Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3472 insertions, 0 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
new file mode 100644
index 000000000..356e289d1
--- /dev/null
+++ b/fs/buffer.c
@@ -0,0 +1,3472 @@
+/*
+ *  linux/fs/buffer.c
+ *
+ *  Copyright (C) 1991, 1992, 2002  Linus Torvalds
+ */
+
+/*
+ * Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
+ *
+ * Removed a lot of unnecessary code and simplified things now that
+ * the buffer cache isn't our primary cache - Andrew Tridgell 12/96
+ *
+ * Speed up hash, lru, and free list operations.  Use gfp() for allocating
+ * hash table, use SLAB cache for buffer heads. SMP threading.  -DaveM
+ *
+ * Added 32k buffer block sizes - these are required older ARM systems. - RMK
+ *
+ * async buffer flushing, 1999 Andrea Arcangeli <andrea@suse.de>
+ */
+
+#include <linux/kernel.h>
+#include <linux/sched/signal.h>
+#include <linux/syscalls.h>
+#include <linux/fs.h>
+#include <linux/iomap.h>
+#include <linux/mm.h>
+#include <linux/percpu.h>
+#include <linux/slab.h>
+#include <linux/capability.h>
+#include <linux/blkdev.h>
+#include <linux/file.h>
+#include <linux/quotaops.h>
+#include <linux/highmem.h>
+#include <linux/export.h>
+#include <linux/backing-dev.h>
+#include <linux/writeback.h>
+#include <linux/hash.h>
+#include <linux/suspend.h>
+#include <linux/buffer_head.h>
+#include <linux/task_io_accounting_ops.h>
+#include <linux/bio.h>
+#include <linux/cpu.h>
+#include <linux/bitops.h>
+#include <linux/mpage.h>
+#include <linux/bit_spinlock.h>
+#include <linux/pagevec.h>
+#include <linux/sched/mm.h>
+#include <trace/events/block.h>
+
+static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
+static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
+			 enum rw_hint hint, struct writeback_control *wbc);
+
+#define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
+
+inline void touch_buffer(struct buffer_head *bh)
+{
+	trace_block_touch_buffer(bh);
+	mark_page_accessed(bh->b_page);
+}
+EXPORT_SYMBOL(touch_buffer);
+
+void __lock_buffer(struct buffer_head *bh)
+{
+	wait_on_bit_lock_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
+}
+EXPORT_SYMBOL(__lock_buffer);
+
+void unlock_buffer(struct buffer_head *bh)
+{
+	clear_bit_unlock(BH_Lock, &bh->b_state);
+	smp_mb__after_atomic();
+	wake_up_bit(&bh->b_state, BH_Lock);
+}
+EXPORT_SYMBOL(unlock_buffer);
+
+/*
+ * Returns if the page has dirty or writeback buffers. If all the buffers
+ * are unlocked and clean then the PageDirty information is stale. If
+ * any of the pages are locked, it is assumed they are locked for IO.
+ */
+void buffer_check_dirty_writeback(struct page *page,
+				     bool *dirty, bool *writeback)
+{
+	struct buffer_head *head, *bh;
+	*dirty = false;
+	*writeback = false;
+
+	BUG_ON(!PageLocked(page));
+
+	if (!page_has_buffers(page))
+		return;
+
+	if (PageWriteback(page))
+		*writeback = true;
+
+	head = page_buffers(page);
+	bh = head;
+	do {
+		if (buffer_locked(bh))
+			*writeback = true;
+
+		if (buffer_dirty(bh))
+			*dirty = true;
+
+		bh = bh->b_this_page;
+	} while (bh != head);
+}
+EXPORT_SYMBOL(buffer_check_dirty_writeback);
+
+/*
+ * Block until a buffer comes unlocked.  This doesn't stop it
+ * from becoming locked again - you have to lock it yourself
+ * if you want to preserve its state.
+ */
+void __wait_on_buffer(struct buffer_head * bh)
+{
+	wait_on_bit_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
+}
+EXPORT_SYMBOL(__wait_on_buffer);
+
+static void
+__clear_page_buffers(struct page *page)
+{
+	ClearPagePrivate(page);
+	set_page_private(page, 0);
+	put_page(page);
+}
+
+static void buffer_io_error(struct buffer_head *bh, char *msg)
+{
+	if (!test_bit(BH_Quiet, &bh->b_state))
+		printk_ratelimited(KERN_ERR
+			"Buffer I/O error on dev %pg, logical block %llu%s\n",
+			bh->b_bdev, (unsigned long long)bh->b_blocknr, msg);
+}
+
+/*
+ * End-of-IO handler helper function which does not touch the bh after
+ * unlocking it.
+ * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
+ * a race there is benign: unlock_buffer() only use the bh's address for
+ * hashing after unlocking the buffer, so it doesn't actually touch the bh
+ * itself.
+ */
+static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
+{
+	if (uptodate) {
+		set_buffer_uptodate(bh);
+	} else {
+		/* This happens, due to failed read-ahead attempts. */
+		clear_buffer_uptodate(bh);
+	}
+	unlock_buffer(bh);
+}
+
+/*
+ * Default synchronous end-of-IO handler..  Just mark it up-to-date and
+ * unlock the buffer. This is what ll_rw_block uses too.
+ */
+void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
+{
+	__end_buffer_read_notouch(bh, uptodate);
+	put_bh(bh);
+}
+EXPORT_SYMBOL(end_buffer_read_sync);
+
+void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
+{
+	if (uptodate) {
+		set_buffer_uptodate(bh);
+	} else {
+		buffer_io_error(bh, ", lost sync page write");
+		mark_buffer_write_io_error(bh);
+		clear_buffer_uptodate(bh);
+	}
+	unlock_buffer(bh);
+	put_bh(bh);
+}
+EXPORT_SYMBOL(end_buffer_write_sync);
+
+/*
+ * Various filesystems appear to want __find_get_block to be non-blocking.
+ * But it's the page lock which protects the buffers.  To get around this,
+ * we get exclusion from try_to_free_buffers with the blockdev mapping's
+ * private_lock.
+ *
+ * Hack idea: for the blockdev mapping, private_lock contention
+ * may be quite high.  This code could TryLock the page, and if that
+ * succeeds, there is no need to take private_lock.
+ */
+static struct buffer_head *
+__find_get_block_slow(struct block_device *bdev, sector_t block)
+{
+	struct inode *bd_inode = bdev->bd_inode;
+	struct address_space *bd_mapping = bd_inode->i_mapping;
+	struct buffer_head *ret = NULL;
+	pgoff_t index;
+	struct buffer_head *bh;
+	struct buffer_head *head;
+	struct page *page;
+	int all_mapped = 1;
+	static DEFINE_RATELIMIT_STATE(last_warned, HZ, 1);
+
+	index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
+	page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
+	if (!page)
+		goto out;
+
+	spin_lock(&bd_mapping->private_lock);
+	if (!page_has_buffers(page))
+		goto out_unlock;
+	head = page_buffers(page);
+	bh = head;
+	do {
+		if (!buffer_mapped(bh))
+			all_mapped = 0;
+		else if (bh->b_blocknr == block) {
+			ret = bh;
+			get_bh(bh);
+			goto out_unlock;
+		}
+		bh = bh->b_this_page;
+	} while (bh != head);
+
+	/* we might be here because some of the buffers on this page are
+	 * not mapped.  This is due to various races between
+	 * file io on the block device and getblk.  It gets dealt with
+	 * elsewhere, don't buffer_error if we had some unmapped buffers
+	 */
+	ratelimit_set_flags(&last_warned, RATELIMIT_MSG_ON_RELEASE);
+	if (all_mapped && __ratelimit(&last_warned)) {
+		printk("__find_get_block_slow() failed. block=%llu, "
+		       "b_blocknr=%llu, b_state=0x%08lx, b_size=%zu, "
+		       "device %pg blocksize: %d\n",
+		       (unsigned long long)block,
+		       (unsigned long long)bh->b_blocknr,
+		       bh->b_state, bh->b_size, bdev,
+		       1 << bd_inode->i_blkbits);
+	}
+out_unlock:
+	spin_unlock(&bd_mapping->private_lock);
+	put_page(page);
+out:
+	return ret;
+}
+
+/*
+ * I/O completion handler for block_read_full_page() - pages
+ * which come unlocked at the end of I/O.
+ */
+static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
+{
+	unsigned long flags;
+	struct buffer_head *first;
+	struct buffer_head *tmp;
+	struct page *page;
+	int page_uptodate = 1;
+
+	BUG_ON(!buffer_async_read(bh));
+
+	page = bh->b_page;
+	if (uptodate) {
+		set_buffer_uptodate(bh);
+	} else {
+		clear_buffer_uptodate(bh);
+		buffer_io_error(bh, ", async page read");
+		SetPageError(page);
+	}
+
+	/*
+	 * Be _very_ careful from here on. Bad things can happen if
+	 * two buffer heads end IO at almost the same time and both
+	 * decide that the page is now completely done.
+	 */
+	first = page_buffers(page);
+	local_irq_save(flags);
+	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
+	clear_buffer_async_read(bh);
+	unlock_buffer(bh);
+	tmp = bh;
+	do {
+		if (!buffer_uptodate(tmp))
+			page_uptodate = 0;
+		if (buffer_async_read(tmp)) {
+			BUG_ON(!buffer_locked(tmp));
+			goto still_busy;
+		}
+		tmp = tmp->b_this_page;
+	} while (tmp != bh);
+	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
+	local_irq_restore(flags);
+
+	/*
+	 * If none of the buffers had errors and they are all
+	 * uptodate then we can set the page uptodate.
+	 */
+	if (page_uptodate && !PageError(page))
+		SetPageUptodate(page);
+	unlock_page(page);
+	return;
+
+still_busy:
+	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
+	local_irq_restore(flags);
+	return;
+}
+
+/*
+ * Completion handler for block_write_full_page() - pages which are unlocked
+ * during I/O, and which have PageWriteback cleared upon I/O completion.
+ */
+void end_buffer_async_write(struct buffer_head *bh, int uptodate)
+{
+	unsigned long flags;
+	struct buffer_head *first;
+	struct buffer_head *tmp;
+	struct page *page;
+
+	BUG_ON(!buffer_async_write(bh));
+
+	page = bh->b_page;
+	if (uptodate) {
+		set_buffer_uptodate(bh);
+	} else {
+		buffer_io_error(bh, ", lost async page write");
+		mark_buffer_write_io_error(bh);
+		clear_buffer_uptodate(bh);
+		SetPageError(page);
+	}
+
+	first = page_buffers(page);
+	local_irq_save(flags);
+	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
+
+	clear_buffer_async_write(bh);
+	unlock_buffer(bh);
+	tmp = bh->b_this_page;
+	while (tmp != bh) {
+		if (buffer_async_write(tmp)) {
+			BUG_ON(!buffer_locked(tmp));
+			goto still_busy;
+		}
+		tmp = tmp->b_this_page;
+	}
+	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
+	local_irq_restore(flags);
+	end_page_writeback(page);
+	return;
+
+still_busy:
+	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
+	local_irq_restore(flags);
+	return;
+}
+EXPORT_SYMBOL(end_buffer_async_write);
+
+/*
+ * If a page's buffers are under async readin (end_buffer_async_read
+ * completion) then there is a possibility that another thread of
+ * control could lock one of the buffers after it has completed
+ * but while some of the other buffers have not completed.  This
+ * locked buffer would confuse end_buffer_async_read() into not unlocking
+ * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
+ * that this buffer is not under async I/O.
+ *
+ * The page comes unlocked when it has no locked buffer_async buffers
+ * left.
+ *
+ * PageLocked prevents anyone starting new async I/O reads any of
+ * the buffers.
+ *
+ * PageWriteback is used to prevent simultaneous writeout of the same
+ * page.
+ *
+ * PageLocked prevents anyone from starting writeback of a page which is
+ * under read I/O (PageWriteback is only ever set against a locked page).
+ */
+static void mark_buffer_async_read(struct buffer_head *bh)
+{
+	bh->b_end_io = end_buffer_async_read;
+	set_buffer_async_read(bh);
+}
+
+static void mark_buffer_async_write_endio(struct buffer_head *bh,
+					  bh_end_io_t *handler)
+{
+	bh->b_end_io = handler;
+	set_buffer_async_write(bh);
+}
+
+void mark_buffer_async_write(struct buffer_head *bh)
+{
+	mark_buffer_async_write_endio(bh, end_buffer_async_write);
+}
+EXPORT_SYMBOL(mark_buffer_async_write);
+
+
+/*
+ * fs/buffer.c contains helper functions for buffer-backed address space's
+ * fsync functions.  A common requirement for buffer-based filesystems is
+ * that certain data from the backing blockdev needs to be written out for
+ * a successful fsync().  For example, ext2 indirect blocks need to be
+ * written back and waited upon before fsync() returns.
+ *
+ * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
+ * inode_has_buffers() and invalidate_inode_buffers() are provided for the
+ * management of a list of dependent buffers at ->i_mapping->private_list.
+ *
+ * Locking is a little subtle: try_to_free_buffers() will remove buffers
+ * from their controlling inode's queue when they are being freed.  But
+ * try_to_free_buffers() will be operating against the *blockdev* mapping
+ * at the time, not against the S_ISREG file which depends on those buffers.
+ * So the locking for private_list is via the private_lock in the address_space
+ * which backs the buffers.  Which is different from the address_space 
+ * against which the buffers are listed.  So for a particular address_space,
+ * mapping->private_lock does *not* protect mapping->private_list!  In fact,
+ * mapping->private_list will always be protected by the backing blockdev's
+ * ->private_lock.
