Merge branch 'writeback-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...
[linux-3.10.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 #include <linux/cleancache.h>
45
46 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
47
48 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
49
50 inline void
51 init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
52 {
53         bh->b_end_io = handler;
54         bh->b_private = private;
55 }
56 EXPORT_SYMBOL(init_buffer);
57
58 static int sleep_on_buffer(void *word)
59 {
60         io_schedule();
61         return 0;
62 }
63
64 void __lock_buffer(struct buffer_head *bh)
65 {
66         wait_on_bit_lock(&bh->b_state, BH_Lock, sleep_on_buffer,
67                                                         TASK_UNINTERRUPTIBLE);
68 }
69 EXPORT_SYMBOL(__lock_buffer);
70
71 void unlock_buffer(struct buffer_head *bh)
72 {
73         clear_bit_unlock(BH_Lock, &bh->b_state);
74         smp_mb__after_clear_bit();
75         wake_up_bit(&bh->b_state, BH_Lock);
76 }
77 EXPORT_SYMBOL(unlock_buffer);
78
79 /*
80  * Block until a buffer comes unlocked.  This doesn't stop it
81  * from becoming locked again - you have to lock it yourself
82  * if you want to preserve its state.
83  */
84 void __wait_on_buffer(struct buffer_head * bh)
85 {
86         wait_on_bit(&bh->b_state, BH_Lock, sleep_on_buffer, TASK_UNINTERRUPTIBLE);
87 }
88 EXPORT_SYMBOL(__wait_on_buffer);
89
90 static void
91 __clear_page_buffers(struct page *page)
92 {
93         ClearPagePrivate(page);
94         set_page_private(page, 0);
95         page_cache_release(page);
96 }
97
98
99 static int quiet_error(struct buffer_head *bh)
100 {
101         if (!test_bit(BH_Quiet, &bh->b_state) && printk_ratelimit())
102                 return 0;
103         return 1;
104 }
105
106
107 static void buffer_io_error(struct buffer_head *bh)
108 {
109         char b[BDEVNAME_SIZE];
110         printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
111                         bdevname(bh->b_bdev, b),
112                         (unsigned long long)bh->b_blocknr);
113 }
114
115 /*
116  * End-of-IO handler helper function which does not touch the bh after
117  * unlocking it.
118  * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
119  * a race there is benign: unlock_buffer() only use the bh's address for
120  * hashing after unlocking the buffer, so it doesn't actually touch the bh
121  * itself.
122  */
123 static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
124 {
125         if (uptodate) {
126                 set_buffer_uptodate(bh);
127         } else {
128                 /* This happens, due to failed READA attempts. */
129                 clear_buffer_uptodate(bh);
130         }
131         unlock_buffer(bh);
132 }
133
134 /*
135  * Default synchronous end-of-IO handler..  Just mark it up-to-date and
136  * unlock the buffer. This is what ll_rw_block uses too.
137  */
138 void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
139 {
140         __end_buffer_read_notouch(bh, uptodate);
141         put_bh(bh);
142 }
143 EXPORT_SYMBOL(end_buffer_read_sync);
144
145 void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
146 {
147         char b[BDEVNAME_SIZE];
148
149         if (uptodate) {
150                 set_buffer_uptodate(bh);
151         } else {
152                 if (!quiet_error(bh)) {
153                         buffer_io_error(bh);
154                         printk(KERN_WARNING "lost page write due to "
155                                         "I/O error on %s\n",
156                                        bdevname(bh->b_bdev, b));
157                 }
158                 set_buffer_write_io_error(bh);
159                 clear_buffer_uptodate(bh);
160         }
161         unlock_buffer(bh);
162         put_bh(bh);
163 }
164 EXPORT_SYMBOL(end_buffer_write_sync);
165
166 /*
167  * Various filesystems appear to want __find_get_block to be non-blocking.
168  * But it's the page lock which protects the buffers.  To get around this,
169  * we get exclusion from try_to_free_buffers with the blockdev mapping's
170  * private_lock.
171  *
172  * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
173  * may be quite high.  This code could TryLock the page, and if that
174  * succeeds, there is no need to take private_lock. (But if
175  * private_lock is contended then so is mapping->tree_lock).
176  */
177 static struct buffer_head *
178 __find_get_block_slow(struct block_device *bdev, sector_t block)
179 {
180         struct inode *bd_inode = bdev->bd_inode;
181         struct address_space *bd_mapping = bd_inode->i_mapping;
182         struct buffer_head *ret = NULL;
183         pgoff_t index;
184         struct buffer_head *bh;
185         struct buffer_head *head;
186         struct page *page;
187         int all_mapped = 1;
188
189         index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
190         page = find_get_page(bd_mapping, index);
191         if (!page)
192                 goto out;
193
194         spin_lock(&bd_mapping->private_lock);
195         if (!page_has_buffers(page))
196                 goto out_unlock;
197         head = page_buffers(page);
198         bh = head;
199         do {
200                 if (!buffer_mapped(bh))
201                         all_mapped = 0;
202                 else if (bh->b_blocknr == block) {
203                         ret = bh;
204                         get_bh(bh);
205                         goto out_unlock;
206                 }
207                 bh = bh->b_this_page;
208         } while (bh != head);
209
210         /* we might be here because some of the buffers on this page are
211          * not mapped.  This is due to various races between
212          * file io on the block device and getblk.  It gets dealt with
213          * elsewhere, don't buffer_error if we had some unmapped buffers
214          */
215         if (all_mapped) {
216                 char b[BDEVNAME_SIZE];
217
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 %s blocksize: %d\n", bdevname(bdev, b),
225                         1 << bd_inode->i_blkbits);
226         }
227 out_unlock:
228         spin_unlock(&bd_mapping->private_lock);
229         page_cache_release(page);
230 out:
231         return ret;
232 }
233
234 /* If invalidate_buffers() will trash dirty buffers, it means some kind
235    of fs corruption is going on. Trashing dirty data always imply losing
236    information that was supposed to be just stored on the physical layer
237    by the user.
238
239    Thus invalidate_buffers in general usage is not allwowed to trash
240    dirty buffers. For example ioctl(FLSBLKBUF) expects dirty data to
241    be preserved.  These buffers are simply skipped.
242   
243    We also skip buffers which are still in use.  For example this can
244    happen if a userspace program is reading the block device.
245
246    NOTE: In the case where the user removed a removable-media-disk even if
247    there's still dirty data not synced on disk (due a bug in the device driver
248    or due an error of the user), by not destroying the dirty buffers we could
249    generate corruption also on the next media inserted, thus a parameter is
250    necessary to handle this case in the most safe way possible (trying
251    to not corrupt also the new disk inserted with the data belonging to
252    the old now corrupted disk). Also for the ramdisk the natural thing
253    to do in order to release the ramdisk memory is to destroy dirty buffers.
254
255    These are two special cases. Normal usage imply the device driver
256    to issue a sync on the device (without waiting I/O completion) and
257    then an invalidate_buffers call that doesn't trash dirty buffers.
258
259    For handling cache coherency with the blkdev pagecache the 'update' case
260    is been introduced. It is needed to re-read from disk any pinned
261    buffer. NOTE: re-reading from disk is destructive so we can do it only
262    when we assume nobody is changing the buffercache under our I/O and when
263    we think the disk contains more recent information than the buffercache.
264    The update == 1 pass marks the buffers we need to update, the update == 2
265    pass does the actual I/O. */
266 void invalidate_bdev(struct block_device *bdev)
267 {
268         struct address_space *mapping = bdev->bd_inode->i_mapping;
269
270         if (mapping->nrpages == 0)
271                 return;
272
273         invalidate_bh_lrus();
274         lru_add_drain_all();    /* make sure all lru add caches are flushed */
275         invalidate_mapping_pages(mapping, 0, -1);
276         /* 99% of the time, we don't need to flush the cleancache on the bdev.
277          * But, for the strange corners, lets be cautious
278          */
279         cleancache_flush_inode(mapping);
280 }
281 EXPORT_SYMBOL(invalidate_bdev);
282
283 /*
284  * Kick the writeback threads then try to free up some ZONE_NORMAL memory.
285  */
286 static void free_more_memory(void)
287 {
288         struct zone *zone;
289         int nid;
290
291         wakeup_flusher_threads(1024, WB_REASON_FREE_MORE_MEM);
292         yield();
293
294         for_each_online_node(nid) {
295                 (void)first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
296                                                 gfp_zone(GFP_NOFS), NULL,
297                                                 &zone);
298                 if (zone)
299                         try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
300                                                 GFP_NOFS, NULL);
301         }
302 }
303
304 /*
305  * I/O completion handler for block_read_full_page() - pages
306  * which come unlocked at the end of I/O.
307  */
308 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
309 {
310         unsigned long flags;
311         struct buffer_head *first;
312         struct buffer_head *tmp;
313         struct page *page;
314         int page_uptodate = 1;
315
316         BUG_ON(!buffer_async_read(bh));
317
318         page = bh->b_page;
319         if (uptodate) {
320                 set_buffer_uptodate(bh);
321         } else {
322                 clear_buffer_uptodate(bh);
323                 if (!quiet_error(bh))
324                         buffer_io_error(bh);
325                 SetPageError(page);
326         }
327
328         /*
329          * Be _very_ careful from here on. Bad things can happen if
330          * two buffer heads end IO at almost the same time and both
331          * decide that the page is now completely done.
332          */
333         first = page_buffers(page);
334         local_irq_save(flags);
335         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
336         clear_buffer_async_read(bh);
337         unlock_buffer(bh);
338         tmp = bh;
339         do {
340                 if (!buffer_uptodate(tmp))
341                         page_uptodate = 0;
342                 if (buffer_async_read(tmp)) {
343                         BUG_ON(!buffer_locked(tmp));
344                         goto still_busy;
345                 }
346                 tmp = tmp->b_this_page;
347         } while (tmp != bh);
348         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
349         local_irq_restore(flags);
350
351         /*
352          * If none of the buffers had errors and they are all
353          * uptodate then we can set the page uptodate.
354          */
355         if (page_uptodate && !PageError(page))
356                 SetPageUptodate(page);
357         unlock_page(page);
358         return;
359
360 still_busy:
361         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
362         local_irq_restore(flags);
363         return;
364 }
365
366 /*
367  * Completion handler for block_write_full_page() - pages which are unlocked
368  * during I/O, and which have PageWriteback cleared upon I/O completion.
369  */
370 void end_buffer_async_write(struct buffer_head *bh, int uptodate)
371 {
372         char b[BDEVNAME_SIZE];
373         unsigned long flags;
374         struct buffer_head *first;
375         struct buffer_head *tmp;
376         struct page *page;
377
378         BUG_ON(!buffer_async_write(bh));
379
380         page = bh->b_page;
381         if (uptodate) {
382                 set_buffer_uptodate(bh);
383         } else {
384                 if (!quiet_error(bh)) {
385                         buffer_io_error(bh);
386                         printk(KERN_WARNING "lost page write due to "
387                                         "I/O error on %s\n",
388                                bdevname(bh->b_bdev, b));
389                 }
390                 set_bit(AS_EIO, &page->mapping->flags);
391                 set_buffer_write_io_error(bh);
392                 clear_buffer_uptodate(bh);
393                 SetPageError(page);
394         }
395
396         first = page_buffers(page);
397         local_irq_save(flags);
398         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
399
400         clear_buffer_async_write(bh);
401         unlock_buffer(bh);
402         tmp = bh->b_this_page;
403         while (tmp != bh) {
404                 if (buffer_async_write(tmp)) {
405                         BUG_ON(!buffer_locked(tmp));
406                         goto still_busy;
407                 }
408                 tmp = tmp->b_this_page;
409         }
410         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
411         local_irq_restore(flags);
412         end_page_writeback(page);
413         return;
414
415 still_busy:
416         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
417         local_irq_restore(flags);
418         return;
419 }
420 EXPORT_SYMBOL(end_buffer_async_write);
421
422 /*
423  * If a page's buffers are under async readin (end_buffer_async_read
424  * completion) then there is a possibility that another thread of
425  * control could lock one of the buffers after it has completed
426  * but while some of the other buffers have not completed.  This
427  * locked buffer would confuse end_buffer_async_read() into not unlocking
428  * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
429  * that this buffer is not under async I/O.
430  *
431  * The page comes unlocked when it has no locked buffer_async buffers
432  * left.
433  *
434  * PageLocked prevents anyone starting new async I/O reads any of
435  * the buffers.
436  *
437  * PageWriteback is used to prevent simultaneous writeout of the same
438  * page.
439  *
440  * PageLocked prevents anyone from starting writeback of a page which is
441  * under read I/O (PageWriteback is only ever set against a locked page).
442  */
443 static void mark_buffer_async_read(struct buffer_head *bh)
444 {
445         bh->b_end_io = end_buffer_async_read;
446         set_buffer_async_read(bh);
447 }
448
449 static void mark_buffer_async_write_endio(struct buffer_head *bh,
450                                           bh_end_io_t *handler)
451 {
452         bh->b_end_io = handler;
453         set_buffer_async_write(bh);
454 }
455
456 void mark_buffer_async_write(struct buffer_head *bh)
457 {
458         mark_buffer_async_write_endio(bh, end_buffer_async_write);
459 }
460 EXPORT_SYMBOL(mark_buffer_async_write);
461
462
463 /*
464  * fs/buffer.c contains helper functions for buffer-backed address space's
465  * fsync functions.  A common requirement for buffer-based filesystems is
466  * that certain data from the backing blockdev needs to be written out for
467  * a successful fsync().  For example, ext2 indirect blocks need to be
468  * written back and waited upon before fsync() returns.
469  *
470  * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
471  * inode_has_buffers() and invalidate_inode_buffers() are provided for the
472  * management of a list of dependent buffers at ->i_mapping->private_list.
