4 * Copyright (C) 1991, 1992, 2002 Linus Torvalds
8 * Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
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
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
16 * Added 32k buffer block sizes - these are required older ARM systems. - RMK
18 * async buffer flushing, 1999 Andrea Arcangeli <andrea@suse.de>
21 #include <linux/kernel.h>
22 #include <linux/syscalls.h>
25 #include <linux/percpu.h>
26 #include <linux/slab.h>
27 #include <linux/capability.h>
28 #include <linux/blkdev.h>
29 #include <linux/file.h>
30 #include <linux/quotaops.h>
31 #include <linux/highmem.h>
32 #include <linux/export.h>
33 #include <linux/backing-dev.h>
34 #include <linux/writeback.h>
35 #include <linux/hash.h>
36 #include <linux/suspend.h>
37 #include <linux/buffer_head.h>
38 #include <linux/task_io_accounting_ops.h>
39 #include <linux/bio.h>
40 #include <linux/notifier.h>
41 #include <linux/cpu.h>
42 #include <linux/bitops.h>
43 #include <linux/mpage.h>
44 #include <linux/bit_spinlock.h>
45 #include <trace/events/block.h>
47 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
48 static int submit_bh_wbc(int rw, struct buffer_head *bh,
49 unsigned long bio_flags,
50 struct writeback_control *wbc);
52 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
54 void init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
56 bh->b_end_io = handler;
57 bh->b_private = private;
59 EXPORT_SYMBOL(init_buffer);
61 inline void touch_buffer(struct buffer_head *bh)
63 trace_block_touch_buffer(bh);
64 mark_page_accessed(bh->b_page);
66 EXPORT_SYMBOL(touch_buffer);
68 void __lock_buffer(struct buffer_head *bh)
70 wait_on_bit_lock_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
72 EXPORT_SYMBOL(__lock_buffer);
74 void unlock_buffer(struct buffer_head *bh)
76 clear_bit_unlock(BH_Lock, &bh->b_state);
77 smp_mb__after_atomic();
78 wake_up_bit(&bh->b_state, BH_Lock);
80 EXPORT_SYMBOL(unlock_buffer);
83 * Returns if the page has dirty or writeback buffers. If all the buffers
84 * are unlocked and clean then the PageDirty information is stale. If
85 * any of the pages are locked, it is assumed they are locked for IO.
87 void buffer_check_dirty_writeback(struct page *page,
88 bool *dirty, bool *writeback)
90 struct buffer_head *head, *bh;
94 BUG_ON(!PageLocked(page));
96 if (!page_has_buffers(page))
99 if (PageWriteback(page))
102 head = page_buffers(page);
105 if (buffer_locked(bh))
108 if (buffer_dirty(bh))
111 bh = bh->b_this_page;
112 } while (bh != head);
114 EXPORT_SYMBOL(buffer_check_dirty_writeback);
117 * Block until a buffer comes unlocked. This doesn't stop it
118 * from becoming locked again - you have to lock it yourself
119 * if you want to preserve its state.
121 void __wait_on_buffer(struct buffer_head * bh)
123 wait_on_bit_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
125 EXPORT_SYMBOL(__wait_on_buffer);
128 __clear_page_buffers(struct page *page)
130 ClearPagePrivate(page);
131 set_page_private(page, 0);
132 page_cache_release(page);
135 static void buffer_io_error(struct buffer_head *bh, char *msg)
137 char b[BDEVNAME_SIZE];
139 if (!test_bit(BH_Quiet, &bh->b_state))
140 printk_ratelimited(KERN_ERR
141 "Buffer I/O error on dev %s, logical block %llu%s\n",
142 bdevname(bh->b_bdev, b),
143 (unsigned long long)bh->b_blocknr, msg);
147 * End-of-IO handler helper function which does not touch the bh after
149 * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
150 * a race there is benign: unlock_buffer() only use the bh's address for
151 * hashing after unlocking the buffer, so it doesn't actually touch the bh
154 static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
157 set_buffer_uptodate(bh);
159 /* This happens, due to failed READA attempts. */
160 clear_buffer_uptodate(bh);
166 * Default synchronous end-of-IO handler.. Just mark it up-to-date and
167 * unlock the buffer. This is what ll_rw_block uses too.
169 void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
171 __end_buffer_read_notouch(bh, uptodate);
174 EXPORT_SYMBOL(end_buffer_read_sync);
176 void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
179 set_buffer_uptodate(bh);
181 buffer_io_error(bh, ", lost sync page write");
182 set_buffer_write_io_error(bh);
183 clear_buffer_uptodate(bh);
188 EXPORT_SYMBOL(end_buffer_write_sync);
191 * Various filesystems appear to want __find_get_block to be non-blocking.
192 * But it's the page lock which protects the buffers. To get around this,
193 * we get exclusion from try_to_free_buffers with the blockdev mapping's
196 * Hack idea: for the blockdev mapping, i_bufferlist_lock contention
197 * may be quite high. This code could TryLock the page, and if that
198 * succeeds, there is no need to take private_lock. (But if
199 * private_lock is contended then so is mapping->tree_lock).
201 static struct buffer_head *
202 __find_get_block_slow(struct block_device *bdev, sector_t block)
204 struct inode *bd_inode = bdev->bd_inode;
205 struct address_space *bd_mapping = bd_inode->i_mapping;
206 struct buffer_head *ret = NULL;
208 struct buffer_head *bh;
209 struct buffer_head *head;
213 index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
214 page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
218 spin_lock(&bd_mapping->private_lock);
219 if (!page_has_buffers(page))
221 head = page_buffers(page);
224 if (!buffer_mapped(bh))
226 else if (bh->b_blocknr == block) {
231 bh = bh->b_this_page;
232 } while (bh != head);
234 /* we might be here because some of the buffers on this page are
235 * not mapped. This is due to various races between
236 * file io on the block device and getblk. It gets dealt with
237 * elsewhere, don't buffer_error if we had some unmapped buffers
240 char b[BDEVNAME_SIZE];
242 printk("__find_get_block_slow() failed. "
243 "block=%llu, b_blocknr=%llu\n",
244 (unsigned long long)block,
245 (unsigned long long)bh->b_blocknr);
246 printk("b_state=0x%08lx, b_size=%zu\n",
247 bh->b_state, bh->b_size);
248 printk("device %s blocksize: %d\n", bdevname(bdev, b),
249 1 << bd_inode->i_blkbits);
252 spin_unlock(&bd_mapping->private_lock);
253 page_cache_release(page);
259 * Kick the writeback threads then try to free up some ZONE_NORMAL memory.
261 static void free_more_memory(void)
266 wakeup_flusher_threads(1024, WB_REASON_FREE_MORE_MEM);
269 for_each_online_node(nid) {
270 (void)first_zones_zonelist(node_zonelist(nid, GFP_NOFS),
271 gfp_zone(GFP_NOFS), NULL,
274 try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
280 * I/O completion handler for block_read_full_page() - pages
281 * which come unlocked at the end of I/O.
283 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
286 struct buffer_head *first;
287 struct buffer_head *tmp;
289 int page_uptodate = 1;
291 BUG_ON(!buffer_async_read(bh));
295 set_buffer_uptodate(bh);
297 clear_buffer_uptodate(bh);
298 buffer_io_error(bh, ", async page read");
303 * Be _very_ careful from here on. Bad things can happen if
304 * two buffer heads end IO at almost the same time and both
305 * decide that the page is now completely done.
307 first = page_buffers(page);
308 flags = bh_uptodate_lock_irqsave(first);
309 clear_buffer_async_read(bh);
313 if (!buffer_uptodate(tmp))
315 if (buffer_async_read(tmp)) {
316 BUG_ON(!buffer_locked(tmp));
319 tmp = tmp->b_this_page;
321 bh_uptodate_unlock_irqrestore(first, flags);
324 * If none of the buffers had errors and they are all
325 * uptodate then we can set the page uptodate.
327 if (page_uptodate && !PageError(page))
328 SetPageUptodate(page);
333 bh_uptodate_unlock_irqrestore(first, flags);
337 * Completion handler for block_write_full_page() - pages which are unlocked
338 * during I/O, and which have PageWriteback cleared upon I/O completion.
340 void end_buffer_async_write(struct buffer_head *bh, int uptodate)
343 struct buffer_head *first;
344 struct buffer_head *tmp;
347 BUG_ON(!buffer_async_write(bh));
351 set_buffer_uptodate(bh);
353 buffer_io_error(bh, ", lost async page write");
354 set_bit(AS_EIO, &page->mapping->flags);
355 set_buffer_write_io_error(bh);
356 clear_buffer_uptodate(bh);
360 first = page_buffers(page);
361 flags = bh_uptodate_lock_irqsave(first);
363 clear_buffer_async_write(bh);
365 tmp = bh->b_this_page;
367 if (buffer_async_write(tmp)) {
368 BUG_ON(!buffer_locked(tmp));
371 tmp = tmp->b_this_page;
373 bh_uptodate_unlock_irqrestore(first, flags);
374 end_page_writeback(page);
378 bh_uptodate_unlock_irqrestore(first, flags);
380 EXPORT_SYMBOL(end_buffer_async_write);
383 * If a page's buffers are under async readin (end_buffer_async_read
384 * completion) then there is a possibility that another thread of
385 * control could lock one of the buffers after it has completed
386 * but while some of the other buffers have not completed. This
387 * locked buffer would confuse end_buffer_async_read() into not unlocking
388 * the page. So the absence of BH_Async_Read tells end_buffer_async_read()
389 * that this buffer is not under async I/O.
391 * The page comes unlocked when it has no locked buffer_async buffers
394 * PageLocked prevents anyone starting new async I/O reads any of
397 * PageWriteback is used to prevent simultaneous writeout of the same
400 * PageLocked prevents anyone from starting writeback of a page which is
401 * under read I/O (PageWriteback is only ever set against a locked page).
403 static void mark_buffer_async_read(struct buffer_head *bh)
405 bh->b_end_io = end_buffer_async_read;
406 set_buffer_async_read(bh);
409 static void mark_buffer_async_write_endio(struct buffer_head *bh,
410 bh_end_io_t *handler)
412 bh->b_end_io = handler;
413 set_buffer_async_write(bh);
416 void mark_buffer_async_write(struct buffer_head *bh)
418 mark_buffer_async_write_endio(bh, end_buffer_async_write);
420 EXPORT_SYMBOL(mark_buffer_async_write);
424 * fs/buffer.c contains helper functions for buffer-backed address space's
425 * fsync functions. A common requirement for buffer-based filesystems is
426 * that certain data from the backing blockdev needs to be written out for
427 * a successful fsync(). For example, ext2 indirect blocks need to be
428 * written back and waited upon before fsync() returns.
430 * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
431 * inode_has_buffers() and invalidate_inode_buffers() are provided for the
432 * management of a list of dependent buffers at ->i_mapping->private_list.
