev, sector_t block, int size)
1036 {
1037         struct page *page;
1038         pgoff_t index;
1039         int sizebits;
1040
1041         sizebits = -1;
1042         do {
1043                 sizebits++;
1044         } while ((size << sizebits) < PAGE_SIZE);
1045
1046         index = block >> sizebits;
1047
1048         /*
1049          * Check for a block which wants to lie outside our maximum possible
1050          * pagecache index.  (this comparison is done using sector_t types).
1051          */
1052         if (unlikely(index != block >> sizebits)) {
1053                 char b[BDEVNAME_SIZE];
1054
1055                 printk(KERN_ERR "%s: requested out-of-range block %llu for "
1056                         "device %s\n",
1057                         __func__, (unsigned long long)block,
1058                         bdevname(bdev, b));
1059                 return -EIO;
1060         }
1061         block = index << sizebits;
1062         /* Create a page with the proper size buffers.. */
1063         page = grow_dev_page(bdev, block, index, size);
1064         if (!page)
1065                 return 0;
1066         unlock_page(page);
1067         page_cache_release(page);
1068         return 1;
1069 }
1070
1071 static struct buffer_head *
1072 __getblk_slow(struct block_device *bdev, sector_t block, int size)
1073 {
1074         /* Size must be multiple of hard sectorsize */
1075         if (unlikely(size & (bdev_hardsect_size(bdev)-1) ||
1076                         (size < 512 || size > PAGE_SIZE))) {
1077                 printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1078                                         size);
1079                 printk(KERN_ERR "hardsect size: %d\n",
1080                                         bdev_hardsect_size(bdev));
1081
1082                 dump_stack();
1083                 return NULL;
1084         }
1085
1086         for (;;) {
1087                 struct buffer_head * bh;
1088                 int ret;
1089
1090                 bh = __find_get_block(bdev, block, size);
1091                 if (bh)
1092                         return bh;
1093
1094                 ret = grow_buffers(bdev, block, size);
1095                 if (ret < 0)
1096                         return NULL;
1097                 if (ret == 0)
1098                         free_more_memory();
1099         }
1100 }
1101
1102 /*
1103  * The relationship between dirty buffers and dirty pages:
1104  *
1105  * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1106  * the page is tagged dirty in its radix tree.
1107  *
1108  * At all times, the dirtiness of the buffers represents the dirtiness of
1109  * subsections of the page.  If the page has buffers, the page dirty bit is
1110  * merely a hint about the true dirty state.
1111  *
1112  * When a page is set dirty in its entirety, all its buffers are marked dirty
1113  * (if the page has buffers).
1114  *
1115  * When a buffer is marked dirty, its page is dirtied, but the page's other
1116  * buffers are not.
1117  *
1118  * Also.  When blockdev buffers are explicitly read with bread(), they
1119  * individually become uptodate.  But their backing page remains not
1120  * uptodate - even if all of its buffers are uptodate.  A subsequent
1121  * block_read_full_page() against that page will discover all the uptodate
1122  * buffers, will set the page uptodate and will perform no I/O.
1123  */
1124
1125 /**
1126  * mark_buffer_dirty - mark a buffer_head as needing writeout
1127  * @bh: the buffer_head to mark dirty
1128  *
1129  * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1130  * backing page dirty, then tag the page as dirty in its address_space's radix
1131  * tree and then attach the address_space's inode to its superblock's dirty
1132  * inode list.
1133  *
1134  * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1135  * mapping->tree_lock and the global inode_lock.
1136  */
1137 void mark_buffer_dirty(struct buffer_head *bh)
1138 {
1139         WARN_ON_ONCE(!buffer_uptodate(bh));
1140
1141         /*
1142          * Very *carefully* optimize the it-is-already-dirty case.
1143          *
1144          * Don't let the final "is it dirty" escape to before we
1145          * perhaps modified the buffer.
1146          */
1147         if (buffer_dirty(bh)) {
1148                 smp_mb();
1149                 if (buffer_dirty(bh))
1150                         return;
1151         }
1152
1153         if (!test_set_buffer_dirty(bh)) {
1154                 struct page *page = bh->b_page;
1155                 if (!TestSetPageDirty(page))
1156                         __set_page_dirty(page, page_mapping(page), 0);
1157         }
1158 }
1159
1160 /*
1161  * Decrement a buffer_head's reference count.  If all buffers against a page
1162  * have zero reference count, are clean and unlocked, and if the page is clean
1163  * and unlocked then try_to_free_buffers() may strip the buffers from the page
1164  * in preparation for freeing it (sometimes, rarely, buffers are removed from
1165  * a page but it ends up not being freed, and buffers may later be reattached).
1166  */
1167 void __brelse(struct buffer_head * buf)
1168 {
1169         if (atomic_read(&buf->b_count)) {
1170                 put_bh(buf);
1171                 return;
1172         }
1173         WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1174 }
1175
1176 /*
1177  * bforget() is like brelse(), except it discards any
1178  * potentially dirty data.
1179  */
1180 void __bforget(struct buffer_head *bh)
1181 {
1182         clear_buffer_dirty(bh);
1183         if (bh->b_assoc_map) {
1184                 struct address_space *buffer_mapping = bh->b_page->mapping;
1185
1186                 spin_lock(&buffer_mapping->private_lock);
1187                 list_del_init(&bh->b_assoc_buffers);
1188                 bh->b_assoc_map = NULL;
1189                 spin_unlock(&buffer_mapping->private_lock);
1190         }
1191         __brelse(bh);
1192 }
1193
1194 static struct buffer_head *__bread_slow(struct buffer_head *bh)
1195 {
1196         lock_buffer(bh);
1197         if (buffer_uptodate(bh)) {
1198                 unlock_buffer(bh);
1199                 return bh;
1200         } else {
1201                 get_bh(bh);
1202                 bh->b_end_io = end_buffer_read_sync;
1203                 submit_bh(READ, bh);
1204                 wait_on_buffer(bh);
1205                 if (buffer_uptodate(bh))
1206                         return bh;
1207         }
1208         brelse(bh);
1209         return NULL;
1210 }
1211
1212 /*
1213  * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1214  * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1215  * refcount elevated by one when they're in an LRU.  A buffer can only appear
1216  * once in a particular CPU's LRU.  A single buffer can be present in multiple
1217  * CPU's LRUs at the same time.
1218  *
1219  * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1220  * sb_find_get_block().
1221  *
1222  * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1223  * a local interrupt disable for that.
1224  */
1225
1226 #define BH_LRU_SIZE     8
1227
1228 struct bh_lru {
1229         struct buffer_head *bhs[BH_LRU_SIZE];
1230 };
1231
1232 static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1233
1234 #ifdef CONFIG_SMP
1235 #define bh_lru_lock()   local_irq_disable()
1236 #define bh_lru_unlock() local_irq_enable()
1237 #else
1238 #define bh_lru_lock()   preempt_disable()
1239 #define bh_lru_unlock() preempt_enable()
1240 #endif
1241
1242 static inline void check_irqs_on(void)
1243 {
1244 #ifdef irqs_disabled
1245         BUG_ON(irqs_disabled());
1246 #endif
1247 }
1248
1249 /*
1250  * The LRU management algorithm is dopey-but-simple.  Sorry.
1251  */
1252 static void bh_lru_install(struct buffer_head *bh)
1253 {
1254         struct buffer_head *evictee = NULL;
1255         struct bh_lru *lru;
1256
1257         check_irqs_on();
1258         bh_lru_lock();
1259         lru = &__get_cpu_var(bh_lrus);
1260         if (lru->bhs[0] != bh) {
1261                 struct buffer_head *bhs[BH_LRU_SIZE];
1262                 int in;
1263                 int out = 0;
1264
1265                 get_bh(bh);
1266                 bhs[out++] = bh;
1267                 for (in = 0; in < BH_LRU_SIZE; in++) {
1268                         struct buffer_head *bh2 = lru->bhs[in];
1269
1270                         if (bh2 == bh) {
1271                                 __brelse(bh2);
1272                         } else {
1273                                 if (out >= BH_LRU_SIZE) {
1274                                         BUG_ON(evictee != NULL);
1275                                         evictee = bh2;
1276                                 } else {
1277                                         bhs[out++] = bh2;
1278                                 }
1279                         }
1280                 }
1281                 while (out < BH_LRU_SIZE)
1282                         bhs[out++] = NULL;
1283                 memcpy(lru->bhs, bhs, sizeof(bhs));
1284         }
1285         bh_lru_unlock();
1286
1287         if (evictee)
1288                 __brelse(evictee);
1289 }
1290
1291 /*
1292  * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1293  */
1294 static struct buffer_head *
1295 lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1296 {
1297         struct buffer_head *ret = NULL;
1298         struct bh_lru *lru;
1299         unsigned int i;
1300
1301         check_irqs_on();
1302         bh_lru_lock();
1303         lru = &__get_cpu_var(bh_lrus);
1304         for (i = 0; i < BH_LRU_SIZE; i++) {
1305                 struct buffer_head *bh = lru->bhs[i];
1306
1307                 if (bh && bh->b_bdev == bdev &&
1308                                 bh->b_blocknr == block && bh->b_size == size) {
1309                         if (i) {
1310                                 while (i) {
1311                                         lru->bhs[i] = lru->bhs[i - 1];
1312                                         i--;
1313                                 }
1314                                 lru->bhs[0] = bh;
1315                         }
1316                         get_bh(bh);
1317                         ret = bh;
1318                         break;
1319                 }
1320         }
1321         bh_lru_unlock();
1322         return ret;
1323 }
1324
1325 /*
1326  * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1327  * it in the LRU and mark it as accessed.  If it is not present then return
1328  * NULL
1329  */
1330 struct buffer_head *
1331 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1332 {
1333         struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1334
1335         if (bh == NULL) {
1336                 bh = __find_get_block_slow(bdev, block);
1337                 if (bh)
1338                         bh_lru_install(bh);
1339         }
1340         if (bh)
1341                 touch_buffer(bh);
1342         return bh;
1343 }
1344 EXPORT_SYMBOL(__find_get_block);
1345
1346 /*
1347  * __getblk will locate (and, if necessary, create) the buffer_head
1348  * which corresponds to the passed block_device, block and size. The
1349  * returned buffer has its reference count incremented.