473  *
474  * Locking is a little subtle: try_to_free_buffers() will remove buffers
475  * from their controlling inode's queue when they are being freed.  But
476  * try_to_free_buffers() will be operating against the *blockdev* mapping
477  * at the time, not against the S_ISREG file which depends on those buffers.
478  * So the locking for private_list is via the private_lock in the address_space
479  * which backs the buffers.  Which is different from the address_space 
480  * against which the buffers are listed.  So for a particular address_space,
481  * mapping->private_lock does *not* protect mapping->private_list!  In fact,
482  * mapping->private_list will always be protected by the backing blockdev's
483  * ->private_lock.
484  *
485  * Which introduces a requirement: all buffers on an address_space's
486  * ->private_list must be from the same address_space: the blockdev's.
487  *
488  * address_spaces which do not place buffers at ->private_list via these
489  * utility functions are free to use private_lock and private_list for
490  * whatever they want.  The only requirement is that list_empty(private_list)
491  * be true at clear_inode() time.
492  *
493  * FIXME: clear_inode should not call invalidate_inode_buffers().  The
494  * filesystems should do that.  invalidate_inode_buffers() should just go
495  * BUG_ON(!list_empty).
496  *
497  * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
498  * take an address_space, not an inode.  And it should be called
499  * mark_buffer_dirty_fsync() to clearly define why those buffers are being
500  * queued up.
501  *
502  * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
503  * list if it is already on a list.  Because if the buffer is on a list,
504  * it *must* already be on the right one.  If not, the filesystem is being
505  * silly.  This will save a ton of locking.  But first we have to ensure
506  * that buffers are taken *off* the old inode's list when they are freed
507  * (presumably in truncate).  That requires careful auditing of all
508  * filesystems (do it inside bforget()).  It could also be done by bringing
509  * b_inode back.
510  */
511
512 /*
513  * The buffer's backing address_space's private_lock must be held
514  */
515 static void __remove_assoc_queue(struct buffer_head *bh)
516 {
517         list_del_init(&bh->b_assoc_buffers);
518         WARN_ON(!bh->b_assoc_map);
519         if (buffer_write_io_error(bh))
520                 set_bit(AS_EIO, &bh->b_assoc_map->flags);
521         bh->b_assoc_map = NULL;
522 }
523
524 int inode_has_buffers(struct inode *inode)
525 {
526         return !list_empty(&inode->i_data.private_list);
527 }
528
529 /*
530  * osync is designed to support O_SYNC io.  It waits synchronously for
531  * all already-submitted IO to complete, but does not queue any new
532  * writes to the disk.
533  *
534  * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
535  * you dirty the buffers, and then use osync_inode_buffers to wait for
536  * completion.  Any other dirty buffers which are not yet queued for
537  * write will not be flushed to disk by the osync.
538  */
539 static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
540 {
541         struct buffer_head *bh;
542         struct list_head *p;
543         int err = 0;
544
545         spin_lock(lock);
546 repeat:
547         list_for_each_prev(p, list) {
548                 bh = BH_ENTRY(p);
549                 if (buffer_locked(bh)) {
550                         get_bh(bh);
551                         spin_unlock(lock);
552                         wait_on_buffer(bh);
553                         if (!buffer_uptodate(bh))
554                                 err = -EIO;
555                         brelse(bh);
556                         spin_lock(lock);
557                         goto repeat;
558                 }
559         }
560         spin_unlock(lock);
561         return err;
562 }
563
564 static void do_thaw_one(struct super_block *sb, void *unused)
565 {
566         char b[BDEVNAME_SIZE];
567         while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
568                 printk(KERN_WARNING "Emergency Thaw on %s\n",
569                        bdevname(sb->s_bdev, b));
570 }
571
572 static void do_thaw_all(struct work_struct *work)
573 {
574         iterate_supers(do_thaw_one, NULL);
575         kfree(work);
576         printk(KERN_WARNING "Emergency Thaw complete\n");
577 }
578
579 /**
580  * emergency_thaw_all -- forcibly thaw every frozen filesystem
581  *
582  * Used for emergency unfreeze of all filesystems via SysRq
583  */
584 void emergency_thaw_all(void)
585 {
586         struct work_struct *work;
587
588         work = kmalloc(sizeof(*work), GFP_ATOMIC);
589         if (work) {
590                 INIT_WORK(work, do_thaw_all);
591                 schedule_work(work);
592         }
593 }
594
595 /**
596  * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
597  * @mapping: the mapping which wants those buffers written
598  *
599  * Starts I/O against the buffers at mapping->private_list, and waits upon
600  * that I/O.
601  *
602  * Basically, this is a convenience function for fsync().
603  * @mapping is a file or directory which needs those buffers to be written for
604  * a successful fsync().
605  */
606 int sync_mapping_buffers(struct address_space *mapping)
607 {
608         struct address_space *buffer_mapping = mapping->assoc_mapping;
609
610         if (buffer_mapping == NULL || list_empty(&mapping->private_list))
611                 return 0;
612
613         return fsync_buffers_list(&buffer_mapping->private_lock,
614                                         &mapping->private_list);
615 }
616 EXPORT_SYMBOL(sync_mapping_buffers);
617
618 /*
619  * Called when we've recently written block `bblock', and it is known that
620  * `bblock' was for a buffer_boundary() buffer.  This means that the block at
621  * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
622  * dirty, schedule it for IO.  So that indirects merge nicely with their data.
623  */
624 void write_boundary_block(struct block_device *bdev,
625                         sector_t bblock, unsigned blocksize)
626 {
627         struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
628         if (bh) {
629                 if (buffer_dirty(bh))
630                         ll_rw_block(WRITE, 1, &bh);
631                 put_bh(bh);
632         }
633 }
634
635 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
636 {
637         struct address_space *mapping = inode->i_mapping;
638         struct address_space *buffer_mapping = bh->b_page->mapping;
639
640         mark_buffer_dirty(bh);
641         if (!mapping->assoc_mapping) {
642                 mapping->assoc_mapping = buffer_mapping;
643         } else {
644                 BUG_ON(mapping->assoc_mapping != buffer_mapping);
645         }
646         if (!bh->b_assoc_map) {
647                 spin_lock(&buffer_mapping->private_lock);
648                 list_move_tail(&bh->b_assoc_buffers,
649                                 &mapping->private_list);
650                 bh->b_assoc_map = mapping;
651                 spin_unlock(&buffer_mapping->private_lock);
652         }
653 }
654 EXPORT_SYMBOL(mark_buffer_dirty_inode);
655
656 /*
657  * Mark the page dirty, and set it dirty in the radix tree, and mark the inode
658  * dirty.
659  *
660  * If warn is true, then emit a warning if the page is not uptodate and has
661  * not been truncated.
662  */
663 static void __set_page_dirty(struct page *page,
664                 struct address_space *mapping, int warn)
665 {
666         spin_lock_irq(&mapping->tree_lock);
667         if (page->mapping) {    /* Race with truncate? */
668                 WARN_ON_ONCE(warn && !PageUptodate(page));
669                 account_page_dirtied(page, mapping);
670                 radix_tree_tag_set(&mapping->page_tree,
671                                 page_index(page), PAGECACHE_TAG_DIRTY);
672         }
673         spin_unlock_irq(&mapping->tree_lock);
674         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
675 }
676
677 /*
678  * Add a page to the dirty page list.
679  *
680  * It is a sad fact of life that this function is called from several places
681  * deeply under spinlocking.  It may not sleep.
682  *
683  * If the page has buffers, the uptodate buffers are set dirty, to preserve
684  * dirty-state coherency between the page and the buffers.  It the page does
685  * not have buffers then when they are later attached they will all be set
686  * dirty.
687  *
688  * The buffers are dirtied before the page is dirtied.  There's a small race
689  * window in which a writepage caller may see the page cleanness but not the
690  * buffer dirtiness.  That's fine.  If this code were to set the page dirty
691  * before the buffers, a concurrent writepage caller could clear the page dirty
692  * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
693  * page on the dirty page list.
694  *
695  * We use private_lock to lock against try_to_free_buffers while using the
696  * page's buffer list.  Also use this to protect against clean buffers being
697  * added to the page after it was set dirty.
698  *
699  * FIXME: may need to call ->reservepage here as well.  That's rather up to the
700  * address_space though.
701  */
702 int __set_page_dirty_buffers(struct page *page)
703 {
704         int newly_dirty;
705         struct address_space *mapping = page_mapping(page);
706
707         if (unlikely(!mapping))
708                 return !TestSetPageDirty(page);
709
710         spin_lock(&mapping->private_lock);
711         if (page_has_buffers(page)) {
712                 struct buffer_head *head = page_buffers(page);
713                 struct buffer_head *bh = head;
714
715                 do {
716                         set_buffer_dirty(bh);
717                         bh = bh->b_this_page;
718                 } while (bh != head);
719         }
720         newly_dirty = !TestSetPageDirty(page);
721         spin_unlock(&mapping->private_lock);
722
723         if (newly_dirty)
724                 __set_page_dirty(page, mapping, 1);
725         return newly_dirty;
726 }
727 EXPORT_SYMBOL(__set_page_dirty_buffers);
728
729 /*
730  * Write out and wait upon a list of buffers.
731  *
732  * We have conflicting pressures: we want to make sure that all
733  * initially dirty buffers get waited on, but that any subsequently
734  * dirtied buffers don't.  After all, we don't want fsync to last
735  * forever if somebody is actively writing to the file.
736  *
737  * Do this in two main stages: first we copy dirty buffers to a
738  * temporary inode list, queueing the writes as we go.  Then we clean
739  * up, waiting for those writes to complete.
740  * 
741  * During this second stage, any subsequent updates to the file may end
742  * up refiling the buffer on the original inode's dirty list again, so
743  * there is a chance we will end up with a buffer queued for write but
744  * not yet completed on that list.  So, as a final cleanup we go through
745  * the osync code to catch these locked, dirty buffers without requeuing
746  * any newly dirty buffers for write.
747  */
748 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
749 {
750         struct buffer_head *bh;
751         struct list_head tmp;
752         struct address_space *mapping;
753         int err = 0, err2;
754         struct blk_plug plug;
755
756         INIT_LIST_HEAD(&tmp);
757         blk_start_plug(&plug);
758
759         spin_lock(lock);
760         while (!list_empty(list)) {
761                 bh = BH_ENTRY(list->next);
762                 mapping = bh->b_assoc_map;
763                 __remove_assoc_queue(bh);
764                 /* Avoid race with mark_buffer_dirty_inode() which does
765                  * a lockless check and we rely on seeing the dirty bit */
766                 smp_mb();
767                 if (buffer_dirty(bh) || buffer_locked(bh)) {
768                         list_add(&bh->b_assoc_buffers, &tmp);
769                         bh->b_assoc_map = mapping;
770                         if (buffer_dirty(bh)) {
771                                 get_bh(bh);
772                                 spin_unlock(lock);
773                                 /*
774                                  * Ensure any pending I/O completes so that
775                                  * write_dirty_buffer() actually writes the
776                                  * current contents - it is a noop if I/O is
777                                  * still in flight on potentially older
778                                  * contents.
779                                  */
780                                 write_dirty_buffer(bh, WRITE_SYNC);
781
782                                 /*
783                                  * Kick off IO for the previous mapping. Note
784                                  * that we will not run the very last mapping,
785                                  * wait_on_buffer() will do that for us
786                                  * through sync_buffer().
787                                  */
788                                 brelse(bh);
789                                 spin_lock(lock);
790                         }
791                 }
792         }
793
794         spin_unlock(lock);
795         blk_finish_plug(&plug);
796         spin_lock(lock);
797
798         while (!list_empty(&tmp)) {
799                 bh = BH_ENTRY(tmp.prev);
800                 get_bh(bh);
801                 mapping = bh->b_assoc_map;
802                 __remove_assoc_queue(bh);
803                 /* Avoid race with mark_buffer_dirty_inode() which does
804                  * a lockless check and we rely on seeing the dirty bit */
805                 smp_mb();
806                 if (buffer_dirty(bh)) {
807                         list_add(&bh->b_assoc_buffers,
808                                  &mapping->private_list);
809                         bh->b_assoc_map = mapping;
810                 }
811                 spin_unlock(lock);
812                 wait_on_buffer(bh);
813                 if (!buffer_uptodate(bh))
814                         err = -EIO;
815                 brelse(bh);
816                 spin_lock(lock);
817         }
818         
819         spin_unlock(lock);
820         err2 = osync_buffers_list(lock, list);
821         if (err)
822                 return err;
823         else
824                 return err2;
825 }
826
827 /*
828  * Invalidate any and all dirty buffers on a given inode.  We are
829  * probably unmounting the fs, but that doesn't mean we have already
830  * done a sync().  Just drop the buffers from the inode list.
831  *
832  * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
833  * assumes that all the buffers are against the blockdev.  Not true
834  * for reiserfs.
835  */
836 void invalidate_inode_buffers(struct inode *inode)
837 {
838         if (inode_has_buffers(inode)) {
839                 struct address_space *mapping = &inode->i_data;
840                 struct list_head *list = &mapping->private_list;
841                 struct address_space *buffer_mapping = mapping->assoc_mapping;
842
843                 spin_lock(&buffer_mapping->private_lock);
844                 while (!list_empty(list))
845                         __remove_assoc_queue(BH_ENTRY(list->next));
846                 spin_unlock(&buffer_mapping->private_lock);
847         }
848 }
849 EXPORT_SYMBOL(invalidate_inode_buffers);
850
851 /*
852  * Remove any clean buffers from the inode's buffer list.  This is called
853  * when we're trying to free the inode itself.  Those buffers can pin it.
854  *
855  * Returns true if all buffers were removed.
