Re: [PATCH bpf-next v1 2/8] libbpf: tie struct_ops programs to kernel BTF ids, not to local ids

[Martin KaFai Lau <martin.lau@linux.dev>]

On 2/27/24 12:45 PM, Eduard Zingerman wrote:
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index abe663927013..c239b75d5816 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1134,8 +1134,27 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map)
>   
>   			if (mod_btf)
>   				prog->attach_btf_obj_fd = mod_btf->fd;
> -			prog->attach_btf_id = kern_type_id;
> -			prog->expected_attach_type = kern_member_idx;
> +
> +			/* if we haven't yet processed this BPF program, record proper
> +			 * attach_btf_id and member_idx
> +			 */
> +			if (!prog->attach_btf_id) {
> +				prog->attach_btf_id = kern_type_id;
> +				prog->expected_attach_type = kern_member_idx;
> +			}
> +
> +			/* struct_ops BPF prog can be re-used between multiple
> +			 * .struct_ops & .struct_ops.link as long as it's the
> +			 * same struct_ops struct definition and the same
> +			 * function pointer field
> +			 */
> +			if (prog->attach_btf_id != kern_type_id ||
> +			    prog->expected_attach_type != kern_member_idx) {
> +				pr_warn("struct_ops reloc %s: cannot use prog %s in sec %s with type %u attach_btf_id %u expected_attach_type %u for func ptr %s\n",

The patch lgtm. A nit is s/reloc/init_kern/.

> +					map->name, prog->name, prog->sec_name, prog->type,
> +					prog->attach_btf_id, prog->expected_attach_type, mname);
> +				return -EINVAL;
> +			}
>   
>   			st_ops->kern_func_off[i] = kern_data_off + kern_moff;