1350  *
1351  * __getblk() cannot fail - it just keeps trying.  If you pass it an
1352  * illegal block number, __getblk() will happily return a buffer_head
1353  * which represents the non-existent block.  Very weird.
1354  *
1355  * __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
1356  * attempt is failing.  FIXME, perhaps?
1357  */
1358 struct buffer_head *
1359 __getblk(struct block_device *bdev, sector_t block, unsigned size)
1360 {
1361         struct buffer_head *bh = __find_get_block(bdev, block, size);
1362
1363         might_sleep();
1364         if (bh == NULL)
1365                 bh = __getblk_slow(bdev, block, size);
1366         return bh;
1367 }
1368 EXPORT_SYMBOL(__getblk);
1369
1370 /*
1371  * Do async read-ahead on a buffer..
1372  */
1373 void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1374 {
1375         struct buffer_head *bh = __getblk(bdev, block, size);
1376         if (likely(bh)) {
1377                 ll_rw_block(READA, 1, &bh);
1378                 brelse(bh);
1379         }
1380 }
1381 EXPORT_SYMBOL(__breadahead);
1382
1383 /**
1384  *  __bread() - reads a specified block and returns the bh
1385  *  @bdev: the block_device to read from
1386  *  @block: number of block
1387  *  @size: size (in bytes) to read
1388  * 
1389  *  Reads a specified block, and returns buffer head that contains it.
1390  *  It returns NULL if the block was unreadable.
1391  */
1392 struct buffer_head *
1393 __bread(struct block_device *bdev, sector_t block, unsigned size)
1394 {
1395         struct buffer_head *bh = __getblk(bdev, block, size);
1396
1397         if (likely(bh) && !buffer_uptodate(bh))
1398                 bh = __bread_slow(bh);
1399         return bh;
1400 }
1401 EXPORT_SYMBOL(__bread);
1402
1403 /*
1404  * invalidate_bh_lrus() is called rarely - but not only at unmount.
1405  * This doesn't race because it runs in each cpu either in irq
1406  * or with preempt disabled.
1407  */
1408 static void invalidate_bh_lru(void *arg)
1409 {
1410         struct bh_lru *b = &get_cpu_var(bh_lrus);
1411         int i;
1412
1413         for (i = 0; i < BH_LRU_SIZE; i++) {
1414                 brelse(b->bhs[i]);
1415                 b->bhs[i] = NULL;
1416         }
1417         put_cpu_var(bh_lrus);
1418 }
1419         
1420 void invalidate_bh_lrus(void)
1421 {
1422         on_each_cpu(invalidate_bh_lru, NULL, 1);
1423 }
1424 EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1425
1426 void set_bh_page(struct buffer_head *bh,
1427                 struct page *page, unsigned long offset)
1428 {
1429         bh->b_page = page;
1430         BUG_ON(offset >= PAGE_SIZE);
1431         if (PageHighMem(page))
1432                 /*
1433                  * This catches illegal uses and preserves the offset:
1434                  */
1435                 bh->b_data = (char *)(0 + offset);
1436         else
1437                 bh->b_data = page_address(page) + offset;
1438 }
1439 EXPORT_SYMBOL(set_bh_page);
1440
1441 /*
1442  * Called when truncating a buffer on a page completely.
1443  */
1444 static void discard_buffer(struct buffer_head * bh)
1445 {
1446         lock_buffer(bh);
1447         clear_buffer_dirty(bh);
1448         bh->b_bdev = NULL;
1449         clear_buffer_mapped(bh);
1450         clear_buffer_req(bh);
1451         clear_buffer_new(bh);
1452         clear_buffer_delay(bh);
1453         clear_buffer_unwritten(bh);
1454         unlock_buffer(bh);
1455 }
1456
1457 /**
1458  * block_invalidatepage - invalidate part of all of a buffer-backed page
1459  *
1460  * @page: the page which is affected
1461  * @offset: the index of the truncation point
1462  *
1463  * block_invalidatepage() is called when all or part of the page has become
1464  * invalidatedby a truncate operation.
1465  *
1466  * block_invalidatepage() does not have to release all buffers, but it must
1467  * ensure that no dirty buffer is left outside @offset and that no I/O
1468  * is underway against any of the blocks which are outside the truncation
1469  * point.  Because the caller is about to free (and possibly reuse) those
1470  * blocks on-disk.
1471  */
1472 void block_invalidatepage(struct page *page, unsigned long offset)
1473 {
1474         struct buffer_head *head, *bh, *next;
1475         unsigned int curr_off = 0;
1476
1477         BUG_ON(!PageLocked(page));
1478         if (!page_has_buffers(page))
1479                 goto out;
1480
1481         head = page_buffers(page);
1482         bh = head;
1483         do {
1484                 unsigned int next_off = curr_off + bh->b_size;
1485                 next = bh->b_this_page;
1486
1487                 /*
1488                  * is this block fully invalidated?
1489                  */
1490                 if (offset <= curr_off)
1491                         discard_buffer(bh);
1492                 curr_off = next_off;
1493                 bh = next;
1494         } while (bh != head);
1495
1496         /*
1497          * We release buffers only if the entire page is being invalidated.
1498          * The get_block cached value has been unconditionally invalidated,
1499          * so real IO is not possible anymore.
1500          */
1501         if (offset == 0)
1502                 try_to_release_page(page, 0);
1503 out:
1504         return;
1505 }
1506 EXPORT_SYMBOL(block_invalidatepage);
1507
1508 /*
1509  * We attach and possibly dirty the buffers atomically wrt
1510  * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1511  * is already excluded via the page lock.
1512  */
1513 void create_empty_buffers(struct page *page,
1514                         unsigned long blocksize, unsigned long b_state)
1515 {
1516         struct buffer_head *bh, *head, *tail;
1517
1518         head = alloc_page_buffers(page, blocksize, 1);
1519         bh = head;
1520         do {
1521                 bh->b_state |= b_state;
1522                 tail = bh;
1523                 bh = bh->b_this_page;
1524         } while (bh);
1525         tail->b_this_page = head;
1526
1527         spin_lock(&page->mapping->private_lock);
1528         if (PageUptodate(page) || PageDirty(page)) {
1529                 bh = head;
1530                 do {
1531                         if (PageDirty(page))
1532                                 set_buffer_dirty(bh);
1533                         if (PageUptodate(page))
1534                                 set_buffer_uptodate(bh);
1535                         bh = bh->b_this_page;
1536                 } while (bh != head);
1537         }
1538         attach_page_buffers(page, head);
1539         spin_unlock(&page->mapping->private_lock);
1540 }
1541 EXPORT_SYMBOL(create_empty_buffers);
1542
1543 /*
1544  * We are taking a block for data and we don't want any output from any
1545  * buffer-cache aliases starting from return from that function and
1546  * until the moment when something will explicitly mark the buffer
1547  * dirty (hopefully that will not happen until we will free that block ;-)
1548  * We don't even need to mark it not-uptodate - nobody can expect
1549  * anything from a newly allocated buffer anyway. We used to used
1550  * unmap_buffer() for such invalidation, but that was wrong. We definitely
1551  * don't want to mark the alias unmapped, for example - it would confuse
1552  * anyone who might pick it with bread() afterwards...
1553  *
1554  * Also..  Note that bforget() doesn't lock the buffer.  So there can
1555  * be writeout I/O going on against recently-freed buffers.  We don't
1556  * wait on that I/O in bforget() - it's more efficient to wait on the I/O
1557  * only if we really need to.  That happens here.
1558  */
1559 void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1560 {
1561         struct buffer_head *old_bh;
1562
1563         might_sleep();
1564
1565         old_bh = __find_get_block_slow(bdev, block);
1566         if (old_bh) {
1567                 clear_buffer_dirty(old_bh);
1568                 wait_on_buffer(old_bh);
1569                 clear_buffer_req(old_bh);
1570                 __brelse(old_bh);
1571         }
1572 }
1573 EXPORT_SYMBOL(unmap_underlying_metadata);
1574
1575 /*
1576  * NOTE! All mapped/uptodate combinations are valid:
1577  *
1578  *      Mapped  Uptodate        Meaning
1579  *
1580  *      No      No              "unknown" - must do get_block()
1581  *      No      Yes             "hole" - zero-filled
1582  *      Yes     No              "allocated" - allocated on disk, not read in
1583  *      Yes     Yes             "valid" - allocated and up-to-date in memory.
1584  *
1585  * "Dirty" is valid only with the last case (mapped+uptodate).
1586  */
1587
1588 /*
1589  * While block_write_full_page is writing back the dirty buffers under
1590  * the page lock, whoever dirtied the buffers may decide to clean them
1591  * again at any time.  We handle that by only looking at the buffer
1592  * state inside lock_buffer().
1593  *
1594  * If block_write_full_page() is called for regular writeback
1595  * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1596  * locked buffer.   This only can happen if someone has written the buffer
1597  * directly, with submit_bh().  At the address_space level PageWriteback
1598  * prevents this contention from occurring.
1599  *
1600  * If block_write_full_page() is called with wbc->sync_mode ==
1601  * WB_SYNC_ALL, the writes are posted using WRITE_SYNC_PLUG; this
1602  * causes the writes to be flagged as synchronous writes, but the
1603  * block device queue will NOT be unplugged, since usually many pages
1604  * will be pushed to the out before the higher-level caller actually
1605  * waits for the writes to be completed.  The various wait functions,
1606  * such as wait_on_writeback_range() will ultimately call sync_page()
1607  * which will ultimately call blk_run_backing_dev(), which will end up
1608  * unplugging the device queue.
1609  */
1610 static int __block_write_full_page(struct inode *inode, struct page *page,
1611                         get_block_t *get_block, struct writeback_control *wbc)
1612 {
1613         int err;
1614         sector_t block;
1615         sector_t last_block;
1616         struct buffer_head *bh, *head;
1617         const unsigned blocksize = 1 << inode->i_blkbits;
1618         int nr_underway = 0;
1619         int write_op = (wbc->sync_mode == WB_SYNC_ALL ?