+ *
+ * Which introduces a requirement: all buffers on an address_space's
+ * ->private_list must be from the same address_space: the blockdev's.
+ *
+ * address_spaces which do not place buffers at ->private_list via these
+ * utility functions are free to use private_lock and private_list for
+ * whatever they want.  The only requirement is that list_empty(private_list)
+ * be true at clear_inode() time.
+ *
+ * FIXME: clear_inode should not call invalidate_inode_buffers().  The
+ * filesystems should do that.  invalidate_inode_buffers() should just go
+ * BUG_ON(!list_empty).
+ *
+ * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
+ * take an address_space, not an inode.  And it should be called
+ * mark_buffer_dirty_fsync() to clearly define why those buffers are being
+ * queued up.
+ *
+ * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
+ * list if it is already on a list.  Because if the buffer is on a list,
+ * it *must* already be on the right one.  If not, the filesystem is being
+ * silly.  This will save a ton of locking.  But first we have to ensure
+ * that buffers are taken *off* the old inode's list when they are freed
+ * (presumably in truncate).  That requires careful auditing of all
+ * filesystems (do it inside bforget()).  It could also be done by bringing
+ * b_inode back.
+ */
+
+/*
+ * The buffer's backing address_space's private_lock must be held
+ */
+static void __remove_assoc_queue(struct buffer_head *bh)
+{
+	list_del_init(&bh->b_assoc_buffers);
+	WARN_ON(!bh->b_assoc_map);
+	bh->b_assoc_map = NULL;
+}
+
+int inode_has_buffers(struct inode *inode)
+{
+	return !list_empty(&inode->i_data.private_list);
+}
+
+/*
+ * osync is designed to support O_SYNC io.  It waits synchronously for
+ * all already-submitted IO to complete, but does not queue any new
+ * writes to the disk.
+ *
+ * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
+ * you dirty the buffers, and then use osync_inode_buffers to wait for
+ * completion.  Any other dirty buffers which are not yet queued for
+ * write will not be flushed to disk by the osync.
+ */
+static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
+{
+	struct buffer_head *bh;
+	struct list_head *p;
+	int err = 0;
+
+	spin_lock(lock);
+repeat:
+	list_for_each_prev(p, list) {
+		bh = BH_ENTRY(p);
+		if (buffer_locked(bh)) {
+			get_bh(bh);
+			spin_unlock(lock);
+			wait_on_buffer(bh);
+			if (!buffer_uptodate(bh))
+				err = -EIO;
+			brelse(bh);
+			spin_lock(lock);
+			goto repeat;
+		}
+	}
+	spin_unlock(lock);
+	return err;
+}
+
+void emergency_thaw_bdev(struct super_block *sb)
+{
+	while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
+		printk(KERN_WARNING "Emergency Thaw on %pg\n", sb->s_bdev);
+}
+
+/**
+ * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
+ * @mapping: the mapping which wants those buffers written
+ *
+ * Starts I/O against the buffers at mapping->private_list, and waits upon
+ * that I/O.
+ *
+ * Basically, this is a convenience function for fsync().
+ * @mapping is a file or directory which needs those buffers to be written for
+ * a successful fsync().
+ */
+int sync_mapping_buffers(struct address_space *mapping)
+{
+	struct address_space *buffer_mapping = mapping->private_data;
+
+	if (buffer_mapping == NULL || list_empty(&mapping->private_list))
+		return 0;
+
+	return fsync_buffers_list(&buffer_mapping->private_lock,
+					&mapping->private_list);
+}
+EXPORT_SYMBOL(sync_mapping_buffers);
+
+/*
+ * Called when we've recently written block `bblock', and it is known that
+ * `bblock' was for a buffer_boundary() buffer.  This means that the block at
+ * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
+ * dirty, schedule it for IO.  So that indirects merge nicely with their data.
+ */
+void write_boundary_block(struct block_device *bdev,
+			sector_t bblock, unsigned blocksize)
+{
+	struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
+	if (bh) {
+		if (buffer_dirty(bh))
+			ll_rw_block(REQ_OP_WRITE, 0, 1, &bh);
+		put_bh(bh);
+	}
+}
+
+void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
+{
+	struct address_space *mapping = inode->i_mapping;
+	struct address_space *buffer_mapping = bh->b_page->mapping;
+
+	mark_buffer_dirty(bh);
+	if (!mapping->private_data) {
+		mapping->private_data = buffer_mapping;
+	} else {
+		BUG_ON(mapping->private_data != buffer_mapping);
+	}
+	if (!bh->b_assoc_map) {
+		spin_lock(&buffer_mapping->private_lock);
+		list_move_tail(&bh->b_assoc_buffers,
+				&mapping->private_list);
+		bh->b_assoc_map = mapping;
+		spin_unlock(&buffer_mapping->private_lock);
+	}
+}
+EXPORT_SYMBOL(mark_buffer_dirty_inode);
+
+/*
+ * Mark the page dirty, and set it dirty in the radix tree, and mark the inode
+ * dirty.
+ *
+ * If warn is true, then emit a warning if the page is not uptodate and has
+ * not been truncated.
+ *
+ * The caller must hold lock_page_memcg().
+ */
+void __set_page_dirty(struct page *page, struct address_space *mapping,
+			     int warn)
+{
+	unsigned long flags;
+
+	xa_lock_irqsave(&mapping->i_pages, flags);
+	if (page->mapping) {	/* Race with truncate? */
+		WARN_ON_ONCE(warn && !PageUptodate(page));
+		account_page_dirtied(page, mapping);
+		radix_tree_tag_set(&mapping->i_pages,
+				page_index(page), PAGECACHE_TAG_DIRTY);
+	}
+	xa_unlock_irqrestore(&mapping->i_pages, flags);
+}
+EXPORT_SYMBOL_GPL(__set_page_dirty);
+
+/*
+ * Add a page to the dirty page list.
+ *
+ * It is a sad fact of life that this function is called from several places
+ * deeply under spinlocking.  It may not sleep.
+ *
+ * If the page has buffers, the uptodate buffers are set dirty, to preserve
+ * dirty-state coherency between the page and the buffers.  It the page does
+ * not have buffers then when they are later attached they will all be set
+ * dirty.
+ *
+ * The buffers are dirtied before the page is dirtied.  There's a small race
+ * window in which a writepage caller may see the page cleanness but not the
+ * buffer dirtiness.  That's fine.  If this code were to set the page dirty
+ * before the buffers, a concurrent writepage caller could clear the page dirty
+ * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
+ * page on the dirty page list.
+ *
+ * We use private_lock to lock against try_to_free_buffers while using the
+ * page's buffer list.  Also use this to protect against clean buffers being
+ * added to the page after it was set dirty.
+ *
+ * FIXME: may need to call ->reservepage here as well.  That's rather up to the
+ * address_space though.
+ */
+int __set_page_dirty_buffers(struct page *page)
+{
+	int newly_dirty;
+	struct address_space *mapping = page_mapping(page);
+
+	if (unlikely(!mapping))
+		return !TestSetPageDirty(page);
+
+	spin_lock(&mapping->private_lock);
+	if (page_has_buffers(page)) {
+		struct buffer_head *head = page_buffers(page);
+		struct buffer_head *bh = head;
+
+		do {
+			set_buffer_dirty(bh);
+			bh = bh->b_this_page;
+		} while (bh != head);
+	}
+	/*
+	 * Lock out page->mem_cgroup migration to keep PageDirty
+	 * synchronized with per-memcg dirty page counters.
+	 */
+	lock_page_memcg(page);
+	newly_dirty = !TestSetPageDirty(page);
+	spin_unlock(&mapping->private_lock);
+
+	if (newly_dirty)
+		__set_page_dirty(page, mapping, 1);
+
+	unlock_page_memcg(page);
+
+	if (newly_dirty)
+		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+
+	return newly_dirty;
+}
+EXPORT_SYMBOL(__set_page_dirty_buffers);
+
+/*
+ * Write out and wait upon a list of buffers.
+ *
+ * We have conflicting pressures: we want to make sure that all
+ * initially dirty buffers get waited on, but that any subsequently
+ * dirtied buffers don't.  After all, we don't want fsync to last
+ * forever if somebody is actively writing to the file.
+ *
+ * Do this in two main stages: first we copy dirty buffers to a
+ * temporary inode list, queueing the writes as we go.  Then we clean
+ * up, waiting for those writes to complete.
+ * 
+ * During this second stage, any subsequent updates to the file may end
+ * up refiling the buffer on the original inode's dirty list again, so
+ * there is a chance we will end up with a buffer queued for write but
+ * not yet completed on that list.  So, as a final cleanup we go through
+ * the osync code to catch these locked, dirty buffers without requeuing
+ * any newly dirty buffers for write.
+ */
+static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
+{
+	struct buffer_head *bh;
+	struct list_head tmp;
+	struct address_space *mapping;
+	int err = 0, err2;
+	struct blk_plug plug;
+
+	INIT_LIST_HEAD(&tmp);
+	blk_start_plug(&plug);
+
+	spin_lock(lock);
+	while (!list_empty(list)) {
+		bh = BH_ENTRY(list->next);
+		mapping = bh->b_assoc_map;
+		__remove_assoc_queue(bh);
+		/* Avoid race with mark_buffer_dirty_inode() which does
+		 * a lockless check and we rely on seeing the dirty bit */
+		smp_mb();
+		if (buffer_dirty(bh) || buffer_locked(bh)) {
+			list_add(&bh->b_assoc_buffers, &tmp);
+			bh->b_assoc_map = mapping;
+			if (buffer_dirty(bh)) {
+				get_bh(bh);
+				spin_unlock(lock);
+				/*
+				 * Ensure any pending I/O completes so that
+				 * write_dirty_buffer() actually writes the
+				 * current contents - it is a noop if I/O is
+				 * still in flight on potentially older
+				 * contents.
+				 */
+				write_dirty_buffer(bh, REQ_SYNC);
+
+				/*
+				 * Kick off IO for the previous mapping. Note
+				 * that we will not run the very last mapping,
+				 * wait_on_buffer() will do that for us
+				 * through sync_buffer().
+				 */
+				brelse(bh);
+				spin_lock(lock);
+			}
+		}
+	}
+
+	spin_unlock(lock);
+	blk_finish_plug(&plug);
+	spin_lock(lock);
+
+	while (!list_empty(&tmp)) {
+		bh = BH_ENTRY(tmp.prev);
+		get_bh(bh);
+		mapping = bh->b_assoc_map;
+		__remove_assoc_queue(bh);
+		/* Avoid race with mark_buffer_dirty_inode() which does
+		 * a lockless check and we rely on seeing the dirty bit */
+		smp_mb();
+		if (buffer_dirty(bh)) {
+			list_add(&bh->b_assoc_buffers,
+				 &mapping->private_list);
+			bh->b_assoc_map = mapping;
+		}
+		spin_unlock(lock);
+		wait_on_buffer(bh);
+		if (!buffer_uptodate(bh))
+			err = -EIO;
+		brelse(bh);
+		spin_lock(lock);
+	}
+	
+	spin_unlock(lock);
+	err2 = osync_buffers_list(lock, list);
+	if (err)
+		return err;
+	else
+		return err2;
+}
+
+/*
+ * Invalidate any and all dirty buffers on a given inode.  We are
+ * probably unmounting the fs, but that doesn't mean we have already
+ * done a sync().  Just drop the buffers from the inode list.
+ *
+ * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
+ * assumes that all the buffers are against the blockdev.  Not true
+ * for reiserfs.
+ */
+void invalidate_inode_buffers(struct inode *inode)
+{
+	if (inode_has_buffers(inode)) {
+		struct address_space *mapping = &inode->i_data;
+		struct list_head *list = &mapping->private_list;
+		struct address_space *buffer_mapping = mapping->private_data;
+
+		spin_lock(&buffer_mapping->private_lock);
+		while (!list_empty(list))
+			__remove_assoc_queue(BH_ENTRY(list->next));
+		spin_unlock(&buffer_mapping->private_lock);
+	}
+}
+EXPORT_SYMBOL(invalidate_inode_buffers);
+
+/*
+ * Remove any clean buffers from the inode's buffer list.  This is called
+ * when we're trying to free the inode itself.  Those buffers can pin it.
+ *
+ * Returns true if all buffers were removed.
+ */
+int remove_inode_buffers(struct inode *inode)
+{
+	int ret = 1;
+
+	if (inode_has_buffers(inode)) {
+		struct address_space *mapping = &inode->i_data;
+		struct list_head *list = &mapping->private_list;
+		struct address_space *buffer_mapping = mapping->private_data;
+
+		spin_lock(&buffer_mapping->private_lock);
+		while (!list_empty(list)) {
+			struct buffer_head *bh = BH_ENTRY(list->next);
+			if (buffer_dirty(bh)) {
+				ret = 0;
+				break;
+			}
+			__remove_assoc_queue(bh);
+		}
+		spin_unlock(&buffer_mapping->private_lock);
+	}
+	return ret;
+}
+
+/*
+ * Create the appropriate buffers when given a page for data area and
+ * the size of each buffer.. Use the bh->b_this_page linked list to
+ * follow the buffers created.  Return NULL if unable to create more
+ * buffers.
+ *
+ * The retry flag is used to differentiate async IO (paging, swapping)
+ * which may not fail from ordinary buffer allocations.
