hfs_ext_find_block
dblock = hfs_ext_find_block(HFS_I(tree->inode)->first_extents, 0);
dblock = hfs_ext_find_block(HFS_I(inode)->first_extents, ablock);
dblock = hfs_ext_find_block(HFS_I(inode)->cached_extents,
extern u16 hfs_ext_find_block(struct hfs_extent *ext, u16 off);