code from btrfs-tools/sys-linux (which happens to be same/very similar to each other)
1) btrfs_sb_offset() - same as btrfs-tools::btrfs_sb_offset()
2) bin_search()  - same as generic_bin_search() in btrfs-tools (or bin_search() in btrfs patch for grub-legacy)
3) btrfs_chunk_item_size() - same as btrfs-tools::btrfs_chunk_item_size()
4) btrfs_read_sys_chunk_array() - based on btrfs-tools::btrfs_read_sys_array() - (single device support), except that insert_map() is used to keep the mappings in an array instead of inserting in tree.
5) btrfs_read_chunk_tree() - based on btrfs-tools::btrfs_read_chunk_tree() (single device support), except that insert_map() is used to keep the mappings in an array instead of inserting in tree.

code from syslinux:
1) logical_physical()  
2) btrfs_comp_keys_type()
4) search_tree()
5) next_leaf()
6) insert_map()


from the linux kernel:
1) btrfs_name_hash() - same as linux-2.6::btrfs_name_hash()
2) btrfs_comp_keys() - same as linux-2.6::btrfs_comp_cpu_keys()

what is different:
1) btrfs_get_fs_tree() - name is same as in syslinux, but the implementation is different
2) cache implementation()
3) btrfs_init_fs()
4) get_component()
5) btrfs_match_dir_item_name()
6) read_extent()
7) read_file_inr()
8) change_fs_root()
9) get_ino_cache()
10) get_parent()
11) insert_new_cache_item()
12) stripped_len()
13) search_path()
14) follow_link()
15) get_resolved_inum()
16) search_comp()
17) init_file()
18) grub_btrfs_open()
19) get_item_key()
20) grub_btrfs_read()
21) get_dirent_info()
22) btrfs_print_dir_item_names()
23) read_dir()
24) grub_btrfs_dir()
25) grub_btrfs_close()
26) grub_btrfs_label()
27) grub_btrfs_uuid()
28) grub_btrfs_mtime()
* Every function that starts with grub is grub dependent. Every other function could be used by other boot loaders as well.