+ */
+struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
+		bool retry)
+{
+	struct buffer_head *bh, *head;
+	gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
+	long offset;
+	struct mem_cgroup *memcg;
+
+	if (retry)
+		gfp |= __GFP_NOFAIL;
+
+	memcg = get_mem_cgroup_from_page(page);
+	memalloc_use_memcg(memcg);
+
+	head = NULL;
+	offset = PAGE_SIZE;
+	while ((offset -= size) >= 0) {
+		bh = alloc_buffer_head(gfp);
+		if (!bh)
+			goto no_grow;
+
+		bh->b_this_page = head;
+		bh->b_blocknr = -1;
+		head = bh;
+
+		bh->b_size = size;
+
+		/* Link the buffer to its page */
+		set_bh_page(bh, page, offset);
+	}
+out:
+	memalloc_unuse_memcg();
+	mem_cgroup_put(memcg);
+	return head;
+/*
+ * In case anything failed, we just free everything we got.
+ */
+no_grow:
+	if (head) {
+		do {
+			bh = head;
+			head = head->b_this_page;
+			free_buffer_head(bh);
+		} while (head);
+	}
+
+	goto out;
+}
+EXPORT_SYMBOL_GPL(alloc_page_buffers);
+
+static inline void
+link_dev_buffers(struct page *page, struct buffer_head *head)
+{
+	struct buffer_head *bh, *tail;
+
+	bh = head;
+	do {
+		tail = bh;
+		bh = bh->b_this_page;
+	} while (bh);
+	tail->b_this_page = head;
+	attach_page_buffers(page, head);
+}
+
+static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
+{
+	sector_t retval = ~((sector_t)0);
+	loff_t sz = i_size_read(bdev->bd_inode);
+
+	if (sz) {
+		unsigned int sizebits = blksize_bits(size);
+		retval = (sz >> sizebits);
+	}
+	return retval;
+}
+
+/*
+ * Initialise the state of a blockdev page's buffers.
+ */ 
+static sector_t
+init_page_buffers(struct page *page, struct block_device *bdev,
+			sector_t block, int size)
+{
+	struct buffer_head *head = page_buffers(page);
+	struct buffer_head *bh = head;
+	int uptodate = PageUptodate(page);
+	sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
+
+	do {
+		if (!buffer_mapped(bh)) {
+			bh->b_end_io = NULL;
+			bh->b_private = NULL;
+			bh->b_bdev = bdev;
+			bh->b_blocknr = block;
+			if (uptodate)
+				set_buffer_uptodate(bh);
+			if (block < end_block)
+				set_buffer_mapped(bh);
+		}
+		block++;
+		bh = bh->b_this_page;
+	} while (bh != head);
+
+	/*
+	 * Caller needs to validate requested block against end of device.
+	 */
+	return end_block;
+}
+
+/*
+ * Create the page-cache page that contains the requested block.
+ *
+ * This is used purely for blockdev mappings.
+ */
+static int
+grow_dev_page(struct block_device *bdev, sector_t block,
+	      pgoff_t index, int size, int sizebits, gfp_t gfp)
+{
+	struct inode *inode = bdev->bd_inode;
+	struct page *page;
+	struct buffer_head *bh;
+	sector_t end_block;
+	int ret = 0;		/* Will call free_more_memory() */
+	gfp_t gfp_mask;
+
+	gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) | gfp;
+
+	/*
+	 * XXX: __getblk_slow() can not really deal with failure and
+	 * will endlessly loop on improvised global reclaim.  Prefer
+	 * looping in the allocator rather than here, at least that
+	 * code knows what it's doing.
+	 */
+	gfp_mask |= __GFP_NOFAIL;
+
+	page = find_or_create_page(inode->i_mapping, index, gfp_mask);
+
+	BUG_ON(!PageLocked(page));
+
+	if (page_has_buffers(page)) {
+		bh = page_buffers(page);
+		if (bh->b_size == size) {
+			end_block = init_page_buffers(page, bdev,
+						(sector_t)index << sizebits,
+						size);
+			goto done;
+		}
+		if (!try_to_free_buffers(page))
+			goto failed;
+	}
+
+	/*
+	 * Allocate some buffers for this page
+	 */
+	bh = alloc_page_buffers(page, size, true);
+
+	/*
+	 * Link the page to the buffers and initialise them.  Take the
+	 * lock to be atomic wrt __find_get_block(), which does not
+	 * run under the page lock.
+	 */
+	spin_lock(&inode->i_mapping->private_lock);
+	link_dev_buffers(page, bh);
+	end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
+			size);
+	spin_unlock(&inode->i_mapping->private_lock);
+done:
+	ret = (block < end_block) ? 1 : -ENXIO;
+failed:
+	unlock_page(page);
+	put_page(page);
+	return ret;
+}
+
+/*
+ * Create buffers for the specified block device block's page.  If
+ * that page was dirty, the buffers are set dirty also.
+ */
+static int
+grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
+{
+	pgoff_t index;
+	int sizebits;
+
+	sizebits = -1;
+	do {
+		sizebits++;
+	} while ((size << sizebits) < PAGE_SIZE);
+
+	index = block >> sizebits;
+
+	/*
+	 * Check for a block which wants to lie outside our maximum possible
+	 * pagecache index.  (this comparison is done using sector_t types).
+	 */
+	if (unlikely(index != block >> sizebits)) {
+		printk(KERN_ERR "%s: requested out-of-range block %llu for "
+			"device %pg\n",
+			__func__, (unsigned long long)block,
+			bdev);
+		return -EIO;
+	}
+
+	/* Create a page with the proper size buffers.. */
+	return grow_dev_page(bdev, block, index, size, sizebits, gfp);
+}
+
+static struct buffer_head *
+__getblk_slow(struct block_device *bdev, sector_t block,
+	     unsigned size, gfp_t gfp)
+{
+	/* Size must be multiple of hard sectorsize */
+	if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
+			(size < 512 || size > PAGE_SIZE))) {
+		printk(KERN_ERR "getblk(): invalid block size %d requested\n",
+					size);
+		printk(KERN_ERR "logical block size: %d\n",
+					bdev_logical_block_size(bdev));
+
+		dump_stack();
+		return NULL;
+	}
+
+	for (;;) {
+		struct buffer_head *bh;
+		int ret;
+
+		bh = __find_get_block(bdev, block, size);
+		if (bh)
+			return bh;
+
+		ret = grow_buffers(bdev, block, size, gfp);
+		if (ret < 0)
+			return NULL;
+	}
+}
+
+/*
+ * The relationship between dirty buffers and dirty pages:
+ *
+ * Whenever a page has any dirty buffers, the page's dirty bit is set, and
+ * the page is tagged dirty in its radix tree.
+ *
+ * At all times, the dirtiness of the buffers represents the dirtiness of
+ * subsections of the page.  If the page has buffers, the page dirty bit is
+ * merely a hint about the true dirty state.
+ *
+ * When a page is set dirty in its entirety, all its buffers are marked dirty
+ * (if the page has buffers).
+ *
+ * When a buffer is marked dirty, its page is dirtied, but the page's other
+ * buffers are not.
+ *
+ * Also.  When blockdev buffers are explicitly read with bread(), they
+ * individually become uptodate.  But their backing page remains not
+ * uptodate - even if all of its buffers are uptodate.  A subsequent
+ * block_read_full_page() against that page will discover all the uptodate
+ * buffers, will set the page uptodate and will perform no I/O.
+ */
+
+/**
+ * mark_buffer_dirty - mark a buffer_head as needing writeout
+ * @bh: the buffer_head to mark dirty
+ *
+ * mark_buffer_dirty() will set the dirty bit against the buffer, then set its
+ * backing page dirty, then tag the page as dirty in its address_space's radix
+ * tree and then attach the address_space's inode to its superblock's dirty
+ * inode list.
+ *
+ * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
+ * i_pages lock and mapping->host->i_lock.
+ */
+void mark_buffer_dirty(struct buffer_head *bh)
+{
+	WARN_ON_ONCE(!buffer_uptodate(bh));
+
+	trace_block_dirty_buffer(bh);
+
+	/*
+	 * Very *carefully* optimize the it-is-already-dirty case.
+	 *
+	 * Don't let the final "is it dirty" escape to before we
+	 * perhaps modified the buffer.
+	 */
+	if (buffer_dirty(bh)) {
+		smp_mb();
+		if (buffer_dirty(bh))
+			return;
+	}
+
+	if (!test_set_buffer_dirty(bh)) {
+		struct page *page = bh->b_page;
+		struct address_space *mapping = NULL;
+
+		lock_page_memcg(page);
+		if (!TestSetPageDirty(page)) {
+			mapping = page_mapping(page);
+			if (mapping)
+				__set_page_dirty(page, mapping, 0);
+		}
+		unlock_page_memcg(page);
+		if (mapping)
+			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+	}
+}
+EXPORT_SYMBOL(mark_buffer_dirty);
+
+void mark_buffer_write_io_error(struct buffer_head *bh)
+{
+	set_buffer_write_io_error(bh);
+	/* FIXME: do we need to set this in both places? */
+	if (bh->b_page && bh->b_page->mapping)
+		mapping_set_error(bh->b_page->mapping, -EIO);
+	if (bh->b_assoc_map)
+		mapping_set_error(bh->b_assoc_map, -EIO);
+}
+EXPORT_SYMBOL(mark_buffer_write_io_error);
+
+/*
+ * Decrement a buffer_head's reference count.  If all buffers against a page
+ * have zero reference count, are clean and unlocked, and if the page is clean
+ * and unlocked then try_to_free_buffers() may strip the buffers from the page
+ * in preparation for freeing it (sometimes, rarely, buffers are removed from
+ * a page but it ends up not being freed, and buffers may later be reattached).
+ */
+void __brelse(struct buffer_head * buf)
+{
+	if (atomic_read(&buf->b_count)) {
+		put_bh(buf);
+		return;
+	}
+	WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
+}
+EXPORT_SYMBOL(__brelse);
+
+/*
+ * bforget() is like brelse(), except it discards any
+ * potentially dirty data.
+ */
+void __bforget(struct buffer_head *bh)
+{
+	clear_buffer_dirty(bh);
+	if (bh->b_assoc_map) {
+		struct address_space *buffer_mapping = bh->b_page->mapping;
+
+		spin_lock(&buffer_mapping->private_lock);
+		list_del_init(&bh->b_assoc_buffers);
+		bh->b_assoc_map = NULL;
+		spin_unlock(&buffer_mapping->private_lock);
+	}
+	__brelse(bh);
+}
+EXPORT_SYMBOL(__bforget);
+
+static struct buffer_head *__bread_slow(struct buffer_head *bh)
+{
+	lock_buffer(bh);
+	if (buffer_uptodate(bh)) {
+		unlock_buffer(bh);
+		return bh;
+	} else {
+		get_bh(bh);
+		bh->b_end_io = end_buffer_read_sync;
+		submit_bh(REQ_OP_READ, 0, bh);
+		wait_on_buffer(bh);
+		if (buffer_uptodate(bh))
+			return bh;
+	}
+	brelse(bh);
+	return NULL;
+}
+
+/*
+ * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
+ * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
+ * refcount elevated by one when they're in an LRU.  A buffer can only appear
+ * once in a particular CPU's LRU.  A single buffer can be present in multiple
+ * CPU's LRUs at the same time.
+ *
+ * This is a transparent caching front-end to sb_bread(), sb_getblk() and
+ * sb_find_get_block().
+ *
+ * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
+ * a local interrupt disable for that.
+ */
+
+#define BH_LRU_SIZE	16
+
+struct bh_lru {
+	struct buffer_head *bhs[BH_LRU_SIZE];
+};
+
+static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
+
+#ifdef CONFIG_SMP
+#define bh_lru_lock()	local_irq_disable()
+#define bh_lru_unlock()	local_irq_enable()
+#else
+#define bh_lru_lock()	preempt_disable()
+#define bh_lru_unlock()	preempt_enable()
+#endif
+
+static inline void check_irqs_on(void)
+{
+#ifdef irqs_disabled
+	BUG_ON(irqs_disabled());
+#endif
+}
+
+/*
+ * Install a buffer_head into this cpu's LRU.  If not already in the LRU, it is
+ * inserted at the front, and the buffer_head at the back if any is evicted.
+ * Or, if already in the LRU it is moved to the front.
+ */
+static void bh_lru_install(struct buffer_head *bh)
+{
+	struct buffer_head *evictee = bh;
+	struct bh_lru *b;
+	int i;
+
+	check_irqs_on();
+	bh_lru_lock();
+
+	b = this_cpu_ptr(&bh_lrus);
+	for (i = 0; i < BH_LRU_SIZE; i++) {
+		swap(evictee, b->bhs[i]);
+		if (evictee == bh) {
+			bh_lru_unlock();
+			return;
+		}
+	}
+
+	get_bh(bh);
+	bh_lru_unlock();
+	brelse(evictee);
+}
+
+/*
+ * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
+ */
+static struct buffer_head *
+lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
+{
+	struct buffer_head *ret = NULL;
+	unsigned int i;
+
+	check_irqs_on();
+	bh_lru_lock();
+	for (i = 0; i < BH_LRU_SIZE; i++) {
+		struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
+
+		if (bh && bh->b_blocknr == block && bh->b_bdev == bdev &&
+		    bh->b_size == size) {
+			if (i) {
+				while (i) {
+					__this_cpu_write(bh_lrus.bhs[i],
+						__this_cpu_read(bh_lrus.bhs[i - 1]));
+					i--;
+				}
+				__this_cpu_write(bh_lrus.bhs[0], bh);
+			}
+			get_bh(bh);
+			ret = bh;
+			break;
+		}
+	}
+	bh_lru_unlock();
+	return ret;
+}
+
+/*
+ * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
+ * it in the LRU and mark it as accessed.  If it is not present then return
+ * NULL
+ */
+struct buffer_head *
+__find_get_block(struct block_device *bdev, sector_t block, unsigned size)
+{
+	struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
+
+	if (bh == NULL) {
+		/* __find_get_block_slow will mark the page accessed */
+		bh = __find_get_block_slow(bdev, block);
+		if (bh)
+			bh_lru_install(bh);
+	} else
+		touch_buffer(bh);
+
+	return bh;
+}
+EXPORT_SYMBOL(__find_get_block);
+
+/*
+ * __getblk_gfp() will locate (and, if necessary, create) the buffer_head
+ * which corresponds to the passed block_device, block and size. The
+ * returned buffer has its reference count incremented.
