num_maps = (blocks + BLOCKS_PER_MAP-1)/ BLOCKS_PER_MAP;
f->file_map = malloc(num_maps * sizeof(long));
f->num_maps = num_maps;
num_maps = (blocks + BLOCKS_PER_MAP-1)/ BLOCKS_PER_MAP;
f->file_map = malloc(num_maps * sizeof(long));
f->num_maps = num_maps;