1620                         WRITE_SYNC_PLUG : WRITE);
1621
1622         BUG_ON(!PageLocked(page));
1623
1624         last_block = (i_size_read(inode) - 1) >> inode->i_blkbits;
1625
1626         if (!page_has_buffers(page)) {
1627                 create_empty_buffers(page, blocksize,
1628                                         (1 << BH_Dirty)|(1 << BH_Uptodate));
1629         }
1630
1631         /*
1632          * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1633          * here, and the (potentially unmapped) buffers may become dirty at
1634          * any time.  If a buffer becomes dirty here after we've inspected it
1635          * then we just miss that fact, and the page stays dirty.
1636          *
1637          * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1638          * handle that here by just cleaning them.
1639          */
1640
1641         block = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
1642         head = page_buffers(page);
1643         bh = head;
1644
1645         /*
1646          * Get all the dirty buffers mapped to disk addresses and
1647          * handle any aliases from the underlying blockdev's mapping.
1648          */
1649         do {
1650                 if (block > last_block) {
1651                         /*
1652                          * mapped buffers outside i_size will occur, because
1653                          * this page can be outside i_size when there is a
1654                          * truncate in progress.
1655                          */
1656                         /*
1657                          * The buffer was zeroed by block_write_full_page()
1658                          */
1659                         clear_buffer_dirty(bh);
1660                         set_buffer_uptodate(bh);
1661                 } else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1662                            buffer_dirty(bh)) {
1663                         WARN_ON(bh->b_size != blocksize);
1664                         err = get_block(inode, block, bh, 1);
1665                         if (err)
1666                                 goto recover;
1667                         clear_buffer_delay(bh);
1668                         if (buffer_new(bh)) {
1669                                 /* blockdev mappings never come here */
1670                                 clear_buffer_new(bh);
1671                                 unmap_underlying_metadata(bh->b_bdev,
1672                                                         bh->b_blocknr);
1673                         }
1674                 }
1675                 bh = bh->b_this_page;
1676                 block++;
1677         } while (bh != head);
1678
1679         do {
1680                 if (!buffer_mapped(bh))
1681                         continue;
1682                 /*
1683                  * If it's a fully non-blocking write attempt and we cannot
1684                  * lock the buffer then redirty the page.  Note that this can
1685                  * potentially cause a busy-wait loop from pdflush and kswapd
1686                  * activity, but those code paths have their own higher-level
1687                  * throttling.
1688                  */
1689                 if (wbc->sync_mode != WB_SYNC_NONE || !wbc->nonblocking) {
1690                         lock_buffer(bh);
1691                 } else if (!trylock_buffer(bh)) {
1692                         redirty_page_for_writepage(wbc, page);
1693                         continue;
1694                 }
1695                 if (test_clear_buffer_dirty(bh)) {
1696                         mark_buffer_async_write(bh);
1697                 } else {
1698                         unlock_buffer(bh);
1699                 }
1700         } while ((bh = bh->b_this_page) != head);
1701
1702         /*
1703          * The page and its buffers are protected by PageWriteback(), so we can
1704          * drop the bh refcounts early.
1705          */
1706         BUG_ON(PageWriteback(page));
1707         set_page_writeback(page);
1708
1709         do {
1710                 struct buffer_head *next = bh->b_this_page;
1711                 if (buffer_async_write(bh)) {
1712                         submit_bh(write_op, bh);
1713                         nr_underway++;
1714                 }
1715                 bh = next;
1716         } while (bh != head);
1717         unlock_page(page);
1718
1719         err = 0;
1720 done:
1721         if (nr_underway == 0) {
1722                 /*
1723                  * The page was marked dirty, but the buffers were
1724                  * clean.  Someone wrote them back by hand with
1725                  * ll_rw_block/submit_bh.  A rare case.
1726                  */
1727                 end_page_writeback(page);
1728
1729                 /*
1730                  * The page and buffer_heads can be released at any time from
1731                  * here on.
1732                  */
1733         }
1734         return err;
1735
1736 recover:
1737         /*
1738          * ENOSPC, or some other error.  We may already have added some
1739          * blocks to the file, so we need to write these out to avoid
1740          * exposing stale data.
1741          * The page is currently locked and not marked for writeback
1742          */
1743         bh = head;
1744         /* Recovery: lock and submit the mapped buffers */
1745         do {
1746                 if (buffer_mapped(bh) && buffer_dirty(bh) &&
1747                     !buffer_delay(bh)) {
1748                         lock_buffer(bh);
1749                         mark_buffer_async_write(bh);
1750                 } else {
1751                         /*
1752                          * The buffer may have been set dirty during
1753                          * attachment to a dirty page.
1754                          */
1755                         clear_buffer_dirty(bh);
1756                 }
1757         } while ((bh = bh->b_this_page) != head);
1758         SetPageError(page);
1759         BUG_ON(PageWriteback(page));
1760         mapping_set_error(page->mapping, err);
1761         set_page_writeback(page);
1762         do {
1763                 struct buffer_head *next = bh->b_this_page;
1764                 if (buffer_async_write(bh)) {
1765                         clear_buffer_dirty(bh);
1766                         submit_bh(write_op, bh);
1767                         nr_underway++;
1768                 }
1769                 bh = next;
1770         } while (bh != head);
1771         unlock_page(page);
1772         goto done;
1773 }
1774
1775 /*
1776  * If a page has any new buffers, zero them out here, and mark them uptodate
1777  * and dirty so they'll be written out (in order to prevent uninitialised
1778  * block data from leaking). And clear the new bit.
1779  */
1780 void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1781 {
1782         unsigned int block_start, block_end;
1783         struct buffer_head *head, *bh;
1784
1785         BUG_ON(!PageLocked(page));
1786         if (!page_has_buffers(page))
1787                 return;
1788
1789         bh = head = page_buffers(page);
1790         block_start = 0;
1791         do {
1792                 block_end = block_start + bh->b_size;
1793
1794                 if (buffer_new(bh)) {
1795                         if (block_end > from && block_start < to) {
1796                                 if (!PageUptodate(page)) {
1797                                         unsigned start, size;
1798
1799                                         start = max(from, block_start);
1800                                         size = min(to, block_end) - start;
1801
1802                                         zero_user(page, start, size);
1803                                         set_buffer_uptodate(bh);
1804                                 }
1805
1806                                 clear_buffer_new(bh);
1807                                 mark_buffer_dirty(bh);
1808                         }
1809                 }
1810
1811                 block_start = block_end;
1812                 bh = bh->b_this_page;
1813         } while (bh != head);
1814 }
1815 EXPORT_SYMBOL(page_zero_new_buffers);
1816
1817 static int __block_prepare_write(struct inode *inode, struct page *page,
1818                 unsigned from, unsigned to, get_block_t *get_block)
1819 {
1820         unsigned block_start, block_end;
1821         sector_t block;
1822         int err = 0;
1823         unsigned blocksize, bbits;
1824         struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1825
1826         BUG_ON(!PageLocked(page));
1827         BUG_ON(from > PAGE_CACHE_SIZE);
1828         BUG_ON(to > PAGE_CACHE_SIZE);
1829         BUG_ON(from > to);
1830
1831         blocksize = 1 << inode->i_blkbits;
1832         if (!page_has_buffers(page))
1833                 create_empty_buffers(page, blocksize, 0);
1834         head = page_buffers(page);
1835
1836         bbits = inode->i_blkbits;
1837         block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1838
1839         for(bh = head, block_start = 0; bh != head || !block_start;
1840             block++, block_start=block_end, bh = bh->b_this_page) {
1841                 block_end = block_start + blocksize;
1842                 if (block_end <= from || block_start >= to) {
1843                         if (PageUptodate(page)) {
1844                                 if (!buffer_uptodate(bh))
1845                                         set_buffer_uptodate(bh);
1846                         }
1847                         continue;
1848                 }
1849                 if (buffer_new(bh))
1850                         clear_buffer_new(bh);
1851                 if (!buffer_mapped(bh)) {
1852                         WARN_ON(bh->b_size != blocksize);
1853                         err = get_block(inode, block, bh, 1);
1854                         if (err)
1855                                 break;
1856                         if (buffer_new(bh)) {
1857                                 unmap_underlying_metadata(bh->b_bdev,
1858                                                         bh->b_blocknr);
1859                                 if (PageUptodate(page)) {
1860                                         clear_buffer_new(bh);
1861                                         set_buffer_uptodate(bh);
1862                                         mark_buffer_dirty(bh);
1863                                         continue;
1864                                 }
1865                                 if (block_end > to || block_start < from)
1866                                         zero_user_segments(page,
1867                                                 to, block_end,
1868                                                 block_start, from);
1869                                 continue;
1870                         }
1871                 }
1872                 if (PageUptodate(page)) {
1873                         if (!buffer_uptodate(bh))
1874                                 set_buffer_uptodate(bh);
1875                         continue; 
1876                 }
1877                 if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1878                     !buffer_unwritten(bh) &&
1879                      (block_start < from || block_end > to)) {
1880                         ll_rw_block(READ, 1, &bh);
1881                         *wait_bh++=bh;
1882                 }
1883         }
1884         /*
1885          * If we issued read requests - let them complete.
1886          */
1887         while(wait_bh > wait) {
1888                 wait_on_buffer(*--wait_bh);
1889                 if (!buffer_uptodate(*wait_bh))
1890                         err = -EIO;
1891         }
1892         if (unlikely(err))
1893                 page_zero_new_buffers(page, from, to);
1894         return err;
1895 }
1896
1897 static int __block_commit_write(struct inode *inode, struct page *page,
1898                 unsigned from, unsigned to)
1899 {
1900         unsigned block_start, block_end;
1901         int partial = 0;
1902         unsigned blocksize;
1903         struct buffer_head *bh, *head;
1904
1905         blocksize = 1 << inode->i_blkbits;
1906
1907         for(bh = head = page_buffers(page), block_start = 0;
1908             bh != head || !block_start;
1909             block_start=block_end, bh = bh->b_this_page) {
1910                 block_end = block_start + blocksize;
1911                 if (block_end <= from || block_start >= to) {
1912                         if (!buffer_uptodate(bh))
1913                                 partial = 1;
1914                 } else {
1915                         set_buffer_uptodate(bh);
1916                         mark_buffer_dirty(bh);
1917                 }
1918                 clear_buffer_new(bh);
1919         }
1920
1921         /*
1922          * If this is a partial write which happened to make all buffers
1923          * uptodate then we can optimize away a bogus readpage() for
1924          * the next read(). Here we 'discover' whether the page went
1925          * uptodate as a result of this (potentially partial) write.