+ *
+ * __getblk_gfp() will lock up the machine if grow_dev_page's
+ * try_to_free_buffers() attempt is failing.  FIXME, perhaps?
+ */
+struct buffer_head *
+__getblk_gfp(struct block_device *bdev, sector_t block,
+	     unsigned size, gfp_t gfp)
+{
+	struct buffer_head *bh = __find_get_block(bdev, block, size);
+
+	might_sleep();
+	if (bh == NULL)
+		bh = __getblk_slow(bdev, block, size, gfp);
+	return bh;
+}
+EXPORT_SYMBOL(__getblk_gfp);
+
+/*
+ * Do async read-ahead on a buffer..
+ */
+void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
+{
+	struct buffer_head *bh = __getblk(bdev, block, size);
+	if (likely(bh)) {
+		ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
+		brelse(bh);
+	}
+}
+EXPORT_SYMBOL(__breadahead);
+
+void __breadahead_gfp(struct block_device *bdev, sector_t block, unsigned size,
+		      gfp_t gfp)
+{
+	struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
+	if (likely(bh)) {
+		ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
+		brelse(bh);
+	}
+}
+EXPORT_SYMBOL(__breadahead_gfp);
+
+/**
+ *  __bread_gfp() - reads a specified block and returns the bh
+ *  @bdev: the block_device to read from
+ *  @block: number of block
+ *  @size: size (in bytes) to read
+ *  @gfp: page allocation flag
+ *
+ *  Reads a specified block, and returns buffer head that contains it.
+ *  The page cache can be allocated from non-movable area
+ *  not to prevent page migration if you set gfp to zero.
+ *  It returns NULL if the block was unreadable.
+ */
+struct buffer_head *
+__bread_gfp(struct block_device *bdev, sector_t block,
+		   unsigned size, gfp_t gfp)
+{
+	struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
+
+	if (likely(bh) && !buffer_uptodate(bh))
+		bh = __bread_slow(bh);
+	return bh;
+}
+EXPORT_SYMBOL(__bread_gfp);
+
+/*
+ * invalidate_bh_lrus() is called rarely - but not only at unmount.
+ * This doesn't race because it runs in each cpu either in irq
+ * or with preempt disabled.
+ */
+static void invalidate_bh_lru(void *arg)
+{
+	struct bh_lru *b = &get_cpu_var(bh_lrus);
+	int i;
+
+	for (i = 0; i < BH_LRU_SIZE; i++) {
+		brelse(b->bhs[i]);
+		b->bhs[i] = NULL;
+	}
+	put_cpu_var(bh_lrus);
+}
+
+static bool has_bh_in_lru(int cpu, void *dummy)
+{
+	struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
+	int i;
+	
+	for (i = 0; i < BH_LRU_SIZE; i++) {
+		if (b->bhs[i])
+			return 1;
+	}
+
+	return 0;
+}
+
+void invalidate_bh_lrus(void)
+{
+	on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
+}
+EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
+
+void set_bh_page(struct buffer_head *bh,
+		struct page *page, unsigned long offset)
+{
+	bh->b_page = page;
+	BUG_ON(offset >= PAGE_SIZE);
+	if (PageHighMem(page))
+		/*
+		 * This catches illegal uses and preserves the offset:
+		 */
+		bh->b_data = (char *)(0 + offset);
+	else
+		bh->b_data = page_address(page) + offset;
+}
+EXPORT_SYMBOL(set_bh_page);
+
+/*
+ * Called when truncating a buffer on a page completely.
+ */
+
+/* Bits that are cleared during an invalidate */
+#define BUFFER_FLAGS_DISCARD \
+	(1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
+	 1 << BH_Delay | 1 << BH_Unwritten)
+
+static void discard_buffer(struct buffer_head * bh)
+{
+	unsigned long b_state, b_state_old;
+
+	lock_buffer(bh);
+	clear_buffer_dirty(bh);
+	bh->b_bdev = NULL;
+	b_state = bh->b_state;
+	for (;;) {
+		b_state_old = cmpxchg(&bh->b_state, b_state,
+				      (b_state & ~BUFFER_FLAGS_DISCARD));
+		if (b_state_old == b_state)
+			break;
+		b_state = b_state_old;
+	}
+	unlock_buffer(bh);
+}
+
+/**
+ * block_invalidatepage - invalidate part or all of a buffer-backed page
+ *
+ * @page: the page which is affected
+ * @offset: start of the range to invalidate
+ * @length: length of the range to invalidate
+ *
+ * block_invalidatepage() is called when all or part of the page has become
+ * invalidated by a truncate operation.
+ *
+ * block_invalidatepage() does not have to release all buffers, but it must
+ * ensure that no dirty buffer is left outside @offset and that no I/O
+ * is underway against any of the blocks which are outside the truncation
+ * point.  Because the caller is about to free (and possibly reuse) those
+ * blocks on-disk.
+ */
+void block_invalidatepage(struct page *page, unsigned int offset,
+			  unsigned int length)
+{
+	struct buffer_head *head, *bh, *next;
+	unsigned int curr_off = 0;
+	unsigned int stop = length + offset;
+
+	BUG_ON(!PageLocked(page));
+	if (!page_has_buffers(page))
+		goto out;
+
+	/*
+	 * Check for overflow
+	 */
+	BUG_ON(stop > PAGE_SIZE || stop < length);
+
+	head = page_buffers(page);
+	bh = head;
+	do {
+		unsigned int next_off = curr_off + bh->b_size;
+		next = bh->b_this_page;
+
+		/*
+		 * Are we still fully in range ?
+		 */
+		if (next_off > stop)
+			goto out;
+
+		/*
+		 * is this block fully invalidated?
+		 */
+		if (offset <= curr_off)
+			discard_buffer(bh);
+		curr_off = next_off;
+		bh = next;
+	} while (bh != head);
+
+	/*
+	 * We release buffers only if the entire page is being invalidated.
+	 * The get_block cached value has been unconditionally invalidated,
+	 * so real IO is not possible anymore.
+	 */
+	if (length == PAGE_SIZE)
+		try_to_release_page(page, 0);
+out:
+	return;
+}
+EXPORT_SYMBOL(block_invalidatepage);
+
+
+/*
+ * We attach and possibly dirty the buffers atomically wrt
+ * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
+ * is already excluded via the page lock.
+ */
+void create_empty_buffers(struct page *page,
+			unsigned long blocksize, unsigned long b_state)
+{
+	struct buffer_head *bh, *head, *tail;
+
+	head = alloc_page_buffers(page, blocksize, true);
+	bh = head;
+	do {
+		bh->b_state |= b_state;
+		tail = bh;
+		bh = bh->b_this_page;
+	} while (bh);
+	tail->b_this_page = head;
+
+	spin_lock(&page->mapping->private_lock);
+	if (PageUptodate(page) || PageDirty(page)) {
+		bh = head;
+		do {
+			if (PageDirty(page))
+				set_buffer_dirty(bh);
+			if (PageUptodate(page))
+				set_buffer_uptodate(bh);
+			bh = bh->b_this_page;
+		} while (bh != head);
+	}
+	attach_page_buffers(page, head);
+	spin_unlock(&page->mapping->private_lock);
+}
+EXPORT_SYMBOL(create_empty_buffers);
+
+/**
+ * clean_bdev_aliases: clean a range of buffers in block device
+ * @bdev: Block device to clean buffers in
+ * @block: Start of a range of blocks to clean
+ * @len: Number of blocks to clean
+ *
+ * We are taking a range of blocks for data and we don't want writeback of any
+ * buffer-cache aliases starting from return from this function and until the
+ * moment when something will explicitly mark the buffer dirty (hopefully that
+ * will not happen until we will free that block ;-) We don't even need to mark
+ * it not-uptodate - nobody can expect anything from a newly allocated buffer
+ * anyway. We used to use unmap_buffer() for such invalidation, but that was
+ * wrong. We definitely don't want to mark the alias unmapped, for example - it
+ * would confuse anyone who might pick it with bread() afterwards...
+ *
+ * Also..  Note that bforget() doesn't lock the buffer.  So there can be
+ * writeout I/O going on against recently-freed buffers.  We don't wait on that
+ * I/O in bforget() - it's more efficient to wait on the I/O only if we really
+ * need to.  That happens here.
+ */
+void clean_bdev_aliases(struct block_device *bdev, sector_t block, sector_t len)
+{
+	struct inode *bd_inode = bdev->bd_inode;
+	struct address_space *bd_mapping = bd_inode->i_mapping;
+	struct pagevec pvec;
+	pgoff_t index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
+	pgoff_t end;
+	int i, count;
+	struct buffer_head *bh;
+	struct buffer_head *head;
+
+	end = (block + len - 1) >> (PAGE_SHIFT - bd_inode->i_blkbits);
+	pagevec_init(&pvec);
+	while (pagevec_lookup_range(&pvec, bd_mapping, &index, end)) {
+		count = pagevec_count(&pvec);
+		for (i = 0; i < count; i++) {
+			struct page *page = pvec.pages[i];
+
+			if (!page_has_buffers(page))
+				continue;
+			/*
+			 * We use page lock instead of bd_mapping->private_lock
+			 * to pin buffers here since we can afford to sleep and
+			 * it scales better than a global spinlock lock.
+			 */
+			lock_page(page);
+			/* Recheck when the page is locked which pins bhs */
+			if (!page_has_buffers(page))
+				goto unlock_page;
+			head = page_buffers(page);
+			bh = head;
+			do {
+				if (!buffer_mapped(bh) || (bh->b_blocknr < block))
+					goto next;
+				if (bh->b_blocknr >= block + len)
+					break;
+				clear_buffer_dirty(bh);
+				wait_on_buffer(bh);
+				clear_buffer_req(bh);
+next:
+				bh = bh->b_this_page;
+			} while (bh != head);
+unlock_page:
+			unlock_page(page);
+		}
+		pagevec_release(&pvec);
+		cond_resched();
+		/* End of range already reached? */
+		if (index > end || !index)
+			break;
+	}
+}
+EXPORT_SYMBOL(clean_bdev_aliases);
+
+/*
+ * Size is a power-of-two in the range 512..PAGE_SIZE,
+ * and the case we care about most is PAGE_SIZE.
+ *
+ * So this *could* possibly be written with those
+ * constraints in mind (relevant mostly if some
+ * architecture has a slow bit-scan instruction)
+ */
+static inline int block_size_bits(unsigned int blocksize)
+{
+	return ilog2(blocksize);
+}
+
+static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
+{
+	BUG_ON(!PageLocked(page));
+
+	if (!page_has_buffers(page))
+		create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
+				     b_state);
+	return page_buffers(page);
+}
+
+/*
+ * NOTE! All mapped/uptodate combinations are valid:
+ *
+ *	Mapped	Uptodate	Meaning
+ *
+ *	No	No		"unknown" - must do get_block()
+ *	No	Yes		"hole" - zero-filled
+ *	Yes	No		"allocated" - allocated on disk, not read in
+ *	Yes	Yes		"valid" - allocated and up-to-date in memory.
+ *
+ * "Dirty" is valid only with the last case (mapped+uptodate).
+ */
+
+/*
+ * While block_write_full_page is writing back the dirty buffers under
+ * the page lock, whoever dirtied the buffers may decide to clean them
+ * again at any time.  We handle that by only looking at the buffer
+ * state inside lock_buffer().
+ *
+ * If block_write_full_page() is called for regular writeback
+ * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
+ * locked buffer.   This only can happen if someone has written the buffer
+ * directly, with submit_bh().  At the address_space level PageWriteback
+ * prevents this contention from occurring.
+ *
+ * If block_write_full_page() is called with wbc->sync_mode ==
+ * WB_SYNC_ALL, the writes are posted using REQ_SYNC; this
+ * causes the writes to be flagged as synchronous writes.
+ */
+int __block_write_full_page(struct inode *inode, struct page *page,
+			get_block_t *get_block, struct writeback_control *wbc,
+			bh_end_io_t *handler)
+{
+	int err;
+	sector_t block;
+	sector_t last_block;
+	struct buffer_head *bh, *head;
+	unsigned int blocksize, bbits;
+	int nr_underway = 0;
+	int write_flags = wbc_to_write_flags(wbc);
+
+	head = create_page_buffers(page, inode,
+					(1 << BH_Dirty)|(1 << BH_Uptodate));
+
+	/*
+	 * Be very careful.  We have no exclusion from __set_page_dirty_buffers
+	 * here, and the (potentially unmapped) buffers may become dirty at
+	 * any time.  If a buffer becomes dirty here after we've inspected it
+	 * then we just miss that fact, and the page stays dirty.
+	 *
+	 * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
+	 * handle that here by just cleaning them.
+	 */
+
+	bh = head;
+	blocksize = bh->b_size;
+	bbits = block_size_bits(blocksize);
+
+	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
+	last_block = (i_size_read(inode) - 1) >> bbits;
+
+	/*
+	 * Get all the dirty buffers mapped to disk addresses and
+	 * handle any aliases from the underlying blockdev's mapping.
+	 */
+	do {
+		if (block > last_block) {
+			/*
+			 * mapped buffers outside i_size will occur, because
+			 * this page can be outside i_size when there is a
+			 * truncate in progress.