856  */
857 int remove_inode_buffers(struct inode *inode)
858 {
859         int ret = 1;
860
861         if (inode_has_buffers(inode)) {
862                 struct address_space *mapping = &inode->i_data;
863                 struct list_head *list = &mapping->private_list;
864                 struct address_space *buffer_mapping = mapping->assoc_mapping;
865
866                 spin_lock(&buffer_mapping->private_lock);
867                 while (!list_empty(list)) {
868                         struct buffer_head *bh = BH_ENTRY(list->next);
869                         if (buffer_dirty(bh)) {
870                                 ret = 0;
871                                 break;
872                         }
873                         __remove_assoc_queue(bh);
874                 }
875                 spin_unlock(&buffer_mapping->private_lock);
876         }
877         return ret;
878 }
879
880 /*
881  * Create the appropriate buffers when given a page for data area and
882  * the size of each buffer.. Use the bh->b_this_page linked list to
883  * follow the buffers created.  Return NULL if unable to create more
884  * buffers.
885  *
886  * The retry flag is used to differentiate async IO (paging, swapping)
887  * which may not fail from ordinary buffer allocations.
888  */
889 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
890                 int retry)
891 {
892         struct buffer_head *bh, *head;
893         long offset;
894
895 try_again:
896         head = NULL;
897         offset = PAGE_SIZE;
898         while ((offset -= size) >= 0) {
899                 bh = alloc_buffer_head(GFP_NOFS);
900                 if (!bh)
901                         goto no_grow;
902
903                 bh->b_bdev = NULL;
904                 bh->b_this_page = head;
905                 bh->b_blocknr = -1;
906                 head = bh;
907
908                 bh->b_state = 0;
909                 atomic_set(&bh->b_count, 0);
910                 bh->b_size = size;
911
912                 /* Link the buffer to its page */
913                 set_bh_page(bh, page, offset);
914
915                 init_buffer(bh, NULL, NULL);
916         }
917         return head;
918 /*
919  * In case anything failed, we just free everything we got.
920  */
921 no_grow:
922         if (head) {
923                 do {
924                         bh = head;
925                         head = head->b_this_page;
926                         free_buffer_head(bh);
927                 } while (head);
928         }
929
930         /*
931          * Return failure for non-async IO requests.  Async IO requests
932          * are not allowed to fail, so we have to wait until buffer heads
933          * become available.  But we don't want tasks sleeping with 
934          * partially complete buffers, so all were released above.
935          */
936         if (!retry)
937                 return NULL;
938
939         /* We're _really_ low on memory. Now we just
940          * wait for old buffer heads to become free due to
941          * finishing IO.  Since this is an async request and
942          * the reserve list is empty, we're sure there are 
943          * async buffer heads in use.
944          */
945         free_more_memory();
946         goto try_again;
947 }
948 EXPORT_SYMBOL_GPL(alloc_page_buffers);
949
950 static inline void
951 link_dev_buffers(struct page *page, struct buffer_head *head)
952 {
953         struct buffer_head *bh, *tail;
954
955         bh = head;
956         do {
957                 tail = bh;
958                 bh = bh->b_this_page;
959         } while (bh);
960         tail->b_this_page = head;
961         attach_page_buffers(page, head);
962 }
963
964 /*
965  * Initialise the state of a blockdev page's buffers.
966  */ 
967 static void
968 init_page_buffers(struct page *page, struct block_device *bdev,
969                         sector_t block, int size)
970 {
971         struct buffer_head *head = page_buffers(page);
972         struct buffer_head *bh = head;
973         int uptodate = PageUptodate(page);
974
975         do {
976                 if (!buffer_mapped(bh)) {
977                         init_buffer(bh, NULL, NULL);
978                         bh->b_bdev = bdev;
979                         bh->b_blocknr = block;
980                         if (uptodate)
981                                 set_buffer_uptodate(bh);
982                         set_buffer_mapped(bh);
983                 }
984                 block++;
985                 bh = bh->b_this_page;
986         } while (bh != head);
987 }
988
989 /*
990  * Create the page-cache page that contains the requested block.
991  *
992  * This is user purely for blockdev mappings.
993  */
994 static struct page *
995 grow_dev_page(struct block_device *bdev, sector_t block,
996                 pgoff_t index, int size)
997 {
998         struct inode *inode = bdev->bd_inode;
999         struct page *page;
1000         struct buffer_head *bh;
1001
1002         page = find_or_create_page(inode->i_mapping, index,
1003                 (mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS)|__GFP_MOVABLE);
1004         if (!page)
1005                 return NULL;
1006
1007         BUG_ON(!PageLocked(page));
1008
1009         if (page_has_buffers(page)) {
1010                 bh = page_buffers(page);
1011                 if (bh->b_size == size) {
1012                         init_page_buffers(page, bdev, block, size);
1013                         return page;
1014                 }
1015                 if (!try_to_free_buffers(page))
1016                         goto failed;
1017         }
1018
1019         /*
1020          * Allocate some buffers for this page
1021          */
1022         bh = alloc_page_buffers(page, size, 0);
1023         if (!bh)
1024                 goto failed;
1025
1026         /*
1027          * Link the page to the buffers and initialise them.  Take the
1028          * lock to be atomic wrt __find_get_block(), which does not
1029          * run under the page lock.
1030          */
1031         spin_lock(&inode->i_mapping->private_lock);
1032         link_dev_buffers(page, bh);
1033         init_page_buffers(page, bdev, block, size);
1034         spin_unlock(&inode->i_mapping->private_lock);
1035         return page;
1036
1037 failed:
1038         BUG();
1039         unlock_page(page);
1040         page_cache_release(page);
1041         return NULL;
1042 }
1043
1044 /*
1045  * Create buffers for the specified block device block's page.  If
1046  * that page was dirty, the buffers are set dirty also.
1047  */
1048 static int
1049 grow_buffers(struct block_device *bdev, sector_t block, int size)
1050 {
1051         struct page *page;
1052         pgoff_t index;
1053         int sizebits;
1054
1055         sizebits = -1;
1056         do {
1057                 sizebits++;
1058         } while ((size << sizebits) < PAGE_SIZE);
1059
1060         index = block >> sizebits;
1061
1062         /*
1063          * Check for a block which wants to lie outside our maximum possible
1064          * pagecache index.  (this comparison is done using sector_t types).
1065          */
1066         if (unlikely(index != block >> sizebits)) {
1067                 char b[BDEVNAME_SIZE];
1068
1069                 printk(KERN_ERR "%s: requested out-of-range block %llu for "
1070                         "device %s\n",
1071                         __func__, (unsigned long long)block,
1072                         bdevname(bdev, b));
1073                 return -EIO;
1074         }
1075         block = index << sizebits;
1076         /* Create a page with the proper size buffers.. */
1077         page = grow_dev_page(bdev, block, index, size);
1078         if (!page)
1079                 return 0;
1080         unlock_page(page);
1081         page_cache_release(page);
1082         return 1;
1083 }
1084
1085 static struct buffer_head *
1086 __getblk_slow(struct block_device *bdev, sector_t block, int size)
1087 {
1088         /* Size must be multiple of hard sectorsize */
1089         if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
1090                         (size < 512 || size > PAGE_SIZE))) {
1091                 printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1092                                         size);
1093                 printk(KERN_ERR "logical block size: %d\n",
1094                                         bdev_logical_block_size(bdev));
1095
1096                 dump_stack();
1097                 return NULL;
1098         }
1099
1100         for (;;) {
1101                 struct buffer_head * bh;
1102                 int ret;
1103
1104                 bh = __find_get_block(bdev, block, size);
1105                 if (bh)
1106                         return bh;
1107
1108                 ret = grow_buffers(bdev, block, size);
1109                 if (ret < 0)
1110                         return NULL;
1111                 if (ret == 0)
1112                         free_more_memory();
1113         }
1114 }
1115
1116 /*
1117  * The relationship between dirty buffers and dirty pages:
1118  *
1119  * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1120  * the page is tagged dirty in its radix tree.
1121  *
1122  * At all times, the dirtiness of the buffers represents the dirtiness of
1123  * subsections of the page.  If the page has buffers, the page dirty bit is
1124  * merely a hint about the true dirty state.
1125  *
1126  * When a page is set dirty in its entirety, all its buffers are marked dirty
1127  * (if the page has buffers).
1128  *
1129  * When a buffer is marked dirty, its page is dirtied, but the page's other
1130  * buffers are not.
1131  *
1132  * Also.  When blockdev buffers are explicitly read with bread(), they
1133  * individually become uptodate.  But their backing page remains not
1134  * uptodate - even if all of its buffers are uptodate.  A subsequent
1135  * block_read_full_page() against that page will discover all the uptodate
1136  * buffers, will set the page uptodate and will perform no I/O.
1137  */
1138
1139 /**
1140  * mark_buffer_dirty - mark a buffer_head as needing writeout
1141  * @bh: the buffer_head to mark dirty
1142  *
1143  * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1144  * backing page dirty, then tag the page as dirty in its address_space's radix
1145  * tree and then attach the address_space's inode to its superblock's dirty
1146  * inode list.
1147  *
1148  * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1149  * mapping->tree_lock and mapping->host->i_lock.
1150  */
1151 void mark_buffer_dirty(struct buffer_head *bh)
1152 {
1153         WARN_ON_ONCE(!buffer_uptodate(bh));
1154
1155         /*
1156          * Very *carefully* optimize the it-is-already-dirty case.
1157          *
1158          * Don't let the final "is it dirty" escape to before we
1159          * perhaps modified the buffer.
1160          */
1161         if (buffer_dirty(bh)) {
1162                 smp_mb();
1163                 if (buffer_dirty(bh))
1164                         return;
1165         }
1166
1167         if (!test_set_buffer_dirty(bh)) {
1168                 struct page *page = bh->b_page;
1169                 if (!TestSetPageDirty(page)) {
1170                         struct address_space *mapping = page_mapping(page);
1171                         if (mapping)
1172                                 __set_page_dirty(page, mapping, 0);
1173                 }
1174         }
1175 }
1176 EXPORT_SYMBOL(mark_buffer_dirty);
1177
1178 /*
1179  * Decrement a buffer_head's reference count.  If all buffers against a page
1180  * have zero reference count, are clean and unlocked, and if the page is clean
1181  * and unlocked then try_to_free_buffers() may strip the buffers from the page
1182  * in preparation for freeing it (sometimes, rarely, buffers are removed from
1183  * a page but it ends up not being freed, and buffers may later be reattached).
1184  */
1185 void __brelse(struct buffer_head * buf)
1186 {
1187         if (atomic_read(&buf->b_count)) {
1188                 put_bh(buf);
1189                 return;
1190         }
1191         WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1192 }
1193 EXPORT_SYMBOL(__brelse);
1194
1195 /*
1196  * bforget() is like brelse(), except it discards any
1197  * potentially dirty data.
1198  */
1199 void __bforget(struct buffer_head *bh)
1200 {
1201         clear_buffer_dirty(bh);
1202         if (bh->b_assoc_map) {
1203                 struct address_space *buffer_mapping = bh->b_page->mapping;
1204
1205                 spin_lock(&buffer_mapping->private_lock);
1206                 list_del_init(&bh->b_assoc_buffers);
1207                 bh->b_assoc_map = NULL;
1208                 spin_unlock(&buffer_mapping->private_lock);
1209         }
1210         __brelse(bh);
1211 }
1212 EXPORT_SYMBOL(__bforget);
1213
1214 static struct buffer_head *__bread_slow(struct buffer_head *bh)
1215 {
1216         lock_buffer(bh);
1217         if (buffer_uptodate(bh)) {
1218                 unlock_buffer(bh);
1219                 return bh;
1220         } else {
1221                 get_bh(bh);
1222                 bh->b_end_io = end_buffer_read_sync;
1223                 submit_bh(READ, bh);
1224                 wait_on_buffer(bh);
1225                 if (buffer_uptodate(bh))
1226                         return bh;
1227         }
1228         brelse(bh);
1229         return NULL;
1230 }
1231
1232 /*
1233  * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1234  * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1235  * refcount elevated by one when they're in an LRU.  A buffer can only appear
1236  * once in a particular CPU's LRU.  A single buffer can be present in multiple
1237  * CPU's LRUs at the same time.
1238  *
1239  * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1240  * sb_find_get_block().
1241  *
1242  * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1243  * a local interrupt disable for that.
1244  */
1245
1246 #define BH_LRU_SIZE     8
1247
1248 struct bh_lru {
1249         struct buffer_head *bhs[BH_LRU_SIZE];
1250 };
1251
1252 static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1253
1254 #ifdef CONFIG_SMP
1255 #define bh_lru_lock()   local_irq_disable()
1256 #define bh_lru_unlock() local_irq_enable()
1257 #else
1258 #define bh_lru_lock()   preempt_disable()
1259 #define bh_lru_unlock() preempt_enable()
1260 #endif
1261
1262 static inline void check_irqs_on(void)
1263 {
1264 #ifdef irqs_disabled
1265         BUG_ON(irqs_disabled());
1266 #endif
1267 }
1268
1269 /*
1270  * The LRU management algorithm is dopey-but-simple.  Sorry.
