diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
new file mode 100644
index 0000000..f2fb40c
--- /dev/null
+++ b/fs/ocfs2/extent_map.c
@@ -0,0 +1,994 @@
+/* -*- mode: c; c-basic-offset: 8; -*-
+ * vim: noexpandtab sw=8 ts=8 sts=0:
+ *
+ * extent_map.c
+ *
+ * In-memory extent map for OCFS2.  Man, this code was prettier in
+ * the library.
+ *
+ * Copyright (C) 2004 Oracle.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License, version 2,  as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/rbtree.h>
+
+#define MLOG_MASK_PREFIX ML_EXTENT_MAP
+#include <cluster/masklog.h>
+
+#include "ocfs2.h"
+
+#include "extent_map.h"
+#include "inode.h"
+#include "super.h"
+
+#include "buffer_head_io.h"
+
+
+/*
+ * SUCK SUCK SUCK
+ * Our headers are so bad that struct ocfs2_extent_map is in ocfs.h
+ */
+
+struct ocfs2_extent_map_entry {
+	struct rb_node e_node;
+	int e_tree_depth;
+	struct ocfs2_extent_rec e_rec;
+};
+
+struct ocfs2_em_insert_context {
+	int need_left;
+	int need_right;
+	struct ocfs2_extent_map_entry *new_ent;
+	struct ocfs2_extent_map_entry *old_ent;
+	struct ocfs2_extent_map_entry *left_ent;
+	struct ocfs2_extent_map_entry *right_ent;
+};
+
+static kmem_cache_t *ocfs2_em_ent_cachep = NULL;
+
+
+static struct ocfs2_extent_map_entry *
+ocfs2_extent_map_lookup(struct ocfs2_extent_map *em,
+			u32 cpos, u32 clusters,
+			struct rb_node ***ret_p,
+			struct rb_node **ret_parent);
+static int ocfs2_extent_map_insert(struct inode *inode,
+				   struct ocfs2_extent_rec *rec,
+				   int tree_depth);
+static int ocfs2_extent_map_insert_entry(struct ocfs2_extent_map *em,
+					 struct ocfs2_extent_map_entry *ent);
+static int ocfs2_extent_map_find_leaf(struct inode *inode,
+				      u32 cpos, u32 clusters,
+				      struct ocfs2_extent_list *el);
+static int ocfs2_extent_map_lookup_read(struct inode *inode,
+					u32 cpos, u32 clusters,
+					struct ocfs2_extent_map_entry **ret_ent);
+static int ocfs2_extent_map_try_insert(struct inode *inode,
+				       struct ocfs2_extent_rec *rec,
+				       int tree_depth,
+				       struct ocfs2_em_insert_context *ctxt);
+
+/* returns 1 only if the rec contains all the given clusters -- that is that
+ * rec's cpos is <= the cluster cpos and that the rec endpoint (cpos +
+ * clusters) is >= the argument's endpoint */
+static int ocfs2_extent_rec_contains_clusters(struct ocfs2_extent_rec *rec,
+					      u32 cpos, u32 clusters)
+{
+	if (le32_to_cpu(rec->e_cpos) > cpos)
+		return 0;
+	if (cpos + clusters > le32_to_cpu(rec->e_cpos) + 
+			      le32_to_cpu(rec->e_clusters))
+		return 0;
+	return 1;
+}
+
+
+/*
+ * Find an entry in the tree that intersects the region passed in.
+ * Note that this will find straddled intervals, it is up to the
+ * callers to enforce any boundary conditions.
+ *
+ * Callers must hold ip_lock.  This lookup is not guaranteed to return
+ * a tree_depth 0 match, and as such can race inserts if the lock
+ * were not held.
+ *
+ * The rb_node garbage lets insertion share the search.  Trivial
+ * callers pass NULL.
+ */
+static struct ocfs2_extent_map_entry *
+ocfs2_extent_map_lookup(struct ocfs2_extent_map *em,
+			u32 cpos, u32 clusters,
+			struct rb_node ***ret_p,
+			struct rb_node **ret_parent)
+{
+	struct rb_node **p = &em->em_extents.rb_node;
+	struct rb_node *parent = NULL;
+	struct ocfs2_extent_map_entry *ent = NULL;
+
+	while (*p)
+	{
+		parent = *p;
+		ent = rb_entry(parent, struct ocfs2_extent_map_entry,
+			       e_node);
+		if ((cpos + clusters) <= le32_to_cpu(ent->e_rec.e_cpos)) {
+			p = &(*p)->rb_left;
+			ent = NULL;
+		} else if (cpos >= (le32_to_cpu(ent->e_rec.e_cpos) +
+				    le32_to_cpu(ent->e_rec.e_clusters))) {
+			p = &(*p)->rb_right;
+			ent = NULL;
+		} else
+			break;
+	}
+
+	if (ret_p != NULL)
+		*ret_p = p;
+	if (ret_parent != NULL)
+		*ret_parent = parent;
+	return ent;
+}
+
+/*
+ * Find the leaf containing the interval we want.  While we're on our
+ * way down the tree, fill in every record we see at any depth, because
+ * we might want it later.
