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Linux/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/iomap.h>
 25 #include <linux/mm.h>
 26 #include <linux/percpu.h>
 27 #include <linux/slab.h>
 28 #include <linux/capability.h>
 29 #include <linux/blkdev.h>
 30 #include <linux/file.h>
 31 #include <linux/quotaops.h>
 32 #include <linux/highmem.h>
 33 #include <linux/export.h>
 34 #include <linux/backing-dev.h>
 35 #include <linux/writeback.h>
 36 #include <linux/hash.h>
 37 #include <linux/suspend.h>
 38 #include <linux/buffer_head.h>
 39 #include <linux/task_io_accounting_ops.h>
 40 #include <linux/bio.h>
 41 #include <linux/notifier.h>
 42 #include <linux/cpu.h>
 43 #include <linux/bitops.h>
 44 #include <linux/mpage.h>
 45 #include <linux/bit_spinlock.h>
 46 #include <linux/pagevec.h>
 47 #include <trace/events/block.h>
 48 
 49 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
 50 static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
 51                          unsigned long bio_flags,
 52                          struct writeback_control *wbc);
 53 
 54 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
 55 
 56 void init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
 57 {
 58         bh->b_end_io = handler;
 59         bh->b_private = private;
 60 }
 61 EXPORT_SYMBOL(init_buffer);
 62 
 63 inline void touch_buffer(struct buffer_head *bh)
 64 {
 65         trace_block_touch_buffer(bh);
 66         mark_page_accessed(bh->b_page);
 67 }
 68 EXPORT_SYMBOL(touch_buffer);
 69 
 70 void __lock_buffer(struct buffer_head *bh)
 71 {
 72         wait_on_bit_lock_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
 73 }
 74 EXPORT_SYMBOL(__lock_buffer);
 75 
 76 void unlock_buffer(struct buffer_head *bh)
 77 {
 78         clear_bit_unlock(BH_Lock, &bh->b_state);
 79         smp_mb__after_atomic();
 80         wake_up_bit(&bh->b_state, BH_Lock);
 81 }
 82 EXPORT_SYMBOL(unlock_buffer);
 83 
 84 /*
 85  * Returns if the page has dirty or writeback buffers. If all the buffers
 86  * are unlocked and clean then the PageDirty information is stale. If
 87  * any of the pages are locked, it is assumed they are locked for IO.
 88  */
 89 void buffer_check_dirty_writeback(struct page *page,
 90                                      bool *dirty, bool *writeback)
 91 {
 92         struct buffer_head *head, *bh;
 93         *dirty = false;
 94         *writeback = false;
 95 
 96         BUG_ON(!PageLocked(page));
 97 
 98         if (!page_has_buffers(page))
 99                 return;
100 
101         if (PageWriteback(page))
102                 *writeback = true;
103 
104         head = page_buffers(page);
105         bh = head;
106         do {
107                 if (buffer_locked(bh))
108                         *writeback = true;
109 
110                 if (buffer_dirty(bh))
111                         *dirty = true;
112 
113                 bh = bh->b_this_page;
114         } while (bh != head);
115 }
116 EXPORT_SYMBOL(buffer_check_dirty_writeback);
117 
118 /*
119  * Block until a buffer comes unlocked.  This doesn't stop it
120  * from becoming locked again - you have to lock it yourself
121  * if you want to preserve its state.
122  */
123 void __wait_on_buffer(struct buffer_head * bh)
124 {
125         wait_on_bit_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
126 }
127 EXPORT_SYMBOL(__wait_on_buffer);
128 
129 static void
130 __clear_page_buffers(struct page *page)
131 {
132         ClearPagePrivate(page);
133         set_page_private(page, 0);
134         put_page(page);
135 }
136 
137 static void buffer_io_error(struct buffer_head *bh, char *msg)
138 {
139         if (!test_bit(BH_Quiet, &bh->b_state))
140                 printk_ratelimited(KERN_ERR
141                         "Buffer I/O error on dev %pg, logical block %llu%s\n",
142                         bh->b_bdev, (unsigned long long)bh->b_blocknr, msg);
143 }
144 
145 /*
146  * End-of-IO handler helper function which does not touch the bh after
147  * unlocking it.
148  * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
149  * a race there is benign: unlock_buffer() only use the bh's address for
150  * hashing after unlocking the buffer, so it doesn't actually touch the bh
151  * itself.
152  */
153 static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
154 {
155         if (uptodate) {
156                 set_buffer_uptodate(bh);
157         } else {
158                 /* This happens, due to failed read-ahead attempts. */
159                 clear_buffer_uptodate(bh);
160         }
161         unlock_buffer(bh);
162 }
163 
164 /*
165  * Default synchronous end-of-IO handler..  Just mark it up-to-date and
166  * unlock the buffer. This is what ll_rw_block uses too.
167  */
168 void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
169 {
170         __end_buffer_read_notouch(bh, uptodate);
171         put_bh(bh);
172 }
173 EXPORT_SYMBOL(end_buffer_read_sync);
174 
175 void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
176 {
177         if (uptodate) {
178                 set_buffer_uptodate(bh);
179         } else {
180                 buffer_io_error(bh, ", lost sync page write");
181                 set_buffer_write_io_error(bh);
182                 clear_buffer_uptodate(bh);
183         }
184         unlock_buffer(bh);
185         put_bh(bh);
186 }
187 EXPORT_SYMBOL(end_buffer_write_sync);
188 
189 /*
190  * Various filesystems appear to want __find_get_block to be non-blocking.
191  * But it's the page lock which protects the buffers.  To get around this,
192  * we get exclusion from try_to_free_buffers with the blockdev mapping's
193  * private_lock.
194  *
195  * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
196  * may be quite high.  This code could TryLock the page, and if that
197  * succeeds, there is no need to take private_lock. (But if
198  * private_lock is contended then so is mapping->tree_lock).
199  */
200 static struct buffer_head *
201 __find_get_block_slow(struct block_device *bdev, sector_t block)
202 {
203         struct inode *bd_inode = bdev->bd_inode;
204         struct address_space *bd_mapping = bd_inode->i_mapping;
205         struct buffer_head *ret = NULL;
206         pgoff_t index;
207         struct buffer_head *bh;
208         struct buffer_head *head;
209         struct page *page;
210         int all_mapped = 1;
211 
212         index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
213         page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
214         if (!page)
215                 goto out;
216 
217         spin_lock(&bd_mapping->private_lock);
218         if (!page_has_buffers(page))
219                 goto out_unlock;
220         head = page_buffers(page);
221         bh = head;
222         do {
223                 if (!buffer_mapped(bh))
224                         all_mapped = 0;
225                 else if (bh->b_blocknr == block) {
226                         ret = bh;
227                         get_bh(bh);
228                         goto out_unlock;
229                 }
230                 bh = bh->b_this_page;
231         } while (bh != head);
232 
233         /* we might be here because some of the buffers on this page are
234          * not mapped.  This is due to various races between
235          * file io on the block device and getblk.  It gets dealt with
236          * elsewhere, don't buffer_error if we had some unmapped buffers
237          */
238         if (all_mapped) {
239                 printk("__find_get_block_slow() failed. "
240                         "block=%llu, b_blocknr=%llu\n",
241                         (unsigned long long)block,
242                         (unsigned long long)bh->b_blocknr);
243                 printk("b_state=0x%08lx, b_size=%zu\n",
244                         bh->b_state, bh->b_size);
245                 printk("device %pg blocksize: %d\n", bdev,
246                         1 << bd_inode->i_blkbits);
247         }
248 out_unlock:
249         spin_unlock(&bd_mapping->private_lock);
250         put_page(page);
251 out:
252         return ret;
253 }
254 
255 /*
256  * Kick the writeback threads then try to free up some ZONE_NORMAL memory.
257  */
258 static void free_more_memory(void)
259 {
260         struct zoneref *z;
261         int nid;
262 
263         wakeup_flusher_threads(1024, WB_REASON_FREE_MORE_MEM);
264         yield();
265 
266         for_each_online_node(nid) {
267 
268                 z = first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
269                                                 gfp_zone(GFP_NOFS), NULL);
270                 if (z->zone)
271                         try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
272                                                 GFP_NOFS, NULL);
273         }
274 }
275 
276 /*
277  * I/O completion handler for block_read_full_page() - pages
278  * which come unlocked at the end of I/O.
279  */
280 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
281 {
282         unsigned long flags;
283         struct buffer_head *first;
284         struct buffer_head *tmp;
285         struct page *page;
286         int page_uptodate = 1;
287 
288         BUG_ON(!buffer_async_read(bh));
289 
290         page = bh->b_page;
291         if (uptodate) {
292                 set_buffer_uptodate(bh);
293         } else {
294                 clear_buffer_uptodate(bh);
295                 buffer_io_error(bh, ", async page read");
296                 SetPageError(page);
297         }
298 
299         /*
300          * Be _very_ careful from here on. Bad things can happen if
301          * two buffer heads end IO at almost the same time and both
302          * decide that the page is now completely done.
303          */
304         first = page_buffers(page);
305         local_irq_save(flags);
306         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
307         clear_buffer_async_read(bh);
308         unlock_buffer(bh);
309         tmp = bh;
310         do {
311                 if (!buffer_uptodate(tmp))
312                         page_uptodate = 0;
313                 if (buffer_async_read(tmp)) {
314                         BUG_ON(!buffer_locked(tmp));
315                         goto still_busy;
316                 }
317                 tmp = tmp->b_this_page;
318         } while (tmp != bh);
319         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
320         local_irq_restore(flags);
321 
322         /*
323          * If none of the buffers had errors and they are all
324          * uptodate then we can set the page uptodate.
325          */
326         if (page_uptodate && !PageError(page))
327                 SetPageUptodate(page);
328         unlock_page(page);
329         return;
330 
331 still_busy:
332         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
333         local_irq_restore(flags);
334         return;
335 }
336 
337 /*
338  * Completion handler for block_write_full_page() - pages which are unlocked
339  * during I/O, and which have PageWriteback cleared upon I/O completion.
340  */
341 void end_buffer_async_write(struct buffer_head *bh, int uptodate)
342 {
343         unsigned long flags;
344         struct buffer_head *first;
345         struct buffer_head *tmp;
346         struct page *page;
347 
348         BUG_ON(!buffer_async_write(bh));
349 
350         page = bh->b_page;
351         if (uptodate) {
352                 set_buffer_uptodate(bh);
353         } else {
354                 buffer_io_error(bh, ", lost async page write");
355                 mapping_set_error(page->mapping, -EIO);
356                 set_buffer_write_io_error(bh);
357                 clear_buffer_uptodate(bh);
358                 SetPageError(page);
359         }
360 
361         first = page_buffers(page);
362         local_irq_save(flags);
363         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
364 
365         clear_buffer_async_write(bh);
366         unlock_buffer(bh);
367         tmp = bh->b_this_page;
368         while (tmp != bh) {
369                 if (buffer_async_write(tmp)) {
370                         BUG_ON(!buffer_locked(tmp));
371                         goto still_busy;
372                 }
373                 tmp = tmp->b_this_page;
374         }
375         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
376         local_irq_restore(flags);
377         end_page_writeback(page);
378         return;
379 
380 still_busy:
381         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
382         local_irq_restore(flags);
383         return;
384 }
385 EXPORT_SYMBOL(end_buffer_async_write);
386 
387 /*
388  * If a page's buffers are under async readin (end_buffer_async_read
389  * completion) then there is a possibility that another thread of
390  * control could lock one of the buffers after it has completed
391  * but while some of the other buffers have not completed.  This
392  * locked buffer would confuse end_buffer_async_read() into not unlocking
393  * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
394  * that this buffer is not under async I/O.
395  *
396  * The page comes unlocked when it has no locked buffer_async buffers
397  * left.
398  *
399  * PageLocked prevents anyone starting new async I/O reads any of
400  * the buffers.
401  *
402  * PageWriteback is used to prevent simultaneous writeout of the same
403  * page.
404  *
405  * PageLocked prevents anyone from starting writeback of a page which is
406  * under read I/O (PageWriteback is only ever set against a locked page).
407  */
408 static void mark_buffer_async_read(struct buffer_head *bh)
409 {
410         bh->b_end_io = end_buffer_async_read;
411         set_buffer_async_read(bh);
412 }
413 
414 static void mark_buffer_async_write_endio(struct buffer_head *bh,
415                                           bh_end_io_t *handler)
416 {
417         bh->b_end_io = handler;
418         set_buffer_async_write(bh);
419 }
420 
421 void mark_buffer_async_write(struct buffer_head *bh)
422 {
423         mark_buffer_async_write_endio(bh, end_buffer_async_write);
424 }
425 EXPORT_SYMBOL(mark_buffer_async_write);
426 
427 
428 /*
429  * fs/buffer.c contains helper functions for buffer-backed address space's
430  * fsync functions.  A common requirement for buffer-based filesystems is
431  * that certain data from the backing blockdev needs to be written out for
432  * a successful fsync().  For example, ext2 indirect blocks need to be
433  * written back and waited upon before fsync() returns.
434  *
435  * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
436  * inode_has_buffers() and invalidate_inode_buffers() are provided for the
437  * management of a list of dependent buffers at ->i_mapping->private_list.
438  *
439  * Locking is a little subtle: try_to_free_buffers() will remove buffers
440  * from their controlling inode's queue when they are being freed.  But
441  * try_to_free_buffers() will be operating against the *blockdev* mapping
442  * at the time, not against the S_ISREG file which depends on those buffers.
443  * So the locking for private_list is via the private_lock in the address_space
444  * which backs the buffers.  Which is different from the address_space 
445  * against which the buffers are listed.  So for a particular address_space,
446  * mapping->private_lock does *not* protect mapping->private_list!  In fact,
447  * mapping->private_list will always be protected by the backing blockdev's
448  * ->private_lock.
449  *
450  * Which introduces a requirement: all buffers on an address_space's
451  * ->private_list must be from the same address_space: the blockdev's.
452  *
453  * address_spaces which do not place buffers at ->private_list via these
454  * utility functions are free to use private_lock and private_list for
455  * whatever they want.  The only requirement is that list_empty(private_list)
456  * be true at clear_inode() time.
457  *
458  * FIXME: clear_inode should not call invalidate_inode_buffers().  The
459  * filesystems should do that.  invalidate_inode_buffers() should just go
460  * BUG_ON(!list_empty).
461  *
462  * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
463  * take an address_space, not an inode.  And it should be called
464  * mark_buffer_dirty_fsync() to clearly define why those buffers are being
465  * queued up.
466  *
467  * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
468  * list if it is already on a list.  Because if the buffer is on a list,
469  * it *must* already be on the right one.  If not, the filesystem is being
470  * silly.  This will save a ton of locking.  But first we have to ensure
471  * that buffers are taken *off* the old inode's list when they are freed
472  * (presumably in truncate).  That requires careful auditing of all
473  * filesystems (do it inside bforget()).  It could also be done by bringing
474  * b_inode back.
