diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
index 6336021..df065dd 100644
--- a/fs/btrfs/Makefile
+++ b/fs/btrfs/Makefile
@@ -4,8 +4,8 @@
 .c.o:
 	$(CC) $(CFLAGS) -c $<
 
-ctree: ctree.o disk-io.h ctree.h disk-io.o radix-tree.o radix-tree.h
-	gcc $(CFLAGS) -o ctree ctree.o disk-io.o radix-tree.o
+ctree: ctree.o disk-io.h ctree.h disk-io.o radix-tree.o radix-tree.h mkfs.o
+	gcc $(CFLAGS) -o ctree ctree.o disk-io.o radix-tree.o mkfs.o
 
 clean:
 	rm ctree *.o
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 6b64f49..2177744 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -5,6 +5,8 @@
 #include "ctree.h"
 #include "disk-io.h"
 
+static int refill_alloc_extent(struct ctree_root *root);
+
 static inline void init_path(struct ctree_path *p)
 {
 	memset(p, 0, sizeof(*p));
@@ -29,7 +31,7 @@
 {
 	unsigned int nr = leaf->header.nritems;
 	if (nr == 0)
-		return ARRAY_SIZE(leaf->data);
+		return sizeof(leaf->data);
 	return leaf->items[nr-1].offset;
 }
 
@@ -421,7 +423,7 @@
 	 * due to splitting.  Once we've done all the splitting required
 	 * do the inserts based on the data in the bal array.
 	 */
-	memset(bal, 0, ARRAY_SIZE(bal));
+	memset(bal, 0, sizeof(bal));
 	while(t && t->node.header.nritems == NODEPTRS_PER_BLOCK) {
 		c = &t->node;
 		if (push_node_left(root, path,
@@ -756,6 +758,7 @@
 	if (leaf_free_space(leaf) < 0)
 		BUG();
 	release_path(root, &path);
+	refill_alloc_extent(root);
 	return 0;
 }
 
@@ -884,6 +887,135 @@
 	return 0;
 }
 
+int next_leaf(struct ctree_root *root, struct ctree_path *path)
+{
+	int slot;
+	int level = 1;
+	u64 blocknr;
+	struct tree_buffer *c;
+	struct tree_buffer *next;
+
+	while(level < MAX_LEVEL) {
+		if (!path->nodes[level])
+			return -1;
+		slot = path->slots[level] + 1;
+		c = path->nodes[level];
+		if (slot >= c->node.header.nritems) {
+			level++;
+			continue;
+		}
+		blocknr = c->node.blockptrs[slot];
+		next = read_tree_block(root, blocknr);
+		break;
+	}
+	path->slots[level] = slot;
+	while(1) {
+		level--;
+		c = path->nodes[level];
+		tree_block_release(root, c);
+		path->nodes[level] = next;
+		path->slots[level] = 0;
+		if (!level)
+			break;
+		next = read_tree_block(root, next->node.blockptrs[0]);
+	}
+	return 0;
+}
+
+int alloc_extent(struct ctree_root *root, u64 num_blocks, u64 search_start,
+		 u64 search_end, u64 owner, struct key *ins)
+{
+	struct ctree_path path;
+	struct key *key;
+	int ret;
+	u64 hole_size = 0;
+	int slot = 0;
+	u64 last_block;
+	int start_found = 0;
+	struct leaf *l;
+	struct extent_item extent_item;
+
+	init_path(&path);
+	ins->objectid = search_start;
+	ins->offset = 0;
+	ins->flags = 0;
+
+	ret = search_slot(root, ins, &path);
+	while (1) {
+		l = &path.nodes[0]->leaf;
+		slot = path.slots[0];
+		if (!l) {
+			// FIXME allocate root
+		}
+		if (slot >= l->header.nritems) {
+			ret = next_leaf(root, &path);
+			if (ret == 0)
+				continue;
+			if (!start_found) {
+				ins->objectid = search_start;
+				ins->offset = num_blocks;
+				hole_size = search_end - search_start;
+				goto insert;
+			}
+			ins->objectid = last_block;
+			ins->offset = num_blocks;
+			hole_size = search_end - last_block;
+			goto insert;
+		}
+		key = &l->items[slot].key;
+		if (start_found) {
+			hole_size = key->objectid - last_block;
+			if (hole_size > num_blocks) {
+				ins->objectid = last_block;
+				ins->offset = num_blocks;
+				goto insert;
+			}
+		} else
+			start_found = 1;
+		last_block = key->objectid + key->offset;
+		path.slots[0]++;
+		printf("last block is not %lu\n", last_block);
+	}
+	// FIXME -ENOSPC
+insert:
+	extent_item.refs = 1;
+	extent_item.owner = owner;
+	ret = insert_item(root, ins, &extent_item, sizeof(extent_item));
+	return ret;
+}
+
+static int refill_alloc_extent(struct ctree_root *root)
+{
+	struct alloc_extent *ae = root->alloc_extent;
+	struct key key;
+	int ret;
+	int min_blocks = MAX_LEVEL * 2;
+
+	printf("refill alloc root %p, numused %lu total %lu\n", root, ae->num_used, ae->num_blocks);
+	if (ae->num_blocks > ae->num_used && ae->num_blocks - ae->num_used >
+	    min_blocks)
+		return 0;
+	ae = root->reserve_extent;
+	if (ae->num_blocks > ae->num_used) {
+		if (root->alloc_extent->num_blocks == 0) {
+			/* we should swap reserve/alloc_extent when alloc
+			 * fills up
+			 */
+			BUG();
+		}
+		if (ae->num_blocks - ae->num_used < min_blocks)
+			BUG();
+		return 0;
+	}
+	// FIXME, this recurses
+	ret = alloc_extent(root->extent_root,
+			   min_blocks * 2, 0, (unsigned long)-1, 0, &key);
+	ae->blocknr = key.objectid;
+	ae->num_blocks = key.offset;
+	ae->num_used = 0;
+	return ret;
+}
+
 void print_leaf(struct leaf *l)
 {
 	int i;
@@ -948,8 +1080,8 @@
 
