Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 3152 insertions, 0 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
new file mode 100644
index 000000000000..f961605a904b
--- /dev/null
+++ b/fs/buffer.c
@@ -0,0 +1,3152 @@
+/*
+ *  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/config.h>
+#include <linux/kernel.h>
+#include <linux/syscalls.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/percpu.h>
+#include <linux/slab.h>
+#include <linux/smp_lock.h>
+#include <linux/blkdev.h>
+#include <linux/file.h>
+#include <linux/quotaops.h>
+#include <linux/highmem.h>
+#include <linux/module.h>
+#include <linux/writeback.h>
+#include <linux/hash.h>
+#include <linux/suspend.h>
+#include <linux/buffer_head.h>
+#include <linux/bio.h>
+#include <linux/notifier.h>
+#include <linux/cpu.h>
+#include <linux/bitops.h>
+#include <linux/mpage.h>
+
+static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
+static void invalidate_bh_lrus(void);
+
+#define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
+
+inline void
+init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
+{
+	bh->b_end_io = handler;
+	bh->b_private = private;
+}
+
+static int sync_buffer(void *word)
+{
+	struct block_device *bd;
+	struct buffer_head *bh
+		= container_of(word, struct buffer_head, b_state);
+
+	smp_mb();
+	bd = bh->b_bdev;
+	if (bd)
+		blk_run_address_space(bd->bd_inode->i_mapping);
+	io_schedule();
+	return 0;
+}
+
+void fastcall __lock_buffer(struct buffer_head *bh)
+{
+	wait_on_bit_lock(&bh->b_state, BH_Lock, sync_buffer,
+							TASK_UNINTERRUPTIBLE);
+}
+EXPORT_SYMBOL(__lock_buffer);
+
+void fastcall unlock_buffer(struct buffer_head *bh)
+{
+	clear_buffer_locked(bh);
+	smp_mb__after_clear_bit();
+	wake_up_bit(&bh->b_state, BH_Lock);
+}
+
+/*
+ * 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(&bh->b_state, BH_Lock, sync_buffer, TASK_UNINTERRUPTIBLE);
+}
+
+static void
+__clear_page_buffers(struct page *page)
+{
+	ClearPagePrivate(page);
+	page->private = 0;
+	page_cache_release(page);
+}
+
+static void buffer_io_error(struct buffer_head *bh)
+{
+	char b[BDEVNAME_SIZE];
+
+	printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
+			bdevname(bh->b_bdev, b),
+			(unsigned long long)bh->b_blocknr);
+}
+
+/*
+ * 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)
+{
+	if (uptodate) {
+		set_buffer_uptodate(bh);
+	} else {
+		/* This happens, due to failed READA attempts. */
+		clear_buffer_uptodate(bh);
+	}
+	unlock_buffer(bh);
+	put_bh(bh);
+}
+
+void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
+{
+	char b[BDEVNAME_SIZE];
+
+	if (uptodate) {
+		set_buffer_uptodate(bh);
+	} else {
+		if (!buffer_eopnotsupp(bh) && printk_ratelimit()) {
+			buffer_io_error(bh);
+			printk(KERN_WARNING "lost page write due to "
+					"I/O error on %s\n",
+				       bdevname(bh->b_bdev, b));
+		}
+		set_buffer_write_io_error(bh);
+		clear_buffer_uptodate(bh);
+	}
+	unlock_buffer(bh);
+	put_bh(bh);
+}
+
+/*
+ * Write out and wait upon all the dirty data associated with a block
+ * device via its mapping.  Does not take the superblock lock.
+ */
+int sync_blockdev(struct block_device *bdev)
+{
+	int ret = 0;
+
+	if (bdev) {
+		int err;
+
+		ret = filemap_fdatawrite(bdev->bd_inode->i_mapping);
+		err = filemap_fdatawait(bdev->bd_inode->i_mapping);
+		if (!ret)
+			ret = err;
+	}
+	return ret;
+}
+EXPORT_SYMBOL(sync_blockdev);
+
+/*
+ * Write out and wait upon all dirty data associated with this
+ * superblock.  Filesystem data as well as the underlying block
+ * device.  Takes the superblock lock.
+ */
+int fsync_super(struct super_block *sb)
+{
+	sync_inodes_sb(sb, 0);
+	DQUOT_SYNC(sb);
+	lock_super(sb);
+	if (sb->s_dirt && sb->s_op->write_super)
+		sb->s_op->write_super(sb);
+	unlock_super(sb);
+	if (sb->s_op->sync_fs)
+		sb->s_op->sync_fs(sb, 1);
+	sync_blockdev(sb->s_bdev);
+	sync_inodes_sb(sb, 1);
+
+	return sync_blockdev(sb->s_bdev);
+}
+
+/*
+ * Write out and wait upon all dirty data associated with this
+ * device.   Filesystem data as well as the underlying block
+ * device.  Takes the superblock lock.
+ */
+int fsync_bdev(struct block_device *bdev)
+{
+	struct super_block *sb = get_super(bdev);
+	if (sb) {
+		int res = fsync_super(sb);
+		drop_super(sb);
+		return res;
+	}
+	return sync_blockdev(bdev);
+}
+
+/**
+ * freeze_bdev  --  lock a filesystem and force it into a consistent state
+ * @bdev:	blockdevice to lock
+ *
+ * This takes the block device bd_mount_sem to make sure no new mounts
+ * happen on bdev until thaw_bdev() is called.
+ * If a superblock is found on this device, we take the s_umount semaphore
+ * on it to make sure nobody unmounts until the snapshot creation is done.
+ */
+struct super_block *freeze_bdev(struct block_device *bdev)
+{
+	struct super_block *sb;
+
+	down(&bdev->bd_mount_sem);
+	sb = get_super(bdev);
+	if (sb && !(sb->s_flags & MS_RDONLY)) {
+		sb->s_frozen = SB_FREEZE_WRITE;
+		wmb();
+
+		sync_inodes_sb(sb, 0);
+		DQUOT_SYNC(sb);
+
+		lock_super(sb);
+		if (sb->s_dirt && sb->s_op->write_super)
+			sb->s_op->write_super(sb);
+		unlock_super(sb);
+
+		if (sb->s_op->sync_fs)
+			sb->s_op->sync_fs(sb, 1);
+
+		sync_blockdev(sb->s_bdev);
+		sync_inodes_sb(sb, 1);
+
+		sb->s_frozen = SB_FREEZE_TRANS;
+		wmb();
+
+		sync_blockdev(sb->s_bdev);
+
+		if (sb->s_op->write_super_lockfs)
+			sb->s_op->write_super_lockfs(sb);
+	}
+
+	sync_blockdev(bdev);
+	return sb;	/* thaw_bdev releases s->s_umount and bd_mount_sem */
+}
+EXPORT_SYMBOL(freeze_bdev);
+
+/**
+ * thaw_bdev  -- unlock filesystem
+ * @bdev:	blockdevice to unlock
+ * @sb:		associated superblock
+ *
+ * Unlocks the filesystem and marks it writeable again after freeze_bdev().
+ */
+void thaw_bdev(struct block_device *bdev, struct super_block *sb)
+{
+	if (sb) {
+		BUG_ON(sb->s_bdev != bdev);
+
+		if (sb->s_op->unlockfs)
+			sb->s_op->unlockfs(sb);
+		sb->s_frozen = SB_UNFROZEN;
+		wmb();
+		wake_up(&sb->s_wait_unfrozen);
+		drop_super(sb);
+	}
+
+	up(&bdev->bd_mount_sem);
+}
+EXPORT_SYMBOL(thaw_bdev);
+
+/*
+ * sync everything.  Start out by waking pdflush, because that writes back
+ * all queues in parallel.
