Re: [PATCH bpf-next v2] bpftool: Show map IDs along with struct_ops links.

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

On 4/20/23 16:41, Andrii Nakryiko wrote:
> On Tue, Apr 18, 2023 at 5:37 PM Kui-Feng Lee <thinker.li@gmail.com> 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..8eb8520bd7b4 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_id %u  ", info->struct_ops.map_id);
>> +       else
>> +               printf("prog %u  ", info->prog_id);
> 
> if we output "prog %u" for prog_id, shouldn't we just output "map %u"
> for map_id?

"map" make sense to me.

> 
>>   }
>>
>>   static void show_link_attach_type_plain(__u32 attach_type)
>> --
>> 2.34.1
>>