475  */
476 
477 /*
478  * The buffer's backing address_space's private_lock must be held
479  */
480 static void __remove_assoc_queue(struct buffer_head *bh)
481 {
482         list_del_init(&bh->b_assoc_buffers);
483         WARN_ON(!bh->b_assoc_map);
484         if (buffer_write_io_error(bh))
485                 set_bit(AS_EIO, &bh->b_assoc_map->flags);
486         bh->b_assoc_map = NULL;
487 }
488 
489 int inode_has_buffers(struct inode *inode)
490 {
491         return !list_empty(&inode->i_data.private_list);
492 }
493 
494 /*
495  * osync is designed to support O_SYNC io.  It waits synchronously for
496  * all already-submitted IO to complete, but does not queue any new
497  * writes to the disk.
498  *
499  * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
500  * you dirty the buffers, and then use osync_inode_buffers to wait for
501  * completion.  Any other dirty buffers which are not yet queued for
502  * write will not be flushed to disk by the osync.
503  */
504 static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
505 {
506         struct buffer_head *bh;
507         struct list_head *p;
508         int err = 0;
509 
510         spin_lock(lock);
511 repeat:
512         list_for_each_prev(p, list) {
513                 bh = BH_ENTRY(p);
514                 if (buffer_locked(bh)) {
515                         get_bh(bh);
516                         spin_unlock(lock);
517                         wait_on_buffer(bh);
518                         if (!buffer_uptodate(bh))
519                                 err = -EIO;
520                         brelse(bh);
521                         spin_lock(lock);
522                         goto repeat;
523                 }
524         }
525         spin_unlock(lock);
526         return err;
527 }
528 
529 static void do_thaw_one(struct super_block *sb, void *unused)
530 {
531         while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
532                 printk(KERN_WARNING "Emergency Thaw on %pg\n", sb->s_bdev);
533 }
534 
535 static void do_thaw_all(struct work_struct *work)
536 {
537         iterate_supers(do_thaw_one, NULL);
538         kfree(work);
539         printk(KERN_WARNING "Emergency Thaw complete\n");
540 }
541 
542 /**
543  * emergency_thaw_all -- forcibly thaw every frozen filesystem
544  *
545  * Used for emergency unfreeze of all filesystems via SysRq
546  */
547 void emergency_thaw_all(void)
548 {
549         struct work_struct *work;
550 
551         work = kmalloc(sizeof(*work), GFP_ATOMIC);
552         if (work) {
553                 INIT_WORK(work, do_thaw_all);
554                 schedule_work(work);
555         }
556 }
557 
558 /**
559  * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
560  * @mapping: the mapping which wants those buffers written
561  *
562  * Starts I/O against the buffers at mapping->private_list, and waits upon
563  * that I/O.
564  *
565  * Basically, this is a convenience function for fsync().
566  * @mapping is a file or directory which needs those buffers to be written for
567  * a successful fsync().
568  */
569 int sync_mapping_buffers(struct address_space *mapping)
570 {
571         struct address_space *buffer_mapping = mapping->private_data;
572 
573         if (buffer_mapping == NULL || list_empty(&mapping->private_list))
574                 return 0;
575 
576         return fsync_buffers_list(&buffer_mapping->private_lock,
577                                         &mapping->private_list);
578 }
579 EXPORT_SYMBOL(sync_mapping_buffers);
580 
581 /*
582  * Called when we've recently written block `bblock', and it is known that
583  * `bblock' was for a buffer_boundary() buffer.  This means that the block at
584  * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
585  * dirty, schedule it for IO.  So that indirects merge nicely with their data.
586  */
587 void write_boundary_block(struct block_device *bdev,
588                         sector_t bblock, unsigned blocksize)
589 {
590         struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
591         if (bh) {
592                 if (buffer_dirty(bh))
593                         ll_rw_block(REQ_OP_WRITE, 0, 1, &bh);
594                 put_bh(bh);
595         }
596 }
597 
598 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
599 {
600         struct address_space *mapping = inode->i_mapping;
601         struct address_space *buffer_mapping = bh->b_page->mapping;
602 
603         mark_buffer_dirty(bh);
604         if (!mapping->private_data) {
605                 mapping->private_data = buffer_mapping;
606         } else {
607                 BUG_ON(mapping->private_data != buffer_mapping);
608         }
609         if (!bh->b_assoc_map) {
610                 spin_lock(&buffer_mapping->private_lock);
611                 list_move_tail(&bh->b_assoc_buffers,
612                                 &mapping->private_list);
613                 bh->b_assoc_map = mapping;
614                 spin_unlock(&buffer_mapping->private_lock);
615         }
616 }
617 EXPORT_SYMBOL(mark_buffer_dirty_inode);
618 
619 /*
620  * Mark the page dirty, and set it dirty in the radix tree, and mark the inode
621  * dirty.
622  *
623  * If warn is true, then emit a warning if the page is not uptodate and has
624  * not been truncated.
625  *
626  * The caller must hold lock_page_memcg().
627  */
628 static void __set_page_dirty(struct page *page, struct address_space *mapping,
629                              int warn)
630 {
631         unsigned long flags;
632 
633         spin_lock_irqsave(&mapping->tree_lock, flags);
634         if (page->mapping) {    /* Race with truncate? */
635                 WARN_ON_ONCE(warn && !PageUptodate(page));
636                 account_page_dirtied(page, mapping);
637                 radix_tree_tag_set(&mapping->page_tree,
638                                 page_index(page), PAGECACHE_TAG_DIRTY);
639         }
640         spin_unlock_irqrestore(&mapping->tree_lock, flags);
641 }
642 
643 /*
644  * Add a page to the dirty page list.
645  *
646  * It is a sad fact of life that this function is called from several places
647  * deeply under spinlocking.  It may not sleep.
648  *
649  * If the page has buffers, the uptodate buffers are set dirty, to preserve
650  * dirty-state coherency between the page and the buffers.  It the page does
651  * not have buffers then when they are later attached they will all be set
652  * dirty.
653  *
654  * The buffers are dirtied before the page is dirtied.  There's a small race
655  * window in which a writepage caller may see the page cleanness but not the
656  * buffer dirtiness.  That's fine.  If this code were to set the page dirty
657  * before the buffers, a concurrent writepage caller could clear the page dirty
658  * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
659  * page on the dirty page list.
660  *
661  * We use private_lock to lock against try_to_free_buffers while using the
662  * page's buffer list.  Also use this to protect against clean buffers being
663  * added to the page after it was set dirty.
664  *
665  * FIXME: may need to call ->reservepage here as well.  That's rather up to the
666  * address_space though.
667  */
668 int __set_page_dirty_buffers(struct page *page)
669 {
670         int newly_dirty;
671         struct address_space *mapping = page_mapping(page);
672 
673         if (unlikely(!mapping))
674                 return !TestSetPageDirty(page);
675 
676         spin_lock(&mapping->private_lock);
677         if (page_has_buffers(page)) {
678                 struct buffer_head *head = page_buffers(page);
679                 struct buffer_head *bh = head;
680 
681                 do {
682                         set_buffer_dirty(bh);
683                         bh = bh->b_this_page;
684                 } while (bh != head);
685         }
686         /*
687          * Lock out page->mem_cgroup migration to keep PageDirty
688          * synchronized with per-memcg dirty page counters.
689          */
690         lock_page_memcg(page);
691         newly_dirty = !TestSetPageDirty(page);
692         spin_unlock(&mapping->private_lock);
693 
694         if (newly_dirty)
695                 __set_page_dirty(page, mapping, 1);
696 
697         unlock_page_memcg(page);
698 
699         if (newly_dirty)
700                 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
701 
702         return newly_dirty;
703 }
704 EXPORT_SYMBOL(__set_page_dirty_buffers);
705 
706 /*
707  * Write out and wait upon a list of buffers.
708  *
709  * We have conflicting pressures: we want to make sure that all
710  * initially dirty buffers get waited on, but that any subsequently
711  * dirtied buffers don't.  After all, we don't want fsync to last
712  * forever if somebody is actively writing to the file.
713  *
714  * Do this in two main stages: first we copy dirty buffers to a
715  * temporary inode list, queueing the writes as we go.  Then we clean
716  * up, waiting for those writes to complete.
717  * 
718  * During this second stage, any subsequent updates to the file may end
719  * up refiling the buffer on the original inode's dirty list again, so
720  * there is a chance we will end up with a buffer queued for write but
721  * not yet completed on that list.  So, as a final cleanup we go through
722  * the osync code to catch these locked, dirty buffers without requeuing
723  * any newly dirty buffers for write.
724  */
725 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
726 {
727         struct buffer_head *bh;
728         struct list_head tmp;
729         struct address_space *mapping;
730         int err = 0, err2;
731         struct blk_plug plug;
732 
733         INIT_LIST_HEAD(&tmp);
734         blk_start_plug(&plug);
735 
736         spin_lock(lock);
737         while (!list_empty(list)) {
738                 bh = BH_ENTRY(list->next);
739                 mapping = bh->b_assoc_map;
740                 __remove_assoc_queue(bh);
741                 /* Avoid race with mark_buffer_dirty_inode() which does
742                  * a lockless check and we rely on seeing the dirty bit */
743                 smp_mb();
744                 if (buffer_dirty(bh) || buffer_locked(bh)) {
745                         list_add(&bh->b_assoc_buffers, &tmp);
746                         bh->b_assoc_map = mapping;
747                         if (buffer_dirty(bh)) {
748                                 get_bh(bh);
749                                 spin_unlock(lock);
750                                 /*
751                                  * Ensure any pending I/O completes so that
752                                  * write_dirty_buffer() actually writes the
753                                  * current contents - it is a noop if I/O is
754                                  * still in flight on potentially older
755                                  * contents.
756                                  */
757                                 write_dirty_buffer(bh, REQ_SYNC);
758 
759                                 /*
760                                  * Kick off IO for the previous mapping. Note
761                                  * that we will not run the very last mapping,
762                                  * wait_on_buffer() will do that for us
763                                  * through sync_buffer().
764                                  */
765                                 brelse(bh);
766                                 spin_lock(lock);
767                         }
768                 }
769         }
770 
771         spin_unlock(lock);
772         blk_finish_plug(&plug);
773         spin_lock(lock);
774 
775         while (!list_empty(&tmp)) {
776                 bh = BH_ENTRY(tmp.prev);
777                 get_bh(bh);
778                 mapping = bh->b_assoc_map;
779                 __remove_assoc_queue(bh);
780                 /* Avoid race with mark_buffer_dirty_inode() which does
781                  * a lockless check and we rely on seeing the dirty bit */
782                 smp_mb();
783                 if (buffer_dirty(bh)) {
784                         list_add(&bh->b_assoc_buffers,
785                                  &mapping->private_list);
786                         bh->b_assoc_map = mapping;
787                 }
788                 spin_unlock(lock);
789                 wait_on_buffer(bh);
790                 if (!buffer_uptodate(bh))
791                         err = -EIO;
792                 brelse(bh);
793                 spin_lock(lock);
794         }
795         
796         spin_unlock(lock);
797         err2 = osync_buffers_list(lock, list);
798         if (err)
799                 return err;
800         else
801                 return err2;
802 }
803 
804 /*
805  * Invalidate any and all dirty buffers on a given inode.  We are
806  * probably unmounting the fs, but that doesn't mean we have already
807  * done a sync().  Just drop the buffers from the inode list.
808  *
809  * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
810  * assumes that all the buffers are against the blockdev.  Not true
811  * for reiserfs.
812  */
813 void invalidate_inode_buffers(struct inode *inode)
814 {
815         if (inode_has_buffers(inode)) {
816                 struct address_space *mapping = &inode->i_data;
817                 struct list_head *list = &mapping->private_list;
818                 struct address_space *buffer_mapping = mapping->private_data;
819 
820                 spin_lock(&buffer_mapping->private_lock);
821                 while (!list_empty(list))
822                         __remove_assoc_queue(BH_ENTRY(list->next));
823                 spin_unlock(&buffer_mapping->private_lock);
824         }
825 }
826 EXPORT_SYMBOL(invalidate_inode_buffers);
827 
828 /*
829  * Remove any clean buffers from the inode's buffer list.  This is called
830  * when we're trying to free the inode itself.  Those buffers can pin it.
831  *
832  * Returns true if all buffers were removed.
833  */
834 int remove_inode_buffers(struct inode *inode)
835 {
836         int ret = 1;
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->private_data;
842 
843                 spin_lock(&buffer_mapping->private_lock);
844                 while (!list_empty(list)) {
845                         struct buffer_head *bh = BH_ENTRY(list->next);
846                         if (buffer_dirty(bh)) {
847                                 ret = 0;
848                                 break;
849                         }
850                         __remove_assoc_queue(bh);
851                 }
852                 spin_unlock(&buffer_mapping->private_lock);
853         }
854         return ret;
855 }
856 
857 /*
858  * Create the appropriate buffers when given a page for data area and
859  * the size of each buffer.. Use the bh->b_this_page linked list to
860  * follow the buffers created.  Return NULL if unable to create more
861  * buffers.
862  *
863  * The retry flag is used to differentiate async IO (paging, swapping)
864  * which may not fail from ordinary buffer allocations.
865  */
866 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
867                 int retry)
868 {
869         struct buffer_head *bh, *head;
870         long offset;
871 
872 try_again:
873         head = NULL;
874         offset = PAGE_SIZE;
875         while ((offset -= size) >= 0) {
876                 bh = alloc_buffer_head(GFP_NOFS);
877                 if (!bh)
878                         goto no_grow;
879 
880                 bh->b_this_page = head;
881                 bh->b_blocknr = -1;
882                 head = bh;
883 
884                 bh->b_size = size;
885 
886                 /* Link the buffer to its page */
887                 set_bh_page(bh, page, offset);
888         }
889         return head;
890 /*
891  * In case anything failed, we just free everything we got.
892  */
893 no_grow:
894         if (head) {
895                 do {
896                         bh = head;
897                         head = head->b_this_page;
898                         free_buffer_head(bh);
899                 } while (head);
900         }
901 
902         /*
903          * Return failure for non-async IO requests.  Async IO requests
904          * are not allowed to fail, so we have to wait until buffer heads
905          * become available.  But we don't want tasks sleeping with 
906          * partially complete buffers, so all were released above.
907          */
908         if (!retry)
909                 return NULL;
910 
911         /* We're _really_ low on memory. Now we just
912          * wait for old buffer heads to become free due to
913          * finishing IO.  Since this is an async request and
914          * the reserve list is empty, we're sure there are 
915          * async buffer heads in use.