+ */
+static void do_sync(unsigned long wait)
+{
+	wakeup_bdflush(0);
+	sync_inodes(0);		/* All mappings, inodes and their blockdevs */
+	DQUOT_SYNC(NULL);
+	sync_supers();		/* Write the superblocks */
+	sync_filesystems(0);	/* Start syncing the filesystems */
+	sync_filesystems(wait);	/* Waitingly sync the filesystems */
+	sync_inodes(wait);	/* Mappings, inodes and blockdevs, again. */
+	if (!wait)
+		printk("Emergency Sync complete\n");
+	if (unlikely(laptop_mode))
+		laptop_sync_completion();
+}
+
+asmlinkage long sys_sync(void)
+{
+	do_sync(1);
+	return 0;
+}
+
+void emergency_sync(void)
+{
+	pdflush_operation(do_sync, 0);
+}
+
+/*
+ * Generic function to fsync a file.
+ *
+ * filp may be NULL if called via the msync of a vma.
+ */
+ 
+int file_fsync(struct file *filp, struct dentry *dentry, int datasync)
+{
+	struct inode * inode = dentry->d_inode;
+	struct super_block * sb;
+	int ret, err;
+
+	/* sync the inode to buffers */
+	ret = write_inode_now(inode, 0);
+
+	/* sync the superblock to buffers */
+	sb = inode->i_sb;
+	lock_super(sb);
+	if (sb->s_op->write_super)
+		sb->s_op->write_super(sb);
+	unlock_super(sb);
+
+	/* .. finally sync the buffers to disk */
+	err = sync_blockdev(sb->s_bdev);
+	if (!ret)
+		ret = err;
+	return ret;
+}
+
+asmlinkage long sys_fsync(unsigned int fd)
+{
+	struct file * file;
+	struct address_space *mapping;
+	int ret, err;
+
+	ret = -EBADF;
+	file = fget(fd);
+	if (!file)
+		goto out;
+
+	mapping = file->f_mapping;
+
+	ret = -EINVAL;
+	if (!file->f_op || !file->f_op->fsync) {
+		/* Why?  We can still call filemap_fdatawrite */
+		goto out_putf;
+	}
+
+	current->flags |= PF_SYNCWRITE;
+	ret = filemap_fdatawrite(mapping);
+
+	/*
+	 * We need to protect against concurrent writers,
+	 * which could cause livelocks in fsync_buffers_list
+	 */
+	down(&mapping->host->i_sem);
+	err = file->f_op->fsync(file, file->f_dentry, 0);
+	if (!ret)
+		ret = err;
+	up(&mapping->host->i_sem);
+	err = filemap_fdatawait(mapping);
+	if (!ret)
+		ret = err;
+	current->flags &= ~PF_SYNCWRITE;
+
+out_putf:
+	fput(file);
+out:
+	return ret;
+}
+
+asmlinkage long sys_fdatasync(unsigned int fd)
+{
+	struct file * file;
+	struct address_space *mapping;
+	int ret, err;
+
+	ret = -EBADF;
+	file = fget(fd);
+	if (!file)
+		goto out;
+
+	ret = -EINVAL;
+	if (!file->f_op || !file->f_op->fsync)
+		goto out_putf;
+
+	mapping = file->f_mapping;
+
+	current->flags |= PF_SYNCWRITE;
+	ret = filemap_fdatawrite(mapping);
+	down(&mapping->host->i_sem);
+	err = file->f_op->fsync(file, file->f_dentry, 1);
+	if (!ret)
+		ret = err;
+	up(&mapping->host->i_sem);
+	err = filemap_fdatawait(mapping);
+	if (!ret)
+		ret = err;
+	current->flags &= ~PF_SYNCWRITE;
+
+out_putf:
+	fput(file);
+out:
+	return ret;
+}
+
+/*
+ * 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, i_bufferlist_lock contention
+ * may be quite high.  This code could TryLock the page, and if that
+ * succeeds, there is no need to take private_lock. (But if
+ * private_lock is contended then so is mapping->tree_lock).
+ */
+static struct buffer_head *
+__find_get_block_slow(struct block_device *bdev, sector_t block, int unused)
+{
+	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;
+
+	index = block >> (PAGE_CACHE_SHIFT - bd_inode->i_blkbits);
+	page = find_get_page(bd_mapping, index);
+	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 (bh->b_blocknr == block) {
+			ret = bh;
+			get_bh(bh);
+			goto out_unlock;
+		}
+		if (!buffer_mapped(bh))
+			all_mapped = 0;
+		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
+	 */
+	if (all_mapped) {
+		printk("__find_get_block_slow() failed. "
+			"block=%llu, b_blocknr=%llu\n",
+			(unsigned long long)block, (unsigned long long)bh->b_blocknr);
+		printk("b_state=0x%08lx, b_size=%u\n", bh->b_state, bh->b_size);
+		printk("device blocksize: %d\n", 1 << bd_inode->i_blkbits);
+	}
+out_unlock:
+	spin_unlock(&bd_mapping->private_lock);
+	page_cache_release(page);
+out:
+	return ret;
+}
+
+/* If invalidate_buffers() will trash dirty buffers, it means some kind
+   of fs corruption is going on. Trashing dirty data always imply losing
+   information that was supposed to be just stored on the physical layer
+   by the user.
+
+   Thus invalidate_buffers in general usage is not allwowed to trash
+   dirty buffers. For example ioctl(FLSBLKBUF) expects dirty data to
+   be preserved.  These buffers are simply skipped.
+  
+   We also skip buffers which are still in use.  For example this can
+   happen if a userspace program is reading the block device.
+
+   NOTE: In the case where the user removed a removable-media-disk even if
+   there's still dirty data not synced on disk (due a bug in the device driver
+   or due an error of the user), by not destroying the dirty buffers we could
+   generate corruption also on the next media inserted, thus a parameter is
+   necessary to handle this case in the most safe way possible (trying
+   to not corrupt also the new disk inserted with the data belonging to
+   the old now corrupted disk). Also for the ramdisk the natural thing
+   to do in order to release the ramdisk memory is to destroy dirty buffers.
+
+   These are two special cases. Normal usage imply the device driver
+   to issue a sync on the device (without waiting I/O completion) and
+   then an invalidate_buffers call that doesn't trash dirty buffers.
+
+   For handling cache coherency with the blkdev pagecache the 'update' case
+   is been introduced. It is needed to re-read from disk any pinned
+   buffer. NOTE: re-reading from disk is destructive so we can do it only
+   when we assume nobody is changing the buffercache under our I/O and when
+   we think the disk contains more recent information than the buffercache.
+   The update == 1 pass marks the buffers we need to update, the update == 2
+   pass does the actual I/O. */
+void invalidate_bdev(struct block_device *bdev, int destroy_dirty_buffers)
+{
+	invalidate_bh_lrus();
+	/*
+	 * FIXME: what about destroy_dirty_buffers?
+	 * We really want to use invalidate_inode_pages2() for
+	 * that, but not until that's cleaned up.
+	 */
+	invalidate_inode_pages(bdev->bd_inode->i_mapping);
+}
+
+/*
+ * Kick pdflush then try to free up some ZONE_NORMAL memory.
+ */
+static void free_more_memory(void)
+{
+	struct zone **zones;
+	pg_data_t *pgdat;
+
+	wakeup_bdflush(1024);
+	yield();
+
+	for_each_pgdat(pgdat) {
+		zones = pgdat->node_zonelists[GFP_NOFS&GFP_ZONEMASK].zones;
+		if (*zones)
+			try_to_free_pages(zones, GFP_NOFS, 0);
+	}
+}
+
+/*
+ * 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)
+{
+	static DEFINE_SPINLOCK(page_uptodate_lock);
+	unsigned long flags;
+	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);
+		if (printk_ratelimit())
+			buffer_io_error(bh);
+		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.