1271  */
1272 static void bh_lru_install(struct buffer_head *bh)
1273 {
1274         struct buffer_head *evictee = NULL;
1275
1276         check_irqs_on();
1277         bh_lru_lock();
1278         if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
1279                 struct buffer_head *bhs[BH_LRU_SIZE];
1280                 int in;
1281                 int out = 0;
1282
1283                 get_bh(bh);
1284                 bhs[out++] = bh;
1285                 for (in = 0; in < BH_LRU_SIZE; in++) {
1286                         struct buffer_head *bh2 =
1287                                 __this_cpu_read(bh_lrus.bhs[in]);
1288
1289                         if (bh2 == bh) {
1290                                 __brelse(bh2);
1291                         } else {
1292                                 if (out >= BH_LRU_SIZE) {
1293                                         BUG_ON(evictee != NULL);
1294                                         evictee = bh2;
1295                                 } else {
1296                                         bhs[out++] = bh2;
1297                                 }
1298                         }
1299                 }
1300                 while (out < BH_LRU_SIZE)
1301                         bhs[out++] = NULL;
1302                 memcpy(__this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
1303         }
1304         bh_lru_unlock();
1305
1306         if (evictee)
1307                 __brelse(evictee);
1308 }
1309
1310 /*
1311  * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1312  */
1313 static struct buffer_head *
1314 lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1315 {
1316         struct buffer_head *ret = NULL;
1317         unsigned int i;
1318
1319         check_irqs_on();
1320         bh_lru_lock();
1321         for (i = 0; i < BH_LRU_SIZE; i++) {
1322                 struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1323
1324                 if (bh && bh->b_bdev == bdev &&
1325                                 bh->b_blocknr == block && bh->b_size == size) {
1326                         if (i) {
1327                                 while (i) {
1328                                         __this_cpu_write(bh_lrus.bhs[i],
1329                                                 __this_cpu_read(bh_lrus.bhs[i - 1]));
1330                                         i--;
1331                                 }
1332                                 __this_cpu_write(bh_lrus.bhs[0], bh);
1333                         }
1334                         get_bh(bh);
1335                         ret = bh;
1336                         break;
1337                 }
1338         }
1339         bh_lru_unlock();
1340         return ret;
1341 }
1342
1343 /*
1344  * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1345  * it in the LRU and mark it as accessed.  If it is not present then return
1346  * NULL
1347  */
1348 struct buffer_head *
1349 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1350 {
1351         struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1352
1353         if (bh == NULL) {
1354                 bh = __find_get_block_slow(bdev, block);
1355                 if (bh)
1356                         bh_lru_install(bh);
1357         }
1358         if (bh)
1359                 touch_buffer(bh);
1360         return bh;
1361 }
1362 EXPORT_SYMBOL(__find_get_block);
1363
1364 /*
1365  * __getblk will locate (and, if necessary, create) the buffer_head
1366  * which corresponds to the passed block_device, block and size. The
1367  * returned buffer has its reference count incremented.
1368  *
1369  * __getblk() cannot fail - it just keeps trying.  If you pass it an
1370  * illegal block number, __getblk() will happily return a buffer_head
1371  * which represents the non-existent block.  Very weird.
1372  *
1373  * __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
1374  * attempt is failing.  FIXME, perhaps?
1375  */
1376 struct buffer_head *
1377 __getblk(struct block_device *bdev, sector_t block, unsigned size)
1378 {
1379         struct buffer_head *bh = __find_get_block(bdev, block, size);
1380
1381         might_sleep();
1382         if (bh == NULL)
1383                 bh = __getblk_slow(bdev, block, size);
1384         return bh;
1385 }
1386 EXPORT_SYMBOL(__getblk);
1387
1388 /*
1389  * Do async read-ahead on a buffer..
1390  */
1391 void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1392 {
1393         struct buffer_head *bh = __getblk(bdev, block, size);
1394         if (likely(bh)) {
1395                 ll_rw_block(READA, 1, &bh);
1396                 brelse(bh);
1397         }
1398 }
1399 EXPORT_SYMBOL(__breadahead);
1400
1401 /**
1402  *  __bread() - reads a specified block and returns the bh
1403  *  @bdev: the block_device to read from
1404  *  @block: number of block
1405  *  @size: size (in bytes) to read
1406  * 
1407  *  Reads a specified block, and returns buffer head that contains it.
1408  *  It returns NULL if the block was unreadable.
1409  */
1410 struct buffer_head *
1411 __bread(struct block_device *bdev, sector_t block, unsigned size)
1412 {
1413         struct buffer_head *bh = __getblk(bdev, block, size);
1414
1415         if (likely(bh) && !buffer_uptodate(bh))
1416                 bh = __bread_slow(bh);
1417         return bh;
1418 }
1419 EXPORT_SYMBOL(__bread);
1420
1421 /*
1422  * invalidate_bh_lrus() is called rarely - but not only at unmount.
1423  * This doesn't race because it runs in each cpu either in irq
1424  * or with preempt disabled.
1425  */
1426 static void invalidate_bh_lru(void *arg)
1427 {
1428         struct bh_lru *b = &get_cpu_var(bh_lrus);
1429         int i;
1430
1431         for (i = 0; i < BH_LRU_SIZE; i++) {
1432                 brelse(b->bhs[i]);
1433                 b->bhs[i] = NULL;
1434         }
1435         put_cpu_var(bh_lrus);
1436 }
1437         
1438 void invalidate_bh_lrus(void)
1439 {
1440         on_each_cpu(invalidate_bh_lru, NULL, 1);
1441 }
1442 EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1443
1444 void set_bh_page(struct buffer_head *bh,
1445                 struct page *page, unsigned long offset)
1446 {
1447         bh->b_page = page;
1448         BUG_ON(offset >= PAGE_SIZE);
1449         if (PageHighMem(page))
1450                 /*
1451                  * This catches illegal uses and preserves the offset:
1452                  */
1453                 bh->b_data = (char *)(0 + offset);
1454         else
1455                 bh->b_data = page_address(page) + offset;
1456 }
1457 EXPORT_SYMBOL(set_bh_page);
1458
1459 /*
1460  * Called when truncating a buffer on a page completely.
1461  */
1462 static void discard_buffer(struct buffer_head * bh)
1463 {
1464         lock_buffer(bh);
1465         clear_buffer_dirty(bh);
1466         bh->b_bdev = NULL;
1467         clear_buffer_mapped(bh);
1468         clear_buffer_req(bh);
1469         clear_buffer_new(bh);
1470         clear_buffer_delay(bh);
1471         clear_buffer_unwritten(bh);
1472         unlock_buffer(bh);
1473 }
1474
1475 /**
1476  * block_invalidatepage - invalidate part or all of a buffer-backed page
1477  *
1478  * @page: the page which is affected
1479  * @offset: the index of the truncation point
1480  *
1481  * block_invalidatepage() is called when all or part of the page has become
1482  * invalidated by a truncate operation.
1483  *
1484  * block_invalidatepage() does not have to release all buffers, but it must
1485  * ensure that no dirty buffer is left outside @offset and that no I/O
1486  * is underway against any of the blocks which are outside the truncation
1487  * point.  Because the caller is about to free (and possibly reuse) those
1488  * blocks on-disk.
1489  */
1490 void block_invalidatepage(struct page *page, unsigned long offset)
1491 {
1492         struct buffer_head *head, *bh, *next;
1493         unsigned int curr_off = 0;
1494
1495         BUG_ON(!PageLocked(page));
1496         if (!page_has_buffers(page))
1497                 goto out;
1498
1499         head = page_buffers(page);
1500         bh = head;
1501         do {
1502                 unsigned int next_off = curr_off + bh->b_size;
1503                 next = bh->b_this_page;
1504
1505                 /*
1506                  * is this block fully invalidated?
1507                  */
1508                 if (offset <= curr_off)
1509                         discard_buffer(bh);
1510                 curr_off = next_off;
1511                 bh = next;
1512         } while (bh != head);
1513
1514         /*
1515          * We release buffers only if the entire page is being invalidated.
1516          * The get_block cached value has been unconditionally invalidated,
1517          * so real IO is not possible anymore.
1518          */
1519         if (offset == 0)
1520                 try_to_release_page(page, 0);
1521 out:
1522         return;
1523 }
1524 EXPORT_SYMBOL(block_invalidatepage);
1525
1526 /*
1527  * We attach and possibly dirty the buffers atomically wrt
1528  * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1529  * is already excluded via the page lock.
1530  */
1531 void create_empty_buffers(struct page *page,
1532                         unsigned long blocksize, unsigned long b_state)
1533 {
1534         struct buffer_head *bh, *head, *tail;
1535
1536         head = alloc_page_buffers(page, blocksize, 1);
1537         bh = head;
1538         do {
1539                 bh->b_state |= b_state;
1540                 tail = bh;
1541                 bh = bh->b_this_page;
1542         } while (bh);
1543         tail->b_this_page = head;
1544
1545         spin_lock(&page->mapping->private_lock);
1546         if (PageUptodate(page) || PageDirty(page)) {
1547                 bh = head;
1548                 do {
1549                         if (PageDirty(page))
1550                                 set_buffer_dirty(bh);
1551                         if (PageUptodate(page))
1552                                 set_buffer_uptodate(bh);
1553                         bh = bh->b_this_page;
1554                 } while (bh != head);
1555         }
1556         attach_page_buffers(page, head);
1557         spin_unlock(&page->mapping->private_lock);
1558 }
1559 EXPORT_SYMBOL(create_empty_buffers);
1560
1561 /*
1562  * We are taking a block for data and we don't want any output from any
1563  * buffer-cache aliases starting from return from that function and
1564  * until the moment when something will explicitly mark the buffer
1565  * dirty (hopefully that will not happen until we will free that block ;-)
1566  * We don't even need to mark it not-uptodate - nobody can expect
1567  * anything from a newly allocated buffer anyway. We used to used
1568  * unmap_buffer() for such invalidation, but that was wrong. We definitely
1569  * don't want to mark the alias unmapped, for example - it would confuse
1570  * anyone who might pick it with bread() afterwards...
1571  *
1572  * Also..  Note that bforget() doesn't lock the buffer.  So there can
1573  * be writeout I/O going on against recently-freed buffers.  We don't
1574  * wait on that I/O in bforget() - it's more efficient to wait on the I/O
1575  * only if we really need to.  That happens here.
1576  */
1577 void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1578 {
1579         struct buffer_head *old_bh;
1580
1581         might_sleep();
1582
1583         old_bh = __find_get_block_slow(bdev, block);
1584         if (old_bh) {
1585                 clear_buffer_dirty(old_bh);
1586                 wait_on_buffer(old_bh);
1587                 clear_buffer_req(old_bh);
1588                 __brelse(old_bh);
1589         }
1590 }
1591 EXPORT_SYMBOL(unmap_underlying_metadata);
1592
1593 /*
1594  * NOTE! All mapped/uptodate combinations are valid:
1595  *
1596  *      Mapped  Uptodate        Meaning
1597  *
1598  *      No      No              "unknown" - must do get_block()
1599  *      No      Yes             "hole" - zero-filled
1600  *      Yes     No              "allocated" - allocated on disk, not read in
1601  *      Yes     Yes             "valid" - allocated and up-to-date in memory.
1602  *
1603  * "Dirty" is valid only with the last case (mapped+uptodate).
1604  */
1605
1606 /*
1607  * While block_write_full_page is writing back the dirty buffers under
1608  * the page lock, whoever dirtied the buffers may decide to clean them
1609  * again at any time.  We handle that by only looking at the buffer
1610  * state inside lock_buffer().
1611  *
1612  * If block_write_full_page() is called for regular writeback
1613  * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1614  * locked buffer.   This only can happen if someone has written the buffer
1615  * directly, with submit_bh().  At the address_space level PageWriteback
1616  * prevents this contention from occurring.
1617  *
1618  * If block_write_full_page() is called with wbc->sync_mode ==
1619  * WB_SYNC_ALL, the writes are posted using WRITE_SYNC; this
1620  * causes the writes to be flagged as synchronous writes.
1621  */
1622 static int __block_write_full_page(struct inode *inode, struct page *page,
1623                         get_block_t *get_block, struct writeback_control *wbc,
1624                         bh_end_io_t *handler)
1625 {
1626         int err;
1627         sector_t block;
1628         sector_t last_block;
1629         struct buffer_head *bh, *head;
1630         const unsigned blocksize = 1 << inode->i_blkbits;
1631         int nr_underway = 0;
1632         int write_op = (wbc->sync_mode == WB_SYNC_ALL ?
1633                         WRITE_SYNC : WRITE);
1634
1635         BUG_ON(!PageLocked(page));
1636
1637         last_block = (i_size_read(inode) - 1) >> inode->i_blkbits;
1638
1639         if (!page_has_buffers(page)) {
1640                 create_empty_buffers(page, blocksize,
1641                                         (1 << BH_Dirty)|(1 << BH_Uptodate));
1642         }
1643
1644         /*
1645          * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1646          * here, and the (potentially unmapped) buffers may become dirty at
1647          * any time.  If a buffer becomes dirty here after we've inspected it
1648          * then we just miss that fact, and the page stays dirty.
1649          *
1650          * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1651          * handle that here by just cleaning them.
1652          */
1653
1654         block = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
1655         head = page_buffers(page);
1656         bh = head;
1657
1658         /*
1659          * Get all the dirty buffers mapped to disk addresses and
1660          * handle any aliases from the underlying blockdev's mapping.
1661          */
1662         do {
1663                 if (block > last_block) {
1664                         /*
1665                          * mapped buffers outside i_size will occur, because
1666                          * this page can be outside i_size when there is a
1667                          * truncate in progress.
1668                          */
1669                         /*
1670                          * The buffer was zeroed by block_write_full_page()
1671                          */
1672                         clear_buffer_dirty(bh);
1673                         set_buffer_uptodate(bh);
1674                 } else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1675                            buffer_dirty(bh)) {
1676                         WARN_ON(bh->b_size != blocksize);
1677                         err = get_block(inode, block, bh, 1);
1678                         if (err)
1679                                 goto recover;
1680                         clear_buffer_delay(bh);
1681                         if (buffer_new(bh)) {
1682                                 /* blockdev mappings never come here */
1683                                 clear_buffer_new(bh);
1684                                 unmap_underlying_metadata(bh->b_bdev,
1685                                                         bh->b_blocknr);
1686                         }
1687                 }
1688                 bh = bh->b_this_page;
1689                 block++;
1690         } while (bh != head);
1691
1692         do {
1693                 if (!buffer_mapped(bh))
1694                         continue;
1695                 /*
1696                  * If it's a fully non-blocking write attempt and we cannot
1697                  * lock the buffer then redirty the page.  Note that this can
1698                  * potentially cause a busy-wait loop from writeback threads
1699                  * and kswapd activity, but those code paths have their own
1700                  * higher-level throttling.