1926          */
1927         if (!partial)
1928                 SetPageUptodate(page);
1929         return 0;
1930 }
1931
1932 /*
1933  * block_write_begin takes care of the basic task of block allocation and
1934  * bringing partial write blocks uptodate first.
1935  *
1936  * If *pagep is not NULL, then block_write_begin uses the locked page
1937  * at *pagep rather than allocating its own. In this case, the page will
1938  * not be unlocked or deallocated on failure.
1939  */
1940 int block_write_begin(struct file *file, struct address_space *mapping,
1941                         loff_t pos, unsigned len, unsigned flags,
1942                         struct page **pagep, void **fsdata,
1943                         get_block_t *get_block)
1944 {
1945         struct inode *inode = mapping->host;
1946         int status = 0;
1947         struct page *page;
1948         pgoff_t index;
1949         unsigned start, end;
1950         int ownpage = 0;
1951
1952         index = pos >> PAGE_CACHE_SHIFT;
1953         start = pos & (PAGE_CACHE_SIZE - 1);
1954         end = start + len;
1955
1956         page = *pagep;
1957         if (page == NULL) {
1958                 ownpage = 1;
1959                 page = grab_cache_page_write_begin(mapping, index, flags);
1960                 if (!page) {
1961                         status = -ENOMEM;
1962                         goto out;
1963                 }
1964                 *pagep = page;
1965         } else
1966                 BUG_ON(!PageLocked(page));
1967
1968         status = __block_prepare_write(inode, page, start, end, get_block);
1969         if (unlikely(status)) {
1970                 ClearPageUptodate(page);
1971
1972                 if (ownpage) {
1973                         unlock_page(page);
1974                         page_cache_release(page);
1975                         *pagep = NULL;
1976
1977                         /*
1978                          * prepare_write() may have instantiated a few blocks
1979                          * outside i_size.  Trim these off again. Don't need
1980                          * i_size_read because we hold i_mutex.
1981                          */
1982                         if (pos + len > inode->i_size)
1983                                 vmtruncate(inode, inode->i_size);
1984                 }
1985         }
1986
1987 out:
1988         return status;
1989 }
1990 EXPORT_SYMBOL(block_write_begin);
1991
1992 int block_write_end(struct file *file, struct address_space *mapping,
1993                         loff_t pos, unsigned len, unsigned copied,
1994                         struct page *page, void *fsdata)
1995 {
1996         struct inode *inode = mapping->host;
1997         unsigned start;
1998
1999         start = pos & (PAGE_CACHE_SIZE - 1);
2000
2001         if (unlikely(copied < len)) {
2002                 /*
2003                  * The buffers that were written will now be uptodate, so we
2004                  * don't have to worry about a readpage reading them and
2005                  * overwriting a partial write. However if we have encountered
2006                  * a short write and only partially written into a buffer, it
2007                  * will not be marked uptodate, so a readpage might come in and
2008                  * destroy our partial write.
2009                  *
2010                  * Do the simplest thing, and just treat any short write to a
2011                  * non uptodate page as a zero-length write, and force the
2012                  * caller to redo the whole thing.
2013                  */
2014                 if (!PageUptodate(page))
2015                         copied = 0;
2016
2017                 page_zero_new_buffers(page, start+copied, start+len);
2018         }
2019         flush_dcache_page(page);
2020
2021         /* This could be a short (even 0-length) commit */
2022         __block_commit_write(inode, page, start, start+copied);
2023
2024         return copied;
2025 }
2026 EXPORT_SYMBOL(block_write_end);
2027
2028 int generic_write_end(struct file *file, struct address_space *mapping,
2029                         loff_t pos, unsigned len, unsigned copied,
2030                         struct page *page, void *fsdata)
2031 {
2032         struct inode *inode = mapping->host;
2033         int i_size_changed = 0;
2034
2035         copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2036
2037         /*
2038          * No need to use i_size_read() here, the i_size
2039          * cannot change under us because we hold i_mutex.
2040          *
2041          * But it's important to update i_size while still holding page lock:
2042          * page writeout could otherwise come in and zero beyond i_size.
2043          */
2044         if (pos+copied > inode->i_size) {
2045                 i_size_write(inode, pos+copied);
2046                 i_size_changed = 1;
2047         }
2048
2049         unlock_page(page);
2050         page_cache_release(page);
2051
2052         /*
2053          * Don't mark the inode dirty under page lock. First, it unnecessarily
2054          * makes the holding time of page lock longer. Second, it forces lock
2055          * ordering of page lock and transaction start for journaling
2056          * filesystems.
2057          */
2058         if (i_size_changed)
2059                 mark_inode_dirty(inode);
2060
2061         return copied;
2062 }
2063 EXPORT_SYMBOL(generic_write_end);
2064
2065 /*
2066  * block_is_partially_uptodate checks whether buffers within a page are
2067  * uptodate or not.
2068  *
2069  * Returns true if all buffers which correspond to a file portion
2070  * we want to read are uptodate.
2071  */
2072 int block_is_partially_uptodate(struct page *page, read_descriptor_t *desc,
2073                                         unsigned long from)
2074 {
2075         struct inode *inode = page->mapping->host;
2076         unsigned block_start, block_end, blocksize;
2077         unsigned to;
2078         struct buffer_head *bh, *head;
2079         int ret = 1;
2080
2081         if (!page_has_buffers(page))
2082                 return 0;
2083
2084         blocksize = 1 << inode->i_blkbits;
2085         to = min_t(unsigned, PAGE_CACHE_SIZE - from, desc->count);
2086         to = from + to;
2087         if (from < blocksize && to > PAGE_CACHE_SIZE - blocksize)
2088                 return 0;
2089
2090         head = page_buffers(page);
2091         bh = head;
2092         block_start = 0;
2093         do {
2094                 block_end = block_start + blocksize;
2095                 if (block_end > from && block_start < to) {
2096                         if (!buffer_uptodate(bh)) {
2097                                 ret = 0;
2098                                 break;
2099                         }
2100                         if (block_end >= to)
2101                                 break;
2102                 }
2103                 block_start = block_end;
2104                 bh = bh->b_this_page;
2105         } while (bh != head);
2106
2107         return ret;
2108 }
2109 EXPORT_SYMBOL(block_is_partially_uptodate);
2110
2111 /*
2112  * Generic "read page" function for block devices that have the normal
2113  * get_block functionality. This is most of the block device filesystems.
2114  * Reads the page asynchronously --- the unlock_buffer() and
2115  * set/clear_buffer_uptodate() functions propagate buffer state into the
2116  * page struct once IO has completed.
2117  */
2118 int block_read_full_page(struct page *page, get_block_t *get_block)
2119 {
2120         struct inode *inode = page->mapping->host;
2121         sector_t iblock, lblock;
2122         struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2123         unsigned int blocksize;
2124         int nr, i;
2125         int fully_mapped = 1;
2126
2127         BUG_ON(!PageLocked(page));
2128         blocksize = 1 << inode->i_blkbits;
2129         if (!page_has_buffers(page))
2130                 create_empty_buffers(page, blocksize, 0);
2131         head = page_buffers(page);
2132
2133         iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2134         lblock = (i_size_read(inode)+blocksize-1) >> inode->i_blkbits;
2135         bh = head;
2136         nr = 0;
2137         i = 0;
2138
2139         do {
2140                 if (buffer_uptodate(bh))
2141                         continue;
2142
2143                 if (!buffer_mapped(bh)) {
2144                         int err = 0;
2145
2146                         fully_mapped = 0;
2147                         if (iblock < lblock) {
2148                                 WARN_ON(bh->b_size != blocksize);
2149                                 err = get_block(inode, iblock, bh, 0);
2150                                 if (err)
2151                                         SetPageError(page);
2152                         }
2153                         if (!buffer_mapped(bh)) {
2154                                 zero_user(page, i * blocksize, blocksize);
2155                                 if (!err)
2156                                         set_buffer_uptodate(bh);
2157                                 continue;
2158                         }
2159                         /*
2160                          * get_block() might have updated the buffer
2161                          * synchronously
2162                          */
2163                         if (buffer_uptodate(bh))
2164                                 continue;
2165                 }
2166                 arr[nr++] = bh;
2167         } while (i++, iblock++, (bh = bh->b_this_page) != head);
2168
2169         if (fully_mapped)
2170                 SetPageMappedToDisk(page);
2171
2172         if (!nr) {
2173                 /*
2174                  * All buffers are uptodate - we can set the page uptodate
2175                  * as well. But not if get_block() returned an error.
2176                  */
2177                 if (!PageError(page))
2178                         SetPageUptodate(page);
2179                 unlock_page(page);
2180                 return 0;
2181         }
2182
2183         /* Stage two: lock the buffers */
2184         for (i = 0; i < nr; i++) {
2185                 bh = arr[i];
2186                 lock_buffer(bh);
2187                 mark_buffer_async_read(bh);
2188         }
2189
2190         /*
2191          * Stage 3: start the IO.  Check for uptodateness
2192          * inside the buffer lock in case another process reading
2193          * the underlying blockdev brought it uptodate (the sct fix).
2194          */
2195         for (i = 0; i < nr; i++) {
2196                 bh = arr[i];
2197                 if (buffer_uptodate(bh))
2198                         end_buffer_async_read(bh, 1);
2199                 else
2200                         submit_bh(READ, bh);
2201         }
2202         return 0;
2203 }
2204
2205 /* utility function for filesystems that need to do work on expanding
2206  * truncates.  Uses filesystem pagecache writes to allow the filesystem to
2207  * deal with the hole.  