+	 */
+	spin_lock_irqsave(&page_uptodate_lock, flags);
+	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);
+	spin_unlock_irqrestore(&page_uptodate_lock, 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:
+	spin_unlock_irqrestore(&page_uptodate_lock, 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)
+{
+	char b[BDEVNAME_SIZE];
+	static DEFINE_SPINLOCK(page_uptodate_lock);
+	unsigned long flags;
+	struct buffer_head *tmp;
+	struct page *page;
+
+	BUG_ON(!buffer_async_write(bh));
+
+	page = bh->b_page;
+	if (uptodate) {
+		set_buffer_uptodate(bh);
+	} else {
+		if (printk_ratelimit()) {
+			buffer_io_error(bh);
+			printk(KERN_WARNING "lost page write due to "
+					"I/O error on %s\n",
+			       bdevname(bh->b_bdev, b));
+		}
+		set_bit(AS_EIO, &page->mapping->flags);
+		clear_buffer_uptodate(bh);
+		SetPageError(page);
+	}
+
+	spin_lock_irqsave(&page_uptodate_lock, flags);
+	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;
+	}
+	spin_unlock_irqrestore(&page_uptodate_lock, flags);
+	end_page_writeback(page);
+	return;
+
+still_busy:
+	spin_unlock_irqrestore(&page_uptodate_lock, flags);
+	return;
+}
+
+/*
+ * 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);
+}
+
+void mark_buffer_async_write(struct buffer_head *bh)
+{
+	bh->b_end_io = end_buffer_async_write;
+	set_buffer_async_write(bh);
+}
+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 inline void __remove_assoc_queue(struct buffer_head *bh)
+{
+	list_del_init(&bh->b_assoc_buffers);
+}
+
+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;
+}
+
+/**
+ * sync_mapping_buffers - write out and wait upon a mapping's "associated"
+ *                        buffers
+ * @buffer_mapping - the mapping which backs the buffers' data
+ * @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().  @buffer_mapping is
+ * the blockdev which "owns" the buffers and @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->assoc_mapping;
+
+	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(WRITE, 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->assoc_mapping) {
+		mapping->assoc_mapping = buffer_mapping;
+	} else {
+		if (mapping->assoc_mapping != buffer_mapping)
+			BUG();
+	}
+	if (list_empty(&bh->b_assoc_buffers)) {
+		spin_lock(&buffer_mapping->private_lock);
+		list_move_tail(&bh->b_assoc_buffers,
+				&mapping->private_list);
+		spin_unlock(&buffer_mapping->private_lock);
+	}
+}
+EXPORT_SYMBOL(mark_buffer_dirty_inode);
+
+/*
+ * 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)
+{
+	struct address_space * const mapping = page->mapping;
+
+	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);
+	}
+	spin_unlock(&mapping->private_lock);
+
+	if (!TestSetPageDirty(page)) {
+		write_lock_irq(&mapping->tree_lock);
+		if (page->mapping) {	/* Race with truncate? */
+			if (mapping_cap_account_dirty(mapping))
+				inc_page_state(nr_dirty);
+			radix_tree_tag_set(&mapping->page_tree,
+						page_index(page),
+						PAGECACHE_TAG_DIRTY);
+		}
+		write_unlock_irq(&mapping->tree_lock);
+		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+	}
+	
+	return 0;
+}
+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;
+	int err = 0, err2;
+
+	INIT_LIST_HEAD(&tmp);
+
+	spin_lock(lock);
+	while (!list_empty(list)) {
+		bh = BH_ENTRY(list->next);
+		list_del_init(&bh->b_assoc_buffers);
+		if (buffer_dirty(bh) || buffer_locked(bh)) {
+			list_add(&bh->b_assoc_buffers, &tmp);
+			if (buffer_dirty(bh)) {
+				get_bh(bh);
+				spin_unlock(lock);
+				/*
+				 * Ensure any pending I/O completes so that
+				 * ll_rw_block() actually writes the current
+				 * contents - it is a noop if I/O is still in
+				 * flight on potentially older contents.
+				 */
+				wait_on_buffer(bh);
+				ll_rw_block(WRITE, 1, &bh);
+				brelse(bh);
+				spin_lock(lock);
+			}
+		}
+	}
+
+	while (!list_empty(&tmp)) {
+		bh = BH_ENTRY(tmp.prev);
+		__remove_assoc_queue(bh);
+		get_bh(bh);
+		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->assoc_mapping;
+
+		spin_lock(&buffer_mapping->private_lock);
+		while (!list_empty(list))
+			__remove_assoc_queue(BH_ENTRY(list->next));
+		spin_unlock(&buffer_mapping->private_lock);
+	}
+}
+
+/*
+ * 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->assoc_mapping;
+
+		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,
+		int retry)
+{
+	struct buffer_head *bh, *head;
+	long offset;
+
+try_again:
+	head = NULL;
+	offset = PAGE_SIZE;
+	while ((offset -= size) >= 0) {
+		bh = alloc_buffer_head(GFP_NOFS);
+		if (!bh)
+			goto no_grow;
+
+		bh->b_bdev = NULL;
+		bh->b_this_page = head;
+		bh->b_blocknr = -1;
+		head = bh;
+
+		bh->b_state = 0;
+		atomic_set(&bh->b_count, 0);
+		bh->b_size = size;
+
+		/* Link the buffer to its page */
+		set_bh_page(bh, page, offset);
+
+		bh->b_end_io = NULL;
+	}
+	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);
+	}
+
+	/*
+	 * Return failure for non-async IO requests.  Async IO requests
+	 * are not allowed to fail, so we have to wait until buffer heads
+	 * become available.  But we don't want tasks sleeping with 
+	 * partially complete buffers, so all were released above.
+	 */
+	if (!retry)
+		return NULL;
+
+	/* We're _really_ low on memory. Now we just
+	 * wait for old buffer heads to become free due to
+	 * finishing IO.  Since this is an async request and
+	 * the reserve list is empty, we're sure there are 
+	 * async buffer heads in use.
+	 */
+	free_more_memory();
+	goto try_again;
+}
+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);
+}
+
+/*
+ * Initialise the state of a blockdev page's buffers.
+ */ 
+static void
+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);
+
+	do {
+		if (!buffer_mapped(bh)) {
+			init_buffer(bh, NULL, NULL);
+			bh->b_bdev = bdev;
+			bh->b_blocknr = block;
+			if (uptodate)
+				set_buffer_uptodate(bh);
+			set_buffer_mapped(bh);
+		}
+		block++;
+		bh = bh->b_this_page;
+	} while (bh != head);
+}
+
+/*
+ * Create the page-cache page that contains the requested block.
+ *
+ * This is user purely for blockdev mappings.
+ */
+static struct page *
+grow_dev_page(struct block_device *bdev, sector_t block,
+		pgoff_t index, int size)
+{
+	struct inode *inode = bdev->bd_inode;
+	struct page *page;
+	struct buffer_head *bh;
+
+	page = find_or_create_page(inode->i_mapping, index, GFP_NOFS);
+	if (!page)
+		return NULL;
+
+	if (!PageLocked(page))
+		BUG();
+
+	if (page_has_buffers(page)) {
+		bh = page_buffers(page);
+		if (bh->b_size == size) {
+			init_page_buffers(page, bdev, block, size);
+			return page;
+		}
+		if (!try_to_free_buffers(page))
+			goto failed;
+	}
+
+	/*
+	 * Allocate some buffers for this page
+	 */
+	bh = alloc_page_buffers(page, size, 0);
+	if (!bh)
+		goto failed;
+
+	/*
+	 * 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);
+	init_page_buffers(page, bdev, block, size);
+	spin_unlock(&inode->i_mapping->private_lock);
+	return page;
+
+failed:
+	BUG();
+	unlock_page(page);
+	page_cache_release(page);
+	return NULL;
+}
+
+/*
+ * Create buffers for the specified block device block's page.  If
+ * that page was dirty, the buffers are set dirty also.
+ *
+ * Except that's a bug.  Attaching dirty buffers to a dirty
+ * blockdev's page can result in filesystem corruption, because
+ * some of those buffers may be aliases of filesystem data.
+ * grow_dev_page() will go BUG() if this happens.