434 * Locking is a little subtle: try_to_free_buffers() will remove buffers
435 * from their controlling inode's queue when they are being freed. But
436 * try_to_free_buffers() will be operating against the *blockdev* mapping
437 * at the time, not against the S_ISREG file which depends on those buffers.
438 * So the locking for private_list is via the private_lock in the address_space
439 * which backs the buffers. Which is different from the address_space
440 * against which the buffers are listed. So for a particular address_space,
441 * mapping->private_lock does *not* protect mapping->private_list! In fact,
442 * mapping->private_list will always be protected by the backing blockdev's
445 * Which introduces a requirement: all buffers on an address_space's
446 * ->private_list must be from the same address_space: the blockdev's.
448 * address_spaces which do not place buffers at ->private_list via these
449 * utility functions are free to use private_lock and private_list for
450 * whatever they want. The only requirement is that list_empty(private_list)
451 * be true at clear_inode() time.
453 * FIXME: clear_inode should not call invalidate_inode_buffers(). The
454 * filesystems should do that. invalidate_inode_buffers() should just go
455 * BUG_ON(!list_empty).
457 * FIXME: mark_buffer_dirty_inode() is a data-plane operation. It should
458 * take an address_space, not an inode. And it should be called
459 * mark_buffer_dirty_fsync() to clearly define why those buffers are being
462 * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
463 * list if it is already on a list. Because if the buffer is on a list,
464 * it *must* already be on the right one. If not, the filesystem is being
465 * silly. This will save a ton of locking. But first we have to ensure
466 * that buffers are taken *off* the old inode's list when they are freed
467 * (presumably in truncate). That requires careful auditing of all
468 * filesystems (do it inside bforget()). It could also be done by bringing
473 * The buffer's backing address_space's private_lock must be held
475 static void __remove_assoc_queue(struct buffer_head *bh)
477 list_del_init(&bh->b_assoc_buffers);
478 WARN_ON(!bh->b_assoc_map);
479 if (buffer_write_io_error(bh))
480 set_bit(AS_EIO, &bh->b_assoc_map->flags);
481 bh->b_assoc_map = NULL;
484 int inode_has_buffers(struct inode *inode)
486 return !list_empty(&inode->i_data.private_list);
490 * osync is designed to support O_SYNC io. It waits synchronously for
491 * all already-submitted IO to complete, but does not queue any new
492 * writes to the disk.
494 * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
495 * you dirty the buffers, and then use osync_inode_buffers to wait for
496 * completion. Any other dirty buffers which are not yet queued for
497 * write will not be flushed to disk by the osync.
499 static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
501 struct buffer_head *bh;
507 list_for_each_prev(p, list) {
509 if (buffer_locked(bh)) {
513 if (!buffer_uptodate(bh))
524 static void do_thaw_one(struct super_block *sb, void *unused)
526 char b[BDEVNAME_SIZE];
527 while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
528 printk(KERN_WARNING "Emergency Thaw on %s\n",
529 bdevname(sb->s_bdev, b));
532 static void do_thaw_all(struct work_struct *work)
534 iterate_supers(do_thaw_one, NULL);
536 printk(KERN_WARNING "Emergency Thaw complete\n");
540 * emergency_thaw_all -- forcibly thaw every frozen filesystem
542 * Used for emergency unfreeze of all filesystems via SysRq
544 void emergency_thaw_all(void)
546 struct work_struct *work;
548 work = kmalloc(sizeof(*work), GFP_ATOMIC);
550 INIT_WORK(work, do_thaw_all);
556 * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
557 * @mapping: the mapping which wants those buffers written
559 * Starts I/O against the buffers at mapping->private_list, and waits upon
562 * Basically, this is a convenience function for fsync().
563 * @mapping is a file or directory which needs those buffers to be written for
564 * a successful fsync().
566 int sync_mapping_buffers(struct address_space *mapping)
568 struct address_space *buffer_mapping = mapping->private_data;
570 if (buffer_mapping == NULL || list_empty(&mapping->private_list))
573 return fsync_buffers_list(&buffer_mapping->private_lock,
574 &mapping->private_list);
576 EXPORT_SYMBOL(sync_mapping_buffers);
579 * Called when we've recently written block `bblock', and it is known that
580 * `bblock' was for a buffer_boundary() buffer. This means that the block at
581 * `bblock + 1' is probably a dirty indirect block. Hunt it down and, if it's
582 * dirty, schedule it for IO. So that indirects merge nicely with their data.
584 void write_boundary_block(struct block_device *bdev,
585 sector_t bblock, unsigned blocksize)
587 struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
589 if (buffer_dirty(bh))
590 ll_rw_block(WRITE, 1, &bh);
595 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
597 struct address_space *mapping = inode->i_mapping;
598 struct address_space *buffer_mapping = bh->b_page->mapping;
600 mark_buffer_dirty(bh);
601 if (!mapping->private_data) {
602 mapping->private_data = buffer_mapping;
604 BUG_ON(mapping->private_data != buffer_mapping);
606 if (!bh->b_assoc_map) {
607 spin_lock(&buffer_mapping->private_lock);
608 list_move_tail(&bh->b_assoc_buffers,
609 &mapping->private_list);
610 bh->b_assoc_map = mapping;
611 spin_unlock(&buffer_mapping->private_lock);
614 EXPORT_SYMBOL(mark_buffer_dirty_inode);
617 * Mark the page dirty, and set it dirty in the radix tree, and mark the inode
620 * If warn is true, then emit a warning if the page is not uptodate and has
621 * not been truncated.
623 * The caller must hold mem_cgroup_begin_page_stat() lock.
625 static void __set_page_dirty(struct page *page, struct address_space *mapping,
626 struct mem_cgroup *memcg, int warn)
630 spin_lock_irqsave(&mapping->tree_lock, flags);
631 if (page->mapping) { /* Race with truncate? */
632 WARN_ON_ONCE(warn && !PageUptodate(page));
633 account_page_dirtied(page, mapping, memcg);
634 radix_tree_tag_set(&mapping->page_tree,
635 page_index(page), PAGECACHE_TAG_DIRTY);
637 spin_unlock_irqrestore(&mapping->tree_lock, flags);
641 * Add a page to the dirty page list.
643 * It is a sad fact of life that this function is called from several places
644 * deeply under spinlocking. It may not sleep.
646 * If the page has buffers, the uptodate buffers are set dirty, to preserve
647 * dirty-state coherency between the page and the buffers. It the page does
648 * not have buffers then when they are later attached they will all be set
651 * The buffers are dirtied before the page is dirtied. There's a small race
652 * window in which a writepage caller may see the page cleanness but not the
653 * buffer dirtiness. That's fine. If this code were to set the page dirty
654 * before the buffers, a concurrent writepage caller could clear the page dirty
655 * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
656 * page on the dirty page list.
658 * We use private_lock to lock against try_to_free_buffers while using the
659 * page's buffer list. Also use this to protect against clean buffers being
660 * added to the page after it was set dirty.
662 * FIXME: may need to call ->reservepage here as well. That's rather up to the
663 * address_space though.
665 int __set_page_dirty_buffers(struct page *page)
668 struct mem_cgroup *memcg;
669 struct address_space *mapping = page_mapping(page);
671 if (unlikely(!mapping))
672 return !TestSetPageDirty(page);
674 spin_lock(&mapping->private_lock);
675 if (page_has_buffers(page)) {
676 struct buffer_head *head = page_buffers(page);
677 struct buffer_head *bh = head;
680 set_buffer_dirty(bh);
681 bh = bh->b_this_page;
682 } while (bh != head);
685 * Use mem_group_begin_page_stat() to keep PageDirty synchronized with
686 * per-memcg dirty page counters.
688 memcg = mem_cgroup_begin_page_stat(page);
689 newly_dirty = !TestSetPageDirty(page);
690 spin_unlock(&mapping->private_lock);
693 __set_page_dirty(page, mapping, memcg, 1);
695 mem_cgroup_end_page_stat(memcg);
698 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
702 EXPORT_SYMBOL(__set_page_dirty_buffers);
705 * Write out and wait upon a list of buffers.
707 * We have conflicting pressures: we want to make sure that all
708 * initially dirty buffers get waited on, but that any subsequently
709 * dirtied buffers don't. After all, we don't want fsync to last
710 * forever if somebody is actively writing to the file.
712 * Do this in two main stages: first we copy dirty buffers to a
713 * temporary inode list, queueing the writes as we go. Then we clean
714 * up, waiting for those writes to complete.
716 * During this second stage, any subsequent updates to the file may end
717 * up refiling the buffer on the original inode's dirty list again, so
718 * there is a chance we will end up with a buffer queued for write but
719 * not yet completed on that list. So, as a final cleanup we go through
720 * the osync code to catch these locked, dirty buffers without requeuing
721 * any newly dirty buffers for write.
723 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
725 struct buffer_head *bh;
726 struct list_head tmp;
727 struct address_space *mapping;
729 struct blk_plug plug;
731 INIT_LIST_HEAD(&tmp);
732 blk_start_plug(&plug);
735 while (!list_empty(list)) {
736 bh = BH_ENTRY(list->next);
737 mapping = bh->b_assoc_map;
738 __remove_assoc_queue(bh);
739 /* Avoid race with mark_buffer_dirty_inode() which does
740 * a lockless check and we rely on seeing the dirty bit */
742 if (buffer_dirty(bh) || buffer_locked(bh)) {
743 list_add(&bh->b_assoc_buffers, &tmp);
744 bh->b_assoc_map = mapping;
745 if (buffer_dirty(bh)) {
749 * Ensure any pending I/O completes so that
750 * write_dirty_buffer() actually writes the
751 * current contents - it is a noop if I/O is
752 * still in flight on potentially older
755 write_dirty_buffer(bh, WRITE_SYNC);
758 * Kick off IO for the previous mapping. Note
759 * that we will not run the very last mapping,
760 * wait_on_buffer() will do that for us
761 * through sync_buffer().
770 blk_finish_plug(&plug);
773 while (!list_empty(&tmp)) {
774 bh = BH_ENTRY(tmp.prev);
776 mapping = bh->b_assoc_map;
777 __remove_assoc_queue(bh);
778 /* Avoid race with mark_buffer_dirty_inode() which does
779 * a lockless check and we rely on seeing the dirty bit */
781 if (buffer_dirty(bh)) {
782 list_add(&bh->b_assoc_buffers,
783 &mapping->private_list);
784 bh->b_assoc_map = mapping;
788 if (!buffer_uptodate(bh))
795 err2 = osync_buffers_list(lock, list);
803 * Invalidate any and all dirty buffers on a given inode. We are
804 * probably unmounting the fs, but that doesn't mean we have already
805 * done a sync(). Just drop the buffers from the inode list.