916          */
917         free_more_memory();
918         goto try_again;
919 }
920 EXPORT_SYMBOL_GPL(alloc_page_buffers);
921 
922 static inline void
923 link_dev_buffers(struct page *page, struct buffer_head *head)
924 {
925         struct buffer_head *bh, *tail;
926 
927         bh = head;
928         do {
929                 tail = bh;
930                 bh = bh->b_this_page;
931         } while (bh);
932         tail->b_this_page = head;
933         attach_page_buffers(page, head);
934 }
935 
936 static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
937 {
938         sector_t retval = ~((sector_t)0);
939         loff_t sz = i_size_read(bdev->bd_inode);
940 
941         if (sz) {
942                 unsigned int sizebits = blksize_bits(size);
943                 retval = (sz >> sizebits);
944         }
945         return retval;
946 }
947 
948 /*
949  * Initialise the state of a blockdev page's buffers.
950  */ 
951 static sector_t
952 init_page_buffers(struct page *page, struct block_device *bdev,
953                         sector_t block, int size)
954 {
955         struct buffer_head *head = page_buffers(page);
956         struct buffer_head *bh = head;
957         int uptodate = PageUptodate(page);
958         sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
959 
960         do {
961                 if (!buffer_mapped(bh)) {
962                         init_buffer(bh, NULL, NULL);
963                         bh->b_bdev = bdev;
964                         bh->b_blocknr = block;
965                         if (uptodate)
966                                 set_buffer_uptodate(bh);
967                         if (block < end_block)
968                                 set_buffer_mapped(bh);
969                 }
970                 block++;
971                 bh = bh->b_this_page;
972         } while (bh != head);
973 
974         /*
975          * Caller needs to validate requested block against end of device.
976          */
977         return end_block;
978 }
979 
980 /*
981  * Create the page-cache page that contains the requested block.
982  *
983  * This is used purely for blockdev mappings.
984  */
985 static int
986 grow_dev_page(struct block_device *bdev, sector_t block,
987               pgoff_t index, int size, int sizebits, gfp_t gfp)
988 {
989         struct inode *inode = bdev->bd_inode;
990         struct page *page;
991         struct buffer_head *bh;
992         sector_t end_block;
993         int ret = 0;            /* Will call free_more_memory() */
994         gfp_t gfp_mask;
995 
996         gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) | gfp;
997 
998         /*
999          * XXX: __getblk_slow() can not really deal with failure and
1000          * will endlessly loop on improvised global reclaim.  Prefer
1001          * looping in the allocator rather than here, at least that
1002          * code knows what it's doing.
1003          */
1004         gfp_mask |= __GFP_NOFAIL;
1005 
1006         page = find_or_create_page(inode->i_mapping, index, gfp_mask);
1007         if (!page)
1008                 return ret;
1009 
1010         BUG_ON(!PageLocked(page));
1011 
1012         if (page_has_buffers(page)) {
1013                 bh = page_buffers(page);
1014                 if (bh->b_size == size) {
1015                         end_block = init_page_buffers(page, bdev,
1016                                                 (sector_t)index << sizebits,
1017                                                 size);
1018                         goto done;
1019                 }
1020                 if (!try_to_free_buffers(page))
1021                         goto failed;
1022         }
1023 
1024         /*
1025          * Allocate some buffers for this page
1026          */
1027         bh = alloc_page_buffers(page, size, 0);
1028         if (!bh)
1029                 goto failed;
1030 
1031         /*
1032          * Link the page to the buffers and initialise them.  Take the
1033          * lock to be atomic wrt __find_get_block(), which does not
1034          * run under the page lock.
1035          */
1036         spin_lock(&inode->i_mapping->private_lock);
1037         link_dev_buffers(page, bh);
1038         end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
1039                         size);
1040         spin_unlock(&inode->i_mapping->private_lock);
1041 done:
1042         ret = (block < end_block) ? 1 : -ENXIO;
1043 failed:
1044         unlock_page(page);
1045         put_page(page);
1046         return ret;
1047 }
1048 
1049 /*
1050  * Create buffers for the specified block device block's page.  If
1051  * that page was dirty, the buffers are set dirty also.
1052  */
1053 static int
1054 grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
1055 {
1056         pgoff_t index;
1057         int sizebits;
1058 
1059         sizebits = -1;
1060         do {
1061                 sizebits++;
1062         } while ((size << sizebits) < PAGE_SIZE);
1063 
1064         index = block >> sizebits;
1065 
1066         /*
1067          * Check for a block which wants to lie outside our maximum possible
1068          * pagecache index.  (this comparison is done using sector_t types).
1069          */
1070         if (unlikely(index != block >> sizebits)) {
1071                 printk(KERN_ERR "%s: requested out-of-range block %llu for "
1072                         "device %pg\n",
1073                         __func__, (unsigned long long)block,
1074                         bdev);
1075                 return -EIO;
1076         }
1077 
1078         /* Create a page with the proper size buffers.. */
1079         return grow_dev_page(bdev, block, index, size, sizebits, gfp);
1080 }
1081 
1082 static struct buffer_head *
1083 __getblk_slow(struct block_device *bdev, sector_t block,
1084              unsigned size, gfp_t gfp)
1085 {
1086         /* Size must be multiple of hard sectorsize */
1087         if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
1088                         (size < 512 || size > PAGE_SIZE))) {
1089                 printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1090                                         size);
1091                 printk(KERN_ERR "logical block size: %d\n",
1092                                         bdev_logical_block_size(bdev));
1093 
1094                 dump_stack();
1095                 return NULL;
1096         }
1097 
1098         for (;;) {
1099                 struct buffer_head *bh;
1100                 int ret;
1101 
1102                 bh = __find_get_block(bdev, block, size);
1103                 if (bh)
1104                         return bh;
1105 
1106                 ret = grow_buffers(bdev, block, size, gfp);
1107                 if (ret < 0)
1108                         return NULL;
1109                 if (ret == 0)
1110                         free_more_memory();
1111         }
1112 }
1113 
1114 /*
1115  * The relationship between dirty buffers and dirty pages:
1116  *
1117  * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1118  * the page is tagged dirty in its radix tree.
1119  *
1120  * At all times, the dirtiness of the buffers represents the dirtiness of
1121  * subsections of the page.  If the page has buffers, the page dirty bit is
1122  * merely a hint about the true dirty state.
1123  *
1124  * When a page is set dirty in its entirety, all its buffers are marked dirty
1125  * (if the page has buffers).
1126  *
1127  * When a buffer is marked dirty, its page is dirtied, but the page's other
1128  * buffers are not.
1129  *
1130  * Also.  When blockdev buffers are explicitly read with bread(), they
1131  * individually become uptodate.  But their backing page remains not
1132  * uptodate - even if all of its buffers are uptodate.  A subsequent
1133  * block_read_full_page() against that page will discover all the uptodate
1134  * buffers, will set the page uptodate and will perform no I/O.
1135  */
1136 
1137 /**
1138  * mark_buffer_dirty - mark a buffer_head as needing writeout
1139  * @bh: the buffer_head to mark dirty
1140  *
1141  * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1142  * backing page dirty, then tag the page as dirty in its address_space's radix
1143  * tree and then attach the address_space's inode to its superblock's dirty
1144  * inode list.
1145  *
1146  * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1147  * mapping->tree_lock and mapping->host->i_lock.
1148  */
1149 void mark_buffer_dirty(struct buffer_head *bh)
1150 {
1151         WARN_ON_ONCE(!buffer_uptodate(bh));
1152 
1153         trace_block_dirty_buffer(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                 struct address_space *mapping = NULL;
1170 
1171                 lock_page_memcg(page);
1172                 if (!TestSetPageDirty(page)) {
1173                         mapping = page_mapping(page);
1174                         if (mapping)
1175                                 __set_page_dirty(page, mapping, 0);
1176                 }
1177                 unlock_page_memcg(page);
1178                 if (mapping)
1179                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1180         }
1181 }
1182 EXPORT_SYMBOL(mark_buffer_dirty);
1183 
1184 /*
1185  * Decrement a buffer_head's reference count.  If all buffers against a page
1186  * have zero reference count, are clean and unlocked, and if the page is clean
1187  * and unlocked then try_to_free_buffers() may strip the buffers from the page
1188  * in preparation for freeing it (sometimes, rarely, buffers are removed from
1189  * a page but it ends up not being freed, and buffers may later be reattached).
1190  */
1191 void __brelse(struct buffer_head * buf)
1192 {
1193         if (atomic_read(&buf->b_count)) {
1194                 put_bh(buf);
1195                 return;
1196         }
1197         WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1198 }
1199 EXPORT_SYMBOL(__brelse);
1200 
1201 /*
1202  * bforget() is like brelse(), except it discards any
1203  * potentially dirty data.
1204  */
1205 void __bforget(struct buffer_head *bh)
1206 {
1207         clear_buffer_dirty(bh);
1208         if (bh->b_assoc_map) {
1209                 struct address_space *buffer_mapping = bh->b_page->mapping;
1210 
1211                 spin_lock(&buffer_mapping->private_lock);
1212                 list_del_init(&bh->b_assoc_buffers);
1213                 bh->b_assoc_map = NULL;
1214                 spin_unlock(&buffer_mapping->private_lock);
1215         }
1216         __brelse(bh);
1217 }
1218 EXPORT_SYMBOL(__bforget);
1219 
1220 static struct buffer_head *__bread_slow(struct buffer_head *bh)
1221 {
1222         lock_buffer(bh);
1223         if (buffer_uptodate(bh)) {
1224                 unlock_buffer(bh);
1225                 return bh;
1226         } else {
1227                 get_bh(bh);
1228                 bh->b_end_io = end_buffer_read_sync;
1229                 submit_bh(REQ_OP_READ, 0, bh);
1230                 wait_on_buffer(bh);
1231                 if (buffer_uptodate(bh))
1232                         return bh;
1233         }
1234         brelse(bh);
1235         return NULL;
1236 }
1237 
1238 /*
1239  * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1240  * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1241  * refcount elevated by one when they're in an LRU.  A buffer can only appear
1242  * once in a particular CPU's LRU.  A single buffer can be present in multiple
1243  * CPU's LRUs at the same time.
1244  *
1245  * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1246  * sb_find_get_block().
1247  *
1248  * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1249  * a local interrupt disable for that.
1250  */
1251 
1252 #define BH_LRU_SIZE     16
1253 
1254 struct bh_lru {
1255         struct buffer_head *bhs[BH_LRU_SIZE];
1256 };
1257 
1258 static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1259 
1260 #ifdef CONFIG_SMP
1261 #define bh_lru_lock()   local_irq_disable()
1262 #define bh_lru_unlock() local_irq_enable()
1263 #else
1264 #define bh_lru_lock()   preempt_disable()
1265 #define bh_lru_unlock() preempt_enable()
1266 #endif
1267 
1268 static inline void check_irqs_on(void)
1269 {
1270 #ifdef irqs_disabled
1271         BUG_ON(irqs_disabled());
1272 #endif
1273 }
1274 
1275 /*
1276  * The LRU management algorithm is dopey-but-simple.  Sorry.
1277  */
1278 static void bh_lru_install(struct buffer_head *bh)
1279 {
1280         struct buffer_head *evictee = NULL;
1281 
1282         check_irqs_on();
1283         bh_lru_lock();
1284         if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
1285                 struct buffer_head *bhs[BH_LRU_SIZE];
1286                 int in;
1287                 int out = 0;
1288 
1289                 get_bh(bh);
1290                 bhs[out++] = bh;
1291                 for (in = 0; in < BH_LRU_SIZE; in++) {
1292                         struct buffer_head *bh2 =
1293                                 __this_cpu_read(bh_lrus.bhs[in]);
1294 
1295                         if (bh2 == bh) {
1296                                 __brelse(bh2);
1297                         } else {
1298                                 if (out >= BH_LRU_SIZE) {
1299                                         BUG_ON(evictee != NULL);
1300                                         evictee = bh2;
1301                                 } else {
1302                                         bhs[out++] = bh2;
1303                                 }
1304                         }
1305                 }
1306                 while (out < BH_LRU_SIZE)
1307                         bhs[out++] = NULL;
1308                 memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
1309         }
1310         bh_lru_unlock();
1311 
1312         if (evictee)
1313                 __brelse(evictee);
1314 }
1315 
1316 /*
1317  * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1318  */
1319 static struct buffer_head *
1320 lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1321 {
1322         struct buffer_head *ret = NULL;
1323         unsigned int i;
1324 
1325         check_irqs_on();
1326         bh_lru_lock();
1327         for (i = 0; i < BH_LRU_SIZE; i++) {
1328                 struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1329 
1330                 if (bh && bh->b_blocknr == block && bh->b_bdev == bdev &&
1331                     bh->b_size == size) {
1332                         if (i) {
1333                                 while (i) {
1334                                         __this_cpu_write(bh_lrus.bhs[i],
1335                                                 __this_cpu_read(bh_lrus.bhs[i - 1]));
1336                                         i--;
1337                                 }
1338                                 __this_cpu_write(bh_lrus.bhs[0], bh);
1339                         }
1340                         get_bh(bh);
1341                         ret = bh;
1342                         break;
1343                 }
1344         }
1345         bh_lru_unlock();
1346         return ret;
1347 }
1348 
1349 /*
1350  * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1351  * it in the LRU and mark it as accessed.  If it is not present then return
1352  * NULL
1353  */
1354 struct buffer_head *
1355 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1356 {
1357         struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1358 
1359         if (bh == NULL) {
1360                 /* __find_get_block_slow will mark the page accessed */
1361                 bh = __find_get_block_slow(bdev, block);
1362                 if (bh)
1363                         bh_lru_install(bh);
1364         } else
1365                 touch_buffer(bh);
1366 
1367         return bh;
1368 }
1369 EXPORT_SYMBOL(__find_get_block);
1370 
1371 /*
1372  * __getblk_gfp() will locate (and, if necessary, create) the buffer_head
1373  * which corresponds to the passed block_device, block and size. The
1374  * returned buffer has its reference count incremented.
1375  *
1376  * __getblk_gfp() will lock up the machine if grow_dev_page's
1377  * try_to_free_buffers() attempt is failing.  FIXME, perhaps?
1378  */
1379 struct buffer_head *
1380 __getblk_gfp(struct block_device *bdev, sector_t block,
1381              unsigned size, gfp_t gfp)
1382 {
1383         struct buffer_head *bh = __find_get_block(bdev, block, size);
1384 
1385         might_sleep();
1386         if (bh == NULL)
1387                 bh = __getblk_slow(bdev, block, size, gfp);
1388         return bh;
1389 }
1390 EXPORT_SYMBOL(__getblk_gfp);
1391 
1392 /*
1393  * Do async read-ahead on a buffer..
1394  */
1395 void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1396 {
1397         struct buffer_head *bh = __getblk(bdev, block, size);
1398         if (likely(bh)) {
1399                 ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
1400                 brelse(bh);
1401         }
1402 }
1403 EXPORT_SYMBOL(__breadahead);
1404 
1405 /**
1406  *  __bread_gfp() - reads a specified block and returns the bh
1407  *  @bdev: the block_device to read from
1408  *  @block: number of block
1409  *  @size: size (in bytes) to read
1410  *  @gfp: page allocation flag
1411  *
1412  *  Reads a specified block, and returns buffer head that contains it.