+ */
+static inline int
+grow_buffers(struct block_device *bdev, sector_t block, int size)
+{
+	struct page *page;
+	pgoff_t index;
+	int sizebits;
+
+	sizebits = -1;
+	do {
+		sizebits++;
+	} while ((size << sizebits) < PAGE_SIZE);
+
+	index = block >> sizebits;
+	block = index << sizebits;
+
+	/* Create a page with the proper size buffers.. */
+	page = grow_dev_page(bdev, block, index, size);
+	if (!page)
+		return 0;
+	unlock_page(page);
+	page_cache_release(page);
+	return 1;
+}
+
+struct buffer_head *
+__getblk_slow(struct block_device *bdev, sector_t block, int size)
+{
+	/* Size must be multiple of hard sectorsize */
+	if (unlikely(size & (bdev_hardsect_size(bdev)-1) ||
+			(size < 512 || size > PAGE_SIZE))) {
+		printk(KERN_ERR "getblk(): invalid block size %d requested\n",
+					size);
+		printk(KERN_ERR "hardsect size: %d\n",
+					bdev_hardsect_size(bdev));
+
+		dump_stack();
+		return NULL;
+	}
+
+	for (;;) {
+		struct buffer_head * bh;
+
+		bh = __find_get_block(bdev, block, size);
+		if (bh)
+			return bh;
+
+		if (!grow_buffers(bdev, block, size))
+			free_more_memory();
+	}
+}
+
+/*
+ * 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
+ *
+ * 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,
+ * mapping->tree_lock and the global inode_lock.
+ */
+void fastcall mark_buffer_dirty(struct buffer_head *bh)
+{
+	if (!buffer_dirty(bh) && !test_set_buffer_dirty(bh))
+		__set_page_dirty_nobuffers(bh->b_page);
+}
+
+/*
+ * 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;
+	}
+	printk(KERN_ERR "VFS: brelse: Trying to free free buffer\n");
+	WARN_ON(1);
+}
+
+/*
+ * bforget() is like brelse(), except it discards any
+ * potentially dirty data.
+ */
+void __bforget(struct buffer_head *bh)
+{
+	clear_buffer_dirty(bh);
+	if (!list_empty(&bh->b_assoc_buffers)) {
+		struct address_space *buffer_mapping = bh->b_page->mapping;
+
+		spin_lock(&buffer_mapping->private_lock);
+		list_del_init(&bh->b_assoc_buffers);
+		spin_unlock(&buffer_mapping->private_lock);
+	}
+	__brelse(bh);
+}
+
+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(READ, 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	8
+
+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
+}
+
+/*
+ * The LRU management algorithm is dopey-but-simple.  Sorry.
+ */
+static void bh_lru_install(struct buffer_head *bh)
+{
+	struct buffer_head *evictee = NULL;
+	struct bh_lru *lru;
+
+	check_irqs_on();
+	bh_lru_lock();
+	lru = &__get_cpu_var(bh_lrus);
+	if (lru->bhs[0] != bh) {
+		struct buffer_head *bhs[BH_LRU_SIZE];
+		int in;
+		int out = 0;
+
+		get_bh(bh);
+		bhs[out++] = bh;
+		for (in = 0; in < BH_LRU_SIZE; in++) {
+			struct buffer_head *bh2 = lru->bhs[in];
+
+			if (bh2 == bh) {
+				__brelse(bh2);
+			} else {
+				if (out >= BH_LRU_SIZE) {
+					BUG_ON(evictee != NULL);
+					evictee = bh2;
+				} else {
+					bhs[out++] = bh2;
+				}
+			}
+		}
+		while (out < BH_LRU_SIZE)
+			bhs[out++] = NULL;
+		memcpy(lru->bhs, bhs, sizeof(bhs));
+	}
+	bh_lru_unlock();
+
+	if (evictee)
+		__brelse(evictee);
+}
+
+/*
+ * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
+ */
+static inline struct buffer_head *
+lookup_bh_lru(struct block_device *bdev, sector_t block, int size)
+{
+	struct buffer_head *ret = NULL;
+	struct bh_lru *lru;
+	int i;
+
+	check_irqs_on();
+	bh_lru_lock();
+	lru = &__get_cpu_var(bh_lrus);
+	for (i = 0; i < BH_LRU_SIZE; i++) {
+		struct buffer_head *bh = lru->bhs[i];
+
+		if (bh && bh->b_bdev == bdev &&
+				bh->b_blocknr == block && bh->b_size == size) {
+			if (i) {
+				while (i) {
+					lru->bhs[i] = lru->bhs[i - 1];
+					i--;
+				}
+				lru->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, int size)
+{
+	struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
+
+	if (bh == NULL) {
+		bh = __find_get_block_slow(bdev, block, size);
+		if (bh)
+			bh_lru_install(bh);
+	}
+	if (bh)
+		touch_buffer(bh);
+	return bh;
+}
+EXPORT_SYMBOL(__find_get_block);
+
+/*
+ * __getblk 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() cannot fail - it just keeps trying.  If you pass it an
+ * illegal block number, __getblk() will happily return a buffer_head
+ * which represents the non-existent block.  Very weird.
+ *
+ * __getblk() will lock up the machine if grow_dev_page's try_to_free_buffers()
+ * attempt is failing.  FIXME, perhaps?
+ */
+struct buffer_head *
+__getblk(struct block_device *bdev, sector_t block, int size)
+{
+	struct buffer_head *bh = __find_get_block(bdev, block, size);
+
+	might_sleep();
+	if (bh == NULL)
+		bh = __getblk_slow(bdev, block, size);
+	return bh;
+}
+EXPORT_SYMBOL(__getblk);
+
+/*
+ * Do async read-ahead on a buffer..
+ */
+void __breadahead(struct block_device *bdev, sector_t block, int size)
+{
+	struct buffer_head *bh = __getblk(bdev, block, size);
+	ll_rw_block(READA, 1, &bh);
+	brelse(bh);
+}
+EXPORT_SYMBOL(__breadahead);
+
+/**
+ *  __bread() - reads a specified block and returns the bh
+ *  @block: number of block
+ *  @size: size (in bytes) to read
+ * 
+ *  Reads a specified block, and returns buffer head that contains it.
+ *  It returns NULL if the block was unreadable.
+ */
+struct buffer_head *
+__bread(struct block_device *bdev, sector_t block, int size)
+{
+	struct buffer_head *bh = __getblk(bdev, block, size);
+
+	if (!buffer_uptodate(bh))
+		bh = __bread_slow(bh);
+	return bh;
+}
+EXPORT_SYMBOL(__bread);
+
+/*
+ * 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 void invalidate_bh_lrus(void)
+{
+	on_each_cpu(invalidate_bh_lru, NULL, 1, 1);
+}
+
+void set_bh_page(struct buffer_head *bh,
+		struct page *page, unsigned long offset)
+{
+	bh->b_page = page;
+	if (offset >= PAGE_SIZE)
+		BUG();
+	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.
+ */
+static inline void discard_buffer(struct buffer_head * bh)
+{
+	lock_buffer(bh);
+	clear_buffer_dirty(bh);
+	bh->b_bdev = NULL;
+	clear_buffer_mapped(bh);
+	clear_buffer_req(bh);
+	clear_buffer_new(bh);
+	clear_buffer_delay(bh);
+	unlock_buffer(bh);
+}
+
+/**
+ * try_to_release_page() - release old fs-specific metadata on a page
+ *
+ * @page: the page which the kernel is trying to free
+ * @gfp_mask: memory allocation flags (and I/O mode)
+ *
+ * The address_space is to try to release any data against the page
+ * (presumably at page->private).  If the release was successful, return `1'.
+ * Otherwise return zero.
+ *
+ * The @gfp_mask argument specifies whether I/O may be performed to release
+ * this page (__GFP_IO), and whether the call may block (__GFP_WAIT).
+ *
+ * NOTE: @gfp_mask may go away, and this function may become non-blocking.
+ */
+int try_to_release_page(struct page *page, int gfp_mask)
+{
+	struct address_space * const mapping = page->mapping;
+
+	BUG_ON(!PageLocked(page));
+	if (PageWriteback(page))
+		return 0;
+	
+	if (mapping && mapping->a_ops->releasepage)
+		return mapping->a_ops->releasepage(page, gfp_mask);
+	return try_to_free_buffers(page);
+}
+EXPORT_SYMBOL(try_to_release_page);
+
+/**
+ * block_invalidatepage - invalidate part of all of a buffer-backed page
+ *
+ * @page: the page which is affected
+ * @offset: the index of the truncation point
+ *
+ * block_invalidatepage() is called when all or part of the page has become
+ * invalidatedby 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.