+			 */
+			/*
+			 * The buffer was zeroed by block_write_full_page()
+			 */
+			clear_buffer_dirty(bh);
+			set_buffer_uptodate(bh);
+		} else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
+			   buffer_dirty(bh)) {
+			WARN_ON(bh->b_size != blocksize);
+			err = get_block(inode, block, bh, 1);
+			if (err)
+				goto recover;
+			clear_buffer_delay(bh);
+			if (buffer_new(bh)) {
+				/* blockdev mappings never come here */
+				clear_buffer_new(bh);
+				clean_bdev_bh_alias(bh);
+			}
+		}
+		bh = bh->b_this_page;
+		block++;
+	} while (bh != head);
+
+	do {
+		if (!buffer_mapped(bh))
+			continue;
+		/*
+		 * If it's a fully non-blocking write attempt and we cannot
+		 * lock the buffer then redirty the page.  Note that this can
+		 * potentially cause a busy-wait loop from writeback threads
+		 * and kswapd activity, but those code paths have their own
+		 * higher-level throttling.
+		 */
+		if (wbc->sync_mode != WB_SYNC_NONE) {
+			lock_buffer(bh);
+		} else if (!trylock_buffer(bh)) {
+			redirty_page_for_writepage(wbc, page);
+			continue;
+		}
+		if (test_clear_buffer_dirty(bh)) {
+			mark_buffer_async_write_endio(bh, handler);
+		} else {
+			unlock_buffer(bh);
+		}
+	} while ((bh = bh->b_this_page) != head);
+
+	/*
+	 * The page and its buffers are protected by PageWriteback(), so we can
+	 * drop the bh refcounts early.
+	 */
+	BUG_ON(PageWriteback(page));
+	set_page_writeback(page);
+
+	do {
+		struct buffer_head *next = bh->b_this_page;
+		if (buffer_async_write(bh)) {
+			submit_bh_wbc(REQ_OP_WRITE, write_flags, bh,
+					inode->i_write_hint, wbc);
+			nr_underway++;
+		}
+		bh = next;
+	} while (bh != head);
+	unlock_page(page);
+
+	err = 0;
+done:
+	if (nr_underway == 0) {
+		/*
+		 * The page was marked dirty, but the buffers were
+		 * clean.  Someone wrote them back by hand with
+		 * ll_rw_block/submit_bh.  A rare case.
+		 */
+		end_page_writeback(page);
+
+		/*
+		 * The page and buffer_heads can be released at any time from
+		 * here on.
+		 */
+	}
+	return err;
+
+recover:
+	/*
+	 * ENOSPC, or some other error.  We may already have added some
+	 * blocks to the file, so we need to write these out to avoid
+	 * exposing stale data.
+	 * The page is currently locked and not marked for writeback
+	 */
+	bh = head;
+	/* Recovery: lock and submit the mapped buffers */
+	do {
+		if (buffer_mapped(bh) && buffer_dirty(bh) &&
+		    !buffer_delay(bh)) {
+			lock_buffer(bh);
+			mark_buffer_async_write_endio(bh, handler);
+		} else {
+			/*
+			 * The buffer may have been set dirty during
+			 * attachment to a dirty page.
+			 */
+			clear_buffer_dirty(bh);
+		}
+	} while ((bh = bh->b_this_page) != head);
+	SetPageError(page);
+	BUG_ON(PageWriteback(page));
+	mapping_set_error(page->mapping, err);
+	set_page_writeback(page);
+	do {
+		struct buffer_head *next = bh->b_this_page;
+		if (buffer_async_write(bh)) {
+			clear_buffer_dirty(bh);
+			submit_bh_wbc(REQ_OP_WRITE, write_flags, bh,
+					inode->i_write_hint, wbc);
+			nr_underway++;
+		}
+		bh = next;
+	} while (bh != head);
+	unlock_page(page);
+	goto done;
+}
+EXPORT_SYMBOL(__block_write_full_page);
+
+/*
+ * If a page has any new buffers, zero them out here, and mark them uptodate
+ * and dirty so they'll be written out (in order to prevent uninitialised
+ * block data from leaking). And clear the new bit.
+ */
+void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
+{
+	unsigned int block_start, block_end;
+	struct buffer_head *head, *bh;
+
+	BUG_ON(!PageLocked(page));
+	if (!page_has_buffers(page))
+		return;
+
+	bh = head = page_buffers(page);
+	block_start = 0;
+	do {
+		block_end = block_start + bh->b_size;
+
+		if (buffer_new(bh)) {
+			if (block_end > from && block_start < to) {
+				if (!PageUptodate(page)) {
+					unsigned start, size;
+
+					start = max(from, block_start);
+					size = min(to, block_end) - start;
+
+					zero_user(page, start, size);
+					set_buffer_uptodate(bh);
+				}
+
+				clear_buffer_new(bh);
+				mark_buffer_dirty(bh);
+			}
+		}
+
+		block_start = block_end;
+		bh = bh->b_this_page;
+	} while (bh != head);
+}
+EXPORT_SYMBOL(page_zero_new_buffers);
+
+static void
+iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
+		struct iomap *iomap)
+{
+	loff_t offset = block << inode->i_blkbits;
+
+	bh->b_bdev = iomap->bdev;
+
+	/*
+	 * Block points to offset in file we need to map, iomap contains
+	 * the offset at which the map starts. If the map ends before the
+	 * current block, then do not map the buffer and let the caller
+	 * handle it.
+	 */
+	BUG_ON(offset >= iomap->offset + iomap->length);
+
+	switch (iomap->type) {
+	case IOMAP_HOLE:
+		/*
+		 * If the buffer is not up to date or beyond the current EOF,
+		 * we need to mark it as new to ensure sub-block zeroing is
+		 * executed if necessary.
+		 */
+		if (!buffer_uptodate(bh) ||
+		    (offset >= i_size_read(inode)))
+			set_buffer_new(bh);
+		break;
+	case IOMAP_DELALLOC:
+		if (!buffer_uptodate(bh) ||
+		    (offset >= i_size_read(inode)))
+			set_buffer_new(bh);
+		set_buffer_uptodate(bh);
+		set_buffer_mapped(bh);
+		set_buffer_delay(bh);
+		break;
+	case IOMAP_UNWRITTEN:
+		/*
+		 * For unwritten regions, we always need to ensure that regions
+		 * in the block we are not writing to are zeroed. Mark the
+		 * buffer as new to ensure this.
+		 */
+		set_buffer_new(bh);
+		set_buffer_unwritten(bh);
+		/* FALLTHRU */
+	case IOMAP_MAPPED:
+		if ((iomap->flags & IOMAP_F_NEW) ||
+		    offset >= i_size_read(inode))
+			set_buffer_new(bh);
+		bh->b_blocknr = (iomap->addr + offset - iomap->offset) >>
+				inode->i_blkbits;
+		set_buffer_mapped(bh);
+		break;
+	}
+}
+
+int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
+		get_block_t *get_block, struct iomap *iomap)
+{
+	unsigned from = pos & (PAGE_SIZE - 1);
+	unsigned to = from + len;
+	struct inode *inode = page->mapping->host;
+	unsigned block_start, block_end;
+	sector_t block;
+	int err = 0;
+	unsigned blocksize, bbits;
+	struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
+
+	BUG_ON(!PageLocked(page));
+	BUG_ON(from > PAGE_SIZE);
+	BUG_ON(to > PAGE_SIZE);
+	BUG_ON(from > to);
+
+	head = create_page_buffers(page, inode, 0);
+	blocksize = head->b_size;
+	bbits = block_size_bits(blocksize);
+
+	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
+
+	for(bh = head, block_start = 0; bh != head || !block_start;
+	    block++, block_start=block_end, bh = bh->b_this_page) {
+		block_end = block_start + blocksize;
+		if (block_end <= from || block_start >= to) {
+			if (PageUptodate(page)) {
+				if (!buffer_uptodate(bh))
+					set_buffer_uptodate(bh);
+			}
+			continue;
+		}
+		if (buffer_new(bh))
+			clear_buffer_new(bh);
+		if (!buffer_mapped(bh)) {
+			WARN_ON(bh->b_size != blocksize);
+			if (get_block) {
+				err = get_block(inode, block, bh, 1);
+				if (err)
+					break;
+			} else {
+				iomap_to_bh(inode, block, bh, iomap);
+			}
+
+			if (buffer_new(bh)) {
+				clean_bdev_bh_alias(bh);
+				if (PageUptodate(page)) {
+					clear_buffer_new(bh);
+					set_buffer_uptodate(bh);
+					mark_buffer_dirty(bh);
+					continue;
+				}
+				if (block_end > to || block_start < from)
+					zero_user_segments(page,
+						to, block_end,
+						block_start, from);
+				continue;
+			}
+		}
+		if (PageUptodate(page)) {
+			if (!buffer_uptodate(bh))
+				set_buffer_uptodate(bh);
+			continue; 
+		}
+		if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
+		    !buffer_unwritten(bh) &&
+		     (block_start < from || block_end > to)) {
+			ll_rw_block(REQ_OP_READ, 0, 1, &bh);
+			*wait_bh++=bh;
+		}
+	}
+	/*
+	 * If we issued read requests - let them complete.
+	 */
+	while(wait_bh > wait) {
+		wait_on_buffer(*--wait_bh);
+		if (!buffer_uptodate(*wait_bh))
+			err = -EIO;
+	}
+	if (unlikely(err))
+		page_zero_new_buffers(page, from, to);
+	return err;
+}
+
+int __block_write_begin(struct page *page, loff_t pos, unsigned len,
+		get_block_t *get_block)
+{
+	return __block_write_begin_int(page, pos, len, get_block, NULL);
+}
+EXPORT_SYMBOL(__block_write_begin);
+
+static int __block_commit_write(struct inode *inode, struct page *page,
+		unsigned from, unsigned to)
+{
+	unsigned block_start, block_end;
+	int partial = 0;
+	unsigned blocksize;
+	struct buffer_head *bh, *head;
+
+	bh = head = page_buffers(page);
+	blocksize = bh->b_size;
+
+	block_start = 0;
+	do {
+		block_end = block_start + blocksize;
+		if (block_end <= from || block_start >= to) {
+			if (!buffer_uptodate(bh))
+				partial = 1;
+		} else {
+			set_buffer_uptodate(bh);
+			mark_buffer_dirty(bh);
+		}
+		clear_buffer_new(bh);
+
+		block_start = block_end;
+		bh = bh->b_this_page;
+	} while (bh != head);
+
+	/*
+	 * If this is a partial write which happened to make all buffers
+	 * uptodate then we can optimize away a bogus readpage() for
+	 * the next read(). Here we 'discover' whether the page went
+	 * uptodate as a result of this (potentially partial) write.
+	 */
+	if (!partial)
+		SetPageUptodate(page);
+	return 0;
+}
+
+/*
+ * block_write_begin takes care of the basic task of block allocation and
+ * bringing partial write blocks uptodate first.
+ *
+ * The filesystem needs to handle block truncation upon failure.
+ */
+int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
+		unsigned flags, struct page **pagep, get_block_t *get_block)
+{
+	pgoff_t index = pos >> PAGE_SHIFT;
+	struct page *page;
+	int status;
+
+	page = grab_cache_page_write_begin(mapping, index, flags);
+	if (!page)
+		return -ENOMEM;
+
+	status = __block_write_begin(page, pos, len, get_block);
+	if (unlikely(status)) {
+		unlock_page(page);
+		put_page(page);
+		page = NULL;
+	}
+
+	*pagep = page;
+	return status;
+}
+EXPORT_SYMBOL(block_write_begin);
+
+int __generic_write_end(struct inode *inode, loff_t pos, unsigned copied,
+		struct page *page)
+{
+	loff_t old_size = inode->i_size;
+	bool i_size_changed = false;
+
+	/*
+	 * No need to use i_size_read() here, the i_size cannot change under us
+	 * because we hold i_rwsem.
+	 *
+	 * But it's important to update i_size while still holding page lock:
+	 * page writeout could otherwise come in and zero beyond i_size.
+	 */
+	if (pos + copied > inode->i_size) {
+		i_size_write(inode, pos + copied);
+		i_size_changed = true;
+	}
+
+	unlock_page(page);
+	put_page(page);
+
+	if (old_size < pos)
+		pagecache_isize_extended(inode, old_size, pos);
+	/*
+	 * Don't mark the inode dirty under page lock. First, it unnecessarily
+	 * makes the holding time of page lock longer. Second, it forces lock
+	 * ordering of page lock and transaction start for journaling
+	 * filesystems.
+	 */
+	if (i_size_changed)
+		mark_inode_dirty(inode);
+	return copied;
+}
+
+int block_write_end(struct file *file, struct address_space *mapping,
+			loff_t pos, unsigned len, unsigned copied,
+			struct page *page, void *fsdata)
+{
+	struct inode *inode = mapping->host;
+	unsigned start;
+
+	start = pos & (PAGE_SIZE - 1);
+
+	if (unlikely(copied < len)) {
+		/*
+		 * The buffers that were written will now be uptodate, so we
+		 * don't have to worry about a readpage reading them and
+		 * overwriting a partial write. However if we have encountered
+		 * a short write and only partially written into a buffer, it
+		 * will not be marked uptodate, so a readpage might come in and
+		 * destroy our partial write.
+		 *
+		 * Do the simplest thing, and just treat any short write to a
+		 * non uptodate page as a zero-length write, and force the
+		 * caller to redo the whole thing.