1413  *  The page cache can be allocated from non-movable area
1414  *  not to prevent page migration if you set gfp to zero.
1415  *  It returns NULL if the block was unreadable.
1416  */
1417 struct buffer_head *
1418 __bread_gfp(struct block_device *bdev, sector_t block,
1419                    unsigned size, gfp_t gfp)
1420 {
1421         struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
1422 
1423         if (likely(bh) && !buffer_uptodate(bh))
1424                 bh = __bread_slow(bh);
1425         return bh;
1426 }
1427 EXPORT_SYMBOL(__bread_gfp);
1428 
1429 /*
1430  * invalidate_bh_lrus() is called rarely - but not only at unmount.
1431  * This doesn't race because it runs in each cpu either in irq
1432  * or with preempt disabled.
1433  */
1434 static void invalidate_bh_lru(void *arg)
1435 {
1436         struct bh_lru *b = &get_cpu_var(bh_lrus);
1437         int i;
1438 
1439         for (i = 0; i < BH_LRU_SIZE; i++) {
1440                 brelse(b->bhs[i]);
1441                 b->bhs[i] = NULL;
1442         }
1443         put_cpu_var(bh_lrus);
1444 }
1445 
1446 static bool has_bh_in_lru(int cpu, void *dummy)
1447 {
1448         struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1449         int i;
1450         
1451         for (i = 0; i < BH_LRU_SIZE; i++) {
1452                 if (b->bhs[i])
1453                         return 1;
1454         }
1455 
1456         return 0;
1457 }
1458 
1459 void invalidate_bh_lrus(void)
1460 {
1461         on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1462 }
1463 EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1464 
1465 void set_bh_page(struct buffer_head *bh,
1466                 struct page *page, unsigned long offset)
1467 {
1468         bh->b_page = page;
1469         BUG_ON(offset >= PAGE_SIZE);
1470         if (PageHighMem(page))
1471                 /*
1472                  * This catches illegal uses and preserves the offset:
1473                  */
1474                 bh->b_data = (char *)(0 + offset);
1475         else
1476                 bh->b_data = page_address(page) + offset;
1477 }
1478 EXPORT_SYMBOL(set_bh_page);
1479 
1480 /*
1481  * Called when truncating a buffer on a page completely.
1482  */
1483 
1484 /* Bits that are cleared during an invalidate */
1485 #define BUFFER_FLAGS_DISCARD \
1486         (1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
1487          1 << BH_Delay | 1 << BH_Unwritten)
1488 
1489 static void discard_buffer(struct buffer_head * bh)
1490 {
1491         unsigned long b_state, b_state_old;
1492 
1493         lock_buffer(bh);
1494         clear_buffer_dirty(bh);
1495         bh->b_bdev = NULL;
1496         b_state = bh->b_state;
1497         for (;;) {
1498                 b_state_old = cmpxchg(&bh->b_state, b_state,
1499                                       (b_state & ~BUFFER_FLAGS_DISCARD));
1500                 if (b_state_old == b_state)
1501                         break;
1502                 b_state = b_state_old;
1503         }
1504         unlock_buffer(bh);
1505 }
1506 
1507 /**
1508  * block_invalidatepage - invalidate part or all of a buffer-backed page
1509  *
1510  * @page: the page which is affected
1511  * @offset: start of the range to invalidate
1512  * @length: length of the range to invalidate
1513  *
1514  * block_invalidatepage() is called when all or part of the page has become
1515  * invalidated by a truncate operation.
1516  *
1517  * block_invalidatepage() does not have to release all buffers, but it must
1518  * ensure that no dirty buffer is left outside @offset and that no I/O
1519  * is underway against any of the blocks which are outside the truncation
1520  * point.  Because the caller is about to free (and possibly reuse) those
1521  * blocks on-disk.
1522  */
1523 void block_invalidatepage(struct page *page, unsigned int offset,
1524                           unsigned int length)
1525 {
1526         struct buffer_head *head, *bh, *next;
1527         unsigned int curr_off = 0;
1528         unsigned int stop = length + offset;
1529 
1530         BUG_ON(!PageLocked(page));
1531         if (!page_has_buffers(page))
1532                 goto out;
1533 
1534         /*
1535          * Check for overflow
1536          */
1537         BUG_ON(stop > PAGE_SIZE || stop < length);
1538 
1539         head = page_buffers(page);
1540         bh = head;
1541         do {
1542                 unsigned int next_off = curr_off + bh->b_size;
1543                 next = bh->b_this_page;
1544 
1545                 /*
1546                  * Are we still fully in range ?
1547                  */
1548                 if (next_off > stop)
1549                         goto out;
1550 
1551                 /*
1552                  * is this block fully invalidated?
1553                  */
1554                 if (offset <= curr_off)
1555                         discard_buffer(bh);
1556                 curr_off = next_off;
1557                 bh = next;
1558         } while (bh != head);
1559 
1560         /*
1561          * We release buffers only if the entire page is being invalidated.
1562          * The get_block cached value has been unconditionally invalidated,
1563          * so real IO is not possible anymore.
1564          */
1565         if (offset == 0)
1566                 try_to_release_page(page, 0);
1567 out:
1568         return;
1569 }
1570 EXPORT_SYMBOL(block_invalidatepage);
1571 
1572 
1573 /*
1574  * We attach and possibly dirty the buffers atomically wrt
1575  * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1576  * is already excluded via the page lock.
1577  */
1578 void create_empty_buffers(struct page *page,
1579                         unsigned long blocksize, unsigned long b_state)
1580 {
1581         struct buffer_head *bh, *head, *tail;
1582 
1583         head = alloc_page_buffers(page, blocksize, 1);
1584         bh = head;
1585         do {
1586                 bh->b_state |= b_state;
1587                 tail = bh;
1588                 bh = bh->b_this_page;
1589         } while (bh);
1590         tail->b_this_page = head;
1591 
1592         spin_lock(&page->mapping->private_lock);
1593         if (PageUptodate(page) || PageDirty(page)) {
1594                 bh = head;
1595                 do {
1596                         if (PageDirty(page))
1597                                 set_buffer_dirty(bh);
1598                         if (PageUptodate(page))
1599                                 set_buffer_uptodate(bh);
1600                         bh = bh->b_this_page;
1601                 } while (bh != head);
1602         }
1603         attach_page_buffers(page, head);
1604         spin_unlock(&page->mapping->private_lock);
1605 }
1606 EXPORT_SYMBOL(create_empty_buffers);
1607 
1608 /**
1609  * clean_bdev_aliases: clean a range of buffers in block device
1610  * @bdev: Block device to clean buffers in
1611  * @block: Start of a range of blocks to clean
1612  * @len: Number of blocks to clean
1613  *
1614  * We are taking a range of blocks for data and we don't want writeback of any
1615  * buffer-cache aliases starting from return from this function and until the
1616  * moment when something will explicitly mark the buffer dirty (hopefully that
1617  * will not happen until we will free that block ;-) We don't even need to mark
1618  * it not-uptodate - nobody can expect anything from a newly allocated buffer
1619  * anyway. We used to use unmap_buffer() for such invalidation, but that was
1620  * wrong. We definitely don't want to mark the alias unmapped, for example - it
1621  * would confuse anyone who might pick it with bread() afterwards...
1622  *
1623  * Also..  Note that bforget() doesn't lock the buffer.  So there can be
1624  * writeout I/O going on against recently-freed buffers.  We don't wait on that
1625  * I/O in bforget() - it's more efficient to wait on the I/O only if we really
1626  * need to.  That happens here.
1627  */
1628 void clean_bdev_aliases(struct block_device *bdev, sector_t block, sector_t len)
1629 {
1630         struct inode *bd_inode = bdev->bd_inode;
1631         struct address_space *bd_mapping = bd_inode->i_mapping;
1632         struct pagevec pvec;
1633         pgoff_t index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
1634         pgoff_t end;
1635         int i;
1636         struct buffer_head *bh;
1637         struct buffer_head *head;
1638 
1639         end = (block + len - 1) >> (PAGE_SHIFT - bd_inode->i_blkbits);
1640         pagevec_init(&pvec, 0);
1641         while (index <= end && pagevec_lookup(&pvec, bd_mapping, index,
1642                         min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
1643                 for (i = 0; i < pagevec_count(&pvec); i++) {
1644                         struct page *page = pvec.pages[i];
1645 
1646                         index = page->index;
1647                         if (index > end)
1648                                 break;
1649                         if (!page_has_buffers(page))
1650                                 continue;
1651                         /*
1652                          * We use page lock instead of bd_mapping->private_lock
1653                          * to pin buffers here since we can afford to sleep and
1654                          * it scales better than a global spinlock lock.
1655                          */
1656                         lock_page(page);
1657                         /* Recheck when the page is locked which pins bhs */
1658                         if (!page_has_buffers(page))
1659                                 goto unlock_page;
1660                         head = page_buffers(page);
1661                         bh = head;
1662                         do {
1663                                 if (!buffer_mapped(bh) || (bh->b_blocknr < block))
1664                                         goto next;
1665                                 if (bh->b_blocknr >= block + len)
1666                                         break;
1667                                 clear_buffer_dirty(bh);
1668                                 wait_on_buffer(bh);
1669                                 clear_buffer_req(bh);
1670 next:
1671                                 bh = bh->b_this_page;
1672                         } while (bh != head);
1673 unlock_page:
1674                         unlock_page(page);
1675                 }
1676                 pagevec_release(&pvec);
1677                 cond_resched();
1678                 index++;
1679         }
1680 }
1681 EXPORT_SYMBOL(clean_bdev_aliases);
1682 
1683 /*
1684  * Size is a power-of-two in the range 512..PAGE_SIZE,
1685  * and the case we care about most is PAGE_SIZE.
1686  *
1687  * So this *could* possibly be written with those
1688  * constraints in mind (relevant mostly if some
1689  * architecture has a slow bit-scan instruction)
1690  */
1691 static inline int block_size_bits(unsigned int blocksize)
1692 {
1693         return ilog2(blocksize);
1694 }
1695 
1696 static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
1697 {
1698         BUG_ON(!PageLocked(page));
1699 
1700         if (!page_has_buffers(page))
1701                 create_empty_buffers(page, 1 << ACCESS_ONCE(inode->i_blkbits), b_state);
1702         return page_buffers(page);
1703 }
1704 
1705 /*
1706  * NOTE! All mapped/uptodate combinations are valid:
1707  *
1708  *      Mapped  Uptodate        Meaning
1709  *
1710  *      No      No              "unknown" - must do get_block()
1711  *      No      Yes             "hole" - zero-filled
1712  *      Yes     No              "allocated" - allocated on disk, not read in
1713  *      Yes     Yes             "valid" - allocated and up-to-date in memory.
1714  *
1715  * "Dirty" is valid only with the last case (mapped+uptodate).
1716  */
1717 
1718 /*
1719  * While block_write_full_page is writing back the dirty buffers under
1720  * the page lock, whoever dirtied the buffers may decide to clean them
1721  * again at any time.  We handle that by only looking at the buffer
1722  * state inside lock_buffer().
1723  *
1724  * If block_write_full_page() is called for regular writeback
1725  * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1726  * locked buffer.   This only can happen if someone has written the buffer
1727  * directly, with submit_bh().  At the address_space level PageWriteback
1728  * prevents this contention from occurring.
1729  *
1730  * If block_write_full_page() is called with wbc->sync_mode ==
1731  * WB_SYNC_ALL, the writes are posted using REQ_SYNC; this
1732  * causes the writes to be flagged as synchronous writes.
1733  */
1734 int __block_write_full_page(struct inode *inode, struct page *page,
1735                         get_block_t *get_block, struct writeback_control *wbc,
1736                         bh_end_io_t *handler)
1737 {
1738         int err;
1739         sector_t block;
1740         sector_t last_block;
1741         struct buffer_head *bh, *head;
1742         unsigned int blocksize, bbits;
1743         int nr_underway = 0;
1744         int write_flags = wbc_to_write_flags(wbc);
1745 
1746         head = create_page_buffers(page, inode,
1747                                         (1 << BH_Dirty)|(1 << BH_Uptodate));
1748 
1749         /*
1750          * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1751          * here, and the (potentially unmapped) buffers may become dirty at
1752          * any time.  If a buffer becomes dirty here after we've inspected it
1753          * then we just miss that fact, and the page stays dirty.
1754          *
1755          * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1756          * handle that here by just cleaning them.
1757          */
1758 
1759         bh = head;
1760         blocksize = bh->b_size;
1761         bbits = block_size_bits(blocksize);
1762 
1763         block = (sector_t)page->index << (PAGE_SHIFT - bbits);
1764         last_block = (i_size_read(inode) - 1) >> bbits;
1765 
1766         /*
1767          * Get all the dirty buffers mapped to disk addresses and
1768          * handle any aliases from the underlying blockdev's mapping.
1769          */
1770         do {
1771                 if (block > last_block) {
1772                         /*
1773                          * mapped buffers outside i_size will occur, because
1774                          * this page can be outside i_size when there is a
1775                          * truncate in progress.
1776                          */
1777                         /*
1778                          * The buffer was zeroed by block_write_full_page()
1779                          */
1780                         clear_buffer_dirty(bh);
1781                         set_buffer_uptodate(bh);
1782                 } else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1783                            buffer_dirty(bh)) {
1784                         WARN_ON(bh->b_size != blocksize);
1785                         err = get_block(inode, block, bh, 1);
1786                         if (err)
1787                                 goto recover;
1788                         clear_buffer_delay(bh);
1789                         if (buffer_new(bh)) {
1790                                 /* blockdev mappings never come here */
1791                                 clear_buffer_new(bh);
1792                                 clean_bdev_bh_alias(bh);
1793                         }
1794                 }
1795                 bh = bh->b_this_page;
1796                 block++;
1797         } while (bh != head);
1798 
1799         do {
1800                 if (!buffer_mapped(bh))
1801                         continue;
1802                 /*
1803                  * If it's a fully non-blocking write attempt and we cannot
1804                  * lock the buffer then redirty the page.  Note that this can
1805                  * potentially cause a busy-wait loop from writeback threads
1806                  * and kswapd activity, but those code paths have their own
1807                  * higher-level throttling.
1808                  */
1809                 if (wbc->sync_mode != WB_SYNC_NONE) {
1810                         lock_buffer(bh);
1811                 } else if (!trylock_buffer(bh)) {
1812                         redirty_page_for_writepage(wbc, page);
1813                         continue;
1814                 }
1815                 if (test_clear_buffer_dirty(bh)) {
1816                         mark_buffer_async_write_endio(bh, handler);
1817                 } else {
1818                         unlock_buffer(bh);
1819                 }
1820         } while ((bh = bh->b_this_page) != head);
1821 
1822         /*
1823          * The page and its buffers are protected by PageWriteback(), so we can
1824          * drop the bh refcounts early.