1701                  */
1702                 if (wbc->sync_mode != WB_SYNC_NONE) {
1703                         lock_buffer(bh);
1704                 } else if (!trylock_buffer(bh)) {
1705                         redirty_page_for_writepage(wbc, page);
1706                         continue;
1707                 }
1708                 if (test_clear_buffer_dirty(bh)) {
1709                         mark_buffer_async_write_endio(bh, handler);
1710                 } else {
1711                         unlock_buffer(bh);
1712                 }
1713         } while ((bh = bh->b_this_page) != head);
1714
1715         /*
1716          * The page and its buffers are protected by PageWriteback(), so we can
1717          * drop the bh refcounts early.
1718          */
1719         BUG_ON(PageWriteback(page));
1720         set_page_writeback(page);
1721
1722         do {
1723                 struct buffer_head *next = bh->b_this_page;
1724                 if (buffer_async_write(bh)) {
1725                         submit_bh(write_op, bh);
1726                         nr_underway++;
1727                 }
1728                 bh = next;
1729         } while (bh != head);
1730         unlock_page(page);
1731
1732         err = 0;
1733 done:
1734         if (nr_underway == 0) {
1735                 /*
1736                  * The page was marked dirty, but the buffers were
1737                  * clean.  Someone wrote them back by hand with
1738                  * ll_rw_block/submit_bh.  A rare case.
1739                  */
1740                 end_page_writeback(page);
1741
1742                 /*
1743                  * The page and buffer_heads can be released at any time from
1744                  * here on.
1745                  */
1746         }
1747         return err;
1748
1749 recover:
1750         /*
1751          * ENOSPC, or some other error.  We may already have added some
1752          * blocks to the file, so we need to write these out to avoid
1753          * exposing stale data.
1754          * The page is currently locked and not marked for writeback
1755          */
1756         bh = head;
1757         /* Recovery: lock and submit the mapped buffers */
1758         do {
1759                 if (buffer_mapped(bh) && buffer_dirty(bh) &&
1760                     !buffer_delay(bh)) {
1761                         lock_buffer(bh);
1762                         mark_buffer_async_write_endio(bh, handler);
1763                 } else {
1764                         /*
1765                          * The buffer may have been set dirty during
1766                          * attachment to a dirty page.
1767                          */
1768                         clear_buffer_dirty(bh);
1769                 }
1770         } while ((bh = bh->b_this_page) != head);
1771         SetPageError(page);
1772         BUG_ON(PageWriteback(page));
1773         mapping_set_error(page->mapping, err);
1774         set_page_writeback(page);
1775         do {
1776                 struct buffer_head *next = bh->b_this_page;
1777                 if (buffer_async_write(bh)) {
1778                         clear_buffer_dirty(bh);
1779                         submit_bh(write_op, bh);
1780                         nr_underway++;
1781                 }
1782                 bh = next;
1783         } while (bh != head);
1784         unlock_page(page);
1785         goto done;
1786 }
1787
1788 /*
1789  * If a page has any new buffers, zero them out here, and mark them uptodate
1790  * and dirty so they'll be written out (in order to prevent uninitialised
1791  * block data from leaking). And clear the new bit.
1792  */
1793 void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1794 {
1795         unsigned int block_start, block_end;
1796         struct buffer_head *head, *bh;
1797
1798         BUG_ON(!PageLocked(page));
1799         if (!page_has_buffers(page))
1800                 return;
1801
1802         bh = head = page_buffers(page);
1803         block_start = 0;
1804         do {
1805                 block_end = block_start + bh->b_size;
1806
1807                 if (buffer_new(bh)) {
1808                         if (block_end > from && block_start < to) {
1809                                 if (!PageUptodate(page)) {
1810                                         unsigned start, size;
1811
1812                                         start = max(from, block_start);
1813                                         size = min(to, block_end) - start;
1814
1815                                         zero_user(page, start, size);
1816                                         set_buffer_uptodate(bh);
1817                                 }
1818
1819                                 clear_buffer_new(bh);
1820                                 mark_buffer_dirty(bh);
1821                         }
1822                 }
1823
1824                 block_start = block_end;
1825                 bh = bh->b_this_page;
1826         } while (bh != head);
1827 }
1828 EXPORT_SYMBOL(page_zero_new_buffers);
1829
1830 int __block_write_begin(struct page *page, loff_t pos, unsigned len,
1831                 get_block_t *get_block)
1832 {
1833         unsigned from = pos & (PAGE_CACHE_SIZE - 1);
1834         unsigned to = from + len;
1835         struct inode *inode = page->mapping->host;
1836         unsigned block_start, block_end;
1837         sector_t block;
1838         int err = 0;
1839         unsigned blocksize, bbits;
1840         struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1841
1842         BUG_ON(!PageLocked(page));
1843         BUG_ON(from > PAGE_CACHE_SIZE);
1844         BUG_ON(to > PAGE_CACHE_SIZE);
1845         BUG_ON(from > to);
1846
1847         blocksize = 1 << inode->i_blkbits;
1848         if (!page_has_buffers(page))
1849                 create_empty_buffers(page, blocksize, 0);
1850         head = page_buffers(page);
1851
1852         bbits = inode->i_blkbits;
1853         block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1854
1855         for(bh = head, block_start = 0; bh != head || !block_start;
1856             block++, block_start=block_end, bh = bh->b_this_page) {
1857                 block_end = block_start + blocksize;
1858                 if (block_end <= from || block_start >= to) {
1859                         if (PageUptodate(page)) {
1860                                 if (!buffer_uptodate(bh))
1861                                         set_buffer_uptodate(bh);
1862                         }
1863                         continue;
1864                 }
1865                 if (buffer_new(bh))
1866                         clear_buffer_new(bh);
1867                 if (!buffer_mapped(bh)) {
1868                         WARN_ON(bh->b_size != blocksize);
1869                         err = get_block(inode, block, bh, 1);
1870                         if (err)
1871                                 break;
1872                         if (buffer_new(bh)) {
1873                                 unmap_underlying_metadata(bh->b_bdev,
1874                                                         bh->b_blocknr);
1875                                 if (PageUptodate(page)) {
1876                                         clear_buffer_new(bh);
1877                                         set_buffer_uptodate(bh);
1878                                         mark_buffer_dirty(bh);
1879                                         continue;
1880                                 }
1881                                 if (block_end > to || block_start < from)
1882                                         zero_user_segments(page,
1883                                                 to, block_end,
1884                                                 block_start, from);
1885                                 continue;
1886                         }
1887                 }
1888                 if (PageUptodate(page)) {
1889                         if (!buffer_uptodate(bh))
1890                                 set_buffer_uptodate(bh);
1891                         continue; 
1892                 }
1893                 if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1894                     !buffer_unwritten(bh) &&
1895                      (block_start < from || block_end > to)) {
1896                         ll_rw_block(READ, 1, &bh);
1897                         *wait_bh++=bh;
1898                 }
1899         }
1900         /*
1901          * If we issued read requests - let them complete.
1902          */
1903         while(wait_bh > wait) {
1904                 wait_on_buffer(*--wait_bh);
1905                 if (!buffer_uptodate(*wait_bh))
1906                         err = -EIO;
1907         }
1908         if (unlikely(err))
1909                 page_zero_new_buffers(page, from, to);
1910         return err;
1911 }
1912 EXPORT_SYMBOL(__block_write_begin);
1913
1914 static int __block_commit_write(struct inode *inode, struct page *page,
1915                 unsigned from, unsigned to)
1916 {
1917         unsigned block_start, block_end;
1918         int partial = 0;
1919         unsigned blocksize;
1920         struct buffer_head *bh, *head;
1921
1922         blocksize = 1 << inode->i_blkbits;
1923
1924         for(bh = head = page_buffers(page), block_start = 0;
1925             bh != head || !block_start;
1926             block_start=block_end, bh = bh->b_this_page) {
1927                 block_end = block_start + blocksize;
1928                 if (block_end <= from || block_start >= to) {
1929                         if (!buffer_uptodate(bh))
1930                                 partial = 1;
1931                 } else {
1932                         set_buffer_uptodate(bh);
1933                         mark_buffer_dirty(bh);
1934                 }
1935                 clear_buffer_new(bh);
1936         }
1937
1938         /*
1939          * If this is a partial write which happened to make all buffers
1940          * uptodate then we can optimize away a bogus readpage() for
1941          * the next read(). Here we 'discover' whether the page went
1942          * uptodate as a result of this (potentially partial) write.
1943          */
1944         if (!partial)
1945                 SetPageUptodate(page);
1946         return 0;
1947 }
1948
1949 /*
1950  * block_write_begin takes care of the basic task of block allocation and
1951  * bringing partial write blocks uptodate first.
1952  *
1953  * The filesystem needs to handle block truncation upon failure.
1954  */
1955 int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
1956                 unsigned flags, struct page **pagep, get_block_t *get_block)
1957 {
1958         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
1959         struct page *page;
1960         int status;
1961
1962         page = grab_cache_page_write_begin(mapping, index, flags);
1963         if (!page)
1964                 return -ENOMEM;
1965
1966         status = __block_write_begin(page, pos, len, get_block);
1967         if (unlikely(status)) {
1968                 unlock_page(page);
1969                 page_cache_release(page);
1970                 page = NULL;
1971         }
1972
1973         *pagep = page;
1974         return status;
1975 }
1976 EXPORT_SYMBOL(block_write_begin);
1977
1978 int block_write_end(struct file *file, struct address_space *mapping,
1979                         loff_t pos, unsigned len, unsigned copied,
1980                         struct page *page, void *fsdata)
1981 {
1982         struct inode *inode = mapping->host;
1983         unsigned start;
1984
1985         start = pos & (PAGE_CACHE_SIZE - 1);
1986
1987         if (unlikely(copied < len)) {
1988                 /*
1989                  * The buffers that were written will now be uptodate, so we
1990                  * don't have to worry about a readpage reading them and
1991                  * overwriting a partial write. However if we have encountered
1992                  * a short write and only partially written into a buffer, it
1993                  * will not be marked uptodate, so a readpage might come in and
1994                  * destroy our partial write.
1995                  *
1996                  * Do the simplest thing, and just treat any short write to a
1997                  * non uptodate page as a zero-length write, and force the
1998                  * caller to redo the whole thing.
1999                  */
2000                 if (!PageUptodate(page))
2001                         copied = 0;
2002
2003                 page_zero_new_buffers(page, start+copied, start+len);
2004         }
2005         flush_dcache_page(page);
2006
2007         /* This could be a short (even 0-length) commit */
2008         __block_commit_write(inode, page, start, start+copied);
2009
2010         return copied;
2011 }
2012 EXPORT_SYMBOL(block_write_end);
2013
2014 int generic_write_end(struct file *file, struct address_space *mapping,
2015                         loff_t pos, unsigned len, unsigned copied,
2016                         struct page *page, void *fsdata)
2017 {
2018         struct inode *inode = mapping->host;
2019         int i_size_changed = 0;
2020
2021         copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2022
2023         /*
2024          * No need to use i_size_read() here, the i_size
2025          * cannot change under us because we hold i_mutex.
2026          *
2027          * But it's important to update i_size while still holding page lock:
2028          * page writeout could otherwise come in and zero beyond i_size.
2029          */
2030         if (pos+copied > inode->i_size) {
2031                 i_size_write(inode, pos+copied);
2032                 i_size_changed = 1;
2033         }
2034
2035         unlock_page(page);
2036         page_cache_release(page);
2037
2038         /*
2039          * Don't mark the inode dirty under page lock. First, it unnecessarily
2040          * makes the holding time of page lock longer. Second, it forces lock
2041          * ordering of page lock and transaction start for journaling
2042          * filesystems.
2043          */
2044         if (i_size_changed)
2045                 mark_inode_dirty(inode);
2046
2047         return copied;
2048 }
2049 EXPORT_SYMBOL(generic_write_end);
2050
2051 /*
2052  * block_is_partially_uptodate checks whether buffers within a page are
2053  * uptodate or not.
2054  *
2055  * Returns true if all buffers which correspond to a file portion
2056  * we want to read are uptodate.
2057  */
2058 int block_is_partially_uptodate(struct page *page, read_descriptor_t *desc,
2059                                         unsigned long from)
2060 {
2061         struct inode *inode = page->mapping->host;
2062         unsigned block_start, block_end, blocksize;
2063         unsigned to;
2064         struct buffer_head *bh, *head;
2065         int ret = 1;
2066
2067         if (!page_has_buffers(page))
2068                 return 0;
2069
2070         blocksize = 1 << inode->i_blkbits;
2071         to = min_t(unsigned, PAGE_CACHE_SIZE - from, desc->count);
2072         to = from + to;
2073         if (from < blocksize && to > PAGE_CACHE_SIZE - blocksize)
2074                 return 0;
2075
2076         head = page_buffers(page);
2077         bh = head;
2078         block_start = 0;
2079         do {
2080                 block_end = block_start + blocksize;
2081                 if (block_end > from && block_start < to) {
2082                         if (!buffer_uptodate(bh)) {
2083                                 ret = 0;
2084                                 break;
2085                         }
2086                         if (block_end >= to)
2087                                 break;
2088                 }
2089                 block_start = block_end;
2090                 bh = bh->b_this_page;
2091         } while (bh != head);
2092
2093         return ret;
2094 }
2095 EXPORT_SYMBOL(block_is_partially_uptodate);
2096
2097 /*
2098  * Generic "read page" function for block devices that have the normal
2099  * get_block functionality. This is most of the block device filesystems.
