write_extent_buffer(c, root->fs_info->fsid,
                            (unsigned long)btrfs_header_fsid(c),
                            BTRFS_FSID_SIZE);
+
+       write_extent_buffer(c, root->fs_info->chunk_tree_uuid,
+                           (unsigned long)btrfs_header_chunk_tree_uuid(c),
+                           BTRFS_UUID_SIZE);
+
        btrfs_set_node_key(c, &lower_key, 0);
        btrfs_set_node_blockptr(c, 0, lower->start);
        lower_gen = btrfs_header_generation(lower);
        write_extent_buffer(split, root->fs_info->fsid,
                            (unsigned long)btrfs_header_fsid(split),
                            BTRFS_FSID_SIZE);
+       write_extent_buffer(split, root->fs_info->chunk_tree_uuid,
+                           (unsigned long)btrfs_header_chunk_tree_uuid(split),
+                           BTRFS_UUID_SIZE);
 
        mid = (c_nritems + 1) / 2;
 
        write_extent_buffer(right, root->fs_info->fsid,
                            (unsigned long)btrfs_header_fsid(right),
                            BTRFS_FSID_SIZE);
+
+       write_extent_buffer(right, root->fs_info->chunk_tree_uuid,
+                           (unsigned long)btrfs_header_chunk_tree_uuid(right),
+                           BTRFS_UUID_SIZE);
        if (mid <= slot) {
                if (nritems == 1 ||
                    leaf_space_used(l, mid, nritems - mid) + space_needed >
 
  * All files have objectids higher than this.
  */
 #define BTRFS_FIRST_FREE_OBJECTID 256ULL
+#define BTRFS_FIRST_CHUNK_TREE_OBJECTID 256ULL
 
 
 /*
        struct extent_map_tree map_tree;
 };
 
-#define BTRFS_DEV_UUID_SIZE 16
+#define BTRFS_UUID_SIZE 16
 struct btrfs_dev_item {
        /* the internal btrfs device id */
        __le64 devid;
        /* type and info about this device */
        __le64 type;
 
+       /* grouping information for allocation decisions */
+       __le32 dev_group;
+
+       /* seek speed 0-100 where 100 is fastest */
+       u8 seek_speed;
+
+       /* bandwidth 0-100 where 100 is fastest */
+       u8 bandwidth;
+
        /* btrfs generated uuid for this device */
-       u8 uuid[BTRFS_DEV_UUID_SIZE];
+       u8 uuid[BTRFS_UUID_SIZE];
 } __attribute__ ((__packed__));
 
 struct btrfs_stripe {
        __le64 devid;
        __le64 offset;
+       u8 dev_uuid[BTRFS_UUID_SIZE];
 } __attribute__ ((__packed__));
 
 struct btrfs_chunk {
+       /* size of this chunk in bytes */
+       __le64 length;
+
+       /* objectid of the root referencing this chunk */
        __le64 owner;
+
        __le64 stripe_len;
        __le64 type;
 
  * every tree block (leaf or node) starts with this header.
  */
 struct btrfs_header {
+       /* these first four must match the super block */
        u8 csum[BTRFS_CSUM_SIZE];
        u8 fsid[BTRFS_FSID_SIZE]; /* FS specific uuid */
        __le64 bytenr; /* which block this node is supposed to live in */
        __le64 flags;
+
+       /* allowed to be different from the super from here on down */
+       u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
        __le64 generation;
        __le64 owner;
        __le32 nritems;
        u8 fsid[16];    /* FS specific uuid */
        __le64 bytenr; /* this block number */
        __le64 flags;
+
+       /* allowed to be different from the btrfs_header from here own down */
        __le64 magic;
        __le64 generation;
        __le64 root;
 
 /* dev extents record free space on individual devices.  The owner
  * field points back to the chunk allocation mapping tree that allocated
- * the extent
+ * the extent.  The chunk tree uuid field is a way to double check the owner
  */
 struct btrfs_dev_extent {
-       __le64 owner;
+       __le64 chunk_tree;
+       __le64 chunk_objectid;
+       __le64 chunk_offset;
        __le64 length;
+       u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
 } __attribute__ ((__packed__));
 
