Re: [PATCH bpf-next v3] bpftool: Show map IDs along with struct_ops links.

[Kui-Feng Lee <sinquersw@gmail.com>]

Due to a confliction, I have rebased this patch and sent v4.

On 4/21/23 11:17, Kui-Feng Lee wrote:
> A new link type, BPF_LINK_TYPE_STRUCT_OPS, was added to attach
> struct_ops to links. (226bc6ae6405) It would be helpful for users to
> know which map is associated with the link.
> 
> The assumption was that every link is associated with a BPF program, but
> this does not hold true for struct_ops. It would be better to display
> map_id instead of prog_id for struct_ops links. However, some tools may
> rely on the old assumption and need a prog_id.  The discussion on the
> mailing list suggests that tools should parse JSON format. We will maintain
> the existing JSON format by adding a map_id without removing prog_id. As
> for plain text format, we will remove prog_id from the header line and add
> a map_id for struct_ops links.
> 
> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
> Reviewed-by: Quentin Monnet <quentin@isovalent.com>
> ---
>   tools/bpf/bpftool/link.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
> index f985b79cca27..c79f2e8927d6 100644
> --- a/tools/bpf/bpftool/link.c
> +++ b/tools/bpf/bpftool/link.c
> @@ -195,6 +195,10 @@ static int show_link_close_json(int fd, struct bpf_link_info *info)
>   				 info->netns.netns_ino);
>   		show_link_attach_type_json(info->netns.attach_type, json_wtr);
>   		break;
> +	case BPF_LINK_TYPE_STRUCT_OPS:
> +		jsonw_uint_field(json_wtr, "map_id",
> +				 info->struct_ops.map_id);
> +		break;
>   	default:
>   		break;
>   	}
> @@ -227,7 +231,10 @@ static void show_link_header_plain(struct bpf_link_info *info)
>   	else
>   		printf("type %u  ", info->type);
>   
> -	printf("prog %u  ", info->prog_id);
> +	if (info->type == BPF_LINK_TYPE_STRUCT_OPS)
> +		printf("map %u  ", info->struct_ops.map_id);
> +	else
> +		printf("prog %u  ", info->prog_id);
>   }
>   
>   static void show_link_attach_type_plain(__u32 attach_type)