2100  * Reads the page asynchronously --- the unlock_buffer() and
2101  * set/clear_buffer_uptodate() functions propagate buffer state into the
2102  * page struct once IO has completed.
2103  */
2104 int block_read_full_page(struct page *page, get_block_t *get_block)
2105 {
2106         struct inode *inode = page->mapping->host;
2107         sector_t iblock, lblock;
2108         struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2109         unsigned int blocksize;
2110         int nr, i;
2111         int fully_mapped = 1;
2112
2113         BUG_ON(!PageLocked(page));
2114         blocksize = 1 << inode->i_blkbits;
2115         if (!page_has_buffers(page))
2116                 create_empty_buffers(page, blocksize, 0);
2117         head = page_buffers(page);
2118
2119         iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2120         lblock = (i_size_read(inode)+blocksize-1) >> inode->i_blkbits;
2121         bh = head;
2122         nr = 0;
2123         i = 0;
2124
2125         do {
2126                 if (buffer_uptodate(bh))
2127                         continue;
2128
2129                 if (!buffer_mapped(bh)) {
2130                         int err = 0;
2131
2132                         fully_mapped = 0;
2133                         if (iblock < lblock) {
2134                                 WARN_ON(bh->b_size != blocksize);
2135                                 err = get_block(inode, iblock, bh, 0);
2136                                 if (err)
2137                                         SetPageError(page);
2138                         }
2139                         if (!buffer_mapped(bh)) {
2140                                 zero_user(page, i * blocksize, blocksize);
2141                                 if (!err)
2142                                         set_buffer_uptodate(bh);
2143                                 continue;
2144                         }
2145                         /*
2146                          * get_block() might have updated the buffer
2147                          * synchronously
2148                          */
2149                         if (buffer_uptodate(bh))
2150                                 continue;
2151                 }
2152                 arr[nr++] = bh;
2153         } while (i++, iblock++, (bh = bh->b_this_page) != head);
2154
2155         if (fully_mapped)
2156                 SetPageMappedToDisk(page);
2157
2158         if (!nr) {
2159                 /*
2160                  * All buffers are uptodate - we can set the page uptodate
2161                  * as well. But not if get_block() returned an error.
2162                  */
2163                 if (!PageError(page))
2164                         SetPageUptodate(page);
2165                 unlock_page(page);
2166                 return 0;
2167         }
2168
2169         /* Stage two: lock the buffers */
2170         for (i = 0; i < nr; i++) {
2171                 bh = arr[i];
2172                 lock_buffer(bh);
2173                 mark_buffer_async_read(bh);
2174         }
2175
2176         /*
2177          * Stage 3: start the IO.  Check for uptodateness
2178          * inside the buffer lock in case another process reading
2179          * the underlying blockdev brought it uptodate (the sct fix).
2180          */
2181         for (i = 0; i < nr; i++) {
2182                 bh = arr[i];
2183                 if (buffer_uptodate(bh))
2184                         end_buffer_async_read(bh, 1);
2185                 else
2186                         submit_bh(READ, bh);
2187         }
2188         return 0;
2189 }
2190 EXPORT_SYMBOL(block_read_full_page);
2191
2192 /* utility function for filesystems that need to do work on expanding
2193  * truncates.  Uses filesystem pagecache writes to allow the filesystem to
2194  * deal with the hole.  
2195  */
2196 int generic_cont_expand_simple(struct inode *inode, loff_t size)
2197 {
2198         struct address_space *mapping = inode->i_mapping;
2199         struct page *page;
2200         void *fsdata;
2201         int err;
2202
2203         err = inode_newsize_ok(inode, size);
2204         if (err)
2205                 goto out;
2206
2207         err = pagecache_write_begin(NULL, mapping, size, 0,
2208                                 AOP_FLAG_UNINTERRUPTIBLE|AOP_FLAG_CONT_EXPAND,
2209                                 &page, &fsdata);
2210         if (err)
2211                 goto out;
2212
2213         err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2214         BUG_ON(err > 0);
2215
2216 out:
2217         return err;
2218 }
2219 EXPORT_SYMBOL(generic_cont_expand_simple);
2220
2221 static int cont_expand_zero(struct file *file, struct address_space *mapping,
2222                             loff_t pos, loff_t *bytes)
2223 {
2224         struct inode *inode = mapping->host;
2225         unsigned blocksize = 1 << inode->i_blkbits;
2226         struct page *page;
2227         void *fsdata;
2228         pgoff_t index, curidx;
2229         loff_t curpos;
2230         unsigned zerofrom, offset, len;
2231         int err = 0;
2232
2233         index = pos >> PAGE_CACHE_SHIFT;
2234         offset = pos & ~PAGE_CACHE_MASK;
2235
2236         while (index > (curidx = (curpos = *bytes)>>PAGE_CACHE_SHIFT)) {
2237                 zerofrom = curpos & ~PAGE_CACHE_MASK;
2238                 if (zerofrom & (blocksize-1)) {
2239                         *bytes |= (blocksize-1);
2240                         (*bytes)++;
2241                 }
2242                 len = PAGE_CACHE_SIZE - zerofrom;
2243
2244                 err = pagecache_write_begin(file, mapping, curpos, len,
2245                                                 AOP_FLAG_UNINTERRUPTIBLE,
2246                                                 &page, &fsdata);
2247                 if (err)
2248                         goto out;
2249                 zero_user(page, zerofrom, len);
2250                 err = pagecache_write_end(file, mapping, curpos, len, len,
2251                                                 page, fsdata);
2252                 if (err < 0)
2253                         goto out;
2254                 BUG_ON(err != len);
2255                 err = 0;
2256
2257                 balance_dirty_pages_ratelimited(mapping);
2258         }
2259
2260         /* page covers the boundary, find the boundary offset */
2261         if (index == curidx) {
2262                 zerofrom = curpos & ~PAGE_CACHE_MASK;
2263                 /* if we will expand the thing last block will be filled */
2264                 if (offset <= zerofrom) {
2265                         goto out;
2266                 }
2267                 if (zerofrom & (blocksize-1)) {
2268                         *bytes |= (blocksize-1);
2269                         (*bytes)++;
2270                 }
2271                 len = offset - zerofrom;
2272
2273                 err = pagecache_write_begin(file, mapping, curpos, len,
2274                                                 AOP_FLAG_UNINTERRUPTIBLE,
2275                                                 &page, &fsdata);
2276                 if (err)
2277                         goto out;
2278                 zero_user(page, zerofrom, len);
2279                 err = pagecache_write_end(file, mapping, curpos, len, len,
2280                                                 page, fsdata);
2281                 if (err < 0)
2282                         goto out;
2283                 BUG_ON(err != len);
2284                 err = 0;
2285         }
2286 out:
2287         return err;
2288 }
2289
2290 /*
2291  * For moronic filesystems that do not allow holes in file.
2292  * We may have to extend the file.
2293  */
2294 int cont_write_begin(struct file *file, struct address_space *mapping,
2295                         loff_t pos, unsigned len, unsigned flags,
2296                         struct page **pagep, void **fsdata,
2297                         get_block_t *get_block, loff_t *bytes)
2298 {
2299         struct inode *inode = mapping->host;
2300         unsigned blocksize = 1 << inode->i_blkbits;
2301         unsigned zerofrom;
2302         int err;
2303
2304         err = cont_expand_zero(file, mapping, pos, bytes);
2305         if (err)
2306                 return err;
2307
2308         zerofrom = *bytes & ~PAGE_CACHE_MASK;
2309         if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2310                 *bytes |= (blocksize-1);
2311                 (*bytes)++;
2312         }
2313
2314         return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2315 }
2316 EXPORT_SYMBOL(cont_write_begin);
2317
2318 int block_commit_write(struct page *page, unsigned from, unsigned to)
2319 {
2320         struct inode *inode = page->mapping->host;
2321         __block_commit_write(inode,page,from,to);
2322         return 0;
2323 }
2324 EXPORT_SYMBOL(block_commit_write);
2325
2326 /*
2327  * block_page_mkwrite() is not allowed to change the file size as it gets
2328  * called from a page fault handler when a page is first dirtied. Hence we must
2329  * be careful to check for EOF conditions here. We set the page up correctly
2330  * for a written page which means we get ENOSPC checking when writing into
2331  * holes and correct delalloc and unwritten extent mapping on filesystems that
2332  * support these features.
2333  *
2334  * We are not allowed to take the i_mutex here so we have to play games to
2335  * protect against truncate races as the page could now be beyond EOF.  Because
2336  * truncate writes the inode size before removing pages, once we have the
2337  * page lock we can determine safely if the page is beyond EOF. If it is not
2338  * beyond EOF, then the page is guaranteed safe against truncation until we
2339  * unlock the page.
2340  *
2341  * Direct callers of this function should call vfs_check_frozen() so that page
2342  * fault does not busyloop until the fs is thawed.
2343  */
2344 int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2345                          get_block_t get_block)
2346 {
2347         struct page *page = vmf->page;
2348         struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
2349         unsigned long end;
2350         loff_t size;
2351         int ret;
2352
2353         lock_page(page);
2354         size = i_size_read(inode);
2355         if ((page->mapping != inode->i_mapping) ||
2356             (page_offset(page) > size)) {
2357                 /* We overload EFAULT to mean page got truncated */
2358                 ret = -EFAULT;
2359                 goto out_unlock;
2360         }
2361
2362         /* page is wholly or partially inside EOF */
2363         if (((page->index + 1) << PAGE_CACHE_SHIFT) > size)
2364                 end = size & ~PAGE_CACHE_MASK;
2365         else
2366                 end = PAGE_CACHE_SIZE;
2367
2368         ret = __block_write_begin(page, 0, end, get_block);
2369         if (!ret)
2370                 ret = block_commit_write(page, 0, end);
2371
2372         if (unlikely(ret < 0))
2373                 goto out_unlock;
2374         /*
2375          * Freezing in progress? We check after the page is marked dirty and
2376          * with page lock held so if the test here fails, we are sure freezing
2377          * code will wait during syncing until the page fault is done - at that
2378          * point page will be dirty and unlocked so freezing code will write it
2379          * and writeprotect it again.
2380          */
2381         set_page_dirty(page);
2382         if (inode->i_sb->s_frozen != SB_UNFROZEN) {
2383                 ret = -EAGAIN;
2384                 goto out_unlock;
2385         }
2386         wait_on_page_writeback(page);
2387         return 0;
2388 out_unlock:
2389         unlock_page(page);
2390         return ret;
2391 }
2392 EXPORT_SYMBOL(__block_page_mkwrite);
2393
2394 int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2395                    get_block_t get_block)
2396 {
2397         int ret;
2398         struct super_block *sb = vma->vm_file->f_path.dentry->d_inode->i_sb;
2399
2400         /*
2401          * This check is racy but catches the common case. The check in
2402          * __block_page_mkwrite() is reliable.
2403          */
2404         vfs_check_frozen(sb, SB_FREEZE_WRITE);
2405         ret = __block_page_mkwrite(vma, vmf, get_block);
2406         return block_page_mkwrite_return(ret);
2407 }
2408 EXPORT_SYMBOL(block_page_mkwrite);
2409
2410 /*
2411  * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2412  * immediately, while under the page lock.  So it needs a special end_io
2413  * handler which does not touch the bh after unlocking it.
2414  */
2415 static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2416 {
2417         __end_buffer_read_notouch(bh, uptodate);
2418 }
2419
2420 /*
2421  * Attach the singly-linked list of buffers created by nobh_write_begin, to
2422  * the page (converting it to circular linked list and taking care of page
2423  * dirty races).
2424  */
2425 static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2426 {
2427         struct buffer_head *bh;
2428
2429         BUG_ON(!PageLocked(page));
2430
2431         spin_lock(&page->mapping->private_lock);
2432         bh = head;
2433         do {
2434                 if (PageDirty(page))
2435                         set_buffer_dirty(bh);
2436                 if (!bh->b_this_page)
2437                         bh->b_this_page = head;
2438                 bh = bh->b_this_page;
2439         } while (bh != head);
2440         attach_page_buffers(page, head);
2441         spin_unlock(&page->mapping->private_lock);
2442 }
2443
2444 /*
2445  * On entry, the page is fully not uptodate.
2446  * On exit the page is fully uptodate in the areas outside (from,to)
2447  * The filesystem needs to handle block truncation upon failure.
2448  */
2449 int nobh_write_begin(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                 ret = __block_write_begin(page, pos, len, get_block);
2480                 if (unlikely(ret))
2481                         goto out_release;
2482                 return ret;
2483         }
2484
2485         if (PageMappedToDisk(page))
2486                 return 0;
2487
2488         /*
2489          * Allocate buffers so that we can keep track of state, and potentially
2490          * attach them to the page if an error occurs. In the common case of
2491          * no error, they will just be freed again without ever being attached
2492          * to the page (which is all OK, because we're under the page lock).
2493          *
2494          * Be careful: the buffer linked list is a NULL terminated one, rather
2495          * than the circular one we're used to.
2496          */
2497         head = alloc_page_buffers(page, blocksize, 0);
2498         if (!head) {
2499                 ret = -ENOMEM;
2500                 goto out_release;
2501         }
2502
2503         block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
2504
2505         /*
2506          * We loop across all blocks in the page, whether or not they are
2507          * part of the affected region.  This is so we can discover if the
2508          * page is fully mapped-to-disk.