807 * NOTE: we take the inode's blockdev's mapping's private_lock. Which
808 * assumes that all the buffers are against the blockdev. Not true
811 void invalidate_inode_buffers(struct inode *inode)
813 if (inode_has_buffers(inode)) {
814 struct address_space *mapping = &inode->i_data;
815 struct list_head *list = &mapping->private_list;
816 struct address_space *buffer_mapping = mapping->private_data;
818 spin_lock(&buffer_mapping->private_lock);
819 while (!list_empty(list))
820 __remove_assoc_queue(BH_ENTRY(list->next));
821 spin_unlock(&buffer_mapping->private_lock);
824 EXPORT_SYMBOL(invalidate_inode_buffers);
827 * Remove any clean buffers from the inode's buffer list. This is called
828 * when we're trying to free the inode itself. Those buffers can pin it.
830 * Returns true if all buffers were removed.
832 int remove_inode_buffers(struct inode *inode)
836 if (inode_has_buffers(inode)) {
837 struct address_space *mapping = &inode->i_data;
838 struct list_head *list = &mapping->private_list;
839 struct address_space *buffer_mapping = mapping->private_data;
841 spin_lock(&buffer_mapping->private_lock);
842 while (!list_empty(list)) {
843 struct buffer_head *bh = BH_ENTRY(list->next);
844 if (buffer_dirty(bh)) {
848 __remove_assoc_queue(bh);
850 spin_unlock(&buffer_mapping->private_lock);
856 * Create the appropriate buffers when given a page for data area and
857 * the size of each buffer.. Use the bh->b_this_page linked list to
858 * follow the buffers created. Return NULL if unable to create more
861 * The retry flag is used to differentiate async IO (paging, swapping)
862 * which may not fail from ordinary buffer allocations.
864 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
867 struct buffer_head *bh, *head;
873 while ((offset -= size) >= 0) {
874 bh = alloc_buffer_head(GFP_NOFS);
878 bh->b_this_page = head;
884 /* Link the buffer to its page */
885 set_bh_page(bh, page, offset);
889 * In case anything failed, we just free everything we got.
895 head = head->b_this_page;
896 free_buffer_head(bh);
901 * Return failure for non-async IO requests. Async IO requests
902 * are not allowed to fail, so we have to wait until buffer heads
903 * become available. But we don't want tasks sleeping with
904 * partially complete buffers, so all were released above.
909 /* We're _really_ low on memory. Now we just
910 * wait for old buffer heads to become free due to
911 * finishing IO. Since this is an async request and
912 * the reserve list is empty, we're sure there are
913 * async buffer heads in use.
918 EXPORT_SYMBOL_GPL(alloc_page_buffers);
921 link_dev_buffers(struct page *page, struct buffer_head *head)
923 struct buffer_head *bh, *tail;
928 bh = bh->b_this_page;
930 tail->b_this_page = head;
931 attach_page_buffers(page, head);
934 static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
936 sector_t retval = ~((sector_t)0);
937 loff_t sz = i_size_read(bdev->bd_inode);
940 unsigned int sizebits = blksize_bits(size);
941 retval = (sz >> sizebits);
947 * Initialise the state of a blockdev page's buffers.
950 init_page_buffers(struct page *page, struct block_device *bdev,
951 sector_t block, int size)
953 struct buffer_head *head = page_buffers(page);
954 struct buffer_head *bh = head;
955 int uptodate = PageUptodate(page);
956 sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
959 if (!buffer_mapped(bh)) {
960 init_buffer(bh, NULL, NULL);
962 bh->b_blocknr = block;
964 set_buffer_uptodate(bh);
965 if (block < end_block)
966 set_buffer_mapped(bh);
969 bh = bh->b_this_page;
970 } while (bh != head);
973 * Caller needs to validate requested block against end of device.
979 * Create the page-cache page that contains the requested block.
981 * This is used purely for blockdev mappings.
984 grow_dev_page(struct block_device *bdev, sector_t block,
985 pgoff_t index, int size, int sizebits, gfp_t gfp)
987 struct inode *inode = bdev->bd_inode;
989 struct buffer_head *bh;
991 int ret = 0; /* Will call free_more_memory() */
994 gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) | gfp;
997 * XXX: __getblk_slow() can not really deal with failure and
998 * will endlessly loop on improvised global reclaim. Prefer
999 * looping in the allocator rather than here, at least that
1000 * code knows what it's doing.
1002 gfp_mask |= __GFP_NOFAIL;
1004 page = find_or_create_page(inode->i_mapping, index, gfp_mask);
1008 BUG_ON(!PageLocked(page));
1010 if (page_has_buffers(page)) {
1011 bh = page_buffers(page);
1012 if (bh->b_size == size) {
1013 end_block = init_page_buffers(page, bdev,
1014 (sector_t)index << sizebits,
1018 if (!try_to_free_buffers(page))
1023 * Allocate some buffers for this page
1025 bh = alloc_page_buffers(page, size, 0);
1030 * Link the page to the buffers and initialise them. Take the
1031 * lock to be atomic wrt __find_get_block(), which does not
1032 * run under the page lock.
1034 spin_lock(&inode->i_mapping->private_lock);
1035 link_dev_buffers(page, bh);
1036 end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
1038 spin_unlock(&inode->i_mapping->private_lock);
1040 ret = (block < end_block) ? 1 : -ENXIO;
1043 page_cache_release(page);
1048 * Create buffers for the specified block device block's page. If
1049 * that page was dirty, the buffers are set dirty also.
1052 grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
1060 } while ((size << sizebits) < PAGE_SIZE);
1062 index = block >> sizebits;
1065 * Check for a block which wants to lie outside our maximum possible
1066 * pagecache index. (this comparison is done using sector_t types).
1068 if (unlikely(index != block >> sizebits)) {
1069 char b[BDEVNAME_SIZE];
1071 printk(KERN_ERR "%s: requested out-of-range block %llu for "
1073 __func__, (unsigned long long)block,
1078 /* Create a page with the proper size buffers.. */
1079 return grow_dev_page(bdev, block, index, size, sizebits, gfp);
1082 struct buffer_head *
1083 __getblk_slow(struct block_device *bdev, sector_t block,
1084 unsigned size, gfp_t gfp)
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",
1091 printk(KERN_ERR "logical block size: %d\n",
1092 bdev_logical_block_size(bdev));
1099 struct buffer_head *bh;
1102 bh = __find_get_block(bdev, block, size);
1106 ret = grow_buffers(bdev, block, size, gfp);
1113 EXPORT_SYMBOL(__getblk_slow);
1116 * The relationship between dirty buffers and dirty pages:
1118 * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1119 * the page is tagged dirty in its radix tree.
1121 * At all times, the dirtiness of the buffers represents the dirtiness of
1122 * subsections of the page. If the page has buffers, the page dirty bit is
1123 * merely a hint about the true dirty state.
1125 * When a page is set dirty in its entirety, all its buffers are marked dirty
1126 * (if the page has buffers).
1128 * When a buffer is marked dirty, its page is dirtied, but the page's other
1131 * Also. When blockdev buffers are explicitly read with bread(), they
1132 * individually become uptodate. But their backing page remains not
1133 * uptodate - even if all of its buffers are uptodate. A subsequent
1134 * block_read_full_page() against that page will discover all the uptodate
1135 * buffers, will set the page uptodate and will perform no I/O.
1139 * mark_buffer_dirty - mark a buffer_head as needing writeout
1140 * @bh: the buffer_head to mark dirty
1142 * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
1143 * backing page dirty, then tag the page as dirty in its address_space's radix
1144 * tree and then attach the address_space's inode to its superblock's dirty
1147 * mark_buffer_dirty() is atomic. It takes bh->b_page->mapping->private_lock,
1148 * mapping->tree_lock and mapping->host->i_lock.
1150 void mark_buffer_dirty(struct buffer_head *bh)
1152 WARN_ON_ONCE(!buffer_uptodate(bh));
1154 trace_block_dirty_buffer(bh);
1157 * Very *carefully* optimize the it-is-already-dirty case.
1159 * Don't let the final "is it dirty" escape to before we
1160 * perhaps modified the buffer.
1162 if (buffer_dirty(bh)) {
1164 if (buffer_dirty(bh))
1168 if (!test_set_buffer_dirty(bh)) {
1169 struct page *page = bh->b_page;
1170 struct address_space *mapping = NULL;
1171 struct mem_cgroup *memcg;
1173 memcg = mem_cgroup_begin_page_stat(page);
1174 if (!TestSetPageDirty(page)) {
1175 mapping = page_mapping(page);
1177 __set_page_dirty(page, mapping, memcg, 0);
1179 mem_cgroup_end_page_stat(memcg);
1181 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1184 EXPORT_SYMBOL(mark_buffer_dirty);
1187 * Decrement a buffer_head's reference count. If all buffers against a page
1188 * have zero reference count, are clean and unlocked, and if the page is clean
1189 * and unlocked then try_to_free_buffers() may strip the buffers from the page
1190 * in preparation for freeing it (sometimes, rarely, buffers are removed from
1191 * a page but it ends up not being freed, and buffers may later be reattached).
1193 void __brelse(struct buffer_head * buf)
1195 if (atomic_read(&buf->b_count)) {
1199 WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1201 EXPORT_SYMBOL(__brelse);
1204 * bforget() is like brelse(), except it discards any
1205 * potentially dirty data.
1207 void __bforget(struct buffer_head *bh)
1209 clear_buffer_dirty(bh);
1210 if (bh->b_assoc_map) {
1211 struct address_space *buffer_mapping = bh->b_page->mapping;
1213 spin_lock(&buffer_mapping->private_lock);
1214 list_del_init(&bh->b_assoc_buffers);
1215 bh->b_assoc_map = NULL;
1216 spin_unlock(&buffer_mapping->private_lock);
1220 EXPORT_SYMBOL(__bforget);
1222 static struct buffer_head *__bread_slow(struct buffer_head *bh)
1225 if (buffer_uptodate(bh)) {
1230 bh->b_end_io = end_buffer_read_sync;
1231 submit_bh(READ, bh);
1233 if (buffer_uptodate(bh))
1241 * Per-cpu buffer LRU implementation. To reduce the cost of __find_get_block().
1242 * The bhs[] array is sorted - newest buffer is at bhs[0]. Buffers have their
1243 * refcount elevated by one when they're in an LRU. A buffer can only appear
1244 * once in a particular CPU's LRU. A single buffer can be present in multiple
1245 * CPU's LRUs at the same time.
1247 * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1248 * sb_find_get_block().
1250 * The LRUs themselves only need locking against invalidate_bh_lrus. We use
1251 * a local interrupt disable for that.
1254 #define BH_LRU_SIZE 16
1257 struct buffer_head *bhs[BH_LRU_SIZE];
1260 static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1263 #define bh_lru_lock() local_irq_disable()
1264 #define bh_lru_unlock() local_irq_enable()
1266 #define bh_lru_lock() preempt_disable()
1267 #define bh_lru_unlock() preempt_enable()
1270 static inline void check_irqs_on(void)
1272 #ifdef irqs_disabled
1273 BUG_ON(irqs_disabled());
1278 * The LRU management algorithm is dopey-but-simple. Sorry.