+ *
+ * Note that this code is run without ip_lock.  That's because it
+ * sleeps while reading.  If someone is also filling the extent list at
+ * the same time we are, we might have to restart.
+ */
+static int ocfs2_extent_map_find_leaf(struct inode *inode,
+				      u32 cpos, u32 clusters,
+				      struct ocfs2_extent_list *el)
+{
+	int i, ret;
+	struct buffer_head *eb_bh = NULL;
+	u64 blkno;
+	u32 rec_end;
+	struct ocfs2_extent_block *eb;
+	struct ocfs2_extent_rec *rec;
+
+	/*
+	 * The bh data containing the el cannot change here, because
+	 * we hold alloc_sem.  So we can do this without other
+	 * locks.
+	 */
+	while (el->l_tree_depth)
+	{
+		blkno = 0;
+		for (i = 0; i < le16_to_cpu(el->l_next_free_rec); i++) {
+			rec = &el->l_recs[i];
+			rec_end = (le32_to_cpu(rec->e_cpos) +
+				   le32_to_cpu(rec->e_clusters));
+
+			ret = -EBADR;
+			if (rec_end > OCFS2_I(inode)->ip_clusters) {
+				mlog_errno(ret);
+				goto out_free;
+			}
+
+			if (rec_end <= cpos) {
+				ret = ocfs2_extent_map_insert(inode, rec,
+						le16_to_cpu(el->l_tree_depth));
+				if (ret && (ret != -EEXIST)) {
+					mlog_errno(ret);
+					goto out_free;
+				}
+				continue;
+			}
+			if ((cpos + clusters) <= le32_to_cpu(rec->e_cpos)) {
+				ret = ocfs2_extent_map_insert(inode, rec,
+						le16_to_cpu(el->l_tree_depth));
+				if (ret && (ret != -EEXIST)) {
+					mlog_errno(ret);
+					goto out_free;
+				}
+				continue;
+			}
+
+			/*
+			 * We've found a record that matches our
+			 * interval.  We don't insert it because we're
+			 * about to traverse it.
+			 */
+
+			/* Check to see if we're stradling */
+			ret = -ESRCH;
+			if (!ocfs2_extent_rec_contains_clusters(rec,
+							        cpos,
+								clusters)) {
+				mlog_errno(ret);
+				goto out_free;
+			}
+
+			/*
+			 * If we've already found a record, the el has
+			 * two records covering the same interval.
+			 * EEEK!
+			 */
+			ret = -EBADR;
+			if (blkno) {
+				mlog_errno(ret);
+				goto out_free;
+			}
+
+			blkno = le64_to_cpu(rec->e_blkno);
+		}
+
+		/*
+		 * We don't support holes, and we're still up
+		 * in the branches, so we'd better have found someone
+		 */
+		ret = -EBADR;
+		if (!blkno) {
+			mlog_errno(ret);
+			goto out_free;
+		}
+
+		if (eb_bh) {
+			brelse(eb_bh);
+			eb_bh = NULL;
+		}
+		ret = ocfs2_read_block(OCFS2_SB(inode->i_sb),
+				       blkno, &eb_bh, OCFS2_BH_CACHED,
+				       inode);
+		if (ret) {
+			mlog_errno(ret);
+			goto out_free;
+		}
+		eb = (struct ocfs2_extent_block *)eb_bh->b_data;
+		if (!OCFS2_IS_VALID_EXTENT_BLOCK(eb)) {
+			OCFS2_RO_ON_INVALID_EXTENT_BLOCK(inode->i_sb, eb);
+			ret = -EIO;
+			goto out_free;
+		}
+		el = &eb->h_list;
+	}
+
+	if (el->l_tree_depth)
+		BUG();
+
+	for (i = 0; i < le16_to_cpu(el->l_next_free_rec); i++) {
+		rec = &el->l_recs[i];
+		ret = ocfs2_extent_map_insert(inode, rec,
+					      le16_to_cpu(el->l_tree_depth));
+		if (ret) {
+			mlog_errno(ret);
+			goto out_free;
+		}
+	}
+
+	ret = 0;
+
+out_free:
+	if (eb_bh)
+		brelse(eb_bh);
+
+	return ret;
+}
+
+/*
+ * This lookup actually will read from disk.  It has one invariant:
+ * It will never re-traverse blocks.  This means that all inserts should
+ * be new regions or more granular regions (both allowed by insert).
