Re: [PATCH bpf-next v3 3/7] bpf: create repeated fields for arrays.

[Eduard Zingerman <eddyz87@xxxxxxxxx>]

On Wed, 2024-05-01 at 13:47 -0700, Kui-Feng Lee wrote:

I think this looks good for repeating fields of nested arrays
(w/o visiting nested structures), two nits below.

> @@ -3575,6 +3628,19 @@ static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
>  	for_each_vsi(i, t, vsi) {
>  		const struct btf_type *var = btf_type_by_id(btf, vsi->type);
>  		const struct btf_type *var_type = btf_type_by_id(btf, var->type);
> +		const struct btf_array *array;
> +		u32 j, nelems = 1;
> +
> +		/* Walk into array types to find the element type and the
> +		 * number of elements in the (flattened) array.
> +		 */
> +		for (j = 0; j < MAX_RESOLVE_DEPTH && btf_type_is_array(var_type); j++) {
> +			array = btf_array(var_type);
> +			nelems *= array->nelems;
> +			var_type = btf_type_by_id(btf, array->type);
> +		}
> +		if (nelems == 0)
> +			continue;

Nit: Should this return an error if j == MAX_RESOLVE_DEPTH after the loop?

>  
>  		field_type = btf_get_field_type(__btf_name_by_offset(btf, var_type->name_off),
>  						field_mask, &seen_mask, &align, &sz);
> @@ -3584,7 +3650,7 @@ static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
>  			return field_type;
>  
>  		off = vsi->offset;
> -		if (vsi->size != sz)
> +		if (vsi->size != sz * nelems)
>  			continue;
>  		if (off % align)
>  			continue;
> @@ -3624,9 +3690,14 @@ static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
>  
>  		if (ret == BTF_FIELD_IGNORE)
>  			continue;
> -		if (idx >= info_cnt)
> +		if (idx + nelems > info_cnt)
>  			return -E2BIG;

Nit: This is bounded by BTF_FIELDS_MAX which has value of 11,
     would that be enough?

> -		++idx;
> +		if (nelems > 1) {
> +			ret = btf_repeat_field(info, idx, nelems - 1, sz);
> +			if (ret < 0)
> +				return ret;
> +		}
> +		idx += nelems;
>  	}
>  	return idx;
>  }