1825          */
1826         BUG_ON(PageWriteback(page));
1827         set_page_writeback(page);
1828 
1829         do {
1830                 struct buffer_head *next = bh->b_this_page;
1831                 if (buffer_async_write(bh)) {
1832                         submit_bh_wbc(REQ_OP_WRITE, write_flags, bh, 0, wbc);
1833                         nr_underway++;
1834                 }
1835                 bh = next;
1836         } while (bh != head);
1837         unlock_page(page);
1838 
1839         err = 0;
1840 done:
1841         if (nr_underway == 0) {
1842                 /*
1843                  * The page was marked dirty, but the buffers were
1844                  * clean.  Someone wrote them back by hand with
1845                  * ll_rw_block/submit_bh.  A rare case.
1846                  */
1847                 end_page_writeback(page);
1848 
1849                 /*
1850                  * The page and buffer_heads can be released at any time from
1851                  * here on.
1852                  */
1853         }
1854         return err;
1855 
1856 recover:
1857         /*
1858          * ENOSPC, or some other error.  We may already have added some
1859          * blocks to the file, so we need to write these out to avoid
1860          * exposing stale data.
1861          * The page is currently locked and not marked for writeback
1862          */
1863         bh = head;
1864         /* Recovery: lock and submit the mapped buffers */
1865         do {
1866                 if (buffer_mapped(bh) && buffer_dirty(bh) &&
1867                     !buffer_delay(bh)) {
1868                         lock_buffer(bh);
1869                         mark_buffer_async_write_endio(bh, handler);
1870                 } else {
1871                         /*
1872                          * The buffer may have been set dirty during
1873                          * attachment to a dirty page.
1874                          */
1875                         clear_buffer_dirty(bh);
1876                 }
1877         } while ((bh = bh->b_this_page) != head);
1878         SetPageError(page);
1879         BUG_ON(PageWriteback(page));
1880         mapping_set_error(page->mapping, err);
1881         set_page_writeback(page);
1882         do {
1883                 struct buffer_head *next = bh->b_this_page;
1884                 if (buffer_async_write(bh)) {
1885                         clear_buffer_dirty(bh);
1886                         submit_bh_wbc(REQ_OP_WRITE, write_flags, bh, 0, wbc);
1887                         nr_underway++;
1888                 }
1889                 bh = next;
1890         } while (bh != head);
1891         unlock_page(page);
1892         goto done;
1893 }
1894 EXPORT_SYMBOL(__block_write_full_page);
1895 
1896 /*
1897  * If a page has any new buffers, zero them out here, and mark them uptodate
1898  * and dirty so they'll be written out (in order to prevent uninitialised
1899  * block data from leaking). And clear the new bit.
1900  */
1901 void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1902 {
1903         unsigned int block_start, block_end;
1904         struct buffer_head *head, *bh;
1905 
1906         BUG_ON(!PageLocked(page));
1907         if (!page_has_buffers(page))
1908                 return;
1909 
1910         bh = head = page_buffers(page);
1911         block_start = 0;
1912         do {
1913                 block_end = block_start + bh->b_size;
1914 
1915                 if (buffer_new(bh)) {
1916                         if (block_end > from && block_start < to) {
1917                                 if (!PageUptodate(page)) {
1918                                         unsigned start, size;
1919 
1920                                         start = max(from, block_start);
1921                                         size = min(to, block_end) - start;
1922 
1923                                         zero_user(page, start, size);
1924                                         set_buffer_uptodate(bh);
1925                                 }
1926 
1927                                 clear_buffer_new(bh);
1928                                 mark_buffer_dirty(bh);
1929                         }
1930                 }
1931 
1932                 block_start = block_end;
1933                 bh = bh->b_this_page;
1934         } while (bh != head);
1935 }
1936 EXPORT_SYMBOL(page_zero_new_buffers);
1937 
1938 static void
1939 iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
1940                 struct iomap *iomap)
1941 {
1942         loff_t offset = block << inode->i_blkbits;
1943 
1944         bh->b_bdev = iomap->bdev;
1945 
1946         /*
1947          * Block points to offset in file we need to map, iomap contains
1948          * the offset at which the map starts. If the map ends before the
1949          * current block, then do not map the buffer and let the caller
1950          * handle it.
1951          */
1952         BUG_ON(offset >= iomap->offset + iomap->length);
1953 
1954         switch (iomap->type) {
1955         case IOMAP_HOLE:
1956                 /*
1957                  * If the buffer is not up to date or beyond the current EOF,
1958                  * we need to mark it as new to ensure sub-block zeroing is
1959                  * executed if necessary.
1960                  */
1961                 if (!buffer_uptodate(bh) ||
1962                     (offset >= i_size_read(inode)))
1963                         set_buffer_new(bh);
1964                 break;
1965         case IOMAP_DELALLOC:
1966                 if (!buffer_uptodate(bh) ||
1967                     (offset >= i_size_read(inode)))
1968                         set_buffer_new(bh);
1969                 set_buffer_uptodate(bh);
1970                 set_buffer_mapped(bh);
1971                 set_buffer_delay(bh);
1972                 break;
1973         case IOMAP_UNWRITTEN:
1974                 /*
1975                  * For unwritten regions, we always need to ensure that
1976                  * sub-block writes cause the regions in the block we are not
1977                  * writing to are zeroed. Set the buffer as new to ensure this.
1978                  */
1979                 set_buffer_new(bh);
1980                 set_buffer_unwritten(bh);
1981                 /* FALLTHRU */
1982         case IOMAP_MAPPED:
1983                 if (offset >= i_size_read(inode))
1984                         set_buffer_new(bh);
1985                 bh->b_blocknr = (iomap->blkno >> (inode->i_blkbits - 9)) +
1986                                 ((offset - iomap->offset) >> inode->i_blkbits);
1987                 set_buffer_mapped(bh);
1988                 break;
1989         }
1990 }
1991 
1992 int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
1993                 get_block_t *get_block, struct iomap *iomap)
1994 {
1995         unsigned from = pos & (PAGE_SIZE - 1);
1996         unsigned to = from + len;
1997         struct inode *inode = page->mapping->host;
1998         unsigned block_start, block_end;
1999         sector_t block;
2000         int err = 0;
2001         unsigned blocksize, bbits;
2002         struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
2003 
2004         BUG_ON(!PageLocked(page));
2005         BUG_ON(from > PAGE_SIZE);
2006         BUG_ON(to > PAGE_SIZE);
2007         BUG_ON(from > to);
2008 
2009         head = create_page_buffers(page, inode, 0);
2010         blocksize = head->b_size;
2011         bbits = block_size_bits(blocksize);
2012 
2013         block = (sector_t)page->index << (PAGE_SHIFT - bbits);
2014 
2015         for(bh = head, block_start = 0; bh != head || !block_start;
2016             block++, block_start=block_end, bh = bh->b_this_page) {
2017                 block_end = block_start + blocksize;
2018                 if (block_end <= from || block_start >= to) {
2019                         if (PageUptodate(page)) {
2020                                 if (!buffer_uptodate(bh))
2021                                         set_buffer_uptodate(bh);
2022                         }
2023                         continue;
2024                 }
2025                 if (buffer_new(bh))
2026                         clear_buffer_new(bh);
2027                 if (!buffer_mapped(bh)) {
2028                         WARN_ON(bh->b_size != blocksize);
2029                         if (get_block) {
2030                                 err = get_block(inode, block, bh, 1);
2031                                 if (err)
2032                                         break;
2033                         } else {
2034                                 iomap_to_bh(inode, block, bh, iomap);
2035                         }
2036 
2037                         if (buffer_new(bh)) {
2038                                 clean_bdev_bh_alias(bh);
2039                                 if (PageUptodate(page)) {
2040                                         clear_buffer_new(bh);
2041                                         set_buffer_uptodate(bh);
2042                                         mark_buffer_dirty(bh);
2043                                         continue;
2044                                 }
2045                                 if (block_end > to || block_start < from)
2046                                         zero_user_segments(page,
2047                                                 to, block_end,
2048                                                 block_start, from);
2049                                 continue;
2050                         }
2051                 }
2052                 if (PageUptodate(page)) {
2053                         if (!buffer_uptodate(bh))
2054                                 set_buffer_uptodate(bh);
2055                         continue; 
2056                 }
2057                 if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
2058                     !buffer_unwritten(bh) &&
2059                      (block_start < from || block_end > to)) {
2060                         ll_rw_block(REQ_OP_READ, 0, 1, &bh);
2061                         *wait_bh++=bh;
2062                 }
2063         }
2064         /*
2065          * If we issued read requests - let them complete.
2066          */
2067         while(wait_bh > wait) {
2068                 wait_on_buffer(*--wait_bh);
2069                 if (!buffer_uptodate(*wait_bh))
2070                         err = -EIO;
2071         }
2072         if (unlikely(err))
2073                 page_zero_new_buffers(page, from, to);
2074         return err;
2075 }
2076 
2077 int __block_write_begin(struct page *page, loff_t pos, unsigned len,
2078                 get_block_t *get_block)
2079 {
2080         return __block_write_begin_int(page, pos, len, get_block, NULL);
2081 }
2082 EXPORT_SYMBOL(__block_write_begin);
2083 
2084 static int __block_commit_write(struct inode *inode, struct page *page,
2085                 unsigned from, unsigned to)
2086 {
2087         unsigned block_start, block_end;
2088         int partial = 0;
2089         unsigned blocksize;
2090         struct buffer_head *bh, *head;
2091 
2092         bh = head = page_buffers(page);
2093         blocksize = bh->b_size;
2094 
2095         block_start = 0;
2096         do {
2097                 block_end = block_start + blocksize;
2098                 if (block_end <= from || block_start >= to) {
2099                         if (!buffer_uptodate(bh))
2100                                 partial = 1;
2101                 } else {
2102                         set_buffer_uptodate(bh);
2103                         mark_buffer_dirty(bh);
2104                 }
2105                 clear_buffer_new(bh);
2106 
2107                 block_start = block_end;
2108                 bh = bh->b_this_page;
2109         } while (bh != head);
2110 
2111         /*
2112          * If this is a partial write which happened to make all buffers
2113          * uptodate then we can optimize away a bogus readpage() for
2114          * the next read(). Here we 'discover' whether the page went
2115          * uptodate as a result of this (potentially partial) write.
2116          */
2117         if (!partial)
2118                 SetPageUptodate(page);
2119         return 0;
2120 }
2121 
2122 /*
2123  * block_write_begin takes care of the basic task of block allocation and
2124  * bringing partial write blocks uptodate first.
2125  *
2126  * The filesystem needs to handle block truncation upon failure.
2127  */
2128 int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
2129                 unsigned flags, struct page **pagep, get_block_t *get_block)
2130 {
2131         pgoff_t index = pos >> PAGE_SHIFT;
2132         struct page *page;
2133         int status;
2134 
2135         page = grab_cache_page_write_begin(mapping, index, flags);
2136         if (!page)
2137                 return -ENOMEM;
2138 
2139         status = __block_write_begin(page, pos, len, get_block);
2140         if (unlikely(status)) {
2141                 unlock_page(page);
2142                 put_page(page);
2143                 page = NULL;
2144         }
2145 
2146         *pagep = page;
2147         return status;
2148 }
2149 EXPORT_SYMBOL(block_write_begin);
2150 
2151 int block_write_end(struct file *file, struct address_space *mapping,
2152                         loff_t pos, unsigned len, unsigned copied,
2153                         struct page *page, void *fsdata)
2154 {
2155         struct inode *inode = mapping->host;
2156         unsigned start;
2157 
2158         start = pos & (PAGE_SIZE - 1);
2159 
2160         if (unlikely(copied < len)) {
2161                 /*
2162                  * The buffers that were written will now be uptodate, so we
2163                  * don't have to worry about a readpage reading them and
2164                  * overwriting a partial write. However if we have encountered
2165                  * a short write and only partially written into a buffer, it
2166                  * will not be marked uptodate, so a readpage might come in and
2167                  * destroy our partial write.
2168                  *
2169                  * Do the simplest thing, and just treat any short write to a
2170                  * non uptodate page as a zero-length write, and force the
2171                  * caller to redo the whole thing.
2172                  */
2173                 if (!PageUptodate(page))
2174                         copied = 0;
2175 
2176                 page_zero_new_buffers(page, start+copied, start+len);
2177         }
2178         flush_dcache_page(page);
2179 
2180         /* This could be a short (even 0-length) commit */
2181         __block_commit_write(inode, page, start, start+copied);
2182 
2183         return copied;
2184 }
2185 EXPORT_SYMBOL(block_write_end);
2186 
2187 int generic_write_end(struct file *file, struct address_space *mapping,
2188                         loff_t pos, unsigned len, unsigned copied,
2189                         struct page *page, void *fsdata)
2190 {
2191         struct inode *inode = mapping->host;
2192         loff_t old_size = inode->i_size;
2193         int i_size_changed = 0;
2194 
2195         copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2196 
2197         /*
2198          * No need to use i_size_read() here, the i_size
2199          * cannot change under us because we hold i_mutex.
2200          *
2201          * But it's important to update i_size while still holding page lock:
2202          * page writeout could otherwise come in and zero beyond i_size.
2203          */
2204         if (pos+copied > inode->i_size) {
2205                 i_size_write(inode, pos+copied);
2206                 i_size_changed = 1;
2207         }
2208 
2209         unlock_page(page);
2210         put_page(page);
2211 
2212         if (old_size < pos)
2213                 pagecache_isize_extended(inode, old_size, pos);
2214         /*
2215          * Don't mark the inode dirty under page lock. First, it unnecessarily
2216          * makes the holding time of page lock longer. Second, it forces lock
2217          * ordering of page lock and transaction start for journaling
2218          * filesystems.
2219          */
2220         if (i_size_changed)
2221                 mark_inode_dirty(inode);
2222 
2223         return copied;
2224 }
2225 EXPORT_SYMBOL(generic_write_end);
2226 
2227 /*
2228  * block_is_partially_uptodate checks whether buffers within a page are
2229  * uptodate or not.
2230  *
2231  * Returns true if all buffers which correspond to a file portion
2232  * we want to read are uptodate.