+ */
+static int ocfs2_extent_map_lookup_read(struct inode *inode,
+					u32 cpos,
+					u32 clusters,
+					struct ocfs2_extent_map_entry **ret_ent)
+{
+	int ret;
+	u64 blkno;
+	struct ocfs2_extent_map *em = &OCFS2_I(inode)->ip_map;
+	struct ocfs2_extent_map_entry *ent;
+	struct buffer_head *bh = NULL;
+	struct ocfs2_extent_block *eb;
+	struct ocfs2_dinode *di;
+	struct ocfs2_extent_list *el;
+
+	spin_lock(&OCFS2_I(inode)->ip_lock);
+	ent = ocfs2_extent_map_lookup(em, cpos, clusters, NULL, NULL);
+	if (ent) {
+		if (!ent->e_tree_depth) {
+			spin_unlock(&OCFS2_I(inode)->ip_lock);
+			*ret_ent = ent;
+			return 0;
+		}
+		blkno = le64_to_cpu(ent->e_rec.e_blkno);
+		spin_unlock(&OCFS2_I(inode)->ip_lock);
+
+		ret = ocfs2_read_block(OCFS2_SB(inode->i_sb), blkno, &bh,
+				       OCFS2_BH_CACHED, inode);
+		if (ret) {
+			mlog_errno(ret);
+			if (bh)
+				brelse(bh);
+			return ret;
+		}
+		eb = (struct ocfs2_extent_block *)bh->b_data;
+		if (!OCFS2_IS_VALID_EXTENT_BLOCK(eb)) {
+			OCFS2_RO_ON_INVALID_EXTENT_BLOCK(inode->i_sb, eb);
+			brelse(bh);
+			return -EIO;
+		}
+		el = &eb->h_list;
+	} else {
+		spin_unlock(&OCFS2_I(inode)->ip_lock);
+
+		ret = ocfs2_read_block(OCFS2_SB(inode->i_sb),
+				       OCFS2_I(inode)->ip_blkno, &bh,
+				       OCFS2_BH_CACHED, inode);
+		if (ret) {
+			mlog_errno(ret);
+			if (bh)
+				brelse(bh);
+			return ret;
+		}
+		di = (struct ocfs2_dinode *)bh->b_data;
+		if (!OCFS2_IS_VALID_DINODE(di)) {
+			brelse(bh);
+			OCFS2_RO_ON_INVALID_DINODE(inode->i_sb, di);
+			return -EIO;
+		}
+		el = &di->id2.i_list;
+	}
+
+	ret = ocfs2_extent_map_find_leaf(inode, cpos, clusters, el);
+	brelse(bh);
+	if (ret) {
+		mlog_errno(ret);
+		return ret;
+	}
+
+	ent = ocfs2_extent_map_lookup(em, cpos, clusters, NULL, NULL);
+	if (!ent) {
+		ret = -ESRCH;
+		mlog_errno(ret);
+		return ret;
+	}
+
+	if (ent->e_tree_depth)
+		BUG();  /* FIXME: Make sure this isn't a corruption */
+
+	*ret_ent = ent;
+
+	return 0;
+}
+
+/*
+ * Callers must hold ip_lock.  This can insert pieces of the tree,
+ * thus racing lookup if the lock weren't held.
+ */
+static int ocfs2_extent_map_insert_entry(struct ocfs2_extent_map *em,
+					 struct ocfs2_extent_map_entry *ent)
+{
+	struct rb_node **p, *parent;
+	struct ocfs2_extent_map_entry *old_ent;
+
+	old_ent = ocfs2_extent_map_lookup(em, le32_to_cpu(ent->e_rec.e_cpos),
+					  le32_to_cpu(ent->e_rec.e_clusters),
+					  &p, &parent);
+	if (old_ent)
+		return -EEXIST;
+
+	rb_link_node(&ent->e_node, parent, p);
+	rb_insert_color(&ent->e_node, &em->em_extents);
+
+	return 0;
+}
+
+
+/*
+ * Simple rule: on any return code other than -EAGAIN, anything left
+ * in the insert_context will be freed.
