Re: [PATCH bpf-next 2/2] bpftool: Show target_{obj,btf}_id in tracing link info

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2023-05-16 12:39 UTC+0000 ~ Yafang Shao <laoar.shao@xxxxxxxxx>
> The target_btf_id can help us understand which kernel function is
> linked by a tracing prog. The target_btf_id and target_obj_id have
> already been exposed to userspace, so we just need to show them.
> 
> The result as follows,
> 
> $ tools/bpf/bpftool/bpftool link show
> 2: tracing  prog 13
>         prog_type tracing  attach_type trace_fentry
>         target_obj_id 1  target_btf_id 13964
>         pids trace(10673)
> 
> $ tools/bpf/bpftool/bpftool link show -j
> [{"id":2,"type":"tracing","prog_id":13,"prog_type":"tracing","attach_type":"trace_fentry","target_obj_id":1,"target_btf_id":13964,"pids":[{"pid":10673,"comm":"trace"}]}]
> 
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> Acked-by: Song Liu <song@xxxxxxxxxx>
> ---
>  tools/bpf/bpftool/link.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
> index 243b74e..cfe896f 100644
> --- a/tools/bpf/bpftool/link.c
> +++ b/tools/bpf/bpftool/link.c
> @@ -195,6 +195,8 @@ static int show_link_close_json(int fd, struct bpf_link_info *info)
>  
>  		show_link_attach_type_json(info->tracing.attach_type,
>  					   json_wtr);
> +		jsonw_uint_field(json_wtr, "target_obj_id", info->tracing.target_obj_id);
> +		jsonw_uint_field(json_wtr, "target_btf_id", info->tracing.target_btf_id);
>  		break;
>  	case BPF_LINK_TYPE_CGROUP:
>  		jsonw_lluint_field(json_wtr, "cgroup_id",
> @@ -375,6 +377,8 @@ static int show_link_close_plain(int fd, struct bpf_link_info *info)
>  			printf("\n\tprog_type %u  ", prog_info.type);
>  
>  		show_link_attach_type_plain(info->tracing.attach_type);
> +		printf("\n\ttarget_obj_id %u  target_btf_id %u  ",
> +			   info->tracing.target_obj_id, info->tracing.target_btf_id);

Older kernels won't share this info, so maybe we can skip this printf()
in plain output if the target object and BTF ids are 0?

>  		break;
>  	case BPF_LINK_TYPE_CGROUP:
>  		printf("\n\tcgroup_id %zu  ", (size_t)info->cgroup.cgroup_id);





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