 /* for testing only */
 int next_key(int i, int max_key) {
-	return rand() % max_key;
-	// return i;
+	// return rand() % max_key;
+	return i;
 }
 
 int main() {
@@ -960,7 +1092,7 @@
 	int i;
 	int num;
 	int ret;
-	int run_size = 25000;
+	int run_size = 256;
 	int max_key = 100000000;
 	int tree_size = 0;
 	struct ctree_path path;
@@ -980,10 +1112,20 @@
 		ins.objectid = num;
 		ins.offset = 0;
 		ins.flags = 0;
+		printf("insert %d\n", i);
 		ret = insert_item(root, &ins, buf, strlen(buf));
 		if (!ret)
 			tree_size++;
+		printf("done insert %d\n", i);
 	}
+	printf("root used: %lu\n", root->alloc_extent->num_used);
+	printf("root tree\n");
+	print_tree(root, root->node);
+	printf("map tree\n");
+	printf("map used: %lu\n", root->extent_root->alloc_extent->num_used);
+	print_tree(root->extent_root, root->extent_root->node);
+	exit(1);
+
 	close_ctree(root);
 	root = open_ctree("dbfile");
 	printf("starting search\n");
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 586bf18..b737925 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1,7 +1,7 @@
 #ifndef __CTREE__
 #define __CTREE__
 
-#define CTREE_BLOCKSIZE 4096
+#define CTREE_BLOCKSIZE 256
 
 struct key {
 	u64 objectid;
@@ -22,18 +22,41 @@
 #define NODEPTRS_PER_BLOCK ((CTREE_BLOCKSIZE - sizeof(struct header)) / \
 			    (sizeof(struct key) + sizeof(u64)))
 
-#define LEVEL_BITS 3
-#define MAX_LEVEL (1 << LEVEL_BITS)
+#define MAX_LEVEL 8
 #define node_level(f) ((f) & (MAX_LEVEL-1))
 #define is_leaf(f) (node_level(f) == 0)
 
 struct tree_buffer;
+
+struct alloc_extent {
+	u64 blocknr;
+	u64 num_blocks;
+	u64 num_used;
+} __attribute__ ((__packed__));
+
 struct ctree_root {
 	struct tree_buffer *node;
+	struct ctree_root *extent_root;
+	struct alloc_extent *alloc_extent;
+	struct alloc_extent *reserve_extent;
 	int fp;
 	struct radix_tree_root cache_radix;
+	struct alloc_extent ai1;
+	struct alloc_extent ai2;
 };
 
+struct ctree_root_info {
+	u64 fsid[2]; /* FS specific uuid */
+	u64 blocknr; /* blocknr of this block */
+	u64 objectid; /* inode number of this root */
+	u64 tree_root; /* the tree root */
+	u32 csum;
+	u32 ham;
+	struct alloc_extent alloc_extent;
+	struct alloc_extent reserve_extent;
+	u64 snapuuid[2]; /* root specific uuid */
+} __attribute__ ((__packed__));
+
 struct item {
 	struct key key;
 	u16 offset;
@@ -55,6 +78,11 @@
 	u64 blockptrs[NODEPTRS_PER_BLOCK];
 } __attribute__ ((__packed__));
 
+struct extent_item {
+	u32 refs;
+	u64 owner;
+} __attribute__ ((__packed__));
+
 struct ctree_path {
 	struct tree_buffer *nodes[MAX_LEVEL];
 	int slots[MAX_LEVEL];
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 8d51a07..653f18a 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -12,25 +12,27 @@
 
 static int allocated_blocks = 0;
 
-struct ctree_header {
-	u64 root_block;
-} __attribute__ ((__packed__));
-
 static int get_free_block(struct ctree_root *root, u64 *block)
 {
 	struct stat st;
 	int ret;
 