1280 static void bh_lru_install(struct buffer_head *bh)
1282 struct buffer_head *evictee = NULL;
1286 if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
1287 struct buffer_head *bhs[BH_LRU_SIZE];
1293 for (in = 0; in < BH_LRU_SIZE; in++) {
1294 struct buffer_head *bh2 =
1295 __this_cpu_read(bh_lrus.bhs[in]);
1300 if (out >= BH_LRU_SIZE) {
1301 BUG_ON(evictee != NULL);
1308 while (out < BH_LRU_SIZE)
1310 memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
1319 * Look up the bh in this cpu's LRU. If it's there, move it to the head.
1321 static struct buffer_head *
1322 lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1324 struct buffer_head *ret = NULL;
1329 for (i = 0; i < BH_LRU_SIZE; i++) {
1330 struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1332 if (bh && bh->b_blocknr == block && bh->b_bdev == bdev &&
1333 bh->b_size == size) {
1336 __this_cpu_write(bh_lrus.bhs[i],
1337 __this_cpu_read(bh_lrus.bhs[i - 1]));
1340 __this_cpu_write(bh_lrus.bhs[0], bh);
1352 * Perform a pagecache lookup for the matching buffer. If it's there, refresh
1353 * it in the LRU and mark it as accessed. If it is not present then return
1356 struct buffer_head *
1357 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1359 struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1362 /* __find_get_block_slow will mark the page accessed */
1363 bh = __find_get_block_slow(bdev, block);
1371 EXPORT_SYMBOL(__find_get_block);
1374 * __getblk_gfp() will locate (and, if necessary, create) the buffer_head
1375 * which corresponds to the passed block_device, block and size. The
1376 * returned buffer has its reference count incremented.
1378 * __getblk_gfp() will lock up the machine if grow_dev_page's
1379 * try_to_free_buffers() attempt is failing. FIXME, perhaps?
1381 struct buffer_head *
1382 __getblk_gfp(struct block_device *bdev, sector_t block,
1383 unsigned size, gfp_t gfp)
1385 struct buffer_head *bh = __find_get_block(bdev, block, size);
1389 bh = __getblk_slow(bdev, block, size, gfp);
1392 EXPORT_SYMBOL(__getblk_gfp);
1395 * Do async read-ahead on a buffer..
1397 void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1399 struct buffer_head *bh = __getblk(bdev, block, size);
1401 ll_rw_block(READA, 1, &bh);
1405 EXPORT_SYMBOL(__breadahead);
1408 * __bread_gfp() - reads a specified block and returns the bh
1409 * @bdev: the block_device to read from
1410 * @block: number of block
1411 * @size: size (in bytes) to read
1412 * @gfp: page allocation flag
1414 * Reads a specified block, and returns buffer head that contains it.
1415 * The page cache can be allocated from non-movable area
1416 * not to prevent page migration if you set gfp to zero.
1417 * It returns NULL if the block was unreadable.
1419 struct buffer_head *
1420 __bread_gfp(struct block_device *bdev, sector_t block,
1421 unsigned size, gfp_t gfp)
1423 struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
1425 if (likely(bh) && !buffer_uptodate(bh))
1426 bh = __bread_slow(bh);
1429 EXPORT_SYMBOL(__bread_gfp);
1432 * invalidate_bh_lrus() is called rarely - but not only at unmount.
1433 * This doesn't race because it runs in each cpu either in irq
1434 * or with preempt disabled.
1436 static void invalidate_bh_lru(void *arg)
1438 struct bh_lru *b = &get_cpu_var(bh_lrus);
1441 for (i = 0; i < BH_LRU_SIZE; i++) {
1445 put_cpu_var(bh_lrus);
1448 static bool has_bh_in_lru(int cpu, void *dummy)
1450 struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1453 for (i = 0; i < BH_LRU_SIZE; i++) {
1461 void invalidate_bh_lrus(void)
1463 on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1465 EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1467 void set_bh_page(struct buffer_head *bh,
1468 struct page *page, unsigned long offset)
1471 BUG_ON(offset >= PAGE_SIZE);
1472 if (PageHighMem(page))
1474 * This catches illegal uses and preserves the offset:
1476 bh->b_data = (char *)(0 + offset);
1478 bh->b_data = page_address(page) + offset;
1480 EXPORT_SYMBOL(set_bh_page);
1483 * Called when truncating a buffer on a page completely.
1486 /* Bits that are cleared during an invalidate */
1487 #define BUFFER_FLAGS_DISCARD \
1488 (1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
1489 1 << BH_Delay | 1 << BH_Unwritten)
1491 static void discard_buffer(struct buffer_head * bh)
1493 unsigned long b_state, b_state_old;
1496 clear_buffer_dirty(bh);
1498 b_state = bh->b_state;
1500 b_state_old = cmpxchg(&bh->b_state, b_state,
1501 (b_state & ~BUFFER_FLAGS_DISCARD));
1502 if (b_state_old == b_state)
1504 b_state = b_state_old;
1510 * block_invalidatepage - invalidate part or all of a buffer-backed page
1512 * @page: the page which is affected
1513 * @offset: start of the range to invalidate
1514 * @length: length of the range to invalidate
1516 * block_invalidatepage() is called when all or part of the page has become
1517 * invalidated by a truncate operation.
1519 * block_invalidatepage() does not have to release all buffers, but it must
1520 * ensure that no dirty buffer is left outside @offset and that no I/O
1521 * is underway against any of the blocks which are outside the truncation
1522 * point. Because the caller is about to free (and possibly reuse) those
1525 void block_invalidatepage(struct page *page, unsigned int offset,
1526 unsigned int length)
1528 struct buffer_head *head, *bh, *next;
1529 unsigned int curr_off = 0;
1530 unsigned int stop = length + offset;
1532 BUG_ON(!PageLocked(page));
1533 if (!page_has_buffers(page))
1537 * Check for overflow
1539 BUG_ON(stop > PAGE_CACHE_SIZE || stop < length);
1541 head = page_buffers(page);
1544 unsigned int next_off = curr_off + bh->b_size;
1545 next = bh->b_this_page;
1548 * Are we still fully in range ?
1550 if (next_off > stop)
1554 * is this block fully invalidated?
1556 if (offset <= curr_off)
1558 curr_off = next_off;
1560 } while (bh != head);
1563 * We release buffers only if the entire page is being invalidated.
1564 * The get_block cached value has been unconditionally invalidated,
1565 * so real IO is not possible anymore.
1568 try_to_release_page(page, 0);
1572 EXPORT_SYMBOL(block_invalidatepage);
1576 * We attach and possibly dirty the buffers atomically wrt
1577 * __set_page_dirty_buffers() via private_lock. try_to_free_buffers
1578 * is already excluded via the page lock.
1580 void create_empty_buffers(struct page *page,
1581 unsigned long blocksize, unsigned long b_state)
1583 struct buffer_head *bh, *head, *tail;
1585 head = alloc_page_buffers(page, blocksize, 1);
1588 bh->b_state |= b_state;
1590 bh = bh->b_this_page;
1592 tail->b_this_page = head;
1594 spin_lock(&page->mapping->private_lock);
1595 if (PageUptodate(page) || PageDirty(page)) {
1598 if (PageDirty(page))
1599 set_buffer_dirty(bh);
1600 if (PageUptodate(page))
1601 set_buffer_uptodate(bh);
1602 bh = bh->b_this_page;
1603 } while (bh != head);
1605 attach_page_buffers(page, head);
1606 spin_unlock(&page->mapping->private_lock);
1608 EXPORT_SYMBOL(create_empty_buffers);
1611 * We are taking a block for data and we don't want any output from any
1612 * buffer-cache aliases starting from return from that function and
1613 * until the moment when something will explicitly mark the buffer
1614 * dirty (hopefully that will not happen until we will free that block ;-)
1615 * We don't even need to mark it not-uptodate - nobody can expect
1616 * anything from a newly allocated buffer anyway. We used to used
1617 * unmap_buffer() for such invalidation, but that was wrong. We definitely
1618 * don't want to mark the alias unmapped, for example - it would confuse
1619 * anyone who might pick it with bread() afterwards...
1621 * Also.. Note that bforget() doesn't lock the buffer. So there can
1622 * be writeout I/O going on against recently-freed buffers. We don't
1623 * wait on that I/O in bforget() - it's more efficient to wait on the I/O
1624 * only if we really need to. That happens here.
1626 void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
1628 struct buffer_head *old_bh;
1632 old_bh = __find_get_block_slow(bdev, block);
1634 clear_buffer_dirty(old_bh);
1635 wait_on_buffer(old_bh);
1636 clear_buffer_req(old_bh);
1640 EXPORT_SYMBOL(unmap_underlying_metadata);
1643 * Size is a power-of-two in the range 512..PAGE_SIZE,
1644 * and the case we care about most is PAGE_SIZE.
1646 * So this *could* possibly be written with those
1647 * constraints in mind (relevant mostly if some
1648 * architecture has a slow bit-scan instruction)
1650 static inline int block_size_bits(unsigned int blocksize)
1652 return ilog2(blocksize);
1655 static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
1657 BUG_ON(!PageLocked(page));
1659 if (!page_has_buffers(page))
1660 create_empty_buffers(page, 1 << ACCESS_ONCE(inode->i_blkbits), b_state);
1661 return page_buffers(page);
1665 * NOTE! All mapped/uptodate combinations are valid:
1667 * Mapped Uptodate Meaning
1669 * No No "unknown" - must do get_block()
1670 * No Yes "hole" - zero-filled
1671 * Yes No "allocated" - allocated on disk, not read in
1672 * Yes Yes "valid" - allocated and up-to-date in memory.
1674 * "Dirty" is valid only with the last case (mapped+uptodate).
1678 * While block_write_full_page is writing back the dirty buffers under
1679 * the page lock, whoever dirtied the buffers may decide to clean them
1680 * again at any time. We handle that by only looking at the buffer
1681 * state inside lock_buffer().
1683 * If block_write_full_page() is called for regular writeback
1684 * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1685 * locked buffer. This only can happen if someone has written the buffer
1686 * directly, with submit_bh(). At the address_space level PageWriteback
1687 * prevents this contention from occurring.
1689 * If block_write_full_page() is called with wbc->sync_mode ==
1690 * WB_SYNC_ALL, the writes are posted using WRITE_SYNC; this
1691 * causes the writes to be flagged as synchronous writes.