+ */
+static int ocfs2_extent_map_try_insert(struct inode *inode,
+				       struct ocfs2_extent_rec *rec,
+				       int tree_depth,
+				       struct ocfs2_em_insert_context *ctxt)
+{
+	int ret;
+	struct ocfs2_extent_map *em = &OCFS2_I(inode)->ip_map;
+	struct ocfs2_extent_map_entry *old_ent;
+
+	ctxt->need_left = 0;
+	ctxt->need_right = 0;
+	ctxt->old_ent = NULL;
+
+	spin_lock(&OCFS2_I(inode)->ip_lock);
+	ret = ocfs2_extent_map_insert_entry(em, ctxt->new_ent);
+	if (!ret) {
+		ctxt->new_ent = NULL;
+		goto out_unlock;
+	}
+
+	old_ent = ocfs2_extent_map_lookup(em, le32_to_cpu(rec->e_cpos),
+					  le32_to_cpu(rec->e_clusters), NULL,
+					  NULL);
+
+	if (!old_ent)
+		BUG();
+
+	ret = -EEXIST;
+	if (old_ent->e_tree_depth < tree_depth)
+		goto out_unlock;
+
+	if (old_ent->e_tree_depth == tree_depth) {
+		if (!memcmp(rec, &old_ent->e_rec,
+			    sizeof(struct ocfs2_extent_rec)))
+			ret = 0;
+
+		/* FIXME: Should this be ESRCH/EBADR??? */
+		goto out_unlock;
+	}
+
+	/*
+	 * We do it in this order specifically so that no actual tree
+	 * changes occur until we have all the pieces we need.  We
+	 * don't want malloc failures to leave an inconsistent tree.
+	 * Whenever we drop the lock, another process could be
+	 * inserting.  Also note that, if another process just beat us
+	 * to an insert, we might not need the same pieces we needed
+	 * the first go round.  In the end, the pieces we need will
+	 * be used, and the pieces we don't will be freed.
+	 */
+	ctxt->need_left = !!(le32_to_cpu(rec->e_cpos) >
+			     le32_to_cpu(old_ent->e_rec.e_cpos));
+	ctxt->need_right = !!((le32_to_cpu(old_ent->e_rec.e_cpos) +
+			       le32_to_cpu(old_ent->e_rec.e_clusters)) >
+			      (le32_to_cpu(rec->e_cpos) + le32_to_cpu(rec->e_clusters)));
+	ret = -EAGAIN;
+	if (ctxt->need_left) {
+		if (!ctxt->left_ent)
+			goto out_unlock;
+		*(ctxt->left_ent) = *old_ent;
+		ctxt->left_ent->e_rec.e_clusters =
+			cpu_to_le32(le32_to_cpu(rec->e_cpos) -
+				    le32_to_cpu(ctxt->left_ent->e_rec.e_cpos));
+	}
+	if (ctxt->need_right) {
+		if (!ctxt->right_ent)
+			goto out_unlock;
+		*(ctxt->right_ent) = *old_ent;
+		ctxt->right_ent->e_rec.e_cpos =
+			cpu_to_le32(le32_to_cpu(rec->e_cpos) +
+				    le32_to_cpu(rec->e_clusters));
+		ctxt->right_ent->e_rec.e_clusters =
+			cpu_to_le32((le32_to_cpu(old_ent->e_rec.e_cpos) +
+				     le32_to_cpu(old_ent->e_rec.e_clusters)) -
+				    le32_to_cpu(ctxt->right_ent->e_rec.e_cpos));
+	}
+
+	rb_erase(&old_ent->e_node, &em->em_extents);
+	/* Now that he's erased, set him up for deletion */
+	ctxt->old_ent = old_ent;
+
+	if (ctxt->need_left) {
+		ret = ocfs2_extent_map_insert_entry(em,
+						    ctxt->left_ent);
+		if (ret)
+			goto out_unlock;
+		ctxt->left_ent = NULL;
+	}
+