2208  */
2209 int generic_cont_expand_simple(struct inode *inode, loff_t size)
2210 {
2211         struct address_space *mapping = inode->i_mapping;
2212         struct page *page;
2213         void *fsdata;
2214         unsigned long limit;
2215         int err;
2216
2217         err = -EFBIG;
2218         limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
2219         if (limit != RLIM_INFINITY && size > (loff_t)limit) {
2220                 send_sig(SIGXFSZ, current, 0);
2221                 goto out;
2222         }
2223         if (size > inode->i_sb->s_maxbytes)
2224                 goto out;
2225
2226         err = pagecache_write_begin(NULL, mapping, size, 0,
2227                                 AOP_FLAG_UNINTERRUPTIBLE|AOP_FLAG_CONT_EXPAND,
2228                                 &page, &fsdata);
2229         if (err)
2230                 goto out;
2231
2232         err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2233         BUG_ON(err > 0);
2234
2235 out:
2236         return err;
2237 }
2238
2239 static int cont_expand_zero(struct file *file, struct address_space *mapping,
2240                             loff_t pos, loff_t *bytes)
2241 {
2242         struct inode *inode = mapping->host;
2243         unsigned blocksize = 1 << inode->i_blkbits;
2244         struct page *page;
2245         void *fsdata;
2246         pgoff_t index, curidx;
2247         loff_t curpos;
2248         unsigned zerofrom, offset, len;
2249         int err = 0;
2250
2251         index = pos >> PAGE_CACHE_SHIFT;
2252         offset = pos & ~PAGE_CACHE_MASK;
2253
2254         while (index > (curidx = (curpos = *bytes)>>PAGE_CACHE_SHIFT)) {
2255                 zerofrom = curpos & ~PAGE_CACHE_MASK;
2256                 if (zerofrom & (blocksize-1)) {
2257                         *bytes |= (blocksize-1);
2258                         (*bytes)++;
2259                 }
2260                 len = PAGE_CACHE_SIZE - zerofrom;
2261
2262                 err = pagecache_write_begin(file, mapping, curpos, len,
2263                                                 AOP_FLAG_UNINTERRUPTIBLE,
2264                                                 &page, &fsdata);
2265                 if (err)
2266                         goto out;
2267                 zero_user(page, zerofrom, len);
2268                 err = pagecache_write_end(file, mapping, curpos, len, len,
2269                                                 page, fsdata);
2270                 if (err < 0)
2271                         goto out;
2272                 BUG_ON(err != len);
2273                 err = 0;
2274
2275                 balance_dirty_pages_ratelimited(mapping);
2276         }
2277
2278         /* page covers the boundary, find the boundary offset */
2279         if (index == curidx) {
2280                 zerofrom = curpos & ~PAGE_CACHE_MASK;
2281                 /* if we will expand the thing last block will be filled */
2282                 if (offset <= zerofrom) {
2283                         goto out;
2284                 }
2285                 if (zerofrom & (blocksize-1)) {
2286                         *bytes |= (blocksize-1);
2287                         (*bytes)++;
2288                 }
2289                 len = offset - zerofrom;
2290
2291                 err = pagecache_write_begin(file, mapping, curpos, len,
2292                                                 AOP_FLAG_UNINTERRUPTIBLE,
2293                                                 &page, &fsdata);
2294                 if (err)
2295                         goto out;
2296                 zero_user(page, zerofrom, len);
2297                 err = pagecache_write_end(file, mapping, curpos, len, len,
2298                                                 page, fsdata);
2299                 if (err < 0)
2300                         goto out;
2301                 BUG_ON(err != len);
2302                 err = 0;
2303         }
2304 out:
2305         return err;
2306 }
2307
2308 /*
2309  * For moronic filesystems that do not allow holes in file.
2310  * We may have to extend the file.
2311  */
2312 int cont_write_begin(struct file *file, struct address_space *mapping,
2313                         loff_t pos, unsigned len, unsigned flags,
2314                         struct page **pagep, void **fsdata,
2315                         get_block_t *get_block, loff_t *bytes)
2316 {
2317         struct inode *inode = mapping->host;
2318         unsigned blocksize = 1 << inode->i_blkbits;
2319         unsigned zerofrom;
2320         int err;
2321
2322         err = cont_expand_zero(file, mapping, pos, bytes);
2323         if (err)
2324                 goto out;
2325
2326         zerofrom = *bytes & ~PAGE_CACHE_MASK;
2327         if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2328                 *bytes |= (blocksize-1);
2329                 (*bytes)++;
2330         }
2331
2332         *pagep = NULL;
2333         err = block_write_begin(file, mapping, pos, len,
2334                                 flags, pagep, fsdata, get_block);
2335 out:
2336         return err;
2337 }
2338
2339 int block_prepare_write(struct page *page, unsigned from, unsigned to,
2340                         get_block_t *get_block)
2341 {
2342         struct inode *inode = page->mapping->host;
2343         int err = __block_prepare_write(inode, page, from, to, get_block);
2344         if (err)
2345                 ClearPageUptodate(page);
2346         return err;
2347 }
2348
2349 int block_commit_write(struct page *page, unsigned from, unsigned to)
2350 {
2351         struct inode *inode = page->mapping->host;
2352         __block_commit_write(inode,page,from,to);
2353         return 0;
2354 }
2355
2356 /*
2357  * block_page_mkwrite() is not allowed to change the file size as it gets
2358  * called from a page fault handler when a page is first dirtied. Hence we must
2359  * be careful to check for EOF conditions here. We set the page up correctly
2360  * for a written page which means we get ENOSPC checking when writing into
2361  * holes and correct delalloc and unwritten extent mapping on filesystems that
2362  * support these features.
2363  *
2364  * We are not allowed to take the i_mutex here so we have to play games to
2365  * protect against truncate races as the page could now be beyond EOF.  Because
2366  * vmtruncate() writes the inode size before removing pages, once we have the
2367  * page lock we can determine safely if the page is beyond EOF. If it is not
2368  * beyond EOF, then the page is guaranteed safe against truncation until we
2369  * unlock the page.
2370  */
2371 int
2372 block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2373                    get_block_t get_block)
2374 {
2375         struct page *page = vmf->page;
2376         struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
2377         unsigned long end;
2378         loff_t size;
2379         int ret = VM_FAULT_NOPAGE; /* make the VM retry the fault */
2380
2381         lock_page(page);
2382         size = i_size_read(inode);
2383         if ((page->mapping != inode->i_mapping) ||
2384             (page_offset(page) > size)) {
2385                 /* page got truncated out from underneath us */
2386                 goto out_unlock;
2387         }
2388
2389         /* page is wholly or partially inside EOF */
2390         if (((page->index + 1) << PAGE_CACHE_SHIFT) > size)
2391                 end = size & ~PAGE_CACHE_MASK;
2392         else
2393                 end = PAGE_CACHE_SIZE;
2394
2395         ret = block_prepare_write(page, 0, end, get_block);
2396         if (!ret)
2397                 ret = block_commit_write(page, 0, end);
2398
2399         if (unlikely(ret)) {
2400                 if (ret == -ENOMEM)
2401                         ret = VM_FAULT_OOM;
2402                 else /* -ENOSPC, -EIO, etc */
2403                         ret = VM_FAULT_SIGBUS;
2404         }
2405
2406 out_unlock:
2407         unlock_page(page);
2408         return ret;
2409 }
2410
2411 /*
2412  * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2413  * immediately, while under the page lock.  So it needs a special end_io
2414  * handler which does not touch the bh after unlocking it.
2415  */
2416 static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2417 {
2418         __end_buffer_read_notouch(bh, uptodate);
2419 }
2420
2421 /*
2422  * Attach the singly-linked list of buffers created by nobh_write_begin, to
2423  * the page (converting it to circular linked list and taking care of page
2424  * dirty races).
2425  */
2426 static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2427 {
2428         struct buffer_head *bh;
2429
2430         BUG_ON(!PageLocked(page));
2431
2432         spin_lock(&page->mapping->private_lock);
2433         bh = head;
2434         do {
2435                 if (PageDirty(page))
2436                         set_buffer_dirty(bh);
2437                 if (!bh->b_this_page)
2438                         bh->b_this_page = head;
2439                 bh = bh->b_this_page;
2440         } while (bh != head);
2441         attach_page_buffers(page, head);
2442         spin_unlock(&page->mapping->private_lock);
2443 }
2444
2445 /*
2446  * On entry, the page is fully not uptodate.
2447  * On exit the page is fully uptodate in the areas outside (from,to)
2448  */
2449 int nobh_write_begin(struct file *file, struct address_space *mapping,
2450                         loff_t pos, unsigned len, unsigned flags,
2451                         struct page **pagep, void **fsdata,
2452                         get_block_t *get_block)
2453 {
2454         struct inode *inode = mapping->host;
2455         const unsigned blkbits = inode->i_blkbits;
2456         const unsigned blocksize = 1 << blkbits;
2457         struct buffer_head *head, *bh;
2458         struct page *page;
2459         pgoff_t index;
2460         unsigned from, to;
2461         unsigned block_in_page;
2462         unsigned block_start, block_end;
2463         sector_t block_in_file;
2464         int nr_reads = 0;
2465         int ret = 0;
2466         int is_mapped_to_disk = 1;
2467
2468         index = pos >> PAGE_CACHE_SHIFT;
2469         from = pos & (PAGE_CACHE_SIZE - 1);
2470         to = from + len;
2471
2472         page = grab_cache_page_write_begin(mapping, index, flags);
2473         if (!page)
2474                 return -ENOMEM;
2475         *pagep = page;
2476         *fsdata = NULL;
2477
2478         if (page_has_buffers(page)) {
2479                 unlock_page(page);
2480                 page_cache_release(page);
2481                 *pagep = NULL;
2482                 return block_write_begin(file, mapping, pos, len, flags, pagep,
2483                                         fsdata, get_block);
2484         }
2485
2486         if (PageMappedToDisk(page))
2487                 return 0;
2488
2489         /*
2490          * Allocate buffers so that we can keep track of state, and potentially
2491          * attach them to the page if an error occurs. In the common case of
2492          * no error, they will just be freed again without ever being attached
2493          * to the page (which is all OK, because we're under the page lock).