2233  */
2234 int block_is_partially_uptodate(struct page *page, unsigned long from,
2235                                         unsigned long count)
2236 {
2237         unsigned block_start, block_end, blocksize;
2238         unsigned to;
2239         struct buffer_head *bh, *head;
2240         int ret = 1;
2241 
2242         if (!page_has_buffers(page))
2243                 return 0;
2244 
2245         head = page_buffers(page);
2246         blocksize = head->b_size;
2247         to = min_t(unsigned, PAGE_SIZE - from, count);
2248         to = from + to;
2249         if (from < blocksize && to > PAGE_SIZE - blocksize)
2250                 return 0;
2251 
2252         bh = head;
2253         block_start = 0;
2254         do {
2255                 block_end = block_start + blocksize;
2256                 if (block_end > from && block_start < to) {
2257                         if (!buffer_uptodate(bh)) {
2258                                 ret = 0;
2259                                 break;
2260                         }
2261                         if (block_end >= to)
2262                                 break;
2263                 }
2264                 block_start = block_end;
2265                 bh = bh->b_this_page;
2266         } while (bh != head);
2267 
2268         return ret;
2269 }
2270 EXPORT_SYMBOL(block_is_partially_uptodate);
2271 
2272 /*
2273  * Generic "read page" function for block devices that have the normal
2274  * get_block functionality. This is most of the block device filesystems.
2275  * Reads the page asynchronously --- the unlock_buffer() and
2276  * set/clear_buffer_uptodate() functions propagate buffer state into the
2277  * page struct once IO has completed.
2278  */
2279 int block_read_full_page(struct page *page, get_block_t *get_block)
2280 {
2281         struct inode *inode = page->mapping->host;
2282         sector_t iblock, lblock;
2283         struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2284         unsigned int blocksize, bbits;
2285         int nr, i;
2286         int fully_mapped = 1;
2287 
2288         head = create_page_buffers(page, inode, 0);
2289         blocksize = head->b_size;
2290         bbits = block_size_bits(blocksize);
2291 
2292         iblock = (sector_t)page->index << (PAGE_SHIFT - bbits);
2293         lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2294         bh = head;
2295         nr = 0;
2296         i = 0;
2297 
2298         do {
2299                 if (buffer_uptodate(bh))
2300                         continue;
2301 
2302                 if (!buffer_mapped(bh)) {
2303                         int err = 0;
2304 
2305                         fully_mapped = 0;
2306                         if (iblock < lblock) {
2307                                 WARN_ON(bh->b_size != blocksize);
2308                                 err = get_block(inode, iblock, bh, 0);
2309                                 if (err)
2310                                         SetPageError(page);
2311                         }
2312                         if (!buffer_mapped(bh)) {
2313                                 zero_user(page, i * blocksize, blocksize);
2314                                 if (!err)
2315                                         set_buffer_uptodate(bh);
2316                                 continue;
2317                         }
2318                         /*
2319                          * get_block() might have updated the buffer
2320                          * synchronously
2321                          */
2322                         if (buffer_uptodate(bh))
2323                                 continue;
2324                 }
2325                 arr[nr++] = bh;
2326         } while (i++, iblock++, (bh = bh->b_this_page) != head);
2327 
2328         if (fully_mapped)
2329                 SetPageMappedToDisk(page);
2330 
2331         if (!nr) {
2332                 /*
2333                  * All buffers are uptodate - we can set the page uptodate
2334                  * as well. But not if get_block() returned an error.
2335                  */
2336                 if (!PageError(page))
2337                         SetPageUptodate(page);
2338                 unlock_page(page);
2339                 return 0;
2340         }
2341 
2342         /* Stage two: lock the buffers */
2343         for (i = 0; i < nr; i++) {
2344                 bh = arr[i];
2345                 lock_buffer(bh);
2346                 mark_buffer_async_read(bh);
2347         }
2348 
2349         /*
2350          * Stage 3: start the IO.  Check for uptodateness
2351          * inside the buffer lock in case another process reading
2352          * the underlying blockdev brought it uptodate (the sct fix).
2353          */
2354         for (i = 0; i < nr; i++) {
2355                 bh = arr[i];
2356                 if (buffer_uptodate(bh))
2357                         end_buffer_async_read(bh, 1);
2358                 else
2359                         submit_bh(REQ_OP_READ, 0, bh);
2360         }
2361         return 0;
2362 }
2363 EXPORT_SYMBOL(block_read_full_page);
2364 
2365 /* utility function for filesystems that need to do work on expanding
2366  * truncates.  Uses filesystem pagecache writes to allow the filesystem to
2367  * deal with the hole.  
2368  */
2369 int generic_cont_expand_simple(struct inode *inode, loff_t size)
2370 {
2371         struct address_space *mapping = inode->i_mapping;
2372         struct page *page;
2373         void *fsdata;
2374         int err;
2375 
2376         err = inode_newsize_ok(inode, size);
2377         if (err)
2378                 goto out;
2379 
2380         err = pagecache_write_begin(NULL, mapping, size, 0,
2381                                 AOP_FLAG_UNINTERRUPTIBLE|AOP_FLAG_CONT_EXPAND,
2382                                 &page, &fsdata);
2383         if (err)
2384                 goto out;
2385 
2386         err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2387         BUG_ON(err > 0);
2388 
2389 out:
2390         return err;
2391 }
2392 EXPORT_SYMBOL(generic_cont_expand_simple);
2393 
2394 static int cont_expand_zero(struct file *file, struct address_space *mapping,
2395                             loff_t pos, loff_t *bytes)
2396 {
2397         struct inode *inode = mapping->host;
2398         unsigned blocksize = 1 << inode->i_blkbits;
2399         struct page *page;
2400         void *fsdata;
2401         pgoff_t index, curidx;
2402         loff_t curpos;
2403         unsigned zerofrom, offset, len;
2404         int err = 0;
2405 
2406         index = pos >> PAGE_SHIFT;
2407         offset = pos & ~PAGE_MASK;
2408 
2409         while (index > (curidx = (curpos = *bytes)>>PAGE_SHIFT)) {
2410                 zerofrom = curpos & ~PAGE_MASK;
2411                 if (zerofrom & (blocksize-1)) {
2412                         *bytes |= (blocksize-1);
2413                         (*bytes)++;
2414                 }
2415                 len = PAGE_SIZE - zerofrom;
2416 
2417                 err = pagecache_write_begin(file, mapping, curpos, len,
2418                                                 AOP_FLAG_UNINTERRUPTIBLE,
2419                                                 &page, &fsdata);
2420                 if (err)
2421                         goto out;
2422                 zero_user(page, zerofrom, len);
2423                 err = pagecache_write_end(file, mapping, curpos, len, len,
2424                                                 page, fsdata);
2425                 if (err < 0)
2426                         goto out;
2427                 BUG_ON(err != len);
2428                 err = 0;
2429 
2430                 balance_dirty_pages_ratelimited(mapping);
2431 
2432                 if (unlikely(fatal_signal_pending(current))) {
2433                         err = -EINTR;
2434                         goto out;
2435                 }
2436         }
2437 
2438         /* page covers the boundary, find the boundary offset */
2439         if (index == curidx) {
2440                 zerofrom = curpos & ~PAGE_MASK;
2441                 /* if we will expand the thing last block will be filled */
2442                 if (offset <= zerofrom) {
2443                         goto out;
2444                 }
2445                 if (zerofrom & (blocksize-1)) {
2446                         *bytes |= (blocksize-1);
2447                         (*bytes)++;
2448                 }
2449                 len = offset - zerofrom;
2450 
2451                 err = pagecache_write_begin(file, mapping, curpos, len,
2452                                                 AOP_FLAG_UNINTERRUPTIBLE,
2453                                                 &page, &fsdata);
2454                 if (err)
2455                         goto out;
2456                 zero_user(page, zerofrom, len);
2457                 err = pagecache_write_end(file, mapping, curpos, len, len,
2458                                                 page, fsdata);
2459                 if (err < 0)
2460                         goto out;
2461                 BUG_ON(err != len);
2462                 err = 0;
2463         }
2464 out:
2465         return err;
2466 }
2467 
2468 /*
2469  * For moronic filesystems that do not allow holes in file.
2470  * We may have to extend the file.
2471  */
2472 int cont_write_begin(struct file *file, struct address_space *mapping,
2473                         loff_t pos, unsigned len, unsigned flags,
2474                         struct page **pagep, void **fsdata,
2475                         get_block_t *get_block, loff_t *bytes)
2476 {
2477         struct inode *inode = mapping->host;
2478         unsigned blocksize = 1 << inode->i_blkbits;
2479         unsigned zerofrom;
2480         int err;
2481 
2482         err = cont_expand_zero(file, mapping, pos, bytes);
2483         if (err)
2484                 return err;
2485 
2486         zerofrom = *bytes & ~PAGE_MASK;
2487         if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2488                 *bytes |= (blocksize-1);
2489                 (*bytes)++;
2490         }
2491 
2492         return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2493 }
2494 EXPORT_SYMBOL(cont_write_begin);
2495 
2496 int block_commit_write(struct page *page, unsigned from, unsigned to)
2497 {
2498         struct inode *inode = page->mapping->host;
2499         __block_commit_write(inode,page,from,to);
2500         return 0;
2501 }
2502 EXPORT_SYMBOL(block_commit_write);
2503 
2504 /*
2505  * block_page_mkwrite() is not allowed to change the file size as it gets
2506  * called from a page fault handler when a page is first dirtied. Hence we must
2507  * be careful to check for EOF conditions here. We set the page up correctly
2508  * for a written page which means we get ENOSPC checking when writing into
2509  * holes and correct delalloc and unwritten extent mapping on filesystems that
2510  * support these features.
2511  *
2512  * We are not allowed to take the i_mutex here so we have to play games to
2513  * protect against truncate races as the page could now be beyond EOF.  Because
2514  * truncate writes the inode size before removing pages, once we have the
2515  * page lock we can determine safely if the page is beyond EOF. If it is not
2516  * beyond EOF, then the page is guaranteed safe against truncation until we
2517  * unlock the page.
2518  *
2519  * Direct callers of this function should protect against filesystem freezing
2520  * using sb_start_pagefault() - sb_end_pagefault() functions.
2521  */
2522 int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2523                          get_block_t get_block)
2524 {
2525         struct page *page = vmf->page;
2526         struct inode *inode = file_inode(vma->vm_file);
2527         unsigned long end;
2528         loff_t size;
2529         int ret;
2530 
2531         lock_page(page);
2532         size = i_size_read(inode);
2533         if ((page->mapping != inode->i_mapping) ||
2534             (page_offset(page) > size)) {
2535                 /* We overload EFAULT to mean page got truncated */
2536                 ret = -EFAULT;
2537                 goto out_unlock;
2538         }
2539 
2540         /* page is wholly or partially inside EOF */
2541         if (((page->index + 1) << PAGE_SHIFT) > size)
2542                 end = size & ~PAGE_MASK;
2543         else
2544                 end = PAGE_SIZE;
2545 
2546         ret = __block_write_begin(page, 0, end, get_block);
2547         if (!ret)
2548                 ret = block_commit_write(page, 0, end);
2549 
2550         if (unlikely(ret < 0))
2551                 goto out_unlock;
2552         set_page_dirty(page);
2553         wait_for_stable_page(page);
2554         return 0;
2555 out_unlock:
2556         unlock_page(page);
2557         return ret;
2558 }
2559 EXPORT_SYMBOL(block_page_mkwrite);
2560 
2561 /*
2562  * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2563  * immediately, while under the page lock.  So it needs a special end_io
2564  * handler which does not touch the bh after unlocking it.
2565  */
2566 static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2567 {
2568         __end_buffer_read_notouch(bh, uptodate);
2569 }
2570 
2571 /*
2572  * Attach the singly-linked list of buffers created by nobh_write_begin, to
2573  * the page (converting it to circular linked list and taking care of page
2574  * dirty races).
2575  */
2576 static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2577 {
2578         struct buffer_head *bh;
2579 
2580         BUG_ON(!PageLocked(page));
2581 
2582         spin_lock(&page->mapping->private_lock);
2583         bh = head;
2584         do {
2585                 if (PageDirty(page))
2586                         set_buffer_dirty(bh);
2587                 if (!bh->b_this_page)
2588                         bh->b_this_page = head;
2589                 bh = bh->b_this_page;
2590         } while (bh != head);
2591         attach_page_buffers(page, head);
2592         spin_unlock(&page->mapping->private_lock);
2593 }
2594 
2595 /*
2596  * On entry, the page is fully not uptodate.
2597  * On exit the page is fully uptodate in the areas outside (from,to)
2598  * The filesystem needs to handle block truncation upon failure.
2599  */
2600 int nobh_write_begin(struct address_space *mapping,
2601                         loff_t pos, unsigned len, unsigned flags,
2602                         struct page **pagep, void **fsdata,
2603                         get_block_t *get_block)
2604 {
2605         struct inode *inode = mapping->host;
2606         const unsigned blkbits = inode->i_blkbits;
2607         const unsigned blocksize = 1 << blkbits;
2608         struct buffer_head *head, *bh;
2609         struct page *page;
2610         pgoff_t index;
2611         unsigned from, to;
2612         unsigned block_in_page;
2613         unsigned block_start, block_end;
2614         sector_t block_in_file;
2615         int nr_reads = 0;
2616         int ret = 0;
2617         int is_mapped_to_disk = 1;
2618 
2619         index = pos >> PAGE_SHIFT;
2620         from = pos & (PAGE_SIZE - 1);
2621         to = from + len;
2622 
2623         page = grab_cache_page_write_begin(mapping, index, flags);
2624         if (!page)
2625                 return -ENOMEM;
2626         *pagep = page;
2627         *fsdata = NULL;
2628 
2629         if (page_has_buffers(page)) {
2630                 ret = __block_write_begin(page, pos, len, get_block);
2631                 if (unlikely(ret))
2632                         goto out_release;
2633                 return ret;
2634         }
2635 
2636         if (PageMappedToDisk(page))
2637                 return 0;
2638 
2639         /*
2640          * Allocate buffers so that we can keep track of state, and potentially
2641          * attach them to the page if an error occurs. In the common case of
2642          * no error, they will just be freed again without ever being attached
2643          * to the page (which is all OK, because we're under the page lock).
2644          *
2645          * Be careful: the buffer linked list is a NULL terminated one, rather
2646          * than the circular one we're used to.
2647          */
2648         head = alloc_page_buffers(page, blocksize, 0);
2649         if (!head) {
2650                 ret = -ENOMEM;
2651                 goto out_release;
2652         }
2653 
2654         block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
2655 
2656         /*
2657          * We loop across all blocks in the page, whether or not they are
2658          * part of the affected region.  This is so we can discover if the
2659          * page is fully mapped-to-disk.