-
 struct btrfs_inode_ref {
        __le16 name_len;
        /* name goes here */
 
 struct btrfs_block_group_item {
        __le64 used;
-       __le64 chunk_tree;
        __le64 chunk_objectid;
        __le64 flags;
 } __attribute__ ((__packed__));
 struct btrfs_fs_devices;
 struct btrfs_fs_info {
        u8 fsid[BTRFS_FSID_SIZE];
+       u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
        struct btrfs_root *extent_root;
        struct btrfs_root *tree_root;
        struct btrfs_root *chunk_root;
 BTRFS_SETGET_FUNCS(device_io_width, struct btrfs_dev_item, io_width, 32);
 BTRFS_SETGET_FUNCS(device_sector_size, struct btrfs_dev_item, sector_size, 32);
 BTRFS_SETGET_FUNCS(device_id, struct btrfs_dev_item, devid, 64);
+BTRFS_SETGET_FUNCS(device_group, struct btrfs_dev_item, dev_group, 32);
+BTRFS_SETGET_FUNCS(device_seek_speed, struct btrfs_dev_item, seek_speed, 8);
+BTRFS_SETGET_FUNCS(device_bandwidth, struct btrfs_dev_item, bandwidth, 8);
 
 BTRFS_SETGET_STACK_FUNCS(stack_device_type, struct btrfs_dev_item, type, 64);
 BTRFS_SETGET_STACK_FUNCS(stack_device_total_bytes, struct btrfs_dev_item,
 BTRFS_SETGET_STACK_FUNCS(stack_device_sector_size, struct btrfs_dev_item,
                         sector_size, 32);
 BTRFS_SETGET_STACK_FUNCS(stack_device_id, struct btrfs_dev_item, devid, 64);
+BTRFS_SETGET_STACK_FUNCS(stack_device_group, struct btrfs_dev_item,
+                        dev_group, 32);
+BTRFS_SETGET_STACK_FUNCS(stack_device_seek_speed, struct btrfs_dev_item,
+                        seek_speed, 8);
+BTRFS_SETGET_STACK_FUNCS(stack_device_bandwidth, struct btrfs_dev_item,
+                        bandwidth, 8);
 
 static inline char *btrfs_device_uuid(struct btrfs_dev_item *d)
 {
        return (char *)d + offsetof(struct btrfs_dev_item, uuid);
 }
 
+BTRFS_SETGET_FUNCS(chunk_length, struct btrfs_chunk, length, 64);
 BTRFS_SETGET_FUNCS(chunk_owner, struct btrfs_chunk, owner, 64);
 BTRFS_SETGET_FUNCS(chunk_stripe_len, struct btrfs_chunk, stripe_len, 64);
 BTRFS_SETGET_FUNCS(chunk_io_align, struct btrfs_chunk, io_align, 32);
 BTRFS_SETGET_FUNCS(stripe_devid, struct btrfs_stripe, devid, 64);
 BTRFS_SETGET_FUNCS(stripe_offset, struct btrfs_stripe, offset, 64);
 
+static inline char *btrfs_stripe_dev_uuid(struct btrfs_stripe *s)
+{
+       return (char *)s + offsetof(struct btrfs_stripe, dev_uuid);
+}
+
+BTRFS_SETGET_STACK_FUNCS(stack_chunk_length, struct btrfs_chunk, length, 64);
 BTRFS_SETGET_STACK_FUNCS(stack_chunk_owner, struct btrfs_chunk, owner, 64);
 BTRFS_SETGET_STACK_FUNCS(stack_chunk_stripe_len, struct btrfs_chunk,
                         stripe_len, 64);
                         used, 64);
 BTRFS_SETGET_FUNCS(disk_block_group_used, struct btrfs_block_group_item,
                         used, 64);
-BTRFS_SETGET_STACK_FUNCS(block_group_chunk_tree, struct btrfs_block_group_item,
-                        chunk_tree, 64);
-BTRFS_SETGET_FUNCS(disk_block_group_chunk_tree, struct btrfs_block_group_item,
-                        chunk_tree, 64);
 BTRFS_SETGET_STACK_FUNCS(block_group_chunk_objectid,
                        struct btrfs_block_group_item, chunk_objectid, 64);
-BTRFS_SETGET_FUNCS(disk_block_group_chunk_objecitd,
+
+BTRFS_SETGET_FUNCS(disk_block_group_chunk_objectid,
                   struct btrfs_block_group_item, chunk_objectid, 64);
 BTRFS_SETGET_FUNCS(disk_block_group_flags,
                   struct btrfs_block_group_item, flags, 64);
 BTRFS_SETGET_FUNCS(extent_refs, struct btrfs_extent_item, refs, 32);
 