2494          *
2495          * Be careful: the buffer linked list is a NULL terminated one, rather
2496          * than the circular one we're used to.
2497          */
2498         head = alloc_page_buffers(page, blocksize, 0);
2499         if (!head) {
2500                 ret = -ENOMEM;
2501                 goto out_release;
2502         }
2503
2504         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
2505
2506         /*
2507          * We loop across all blocks in the page, whether or not they are
2508          * part of the affected region.  This is so we can discover if the
2509          * page is fully mapped-to-disk.
2510          */
2511         for (block_start = 0, block_in_page = 0, bh = head;
2512                   block_start < PAGE_CACHE_SIZE;
2513                   block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2514                 int create;
2515
2516                 block_end = block_start + blocksize;
2517                 bh->b_state = 0;
2518                 create = 1;
2519                 if (block_start >= to)
2520                         create = 0;
2521                 ret = get_block(inode, block_in_file + block_in_page,
2522                                         bh, create);
2523                 if (ret)
2524                         goto failed;
2525                 if (!buffer_mapped(bh))
2526                         is_mapped_to_disk = 0;
2527                 if (buffer_new(bh))
2528                         unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
2529                 if (PageUptodate(page)) {
2530                         set_buffer_uptodate(bh);
2531                         continue;
2532                 }
2533                 if (buffer_new(bh) || !buffer_mapped(bh)) {
2534                         zero_user_segments(page, block_start, from,
2535                                                         to, block_end);
2536                         continue;
2537                 }
2538                 if (buffer_uptodate(bh))
2539                         continue;       /* reiserfs does this */
2540                 if (block_start < from || block_end > to) {
2541                         lock_buffer(bh);
2542                         bh->b_end_io = end_buffer_read_nobh;
2543                         submit_bh(READ, bh);
2544                         nr_reads++;
2545                 }
2546         }
2547
2548         if (nr_reads) {
2549                 /*
2550                  * The page is locked, so these buffers are protected from
2551                  * any VM or truncate activity.  Hence we don't need to care
2552                  * for the buffer_head refcounts.
2553                  */
2554                 for (bh = head; bh; bh = bh->b_this_page) {
2555                         wait_on_buffer(bh);
2556                         if (!buffer_uptodate(bh))
2557                                 ret = -EIO;
2558                 }
2559                 if (ret)
2560                         goto failed;
2561         }
2562
2563         if (is_mapped_to_disk)
2564                 SetPageMappedToDisk(page);
2565
2566         *fsdata = head; /* to be released by nobh_write_end */
2567
2568         return 0;
2569
2570 failed:
2571         BUG_ON(!ret);
2572         /*
2573          * Error recovery is a bit difficult. We need to zero out blocks that
2574          * were newly allocated, and dirty them to ensure they get written out.
2575          * Buffers need to be attached to the page at this point, otherwise
2576          * the handling of potential IO errors during writeout would be hard
2577          * (could try doing synchronous writeout, but what if that fails too?)
2578          */
2579         attach_nobh_buffers(page, head);
2580         page_zero_new_buffers(page, from, to);
2581
2582 out_release:
2583         unlock_page(page);
2584         page_cache_release(page);
2585         *pagep = NULL;
2586
2587         if (pos + len > inode->i_size)
2588                 vmtruncate(inode, inode->i_size);
2589
2590         return ret;
2591 }
2592 EXPORT_SYMBOL(nobh_write_begin);
2593
2594 int nobh_write_end(struct file *file, struct address_space *mapping,
2595                         loff_t pos, unsigned len, unsigned copied,
2596                         struct page *page, void *fsdata)
2597 {
2598         struct inode *inode = page->mapping->host;
2599         struct buffer_head *head = fsdata;
2600         struct buffer_head *bh;
2601         BUG_ON(fsdata != NULL && page_has_buffers(page));
2602
2603         if (unlikely(copied < len) && head)
2604                 attach_nobh_buffers(page, head);
2605         if (page_has_buffers(page))
2606                 return generic_write_end(file, mapping, pos, len,
2607                                         copied, page, fsdata);
2608
2609         SetPageUptodate(page);
2610         set_page_dirty(page);
2611         if (pos+copied > inode->i_size) {
2612                 i_size_write(inode, pos+copied);
2613                 mark_inode_dirty(inode);
2614         }
2615
2616         unlock_page(page);
2617         page_cache_release(page);
2618
2619         while (head) {
2620                 bh = head;
2621                 head = head->b_this_page;
2622                 free_buffer_head(bh);
2623         }
2624
2625         return copied;
2626 }
2627 EXPORT_SYMBOL(nobh_write_end);
2628
2629 /*
2630  * nobh_writepage() - based on block_full_write_page() except
2631  * that it tries to operate without attaching bufferheads to
2632  * the page.
2633  */
2634 int nobh_writepage(struct page *page, get_block_t *get_block,
2635                         struct writeback_control *wbc)
2636 {
2637         struct inode * const inode = page->mapping->host;
2638         loff_t i_size = i_size_read(inode);
2639         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2640         unsigned offset;
2641         int ret;
2642
2643         /* Is the page fully inside i_size? */
2644         if (page->index < end_index)
2645                 goto out;
2646
2647         /* Is the page fully outside i_size? (truncate in progress) */
2648         offset = i_size & (PAGE_CACHE_SIZE-1);
2649         if (page->index >= end_index+1 || !offset) {
2650                 /*
2651                  * The page may have dirty, unmapped buffers.  For example,
2652                  * they may have been added in ext3_writepage().  Make them
2653                  * freeable here, so the page does not leak.
2654                  */
2655 #if 0
2656                 /* Not really sure about this  - do we need this ? */
2657                 if (page->mapping->a_ops->invalidatepage)
2658                         page->mapping->a_ops->invalidatepage(page, offset);
2659 #endif
2660                 unlock_page(page);
2661                 return 0; /* don't care */
2662         }
2663
2664         /*
2665          * The page straddles i_size.  It must be zeroed out on each and every
2666          * writepage invocation because it may be mmapped.  "A file is mapped
2667          * in multiples of the page size.  For a file that is not a multiple of
2668          * the  page size, the remaining memory is zeroed when mapped, and
2669          * writes to that region are not written out to the file."
2670          */
2671         zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2672 out:
2673         ret = mpage_writepage(page, get_block, wbc);
2674         if (ret == -EAGAIN)
2675                 ret = __block_write_full_page(inode, page, get_block, wbc);
2676         return ret;
2677 }
2678 EXPORT_SYMBOL(nobh_writepage);
2679
2680 int nobh_truncate_page(struct address_space *mapping,
2681                         loff_t from, get_block_t *get_block)
2682 {
2683         pgoff_t index = from >> PAGE_CACHE_SHIFT;
2684         unsigned offset = from & (PAGE_CACHE_SIZE-1);
2685         unsigned blocksize;
2686         sector_t iblock;
2687         unsigned length, pos;
2688         struct inode *inode = mapping->host;
2689         struct page *page;
2690         struct buffer_head map_bh;
2691         int err;
2692
2693         blocksize = 1 << inode->i_blkbits;
2694         length = offset & (blocksize - 1);
2695
2696         /* Block boundary? Nothing to do */
2697         if (!length)
2698                 return 0;
2699
2700         length = blocksize - length;
2701         iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2702
2703         page = grab_cache_page(mapping, index);
2704         err = -ENOMEM;
2705         if (!page)
2706                 goto out;
2707
2708         if (page_has_buffers(page)) {
2709 has_buffers:
2710                 unlock_page(page);
2711                 page_cache_release(page);
2712                 return block_truncate_page(mapping, from, get_block);
2713         }
2714
2715         /* Find the buffer that contains "offset" */
2716         pos = blocksize;
2717         while (offset >= pos) {
2718                 iblock++;
2719                 pos += blocksize;
2720         }
2721
2722         err = get_block(inode, iblock, &map_bh, 0);
2723         if (err)
2724                 goto unlock;
2725         /* unmapped? It's a hole - nothing to do */
2726         if (!buffer_mapped(&map_bh))
2727                 goto unlock;
2728
2729         /* Ok, it's mapped. Make sure it's up-to-date */
2730         if (!PageUptodate(page)) {
2731                 err = mapping->a_ops->readpage(NULL, page);
2732                 if (err) {
2733                         page_cache_release(page);
2734                         goto out;
2735                 }
2736                 lock_page(page);
2737                 if (!PageUptodate(page)) {
2738                         err = -EIO;
2739                         goto unlock;
2740                 }
2741                 if (page_has_buffers(page))
2742                         goto has_buffers;
2743         }
2744         zero_user(page, offset, length);
2745         set_page_dirty(page);
2746         err = 0;
2747
2748 unlock:
2749         unlock_page(page);
2750         page_cache_release(page);
2751 out:
2752         return err;
2753 }
2754 EXPORT_SYMBOL(nobh_truncate_page);
2755
2756 int block_truncate_page(struct address_space *mapping,
2757                         loff_t from, get_block_t *get_block)
2758 {
2759         pgoff_t index = from >> PAGE_CACHE_SHIFT;
2760         unsigned offset = from & (PAGE_CACHE_SIZE-1);
2761         unsigned blocksize;
2762         sector_t iblock;
2763         unsigned length, pos;
2764         struct inode *inode = mapping->host;
2765         struct page *page;
2766         struct buffer_head *bh;
2767         int err;
2768
2769         blocksize = 1 << inode->i_blkbits;
2770         length = offset & (blocksize - 1);
2771
2772         /* Block boundary? Nothing to do */
2773         if (!length)
2774                 return 0;
2775
2776         length = blocksize - length;
2777         iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2778         
2779         page = grab_cache_page(mapping, index);
2780         err = -ENOMEM;
2781         if (!page)
2782                 goto out;
2783
2784         if (!page_has_buffers(page))
2785                 create_empty_buffers(page, blocksize, 0);
2786
2787         /* Find the buffer that contains "offset" */
2788         bh = page_buffers(page);
2789         pos = blocksize;
2790         while (offset >= pos) {
2791                 bh = bh->b_this_page;
2792                 iblock++;
2793                 pos += blocksize;
2794         }
2795
2796         err = 0;
2797         if (!buffer_mapped(bh)) {
2798                 WARN_ON(bh->b_size != blocksize);
2799                 err = get_block(inode, iblock, bh, 0);
2800                 if (err)
2801                         goto unlock;
2802                 /* unmapped? It's a hole - nothing to do */
2803                 if (!buffer_mapped(bh))
2804                         goto unlock;
2805         }
2806
2807         /* Ok, it's mapped. Make sure it's up-to-date */
2808         if (PageUptodate(page))
2809                 set_buffer_uptodate(bh);
2810
2811         if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2812                 err = -EIO;
2813                 ll_rw_block(READ, 1, &bh);
2814                 wait_on_buffer(bh);
2815                 /* Uhhuh. Read error. Complain and punt. */
2816                 if (!buffer_uptodate(bh))
2817                         goto unlock;
2818         }
2819
2820         zero_user(page, offset, length);
2821         mark_buffer_dirty(bh);
2822         err = 0;
2823
2824 unlock:
2825         unlock_page(page);
2826         page_cache_release(page);
2827 out:
2828         return err;
2829 }
2830
2831 /*
2832  * The generic ->writepage function for buffer-backed address_spaces
2833  */
2834 int block_write_full_page(struct page *page, get_block_t *get_block,
2835                         struct writeback_control *wbc)
2836 {
2837         struct inode * const inode = page->mapping->host;
2838         loff_t i_size = i_size_read(inode);
2839         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2840         unsigned offset;
2841
2842         /* Is the page fully inside i_size? */
2843         if (page->index < end_index)
2844                 return __block_write_full_page(inode, page, get_block, wbc);
2845
2846         /* Is the page fully outside i_size? (truncate in progress) */
2847         offset = i_size & (PAGE_CACHE_SIZE-1);
2848         if (page->index >= end_index+1 || !offset) {
2849                 /*
2850                  * The page may have dirty, unmapped buffers.  For example,
2851                  * they may have been added in ext3_writepage().  Make them
2852                  * freeable here, so the page does not leak.
