find_wl_entry
e = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF,
e = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF, 0);
e = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF, 0);
e2 = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF, 0);
e = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF, 0);
e = find_wl_entry(ubi, root, WL_FREE_MAX_DIFF/2, 0);