next_slab
struct vdo_slab *slab = next_slab(&iterator);
struct vdo_slab *slab = next_slab(&iterator);
slab = next_slab(&allocator->slabs_to_erase);
slab_count_t slab_number = next_slab(&iterator)->slab_number;
struct vdo_slab *slab = next_slab(&iterator);
int result = allocate_slab_counters(next_slab(&iterator));