2853                  */
2854                 do_invalidatepage(page, 0);
2855                 unlock_page(page);
2856                 return 0; /* don't care */
2857         }
2858
2859         /*
2860          * The page straddles i_size.  It must be zeroed out on each and every
2861          * writepage invokation because it may be mmapped.  "A file is mapped
2862          * in multiples of the page size.  For a file that is not a multiple of
2863          * the  page size, the remaining memory is zeroed when mapped, and
2864          * writes to that region are not written out to the file."
2865          */
2866         zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2867         return __block_write_full_page(inode, page, get_block, wbc);
2868 }
2869
2870 sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2871                             get_block_t *get_block)
2872 {
2873         struct buffer_head tmp;
2874         struct inode *inode = mapping->host;
2875         tmp.b_state = 0;
2876         tmp.b_blocknr = 0;
2877         tmp.b_size = 1 << inode->i_blkbits;
2878         get_block(inode, block, &tmp, 0);
2879         return tmp.b_blocknr;
2880 }
2881
2882 static void end_bio_bh_io_sync(struct bio *bio, int err)
2883 {
2884         struct buffer_head *bh = bio->bi_private;
2885
2886         if (err == -EOPNOTSUPP) {
2887                 set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
2888                 set_bit(BH_Eopnotsupp, &bh->b_state);
2889         }
2890
2891         if (unlikely (test_bit(BIO_QUIET,&bio->bi_flags)))
2892                 set_bit(BH_Quiet, &bh->b_state);
2893
2894         bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
2895         bio_put(bio);
2896 }
2897
2898 int submit_bh(int rw, struct buffer_head * bh)
2899 {
2900         struct bio *bio;
2901         int ret = 0;
2902
2903         BUG_ON(!buffer_locked(bh));
2904         BUG_ON(!buffer_mapped(bh));
2905         BUG_ON(!bh->b_end_io);
2906
2907         /*
2908          * Mask in barrier bit for a write (could be either a WRITE or a
2909          * WRITE_SYNC
2910          */
2911         if (buffer_ordered(bh) && (rw & WRITE))
2912                 rw |= WRITE_BARRIER;
2913
2914         /*
2915          * Only clear out a write error when rewriting
2916          */
2917         if (test_set_buffer_req(bh) && (rw & WRITE))
2918                 clear_buffer_write_io_error(bh);
2919
2920         /*
2921          * from here on down, it's all bio -- do the initial mapping,
2922          * submit_bio -> generic_make_request may further map this bio around
2923          */
2924         bio = bio_alloc(GFP_NOIO, 1);
2925
2926         bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
2927         bio->bi_bdev = bh->b_bdev;
2928         bio->bi_io_vec[0].bv_page = bh->b_page;
2929         bio->bi_io_vec[0].bv_len = bh->b_size;
2930         bio->bi_io_vec[0].bv_offset = bh_offset(bh);
2931
2932         bio->bi_vcnt = 1;
2933         bio->bi_idx = 0;
2934         bio->bi_size = bh->b_size;
2935
2936         bio->bi_end_io = end_bio_bh_io_sync;
2937         bio->bi_private = bh;
2938
2939         bio_get(bio);
2940         submit_bio(rw, bio);
2941
2942         if (bio_flagged(bio, BIO_EOPNOTSUPP))
2943                 ret = -EOPNOTSUPP;
2944
2945         bio_put(bio);
2946         return ret;
2947 }
2948
2949 /**
2950  * ll_rw_block: low-level access to block devices (DEPRECATED)
2951  * @rw: whether to %READ or %WRITE or %SWRITE or maybe %READA (readahead)
2952  * @nr: number of &struct buffer_heads in the array
2953  * @bhs: array of pointers to &struct buffer_head
2954  *
2955  * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
2956  * requests an I/O operation on them, either a %READ or a %WRITE.  The third
2957  * %SWRITE is like %WRITE only we make sure that the *current* data in buffers
2958  * are sent to disk. The fourth %READA option is described in the documentation
2959  * for generic_make_request() which ll_rw_block() calls.
2960  *
2961  * This function drops any buffer that it cannot get a lock on (with the
2962  * BH_Lock state bit) unless SWRITE is required, any buffer that appears to be
2963  * clean when doing a write request, and any buffer that appears to be
2964  * up-to-date when doing read request.  Further it marks as clean buffers that
2965  * are processed for writing (the buffer cache won't assume that they are
2966  * actually clean until the buffer gets unlocked).
2967  *
2968  * ll_rw_block sets b_end_io to simple completion handler that marks
2969  * the buffer up-to-date (if approriate), unlocks the buffer and wakes
2970  * any waiters. 
2971  *
2972  * All of the buffers must be for the same device, and must also be a
2973  * multiple of the current approved size for the device.
2974  */
2975 void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
2976 {
2977         int i;
2978
2979         for (i = 0; i < nr; i++) {
2980                 struct buffer_head *bh = bhs[i];
2981
2982                 if (rw == SWRITE || rw == SWRITE_SYNC || rw == SWRITE_SYNC_PLUG)
2983                         lock_buffer(bh);
2984                 else if (!trylock_buffer(bh))
2985                         continue;
2986
2987                 if (rw == WRITE || rw == SWRITE || rw == SWRITE_SYNC ||
2988                     rw == SWRITE_SYNC_PLUG) {
2989                         if (test_clear_buffer_dirty(bh)) {
2990                                 bh->b_end_io = end_buffer_write_sync;
2991                                 get_bh(bh);
2992                                 if (rw == SWRITE_SYNC)
2993                                         submit_bh(WRITE_SYNC, bh);
2994                                 else
2995                                         submit_bh(WRITE, bh);
2996                                 continue;
2997                         }
2998                 } else {
2999                         if (!buffer_uptodate(bh)) {
3000                                 bh->b_end_io = end_buffer_read_sync;
3001                                 get_bh(bh);
3002                                 submit_bh(rw, bh);
3003                                 continue;
3004                         }
3005                 }
3006                 unlock_buffer(bh);
3007         }
3008 }
3009
3010 /*
3011  * For a data-integrity writeout, we need to wait upon any in-progress I/O
3012  * and then start new I/O and then wait upon it.  The caller must have a ref on
3013  * the buffer_head.
3014  */
3015 int sync_dirty_buffer(struct buffer_head *bh)
3016 {
3017         int ret = 0;
3018
3019         WARN_ON(atomic_read(&bh->b_count) < 1);
3020         lock_buffer(bh);
3021         if (test_clear_buffer_dirty(bh)) {
3022                 get_bh(bh);
3023                 bh->b_end_io = end_buffer_write_sync;
3024                 ret = submit_bh(WRITE_SYNC, bh);
3025                 wait_on_buffer(bh);
3026                 if (buffer_eopnotsupp(bh)) {
3027                         clear_buffer_eopnotsupp(bh);
3028                         ret = -EOPNOTSUPP;
3029                 }
3030                 if (!ret && !buffer_uptodate(bh))
3031                         ret = -EIO;
3032         } else {
3033                 unlock_buffer(bh);
3034         }
3035         return ret;
3036 }
3037
3038 /*
3039  * try_to_free_buffers() checks if all the buffers on this particular page
3040  * are unused, and releases them if so.
3041  *
3042  * Exclusion against try_to_free_buffers may be obtained by either
3043  * locking the page or by holding its mapping's private_lock.
3044  *
3045  * If the page is dirty but all the buffers are clean then we need to
3046  * be sure to mark the page clean as well.  This is because the page
3047  * may be against a block device, and a later reattachment of buffers
3048  * to a dirty page will set *all* buffers dirty.  Which would corrupt
3049  * filesystem data on the same device.
3050  *
3051  * The same applies to regular filesystem pages: if all the buffers are
3052  * clean then we set the page clean and proceed.  To do that, we require
3053  * total exclusion from __set_page_dirty_buffers().  That is obtained with
3054  * private_lock.
3055  *
3056  * try_to_free_buffers() is non-blocking.
