Re: [PATCH bpf-next v7 4/8] libbpf: Create a bpf_link in bpf_map__attach_struct_ops().

[Martin KaFai Lau <martin.lau@xxxxxxxxx>]

On 3/15/23 7:36 PM, Kui-Feng Lee wrote:
> @@ -11590,31 +11631,32 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
>   	if (!link)
>   		return libbpf_err_ptr(-EINVAL);
>   
> -	st_ops = map->st_ops;
> -	for (i = 0; i < btf_vlen(st_ops->type); i++) {
> -		struct bpf_program *prog = st_ops->progs[i];
> -		void *kern_data;
> -		int prog_fd;
> +	/* kern_vdata should be prepared during the loading phase. */
> +	err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
> +	if (err) {

It should not fail for BPF_F_LINK struct_ops when err is EBUSY.
The struct_ops map can attach, detach, and then attach again.

It needs a test for this case.

> +		free(link);
> +		return libbpf_err_ptr(err);
> +	}