+	if (ctxt->need_right) {
+		ret = ocfs2_extent_map_insert_entry(em,
+						    ctxt->right_ent);
+		if (ret)
+			goto out_unlock;
+		ctxt->right_ent = NULL;
+	}
+
+	ret = ocfs2_extent_map_insert_entry(em, ctxt->new_ent);
+
+	if (!ret)
+		ctxt->new_ent = NULL;
+
+out_unlock:
+	spin_unlock(&OCFS2_I(inode)->ip_lock);
+
+	return ret;
+}
+
+
+static int ocfs2_extent_map_insert(struct inode *inode,
+				   struct ocfs2_extent_rec *rec,
+				   int tree_depth)
+{
+	int ret;
+	struct ocfs2_em_insert_context ctxt = {0, };
+
+	if ((le32_to_cpu(rec->e_cpos) + le32_to_cpu(rec->e_clusters)) >
+	    OCFS2_I(inode)->ip_map.em_clusters) {
+		ret = -EBADR;
+		mlog_errno(ret);
+		return ret;
+	}
+
+	/* Zero e_clusters means a truncated tail record.  It better be EOF */
+	if (!rec->e_clusters) {
+		if ((le32_to_cpu(rec->e_cpos) + le32_to_cpu(rec->e_clusters)) !=
+		    OCFS2_I(inode)->ip_map.em_clusters) {
+			ret = -EBADR;
+			mlog_errno(ret);
+			return ret;
+		}
+
+		/* Ignore the truncated tail */
+		return 0;
+	}
+
+	ret = -ENOMEM;
+	ctxt.new_ent = kmem_cache_alloc(ocfs2_em_ent_cachep,
+					GFP_KERNEL);
+	if (!ctxt.new_ent) {
+		mlog_errno(ret);
+		return ret;
+	}
+
+	ctxt.new_ent->e_rec = *rec;
+	ctxt.new_ent->e_tree_depth = tree_depth;
+
+	do {
+		ret = -ENOMEM;
+		if (ctxt.need_left && !ctxt.left_ent) {
+			ctxt.left_ent =
+				kmem_cache_alloc(ocfs2_em_ent_cachep,
+						 GFP_KERNEL);
+			if (!ctxt.left_ent)
+				break;
+		}
+		if (ctxt.need_right && !ctxt.right_ent) {
+			ctxt.right_ent =
+				kmem_cache_alloc(ocfs2_em_ent_cachep,
+						 GFP_KERNEL);
+			if (!ctxt.right_ent)
+				break;
+		}
+
+		ret = ocfs2_extent_map_try_insert(inode, rec,
+						  tree_depth, &ctxt);
+	} while (ret == -EAGAIN);
+
+	if (ret < 0)
+		mlog_errno(ret);
+
+	if (ctxt.left_ent)
+		kmem_cache_free(ocfs2_em_ent_cachep, ctxt.left_ent);
+	if (ctxt.right_ent)
+		kmem_cache_free(ocfs2_em_ent_cachep, ctxt.right_ent);
+	if (ctxt.old_ent)
+		kmem_cache_free(ocfs2_em_ent_cachep, ctxt.old_ent);
+	if (ctxt.new_ent)
+		kmem_cache_free(ocfs2_em_ent_cachep, ctxt.new_ent);
+
+	return ret;
+}
+
+/*
+ * Append this record to the tail of the extent map.  It must be
+ * tree_depth 0.  The record might be an extension of an existing
+ * record, and as such that needs to be handled.  eg:
+ *
+ * Existing record in the extent map:
+ *
+ *	cpos = 10, len = 10
+ * 	|---------|
+ *
+ * New Record:
+ *
+ *	cpos = 10, len = 20
+ * 	|------------------|
+ *
+ * The passed record is the new on-disk record.  The new_clusters value
+ * is how many clusters were added to the file.  If the append is a
+ * contiguous append, the new_clusters has been added to
+ * rec->e_clusters.  If the append is an entirely new extent, then
+ * rec->e_clusters is == new_clusters.