+		 */
+		if (!PageUptodate(page))
+			copied = 0;
+
+		page_zero_new_buffers(page, start+copied, start+len);
+	}
+	flush_dcache_page(page);
+
+	/* This could be a short (even 0-length) commit */
+	__block_commit_write(inode, page, start, start+copied);
+
+	return copied;
+}
+EXPORT_SYMBOL(block_write_end);
+
+int generic_write_end(struct file *file, struct address_space *mapping,
+			loff_t pos, unsigned len, unsigned copied,
+			struct page *page, void *fsdata)
+{
+	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
+	return __generic_write_end(mapping->host, pos, copied, page);
+}
+EXPORT_SYMBOL(generic_write_end);
+
+/*
+ * block_is_partially_uptodate checks whether buffers within a page are
+ * uptodate or not.
+ *
+ * Returns true if all buffers which correspond to a file portion
+ * we want to read are uptodate.
+ */
+int block_is_partially_uptodate(struct page *page, unsigned long from,
+					unsigned long count)
+{
+	unsigned block_start, block_end, blocksize;
+	unsigned to;
+	struct buffer_head *bh, *head;
+	int ret = 1;
+
+	if (!page_has_buffers(page))
+		return 0;
+
+	head = page_buffers(page);
+	blocksize = head->b_size;
+	to = min_t(unsigned, PAGE_SIZE - from, count);
+	to = from + to;
+	if (from < blocksize && to > PAGE_SIZE - blocksize)
+		return 0;
+
+	bh = head;
+	block_start = 0;
+	do {
+		block_end = block_start + blocksize;
+		if (block_end > from && block_start < to) {
+			if (!buffer_uptodate(bh)) {
+				ret = 0;
+				break;
+			}
+			if (block_end >= to)
+				break;
+		}
+		block_start = block_end;
+		bh = bh->b_this_page;
+	} while (bh != head);
+
+	return ret;
+}
+EXPORT_SYMBOL(block_is_partially_uptodate);
+
+/*
+ * Generic "read page" function for block devices that have the normal
+ * get_block functionality. This is most of the block device filesystems.
+ * Reads the page asynchronously --- the unlock_buffer() and
+ * set/clear_buffer_uptodate() functions propagate buffer state into the
+ * page struct once IO has completed.
+ */
+int block_read_full_page(struct page *page, get_block_t *get_block)
+{
+	struct inode *inode = page->mapping->host;
+	sector_t iblock, lblock;
+	struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
+	unsigned int blocksize, bbits;
+	int nr, i;
+	int fully_mapped = 1;
+
+	head = create_page_buffers(page, inode, 0);
+	blocksize = head->b_size;
+	bbits = block_size_bits(blocksize);
+
+	iblock = (sector_t)page->index << (PAGE_SHIFT - bbits);
+	lblock = (i_size_read(inode)+blocksize-1) >> bbits;
+	bh = head;
+	nr = 0;
+	i = 0;
+
+	do {
+		if (buffer_uptodate(bh))
+			continue;
+
+		if (!buffer_mapped(bh)) {
+			int err = 0;
+
+			fully_mapped = 0;
+			if (iblock < lblock) {
+				WARN_ON(bh->b_size != blocksize);
+				err = get_block(inode, iblock, bh, 0);
+				if (err)
+					SetPageError(page);
+			}
+			if (!buffer_mapped(bh)) {
+				zero_user(page, i * blocksize, blocksize);
+				if (!err)
+					set_buffer_uptodate(bh);
+				continue;
+			}
+			/*
+			 * get_block() might have updated the buffer
+			 * synchronously
+			 */
+			if (buffer_uptodate(bh))
+				continue;
+		}
+		arr[nr++] = bh;
+	} while (i++, iblock++, (bh = bh->b_this_page) != head);
+
+	if (fully_mapped)
+		SetPageMappedToDisk(page);
+
+	if (!nr) {
+		/*
+		 * All buffers are uptodate - we can set the page uptodate
+		 * as well. But not if get_block() returned an error.
+		 */
+		if (!PageError(page))
+			SetPageUptodate(page);
+		unlock_page(page);
+		return 0;
+	}
+
+	/* Stage two: lock the buffers */
+	for (i = 0; i < nr; i++) {
+		bh = arr[i];
+		lock_buffer(bh);
+		mark_buffer_async_read(bh);
+	}
+
+	/*
+	 * Stage 3: start the IO.  Check for uptodateness
+	 * inside the buffer lock in case another process reading
+	 * the underlying blockdev brought it uptodate (the sct fix).
+	 */
+	for (i = 0; i < nr; i++) {
+		bh = arr[i];
+		if (buffer_uptodate(bh))
+			end_buffer_async_read(bh, 1);
+		else
+			submit_bh(REQ_OP_READ, 0, bh);
+	}
+	return 0;
+}
+EXPORT_SYMBOL(block_read_full_page);
+
+/* utility function for filesystems that need to do work on expanding
+ * truncates.  Uses filesystem pagecache writes to allow the filesystem to
+ * deal with the hole.  
+ */
+int generic_cont_expand_simple(struct inode *inode, loff_t size)
+{
+	struct address_space *mapping = inode->i_mapping;
+	struct page *page;
+	void *fsdata;
+	int err;
+
+	err = inode_newsize_ok(inode, size);
+	if (err)
+		goto out;
+
+	err = pagecache_write_begin(NULL, mapping, size, 0,
+				    AOP_FLAG_CONT_EXPAND, &page, &fsdata);
+	if (err)
+		goto out;
+
+	err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
+	BUG_ON(err > 0);
+
+out:
+	return err;
+}
+EXPORT_SYMBOL(generic_cont_expand_simple);
+
+static int cont_expand_zero(struct file *file, struct address_space *mapping,
+			    loff_t pos, loff_t *bytes)
+{
+	struct inode *inode = mapping->host;
+	unsigned int blocksize = i_blocksize(inode);
+	struct page *page;
+	void *fsdata;
+	pgoff_t index, curidx;
+	loff_t curpos;
+	unsigned zerofrom, offset, len;
+	int err = 0;
+
+	index = pos >> PAGE_SHIFT;
+	offset = pos & ~PAGE_MASK;
+
+	while (index > (curidx = (curpos = *bytes)>>PAGE_SHIFT)) {
+		zerofrom = curpos & ~PAGE_MASK;
+		if (zerofrom & (blocksize-1)) {
+			*bytes |= (blocksize-1);
+			(*bytes)++;
+		}
+		len = PAGE_SIZE - zerofrom;
+
+		err = pagecache_write_begin(file, mapping, curpos, len, 0,
+					    &page, &fsdata);
+		if (err)
+			goto out;
+		zero_user(page, zerofrom, len);
+		err = pagecache_write_end(file, mapping, curpos, len, len,
+						page, fsdata);
+		if (err < 0)
+			goto out;
+		BUG_ON(err != len);
+		err = 0;
+
+		balance_dirty_pages_ratelimited(mapping);
+
+		if (unlikely(fatal_signal_pending(current))) {
+			err = -EINTR;
+			goto out;
+		}
+	}
+
+	/* page covers the boundary, find the boundary offset */
+	if (index == curidx) {
+		zerofrom = curpos & ~PAGE_MASK;
+		/* if we will expand the thing last block will be filled */
+		if (offset <= zerofrom) {
+			goto out;
+		}
+		if (zerofrom & (blocksize-1)) {
+			*bytes |= (blocksize-1);
+			(*bytes)++;
+		}
+		len = offset - zerofrom;
+
+		err = pagecache_write_begin(file, mapping, curpos, len, 0,
+					    &page, &fsdata);
+		if (err)
+			goto out;
+		zero_user(page, zerofrom, len);
+		err = pagecache_write_end(file, mapping, curpos, len, len,
+						page, fsdata);
+		if (err < 0)
+			goto out;
+		BUG_ON(err != len);
+		err = 0;
+	}
+out:
+	return err;
+}
+
+/*
+ * For moronic filesystems that do not allow holes in file.
+ * We may have to extend the file.
+ */
+int cont_write_begin(struct file *file, struct address_space *mapping,
+			loff_t pos, unsigned len, unsigned flags,
+			struct page **pagep, void **fsdata,
+			get_block_t *get_block, loff_t *bytes)
+{
+	struct inode *inode = mapping->host;
+	unsigned int blocksize = i_blocksize(inode);
+	unsigned int zerofrom;
+	int err;
+
+	err = cont_expand_zero(file, mapping, pos, bytes);
+	if (err)
+		return err;
+
+	zerofrom = *bytes & ~PAGE_MASK;
+	if (pos+len > *bytes && zerofrom & (blocksize-1)) {
+		*bytes |= (blocksize-1);
+		(*bytes)++;
+	}
+
+	return block_write_begin(mapping, pos, len, flags, pagep, get_block);
+}
+EXPORT_SYMBOL(cont_write_begin);
+
+int block_commit_write(struct page *page, unsigned from, unsigned to)
+{
+	struct inode *inode = page->mapping->host;
+	__block_commit_write(inode,page,from,to);
+	return 0;
+}
+EXPORT_SYMBOL(block_commit_write);
+
+/*
+ * block_page_mkwrite() is not allowed to change the file size as it gets
+ * called from a page fault handler when a page is first dirtied. Hence we must
+ * be careful to check for EOF conditions here. We set the page up correctly
+ * for a written page which means we get ENOSPC checking when writing into
+ * holes and correct delalloc and unwritten extent mapping on filesystems that
+ * support these features.
+ *
+ * We are not allowed to take the i_mutex here so we have to play games to
+ * protect against truncate races as the page could now be beyond EOF.  Because
+ * truncate writes the inode size before removing pages, once we have the
+ * page lock we can determine safely if the page is beyond EOF. If it is not
+ * beyond EOF, then the page is guaranteed safe against truncation until we
+ * unlock the page.
+ *
+ * Direct callers of this function should protect against filesystem freezing
+ * using sb_start_pagefault() - sb_end_pagefault() functions.
+ */
+int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
+			 get_block_t get_block)
+{
+	struct page *page = vmf->page;
+	struct inode *inode = file_inode(vma->vm_file);
+	unsigned long end;
+	loff_t size;
+	int ret;
+
+	lock_page(page);
+	size = i_size_read(inode);
+	if ((page->mapping != inode->i_mapping) ||
+	    (page_offset(page) > size)) {
+		/* We overload EFAULT to mean page got truncated */
+		ret = -EFAULT;
+		goto out_unlock;
+	}
+
+	/* page is wholly or partially inside EOF */
+	if (((page->index + 1) << PAGE_SHIFT) > size)
+		end = size & ~PAGE_MASK;
+	else
+		end = PAGE_SIZE;
+
+	ret = __block_write_begin(page, 0, end, get_block);
+	if (!ret)
+		ret = block_commit_write(page, 0, end);
+
+	if (unlikely(ret < 0))
+		goto out_unlock;
+	set_page_dirty(page);
+	wait_for_stable_page(page);
+	return 0;
+out_unlock:
+	unlock_page(page);
+	return ret;
+}
+EXPORT_SYMBOL(block_page_mkwrite);
+
+/*
+ * nobh_write_begin()'s prereads are special: the buffer_heads are freed
+ * immediately, while under the page lock.  So it needs a special end_io
+ * handler which does not touch the bh after unlocking it.
+ */
+static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
+{
+	__end_buffer_read_notouch(bh, uptodate);
+}
+
+/*
+ * Attach the singly-linked list of buffers created by nobh_write_begin, to
+ * the page (converting it to circular linked list and taking care of page
+ * dirty races).
+ */
+static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
+{
+	struct buffer_head *bh;
+
+	BUG_ON(!PageLocked(page));
+
+	spin_lock(&page->mapping->private_lock);
+	bh = head;
+	do {
+		if (PageDirty(page))
+			set_buffer_dirty(bh);
+		if (!bh->b_this_page)
+			bh->b_this_page = head;
+		bh = bh->b_this_page;
+	} while (bh != head);
+	attach_page_buffers(page, head);
+	spin_unlock(&page->mapping->private_lock);
+}
+
+/*
+ * On entry, the page is fully not uptodate.
+ * On exit the page is fully uptodate in the areas outside (from,to)
+ * The filesystem needs to handle block truncation upon failure.
+ */
+int nobh_write_begin(struct address_space *mapping,
+			loff_t pos, unsigned len, unsigned flags,
+			struct page **pagep, void **fsdata,
+			get_block_t *get_block)
+{
+	struct inode *inode = mapping->host;
+	const unsigned blkbits = inode->i_blkbits;
+	const unsigned blocksize = 1 << blkbits;
+	struct buffer_head *head, *bh;
+	struct page *page;
+	pgoff_t index;
+	unsigned from, to;
+	unsigned block_in_page;
+	unsigned block_start, block_end;
+	sector_t block_in_file;
+	int nr_reads = 0;
+	int ret = 0;
+	int is_mapped_to_disk = 1;
+
+	index = pos >> PAGE_SHIFT;
+	from = pos & (PAGE_SIZE - 1);
+	to = from + len;
+
+	page = grab_cache_page_write_begin(mapping, index, flags);
+	if (!page)
+		return -ENOMEM;
+	*pagep = page;
+	*fsdata = NULL;
+
+	if (page_has_buffers(page)) {
+		ret = __block_write_begin(page, pos, len, get_block);
+		if (unlikely(ret))
+			goto out_release;
+		return ret;
+	}
+
+	if (PageMappedToDisk(page))
+		return 0;
+
+	/*
+	 * Allocate buffers so that we can keep track of state, and potentially
+	 * attach them to the page if an error occurs. In the common case of
+	 * no error, they will just be freed again without ever being attached
+	 * to the page (which is all OK, because we're under the page lock).
+	 *
+	 * Be careful: the buffer linked list is a NULL terminated one, rather
+	 * than the circular one we're used to.