+ */
+int block_invalidatepage(struct page *page, unsigned long offset)
+{
+	struct buffer_head *head, *bh, *next;
+	unsigned int curr_off = 0;
+	int ret = 1;
+
+	BUG_ON(!PageLocked(page));
+	if (!page_has_buffers(page))
+		goto out;
+
+	head = page_buffers(page);
+	bh = head;
+	do {
+		unsigned int next_off = curr_off + bh->b_size;
+		next = bh->b_this_page;
+
+		/*
+		 * 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 (offset == 0)
+		ret = try_to_release_page(page, 0);
+out:
+	return ret;
+}
+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, 1);
+	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);
+
+/*
+ * We are taking a block for data and we don't want any output from any
+ * buffer-cache aliases starting from return from that 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 used
+ * 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 unmap_underlying_metadata(struct block_device *bdev, sector_t block)
+{
+	struct buffer_head *old_bh;
+
+	might_sleep();
+
+	old_bh = __find_get_block_slow(bdev, block, 0);
+	if (old_bh) {
+		clear_buffer_dirty(old_bh);
+		wait_on_buffer(old_bh);
+		clear_buffer_req(old_bh);
+		__brelse(old_bh);
+	}
+}
+EXPORT_SYMBOL(unmap_underlying_metadata);
+
+/*
+ * 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.
+ */
+static int __block_write_full_page(struct inode *inode, struct page *page,
+			get_block_t *get_block, struct writeback_control *wbc)
+{
+	int err;
+	sector_t block;
+	sector_t last_block;
+	struct buffer_head *bh, *head;
+	int nr_underway = 0;
+
+	BUG_ON(!PageLocked(page));
+
+	last_block = (i_size_read(inode) - 1) >> inode->i_blkbits;
+
+	if (!page_has_buffers(page)) {
+		create_empty_buffers(page, 1 << inode->i_blkbits,
+					(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.
+	 */
+
+	block = page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
+	head = page_buffers(page);
+	bh = head;
+
+	/*
+	 * 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_dirty(bh)) {
+			err = get_block(inode, block, bh, 1);
+			if (err)
+				goto recover;
+			if (buffer_new(bh)) {
+				/* blockdev mappings never come here */
+				clear_buffer_new(bh);
+				unmap_underlying_metadata(bh->b_bdev,
+							bh->b_blocknr);
+			}
+		}
+		bh = bh->b_this_page;
+		block++;
+	} while (bh != head);
+
+	do {
+		get_bh(bh);
+		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 pdflush and kswapd
+		 * activity, but those code paths have their own higher-level
+		 * throttling.
+		 */
+		if (wbc->sync_mode != WB_SYNC_NONE || !wbc->nonblocking) {
+			lock_buffer(bh);
+		} else if (test_set_buffer_locked(bh)) {
+			redirty_page_for_writepage(wbc, page);
+			continue;
+		}
+		if (test_clear_buffer_dirty(bh)) {
+			mark_buffer_async_write(bh);
+		} 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);
+	unlock_page(page);
+
+	do {
+		struct buffer_head *next = bh->b_this_page;
+		if (buffer_async_write(bh)) {
+			submit_bh(WRITE, bh);
+			nr_underway++;
+		}
+		put_bh(bh);
+		bh = next;
+	} while (bh != head);
+
+	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.
+		 */
+		int uptodate = 1;
+		do {
+			if (!buffer_uptodate(bh)) {
+				uptodate = 0;
+				break;
+			}
+			bh = bh->b_this_page;
+		} while (bh != head);
+		if (uptodate)
+			SetPageUptodate(page);
+		end_page_writeback(page);
+		/*
+		 * The page and buffer_heads can be released at any time from
+		 * here on.
+		 */
+		wbc->pages_skipped++;	/* We didn't write this page */
+	}
+	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 {
+		get_bh(bh);
+		if (buffer_mapped(bh) && buffer_dirty(bh)) {
+			lock_buffer(bh);
+			mark_buffer_async_write(bh);
+		} 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));
+	set_page_writeback(page);
+	unlock_page(page);
+	do {
+		struct buffer_head *next = bh->b_this_page;
+		if (buffer_async_write(bh)) {
+			clear_buffer_dirty(bh);
+			submit_bh(WRITE, bh);
+			nr_underway++;
+		}
+		put_bh(bh);
+		bh = next;
+	} while (bh != head);
+	goto done;
+}
+
+static int __block_prepare_write(struct inode *inode, struct page *page,
+		unsigned from, unsigned to, get_block_t *get_block)
+{
+	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_CACHE_SIZE);
+	BUG_ON(to > PAGE_CACHE_SIZE);
+	BUG_ON(from > to);
+
+	blocksize = 1 << inode->i_blkbits;
+	if (!page_has_buffers(page))
+		create_empty_buffers(page, blocksize, 0);
+	head = page_buffers(page);
+
+	bbits = inode->i_blkbits;
+	block = (sector_t)page->index << (PAGE_CACHE_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)) {
+			err = get_block(inode, block, bh, 1);
+			if (err)
+				goto out;
+			if (buffer_new(bh)) {
+				clear_buffer_new(bh);
+				unmap_underlying_metadata(bh->b_bdev,
+							bh->b_blocknr);
+				if (PageUptodate(page)) {
+					set_buffer_uptodate(bh);
+					continue;
+				}
+				if (block_end > to || block_start < from) {
+					void *kaddr;
+
+					kaddr = kmap_atomic(page, KM_USER0);
+					if (block_end > to)
+						memset(kaddr+to, 0,
+							block_end-to);
+					if (block_start < from)
+						memset(kaddr+block_start,
+							0, from-block_start);
+					flush_dcache_page(page);
+					kunmap_atomic(kaddr, KM_USER0);
+				}
+				continue;
+			}
+		}
+		if (PageUptodate(page)) {
+			if (!buffer_uptodate(bh))
+				set_buffer_uptodate(bh);
+			continue; 
+		}
+		if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
+		     (block_start < from || block_end > to)) {
+			ll_rw_block(READ, 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))
+			return -EIO;
+	}
+	return 0;
+out:
+	/*
+	 * Zero out any newly allocated blocks to avoid exposing stale
+	 * data.  If BH_New is set, we know that the block was newly
+	 * allocated in the above loop.
+	 */
+	bh = head;
+	block_start = 0;
+	do {
+		block_end = block_start+blocksize;
+		if (block_end <= from)
+			goto next_bh;
+		if (block_start >= to)
+			break;
+		if (buffer_new(bh)) {
+			void *kaddr;
+
+			clear_buffer_new(bh);
+			kaddr = kmap_atomic(page, KM_USER0);
+			memset(kaddr+block_start, 0, bh->b_size);
+			kunmap_atomic(kaddr, KM_USER0);
+			set_buffer_uptodate(bh);
+			mark_buffer_dirty(bh);
+		}
+next_bh:
+		block_start = block_end;
+		bh = bh->b_this_page;
+	} while (bh != head);
+	return err;
+}
+
+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;
+
+	blocksize = 1 << inode->i_blkbits;
+
+	for(bh = head = page_buffers(page), block_start = 0;
+	    bh != head || !block_start;
+	    block_start=block_end, bh = bh->b_this_page) {
+		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);
+		}
+	}
+
+	/*
+	 * 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;
+}
+
+/*
+ * 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;
+	int nr, i;
+	int fully_mapped = 1;
+
+	if (!PageLocked(page))
+		PAGE_BUG(page);
+	blocksize = 1 << inode->i_blkbits;
+	if (!page_has_buffers(page))
+		create_empty_buffers(page, blocksize, 0);
+	head = page_buffers(page);
+
+	iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
+	lblock = (i_size_read(inode)+blocksize-1) >> inode->i_blkbits;
+	bh = head;
+	nr = 0;
+	i = 0;
+
+	do {
+		if (buffer_uptodate(bh))
+			continue;
+
+		if (!buffer_mapped(bh)) {
+			fully_mapped = 0;
+			if (iblock < lblock) {
+				if (get_block(inode, iblock, bh, 0))
+					SetPageError(page);
+			}
+			if (!buffer_mapped(bh)) {
+				void *kaddr = kmap_atomic(page, KM_USER0);
+				memset(kaddr + i * blocksize, 0, blocksize);
+				flush_dcache_page(page);
+				kunmap_atomic(kaddr, KM_USER0);
+				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(READ, bh);
+	}
+	return 0;
+}
+
+/* utility function for filesystems that need to do work on expanding
+ * truncates.  Uses prepare/commit_write to allow the filesystem to
+ * deal with the hole.  