+ */
+int ocfs2_extent_map_append(struct inode *inode,
+			    struct ocfs2_extent_rec *rec,
+			    u32 new_clusters)
+{
+	int ret;
+	struct ocfs2_extent_map *em = &OCFS2_I(inode)->ip_map;
+	struct ocfs2_extent_map_entry *ent;
+	struct ocfs2_extent_rec *old;
+
+	BUG_ON(!new_clusters);
+	BUG_ON(le32_to_cpu(rec->e_clusters) < new_clusters);
+
+	if (em->em_clusters < OCFS2_I(inode)->ip_clusters) {
+		/*
+		 * Size changed underneath us on disk.  Drop any
+		 * straddling records and update our idea of
+		 * i_clusters
+		 */
+		ocfs2_extent_map_drop(inode, em->em_clusters - 1);
+		em->em_clusters = OCFS2_I(inode)->ip_clusters;
+	}
+
+	mlog_bug_on_msg((le32_to_cpu(rec->e_cpos) +
+			 le32_to_cpu(rec->e_clusters)) !=
+			(em->em_clusters + new_clusters),
+			"Inode %"MLFu64":\n"
+			"rec->e_cpos = %u + rec->e_clusters = %u = %u\n"
+			"em->em_clusters = %u + new_clusters = %u = %u\n",
+			OCFS2_I(inode)->ip_blkno,
+			le32_to_cpu(rec->e_cpos), le32_to_cpu(rec->e_clusters),
+			le32_to_cpu(rec->e_cpos) + le32_to_cpu(rec->e_clusters),
+			em->em_clusters, new_clusters,
+			em->em_clusters + new_clusters);
+
+	em->em_clusters += new_clusters;
+
+	ret = -ENOENT;
+	if (le32_to_cpu(rec->e_clusters) > new_clusters) {
+		/* This is a contiguous append */
+		ent = ocfs2_extent_map_lookup(em, le32_to_cpu(rec->e_cpos), 1,
+					      NULL, NULL);
+		if (ent) {
+			old = &ent->e_rec;
+			BUG_ON((le32_to_cpu(rec->e_cpos) +
+				le32_to_cpu(rec->e_clusters)) !=
+				 (le32_to_cpu(old->e_cpos) +
+				  le32_to_cpu(old->e_clusters) +
+				  new_clusters));
+			if (ent->e_tree_depth == 0) {
+				BUG_ON(le32_to_cpu(old->e_cpos) !=
+				       le32_to_cpu(rec->e_cpos));
+				BUG_ON(le64_to_cpu(old->e_blkno) !=
+				       le64_to_cpu(rec->e_blkno));
+				ret = 0;
+			}
+			/*
+			 * Let non-leafs fall through as -ENOENT to
+			 * force insertion of the new leaf.
+			 */
+			le32_add_cpu(&old->e_clusters, new_clusters);
+		}
+	}
+
+	if (ret == -ENOENT)
+		ret = ocfs2_extent_map_insert(inode, rec, 0);
+	if (ret < 0)
+		mlog_errno(ret);
+	return ret;
+}
+
+#if 0
+/* Code here is included but defined out as it completes the extent
+ * map api and may be used in the future. */
+
+/*
+ * Look up the record containing this cluster offset.  This record is
+ * part of the extent map.  Do not free it.  Any changes you make to
+ * it will reflect in the extent map.  So, if your last extent
+ * is (cpos = 10, clusters = 10) and you truncate the file by 5
+ * clusters, you can do:
+ *
+ * ret = ocfs2_extent_map_get_rec(em, orig_size - 5, &rec);
+ * rec->e_clusters -= 5;
+ *
+ * The lookup does not read from disk.  If the map isn't filled in for
+ * an entry, you won't find it.
+ *
+ * Also note that the returned record is valid until alloc_sem is
+ * dropped.  After that, truncate and extend can happen.  Caveat Emptor.
+ */
+int ocfs2_extent_map_get_rec(struct inode *inode, u32 cpos,
+			     struct ocfs2_extent_rec **rec,
+			     int *tree_depth)
+{
+	int ret = -ENOENT;
+	struct ocfs2_extent_map *em = &OCFS2_I(inode)->ip_map;
+	struct ocfs2_extent_map_entry *ent;
+
+	*rec = NULL;
+
+	if (cpos >= OCFS2_I(inode)->ip_clusters)
+		return -EINVAL;
+
+	if (cpos >= em->em_clusters) {
+		/*
+		 * Size changed underneath us on disk.  Drop any
+		 * straddling records and update our idea of
+		 * i_clusters