1693 static int __block_write_full_page(struct inode *inode, struct page *page,
1694 get_block_t *get_block, struct writeback_control *wbc,
1695 bh_end_io_t *handler)
1699 sector_t last_block;
1700 struct buffer_head *bh, *head;
1701 unsigned int blocksize, bbits;
1702 int nr_underway = 0;
1703 int write_op = (wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE);
1705 head = create_page_buffers(page, inode,
1706 (1 << BH_Dirty)|(1 << BH_Uptodate));
1709 * Be very careful. We have no exclusion from __set_page_dirty_buffers
1710 * here, and the (potentially unmapped) buffers may become dirty at
1711 * any time. If a buffer becomes dirty here after we've inspected it
1712 * then we just miss that fact, and the page stays dirty.
1714 * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1715 * handle that here by just cleaning them.
1719 blocksize = bh->b_size;
1720 bbits = block_size_bits(blocksize);
1722 block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1723 last_block = (i_size_read(inode) - 1) >> bbits;
1726 * Get all the dirty buffers mapped to disk addresses and
1727 * handle any aliases from the underlying blockdev's mapping.
1730 if (block > last_block) {
1732 * mapped buffers outside i_size will occur, because
1733 * this page can be outside i_size when there is a
1734 * truncate in progress.
1737 * The buffer was zeroed by block_write_full_page()
1739 clear_buffer_dirty(bh);
1740 set_buffer_uptodate(bh);
1741 } else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1743 WARN_ON(bh->b_size != blocksize);
1744 err = get_block(inode, block, bh, 1);
1747 clear_buffer_delay(bh);
1748 if (buffer_new(bh)) {
1749 /* blockdev mappings never come here */
1750 clear_buffer_new(bh);
1751 unmap_underlying_metadata(bh->b_bdev,
1755 bh = bh->b_this_page;
1757 } while (bh != head);
1760 if (!buffer_mapped(bh))
1763 * If it's a fully non-blocking write attempt and we cannot
1764 * lock the buffer then redirty the page. Note that this can
1765 * potentially cause a busy-wait loop from writeback threads
1766 * and kswapd activity, but those code paths have their own
1767 * higher-level throttling.
1769 if (wbc->sync_mode != WB_SYNC_NONE) {
1771 } else if (!trylock_buffer(bh)) {
1772 redirty_page_for_writepage(wbc, page);
1775 if (test_clear_buffer_dirty(bh)) {
1776 mark_buffer_async_write_endio(bh, handler);
1780 } while ((bh = bh->b_this_page) != head);
1783 * The page and its buffers are protected by PageWriteback(), so we can
1784 * drop the bh refcounts early.
1786 BUG_ON(PageWriteback(page));
1787 set_page_writeback(page);
1790 struct buffer_head *next = bh->b_this_page;
1791 if (buffer_async_write(bh)) {
1792 submit_bh_wbc(write_op, bh, 0, wbc);
1796 } while (bh != head);
1801 if (nr_underway == 0) {
1803 * The page was marked dirty, but the buffers were
1804 * clean. Someone wrote them back by hand with
1805 * ll_rw_block/submit_bh. A rare case.
1807 end_page_writeback(page);
1810 * The page and buffer_heads can be released at any time from
1818 * ENOSPC, or some other error. We may already have added some
1819 * blocks to the file, so we need to write these out to avoid
1820 * exposing stale data.
1821 * The page is currently locked and not marked for writeback
1824 /* Recovery: lock and submit the mapped buffers */
1826 if (buffer_mapped(bh) && buffer_dirty(bh) &&
1827 !buffer_delay(bh)) {
1829 mark_buffer_async_write_endio(bh, handler);
1832 * The buffer may have been set dirty during
1833 * attachment to a dirty page.
1835 clear_buffer_dirty(bh);
1837 } while ((bh = bh->b_this_page) != head);
1839 BUG_ON(PageWriteback(page));
1840 mapping_set_error(page->mapping, err);
1841 set_page_writeback(page);
1843 struct buffer_head *next = bh->b_this_page;
1844 if (buffer_async_write(bh)) {
1845 clear_buffer_dirty(bh);
1846 submit_bh_wbc(write_op, bh, 0, wbc);
1850 } while (bh != head);
1856 * If a page has any new buffers, zero them out here, and mark them uptodate
1857 * and dirty so they'll be written out (in order to prevent uninitialised
1858 * block data from leaking). And clear the new bit.
1860 void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1862 unsigned int block_start, block_end;
1863 struct buffer_head *head, *bh;
1865 BUG_ON(!PageLocked(page));
1866 if (!page_has_buffers(page))
1869 bh = head = page_buffers(page);
1872 block_end = block_start + bh->b_size;
1874 if (buffer_new(bh)) {
1875 if (block_end > from && block_start < to) {
1876 if (!PageUptodate(page)) {
1877 unsigned start, size;
1879 start = max(from, block_start);
1880 size = min(to, block_end) - start;
1882 zero_user(page, start, size);
1883 set_buffer_uptodate(bh);
1886 clear_buffer_new(bh);
1887 mark_buffer_dirty(bh);
1891 block_start = block_end;
1892 bh = bh->b_this_page;
1893 } while (bh != head);
1895 EXPORT_SYMBOL(page_zero_new_buffers);
1897 int __block_write_begin(struct page *page, loff_t pos, unsigned len,
1898 get_block_t *get_block)
1900 unsigned from = pos & (PAGE_CACHE_SIZE - 1);
1901 unsigned to = from + len;
1902 struct inode *inode = page->mapping->host;
1903 unsigned block_start, block_end;
1906 unsigned blocksize, bbits;
1907 struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1909 BUG_ON(!PageLocked(page));
1910 BUG_ON(from > PAGE_CACHE_SIZE);
1911 BUG_ON(to > PAGE_CACHE_SIZE);
1914 head = create_page_buffers(page, inode, 0);
1915 blocksize = head->b_size;
1916 bbits = block_size_bits(blocksize);
1918 block = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
1920 for(bh = head, block_start = 0; bh != head || !block_start;
1921 block++, block_start=block_end, bh = bh->b_this_page) {
1922 block_end = block_start + blocksize;
1923 if (block_end <= from || block_start >= to) {
1924 if (PageUptodate(page)) {
1925 if (!buffer_uptodate(bh))
1926 set_buffer_uptodate(bh);
1931 clear_buffer_new(bh);
1932 if (!buffer_mapped(bh)) {
1933 WARN_ON(bh->b_size != blocksize);
1934 err = get_block(inode, block, bh, 1);
1937 if (buffer_new(bh)) {
1938 unmap_underlying_metadata(bh->b_bdev,
1940 if (PageUptodate(page)) {
1941 clear_buffer_new(bh);
1942 set_buffer_uptodate(bh);
1943 mark_buffer_dirty(bh);
1946 if (block_end > to || block_start < from)
1947 zero_user_segments(page,
1953 if (PageUptodate(page)) {
1954 if (!buffer_uptodate(bh))
1955 set_buffer_uptodate(bh);
1958 if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
1959 !buffer_unwritten(bh) &&
1960 (block_start < from || block_end > to)) {
1961 ll_rw_block(READ, 1, &bh);
1966 * If we issued read requests - let them complete.
1968 while(wait_bh > wait) {
1969 wait_on_buffer(*--wait_bh);
1970 if (!buffer_uptodate(*wait_bh))
1974 page_zero_new_buffers(page, from, to);
1977 EXPORT_SYMBOL(__block_write_begin);
1979 static int __block_commit_write(struct inode *inode, struct page *page,
1980 unsigned from, unsigned to)
1982 unsigned block_start, block_end;
1985 struct buffer_head *bh, *head;
1987 bh = head = page_buffers(page);
1988 blocksize = bh->b_size;
1992 block_end = block_start + blocksize;
1993 if (block_end <= from || block_start >= to) {
1994 if (!buffer_uptodate(bh))
1997 set_buffer_uptodate(bh);
1998 mark_buffer_dirty(bh);
2000 clear_buffer_new(bh);
2002 block_start = block_end;
2003 bh = bh->b_this_page;
2004 } while (bh != head);
2007 * If this is a partial write which happened to make all buffers
2008 * uptodate then we can optimize away a bogus readpage() for
2009 * the next read(). Here we 'discover' whether the page went
2010 * uptodate as a result of this (potentially partial) write.
2013 SetPageUptodate(page);
2018 * block_write_begin takes care of the basic task of block allocation and
2019 * bringing partial write blocks uptodate first.
2021 * The filesystem needs to handle block truncation upon failure.
2023 int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
2024 unsigned flags, struct page **pagep, get_block_t *get_block)
2026 pgoff_t index = pos >> PAGE_CACHE_SHIFT;
2030 page = grab_cache_page_write_begin(mapping, index, flags);
2034 status = __block_write_begin(page, pos, len, get_block);
2035 if (unlikely(status)) {
2037 page_cache_release(page);
2044 EXPORT_SYMBOL(block_write_begin);
2046 int block_write_end(struct file *file, struct address_space *mapping,
2047 loff_t pos, unsigned len, unsigned copied,
2048 struct page *page, void *fsdata)
2050 struct inode *inode = mapping->host;
2053 start = pos & (PAGE_CACHE_SIZE - 1);
2055 if (unlikely(copied < len)) {
2057 * The buffers that were written will now be uptodate, so we
2058 * don't have to worry about a readpage reading them and
2059 * overwriting a partial write. However if we have encountered
2060 * a short write and only partially written into a buffer, it
2061 * will not be marked uptodate, so a readpage might come in and
2062 * destroy our partial write.
2064 * Do the simplest thing, and just treat any short write to a
2065 * non uptodate page as a zero-length write, and force the
2066 * caller to redo the whole thing.
2068 if (!PageUptodate(page))
2071 page_zero_new_buffers(page, start+copied, start+len);
2073 flush_dcache_page(page);
2075 /* This could be a short (even 0-length) commit */
2076 __block_commit_write(inode, page, start, start+copied);
2080 EXPORT_SYMBOL(block_write_end);
2082 int generic_write_end(struct file *file, struct address_space *mapping,
2083 loff_t pos, unsigned len, unsigned copied,
2084 struct page *page, void *fsdata)
2086 struct inode *inode = mapping->host;
2087 loff_t old_size = inode->i_size;
2088 int i_size_changed = 0;
2090 copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2093 * No need to use i_size_read() here, the i_size
2094 * cannot change under us because we hold i_mutex.
2096 * But it's important to update i_size while still holding page lock:
2097 * page writeout could otherwise come in and zero beyond i_size.
2099 if (pos+copied > inode->i_size) {
2100 i_size_write(inode, pos+copied);
2105 page_cache_release(page);
2108 pagecache_isize_extended(inode, old_size, pos);
2110 * Don't mark the inode dirty under page lock. First, it unnecessarily
2111 * makes the holding time of page lock longer. Second, it forces lock
2112 * ordering of page lock and transaction start for journaling
2116 mark_inode_dirty(inode);
2120 EXPORT_SYMBOL(generic_write_end);
2123 * block_is_partially_uptodate checks whether buffers within a page are
2126 * Returns true if all buffers which correspond to a file portion
2127 * we want to read are uptodate.