2509          */
2510         for (block_start = 0, block_in_page = 0, bh = head;
2511                   block_start < PAGE_CACHE_SIZE;
2512                   block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2513                 int create;
2514
2515                 block_end = block_start + blocksize;
2516                 bh->b_state = 0;
2517                 create = 1;
2518                 if (block_start >= to)
2519                         create = 0;
2520                 ret = get_block(inode, block_in_file + block_in_page,
2521                                         bh, create);
2522                 if (ret)
2523                         goto failed;
2524                 if (!buffer_mapped(bh))
2525                         is_mapped_to_disk = 0;
2526                 if (buffer_new(bh))
2527                         unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
2528                 if (PageUptodate(page)) {
2529                         set_buffer_uptodate(bh);
2530                         continue;
2531                 }
2532                 if (buffer_new(bh) || !buffer_mapped(bh)) {
2533                         zero_user_segments(page, block_start, from,
2534                                                         to, block_end);
2535                         continue;
2536                 }
2537                 if (buffer_uptodate(bh))
2538                         continue;       /* reiserfs does this */
2539                 if (block_start < from || block_end > to) {
2540                         lock_buffer(bh);
2541                         bh->b_end_io = end_buffer_read_nobh;
2542                         submit_bh(READ, bh);
2543                         nr_reads++;
2544                 }
2545         }
2546
2547         if (nr_reads) {
2548                 /*
2549                  * The page is locked, so these buffers are protected from
2550                  * any VM or truncate activity.  Hence we don't need to care
2551                  * for the buffer_head refcounts.
2552                  */
2553                 for (bh = head; bh; bh = bh->b_this_page) {
2554                         wait_on_buffer(bh);
2555                         if (!buffer_uptodate(bh))
2556                                 ret = -EIO;
2557                 }
2558                 if (ret)
2559                         goto failed;
2560         }
2561
2562         if (is_mapped_to_disk)
2563                 SetPageMappedToDisk(page);
2564
2565         *fsdata = head; /* to be released by nobh_write_end */
2566
2567         return 0;
2568
2569 failed:
2570         BUG_ON(!ret);
2571         /*
2572          * Error recovery is a bit difficult. We need to zero out blocks that
2573          * were newly allocated, and dirty them to ensure they get written out.
2574          * Buffers need to be attached to the page at this point, otherwise
2575          * the handling of potential IO errors during writeout would be hard
2576          * (could try doing synchronous writeout, but what if that fails too?)
2577          */
2578         attach_nobh_buffers(page, head);
2579         page_zero_new_buffers(page, from, to);
2580
2581 out_release:
2582         unlock_page(page);
2583         page_cache_release(page);
2584         *pagep = NULL;
2585
2586         return ret;
2587 }
2588 EXPORT_SYMBOL(nobh_write_begin);
2589
2590 int nobh_write_end(struct file *file, struct address_space *mapping,
2591                         loff_t pos, unsigned len, unsigned copied,
2592                         struct page *page, void *fsdata)
2593 {
2594         struct inode *inode = page->mapping->host;
2595         struct buffer_head *head = fsdata;
2596         struct buffer_head *bh;
2597         BUG_ON(fsdata != NULL && page_has_buffers(page));
2598
2599         if (unlikely(copied < len) && head)
2600                 attach_nobh_buffers(page, head);
2601         if (page_has_buffers(page))
2602                 return generic_write_end(file, mapping, pos, len,
2603                                         copied, page, fsdata);
2604
2605         SetPageUptodate(page);
2606         set_page_dirty(page);
2607         if (pos+copied > inode->i_size) {
2608                 i_size_write(inode, pos+copied);
2609                 mark_inode_dirty(inode);
2610         }
2611
2612         unlock_page(page);
2613         page_cache_release(page);
2614
2615         while (head) {
2616                 bh = head;
2617                 head = head->b_this_page;
2618                 free_buffer_head(bh);
2619         }
2620
2621         return copied;
2622 }
2623 EXPORT_SYMBOL(nobh_write_end);
2624
2625 /*
2626  * nobh_writepage() - based on block_full_write_page() except
2627  * that it tries to operate without attaching bufferheads to
2628  * the page.
2629  */
2630 int nobh_writepage(struct page *page, get_block_t *get_block,
2631                         struct writeback_control *wbc)
2632 {
2633         struct inode * const inode = page->mapping->host;
2634         loff_t i_size = i_size_read(inode);
2635         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2636         unsigned offset;
2637         int ret;
2638
2639         /* Is the page fully inside i_size? */
2640         if (page->index < end_index)
2641                 goto out;
2642
2643         /* Is the page fully outside i_size? (truncate in progress) */
2644         offset = i_size & (PAGE_CACHE_SIZE-1);
2645         if (page->index >= end_index+1 || !offset) {
2646                 /*
2647                  * The page may have dirty, unmapped buffers.  For example,
2648                  * they may have been added in ext3_writepage().  Make them
2649                  * freeable here, so the page does not leak.
2650                  */
2651 #if 0
2652                 /* Not really sure about this  - do we need this ? */
2653                 if (page->mapping->a_ops->invalidatepage)
2654                         page->mapping->a_ops->invalidatepage(page, offset);
2655 #endif
2656                 unlock_page(page);
2657                 return 0; /* don't care */
2658         }
2659
2660         /*
2661          * The page straddles i_size.  It must be zeroed out on each and every
2662          * writepage invocation because it may be mmapped.  "A file is mapped
2663          * in multiples of the page size.  For a file that is not a multiple of
2664          * the  page size, the remaining memory is zeroed when mapped, and
2665          * writes to that region are not written out to the file."
2666          */
2667         zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2668 out:
2669         ret = mpage_writepage(page, get_block, wbc);
2670         if (ret == -EAGAIN)
2671                 ret = __block_write_full_page(inode, page, get_block, wbc,
2672                                               end_buffer_async_write);
2673         return ret;
2674 }
2675 EXPORT_SYMBOL(nobh_writepage);
2676
2677 int nobh_truncate_page(struct address_space *mapping,
2678                         loff_t from, get_block_t *get_block)
2679 {
2680         pgoff_t index = from >> PAGE_CACHE_SHIFT;
2681         unsigned offset = from & (PAGE_CACHE_SIZE-1);
2682         unsigned blocksize;
2683         sector_t iblock;
2684         unsigned length, pos;
2685         struct inode *inode = mapping->host;
2686         struct page *page;
2687         struct buffer_head map_bh;
2688         int err;
2689
2690         blocksize = 1 << inode->i_blkbits;
2691         length = offset & (blocksize - 1);
2692
2693         /* Block boundary? Nothing to do */
2694         if (!length)
2695                 return 0;
2696
2697         length = blocksize - length;
2698         iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2699
2700         page = grab_cache_page(mapping, index);
2701         err = -ENOMEM;
2702         if (!page)
2703                 goto out;
2704
2705         if (page_has_buffers(page)) {
2706 has_buffers:
2707                 unlock_page(page);
2708                 page_cache_release(page);
2709                 return block_truncate_page(mapping, from, get_block);
2710         }
2711
2712         /* Find the buffer that contains "offset" */
2713         pos = blocksize;
2714         while (offset >= pos) {
2715                 iblock++;
2716                 pos += blocksize;
2717         }
2718
2719         map_bh.b_size = blocksize;
2720         map_bh.b_state = 0;
2721         err = get_block(inode, iblock, &map_bh, 0);
2722         if (err)
2723                 goto unlock;
2724         /* unmapped? It's a hole - nothing to do */
2725         if (!buffer_mapped(&map_bh))
2726                 goto unlock;
2727
2728         /* Ok, it's mapped. Make sure it's up-to-date */
2729         if (!PageUptodate(page)) {
2730                 err = mapping->a_ops->readpage(NULL, page);
2731                 if (err) {
2732                         page_cache_release(page);
2733                         goto out;
2734                 }
2735                 lock_page(page);
2736                 if (!PageUptodate(page)) {
2737                         err = -EIO;
2738                         goto unlock;
2739                 }
2740                 if (page_has_buffers(page))
2741                         goto has_buffers;
2742         }
2743         zero_user(page, offset, length);
2744         set_page_dirty(page);
2745         err = 0;
2746
2747 unlock:
2748         unlock_page(page);
2749         page_cache_release(page);
2750 out:
2751         return err;
2752 }
2753 EXPORT_SYMBOL(nobh_truncate_page);
2754
2755 int block_truncate_page(struct address_space *mapping,
2756                         loff_t from, get_block_t *get_block)
2757 {
2758         pgoff_t index = from >> PAGE_CACHE_SHIFT;
2759         unsigned offset = from & (PAGE_CACHE_SIZE-1);
2760         unsigned blocksize;
2761         sector_t iblock;
2762         unsigned length, pos;
2763         struct inode *inode = mapping->host;
2764         struct page *page;
2765         struct buffer_head *bh;
2766         int err;
2767
2768         blocksize = 1 << inode->i_blkbits;
2769         length = offset & (blocksize - 1);
2770
2771         /* Block boundary? Nothing to do */
2772         if (!length)
2773                 return 0;
2774
2775         length = blocksize - length;
2776         iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2777         
2778         page = grab_cache_page(mapping, index);
2779         err = -ENOMEM;
2780         if (!page)
2781                 goto out;
2782
2783         if (!page_has_buffers(page))
2784                 create_empty_buffers(page, blocksize, 0);
2785
2786         /* Find the buffer that contains "offset" */
2787         bh = page_buffers(page);
2788         pos = blocksize;
2789         while (offset >= pos) {
2790                 bh = bh->b_this_page;
2791                 iblock++;
2792                 pos += blocksize;
2793         }
2794
2795         err = 0;
2796         if (!buffer_mapped(bh)) {
2797                 WARN_ON(bh->b_size != blocksize);
2798                 err = get_block(inode, iblock, bh, 0);
2799                 if (err)
2800                         goto unlock;
2801                 /* unmapped? It's a hole - nothing to do */
2802                 if (!buffer_mapped(bh))
2803                         goto unlock;
2804         }
2805
2806         /* Ok, it's mapped. Make sure it's up-to-date */
2807         if (PageUptodate(page))
2808                 set_buffer_uptodate(bh);
2809
2810         if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2811                 err = -EIO;
2812                 ll_rw_block(READ, 1, &bh);
2813                 wait_on_buffer(bh);
2814                 /* Uhhuh. Read error. Complain and punt. */
2815                 if (!buffer_uptodate(bh))
2816                         goto unlock;
2817         }
2818
2819         zero_user(page, offset, length);
2820         mark_buffer_dirty(bh);
2821         err = 0;
2822
2823 unlock:
2824         unlock_page(page);
2825         page_cache_release(page);
2826 out:
2827         return err;
2828 }
2829 EXPORT_SYMBOL(block_truncate_page);
2830
2831 /*
2832  * The generic ->writepage function for buffer-backed address_spaces
2833  * this form passes in the end_io handler used to finish the IO.
2834  */
2835 int block_write_full_page_endio(struct page *page, get_block_t *get_block,
2836                         struct writeback_control *wbc, bh_end_io_t *handler)
2837 {
2838         struct inode * const inode = page->mapping->host;
2839         loff_t i_size = i_size_read(inode);
2840         const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2841         unsigned offset;
2842
2843         /* Is the page fully inside i_size? */
2844         if (page->index < end_index)
2845                 return __block_write_full_page(inode, page, get_block, wbc,
2846                                                handler);
2847
2848         /* Is the page fully outside i_size? (truncate in progress) */
2849         offset = i_size & (PAGE_CACHE_SIZE-1);
2850         if (page->index >= end_index+1 || !offset) {
2851                 /*
2852                  * The page may have dirty, unmapped buffers.  For example,
2853                  * they may have been added in ext3_writepage().  Make them
2854                  * freeable here, so the page does not leak.
2855                  */
2856                 do_invalidatepage(page, 0);
2857                 unlock_page(page);
2858                 return 0; /* don't care */
2859         }
2860
2861         /*
2862          * The page straddles i_size.  It must be zeroed out on each and every
2863          * writepage invocation because it may be mmapped.  "A file is mapped
2864          * in multiples of the page size.  For a file that is not a multiple of
2865          * the  page size, the remaining memory is zeroed when mapped, and
2866          * writes to that region are not written out to the file."
2867          */
2868         zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2869         return __block_write_full_page(inode, page, get_block, wbc, handler);
2870 }
2871 EXPORT_SYMBOL(block_write_full_page_endio);
2872
2873 /*
2874  * The generic ->writepage function for buffer-backed address_spaces
2875  */
2876 int block_write_full_page(struct page *page, get_block_t *get_block,
2877                         struct writeback_control *wbc)
2878 {
2879         return block_write_full_page_endio(page, get_block, wbc,
2880                                            end_buffer_async_write);
2881 }
2882 EXPORT_SYMBOL(block_write_full_page);
2883
2884 sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2885                             get_block_t *get_block)
2886 {
2887         struct buffer_head tmp;
2888         struct inode *inode = mapping->host;
2889         tmp.b_state = 0;
2890         tmp.b_blocknr = 0;
2891         tmp.b_size = 1 << inode->i_blkbits;
2892         get_block(inode, block, &tmp, 0);
2893         return tmp.b_blocknr;
2894 }
2895 EXPORT_SYMBOL(generic_block_bmap);
2896
2897 static void end_bio_bh_io_sync(struct bio *bio, int err)
2898 {
2899         struct buffer_head *bh = bio->bi_private;
2900
2901         if (err == -EOPNOTSUPP) {
2902                 set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
2903         }
2904
2905         if (unlikely (test_bit(BIO_QUIET,&bio->bi_flags)))
2906                 set_bit(BH_Quiet, &bh->b_state);
2907
2908         bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
2909         bio_put(bio);
2910 }
2911
2912 int submit_bh(int rw, struct buffer_head * bh)
2913 {
2914         struct bio *bio;
2915         int ret = 0;
2916
2917         BUG_ON(!buffer_locked(bh));
2918         BUG_ON(!buffer_mapped(bh));
2919         BUG_ON(!bh->b_end_io);
2920         BUG_ON(buffer_delay(bh));
2921         BUG_ON(buffer_unwritten(bh));
2922
2923         /*
2924          * Only clear out a write error when rewriting
2925          */
2926         if (test_set_buffer_req(bh) && (rw & WRITE))
2927                 clear_buffer_write_io_error(bh);
2928
2929         /*
2930          * from here on down, it's all bio -- do the initial mapping,
2931          * submit_bio -> generic_make_request may further map this bio around
2932          */
2933         bio = bio_alloc(GFP_NOIO, 1);
2934
2935         bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
2936         bio->bi_bdev = bh->b_bdev;
2937         bio->bi_io_vec[0].bv_page = bh->b_page;
2938         bio->bi_io_vec[0].bv_len = bh->b_size;
2939         bio->bi_io_vec[0].bv_offset = bh_offset(bh);
2940
2941         bio->bi_vcnt = 1;
2942         bio->bi_idx = 0;
2943         bio->bi_size = bh->b_size;
2944
2945         bio->bi_end_io = end_bio_bh_io_sync;
2946         bio->bi_private = bh;
2947
2948         bio_get(bio);
2949         submit_bio(rw, bio);
2950
2951         if (bio_flagged(bio, BIO_EOPNOTSUPP))
2952                 ret = -EOPNOTSUPP;
2953
2954         bio_put(bio);
2955         return ret;
2956 }
2957 EXPORT_SYMBOL(submit_bh);
2958
2959 /**
2960  * ll_rw_block: low-level access to block devices (DEPRECATED)
2961  * @rw: whether to %READ or %WRITE or maybe %READA (readahead)
2962  * @nr: number of &struct buffer_heads in the array
2963  * @bhs: array of pointers to &struct buffer_head
2964  *
2965  * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
2966  * requests an I/O operation on them, either a %READ or a %WRITE.  The third
2967  * %READA option is described in the documentation for generic_make_request()
2968  * which ll_rw_block() calls.