+		 */
+		ocfs2_extent_map_drop(inode, em->em_clusters - 1);
+		em->em_clusters = OCFS2_I(inode)->ip_clusters ;
+	}
+
+	ent = ocfs2_extent_map_lookup(&OCFS2_I(inode)->ip_map, cpos, 1,
+				      NULL, NULL);
+
+	if (ent) {
+		*rec = &ent->e_rec;
+		if (tree_depth)
+			*tree_depth = ent->e_tree_depth;
+		ret = 0;
+	}
+
+	return ret;
+}
+
+int ocfs2_extent_map_get_clusters(struct inode *inode,
+				  u32 v_cpos, int count,
+				  u32 *p_cpos, int *ret_count)
+{
+	int ret;
+	u32 coff, ccount;
+	struct ocfs2_extent_map *em = &OCFS2_I(inode)->ip_map;
+	struct ocfs2_extent_map_entry *ent = NULL;
+
+	*p_cpos = ccount = 0;
+
+	if ((v_cpos + count) > OCFS2_I(inode)->ip_clusters)
+		return -EINVAL;
+
+	if ((v_cpos + count) > em->em_clusters) {
+		/*
+		 * Size changed underneath us on disk.  Drop any
+		 * straddling records and update our idea of
+		 * i_clusters
+		 */
+		ocfs2_extent_map_drop(inode, em->em_clusters - 1);
+		em->em_clusters = OCFS2_I(inode)->ip_clusters;
+	}
+
+
+	ret = ocfs2_extent_map_lookup_read(inode, v_cpos, count, &ent);
+	if (ret)
+		return ret;
+
+	if (ent) {
+		/* We should never find ourselves straddling an interval */
+		if (!ocfs2_extent_rec_contains_clusters(&ent->e_rec,
+							v_cpos,
+							count))
+			return -ESRCH;
+
+		coff = v_cpos - le32_to_cpu(ent->e_rec.e_cpos);
+		*p_cpos = ocfs2_blocks_to_clusters(inode->i_sb,
+				le64_to_cpu(ent->e_rec.e_blkno)) +
+			  coff;
+
+		if (ret_count)
+			*ret_count = le32_to_cpu(ent->e_rec.e_clusters) - coff;
+
+		return 0;
+	}
+
+
+	return -ENOENT;
+}
+
+#endif  /*  0  */
+
+int ocfs2_extent_map_get_blocks(struct inode *inode,
+				u64 v_blkno, int count,
+				u64 *p_blkno, int *ret_count)
+{
+	int ret;
+	u64 boff;
+	u32 cpos, clusters;
+	int bpc = ocfs2_clusters_to_blocks(inode->i_sb, 1);
+	struct ocfs2_extent_map_entry *ent = NULL;
+	struct ocfs2_extent_map *em = &OCFS2_I(inode)->ip_map;
+	struct ocfs2_extent_rec *rec;
+
+	*p_blkno = 0;
+
+	cpos = ocfs2_blocks_to_clusters(inode->i_sb, v_blkno);
+	clusters = ocfs2_blocks_to_clusters(inode->i_sb,
+					    (u64)count + bpc - 1);
+	if ((cpos + clusters) > OCFS2_I(inode)->ip_clusters) {
+		ret = -EINVAL;
+		mlog_errno(ret);
+		return ret;
+	}
+
+	if ((cpos + clusters) > em->em_clusters) {
+		/*
+		 * Size changed underneath us on disk.  Drop any
+		 * straddling records and update our idea of
+		 * i_clusters
+		 */
+		ocfs2_extent_map_drop(inode, em->em_clusters - 1);
+		em->em_clusters = OCFS2_I(inode)->ip_clusters;
+	}
+
+	ret = ocfs2_extent_map_lookup_read(inode, cpos, clusters, &ent);
+	if (ret) {
+		mlog_errno(ret);
+		return ret;
+	}
+
+	if (ent)
+	{
+		rec = &ent->e_rec;
+
+		/* We should never find ourselves straddling an interval */
+		if (!ocfs2_extent_rec_contains_clusters(rec, cpos, clusters)) {
+			ret = -ESRCH;
+			mlog_errno(ret);
+			return ret;
+		}
+
+		boff = ocfs2_clusters_to_blocks(inode->i_sb, cpos -
+						le32_to_cpu(rec->e_cpos));
+		boff += (v_blkno & (u64)(bpc - 1));
+		*p_blkno = le64_to_cpu(rec->e_blkno) + boff;
+
+		if (ret_count) {
+			*ret_count = ocfs2_clusters_to_blocks(inode->i_sb,
+					le32_to_cpu(rec->e_clusters)) - boff;
+		}
+
+		return 0;
+	}
+
+	return -ENOENT;
+}
+
+int ocfs2_extent_map_init(struct inode *inode)
+{
+	struct ocfs2_extent_map *em = &OCFS2_I(inode)->ip_map;
+
+	em->em_extents = RB_ROOT;
