int lock_extent(struct extent_io_tree *tree, u64 start, u64 end, gfp_t mask);
int unlock_extent(struct extent_io_tree *tree, u64 start, u64 end, gfp_t mask);
int extent_read_full_page(struct extent_io_tree *tree, struct page *page,
int lock_extent(struct extent_io_tree *tree, u64 start, u64 end, gfp_t mask);
int unlock_extent(struct extent_io_tree *tree, u64 start, u64 end, gfp_t mask);
int extent_read_full_page(struct extent_io_tree *tree, struct page *page,