2969  *
2970  * This function drops any buffer that it cannot get a lock on (with the
2971  * BH_Lock state bit), any buffer that appears to be clean when doing a write
2972  * request, and any buffer that appears to be up-to-date when doing read
2973  * request.  Further it marks as clean buffers that are processed for
2974  * writing (the buffer cache won't assume that they are actually clean
2975  * until the buffer gets unlocked).
2976  *
2977  * ll_rw_block sets b_end_io to simple completion handler that marks
2978  * the buffer up-to-date (if approriate), unlocks the buffer and wakes
2979  * any waiters. 
2980  *
2981  * All of the buffers must be for the same device, and must also be a
2982  * multiple of the current approved size for the device.
2983  */
2984 void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
2985 {
2986         int i;
2987
2988         for (i = 0; i < nr; i++) {
2989                 struct buffer_head *bh = bhs[i];
2990
2991                 if (!trylock_buffer(bh))
2992                         continue;
2993                 if (rw == WRITE) {
2994                         if (test_clear_buffer_dirty(bh)) {
2995                                 bh->b_end_io = end_buffer_write_sync;
2996                                 get_bh(bh);
2997                                 submit_bh(WRITE, bh);
2998                                 continue;
2999                         }
3000                 } else {
3001                         if (!buffer_uptodate(bh)) {
3002                                 bh->b_end_io = end_buffer_read_sync;
3003                                 get_bh(bh);
3004                                 submit_bh(rw, bh);
3005                                 continue;
3006                         }
3007                 }
3008                 unlock_buffer(bh);
3009         }
3010 }
3011 EXPORT_SYMBOL(ll_rw_block);
3012
3013 void write_dirty_buffer(struct buffer_head *bh, int rw)
3014 {
3015         lock_buffer(bh);
3016         if (!test_clear_buffer_dirty(bh)) {
3017                 unlock_buffer(bh);
3018                 return;
3019         }
3020         bh->b_end_io = end_buffer_write_sync;
3021         get_bh(bh);
3022         submit_bh(rw, bh);
3023 }
3024 EXPORT_SYMBOL(write_dirty_buffer);
3025
3026 /*
3027  * For a data-integrity writeout, we need to wait upon any in-progress I/O
3028  * and then start new I/O and then wait upon it.  The caller must have a ref on
3029  * the buffer_head.
3030  */
3031 int __sync_dirty_buffer(struct buffer_head *bh, int rw)
3032 {
3033         int ret = 0;
3034
3035         WARN_ON(atomic_read(&bh->b_count) < 1);
3036         lock_buffer(bh);
3037         if (test_clear_buffer_dirty(bh)) {
3038                 get_bh(bh);
3039                 bh->b_end_io = end_buffer_write_sync;
3040                 ret = submit_bh(rw, bh);
3041                 wait_on_buffer(bh);
3042                 if (!ret && !buffer_uptodate(bh))
3043                         ret = -EIO;
3044         } else {
3045                 unlock_buffer(bh);
3046         }
3047         return ret;
3048 }
3049 EXPORT_SYMBOL(__sync_dirty_buffer);
3050
3051 int sync_dirty_buffer(struct buffer_head *bh)
3052 {
3053         return __sync_dirty_buffer(bh, WRITE_SYNC);
3054 }
3055 EXPORT_SYMBOL(sync_dirty_buffer);
3056
3057 /*
3058  * try_to_free_buffers() checks if all the buffers on this particular page
3059  * are unused, and releases them if so.
3060  *
3061  * Exclusion against try_to_free_buffers may be obtained by either
3062  * locking the page or by holding its mapping's private_lock.
3063  *
3064  * If the page is dirty but all the buffers are clean then we need to
3065  * be sure to mark the page clean as well.  This is because the page
3066  * may be against a block device, and a later reattachment of buffers
3067  * to a dirty page will set *all* buffers dirty.  Which would corrupt
3068  * filesystem data on the same device.
3069  *
3070  * The same applies to regular filesystem pages: if all the buffers are
3071  * clean then we set the page clean and proceed.  To do that, we require
3072  * total exclusion from __set_page_dirty_buffers().  That is obtained with
3073  * private_lock.
3074  *
3075  * try_to_free_buffers() is non-blocking.
3076  */
3077 static inline int buffer_busy(struct buffer_head *bh)
3078 {
3079         return atomic_read(&bh->b_count) |
3080                 (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3081 }
3082
3083 static int
3084 drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
3085 {
3086         struct buffer_head *head = page_buffers(page);
3087         struct buffer_head *bh;
3088
3089         bh = head;
3090         do {
3091                 if (buffer_write_io_error(bh) && page->mapping)
3092                         set_bit(AS_EIO, &page->mapping->flags);
3093                 if (buffer_busy(bh))
3094                         goto failed;
3095                 bh = bh->b_this_page;
3096         } while (bh != head);
3097
3098         do {
3099                 struct buffer_head *next = bh->b_this_page;
3100
3101                 if (bh->b_assoc_map)
3102                         __remove_assoc_queue(bh);
3103                 bh = next;
3104         } while (bh != head);
3105         *buffers_to_free = head;
3106         __clear_page_buffers(page);
3107         return 1;
3108 failed:
3109         return 0;
3110 }
3111
3112 int try_to_free_buffers(struct page *page)
3113 {
3114         struct address_space * const mapping = page->mapping;
3115         struct buffer_head *buffers_to_free = NULL;
3116         int ret = 0;
3117
3118         BUG_ON(!PageLocked(page));
3119         if (PageWriteback(page))
3120                 return 0;
3121
3122         if (mapping == NULL) {          /* can this still happen? */
3123                 ret = drop_buffers(page, &buffers_to_free);
3124                 goto out;
3125         }
3126
3127         spin_lock(&mapping->private_lock);
3128         ret = drop_buffers(page, &buffers_to_free);
3129
3130         /*
3131          * If the filesystem writes its buffers by hand (eg ext3)
3132          * then we can have clean buffers against a dirty page.  We
3133          * clean the page here; otherwise the VM will never notice
3134          * that the filesystem did any IO at all.
3135          *
3136          * Also, during truncate, discard_buffer will have marked all
3137          * the page's buffers clean.  We discover that here and clean
3138          * the page also.
3139          *
3140          * private_lock must be held over this entire operation in order
3141          * to synchronise against __set_page_dirty_buffers and prevent the
3142          * dirty bit from being lost.
3143          */
3144         if (ret)
3145                 cancel_dirty_page(page, PAGE_CACHE_SIZE);
3146         spin_unlock(&mapping->private_lock);
3147 out:
3148         if (buffers_to_free) {
3149                 struct buffer_head *bh = buffers_to_free;
3150
3151                 do {
3152                         struct buffer_head *next = bh->b_this_page;
3153                         free_buffer_head(bh);
3154                         bh = next;
3155                 } while (bh != buffers_to_free);
3156         }
3157         return ret;
3158 }
3159 EXPORT_SYMBOL(try_to_free_buffers);
3160
3161 /*
3162  * There are no bdflush tunables left.  But distributions are
3163  * still running obsolete flush daemons, so we terminate them here.
3164  *
3165  * Use of bdflush() is deprecated and will be removed in a future kernel.
3166  * The `flush-X' kernel threads fully replace bdflush daemons and this call.
3167  */
3168 SYSCALL_DEFINE2(bdflush, int, func, long, data)
3169 {
3170         static int msg_count;
3171
3172         if (!capable(CAP_SYS_ADMIN))
3173                 return -EPERM;
3174
3175         if (msg_count < 5) {
3176                 msg_count++;
3177                 printk(KERN_INFO
3178                         "warning: process `%s' used the obsolete bdflush"
3179                         " system call\n", current->comm);
3180                 printk(KERN_INFO "Fix your initscripts?\n");
3181         }
3182
3183         if (func == 1)
3184                 do_exit(0);
3185         return 0;
3186 }
3187
3188 /*
3189  * Buffer-head allocation
3190  */
3191 static struct kmem_cache *bh_cachep;
3192
3193 /*
3194  * Once the number of bh's in the machine exceeds this level, we start
3195  * stripping them in writeback.
3196  */
3197 static int max_buffer_heads;
3198
3199 int buffer_heads_over_limit;
3200
3201 struct bh_accounting {
3202         int nr;                 /* Number of live bh's */
3203         int ratelimit;          /* Limit cacheline bouncing */
3204 };
3205
3206 static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3207
3208 static void recalc_bh_state(void)
3209 {
3210         int i;
3211         int tot = 0;
3212
3213         if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3214                 return;
3215         __this_cpu_write(bh_accounting.ratelimit, 0);
3216         for_each_online_cpu(i)
3217                 tot += per_cpu(bh_accounting, i).nr;
3218         buffer_heads_over_limit = (tot > max_buffer_heads);
3219 }
3220
3221 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3222 {
3223         struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3224         if (ret) {
3225                 INIT_LIST_HEAD(&ret->b_assoc_buffers);
3226                 preempt_disable();
3227                 __this_cpu_inc(bh_accounting.nr);
3228                 recalc_bh_state();
3229                 preempt_enable();
3230         }
3231         return ret;
3232 }
3233 EXPORT_SYMBOL(alloc_buffer_head);
3234
3235 void free_buffer_head(struct buffer_head *bh)
3236 {
3237         BUG_ON(!list_empty(&bh->b_assoc_buffers));
3238         kmem_cache_free(bh_cachep, bh);
3239         preempt_disable();
3240         __this_cpu_dec(bh_accounting.nr);
3241         recalc_bh_state();
3242         preempt_enable();
3243 }
3244 EXPORT_SYMBOL(free_buffer_head);
3245
3246 static void buffer_exit_cpu(int cpu)
3247 {
3248         int i;
3249         struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3250
3251         for (i = 0; i < BH_LRU_SIZE; i++) {
3252                 brelse(b->bhs[i]);
3253                 b->bhs[i] = NULL;
3254         }
3255         this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3256         per_cpu(bh_accounting, cpu).nr = 0;
3257 }
3258
3259 static int buffer_cpu_notify(struct notifier_block *self,
3260                               unsigned long action, void *hcpu)
3261 {
3262         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN)
3263                 buffer_exit_cpu((unsigned long)hcpu);
3264         return NOTIFY_OK;
3265 }
3266
3267 /**
3268  * bh_uptodate_or_lock - Test whether the buffer is uptodate
3269  * @bh: struct buffer_head
3270  *
3271  * Return true if the buffer is up-to-date and false,
3272  * with the buffer locked, if not.
3273  */
3274 int bh_uptodate_or_lock(struct buffer_head *bh)
3275 {
3276         if (!buffer_uptodate(bh)) {
3277                 lock_buffer(bh);
3278                 if (!buffer_uptodate(bh))
3279                         return 0;
3280                 unlock_buffer(bh);
3281         }
3282         return 1;
3283 }
3284 EXPORT_SYMBOL(bh_uptodate_or_lock);
3285
3286 /**
3287  * bh_submit_read - Submit a locked buffer for reading
3288  * @bh: struct buffer_head
3289  *
3290  * Returns zero on success and -EIO on error.
3291  */
3292 int bh_submit_read(struct buffer_head *bh)
3293 {
3294         BUG_ON(!buffer_locked(bh));
3295
3296         if (buffer_uptodate(bh)) {
3297                 unlock_buffer(bh);
3298                 return 0;
3299         }
3300
3301         get_bh(bh);
3302         bh->b_end_io = end_buffer_read_sync;
3303         submit_bh(READ, bh);
3304         wait_on_buffer(bh);
3305         if (buffer_uptodate(bh))
3306                 return 0;
3307         return -EIO;
3308 }
3309 EXPORT_SYMBOL(bh_submit_read);
3310
3311 void __init buffer_init(void)
3312 {
3313         int nrpages;
3314
3315         bh_cachep = kmem_cache_create("buffer_head",
3316                         sizeof(struct buffer_head), 0,
3317                                 (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3318                                 SLAB_MEM_SPREAD),
3319                                 NULL);
3320
3321         /*
3322          * Limit the bh occupancy to 10% of ZONE_NORMAL
3323          */
3324         nrpages = (nr_free_buffer_pages() * 10) / 100;
3325         max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3326         hotcpu_notifier(buffer_cpu_notify, 0);
3327 }