2129 int block_is_partially_uptodate(struct page *page, unsigned long from,
2130 unsigned long count)
2132 unsigned block_start, block_end, blocksize;
2134 struct buffer_head *bh, *head;
2137 if (!page_has_buffers(page))
2140 head = page_buffers(page);
2141 blocksize = head->b_size;
2142 to = min_t(unsigned, PAGE_CACHE_SIZE - from, count);
2144 if (from < blocksize && to > PAGE_CACHE_SIZE - blocksize)
2150 block_end = block_start + blocksize;
2151 if (block_end > from && block_start < to) {
2152 if (!buffer_uptodate(bh)) {
2156 if (block_end >= to)
2159 block_start = block_end;
2160 bh = bh->b_this_page;
2161 } while (bh != head);
2165 EXPORT_SYMBOL(block_is_partially_uptodate);
2168 * Generic "read page" function for block devices that have the normal
2169 * get_block functionality. This is most of the block device filesystems.
2170 * Reads the page asynchronously --- the unlock_buffer() and
2171 * set/clear_buffer_uptodate() functions propagate buffer state into the
2172 * page struct once IO has completed.
2174 int block_read_full_page(struct page *page, get_block_t *get_block)
2176 struct inode *inode = page->mapping->host;
2177 sector_t iblock, lblock;
2178 struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2179 unsigned int blocksize, bbits;
2181 int fully_mapped = 1;
2183 head = create_page_buffers(page, inode, 0);
2184 blocksize = head->b_size;
2185 bbits = block_size_bits(blocksize);
2187 iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - bbits);
2188 lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2194 if (buffer_uptodate(bh))
2197 if (!buffer_mapped(bh)) {
2201 if (iblock < lblock) {
2202 WARN_ON(bh->b_size != blocksize);
2203 err = get_block(inode, iblock, bh, 0);
2207 if (!buffer_mapped(bh)) {
2208 zero_user(page, i * blocksize, blocksize);
2210 set_buffer_uptodate(bh);
2214 * get_block() might have updated the buffer
2217 if (buffer_uptodate(bh))
2221 } while (i++, iblock++, (bh = bh->b_this_page) != head);
2224 SetPageMappedToDisk(page);
2228 * All buffers are uptodate - we can set the page uptodate
2229 * as well. But not if get_block() returned an error.
2231 if (!PageError(page))
2232 SetPageUptodate(page);
2237 /* Stage two: lock the buffers */
2238 for (i = 0; i < nr; i++) {
2241 mark_buffer_async_read(bh);
2245 * Stage 3: start the IO. Check for uptodateness
2246 * inside the buffer lock in case another process reading
2247 * the underlying blockdev brought it uptodate (the sct fix).
2249 for (i = 0; i < nr; i++) {
2251 if (buffer_uptodate(bh))
2252 end_buffer_async_read(bh, 1);
2254 submit_bh(READ, bh);
2258 EXPORT_SYMBOL(block_read_full_page);
2260 /* utility function for filesystems that need to do work on expanding
2261 * truncates. Uses filesystem pagecache writes to allow the filesystem to
2262 * deal with the hole.
2264 int generic_cont_expand_simple(struct inode *inode, loff_t size)
2266 struct address_space *mapping = inode->i_mapping;
2271 err = inode_newsize_ok(inode, size);
2275 err = pagecache_write_begin(NULL, mapping, size, 0,
2276 AOP_FLAG_UNINTERRUPTIBLE|AOP_FLAG_CONT_EXPAND,
2281 err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2287 EXPORT_SYMBOL(generic_cont_expand_simple);
2289 static int cont_expand_zero(struct file *file, struct address_space *mapping,
2290 loff_t pos, loff_t *bytes)
2292 struct inode *inode = mapping->host;
2293 unsigned blocksize = 1 << inode->i_blkbits;
2296 pgoff_t index, curidx;
2298 unsigned zerofrom, offset, len;
2301 index = pos >> PAGE_CACHE_SHIFT;
2302 offset = pos & ~PAGE_CACHE_MASK;
2304 while (index > (curidx = (curpos = *bytes)>>PAGE_CACHE_SHIFT)) {
2305 zerofrom = curpos & ~PAGE_CACHE_MASK;
2306 if (zerofrom & (blocksize-1)) {
2307 *bytes |= (blocksize-1);
2310 len = PAGE_CACHE_SIZE - zerofrom;
2312 err = pagecache_write_begin(file, mapping, curpos, len,
2313 AOP_FLAG_UNINTERRUPTIBLE,
2317 zero_user(page, zerofrom, len);
2318 err = pagecache_write_end(file, mapping, curpos, len, len,
2325 balance_dirty_pages_ratelimited(mapping);
2327 if (unlikely(fatal_signal_pending(current))) {
2333 /* page covers the boundary, find the boundary offset */
2334 if (index == curidx) {
2335 zerofrom = curpos & ~PAGE_CACHE_MASK;
2336 /* if we will expand the thing last block will be filled */
2337 if (offset <= zerofrom) {
2340 if (zerofrom & (blocksize-1)) {
2341 *bytes |= (blocksize-1);
2344 len = offset - zerofrom;
2346 err = pagecache_write_begin(file, mapping, curpos, len,
2347 AOP_FLAG_UNINTERRUPTIBLE,
2351 zero_user(page, zerofrom, len);
2352 err = pagecache_write_end(file, mapping, curpos, len, len,
2364 * For moronic filesystems that do not allow holes in file.
2365 * We may have to extend the file.
2367 int cont_write_begin(struct file *file, struct address_space *mapping,
2368 loff_t pos, unsigned len, unsigned flags,
2369 struct page **pagep, void **fsdata,
2370 get_block_t *get_block, loff_t *bytes)
2372 struct inode *inode = mapping->host;
2373 unsigned blocksize = 1 << inode->i_blkbits;
2377 err = cont_expand_zero(file, mapping, pos, bytes);
2381 zerofrom = *bytes & ~PAGE_CACHE_MASK;
2382 if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2383 *bytes |= (blocksize-1);
2387 return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2389 EXPORT_SYMBOL(cont_write_begin);
2391 int block_commit_write(struct page *page, unsigned from, unsigned to)
2393 struct inode *inode = page->mapping->host;
2394 __block_commit_write(inode,page,from,to);
2397 EXPORT_SYMBOL(block_commit_write);
2400 * block_page_mkwrite() is not allowed to change the file size as it gets
2401 * called from a page fault handler when a page is first dirtied. Hence we must
2402 * be careful to check for EOF conditions here. We set the page up correctly
2403 * for a written page which means we get ENOSPC checking when writing into
2404 * holes and correct delalloc and unwritten extent mapping on filesystems that
2405 * support these features.
2407 * We are not allowed to take the i_mutex here so we have to play games to
2408 * protect against truncate races as the page could now be beyond EOF. Because
2409 * truncate writes the inode size before removing pages, once we have the
2410 * page lock we can determine safely if the page is beyond EOF. If it is not
2411 * beyond EOF, then the page is guaranteed safe against truncation until we
2414 * Direct callers of this function should protect against filesystem freezing
2415 * using sb_start_pagefault() - sb_end_pagefault() functions.
2417 int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2418 get_block_t get_block)
2420 struct page *page = vmf->page;
2421 struct inode *inode = file_inode(vma->vm_file);
2427 size = i_size_read(inode);
2428 if ((page->mapping != inode->i_mapping) ||
2429 (page_offset(page) > size)) {
2430 /* We overload EFAULT to mean page got truncated */
2435 /* page is wholly or partially inside EOF */
2436 if (((page->index + 1) << PAGE_CACHE_SHIFT) > size)
2437 end = size & ~PAGE_CACHE_MASK;
2439 end = PAGE_CACHE_SIZE;
2441 ret = __block_write_begin(page, 0, end, get_block);
2443 ret = block_commit_write(page, 0, end);
2445 if (unlikely(ret < 0))
2447 set_page_dirty(page);
2448 wait_for_stable_page(page);
2454 EXPORT_SYMBOL(block_page_mkwrite);
2457 * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2458 * immediately, while under the page lock. So it needs a special end_io
2459 * handler which does not touch the bh after unlocking it.
2461 static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2463 __end_buffer_read_notouch(bh, uptodate);
2467 * Attach the singly-linked list of buffers created by nobh_write_begin, to
2468 * the page (converting it to circular linked list and taking care of page
2471 static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2473 struct buffer_head *bh;
2475 BUG_ON(!PageLocked(page));
2477 spin_lock(&page->mapping->private_lock);
2480 if (PageDirty(page))
2481 set_buffer_dirty(bh);
2482 if (!bh->b_this_page)
2483 bh->b_this_page = head;
2484 bh = bh->b_this_page;
2485 } while (bh != head);
2486 attach_page_buffers(page, head);
2487 spin_unlock(&page->mapping->private_lock);
2491 * On entry, the page is fully not uptodate.
2492 * On exit the page is fully uptodate in the areas outside (from,to)
2493 * The filesystem needs to handle block truncation upon failure.
2495 int nobh_write_begin(struct address_space *mapping,
2496 loff_t pos, unsigned len, unsigned flags,
2497 struct page **pagep, void **fsdata,
2498 get_block_t *get_block)
2500 struct inode *inode = mapping->host;
2501 const unsigned blkbits = inode->i_blkbits;
2502 const unsigned blocksize = 1 << blkbits;
2503 struct buffer_head *head, *bh;
2507 unsigned block_in_page;
2508 unsigned block_start, block_end;
2509 sector_t block_in_file;
2512 int is_mapped_to_disk = 1;
2514 index = pos >> PAGE_CACHE_SHIFT;
2515 from = pos & (PAGE_CACHE_SIZE - 1);
2518 page = grab_cache_page_write_begin(mapping, index, flags);
2524 if (page_has_buffers(page)) {
2525 ret = __block_write_begin(page, pos, len, get_block);
2531 if (PageMappedToDisk(page))
2535 * Allocate buffers so that we can keep track of state, and potentially
2536 * attach them to the page if an error occurs. In the common case of
2537 * no error, they will just be freed again without ever being attached
2538 * to the page (which is all OK, because we're under the page lock).
2540 * Be careful: the buffer linked list is a NULL terminated one, rather
2541 * than the circular one we're used to.
2543 head = alloc_page_buffers(page, blocksize, 0);
2549 block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
2552 * We loop across all blocks in the page, whether or not they are
2553 * part of the affected region. This is so we can discover if the
2554 * page is fully mapped-to-disk.