2660          */
2661         for (block_start = 0, block_in_page = 0, bh = head;
2662                   block_start < PAGE_SIZE;
2663                   block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2664                 int create;
2665 
2666                 block_end = block_start + blocksize;
2667                 bh->b_state = 0;
2668                 create = 1;
2669                 if (block_start >= to)
2670                         create = 0;
2671                 ret = get_block(inode, block_in_file + block_in_page,
2672                                         bh, create);
2673                 if (ret)
2674                         goto failed;
2675                 if (!buffer_mapped(bh))
2676                         is_mapped_to_disk = 0;
2677                 if (buffer_new(bh))
2678                         clean_bdev_bh_alias(bh);
2679                 if (PageUptodate(page)) {
2680                         set_buffer_uptodate(bh);
2681                         continue;
2682                 }
2683                 if (buffer_new(bh) || !buffer_mapped(bh)) {
2684                         zero_user_segments(page, block_start, from,
2685                                                         to, block_end);
2686                         continue;
2687                 }
2688                 if (buffer_uptodate(bh))
2689                         continue;       /* reiserfs does this */
2690                 if (block_start < from || block_end > to) {
2691                         lock_buffer(bh);
2692                         bh->b_end_io = end_buffer_read_nobh;
2693                         submit_bh(REQ_OP_READ, 0, bh);
2694                         nr_reads++;
2695                 }
2696         }
2697 
2698         if (nr_reads) {
2699                 /*
2700                  * The page is locked, so these buffers are protected from
2701                  * any VM or truncate activity.  Hence we don't need to care
2702                  * for the buffer_head refcounts.
2703                  */
2704                 for (bh = head; bh; bh = bh->b_this_page) {
2705                         wait_on_buffer(bh);
2706                         if (!buffer_uptodate(bh))
2707                                 ret = -EIO;
2708                 }
2709                 if (ret)
2710                         goto failed;
2711         }
2712 
2713         if (is_mapped_to_disk)
2714                 SetPageMappedToDisk(page);
2715 
2716         *fsdata = head; /* to be released by nobh_write_end */
2717 
2718         return 0;
2719 
2720 failed:
2721         BUG_ON(!ret);
2722         /*
2723          * Error recovery is a bit difficult. We need to zero out blocks that
2724          * were newly allocated, and dirty them to ensure they get written out.
2725          * Buffers need to be attached to the page at this point, otherwise
2726          * the handling of potential IO errors during writeout would be hard
2727          * (could try doing synchronous writeout, but what if that fails too?)
2728          */
2729         attach_nobh_buffers(page, head);
2730         page_zero_new_buffers(page, from, to);
2731 
2732 out_release:
2733         unlock_page(page);
2734         put_page(page);
2735         *pagep = NULL;
2736 
2737         return ret;
2738 }
2739 EXPORT_SYMBOL(nobh_write_begin);
2740 
2741 int nobh_write_end(struct file *file, struct address_space *mapping,
2742                         loff_t pos, unsigned len, unsigned copied,
2743                         struct page *page, void *fsdata)
2744 {
2745         struct inode *inode = page->mapping->host;
2746         struct buffer_head *head = fsdata;
2747         struct buffer_head *bh;
2748         BUG_ON(fsdata != NULL && page_has_buffers(page));
2749 
2750         if (unlikely(copied < len) && head)
2751                 attach_nobh_buffers(page, head);
2752         if (page_has_buffers(page))
2753                 return generic_write_end(file, mapping, pos, len,
2754                                         copied, page, fsdata);
2755 
2756         SetPageUptodate(page);
2757         set_page_dirty(page);
2758         if (pos+copied > inode->i_size) {
2759                 i_size_write(inode, pos+copied);
2760                 mark_inode_dirty(inode);
2761         }
2762 
2763         unlock_page(page);
2764         put_page(page);
2765 
2766         while (head) {
2767                 bh = head;
2768                 head = head->b_this_page;
2769                 free_buffer_head(bh);
2770         }
2771 
2772         return copied;
2773 }
2774 EXPORT_SYMBOL(nobh_write_end);
2775 
2776 /*
2777  * nobh_writepage() - based on block_full_write_page() except
2778  * that it tries to operate without attaching bufferheads to
2779  * the page.
2780  */
2781 int nobh_writepage(struct page *page, get_block_t *get_block,
2782                         struct writeback_control *wbc)
2783 {
2784         struct inode * const inode = page->mapping->host;
2785         loff_t i_size = i_size_read(inode);
2786         const pgoff_t end_index = i_size >> PAGE_SHIFT;
2787         unsigned offset;
2788         int ret;
2789 
2790         /* Is the page fully inside i_size? */
2791         if (page->index < end_index)
2792                 goto out;
2793 
2794         /* Is the page fully outside i_size? (truncate in progress) */
2795         offset = i_size & (PAGE_SIZE-1);
2796         if (page->index >= end_index+1 || !offset) {
2797                 /*
2798                  * The page may have dirty, unmapped buffers.  For example,
2799                  * they may have been added in ext3_writepage().  Make them
2800                  * freeable here, so the page does not leak.
2801                  */
2802 #if 0
2803                 /* Not really sure about this  - do we need this ? */
2804                 if (page->mapping->a_ops->invalidatepage)
2805                         page->mapping->a_ops->invalidatepage(page, offset);
2806 #endif
2807                 unlock_page(page);
2808                 return 0; /* don't care */
2809         }
2810 
2811         /*
2812          * The page straddles i_size.  It must be zeroed out on each and every
2813          * writepage invocation because it may be mmapped.  "A file is mapped
2814          * in multiples of the page size.  For a file that is not a multiple of
2815          * the  page size, the remaining memory is zeroed when mapped, and
2816          * writes to that region are not written out to the file."
2817          */
2818         zero_user_segment(page, offset, PAGE_SIZE);
2819 out:
2820         ret = mpage_writepage(page, get_block, wbc);
2821         if (ret == -EAGAIN)
2822                 ret = __block_write_full_page(inode, page, get_block, wbc,
2823                                               end_buffer_async_write);
2824         return ret;
2825 }
2826 EXPORT_SYMBOL(nobh_writepage);
2827 
2828 int nobh_truncate_page(struct address_space *mapping,
2829                         loff_t from, get_block_t *get_block)
2830 {
2831         pgoff_t index = from >> PAGE_SHIFT;
2832         unsigned offset = from & (PAGE_SIZE-1);
2833         unsigned blocksize;
2834         sector_t iblock;
2835         unsigned length, pos;
2836         struct inode *inode = mapping->host;
2837         struct page *page;
2838         struct buffer_head map_bh;
2839         int err;
2840 
2841         blocksize = 1 << inode->i_blkbits;
2842         length = offset & (blocksize - 1);
2843 
2844         /* Block boundary? Nothing to do */
2845         if (!length)
2846                 return 0;
2847 
2848         length = blocksize - length;
2849         iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2850 
2851         page = grab_cache_page(mapping, index);
2852         err = -ENOMEM;
2853         if (!page)
2854                 goto out;
2855 
2856         if (page_has_buffers(page)) {
2857 has_buffers:
2858                 unlock_page(page);
2859                 put_page(page);
2860                 return block_truncate_page(mapping, from, get_block);
2861         }
2862 
2863         /* Find the buffer that contains "offset" */
2864         pos = blocksize;
2865         while (offset >= pos) {
2866                 iblock++;
2867                 pos += blocksize;
2868         }
2869 
2870         map_bh.b_size = blocksize;
2871         map_bh.b_state = 0;
2872         err = get_block(inode, iblock, &map_bh, 0);
2873         if (err)
2874                 goto unlock;
2875         /* unmapped? It's a hole - nothing to do */
2876         if (!buffer_mapped(&map_bh))
2877                 goto unlock;
2878 
2879         /* Ok, it's mapped. Make sure it's up-to-date */
2880         if (!PageUptodate(page)) {
2881                 err = mapping->a_ops->readpage(NULL, page);
2882                 if (err) {
2883                         put_page(page);
2884                         goto out;
2885                 }
2886                 lock_page(page);
2887                 if (!PageUptodate(page)) {
2888                         err = -EIO;
2889                         goto unlock;
2890                 }
2891                 if (page_has_buffers(page))
2892                         goto has_buffers;
2893         }
2894         zero_user(page, offset, length);
2895         set_page_dirty(page);
2896         err = 0;
2897 
2898 unlock:
2899         unlock_page(page);
2900         put_page(page);
2901 out:
2902         return err;
2903 }
2904 EXPORT_SYMBOL(nobh_truncate_page);
2905 
2906 int block_truncate_page(struct address_space *mapping,
2907                         loff_t from, get_block_t *get_block)
2908 {
2909         pgoff_t index = from >> PAGE_SHIFT;
2910         unsigned offset = from & (PAGE_SIZE-1);
2911         unsigned blocksize;
2912         sector_t iblock;
2913         unsigned length, pos;
2914         struct inode *inode = mapping->host;
2915         struct page *page;
2916         struct buffer_head *bh;
2917         int err;
2918 
2919         blocksize = 1 << inode->i_blkbits;
2920         length = offset & (blocksize - 1);
2921 
2922         /* Block boundary? Nothing to do */
2923         if (!length)
2924                 return 0;
2925 
2926         length = blocksize - length;
2927         iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2928         
2929         page = grab_cache_page(mapping, index);
2930         err = -ENOMEM;
2931         if (!page)
2932                 goto out;
2933 
2934         if (!page_has_buffers(page))
2935                 create_empty_buffers(page, blocksize, 0);
2936 
2937         /* Find the buffer that contains "offset" */
2938         bh = page_buffers(page);
2939         pos = blocksize;
2940         while (offset >= pos) {
2941                 bh = bh->b_this_page;
2942                 iblock++;
2943                 pos += blocksize;
2944         }
2945 
2946         err = 0;
2947         if (!buffer_mapped(bh)) {
2948                 WARN_ON(bh->b_size != blocksize);
2949                 err = get_block(inode, iblock, bh, 0);
2950                 if (err)
2951                         goto unlock;
2952                 /* unmapped? It's a hole - nothing to do */
2953                 if (!buffer_mapped(bh))
2954                         goto unlock;
2955         }
2956 
2957         /* Ok, it's mapped. Make sure it's up-to-date */
2958         if (PageUptodate(page))
2959                 set_buffer_uptodate(bh);
2960 
2961         if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2962                 err = -EIO;
2963                 ll_rw_block(REQ_OP_READ, 0, 1, &bh);
2964                 wait_on_buffer(bh);
2965                 /* Uhhuh. Read error. Complain and punt. */
2966                 if (!buffer_uptodate(bh))
2967                         goto unlock;
2968         }
2969 
2970         zero_user(page, offset, length);
2971         mark_buffer_dirty(bh);
2972         err = 0;
2973 
2974 unlock:
2975         unlock_page(page);
2976         put_page(page);
2977 out:
2978         return err;
2979 }
2980 EXPORT_SYMBOL(block_truncate_page);
2981 
2982 /*
2983  * The generic ->writepage function for buffer-backed address_spaces
2984  */
2985 int block_write_full_page(struct page *page, get_block_t *get_block,
2986                         struct writeback_control *wbc)
2987 {
2988         struct inode * const inode = page->mapping->host;
2989         loff_t i_size = i_size_read(inode);
2990         const pgoff_t end_index = i_size >> PAGE_SHIFT;
2991         unsigned offset;
2992 
2993         /* Is the page fully inside i_size? */
2994         if (page->index < end_index)
2995                 return __block_write_full_page(inode, page, get_block, wbc,
2996                                                end_buffer_async_write);
2997 
2998         /* Is the page fully outside i_size? (truncate in progress) */
2999         offset = i_size & (PAGE_SIZE-1);
3000         if (page->index >= end_index+1 || !offset) {
3001                 /*
3002                  * The page may have dirty, unmapped buffers.  For example,
3003                  * they may have been added in ext3_writepage().  Make them
3004                  * freeable here, so the page does not leak.
3005                  */
3006                 do_invalidatepage(page, 0, PAGE_SIZE);
3007                 unlock_page(page);
3008                 return 0; /* don't care */
3009         }
3010 
3011         /*
3012          * The page straddles i_size.  It must be zeroed out on each and every
3013          * writepage invocation because it may be mmapped.  "A file is mapped
3014          * in multiples of the page size.  For a file that is not a multiple of
3015          * the  page size, the remaining memory is zeroed when mapped, and
3016          * writes to that region are not written out to the file."
3017          */
3018         zero_user_segment(page, offset, PAGE_SIZE);
3019         return __block_write_full_page(inode, page, get_block, wbc,
3020                                                         end_buffer_async_write);
3021 }
3022 EXPORT_SYMBOL(block_write_full_page);
3023 
3024 sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
3025                             get_block_t *get_block)
3026 {
3027         struct buffer_head tmp;
3028         struct inode *inode = mapping->host;
3029         tmp.b_state = 0;
3030         tmp.b_blocknr = 0;
3031         tmp.b_size = 1 << inode->i_blkbits;
3032         get_block(inode, block, &tmp, 0);
3033         return tmp.b_blocknr;
3034 }
3035 EXPORT_SYMBOL(generic_block_bmap);
3036 
3037 static void end_bio_bh_io_sync(struct bio *bio)
3038 {
3039         struct buffer_head *bh = bio->bi_private;
3040 
3041         if (unlikely(bio_flagged(bio, BIO_QUIET)))
3042                 set_bit(BH_Quiet, &bh->b_state);
3043 
3044         bh->b_end_io(bh, !bio->bi_error);
3045         bio_put(bio);
3046 }
3047 
3048 /*
3049  * This allows us to do IO even on the odd last sectors
3050  * of a device, even if the block size is some multiple
3051  * of the physical sector size.
3052  *
3053  * We'll just truncate the bio to the size of the device,
3054  * and clear the end of the buffer head manually.
3055  *
3056  * Truly out-of-range accesses will turn into actual IO
3057  * errors, this only handles the "we need to be able to
3058  * do IO at the final sector" case.
3059  */
3060 void guard_bio_eod(int op, struct bio *bio)
3061 {
3062         sector_t maxsector;
3063         struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
3064         unsigned truncated_bytes;
3065 
3066         maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
3067         if (!maxsector)
3068                 return;
3069 
3070         /*
3071          * If the *whole* IO is past the end of the device,
3072          * let it through, and the IO layer will turn it into
3073          * an EIO.