 /* struct btrfs_dev_extent */
-BTRFS_SETGET_FUNCS(dev_extent_owner, struct btrfs_dev_extent, owner, 64);
+BTRFS_SETGET_FUNCS(dev_extent_chunk_tree, struct btrfs_dev_extent,
+                  chunk_tree, 64);
+BTRFS_SETGET_FUNCS(dev_extent_chunk_objectid, struct btrfs_dev_extent,
+                  chunk_objectid, 64);
+BTRFS_SETGET_FUNCS(dev_extent_chunk_offset, struct btrfs_dev_extent,
+                  chunk_offset, 64);
 BTRFS_SETGET_FUNCS(dev_extent_length, struct btrfs_dev_extent, length, 64);
 
+static inline u8 *btrfs_dev_extent_chunk_tree_uuid(struct btrfs_dev_extent *dev)
+{
+       unsigned long ptr = offsetof(struct btrfs_dev_extent, chunk_tree_uuid);
+       return (u8 *)((unsigned long)dev + ptr);
+}
+
 /* struct btrfs_extent_ref */
 BTRFS_SETGET_FUNCS(ref_root, struct btrfs_extent_ref, root, 64);
 BTRFS_SETGET_FUNCS(ref_generation, struct btrfs_extent_ref, generation, 64);
        return (u8 *)ptr;
 }
 
+static inline u8 *btrfs_header_chunk_tree_uuid(struct extent_buffer *eb)
+{
+       unsigned long ptr = offsetof(struct btrfs_header, chunk_tree_uuid);
+       return (u8 *)ptr;
+}
+
 static inline u8 *btrfs_super_fsid(struct extent_buffer *eb)
 {
        unsigned long ptr = offsetof(struct btrfs_super_block, fsid);
 int btrfs_read_block_groups(struct btrfs_root *root);
 int btrfs_make_block_group(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root, u64 bytes_used,
-                          u64 type, u64 chunk_tree, u64 chunk_objectid,
+                          u64 type, u64 chunk_objectid, u64 chunk_offset,
                           u64 size);
 /* ctree.c */
 int btrfs_previous_item(struct btrfs_root *root,
 
                                           blocksize);
        BUG_ON(!chunk_root->node);
 
+       read_extent_buffer(chunk_root->node, fs_info->chunk_tree_uuid,
+                (unsigned long)btrfs_header_chunk_tree_uuid(chunk_root->node),
+                BTRFS_UUID_SIZE);
+
        ret = btrfs_read_chunk_tree(chunk_root);
        BUG_ON(ret);
 
                btrfs_set_device_sector_size(sb, dev_item, dev->sector_size);
                write_extent_buffer(sb, dev->uuid,
                                    (unsigned long)btrfs_device_uuid(dev_item),
-                                   BTRFS_DEV_UUID_SIZE);
+                                   BTRFS_UUID_SIZE);
 
                btrfs_set_header_flag(sb, BTRFS_HEADER_FLAG_WRITTEN);
                csum_tree_block(root, sb, 0);
 
                                 btrfs_root *extent_root);
 static int del_pending_extents(struct btrfs_trans_handle *trans, struct
                               btrfs_root *extent_root);
-int btrfs_make_block_group(struct btrfs_trans_handle *trans,
-                          struct btrfs_root *root, u64 bytes_used,
-                          u64 type, u64 chunk_tree, u64 chunk_objectid,
-                          u64 size);
 
 
 static int cache_block_group(struct btrfs_root *root,
                ret = get_state_private(block_group_cache, start, &ptr);
                if (ret)
                        break;
-
                cache = (struct btrfs_block_group_cache *)(unsigned long)ptr;
                err = write_one_cache_group(trans, root,
                                            path, cache);
        BUG_ON(ret);
 
        ret = btrfs_make_block_group(trans, extent_root, 0, flags,
-                    extent_root->fs_info->chunk_root->root_key.objectid,
-                    start, num_bytes);
+                    BTRFS_FIRST_CHUNK_TREE_OBJECTID, start, num_bytes);
        BUG_ON(ret);
 