2556 for (block_start = 0, block_in_page = 0, bh = head;
2557 block_start < PAGE_CACHE_SIZE;
2558 block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2561 block_end = block_start + blocksize;
2564 if (block_start >= to)
2566 ret = get_block(inode, block_in_file + block_in_page,
2570 if (!buffer_mapped(bh))
2571 is_mapped_to_disk = 0;
2573 unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
2574 if (PageUptodate(page)) {
2575 set_buffer_uptodate(bh);
2578 if (buffer_new(bh) || !buffer_mapped(bh)) {
2579 zero_user_segments(page, block_start, from,
2583 if (buffer_uptodate(bh))
2584 continue; /* reiserfs does this */
2585 if (block_start < from || block_end > to) {
2587 bh->b_end_io = end_buffer_read_nobh;
2588 submit_bh(READ, bh);
2595 * The page is locked, so these buffers are protected from
2596 * any VM or truncate activity. Hence we don't need to care
2597 * for the buffer_head refcounts.
2599 for (bh = head; bh; bh = bh->b_this_page) {
2601 if (!buffer_uptodate(bh))
2608 if (is_mapped_to_disk)
2609 SetPageMappedToDisk(page);
2611 *fsdata = head; /* to be released by nobh_write_end */
2618 * Error recovery is a bit difficult. We need to zero out blocks that
2619 * were newly allocated, and dirty them to ensure they get written out.
2620 * Buffers need to be attached to the page at this point, otherwise
2621 * the handling of potential IO errors during writeout would be hard
2622 * (could try doing synchronous writeout, but what if that fails too?)
2624 attach_nobh_buffers(page, head);
2625 page_zero_new_buffers(page, from, to);
2629 page_cache_release(page);
2634 EXPORT_SYMBOL(nobh_write_begin);
2636 int nobh_write_end(struct file *file, struct address_space *mapping,
2637 loff_t pos, unsigned len, unsigned copied,
2638 struct page *page, void *fsdata)
2640 struct inode *inode = page->mapping->host;
2641 struct buffer_head *head = fsdata;
2642 struct buffer_head *bh;
2643 BUG_ON(fsdata != NULL && page_has_buffers(page));
2645 if (unlikely(copied < len) && head)
2646 attach_nobh_buffers(page, head);
2647 if (page_has_buffers(page))
2648 return generic_write_end(file, mapping, pos, len,
2649 copied, page, fsdata);
2651 SetPageUptodate(page);
2652 set_page_dirty(page);
2653 if (pos+copied > inode->i_size) {
2654 i_size_write(inode, pos+copied);
2655 mark_inode_dirty(inode);
2659 page_cache_release(page);
2663 head = head->b_this_page;
2664 free_buffer_head(bh);
2669 EXPORT_SYMBOL(nobh_write_end);
2672 * nobh_writepage() - based on block_full_write_page() except
2673 * that it tries to operate without attaching bufferheads to
2676 int nobh_writepage(struct page *page, get_block_t *get_block,
2677 struct writeback_control *wbc)
2679 struct inode * const inode = page->mapping->host;
2680 loff_t i_size = i_size_read(inode);
2681 const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2685 /* Is the page fully inside i_size? */
2686 if (page->index < end_index)
2689 /* Is the page fully outside i_size? (truncate in progress) */
2690 offset = i_size & (PAGE_CACHE_SIZE-1);
2691 if (page->index >= end_index+1 || !offset) {
2693 * The page may have dirty, unmapped buffers. For example,
2694 * they may have been added in ext3_writepage(). Make them
2695 * freeable here, so the page does not leak.
2698 /* Not really sure about this - do we need this ? */
2699 if (page->mapping->a_ops->invalidatepage)
2700 page->mapping->a_ops->invalidatepage(page, offset);
2703 return 0; /* don't care */
2707 * The page straddles i_size. It must be zeroed out on each and every
2708 * writepage invocation because it may be mmapped. "A file is mapped
2709 * in multiples of the page size. For a file that is not a multiple of
2710 * the page size, the remaining memory is zeroed when mapped, and
2711 * writes to that region are not written out to the file."
2713 zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2715 ret = mpage_writepage(page, get_block, wbc);
2717 ret = __block_write_full_page(inode, page, get_block, wbc,
2718 end_buffer_async_write);
2721 EXPORT_SYMBOL(nobh_writepage);
2723 int nobh_truncate_page(struct address_space *mapping,
2724 loff_t from, get_block_t *get_block)
2726 pgoff_t index = from >> PAGE_CACHE_SHIFT;
2727 unsigned offset = from & (PAGE_CACHE_SIZE-1);
2730 unsigned length, pos;
2731 struct inode *inode = mapping->host;
2733 struct buffer_head map_bh;
2736 blocksize = 1 << inode->i_blkbits;
2737 length = offset & (blocksize - 1);
2739 /* Block boundary? Nothing to do */
2743 length = blocksize - length;
2744 iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2746 page = grab_cache_page(mapping, index);
2751 if (page_has_buffers(page)) {
2754 page_cache_release(page);
2755 return block_truncate_page(mapping, from, get_block);
2758 /* Find the buffer that contains "offset" */
2760 while (offset >= pos) {
2765 map_bh.b_size = blocksize;
2767 err = get_block(inode, iblock, &map_bh, 0);
2770 /* unmapped? It's a hole - nothing to do */
2771 if (!buffer_mapped(&map_bh))
2774 /* Ok, it's mapped. Make sure it's up-to-date */
2775 if (!PageUptodate(page)) {
2776 err = mapping->a_ops->readpage(NULL, page);
2778 page_cache_release(page);
2782 if (!PageUptodate(page)) {
2786 if (page_has_buffers(page))
2789 zero_user(page, offset, length);
2790 set_page_dirty(page);
2795 page_cache_release(page);
2799 EXPORT_SYMBOL(nobh_truncate_page);
2801 int block_truncate_page(struct address_space *mapping,
2802 loff_t from, get_block_t *get_block)
2804 pgoff_t index = from >> PAGE_CACHE_SHIFT;
2805 unsigned offset = from & (PAGE_CACHE_SIZE-1);
2808 unsigned length, pos;
2809 struct inode *inode = mapping->host;
2811 struct buffer_head *bh;
2814 blocksize = 1 << inode->i_blkbits;
2815 length = offset & (blocksize - 1);
2817 /* Block boundary? Nothing to do */
2821 length = blocksize - length;
2822 iblock = (sector_t)index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
2824 page = grab_cache_page(mapping, index);
2829 if (!page_has_buffers(page))
2830 create_empty_buffers(page, blocksize, 0);
2832 /* Find the buffer that contains "offset" */
2833 bh = page_buffers(page);
2835 while (offset >= pos) {
2836 bh = bh->b_this_page;
2842 if (!buffer_mapped(bh)) {
2843 WARN_ON(bh->b_size != blocksize);
2844 err = get_block(inode, iblock, bh, 0);
2847 /* unmapped? It's a hole - nothing to do */
2848 if (!buffer_mapped(bh))
2852 /* Ok, it's mapped. Make sure it's up-to-date */
2853 if (PageUptodate(page))
2854 set_buffer_uptodate(bh);
2856 if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2858 ll_rw_block(READ, 1, &bh);
2860 /* Uhhuh. Read error. Complain and punt. */
2861 if (!buffer_uptodate(bh))
2865 zero_user(page, offset, length);
2866 mark_buffer_dirty(bh);
2871 page_cache_release(page);
2875 EXPORT_SYMBOL(block_truncate_page);
2878 * The generic ->writepage function for buffer-backed address_spaces
2880 int block_write_full_page(struct page *page, get_block_t *get_block,
2881 struct writeback_control *wbc)
2883 struct inode * const inode = page->mapping->host;
2884 loff_t i_size = i_size_read(inode);
2885 const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
2888 /* Is the page fully inside i_size? */
2889 if (page->index < end_index)
2890 return __block_write_full_page(inode, page, get_block, wbc,
2891 end_buffer_async_write);
2893 /* Is the page fully outside i_size? (truncate in progress) */
2894 offset = i_size & (PAGE_CACHE_SIZE-1);
2895 if (page->index >= end_index+1 || !offset) {
2897 * The page may have dirty, unmapped buffers. For example,
2898 * they may have been added in ext3_writepage(). Make them
2899 * freeable here, so the page does not leak.
2901 do_invalidatepage(page, 0, PAGE_CACHE_SIZE);
2903 return 0; /* don't care */
2907 * The page straddles i_size. It must be zeroed out on each and every
2908 * writepage invocation because it may be mmapped. "A file is mapped
2909 * in multiples of the page size. For a file that is not a multiple of
2910 * the page size, the remaining memory is zeroed when mapped, and
2911 * writes to that region are not written out to the file."
2913 zero_user_segment(page, offset, PAGE_CACHE_SIZE);
2914 return __block_write_full_page(inode, page, get_block, wbc,
2915 end_buffer_async_write);
2917 EXPORT_SYMBOL(block_write_full_page);
2919 sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2920 get_block_t *get_block)
2922 struct buffer_head tmp;
2923 struct inode *inode = mapping->host;
2926 tmp.b_size = 1 << inode->i_blkbits;
2927 get_block(inode, block, &tmp, 0);
2928 return tmp.b_blocknr;
2930 EXPORT_SYMBOL(generic_block_bmap);
2932 static void end_bio_bh_io_sync(struct bio *bio)
2934 struct buffer_head *bh = bio->bi_private;
2936 if (unlikely(bio_flagged(bio, BIO_QUIET)))
2937 set_bit(BH_Quiet, &bh->b_state);
2939 bh->b_end_io(bh, !bio->bi_error);
2944 * This allows us to do IO even on the odd last sectors
2945 * of a device, even if the block size is some multiple
2946 * of the physical sector size.
2948 * We'll just truncate the bio to the size of the device,
2949 * and clear the end of the buffer head manually.
2951 * Truly out-of-range accesses will turn into actual IO
2952 * errors, this only handles the "we need to be able to
2953 * do IO at the final sector" case.