+ */
+int generic_cont_expand(struct inode *inode, loff_t size)
+{
+	struct address_space *mapping = inode->i_mapping;
+	struct page *page;
+	unsigned long index, offset, limit;
+	int err;
+
+	err = -EFBIG;
+        limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
+	if (limit != RLIM_INFINITY && size > (loff_t)limit) {
+		send_sig(SIGXFSZ, current, 0);
+		goto out;
+	}
+	if (size > inode->i_sb->s_maxbytes)
+		goto out;
+
+	offset = (size & (PAGE_CACHE_SIZE-1)); /* Within page */
+
+	/* ugh.  in prepare/commit_write, if from==to==start of block, we 
+	** skip the prepare.  make sure we never send an offset for the start
+	** of a block
+	*/
+	if ((offset & (inode->i_sb->s_blocksize - 1)) == 0) {
+		offset++;
+	}
+	index = size >> PAGE_CACHE_SHIFT;
+	err = -ENOMEM;
+	page = grab_cache_page(mapping, index);
+	if (!page)
+		goto out;
+	err = mapping->a_ops->prepare_write(NULL, page, offset, offset);
+	if (!err) {
+		err = mapping->a_ops->commit_write(NULL, page, offset, offset);
+	}
+	unlock_page(page);
+	page_cache_release(page);
+	if (err > 0)
+		err = 0;
+out:
+	return err;
+}
+
+/*
+ * For moronic filesystems that do not allow holes in file.
+ * We may have to extend the file.
+ */
+
+int cont_prepare_write(struct page *page, unsigned offset,
+		unsigned to, get_block_t *get_block, loff_t *bytes)
+{
+	struct address_space *mapping = page->mapping;
+	struct inode *inode = mapping->host;
+	struct page *new_page;
+	pgoff_t pgpos;
+	long status;
+	unsigned zerofrom;
+	unsigned blocksize = 1 << inode->i_blkbits;
+	void *kaddr;
+
+	while(page->index > (pgpos = *bytes>>PAGE_CACHE_SHIFT)) {
+		status = -ENOMEM;
+		new_page = grab_cache_page(mapping, pgpos);
+		if (!new_page)
+			goto out;
+		/* we might sleep */
+		if (*bytes>>PAGE_CACHE_SHIFT != pgpos) {
+			unlock_page(new_page);
+			page_cache_release(new_page);
+			continue;
+		}
+		zerofrom = *bytes & ~PAGE_CACHE_MASK;
+		if (zerofrom & (blocksize-1)) {
+			*bytes |= (blocksize-1);
+			(*bytes)++;
+		}
+		status = __block_prepare_write(inode, new_page, zerofrom,
+						PAGE_CACHE_SIZE, get_block);
+		if (status)
+			goto out_unmap;
+		kaddr = kmap_atomic(new_page, KM_USER0);
+		memset(kaddr+zerofrom, 0, PAGE_CACHE_SIZE-zerofrom);
+		flush_dcache_page(new_page);
+		kunmap_atomic(kaddr, KM_USER0);
+		generic_commit_write(NULL, new_page, zerofrom, PAGE_CACHE_SIZE);
+		unlock_page(new_page);
+		page_cache_release(new_page);
+	}
+
+	if (page->index < pgpos) {
+		/* completely inside the area */
+		zerofrom = offset;
+	} else {
+		/* page covers the boundary, find the boundary offset */
+		zerofrom = *bytes & ~PAGE_CACHE_MASK;
+
+		/* if we will expand the thing last block will be filled */
+		if (to > zerofrom && (zerofrom & (blocksize-1))) {
+			*bytes |= (blocksize-1);
+			(*bytes)++;
+		}
+
+		/* starting below the boundary? Nothing to zero out */
+		if (offset <= zerofrom)
+			zerofrom = offset;
+	}
+	status = __block_prepare_write(inode, page, zerofrom, to, get_block);
+	if (status)
+		goto out1;
+	if (zerofrom < offset) {
+		kaddr = kmap_atomic(page, KM_USER0);
+		memset(kaddr+zerofrom, 0, offset-zerofrom);
+		flush_dcache_page(page);
+		kunmap_atomic(kaddr, KM_USER0);
+		__block_commit_write(inode, page, zerofrom, offset);
+	}
+	return 0;
+out1:
+	ClearPageUptodate(page);
+	return status;
+
+out_unmap:
+	ClearPageUptodate(new_page);
+	unlock_page(new_page);
+	page_cache_release(new_page);
+out:
+	return status;
+}
+
+int block_prepare_write(struct page *page, unsigned from, unsigned to,
+			get_block_t *get_block)
+{
+	struct inode *inode = page->mapping->host;
+	int err = __block_prepare_write(inode, page, from, to, get_block);
+	if (err)
+		ClearPageUptodate(page);
+	return err;
+}
+
+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;
+}
+
+int generic_commit_write(struct file *file, struct page *page,
+		unsigned from, unsigned to)
+{
+	struct inode *inode = page->mapping->host;
+	loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
+	__block_commit_write(inode,page,from,to);
+	/*
+	 * No need to use i_size_read() here, the i_size
+	 * cannot change under us because we hold i_sem.
+	 */
+	if (pos > inode->i_size) {
+		i_size_write(inode, pos);
+		mark_inode_dirty(inode);
+	}
+	return 0;
+}
+
+
+/*
+ * nobh_prepare_write()'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.
+ *
+ * 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_nobh(struct buffer_head *bh, int uptodate)
+{
+	if (uptodate) {
+		set_buffer_uptodate(bh);
+	} else {
+		/* This happens, due to failed READA attempts. */
+		clear_buffer_uptodate(bh);
+	}
+	unlock_buffer(bh);
+}
+
+/*
+ * On entry, the page is fully not uptodate.
+ * On exit the page is fully uptodate in the areas outside (from,to)
+ */
+int nobh_prepare_write(struct page *page, unsigned from, unsigned to,
+			get_block_t *get_block)
+{
+	struct inode *inode = page->mapping->host;
+	const unsigned blkbits = inode->i_blkbits;
+	const unsigned blocksize = 1 << blkbits;
+	struct buffer_head map_bh;
+	struct buffer_head *read_bh[MAX_BUF_PER_PAGE];
+	unsigned block_in_page;
+	unsigned block_start;
+	sector_t block_in_file;
+	char *kaddr;
+	int nr_reads = 0;
+	int i;
+	int ret = 0;
+	int is_mapped_to_disk = 1;
+	int dirtied_it = 0;
+
+	if (PageMappedToDisk(page))
+		return 0;
+
+	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
+	map_bh.b_page = page;
+
+	/*
+	 * 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;
+		  block_start < PAGE_CACHE_SIZE;
+		  block_in_page++, block_start += blocksize) {
+		unsigned block_end = block_start + blocksize;
+		int create;
+
+		map_bh.b_state = 0;
+		create = 1;
+		if (block_start >= to)
+			create = 0;
+		ret = get_block(inode, block_in_file + block_in_page,
+					&map_bh, create);
+		if (ret)
+			goto failed;
+		if (!buffer_mapped(&map_bh))
+			is_mapped_to_disk = 0;
+		if (buffer_new(&map_bh))
+			unmap_underlying_metadata(map_bh.b_bdev,
+							map_bh.b_blocknr);
+		if (PageUptodate(page))
+			continue;
+		if (buffer_new(&map_bh) || !buffer_mapped(&map_bh)) {
+			kaddr = kmap_atomic(page, KM_USER0);
+			if (block_start < from) {
+				memset(kaddr+block_start, 0, from-block_start);
+				dirtied_it = 1;
+			}
+			if (block_end > to) {
+				memset(kaddr + to, 0, block_end - to);
+				dirtied_it = 1;
+			}
+			flush_dcache_page(page);
+			kunmap_atomic(kaddr, KM_USER0);
+			continue;
+		}
+		if (buffer_uptodate(&map_bh))
+			continue;	/* reiserfs does this */
+		if (block_start < from || block_end > to) {
+			struct buffer_head *bh = alloc_buffer_head(GFP_NOFS);
+
+			if (!bh) {
+				ret = -ENOMEM;
+				goto failed;
+			}
+			bh->b_state = map_bh.b_state;
+			atomic_set(&bh->b_count, 0);
+			bh->b_this_page = NULL;
+			bh->b_page = page;
+			bh->b_blocknr = map_bh.b_blocknr;
+			bh->b_size = blocksize;
+			bh->b_data = (char *)(long)block_start;
+			bh->b_bdev = map_bh.b_bdev;
+			bh->b_private = NULL;
+			read_bh[nr_reads++] = bh;
+		}
+	}
+
+	if (nr_reads) {
+		struct buffer_head *bh;
+
+		/*
+		 * 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 (i = 0; i < nr_reads; i++) {
+			bh = read_bh[i];
+			lock_buffer(bh);
+			bh->b_end_io = end_buffer_read_nobh;
+			submit_bh(READ, bh);
+		}
+		for (i = 0; i < nr_reads; i++) {
+			bh = read_bh[i];
+			wait_on_buffer(bh);
+			if (!buffer_uptodate(bh))
+				ret = -EIO;
+			free_buffer_head(bh);
+			read_bh[i] = NULL;
+		}
+		if (ret)
+			goto failed;
+	}
+
+	if (is_mapped_to_disk)
+		SetPageMappedToDisk(page);
+	SetPageUptodate(page);
+
+	/*
+	 * Setting the page dirty here isn't necessary for the prepare_write
+	 * function - commit_write will do that.  But if/when this function is
+	 * used within the pagefault handler to ensure that all mmapped pages
+	 * have backing space in the filesystem, we will need to dirty the page
+	 * if its contents were altered.