+	if (root->alloc_extent->num_used >= root->alloc_extent->num_blocks)
+		return -1;
+
+	*block = root->alloc_extent->blocknr + root->alloc_extent->num_used;
+	root->alloc_extent->num_used += 1;
+	if (root->alloc_extent->num_used >= root->alloc_extent->num_blocks) {
+		struct alloc_extent *ae = root->alloc_extent;
+		root->alloc_extent = root->reserve_extent;
+		root->reserve_extent = ae;
+		ae->num_blocks = 0;
+	}
 	st.st_size = 0;
 	ret = fstat(root->fp, &st);
-	if (st.st_size > sizeof(struct ctree_header)) {
-		*block = (st.st_size -
-			sizeof(struct ctree_header)) / CTREE_BLOCKSIZE;
-	} else {
-		*block = 0;
-	}
-	ret = ftruncate(root->fp, sizeof(struct ctree_header) + (*block + 1) *
-			CTREE_BLOCKSIZE);
+	if (st.st_size < (*block + 1) * CTREE_BLOCKSIZE)
+		ret = ftruncate(root->fp,
+				(*block + 1) * CTREE_BLOCKSIZE);
 	return ret;
 }
 
@@ -72,7 +74,7 @@
 
 struct tree_buffer *read_tree_block(struct ctree_root *root, u64 blocknr)
 {
-	loff_t offset = blocknr * CTREE_BLOCKSIZE + sizeof(struct ctree_header);
+	loff_t offset = blocknr * CTREE_BLOCKSIZE;
 	struct tree_buffer *buf;
 	int ret;
 
@@ -101,7 +103,7 @@
 int write_tree_block(struct ctree_root *root, struct tree_buffer *buf)
 {
 	u64 blocknr = buf->blocknr;
-	loff_t offset = blocknr * CTREE_BLOCKSIZE + sizeof(struct ctree_header);
+	loff_t offset = blocknr * CTREE_BLOCKSIZE;
 	int ret;
 
 	if (buf->blocknr != buf->node.header.blocknr)
@@ -114,11 +116,32 @@
 	return 0;
 }
 
+struct ctree_super_block {
+	struct ctree_root_info root_info;
+	struct ctree_root_info extent_info;
+} __attribute__ ((__packed__));
+
+static int __setup_root(struct ctree_root *root, struct ctree_root *extent_root,
+			struct ctree_root_info *info, int fp)
+{
+	root->fp = fp;
+	root->node = read_tree_block(root, info->tree_root);
+	root->extent_root = extent_root;
+	memcpy(&root->ai1, &info->alloc_extent, sizeof(info->alloc_extent));
+	memcpy(&root->ai2, &info->reserve_extent, sizeof(info->reserve_extent));
+	root->alloc_extent = &root->ai1;
+	root->reserve_extent = &root->ai2;
+	INIT_RADIX_TREE(&root->cache_radix, GFP_KERNEL);
+	printf("setup done reading root %p, used %lu\n", root, root->alloc_extent->num_used);
+	return 0;
+}
+
 struct ctree_root *open_ctree(char *filename)
 {
 	struct ctree_root *root = malloc(sizeof(struct ctree_root));
+	struct ctree_root *extent_root = malloc(sizeof(struct ctree_root));
+	struct ctree_super_block super;
 	int fp;
-	u64 root_block;
 	int ret;
 
 	fp = open(filename, O_CREAT | O_RDWR);
@@ -126,14 +149,20 @@
 		free(root);
 		return NULL;
 	}
-	root->fp = fp;
-	INIT_RADIX_TREE(&root->cache_radix, GFP_KERNEL);
-	ret = pread(fp, &root_block, sizeof(u64), 0);
-	if (ret == sizeof(u64)) {
-		printf("reading root node at block %lu\n", root_block);
-		root->node = read_tree_block(root, root_block);
-	} else
-		root->node = NULL;
+	ret = pread(fp, &super, sizeof(struct ctree_super_block),
+		     CTREE_SUPER_INFO_OFFSET(CTREE_BLOCKSIZE));
+	if (ret == 0) {
+		ret = mkfs(fp);
+		if (ret)
+			return NULL;
+		ret = pread(fp, &super, sizeof(struct ctree_super_block),
+			     CTREE_SUPER_INFO_OFFSET(CTREE_BLOCKSIZE));
+		if (ret != sizeof(struct ctree_super_block))
+			return NULL;
+	}
+	BUG_ON(ret < 0);
+	__setup_root(root, extent_root, &super.root_info, fp);
+	__setup_root(extent_root, extent_root, &super.extent_info, fp);
 	return root;
 }
 
@@ -160,6 +189,7 @@
 
 void tree_block_release(struct ctree_root *root, struct tree_buffer *buf)
 {
+	return;
 	buf->count--;
 	if (buf->count == 0) {
 		if (!radix_tree_lookup(&root->cache_radix, buf->blocknr))
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index ee95fa0..41acb65 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -17,5 +17,8 @@
 void tree_block_release(struct ctree_root *root, struct tree_buffer *buf);
 struct tree_buffer *alloc_free_block(struct ctree_root *root);
 int update_root_block(struct ctree_root *root);
+int mkfs(int fd);
+
+#define CTREE_SUPER_INFO_OFFSET(bs) (16 * (bs))
 
 #endif