        return 0;
 
 int btrfs_make_block_group(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root, u64 bytes_used,
-                          u64 type, u64 chunk_tree, u64 chunk_objectid,
+                          u64 type, u64 chunk_objectid, u64 chunk_offset,
                           u64 size)
 {
        int ret;
 
        cache = kmalloc(sizeof(*cache), GFP_NOFS);
        BUG_ON(!cache);
-       cache->key.objectid = chunk_objectid;
+       cache->key.objectid = chunk_offset;
        cache->key.offset = size;
        cache->cached = 0;
        cache->pinned = 0;
+
        btrfs_set_key_type(&cache->key, BTRFS_BLOCK_GROUP_ITEM_KEY);
        memset(&cache->item, 0, sizeof(cache->item));
        btrfs_set_block_group_used(&cache->item, bytes_used);
-       btrfs_set_block_group_chunk_tree(&cache->item, chunk_tree);
        btrfs_set_block_group_chunk_objectid(&cache->item, chunk_objectid);
        cache->flags = type;
        btrfs_set_block_group_flags(&cache->item, type);
        BUG_ON(ret);
 
        bit = block_group_state_bits(type);
-       set_extent_bits(block_group_cache, chunk_objectid,
-                       chunk_objectid + size - 1,
+       set_extent_bits(block_group_cache, chunk_offset,
+                       chunk_offset + size - 1,
                        bit | EXTENT_LOCKED, GFP_NOFS);
-       set_state_private(block_group_cache, chunk_objectid,
-                         (unsigned long)cache);
 
+       set_state_private(block_group_cache, chunk_offset,
+                         (unsigned long)cache);
        ret = btrfs_insert_item(trans, extent_root, &cache->key, &cache->item,
                                sizeof(cache->item));
        BUG_ON(ret);
 
 {
        int num_stripes = btrfs_chunk_num_stripes(eb, chunk);
        int i;
-       printk("\t\tchunk owner %llu type %llu num_stripes %d\n",
+       printk("\t\tchunk length %llu owner %llu type %llu num_stripes %d\n",
+              (unsigned long long)btrfs_chunk_length(eb, chunk),
               (unsigned long long)btrfs_chunk_owner(eb, chunk),
               (unsigned long long)btrfs_chunk_type(eb, chunk),
               num_stripes);
                case BTRFS_DEV_EXTENT_KEY:
                        dev_extent = btrfs_item_ptr(l, i,
                                                    struct btrfs_dev_extent);
-                       printk("\t\tdev extent owner %llu length %llu\n",
-                              (unsigned long long)btrfs_dev_extent_owner(l, dev_extent),
-                              (unsigned long long)btrfs_dev_extent_length(l, dev_extent));
+                       printk("\t\tdev extent chunk_tree %llu\n"
+                              "\t\tchunk objectid %llu chunk offset %llu "
+                              "length %llu\n",
+                              (unsigned long long)
+                              btrfs_dev_extent_chunk_tree(l, dev_extent),
+                              (unsigned long long)
+                              btrfs_dev_extent_chunk_objectid(l, dev_extent),
+                              (unsigned long long)
+                              btrfs_dev_extent_chunk_offset(l, dev_extent),
+                              (unsigned long long)
+                              btrfs_dev_extent_length(l, dev_extent));
                };
        }
 }
 
 void btrfs_print_tree(struct btrfs_root *root, struct extent_buffer *c)
 {
-       int i;
-       u32 nr;
+       int i; u32 nr;
        struct btrfs_key key;
        int level;
 
 
        list_for_each(cur, head) {
                device = list_entry(cur, struct btrfs_device, dev_list);
                bdev = open_bdev_excl(device->name, flags, holder);
-printk("opening %s devid %Lu\n", device->name, device->devid);
+
                if (IS_ERR(bdev)) {
                        printk("open %s failed\n", device->name);
                        ret = PTR_ERR(bdev);
                        fs_devices->latest_bdev = bdev;
                if (device->devid == fs_devices->lowest_devid) {
                        fs_devices->lowest_bdev = bdev;
-printk("lowest bdev %s\n", device->name);
                }
                device->bdev = bdev;
        }
 