3057  */
3058 static inline int buffer_busy(struct buffer_head *bh)
3059 {
3060         return atomic_read(&bh->b_count) |
3061                 (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3062 }
3063
3064 static int
3065 drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
3066 {
3067         struct buffer_head *head = page_buffers(page);
3068         struct buffer_head *bh;
3069
3070         bh = head;
3071         do {
3072                 if (buffer_write_io_error(bh) && page->mapping)
3073                         set_bit(AS_EIO, &page->mapping->flags);
3074                 if (buffer_busy(bh))
3075                         goto failed;
3076                 bh = bh->b_this_page;
3077         } while (bh != head);
3078
3079         do {
3080                 struct buffer_head *next = bh->b_this_page;
3081
3082                 if (bh->b_assoc_map)
3083                         __remove_assoc_queue(bh);
3084                 bh = next;
3085         } while (bh != head);
3086         *buffers_to_free = head;
3087         __clear_page_buffers(page);
3088         return 1;
3089 failed:
3090         return 0;
3091 }
3092
3093 int try_to_free_buffers(struct page *page)
3094 {
3095         struct address_space * const mapping = page->mapping;
3096         struct buffer_head *buffers_to_free = NULL;
3097         int ret = 0;
3098
3099         BUG_ON(!PageLocked(page));
3100         if (PageWriteback(page))
3101                 return 0;
3102
3103         if (mapping == NULL) {          /* can this still happen? */
3104                 ret = drop_buffers(page, &buffers_to_free);
3105                 goto out;
3106         }
3107
3108         spin_lock(&mapping->private_lock);
3109         ret = drop_buffers(page, &buffers_to_free);
3110
3111         /*
3112          * If the filesystem writes its buffers by hand (eg ext3)
3113          * then we can have clean buffers against a dirty page.  We
3114          * clean the page here; otherwise the VM will never notice
3115          * that the filesystem did any IO at all.
3116          *
3117          * Also, during truncate, discard_buffer will have marked all
3118          * the page's buffers clean.  We discover that here and clean
3119          * the page also.
3120          *
3121          * private_lock must be held over this entire operation in order
3122          * to synchronise against __set_page_dirty_buffers and prevent the
3123          * dirty bit from being lost.
3124          */
3125         if (ret)
3126                 cancel_dirty_page(page, PAGE_CACHE_SIZE);
3127         spin_unlock(&mapping->private_lock);
3128 out:
3129         if (buffers_to_free) {
3130                 struct buffer_head *bh = buffers_to_free;
3131
3132                 do {
3133                         struct buffer_head *next = bh->b_this_page;
3134                         free_buffer_head(bh);
3135                         bh = next;
3136                 } while (bh != buffers_to_free);
3137         }
3138         return ret;
3139 }
3140 EXPORT_SYMBOL(try_to_free_buffers);
3141
3142 void block_sync_page(struct page *page)
3143 {
3144         struct address_space *mapping;
3145
3146         smp_mb();
3147         mapping = page_mapping(page);
3148         if (mapping)
3149                 blk_run_backing_dev(mapping->backing_dev_info, page);
3150 }
3151
3152 /*
3153  * There are no bdflush tunables left.  But distributions are
3154  * still running obsolete flush daemons, so we terminate them here.
3155  *
3156  * Use of bdflush() is deprecated and will be removed in a future kernel.
3157  * The `pdflush' kernel threads fully replace bdflush daemons and this call.
3158  */
3159 SYSCALL_DEFINE2(bdflush, int, func, long, data)
3160 {
3161         static int msg_count;
3162
3163         if (!capable(CAP_SYS_ADMIN))
3164                 return -EPERM;
3165
3166         if (msg_count < 5) {
3167                 msg_count++;
3168                 printk(KERN_INFO
3169                         "warning: process `%s' used the obsolete bdflush"
3170                         " system call\n", current->comm);
3171                 printk(KERN_INFO "Fix your initscripts?\n");
3172         }
3173
3174         if (func == 1)
3175                 do_exit(0);
3176         return 0;
3177 }
3178
3179 /*
3180  * Buffer-head allocation
3181  */
3182 static struct kmem_cache *bh_cachep;
3183
3184 /*
3185  * Once the number of bh's in the machine exceeds this level, we start
3186  * stripping them in writeback.
3187  */
3188 static int max_buffer_heads;
3189
3190 int buffer_heads_over_limit;
3191
3192 struct bh_accounting {
3193         int nr;                 /* Number of live bh's */
3194         int ratelimit;          /* Limit cacheline bouncing */
3195 };
3196
3197 static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3198
3199 static void recalc_bh_state(void)
3200 {
3201         int i;
3202         int tot = 0;
3203
3204         if (__get_cpu_var(bh_accounting).ratelimit++ < 4096)
3205                 return;
3206         __get_cpu_var(bh_accounting).ratelimit = 0;
3207         for_each_online_cpu(i)
3208                 tot += per_cpu(bh_accounting, i).nr;
3209         buffer_heads_over_limit = (tot > max_buffer_heads);
3210 }
3211         
3212 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3213 {
3214         struct buffer_head *ret = kmem_cache_alloc(bh_cachep, gfp_flags);
3215         if (ret) {
3216                 INIT_LIST_HEAD(&ret->b_assoc_buffers);
3217                 get_cpu_var(bh_accounting).nr++;
3218                 recalc_bh_state();
3219                 put_cpu_var(bh_accounting);
3220         }
3221         return ret;
3222 }
3223 EXPORT_SYMBOL(alloc_buffer_head);
3224
3225 void free_buffer_head(struct buffer_head *bh)
3226 {
3227         BUG_ON(!list_empty(&bh->b_assoc_buffers));
3228         kmem_cache_free(bh_cachep, bh);
3229         get_cpu_var(bh_accounting).nr--;
3230         recalc_bh_state();
3231         put_cpu_var(bh_accounting);
3232 }
3233 EXPORT_SYMBOL(free_buffer_head);
3234
3235 static void buffer_exit_cpu(int cpu)
3236 {
3237         int i;
3238         struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3239
3240         for (i = 0; i < BH_LRU_SIZE; i++) {
3241                 brelse(b->bhs[i]);
3242                 b->bhs[i] = NULL;
3243         }
3244         get_cpu_var(bh_accounting).nr += per_cpu(bh_accounting, cpu).nr;
3245         per_cpu(bh_accounting, cpu).nr = 0;
3246         put_cpu_var(bh_accounting);
3247 }
3248
3249 static int buffer_cpu_notify(struct notifier_block *self,
3250                               unsigned long action, void *hcpu)
3251 {
3252         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN)
3253                 buffer_exit_cpu((unsigned long)hcpu);
3254         return NOTIFY_OK;
3255 }
3256
3257 /**
3258  * bh_uptodate_or_lock - Test whether the buffer is uptodate
3259  * @bh: struct buffer_head
3260  *
3261  * Return true if the buffer is up-to-date and false,
3262  * with the buffer locked, if not.
3263  */
3264 int bh_uptodate_or_lock(struct buffer_head *bh)
3265 {
3266         if (!buffer_uptodate(bh)) {
3267                 lock_buffer(bh);
3268                 if (!buffer_uptodate(bh))
3269                         return 0;
3270                 unlock_buffer(bh);
3271         }
3272         return 1;
3273 }
3274 EXPORT_SYMBOL(bh_uptodate_or_lock);
3275
3276 /**
3277  * bh_submit_read - Submit a locked buffer for reading
3278  * @bh: struct buffer_head
3279  *
3280  * Returns zero on success and -EIO on error.
3281  */
3282 int bh_submit_read(struct buffer_head *bh)
3283 {
3284         BUG_ON(!buffer_locked(bh));
3285
3286         if (buffer_uptodate(bh)) {
3287                 unlock_buffer(bh);
3288                 return 0;
3289         }
3290
3291         get_bh(bh);
3292         bh->b_end_io = end_buffer_read_sync;
3293         submit_bh(READ, bh);
3294         wait_on_buffer(bh);
3295         if (buffer_uptodate(bh))
3296                 return 0;
3297         return -EIO;
3298 }
3299 EXPORT_SYMBOL(bh_submit_read);
3300
3301 static void
3302 init_buffer_head(void *data)
3303 {
3304         struct buffer_head *bh = data;
3305
3306         memset(bh, 0, sizeof(*bh));
3307         INIT_LIST_HEAD(&bh->b_assoc_buffers);
3308 }
3309
3310 void __init buffer_init(void)
3311 {
3312         int nrpages;
3313
3314         bh_cachep = kmem_cache_create("buffer_head",
3315                         sizeof(struct buffer_head), 0,
3316                                 (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3317                                 SLAB_MEM_SPREAD),
3318                                 init_buffer_head);
3319
3320         /*
3321          * Limit the bh occupancy to 10% of ZONE_NORMAL
3322          */
3323         nrpages = (nr_free_buffer_pages() * 10) / 100;
3324         max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3325         hotcpu_notifier(buffer_cpu_notify, 0);
3326 }
3327
3328 EXPORT_SYMBOL(__bforget);
3329 EXPORT_SYMBOL(__brelse);
3330 EXPORT_SYMBOL(__wait_on_buffer);
3331 EXPORT_SYMBOL(block_commit_write);
3332 EXPORT_SYMBOL(block_prepare_write);
3333 EXPORT_SYMBOL(block_page_mkwrite);
3334 EXPORT_SYMBOL(block_read_full_page);
3335 EXPORT_SYMBOL(block_sync_page);
3336 EXPORT_SYMBOL(block_truncate_page);
3337 EXPORT_SYMBOL(block_write_full_page);
3338 EXPORT_SYMBOL(cont_write_begin);
3339 EXPORT_SYMBOL(end_buffer_read_sync);
3340 EXPORT_SYMBOL(end_buffer_write_sync);
3341 EXPORT_SYMBOL(file_fsync);
3342 EXPORT_SYMBOL(generic_block_bmap);
3343 EXPORT_SYMBOL(generic_cont_expand_simple);
3344 EXPORT_SYMBOL(init_buffer);
3345 EXPORT_SYMBOL(invalidate_bdev);
3346 EXPORT_SYMBOL(ll_rw_block);
3347 EXPORT_SYMBOL(mark_buffer_dirty);
3348 EXPORT_SYMBOL(submit_bh);
3349 EXPORT_SYMBOL(sync_dirty_buffer);
3350 EXPORT_SYMBOL(unlock_buffer);