+	em->em_clusters = 0;
+
+	return 0;
+}
+
+/* Needs the lock */
+static void __ocfs2_extent_map_drop(struct inode *inode,
+				    u32 new_clusters,
+				    struct rb_node **free_head,
+				    struct ocfs2_extent_map_entry **tail_ent)
+{
+	struct rb_node *node, *next;
+	struct ocfs2_extent_map *em = &OCFS2_I(inode)->ip_map;
+	struct ocfs2_extent_map_entry *ent;
+
+	*free_head = NULL;
+
+	ent = NULL;
+	node = rb_last(&em->em_extents);
+	while (node)
+	{
+		next = rb_prev(node);
+
+		ent = rb_entry(node, struct ocfs2_extent_map_entry,
+			       e_node);
+		if (le32_to_cpu(ent->e_rec.e_cpos) < new_clusters)
+			break;
+
+		rb_erase(&ent->e_node, &em->em_extents);
+
+		node->rb_right = *free_head;
+		*free_head = node;
+
+		ent = NULL;
+		node = next;
+	}
+
+	/* Do we have an entry straddling new_clusters? */
+	if (tail_ent) {
+		if (ent &&
+		    ((le32_to_cpu(ent->e_rec.e_cpos) +
+		      le32_to_cpu(ent->e_rec.e_clusters)) > new_clusters))
+			*tail_ent = ent;
+		else
+			*tail_ent = NULL;
+	}
+}
+
+static void __ocfs2_extent_map_drop_cleanup(struct rb_node *free_head)
+{
+	struct rb_node *node;
+	struct ocfs2_extent_map_entry *ent;
+
+	while (free_head) {
+		node = free_head;
+		free_head = node->rb_right;
+
+		ent = rb_entry(node, struct ocfs2_extent_map_entry,
+			       e_node);
+		kmem_cache_free(ocfs2_em_ent_cachep, ent);
+	}
+}
+
+/*
+ * Remove all entries past new_clusters, inclusive of an entry that
+ * contains new_clusters.  This is effectively a cache forget.
+ *
+ * If you want to also clip the last extent by some number of clusters,
+ * you need to call ocfs2_extent_map_trunc().
+ * This code does not check or modify ip_clusters.
+ */
+int ocfs2_extent_map_drop(struct inode *inode, u32 new_clusters)
+{
+	struct rb_node *free_head = NULL;
+	struct ocfs2_extent_map *em = &OCFS2_I(inode)->ip_map;
+	struct ocfs2_extent_map_entry *ent;
+
+	spin_lock(&OCFS2_I(inode)->ip_lock);
+
+	__ocfs2_extent_map_drop(inode, new_clusters, &free_head, &ent);
+
+	if (ent) {
+		rb_erase(&ent->e_node, &em->em_extents);
+		ent->e_node.rb_right = free_head;
+		free_head = &ent->e_node;
+	}
+
+	spin_unlock(&OCFS2_I(inode)->ip_lock);
+
+	if (free_head)
+		__ocfs2_extent_map_drop_cleanup(free_head);
+
+	return 0;
+}
+
+/*
+ * Remove all entries past new_clusters and also clip any extent
+ * straddling new_clusters, if there is one.  This does not check
+ * or modify ip_clusters
+ */
+int ocfs2_extent_map_trunc(struct inode *inode, u32 new_clusters)
+{
+	struct rb_node *free_head = NULL;
+	struct ocfs2_extent_map_entry *ent = NULL;
+
+	spin_lock(&OCFS2_I(inode)->ip_lock);
+
+	__ocfs2_extent_map_drop(inode, new_clusters, &free_head, &ent);
+
+	if (ent)
+		ent->e_rec.e_clusters = cpu_to_le32(new_clusters -
+					       le32_to_cpu(ent->e_rec.e_cpos));
+
+	OCFS2_I(inode)->ip_map.em_clusters = new_clusters;
+
+	spin_unlock(&OCFS2_I(inode)->ip_lock);
+
+	if (free_head)
+		__ocfs2_extent_map_drop_cleanup(free_head);
+
+	return 0;
+}
+
+int __init init_ocfs2_extent_maps(void)
+{
+	ocfs2_em_ent_cachep =
+		kmem_cache_create("ocfs2_em_ent",
+				  sizeof(struct ocfs2_extent_map_entry),
+				  0, SLAB_HWCACHE_ALIGN, NULL, NULL);
+	if (!ocfs2_em_ent_cachep)
+		return -ENOMEM;
+
+	return 0;
+}
+
+void __exit exit_ocfs2_extent_maps(void)
+{
+	kmem_cache_destroy(ocfs2_em_ent_cachep);
+}