 int btrfs_alloc_dev_extent(struct btrfs_trans_handle *trans,
                           struct btrfs_device *device,
-                          u64 owner, u64 num_bytes, u64 *start)
+                          u64 chunk_tree, u64 chunk_objectid,
+                          u64 chunk_offset,
+                          u64 num_bytes, u64 *start)
 {
        int ret;
        struct btrfs_path *path;
        leaf = path->nodes[0];
        extent = btrfs_item_ptr(leaf, path->slots[0],
                                struct btrfs_dev_extent);
-       btrfs_set_dev_extent_owner(leaf, extent, owner);
+       btrfs_set_dev_extent_chunk_tree(leaf, extent, chunk_tree);
+       btrfs_set_dev_extent_chunk_objectid(leaf, extent, chunk_objectid);
+       btrfs_set_dev_extent_chunk_offset(leaf, extent, chunk_offset);
+
+       write_extent_buffer(leaf, root->fs_info->chunk_tree_uuid,
+                   (unsigned long)btrfs_dev_extent_chunk_tree_uuid(extent),
+                   BTRFS_UUID_SIZE);
+
        btrfs_set_dev_extent_length(leaf, extent, num_bytes);
        btrfs_mark_buffer_dirty(leaf);
 err:
        return ret;
 }
 
-static int find_next_chunk(struct btrfs_root *root, u64 *objectid)
+static int find_next_chunk(struct btrfs_root *root, u64 objectid, u64 *offset)
 {
        struct btrfs_path *path;
        int ret;
        struct btrfs_key key;
+       struct btrfs_chunk *chunk;
        struct btrfs_key found_key;
 
        path = btrfs_alloc_path();
        BUG_ON(!path);
 
-       key.objectid = (u64)-1;
+       key.objectid = objectid;
        key.offset = (u64)-1;
        key.type = BTRFS_CHUNK_ITEM_KEY;
 
 
        ret = btrfs_previous_item(root, path, 0, BTRFS_CHUNK_ITEM_KEY);
        if (ret) {
-               *objectid = 0;
+               *offset = 0;
        } else {
                btrfs_item_key_to_cpu(path->nodes[0], &found_key,
                                      path->slots[0]);
-               *objectid = found_key.objectid + found_key.offset;
+               if (found_key.objectid != objectid)
+                       *offset = 0;
+               else {
+                       chunk = btrfs_item_ptr(path->nodes[0], path->slots[0],
+                                              struct btrfs_chunk);
+                       *offset = found_key.offset +
+                               btrfs_chunk_length(path->nodes[0], chunk);
+               }
        }
        ret = 0;
 error:
        btrfs_set_device_sector_size(leaf, dev_item, device->sector_size);
        btrfs_set_device_total_bytes(leaf, dev_item, device->total_bytes);
        btrfs_set_device_bytes_used(leaf, dev_item, device->bytes_used);
+       btrfs_set_device_group(leaf, dev_item, 0);
+       btrfs_set_device_seek_speed(leaf, dev_item, 0);
+       btrfs_set_device_bandwidth(leaf, dev_item, 0);
 
        ptr = (unsigned long)btrfs_device_uuid(dev_item);
-       write_extent_buffer(leaf, device->uuid, ptr, BTRFS_DEV_UUID_SIZE);
+       write_extent_buffer(leaf, device->uuid, ptr, BTRFS_UUID_SIZE);
        btrfs_mark_buffer_dirty(leaf);
        ret = 0;
 
                return -ENOSPC;
        }
 
-       ret = find_next_chunk(chunk_root, &key.objectid);
+       key.objectid = BTRFS_FIRST_CHUNK_TREE_OBJECTID;
+       key.type = BTRFS_CHUNK_ITEM_KEY;
+       ret = find_next_chunk(chunk_root, BTRFS_FIRST_CHUNK_TREE_OBJECTID,
+                             &key.offset);
        if (ret)
                return ret;
 