3074          */
3075         if (unlikely(bio->bi_iter.bi_sector >= maxsector))
3076                 return;
3077 
3078         maxsector -= bio->bi_iter.bi_sector;
3079         if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))
3080                 return;
3081 
3082         /* Uhhuh. We've got a bio that straddles the device size! */
3083         truncated_bytes = bio->bi_iter.bi_size - (maxsector << 9);
3084 
3085         /* Truncate the bio.. */
3086         bio->bi_iter.bi_size -= truncated_bytes;
3087         bvec->bv_len -= truncated_bytes;
3088 
3089         /* ..and clear the end of the buffer for reads */
3090         if (op == REQ_OP_READ) {
3091                 zero_user(bvec->bv_page, bvec->bv_offset + bvec->bv_len,
3092                                 truncated_bytes);
3093         }
3094 }
3095 
3096 static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
3097                          unsigned long bio_flags, struct writeback_control *wbc)
3098 {
3099         struct bio *bio;
3100 
3101         BUG_ON(!buffer_locked(bh));
3102         BUG_ON(!buffer_mapped(bh));
3103         BUG_ON(!bh->b_end_io);
3104         BUG_ON(buffer_delay(bh));
3105         BUG_ON(buffer_unwritten(bh));
3106 
3107         /*
3108          * Only clear out a write error when rewriting
3109          */
3110         if (test_set_buffer_req(bh) && (op == REQ_OP_WRITE))
3111                 clear_buffer_write_io_error(bh);
3112 
3113         /*
3114          * from here on down, it's all bio -- do the initial mapping,
3115          * submit_bio -> generic_make_request may further map this bio around
3116          */
3117         bio = bio_alloc(GFP_NOIO, 1);
3118 
3119         if (wbc) {
3120                 wbc_init_bio(wbc, bio);
3121                 wbc_account_io(wbc, bh->b_page, bh->b_size);
3122         }
3123 
3124         bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
3125         bio->bi_bdev = bh->b_bdev;
3126 
3127         bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
3128         BUG_ON(bio->bi_iter.bi_size != bh->b_size);
3129 
3130         bio->bi_end_io = end_bio_bh_io_sync;
3131         bio->bi_private = bh;
3132         bio->bi_flags |= bio_flags;
3133 
3134         /* Take care of bh's that straddle the end of the device */
3135         guard_bio_eod(op, bio);
3136 
3137         if (buffer_meta(bh))
3138                 op_flags |= REQ_META;
3139         if (buffer_prio(bh))
3140                 op_flags |= REQ_PRIO;
3141         bio_set_op_attrs(bio, op, op_flags);
3142 
3143         submit_bio(bio);
3144         return 0;
3145 }
3146 
3147 int _submit_bh(int op, int op_flags, struct buffer_head *bh,
3148                unsigned long bio_flags)
3149 {
3150         return submit_bh_wbc(op, op_flags, bh, bio_flags, NULL);
3151 }
3152 EXPORT_SYMBOL_GPL(_submit_bh);
3153 
3154 int submit_bh(int op, int op_flags,  struct buffer_head *bh)
3155 {
3156         return submit_bh_wbc(op, op_flags, bh, 0, NULL);
3157 }
3158 EXPORT_SYMBOL(submit_bh);
3159 
3160 /**
3161  * ll_rw_block: low-level access to block devices (DEPRECATED)
3162  * @op: whether to %READ or %WRITE
3163  * @op_flags: req_flag_bits
3164  * @nr: number of &struct buffer_heads in the array
3165  * @bhs: array of pointers to &struct buffer_head
3166  *
3167  * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3168  * requests an I/O operation on them, either a %REQ_OP_READ or a %REQ_OP_WRITE.
3169  * @op_flags contains flags modifying the detailed I/O behavior, most notably
3170  * %REQ_RAHEAD.
3171  *
3172  * This function drops any buffer that it cannot get a lock on (with the
3173  * BH_Lock state bit), any buffer that appears to be clean when doing a write
3174  * request, and any buffer that appears to be up-to-date when doing read
3175  * request.  Further it marks as clean buffers that are processed for
3176  * writing (the buffer cache won't assume that they are actually clean
3177  * until the buffer gets unlocked).
3178  *
3179  * ll_rw_block sets b_end_io to simple completion handler that marks
3180  * the buffer up-to-date (if appropriate), unlocks the buffer and wakes
3181  * any waiters. 
3182  *
3183  * All of the buffers must be for the same device, and must also be a
3184  * multiple of the current approved size for the device.
3185  */
3186 void ll_rw_block(int op, int op_flags,  int nr, struct buffer_head *bhs[])
3187 {
3188         int i;
3189 
3190         for (i = 0; i < nr; i++) {
3191                 struct buffer_head *bh = bhs[i];
3192 
3193                 if (!trylock_buffer(bh))
3194                         continue;
3195                 if (op == WRITE) {
3196                         if (test_clear_buffer_dirty(bh)) {
3197                                 bh->b_end_io = end_buffer_write_sync;
3198                                 get_bh(bh);
3199                                 submit_bh(op, op_flags, bh);
3200                                 continue;
3201                         }
3202                 } else {
3203                         if (!buffer_uptodate(bh)) {
3204                                 bh->b_end_io = end_buffer_read_sync;
3205                                 get_bh(bh);
3206                                 submit_bh(op, op_flags, bh);
3207                                 continue;
3208                         }
3209                 }
3210                 unlock_buffer(bh);
3211         }
3212 }
3213 EXPORT_SYMBOL(ll_rw_block);
3214 
3215 void write_dirty_buffer(struct buffer_head *bh, int op_flags)
3216 {
3217         lock_buffer(bh);
3218         if (!test_clear_buffer_dirty(bh)) {
3219                 unlock_buffer(bh);
3220                 return;
3221         }
3222         bh->b_end_io = end_buffer_write_sync;
3223         get_bh(bh);
3224         submit_bh(REQ_OP_WRITE, op_flags, bh);
3225 }
3226 EXPORT_SYMBOL(write_dirty_buffer);
3227 
3228 /*
3229  * For a data-integrity writeout, we need to wait upon any in-progress I/O
3230  * and then start new I/O and then wait upon it.  The caller must have a ref on
3231  * the buffer_head.
3232  */
3233 int __sync_dirty_buffer(struct buffer_head *bh, int op_flags)
3234 {
3235         int ret = 0;
3236 
3237         WARN_ON(atomic_read(&bh->b_count) < 1);
3238         lock_buffer(bh);
3239         if (test_clear_buffer_dirty(bh)) {
3240                 get_bh(bh);
3241                 bh->b_end_io = end_buffer_write_sync;
3242                 ret = submit_bh(REQ_OP_WRITE, op_flags, bh);
3243                 wait_on_buffer(bh);
3244                 if (!ret && !buffer_uptodate(bh))
3245                         ret = -EIO;
3246         } else {
3247                 unlock_buffer(bh);
3248         }
3249         return ret;
3250 }
3251 EXPORT_SYMBOL(__sync_dirty_buffer);
3252 
3253 int sync_dirty_buffer(struct buffer_head *bh)
3254 {
3255         return __sync_dirty_buffer(bh, REQ_SYNC);
3256 }
3257 EXPORT_SYMBOL(sync_dirty_buffer);
3258 
3259 /*
3260  * try_to_free_buffers() checks if all the buffers on this particular page
3261  * are unused, and releases them if so.
3262  *
3263  * Exclusion against try_to_free_buffers may be obtained by either
3264  * locking the page or by holding its mapping's private_lock.
3265  *
3266  * If the page is dirty but all the buffers are clean then we need to
3267  * be sure to mark the page clean as well.  This is because the page
3268  * may be against a block device, and a later reattachment of buffers
3269  * to a dirty page will set *all* buffers dirty.  Which would corrupt
3270  * filesystem data on the same device.
3271  *
3272  * The same applies to regular filesystem pages: if all the buffers are
3273  * clean then we set the page clean and proceed.  To do that, we require
3274  * total exclusion from __set_page_dirty_buffers().  That is obtained with
3275  * private_lock.
3276  *
3277  * try_to_free_buffers() is non-blocking.
3278  */
3279 static inline int buffer_busy(struct buffer_head *bh)
3280 {
3281         return atomic_read(&bh->b_count) |
3282                 (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3283 }
3284 
3285 static int
3286 drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
3287 {
3288         struct buffer_head *head = page_buffers(page);
3289         struct buffer_head *bh;
3290 
3291         bh = head;
3292         do {
3293                 if (buffer_write_io_error(bh) && page->mapping)
3294                         mapping_set_error(page->mapping, -EIO);
3295                 if (buffer_busy(bh))
3296                         goto failed;
3297                 bh = bh->b_this_page;
3298         } while (bh != head);
3299 
3300         do {
3301                 struct buffer_head *next = bh->b_this_page;
3302 
3303                 if (bh->b_assoc_map)
3304                         __remove_assoc_queue(bh);
3305                 bh = next;
3306         } while (bh != head);
3307         *buffers_to_free = head;
3308         __clear_page_buffers(page);
3309         return 1;
3310 failed:
3311         return 0;
3312 }
3313 
3314 int try_to_free_buffers(struct page *page)
3315 {
3316         struct address_space * const mapping = page->mapping;
3317         struct buffer_head *buffers_to_free = NULL;
3318         int ret = 0;
3319 
3320         BUG_ON(!PageLocked(page));
3321         if (PageWriteback(page))
3322                 return 0;
3323 
3324         if (mapping == NULL) {          /* can this still happen? */
3325                 ret = drop_buffers(page, &buffers_to_free);
3326                 goto out;
3327         }
3328 
3329         spin_lock(&mapping->private_lock);
3330         ret = drop_buffers(page, &buffers_to_free);
3331 
3332         /*
3333          * If the filesystem writes its buffers by hand (eg ext3)
3334          * then we can have clean buffers against a dirty page.  We
3335          * clean the page here; otherwise the VM will never notice
3336          * that the filesystem did any IO at all.
3337          *
3338          * Also, during truncate, discard_buffer will have marked all
3339          * the page's buffers clean.  We discover that here and clean
3340          * the page also.
3341          *
3342          * private_lock must be held over this entire operation in order
3343          * to synchronise against __set_page_dirty_buffers and prevent the
3344          * dirty bit from being lost.
3345          */
3346         if (ret)
3347                 cancel_dirty_page(page);
3348         spin_unlock(&mapping->private_lock);
3349 out:
3350         if (buffers_to_free) {
3351                 struct buffer_head *bh = buffers_to_free;
3352 
3353                 do {
3354                         struct buffer_head *next = bh->b_this_page;
3355                         free_buffer_head(bh);
3356                         bh = next;
3357                 } while (bh != buffers_to_free);
3358         }
3359         return ret;
3360 }
3361 EXPORT_SYMBOL(try_to_free_buffers);
3362 
3363 /*
3364  * There are no bdflush tunables left.  But distributions are
3365  * still running obsolete flush daemons, so we terminate them here.
3366  *
3367  * Use of bdflush() is deprecated and will be removed in a future kernel.
3368  * The `flush-X' kernel threads fully replace bdflush daemons and this call.
3369  */
3370 SYSCALL_DEFINE2(bdflush, int, func, long, data)
3371 {
3372         static int msg_count;
3373 
3374         if (!capable(CAP_SYS_ADMIN))
3375                 return -EPERM;
3376 
3377         if (msg_count < 5) {
3378                 msg_count++;
3379                 printk(KERN_INFO
3380                         "warning: process `%s' used the obsolete bdflush"
3381                         " system call\n", current->comm);
3382                 printk(KERN_INFO "Fix your initscripts?\n");
3383         }
3384 
3385         if (func == 1)
3386                 do_exit(0);
3387         return 0;
3388 }
3389 
3390 /*
3391  * Buffer-head allocation
3392  */
3393 static struct kmem_cache *bh_cachep __read_mostly;
3394 
3395 /*
3396  * Once the number of bh's in the machine exceeds this level, we start
3397  * stripping them in writeback.
3398  */
3399 static unsigned long max_buffer_heads;
3400 
3401 int buffer_heads_over_limit;
3402 
3403 struct bh_accounting {
3404         int nr;                 /* Number of live bh's */
3405         int ratelimit;          /* Limit cacheline bouncing */
3406 };
3407 
3408 static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3409 
3410 static void recalc_bh_state(void)
3411 {
3412         int i;
3413         int tot = 0;
3414 
3415         if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3416                 return;
3417         __this_cpu_write(bh_accounting.ratelimit, 0);
3418         for_each_online_cpu(i)
3419                 tot += per_cpu(bh_accounting, i).nr;
3420         buffer_heads_over_limit = (tot > max_buffer_heads);
3421 }
3422 
3423 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3424 {
3425         struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3426         if (ret) {
3427                 INIT_LIST_HEAD(&ret->b_assoc_buffers);
3428                 preempt_disable();
3429                 __this_cpu_inc(bh_accounting.nr);
3430                 recalc_bh_state();
3431                 preempt_enable();
3432         }
3433         return ret;
3434 }
3435 EXPORT_SYMBOL(alloc_buffer_head);
3436 
3437 void free_buffer_head(struct buffer_head *bh)
3438 {
3439         BUG_ON(!list_empty(&bh->b_assoc_buffers));
3440         kmem_cache_free(bh_cachep, bh);
3441         preempt_disable();
3442         __this_cpu_dec(bh_accounting.nr);
3443         recalc_bh_state();
3444         preempt_enable();
3445 }
3446 EXPORT_SYMBOL(free_buffer_head);
3447 
3448 static int buffer_exit_cpu_dead(unsigned int cpu)
3449 {
3450         int i;
3451         struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3452 
3453         for (i = 0; i < BH_LRU_SIZE; i++) {
3454                 brelse(b->bhs[i]);
3455                 b->bhs[i] = NULL;
3456         }
3457         this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3458         per_cpu(bh_accounting, cpu).nr = 0;
3459         return 0;
3460 }
3461 
3462 /**
3463  * bh_uptodate_or_lock - Test whether the buffer is uptodate
3464  * @bh: struct buffer_head
3465  *
3466  * Return true if the buffer is up-to-date and false,
3467  * with the buffer locked, if not.
3468  */
3469 int bh_uptodate_or_lock(struct buffer_head *bh)
3470 {
3471         if (!buffer_uptodate(bh)) {
3472                 lock_buffer(bh);
3473                 if (!buffer_uptodate(bh))
3474                         return 0;
3475                 unlock_buffer(bh);
3476         }
3477         return 1;
3478 }
3479 EXPORT_SYMBOL(bh_uptodate_or_lock);
3480 
3481 /**
3482  * bh_submit_read - Submit a locked buffer for reading
3483  * @bh: struct buffer_head
3484  *
3485  * Returns zero on success and -EIO on error.
3486  */
3487 int bh_submit_read(struct buffer_head *bh)
3488 {
3489         BUG_ON(!buffer_locked(bh));
3490 
3491         if (buffer_uptodate(bh)) {
3492                 unlock_buffer(bh);
3493                 return 0;
3494         }
3495 
3496         get_bh(bh);
3497         bh->b_end_io = end_buffer_read_sync;
3498         submit_bh(REQ_OP_READ, 0, bh);
3499         wait_on_buffer(bh);
3500         if (buffer_uptodate(bh))
3501                 return 0;
3502         return -EIO;
3503 }
3504 EXPORT_SYMBOL(bh_submit_read);
3505 
3506 void __init buffer_init(void)
3507 {
3508         unsigned long nrpages;
3509         int ret;
3510 
3511         bh_cachep = kmem_cache_create("buffer_head",
3512                         sizeof(struct buffer_head), 0,
3513                                 (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3514                                 SLAB_MEM_SPREAD),
3515                                 NULL);
3516 
3517         /*
3518          * Limit the bh occupancy to 10% of ZONE_NORMAL
3519          */
3520         nrpages = (nr_free_buffer_pages() * 10) / 100;
3521         max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3522         ret = cpuhp_setup_state_nocalls(CPUHP_FS_BUFF_DEAD, "fs/buffer:dead",
3523                                         NULL, buffer_exit_cpu_dead);
3524         WARN_ON(ret < 0);
3525 }
3526 

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