Re: [PATCH bpf-next v9 6/8] libbpf: Update a bpf_link with another struct_ops.

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

On 3/20/23 12:56 PM, Kui-Feng Lee wrote:
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 56a60ab2ca8f..f84d68c049e3 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -11639,6 +11639,11 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
>   
>   	/* kern_vdata should be prepared during the loading phase. */
>   	err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
> +	/* It can be EBUSY if the map has been used to create or
> +	 * update a link before.  We don't allow updating the value of
> +	 * a struct_ops once it is set.  That ensures that the value
> +	 * never changed.  So, it is safe to skip EBUSY.
> +	 */

This belongs to the earlier patch (4?).

>   	if (err && err != -EBUSY) {
>   		free(link);
>   		return libbpf_err_ptr(err);