                *num_bytes = calc_size * num_stripes;
 
        index = 0;
-printk("new chunk type %Lu start %Lu size %Lu\n", type, key.objectid, *num_bytes);
+printk("new chunk type %Lu start %Lu size %Lu\n", type, key.offset, *num_bytes);
        while(index < num_stripes) {
+               struct btrfs_stripe *stripe;
                BUG_ON(list_empty(&private_devs));
                cur = private_devs.next;
                device = list_entry(cur, struct btrfs_device, dev_list);
                        list_move_tail(&device->dev_list, dev_list);
 
                ret = btrfs_alloc_dev_extent(trans, device,
-                                            key.objectid,
-                                            calc_size, &dev_offset);
+                            info->chunk_root->root_key.objectid,
+                            BTRFS_FIRST_CHUNK_TREE_OBJECTID, key.offset,
+                            calc_size, &dev_offset);
                BUG_ON(ret);
-printk("alloc chunk start %Lu size %Lu from dev %Lu type %Lu\n", key.objectid, calc_size, device->devid, type);
+printk("alloc chunk start %Lu size %Lu from dev %Lu type %Lu\n", key.offset, calc_size, device->devid, type);
                device->bytes_used += calc_size;
                ret = btrfs_update_device(trans, device);
                BUG_ON(ret);
 
                map->stripes[index].dev = device;
                map->stripes[index].physical = dev_offset;
-               btrfs_set_stack_stripe_devid(stripes + index, device->devid);
-               btrfs_set_stack_stripe_offset(stripes + index, dev_offset);
+               stripe = stripes + index;
+               btrfs_set_stack_stripe_devid(stripe, device->devid);
+               btrfs_set_stack_stripe_offset(stripe, dev_offset);
+               memcpy(stripe->dev_uuid, device->uuid, BTRFS_UUID_SIZE);
                physical = dev_offset;
                index++;
        }
        BUG_ON(!list_empty(&private_devs));
 
-       /* key.objectid was set above */
-       key.offset = *num_bytes;
-       key.type = BTRFS_CHUNK_ITEM_KEY;
+       /* key was set above */
+       btrfs_set_stack_chunk_length(chunk, *num_bytes);
        btrfs_set_stack_chunk_owner(chunk, extent_root->root_key.objectid);
        btrfs_set_stack_chunk_stripe_len(chunk, stripe_len);
        btrfs_set_stack_chunk_type(chunk, type);
        ret = btrfs_insert_item(trans, chunk_root, &key, chunk,
                                btrfs_chunk_item_size(num_stripes));
        BUG_ON(ret);
-       *start = key.objectid;
+       *start = key.offset;;
 
        em = alloc_extent_map(GFP_NOFS);
        if (!em)
                return -ENOMEM;
        em->bdev = (struct block_device *)map;
-       em->start = key.objectid;
-       em->len = key.offset;
+       em->start = key.offset;
+       em->len = *num_bytes;
        em->block_start = 0;
 
        kfree(chunk);
        int ret;
        int i;
 
-       logical = key->objectid;
-       length = key->offset;
+       logical = key->offset;
+       length = btrfs_chunk_length(leaf, chunk);
        spin_lock(&map_tree->map_tree.lock);
        em = lookup_extent_mapping(&map_tree->map_tree, logical, 1);
        spin_unlock(&map_tree->map_tree.lock);
        device->sector_size = btrfs_device_sector_size(leaf, dev_item);
 
        ptr = (unsigned long)btrfs_device_uuid(dev_item);
-       read_extent_buffer(leaf, device->uuid, ptr, BTRFS_DEV_UUID_SIZE);
+       read_extent_buffer(leaf, device->uuid, ptr, BTRFS_UUID_SIZE);
 
        return 0;
 }
        struct btrfs_device *device;
        u64 devid;
        int ret;
-
        devid = btrfs_device_id(leaf, dev_item);
        device = btrfs_find_device(root, devid);
        if (!device) {
 
        u64 type;
 
        /* physical drive uuid (or lvm uuid) */
-       u8 uuid[BTRFS_DEV_UUID_SIZE];
+       u8 uuid[BTRFS_UUID_SIZE];
 };
 
 struct btrfs_fs_devices {
 
 int btrfs_alloc_dev_extent(struct btrfs_trans_handle *trans,
                           struct btrfs_device *device,
-                          u64 owner, u64 num_bytes, u64 *start);
+                          u64 chunk_tree, u64 chunk_objectid,
+                          u64 chunk_offset,
+                          u64 num_bytes, u64 *start);
 int btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
                    u64 logical, u64 *length,
                    struct btrfs_multi_bio **multi_ret, int mirror_num);