+	 */
+	if (dirtied_it)
+		set_page_dirty(page);
+
+	return 0;
+
+failed:
+	for (i = 0; i < nr_reads; i++) {
+		if (read_bh[i])
+			free_buffer_head(read_bh[i]);
+	}
+
+	/*
+	 * Error recovery is pretty slack.  Clear the page and mark it dirty
+	 * so we'll later zero out any blocks which _were_ allocated.
+	 */
+	kaddr = kmap_atomic(page, KM_USER0);
+	memset(kaddr, 0, PAGE_CACHE_SIZE);
+	kunmap_atomic(kaddr, KM_USER0);
+	SetPageUptodate(page);
+	set_page_dirty(page);
+	return ret;
+}
+EXPORT_SYMBOL(nobh_prepare_write);
+
+int nobh_commit_write(struct file *file, struct page *page,
+		unsigned from, unsigned to)
+{
+	struct inode *inode = page->mapping->host;
+	loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
+
+	set_page_dirty(page);
+	if (pos > inode->i_size) {
+		i_size_write(inode, pos);
+		mark_inode_dirty(inode);
+	}
+	return 0;
+}
+EXPORT_SYMBOL(nobh_commit_write);
+
+/*
+ * 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_CACHE_SHIFT;
+	unsigned offset;
+	void *kaddr;
+	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_CACHE_SIZE-1);
+	if (page->index >= end_index+1 || !offset) {
+		/*
+		 * The page may have dirty, unmapped buffers.  For example,
+		 * they may have been added in ext3_writepage().  Make them
+		 * freeable here, so the page does not leak.
+		 */
+#if 0
+		/* Not really sure about this  - do we need this ? */
+		if (page->mapping->a_ops->invalidatepage)
+			page->mapping->a_ops->invalidatepage(page, offset);
+#endif
+		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."
+	 */
+	kaddr = kmap_atomic(page, KM_USER0);
+	memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
+	flush_dcache_page(page);
+	kunmap_atomic(kaddr, KM_USER0);
+out:
+	ret = mpage_writepage(page, get_block, wbc);
+	if (ret == -EAGAIN)
+		ret = __block_write_full_page(inode, page, get_block, wbc);
+	return ret;
+}
+EXPORT_SYMBOL(nobh_writepage);
+
+/*
+ * This function assumes that ->prepare_write() uses nobh_prepare_write().
+ */
+int nobh_truncate_page(struct address_space *mapping, loff_t from)
+{
+	struct inode *inode = mapping->host;
+	unsigned blocksize = 1 << inode->i_blkbits;
+	pgoff_t index = from >> PAGE_CACHE_SHIFT;
+	unsigned offset = from & (PAGE_CACHE_SIZE-1);
+	unsigned to;
+	struct page *page;
+	struct address_space_operations *a_ops = mapping->a_ops;
+	char *kaddr;
+	int ret = 0;
+
+	if ((offset & (blocksize - 1)) == 0)
+		goto out;
+
+	ret = -ENOMEM;
+	page = grab_cache_page(mapping, index);
+	if (!page)
+		goto out;
+
+	to = (offset + blocksize) & ~(blocksize - 1);
+	ret = a_ops->prepare_write(NULL, page, offset, to);
+	if (ret == 0) {
+		kaddr = kmap_atomic(page, KM_USER0);
+		memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
+		flush_dcache_page(page);
+		kunmap_atomic(kaddr, KM_USER0);
+		set_page_dirty(page);
+	}
+	unlock_page(page);
+	page_cache_release(page);
+out:
+	return ret;
+}
+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_CACHE_SHIFT;
+	unsigned offset = from & (PAGE_CACHE_SIZE-1);
+	unsigned blocksize;
+	pgoff_t iblock;
+	unsigned length, pos;
+	struct inode *inode = mapping->host;
+	struct page *page;
+	struct buffer_head *bh;
+	void *kaddr;
+	int err;
+
+	blocksize = 1 << inode->i_blkbits;
+	length = offset & (blocksize - 1);
+
+	/* Block boundary? Nothing to do */
+	if (!length)
+		return 0;
+
+	length = blocksize - length;
+	iblock = index << (PAGE_CACHE_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)) {
+		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)) {
+		err = -EIO;
+		ll_rw_block(READ, 1, &bh);
+		wait_on_buffer(bh);
+		/* Uhhuh. Read error. Complain and punt. */
+		if (!buffer_uptodate(bh))
+			goto unlock;
+	}
+
+	kaddr = kmap_atomic(page, KM_USER0);
+	memset(kaddr + offset, 0, length);
+	flush_dcache_page(page);
+	kunmap_atomic(kaddr, KM_USER0);
+
+	mark_buffer_dirty(bh);
+	err = 0;
+
+unlock:
+	unlock_page(page);
+	page_cache_release(page);
+out:
+	return err;
+}
+
+/*
+ * 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_CACHE_SHIFT;
+	unsigned offset;
+	void *kaddr;
+
+	/* Is the page fully inside i_size? */
+	if (page->index < end_index)
+		return __block_write_full_page(inode, page, get_block, wbc);
+
+	/* Is the page fully outside i_size? (truncate in progress) */
+	offset = i_size & (PAGE_CACHE_SIZE-1);
+	if (page->index >= end_index+1 || !offset) {
+		/*
+		 * The page may have dirty, unmapped buffers.  For example,
+		 * they may have been added in ext3_writepage().  Make them
+		 * freeable here, so the page does not leak.
+		 */
+		block_invalidatepage(page, 0);
+		unlock_page(page);
+		return 0; /* don't care */
+	}
+
+	/*
+	 * The page straddles i_size.  It must be zeroed out on each and every
+	 * writepage invokation 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."