+	 */
+	head = alloc_page_buffers(page, blocksize, false);
+	if (!head) {
+		ret = -ENOMEM;
+		goto out_release;
+	}
+
+	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
+
+	/*
+	 * We loop across all blocks in the page, whether or not they are
+	 * part of the affected region.  This is so we can discover if the
+	 * page is fully mapped-to-disk.
+	 */
+	for (block_start = 0, block_in_page = 0, bh = head;
+		  block_start < PAGE_SIZE;
+		  block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
+		int create;
+
+		block_end = block_start + blocksize;
+		bh->b_state = 0;
+		create = 1;
+		if (block_start >= to)
+			create = 0;
+		ret = get_block(inode, block_in_file + block_in_page,
+					bh, create);
+		if (ret)
+			goto failed;
+		if (!buffer_mapped(bh))
+			is_mapped_to_disk = 0;
+		if (buffer_new(bh))
+			clean_bdev_bh_alias(bh);
+		if (PageUptodate(page)) {
+			set_buffer_uptodate(bh);
+			continue;
+		}
+		if (buffer_new(bh) || !buffer_mapped(bh)) {
+			zero_user_segments(page, block_start, from,
+							to, block_end);
+			continue;
+		}
+		if (buffer_uptodate(bh))
+			continue;	/* reiserfs does this */
+		if (block_start < from || block_end > to) {
+			lock_buffer(bh);
+			bh->b_end_io = end_buffer_read_nobh;
+			submit_bh(REQ_OP_READ, 0, bh);
+			nr_reads++;
+		}
+	}
+
+	if (nr_reads) {
+		/*
+		 * The page is locked, so these buffers are protected from
+		 * any VM or truncate activity.  Hence we don't need to care
+		 * for the buffer_head refcounts.
+		 */
+		for (bh = head; bh; bh = bh->b_this_page) {
+			wait_on_buffer(bh);
+			if (!buffer_uptodate(bh))
+				ret = -EIO;
+		}
+		if (ret)
+			goto failed;
+	}
+
+	if (is_mapped_to_disk)
+		SetPageMappedToDisk(page);
+
+	*fsdata = head; /* to be released by nobh_write_end */
+
+	return 0;
+
+failed:
+	BUG_ON(!ret);
+	/*
+	 * Error recovery is a bit difficult. We need to zero out blocks that
+	 * were newly allocated, and dirty them to ensure they get written out.
+	 * Buffers need to be attached to the page at this point, otherwise
+	 * the handling of potential IO errors during writeout would be hard
+	 * (could try doing synchronous writeout, but what if that fails too?)
+	 */
+	attach_nobh_buffers(page, head);
+	page_zero_new_buffers(page, from, to);
+
+out_release:
+	unlock_page(page);
+	put_page(page);
+	*pagep = NULL;
+
+	return ret;
+}
+EXPORT_SYMBOL(nobh_write_begin);
+
+int nobh_write_end(struct file *file, struct address_space *mapping,
+			loff_t pos, unsigned len, unsigned copied,
+			struct page *page, void *fsdata)
+{
+	struct inode *inode = page->mapping->host;
+	struct buffer_head *head = fsdata;
+	struct buffer_head *bh;
+	BUG_ON(fsdata != NULL && page_has_buffers(page));
+
+	if (unlikely(copied < len) && head)
+		attach_nobh_buffers(page, head);
+	if (page_has_buffers(page))
+		return generic_write_end(file, mapping, pos, len,
+					copied, page, fsdata);
+
+	SetPageUptodate(page);
+	set_page_dirty(page);
+	if (pos+copied > inode->i_size) {
+		i_size_write(inode, pos+copied);
+		mark_inode_dirty(inode);
+	}
+
+	unlock_page(page);
+	put_page(page);
+
+	while (head) {
+		bh = head;
+		head = head->b_this_page;
+		free_buffer_head(bh);
+	}
+
+	return copied;
+}
+EXPORT_SYMBOL(nobh_write_end);
+
+/*
+ * nobh_writepage() - based on block_full_write_page() except
+ * that it tries to operate without attaching bufferheads to
+ * the page.
+ */
+int nobh_writepage(struct page *page, get_block_t *get_block,
+			struct writeback_control *wbc)
+{
+	struct inode * const inode = page->mapping->host;
+	loff_t i_size = i_size_read(inode);
+	const pgoff_t end_index = i_size >> PAGE_SHIFT;
+	unsigned offset;
+	int ret;
+
+	/* Is the page fully inside i_size? */
+	if (page->index < end_index)
+		goto out;
+
+	/* Is the page fully outside i_size? (truncate in progress) */
+	offset = i_size & (PAGE_SIZE-1);
+	if (page->index >= end_index+1 || !offset) {
+		unlock_page(page);
+		return 0; /* don't care */
+	}
+
+	/*
+	 * The page straddles i_size.  It must be zeroed out on each and every
+	 * writepage invocation because it may be mmapped.  "A file is mapped
+	 * in multiples of the page size.  For a file that is not a multiple of
+	 * the  page size, the remaining memory is zeroed when mapped, and
+	 * writes to that region are not written out to the file."
+	 */
+	zero_user_segment(page, offset, PAGE_SIZE);
+out:
+	ret = mpage_writepage(page, get_block, wbc);
+	if (ret == -EAGAIN)
+		ret = __block_write_full_page(inode, page, get_block, wbc,
+					      end_buffer_async_write);
+	return ret;
+}
+EXPORT_SYMBOL(nobh_writepage);
+
+int nobh_truncate_page(struct address_space *mapping,
+			loff_t from, get_block_t *get_block)
+{
+	pgoff_t index = from >> PAGE_SHIFT;
+	unsigned offset = from & (PAGE_SIZE-1);
+	unsigned blocksize;
+	sector_t iblock;
+	unsigned length, pos;
+	struct inode *inode = mapping->host;
+	struct page *page;
+	struct buffer_head map_bh;
+	int err;
+
+	blocksize = i_blocksize(inode);
+	length = offset & (blocksize - 1);
+
+	/* Block boundary? Nothing to do */
+	if (!length)
+		return 0;
+
+	length = blocksize - length;
+	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
+
+	page = grab_cache_page(mapping, index);
+	err = -ENOMEM;
+	if (!page)
+		goto out;
+
+	if (page_has_buffers(page)) {
+has_buffers:
+		unlock_page(page);
+		put_page(page);
+		return block_truncate_page(mapping, from, get_block);
+	}
+
+	/* Find the buffer that contains "offset" */
+	pos = blocksize;
+	while (offset >= pos) {
+		iblock++;
+		pos += blocksize;
+	}
+
+	map_bh.b_size = blocksize;
+	map_bh.b_state = 0;
+	err = get_block(inode, iblock, &map_bh, 0);
+	if (err)
+		goto unlock;
+	/* unmapped? It's a hole - nothing to do */
+	if (!buffer_mapped(&map_bh))
+		goto unlock;
+
+	/* Ok, it's mapped. Make sure it's up-to-date */
+	if (!PageUptodate(page)) {
+		err = mapping->a_ops->readpage(NULL, page);
+		if (err) {
+			put_page(page);
+			goto out;
+		}
+		lock_page(page);
+		if (!PageUptodate(page)) {
+			err = -EIO;
+			goto unlock;
+		}
+		if (page_has_buffers(page))
+			goto has_buffers;
+	}
+	zero_user(page, offset, length);
+	set_page_dirty(page);
+	err = 0;
+
+unlock:
+	unlock_page(page);
+	put_page(page);
+out:
+	return err;
+}
+EXPORT_SYMBOL(nobh_truncate_page);
+
+int block_truncate_page(struct address_space *mapping,
+			loff_t from, get_block_t *get_block)
+{
+	pgoff_t index = from >> PAGE_SHIFT;
+	unsigned offset = from & (PAGE_SIZE-1);
+	unsigned blocksize;
+	sector_t iblock;
+	unsigned length, pos;
+	struct inode *inode = mapping->host;
+	struct page *page;
+	struct buffer_head *bh;
+	int err;
+
+	blocksize = i_blocksize(inode);
+	length = offset & (blocksize - 1);
+
+	/* Block boundary? Nothing to do */
+	if (!length)
+		return 0;
+
+	length = blocksize - length;
+	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
+	
+	page = grab_cache_page(mapping, index);
+	err = -ENOMEM;
+	if (!page)
+		goto out;
+
+	if (!page_has_buffers(page))
+		create_empty_buffers(page, blocksize, 0);
+
+	/* Find the buffer that contains "offset" */
+	bh = page_buffers(page);
+	pos = blocksize;
+	while (offset >= pos) {
+		bh = bh->b_this_page;
+		iblock++;
+		pos += blocksize;
+	}
+
+	err = 0;
+	if (!buffer_mapped(bh)) {
+		WARN_ON(bh->b_size != blocksize);
+		err = get_block(inode, iblock, bh, 0);
+		if (err)
+			goto unlock;
+		/* unmapped? It's a hole - nothing to do */
+		if (!buffer_mapped(bh))
+			goto unlock;
+	}
+
+	/* Ok, it's mapped. Make sure it's up-to-date */
+	if (PageUptodate(page))
+		set_buffer_uptodate(bh);
+
+	if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
+		err = -EIO;
+		ll_rw_block(REQ_OP_READ, 0, 1, &bh);
+		wait_on_buffer(bh);
+		/* Uhhuh. Read error. Complain and punt. */
+		if (!buffer_uptodate(bh))
+			goto unlock;
+	}
+
+	zero_user(page, offset, length);
+	mark_buffer_dirty(bh);
+	err = 0;
+
+unlock:
+	unlock_page(page);
+	put_page(page);
+out:
+	return err;
+}
+EXPORT_SYMBOL(block_truncate_page);
+
+/*
+ * The generic ->writepage function for buffer-backed address_spaces
+ */
+int block_write_full_page(struct page *page, get_block_t *get_block,
+			struct writeback_control *wbc)
+{
+	struct inode * const inode = page->mapping->host;
+	loff_t i_size = i_size_read(inode);
+	const pgoff_t end_index = i_size >> PAGE_SHIFT;
+	unsigned offset;
+
+	/* Is the page fully inside i_size? */
+	if (page->index < end_index)
+		return __block_write_full_page(inode, page, get_block, wbc,
+					       end_buffer_async_write);
+
+	/* Is the page fully outside i_size? (truncate in progress) */
+	offset = i_size & (PAGE_SIZE-1);
+	if (page->index >= end_index+1 || !offset) {
+		unlock_page(page);
+		return 0; /* don't care */
+	}
+
+	/*
+	 * The page straddles i_size.  It must be zeroed out on each and every
+	 * writepage invocation because it may be mmapped.  "A file is mapped
+	 * in multiples of the page size.  For a file that is not a multiple of
+	 * the  page size, the remaining memory is zeroed when mapped, and
+	 * writes to that region are not written out to the file."
+	 */
+	zero_user_segment(page, offset, PAGE_SIZE);
+	return __block_write_full_page(inode, page, get_block, wbc,
+							end_buffer_async_write);
+}
+EXPORT_SYMBOL(block_write_full_page);
+
+sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
+			    get_block_t *get_block)
+{
+	struct inode *inode = mapping->host;
+	struct buffer_head tmp = {
+		.b_size = i_blocksize(inode),
+	};
+
+	get_block(inode, block, &tmp, 0);
+	return tmp.b_blocknr;
+}
+EXPORT_SYMBOL(generic_block_bmap);
+
+static void end_bio_bh_io_sync(struct bio *bio)
+{
+	struct buffer_head *bh = bio->bi_private;
+
+	if (unlikely(bio_flagged(bio, BIO_QUIET)))
+		set_bit(BH_Quiet, &bh->b_state);
+
+	bh->b_end_io(bh, !bio->bi_status);
+	bio_put(bio);
+}
+
+/*
+ * This allows us to do IO even on the odd last sectors
+ * of a device, even if the block size is some multiple
+ * of the physical sector size.
+ *
+ * We'll just truncate the bio to the size of the device,
+ * and clear the end of the buffer head manually.
+ *
+ * Truly out-of-range accesses will turn into actual IO
+ * errors, this only handles the "we need to be able to
+ * do IO at the final sector" case.
+ */
+void guard_bio_eod(int op, struct bio *bio)
+{
+	sector_t maxsector;
+	struct bio_vec *bvec = bio_last_bvec_all(bio);
+	unsigned truncated_bytes;
+	struct hd_struct *part;
+
+	rcu_read_lock();
+	part = __disk_get_part(bio->bi_disk, bio->bi_partno);
+	if (part)
+		maxsector = part_nr_sects_read(part);
+	else
+		maxsector = get_capacity(bio->bi_disk);
+	rcu_read_unlock();
+
+	if (!maxsector)
+		return;
+
+	/*
+	 * If the *whole* IO is past the end of the device,
+	 * let it through, and the IO layer will turn it into
+	 * an EIO.