2955 void guard_bio_eod(int rw, struct bio *bio)
2958 struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
2959 unsigned truncated_bytes;
2961 maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
2966 * If the *whole* IO is past the end of the device,
2967 * let it through, and the IO layer will turn it into
2970 if (unlikely(bio->bi_iter.bi_sector >= maxsector))
2973 maxsector -= bio->bi_iter.bi_sector;
2974 if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))
2977 /* Uhhuh. We've got a bio that straddles the device size! */
2978 truncated_bytes = bio->bi_iter.bi_size - (maxsector << 9);
2980 /* Truncate the bio.. */
2981 bio->bi_iter.bi_size -= truncated_bytes;
2982 bvec->bv_len -= truncated_bytes;
2984 /* ..and clear the end of the buffer for reads */
2985 if ((rw & RW_MASK) == READ) {
2986 zero_user(bvec->bv_page, bvec->bv_offset + bvec->bv_len,
2991 static int submit_bh_wbc(int rw, struct buffer_head *bh,
2992 unsigned long bio_flags, struct writeback_control *wbc)
2996 BUG_ON(!buffer_locked(bh));
2997 BUG_ON(!buffer_mapped(bh));
2998 BUG_ON(!bh->b_end_io);
2999 BUG_ON(buffer_delay(bh));
3000 BUG_ON(buffer_unwritten(bh));
3003 * Only clear out a write error when rewriting
3005 if (test_set_buffer_req(bh) && (rw & WRITE))
3006 clear_buffer_write_io_error(bh);
3009 * from here on down, it's all bio -- do the initial mapping,
3010 * submit_bio -> generic_make_request may further map this bio around
3012 bio = bio_alloc(GFP_NOIO, 1);
3015 wbc_init_bio(wbc, bio);
3016 wbc_account_io(wbc, bh->b_page, bh->b_size);
3019 bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
3020 bio->bi_bdev = bh->b_bdev;
3022 bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
3023 BUG_ON(bio->bi_iter.bi_size != bh->b_size);
3025 bio->bi_end_io = end_bio_bh_io_sync;
3026 bio->bi_private = bh;
3027 bio->bi_flags |= bio_flags;
3029 /* Take care of bh's that straddle the end of the device */
3030 guard_bio_eod(rw, bio);
3032 if (buffer_meta(bh))
3034 if (buffer_prio(bh))
3037 submit_bio(rw, bio);
3041 int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags)
3043 return submit_bh_wbc(rw, bh, bio_flags, NULL);
3045 EXPORT_SYMBOL_GPL(_submit_bh);
3047 int submit_bh(int rw, struct buffer_head *bh)
3049 return submit_bh_wbc(rw, bh, 0, NULL);
3051 EXPORT_SYMBOL(submit_bh);
3054 * ll_rw_block: low-level access to block devices (DEPRECATED)
3055 * @rw: whether to %READ or %WRITE or maybe %READA (readahead)
3056 * @nr: number of &struct buffer_heads in the array
3057 * @bhs: array of pointers to &struct buffer_head
3059 * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3060 * requests an I/O operation on them, either a %READ or a %WRITE. The third
3061 * %READA option is described in the documentation for generic_make_request()
3062 * which ll_rw_block() calls.
3064 * This function drops any buffer that it cannot get a lock on (with the
3065 * BH_Lock state bit), any buffer that appears to be clean when doing a write
3066 * request, and any buffer that appears to be up-to-date when doing read
3067 * request. Further it marks as clean buffers that are processed for
3068 * writing (the buffer cache won't assume that they are actually clean
3069 * until the buffer gets unlocked).
3071 * ll_rw_block sets b_end_io to simple completion handler that marks
3072 * the buffer up-to-date (if appropriate), unlocks the buffer and wakes
3075 * All of the buffers must be for the same device, and must also be a
3076 * multiple of the current approved size for the device.
3078 void ll_rw_block(int rw, int nr, struct buffer_head *bhs[])
3082 for (i = 0; i < nr; i++) {
3083 struct buffer_head *bh = bhs[i];
3085 if (!trylock_buffer(bh))
3088 if (test_clear_buffer_dirty(bh)) {
3089 bh->b_end_io = end_buffer_write_sync;
3091 submit_bh(WRITE, bh);
3095 if (!buffer_uptodate(bh)) {
3096 bh->b_end_io = end_buffer_read_sync;
3105 EXPORT_SYMBOL(ll_rw_block);
3107 void write_dirty_buffer(struct buffer_head *bh, int rw)
3110 if (!test_clear_buffer_dirty(bh)) {
3114 bh->b_end_io = end_buffer_write_sync;
3118 EXPORT_SYMBOL(write_dirty_buffer);
3121 * For a data-integrity writeout, we need to wait upon any in-progress I/O
3122 * and then start new I/O and then wait upon it. The caller must have a ref on
3125 int __sync_dirty_buffer(struct buffer_head *bh, int rw)
3129 WARN_ON(atomic_read(&bh->b_count) < 1);
3131 if (test_clear_buffer_dirty(bh)) {
3133 bh->b_end_io = end_buffer_write_sync;
3134 ret = submit_bh(rw, bh);
3136 if (!ret && !buffer_uptodate(bh))
3143 EXPORT_SYMBOL(__sync_dirty_buffer);
3145 int sync_dirty_buffer(struct buffer_head *bh)
3147 return __sync_dirty_buffer(bh, WRITE_SYNC);
3149 EXPORT_SYMBOL(sync_dirty_buffer);
3152 * try_to_free_buffers() checks if all the buffers on this particular page
3153 * are unused, and releases them if so.
3155 * Exclusion against try_to_free_buffers may be obtained by either
3156 * locking the page or by holding its mapping's private_lock.
3158 * If the page is dirty but all the buffers are clean then we need to
3159 * be sure to mark the page clean as well. This is because the page
3160 * may be against a block device, and a later reattachment of buffers
3161 * to a dirty page will set *all* buffers dirty. Which would corrupt
3162 * filesystem data on the same device.
3164 * The same applies to regular filesystem pages: if all the buffers are
3165 * clean then we set the page clean and proceed. To do that, we require
3166 * total exclusion from __set_page_dirty_buffers(). That is obtained with
3169 * try_to_free_buffers() is non-blocking.
3171 static inline int buffer_busy(struct buffer_head *bh)
3173 return atomic_read(&bh->b_count) |
3174 (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3178 drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
3180 struct buffer_head *head = page_buffers(page);
3181 struct buffer_head *bh;
3185 if (buffer_write_io_error(bh) && page->mapping)
3186 set_bit(AS_EIO, &page->mapping->flags);
3187 if (buffer_busy(bh))
3189 bh = bh->b_this_page;
3190 } while (bh != head);
3193 struct buffer_head *next = bh->b_this_page;
3195 if (bh->b_assoc_map)
3196 __remove_assoc_queue(bh);
3198 } while (bh != head);
3199 *buffers_to_free = head;
3200 __clear_page_buffers(page);
3206 int try_to_free_buffers(struct page *page)
3208 struct address_space * const mapping = page->mapping;
3209 struct buffer_head *buffers_to_free = NULL;
3212 BUG_ON(!PageLocked(page));
3213 if (PageWriteback(page))
3216 if (mapping == NULL) { /* can this still happen? */
3217 ret = drop_buffers(page, &buffers_to_free);
3221 spin_lock(&mapping->private_lock);
3222 ret = drop_buffers(page, &buffers_to_free);
3225 * If the filesystem writes its buffers by hand (eg ext3)
3226 * then we can have clean buffers against a dirty page. We
3227 * clean the page here; otherwise the VM will never notice
3228 * that the filesystem did any IO at all.
3230 * Also, during truncate, discard_buffer will have marked all
3231 * the page's buffers clean. We discover that here and clean
3234 * private_lock must be held over this entire operation in order
3235 * to synchronise against __set_page_dirty_buffers and prevent the
3236 * dirty bit from being lost.
3239 cancel_dirty_page(page);
3240 spin_unlock(&mapping->private_lock);
3242 if (buffers_to_free) {
3243 struct buffer_head *bh = buffers_to_free;
3246 struct buffer_head *next = bh->b_this_page;
3247 free_buffer_head(bh);
3249 } while (bh != buffers_to_free);
3253 EXPORT_SYMBOL(try_to_free_buffers);
3256 * There are no bdflush tunables left. But distributions are
3257 * still running obsolete flush daemons, so we terminate them here.
3259 * Use of bdflush() is deprecated and will be removed in a future kernel.
3260 * The `flush-X' kernel threads fully replace bdflush daemons and this call.
3262 SYSCALL_DEFINE2(bdflush, int, func, long, data)
3264 static int msg_count;
3266 if (!capable(CAP_SYS_ADMIN))
3269 if (msg_count < 5) {
3272 "warning: process `%s' used the obsolete bdflush"
3273 " system call\n", current->comm);
3274 printk(KERN_INFO "Fix your initscripts?\n");
3283 * Buffer-head allocation
3285 static struct kmem_cache *bh_cachep __read_mostly;
3288 * Once the number of bh's in the machine exceeds this level, we start
3289 * stripping them in writeback.
3291 static unsigned long max_buffer_heads;
3293 int buffer_heads_over_limit;
3295 struct bh_accounting {
3296 int nr; /* Number of live bh's */
3297 int ratelimit; /* Limit cacheline bouncing */
3300 static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3302 static void recalc_bh_state(void)
3307 if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3309 __this_cpu_write(bh_accounting.ratelimit, 0);
3310 for_each_online_cpu(i)
3311 tot += per_cpu(bh_accounting, i).nr;
3312 buffer_heads_over_limit = (tot > max_buffer_heads);
3315 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3317 struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3319 INIT_LIST_HEAD(&ret->b_assoc_buffers);
3320 buffer_head_init_locks(ret);
3322 __this_cpu_inc(bh_accounting.nr);
3328 EXPORT_SYMBOL(alloc_buffer_head);
3330 void free_buffer_head(struct buffer_head *bh)
3332 BUG_ON(!list_empty(&bh->b_assoc_buffers));
3333 kmem_cache_free(bh_cachep, bh);
3335 __this_cpu_dec(bh_accounting.nr);
3339 EXPORT_SYMBOL(free_buffer_head);
3341 static void buffer_exit_cpu(int cpu)
3344 struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3346 for (i = 0; i < BH_LRU_SIZE; i++) {
3350 this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3351 per_cpu(bh_accounting, cpu).nr = 0;
3354 static int buffer_cpu_notify(struct notifier_block *self,
3355 unsigned long action, void *hcpu)
3357 if (action == CPU_DEAD || action == CPU_DEAD_FROZEN)
3358 buffer_exit_cpu((unsigned long)hcpu);
3363 * bh_uptodate_or_lock - Test whether the buffer is uptodate
3364 * @bh: struct buffer_head
3366 * Return true if the buffer is up-to-date and false,
3367 * with the buffer locked, if not.
3369 int bh_uptodate_or_lock(struct buffer_head *bh)
3371 if (!buffer_uptodate(bh)) {
3373 if (!buffer_uptodate(bh))
3379 EXPORT_SYMBOL(bh_uptodate_or_lock);
3382 * bh_submit_read - Submit a locked buffer for reading
3383 * @bh: struct buffer_head
3385 * Returns zero on success and -EIO on error.
3387 int bh_submit_read(struct buffer_head *bh)
3389 BUG_ON(!buffer_locked(bh));
3391 if (buffer_uptodate(bh)) {
3397 bh->b_end_io = end_buffer_read_sync;
3398 submit_bh(READ, bh);
3400 if (buffer_uptodate(bh))
3404 EXPORT_SYMBOL(bh_submit_read);
3406 void __init buffer_init(void)
3408 unsigned long nrpages;
3410 bh_cachep = kmem_cache_create("buffer_head",
3411 sizeof(struct buffer_head), 0,
3412 (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3417 * Limit the bh occupancy to 10% of ZONE_NORMAL
3419 nrpages = (nr_free_buffer_pages() * 10) / 100;
3420 max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3421 hotcpu_notifier(buffer_cpu_notify, 0);