+	 */
+	kaddr = kmap_atomic(page, KM_USER0);
+	memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
+	flush_dcache_page(page);
+	kunmap_atomic(kaddr, KM_USER0);
+	return __block_write_full_page(inode, page, get_block, wbc);
+}
+
+sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
+			    get_block_t *get_block)
+{
+	struct buffer_head tmp;
+	struct inode *inode = mapping->host;
+	tmp.b_state = 0;
+	tmp.b_blocknr = 0;
+	get_block(inode, block, &tmp, 0);
+	return tmp.b_blocknr;
+}
+
+static int end_bio_bh_io_sync(struct bio *bio, unsigned int bytes_done, int err)
+{
+	struct buffer_head *bh = bio->bi_private;
+
+	if (bio->bi_size)
+		return 1;
+
+	if (err == -EOPNOTSUPP) {
+		set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
+		set_bit(BH_Eopnotsupp, &bh->b_state);
+	}
+
+	bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
+	bio_put(bio);
+	return 0;
+}
+
+int submit_bh(int rw, struct buffer_head * bh)
+{
+	struct bio *bio;
+	int ret = 0;
+
+	BUG_ON(!buffer_locked(bh));
+	BUG_ON(!buffer_mapped(bh));
+	BUG_ON(!bh->b_end_io);
+
+	if (buffer_ordered(bh) && (rw == WRITE))
+		rw = WRITE_BARRIER;
+
+	/*
+	 * Only clear out a write error when rewriting, should this
+	 * include WRITE_SYNC as well?
+	 */
+	if (test_set_buffer_req(bh) && (rw == WRITE || rw == WRITE_BARRIER))
+		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);
+
+	bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
+	bio->bi_bdev = bh->b_bdev;
+	bio->bi_io_vec[0].bv_page = bh->b_page;
+	bio->bi_io_vec[0].bv_len = bh->b_size;
+	bio->bi_io_vec[0].bv_offset = bh_offset(bh);
+
+	bio->bi_vcnt = 1;
+	bio->bi_idx = 0;
+	bio->bi_size = bh->b_size;
+
+	bio->bi_end_io = end_bio_bh_io_sync;
+	bio->bi_private = bh;
+
+	bio_get(bio);
+	submit_bio(rw, bio);
+
+	if (bio_flagged(bio, BIO_EOPNOTSUPP))
+		ret = -EOPNOTSUPP;
+
+	bio_put(bio);
+	return ret;
+}
+
+/**
+ * ll_rw_block: low-level access to block devices (DEPRECATED)
+ * @rw: whether to %READ or %WRITE or maybe %READA (readahead)
+ * @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 %READ or a %WRITE.
+ * The third %READA option is described in the documentation for
+ * generic_make_request() which ll_rw_block() calls.
+ *
+ * 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 approriate), 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 rw, int nr, struct buffer_head *bhs[])
+{
+	int i;
+
+	for (i = 0; i < nr; i++) {
+		struct buffer_head *bh = bhs[i];
+
+		if (test_set_buffer_locked(bh))
+			continue;
+
+		get_bh(bh);
+		if (rw == WRITE) {
+			bh->b_end_io = end_buffer_write_sync;
+			if (test_clear_buffer_dirty(bh)) {
+				submit_bh(WRITE, bh);
+				continue;
+			}
+		} else {
+			bh->b_end_io = end_buffer_read_sync;
+			if (!buffer_uptodate(bh)) {
+				submit_bh(rw, bh);
+				continue;
+			}
+		}
+		unlock_buffer(bh);
+		put_bh(bh);
+	}
+}
+
+/*
+ * 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 ret = 0;
+
+	WARN_ON(atomic_read(&bh->b_count) < 1);
+	lock_buffer(bh);
+	if (test_clear_buffer_dirty(bh)) {
+		get_bh(bh);
+		bh->b_end_io = end_buffer_write_sync;
+		ret = submit_bh(WRITE, bh);
+		wait_on_buffer(bh);
+		if (buffer_eopnotsupp(bh)) {
+			clear_buffer_eopnotsupp(bh);
+			ret = -EOPNOTSUPP;
+		}
+		if (!ret && !buffer_uptodate(bh))
+			ret = -EIO;
+	} else {
+		unlock_buffer(bh);
+	}
+	return ret;
+}
+
+/*
+ * 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_write_io_error(bh))
+			set_bit(AS_EIO, &page->mapping->flags);
+		if (buffer_busy(bh))
+			goto failed;
+		bh = bh->b_this_page;
+	} while (bh != head);
+
+	do {
+		struct buffer_head *next = bh->b_this_page;
+
+		if (!list_empty(&bh->b_assoc_buffers))
+			__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 (ret) {
+		/*
+		 * 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 later reattachment of buffers
+		 * could encounter a non-uptodate page, which is unresolvable.
+		 * This only applies in the rare case where try_to_free_buffers
+		 * succeeds but the page is not freed.
+		 */
+		clear_page_dirty(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);
+
+int block_sync_page(struct page *page)
+{
+	struct address_space *mapping;
+
+	smp_mb();
+	mapping = page_mapping(page);
+	if (mapping)
+		blk_run_backing_dev(mapping->backing_dev_info, page);
+	return 0;
+}
+
+/*
+ * 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 `pdflush' kernel threads fully replace bdflush daemons and this call.
+ */
+asmlinkage long sys_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 kmem_cache_t *bh_cachep;
+
+/*
+ * Once the number of bh's in the machine exceeds this level, we start
+ * stripping them in writeback.
+ */
+static int 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 (__get_cpu_var(bh_accounting).ratelimit++ < 4096)
+		return;
+	__get_cpu_var(bh_accounting).ratelimit = 0;
+	for_each_cpu(i)
+		tot += per_cpu(bh_accounting, i).nr;
+	buffer_heads_over_limit = (tot > max_buffer_heads);
+}
+	
+struct buffer_head *alloc_buffer_head(unsigned int __nocast gfp_flags)
+{
+	struct buffer_head *ret = kmem_cache_alloc(bh_cachep, gfp_flags);
+	if (ret) {
+		preempt_disable();
+		__get_cpu_var(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();
+	__get_cpu_var(bh_accounting).nr--;
+	recalc_bh_state();
+	preempt_enable();
+}
+EXPORT_SYMBOL(free_buffer_head);
+
+static void
+init_buffer_head(void *data, kmem_cache_t *cachep, unsigned long flags)
+{
+	if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
+			    SLAB_CTOR_CONSTRUCTOR) {
+		struct buffer_head * bh = (struct buffer_head *)data;
+
+		memset(bh, 0, sizeof(*bh));
+		INIT_LIST_HEAD(&bh->b_assoc_buffers);
+	}
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+static void buffer_exit_cpu(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;
+	}
+}
+
+static int buffer_cpu_notify(struct notifier_block *self,
+			      unsigned long action, void *hcpu)
+{
+	if (action == CPU_DEAD)
+		buffer_exit_cpu((unsigned long)hcpu);
+	return NOTIFY_OK;
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
+void __init buffer_init(void)
+{
+	int nrpages;
+
+	bh_cachep = kmem_cache_create("buffer_head",
+			sizeof(struct buffer_head), 0,
+			SLAB_PANIC, init_buffer_head, 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));
+	hotcpu_notifier(buffer_cpu_notify, 0);
+}
+
+EXPORT_SYMBOL(__bforget);
+EXPORT_SYMBOL(__brelse);
+EXPORT_SYMBOL(__wait_on_buffer);
+EXPORT_SYMBOL(block_commit_write);
+EXPORT_SYMBOL(block_prepare_write);
+EXPORT_SYMBOL(block_read_full_page);
+EXPORT_SYMBOL(block_sync_page);
+EXPORT_SYMBOL(block_truncate_page);
+EXPORT_SYMBOL(block_write_full_page);
+EXPORT_SYMBOL(cont_prepare_write);
+EXPORT_SYMBOL(end_buffer_async_write);
+EXPORT_SYMBOL(end_buffer_read_sync);
+EXPORT_SYMBOL(end_buffer_write_sync);
+EXPORT_SYMBOL(file_fsync);
+EXPORT_SYMBOL(fsync_bdev);
+EXPORT_SYMBOL(generic_block_bmap);
+EXPORT_SYMBOL(generic_commit_write);
+EXPORT_SYMBOL(generic_cont_expand);
+EXPORT_SYMBOL(init_buffer);
+EXPORT_SYMBOL(invalidate_bdev);
+EXPORT_SYMBOL(ll_rw_block);
+EXPORT_SYMBOL(mark_buffer_dirty);
+EXPORT_SYMBOL(submit_bh);
+EXPORT_SYMBOL(sync_dirty_buffer);
+EXPORT_SYMBOL(unlock_buffer);