+	 */
+	if (unlikely(bio->bi_iter.bi_sector >= maxsector))
+		return;
+
+	maxsector -= bio->bi_iter.bi_sector;
+	if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))
+		return;
+
+	/* Uhhuh. We've got a bio that straddles the device size! */
+	truncated_bytes = bio->bi_iter.bi_size - (maxsector << 9);
+
+	/*
+	 * The bio contains more than one segment which spans EOD, just return
+	 * and let IO layer turn it into an EIO
+	 */
+	if (truncated_bytes > bvec->bv_len)
+		return;
+
+	/* Truncate the bio.. */
+	bio->bi_iter.bi_size -= truncated_bytes;
+	bvec->bv_len -= truncated_bytes;
+
+	/* ..and clear the end of the buffer for reads */
+	if (op == REQ_OP_READ) {
+		zero_user(bvec->bv_page, bvec->bv_offset + bvec->bv_len,
+				truncated_bytes);
+	}
+}
+
+static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
+			 enum rw_hint write_hint, struct writeback_control *wbc)
+{
+	struct bio *bio;
+
+	BUG_ON(!buffer_locked(bh));
+	BUG_ON(!buffer_mapped(bh));
+	BUG_ON(!bh->b_end_io);
+	BUG_ON(buffer_delay(bh));
+	BUG_ON(buffer_unwritten(bh));
+
+	/*
+	 * Only clear out a write error when rewriting
+	 */
+	if (test_set_buffer_req(bh) && (op == REQ_OP_WRITE))
+		clear_buffer_write_io_error(bh);
+
+	/*
+	 * from here on down, it's all bio -- do the initial mapping,
+	 * submit_bio -> generic_make_request may further map this bio around
+	 */
+	bio = bio_alloc(GFP_NOIO, 1);
+
+	if (wbc) {
+		wbc_init_bio(wbc, bio);
+		wbc_account_io(wbc, bh->b_page, bh->b_size);
+	}
+
+	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
+	bio_set_dev(bio, bh->b_bdev);
+	bio->bi_write_hint = write_hint;
+
+	bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
+	BUG_ON(bio->bi_iter.bi_size != bh->b_size);
+
+	bio->bi_end_io = end_bio_bh_io_sync;
+	bio->bi_private = bh;
+
+	/* Take care of bh's that straddle the end of the device */
+	guard_bio_eod(op, bio);
+
+	if (buffer_meta(bh))
+		op_flags |= REQ_META;
+	if (buffer_prio(bh))
+		op_flags |= REQ_PRIO;
+	bio_set_op_attrs(bio, op, op_flags);
+
+	submit_bio(bio);
+	return 0;
+}
+
+int submit_bh(int op, int op_flags, struct buffer_head *bh)
+{
+	return submit_bh_wbc(op, op_flags, bh, 0, NULL);
+}
+EXPORT_SYMBOL(submit_bh);
+
+/**
+ * ll_rw_block: low-level access to block devices (DEPRECATED)
+ * @op: whether to %READ or %WRITE
+ * @op_flags: req_flag_bits
+ * @nr: number of &struct buffer_heads in the array
+ * @bhs: array of pointers to &struct buffer_head
+ *
+ * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
+ * requests an I/O operation on them, either a %REQ_OP_READ or a %REQ_OP_WRITE.
+ * @op_flags contains flags modifying the detailed I/O behavior, most notably
+ * %REQ_RAHEAD.
+ *
+ * This function drops any buffer that it cannot get a lock on (with the
+ * BH_Lock state bit), any buffer that appears to be clean when doing a write
+ * request, and any buffer that appears to be up-to-date when doing read
+ * request.  Further it marks as clean buffers that are processed for
+ * writing (the buffer cache won't assume that they are actually clean
+ * until the buffer gets unlocked).
+ *
+ * ll_rw_block sets b_end_io to simple completion handler that marks
+ * the buffer up-to-date (if appropriate), unlocks the buffer and wakes
+ * any waiters. 
+ *
+ * All of the buffers must be for the same device, and must also be a
+ * multiple of the current approved size for the device.
+ */
+void ll_rw_block(int op, int op_flags,  int nr, struct buffer_head *bhs[])
+{
+	int i;
+
+	for (i = 0; i < nr; i++) {
+		struct buffer_head *bh = bhs[i];
+
+		if (!trylock_buffer(bh))
+			continue;
+		if (op == WRITE) {
+			if (test_clear_buffer_dirty(bh)) {
+				bh->b_end_io = end_buffer_write_sync;
+				get_bh(bh);
+				submit_bh(op, op_flags, bh);
+				continue;
+			}
+		} else {
+			if (!buffer_uptodate(bh)) {
+				bh->b_end_io = end_buffer_read_sync;
+				get_bh(bh);
+				submit_bh(op, op_flags, bh);
+				continue;
+			}
+		}
+		unlock_buffer(bh);
+	}
+}
+EXPORT_SYMBOL(ll_rw_block);
+
+void write_dirty_buffer(struct buffer_head *bh, int op_flags)
+{
+	lock_buffer(bh);
+	if (!test_clear_buffer_dirty(bh)) {
+		unlock_buffer(bh);
+		return;
+	}
+	bh->b_end_io = end_buffer_write_sync;
+	get_bh(bh);
+	submit_bh(REQ_OP_WRITE, op_flags, bh);
+}
+EXPORT_SYMBOL(write_dirty_buffer);
+
+/*
+ * For a data-integrity writeout, we need to wait upon any in-progress I/O
+ * and then start new I/O and then wait upon it.  The caller must have a ref on
+ * the buffer_head.
+ */
+int __sync_dirty_buffer(struct buffer_head *bh, int op_flags)
+{
+	int ret = 0;
+
+	WARN_ON(atomic_read(&bh->b_count) < 1);
+	lock_buffer(bh);
+	if (test_clear_buffer_dirty(bh)) {
+		/*
+		 * The bh should be mapped, but it might not be if the
+		 * device was hot-removed. Not much we can do but fail the I/O.
+		 */
+		if (!buffer_mapped(bh)) {
+			unlock_buffer(bh);
+			return -EIO;
+		}
+
+		get_bh(bh);
+		bh->b_end_io = end_buffer_write_sync;
+		ret = submit_bh(REQ_OP_WRITE, op_flags, bh);
+		wait_on_buffer(bh);
+		if (!ret && !buffer_uptodate(bh))
+			ret = -EIO;
+	} else {
+		unlock_buffer(bh);
+	}
+	return ret;
+}
+EXPORT_SYMBOL(__sync_dirty_buffer);
+
+int sync_dirty_buffer(struct buffer_head *bh)
+{
+	return __sync_dirty_buffer(bh, REQ_SYNC);
+}
+EXPORT_SYMBOL(sync_dirty_buffer);
+
+/*
+ * try_to_free_buffers() checks if all the buffers on this particular page
+ * are unused, and releases them if so.
+ *
+ * Exclusion against try_to_free_buffers may be obtained by either
+ * locking the page or by holding its mapping's private_lock.
+ *
+ * If the page is dirty but all the buffers are clean then we need to
+ * be sure to mark the page clean as well.  This is because the page
+ * may be against a block device, and a later reattachment of buffers
+ * to a dirty page will set *all* buffers dirty.  Which would corrupt
+ * filesystem data on the same device.
+ *
+ * The same applies to regular filesystem pages: if all the buffers are
+ * clean then we set the page clean and proceed.  To do that, we require
+ * total exclusion from __set_page_dirty_buffers().  That is obtained with
+ * private_lock.
+ *
+ * try_to_free_buffers() is non-blocking.
+ */
+static inline int buffer_busy(struct buffer_head *bh)
+{
+	return atomic_read(&bh->b_count) |
+		(bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
+}
+
+static int
+drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
+{
+	struct buffer_head *head = page_buffers(page);
+	struct buffer_head *bh;
+
+	bh = head;
+	do {
+		if (buffer_busy(bh))
+			goto failed;
+		bh = bh->b_this_page;
+	} while (bh != head);
+
+	do {
+		struct buffer_head *next = bh->b_this_page;
+
+		if (bh->b_assoc_map)
+			__remove_assoc_queue(bh);
+		bh = next;
+	} while (bh != head);
+	*buffers_to_free = head;
+	__clear_page_buffers(page);
+	return 1;
+failed:
+	return 0;
+}
+
+int try_to_free_buffers(struct page *page)
+{
+	struct address_space * const mapping = page->mapping;
+	struct buffer_head *buffers_to_free = NULL;
+	int ret = 0;
+
+	BUG_ON(!PageLocked(page));
+	if (PageWriteback(page))
+		return 0;
+
+	if (mapping == NULL) {		/* can this still happen? */
+		ret = drop_buffers(page, &buffers_to_free);
+		goto out;
+	}
+
+	spin_lock(&mapping->private_lock);
+	ret = drop_buffers(page, &buffers_to_free);
+
+	/*
+	 * If the filesystem writes its buffers by hand (eg ext3)
+	 * then we can have clean buffers against a dirty page.  We
+	 * clean the page here; otherwise the VM will never notice
+	 * that the filesystem did any IO at all.
+	 *
+	 * Also, during truncate, discard_buffer will have marked all
+	 * the page's buffers clean.  We discover that here and clean
+	 * the page also.
+	 *
+	 * private_lock must be held over this entire operation in order
+	 * to synchronise against __set_page_dirty_buffers and prevent the
+	 * dirty bit from being lost.
+	 */
+	if (ret)
+		cancel_dirty_page(page);
+	spin_unlock(&mapping->private_lock);
+out:
+	if (buffers_to_free) {
+		struct buffer_head *bh = buffers_to_free;
+
+		do {
+			struct buffer_head *next = bh->b_this_page;
+			free_buffer_head(bh);
+			bh = next;
+		} while (bh != buffers_to_free);
+	}
+	return ret;
+}
+EXPORT_SYMBOL(try_to_free_buffers);
+
+/*
+ * There are no bdflush tunables left.  But distributions are
+ * still running obsolete flush daemons, so we terminate them here.
+ *
+ * Use of bdflush() is deprecated and will be removed in a future kernel.
+ * The `flush-X' kernel threads fully replace bdflush daemons and this call.
+ */
+SYSCALL_DEFINE2(bdflush, int, func, long, data)
+{
+	static int msg_count;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (msg_count < 5) {
+		msg_count++;
+		printk(KERN_INFO
+			"warning: process `%s' used the obsolete bdflush"
+			" system call\n", current->comm);
+		printk(KERN_INFO "Fix your initscripts?\n");
+	}
+
+	if (func == 1)
+		do_exit(0);
+	return 0;
+}
+
+/*
+ * Buffer-head allocation
+ */
+static struct kmem_cache *bh_cachep __read_mostly;
+
+/*
+ * Once the number of bh's in the machine exceeds this level, we start
+ * stripping them in writeback.
+ */
+static unsigned long max_buffer_heads;
+
+int buffer_heads_over_limit;
+
+struct bh_accounting {
+	int nr;			/* Number of live bh's */
+	int ratelimit;		/* Limit cacheline bouncing */
+};
+
+static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
+
+static void recalc_bh_state(void)
+{
+	int i;
+	int tot = 0;
+
+	if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
+		return;
+	__this_cpu_write(bh_accounting.ratelimit, 0);
+	for_each_online_cpu(i)
+		tot += per_cpu(bh_accounting, i).nr;
+	buffer_heads_over_limit = (tot > max_buffer_heads);
+}
+
+struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
+{
+	struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
+	if (ret) {
+		INIT_LIST_HEAD(&ret->b_assoc_buffers);
+		preempt_disable();
+		__this_cpu_inc(bh_accounting.nr);
+		recalc_bh_state();
+		preempt_enable();
+	}
+	return ret;
+}
+EXPORT_SYMBOL(alloc_buffer_head);
+
+void free_buffer_head(struct buffer_head *bh)
+{
+	BUG_ON(!list_empty(&bh->b_assoc_buffers));
+	kmem_cache_free(bh_cachep, bh);
+	preempt_disable();
+	__this_cpu_dec(bh_accounting.nr);
+	recalc_bh_state();
+	preempt_enable();
+}
+EXPORT_SYMBOL(free_buffer_head);
+
+static int buffer_exit_cpu_dead(unsigned int cpu)
+{
+	int i;
+	struct bh_lru *b = &per_cpu(bh_lrus, cpu);
+
+	for (i = 0; i < BH_LRU_SIZE; i++) {
+		brelse(b->bhs[i]);
+		b->bhs[i] = NULL;
+	}
+	this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
+	per_cpu(bh_accounting, cpu).nr = 0;
+	return 0;
+}
+
+/**
+ * bh_uptodate_or_lock - Test whether the buffer is uptodate
+ * @bh: struct buffer_head
+ *
+ * Return true if the buffer is up-to-date and false,
+ * with the buffer locked, if not.
+ */
+int bh_uptodate_or_lock(struct buffer_head *bh)
+{
+	if (!buffer_uptodate(bh)) {
+		lock_buffer(bh);
+		if (!buffer_uptodate(bh))
+			return 0;
+		unlock_buffer(bh);
+	}
+	return 1;
+}
+EXPORT_SYMBOL(bh_uptodate_or_lock);
+
+/**
+ * bh_submit_read - Submit a locked buffer for reading
+ * @bh: struct buffer_head
+ *
+ * Returns zero on success and -EIO on error.
+ */
+int bh_submit_read(struct buffer_head *bh)
+{
+	BUG_ON(!buffer_locked(bh));
+
+	if (buffer_uptodate(bh)) {
+		unlock_buffer(bh);
+		return 0;
+	}
+
+	get_bh(bh);
+	bh->b_end_io = end_buffer_read_sync;
+	submit_bh(REQ_OP_READ, 0, bh);
+	wait_on_buffer(bh);
+	if (buffer_uptodate(bh))
+		return 0;
+	return -EIO;
+}
+EXPORT_SYMBOL(bh_submit_read);
+
+void __init buffer_init(void)
+{
+	unsigned long nrpages;
+	int ret;
+
+	bh_cachep = kmem_cache_create("buffer_head",
+			sizeof(struct buffer_head), 0,
+				(SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
+				SLAB_MEM_SPREAD),
+				NULL);
+
+	/*
+	 * Limit the bh occupancy to 10% of ZONE_NORMAL
+	 */
+	nrpages = (nr_free_buffer_pages() * 10) / 100;
+	max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
+	ret = cpuhp_setup_state_nocalls(CPUHP_FS_BUFF_DEAD, "fs/buffer:dead",
+					NULL, buffer_exit_cpu_dead);
+	WARN_ON(ret < 0);
+}